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Composite fast nonsingular terminal sliding mode control of fast steering mirror
LI Zhi-bin, LI Liang, ZHANG Jian-qiang
 doi: 10.37188/CO.2023-0203
Abstract(19) FullText HTML(5) PDF 9740KB(3)
Abstract:

To further enhance the control performance of the precision tracking system for laser communication, this paper studies the control method of the fast steering mirror (FSM) driven by voice coil motor. Aiming at the problems of strong cross coupling characteristics and external disturbances in the FSM, a composite fast nonsingular terminal sliding mode control strategy integrating feedforward decoupling compensation and fixed-time extended state observer is proposed. Firstly, the coupling transfer function matrix model of the FSM with double inputs and double outputs is established by using system identification method, and the feedforward decoupling compensator is designed to compensate for the coupling components and achieve motion decoupling between the X-axis and Y-axis. Secondly, the fixed-time extended state observer is designed for each decoupled single-axis model, to achieve fixed-time estimation of angular velocity and external disturbances simultaneously. Then, the fast nonsingular terminal sliding mode surface is constructed, and the exponential power function is adopted to replace the sign function in control law design, so as to improve the convergence speed of the system and suppress the chattering of sliding mode, the stability of the proposed control system and the finite-time convergence of tracking error are proved based on Lyapunov stability analysis method. Finally, the effectiveness of the proposed composite control strategy is verified by comparative experiments. The experimental results show that under the 100 Hz strong disturbances, the FSM tracking 60 Hz and 120 Hz circular trajectories, the average absolute values of its trajectory tracking error are 0.0036° and 0.0131° respectively, indicating that the system can maintain good tracking performance. The proposed composite control strategy is validated to be effective in meeting the high-precision and strong anti-disturbance requirements of the FSM for laser communication.

Terahertz band-stop filter with H-type structure
CHEN Xiang-xue, FU Zi-qin, WANG Feng-chao, CHEN Jin, YANG Jing
 doi: 10.37188/CO.2023-0179
Abstract(7) FullText HTML(4) PDF 3966KB(0)
Abstract:

In this paper, a metamaterial terahertz band-stop filter is designed based on a symmetrical H-type structure. The continuous metal arm of this H-type structure can flow current, which can provide an effective reference for expanding the application of metamaterial filters in the field of electronics. Using electromagnetic simulation software CST Microwave Studio 2021, the filtering characteristics of the filter were studied, and The geometric parameters of the filter are determined by changing the arm length, period length and double H distance. The results show that the structure can realize the function of polarization selection. Under the condition of y polarization, the filter has no obvious resonance peak in the range of 0.2−2.3 THz, but the transmittance ranges from −15 dB to −3 dB. Under the X-polarization condition, a stopband of 0.15 THz FWHM bandwidth can be obtained at the center frequency of 1.34 THz, and the transmission parameter is about −30 dB. In order to verify the simulation results, the sample of metamaterial filter was prepared by micromachining technology, and the sample was tested by transmissed-terahertz time-domain spectroscopy system. The test results were in good agreement with the simulation results.

An autofocus algorithm for fusing global and local information in ferrographic images
LIU Xin-liang, ZHANG Long-quan, LENG Sheng, WANG Jing-qiu, WANG Xiao-lei
 doi: 10.37188/CO.2023-0124
Abstract(41) FullText HTML(26) PDF 5669KB(6)
Abstract:

To address the issues of large error and slow speed of manual focusing in ferrographic image acquisition, we propose an autofocus method for fusing global and local information in ferrographic images. This method includes two stages. In the first stage, the global autofocus stage, the feature vectors of the whole image is extracted by Convolutional Neural Networks (CNN) , and the features extracted in the focus process is fused by the Gate Recurrent Unit (GRU) to predict global defocusing distance, which serves as coarse focusing. In the local autofocus stage, the feature vector of the wear particle is extracted and the current features is fused with those extracted in the previous focusing process by GRU. the current defocusing distance is predicted by the resulting fused data based on the information of the thickest particle, which facilitates fine focusing. Moreover, we propose a determination method for autofocus direction using Laplacian gradient function to improve autofocus accuracy. Experimental results indicate an autofocus error of 2.51 μm on the test set and a focusing accuracy of 80.1% with a microscope depth of field of 2.0 μm. The average autofocus time is 0.771 s. The automatic ferrographic image acquisition system exhibits excellent performance and offers a practical approach for its implementation.

Vortex phase-shifting digital holography for micro-optical element surface topography
XUE Yi meng, LIU Bing cai, PAN Yong qiang, FANG Xin meng, TIAN Ai ling, ZHANG Rui xuan
 doi: 10.37188/CO.2023-0180
Abstract(15) FullText HTML(3) PDF 5987KB(5)
Abstract:

Non-destructive, non-contact phase-shifting digital holography has distinct advantages in identifying micro-optical components. Because traditional phase-shifting digital holography requires fine control and cumbersome calibration of the phase shifter, its optical path is susceptible to mechanical vibration interference, which reduces the quality of the holographically reproduced image. This paper proposes a vortex phase-shifting digital holography for the micro-optical element surface measurement method with the help of the special phase distribution of vortex light. The method utilizes a helical phase plate to modulate the vortex phase and introduce a high-precision phase shift. Based on the constructed vortex phase-shifting digital holographic microscopy experimental setup, the actual phase shifts between phase-shift interferograms were determined using the interferometric polarity method, the relationship between the rotation angle of the helical phase plate and the phase shift was calibrated, and the feasibility of the vortex phase shift was experimentally verified. Repeated measurement experiments were carried out on the micro-lens arrays, and the measurement results were compared with those of the ZYGO white light interferometer. The results indicate that a single micro-lens's average longitudinal sagittal height is 12.897 μm with an average relative error of 0.155%. The proposed method enables highly precise measurement of the surface topography of micro-optical elements. It offers the advantages of easy operation, high stability, and high accuracy.

All-optical logic gate based on nonlinear effects of two-dimensional photonic crystals
WU Rong, YANG Jian-ye, ZHANG Hao-chen
 doi: 10.37188/CO.EN-2023-0021
Abstract(58) FullText HTML(26) PDF 5976KB(6)
Abstract:

All-optical XOR, NOT and two-input AND logic gates are designed based on the nonlinear effect and linear interference effect of photonic crystals. The complex logic expressions are divided by inversion theorem, and all-optical NOR gate and four-input AND gate logic devices are designed by cascade combination. In this paper, the Finite-Difference Time-Domain (FDTD) method is used to simulate the simulation, and the coupling characteristics of nonlinear annular cavities are analyzed. Then, the above logic devices are designed under the condition that the signal wavelength is 1.47 μm, and more input devices can be designed by expanding the input. The influence of signal power on the logic function of the four-input AND logic devices is analyzed. The results show that when the power of the signal light source is between 1.1 W/μm2 and 3.4 W/μm2, the logical contrast ratio of the output is greater than 10 dB. The response time of the designed device is only 1.6 ps, the occupied area is small, and the device is easy to expand and integrate. It has great application prospect in optical processing systems and integrated optical paths.

Measurement of methane concentration with wide dynamic range using heterodyne phase-sensitive dispersion spectroscopy
ZHOU Chen, MA Liu-hao, WANG Yu
 doi: 10.37188/CO.2023-0177
Abstract(20) FullText HTML(7) PDF 4644KB(4)
Abstract:
Objective

This paper describes the development of dual-sideband beat-suppressed heterodyne phase-sensitive dispersive spectroscopy (HPSDS) for sensitive detection of trace gases across a wide dynamic range, explores the operational characteristics of the electro-optic modulator, and explores bias voltage control methods under sideband suppression mode. The dispersion phase spectral profiles and the corresponding signal-to-noise ratios in both suppression and non-suppression modes were compared before a comprehensive evaluation of the detection performance.

Method

An HPSDS-based detection system was developed based on a near-infrared distributed feedback laser and an electro-optic modulator (EOM). The suppression of the dual-sideband beat was achieved by exploring and analyzing the optimal operational range of the EOM, leading to the optimization of dispersion phase signals with increased amplitude and high signal-to-noise ratio. The dispersion phase signals under typical high-frequency (1.2 GHz) intensity modulation were recorded for different standard methane/nitrogen mixtures. The relationship between the peak-to-peak values of the dispersion phase signals and the varied gas concentrations was then summarized. Meanwhile, wavelength modulation spectroscopy (WMS) experiments were conducted; subsequently, the HPSDS and WMS techniques’ performances were compared in terms of linearity, detection dynamic range, and immunity to optical power fluctuations; finally, the HPSDS-based system's performance was validated under a wide dynamic range and rapid time response was verified by measuring different concentrations of standard gases.

Result

Experimental results indicate that the HPSDS technique exhibits high linearity (R2 = 0.9999), a wide dynamic range (38.5 ppm to 40%), and remarkable immunity to optical power fluctuations.

Conclusion

The dual-sideband-beat-suppression-HPSDS-based methane sensor developed in this study shows great potential for uses involving wide dynamic range detection and on-site practical trace gas detection.

Design and fabrication of liquid crystal wavefront corrector based on mask lithography
DU Ying, CHEN Mei-rui, LIU Yu-tong, CAO Zong-xin, MAO Hong-min, LI Xiao-ping, SUN Hui-juan, CAO Zhao-liang
 doi: 10.37188/CO.2023-0137
Abstract(53) FullText HTML(28) PDF 7894KB(15)
Abstract:

Liquid crystal wavefront correctors (LCWFCs) exhibit high development cost and customization difficulties due to being fabricated based on the process technology of liquid crystal displays. To achieve specialized and low-cost development of LCWFCs, aliquid crystal wavefront corrector is fabricated by using the mask lithography method. Firstly, a 91-pixel passive liquid crystal driving electrode is designed and prepare based on the mask lithography technology and then, packaged as a liquid crystal optical correction unit. A circuit board for driver connection is designed and prepared to connect the optical correction unit and the driving circuit board. Next, the response characteristics of the LCWFC are tested, and the results show that the phase modulation is 5.5 λ, and the response time is 224 ms. Finally, the spherical waves are obtained and the static tilt aberrations are corrected based on Zygo interferometer. The results show that the LCWFC can generate positive and negative defocused wavefronts. Further, after correction of the horizontal tilt aberration, the coefficient of the first term of the Zernike polynomials is decreased from 1.18 to 0.16. Therefore, the aberration is corrected with the amplitude of 86%. This work may provide new ideas for the development of LCWFCs, and then expanding their application fields and scenarios.

A photoacoustic tomography image reconstruction method based on forward imaging model
CHENG Li-jun, SUN Zheng, SUN Mei-chen, HOU Ying-sa
 doi: 10.37188/CO.2023-0114
Abstract(73) FullText HTML(40) PDF 9816KB(18)
Abstract:

Aiming at the issue of degraded image quality in photoacoustic tomography (PAT) caused by the inhomogeneous light fluence distribution, complex optical and acoustic properties of biological tissues, and non-ideal properties of ultrasonic detectors, we propose a comprehensive forward imaging model. The model takes into account variables such as the inhomogeneous light fluence, unsteady speed of sound, spatial and electrical impulse responses of ultrasonic transducers, limited-view scanning, and sparse sampling. The inverse problem of the imaging model is solved by alternate optimization, and images representing optical absorption and SoS distributions are reconstructed simultaneously. The study results indicate that the structural similarity of the reconstructed images of the proposed method can be enhanced by about 83%, 56%, and 22%, in comparison with back projection, time-reversal, and short-lag spatial coherence techniques, respectively. Additionally, the peak signal-to-noise ratio can be improved by approximately 80%, 68% and 58%, respectively. This method considerably enhances the image quality of non-ideal imaging scenarios when compared to traditional techniques.

Research progress of space laser communication networking technology
LIU Zhi, JIANG Qing-fang, LIU Shu-tong, TIAN Shao-qian, LIU Xian-zhu, YU Jia-xin, ZHAO Jian-tong, YAO Haifeng, DONG Ke-yan
 doi: 10.37188/CO.2023-0140
Abstract(15) FullText HTML(13) PDF 9778KB(2)
Abstract:

Laser communication utilizes light waves as the transmission medium. It offers many advantages, including high data rates, expansive bandwidth, compactness, robust interference resistance, and superior confidentiality. It has the critical capability to enable high-speed transmission and secure operation of space information networks. Prominent research institutions have committed to studying a series of challenges that need to be solved in the process of networking laser communication technology, including point-to-multipoint simultaneous laser communication, all-optical switching and forwarding of multi-channel signals within nodes, node dynamic random access, and network topology design. Numerous demonstration and verification experiments have been conducted, with a subset of these research results finding practical applications. Based on the analysis and discussion of space laser communication networking technology, this paper summarizes the development of laser communication networking technology both domestically and internationally, focusing on the application of laser communication networking technology in the fields of satellite constellations, satellite relays, and aviation networks; furthermore, it presents a review of pertinent domestic research methodologies, experimental validations, and technical solutions; finally, it predicts the development trend of laser communication networking technology and applications.

Adjusting the compactness and hydrophobicity of color filters to decrease gas release during TFT-LCD fabrication
LI Ji, ZHANG Xia, FENG Yi, LIAO Chang, ZHANG Jie, YIN Yong-ming, MENG Hong
 doi: 10.37188/CO.EN-2023-0029
Abstract(24) FullText HTML(16) PDF 5305KB(6)
Abstract:

The TFT-LCD industry is moving towards the direction of high efficiency and low costs. During the manufacturing process, it has been found that various photoresists require different vacuum drying time. To reduce manufacturing time and increase panel yields, it is necessary to clarify the factors that can influence and reduce the vacuum time. This paper explored the relationship between pumping time and the properties of photoresist materials. It was found that the thermal stability of the photoresist had a negligible relationship with the pumping time. The compactness and hydrophobicity of the photoresist are highly correlated with the vacuum drying time. High compactness and high hydrophobicity can effectively avoid water vapor intrusion and storage in the photoresist during fabrication and consequently reduce pumping times. Overall, this work could guide the future development of new photoresists for the TFT-LCD industry.

Realization and error analysis of geographical guidance for roll-pitch electro-optical pod
DONG Qi-lin, ZHANG Wei-guo, ZHAO Chuang-she, WANG Chao, YUAN Yi-jie, YI Xing-guo, LIU Wan-gang, CHENG Yong-dong
 doi: 10.37188/CO.2023-0188
Abstract(12) FullText HTML(4) PDF 4515KB(0)
Abstract:

In order to improve the accuracy and success rate of geographical guidance, according to the structural characteristics of the roll-pitch electro-optical pod, a mathematical model of geographical guidance was developed through three steps: first, establishing the coordinate system; second, solving the target coordinates; and third, calculating the frame angle. Speed forward feed and small domain search modes were introduced on this basis. The frame angle calculation error affected by inertial navigation measurement error and target distance was simulated, and the results show that the longitude, latitude, and heading angle errors had a greater influence on the pitch angle calculation error; nonetheless, the errors of elevation and horizontal attitude angle had a greater influence on the calculation error of the roll angle. Improving the positioning accuracy of inertial navigation can further reduce the frame angle calculation error and improve the geographical guidance accuracy; however, when the heading angle decreases below 0.1 degrees and the horizontal attitude angle decreases below 0.05 degrees, then the influence weight of the attitude angle error also decreases. The improvement in guidance accuracy is no longer evident when attitude angle errors are reduced. Increasing target distance sharply decreases the error of frame angle calculation. Finally, the guidance test with pitch and roll mean square errors of less than 0.12 degrees shows the algorithm's accuracy and the simulation analysis's effectiveness.

Polarization spectral image fusion method for hybrid backgrounds of ground objects
LI Ying-chao, ZHAO Zhe-hao, WANG Qi, LIU Jia-nan, SHI Hao-dong, FU Qiang, SUN Hong-yu
 doi: 10.37188/CO.2023-0185
Abstract(12) FullText HTML(7) PDF 8706KB(4)
Abstract:

To address the issues of blurred edge details and poor contrast in multi-scale transform fused images obtained using remote sensing detection methods for mixed background features, an image fusion approach that combines the sparse representation of non-downsampled contour wavelet transform and a guided filter was utilised to enhance the quality and visual appearance of the fused images. This method involved several steps: Firstly, a multi-scale and multi-directional decomposition was performed on both spectral and polarimetric images using non-downsampled contour wavelet transform to isolate the feature information in each subband; secondly, the low-frequency subbands were fused using a sparse representation approach to minimize the loss of contrast in the fused image; additionally, the high-frequency subbands were fused through a bootstrap filter to enhance the detail information and the contours of the image; finally, the low-frequency and high-frequency fusion coefficients were inverted using non-downsampled contour wavelet inversion to generate the final fused image. Analysis indicates that this method has increased the contrast of the fused image by up to 54.5% relative to the original spectral image and by 15.4% compared to the polarimetric image. This has resulted in a fused image in which it is easier to distinguish objects in shadows within a mixed background. This method was used to fuse spectral and polarimetric images captured by a polarimetric spectral imager at different wavelengths, which resulted in true-colour reproduction. These true-colour restored images demonstrate that this fusion method retains environmental information within the mixed background while distinguishing the object from the background, effectively improving the image quality of polarization spectral remote sensing detection imaging. This approach enhances the integrity and authenticity of image information in polarization spectral remote sensing detection imaging, thereby expanding its application scope in remote sensing detection of complex environments and image recognition.

Reconstruction of snapshot multispectral camera images based on an attention residual network
YAN Gang-qi, LIANG Zong-lin, SONG Yan-song, DONG Ke-yan, ZHANG Bo, LIU Tian-ci, ZHANG LEI, WANG Yan-bo
 doi: 10.37188/CO.2023-0196
Abstract(10) FullText HTML(7) PDF 8459KB(2)
Abstract:

With the rapid advancement of spectral imaging technology, the use of multispectral filter array (MSFA) to collect the spatial and spectral information of multispectral images has become a research hotspot. The uses of the original data are limited because of its low sampling rate and strong spectral inter-correlation for reconstruction. Therefore, this paper proposes a multi-branch attention residual network model for spatial-spectral association based on an 8-band 4 × 4 MSFA with all-pass bands. First, the multi-branch model was used to learn the image features after interpolation in each band; second, the feature information of the eight bands and the all-pass band were united by the spatial channel attention model designed in this paper, and the application of multi-layer convolution and the convolutional attention module and the use of residual compensation effectively compensated the color difference of each band and enriched the edge texture-related feature information; finally, the preliminary interpolated full-pass band and the rest of the band feature information were used in feature learning by residual dense blocks without batch normalization on the spatial and spectral correlation of multispectral images to match the spectral information of each band. Experimental results show that the peak signal-to-noise ratio, structural similarity, and spectral angular similarity of the test image under the D65 light source outperform the state-of-the-art deep learning method by 3.46%, 0.27%, and 6%, respectively; in conclusion, this method not only reduces artifacts but also obtains more texture details.

Phase gradient estimation using Bayesian neural network
ZHANG Kang-yang, NI Zi-hao, DONG Bo, BAI Yu-lei
 doi: 10.37188/CO.2023-0168
Abstract(13) FullText HTML(5) PDF 7531KB(3)
Abstract:
Objective

Strain reconstruction is a vital component in the characterization of mechanical properties using phase-contrast optical coherence tomography (PC-OCT). It requires an accurate calculation for gradient distributions on the wrapped phase map. In order to address the challenge of low signal-to-noise ratio (SNR) in phase gradient calculation under severe noise interference, a Bayesian-neural-network-based phase gradient calculation is presented.

Method

Initially, wrapped phase maps with varying levels of speckle noise and their corresponding ideal phase gradient distributions are generated through a computer simulation. These wrapped phase maps and phase gradient distributions serve as the training datasets. Subsequently, the network learns the “end-to-end” relationship between the wrapped phase maps and phase gradient distributions in a noisy environment by utilizing a Bayesian inference theory. Finally, the Bayesian neural network (BNN), after being trained, accurately predicts the high-quality distribution of phase gradients by inputting the measured wrapped phase-difference maps into the network. Additionally, the statistical process introduced by BNN allows for the utilization of model uncertainty in the quantitative assessment of the network predictions’ reliability.

Result

Computer simulation and three-point bending mechanical loading experiment compare the performance of the BNN and the popular vector method. The results indicate that the BNN can enhance the SNR of estimated phase gradients by 8% in the presence of low noise levels. Importantly, the BNN successfully recovers the phase gradients that the vector method is unable to calculate due to the unresolved phase fringes in the presence of strong noise. Moreover, the BNN model uncertainty can be used to quantitatively analyze the prediction errors.

Conclusion

It is expected that the contribution of this work can offer effective strain estimation for PC-OCT, enabling the internal mechanical property characterization to become high-quality and high-reliability.

Tandem pumped Q-switched mode-locked laser operation of Tm:CYA laser
SUN Tangzheng, LI Yunfei, TAN Jingrong, DU Xiaojuan, DING Jiayu, REN Shuting, XU Hao, WANG Chong, YANG Jinfang, ZHANG Mingxia, ZHU Yongle, DONG Zhong, LING Weijun
 doi: 10.37188/CO.2023-0162
Abstract(16) FullText HTML(11) PDF 2637KB(1)
Abstract:

Passively Q-switched mode-locked operation was realized for the first time by inserting a semiconductor saturable absorption mirror (SESAM) mode-locking element into a Tm:CaYALO4(Tm:CYA) laser using in-band pumping technology. The laser cavity adopted an X-type four-mirror cavity structure, and the pump source was an Er:Y3Al5O12(Er:YAG) solid-state laser with a central wavelength of 1650 nm. Output coupling mirrors with transmittances of 0.5%, 1.5%, 3%, and 5% were used to study the laser’s continuous wave (CW) output and mode-locking output characteristics. The experimental results show that the laser has the best output characteristics when an output coupling mirror with a transmittance of 5% is used. The maximum power of 894 mW and the maximum slope efficiency of 16% were obtained when the laser operated in the CW regime. After the CW power was optimized to the highest, the SESAM mode-locked element was added to the optical path. When the absorbed pump power became greater than 1.86 W, the laser operation entered an unstable Q-switched state; when the absorbed pump power increased to 5.7 W, a stable passively Q-switched mode-locked operation was achieved; when the absorbed pump power reached 6.99 W, a mode-locked pulse laser with a maximum output power of 399 mW was obtained by using a 5% output mirror. At that time, the repetition frequency under the Q-switched envelope was 98.11 MHz, the pulse width was 619.4 ps, and the corresponding maximum single pulse energy was 4.07 nJ. The mode-locked pulse modulation depth in a Q-switched envelope was observed to be close to 100%. The experimental results show that same-band pumping technology can be used in lasers to generate Q-switched mode-locked pulses, which provides a new pumping method for generating ultrashort pulse lasers.

Design of optical field of vision imaging for defect detection of paper and transparent film
JIANG Shi-fei, ZHANG Zhao-guo, WANG Fa-an, XIE Kai-ting, WANG Cheng-lin, LI Zhi
 doi: 10.37188/CO.2023-0134
Abstract(37) FullText HTML(31) PDF 5133KB(6)
Abstract:

To achieve synchronous detection of defects in the paper and transparent film layers of packaging boxes, we studied the synchronous imaging of the paper and film defect. Firstly, we established models for a standard sphere integral light field, an ellipsoidal integral light field, and an arc integral light field. We then simulated three different light fields using COMSOL Multiphysics 5.6 and compared their ray angle uniformity and irradiation uniformity. The parameters of ellipsoidal area integral light field are optimized by orthogonal simulation. Secondly, the packaging box was imaged using the ellipsoidal integral light field, the bright and dark field forward lighting. Physical detection and machine vision were used to detect five common defects in the packaging box, including oil stains, pressure marks, openings, bubble wrinkles, and breakages, to verify the effectiveness of defect imaging. The results show that the images can clearly present defect characteristics in the paper base and transparent film layers under ellipsoidal integral light field. The physical detection rates for oil stains, pressure marks, openings, bubble wrinkles, and breakages were 96.2%, 92.5%, 100%, 95%, and 92%, respectively. Anomaly detection rates were 98.6%, 97.5%, 100%, 100%, 98.4%, respectively. Detection rates of defects were 97.6%, 96%, 100%, 97%, and 96%, respectively. Th study indicates that the consistent optical path angle and irradiation intensity result in a uniform ellipsoidal integral light field. Consequently, transparent film imaging of the packaging box shows clear defect characteristics that satisfy the standards for industrial detection application.

A study of tunable narrow-band perfect absorber based on metal-dielectric-metal
WANG Xiao-kun, LI Zhou, LIANG Guo-long
 doi: 10.37188/CO.2023-0125
Abstract(46) FullText HTML(13) PDF 2807KB(13)
Abstract:

To achieve perfect narrowband absorber, we proposed a sample three-layer thin film (MDM) structure and developed a theoretical model. A comprehensive investigation was conducted on this structure through a combination of simulations and theoretical calculations. First, we executed theoretical calculations on the structure using both finite-difference time-domain algorithm (FDTD) and transfer matrix algorithm. The effects of several structural parameters on the absorption spectrum were analyzed in this study. We analyzed and discussed the physical mechanism of narrow band perfect absorber structure caused by the structure. Finally, we successfully used magnetron sputtering as a fabrication method to produce three-layer samples. The experimental results were consistent with the theoretical simulation. Our proposed structure for a narrowband perfect absorber can achieve a maximum narrow bandwidth of approximately 21 nm and a maximum absorption of 99.51%. These results establish a strong basis for related applications by achieving perfect narrowband absorption.

Study and analysis of a miniature self-absorption-free laser-induced breakdown spectroscopy with high-repetition rate acousto-optic gating
CHEN Fei, WANG Shu-qing, CHENG Nian-kai, ZHANG Wan-fei, ZHANG Yan, LIANG Jia-hui, ZHANG Lei, WANG Gang, MA Xiao-fei, LIU Zhen-rong, LUO Xue-bin, YE Ze-fu, ZHU Zhu-jun, YIN Wang-bao, XIAO Lian-tuan, JIA Suo-tang
 doi: 10.37188/CO.2023-0147
Abstract(41) FullText HTML(10) PDF 5507KB(9)
Abstract:

To improve the accuracy of elemental quantitative analysis, to eliminate the self-absorption effect in laser-induced breakdown spectroscopy (LIBS), and to meet the requirement of convenient elemental analysis in industry, the device of self-absorption free laser-induced breakdown spectroscopy (SAF-LIBS) technology needs to be miniaturized. This paper presents a novel quantitative analysis technique, the high repetition rate acousto-optic gated SAF-LIBS method. To enhance integral spectral intensity, a high repetition rate laser is used to produce quasi-continuous plasmas. In addition, an AOM (acousto-optic modulator) serves as an as an optical gating switch, enabling the use of a compact charge-coupled device (CCD) spectrometer and AOM instead of the intensified charge coupled device (ICCD) and medium step grating spectrometer in conventional large-scale SAF-LIBS devices. The results in a self-absorption-free system that is less bulky and less expensive. After optimizing the system parameters, the quantitative analysis and prediction of the Al element in the sample was achieved. Experimental results show that plasma characteristics are impacted by the laser repetition rate, which affects the intensity of spectral signal. The doublet intensity of Al I 394.4 nm and Al I 396.15 nm is enhanced and then diminished at a laser repetition rate ranging from 1 kHz to 50 kHz, with the optimal repetition rate identified as being 10 kHz. The doublet line intensity ratios of Al decrease with delay time under different fiber collection angles. The highest signal-to-noise ratio is achieved at an angle of 45°, while the optimal optically thin time tot is 426 ns at a certain integration time. Al is quantitatively analyzed and predicted at a laser repetition rate of 10 kHz, fiber collection angle of 45°, and delay time of 400 ns. The experimental results show that the calibration curve linearity of R2 is 0.982 and an average absolute prediction error of aluminum is reduced from 0.8% of single LIBS to 0.18%, which is equivalent to that of traditional SAF-LIBS. Additionally, the high repetition rate acousto-optic gating SAF-LIBS not only effectively eliminates continuous background radiation and broadens spectral lines in optically thick plasma, but also offers the advantages of miniaturization, low cost, convenience, and reliability. Therefore, this study plays a significant role in advancing SAF-LIBS technology from laboratory testing to industrial applications.

Indistinguishable points attention-aware network for infrared small object detection
WANG Bo-xiao, SONG Yan-song, DONG Xiao-na
 doi: 10.37188/CO.2023-0178
Abstract(36) FullText HTML(12) PDF 8170KB(2)
Abstract:

As aircraft maneuverability increases, multi-frame infrared small target detection methods are becoming insufficient to meet detection requirements. In recent years, significant progress has been achieved in single-frame infrared small-target detection methods based on deep learning; however, infrared small targets often lack shape features and have blurred boundaries and backgrounds, obstructing accurate segmentation. Based on this, an indistinguishable points attention-aware network for infrared small object detection was proposed. First, potential target areas were acquired through a point-based region proposal module while filtering out redundant backgrounds; then, to achieve high-quality segmentation, the fine mask boundary module determined disordered, non-local indistinguishable points in the coarse mask, fused multi-scale features, and modeled the attention pixel by pixel; finally, the point detection head generated a fine segmentation mask by re-predicting the indistinguishable points’ attention-aware features. The proposed method reached 87.4 mAP and 63.4 mAP on the publicly available datasets NUDT-SIRST and IRDST, and the F-measure reached 0.8935 and 0.7056, respectively. It can achieve accurate segmentation in multi-detection scenarios and multi-target morphology, suppressing false alarm information while controlling the computational overhead.

Rotary error modeling and assembly optimization of parallel structure shafting
DONG Yi-ming, JIANG Bo, LI Xiang-yu, XIE You-jin, LV Tao, RUAN Ping
 doi: 10.37188/CO.2023-0171
Abstract(37) FullText HTML(7) PDF 4179KB(4)
Abstract:

In order to improve the shafting motion accuracy of two-dimensional turntables such as photoelectric theodolites, this paper establishes a mathematical model based on Jacobian-Torsor theory, which can account for both the structural error of parts and the coupling amplification effect. Aiming at a shafting structure with one fixed end and one swimming, an analysis method of partial parallel structure was proposed. Through numerical simulation analysis, the impact of each part’s structural errors on the motion accuracy of the shafting and the optimal shafting assembly scheme were obtained. The results of assembly and adjustment of a photoelectric theodolite with an optical diameter of 650 mm show that assembly optimization improved the motion accuracy of the shaft system by 32.1%. The precision model and optimization method of shafting motion provide a theoretical basis for the shafting adjustment and tolerance design of two-dimensional turntables such as photoelectric theodolites.

Capillary liquid-core optical fiber temperature sensor based on fluorescence intensity ratio
ZHANG Ye-yu, LIU Ting, HUANG Jian-wei, HUANG Xue-zhi, CHEN Ming-jie
 doi: 10.37188/CO.2023-0160
Abstract(27) FullText HTML(12) PDF 5338KB(2)
Abstract:

This paper aims to solve the problem of the complicated preparation of existing optical fiber fluorescence temperature sensing probes. The paper proposes solving this problem with a simple, cost-effective, and high-performance optical fiber fluorescence temperature sensor based on a capillary liquid core. Firstly, a mixed solution consisting of temperature-sensitive rhodamine B and temperature-insensitive rhodamine 123 was used as the temperature-sensitive material and encapsulated in a stainless-steel capillary to prepare a sensing probe. The ratio of the fluorescence emission peak intensities of the two dyes was utilized for temperature sensing. Subsequently, the sensing probe’s mixed solution concentration and capillary structural parameters were optimized. Then, the performance of the sensor was tested. Lastly, the sensor was applied to real-life temperature measurements. The experimental results demonstrate that the sensor has a temperature response range of 30−70 °C and that there is a quadratic correlation between the fluorescence intensity ratio and the temperature, with the fitted correlation coefficient as high as 0.9984. The sensor exhibits excellent accuracy, repeatability, and stability, with more than three months of service time; moreover, it can be well-utilized to detect temperature in daily life. The optical fiber fluorescence temperature sensor shows significant potential for real-time monitoring and remote detection applications

Error modeling of polarization devices in simultaneous phase-shifted lateral shearing interferometry
ZHANG Yu-wen, LIU Bing-cai, WANG Hong-jun, TIAN Ai-ling, REN Ke-xin, WANG-KAI
 doi: 10.37188/CO.2023-0152
Abstract(15) FullText HTML(8) PDF 4106KB(0)
Abstract:

The objective of this paper is to provide a reliable theoretical basis for the selection, mounting, and error compensation of the polarization device in the synchronous phase-shift transverse shear interference system. Based on the Jones matrix principle, this paper constructs an error model of the degree of influence of the errors of quarter-waveplate and polarizer array on the measurement results in the system and quantitatively analyzes how the measurement results are influenced by the following factors: the phase delay error of quarter-waveplate, fast-axis azimuthal angle error, and transmission-axis azimuthal angle error of the polarizer array. The simulation results show that the wavefront measurement errors are 0.00002λ(PV) and 0.000062λ(RMS) when the phase delay error of the quarter-waveplate is within ±1°, 0.0001λ(PV) and 0.00006λ(RMS) when the adjustment accuracy of the quarter-waveplate is within ±2°, and 0.0001λ(PV) and 0.00006λ(RMS) when the azimuthal angle error of the polarizer array is within ±1°. The measurement errors are 0.003λ(PV) and 0.001λ(RMS). According to the simulation results, the polarization components in the measurement system were selected, and at the same time, two polarization components with different levels of accuracy were chosen for comparison experiments. The experimental results indicate the following conclusions: the verification of the validity of the model proposed in this paper through the use of polarization devices with different levels of accuracy, the deviation of the residual values of the experimental results from the residual values of the simulation results in terms of the PV and the RMS values is less than λ/20, and the validity of the model can be verified to a certain extent. The mathematical model proposed in this paper can provide a reliable theoretical basis for the selection of polarization devices in synchronous phase-shifted transverse shear interference systems.

Reflection characteristics of the wall is solved by improved WOA algorithm
ZHANG LU, FAN Jin-haoi, LU Yu-xuan, ZHANG Lei, FU Li
 doi: 10.37188/CO.2023-0095
Abstract(25) FullText HTML(11) PDF 4610KB(3)
Abstract:
Objective

The infrared reflection characteristics of the wall were characterized by the bidirectional reflectance distribution function (BRDF) to solve the reflection characteristics of the wall. BRDF measurement currently has two problems to be addressed: it requires much experimental data and higher accuracy.

Method

By constructing the reflection characteristic test platform of the wall target, an MR170 Fourier infrared spectroradiometer was used to obtain the target radiance at the incident angle and each reflection angle in the 2−15 μm band. For the stealth target, the RBF network was used to fit the radiance at the bands of 3−5 μm and 8−14 μm to eliminate atmospheric interference. Then, the BRDF values of the stealth targets in the above two bands were obtained. To improve the accuracy of the BRDF model, an improved whale optimization algorithm (IWOA) was proposed to invert BRDF model parameters, and a reflectivity-solving method based on BRDF was designed.

Result

The IWOA algorithm has a good effect on the parameter inversion of the BRDF calculation model. According to the reflection method, the reflectance obtained by applying the obtained BRDF data is 0.5496, and the relative error is 6.17%, both of which meet the engineering requirements.

Conclusion

This study can be helpful for the study of the reflection characteristics of stealth wall targets.

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(118) FullText HTML(58) PDF 3337KB(82)
Abstract:

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, we propose an image denoising method by combining 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.

Incident angle-tuned filter based on 1D resonant waveguide grating in full conical mounting
丽娜 樊, 金巧 沙, 召良 曹
 doi: 10.37188/CO.EN.2023-0030
Abstract(27) PDF 488KB(4)
Abstract:
We propose and demonstrate a tunable filter by using full conical mounting. The designed 1D resonant waveguide grating presents a tunable single reflection peak. The peak reflectance can theoretically reach 100%. The resonant wavelength can be tuned from 642.5 nm to 484.6 nm by changing incident angle. The reflection peak is generated by the resonance between 1st-order diffracted wave and fundamental transverse electric (TE) guided mode. This feature is achieved by optimizing the grating thickness to support the TE guided mode and to suppress the transverse magnetic (TM) guided mode. The same concept can be applied to tunable filters with high dynamic range by increasing the thickness and period of grating in equal proportion.
Stability enhancement of broadband absorption in resistive plasmonic absorbing structures
杨 沈, Zhi-feng Lu, Ya-kun Guo, Yun-fei Long, Rui He, Zherui Zhang
 doi: 10.37188/CO.EN.2023-0022
Abstract(24) PDF 213KB(3)
Abstract:
Broadband absorption performance in resistive metamaterial absorber (MA) has always been disturbed by its element of ohmic sheet. To enhance the stable absorption performance, a comprehensive scheme based on the integration of resistive MA and plasmonic structure (PS) is proposed in this paper. Theoretical investigation shows that the multi-resonance can be inspired by the PS based on dispersion engineering, and the localized electric field takes effect on the surface of ohmic sheet accordingly. Simulation and experimental measurement show that the proposed resistive plasmonic absorbing structures (PAS) can achieve stable and highly efficient absorption with the efficiency during the broad frequency band from 7.8 to 40.0GHz with the ohmic sheet ranging from 100 to 250Ω/sq. On illumination, the attempt provides an efficient path to the comprehensive performance optimization based on the integration scheme of PS and MA, enabling a wide range of applications.
Influence of flow channel structure on characteristics of LD pumped flowing-gas rubidium vapor laser
PAN Li, HE Yang, MA Li-guo, JI Yan-hui, LIU Jin-dai, CHEN Fei
 doi: 10.37188/CO.2023-0174
Abstract(58) FullText HTML(33) PDF 5650KB(13)
Abstract:

In order to study the influence of the output performance of the gas flow tract structure on the output performance of the flowing-gas diode pumped alkali laser(FDPAL), this article is combined with the FDPAL theoretical model combined with the FDPAL mid -gas heat transfer, fluid mechanics and laser dynamics process to use side pump Rb vapor FDPAL(Rb-FDPAL) is a simulation object, analyzing the impact of the output performance of the Rb-FDPAL output performance of the gas flow direction, the cross-sectional area and the shape of the runner. The results show that when the horizontal flow method is adopted, when the cross-sectional area of the flow tract and the connection part of the gas flow tract to the steam pool to the masonry structure, the vortex in the vapor is effectively suppressed, the gas flow rate increases, the thermal effect of the steam pool is smaller, Rb-FDPAL's laser output power and slope efficiency are higher, the simulation results are consistent with the experiment.

Advances in data simulation for space-based situational awareness
LUO Xiu-juan, HAO Wei
 doi: 10.37188/CO.2023-0156
Abstract(85) FullText HTML(28) PDF 409KB(25)
Abstract:

The data simulation for space situational awareness (SSA) can provide critical data support for the development, testing, and validation of space surveillance equipment and situational awareness algorithms (including detection, tracking, recognition, and characterization of space object), playing a significant role in building SSA capabilities. Taking the optical data simulation for space-based situational awareness as the research subject, the purpose and main research content of SSA data simulation are presented, and the typical research methods and processes of SSA optical modeling and simulation are set forth. The current research status and progress in domestic and foreign related research are introduced, covering the imaging modeling and simulation achievements of different optical sensing systems such as binocular vision sensors, LiDAR, infrared sensors, visible light telescopes, and star trackers. The development trend of SSA data simulation research is analyzed, providing reference for future research ideas and approaches of SSA data simulation.

Design of terahertz wave imaging optical system with large aperture
CAO Yi-qing, SHEN Zhi-juan
 doi: 10.37188/CO.2023-0129
Abstract(26) FullText HTML(13) PDF 562KB(4)
Abstract:

The Terahertz wave has some characteristics of the high penetration, low energy and fingerprint spectrum, etc., and is widely used in the detection field, therefore, design of Terahertz wave detection optical imaging system is of great significance and wide application prospects. Firstly, referring to the structure of Tessar objective lens consisting of four lenses, applying the aberration theory of paraxial optical system to establish the balance equations of aberration of the system, to give solve function and method of the initial structure parameters of the system, and then, combined with optical design software to further correct the aberration of the system, and finally a Terahertz wave detection optical imaging system with large aperture is designed. The optical system is composed of four coaxial refraction lenses, and its total focal length is 70 mm, F-number is 1.4, full field of view angle is 8°, value of modulation transfer function (MTF) in the range of full field of view angle is greater than 0.32 at the Nyquist frequency of 10 lp/mm, and the root mean square (RMS) radius of the diffused spot in each field of view are all smaller than the airy disk radius, and finally all kinds of tolerances of the system is analyzed and discussed. The design results show that Terahertz wave detection optical imaging system designed in this paper has the characteristics of large aperture, simple and compact structure, light weight, good imaging performance and easy processing, etc., which meets the design requirements, and it has important applications in the field of high resolution detection and other fields in the Terahertz wave band.

Magnetic field sensor utilizing U-Shape Cavity based in-fiber Mach–Zehnder interferometer
鹏程 范
 doi: 10.37188/CO.EN.2023-0015
Abstract(117) PDF 205KB(11)
Abstract:
An optical fiber magnetic field sensor is proposed and experimentally demonstrated by using a U-shape cavity based on in-fiber Mach–Zehnder interferometer (MZI) coated by magnetic fluid (MF). The magnetic field sensor is fabricated by splicing a section of single-mode fiber (SMF) between two sections of SMF with designed fiber geometry relationship. As the geometric symmetry MZI is strongly sensitive to the surrounding refractive index (RI) with a high sensitivity up to -13588nm/RIU and MF’s RI is sensitive to magnetic field, the magnetic field sensing function of the proposed structure is realized. The results show that the magnetic field sensitivity reaches up to 137pm/Oe with magnetic field range from 0 to 250 Oe almost linearly. Our magnetic field measurement structure has a relatively advantages of small size, low cost, easy fabrication, robustness, high sensitivity, good repeatability and easy integration with fiber systems.
A study of active polarization imaging method under strong light background
SHI Hao-dong, XU Jia-wei, ZHANG Jian, WU Hong-bo, WANG Chao, LIU Zhuang, ZHAN Jun-tong, LI Ying-chao, FU Qiang
 doi: 10.37188/CO.2023-0151
Abstract(64) FullText HTML(21) PDF 5740KB(13)
Abstract:

This study proposes an active polarization imaging approach that utilizes laser illumination to tackle the issue of low target detection contrast in strong light backgrounds, which is a challenge in conventional photoelectric detection. The study examines the coupling relationship between the polarization characteristics of three typical target materials and the scattering angle of a laser beam. This is achieved by constructing a laser incident bidirectional reflection distribution model, a laser incident polarization bidirectional reflection distribution model, and a target surface polarization model of laser illumination. Backlight observation experiments are conducted in a controlled darkroom to verify the impact of the scattering angle of the laser beam on the polarization characteristics of the target. The experimental results show an 86.11% increase in target contrast for active polarization imaging under strong light background compared to traditional passive intensity imaging. Additionally, different target materials exhibit differing visible polarization characteristics under varying beam dispersion angles, with metallic materials is higher than that of non-metallic materials. This result aligns with theoretical analysis and support the advantages of active polarization imaging. The outdoor solar backlight observation experiment verifies the applicability of the research method in high-intensity light and long-distance settings. This study can lay a theoretical foundation for improving accurate target perception under a strong light background.

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(81) FullText HTML(50) PDF 4071KB(5)
Abstract:

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.

Simulation and experiment of weak multi-target laser detection in complex hydrology
ZONG Si-guang, YANG Shao-peng, ZHANG Xin, PENG Dan, DUAN Zi-ke, CHEN Bao
 doi: 10.37188/CO.2023-0141
Abstract(37) FullText HTML(37) PDF 6255KB(5)
Abstract:
Objective

Investigating the impact of water quality, target characteristics, and target distance is crucial to assessing the effectiveness of laser detection for weak targets in complex coastal water bodies. This study examines the theoretical and practical significance of understanding these factors in underwater laser detection.

Method

In this study, we establish a laser detection model for detecting weak underwater targets. To verify the detection of weak multi-target laser ranging under different turbidity, we use Monte Carlo simulation. We simulate laser backscattering echo signals of small targets at different distances and analyze the backscattering echo characteristics of multiple targets with various reflection coefficients. Additionally, a smart and portable laser detection system for detecting weak underwater targets has been designed and developed. Laboratory and field lake environment tests were conducted to detect and range multi-target.

Result

In a near-shore lake with a turbidity of 12.87 NTU, the system can effectively detect 3−4 mixed small target groups. These groups have different low reflection coefficients and diameters varying from 80 to 400 μm, all within a range of 10 meters. The average measurement error is ±0.11 m, which is consistent with the theoretical simulation.

Conclusion

The research results serve as a guide for computing links, designing systems, and optimizing parameters for detecting multi-weak underwater targets using blue and green lasers. Furthermore, the results assist in the engineering practice of detecting underwater obstacles in offshore turbid waters.

A study of the baseline construction method for large aperture circular segmented optical systems
AN Qi-chang, WU Xiao-xia, LIU Xin-yue, LI Hong-wen
 doi: 10.37188/CO.2023-0149
Abstract(43) FullText HTML(16) PDF 4092KB(9)
Abstract:

To enhance detection integration and stability benchmark construction for large apertures of segmented telescopes, this study uses local pupil projection to perform pupil alignment mapping. In addition, we construct a system confocal spatial benchmark using a microlens array. With the annular whole-body control mode as our basis, a joint analysis method of confocal and curvature radius enables joint adjustment of the curvature radius and system alignment. Finally, the stripe envelope formed by white light interference is used for detecting coarse common phases, and the channel spectral method is used to obtain precise connection between coarse and fine common phases. Additionally, the spatial confocal reference positioning exhibits an accuracy of less than 125 microns, and the common phase reference has a coverage range better than 0.5 microns within a 20-microns-range. Furthermore, the uncertainty of the spectral reference is less than 5%. We have effectively improved the accuracy of optical system in-situ measurement detection by achieving hierarchical and multimodal suppression of disturbances from different spatiotemporal features. We have shortened the length of the traceability chain and increased the efficiency and accuracy of detection by utilizing the new method of common reference in-situ measurement.

A study of high-precision spherical wave calibration method for shack-hartmann wavefront sensor
BAO Ming-di, SHI Guo-hua, XING Li-na, HE Yi
 doi: 10.37188/CO.2023-0148
Abstract(69) FullText HTML(39) PDF 4655KB(17)
Abstract:

To address the issues of inaccurate measurements and unstable calibration processes in conventional Shack-Hartmann wavefront sensors (SHWFS), we propose a high-precision absolute calibration method using spherical waves generated by the sensor. The SHWFS experiences an extremely precise calibration process with 128×128 sub-apertures. This is achieved using a method of spherical wave obtained through theoretical derivation in conjunction with the constructed experimental device for spherical wave calibration. The structural parameters of the SHWFS (f, w, and L0) are calculated precisely. Also, the measurement accuracy of the SHWFS is verified following calibration. The experimental results demonstrate that by using this method to calibrate the Shack-Hartmann wavefront sensor, its wavefront recovery accuracy reaches a PV of 1.376×10−2λ and an RMS of 4×10−3λ (where λ=625 nm), respectively. Additionally, its repeatability accuracy reaches a PV of 3.2×10−3λ and an RMS of 9.76×10−4λ (where λ=625 nm), respectively. These findings suggest that this method is suitable for enhancing the measurement accuracy of high-precision calibration of SHWFS with large aperture.

Optical Design and Spectral Optimization of Philips Prism 3CMOS Camera
CHEN Su-hao, LÜ Bo, LIU Wei-qi
 doi: 10.37188/CO.2023-0155
Abstract(88) FullText HTML(37) PDF 5024KB(28)
Abstract:

In response to the demand for high imaging quality and high chromaticity in color digital cameras, this paper investigates the optical system design and camera spectral optimization methods of 3CMOS cameras based on Philips prisms. By modeling the optical path of the Philips prism, the structural parameters of the prism were optimized, reducing the volume of the system while ensuring total internal reflection and exit window size. Based on this method, the Philips prism 3CMOS camera optical system was designed, with a field of view angle of 45 ° and a relative aperture of 1/2.8. The system's MTF was greater than 0.4 in the full field of view and full band at Nyquist sampling frequency of 110 lp/mm. Subsequently, based on the fundamental principles of chromaticity, a vector imaging model for Philips prism cameras was established. The problem of thin film spectral shift caused by changes in light incidence angle was analyzed, and a correction model for spectral shift under wide beam conditions was proposed. Four sets of optical thin films in the camera were designed and optimized using this model. Through optical path simulation experiments and color error analysis, based on the optimized camera spectrum, the average color error of the system was reduced by 15.8%, and the color non-uniformity of the image plane was reduced by 60%. The results indicate that the optical system designed in this article has good imaging quality, and the optimized camera spectrum achieves good color performance and uniformity.

Optical system design of hyperspectral imaging spectrometer for trace gas occultation detection
KONG Xiang-jin, LI Bo, LI Han-shuang, WANG Xiao-xu, GU Guo-chao, JIANG Xue
 doi: 10.37188/CO.2023-0153
Abstract(51) FullText HTML(36) PDF 7480KB(13)
Abstract:

Trace gases, as important constituents of the atmosphere, play an important role in the ecology of the planet. In order to realize the requirements of all-weather continuous measurement, wide-band and hyperspectral detection, a hyperspectral imaging spectrometer operating in occultation detection mode is designed in this paper. The system is a dual-channel structure with a common slit, the UV-visible channel adopts a single concave grating, and the infrared channel adopts a structure combining Littrow and immersion grating, which effectively reduces the volume. The software was used to optimize the optical structure, and the optimization results showed that the spectrometer operated in the range of 250-952 nm wavelengths, of which the UV-visible channel operated in the wavelength range of 250-675 nm, the spectral resolution was better than 1 nm, the MTFs were all higher than 0.58 at a Nyquist frequency of 20 lp/mm, and the RMS values at various wavelengths of the full-field-of-view were all less than 21 μm; The infrared channel operates in the wavelength band of 756-952 nm, the spectral resolution is better than 0.2 nm, the MTF is higher than 0.76 at the Nyquist frequency of 20 lp/mm, and the RMS value at each wavelength in the whole field of view is less than 6 μm , all of them meet the design requirements, and this hyperspectral imaging spectrometer system can realize occultation detection of trace gases . It can be seen that the hyperspectral imaging spectrometer system can realize the occultation detection of trace gases.

A red-emitting copolymer phosphors based on bimetallic Eu-Ir complex for Near-UV chip-based LEDs
Zihao Wang, Yamin Yang, 爱琴 张, 并社 许, Jing Jia
 doi: 10.37188/CO.EN.2023-0023
Abstract(39) PDF 1395KB(4)
Abstract:
In this work, a new Eu-Ir bimetallic complex Eu(FIrPic)2(Phen)UA is synthesized using the iridium complex FIrPic as ligands for europium ions, and red-emitting phosphorescent copolymer PM-Eu-Ir is successfully prepared via radical polymerization for commercial near UV chip-based LEDs. The Eu3+ ions could be effectively sensitized by the addition of Ir-complex with the enhancement of ultra-violet light absorption at around 400 nm, without affecting the characteristic fluorescence emission of the Eu3+ ions. The proposed copolymer PM-Eu-Ir exhibits the strongest emission peak at 612 nm with the CIE coordinates (0.461, 0.254) under 365 nm ultra-violet light excitation, which matches well with the 365 nm near-UV chip. The micro-morphology of the red copolymer phosphor PM-Eu-Ir is a typical multilayer spatial network structure, besides having appreciable red emission and the corresponding fluorescence lifetime of 634.54 μs, it also has excellent thermal stability in a wide range of 25~250 ℃.
Design of large aperture terahertz wave imaging optical system
CAO Yi-qing, SHEN Zhi-juan
 doi: 10.37188/CO.2023-0175
Abstract(45) FullText HTML(24) PDF 2929KB(9)
Abstract:

The Terahertz wave possesses characteristics of high penetration, low energy, and fingerprint spectrum, etc., making it widely used in the detection field. Therefore, developing a Terahertz wave detection optical imaging system holds substantial significance and wide application prospects. Firstly, we refer to the structure of Tessar objective lens, which consists four lenses. The balance equations of aberration for the system were established through the application of the aberration theory of the paraxial optical system. Subsequently, we provide a solution function and method of the initial structure parameters of the system. Then, we combine it with optical design software to further correct the aberration of the system. Finally, we design a Terahertz wave detection optical imaging system with a large aperture. The optical system consists of four coaxial refractive lenses with a total focal length of 70 mm, an F-number of 1.4, and a full field of view angle of 8°. The value of modulation transfer function (MTF) in the range of full field of view angle is greater than 0.32 at the Nyquist frequency of 10 lp/mm, and the root mean square (RMS) radius of the diffused spot in each field of view is less than the airy disk radius. Finally, the paper analyzes and discusses the various tolerance types of the system. The results indicate that the Terahertz wave detection optical imaging system, designed in this paper, has a large aperture, a simple, compact form, a lightweight structure, excellent imaging performance and simple processing, which meets the design requirements, and it has important applications in the field of high-resolution detection and other fields within the Terahertz wave band.

An MTF calculation model under the influence of ghost images
XIAO Peng-yi, LIU Ming-xin, YAN Lei, HU Ming-yu, ZHANG Xin
 doi: 10.37188/CO.2023-0121
Abstract(67) FullText HTML(32) PDF 4772KB(12)
Abstract:

Ghost images, as a type of stray light, are caused by residual reflected light between the optical surfaces. These images can degrade image clarity, annihilation targets, and severely affect the performance of optical systems. To investigate the impact of ghost images on optical system performance, we developed a Modulation Transfer Function (MTF) calculation model under the influence of ghost images generated by secondary reflection. This paper first introduces the method of analyzing and describing using the paraxial approximation. Then, starting from the definition of the MTF, and considering the influence of ghost image irradiance on the modulation of the image plane, a calculation model for calculating the MTF under the influence of ghost images is constructed. After performing calculations and comparing them to simulation results, it was found that the maximum mean square error was less than 0.049373, which verifies the accuracy of the model. Furthermore, a detailed analysis was conducted, examining cases that exhibited larger errors and clarifying the range in which this calculation method can be applied The research results indicate that the paraxial approximation method is both accurate and reliable when calculating the MTF under the influence of ghost images is accurate, and is applicable in most cases. This study serves as a valuable exploration in the ghost image analysis of optical systems.

An improved point cloud registration method based on the point-by-point forward method
LI Mao-yue, XU Sheng-bo, MENG Ling-qiang, LIU Zhi-cheng
 doi: 10.37188/CO.2023-0166
Abstract(64) FullText HTML(41) PDF 4847KB(18)
Abstract:

To improve both the efficiency and accuracy of point cloud registration, this study proposed an improved method based on point-by-point advance feature point extraction. Firstly, the point-by-point advance method extracts point cloud feature points rapidly, and greatly reduces the number of point clouds, while retaining the characteristics of the point cloud model. The KN-4PCS algorithm, using normal vector constraints, conducts a preliminary registration of the source and target point cloud. Finally, the fine registration is achieved with the two-way Kd-tree optimized LM-ICP algorithm. In the open point cloud data registration experiment of Stanford University, the average error is reduced by about 70.2% compared with the SAC-IA+ICP algorithm, and the registration time is reduced by about 86.2% and 81.9%, respectively. The algorithm maintains high accuracy and low time consumption even with varying degrees of Gaussian noise. In the point cloud registration experiment of indoor objects, the average registration error was measured to be 0.0742 mm with an average algorithm time of 0.572 s. The comparison and analysis of Stanford open data and real indoor scene object point cloud data shows that this method can effectively improve the efficiency, accuracy, and robustness of point cloud registration. Furthermore, this study establishes a strong foundation for indoor target recognition and pose estimation through the point cloud.

An XY defocus aberration correction method for high-energy lasers
FENG Ya-fei, WEI Cheng-fu, REN Xiao-ming, GUO Jian-zeng, WANG Jie
 doi: 10.37188/CO.2023-0142
Abstract(61) FullText HTML(19) PDF 4520KB(12)
Abstract:

A method for correcting XY defocus aberrations, based on Hartmann-Shack wavefront sensor and two-dimensional beam-shaping light path, was presented due to the large percentage of defocus and 0° astigmatism aberrations with large PV values in high-energy laser beam. The first step is to derive an expression for XY defocus aberrations by linearly combining the defocus and 0° astigmatism terms of Zernike polynomials. The coefficients directly characterize the wavefront peak-to-valley (PV) values of X and Y defocus. At the same time, compensation for XY defocus wavefronts of the laser beam can be achieved by fine-tuning the mirror spacing in the two-dimensional shaping optics of the high-energy laser. Therefore, this study utilizes the Hartmann wavefront sensor to extract the coefficients of XY defocus aberrations from the laser beam. The computer dynamically adjusts the mirror spacing in the two-dimensional shaping optics based on these coefficient values to correct XY defocus aberrations and improve the beam quality of the output laser beam. The results of the experiment showcase a significant decrease in XY defocus aberrations from 5.2 μm and 1.1 μm to less than 0.5 μm, as well as a decrease in β factor from 3.1 to 1.8, resulting in substantial improvement in beam quality.

A point cloud classification downsampling and registration method for artifacts based on curvature features
ZHU Jing-yi, YANG Peng-cheng, MENG Jie, ZHANG Jin-jing, CUI Jia-bao, DAI Yang
 doi: 10.37188/CO.2023-0115
Abstract(63) FullText HTML(28) PDF 4831KB(11)
Abstract:

3D reconstruction is crucial for digitizing artifacts, and the accuracy of 3D point cloud registration is a significant metric for evaluating the reconstruction quality. In practice, artifact point cloud data includes numerous details, and using conventional downsampling methods may result in the loss of such details, thereby affecting registration accuracy. This paper proposes a method for downsampling and registering artifacts point clouds based on curvature features. First, 3D point clouds data of artifacts are obtained using linear matrix laser measurement. Next, the curvature values of all points are calculated, and a curvature threshold is set for point cloud classification. We downsample different point sets based on their feature attributes, with varying weights assigned to retain the shape features and details of the point cloud as much as possible. Finally, point cloud registration is achieved through the use of a rigid transformation model. Compared to the traditional global downsampling ICP method, the downsampling processing before point cloud registration reduces the point cloud data to 1/3 of the original size. The average distance decreases from approximately 0.89 mm to 0.59 mm, while the standard deviation decreases from about 0.29 mm to 0.18 mm. This approach guarantees the accuracy of downsampling and registration and is applicable to various artifacts point cloud data.

An improved phase generated carrier demodulation algorithm of fiber optic fabry-perot sensor
ZHOU Zhen-rui, ZHANG Guo-qiang, QIU Zong-jia, GUO Shao-peng, LI Qun, SHAO Jian, WU Peng, LU Yun-cai
 doi: 10.37188/CO.2023-0108
Abstract(59) FullText HTML(31) PDF 4333KB(14)
Abstract:

To address the issue of non-linear distortion in the Phase Generated Carrier (PGC) demodulation algorithm, we have developed an extrinsic Fabry-Perot Interferometer (EFPI) sensor demodulation system that is based on an improved PGC-Atan algorithm. The theoretical analysis focuses on the nonlinear factors affecting sine and cosine signals used in arctangent operation of the PGC-Atan algorithm. Such factors include deviations from optimal values of the phase modulation depth (C), companion amplitude modulation, and carrier phase delay. As a solution, we propose an improved PGC-Atan algorithm based on a correction coefficient (PGC-CC-Atan) suitable for external modulation or the case of low companion amplitude modulation scenarios. The PGC-CC-Atan algorithm generates a coefficient relating to C and carrier phase delay while excluding nonlinear parameters in the arctangent operation. Furthermore, an improved PGC-Atan algorithm that utilizes an elliptic fitting algorithm (PGC-EF-Atan) is proposed for internal modulation. The ellipse fitting technique is employed to fit the eclipse using the least squares method based on a matrix block decomposition. The pair of signals that are influenced by nonlinear factors are corrected and transformed into orthogonal signals utilizing three parameters of the ellipse. Finally, the correctness of the two improved algorithms is verified through simulations and experiments. The PGC demodulation system comprises a high dv/di VCSEL laser and a conventional cavity length F-P sensor. By comparing the demodulation performance of the PGC-Atan algorithm with that of the two improved algorithms, their effectiveness in suppressing nonlinear distortion is verified. Experimental results indicate that the two improved algorithms exhibit effective demodulation in the presence of nonlinear factors within a specific range of C values. The signal-to-noise and distortion ratio (SINAD) of demodulation result obtained from PGC-EF-Atan algorithm surpasses that of the PGC-CC-Atan algorithm by 11.602 dB, while the THD is reduced by 10.951%. Between the two improved algorithms, the PGC-EF-Atan algorithm possesses superior demodulation linearity, accuracy, and nonlinear distortion suppression performance.

Omnidirectional spatial monocular vision indoor localization measurement based on a two-degree-of-freedom rotary table
WU Jun, WANG Hao-shuang, SHAN Teng-fei, GUO Run-xia, ZHANG Xiao-yu, CHEN Jiu-sheng
 doi: 10.37188/CO.2023-0106
Abstract(50) FullText HTML(37) PDF 3649KB(14)
Abstract:

To address the problem of limited field of view measurement in traditional monocular vision measurement systems, this paper proposes an omnidirectional spatial monocular vision measurement method based on a two-degree-of-freedom rotary table. First, calibrate the rotating axis parameters of the double-degree-of-freedom rotary table. Then, take pictures of the checkerboard calibration plate fixed with the two-degree-of-freedom rotary table using an auxiliary camera. Extract the position coordinates of the checkerboard corner points and convert them to the same camera coordinate system. The direction vector of the initial position axis parameter was obtained through PCA (principal component analysis) plane fitting, and the position parameter in the rotation axis parameter in the initial position was determined using the method of spatial least squares circle fitting. The camera data acquired at various angles is transformed into coordinate system one using the rotary table rotation angle and the Rodrigues formula. This enables measurement of the target in the horizontal and vertical omnidirectional space. Finally, verification of the measurement accuracy of the proposed method was conducted using a high-precision laser rangefinder. Additionally, experiments comparing the omnidirectional spatial measurement ability of the method with the binocular vision measurement system and wMPS measurement system were conducted. The results indicate that the method achieves a measurement accuracy comparable to that of a binocular vision system. However, it also surpasses the binocular vision system in term of measurement range, making it applicable for omnidirectional spatial measurements.

Three-dimensional surface shape reconstruction of fiber bragg gratings in a ring arrangement
WANG Yan, XU Haoyu, WANG Jun-liang, ZHU Wei, JIANG Chao
 doi: 10.37188/CO.2023-0088
Abstract(47) FullText HTML(26) PDF 6516KB(10)
Abstract:

To improve the accuracy of palm surface reconstruction in flexible robot grasp sensing, this study conducts a COMSOL simulation to select a ring arrangement comprising of 7 fiber Bragg grating (FBG) flexible sensors packaged with polydimethylsiloxane (PDMS) on a 436 mm×436 mm×2 mm polypropylene plate. Assuming that the center and two corner ends of the plate were subjected to stress, respectively, we collected sensor data using a fiber grating demodulation instrument during the experiment. The data was continuously interpolated using cubic spline interpolation. Several planes Y intersected with the fitting ring which created a three-dimensional surface. We calculated the point function to obtain the point set and achieve a fitting visual display of the spatial surface. The plate experienced a minimum relative error of 0.549% in end displacement, with a maximum relative error of 8.300%. the center of the surface’s end yielded a minimum absolute error of 0.051 cm, and a maximum absolute error of 1.255 cm. When both corners at the end of the plate are under stress, a minimum relative error of 2.546%, and a maximum relative error of 14.289% arise in plate reconstruction end displacement. The minimum absolute error is 0.005 cm, and the maximum absolute error is 0.729 cm. These experimental results provide a foundation to implement palm grip sensing in flexible robots.

Design of a single sensor based three-band co-aperture optical system
ZHANG Kun, LI Jing-chen, SUN Si, CHEN Qing-rong, YANG Fan
 doi: 10.37188/CO.2023-0098
Abstract(48) FullText HTML(15) PDF 3288KB(9)
Abstract:

The existing multi-band imaging system poses issues of large volume, high power consumption, and difficulty in integrating design. To address these challenges, we proposed a solution in the form of a design methodology for a single sensor based three-band co-aperture imaging optical system. First, a 1×2 multi-band lens array in the aperture stop of the optical system is designed. This array effectively captures both the visible and short-wave infrared bands simultaneously in a single image plane. In addition, the imaging position deviation of the center wavelength of both bands are controlled to within one pixel, resulting in dual-band fusion imaging. To address the issue of different diffraction limits in multi-band imaging, we propose to use the joint optimization method to simultaneously control the off-axis offset and aperture size of the split channel lens array. In addition, we suggest utilizing a dual electric diaphragm to control the switching speed of the three imaging channels. Finally, a single sensor based three-band co-aperture optical system with a focal length of 30 mm and operating bands ranging from 480 to 900 nm, from 900 to 1700 nm, and from 480 to 1700 nm is designed. The system exhibits multiple advantages, such as excellent imaging quality, a compact structure, no moving optical elements, and a rapid switching speed of the imaging band, as indicated by the design and analysis results.

A seawater salinity sensor based on dual peaks resonance long period fiber grating
DU Chao, ZHAO Shuang, SONG Hua-ke, WANG Qiu-yu, JIA Bin, ZHANG Li, CUI Li-qin, ZHAO Qiang, DENG Xiao
 doi: 10.37188/CO.2023-0101
Abstract(81) FullText HTML(37) PDF 5114KB(25)
Abstract:

To develop a highly sensitive seawater salinity sensor, a long period fiber grating (LPFG) was successfully fabricated using CO2 laser technology to function in close proximity to the dispersion turning point (DTP). An LPFG operating near DTP was fabricated in an 80 μm single mode fiber using CO2 laser micromachining technology. This successful endeavor demonstrates the feasibility of developing LPFG with shorter grating period. LPFGs with varying periods were fabricated using a CO2 laser to ensure that the cladding mode LP1,9 was operating near DTP, resulting in higher refractive index sensitivity of LPFG. The average sensitivity of 0.279 nm/‰ can be achieved in the seawater with salinity ranging from 5.001 ‰ to 39.996 ‰, especially with the dual peak resonance LPFG at a period of 115.4 μm, thanks to the dual peak resonance effect. The dual peaks resonance LPFG seawater salinity sensor exhibits high sensitivity and a large attenuation loss, suggesting potential application in seawater salinity monitoring.

分数薛定谔方程中燕尾高斯光束的可控反转与聚焦特性
HongWei Huang, Ke Cheng, YANG Ceng-hao, YAO Na
 doi: 10.37188/CO.EN.2023-0018
Abstract(42) PDF 1153KB(4)
Abstract:
By transferring one-dimensional swallowtail catastrophe to optical field, the evolution dynamics of the swallowtail-Gaussian (SG) beams in fractional Schrödinger equation (FSE) with different potentials, where include the linear, parabolic and Gaussian potential and non-potential cases, are investigated by using the split-step Fourier method.
A simplified method for high temperature calibration in the visible light band
LI Yun-long, LI Zhou, SUN Zhi-yuan, YANG Guo-qing
 doi: 10.37188/CO.2023-0122
Abstract(124) FullText HTML(91) PDF 361KB(25)
Abstract:

In order to improve the visible light band (0.3 μm~0.9 μm) A simplified method for high-temperature calibration in the visible light band has been proposed to improve the efficiency of high-temperature calibration. First of all, a high-temperature calibration model of visible light band with exposure time variable is proposed. Through a large number of experimental data, it is found that the gray value of each channel of RGB camera not only changes linearly with the increase of exposure time, but also changes linearly with the increase of Black-body radiation brightness. Then, the specific form of high-temperature calibration model of visible light band is determined. Then, in order to solve the unknowns in the simplified high-temperature calibration model of visible light band, image data under two exposure times are collected under two Black-body radiation brightness, and then the image data is processed to obtain the high-temperature calibration curve of RGB camera under any exposure time. Finally, a comparison is made between the simplified visible light band high-temperature calibration method proposed in this article and the conventional visible light band high-temperature calibration method based on exposure time. The experimental results show that the maximum relative error between the calculated value of the R channel and the calibrated value is 3.38%, the maximum relative error between the calculated value of the G channel and the calibrated value is 2.56%, and the maximum relative error between the calculated value of the B channel and the calibrated value is −1.14%. Moreover, the relative error between the calculated value of each channel and the calibrated value does not exceed 3.50%. The mathematical model proposed in this article can effectively simplify the traditional high-temperature calibration method, thereby greatly shortening the high-temperature calibration time and improving the calibration efficiency of high-temperature calibration.

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(60) FullText HTML(30) PDF 9253KB(28)
Abstract:

Small size parts have a small surface area and complex structure. The traditional mark splicing method needs to manually paste marks on the surface of parts, resulting in missing the measurement data of the surface and becoming holes. The feature splicing method requires the surface of parts to have easily distinguishable geometric or distance features, which are not suitable for rotating parts containing repetitive features. We propose a scanning measurement method without marks based on mechanical splicing, which does not need to paste marks or depend on the surface features of parts. 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.

Propagation properties of one-dimensional vortex array beams in a marine atmosphere
HOU Zheng-cheng, ZHANG Ming-ming, BAI Sheng-chuang, LI Shu-zhen, LIU Jun, HU You-you
 doi: 10.37188/CO.2023-0094
Abstract(88) FullText HTML(54) PDF 4944KB(41)
Abstract:

Compared with a single vortex beam, vortex array beams can expand the transmission capacity of information, and the study of their propagation properties is of great significance for their optical communication applications. In this paper, we select the helical Ince-Gaussian (HIGn,n) modes of ordernand use the power spectrum of the refractive index fluctuations in the marine atmosphere to simulate the turbulence of the marine atmosphere. The changes of intensity, phase, scintillation index and spot centroid wander of a one-dimensional array vortex beam in marine atmospheric turbulence have been investigated systematically by using the phase screen method. We find that (1) when either the turbulence intensity or atmospheric turbulence inner scale is increased, both the scintillation index and spot centroid wander standard deviation of HIGn,n modes are enhanced; (2) the scintillation index of HIGn,n mode with oddndecreases with increasing mode order, and is higher than that of HIGn,n mode with evenn; (3) the HIGn,n mode with ordern>1 has better stability than the LG0,1 mode; and (4) the higher the mode order, the smaller the standard deviation of spot centroid wander of HIGn,n mode. In addition, we have also comparatively studied the propagation performance of the linear array vortex beams (LAVBs) and HIG beams, and found that even though LAVBs have better propagation performance than HIG beams, the unique structures of HIG beams can be applied to different application scenarios. Finally, the effects of ellipticity parameter and elliptic ring number on the propagation of the HIG modes are explored and analyzed. The results show that increasing the ellipticity parameter or elliptic ring number is beneficial to improving the anti-turbulence ability of the HIG modes. The research results obtained in this paper are of guiding significance for the offshore application of vortex beams.

Development of high-precision beam splitter for inter-satellite communication system
WANG Zhen-yu, FU Xiu-hua, LIN Zhao-wen, HUANG Jian-shan, WEI Yu-jun, WU Gui-qing, PAN Yong-gang, DONG Suo-tao, WANG Ben
 doi: 10.37188/CO.2023-0100
Abstract(95) FullText HTML(29) PDF 4306KB(29)
Abstract:

With the rapid development of inter-satellite communication systems, the requirements for data transmission accuracy are constantly increasing. As the core component, the spectral characteristics and surface shape accuracy of the beam splitter directly affect the transmission accuracy of the whole system. In this paper, based on the interference theory of thin film, Ta2O5 and SiO2 were selected as the high and low refractive index film materials for the design of the film system, and electron beam evaporation was used to prepare a high-precision beam splitter on a quartz substrate. At the same time, a surface shape correction model was established based on the principle of film stress compensation to control the surface shape. Through the detection of a spectral analyzer, the transmittance of beam splitter is greater than 98% at 1563 nm and the reflectance is greater than 99% at 1540 nm within the incidence range of 21.5° to 23.5°. The surface shape was measured by laser interferometer, the reflective surface shape accuracy RMS is corrected from λ/10 to λ/90 (λ=632.8 nm), and the transmissive optical surface shape accuracy RMS is λ/90.

Methods for processing renal tissue samples for Single-Slice Dual-Mode optical correlation imaging
GAO Ge, GUO Xiao-guang, WU Jun-nan, CHEN Hai-long, SHI Bing, HUANG Zhen-li
 doi: 10.37188/CO.2023-0105
Abstract(53) FullText HTML(36) PDF 2106KB(22)
Abstract:

Bright-field imaging can provide cellular and histological morphological information, while fluorescence imaging can provide expression information of key proteins. Dual-modal correlation imaging based on both techniques is currently a common method for examining tissue samples in medical and scientific research. In clinical examination, however, correlation imaging between adjacent tissue slices is often used for observation. In such cases, both the tissue structure and the cellular level may be altered more or less, which is unfavorable when the sample volume is insufficient, the number of cells on the slices is limited, or precise point-to-point morphological information is required. Therefore, the development of single-slice dual-modal optical correlation imaging techniques which provides both tissue morphology and the distribution and expression of multiple target proteins on a single slice, can help to more accurately describe tumors and their microenvironment. This technique is particularly important in renal pathological testing where sample size is small. Renal pathology requires the use of bright-field imaging to obtain pathomorphological information of tissues and cells after hematoxylin-eosin staining, while the use of fluorescence imaging to obtain the distribution and expression of multiple target proteins is a mandatory molecular test for renal pathology screening. This paper focuses on the tissue sample processing methods that allow the coexistence of hematoxylin-eosin staining and immunofluorescence staining on the same renal slice. Improvements and comparative evaluations of the staining, de-colorizing and re-staining processes, as well as innovative fusion techniques for single-slice dual-modal imaging.

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(87) FullText HTML(20) PDF 6667KB(39)
Abstract:

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.

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(84) FullText HTML(31) PDF 6453KB(37)
Abstract:

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(73) FullText HTML(31) PDF 4003KB(36)
Abstract:

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.

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(152) PDF 621KB(24)
Abstract:
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.
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(153) FullText HTML(89) PDF 4148KB(182)
Abstract:

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.

Review
On-machine detection technology and application progress of high dynamic range fringe structured light
LIU Ze-long, LI Mao-yue, LU Xin-yuan, ZHANG Ming-lei
2024, 17(1): 1-18.   doi: 10.37188/CO.2023-0068
Abstract(199) FullText HTML(52) PDF 6064KB(116)
Abstract:

Fringe structured light technology is a non-contact measurement method, which has developed rapidly in recent years and provides a new solution for on-machine detection in mechanical processing. However, the accuracy of structured light for on-machine detection 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 structured light detection can reduce the effect of high reflectivity, achieving the measurement of metal parts in complex scenes. This paper introduces the measurement principle of structured light and summarizes the challenges of on-machine detection for HDR structured light. Subsequently, this paper provides a comprehensive review of HDR structured light technology. In the context of on-machine detection of mechanical processing, the HDR technology based on hardware equipment and the HDR technology based on stripe algorithm are discussed and analyzed, respectively. Following this, different technologies are summarized according to the requirements of on-machine detection. The advantages and disadvantages of various methods are presented, and the applicability of on-machine detection 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.

Research progress on the related physical mechanism of laser-induced breakdown spectroscopy
LIU Rui-bin, YIN Yun-song
2024, 17(1): 19-37.   doi: 10.37188/CO.2023-0019
Abstract(177) FullText HTML(44) PDF 1508KB(79)
Abstract:

Laser Induced Breakdown Spectroscopy (LIBS) is a new method for qualitative and quantitative analysis of the constituents of a material using plasma spectra produced by the interaction of a strong pulsed laser with the material. In the process of pulsed laser-induced plasma, different laser parameters (energy, pulse width, wavelength), environmental conditions during the detection process and the properties of the material itself have different degrees of influence on the physical mechanism of laser-induced plasma, which in turn affects the results of LIBS quantitative analysis. We review the physical mechanisms of LIBS technology in the current state, including the basic principles of LIBS, the differences in laser parameters, and the physical mechanisms involved in the differences in environmental and material properties. It provides a basis for a deeper understanding of laser-matter interactions and for improving the detection capabilities of LIBS.

Key technology analysis and research 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
2024, 17(1): 38-51.   doi: 10.37188/CO.2023-0074
Abstract(121) FullText HTML(45) PDF 8949KB(81)
Abstract:

Narrow linewidth fiber lasers, based on the multi-longitudinal-mode oscillator seed source, have obvious advantages in engineering applications and space-limited loading platforms. 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 improvement in output power and affects the purity of laser spectra. In this paper, we introduce four commonly used narrow linewidth seeds. The mechanism and suppression methods of the self-pulse effect in multi-longitudinal mode oscillator seeds are 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.

Original Article
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
2024, 17(1): 52-60.   doi: 10.37188/CO.2023-0039
Abstract(434) FullText HTML(129) PDF 6001KB(218)
Abstract:

We propose a design method for off-axis meta-lens and analyze the effects of numerical aperture, off-axis angle, and incident wavelength on the simulation deviation, resolution and focusing efficiency of off-axis meta-lenses. Several off-axis meta-lenses with parameters NA=0.408 α=13°, NA=0.180 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, the spectral resolution becomes better, 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. This study has an important reference value for theoretical analysis and parameter design of off-axis meta-lens in practical application.

Design and experiment of high-resolution detection imaging system with ultra-thin and ultra-short object-image distance
LI Yan-wei, WU Yan-xiong, CHEN Tai-xi, WEI Hao-dong, XIE Xin-wang, DONG Lei-gang, LI Jun-chi, LI Jian-jie
2024, 17(1): 61-68.   doi: 10.37188/CO.2023-0099
Abstract(112) FullText HTML(43) PDF 10837KB(58)
Abstract:

To shorten the axial and radial dimensions of the 12-inch wafer detection imaging system, a solution combining the small angle prism refraction path and the ultra-short object-image distance lens is proposed. A small angle prism with shape accuracy better than 1/12λ (λ=632.8 nm) is designed to convert the optical path and realize the horizontal arrangement between the lighting system and the imaging lens. The radial size is only 80 mm, which greatly reduces the radial size of the whole system without affecting the imaging quality. At the same time, a small angle of 12° bright field lighting is realized. A symmetrical hybrid optical system with magnification of 0.264 is designed. A pure spherical system is used to obtain a large imaging field of view. The image height is 81.92 mm, and the object-image distance is only 392.5 mm, which greatly reduces the axial size of the whole system. The design results show that the average optical transfer function of the whole imaging system is better than 0.4@100 lp/mm, the relative distortion is better than 0.03%, and the uniformity of the image surface illuminance is better than 50%. The actual test results show that the actual imaging resolution is better than 18.88 μm, which reaches the ultimate resolution of the system. The uniformity of illumination of image surface is 43.3%, which meets the development requirement of uniformity better than 40%. The research results show that the ultra-thin and ultra-short object-image distance imaging system is reasonable and effective, which solves the problem of space size compression of the 12-inch wafer detection imaging system and reduces the development cost. It provides a reference for the development of the imaging system for detecting large objects in short distance.

Design of cooled long-wave infrared optical system with large zooming range
TANG Han, XIA Li-kun, LIU Lian, LIU Yun, LIU Xuan, LIU Yu, ZHANG Run-qi, ZHOU Chun-fen, YANG Kai-yu
2024, 17(1): 69-78.   doi: 10.37188/CO.2023-0052
Abstract(134) FullText HTML(57) PDF 5721KB(59)
Abstract:

Compared with the medium-wave Infrared (MWIR) zoom optical system, the long-wave infrared (LWIR) zoom optical system has fewer available materials and is difficult to athermalize in high and low temperature environments. In this paper, the multi-field zoom optical system is realized by using mechanical compensation zoom technology, and the active compensation athermalization technology is used to make the system image clear in the temperature range of −40 °C—+65 °C, to realize the design of the four-field LWIR optical system with four lenses. The focal lengths of the four fields of view are 25 mm, 109 mm, 275 mm and 400 mm, the zoom ratio is 15, the envelope size of the optical system is 280 mm (L)×200 mm (W), and the total weight of the optical components is 618 g. The optical system has SWaP-C characteristics such as light weight, high performance, and low cost, and will be widely used in security fields such as auxiliary navigation, search, and tracking.

Design of UV-band hyperspectral resolution imaging spectrometer with small F-number and high variable ratio
LIU Yang, LI Bo, LIN Guan-yu, WANG Xiao-xu, LI Han-shuang, GU Guo-chao
2024, 17(1): 79-88.   doi: 10.37188/CO.2023-0037
Abstract(157) FullText HTML(76) PDF 5713KB(112)
Abstract:

Conventional imaging spectrometers generally have low variable ratio, 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 spectral resolution imaging spectrometer, an Offner UV imaging spectrometer with high spectral resolution and high variable ratio 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 for the optimization of the system and improve the imaging quality of the system. The obtained imaging spectrometer works in the 270~300 nm band with a long slit of 40 mm, a spectral resolution better than 0.6 nm, the system variable power ratio less than 0.22, and an F number less than 2. Its Modulation Transfer Function (MTF) is better than 0.9 at a cutoff frequency of 14 lp/mm, and the Root Mean Square (RMS) radius 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 ratio.

Design and optimization of Micro LED vehicle light projection optical system
LI Xiang-lan, JIN Xia, LV Jin-guang, ZHENG Kai-feng, CHEN Yu-peng, ZHAO Bai-xuan, ZHAO Ying-ze, QIN Yu-xin, WANG Wei-biao, LIANG Jing-qiu
2024, 17(1): 89-99.   doi: 10.37188/CO.2023-0063
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Abstract:

This article presents a vehicle headlight projection scheme based on Micro LED arrays. A 200×150 white Micro LED array with pixel size of 80 μm×80 μm is designed as the display light source, and a headlight projection optical system with a field of view of 16°×34° is designed. The object plane tilt angle and optical system structure are optimized. In addition, the inverse distortion processing method and pixel grayscale modulation method are used to solve the trapezoidal distortion and uniformity of illumination of the headlight projection image. A projection experimental platform is built to verify the image correction method. Experimental results show that after correction, the image trapezoidal distortion coefficients p1 and p2 decrease from 0.0932 and 0.3680 to 0.0835 and 0.0373, respectively, and the image plane illumination uniformity increases from 83.2% to 93.2%. This article achieves high light efficiency and low distortion of vehicle headlight projection by optimizing the design of the inclined projection headlight optical system based on Micro LEDs and using image correction methods.

An ultraviolet laser at 228 nm with adjustable repetition rate and narrow pulse width
WANG Jin-yan, MA Fang, ZHENG Lei, TIAN Dong-he, CHEN Xi, ZHENG Quan
2024, 17(1): 100-107.   doi: 10.37188/CO.2023-0058
Abstract(185) FullText HTML(111) PDF 3877KB(112)
Abstract:

Ultraviolet lasers play an important role in the study of ultraviolet resonance Raman spectroscopy. The Raman signals can be enhanced by the resonant Raman effect, thereby reducing the detection limit of Raman measurement. We focus on the study of a narrow-pulse all-solid-state ultraviolet laser with an output wavelength of 228 nm. The Nd:YVO4 is used as the gain medium and the electro-optic Q-switched cavity dumped technique is applied to achieve a fundamental frequency output of 914 nm in pulse width of several nanoseconds. Then, the second-harmonic light is generated by LiB3O5(LBO), and the fourth-harmonic 228 nm UV laser is obtained by beta-barium-borate (BBO) crystal. On this basis, further research has been conducted on the variation of fundamental and second harmonic laser power at different repetition rates. Due to the low gain of Nd:YVO4 at 914 nm, the average power of the laser is saturated and decreases with increased repetition rate. The output efficiency of UV laser is optimized by adjusting the focus lens. At the pump power of 30 W and the repetition frequency of 10 kHz, a 228 nm UV laser output with the highest average power of 84 mW is obtained. The UV laser is continuously adjustable within the range of 5−25 kHz repetition frequency 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.

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
2024, 17(1): 108-117.   doi: 10.37188/CO.2023-0084
Abstract(96) FullText HTML(37) PDF 3771KB(51)
Abstract:

To provide high-quality, intelligent, and healthy lighting sources, a linear dimming mixed 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}' $\end{document} chromaticity coordinates, and the brightness is converted into luminance to make the optimization calculations more accurate. The system adopts the linear dimming method, effectively avoiding the health and safety hazards caused by light source flicker, and effectively solves the problem of large linear dimming chromaticity drift with an optimization algorithm. Experiment results demonstate that the chromatic stability of the mixed light in the mixed lighting system is maintained within the first step of the CIE \begin{document}${u}'{v}' $\end{document} chromaticity diagram in the color temperature range of 2000 K−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 indicates that linear dimming is better than the pulse-width dimming method in keeping the optical chromaticity stable. Theoretical exploration and experimental results demonstrate that the mixed lighting system is simple and feasible, with significant practical value.

A hybrid network based on light self-limited attention for structured light phase and depth estimation
ZHU Xin-jun, ZHAO Hao-miao, WANG Hong-yi, SONG Li-mei, SUN Rui-qun
2024, 17(1): 118-127.   doi: 10.37188/CO.2023-0066
Abstract(152) FullText HTML(58) PDF 5444KB(68)
Abstract:

Phase retrieval and depth estimation are vital to three-dimensional measurement using structured light. Currently, conventional methods for structured light phase retrieval and depth estimation have limited efficiency and are lack of robustness in their results and so on. To improve the reconstruction effect of structured light by deep learning, we propose 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 realize the advantages complementary of CNN and Transformer. The proposed network is experimentally compared with other networks in structured light phase estimation and structured light depth estimation. The experimental results indicate that the proposed network achieves finer detail processing in phase and depth estimation compared to other networks. Specifically, for structured light phase and depth estimation, its accuracy improves by 31% and 26%, respectively. Therefore, the proposed network improves the accuracy of deep neural networks in the structured light phase and depth estimation areas.

Optimal position for suger content detection of Yongquan honey oranges based on hyperspectral imaging technology
LI Bin, WAN Xia, LIU Ai-lun, ZOU Ji-ping, LU Ying-jun, YAO Chi, LIU Yan-de
2024, 17(1): 128-139.   doi: 10.37188/CO.2023-0057
Abstract(120) FullText HTML(77) PDF 4577KB(92)
Abstract:

The objective of this study is to explore the optimal detection location and the best prediction model of the suger level of Yongquan honey oranges, which can provide a theoretical basis for the brix measurement and classification of honey oranges. With the wavelength range of 390.2−981.3 nm hyperspectral imaging system was used to study the best position for detecting the sugar content of Yongquan honey oranges, and the spectral information of the calyx, fruit stem, equator and global of Yongquan honey oranges were combined with their sugar content of corresponding parts to establish its prediction model. The original spectra from the different locations were pre-processed by Standard Normal Variance (SNV) transformation, Multiple Scattering Correction (MSC), baseline calibration (Baseline) and SG smoothing, 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 oranges were found, and the optimal spectral data obtained by the best pre-processing methods were conducted to identify characteristic wavelengths using the Competitive Adaptive Re-weighting Sampling algorithm (CARS) and Uninformative Variable Elimination (UVE). 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 oranges 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 position for measuring the sugar content of honey oranges. This study demonstrates that the prediction models based on different parts of the orange have different effects. Identifying the optimal position and prediction model can provide a theoretical basis for classifying oranges for sugar content testing.

A non-null interferometry for concave aspheric surface
ZHANG Xu, LI Shi-jie, LIU Bing-cai, TIAN Ai-ling, LIANG Hai-feng, CAI Chang-long
2024, 17(1): 140-149.   doi: 10.37188/CO.2023-0042
Abstract(132) FullText HTML(53) PDF 8827KB(68)
Abstract:

To realize the rapid, high-precision, and universal testing of concave aspheric surface, a non-null interferometry method is proposed in this paper, which takes the asphere as a spherical surface and measures it directly with an interferometer. Combined with the corresponding data processing methods, the test results of the aspheric surface are obtained. Firstly, the detection theory of this method is introduced, the calculation and removal models of retrace error and adjustment error are established, and the data processing method of shape error is studied. Secondly, taking two concave aspherical surfaces with different parameters as an example, the retrace error and adjustment error are simulated, which verified the effectiveness of the method. Finally, a non-null interferometry experimental setup of concave aspheric surface is performed, and its shape error is successfully obtained. By comparing the results with autocollimation method or LUPHOScan method, it is shown that the surface distribution and evaluation indicators of the results are highly consistent, which verifies the correctness of this method. This method provides an effective measurement method for concave aspheric surface with high precision, universality, and convenience.

NIR-II fluorescence confocal imaging based on indirect wavefront shaping
TAN Tian, SHI Tian-yue, WU Chang-feng, PENG Hong-shang
2024, 17(1): 150-159.   doi: 10.37188/CO.2023-0070
Abstract(104) FullText HTML(53) PDF 4413KB(45)
Abstract:

Optical aberrations caused by the scattering of biological tissues limit the imaging performance of optical systems. A near-infrared II fluorescence confocal imaging technique based on indirect wavefront shaping was investigated. First, we synthesized a highly efficient near-infrared II range fluorescent probe, where reducing the scattering of biological tissue can realize biopsy imaging with high-contrast. Second, we investigated the adaptive optical method based on 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, near-infrared II fluorescence confocal imaging system based on indirect wavefront shaping was deployed and relevant experiments were conducted. The experimental results indicate that the system effectively compensates for the aberrations induced by air plates, scattering media and mouse skull, and increases the final signal intensity by 1.47, 1.95 and 2.85 times, respectively. As a result, the final imaging quality is significantly enhanced.

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
2024, 17(1): 160-166.   doi: 10.37188/CO.2023-0059
Abstract(158) FullText HTML(47) PDF 5295KB(64)
Abstract:

Cytoendoscopy requires continuous amplification with a maximum magnification rate of about 500 times. Due to optical fiber illumination and stray light, the image has non-uniform illumination that changes with the magnification rate, which affects the observation and judgement of lesions by doctors. Therefore, we propose 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.

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
2024, 17(1): 167-177.   doi: 10.37188/CO.2023-0083
Abstract(121) FullText HTML(59) PDF 4762KB(63)
Abstract:

Remote sensing satellites play a 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. We focus 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 with camera aperture, satellite orbit height and atmospheric coherence length is developed. Finally, the effect of atmospheric turbulence on the Modulation Transfer Function (MTF) is studied. The variation of the relative error of MTF with camera aperture, satellite orbit height and atmospheric coherence length is simulated and analyzed, 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.

Effect of electron irradiation on CsPbBr3 perovskite nanocrystal
ZHANG Bo-wen, HAN Dan, XUE Meng-yun, CAO Rong-xing, LI Hong-xia, ZENG Xiang-hua, XUE Yu-xiong
2024, 17(1): 178-186.   doi: 10.37188/CO.2023-0044
Abstract(232) FullText HTML(180) PDF 8081KB(116)
Abstract:

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, we conducted electron irradiation experiments on CsPbBr3 materials, characterized the microscopic morphology of CsPbBr3 nanocrystals by high-resolution transmission electron microscopy. Moreover, we investigated the variation 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 decrease 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 of the CsPbBr3 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.

Calculation of orbit external heat flow and radiation characteristics of space target
ZHENG Hong-ru, MA Yan, ZHANG Shuai, WANG Jian-chao, QU You-yang
2024, 17(1): 187-197.   doi: 10.37188/CO.2023-0033
Abstract(214) FullText HTML(112) PDF 4986KB(139)
Abstract:

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 external 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 earth-pointing mode. The average surface heat flow value of +YZ side panel decreased by 32.05 W/m2. The temperature characteristics of each surface are given combined with 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 each surface varies greatly over time in the earth-pointing mode, while the heat flow on each surface is relatively stable in the sun-pointing mode. Under both modes, the temperature of the solar panel is higher, the radiation intensity is larger, and it has obvious infrared characteristics, which facilitates infrared observation.

Design of a highly sensitive photoelectric detection circuit for TDLAS gas laser telemetry
PEI Zi-yi, HU Peng-bing, PAN Sun-qiang, QI Hai-yang, LIU Su-mei, LIU Dong
2024, 17(1): 198-208.   doi: 10.37188/CO.2023-0107
Abstract(115) FullText HTML(62) PDF 4629KB(60)
Abstract:

Aming at the characterstics of weak gas laser telemetry optical signals and strong interference from environmental factors, a Highly Sensitive Photoelectric Detection Circuit (HSPDC) for TDLAS laser telemetry based on wavelength modulation technology has been designed and investigated. In addition, a noise suppression method for TDLAS signals based on wavelength modulation technology was determined. The photodiode ideal model is utilized to analyze the linear response characteristics of the photodetector circuit and determine the essential photodiode parameters. Based on the cascade amplification principle, the HSPDC is designed, simulated, and tested, achieving a lower limit of optical power detection of 0.11 nW, a signal attenuation of 0.79 dB (f=10 kHz). The cutoff frequency is one order of magnitude higher than the existing 108 V/A cross-impedance amplification circuit. Therefore, the HSPDC is applicable for high-speed modulation of weak optical signals. The laser telemetry system exhibits excellent detection performance at a modulation frequency of 3 kHz, with a detection sensitivity of 88.66 mV/ppm, a detection limit of less than 0.565 ppm, and a linear fit R2 of 0.9996. The study demonstrates that the HSPDC photoelectric detection circuit has the advantages of fast response, high detection sensitivity and accuracy. Thus, it can be integrated to meet the needs of gas laser telemetry applications.

Detector temperature control system for ultraviolet spectrometer
JIANG Xue, HOU Han, MA Qing-jun, LIN Guan-yu
2024, 17(1): 209-216.   doi: 10.37188/CO.2023-0133
Abstract(87) FullText HTML(49) PDF 2625KB(41)
Abstract:

A temperature control system that employs an incremental PID algorithm based on FPGA technology has been developed to decrease detector noise and dark current while ensure the CMOS detector of the spectrometer obtain more accurate spectrum curve. Considering the current temperature and the control parameters, the appropriate control quantity is calculated to ensure the detector realize the target temperature. Controlling the temperature change rate of the detector is realized through front stage control, effectively solving the problem of overshooting. By adding the anti-integral saturation algorithm and the transition link of the target value, the function of the temperature change rate of the detector is controllable, and the problem of overshoot is solved. Multiple environmental tests conducted on the entire machine indicate that the system can control the temperature of the detector to reach any desired temperature within a specified temperature difference range of 40 °C under the ambient temperature condition in orbit. The sensor temperature has a margin of error of ±0.1 °C. Compared to the conventional analog PID control method, the proposed method offers significant advantages of high sensitivity and strong stability. At a temperature of −10 °C, the noise of the detector is substantially reduced.

Optical simulation design of surface mounted device beads for wide beam and high uniformity display
WEI Wei, CHEN Zhi-zhong, GUO Hao-zhong, JIA Chuan-yu, FANG Fang, ZOU Jun, FANG Qian, WU You, SUN Ming-hao, LI Qian, KUANG Yu-han, YIN Qi-kai, ZHANG Guo-yi
2024, 17(1): 217-225.   doi: 10.37188/CO.EN-2023-0017
Abstract(83) FullText HTML(110) PDF 2200KB(38)
Abstract:

Through analysing the optical requirements of wide beam and high uniformity light beads, which are currently used in displays, and packaging micro Light-Emitting Diode (LED) chips with a novel non-Lambertian distribution, we realized the production of wide beam and high uniformity micro-LED chip light beads. The light output efficiency and beam angle of fixed beads were simulated using brackets made of copper, titanium, aluminium and silver, as well as materials that were completely reflecting and absorbing. The simulations were conducted at various fixture angles, packaging heights, packaging materials, sapphire thicknesses, and patterned sapphire substrate sizes. By adjusting the chip and packaging parameters, we can obtain one, two, or three light beams with Surface Mounted Device (SMD) lamp beads characteristics that provide wide angles, high uniformity, and far-field light distribution. These characteristics can meet the current display requirements for LED and LCD.

Stimulated brillouin scattering in double-clad thulium-doped fiber amplifier
LIU Qing-min, SUN Hui-jie, HOU Shang-lin, LEI Jing-li, WU Gang, YAN Zu-yong
2024, 17(1): 226-237.   doi: 10.37188/CO.EN-2023-0011
Abstract(88) FullText HTML(48) PDF 5581KB(57)
Abstract:

In this paper, the effect of Stimulated Brillouin Scattering(SBS) on the laser output performance in a 2 µm thulium-doped fiber amplifier was analyzed theoretically. The optical mode distribution, 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. The stimulated Brillouin scattering characteristics, including the Brillouin frequency shift and the Brillouin gain spectrum, in the double-clad thulium-doped fiber were numerically simulated in the laser waveband of 1.9−2.1 µm. The influence of stimulated Brillouin scattering on the laser output performance of thulium-doped fiber amplifiers was investigated using the theoretical model of stimulated Brillouin scattering in gain fibers. In the DTDF-10/130 double-clad thulium-doped fiber, a continuous wave with power of 100 W and wavelength of 793 nm is used as a pump to amplify a continuous signal wave with wavelength of 2 µm and power of 0.01 W. The maximum output powers of the signal wave are 25.27 W, 31.08 W and 34.06 W when the pump power filling factors are 0.01, 0.02 and 0.03, respectively. The corresponding optimal double-clad fiber lengths are 2.66 m, 2.02 m and 1.75 m. Additionally, the Stokes optical powers generated by the stimulated Brillouin scattering are 1.68 W, 1.39 W and 1.14 W, respectively. The results show that the double-clad fiber with large pump power filling factor in the thulium-doped fiber amplifier can effectively reduce the fiber length, thus to minimize the influence of stimulated Brillouin scattering on the output power of the signal laser. The numerical model can optimize the fiber length of the fiber amplifier, which is of great significance to improve experimental efficiency and reduce experimental costs.

All-solid-state acousto-optic mode-locked laser operating at 660 nm
WANG Yu-ning, ZHENG Quan, SU Xin, BAI Zhong-shu, ZHANG Xiu-qi, LIU Chao-zhi, LIU Wei
2024, 17(1): 238-244.   doi: 10.37188/CO.EN-2023-0013
Abstract(133) FullText HTML(64) PDF 5116KB(99)
Abstract:

Red lasers with a picosecond pulse width are widely used in various fields such as industrial, medical, scientific research and information strorage due to their narrow pulse width and high peak power. This paper presents an all-solid-state laser, operating at 660 nm with picosecond pulse width, narrow band, and high conversion efficiency, which is demonstrated by the acousto-optic mode-locked (AOML) method. By optimizing the cavity and implementing external frequency doubling with two LiB3O5 (LBO) crystals along with various techniques, a mode-locked red laser source with a maximum output power of 8.6 W is developed. The laser operates in a pulsed side-pumped regime and contains the mode-locked pulses with a frequency of 100 MHz and a pulse width of 887 ps. The optical-to-optical conversion efficiency from 1319 nm to 660 nm can reach up to 41%.

Design of all-optical logic gate based on two-dimensional photonic crystal
WU Rong, ZHANG Hao-chen, YANG Jian-ye
2024, 17(1): 245-251.   doi: 10.37188/CO.EN-2023-0014
Abstract(86) FullText HTML(55) PDF 4696KB(42)
Abstract:

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 a two-dimensional photonic crystal is designed. The band structure of the two-dimensional photonic crystal is analyzed by using the plane wave expansion method. The time-domain finite-difference method and the linear interference effect are used to simulate the stable electric field diagram and the normalized power of the XNOR gate and NAND gates on the Rsoft platform. The simulation results demonstrate 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. On the other hand, 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. It can be seen that the designed structure has a high contrast, short response time, and fast data transmission rate.

On-machine detection technology and application progress of high dynamic range fringe structured light
LIU Ze-long, LI Mao-yue, LU Xin-yuan, ZHANG Ming-lei
2024, 17(1): 1-18.   doi: 10.37188/CO.2023-0068
Abstract(199) FullText HTML(52) PDF 6064KB(116)
Abstract:

Fringe structured light technology is a non-contact measurement method, which has developed rapidly in recent years and provides a new solution for on-machine detection in mechanical processing. However, the accuracy of structured light for on-machine detection 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 structured light detection can reduce the effect of high reflectivity, achieving the measurement of metal parts in complex scenes. This paper introduces the measurement principle of structured light and summarizes the challenges of on-machine detection for HDR structured light. Subsequently, this paper provides a comprehensive review of HDR structured light technology. In the context of on-machine detection of mechanical processing, the HDR technology based on hardware equipment and the HDR technology based on stripe algorithm are discussed and analyzed, respectively. Following this, different technologies are summarized according to the requirements of on-machine detection. The advantages and disadvantages of various methods are presented, and the applicability of on-machine detection 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.

Research progress on the related physical mechanism of laser-induced breakdown spectroscopy
LIU Rui-bin, YIN Yun-song
2024, 17(1): 19-37.   doi: 10.37188/CO.2023-0019
Abstract(177) FullText HTML(44) PDF 1508KB(79)
Abstract:

Laser Induced Breakdown Spectroscopy (LIBS) is a new method for qualitative and quantitative analysis of the constituents of a material using plasma spectra produced by the interaction of a strong pulsed laser with the material. In the process of pulsed laser-induced plasma, different laser parameters (energy, pulse width, wavelength), environmental conditions during the detection process and the properties of the material itself have different degrees of influence on the physical mechanism of laser-induced plasma, which in turn affects the results of LIBS quantitative analysis. We review the physical mechanisms of LIBS technology in the current state, including the basic principles of LIBS, the differences in laser parameters, and the physical mechanisms involved in the differences in environmental and material properties. It provides a basis for a deeper understanding of laser-matter interactions and for improving the detection capabilities of LIBS.

Key technology analysis and research 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
2024, 17(1): 38-51.   doi: 10.37188/CO.2023-0074
Abstract(121) FullText HTML(45) PDF 8949KB(81)
Abstract:

Narrow linewidth fiber lasers, based on the multi-longitudinal-mode oscillator seed source, have obvious advantages in engineering applications and space-limited loading platforms. 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 improvement in output power and affects the purity of laser spectra. In this paper, we introduce four commonly used narrow linewidth seeds. The mechanism and suppression methods of the self-pulse effect in multi-longitudinal mode oscillator seeds are 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.

Development and prospects of enhanced absorption spectroscopy
REN Yi-jie, YAN Chang-xiang, XU Jia-wei
2023, 16(6): 1273-1292.   doi: 10.37188/CO.2022-0246
Abstract(780) FullText HTML(352) PDF 4881KB(367)
Abstract:

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.

Advances in optical fiber tweezer technology based on hetero-core fiber
LI Hong, ZHU Ying-xin, ZHOU Ya-ni, WANG Hai-bo, DONG Ming-li, ZHU Lian-qing
2023, 16(6): 1293-1304.   doi: 10.37188/CO.2023-0016
Abstract(338) FullText HTML(182) PDF 6097KB(200)
Abstract:

Optical fiber tweezers are widely used in biochemical analysis, life sciences, and other fields due to their simple structure, flexible operation, and compact size. The hetero-core structure of the optical fiber probe possesses inherent advantages in near-field evanescent wave optical trapping force, core beam coupling transmission, and cross-synergistic application of microfluidic technology, which can realize the functions of cell and subcellular particle collection and transportation, and can significantly improve the three-dimensional particle trapping capability as well as dynamic manipulation level. In this paper, the structural characteristics and application technology research progress of optical fiber tweezers based on different core structures are reviewed. This paper sorts and compares key technologies, including probe preparation, laser source, and coupling mode, in hetero-core optical fiber tweezers systems. It also summarizes and provides a perspective on the role and development of hetero-core fibers with different structures in optical fiber tweezers.

A review of the effect of GaN-Based Micro-LED sidewall on external quantum efficiency and sidewall treatment techniques
KUANG Hai, HUANG Zhen, XIONG Zhi-hua, LIU Li
2023, 16(6): 1305-1317.   doi: 10.37188/CO.2023-0091
Abstract(297) FullText HTML(60) PDF 4670KB(141)
Abstract:

Micro-LEDs offers the benefits of high brightness, high response frequency, and low power consumption, making them an attractive candidate for future display technologies and Visible Light Communication (VLC) systems. Nonetheless, their low External Quantum Efficiency (EQE) currently impedes their scaled mass production and further applications. In order to break through the bottleneck of low EQE, we conducted an analysis of Micro-LED external quantum efficiency’s contributing factors. The influencing factors for EQE are analyzed. It is concluded that the carrier loss and non-radiative recombination caused by sidewall defects are the main reasons for the decrease in EQE. In addition, we summarized the impact of sidewall defects on carrier transport and composites, and we also reviewed the commonly used sidewall treatment technology and repair methods, and pointed out that the existing sidewall treatment methods are helpful but insufficient for improving EQE, and the mechanism of carrier interaction with sidewall defects is not very clear. It is suggested to carry out a thorough and systematic study on the types and distribution of sidewall defects, the mechanism of carrier and sidewall defects, and the defect repair mode in the sidewall treatment process. Finally, future development trends are projected. This paper offers design ideas and theoretical foundations to enhance the external quantum efficiency and accelerate the process of commercialization and mass production of Micro-LEDs.

Recent advances in metasurfaces for polarization imaging
ZHOU Jun-zhuo, HAO Jia, YU Xiao-chang, ZHOU Jian, DENG Chen-wei, YU Yi-ting
2023, 16(5): 973-995.   doi: 10.37188/CO.2022-0234
Abstract(1385) FullText HTML(656) PDF 6268KB(804)
Abstract:

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.

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
2023, 16(5): 996-1009.   doi: 10.37188/CO.2023-0009
Abstract(501) FullText HTML(287) PDF 6648KB(287)
Abstract:

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.

Research progress of miniature head-mounted single photon fluorescence microscopic imaging technique
FU Qiang, ZHANG Zhi-miao, ZHAO Shang-nan, LIU Yang, DONG Yang
2023, 16(5): 1010-1021.   doi: 10.37188/CO.2023-0007
Abstract(417) FullText HTML(157) PDF 8052KB(216)
Abstract:

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.

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(1121) FullText HTML(414) PDF 11662KB(521)
Abstract:

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(822) FullText HTML(403) PDF 7682KB(544)
Abstract:

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(964) FullText HTML(480) PDF 4220KB(529)
Abstract:

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(1353) FullText HTML(575) PDF 10445KB(681)
Abstract:

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(813) FullText HTML(455) PDF 3656KB(406)
Abstract:

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(2468) FullText HTML(616) PDF 7237KB(1009)
Abstract:

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(919) FullText HTML(465) PDF 12124KB(563)
Abstract:

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(1059) FullText HTML(574) PDF 5785KB(670)
Abstract:

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(738) FullText HTML(364) PDF 6306KB(522)
Abstract:

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(1355) FullText HTML(619) PDF 6214KB(548)
Abstract:

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(2784) FullText HTML(689) PDF 19381KB(1502)
Abstract:

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.

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

CODEN ZGHUC8

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