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NIR-II fluorescence confocal imaging based on indirect wavefront shaping
TAN Tian, SHI Tian-yue, WU Chang-feng, PENG Hong-shang
 doi: 10.37188/CO.2023-0070
Abstract(0) FullText HTML(0) PDF 4814KB(0)

Optical aberrations caused by the scattering of biological tissues limit the imaging performance of optical systems. We have explored a fluorescence confocal imaging technique that utilizes wavefront shaping indirectly, operating in the near-infrared II range. First, we synthesized a highly efficient fluorescent probe in the near-infrared II range, where reducing the scattering of biological tissue can enable high-contrast biopsy imaging. Second, the study investigate the adaptive optical method, utilizing indirect wavefront measurement. The indirect wavefront shaping technology was applied to the laser scanning confocal system, enabling the measurement and compensation of optical aberrations caused by biological tissues, and obtaining imaging of biological tissues with a high signal-to-noise ratio. Finally, an indirect wavefront shaping-based near-infrared II fluorescence confocal imaging system was deployed and relavant experiments were conducted. The experimental outcomes reveal that the system effectively compensates for the aberrations induced by air plates, scattering media and mouse skull, and increases the final signal intensity to 1.47, 1.95 and 2.85 times, respectively. As a result, the final imaging quality is significantly enhanced.

Scanning measurement method of small size parts without marks
MO Cai-li, WANG Li-zhong, ZHAO Jian-bo, WANG Sen, ZHOU Hao-jun, REN Mao-dong
 doi: 10.37188/CO.2023-0103
Abstract(0) FullText HTML(0) PDF 9360KB(0)

Small-size parts have a small surface area and complex structure. The traditional mark splicing method is easy to destroy the measurement data of the surface, and it is not allowed to paste marks on the surface of some parts. The feature splicing method is not applicable to parts with repetitive features. We propose a scanning measurement method without marks based on mechanical splicing. First, the camera calibration method based on photogrammetry is used to reconstruct the high precision 3D coordinates of the target on the calibration board. By tracking the position of the encoded target, the rotation matrix corresponding to different angles of the turntable is established, and the direction vector of the rotation axis and the fixed point coordinates on the axis are solved. Then the synchronous calibration of the rotation axis and the camera is completed. Second, based on the accurate calibration of poses of two rotation axes, the rotation mosaic matrix is constructed by using the turntable angle to realize the rough registration of multi-view point clouds. Finally, based on the Normal Iterative Closest Point (NICP) algorithm, the fine registration of the point clouds is completed. Experimental results show that the angle error between the two rotation axes calibrated by the target tracking method is 0.023° lower than that of the traditional standard ball fitting method. After calibration, the average size error of the standard ball is less than 0.012 mm. In the automatic measurement of small-size parts, the point cloud splicing effect of the mechanical splicing method after fine registration is similar to that of the mark splicing method, and the splicing stability is higher. The mechanical splicing method is suitable for the 3D topography measurement of small-size parts where the marks cannot be pasted.

Analysis of key technologies and progress of high-power narrow linewidth fiber laser based on the multi-longitudinal-mode oscillator seed source
SUN Shi-hao, ZHENG Ye, YU Miao, LI Si-yuan, CAO Yi, WANG Jun-long, WANG Xue-feng
 doi: 10.37188/CO.2023-0074
Abstract(0) FullText HTML(0) PDF 3194KB(0)

Narrow linewidth fiber lasers, which are based on a oscillator seed source with multiple longitudinal-mode, offer substantial advantages for engineering applications and space-limited platform payloads. Additionally, they are considered ideal sub-modules for high-power spectral combinations. The time domain of this type of seed is unstable due to the self-pulse effect, causing significant spectral broadening and stimulated Raman scattering effects during the amplification process, which limits their further application. This paper introduces four commonly used narrow linewidth seeds. The mechanism and suppression methods of the self-pulse effect in multi-longitudinal mode oscillator seeds were analyzed. Critical technologies essential for the optimization and relevant progress of the multi-longitudinal-mode oscillator seed source and amplifier stages are discussed in detail. A future development outlook is also presented. This paper serves as a useful reference for the design of narrow linewidth fiber lasers based on the multi-longitudinal-mode oscillator seed source.

Effect of atmospheric turbulence on imaging quality of high-resolution remote sensing satellites
MAO Hong-min, DING Zhi-ya, YANG Yan-yan, JIANG Su-qi, PENG Jian-tao, CAO Nan, HU Li-fa, CAO Zhao-liang
 doi: 10.37188/CO.2023-0083
Abstract(0) FullText HTML(0) PDF 4763KB(0)

Remote sensing satellites play an crucial role in both national defense and civil exploration. However, the imaging quality of high-resolution remote sensing satellites is significantly affected by atmospheric turbulence. This paper focuses on the impact of camera aperture, satellite orbit altitude and atmospheric turbulence intensity on the imaging quality of space cameras during remote sensing satellite Earth detection. Firstly, the turbulence wavefront simulation method based on the spherical wave model and Kolmogorov turbulence theory is analyzed. Subsequently, the disturbed wavefront, impacted by the camera aperture, satellite orbit height and atmospheric turbulence intensity, is analyzed, and a universal formula is derived. In addition, an equation for imaging resolution, taking into account aperture, satellite orbit height and atmospheric coherence length, is developed. Finally, this study examines the effect of atmospheric turbulence on the modulation transfer function (MTF). The analysis focuses on the relative error of MTF concerning camera aperture, satellite orbit height and atmospheric coherence length, with reference to an MTF value of 0.15. This study provides a theoretical basis for designing, analyzing, and assessing high-resolution remote sensing satellites.

Integrated Nitride optoelectronic chip for motion detection and visible light communication
FENG Xiao-xiao, HAN Ming-yu, CHEN Mei-peng, FANG Qian, WANG Yong-jin, LI Xin
 doi: 10.37188/CO.2023-0028
Abstract(102) FullText HTML(51) PDF 4652KB(90)

The movement of objects is everywhere in nature. With the rapid development of smart vehicle and 6G mobile communications, the demand for highly Integrated Sensing and Communication (ISAC) devices with communication and motion sensing is increasing. Based on the coexistence of luminescence and detection characteristics of GaN multiple quantum wells, an integrated optoelectronic chip based on the epitaxial GaN multiple quantum wells material on sapphire substrate with sensitive motion detection and visible light communication. The transmitter of the optoelectronic chip transmits a visible light signal in blue band to the moving target object. The visible light signal modulated by the motion of the target object is reflected back to the receiver of the chip to stimulate the changing photocurrent. By analyzing the changing photocurrent, the motion of the target object rotating at different speeds can be detected. The change period of the photocurrent curve is consistent with the rotation period of the target object. We also study the optoelectronic characteristics and the visible light communication performance of the optoelectronic chip. This chip can be used as transceiver terminal of visible light communication system and can also process and transmit the motion detection signals collected by the chip. The optoelectronic chip based on GaN multiple quantum wells materials is a highly integrated ISAC terminal device with application value.

High-performance transparent all-carbon photodetectors based on the semiconducting single-walled carbon nanotube/fullerene heterojunctions
ZHANG Luo-xi, YIN Huan, CHEN Yue, ZHU Ming-kui, SU Yan-jie
 doi: 10.37188/CO.2022-0243
Abstract(133) FullText HTML(98) PDF 4200KB(127)

Taking advantage of the high absorption coefficient, excellent photoelectric properties, and high carrier mobility of Single-Walled Carbon NanoTubes (SWCNTs), high-performance, transparent, all-carbon Field-Effect Transistor (FET) photodetector has been constructed with a high transmittance more than 80% in the visible light band, in which semiconducting SWCNT (sc-SWCNT)/fullerene (C60) heterojunctions as the channel materials, patterned metallic SWCNT film as source/drain electrodes, graphene oxide (GO) as the dielectric layer, and Indium Tin Oxide (ITO) as a transparent gate electrode. The electrical test results show that the photodetector exhibits a strong gate-tunable characteristics, and achieves a broadband spectral response from 405 to 1064 nm in the visible-near infrared spectral region. Under 940 nm illumination with a light density of 5 mW/cm2, the maximum photoelectric responsivity of 18.55 A/W and a specific detectivity of 5.35×1011 Jones can be achieved.

Development of a doppler asymmetric spatial heterodyne interferometer for ground-based wind field detection at the 557.7 nm wavelength
LIU Huan, JIANG Lun, ZHANG Xiao-fei, FU Yun, SONG Yan-song, TONG Shou-feng, LIU Xian-zhu
 doi: 10.37188/CO.EN-2022-0018
Abstract(124) FullText HTML(65) PDF 5574KB(168)

A ground-based Doppler Asymmetric Spatial Heterodyne (DASH) interferometer with a high Signal-to-Noise Ratio (SNR) and large etendue (AΩ) with thermal compensation was developed to detect wind field information in the middle atmosphere. The detailed parameters and index of the DASH interferometer were developed for the 557.7 nm oxygen airglow spectral line. The system was designed with an expanded Field Of View (FOV) and thermal compensation. The half-FOV angle reached 2.815°, the etendue was 0.09525 cm2sr, and the system’s SNR was approximately 113.75. Through the thermal compensation design, the final optical path difference with temperature variation (dΔd0/dT) was only 2.224×10−7mm/°C. The optical system was designed and optimized according to the corresponding parameters. Image-side telecentric and bilateral telecentric optical system structures were used in the entrance optics and exit optics, respectively, and parameters such as telecentricity and distortion met the detection requirements. To verify the design results, a ground-based DASH interferometer experimental platform was constructed, and indoor and outdoor ground-based experiments were conducted. In the final experiment, clear interference fringes were obtained, which proves that the system design results of the DASH interferometer are reasonable, and the system’s SNR and etendue meet the detection requirements.

Double-slot ultra-compact polarization beam splitter based on asymmetric hybrid plasmonic structure
WANG Fang, LIU Hua, MA Tao, MA Shou-dao, LIU Yu-fang
 doi: 10.37188/CO.EN.2022-0028
Abstract(252) FullText HTML(172) PDF 4526KB(215)

To improve the extinction ratio of a polarization beam splitter, we propose a dual-slot ultra-compact polarization splitter (PBS) consisting of a hybrid plasma Horizontal Slot Waveguide (HSW) and a silicon nitride hybrid Vertical Slot Waveguide (VSW). The coating material is silicon dioxide, which can prevent the oxidation of the mixed plasma and also facilitate integration with other devices. The mode characteristics of the HSW and VSW are simulated by using the Finite Element Method (FEM). At suitable HSW and VSW widths, the TE polarization modes in HSW and VSW are phase-matched, while the TM polarization modes are phase mismatched. Therefore, the TE mode in an HSW waveguide is strongly coupled with a VSW waveguide by adopting a dual-slot, while the TM mode directly passes through the HSW waveguide. The results show that PBS achieves an Extinction Ratio (ER) of 35.1 dB and an Insertion Loss (IL) of 0.34 dB for the TE mode at 1.55 μm. For the TM mode, PBS reached 40.9 dB for ER and 2.65 dB for IL. The proposed PBS is designed with 100 nm bandwidth, high ER, and low IL, which can be suitable for photonic integrated circuits (PICs).

Decoherence of temporal quantum correlation in electrically controllable quantum-dots molecules
XIE Jia-ling, YAN Kai, TAN Jia, CAO Zhao-liang, HAO Xiang
 doi: 10.37188/CO.EN-2022-0025
Abstract(205) FullText HTML(163) PDF 3972KB(209)

The decoherence of temporal quantum correlation is explored in a voltage-controlled quantum dots molecule coupled to a cavity. The temporal correlation in the optoelectronic hybrid system is studied based on Leggett-Garg inequalities. The inequality violations can be interpreted as the existence of temporal quantum correlation during dynamical evolution. The temporal quantum correlation is enhanced by its electron tunnel’s strength and cavity frequency detuning. It is found that there is no temporal quantum correlation in the regions where the values of spatial quantum correlation are zero and the maximal violations occur in conditions with high values of quantum correlation. In contrast, the spatial quantum coherence can still exsit when the value of temporal quantum correlation is zero. The method of open quantum system dynamic is used to study the effect of reservoir memory on temporal quantum correlation. The temporal quantum correlation can be suppressed due to the spontaneous decay of the quantum dots and cavity leakage. These results are helpful for quantum information processing technology in hybrid quantum systems.

Design of all-optical half-adder based on nonlinear effect and linear interference effect
YANG Jian-ye, WU Rong, ZHANG Hao-chen
 doi: 10.37188/CO.EN.2022-0029
Abstract(67) FullText HTML(45) PDF 3371KB(135)

An all-optical half-adder is designed by combining the nonlinear effect and linear interference effect of photonic crystals. By dividing the light source into two parts equally, the half adder AND gate and XOR gate are designed separately. The nonlinear effect is used to realize the AND gate with high contrast, and the linear interference effect is used to realize the XOR logic, so that the overall response speed of the device is improved. In this design structure, the device only has threshold requirements for the signal light source power. When the signal power is greater than 51.4 mW/μm2, it has stable output and strong anti-interference ability. The designed contrast of the half adder carry output port is 20.69 dB, and the output port contrast is 20.13 dB. The data transfer rate is 0.75 Tbits/s and the occupied area is 623 μm2.

Method for the simultaneous measurement of waveguide propagation loss and bending loss
FAN Zuo-wen, JIA Lian-xi, LI Zhao-yi, ZHOU Jing-jie, CONG Qing-yu, ZENG Xian-feng
 doi: 10.37188/CO.EN.2022-0027
Abstract(102) FullText HTML(72) PDF 3587KB(137)

The propagation loss of a waveguide is a key indicator to evaluate the performance of an integrated optical platform. The commonly used cut-back method for measuring propagation loss requires the introduction of the spiral test structure. In order to remove bending loss, the bending radius is usually designed to be larger but this consequently has a larger footprint. In this paper, we suggested a method to simultaneously measure the propagation loss and bending loss of waveguides with a cut-back structure. According to simulations, the bending loss can be exponentially fitted with the bending radius, which can be further simplified as linear fitting between the natural logarithm of the bending loss and bending radius. A genetic algorithm was used to fit the insertion loss curve of the cut-back structure and the propagation losses and bending loss were calculated. With this method, we measured a cut-back structure of lithium niobate waveguide and got a propagation loss of 0.558 dB/cm and a bending loss of 0.698 dB/90° at a radius of 100 μm and wavelength of 1550 nm. Using this method, we can simultaneously measure waveguide propagation loss and bending loss while mitigating the footprint.

Stabilization method of photoelectric platform based on double speed loop observer
GAO Wen-rui, CUI Hui-min, YIN Kui-ying, ZHAO Jing-jing
 doi: 10.37188/CO.2023-0048
Abstract(61) FullText HTML(30) PDF 4126KB(83)

To achieve high-precision and stable tracking performance, a novel disturbance observer for the photoelectric platform based on dual velocity loops is designed. This method aims to minimize the impact of internal friction torque, external carrier disturbances and sensor noise, thereby enhancing the dynamic response performance of the system. Firstly, the mathematical model of double speed-loop is established. By analyzing the signal spectrum and response performance of various sensors, we have chosen the circular grating sensor with low noise and short delay to replace the traditional measuring machine for closing the inner speed loop. Moreover, the Fiber Optic Gyro (FOG) is utilized for the feedback device of the outer speed loop. Then, a disturbance observer is designed based on the gyro speed signal to observe the disturbance compensation residual in the inner speed loop and the outer carrier disturbance signal, while the feed-forward compensation is performed. The experimental results demonstrate that the double speed loop observer control method can reduce the system regulation time to 45% of the original. When subjected to sinusoidal disturbance signals with varying amplitudes (0.25° to 2°) and frequencies (0.25 Hz to 2 Hz), this method effectively improves the system's ability to suppress disturbances and increases the isolation degree from the initial 20.9 dB to 30 dB. The disturbance observer with double speed loops meets the system requirements of rapid response, stable tracking, high precision and strong anti-disturbance ability of the photoelectric tracking platform.

Expanding the angular bandwidth of augmented reality coupling element volume holographic grating by multiplexing equal-period and variable-inclination-angle interference fringes
PENG Can-fu, LI Wen-hao, ZHANG Wei, CHEN Xing-shuo, LIU Rui, ZHANG Jing-ying, LI Wen-long
 doi: 10.37188/CO.2023-0050
Abstract(76) FullText HTML(52) PDF 5025KB(96)

To improve the field of view of the near-to-eye display imaging system by using the optical waveguide scheme, we propose a method of multiplexing interference fringes with equal periods and variable inclination angles to expand the angular bandwidth of the volume holographic grating for augmented reality glasses coupling element. With this method, the range of incident angles after the expansion mathes the Bragg condition, and the influence of the periodic change on the diffraction angle of the incident light is eliminated, thereby improving the angular response range of the coupling element volume holographic grating and reducing the stray light introduced by grating diffraction. The rigorous coupled wave analysis theory is used to simulate the volume holographic grating multiplexing three interference fringes with equal period and variable inclination angles. Under the TE and TM polarization states at the wavelength of 530 nm, the angular bandwidth of the multiplexed volume holographic grating is 3.6° and 3.3°, respectively. The angular bandwidth of the multiplexed volume holographic grating is twice as large as that of the volume holographic grating recorded with a single interference fringe. This method is expected to break the limitation of the volume holographic grating material on the angular bandwidth of the grating, and can be used to expand the field of view of the near-to-eye display imaging system to achieve lightweight, high-efficiency, large-field-of-view, and low-stray-light augmented reality glasses.

Relationship between the preparation process of the graphene/silicon hetero-junction photodetector and its voltage-current characteristics
YANG Ya-xian, ZHANG Guo-qing
 doi: 10.37188/CO.2022-0259
Abstract(159) FullText HTML(99) PDF 4137KB(140)

Wet transferring two-dimension (2D) material to a semiconductor substrate is a common method to prepare a hetero-junction photodetector. When preparing to wet transfer a hetero-junction, different preparation details have significant effects on the properties of the hetero-junction formed by the 2D materials and semiconductors. In this paper, a series of identical Gr/Si hetero-junction devices were prepared by the wet transfer method and the relationship between its preparation technique and the voltage-current characteristics was studied in detail. The experimental results show that the gradient drying process can significantly reduce the dark current of the Gr/Si hetero-junction photodetector, the optimal drying temperature peak is 170 °C, and the leakage current basically no longer changes above 170 °C. The surface impurities and residual water in the inter-layer of Gr/Si van der Waals hetero-junction has a significant effect on the leakage current of the hetero-junction. The selective etching and annealing process of a Gr/Si van der Waals hetero-junction can also greatly reduce the leakage current. Therefore, a suitable drying process, selective etching process and annealing process are each necessary in the preparation of a Gr/Si hetero-junction photodetector. These results can give reference to the fabrication of two-dimensional material hetero-junction devices by the wet transfer method.

Isolation of single wavelength laser communication terminals
GAO Wei-rao, DONG Ke-yan, JIANG Lun
 doi: 10.37188/CO.2022-0253
Abstract(80) FullText HTML(65) PDF 6100KB(100)

For data communication between single wavelength laser communication terminals, good isolation between signal transmission and reception is the key to establishing duplex bidirectional laser communication. In this paper, with respect to the transmission and reception scheme of a single laser wavelength laser communication terminal and its overall communication performance, the influence of the surface roughness and contamination level of key components on the isolation performance of the laser communication terminal is analyzed. The model parameters are derived from Harvey model and ABg model, and the designed scheme is analyzed using TracePro software. When the surface roughness or contamination level of λ/2 wave plate, λ/4 wave plate and optical antenna structure in the signal transmission channel is improved, the backscattering caused by these elements will reduce the isolation performance in the signal transmission channel. At the same time, the measurement result of laser communication terminal isolation is 77.86 dB, which is basically consistent with the software simulation result of 78.35 dB. This can be applied in laser communication system.

Design and achievement of a device for high-precision ammonia gas detection based on laser spectroscopy
YANG Tian-yue, GONG ting, GUO Gu-qing, SUN Xiao-cong, TIAN Ya-li, QIU Xuan-bing, HE Qiu-sheng, GAO Xiao-ming, LI Chuan-liang
 doi: 10.37188/CO.2023-0023
Abstract(110) FullText HTML(55) PDF 4061KB(119)

Ammonia emission will cause harm to the environment and human health, so it is particularly important that the ammonia concentrations are measured with high precision. Off-Axis Integrating Cavity Output Spectroscopy (OA-ICOS), which has the advantages of high sensitivity and high response speed, is used to design a high-precision ammonia detection device. The gas absorption cell is composed of two high reflection mirrors with a reflectivity of 99.99%, and the base length of the optical resonator is 30 cm. Finally, an optical path of nearly 3000 m was realized. The Distributed Feedback Laser (DFB) with a central wavelength of 1528 nm is tuned to 6548.611 cm−1 and 6548.798 cm−1. The concentration of NH3 is changed from 1×10 −5 to 5×10−5 and is detected under an atmospheric pressure of 18.6 kPa at room temperature. The measurement results show that the linear fit R2 between NH3 concentration and signal amplitude can reach 0.99979. The Allan variance is used to analyze the experimental data, and the minimum detection limit of the system can reach 7×10−9 at 103 s. The experimental results show that the detection device has good stability and high sensitivity, meets the demand for the high-precision detection of ammonia gas, and also provides technical experience for the domestic independent research and development of high-precision detection equipment for trace gases.

Design of an optical power splitter with adjustable split ratio
XIE Feng, ZHU Shuo-long, ZHANG Zhen-rong
 doi: 10.37188/CO.2023-0038
Abstract(138) FullText HTML(81) PDF 4347KB(122)

Traditional analytical theory design scheme faces problems, such as high computational complexity, limited analytical solution, and high time-consumption. To cambat these issues, based on the design of traditional optical devices, a scheme for designing an optical power splitter with adjustable split ratio according to the reverse design method is proposed. In a compact region of 1.92 μm×1.92 μm, Ge2Sb2Se4Te1(GSST) is introduced to change the refractive index distribution of the device. The direct binary search algorithm is utilized to search the optimal state distribution of GSST in crystalline and amorphous states. A T-shaped optical power splitter with adjustable split ratio is designed and implemented for the same device structure. The initial structure, split ratio, phase change material region state distribution, manufacturing tolerance, and light field distribution of the device are simulated and analyzed. The results show the minimum relative errors of the designed optical power splitters with three splitting ratios of 1∶1, 1.5∶1 and 2∶1 between wavelengths 1530 nm and 1560 nm are 0.004%, 0.14% and 0.22%, respectively. The maximum fluctuations of the transmission curve in the manufacturing tolerance range are 0.95 dB, 1.21 dB and 1.18 dB, respectively. The splitter has a compact structure and great potential for applications in optical communication and information processing.

Fiber bragg grating accelerometer based on flexure hinge and bearing
SONG Ying, ZHANG Hao-ran, LI Jian-zhi, SHEN Bo-hao, LIU Zhan-jian
 doi: 10.37188/CO.2022-0252
Abstract(152) FullText HTML(60) PDF 6438KB(128)

We develop a fiber Bragg grating accelerometer based on a bearing and flexure hinge for the measurement of medium-high frequency vibration signals. The mathematical model between its natural frequency and sensitivity and structural parameters is derived based on a mechanical model, and the structural design is optimized based on the theoretical analysis results. With these prerequisites, the sensor was fabricated. Ultimately, its dynamic characteristics are validated using a finite element simulation and vibration experiment. The results show that both its operating frequency range and acceleration sensitivity are 10−1200 Hz and 17.25 pm/g. In addition, this proposed sensor has some advantages such as an error of less than 0.3 g, a good linearity of greater than 0.99, a repeatability error of 2.33%, and it is free of temperature.

Accurate measurement of mouse eye aberration combined with optical mask modulation
WANG Liang, KONG Wen, HE Yi, HUANG Jiang-jie, SHI Guo-hua
 doi: 10.37188/CO.2023-0051
Abstract(67) FullText HTML(43) PDF 4318KB(92)

In order to solve the problem of aberration detection failure caused by double-layer reflected light of the fundus retina in standard animal model mouse during wavefront detection, a mouse eye aberration measurement technique combined with optical mask modulation was proposed to improve the accuracy of wavefront aberration measurement. First, according to the key parameters of mouse retina, we established the optical system model of mouse eye wavefront aberration detection and performed optical simulations. Then, the effects of optical masks with different apertures on the reflection beam of the non-target layer of the retina were analyzed and compared, and then the parameters of the optical mask and the experimental plan were determined. Finally, the wave front aberration detection system of the mouse eye was established, and the wavefront aberration of the mouse eye was measured in vivo. The experimental results show that the optical mask with 0.5 mm aperture can reduce the root mean square error of mouse eye wavefront aberration measurement by 74.9%, which is similar to the shielding effect of non-target layer reflected in 80% of the theoretical simulation. It can effectively block the reflected light from the non-target layer of the mouse retina, improve the detection accuracy of the wavefront aberration of the mouse eye, and lay a foundation for the further realization of high-resolution imaging of the mouse eye.

Multi-channel phase measurement system for the space laser interferometry
ZHANG Qiang-tao, LIU He-shan, LUO Zi-ren
 doi: 10.37188/CO.2022-0258
Abstract(165) FullText HTML(88) PDF 6486KB(126)

In the space gravitational wave detection Taiji mission, a heterodyne laser interferometer is used to detect gravitational wave signals in the middle and low frequency bands. In the Taiji mission, the laser interferometry system is composed of multi-channel interferometers, which involves the phase acquisition and readout of multiple sets of the interference signals. Therefore, the multi-channel phase measurement system is one of the key core technologies of the space laser interferometry. In this paper, a multi-channel phase measurement system is proposed, designed and tested based on the requirements of the Taiji mission and its ground-based laser interferometry experiments. First, the hardware and software design of the multi-channel phase measurement system is given, including hardware architecture design, phase measurement algorithm based on digital phase-locked loop and its implementation on FPGA, software architecture design, etc. Second, a time-domain functional tests of the multi-channel phasemeter are performed, which includes the phase accuracy and linearity. The results show that the dynamic and static phase linearity and accuracy of the multi-channel phase measurement system under different working conditions are good. Finally, the frequency domain noise tests of different channels at different frequencies and different amplitudes are carried out. The results show that the phase noise level of the multi-channel phase meter designed in this paper is better than \begin{document}$ 2{\text{π}} {\text{µ}} {\rm{rad}}/\sqrt{{\rm{Hz}}} $\end{document} in the frequency band of 0.1 mHz−1 Hz. There is good consistency between different channels, and the phase noise introduced by channel differences or ADC chip differences is negligible in the target frequency band. For any interference signal with a frequency between 5−25 MHz, the phasemeter can meet the requirements within the target frequency band. Therefore, the multi-channel phase measurement system meets the requirements of space gravitational wave detection and ground-based interference experiments. At the same time, the research results of this paper also provide an experimental basis for expanding the phase measurement system with more channels in the future.

Measurement and suppression of forward stray light for spaceborne gravitational wave detection
LENG Rong-kuan, WANG Shang, WANG Zhi, CHEN Zhi-wei, FANG Chao
 doi: 10.37188/CO.2022-0251
Abstract(159) FullText HTML(115) PDF 5538KB(132)

In the spaceborne gravitational wave interferometric detection, the problem of stray light has received long-term attention. The laser light emitted by the local interferometer produces backward coherent stray light when passing the telescope while the radiation from space that is incident to the spacecraft produces forward incoherent stray light. Forward incoherent stray light has received less attention at this point, but it is a necessary factor of gravitational-wave telescope design. Therefore, this paper studies stray light produced by space gravitational wave telescopes in orbit. First, the annual solar angle is calculated according to the orbital data of the three-star satellite formation of the Taiji Project, and the solar radiation around the 1064 nm band is evaluated. The baffle shadowing function is derived, which satisfies the requirement for the baffle design. The telescope is then modeled optically and mechanically and scatter measurements are conducted for critical optical components. Finally, the stray light reaching the pupil of the telescope is determined based on the energy of the incident sunlight. The results show that when the angle between the incident light and the optical axis is 60°, the stray radiation at the exit pupil is 3.9×10−12 W, and the corresponding point source transmittance is 8.7×10−9 which meets the requirement for space gravitational waves to detect extremely low levels of stray light.

Infrared small target detection via L1−2 spatial-temporal total variation regularization
ZHAO De-min, SUN Yang, LIN Zai-ping, XIONG Wei
 doi: 10.37188/CO.2022-0229
Abstract(91) FullText HTML(62) PDF 9528KB(111)

To solve the high false alarms caused by complex background clutters in infrared small-target detection, a novel detection method based on \begin{document}${L_{1 - 2}}$\end{document} spatial-temporal total variation regularization is proposed. First, the input infrared image sequence is transformed into a Spatial-Temporal Infrared Patch-Tensor (STIPT) structure. This step can associate the spatial and temporal information by using the high dimensional data structures in the tensor domain. Then, weighted Schatten p-norm and \begin{document}${L_{1 - 2}}$\end{document} spatial-temporal total variation regularization are incorporated to recover the low-rank background component to preserve the strong edges and corners, which can improve the accuracy of sparse target component recovery. Finally, the STIPT structure can be transformed into an infrared image sequence by the inverse operator, and an adaptive threshold segmentation is used to obtain the real target. The method is verified using a contrast test with other five methods, and the experimental results show that the false alarm rate by this method decreases to 71.4%, 71.7%, 68.5%, 74.3% and 20.47% compared with the Maxemeidan, Tophat, LIRDNet, DNANet and WSNMSTIPT algorithms. The time cost also decreased to 42.4%, 82.9% and 28.7% of that of the Maxemeidan, DNANet and WSNMSTIPT. The extensive experimental results demonstrate the superiority of this method in detection performance, which can greatly improve the accuracy and efficiency of target detection with complex background clutters.

Multispectral demosaicing method based on an improved guided filter
QI Hai-chao, SONG Yan-song, ZHANG Bo, LIANG Zong-lin, YAN Gang-qi, XUE Jia-yin, ZHANG Yi-qun, REN Bin
 doi: 10.37188/CO.2022-0231
Abstract(106) FullText HTML(60) PDF 1867KB(130)

In order to better preserve high-frequency information in demosaicing multispectral images, we propose a new demosaicing method for multispectral images based on an improved guided filter. Firstly, the strong correlation between adjacent pixels based on the autoregressive model is constructed, gradually estimates the model parameters at each pixel, and the optimal estimation value is obtained by minimizing the estimation error in the local window, interpolates the sampling dense band G, and generates high-quality guide images. The windowed intrinsic variation coefficient is then introduced into the penalty factor to obtain a weighted guide filter with edge sensing ability and to reconstruct the remaining sparse sampling bands. Finally, the CAVE dataset and the TokyoTech dataset are used for simulation. The experimental results show that compared with the mainstream five-band multispectral image demosaicing method, the peak signal-to-noise ratio and structure similarity of the reconstructed image in the CAVE dataset and the TokyoTech dataset are improved by 3.40%, 2.02%, 1.34%, 0.30% and 6.11%, 5.95%, 2.28%, 1.42%, respectively. The local structure and color information of the original image are also better preserved, and the edge artifacts and noise are reduced.

Lightweight YOLOv5s vehicle infrared image target detection
LIU Yan-lei, LI Meng-zhe, WANG Xuan-xuan
 doi: 10.37188/CO.2022-0254
Abstract(268) FullText HTML(189) PDF 6346KB(145)

Vehicle infrared image target detection is an important way of road environment perception for autonomous driving. However, existing vehicle infrared image target detection algorithms have defects, such as low memory utilization, complex calculation and low detection accuracy. In order to solve the above problems, an improved YOLOv5s lightweight target detection algorithm is proposed. Firstly, the C3Ghost and Ghost modules are introduced into the YOLOv5s detection network to reduce network complexity. Secondly, the αIoU loss function is introduced to improve the positioning accuracy of the target and the networks training efficiency. Then, the subsampling rate of the network structure is reduced and the KMeans clustering algorithm is used to optimize the prior anchor size to improve the ability to detect of small targets. Finally, coordinate attention and spatial depth convolution modules are respectively introduced into the Backbone and Neck to further optimize the model and improve the feature extraction of the model. The experimental results show that compared with the original YOLOv5s algorithm, the improved algorithm can compress the model size by 78.1%, reduce the number of parameters and Giga Floating-point Operations Per Second by 84.5% and 40.5% respectively, and improve the mean average precision and detection speed by 4.2% and 10.9%, respectively.

Image super-resolution reconstruction with multi-scale attention fusion
CHEN Chun-yi, WU Xin-yi, HU Xiao-juan, YU Hai-yang
 doi: 10.37188/CO.2023-0020
Abstract(208) FullText HTML(95) PDF 6128KB(139)

The resolution of optical imaging is limited by the diffraction limit, system detector size and many other factors. To obtain images with richer details and clearer textures, a multi-scale feature attention fusion residual network was proposed. Firstly, shallow features of the image were extracted using a layer of convolution and then the multi-scale features were extracted by a cascade of multi-scale feature extraction units. The local channel attention module is introduced in the multi-scale feature extraction unit to adaptively correct the weights of feature channels and improve the attention to high frequency information. The shallow features and the output of each multi-scale feature extraction unit were used as hierarchical features for global feature fusion reconstruction. Finally, the hight-resolution image was reconstructed by introducing shallow features and multi-level image features using the residual branch. Charbonnier loss was adopted to make the training more stable and converge faster. Comparative experiments on the international benchmark datasets show that the model outperforms most state-of-the-art methods on objective metrics. Especially on the Set5 data set, the PSNR index of the 4× reconstruction result is increased by 0.39 dB, and the SSIM index is increased to 0.8992, and the subjective visual effect of the algorithm is better.

Super-resolution reconstruction for colorectal endoscopic images based on a residual network
ZHENG Yue-kun, GE Ming-feng, CHANG Zhi-min, DONG Wen-fei
 doi: 10.37188/CO.2022-0247
Abstract(163) FullText HTML(129) PDF 6423KB(128)

In this paper, an image super-resolution reconstruction multi-scale algorithm based on a residual attention network (SMRAN) is proposed to solve the problems caused by low resolutions, less texture information and blurred details in colorectal endoscopic images. Images from the colorectal polyp endoscope image dataset PolypsSet are selected as the raw data for these experiments. A convolutional network is built to extract the shallow features of the low-resolution image and a Res-Sobel block is designed to enhance its edge features. A multi-scale feature fusion block MEB is designed by introducing convolution kernels of different sizes to adaptively extract image features of different scales and obtain effective image information. The Res-Sobel block and multi-scale feature fusion module block MEB are connected through the residual attention network. Finally, a high-resolution image is reconstructed at the sub-pixel convolution layer. When the amplification factor is ×4, the performance of the proposed algorithm on the test set are as follows: the peak signal-to-noise ratio (PSNR) is 34.25 dB and the structural similarity (SSIM) is 0.8675. Compared with the traditional bicubic interpolation algorithm and commonly used deep learning algorithms such as SRCNN and RCAN, the proposed SMRAN algorithm shows better super-resolution reconstruction results on colorectal endoscopic images.

Research progress of miniature head-mounted single photon fluorescence microscopic imaging technique
FU Qiang, ZHANG Zhi-miao, ZHAO Shang-nan, LIU Yang, DONG Yang
 doi: 10.37188/CO.2023-0007
Abstract(109) FullText HTML(51) PDF 8052KB(131)

Miniature head-mounted single-photon fluorescence microscopy is a breakthrough approach for neuroscience research that has emerged in recent years. It can image the neural activity of freely moving vivo animals in real time, providing an unprecedented way to access neural signals and rapidly enhancing the understanding of how the brain works. Driven by the needs of brain science research, there have been many types of miniature head-mounted single-photon fluorescence microscopes, such as high-resolution imaging, wireless recording, 3D imaging, two-region imaging and two-color imaging. In order to have a more comprehensive understanding of this new optical neuroimaging technology, we classify its technologies according to the imaging field of view, introduce the characteristics of different types of micro-head-mounted single-photon fluorescence microscopes reported so far, and focus on the optical system scheme and optical performance parameters used. The advantages and disadvantages of different schemes are analyzed and compared and the future direction of development is described to provide reference for the practical application of brain science researchers.

Review of the cavity-design of high-energy thin-disk laser multi-pass amplifiers
CHEN Yi, SUN Jun-jie, YU Jing-hua, YAO Zhi-huan, ZHANG Yi-wen, YU De-yang, HE Yang, ZHANG Kuo, PAN Qi-kun, CHEN Fei
 doi: 10.37188/CO.2023-0009
Abstract(225) FullText HTML(138) PDF 6648KB(153)

In order to clarify the cavity design methods of thin-disk multi-pass amplifiers, we summarize the different types of thin-disk multi-pass amplifiers and concludes that there are four fundamental design concepts: (1) 4f relay imaging, (2) resonant cavity design/optical Fourier transform, (3) near-collimated beam transmission, and (4) others. Each amplifier design method is described and the current status of its research is listed in as much detail as possible. By comparing the four types of disk multi-pass amplifiers, it is found that the varying methods have distinct advantages and disadvantages. 4f relay imaging requires a vacuum environment to avoid gas ionization at the focal point, making the mechanics and adjustment more difficult; the resonant cavity design/optical Fourier transform concept multi-pass amplifier has a small spot at the mirrors, making it more suitable for lower energy multi-pass amplifiers; the near collimated beam transmission method has great development potential because it does not require a vacuum environment, but accurately controlling the surface shape of the thin-disk is difficult while the laser is operating. Therefore, from the perspective of laser design, it is necessary to continue to optimize the design of the thin-disk multi-pass amplifier to realize the diversification of application scenarios and the sustainable expansion of output energy.

Recent advances in metasurfaces for polarization imaging
ZHOU Jun-zhuo, HAO Jia, YU Xiao-chang, ZHOU Jian, DENG Chen-wei, YU Yi-ting
 doi: 10.37188/CO.2022-0234
Abstract(772) FullText HTML(448) PDF 6268KB(482)

Polarization imaging, a novel photoelectric detection technology, can simultaneously acquire the contour information and polarization features of a scene. For specific application scenarios, polarization imaging has the excellent ability to distinguish different objects and highlight their outlines. Therefore, polarization imaging has been widely applied in the fields of object detection, underwater imaging, life science, environmental monitoring, 3D imaging, etc. Polarization splitting or the filtering device is the core element in a polarization imaging system. The traditional counterpart suffers from a bulky size, poor optical performance, and being sensitive to external disturbances, and can hardly meet the requirements of a highly integrated, highly functional, and highly stable polarization imaging system. A metasurface is a two-dimensional planar photonic device whose comprising units are arranged quasi-periodically at subwavelength intervals, and can finely regulate the amplitude and phase of the light field in different polarization directions. Polarization devices based on metasurface are featured with compactness, lightweight and multi-degree freedom, offering an original solution to ultracompact polarization imaging systems. Targeted at the field of polarization imaging, this paper illustrates the functional theory, developmental process and future tendency of related metasurfaces. We discuss the challenges and prospect on the future of imaging applications and systematic integrations with metasurfaces.

Design of all-optical logic gate based on two-dimensional photonic crystal
Rong Wu, 张皓辰 张, 建业 杨
 doi: 10.37188/CO.EN.2023-0014
Abstract(4) PDF 695KB(0)
By embedding a line defect in a two-dimensional photonic crystal and using linear interference effect and waveguide coupling, an XNOR gate and NAND gate structure based on two-dimensional photonic crystal is designed. The band structure of the two-dimensional photonic crystal is analyzed by the plane wave expansion method. The finite-difference time-domain method and the linear interference effect are used to simulate the stable electric field diagram and the normalized power of the XNOR gate and the NAND gate on the Rsoft platform. The simulation results show that the designed XNOR gate has a contrast of 29.5 dB, a response time of 0.073 ps, and a data transmission rate of 13.7 Tbit / s. The designed NAND gate has a contrast of up to 24.15 dB, a response time of 0.08 ps, and a data transmission rate of 12.5 Tbit / s. These parameters indicate that the designed structure has high contrast, short response time and fast data transmission rate.
SBS in double-clad thulium-doped fiber amplifier
庆敏 刘, 慧杰 孙, 尚林 侯, 景丽 雷, gang wu, zuyong Yan
 doi: 10.37188/CO.EN.2023-0011
Abstract(4) PDF 1511KB(0)
The influence of stimulated Brillouin scattering on laser output performance in 2 µm thulium-doped fiber amplifier was analyzed theoretically. The distribution of optical modes, the effective refractive index, the effective mode field area and the normalized frequency of the double-clad thulium-doped fiber at 793 nm pump wavelength and 1.9~2.1 µm laser waveband were studied.
 doi: 10.37188/CO.2023-0099
Abstract(4) PDF 730KB(0)
 doi: 10.37188/CO.2023-0094
Abstract(4) PDF 1064KB(0)
On-machine verification technology and application progress of high dynamic range fringe structured light
LIU Ze-long, LI Mao-yue, LU Xin-yuan, ZHANG Ming-lei
 doi: 10.37188/CO.2023-0068
Abstract(4) FullText HTML(2) PDF 7626KB(0)

With the development of industrial manufacturing towards intelligence, precision and integration, on-machine verification of the machining process can provide timely feedback on measurement results, compensate and correct processing parameters, thereby aiding in enhancing machining accuracy and efficiency. Fringe structured light technology is a non-contact measurement method, which has developed rapidly in recent years. It has the characteristics of simple measurement principle, low costs, high measurement accuracy and easy integration, which provides a new solution for on-machine verification. However, the accuracy of structural for on-machine verification is compromised by the convoluted lighting in machining environments and metal parts’ high reflectivity, leading to inaccurate measurements. Applying high dynamic range (HDR) technology to structural light detection enables the measurement of metal parts in complex scenes and reduces the effect of high reflectivity. This paper introduces the measurement principle of structured light and summarizes the challenges of on-machine verification for HDR structured light. Subsequently, this paper provides a comprehensive review of HDR structured light technology. Based on the context of on-machine verification, the HDR technology using hardware equipment and the stripe algorithm are discussed and analyzed, respectively. Following this, different technologies are summarized according to the requirements of on-machine verification. The advantages and disadvantages of various methods are presented, and the applicability of on-machine verification is compared. Finally, the potential applications are analyzed, and the technological prospects will be proposed in combination with the research hotspots of advanced manufacturing technology and precision measurement in recent years.

Mixed lighting based on the linear dimming of three-primary-color LEDs
HUANG Tao, XIA Zhen-ping, PENG Zi-xiong, LIU Yu-jie, LI Chao-chao, GU Min-ming
 doi: 10.37188/CO.2023-0084
Abstract(4) FullText HTML(2) PDF 3810KB(1)

In order to provide high-quality, intelligent, and healthy lighting sources, a linear dimming hybrid lighting system is constructed using three-primary-color LED light sources. An optimization method for dimming and color mixing is proposed. The light chromaticity and light intensity of the mixed light source are set by color temperature and brightness level, which makes the mixed lighting effect more in line with the demand of "human-centric lighting". In the intelligent optimization of the system, the color temperature is converted into CIE \begin{document}$ {u}'{v}' $\end{document} chromaticity coordinates, and the luminance is converted into brightness to make the optimization calculations more accurate. The system adopts the linear dimming method, effectively preventing the health and safety risks caused by light source flicker, and effectively solves the problem of large linear dimming chromaticity drift with an optimization algorithm. Experiments demonstate that the chromatic stability of the mixed light in the hybrid lighting system is maintained within the first step of the CIE \begin{document}${u}'{v}' $\end{document} chromaticity diagram between a color temperature range of 2000 K to 8000 K. Moreover, the system exhibits imperceptible color deviation over the entire range of light intensity adjustments at the corresponding color temperature. This finding also indicate that linear dimming hold a superior edge over pulse-width dimming method in keeping the optical chromaticity stable. Theoretical exploration and experimental results demonstrate that the mixed lighting system is straightforword and practical, with significant practical value.

 doi: 10.37188/CO.2022-0257
Abstract(9) PDF 426KB(0)
目的:腔面光学灾变损伤是导致高功率量子阱半导体激光器阈值输出功率限制的关键因素。通过量子阱混杂技术调整半导体激光器腔面局部区域处有源区材料的带隙宽度,形成对输出光透明的非吸收窗口,可提高激光器输出功率。方法:本文基于InGaAs/AlGaAs高功率量子阱半导体激光器初级外延片,以外延Si单晶层作为扩散源,结合快速热退火法开展了杂质诱导量子阱混杂研究。探索了介质层生长温度、介质层厚度、热处理温度、热处理时间等条件对混杂效果的影响。结果:结果表明,50 nm的650 ℃低温外延Si介质层并结合875 ℃/90 s快速热退火处理可在保证光致发光谱形的同时获得约57 nm波长蓝移量。结论:能谱测试结果发现,Si杂质扩散到初级外延片上波导层是导致量子阱混杂效果显著的关键。 关键词:半导体激光器;量子阱混杂;快速热退火;波长蓝移;光致发光谱
Optimization of structural parameters and fabrication of small blazed angle monocrystalline silicon gratings
XU Hao-Yu, JIANG Yan-Xiu, CHEN Xing-Shuo, WANG Rui-Peng, ZHANG Jing, Bayanheshig
 doi: 10.37188/CO.2023-0056
Abstract(8) FullText HTML(2) PDF 6667KB(5)

In order to meet the requirements of the national synchrotron radiation source, the anisotropic wet-etching technology of small blazed angle monocrystalline silicon grating is studied, and the blazed grating suitable for the medium wave soft X-ray band is prepared. Based on the rigorously coupled wave theory, the structural parameters and process tolerance of the small blazed angle grating are designed. In the crystal alignment process, the crystal orientation of the silicon wafer is determined by ring-preetching, and then the grating mask is aligned with the crystal direction of monocrystalline silicon <111> based on the frequency doubling adjustment method. At the same time, the effect of the photoresist ashing technique and the active agent on the groove quality of the grating is investigated, and the scintillating gratings close to the ideal sawtooth groove shape are successfully prepared by the monocrystalline silicon anisotropic wet etching process. The experimental results show that the blazed angle of the prepared grating is 1°, the linear density is 1200 gr/mm, and the root mean square roughness of the blazed surface is less than 0.5nm. This method can be applied to the fabrication of the medium wave soft X-ray band blazed grating, which can greatly reduce the difficulty and cost of fabrication while achieving high diffraction efficiency.

Structured light depth and phase estimation with light self-limited attention for a hybrid network
ZHU Xin-jun, ZHAO Hao-miao, WANG Hong-yi, SONG Li-mei, SUN Rui-qun
 doi: 10.37188/CO.2023-0066
Abstract(6) FullText HTML(3) PDF 5480KB(7)

Phase retrieval and depth estimation are vital to three-dimensional measurement using structured light. Currently, conventional methods used for structured light analysis have limited efficiency and produce unreliable results. To enhance the reconstruction effect of structured light, this paper proposes a hybrid network for structured light phase and depth estimation based on Light Self-Limited Attention (LSLA). Specifically, a CNN-Transformer hybrid module is constructed and integrated into a U-shaped structure to harness the complementary benefits of CNN and Transformer. The network is assessed comparatively with other networks in tasks related to structured light phase estimation and depth estimation. The outcome of the experimental indicates that the suggested network achieves finer detail processing in phase and depth estimation compared to other networks. Specifically, in structured light phase anddepth estimation, its accuracy improves by 31% and 26%, respectively. Therefore, the proposed network improves the accuracy of deep neural networks in the aforementioned areas.

Stereo matching algorithm based on multi-feature SAD-Census transformation
WU Fu-pei, HUANG Geng-nan, LIU Yu-hao, YE Wei-lin, LI Sheng-ping
 doi: 10.37188/CO.2023-0082
Abstract(11) FullText HTML(3) PDF 6453KB(7)

The high mismatch rate of the parallax discontinuity region and the repeated texture region has been a major issue affecting the measurement accuracy of binocular stereo matching. For these reasons, this paper proposes a stereo matching algorithm that utilize multi-feature fusion. Firstly, the weight of neighboring pixels is given using Gaussian weighting method, which optimizes the calculation accuracy of the Sum of Absolute Differences (SAD) algorithm. Based on the Census transformation, the binary chain code technique has been enhanced to fuse the average gray value of neighborhood pixels with the average gray value of gradient image, and then the judgment basis of the left and right image corresponding points is established, and the coding length is optimized. Secondly, an aggregation technique has been developed that combines the cross method and the improved guide filter to redistribute disparity values with the aim of minimizing error. Finally, the initial disparity is obtained by the Winner Take All (WTA) algorithm, and the final disparity results are obtained by the left-right consistency detection method, sub-pixel method, and then a stereo matching algorithm based on the multi-feature SAD Census transform is established. The experimental results show that the average error matching rate of the proposed algorithm is 4.18%, the average error of the 200−900 mm distance is less than 2%, and the maximum error of the actual 3D data measurement is 1.5%, all using the test of the Middlebury dataset. The experimental results verify the effectiveness of the proposed algorithm.

Multi-channel laser beam combining and closed-loop correction technology in visible light band
XU Xin-hang, LI Gao-sheng, HAN Xu-dong
 doi: 10.37188/CO.2023-0077
Abstract(5) FullText HTML(3) PDF 4003KB(7)

To achieve periodic closed-loop correction of multiple visible wavelength lasers, a laser beam combining system is being designed. This system involves independent monitoring and adjusting of beam pointing and position deviation. First, according to the application requirements of the system, the design indexes of the beam combining system and the overall beam combining scheme are proposed. Then, based on the overall beam combining scheme, we establish the beam control model for the beam combining system. Through numerical simulation experiments, we obtain the solution method for beam control of the beam combining system. The closed-loop beam combining system enables independent monitoring of the unit beam’s pointing and position deviation through the respective beam pointing and position monitoring device. The monitoring results are then used to calculate the control quantity of the beam adjusting device. The independent and efficient adjustment of beam pointing, and position deviation is achieved using a two-dimensional swing mirror and a one-dimensional platform, respectively. Finally, a closed-loop beam combining simulation experimental system with beam monitoring and adjustment device was built using tow laser beams of different wavelengths. The periodic closed-loop beam combining system was verified to have an effective beam combing effect. The experimental results demonstrate that over an extended operational period, both lasers achieve precise beam combining with the reference optical path. Furthermore, the beam combining pointing accuracy is better than ±7μrad, and the positioning accuracy is better than ±0.84 mm. The laser beam combining system developed in this study boast high beam combining accuracy, a fast correction speed, and excellent augmentability for multiple laser beams. Besides, it can accomplish periodic closed-loop beam combining of laser beams, ensuring long-term working stability of the combined laser.

All-aluminum high-resolution camera with lightweight and compact size
SUN Jing-xu, XIE Hong-bo, LI Shu-xian, XIE Xin-wang, WANG Shuo, ZHOU Feng
 doi: 10.37188/CO.2023-0062
Abstract(7) FullText HTML(2) PDF 8887KB(7)

In order to meet the urgent need of developing lightweight and compact space cameras quickly, effectively, and rapidly, a detailed comparative analysis is conducted, including optical system forms and imaging systems. The optical system form of RC+ compensation group is determined, and the imaging system of small F#+micropixel is adopted. Compared with the detailed parameters of the DOVE camera, a lightweight all-aluminum high-resolution camera with a resolution of 3.48m at an orbital altitude of 500km is designed. The overall design results of the camera, its optical and optomechanical structure, imaging electronics, and thermal control are described in detail. The optical design results of the RC+ compensation group of F5.6 are obtained. Using RSA-6061 microcrystalline aluminum alloy as the structural material of the mirror, coupled with an integrated high-rigidity hard aluminum alloy structure, the static (gravity and temperature deformation) simulation analysis results meet the optical design tolerance requirements. The dynamic simulation analysis results show that the first order mode is 302.92 Hz, which has a sufficiently high dynamic stiffness and safety redundancy. The imaging electronics using a 3.2 μm large area array 9 K×7 K detector is designed for low noise miniaturization. Thermal control provided by the satellite platform at a temperature level of 20 °C± 4 °C for the camera. Integration test results show that: (1) The RMS wave aberration of the central field of view is λ/15.6, the wavefront aberration of the five fields of view is better than λ/12.3, which ensures high-quality imaging near the diffraction limit of the camera. The measured optical transfer function at Nyquist frequency is 0.217; (2) The maximum sinusoidal vibration of the camera in three directions is amplified 1.17 times, and the first-order mode of the camera is 295 Hz, with a deviation of 2.61% from the simulation result. The structural stiffness is high and the mechanical stability is good. Under vacuum environment of 10−4 Pa and three different temperatures of 16 °C, 20 °C and 24 °C, the image is clear and can distinguish the corresponding resolution plate image at Nyquist frequency; (3) The image of 2 km outfield target is good, as well as clear and distinct grayscale image with sharp shadow boundaries. The all-aluminum high-resolution camera with lightweight and compact size achieves 3.48 m resolution at a track height of 500 km,width of 15 km×15 km and a total weight of 2 kg. The structural rigidity and strength test results meet the requirements of space launch scenarios, and can provide theoretical guidance and engineering reference for the design of lightweight and higher-resolution space cameras.

Non-uniform illumination correction algorithm for cytoendoscopy images based on illumination model
ZOU Hong-bo, ZHANG Biao, WANG Zi-chuan, CHEN Ke, WANG Li-qiang, YUAN Bo
 doi: 10.37188/CO.2023-0059
Abstract(9) FullText HTML(5) PDF 6778KB(8)

Cytoendoscopy requires continuous amplification with a maximum magnification rate of about 500 times. Due to fiber-optic illumination and stray light, the image has non-uniform illumination that changes with the magnification rate, which affects the observation and evaluation of lesions by doctors. Therefore, this paper proposes an image non-uniform illumination correction algorithm based on the illumination model of cytoendoscopy. According to the principle that image information is composed of illumination and reflection components, the algorithm obtains the illumination component of the image through a convolutional neural network, and realizes non-uniform illumination correction based on the two-dimensional Gamma function. Experiments show that the average gradient of the illumination channel and the discrete entropy of the image are 0.22 and 7.89, respectively, after the non-uniform illumination correction by the proposed method, which is superior to the traditional methods such as adaptive histogram equalization, homophobic filtering, single-scale Retinex and the WSI-FCN algorithm based on deep learning.

Modeling and correction of measurement errors based on depth cameras
WEI Rui-li, WANG Ming-jun, ZHOU Yi-ming, YI Fang
 doi: 10.37188/CO.2023-0047
Abstract(11) PDF 0KB(0)

Time of Flight (ToF) depth camera is one of the important means to obtain three-dimensional point cloud data, but ToF depth camera is limited by its own hardware and external environment, and its measurement data has certain errors. Aiming at the unsystematic error of ToF depth camera, this paper experimentally verifies that the color, distance, and relative motion of the measured target affect the data obtained by the depth camera, and the error effects are different. Based on the oscillation error and the fact that each signal can be expressed in the form of a Fourier series, a new measurement error model is proposed to correct the error caused by color and distance. For the error caused by relative motion, a three-dimensional motion blur function is established to recover it. Through the numerical analysis of the established calibration model, the residual error of distance and color is less than 4mm, and the error caused by relative motion is less than 0.7mm. The work done in this paper improves the quality of the measurement data of the ToF depth camera, and provides more accurate data support for 3D point cloud reconstruction and other work.

CCD/EMCCD Photoelectronic Parameter Test System: design and use
吉 沈, Viacheslav V. Zabudsky, Wei-jing Chang, Qi-yue Na, Yun-fei Jian, Oleg V. Rikhalsky, Oleksandr G. Golenkov, Volodymyr P. Reva
 doi: 10.37188/CO.EN.2023-0016
Abstract(19) PDF 621KB(4)
This article describes design and using of the developed equipment that intended for measuring of CCD and EMCCD (electron multiplying charge-coupled device) chips photoelectrical parameters. Test system provides measurements of dark currents, responsivity of output amplifier, efficiency of charge transfer, charge capacity and other parameters testing in automatic and manual mode. The system can be configured for measurements of different format and architecture CCD/EMCCD both on wafer and in package. The developed equipment was used for 576 × 288, 640 × 512, 768 × 576, 1024 × 1024, 1280 × 1024 CCD and EMCCD chip testing and sorting.
The Poynting vectors, spin and orbital angular momentums of uniformly polarized cosh-Pearcey-Gauss beams in the far zone
LIAO Sai, CHENG Ke, HUANG Hong-wei, YANG Ceng-hao, LIANG Meng-ting, SUN Wang-xuan
 doi: 10.37188/CO.EN.2022-0022
Abstract(157) FullText HTML(112) PDF 7309KB(159)

We propose cosh-Pearcey-Gauss beams with uniform polarization, which are mainly modulated by a hyperbolic cosine function (n, Ω) and the angles related to uniform polarization (α, δ). Based on angular spectrum representation and the stationary phase method, the Poynting vector, Spin Angular Momentursl (SAM) and Orbital Angular Momentums (OAMs) in the far zone are studied. The results show that a larger n or Ω in the hyperbolic cosine function can partition the longitudinal Poynting vectors, SAMs and OAMs into more multi-lobed parabolic structures. Different polarizations described by (α, δ) can distinguish their Poynting vectors and angular momentums between the TE and TM terms, though this does not affect the patterns of the whole beam. Furthermore, the weight of the left and right sides of longitudinal Poynting vectors, SAMs and OAMs in TE and TM terms can be modulated by left-handed or right-handed elliptical polarization, respectively. The results in this paper may be useful for information storage and polarization imaging.

All-solid-state Acousto-optic Mode-locked Laser Operating at 660 nm
凝 王, 权 郑, 鑫 苏, 树 柏, 齐 张, 智 刘, 薇 刘
 doi: 10.37188/CO.2023-0013
Abstract(19) PDF 527KB(41)
Red lasers with picosecond pulse width are widely used in industrial, medical, scientific research and information fields due to their narrow pulse width and high peak power. In this paper,an all-solid-state laser operating at 660 nm with picosecond pulse width, narrow-band, high conversion efficiency is demonstrated by Acousto-Optic Mode-Locked(AOML) method. By carefully optimizing the cavity,external frequency doubling with two LiB3O5 (LBO) crystals and adopting various techniques, a mode-locked red laser source with maximum output power of 8.6W is developed. The laser operating pulsed side-pumped regime in which contain a number of mode-locked pulses with the frequency of 100MHz,the pulse width is 887ps .The optical to optical conversion efficiency from 1319 nm to 660 nm is up to 41%.
Thermal design of ground weak force measurement system for inertial sensors
REN Li-min, CHEN Li-heng, MENG Xu, WANG Zhi
 doi: 10.37188/CO.2023-0022
Abstract(34) FullText HTML(22) PDF 4701KB(56)

In order to meet the ultra-high temperature stability requirements of the inertial sensor ground weak force measurement system, the thermal design of the whole system is carried out. Firstly, the structure of ground weak force measurement system of inertial sensor, heat transfer path of sensitive structure and internal heat source are introduced. Secondly, according to the requirements of the thermal control index of the system, a high-precision thermal control method combining the three-stage thermal control structure and proportional integral differential (PID) control algorithm is proposed to reduce the influence of temperature noise on the detection sensitivity of the inertial sensor. Then, UG/NX software is used to establish the finite element model and carry out the thermal analysis calculation under different working conditions, and the temperature change value of the measurement system in the time domain after equilibrium is (1.2−1.6) ×10−5 K. Finally, the temperature distribution of the measurement system in the time domain is described in the frequency domain, and the temperature stability results of the inertial sensor sensing structure are obtained. The analysis results show that under the current thermal control measures, the temperature stability of the inertial sensor sensing structure is better than 10−4 K/Hz1/2, meeting the requirements of thermal control indicators, and the thermal design scheme is reasonable and feasible.

The influence of the number of coupling regions on the output of the ding-shaped microring resonator
Rong Wu, 张皓辰 张
 doi: 10.37188/CO.EN.2023-0009
Abstract(26) PDF 577KB(57)
In order to explore the influence of the number of coupling regions on the output of the ding-shaped microring resonator, the physical model of the ding-shaped microring resonator is established. The physical model of the ding-shaped microring resonator is studied by using the transfer matrix method, and the influence of the number of different coupling regions on the output of the microring resonator is analyzed. The experimental results show that with the increase of the number of coupling regions, the number of resonance peaks increases in the range of 1.54~1.56um working wavelength, the full width at half maximum(FWHM) decreases, the quality factor Q increases, the energy storage performance of the device is better, and the filter effect on a specific wavelength can be realized. The number of coupling regions has a great influence on the performance of the ding-shaped microring resonator. The number of coupling regions is selected according to the actual needs in the design.
Research on infrared radiation characteristics of space target based on ground-based detector
ZHENG Hong-ru, MA Yan, ZHANG Shuai, CHEN Yatao
 doi: 10.37188/CO.2023-0032
Abstract(57) FullText HTML(27) PDF 4737KB(65)

Constructing the radiation characteristics of space targets is of great significance for the development of space situational awareness technology. In this study, we aim to investigate the infrared radiation characteristics of space targets by developing a simulation program based on the finite element method and unstructured tetrahedral mesh. Through vector coordinate transformation, we calculate the orbit external heat flux received by each surface of the target. By combining the surface material properties and bidirectional reflection distribution function (BRDF), we simulate the temperature and infrared radiation characteristics of each target surface were simulated. Furthermore, we analyze the spectral radiation intensity of the target in the ascending and descending orbital arcs under ground-based detection conditions, taking into account the effects of atmospheric attenuation and background radiation. The results show that, for a three-axis stabilized synchronous orbit satellite with solar panels fixed in the flight direction, the temperature variation range of each surface in the sunlight area and the shadow area is small. The detection effect of the long-wave band of 8~14 μm is better than that of the medium-wave band of 3~5 μm, and the maximum radiation intensity is about 770 W/sr. Ground-based infrared spectrum detection is more affected by the atmosphere, and the detection band must be optimally selected.

Design of catadioptric anamorphic optical system
WU Qing, SHI Guang-wei, ZHANG Jian-ping, ZHAO Shang-nan, ZHANG Xin
 doi: 10.37188/CO.2023-0035
Abstract(68) FullText HTML(46) PDF 4956KB(76)

The anamorphic optical system has a two-plane symmetry, with different focal lengths in the two symmetry planes. This system can obtain a wider field of view when using sensors of conventional size. This paper proposes a method for designing catadioptric anamorphic optical systems based on their first-order aberration characteristics. A catadioptric anamorphic optical system is designed by using a biconic surface, with a focal length of 500 mm in the XOZ plane and 1000 mm in the YOZ plane. The system’s F-number is 10, and the full field angle is 1°×1°. The mean value of the full field of view MTF of the system at is higher than 0.3 at 80 lp/mm. The overall structure of the system is compact, and the imaging quality is excellent.

A denoising method combining bitonic filtering and sine-cosine transform for shearography fringe pattern
WU Rong, LU Yang, OUYANG Ai-guo
 doi: 10.37188/CO.2023-0072
Abstract(40) FullText HTML(21) PDF 2358KB(65)

Shearography is a non-contact, full-field, and high-precision optical deformation measurement technology. There is a lot of random noise in the acquired speckle fringe pattern caused by environmental factors, which affects the measurement accuracy. The traditional denoising methods easily cause the fringe information to be lost or even damaged while filtering out the noise. To solve this problem, this paper proposes an image denoising method based on the combination of sine and cosine transform and bitonic filtering. In this method, the phase fringe image is firstly obtained by sine and cosine transform. Secondly, the two images are denoised by the bitonic filtering method respectively. Finally, the filtered two images are merged into the final phase fringe image. Experimental results show that for the filtered phase pattern, the speckle suppression index is 0.999 and the average retention index is 2.995, which prove that the proposed method can improve the quality of the phase pattern better than the traditional denoising method, and can preserve the details and edge information of the phase fringes to a large extent.

Design and optimization of micro LED vehicle light projection optical system
LI Xianglan, LV Jin-guang, ZHENG Kai-feng, CHEN Yu-peng, ZHAO Bai-xuan, ZHAO Ying-ze, QIN Yu-xin, WANG Wei-biao, LIANG Jing-qiu
 doi: 10.37188/CO.2023-0063
Abstract(67) FullText HTML(27) PDF 8045KB(78)

The development of smart cars puts forward higher requirements for intelligent light systems with projection functions. Compared with the vehicle light system using traditional technology, the vehicle light system using Micro LED projection display technology can make the system structure simpler and the light utilization rate higher, which is more conducive to miniaturization, energy saving and integration because of its good self-luminous characteristics. In this paper, we propose a light projection scheme based on Micro LED array, design a 200×150 white Micro LED array with a pixel size of 80 μm×80 μm as the display light source and the field of view angle is 16°×34° object image tilt, and optimize the tilt angle and optical system structure of the object surface. In addition, the reverse distortion processing method and the pixel grayscale modulation method are used to solve the problems of keystone distortion and illumination uniformity of the projected image of the vehicle light, and a projection experimental platform is built to verify the image correction method. The experimental results show that the keystone distortion coefficients of the corrected images in the x and y directions decrease from 0.0932 and 0.3680 to 0.0835 and 0.0373, respectively, and the uniformity of the illumination of the image surface increases from 83.2% to 93.2%. In this paper, the optimization design of the oblique projection vehicle lighting system based on Micro LED and its image correction method are used to realize the projection of the vehicle light with high luminous efficiency and low distortion.

Calculation of orbit heat flow and research on radiation characteristics of space target
ZHENG Hong-ru, MA Yan, ZHANG Shuai, WANG Jian-chao, QU You-yang
 doi: 10.37188/CO.2023-0033
Abstract(64) FullText HTML(47) PDF 4452KB(87)

With the increasingly crowded space resources in low orbit, space situational awareness is an important support for the normal operation of space assets, and optical observation is one of the important means. In this paper, the solar radiation, the earth radiation and the earth albedo radiation received by the space target are simulated by Monte Carlo simulation method, and the simulation program is written based on the unstructured tetrahedral grid, and the calculation results are compared and verified. Furthermore, for the orbit external heat flow received by the sun-synchronous orbit satellite, the grid with solar panels is used to analyze the orbit heat flow received by each surface with or without occlusion. The results show that the average heat flow value of -Y surface decreases by 53.79 W/m2 after considering occlusion in the ground mode. The average surface heat flow value of +Y-Z side panel decreased by 32.05 W/m2. The temperature characteristics of each surface are given based on the properties of surface materials, and the accuracy of the calculation is verified by combining with the on-orbit telemetry data of the solar panel temperature. Finally, the infrared radiation intensity in each direction of the two modes is calculated. The results show that the influence of heat flow on the surface is different under different observation modes. The temperature of the surface varies with time under the earth mode, while the heat flow on the surface is stable under the sun mode. Under the two modes, the temperature of the solar panel is higher, the radiation intensity is larger, and it has obvious infrared characteristics, which is convenient to carry out infrared observation.

Study on laser backscattering characteristics of ship wake bubble target
ZONG Si-guang, ZHANG Xin, YANG Shao-peng, DUAN Zi-ke, CHEN Bao
 doi: 10.37188/CO.2023-0043
Abstract(50) FullText HTML(21) PDF 4993KB(70)

In order to improve the laser wake guidance distance and the detection signal-to-noise ratio, it is of great theoretical and practical value to study the backscattering characteristics of bubble targets with different distances, bubble sizes, bubble number densities, and bubble layer thicknesses.


The laser backscattering characteristics of ship wake bubble targets with different distances, scales, numerical densities, and thicknesses are studied using Monte Carlo simulations and indoor experiments.


When the bubble density is 102−108 m−3 and the thickness of the bubble layer is greater than 0.05 m, there is always an echo signal for both large- and small-scale bubbles. When the thickness of the bubble layer is less than 0.05 m, no echo signal is detected. The thickness of the bubble layer is the greatest impact factor on the backward scattering of bubbles; When the bubble number density is 109 m−3 and the thickness of the bubble layer is below 0.05 m, the pulse width of the large-scale bubble echo signal widens. The number density and scale characteristics of the bubbles have the greatest impact on the backscattering of bubbles.


A laser backscattering measurement system at the scale of typical underwater bubbles is built to verify the influence of different ship wake bubble characteristics on the laser backscattering detection system, which can provide support for the ship wake laser detection project.

Repetition frequency and 228 nm narrow pulse width tunable deep UV laser
WANG Jin-yan, MA Fang, ZHENG Lei, TIAN Dong-he, CHEN Xi, ZHENG Quan
 doi: 10.37188/CO.2023-0058
Abstract(79) FullText HTML(58) PDF 3985KB(73)

Ultraviolet lasers play an important role in the study of ultraviolet resonance Raman spectroscopy. The Raman resonant Raman effect enhance Raman signals and reduces the detection limit of Raman measurement. This paper focuses on the study of an all-solid-state deep-ultraviolet laser with an output wavelength of 228 nm. The laser uses Nd:YVO4 as a gain medium and electro-optic q-switched cavity dumping technique to achieve a fundamental frequency output of 914 nm in pulse widths of several nanoseconds. Then, the second-harmonic generation is achieved by LiB3O5(LBO), and the fourth-harmonic 228 nm UV laser is obtained by beta-barium-borate (BBO). The variation of fundamental and second harmonic laser power at different repetition rates is investigate. The average power of Nd:YVO4 is saturated and decreases with increased repetition rate due to the low gain at 914 nm. The output efficiency of UV laser is optimized by adjusting the focus lens. At the pump power of 30 W, the highest average power of a 228nm UV laser is 84 mW at 10 kHz. The repetition rate of UV laser is continuously adjustable within the range of 5 kHz−25 kHz, and the pulse width is maintained at 2.8 to 2.9 ns which meets the application requirements in the field of UV spectroscopy detection technology.

Design and characteristic analysis of off-axis meta-lens
HU Jin-gao-wa, ZHAO Shang-nan, WANG Ling-jie, YE Hao-kun, ZHANG Jian-ping, ZHANG Xin
 doi: 10.37188/CO.2023-0039
Abstract(67) FullText HTML(33) PDF 7106KB(83)

As a new type of planar optical element, meta-lens can flexibly control the phase, polarization and amplitude of light. They have great potential for device lightweighting and mass manufacturing, and have garnered widespread attention. Off-axis meta-lens, a special type of meta-lens with certain dispersion effect, can be used as a spectral element, providing a unique and feasible way to realize micro instruments. This paper proposes a design method for off-axis meta-lens and analyzes the effects of numerical aperture, off-axis angle, and incident wavelength on the simulation deviation, resolution and focusing efficiency of off-axis meta-lenses, which provides valuable insights for subsequent research and application of off-axis meta-lenses.


Several off-axis meta-lenses with parameters NA=0.408 α=13°, NA=0.18 α=13°, NA=0.408 α=20° were simulated by Lumerical, respectively.


The simulation results indicate that the off-axis angle is directly proportional to the spectral resolution. As the angle increases, t the spectral resolution becomes larger, but the focusing efficiency decreases. A smaller numerical aperture result in a smaller coverage of the phase distribution, leading to a larger deviation between the simulation and theory.


Designers need to reasonably balance parameters such as numerical aperture and off-axis angle according to the requirements to finally achieve the desired effect. The conclusion of this study is an important reference value for theoretical analysis and parameter design of off-axis meta-lens in practical application.

Study on the optimal detection position of brix value of Yongquan honey tangerines based on hyperspectral imaging technology
LI Bin, WAN Xia, LIU Ai-lun, ZOU Ji-ping, LU Ying-jun, YAO Chi, LIU Yan-de
 doi: 10.37188/CO.2023-0057
Abstract(35) FullText HTML(27) PDF 4582KB(69)

The objective of this study is to explore the optimal detection location and the best prediction model of the brix value of Yongquan honey tangerines, which can provide a theoretical basis for the brix measurement and classification of honey tangerines. With the wavelength range of 390.2−981.3 nm hyperspectral imaging system was used to study the best location for detecting the brix of Yongquan honey tangerines, and the spectral information of the calyx, fruit stem, equator and global of Yongquan honey tangerines were combined with their brix values of corresponding parts to establish its prediction model. The original spectra from the different locations were pre-processed by standard normal variance transformation (SNV), multiple scattering correction (MSC), baseline calibration (Baseline) and convolutional smoothing (SG), respectively, and the partial least squares regression (PLSR) and least squares support vector machine (LSSVM) models were established based on the pre-processed spectral data. The best pre-processing methods for different parts of the honey tangerine were found, and the spectral data obtained from these pre-processing methods were analyzed using the competitive adaptive re-weighting algorithm (CARS) and uninformative variable elimination (UVE) to identify characteristic wavelengths. Finally, the PLSR and LSSVM models were established and compared based on the selected spectral data. The results show that the global MSC-CARS-LSSVM model demonstrates the most accurate prediction performance, with a correlation coefficient of Rp=0.955 and an RMSEP value of 0.395. Alternatively, the SNV-PLSR model of the equatorial location of honey tangerines was found to be the next more effective, with a correlation coefficient of Rp=0.936, and an RMSEP value of 0.37. The correlation coefficients of the two prediction models are similar, the equatorial location can be used as the optimal location for measuring the brix of honey tangerines. This study demonstrates that the use of varying segments of the orange impacts the accuracy of prediction models. Identifying the optimal location and prediction model can provide a theoretical basis for classifying oranges for brix testing.

Design of an Optical System for Generating Ring-Shaped Laser Beam
CHEN Bao-hua, WU Quan-ying, TANG Yun-hai, FAN Jun-liu, CHEN Xiao-yi, YU Hao-mo, SUN Yi
 doi: 10.37188/CO.2023-0045
Abstract(64) FullText HTML(33) PDF 5320KB(82)

This paper presents a method for designing a transmissive-reflective combined optical system to generate a focused ring-shaped laser beam. The design aims to achieve a freely adjustable radius for the focused ring-shaped laser beam and ensure uniform beam intensity even after defocusing.


Based on the principle of equal energy splitting, the transmissive system establishes mapping functions for the input and output light projection height. It optimizes the lens parameters to shape the incident Gaussian light into a flat-topped circular shape, thus achieving uniformity of beam intensity. On the other hand, the reflective system uses the adjustable diameter range of the focal plane ring-shaped light and working distance parameters. By applying the principle of geometric ray tracing, it calculates the parameters of the conical reflecting mirror, parabolic cylindrical mirror, and dynamic mirror. This process shapes the flat-topped circular light into a ring-shaped light.


The experimental results show that when the half-apex angle of the dynamic mirror is 16°, the designed system can achieve a freely adjustable radius for the focused ring-shaped laser beam from 15 mm to 30 mm with a size error of not more than 0.05 mm, and the intensity uniformity after defocusing reaches 84%.


The design method can achieve both uniformity of intensity and freedom of size adjustment without replacing the system lens. It has good operability and yields higher precision and efficiency in the processing of ring-shaped light.

Design of UV small f-number high variable power hyperspectral resolution imaging spectrometer
LIU Yang, LI Bo, LIN Guan-yu, WANG Xiao-xu, LI Han-shuang, GU Guo-chao
 doi: 10.37188/CO.2023-0037
Abstract(48) FullText HTML(24) PDF 5840KB(71)

Conventional imaging spectrometers generally have low variable power, which is not conducive to the extended application of large-field, long-slit, multi-channel optical systems. In space remote sensing, the radiation energy of the ultraviolet band is low, which requires the imaging spectrometer to have a smaller F-number. In order to meet the requirement of detecting small F-number of high variable power and high spectral resolution imaging spectrometer, a high spectral resolution Offner UV imaging spectrometer with high variable power is designed in this paper. An improved Offner structure with light and small size is adopted in the rear beam splitting system of the imaging spectrometer. Based on the requirements of variable power ratio and small F-number of the imaging spectrometer, the initial Offner structure parameters are derived theoretically. A meniscus lens is inserted in front of the image to increase the degree of freedom of optimization of the system and improve the imaging quality of the system. The resulting imaging spectrometer works in the 270~300 nm band with a long slit of 40 mm, a spectral resolution better than 0.6 nm, a spectral sampling of 0.15nm, the system variable power ratio less than 0.22, and an F number less than 2. the system modulation transfer function (MTF) is better than 0.9 at a cutoff frequency of 14 lp/mm, and the root mean square radius (RMS) of each field of view in each band is less than 12 μm. This study provides a design scheme for the UV-band hyperspectral detection imaging spectrometer with small F-number and high variable power.

Narcissus suppression of medium-wave infrared imaging system
BU He-yang, YU Lin-yao, TIAN Hao-nan, WANG Jian
 doi: 10.37188/CO.2023-0008
Abstract(49) FullText HTML(31) PDF 8004KB(75)

Narcissus refers to the phenomenon in an infrared system where a cold imaging sensor can "see" its own reflected image by the reflection of the frontal optical surfaces. Control of narcissus is one of the important requirements in the design of the infrared imaging system. A cooled medium-wave infrared imaging system with Cassegrain reflection structure is designed and analyzed to obtain the optical surfaces with serious narcissus. In addition, the narcissus is reduced by Zemax, and the optimization of the system transfer function MTF is taken into account while the narcissus is controlled. The optimized medium-wave infrared imaging system is compared through NARCISSUS macro (narcissus analysis macro), Tracepro modeling software and actual imaging, and it was found that the narcissus induced equivalent temperature difference (NITD) of the detector image surface decrease from 1.0484 K to 0.1576 K. The energy and size of the narcissus spot did not show marked change during the focusing of the system. The optimized optical structure effectively controls the narcissus of the system.

5.2 W high repetition frequency 257 nm deep ultraviolet picosecond laser
FAN Hao-ran, CHEN Xi, ZHENG Lei, XIE Wenxia, JI Xin, ZHENG Quan
 doi: 10.37188/CO.2023-0026
Abstract(52) FullText HTML(39) PDF 3931KB(86)

To improve the detection efficiency of deep ultraviolet laser for semiconductor detection, it is imperative to develop 257 nm deep ultraviolet picosecond laser with high power and high repetition. In this study, a 257 nm deep ultraviolet laser was experimentally investigated based on photonic fiber amplifier and extra-cavity frequency quadrupling. The seed source uses a fiber laser with a central wavelength of 1030 nm and a pulse width of 50ps, delivering a power output of 20 mW and a repetition frequency of 19.8 MHz. High power 1030 nm fundamental frequency crystal light was obtained through a two-stage ytterbium-doped double cladding (65 μm/275 μm) photonic crystal fiber rod amplification structure, and 257 nm deep ultraviolet laser was generated using double frequency crystal LBO and quadruple frequency crystal BBO. The seed source uses a two-stage photonic crystal fiber amplifier to get a 1030 nm laser output power of 86 W. After the laser focusing system, frequency doubling resulted in a second harmonic output of 47.5 W at 515 nm and a fourth harmonic output of 5.2 W at 257 nm.The fourth harmonic conversion efficiency was 6.05%. The experimental results show that this structure can obtain high power 257 nm deep ultraviolet laser output, providing a novel approach to improve the detection efficiency of semiconductor detection lasers.

Multimodal feature fusion based on heterogeneous optical neural networks
ZHENG Yi-zhen, DAI Jian, ZHANG Tian, XU Kun
 doi: 10.37188/CO.2023-0036
Abstract(66) FullText HTML(42) PDF 9046KB(87)

Current study on photonic neural networks mainly focuses on improving the performance of single-modal networks, while study on multimodal information processing is lacking. Compared with single-modal networks, multimodal learning utilizes complementary information between modalities. Therefore, multimodal learning can make the representation learned by the model more complete. In this paper, we propose a method that combines photonic neural networks and multimodal fusion techniques. First, a heterogeneous photonic neural network is constructed by combining a photonic convolutional neural network and a photonic artificial neural network, and multimodal data are processed by the heterogeneous photonic neural network. Second, the fusion performance is enhanced by introducing attention mechanism in the fusion stage. Ultimately, the accuracy of task classification is improved. In the MNIST dataset of handwritten digits classification task, the classification accuracy of the heterogeneous photonic neural network fused by the splicing method is 95.75%; the heterogeneous photonic neural network fused by introducing the attention mechanism is classified with an accuracy of 98.31%, which is better than many current advanced single-modal photonic neural networks. Compared with the electronic heterogeneous neural network, the training speed of the model is improved by 1.7 times; compared with the single-modality photonic neural network model, the heterogeneous photonic neural network can make the representation learned by the model more complete, thus effectively improving the classification accuracy of MNIST dataset of handwritten digits.

Effect of electron irradiation on CsPbBr3 perovskite nanocrystal
ZHANG Bo-wen, HAN Dan, XUE Mengyun, CAO Rongxing, LI Hongxia, ZENG Xianghua, XUE Yu-xiong
 doi: 10.37188/CO.2023-0044
Abstract(63) FullText HTML(98) PDF 6967KB(82)

With excellent optical properties and high carrier mobility, perovskite materials have become highly competitive materials in the field of space solar cells. However, space particle irradiation can change the structure and optical properties of materials, leading to a rapid degradation of device performance. In order to investigate the influence of electron irradiation on the structure and optical properties of CsPbBr3 nanocrystals, this paper conducted electron irradiation experiments on CsPbBr3 materials, characterized the microscopic morphology of CsPbBr3 nanocrystals by high-resolution transmission electron microscopy method. Moreover, this paper investigated the change trend of crystal structure by X-ray diffraction analysis and X-ray photoelectron spectroscopy analysis. The results revealed electron irradiation caused the CsPbBr3 nanocrystals to become rough and significantly reduced in size. The nanocrystal became compact and formed nanocluster under high-dose electron irradiation. Furthermore, the optical properties of CsPbBr3 materials were characterized using steady-state UV-Vis absorption spectra and photoluminescence spectra. The analysis of lattice expansion-induced bandgap changes after irradiation was performed using first principles calculations. It is demonstrated that electron irradiation deepened the color of nanocrystals and affected the light transmittance of CsPbBr3 nanocrystalline, thereby enhancing the optical absorption performance of the samples. However, electron irradiation also led to the decomposition of CsPbBr3 nanocrystals, resulting in a significant reduction in luminescence intensity by 53.7%−78.6% after high-dose irradiation. These findings provide valuable data support for the study of spatial radiation damage mechanisms and the application of perovskite nanocrystals.

Orbital-angular-momentum spectra in coherent optical vortex beam arrays with hybrid states of polarization
Cenghao Yang, Ke Cheng, HongWei Huang, Sai Liao, Mengting Liang, Ling-yun Shu
 doi: 10.37188/CO.EN.2023-0010
Abstract(69) PDF 2197KB(79)
Based on the Huygens-Fresnel principle and the theory of coherent combination, we propose hybridly polarized vortex beam arrays in coherent combinations of radial off-axis Gaussian beamlets with vortex and polarization topological charges (TC). The results show the number of beamlet and hybrid polarization present joint effect in maximal weight of OAM-modes. An increase of weight value at maximal mode is accompanied by the growing number of the beamlet. As the beamlet number increases, hybrid polarization caused by the initial polarization TC does not maintain its advantage in high-purity OAM spectra due to its slow growth of weight value at maximal modes. The maximal mode equals the total TC at central optical vortex (OV) and it is irrelevant to the beamlet number, i.e., nmax=l+η±m. Whereasfor other modes for non-zero weight, their locations are jointly determined by n=l+η±m−αN with vortex, polarization and addition TCs and the number of beamlets.
xiaoli Song, 驰 张, Ya-Wei Guo
 doi: 10.37188/CO.EN.2022-0026
Abstract(35) PDF 685KB(67)
Research progress of optical tweezers with hetero-core fiber
LI Hong, ZHU Ying-xin, ZHOU Ya-ni, WANG Hai-bo, DONG Ming-li, ZHU Lianq-ing
 doi: 10.37188/CO.2023-0016
Abstract(105) FullText HTML(78) PDF 5688KB(89)

Optical fiber tweezers have a simple structure, operate flexibly and are small in size, and are widely used in biochemical analysis, life science and other fields. The optical fiber probe with hetero-core structure has natural advantages in near-field evanescent wave optical trapping, core beam coupling transmission, and cross-synergistic applications of microfluidic technology. It can realize cell and subcellular particle collection and transportation and can significantly improve the three-dimensional capture ability and dynamic manipulation level of particles. In this paper, the structural characteristics and application technology research progress of fiber optical tweezers with different core structures are reviewed. Their key technologies such as probe preparation, laser source and coupling mode are listed and compared. The role and development of hetero-core fibers with different structures in fiber optical tweezers are summarized and predicted.

立发 胡, Lv Jiang, 启立 胡, 星宇 徐, 杨 黄, 吴晶晶 吴, 琳 俞
 doi: 10.37188/CO.EN.2023-0001
Abstract(52) PDF 1074KB(73)
Effect of slit height on the spectral resolution of a monochromator and its verification
ZHANG Jing, ZHANG Bo, LIU Kai, WANG Kai-yang, FENG Shu-long, LI Wen-hao, YAO Xue-feng
 doi: 10.37188/CO.2023-0004
Abstract(130) FullText HTML(100) PDF 5729KB(121)

: Monochromators are widely used in spectral calibration, material analysis and other aspects and research of high spectral resolution monochromator systems is of great significance as a result. Based on the vector grating equation, the influence of the height of the incident slit on the spectral line diffraction of a spectrometer is investigated, and the analytical expressions for diffraction at the same wavelength and the slit height are given. An optimization scheme of the spectral resolution of the monochromator based on the suppression of spectral line diffraction by the slit height is proposed.


: According to the performance index requirements of a highly sensitive and ultra-fast time response detector, a three-grating monochromator optical system with a spectral resolution of 0.1 nm and a band range of 185 nm−900 nm was designed, and a prototype was built to verify the influence of the slit height on spectral line diffraction, and to explore the influence of slit height on spectral resolution.


: The experimental results show that the spectral resolution can be improved from 0.32 nm to 0.1 nm by optimizing the slit height when the slit width is fixed.


: The slit height will affect the spectral resolution of a grating monochromator, and the experimental results can provide a reference for better use of monochromators.

Design of focusing solar simulator based on freeform surface
WEI Xiu-dong, LI Bai-lin, ZHAO Yu-hang, TANG Jian-fang, ZHANG Ji, HUANG Yong-huan, XU Ying-chao
 doi: 10.37188/CO.2022-0207
Abstract(120) FullText HTML(78) PDF 12867KB(117)

The concentrating solar simulator can obtain high-power convergence of solar radiation spots, which has important applications in the fields of solar thermal power generation and thermochemical research. To obtain uniform solar radiation spots, a free-form condenser design method based on non-imaging optics is proposed, and its design principle and specific method are described. A freeform condenser is designed in comparison to a non-coaxial ellipsoidal condenser with the same containment angle, and the correctness of its method of design is verified by simulation analysis. The simulation results show that when a xenon lamp with a rated power of 6 kW is used as the light source, the single-lamp solar simulator composed of a freeform condenser can produce a spot with an average irradiance of 274.4 kW/m2 in the target and a diameter of 60mm. The spot’s unevenness decreases from 18.28% to 5.69% compared with that of a non-coaxial ellipsoidal solar simulator. The seven-lamp solar simulator can produce a spot with an average irradiance of 1.65 MW/m2, with a spot unevenness that decreases from 13.19% to 5.49%.

Development and prospects of enhanced absorption spectroscopy
REN Yi-jie, YAN Chang-xiang, XU Jia-wei
 doi: 10.37188/CO.2022-0246
Abstract(218) FullText HTML(144) PDF 4774KB(146)

Optical path absorption spectroscopy is an important branch of absorption spectroscopy. In recent years, there has been a proliferation of optical path absorption spectroscopy techniques based on different light source technologies, absorption cavity technologies, and detection methods. As the demands on detection sensitivity and absorption optical path length increased, optical path absorption spectroscopy techniques based on the principle of enhanced absorption emerged, including integrated cavity spectroscopy (ICOS), cavity-enhanced absorption spectroscopy (CEAS) and cavity ring-down spectroscopy (CRDS). Enhanced absorption spectroscopy is advantageous for its high spectral resolution, high sensitivity, fast response time, and portability, but it presently lacks a unified concept and clear classification criteria. This paper compares the development history of absorption spectroscopy techniques and clarifies the concept of their multi-optical path. Based on whether resonant absorption occurs in the absorption cavity, the concept of absorption spectroscopy techniques based on resonance is proposed, and the current research status of resonant absorption spectroscopy techniques is analyzed and summarized, and the applications of this technique in various fields are outlined. Finally, the future development of key technologies in resonance absorption spectroscopy is envisioned.

Research on the polarization mode of underwater waves based on atmospheric multiple scattering
GU Jing-qiao, LI Gao-jie, HU Peng-wei, QIAN Jian-qiang
 doi: 10.37188/CO.2022-0223
Abstract(101) FullText HTML(107) PDF 8845KB(108)

Underwater polarized light with certain distribution characteristics is formed when sunlight is scattered by the atmosphere and refracted by the surface of the water. The resulting underwater polarization distribution pattern can be used in navigation. In this paper, an air-water model is proposed to calculate the polarization pattern of sky light under varying wave conditions and simulate the underwater polarization distribution pattern under the influence of wave refraction. Distribution images are simulated for underwater polarization’s degree and angle in conditions with calm water, sinusoidal waves and random waves with different solar altitude angles. The results are verified using underwater experiments. The comparison of the polarization distribution pattern under the waves and that under the calm water show that the proposed model can accurately characterize the characteristics of the polarization distribution pattern under typical wave surfaces, providing a theoretical basis for improving the environmental adaptability of underwater polarization navigation under fluctuating water surface conditions.

Research on the influencing factors of angle measurement accuracy of an interferometer star tracker
RUAN Yu-xiang, DONG Lei
 doi: 10.37188/CO.2022-0232
Abstract(72) FullText HTML(48) PDF 3706KB(111)

In order to improve the traditional attitude measurement accuracy of star sensors, interference angle measuring technology can be combined with a traditional star sensor. Based on the centroid positioning technology of traditional star sensors, the light intensity information of star image points is subdivided to break through the accuracy limitation of centroid positioning and form a highly precise interferometric star sensor with a large field of view. In this paper, the factors that restrict the Angle measurement accuracy of interferometer sensors are deeply studied with particular interest given to the influence of interference fringe segmentation error on angle measurement accuracy. Through research and analysis, we conclude that the asymmetry error is not the main factor affecting the angle measurement accuracy of interferometric sensors. When the mismatch error between the Mohr fringe period and the overall optical dimension of the optical wedge array is less than 1%, the single-factor angle measurement error is less than 0.01". For non-orthogonal error between Mohr fringe orientation and an optical wedge’s array arrangement direction, the accuracy error of single-factor angle measurement is sure to be less than 0.01 when the fringe rotation angle is less than 0.1°. Therefore, the above two main errors should be suppressed in the production and assembly so that the measurement accuracy of the interferometer sensor is closer to the high-precision theoretical value.

Design of optical system for low-sensitivity space gravitational wave telescope
YU Miao, LI Jian-cong, LIN Hong-an, HUANG Yao-zhang, LUO Jia-xiong, WU Yan-xiong, WANG Zhi
 doi: 10.37188/CO.2023-0006
Abstract(135) FullText HTML(73) PDF 7703KB(123)

The Taiji program is a key task for China's space gravitational wave detection, and as an important part of space gravitational wave detection, the telescope's performance will directly affect the accuracy of gravitational wave detection. The existing typical space gravitational wave telescope structure has high secondary mirror sensitivity, which is difficult to meet the manufacturing and adjustment tolerance requirements of larger aperture space gravitational wave telescopes, especially the tolerance requirements for in-orbit stability. In order to solve the above problems, firstly, a new optical system structure of space gravitational wave telescope with intermediate image plane set between three and four mirrors is proposed to reduce the sensitivity of the secondary mirror. Combined with the theoretical method of Gaussian optics, the initial parameters of the structure of the new telescope are theoretically analyzed and calculated. Secondly, through the optimization design, a telescope optical system with a pupil diameter of 400mm, a magnification of 80 times, a scientific field of view of ± 8μrad, and a wavefront error RMS value of better than 0.0063λ was obtained. Finally, the sensitivity evaluation tolerance allocation table of the telescope system is established, and the tolerance of the existing telescope structure and the new telescope structure are compared and analyzed. Compared with the existing telescope structure, the sensitivity of the new telescope structure is reduced by 30.4%. The results show that the new telescope structure has the advantage of low sensitivity, which provides an optimal scheme for the design of space gravitational wave telescopes.

Polarization-multiplexing of a laser based on a bulk Yb:CALGO crystal
JIN Hao-shu, LIU hui, XU Si-yuan, LU Bao-le, BAI Jin-tao
 doi: 10.37188/CO.EN-2023-0005
Abstract(98) FullText HTML(118) PDF 3676KB(120)

The polarization-multiplexing of a laser based on a medium with a large gain bandwidth and a high thermal conductivity can benefit dual-frequency and dual-comb lasers’ spectral bandwidth and power. This paper presents a demonstration of the polarization-multiplexing of a laser based on a bulk Yb:CALGO crystal. The polarization-multiplexing is realized by sandwiching the gain crystal within two 45˚-cut birefringent crystals, forming two orthogonally polarized beams with spatial separation inside and allowing the system to pump the laser at the waist of the cavity mode for more efficient pumping. The laser outputs watt-level power with a slope efficiency exceeding 30%. A dual-frequency operation with terahertz frequency separation is realized by inserting an etalon into the cavity.

Ground principle verification of clock noise transfer for Taiji program
JIANG Qiang, DONG Peng, LIU He-shan, LUO Zi-ren
 doi: 10.37188/CO.2023-0012
Abstract(178) FullText HTML(87) PDF 7740KB(137)

The Taiji Project is a space gravitational wave detection mission proposed by the Chinese Academy of Sciences, which uses the method of laser differential interference to detect pm-level displacement fluctuations caused by gravitational waves between satellites. In order to eliminate the phase measurement error caused by the dissynchronization of the clock between satellites, Taiji Project intends to use the sideband multiplication transfer scheme to measure and eliminate the inter-satellite clock noise. This paper discusses the requirements, principles, and methods of inter-satellite clock noise transmission of the Taiji project, and designs experiments for principle verification. By building an electronics experiment, the limit value of the clock noise of the two systems was tested, the relevant parameters of the experiment were determined, and the principle of the sideband multiplication transfer scheme was verified by further optical experiments. The experimental results show that the clock noise cancellation scheme and related parameters proposed in this paper are reasonable and feasible, and are suitable for the needs of Taiji project. Moreover, in the 0.05 Hz-1 Hz frequency band, the suppression effect of inter-satellite clock noise is better than 2π×10-5 rad/Hz1/2, which meets the noise requirements of Taiji pathfinder and lays an experimental and theoretical foundation for the design of clock noise transmission scheme and parameter of future Taiji Project.

A Novel Methane and Hydrogen sensor with Surface Plasmon Resonance-Based Photonic Quasi-crystal Fiber
LIU Qiang, ZHAO Jin, SUN Yudan, LIU Wei, WANG Jianxin, LIU Chao, LV Jingwei, WANG Shimiao, JIANG Yu, CHU Paul K
 doi: 10.37188/CO.2022-0025
Abstract(110) FullText HTML(67) PDF 4148KB(174)

A novel photonic quasi-crystal fiber (PQF) sensor based on surface plasmon resonance (SPR) is designed for simultaneous detection of methane and hydrogen. In the sensor, Pd-WO3 and cryptophane E doped polysiloxane films deposited on silver films are the hydrogen and methane sensing materials, respectively. The PQF-SPR sensor is analyzed numerically by the full-vector finite element method and excellent sensing performance is demonstrated. The maximum and average hydrogen sensitivities are 0.8 nm/% and 0.65 nm/% in the concentration range of 0% to 3.5% and the maximum and average methane sensitivities are 10 nm/% and 8.81 nm/% in the range between 0% and 3.5%. The sensor provides the capability of detecting multiple gases and has large potential in device miniaturization and remote monitoring.

Original Article
Laser intensity distribution measurement method based on tomographic imaging
WANG Qian, CAI Wei-wei, TAO Bo
2023, 16(4): 743-752.   doi: 10.37188/CO.2022-0016
Abstract(649) FullText HTML(409) PDF 11029KB(392)

In order to accurately measure the laser intensity distribution, we propose a method based on tomographic imaging. Firstly, numerical studies were performed to validate the correctness of the imaging model and convergence of the reconstruction algorithm. Reconstruction errors were less than or equal to 7.02% with different laser intensity distribution phantoms employed and less than 8.5% with the addition of different random noise levels under 10%. Additionally, a demonstration experiment was performed with the employment of a customized fiber bundle to realize the measurement from seven views. Seven views are distributed along a semi-circle plane which is perpendicular to the propagation direction of the laser beam. The distance from the laser beam to each view is nearly 160 mm and the angle coverage range of the seven views is about 150°. Laser-induced fluorescence obtained after the laser passed through a rhodamine-ethanol solution was collected by the tomographic imaging system. Then, the laser intensity distribution was obtained through absorption-corrected three-dimensional (3D) reconstruction. The correlation of the projection and re-projection of the one view was used to quantitatively access the accuracy after the other six views were adopted in the reconstruction. The results show the feasibility of the method with a correlation coefficient of 0.9802. It can be predicted that the 3D laser intensity measurement scheme proposed in this work has a broad prospect in the field of laser applications.

Laser Doppler velocimetry with a dual polarization structure
TAO Shan-jing, ZHEN Sheng-lai, FANG Jian, CHEN Xin, LV Tao, YU Ben-Li
2023, 16(4): 753-764.   doi: 10.37188/CO.2022-0211
Abstract(246) FullText HTML(114) PDF 4970KB(243)

In order to eliminate the uncertainty caused by the inclination of a beam, a dual polarization laser Doppler velocimetry system is established. We use a structure with two beams and two probes to detect the motion of the object. Firstly, the angle between the two beams is obtained by a calibration experiment. For any beam inclination, the scattered beam on the surface of a moving object is collected by a dual-probe device, and the Doppler shift of the two interference signals is obtained by combining the dual polarization optical path structure. Then, the refined framing algorithm is applied to demodulate the two interference signals in real time. The real speed of the object is obtained through the synthesis of the two speed components. The experimental results show that the average deviation between the measured value and the theoretical value can reach 1%−5% when the speed is within the range of 10 mm/min~1500 mm/min. In the process of non-stationary motion, the mean RMSE of the v-t image corrected by the refining frame segmentation algorithm is 1.19 mm/min. The system’s structure meets the requirements of stability and reliability, high precision and strong anti-interference ability in speed measurement.

Ground electronics verification of inter-satellites laser ranging in the Taiji program
DENG Ru-jie, ZHANG Yi-bin, LIU He-shan, LUO Zi-ren
2023, 16(4): 765-776.   doi: 10.37188/CO.2022-0041
Abstract(688) FullText HTML(356) PDF 7317KB(376)

In the Taiji program, laser interferometry is utilized to detect the tiny displacement produced by the gravitational wave signals. Due to the large-scale unequal arm, the laser frequency noise is the largest noise budget in the space interferometer system. To reduce the influence of laser frequency noise, a technology called the Time Delay Interferometry (TDI) is utilized to deal with it. The TDI is a kind of data post-processing method, which forms the new data stream by the method of the time delay to initial data. But the premise of TDI needs to obtain accurate absolute arm length between satellites. Thus, for that requirement, we discuss the ranging system scheme and implement a ground electronics verification experiment. The ranging system is based on Direct Sequence Spread Spectrum (DS/SS) modulation, and it mainly includes three parts, which are the signal structure, a Delay Locked Loop (DLL), and a data processing algorithm. In DS/SS modulation, types of pseudo-random code can make a difference to the quality of correlation and the ranging accuracy. Therefore, to design the optimal pseudo-random code, we compare the correlation and flexibility in choosing lengths of the m sequence, gold sequence, and Weil code. Weil code that has a shift-cutoff combination with the best autocorrelation is chosen as the ranging code. The ground electronics verification experiment is set up for simulating the physical process of signal transmission and verifying system performance. The main device of the experiment is a FPGA card based on the K7 chip from Xilinx, which is used to simulate the function of communication and ranging between satellites. Meanwhile, we change the length of the Radio Frequency (RF) coaxial cable to correspond to different ranges. The experimental process can be summarized as follows. Firstly, 16-bit data at 24.4 kbps and 1024-bit Weil code at 1.5625 Mbps are modulated with Binary Phase Shift Keying (BPSK) in the 50 MHz sampling frequency. Then the signal is transmitted through RF coaxial cables of 10 to 60 m in length. In receiving end, the signal is consolidated by DLL and the ranging information is collected. To measure the range accurately, we use a centroid method to optimize the collected data. The results show that the ranging accuracy is better than 1.6 m within 60 m. In conclusion, this experiment proves the principle of the scheme and its feasibility, laying a technical foundation for optical system verification in the future.

A target location method for aerial images through fast iteration of elevation based on DEM
LI Zi-hao, KUANG Hai-peng, ZHANG Hong, ZHUANG Chu-heng
2023, 16(4): 777-787.   doi: 10.37188/CO.2022-0215
Abstract(164) FullText HTML(94) PDF 6346KB(151)

In the positioning process of aerial cameras with large inclination angles, the influence of height error in the earth ellipsoid model can be effectively solved with the help of a digital elevation model (DEM). This is very important for obtaining accurate ground coordinates, especially elevation. Firstly, the orientation of the line-of-sight angle in the geographic coordinate system is solved by transforming homogeneous coordinates according to the position and attitude information of the carrier aircraft and the frame angle information of the aerial camera, and then the longitude and latitude of the target point are determined by a digital elevation model. To overcome the tedious nature of calculating target elevation and the non-convergence in the imaging process, a fast iterative method is proposed to iterate over the target elevation’s value. The difference between the light elevation of the visual axis and the ground elevation is calculated by halving the target elevation. The median elevation difference is calculated iteratively until it is less than a certain threshold. Finally, Monte Carlo analysis was used to analyze the error terms in the whole imaging process. When the convergence threshold is 1/10 DEM in grid accuracy, the iteration efficiency increases by 45.5% and the convergence speed is greatly improved. Through the calculation of the digital elevation model, when the flight height is 15,409 meters and the camera frame’s angle is greater than 74°, a mountainous area’s target circular error probability is less than 200 m which meets the real engineering needs.

Microfluidic-microscopic image deformation correction method for planktonic algal cells
HU Xiang, YIN Gao-fang, ZHAO Nan-jing, HE Qian-feng, LIANG Tian-hong, HUANG Peng, Xu Min, JIA Ren-qing
2023, 16(4): 788-795.   doi: 10.37188/CO.2022-0244
Abstract(186) FullText HTML(107) PDF 3089KB(193)

Flow cytomicrographic analysis is an important development in the automatic identification of planktonic algae in a water column, but the accuracy of this process is affected by the deformation of microscopic images under rapid injection conditions. Based on a microfluidic-microscopic imaging system for planktonic algae, the effects of flow rate on the deformation of microscopic images were investigated by analyzing the deformation of algal cells and image clarity at different injection flow rates. Based on the principle of deformation caused by photographing a moving object using a rolling shutter, a method of image deformation correction with unidirectional offset pixels is proposed and analyzed by comparing its results with images acquired under static conditions of algal cells. The experimental results showed that the average aspect ratio and sharpness of L values for oocystis cell images under static conditions were 1.16 and 116.53, respectively; during the dynamic injection process, the deformation (aspect ratio) of the cell images gradually increased and the sharpness decreased as the flow rate increased; the average values of aspect ratio before and after correction were 1.35 and 1.26 respectively at 95µL/min injection flow rate, and the dispersion of deformation decreased from 0.33 before correction to 0.1. The results are close to that of static cell morphology and the image sharpness is basically same. The results provide a method for improving the accuracy of the automatic identification of planktonic algal cells in a water column.

Imaging and detection method for static interferometric high-temperature temperature field
ZHANG Rui, XU Cheng-yu, WANG Zhi-bin, TANG Wei-ping, XUE Peng, LI Meng-wei
2023, 16(4): 796-801.   doi: 10.37188/CO.2022-0168
Abstract(274) FullText HTML(111) PDF 2942KB(201)

In order to realize the non-contact high-precision measurement of high-temperature temperature fields such as the tail flame, combustion and explosion of aerospace engines, a static interferometric high-temperature temperature field imaging and detection method is studied. Firstly, a static interference high-temperature temperature field detection system is designed. On the basis of theoretical analysis of the measurement principle of high-temperature temperature fields, the relationship between the optical path difference and the temperature at the lowest point of high-temperature interference signal intensity is studied. Secondly, according to the response band of the visible light area array detector and the common temperature range, a static interferometric Savart prism is designed, and temperature field imaging is realized by using it for one-dimensional scanning. Finally, the optical system is designed and the corresponding relationship between the minimum optical path difference of the interference and the temperature is obtained by fitting. From this, the linear fitting formula is obtained. Simulations are conducted to verify the interference signal image where the temperature field after passing through the system reaches the area detector. The static interferometric high-temperature temperature field detection method can achieve the high-precision detection of 1000 K−3000 K temperatures. In the linear region, the temperature measurement resolution is 1.4 K and the temperature measurement relative error is better than 0.8%. This research lays the foundation for high-precision high-temperature temperature field imaging in the military and civilian fields.

High precision structural light scanning viewpoint planning for aircraft blade morphology
LI Mao-yue, CAI Dong-chen, ZHAO Wei-xiang, XIAO Gui-feng
2023, 16(4): 802-815.   doi: 10.37188/CO.2022-0221
Abstract(194) FullText HTML(83) PDF 6409KB(230)

The machining quality and detection accuracy of aero-engine blades have a very important influence on their service life of blades. To improve the accuracy of blade detection, a high-precision scanning viewpoint planning method based on structured light is proposed in this paper. Firstly, coarse model data was obtained by coarse scanning under the overall size of the blade, and the field of view was determined according to the camera resolution and acquisition accuracy. Secondly, an improved Angle Criterion algorithm was used to extract the boundary, and the boundary segmentation points were determined according to the boundary coordinates and the range of the visual field. The coarse model was sliced by the section line method for a surface, and the internal segmentation points were determined according to the slice results to complete the uniform segmentation of point clouds. Then, a directed bounding box was established for the segmented point cloud data to obtain the coordinates of the center point, and the normal vector was statistically analyzed to determine the orientation of the main normal to generate the viewpoint coordinates for high-precision scanning. Finally, the surface morphology of the blade was tested and verified. The experimental results show that the average standard deviation of the proposed method is reduced by 0.0054 mm and the collected viewpoint is reduced by 1/3 compared with the viewpoint acquisition result of the supervoxel segmentation, which has good application prospects in the machining inspection of thin-walled blades.

Fano resonances design of metamaterials based on deep learning
YANG Zhi-hu, FU Jia-hui, ZHANG Yu-ping, ZHANG Hui-yun
2023, 16(4): 816-823.   doi: 10.37188/CO.2022-0208
Abstract(302) FullText HTML(209) PDF 4452KB(239)

In this paper, a metamaterial Fano resonance design method based on deep learning is proposed to obtain high-quality factor (high-Q) resonances with desired characteristics, such as linewidth, amplitude, and spectral position.The deep neural network is used to establish the mapping between the structural parameters and the transmission spectrum curve. In the design, the forward network is used to predict the transmission spectrum, and the inverse network is used to achieve the on-demand design of high Q resonance. The low mean square error ( MSE ) is achieved in the design process, and the mean square error of the training set is 0.007. The results indicate that compared with the traditional design process, using deep learning to guide the design can achieve faster, more accurate, and more convenient purposes. The design of Fano resonance can also be extended to the automatic inverse design of other types of metamaterials, significantly improving the feasibility of more complex metamaterial designs.

High quality factor dual wavelength Fano resonance based on continuous bound states
WANG Lin, DONG Fan-long
2023, 16(4): 824-832.   doi: 10.37188/CO.2022-0166
Abstract(233) FullText HTML(183) PDF 5763KB(222)

In order to improve the quality value (Q) to enhance the coupling between light and matter. In this paper, a dielectric metamaterial with simple structure, low fabrication requirements was proposed. It can excite symmetric protected bound states in the continuum (BICs). The dielectric metamaterial has a planar nanopore plate composed of tetrameric pores. By changing the position of the nanopores, the symmetrical protection BIC can be transformed into the symmetrical protection quasi BIC(QBIC), and then two high Q value Fano resonances can be induced. Through simulation calculation, the Fano resonance Q value can reach 1×e6 when Δ=3 nm. Then, the far-field radiation of QBIC and Fano resonance is decomposed into the contributions of different multipole components. Based on the scattering power and electric field vector distribution, it can be found that the dielectric metamaterials λ1 Fano resonance with high Q value is mainly due to magnetic quadrupole and toroidal dipole, while λ2 Fano resonance has high Q value is mainly due to the toroidal dipole. Finally, the influence of nanopore side length and nanopore filling material on the two Fano resonances is analyzed and calculated. The research in this paper can provide theoretical guidance for the future research and preparation of high Q value optical response devices.

Cophasing error of the Golay3 sparse aperture imaging system
QIAN Jun-hong, ZHANG Rong-zhu
2023, 16(4): 833-842.   doi: 10.37188/CO.2022-0203
Abstract(227) FullText HTML(121) PDF 5588KB(210)

Multiple sub-aperture interference imaging enables the images formed by the sparse aperture imaging system to have a higher resolution after the cophasing error is corrected. In this paper, the MTF and surface target imaging of the system are analyzed with a Golay3 sparse aperture imaging system as the research object when there are different piston and tilt errors among the sub-apertures. A Golay3 sparse aperture imaging system was developed to carry out an imaging experiment with the USAF1951 resolving power test target as the area target. Three-aperture synthetic imaging is achieved by adjusting the position of the plane mirror in the light beam deflection and the adjustment module to correct the piston and tilt errors of the sub-apertures. The results of a theoretical analysis are then verified. According to calculations, the developed system’s angular resolution of 1.38 μrad is close to the equivalent single-aperture imaging system’s theoretical resolution of 1.18 μrad. The developed Golay3 sparse aperture imaging system can correct the cophasing errors and improve the imaging resolution.

An adaptive optics system suitable for near-ground imaging
WANG Hai-ming, QUAN Jia-ning, GE Bao-zhen
2023, 16(4): 843-852.   doi: 10.37188/CO.2022-0230
Abstract(223) FullText HTML(111) PDF 5461KB(226)

In order to overcome the adverse effects of near-ground turbulence on the imaging quality of the optical systems at imaging distances of tens to hundreds of meters, an optical imaging system based on a long focal length telescopic objective lens and an integrated adaptive module is designed. With a system center height of 1.9 m and the imaging distance of 50−200 m, the outdoor imaging experiment of a resolution plate is carried out. The experimental results show that the influence of turbulence on imaging quality is obvious at medium and long distances of 50−200 m near the ground. The experimental system can effectively overcome the influence of turbulence at different distances and improve the consistency of image resolution and clarity. As the imaging distance increases, the influence of turbulence increases, and the system’s correction ability and the imaging quality decrease. The imaging resolution of the system can reach 0.5 mm at an imaging distance of 100 m. Cracks on the surface of a concrete model are observed and corrected at a distance of 200 m. The experimental results show that the system can suppress the influence of turbulence and improve the clarity of the image, which verifies the practical application ability of the system.

Passive athermalization design of a cooled infrared optical system
LI Kang, ZHOU Feng, WANG Bao-hua, GONG Hui, ZHENG Guo-xian
2023, 16(4): 853-860.   doi: 10.37188/CO.2022-0205
Abstract(221) FullText HTML(122) PDF 5867KB(228)

Under conditions with large temperature differences, the imaging quality of an infrared optical system will deteriorate due to severe temperature changes. Large field-of-view medium-wave infrared cameras for airborne forest fire monitoring work in drastically changing environments, so the optical system has high requirements for stray radiation. In order to ensure that the optical system performs stably and with good imaging quality in the large field-of-view and the required large temperature range, a cooled medium-wave infrared optical system is designed based on athermalization and the comprehensive evaluation method of stray radiation based on noise equivalent temperature difference. The optical system consists of 6 lenses and 1 filter with working wavelength of 3.7−4.8 μm, F-number 2.5, focal length 62.5 mm, and field of view 14.36°×10.87°, respectively. The pixel resolution of the medium-wave cooled detector is 640×512. By using a combination of silicon and germanium materials and reasonably distributing the optical power, achromatic aberration and athermalization designs are realized. Through cold reflection optimization and cold aperture matching, stray radiation noise in the system is well-suppressed. By a bit of aspheric optimization, higher-order aberrations are corrected based on the requirements. The results show that the imaging quality of the optical system is stable and good in the temperature range of −55~+70 °C.

Tunable long-wave infrared optical parametric oscillator based on temperature-adjustable ZnGeP2
TIAN Jun-tao, LI Hui, ZHAO Li-li, LI Zhi-yong, WANG Hai, LIU Song-yang, XU Wen-ning, BAI Jin-zhou, TAN Rong-qing
2023, 16(4): 861-867.   doi: 10.37188/CO.2022-0217
Abstract(169) FullText HTML(140) PDF 4082KB(195)

In order to realize tunable longwave infrared laser, we design a ZGP temperature tuned longwave infrared optical parametric oscillator. A Ho:YAG laser with the center wavelength of 2097 nm is used to pump ZGP crystals with different phase matching angles. The temperature adjustable properties of ZGP-OPO is researched by changing the operating temperature of crystal. The laser with a segment continuously tunable range of 7.53−8.77 μm is realized in the temperature range of 15−30°C, with a total tuning range of 1.24 μm. The output power of ZnGeP2-Optical Parametric Oscillator(ZGP-OPO) is greater than 1.503 W over the entire tuning range. The output power is 1.503 W at the idler wavelength of 8.77 μm, and the corresponding slope efficiency and optical conversion efficiency are 12.19% and 6.53%, respectively. The experimental results show that temperature tuning of ZGP is an effective technical method to obtain continuously tunable long-wave infrared laser. This research has potential application value in the field of engineering of tunable long-wave laser.

Repeated zoom accuracy index of an electrowetting lens and its optimization method
HUANG Peng, YANG Xiao-ying, CHEN Bin, SONG Yue
2023, 16(4): 868-877.   doi: 10.37188/CO.2022-0209
Abstract(177) FullText HTML(114) PDF 6746KB(189)

Tacking the research of glass lenses as reference, a statistical data-based index of liquid lens zoom stability and liquid lens repeated zoom accuracy is proposed. An experimental method is presented to optimize the structural parameters and materials of the liquid lens. Firstly, the main factors affecting the accuracy of a liquid lens’ repeat zoom accuracy were obtained through preliminary experimental research, including the polar solution volume, taper and non-polar solution viscosity. Secondly, taking the accuracy of the liquid lens’s repeat zoom accuracy and zoom range as evaluation indicators, it was found that the relationship between the accuracy of the liquid lens’s repeat zoom and the voltage is not monotonic, and that it rises first and then falls. On this basis, through the range analysis and comprehensive balance method, the primary and secondary factors and the optimal combination of parameters is obtained. After that, orthogonal experiments were used to optimize the design parameters. Finally, the effectiveness of this method was verified by experiments. The experimental results show that the repeat zoom accuracy of the optimized liquid lens is 0.2 m−1, and the zoom range is −15.2−5.85 m−1 over the voltage range of 0 to 230 V. It basically meets the requirements of stable and reliable, high precision, and large zoom range for liquid lens zoom.

Real-time measurement for boresight vibration of dual line array surveying and mapping cameras
ZHAI Guo-fang, YU Qing-sheng, WANG Yun-long, GAO Wei-jun
2023, 16(4): 878-888.   doi: 10.37188/CO-2022-0175
Abstract(131) FullText HTML(102) PDF 3131KB(113)

In order to realize the real-time measurement of the boresight vibration of the dual line array surveying and mapping camera, a measurement model of the optical axis of the aerospace line array surveying and mapping camera is established. First, by setting up laser transceivers at both ends of the focal plane of the camera, through the central prism correlation, an angle parameter change measurement model for the two cameras is constructed. An optical axis measurement method for multi-line array cameras based on the dual-vector attitude determination principle is proposed. The calculation expression is given and the algorithm error is analyzed, which is verified by simulation. In addition, the residuals of the two algorithms are simulated and the results show that the simplified algorithm is only in good agreement with the dual vector algorithm in a small measurement range but when the detection range is expanded to 2 seconds, the algorithm in this article can be used to obtain 0.1 arc-second. Finally, the algorithm was tested and verified in a thermal vacuum environment, which verified that the calibration accuracy of the internal and external parameters of the camera using this algorithm reached 0.1 arc-second. The results showed that the angle parameters of the two cameras exhibited the periodicity of the orbit, which provided good conditions for the subsequent development of stereo surveying and mapping tasks.

Angle-multiplexed optically encrypted metasurfaces fabricated by ultrafast laser induced spatially selective-modified nanograting structures
ZHANG Xiao-bin, HAN Wei-na
2023, 16(4): 889-903.   doi: 10.37188/CO.2022-0228
Abstract(222) FullText HTML(153) PDF 6608KB(180)

The optical encrypted metasurface based on one-dimensional grating diffraction requires the processing of mask or unit structure one by one, resulting in low efficiency. In addition, the poor uniformity of the structure formed by conventional ablated LIPSS can also affect device performance. Aming at the above problems, an optical metasurfaces processing method is proposed based on modified structures obtained by picosecond laser direct writing phase-change material Ge2Sb2Te5. Firstly, the dispersion properties of the prepared GST-modified gratings are first characterized, and the angle-multiplexed information encryption metasurfaces are designed by combining the polarization dependence of the modified grating, and the metasurface prepared by the proposed method is further demonstrated. In addition, the performance of encryption under natural light conditions and selective decryption reading and dynamic display under strong light conditions has been achieved. Compared to the conventional processing method, the proposed method can generate a series of grating structures in the form of simultaneous printing in a direct writing process, which improves the processing efficiency. At the same time, the grating structure obtained by processing has good uniformity and consistency, which improves the color rendering effect. A modified grating with an orientation angle difference of 16° is used to realize selective information reading without crosstalk resulting in uniform and bright structural colors. The processing strategy proposed in this paper has a profound application prospect in the fields of anti-counterfeiting, information encryption storage and wearable flexible display devices.

Theoretical design and preparation of high performance MWiR notch filter
SHANG Peng, CHEN Bei-xi, SUN Peng, LIU Hua-song, BAI Jin-lin, JI Yi-qin, CAO Bo, MA Yuan-fei, LIN Quan
2023, 16(4): 904-915.   doi: 10.37188/CO.2022-0193
Abstract(114) FullText HTML(72) PDF 5618KB(249)

In order to effectively suppress the interference of CO2 radiation 4.3 μm on MWiR target signal with wavelength of 3 μm−5 μm, based on the Needle random intercalation optimization algorithm, an accurate inversion correction model for the growth error of multi-layer ultra-thick Ge/Al2O3 films under quartz crystal monitoring is established by the electron beam evaporation method, thus realizing the design, the accurate inversion and the accurate preparation of MWiR notch filter. In order to solve the problem that the surface profile of the MWiR notch filter changes greatly, the preset substrate surface method is used to realize the low surface profile regulation of MWiR notch filter. The results show that the high refractive index Ge film has good deposition stability with the increase of coating time, while the deposition scale factor of low refractive index Al2O3 thin film changes up to 11.9% in a regular gradual trend. For the prepared MWiR notch filter, the average cut-off transmittance is less than 0.3% in the wavelength range of 4.2 μm−4.5 μm, and the average transmittances are more than 95% in the wavelength range of 3.5 μm−4.05 μm and 4.7 μm−5.0 μm. The surface profile of the substrate after coating can be effectively controlled in a small range. The film has good adaptability to complex environment, and has successfully passed the environmental test of firmness, high temperature, low temperature and damp heat specified in GJB 2485-95.

Interferometry of double-sided polished wafer and error analysis
BIAN Xiao-yue, HAN Sen, WU Quan-ying
2023, 16(4): 916-932.   doi: 10.37188/CO.2022-0226
Abstract(286) FullText HTML(196) PDF 6742KB(203)

An interferometric measurement method is proposed to measure the Total Thickness Variation (TTV) and the Bow and Warp in the deformation of a double-sided polished wafer. Two phase-shifting Fizeau interferometers with reference mirrors are used to measure the topography of the front and back surfaces of the wafer simultaneously, and the measured topography of the front and back surfaces of the wafer are combined with the cavity topography of the two interferometers when the wafer is not placed to obtain the surface parameters of the double-sided polished wafer which are not affected by the reference mirror error. In the combined operation, the mapping error is introduced because the two reference mirrors are not precisely aligned, which affects the measurement results of the relevant parameters. To this end, before wafer measurement, the three-point positioning device is fixed between the two reference mirrors, and the position of the two reference mirrors is continuously adjusted based on the three-point circular theorem, which can make the mapping error extremely small, thereby reducing the influence of the mapping error on the measurement results. The experimental results show that the mapping errors of 50 mm wafer transverse and longitudinal directions are 21.592 μm and 37.480 μm, respectively, and the TTV, Bow and Warp are 0.198 μm, −0.326 μm and 1.423 μm, respectively. In order to further verify the effectiveness of the adjustment method, a single interferometer was used to flip the wafer for measurement, and the TTV, Bow and Warp of wafer are 0.208 μm, −0.326 μm and 1.415 μm, respectively. The proposed interferometric method can be easily and quickly used for the measurement of large quantities of large-sized wafers after adjusting the position of two reference mirrors, which improves wafer inspection efficiency. At the same time, it has a superior measurement accuracy.

Coplanar excitation of terahertz spoof surface plasmon and high-Q sensing
YAN De-xian, CHENG Gang, LI Er-ping, LI Xiang-jun, ZHANG Xue-ru, WU Yi-lin
2023, 16(4): 933-947.   doi: 10.37188/CO.2022-0204
Abstract(210) FullText HTML(169) PDF 2122KB(278)

In this paper, the coplanar excitation of terahertz Spoof Surface Plasmon (SSP) realized by using a single-layer grating meta-surface coupling method is proposed, which overcomes the disadvantages such as the reflection measurement when applying the medium couplers. The periodic grating and terahertz SSP composite structure are simultaneously constructed on the monolayer metal structure. When the terahertz waves are incident vertically, the wave vector of grating structures and the wave vector of SSPs are matched, and the SSP mode can be excited. The high Q value resonant peaks can be generated in the transmission spectrum, and the Q factor can reach 1923. The effects of the structural parameters on the grating-coupled meta-surface transmission spectrum and dispersion characteristics are also analyzed. In addition, based on the high Q resonant peak in the transmission spectrum of the designed structure, the high sensing sensitivity is about 67 GHz/RIU at the resonant center frequency of 0.22 THz. The structure proposed in this paper, which realizes terahertz SSP excitation and high Q sensing by treating a single-layer meta-surface structure, exhibits great application potential in many practical applications.

Microwave photonic RF frequency multiplying phase shifter with tunable multiplication factor and a full 360-deg tunable range
YAN Ying, MA Jian-xin
2023, 16(4): 948-960.   doi: 10.37188/CO.EN.2022-0019
Abstract(290) FullText HTML(246) PDF 4944KB(263)

A filterless Microwave Photonic Phase Shifter (MPPS) with a tunable Frequency Multiplication Factor (FMF) and a full 360-deg tunable range is theoretically analyzed and verified by simulation. In the scheme, two parallel Mach-Zehnder Modulators (MZM), cascaded with two Dual-Parallel integrated Mach-Zehnder Modulators (DPMZM) by a 2×2 Optical Coupler (OC), are used to generate the ±1st- to 4th-order sidebands adjustably, and a Phase Modulator (PM) is used to phase shift one of the two lightwaves. After photodetection, the 2nd- to 8th- order harmonics with a continuously tunable phase shift from 0 to 360-deg can be generated by adjusting the RF driving signal and the DC bias voltage of the DPMZM, and the DC voltage of the PM. Simulation results demonstrate that both 360-deg continuously tunable phase shift and frequency multiplication can be implemented. Large Optical Sideband Suppression Ratio (OSSR) and Electrical Spurious Suppression Ratio (ESSR) of around 20 dB can be obtained. The phase shifter wavelength insensitive performance has been also evaluated by simulation.

Double Fano resonance and refractive index sensors based on parallel-arranged Au nanorod dimer metasurface arrays
ZHANG Zhi-dong, ZHANG Hui-nan, LIANG Jie, GE Hai-xia, LIU Yan-li, ZHU Xu-peng
2023, 16(4): 961-971.   doi: 10.37188/CO.EN-2023-0008
Abstract(93) FullText HTML(73) PDF 6310KB(118)

In order to study the coupling and refractive index sensing properties of a metasurface, asymmetric parallel nanorod dimers consisting of two nanorods with different lengths was proposed and designed. In this paper, the finite element method is used to simulate the optical properties and a quasi-static approximation model is used to explain the coupling mechanism of double parallel nanorods. The transmission spectra, electric field at the resonant peak, charge distribution and the influence of structural parameters on the transmission spectra are studied. The electric field distribution is simulated at the resonance wavelength, the electron vibration mode is analyzed, and asymmetric double Fano resonance appears in the transmission spectrum. The results show that the double Fano resonance is generated by the coupling between the nanorods and the substrate, and the double Fano resonance can be regulated by the structural parameters and the refractive index of the surrounding medium. The sensitivity of the refractive index based on the Fano resonance can reach 1.137 μm/RIU. These results provide a theoretical basis for the design of a surface plasmon refractive index sensor.

Recent progress of non-line-of-sight imaging reconstruction algorithms in typical imaging modalities
ZHAO Lu-da, DONG Xiao, XU Shi-long, HU Yi-hua, ZHANG Xin-yuan, ZHONG Yi-cheng
2023, 16(3): 479-499.   doi: 10.37188/CO.2022-0186
Abstract(707) FullText HTML(290) PDF 11662KB(465)

Non-line-of-sight (NLoS) imaging is a promising technique developed in recent years, which can reconstruct hidden scenes by analyzing the information in the intermediate surface, and "see around the corner", and has strong application value in many fields. In this paper, we review the reconstruction algorithm for NLoS imaging tasks. Firstly, considering the crossover and non-independent phenomena existing in the NLoS imaging classification, we use the different features of physical imaging models and algorithm models to reclassify them. Secondly, according to the proposed classification criteria, we respectively review the traditional and deep learning-based NLoS imaging reconstruction algorithms, summarize the state-of-the-art algorithms, and derive the implement principle. We also compare the results of deep learning-based and traditional NLoS imaging reconstruction algorithms for reconstruction tasks. Finally, the current challenges and the future development of NLoS imaging are summarized. Different types of NLoS imaging reconstruction algorithms are comprehensively analyzed in this review, which provides important support for the further development of NLoS imaging reconstruction algorithms.

Research progress of gas detection based on laser-induced thermoelastic spectroscopy
LOU Cun-guang, DAI Jia-liang, LI Rui-kai, LIU Xiu-ling, YAO Jian-quan
2023, 16(2): 229-242.   doi: 10.37188/CO.2022-0137
Abstract(618) FullText HTML(312) PDF 7682KB(501)

Laser-Induced Thermo-Elastic Spectroscopy (LITES) is a new developed gas detection technology based on the thermoelastic effect of Quartz Tuning Forks (QTF). The QTF has the advantages of low cost, small volume, high sensitivity and wide spectral response range, and the LITES is becoming a vital method for trace gas detection. In this paper, the basic principle of gas concentration measuring based on LITES is firstly analyzed. Secondly, from the perspective of various technical methods, this paper introduces the methods for improving the sensitivity of QTF detectors, and reviews the research progress of LITES system in recent years. The performance of these systems is evaluated by the signal amplitude, Signal-to-Noise Ratio (SNR), minimum detection limit, and Normalized Noise Equivalent Absorption (NNEA) coefficient. Finally, the practical application of LITES in the field of gas detection technology is briefly reviewed, and the methods for further improving its sensitivity are summarized and prospected.

Research progress of temperature, humidity and pressure detection technology using raman lidar
LIU Dong, YAO Qing-rui, ZHANG Si-nuo, GAO Jia-xin, WANG Nan-chao, WU Jiang, LIU Chong
2023, 16(2): 243-257.   doi: 10.37188/CO.2022-0145
Abstract(656) FullText HTML(347) PDF 4220KB(459)

Atmospheric temperature, humidity and pressure are deemed important atmospheric parameters. Quickly and accurately understanding the temperature, humidity and pressure information of the atmosphere and their changing trends is of great significance to research on meteorology, climatology, and artificial weather research. Raman lidar can obtain various atmospheric environment-related parameters by separating Raman scattering signal inversion, which can achieve high accuracy detection of atmospheric parameter profile information. Raman lidar has unique advantages and potential in atmospheric temperature, humidity and pressure detection. With an introduction to the principle and inverse analysis algorithm of Raman lidar for atmospheric temperature, humidity and pressure detection, this paper also highlights the advantages and disadvantages along with related advances of spectral devices such as filters, etalons and gratings commonly used in Raman lidar. The detection techniques involved in Raman lidar are also included. Finally, typical applications of meteorological parameter measurements by Raman lidar are shown.

Research progress on high-resolution imaging system for optical remote sensing in aerospace
SU Yun, GE Jing-jing, WANG Ye-chao, WANG Le-ran, WANG Yu, ZHENG Zi-xi, SHAO Xiao-peng
2023, 16(2): 258-282.   doi: 10.37188/CO.2022-0085
Abstract(960) FullText HTML(436) PDF 10445KB(600)

With the continuous development of optical imaging technology and the growing demand for remote sensing applications, cross-scale high-resolution optical technology has been widely used in the field of remote sensing. In order to obtain more detailed information on the target, domestic and foreign researchers have carried out relevant research in different technical directions. In this paper, through the technical classification of remote sensing imaging, we introduce a representative aerospace optical remote sensing high-resolution imaging system. It focuses on monomer structure, block expandable imaging, optical interference synthesis aperture imaging, diffraction main mirror imaging, optical synthetic aperture and other technologies. It provides a new idea for the development of high-resolution optical remote sensing loads on the ground.

Application of laser in the medical field
GU Yong-gang, NIU Jian, YANG Jian, XU Hong-xing
2023, 16(2): 283-295.   doi: 10.37188/CO.2023-0017
Abstract(462) FullText HTML(249) PDF 3656KB(299)

With the rapid development of laser technology, the application of laser in the medical field has gained growing attention. Due to its advantages of non-contact, high precision, low damage, portability and operational flexibility, laser treatment significantly enriches the clinical treatment toolkit. Moreover, it has substituted traditional methods for certain diseases and improved the overall medical treatment capability. Currently, laser treatment has gained increasing market share and has a great potential for even more widespread applications. Here, we introduce the laser treatment technique and the requirements of medical laser systems, expound the current status of the applications of laser treatment in clinical departments in a comprehensive manner, and give suggestions regarding to the problems in the laser treatment field in China.

Bound states in continuum in periodic optical systems
YAO Jian-quan, LI Ji-tao, ZHANG Ya-ting, LI Jie, YUE Zhen, XU Hang, YANG Fan
2023, 16(1): 1-23.   doi: 10.37188/CO.2022-0189
Abstract(1688) FullText HTML(474) PDF 7237KB(819)

Periodic optical systems, such as photonic crystals and optical metamaterials, can localize high-density electromagnetic field energy at subwavelength scales and obtain extremely small mode volumes, so they have great application potential in the field of light manipulation. In recent years, a strong interaction between light and matter in periodic optical systems has been discovered, which is called Bound States in Continuum (BIC). Optics BICs are special electromagnetic eigenstates whose frequencies lie in the radiation continuum but are completely localized, and have shown interesting physics and rich application scenarios. This paper systematically reviews the classification and theory of BICs in periodic optical systems, and summarizes their basic physical properties and the latest application development. BICs in periodic optical systems are injecting new impetus into the fields of integrated optics, information optics, bio-optics, topological optics, and nonlinear optics.

Recent progress on synthesis and optical characterization of two-dimensional Bi2O2Se
XIE Bing, AN Xu-hong, ZHAO Wei-wei, NI Zhen-hua
2023, 16(1): 24-43.   doi: 10.37188/CO.2022-0071
Abstract(670) FullText HTML(390) PDF 12124KB(516)

Two-dimensional (2D) Bi2O2Se has attracted broad attention in the field of electronic and optoelectronic applications in the UV-Vis-NIR region due to its unique crystal structure, energy band, high carrier mobility, and excellent stability. In this paper, we review the recent research progress in the material synthesis and optical characterization of Bi2O2Se. Firstly, the synthetic method and growth mechanism of 2D Bi2O2Se are introduced, including Chemical Vapor Deposition (CVD), wet chemical process, Molecular Beam Epitaxy (MBE) and Pulsed Laser Deposition (PLD), etc. Via steady-state spectrum study, the properties change of 2D Bi2O2Se with thickness change can be studied, such as the band gap. The defect type, temperature coefficient and thermal conductivity of 2D Bi2O2Se material can be further studied by focusing on the crystal vibration mode. Transient spectrum techniques can benefit the study of relaxation process and carriers transport properties in 2D Bi2O2Se materials. Finally, we summarize the existing challenges and application prospects for the promising Bi2O2Se field.

Panoramic endoscopic imaging technology and it’s applications
HUO Jia-yi, LI Mian-hao, WANG Zi-chuan, YUAN Bo, YANG Qing, WANG Li-qiang
2023, 16(1): 44-60.   doi: 10.37188/CO.2022-0074
Abstract(738) FullText HTML(420) PDF 5785KB(612)

Panoramic endoscopic imaging technology can effectively reduce the observation blind area of internal organs. It has many advantages, such as shortening the operation time, reducing the risk of intraoperative bleeding, improving the prognosis and shortening the postoperative recovery time. It has important application value in minimally invasive surgery and preoperative examination. It is a research hotspot in recent years. This paper combs the panoramic endoscopic imaging technology from two aspects: principle and product applications. Firstly, various panoramic endoscopic imaging technologies based on two-dimensional and three-dimensional imaging are reviewed, their implementation methods are described, and their key indexes and performances are analyzed. Secondly, the capsule endoscope, panoramic enteroscope and other different types of products derived from panoramic endoscopic imaging technology are compared and analyzed, and the development trend and application prospect of panoramic endoscopic imaging technology are prospected.

Research progress of monolithic integration master-oscillation power-amplifiers
TAN Man-qing, YOU Dao-ming, GUO Wen-tao, LIU Wei-hua
2023, 16(1): 61-75.   doi: 10.37188/CO.2022-0022
Abstract(580) FullText HTML(293) PDF 6306KB(494)

Besides its advantages in volume, power and beam quality, a monolithic integration Master-Oscillation Power-amplifier (MOPA) can also realize a narrower linewidth and dynamic single-mode by integrating Bragg grating. Its application value is high in the fields of frequency doubling, pumping, optical communication and sensing, which makes it a popular research topic in recent years. This paper firstly went over the mainstream structure and characteristics of monolithic integrated MOPA, including a tapered amplifier, ridge amplifier, Bragg grating and three-section MOPA. Based on their working principles and performance characteristics, we introduce the main research directions and the latest development trends in combination with their problems. Aiming at the problem of beam quality degradation at high power in monolithic integrated MOPA, the optimal design of epitaxial layer structure, facet optical film and electrode aspects are then summarized for monolithic integrated MOPAs. After that, we sort out the research progress of MOPAs with different performance characteristics for various application requirements including high power, narrow linewidth, high beam quality and high brightness. Finally, we prospect the development trend of monolithic integrated MOPA.

Design, preparation and application of orthogonal excitation-emission upconversion nanomaterials
JIA Heng, FENG Xiao-rui, LI Da-guang, QIN Wei-ping, YANG Long, HE Wei-yan, MA Hui-yan, TENG Ying-yue
2023, 16(1): 76-93.   doi: 10.37188/CO.2022-0134
Abstract(1123) FullText HTML(530) PDF 6214KB(511)

Rare earth-doped upconversion luminescence nanomaterials have received considerable attention from researchers due to their great potential for applications in many fields such as information security, biomedicine, optical fiber communication, digital displays, and energy. The recently-developed upconversion luminescence nanoparticles with orthogonal excitation-emission properties have attracted especially strong research interest because their distinct luminescence outputs can be dynamically modulated by switching the excitation conditions. The orthogonal luminescence properties further endow such nanocrystals with a set of new features and functionalities, which largely expands their potential applications. This review summarizes the progress in the development of orthogonal upconversion luminescence of rare earth ions, and provides a systematic discussion on design principles and construction strategies of orthogonal excitation-emission systems based on core-shell structures, as well as introduces their recent advances in various fields of applications including data storage, security anti-counterfeiting, digital displays, sensing, bioimaging and therapy. Furthermore, the prospective opportunities and challenges in the future research of orthogonal luminescence systems are also provided.

Resolution, super-resolution and spatial bandwidth product expansion——some thoughts from the perspective of computational optical imaging
ZUO Chao, CHEN Qian
2022, 15(6): 1105-1166.   doi: 10.37188/CO.2022-0105
Abstract(1816) FullText HTML(457) PDF 19381KB(1175)

Conventional optical imaging is essentially a process of recording and reproducing the intensity signal of a scene in the spatial dimension with direct uniform sampling. In this process, the resolution and information content of imaging are inevitably constrained by several physical limitations such as optical diffraction limit, detector sampling, and spatial bandwidth product of the imaging system. How to break these physical limitations and obtain higher resolution and broader image field of view has been an eternal topic in this field. In this paper, we introduce the basic theories and technologies associated with the resolution, super-resolution, and spatial bandwidth product expansion, as well as some examples in the field of computational optical imaging. By placing these specific cases into the higher dimensional framework of "computational optical imaging", this paper reveals that most of them can be understood as a "spatial bandwidth regulation" scheme, i.e., a process of exploiting the available degrees of freedom of the imaging system to optimally encode, decode, and transmit information within the constraints of the limited spatial bandwidth of the imaging system, or figuratively speaking - "dancing with shackles". This is essentially a legal trade-off and choice between "gain" and "loss" under physical constraints. The conclusions of this paper are expected to provide valuable insights into the design and exploration of new imaging mechanisms and methods for various complex practical imaging applications.

In-vivo across-scales two-photon microscopic imaging technique
CHEN Shuai, REN Lin, ZHOU Zhen-qiao, LI Min, JIA Hong-bo
2022, 15(6): 1167-1181.   doi: 10.37188/CO.2022-0086
Abstract(618) FullText HTML(416) PDF 7155KB(478)

Two-photon microscopy’s ability to maintain good spatial resolution in thick biological tissues has led to its application in in-vivo brain imaging studies soon after its conception. As neural networks have cross-scale multidimensional spatio-temporal properties, two-photon microscopy has developed rapidly and significantly in recent years to meet the demand for in-vivo cross-scale imaging of the brain. This paper firstly introduces the working principle of two-photon microscopy, then reviews the progress of two-photon microscopy from five perspectives: imaging field of view, imaging flux, imaging depth, resolution, miniaturization, and analyzes the difficulties and future challenges of cross-scale two-photon in-vivo microscopic imaging technology.

Multi-channel multiplexing digital holographic imaging for high throughput
HUANG Zheng-zhong, CAO Liang-cai
2022, 15(6): 1182-1193.   doi: 10.37188/CO.2022-0070
Abstract(895) FullText HTML(633) PDF 7127KB(602)

Optical imaging has become the dominant method for characterizing information in biological systems. The rapid, non-destructive and comprehensive characterization of biological samples in recent years has placed high demands on the resolvable volume of imaging systems. Digital holography records an entire complex wavefront including both the amplitude and phase of the light field by interference imaging. Due to fast, non-destructive, and 3D imaging abilities, digital holography has been used in numerous applications such as digital pathology, label-free observation and real-time monitoring of in vitro cells. First, this paper introduces the main ways to achieve high-throughput imaging, and analyzes the advantages of digital holography and the evolution of spatial bandwidth. Secondly, a theoretical framework for high-throughput multi-channel multiplexing digital holography based on the Hilbert transform is presented. Then, an extended field of view digital holographic microscope is introduced based on this theoretical framework. Experimental results indicate that the system achieves 8 times the space-bandwidth product higher than that of conventional off-axis holographic microscopes without sacrificing spatial and temporal resolution. This high-throughput digital holographic multiplexing technology can make full use of the redundant spatial bandwidth of single intensity image, which verifies the feasibility of high-throughput multi-channel multiplexing digital holography.

Large field-of-view optical microscopic imaging technology
WANG Yi-qiang, LIN Fang-rui, HU Rui, LIU Li-wei, QU Jun-le
2022, 15(6): 1194-1210.   doi: 10.37188/CO.2022-0098
Abstract(914) FullText HTML(472) PDF 10167KB(591)

With the characteristics of real-time, high-resolution and non-invasive, optical microscopy can scale from cells, tissues to whole living organisms, which has greatly expanded our understanding to the nature of life. However, due to the limited Space-Bandwidth Product (SBP), it is hard for a conventional optical microscope to achieve a large field of view with a high resolution. This makes it very difficult for microscopic imaging in large field of view biological imaging applications, such as imaging of neural circuits between the synapse of the brain neural networks. Recently, large field-of-view imaging technology has received increasing attention and experienced rapid development. The SBP has been improved ten times or even a hundred times as compared to a traditional optical microscope and the field-of-view has been expanded without sacrificing resolution, which, in turn, has resolved some major problems in biomedical research. This review introduces the progress, characteristics and corresponding biological applications of several typical trans-scale optical imaging techniques in recent years, and gives an outlook on their future development.

Recent progress on the reconstruction algorithms of structured illumination microscopy
ZHOU Bo, WANG Kun-hao, CHEN Liang-yi
2022, 15(6): 1211-1227.   doi: 10.37188/CO.EN.2022-0011
Abstract(423) FullText HTML(366) PDF 6600KB(496)

As an early component of modern Super-Resolution (SR) imaging technology, Structured Illumination Microscopy (SIM) has been developed for nearly twenty years. With up to ~60 nm wavelengths and 564 Hz frame rates, it has recently achieved an optimal combination of spatiotemporal resolution in live cells. Despite these advantages, SIM also suffers disadvantages, some of which originated from the intrinsic reconstruction process. Here we review recent technical advances in SIM, including SR reconstruction, performance evaluation, and its integration with other technologies to provide a practical guide for biologists.

Advances in organic fluorescent probes for super-resolution imaging of cellular lipid droplets
ZHOU Ri, WANG Chen-guang, LU Ge-yu
2022, 15(6): 1228-1242.   doi: 10.37188/CO.2022-0077
Abstract(653) FullText HTML(367) PDF 9403KB(422)

Lipid droplets are a kind of spherical organelle in eukaryotic cells and are relevant to many cellular physiological processes. Fluorescence imaging techniques are one of the most powerful tools to visualize and study lipid droplets. However, conventional wide-field microscopy and confocal microscopy can only provide a resolution of about 250 nm due to the limitation of optical diffraction. This resolution is quite insufficient for visualizing the small lipid droplets, especially the nascent ones (size of about 30~60 nm). Emerging super-resolution microscopes that can break the diffraction limit (such as stimulated emission depletion microscopy, structured illumination microscopy and photoactivated localization microscopy) have gradually attracted much interest in recent years. To obtain high-resolution fluorescence images of lipid droplets, the advanced fluorescent probes which meet the special requirements of the corresponding super-resolution microscopes are highly essential. This review paper will briefly introduce the working principles of various super-resolution microscopes, discuss the special requirements on the photophysical properties of fluorescent probes, and systematically summarize the research progress of super-resolution imaging of lipid droplets by employing these fluorescent probes. Meanwhile, this review will compare the advantages and shortcomings of different super-resolution techniques for lipid droplets imaging, and prospect their future possible trends.

Advances in multi-dimensional single molecule imaging
LI Meng-fan, CHEN Jian-wei, SHI Wei, FU Shuang, LI Yun-ze, LUO Ting-dan, CHEN Jun-fan, LI Yi-ming
2022, 15(6): 1243-1257.   doi: 10.37188/CO.2022-0088
Abstract(424) FullText HTML(391) PDF 8194KB(414)

Single-molecule imaging is widely used for the reconstruction of three-dimensional subcellular structures. The point spread function is an important window to analyze the information of a single molecule. Besides 3D coordinates, it also contains abundant additional information. In this paper, we reviewed the recent progress of multi-dimensional single-molecule imaging, including spatial location, fluorescence wavelength, dipole orientation, interference phase, etc. We also briefly introduced the latest methods for molecule localization and proposed the further directions for its research.

Multi-target panoramic digital pathology: from principle to application
ZHANG Xin-hua, LI Cai-wei, ZHANG Yu, HUANG Sheng-nan, SHI Han, WU Jun-nan, REN Shi-jie, LIU Ke-han, GAO Tong-lu, SHI Bing
2022, 15(6): 1258-1274.   doi: 10.37188/CO.2022-0091
Abstract(1026) FullText HTML(506) PDF 6335KB(478)

Digital pathology has brought new opportunities for remote pathological consultation and joint consultation owing to its convenient storage, management, browsing and transmission. However, because of the limited field of view of a microscope, panoramic imaging cannot be achieved while ensuring a high resolution. The proposal of panoramic digital pathology makes up for this defect and achieves panoramic imaging while ensuring high resolution. However, a single slice can only detect a single target, and disease diagnosis needs to observe the expression of multi-target at the same time. In recent years, multi-target panoramic digital pathology technology has developed rapidly. It has attracted much attention because of its great application potential in drug research and development, clinical research and basic research. Owing to its large field of view, wide range of colors and high flux, the system can detect the expression of various biomarkers on a whole tissue section in situ in a short time to identify the phenotype, abundance, state, and relationship of each cell. Firstly, this paper reviews the development process of digital pathology, panoramic digital pathology and multi-target panoramic digital pathology, as well as the update and iteration of technology in the development process, and illustrates the importance of developing multi-target panoramic digital pathology. Then, the multi-target panoramic digital pathology is described in detail from three perspectives: biological sample preparation, multi-color imaging system and image processing. Next, the applications of multi-target panoramic digital pathology in biomedical fields, such as tumor microenvironments and tumor molecular typing are described. Finally, the advantages, challenges and future development of multi-target panoramic digital pathology are summarized.

Recent development of cryo-correlated light and electron microscopy
LU Jing, LI Wei-xing, XU Xiao-jun, JI Wei
2022, 15(6): 1275-1286.   doi: 10.37188/CO.2022-0095
Abstract(369) FullText HTML(184) PDF 5916KB(321)

Cryo-electron tomography (cryo-ET) has become a cutting-edge technology in life sciences for the investigation of protein complexes directly in their natural state. In cryo-ET, the sample’s thickness must be less than 300 nm and the target molecule must be within the lamella, which is prepared by cryo-Focus Iron Beam (FIB) milling. In order to precisely navigate molecules and to improve the efficiency of sample preparation, cryo-Correlative Light and Electron Microscopy (cryo-CLEM) has been introduced to perform in-situ imaging on the frozen samples. The cryo-CLEM combines the localization advantages of fluorescence imaging with the resolution advantages of electron microscopy. By registering images of light and electrons, frozen samples can be thinned by FIB milling, so the efficiency of cryo-ET sample preparation can be improved. In this paper, we review the latest progress and applications of cryo-CLEM technologies, with a particular focus on super-resolution cryo-CLEM imaging and integrated cryo-CLEM. The advantages and limitations of various methodologies, as well as their application scope, are discussed. A discussion on cryo-CLEM's limitations and potential directions for its future development are also presented.

Trans-scale optical endoscopy imaging technology
WANG Zi-chuan, ZHANG Wei, GUO Fei, JIA Zhi-qiang, WANG Li-qiang, DONG Wen-fei, YANG Qing
2022, 15(6): 1287-1301.   doi: 10.37188/CO.2022-0078
Abstract(843) FullText HTML(514) PDF 8063KB(516)

Due to the advantages of high resolution, multi-scale, multi-dimension, low radiation and easy to integrate, optical imaging technology plays an important role in biomedical field. In the field of endoscopy, how to obtain, process and visualize the endoscopic image information is the core of the problem what optical imaging technology need to solve. The obtaining of trans-scale endoscopic image of patients in the medical clinical is more advantageous to the surgeon for the diagnosis of patients and can improve in accuracy of the operation. The review starts with the application of trans-scale optical imaging technology in the field of endoscopy, focusing on the different optical systems to obtain trans-scale images in clinical endoscopy, including trans-scale optical zoom system, multi-channel imaging system, fiber-scanning imaging system, and expounds its progress and future trends.

Supervisor: Chinese Academy of Sciences

Sponsors: the Changchun Institute of Optics, Fine Mechanics, and Physics (CIOMP), CAS

Editor-in-Chief: Wang Jiaqi, Academician

ISSN 2097-1842

CN 22-1431/O4



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