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Abstract(82) FullText HTML(23) PDF 4435KB(104)
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Aiming at the problem that the optical frequency scanning nonlinearity affects the phase extracting accuracy of the optical Frequency Scanning Interferometry (FSI) signal, and thus reduces the FSI ranging accuracy, a phase-extracting method based on the Complementary Ensemble Empirical Mode Decomposition and Hilbert Transform (CEEMD-HT) algorithm is proposed in this paper. Based on theoretical derivation and simulation analysis of the CEEMD-HT algorithm, the effectiveness of the algorithm in solving the phase of the non-stationary interference signal in scanning-frequency is verified by simulation. Further simulation experiments were implemented by using the real output optical frequency curve obtained with FSI ranging system as the simulation conditions. The simulation results showed that the CEEMD-HT algorithm significantly improved the phase extracting accuracy of the interference signal and that of the FSI ranging. Finally, the proposed interference signal phase-extracting method was verified via the experiment of the FSI ranging system. The results showed that the ranging repeatability of the measurement system based on the CEEMD-HT algorithm was 2.79 μm in the free space measurement range of 2 m. Compared with EMD-HT and direct measurement methods, the ranging repeatability was improved by 5.19 times and 8.28 times, respectively.

Abstract(5) FullText HTML(3) PDF 3676KB(1)
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The polarization-multiplexing of a laser based on a medium with a large gain bandwidth and a high thermal conductivity can benefit dual-frequency and dual-comb lasers’ spectral bandwidth and power. This paper presents a demonstration of the polarization-multiplexing of a laser based on a bulk Yb:CALGO crystal. The polarization-multiplexing is realized by sandwiching the gain crystal within two 45˚-cut birefringent crystals, forming two orthogonally polarized beams with spatial separation inside and allowing the system to pump the laser at the waist of the cavity mode for more efficient pumping. The laser outputs watt-level power with a slope efficiency exceeding 30%. A dual-frequency operation with terahertz frequency separation is realized by inserting an etalon into the cavity.

Abstract(32) FullText HTML(8) PDF 7740KB(14)
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The Taiji Project is a space gravitational wave detection mission proposed by the Chinese Academy of Sciences, which uses the method of laser differential interference to detect pm-level displacement fluctuations caused by gravitational waves between satellites. In order to eliminate the phase measurement error caused by the dissynchronization of the clock between satellites, Taiji Project intends to use the sideband multiplication transfer scheme to measure and eliminate the inter-satellite clock noise. This paper discusses the requirements, principles, and methods of inter-satellite clock noise transmission of the Taiji project, and designs experiments for principle verification. By building an electronics experiment, the limit value of the clock noise of the two systems was tested, the relevant parameters of the experiment were determined, and the principle of the sideband multiplication transfer scheme was verified by further optical experiments. The experimental results show that the clock noise cancellation scheme and related parameters proposed in this paper are reasonable and feasible, and are suitable for the needs of Taiji project. Moreover, in the 0.05 Hz-1 Hz frequency band, the suppression effect of inter-satellite clock noise is better than 2π×10-5 rad/Hz1/2, which meets the noise requirements of Taiji pathfinder and lays an experimental and theoretical foundation for the design of clock noise transmission scheme and parameter of future Taiji Project.

Abstract(19) FullText HTML(8) PDF 2527KB(10)
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Flow cytomicrographic analysis is an important development in the automatic identification of planktonic algae in the water column, where the deformation of microscopic images under rapid injection conditions affects the accuracy of automatic identification of planktonic algae. Based on a microfluidic-microscopic imaging system for planktonic algae, the effect of flow rate on the deformation of microscopic images was investigated by analysing the deformation of algal cells and image clarity at different injection flow rates.Based on the principle of deformation caused by a rolling shutter photographing a moving object, a method of image deformation correction with unidirectional offset pixels is proposed and analysed in comparison with images acquired under static conditions of algal cells.The experimental results showed that the average values of aspect ratio and sharpness of L. oocystis cell images under static conditions were 1.16 and 116.53 respectively; during the dynamic injection process, the deformation (aspect ratio) of cell images gradually increased and the sharpness decreased as the flow rate increased; the average values of aspect ratio before and after correction were 1.35 and 1.26 respectively at 95 µL/min injection flow rate, and the dispersion of deformation decreased from 0.33 before correction to 0.1. The mean value of aspect ratio before and after correction was 1.35 and 1.26 respectively at 95 µL flow rate.The results provide a method for improving the accuracy of automatic identification of planktonic algal cells in the water column.

Abstract(140) FullText HTML(110) PDF 2616KB(162)
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To gain better phase measurement results in nonlinear measurement systems, a phase measurement method that uses dual-frequency grating after reducing the nonlinear effect is proposed. Firstly, the nonlinear effect of the phase measurement system is discussed, the basic reason for the existence of high-order spectra components in the frequency domain is analyzed, and the basic method used to reduce the nonlinear effect and separate fundamental frequency information is given. Then, on the basis of reducing the nonlinear effect’s influence on the system, the basic principle of phase measurement for the fringe image of a measured object using the dual-frequency grating method is analyzed. To verify the correctness and effectiveness of the proposed phase measurement method, a computer simulation and some practical experiments were implemented with good results. In the simulation, the error value of this method was 27.97% for the method with nonlinear influence, and 52.51% for that with almost no nonlinear influence. In the experiment, the effect of phase recovery produces the best results. This shows that phase measurement by the method mentioned in this paper has effective and with a small error.

Abstract(29) FullText HTML(18) PDF 10531KB(32)
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We propose cosh-Pearcey-Gauss beams with uniform polarization, which are mainly modulated by a hyperbolic cosine function (n, Ω) and the angles related to uniform polarization (α, δ). Based on angular spectrum representation and the stationary phase method, the Poynting vector, spin and orbital angular momentum in the far zone are studied. The results show that a larger n or Ω in the hyperbolic cosine function can partition the longitudinal Poynting vectors, SAMs and OAMs into more multi-lobed parabolic structures. Different polarizations described by (α, δ) can distinguish their Poynting vectors and angular momentums between the TE and TM terms, though this does not affect the patterns of the whole beam. Furthermore, the weight of the left and right sides of longitudinal Poynting vectors, SAMs and OAMs in TE and TM terms can be modulated by left-handed or right-handed elliptical polarization, respectively. The results in this paper may be useful for information storage and polarization imaging.

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Abstract(25) FullText HTML(18) PDF 4182KB(30)
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In order to realize tunable longwave infrared laser, this paper designs a ZGP temperature tuned longwave infrared optical parametric oscillator. Using a Ho:YAG laser with the center wavelength of 2097 nm to pump ZGP crystals with different phase matching angles, the laser with a segment continuously tunable range of 7.53−8.77 μm is realized in the temperature range of 15−30°C, with a total tuning range of 1.24 μm. The output power of ZGP - OPO is greater than 1.503 W over the entire tuning range. The output power is 1.503 W at the idler wavelength of 8.77 μm, and the corresponding slope efficiency and optical conversion efficiency are 12.19% and 6.53%, respectively. The experimental results show that temperature tuning of ZGP is an effective technical method to obtain continuously tunable long-wave infrared laser. The research of this experiment has potential application value in the field of engineering of tunable long-wave laser.

Abstract(24) FullText HTML(20) PDF 6895KB(27)
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Optical encryption materials for pattern information have been widely used in anti-counterfeiting, information encryption and storage, and structural color metasurface based on anisotropic functional reuse has been developed. The optical encrypted metasurface based on one-dimensional grating diffraction requires the processing of mask or unit structure one by one, resulting in low limiting efficiency. The structure uniformity of traditional ablated LIPSS is poor, which affects the device performance. Based on the above problems, an optical metasurface machining method based on the modified structure of picosecond laser direct writing phase change material Ge2Sb2Te5 is proposed. Firstly, the dispersion performance of the prepared GST modified gratings was characterized, and combined with the polarization dependence of the modified gratings, the angle-multiplexed information encryption metasurface was designed, and the metasurface prepared by the proposed method was further demonstrated. It realizes the performance of encryption under natural light, selective decryption reading and dynamic display under strong light. Compared with the traditional processing method, the proposed method can generate a series of grating structures in the form of simultaneous printing in a direct writing process, which improves the processing efficiency. At the same time, the grating structure obtained by processing is uniform and consistent, which improves the color rendering effect. The modified grating with 16° difference in orientation Angle realizes the selective information reading without crosstalk, and the obtained structure color is uniform and bright. The processing strategy proposed in this paper has a profound application prospect in the fields of anti-counterfeiting, information encryption storage and wearable flexible display devices. The processing strategy proposed in this paper has a profound application prospect in the fields of anti-counterfeiting information encryption storage and wearable flexible display devices.

Abstract(21) PDF 228KB(16)
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A ground-based Doppler Asymmetric Spatial Heterodyne (DASH) interferometer with high signal-to-noise ratio (SNR) and large etendue（AΩ） with thermal compensation was developed to detect wind field information in the middle atmosphere. The detailed parameters and index of the DASH interferometer were developed for the 557.7 nm oxygen airglow spectral line. The system was designed with an expanded field of view (FOV) and thermal compensation. The half-FOV angle reached 2.815°, the etendue was 0.09525cm2sr, and the system SNR was approximately 113.75. Through the thermal compensation design, the final optical path difference with temperature variation（dΔd0/dT） was only 2.224×10-7mm/℃. The optical system was designed and optimized according to the corresponding parameters. Image-side telecentric and bilateral telecentric optical system structures were used in the entrance optics and exit optics, respectively. And parameters such as telecentricity and distortion met the detection requiremen
Abstract(18) FullText HTML(12) PDF 4924KB(28)
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In order to eliminate the uncertainty caused by the inclination of the beam, a dual polarization laser Doppler velocimetry system is established in this paper. The system uses a dual beam dual probe structure to detect the motion information of the object. Firstly, the included angle of the two beams is accurately obtained through the rotation experiment. For any beam inclination, the dual probe device is used to collect the scattered beam from the moving object surface, and the Doppler frequency shift of the two interference signals is obtained by combining the dual polarization optical path structure. Then, the refined framing algorithm is innovated to demodulate the two interference signals in real time, and the real speed of the object is obtained by synthesizing the two speed components. The experimental results show that the average error between the measured value and the theoretical value can reach 1% ~ 5% when the speed is within the range of 10 mm/min ~ 1500 mm/min. In the process of non-stationary motion, the RMSE average of V-T image corrected by thinning and framing algorithm is 1.19mm/min. The structure of the system meets the requirements of stability and reliability, high accuracy and strong anti-interference ability in speed measurement.

Abstract(34) FullText HTML(47) PDF 4559KB(38)
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In this paper, a metamaterial Fano resonance design method based on deep learning is proposed to obtain high-quality factor (high-Q) resonances with desired characteristics, such as linewidth, amplitude, and spectral position.The deep neural network is used to establish the mapping between the structural parameters and the transmission spectrum curve, and the forward network is used to predict the transmission spectrum.The inverse network achieves the on-demand design of high Q resonance. The low mean square error ( MSE ) is achieved in the design process, and the mean square error of the training set is 0.007.The results indicate that compared with the traditional design process, using deep learning to guide the design can achieve faster, more accurate, and more convenient purposes.The design of Fano resonance can also be extended to the automatic inverse design of other types of metamaterials, significantly improving the feasibility of more complex metamaterial designs.

Abstract(70) FullText HTML(34) PDF 4908KB(57)
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To improve the extinction ratio of a polarization beam splitter, we propose a dual-slot ultra-compact polarization splitter (PBS) consisting of a hybrid plasma horizontal slot waveguide (HSW) and a silicon nitride hybrid vertical slot waveguide (VSW). The coating material is silicon dioxide, which can prevent the oxidation of the mixed plasma and also facilitate integration with other devices. The mode characteristics of the HSW and VSW are simulated by using the finite element method (FEM). At suitable HSW and VSW widths, the TE polarization modes in HSW and VSW are phase-matched, while the TM polarization modes are phase mismatched. Therefore, the TE mode in an HSW waveguide is strongly coupled with a VSW waveguide by adopting a dual-slot, while the TM mode directly passes through the HSW waveguide. The results show that PBS achieves an extinction ratio (ER) of 35.1 dB and an insertion loss (IL) of 0.34 dB for the TE mode at 1.55 μm. For the TM mode, PBS reached 40.9 dB for ER and 2.65 dB for IL. The proposed PBS is designed for the 100 nm bandwidth, high ER, and low IL, which can be suitable for photonic integrated circuits (PICs).

Abstract(43) PDF 651KB(31)
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Abstract(84) FullText HTML(72) PDF 472KB(65)
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The decoherence of temporal quantum correlation is explored in a voltage-controlled quantum dots molecule in a cavity. The temporal correlation in the hybrid system is studied by Leggett-Garg inequalities. The inequality violations can be interpreted as the existence of temporal quantum correlation during dynamical evolution. The temporal quantum correlation is enhanced by its electron tunnel’s strength and cavity frequency detuning. It is found that there is no temporal correlation in the regions where the values of spatial quantum correlation are zero and the maximal violations occur in conditions with high values of quantum coherence. In contrast, spatial coherence can persist at times when no violation is detected. The open quantum system approach is used to investigate the environmental effects on inequality violations. The temporal correlation is suppressed by the spontaneous decay of the quantum dots and cavity leakage. These results are serviceable in processing quantum information in hybrid quantum systems.

Abstract(68) FullText HTML(85) PDF 2470KB(120)
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We propose a “leaf-type” hybrid metamaterial to realize bandwidth-tunable half-wave plate based on vanadium dioxide (VO2) phase transition. The hybrid metamaterial is a hollow “leaf-type” metallic structure and regarded as a dual-band half-wave plate when VO2 film is in the insulating phase. Within 1.01−1.17 THz and 1.47−1.95 THz, it can accomplish y− to x-polarization conversion with a polarization conversion rate over 0.9 and an average relative bandwidth of 26%. The metamaterial becomes a solid core “leaf-type” metallic structure when VO2 is in the metallic phase. Within 1.13−2.80 THz, it can act as a broadband half-wave plate with a relative bandwidth of 85%. The working principle of the bandwidth-tunable half-wave plate is explained by the instantaneous surface current distribution and electric field theory in detail. The proposed “leaf-type” hybrid metamaterial half-wave plate has potential application prospects in THz imaging, sensing and polarization detection.

Abstract(67) FullText HTML(50) PDF 6310KB(57)
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In order to improve the quality value (Q) to enhance the coupling between light and matter. In this paper, a dielectric metamaterial with simple structure, low fabrication requirements was proposed. It can excite symmetric protected bound states in the continuum (BICS). The dielectric metamaterial has a planar nanopore plate composed of tetrameric pores. By changing the position of the nanopores, the symmetrical protection BIC can be transformed into the symmetrical protection quasi BIC(QBIC), and then two high Q value Fano resonances can be induced. Through simulation calculation, the Fano resonance Q value can reach 1e6 when Δ=3 nm. Then, the far-field radiation of QBIC and Fano resonance is decomposed into the contributions of different multipole components. Based on the scattering power and electric field vector distribution, it can be found that the dielectric metamaterials λ1 Fano resonance with high Q value is mainly due to magnetic quadrupole and toroidal dipole, while λ2 Fano resonance has high Q value is mainly due to the toroidal dipole. Finally, the influence of nanopore side length and nanopore filling material on the two Fano resonances is analyzed and calculated. The research in this paper can provide theoretical guidance for the future research and preparation of high Q value optical response devices.

Abstract(63) FullText HTML(37) PDF 2261KB(125)
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In this paper, the coplanar excitation of terahertz Spoof Surface Plasmon (SSP) realized by using a single-layer grating meta-surface coupling method is proposed, which overcomes the disadvantages such as the inconvenience of reflection measurement when applying the medium couplers. The periodic grating and terahertz SSP composite structure are simultaneously constructed on the monolayer metal structure. When the terahertz waves are incident vertically, the wavevector of grating structures and the wavevector of SSPs are matched, and the SSP mode can be excited. The high Q value resonant peaks can be generated in the transmission spectrum, and its factor Q can reach 1923. The effects of the structural parameters on the grating-coupled meta-surface transmission spectrum and dispersion characteristics are also analyzed. In addition, based on the high Q resonant peak in the transmission spectrum of the designed structure, the high sensing sensitivity is about 67 GHz/RIU at the resonant center frequency of 0.22 THz. The structure proposed in this paper, which realizes terahertz SSP excitation and high Q sensing by treating a single-layer meta-surface structure, exhibits great application potential in many practical applications.

Abstract(48) FullText HTML(24) PDF 6739KB(46)
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In order to improve the stability of an electrowetting liquid lens’s zoom, based on the research of glass lenses, a statistical data-based index of liquid lens zoom stability and liquid lens repeated zoom accuracy is proposed. An experimental method is presented to optimize the structural parameters and materials of the liquid lens. Firstly, the main factors affecting the accuracy of a liquid lens’s repeat zoom were obtained through preliminary experimental research, including the polar solution volume, taper and non-polar solution viscosity. Secondly, taking the accuracy of the liquid lens’s repeat zoom and zoom range as evaluation indicators, it was found that the relationship between the accuracy of the liquid lens’s repeat zoom and the voltage is not monotonic, and that it rises first and then falls. On this basis, through the range analysis and comprehensive balance method, the primary and secondary factors and the optimal combination of parameters is obtained. After that, orthogonal experiments were used to optimize the design parameters. Finally, the effectiveness of this method was verified by experiments. The experimental results show that the repeat zoom accuracy of the optimized liquid lens is 0.2 m−1, and the zoom range is −15.2−5.85 m−1 over the voltage range of 0 to 230 V. It basically meets the requirements of stable and reliable liquid lens zoom, high precision, and large zoom range.

Abstract(277) FullText HTML(151) PDF 10063KB(188)
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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.

Abstract(45) FullText HTML(18) PDF 5940KB(52)
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In order to overcome the adverse effects of near-ground turbulence on the imaging quality of the optical systems at imaging distances of tens to hundreds of meters, an optical imaging system based on a long focal length telescopic objective lens and an integrated adaptive module is designed. With a system center height of 1.9 m and the imaging distance of 50~200 m, the outdoor imaging experiment of a resolution plate is carried out. The experimental results show that the influence of turbulence on imaging quality is obvious at medium and long distances of 50~200 m near the ground. The experimental system can effectively overcome the influence of turbulence at different distances and improve the consistency of image resolution and clarity. As the imaging distance increases, the influence of turbulence increases, and the system’s correction ability and the imaging quality decrease. The imaging resolution of the system can reach 0.5 mm at an imaging distance of 100 m. Cracks on the surface of a concrete model are observed and corrected at a distance of 200 m. The experimental results show that the system can suppress the influence of turbulence and improve the clarity of the image, which verifies the practical application ability of the system.

Abstract(38) FullText HTML(20) PDF 5829KB(52)
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Under conditions with large temperature differences in an infrared optical system, its imaging quality will deteriorate due to severe temperature changes. Large field-of-view medium-wave infrared cameras for airborne forest fire monitoring work in drastically changing environments. The system also has high requirements for stray radiation. In order to ensure that the optical system performs stably and with good imaging quality in the large field-of-view and the required large temperature range, a cooled medium-wave infrared optical system is designed based on athermalization and the comprehensive evaluation method of stray radiation based on noise equivalent temperature difference. The optical system consists of 6 lenses and 1 filter whose working wavelength is 3.7~4.8 μm; its F-number, focal length, and field of view are 2.5, 62.5 mm and 14.36°×10.87°, respectively. The pixel resolution of the medium-wave uncooled detector is 640×512. By using a combination of silicon and germanium materials and reasonably distributing the optical power, achromatic aberration and athermalization designs are realized. Through cold reflection optimization and cold aperture matching, stray radiation noise in the system is well-suppressed. By a bit of aspheric optimization, higher-order aberrations are corrected based on the requirements. The results show that the imaging quality of the optical system is stable and good in the temperature range of −55~+70 °C.

Abstract(45) FullText HTML(22) PDF 5665KB(52)
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Multiple sub-aperture interference imaging enables the images formed by the sparse aperture imaging system to have a higher resolution after the cophasing error is corrected. In this paper, the MTF and surface target imaging of the system are analyzed with a Golay3 sparse aperture imaging system as the research object when there are different piston and tilt errors among the sub-apertures. A Golay3 sparse aperture imaging system was developed to carry out an imaging experiment with the USAF1951 resolving power test target as the area target. Three-aperture synthetic imaging is achieved by adjusting the position of the plane mirror in the light beam deflection and the adjustment module to correct the piston and tilt errors of the sub-apertures. The results of a theoretical analysis are then verified. According to calculations, the developed system’s angular resolution of 1.38 urad is close to the equivalent single-aperture imaging system’s theoretical resolution of 1.18 urad. The developed Golay3 sparse aperture imaging system can correct the cophasing errors and improve the imaging resolution.

Abstract(56) FullText HTML(34) PDF 3489KB(46)
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In order to realize the non-contact high-precision measurement of high-temperature temperature fields such as the tail flame, combustion and explosion of aerospace engines, a static interferometric high-temperature temperature field imaging and detection method is studied. Firstly, a static interference high-temperature temperature field detection system is designed. Using a theoretical analysis of the measurement principle of high-temperature temperature fields, the relationship between the optical path difference and the temperature at the lowest point of high-temperature interference signal intensity is studied; Secondly, according to the response band of the visible light area array detector and the common temperature range, a static interferometric Savart prism is designed, and temperature field imaging is realized by using it for one-dimensional scanning; Finally, the optical system is designed and the corresponding relationship between the minimum optical path difference of the interference and the temperature is obtained by fitting. From this, the linear fitting formula is obtained. Simulations are conducted to verify the interference signal image where the temperature field after passing through the system reaches the area detector. The static interferometric high-temperature temperature field detection method can achieve the high-precision detection of 1000 K−3000 K temperatures. In the linear region, the temperature measurement resolution is 1.4 K and the temperature measurement relative error is better than 0.8%. This research lays the foundation for high-precision high-temperature temperature field imaging in the military and civilian fields.

Abstract(52) FullText HTML(22) PDF 3362KB(51)
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In order to reduce influence of background infrared radiation, optical system temperatures below −20 °C were necessary when satellite-borne long-wave infrared imagers worked in orbit. On the base of the weak heat conduction structure, a Ω type flexible sunshield made of MLI was developed and a cryogenic optical system was achieved through direct radiation cooling. Cage-like three-dimensional heat conduction straps made of copper were developed and an isothermal design for the primary barrel was realized. The cryogenic optical system applied to space remote sensing was used for the first time in China when it was tested in orbit with satellite SJ-9B. The results showed the temperature of the whole optical system could be maintained at −35 °C~−20 °C all the time, and the temperature difference in the primary barrel was no more than 4 °C. All flight test data met the temperature requirement of the long-wave infrared imager. The thermal control method is simple and effective, which can provide a reference for the thermal design of similar satellite-borne infrared optical systems.

Abstract(27) FullText HTML(33) PDF 5346KB(103)
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In order to effectively suppress the interference of CO2 radiation from 4.3 μm attachment on 3 μm−5 μm MWiR target signal, based on the Needle random intercalation optimization algorithm, an accurate inversion correction model for the growth error of multi-layer ultra-thick Ge/Al2O3 films under quartz crystal monitoring is established by the electron beam evaporation method, thus realizing the design, the accurate inversion and the accurate preparation of MWiR notch filter; in order to solve the problem that the surface profile of the MWiR notch filter changes greatly, the preset substrate surface method is used to realize the low surface profile regulation of MWiR notch filter. The results show that the high refractive index Ge film has good deposition stability with the increase of coating time, while the deposition scale factor of low refractive index Al2O3 thin film changes up to 11.9% in a regular gradual trend. For the prepared MWiR notch filter, the average cut-off transmittance is <0.3% at 4.2 μm−4.5 μm, and the average transmittances are >95% at 3.5 μm−4.05 μm and 4.7 μm−5.0 μm. The surface profile of the substrate after coating can be effectively controlled in a small range. The film has good adaptability to complex environment, and has successfully passed the environmental test of firmness, high temperature, low temperature and damp heat specified in GJB 2485-95.

Abstract(56) FullText HTML(31) PDF 4148KB(73)
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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.

Abstract(65) FullText HTML(25) PDF 6500KB(72)
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The machining quality and detection accuracy of aero-engine blades have a very important influence on the service life of blades. Aiming at the problem of improving the accuracy of blade detection, a high-precision scanning viewpoint planning method based on structured light was proposed in this paper. Firstly, the coarse model data were obtained by coarse scanning under the overall size of the blade, and the field of view was determined according to the camera resolution and acquisition accuracy. Secondly, the improved Angle Criterion algorithm was used to extract the boundary, and the boundary segmentation points were determined according to the boundary coordinates and the range of visual field. The coarse model was sliced by the section line method of surface, and the internal segmentation points were determined according to the slice results, so as to complete the uniform segmentation of point clouds. Then, a directed bounding box was established for the segmented point cloud data to obtain the coordinates of the center point, and the normal vector was statistically analyzed to determine the orientation of the main normal, so as to generate the viewpoint coordinates of high-precision scanning. Finally, the surface morphology of the blade was tested and verified. The experimental results show that the average standard deviation of the proposed method is reduced by 0.0054mm and the collected viewpoint is reduced by 1/3 compared with the viewpoint acquisition result of the supervoxel segmentation, which has a good application prospect in machining inspection of thin-walled blades.

Abstract(75) FullText HTML(47) PDF 4568KB(90)
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We propose a method for improving the computational efficiency of passively mode-locked fiber laser, which is composed by symmetric split-step Fourier method (SSFM) and the global-error-local-energy (GELE) method for solving propagating equations. Our proposed method relies on the limitation of local energy increment related with global error within a certain value to control the selection of step size. This method has advantage of an automatic step adjustment mechanism. To achieve the same order of computation accuracy, the computational time of our method is 255 s, while SSFM with small constant step size method needs to calculate 3855 s. The computational time of our proposed method is one or two orders of magnitude less than that of the SSFM, which indicates our method can enhance the computational efficiency by a factor up to 10. It could be expanded with high-order algorithms, such as RK4IP, Adams, predictor–corrector, etc. for improving the accuracy.

Abstract(98) FullText HTML(29) PDF 3438KB(101)
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In order to achieve accurate target ranging of weak or surface-free texture features based on a monocular camera, an improved difocus image ranging algorithm based on preserving edge spectral information is presented. By comparing two classical disfocal ranging theories with Fourier transform and Laplace transform as the calculation core, the corresponding definition evaluation function is constructed, select the method based on spectrum definition function with better sensitivity, and select the calculation range of frequency domain by retaining the information on the target edge. To verify the feasibility of the algorithm, 6 sets of different duck eggs samples were used to obtain scattered focus images of different aperture and different distances, and use the improved algorithm to solve the distance of duck eggs from the camera lens. The experimental results show that the improved algorithm based on the edge spectrum preservation has good ranging effect, with a correlation coefficient of 0.986 and Root mean square error (RMSE) of 11.39 mm, and it is found that the range ability can be effectively improved after the image rotation processing of the duck egg image taken at an oblique Angle, the root mean square error 11.39 mm to 8.76 mm, from 2.85% to 2.28% and the correlation coefficient to 0.99. It basically meets the requirements of stability and high accuracy of target ranging with weak or no surface texture features.

Abstract(175) FullText HTML(84) PDF 10303KB(151)
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Non-Line-of-Sight (NLoS) imaging is a promising technique developed in recent years, which can reconstruct hidden scene by analyzing the information in the intermediate surface, and achieve "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 model and algorithm model to reclassify it. 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 push the technical methods. And compared 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 algorithm.

Abstract(111) FullText HTML(45) PDF 4381KB(116)
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Atmospheric turbulence affects the tracking and positioning accuracy of high-resolution remote sensing satellites seriously. This paper focuses on the effects of camera aperture, atmospheric turbulence intensity and satellite orbit height on the positioning accuracy. Firstly, we establish the turbulence model and turbulence simulation method based on Kolmogorov turbulence theory for earth observation. Then, the influence of camera aperture, satellite orbit height and atmospheric coherence length on the positioning accuracy of the satellite is simulated and analyzed, and then, the universal formula is deduced to calculate the tilt aberration of turbulence wavefront. Finally, based on this universal formula, the theoretical calculation formula of jitter is derived for earth observation. The research work can provide a theoretical basis of the influence of atmospheric turbulence for design, analysis and evaluation of very high-resolution remote sensing satellites.

Abstract(87) FullText HTML(51) PDF 4882KB(105)
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In this paper, a multifunctional metamaterial device based on the phase transition properties of vanadium dioxide (VO2) is proposed. The metamaterial structure consists of a top layer with the combined VO2-filled SRR and metal cross, a polyimide (PI) dielectric layer, and a metal substrate. When VO2 is in the insulating state, the cross-polarization conversion function can be realized, and the polarization conversion rate (PCR) is greater than 90% in the range of 0.48−0.87 THz. When VO2 is in the metallic state, the device can realize dual-frequency absorption and high-sensitivity sensing functions. The absorption rates are higher than 88% at the frequencies of 1.64 THz and 2.15 THz. By changing the refractive index of the sample material, the sensing sensitivities at the two related frequencies are about 25.6 GHz/RIU and 159 GHz/RIU, and the Q-factors are 71.34 and 23.12, respectively. The proposed metamaterial multifunctional device exhibits the advantages of simple structure, switchable function, and high-efficiency polarization conversion, and provides potential application values in the future terahertz communication, imaging and other fields.

Abstract(121) FullText HTML(117) PDF 5775KB(104)
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A filterless microwave photonic phase shifter (MPPS) with a tunable frequency multiplication factor (FMF) and a full 360-deg tunable range is theoretically analyzed and verified by simulation. In the scheme, two parallel Mach-Zehnder modulators (MZM), cascaded with two dual-parallel integrated Mach-Zehnder modulators (DPMZM) by a 2×2 optical coupler (OC), are used to generate the ±1st- to 4th-order sidebands adjustably, and a phase modulator (PM) is used to phase shift one of the two lightwaves. After photodetection, the 2nd- to 8th- order harmonics with a continuously tunable phase shift from 0 to 360-deg can be generated by adjusting the RF driving signal and the DC bias voltage of the DPMZM, and the DC voltage of the PM. Simulation results demonstrate that both 360-deg continuously tunable phase shift and frequency multiplication can be implemented. Large Optical Sideband Suppression Ratio (OSSR) and Electrical Spurious Suppression Ratio (ESSR) of around 20 dB can be obtained. The phase shifter wavelength insensitive performance has been also evaluated by simulation.

Abstract(75) FullText HTML(36) PDF 8818KB(101)
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Airborne ambient temperature varies widely and airborne vibration is strong. And the mirror coating temperature is higher, the traditional bonding process will lead to bonding failure. Because of the difference of thermal expansion coefficient between Invar inlay and mirror material, the surface precision of mirror can not meet the requirement of system. Therefore, this paper puts forward a method of bonding the mirror after processing and coating, and designs some important parameters of the adhesive layer. In the scheme, RTV is used as the main binder, the mirror and the inlay are bonded together, and the effect of RTV curing on the structure is alleviated by good elasticity. The thickness of RTV is 1.1 mm, the width of RTV is 7.2 mm and the thickness of epoxy adhesive is 0.022 mm. The simulation results show that the RMS of the mirror shape is 25.91 nm and the first-order frequency of the mirror group mode is 242 Hz under gravity and 60 °C temperature change. The final surface detection RMS is 15.8 nm and the resonance frequency is 213 Hz. The experimental results show that the design of structure and bonding layer can meet the requirements of wide temperature and vibration condition.

Abstract(92) FullText HTML(58) PDF 5571KB(126)
Abstract:

3D reconstruction technology is one of the most popular research directions in machine vision, and has been widely used in the fields of unmanned driving and digital processing and production. Traditional 3D reconstruction methods include depth cameras and multi-line laser scanners, but the point clouds obtained by depth cameras have incomplete and inaccurate information, and the high cost of multi-line laser scanners hinders the application of this technology and Research. To solve the above problems, a three-dimensional reconstruction method based on a rotating two-dimensional laser scanner was proposed. First, a stepper motor was used to drive a 2D laser scanner to rotate to obtain 3D point cloud data. Then, the position of the laser scanner was calibrated by the method of multi-sensor fusion, and the point cloud data matching was completed by the coordinate system transformation. Finally, the collected point cloud data were filtered and simplified. The experimental results show: Reconstruction method compared with depth camera/IMU data fusion, the average error is reduced by 0.93 mm, the average error is 4.24 mm, the accuracy has reached the millimeter level, and the error rate is also controlled within 2%. The cost of the whole set of equipment is also greatly reduced compared to the reconstruction method of the multi-line laser scanner. It basically meets the requirements of retaining the shape characteristics of the object, high precision and low cost.

Abstract(84) FullText HTML(77) PDF 4108KB(124)
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Three-dimensional reconstruction is a common method for cultural relics information conservation, mainly through point cloud alignment technology to reorganize the spatial point cloud information of cultural relics, and its alignment accuracy has an important impact on cultural relics recovery. To address the problems of low accuracy and poor robustness in the alignment of complex point cloud texture features on the surface of cultural relics, this paper proposes a local point cloud alignment method based on normal vector angle and faceted index features. Firstly, the normal vector angle and covariance matrix thresholds are set according to the point cloud planar characteristics, and the point cloud feature points satisfying both features are extracted; secondly, the K-nearest neighbor search extracts the point cloud local feature point set, and the two sets of point cloud center-of-mass positions are overlapped by rigid transformation for coarse alignment; finally, the nearest points are iterated based on ICP for fine alignment. By comparing with the traditional ICP, this method reduces the point cloud alignment error by 3% and reduces the matching time by 50%, which effectively improves the accuracy and efficiency of alignment and enhances the robustness of point cloud alignment.

Abstract(99) FullText HTML(38) PDF 1066KB(128)
Abstract:

Aiming at the problem of sea-sky-line detection in low-contrast infrared images being difficult and easily affected by such interference factors as clouds, strip waves and sea clutter, this paper proposes a method of using polarization difference images for sea-sky-line detection. Firstly, polarization difference imaging (PDI) is used to enhance the local contrast of the sea surface area and the signal-to-noise ratio (SNR) of the sea-sky-line. A method of large-scale local contrast accumulation of the polarization difference images is then used to determine the sea-sky-line area. Finally, the accurate detection of small-scale sea-sky-line is completed via combining the methods of gradient significance and polynomial fitting in the sea-sky-line area. Overall, the methodology integrates multi-dimensional information such as the degree of linear polarization (DOLP) and the angle of polarization (AOP) for sea-sky-line detection, and combines large-scale and small-scale detection, which can effectively overcome the interference of factors such as clouds, strip waves and sea clutter. The experimental results show that the accuracy of this algorithm for sea-sky-line detection is 98.5%, and the average time consumed is 16 ms, and that fast and accurate sea-sky-line detection can be realized through this algorithm, which in turn has wide applicability to different scenes.

Abstract(137) FullText HTML(71) PDF 4131KB(142)
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A new method for measuring the flux distribution of high-magnification convergent radiation spot is proposed. The radiation flux sensor is used to measure the flux density at different positions of the spot, and the calibration curve of the grayscale and flux density at different positions of the spot is fitted by polynomial, and finally the radiation spot is obtained. In order to verify the accuracy and feasibility of the measurement method, a high-magnification convergent radiation spot flux distribution measurement experiment was carried out, and the direct measurement results of the radiant flux sensor were compared. The results show that the measurement results of the new method are consistent with the direct measurement results, and the average deviation is < 0.54%. Through analysis, the measurement uncertainty of this measurement method is 4.35%, and the measurement accuracy is higher than the traditional measurement. The method has been improved to meet the needs of practical applications.

Abstract(113) FullText HTML(75) PDF 6731KB(176)
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Vision-based measurement has good application prospects and far-reaching development significance for advanced manufacturing fields such as aerospace, the military industry and electronic chips. Among them, on-machine 3D vision detection technology based on structured light is one of the hotspots and challenges in the field of precision machining. Based on the on-machine 3D measurement process of structured light, this paper discusses and summarizes the key technologies, including its technical requirements, methods and principles involved, related research status and existing problems in the measurement calibration, phase optimization solution, on-machine 3D point cloud processing and reconstruction of different feature surfaces. Finally, according to the actual needs of relevant technologies in the future, predictions are made with regard to processing field calibration, dynamic real-time 3D reconstruction, sub-micron and nano measurement, and measurement processing integrated data transmission technology, with the corresponding research ideas put forward.

Abstract(129) FullText HTML(79) PDF 9235KB(189)
Abstract:

in order to save the problem of the phase solution in white light interferometry and realize the height measurement of micro morphology, white light interferometry micro measurement algorithm based on principal component analysis was proposed. White light microscopic interference system is used to collect multiple interferograms and reconstruct them into vector form. From a set of interferograms, the background illumination can be estimated by a temporal average, eliminating background light components. Then, the eigenvalues and eigenvectors representing the original data are obtained by matrix operation. Finally, the phase distribution is calculated by arctangent function. Experimental results indicate that the measurement result of standard step height of 956.05 nm by the proposed method is about 953.66 nm, the solution is approximately consistent with the iterative algorithm, in comparison to the iterative algorithm, the average time of the proposed method is 2 orders of magnitude faster. The interference fringes with surface roughness of 0.025 μm were analyzed, the mean of surface roughness calculated by the proposed method was 24.83 nm, and the sample standard deviation is 0.3831 nm. The proposed method improves the deficiency of monochromatic interferometry and has advantages of low computational requirements, fast and high accuracy.

Abstract(108) FullText HTML(58) PDF 5287KB(163)
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In a distance-selected imaging system based on single-photon detection, a short-pulse laser is emitted and between the transmitter and receiver for synchronization control, and the detector operates in photon counting mode and integrates in time to complete the imaging. In this paper, in order to obtain a short pulse laser that meets the system requirements while reducing the system’s size and cost, we propose to apply these two types of narrow pulse generation circuits to single photon distance selective imaging systems. We introduce the principle and design method of both types and verify the system through simulation, physical fabrication and testing. The characteristics of the pulse generator and factors affecting its pulse width and amplitude are analyzed. The physical test results show that the transistor-based method can generate a narrow pulse with a rise time of 903.5 ps, a fall time of 946.1 ps, a pulse width of 824 ps, and an amplitude of 2.46 V; the SRD-based method can generate a narrow pulse with a rise time of 456.8 ps, a fall time of 458.3 ps, a pulse width of 1.5 ns, and an amplitude of 2.38 V; and the repetition frequency of both can reach 50 MHz. Both design methods can be used with external current-driven laser diodes to achieve excellent short pulse laser output.

Abstract(86) FullText HTML(52) PDF 6077KB(158)
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Ammonia gas is an important basic industrial raw material, and realizing its non-contact detection is of great significance for the timely detection of ammonia gas leaks to avoid major safety incidents. Aiming at the shortcoming of conventional ammonia leak detection devices that can only respond when ammonia diffuses to a certain range and makes contact with a sensor, a shuffling self-attention network (SSANet) model is proposed to realize the infrared non-contact detection of ammonia leaks. Due to the high noise and low contrast of ammonia leakage images obtained by infrared cameras, an infrared detection dataset of ammonia leakage was established through non-local mean denoising and contrast-limited adaptive histogram equalization preprocessing. On the basis of YOLOv5s, the SSANet model uses the K-means algorithm to cluster and analyze the candidate frame suitable for the infrared detection of ammonia gas leakage to preset the model’s parameters. Using the lightweight ShuffleNetv2 network, the depth of 3×3 in the Shuffle Block can be adjusted. The separate convolution kernel is replaced with a 5×5 depth, and the feature extraction network is reconstructed with an SK5 Block containing a new convolution module, which makes the model size, calculation and parameters non-intensive while improving the detection accuracy. The Transformer module is used instead of its original version. The C3 module in the network bottleneck module realizes the bottom-up fusion of multi-head attention in the leake area, and further improves the detection accuracy. The experimental results show that the size and parameter requirements of the SSANet model are reduced by 76.40% and 78.30%, respectively, to 3.40 M and 1.53 M compared with the basic model of YOLOv5s; the average detection speed of a single image is increased by 1.10% to 3.20 ms; and the average detection accuracy is increased by 3.50% , reaching 96.30%. This paper provides an effective detection algorithm for the development of a non-contact detection device for ammonia leakage to ensure the safe production and stable operation of ammonia-related enterprises.

Abstract(109) FullText HTML(72) PDF 5011KB(163)
Abstract:
Objective

Aiming at the urgent demand of high-precision optical alignment systems for a domestic infrared focal plane flip chip bonder, an optical alignment system was designed and verified, and the parallel adjustment, optical alignment and coordinate system error compensation algorithms applied to the system were researched.

Method

Firstly, this paper analysed the optical alignment process of a flip chip bonder, then introduced the parallelism adjustment and optical alignment algorithm, and proposed a more reasonable error compensation algorithm according to the test process of the optical alignment system. finally, based on the above calculation algorithm, the optical alignment system was designed including three parts: a collimation system, a microscopic imaging system and a laser ranging system. The functions of parallel coarse adjustment, feature point recognition and parallel fine adjustment were realized.

Results

The experimental results show that the collimation system has a good collimation effect, the microscopic imaging system has high resolution and good imaging quality, and the ranging accuracy of the laser ranging system is 0.084μm.

Conclusion

The designed high-precision optical alignment system solves the urgent need for a domestic infrared focal plane flip chip bonder for high-precision optical alignment systems. It has been applied in a certain types of flip chip bonders, and has very important social significance for improving the independent research and development and production capacity of domestic high-end large-scale integrated circuits.

Abstract(258) FullText HTML(243) PDF 9813KB(135)
Abstract:
In order to accurately measure the laser intensity distribution, this paper proposes a method based on tomographic imaging. Firstly, numerical studies were performed to validate the correctness of the imaging model and convergence of the reconstruction algorithm. Reconstruction errors were less than or equal to 7.02% with different laser intensity distribution phantoms employed and less than 8.5% with the addition of different random noise levels under 10%. Additionally, a demonstration experiment was performed with the employment of a customized fiber bundle to realize the measurement from seven views. Seven views are distributed along a semi-circle plane which is perpendicular to the propagation direction of the laser beam. The distance from the laser beam to each view is nearly 160 mm and the angle coverage range of the seven views is about 150°. Laser-induced fluorescence obtained after the laser passed through a rhodamine-ethanol solution was collected by the tomographic imaging system. Then, the laser intensity distribution was obtained through absorption-corrected three-dimensional (3D) reconstruction. The correlation of the projection and re-projection of the one view was used to quantitatively access the accuracy after the other six views were adopted in the reconstruction. The results show the feasibility of the method with a correlation coefficient of 0.9802. It can be predicted that the 3D laser intensity measurement scheme proposed in this work has a broad prospect in the field of laser applications.
Abstract(467) FullText HTML(237) PDF 7219KB(198)
Abstract:
In the Taiji program, laser interferometry is utilized to detect the tiny displacement produced by the gravitational wave signals. Due to the large-scale unequal arm, the laser frequency noise is the largest noise budget in the space interferometer system. To reduce the influence of laser frequency noise, a technology called the Time Delay Interferometry (TDI) is utilized to deal with it. The TDI is a kind of data post-processing method, which forms the new data stream by the method of the time delay to initial data. But the premise of TDI needs to obtain accurate absolute arm length between satellites. Thus, for that requirement, we discuss the ranging system scheme and implement a ground electronics verification experiment. The ranging system is based on Direct Sequence Spread Spectrum (DS/SS) modulation, and it mainly includes three parts, which are the signal structure, a Delay Locked Loop (DLL), and a data processing algorithm. In DS/SS modulation, types of pseudo-random code can make a difference to the quality of correlation and the ranging accuracy. Therefore, to design the optimal pseudo-random code, we compare the correlation and flexibility in choosing lengths of the m sequence, gold sequence, and Weil code. Weil code that has a shift-cutoff combination with the best autocorrelation is chosen as the ranging code. The ground electronics verification experiment is set up for simulating the physical process of signal transmission and verifying system performance. The main device of the experiment is a FPGA card based on the K7 chip from Xilinx, which is used to simulate the function of communication and ranging between satellites. Meanwhile, we change the length of the Radio Frequency (RF) coaxial cable to correspond to different ranges. The experimental process can be summarized as follows. Firstly, 16-bit data at 24.4 kbps and 1024-bit Weil code at 1.5625 Mbps are modulated with Binary Phase Shift Keying (BPSK) in the 50 MHz sampling frequency. Then the signal is transmitted through RF coaxial cables of 10 to 60 m in length. In receiving end, the signal is consolidated by DLL and the ranging information is collected. To measure the range accurately, we use a centroid method to optimize the collected data. The results show that the ranging accuracy is better than 1.6 m within 60 m. In conclusion, this experiment proves the principle of the scheme and its feasibility, laying a technical foundation for optical system verification in the future.
Abstract(385) FullText HTML(232) PDF 6652KB(160)
Abstract:
In order to improve the performance of lane detection algorithms under complex scenes like obstacles, we have proposed a multi-lane detection method based on dual attention mechanism in this paper. Firstly, we designed a lane segmentation network based on a spatial and channel attention mechanism. With this, we obtain a binary image which shows lane pixels and the background region. Then, we introduced HNet which can output a perspective transformation matrix and transform the image to a bird’s eye view. Next, we did curve fitting and transformed the result back to the original image. Finally, we defined the region between the two-lane lines near the middle of the image as the ego lane. Our algorithm achieves a 96.63% accuracy with real-time performance of 134 FPS on the Tusimple dataset. In addition, it obtains 77.32% of precision on the CULane dataset. The experiments show that our proposed lane detection algorithm can detect multi-lane lines under different scenarios including obstacles. Our proposed algorithm shows more excellent performance compared with the other traditional lane line detection algorithms.
Abstract(230) FullText HTML(140) PDF 4571KB(137)
Abstract:
In order to account for the transverse effect of semiconductor lasers, the dynamic equation of a semiconductor laser with transverse effect is given by modifying the dynamic model describing it, and the influence of the transverse effect on its output characteristics is analyzed. On this basis, the synchronization transmission technology of a semiconductor laser’s output signal with transverse effect is further studied. The results show that the output of the semiconductor laser presents a new spatiotemporal chaotic state after considering the transverse effect, and is very sensitive to the dependence of the initial value. At the same time, whether the synchronization transmission of single-channel or multi-channel signals is carried out by a semiconductor laser, its transmission performance is very stable. The synchronization technology is very simple and easy to apply in practice.
Column
2023, 16(2): 229-242.   doi: 10.37188/CO.2022-0137
Abstract(270) FullText HTML(109) PDF 7682KB(219)
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.

2023, 16(2): 243-257.   doi: 10.37188/CO.2022-0145
Abstract(295) FullText HTML(169) PDF 4220KB(182)
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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.

2023, 16(2): 258-282.   doi: 10.37188/CO.2022-0085
Abstract(375) FullText HTML(227) PDF 10445KB(313)
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.

2023, 16(2): 283-295.   doi: 10.37188/CO.2023-0017
Abstract(101) FullText HTML(40) PDF 3656KB(65)
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.

2023, 16(2): 296-304.   doi: 10.37188/CO.2022-0097
Abstract(145) FullText HTML(95) PDF 5138KB(197)
Abstract:

At present, the simulation research of arc actuators is limited to only obtaining the working characteristics of the plasma generated by the actuator, such as potential, pressure, temperature and velocity, while the plasma state is limited to only diagnosing its electron temperature and electron density by spectrum. The two are separated. This paper attempts to unify the two. Therefore, the arc jet plasma actuator designed here adopts the finite element method to solve the nonlinear multi physical equations. The working characteristics of the arc jet plasma actuator are numerically simulated, and the potential, pressure, temperature and velocity distributions inside the actuator are obtained. On this basis, the electron density is calculated and the simulation calculation model of the plasma state (electron temperature and electron density) of the actuator is obtained from the working condition of the actuator. Then the spectral diagnosis of the jet plasma is carried out by using the emission spectral diagnosis method, and the electron density of plasma is calculated by using the intensity ratio method of discrete spectral lines. The diagnostic experiment of the arc plasma actuator shows that the maximum electron temperature is 10505.8 K and the maximum electron density is 5.75×1022 m−3. For the plasma electron temperature and plasma density under different working conditions, the experimental and simulation results increase with the increase of inlet gas flow and discharge current. It shows that our simulation model of plasma state is reasonable and applicable for our miniaturized arc jet actuator with high jet velocity.

2023, 16(2): 305-317.   doi: 10.37188/CO.2022-0147
Abstract(65) FullText HTML(21) PDF 8466KB(52)
Abstract:

In order to improve the autonomous detection ability of the airborne optronics pod of a UAV under special working conditions, this paper developed a targeting technology suitable for the airborne optronics pod in an actual engineering project, and realized the functional verification on the embedded GPU (Graphics Processing Unit, Jetson-TX2i platform model). Firstly, we proposed an improved SURF (Speeded Up Robust Features) algorithm and GPU-accelerated digital image processing scheme to detect and match the real-time features of two images acquired at different focal lengths. Secondly, geometric cross-ratio invariance was used to correct the position information of distorted feature points at image edges. Finally, we used the least square method to estimate the depth information of the target and combines the quaternion space model to determine the attitude information of the target to determine its position. Experimental results show that the improved SURF algorithm is superior to the classical SURF algorithm in feature matching accuracy and speed. If the corner characteristic position error is controlled within one pixel, the depth error is no more than 2% and the angle errors of azimuth, pitch and roll angles are less than 4°, 5° and 2°, respectively. This error meets the target positioning accuracy requirements of the airborne optronics pod. In addition, when processing a set of images (two frames) at 1080 P resolution, the processing time can be increased to 74 ms through GPU acceleration, which meets the real-time demand for data processing in the airborne optronics pod.

2023, 16(2): 318-328.   doi: 10.37188/CO.2022-0035
Abstract(339) FullText HTML(184) PDF 3582KB(155)
Abstract:

Infrared polarization imaging technology has the advantages of long detection range and high rate of target recognition. However, the polarization characteristics of targets are easily affected by background radiation in complex environments, which significantly reduces the detection capability of infrared polarization equipment. Based on the polarized Bidirectional Reflectance Distribution Function (pBRDF), this paper establishes a calculation model for the target’s Degree of Linear Polarization (DoLP), comprehensively considering the radiation coupling effect between the target and the background. The variation of the target’s DoLP under two conditions - with and without a strong radiation backplate – is then comparatively studied. Additionally, in order to solve problems of land-based and airborne small-angle detection, simulation research is done to find out how the target’s DoLP is influenced by parameters such as the temperatures and the included angle between the target and the backplate. Research results show that the radiation coupling effect significantly reduces the target’s degree of polarization when the temperatures of the target and the backplate are the same, but it does not change the trend of the target’s degree of polarization, which increases with an increase in temperature. When the temperature of the target and the backplate is 30 °C, 40 °C, and 50 °C, the maximum degree of polarization of the target is 63.7%, 44.9%, and 42.2% of those without a strong radiation backplate, respectively. It can be concluded then that the higher the temperature, the stronger the radiation coupling effect between the target and the backplate, and the greater the reduction of the target’s degree of polarization; and that the strength of the radiation coupling effect is not only related to the temperature, but also to the included angle between the target and the backplate. With the increase of the included angle, the target’s DoLP first increases and then decreases, and the maximum value is obtained when the included angle is about 105°. Therefore, the radiation coupling effect changes the target’s DoLP to a certain extent, thereby affecting the detection ability of the infrared polarization equipment. Finally, through building a long-wave infrared polarization imaging system, the established calculation model of the target’s degree of polarization is verified by experiments, whose results are basically consistent with those of the simulation analysis. Overall, the research results in this paper have certain guiding significance for improving the detection and identification capabilities of land-based and airborne infrared polarization equipment.

2023, 16(2): 329-338.   doi: 10.37188/CO.2022-0036
Abstract(217) FullText HTML(161) PDF 5421KB(268)
Abstract:

In order to generate double doughnut-shaped focal spots at adjustable positions along the axial direction, a vortex phase zone plate based on a formula of annular radius derived from vector diffraction integral was designed. The focusing properties of the modulated vortex phase zone plate were further investigated in a tightly focused system. First, integral formulas of linearly and circularly polarized vortex beams were calculated under high NA focusing conditions. Then, the intensity distributions of linearly and circularly polarized vortex beams in a high NA focusing system were simulated by integral formulas with various axial shifting distances and topological charges. Finally, the corresponding experimental results of linearly and circularly polarized light were also given, utilizing a spatial light modulator loaded on double doughnut-shaped phase patterns. The double doughnut-shaped focal spots with a topological charge of 1 and axial distances of ±10 μm and ±15 μm were produced when the incident light was linearly polarized. As well as the double doughnut-shaped focal spots with axial distances of ±20 μm, topological charges of 1−4 were also produced when the incident light was circularly polarized. The simulated and experimental results demonstrated that two doughnut-shape focal spots with controllable axial shifting distances and dark spot sizes could be produced in the tight focusing region of a high NA objective when it is modulated by the vortex phase zone plate. This kind of vortex phase zone plate could be applied in the field of optical micromanipulation, two-beam super-resolution nanolithography, and Stimulated-Emission-Depletion (STED) fluorescence microscopy.

2023, 16(2): 339-347.   doi: 10.37188/CO.2022-0027
Abstract(227) FullText HTML(166) PDF 4695KB(151)
Abstract:

With the continuous development of digital display technology, display methods have also changed. Pepper’s ghost images that adopt modern display methods require the light environment of the exhibition space not only to ensure the effect but also ensure better visual comfort. In order to explore the influence of the lighting environment on the display effect based on Pepper’s ghost images, a virtual imaging display space is set up to analyze the factors and trends affecting the imaging effect, in which 12 sets of LED lighting conditions with different illuminances and color temperatures are generated. 25 observers are selected to conduct a psychophysical experiment. The experiment shows that color temperature has no significant effect on the evaluation of color authenticity, detail expressiveness and stereoscopic expressiveness for Pepper’s ghost images; illumination has no strong effect on the evaluation of the color authenticity of Pepper’s ghost images, but has a significant effect on their detail expressiveness and stereoscopic expressiveness. Under the lighting environment where the color temperature is 3500 K and the illumination is 10 lx, the detailed expressiveness and stereoscopic expressiveness of the display effect are relatively high and the visual comfort of 2500 K and 10 lx is better.

2023, 16(2): 348-357.   doi: 10.37188/CO.2022-0144
Abstract(109) FullText HTML(108) PDF 3900KB(148)
Abstract:

To investigate the multiple scattering transmission characteristics of polarized light in ellipsoidal fine particles, a simulation and experiment verification system for black carbon aerosol particles was established. The polarization transmission characteristic after multiple scattering of the randomly oriented ellipsoidal fine particles are studied by combining the T-matrix with the Monte Carlo method. A half-real simulation testing environment was established to verify the simulation algorithm, and the ellipsoidal fine particles were prepared by extending ganoderma lucidum spores′ burning time. The size distribution and optical thickness of the ellipsoidal fine particles were measured by Malvern Spraytec and a light power meter, respectively. The simulation results can be proven by combining the experiment with the simulation. The results show that with an increase in the concentration of black carbon ellipsoidal fine particles, the Degree Of Polarization (DOP) of the horizontal, vertical, 45° linearly polarized and the right circularly polarized light all decrease, and the polarization preservation ability of three kinds of linear polarizations are basically consistent. The polarization preservation ability of the circularly polarized light gradually exceeds the linearly polarized light with an increase in concentration. The gap between the linear and circular polarizations becomes larger as it reaches its maximum value at 3.12 optical thickness. When the optical thickness is greater than 3.12, the DOP difference between the circularly and the linearly polarized lights tend to be stable. By calculation, the percent agreement between the simulation and the experiment is better than 70.84%. These results can expand the environmental applicable range of polarization detection and provide theoretical support for studying the polarization detection of atmospheric non-spherical particles.

2023, 16(2): 358-365.   doi: 10.37188/CO.2022-0117
Abstract(166) FullText HTML(93) PDF 5570KB(220)
Abstract:

The large aperture sky survey telescope needs closed-loop error correction based on the feedback of its wavefront sensing system, so as to give it a better conform to its limit detection ability. In this paper, firstly, the basic theoretical expression of sub region curvature sensing is derived. Then, a joint simulation model is established. The process of sub region curvature sensing is simulated and analyzed by using a combination of optical design software and numerical calculation software. Finally, by setting up a desktop experiment, the cross-comparison of single- and multi-target curvature sensors is carried out to verify the correctness of the algorithm. Compared to the traditional active optical technology, the method proposed in this paper can improve the detection signal-to-noise ratio and sampling speed by expanding the available guide stars. For the standard wavefront, compared with the single guide star curvature sensor, the error is 0.02 operating wavelengths (RMS), and the error is less than 10%, which can effectively improve the correction ability of the active optical system.

2023, 16(2): 366-372.   doi: 10.37188/CO.2022-0079
Abstract(154) FullText HTML(96) PDF 7174KB(241)
Abstract:

In order to improve the suitability of the fiber hydrophone towing line array, a flexible fiber grating hydrophone array was proposed.The sound pressure sensitivity of three flexible fiber grating hydrophones was calculated according to the mechanical theoretical model, and the influence factors were compared and analyzed. 2-element flexible fiber hydrophone sample arrays with diameters of 10 mm,12 mm and 16 mm were developed through finite element simulation for frequency response analysis. The sensitivity was measured by a vibration liquid column experiment. The experimental results show that the response is flat within the frequency range of 200~800 Hz, and the average sound pressure sensitivities of the hydrophone arrays with different structural parameters are −138.90 dB, −134.71 dB, and −136.12 dB, respectively. The theory and simulation analysis are verified. By further optimizing the material and structure parameters and using weak reflection fiber grating, an integrated flexible hydrophone array with hundreds of elements can be constructed according to the design in this paper.

2023, 16(2): 373-381.   doi: 10.37188/CO.2021-0228
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The damage threshold of an interline transfer CCD irradiated by different wavelength nanosecond Raman lasers was studied and an experiment with 496 nm, 574 nm, 630 nm Raman and multispectral Raman laser-irradiated CCD was carried out. The damage threshold interval of dot damage, line damage and total damage were observed and collected by adjusting the energy of each focused Raman laser. By careful fitting, the damage threshold interval and the damage possibility curve of the CCD at different laser energy densities with each Raman laser were estimated. Results showed that the multispectral Raman laser including a residual pump laser is most effective for damaging the CCD than the monochrome Raman laser, and the 630nm Raman laser acts better than 574 nm and the 496 nm Raman laser. The microscopic images of the damaged CCD were reviewed, and the electronic characters of the damaged CCD were also tested to understand the damage and blindness mechanism of a Raman laser pulse-irradiated CCD.

2023, 16(2): 382-389.   doi: 10.37188/CO.2022-0092
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Measurement repeatability is the largest uncertainty component of a light pressure based measurement device, which directly affects the accuracy of the measurement results. In order to improve the accuracy of the measurement power in the process of high-power laser measurement, a high-power laser measuring device based on light pressure is built. Quality measurement repeatability and laser power measurement repeatability experiments were carried out, and the results of the two experiments were compared and analyzed. The experimental results show that the measurement repeatability of the light pressure measuring device gradually decreased with the increase of the measured mass and the measured laser power, indicating that the light pressure method has more advantages in measuring high-power lasers. In the laser power measurement repeatability experiment, the influence of eccentric loads and airflow disturbance is avoided, so the laser power measurement repeatability is better than the measurement repeatability calculated according to the equivalent mass. The research results have guiding significance for further improving the measurement accuracy of the light pressure method in the future.

2023, 16(2): 390-398.   doi: 10.37188/CO.2022-0089
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Abstract:

Airborne lidar is an important means to achieve long-range accurate atmospheric monitoring. Its laser wavelength is consistent with the absorption spectrum of most atmospheric pollutants and chemical substances, which makes it an important laser source for airborne lidar. However, it is difficult to design a temperature control system for airborne CO2 lasers to work in the −40 °C−55 °C temperature range under the controlled volume and weight conditions. In this paper, we propose a temperature closed-loop control method, in which the laser characteristic and environment temperature are used as input, and a thermo electric cooler and forced air cooling are combined. According to the structure and heat transfer characteristics of the laser, the thermo-electric cooler and the level of forced air cooling, the finite element model of temperature control method is established to optimize the temperature control performance of the laser. In a high temperature environment of 55 °C, the temperature of the laser is controlled at 40 °C after the temperature control system operates for 25 min. In a low temperature environment of −40 °C, the laser temperature is controlled at 25 °C after the temperature control system operates for 20 minutes, which meets the normal working requirements of the laser. According to the laser and the established temperature control method, the experimental research on the working ability of the laser in high and low temperature environment is carried out, the temperature data of the laser in the experimental process is collected, and the laser output power is measured under high and low temperature conditions. The experimental results show that the experimental measured temperature data is consistent with the finite element simulation results and the error between them is less than 10%. The laser using the proposed temperature control method can work steadily, and the output power of the laser is consistent with that of the laser at room temperature.

2023, 16(2): 399-406.   doi: 10.37188/CO.2022-0191
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In order to improve the output performance of a high-power Thulium-Doped Fiber Laser (TDFL) and increase the optical-optical conversion efficiency of the system, a high-power TDFL with an all-fiber Main Oscillation Power Amplification (MOPA) structure was developed, which can operate in both Continuous Wave (CW) and Quasi-Continuous Wave (QCW) modes. First, a laser oscillator was built to study the output characteristics of the seed source laser. Then, a thulium-doped fiber amplifier was built and connected to the laser oscillator to study the output characteristics of the MOPA structured fiber laser. Finally, the pulse characteristics of the MOPA structured fiber laser were analyzed under the QCW modulation mode. The laser oscillator achieved a continuous and stable laser output with a central wavelength of 1940 nm, and the highest average output power was 18.56 W. The slope efficiency was 54.84%, and the spectrum was free of Raman components. Using this low-power continuous laser as the seed source through the homemade thulium-doped fiber amplifier, the average output power could reach 66.9 W, and the slope efficiency was 48.48%. When the system operated in the QCW mode, the frequency and duty cycle can be adjusted, and the peak power was calculated to be 80.3 W when the frequency was 75 Hz and the duty cycle was 10%. This research is of referential significance for the development of higher power MOPA lasers in the 2 μm band.

2023, 16(2): 407-414.   doi: 10.37188/CO.2022-0084
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Aming at the problems of long processing time and low accuracy of the traditional laser spot center positioning algorithm used in a vibrating environment. We proposed a laser spot center positioning method based on a genetic algorithm optimized BP neural network. A BP neural network was applied to predict the spot center position and a genetic algorithm was applied to optimize the neural network. Based on the BP neural network, the gray weighted centroid method, centroid method, Gaussian fitting method were used to obtain the spot center position, and the centroid method was used to obtain the radius of laser spot, on the above basis, we predicted the actual center position of the spot. Genetic algorithms were used to optimize the weights and thresholds of neural networks to improve prediction accuracy. An experimental platform is established to simulate the vibration environment by applying perturbations to the optical system and the data is collected to train neural network and verify the algorithm. The experimental results show that the number of calibration test iterations before and after optimization is 55 and 29, and the average errors are 0.81 pixels and 0.45 pixels, respectively. Under the optimization of the genetic algorithm, the iteration speed and prediction accuracy of the neural network algorithm is improved.

2023, 16(2): 415-424.   doi: 10.37188/CO.2022-0106
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In order to effectively avoid high computational complexity when using Maximum Likelihood (ML) detection, a deep learning-based Spatial Pulse Position Modulation (SPPM) multi-classification detector is proposed by combining a Deep Neural Network (DNN) and step detection. In the detector, the DNN is used to establish a non-linear relationship between the received signal and the PPM symbols. Thereafter, the subsequent received PPM symbols are detected according to this relationship, so as to avoid the exhaustive search process of PPM symbol detection. The simulation results show that with the proposed detector, the SPPM system approximately achieves optimal bit error performance on the premise of greatly reducing detection complexity. Meanwhile, it overcomes the error platform effect caused by K-Means Clustering (KMC) step classification detection. When the PPM order is 64, the computational complexity of the proposal is about 95.45% and 33.54% lower than that of ML detectors and linear equalization DNN detectors, respectively.

2023, 16(2): 425-433.   doi: 10.37188/CO.2021-0210
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Abstract:

In the tower solar thermal power plant, the heliostat mirror shape errors have an important impact on the optical efficiency of the heliostat field, so it is necessary to measure the heliostat surface shape error. The heliostat is generally made up of splicing multiple sub-mirrors, the tilt angle error of the sub-mirror is an important part of the heliostat mirror shape errors. This paper proposes a measurement method for the tilt angle errors of the heliostat sub-mirror based on the photogrammetry. That is, under the condition of known the shape size of the heliostat sub-mirror, the spatial position coordinates of the 4 corner points of the heliostat sub-mirror are calculated by using the principle of photographic imaging. Then the normal direction of the sub-mirror is found, and the tilt angle of the sub-mirror is calculated by using the normal line obtained. Finally, the measurement for the tilt angle error of the heliostat sub-mirror is achieved. In this paper, the measurement principle of the method is elaborated, the calculation formula is derived, and relevant verification experiments were carried out using planar mirrors and cameras. By measuring the plane mirror with different tilt angles at different distances, the deviation between the measured tilt angle and the actual tilt angle of the plane mirror is about 0.1°~0.3°, and the experimental results show that the method can accurately measure the tilt angle error of the sub-mirror of heliostat, thus the correctness and feasibility of the method are verified.

2023, 16(2): 434-446.   doi: 10.37188/CO.2022-0119
Abstract(227) FullText HTML(66) PDF 4159KB(170)
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The refractive index measurements based on traditional wave optical methods are mainly depended on intensity and wavelength detection strategies. Interference spectrometers are widely used as the most ideal wavelength detecting devices. Interference spectrometers measure the signal intensity, analyze the change of fringe numbers and the corresponding optical path difference by means of optical power meter, and then calculate the wavelength of signal light. Therefore, its essence is still based on intensity detection. However, the resolution of interference signal in intensity detection is restricted by classical diffraction limit, thus its resolution is difficult to further improve. In order to solve this bottleneck, parity detection which could break through the classical resolution limit and realize super-resolution refractive index measurement is proposed in this paper. According to the quantum detection and estimation theory, the expressions for signals and their corresponding sensitivities of refractive index measurement with parity and intensity detections were derived respectively and their numerical comparison analysis was carried out. In addition, the effects of loss on resolution and sensitivity of the output signal were investigated. Numerical results show that the resolution of parity detection is \begin{document}${\text{2{\text{π}}}}\sqrt N$\end{document} times that of intensity detection, achieving super-resolution refractive index measurement. Moreover, the optimal sensitivity reaches the refractive index measurement shot noise limit \begin{document}${\lambda \mathord{\left/ {\vphantom {\lambda {\left( {2{\text{π}} l\sqrt N } \right)}}} \right. } {\left( {2{\text{π}} l\sqrt N } \right)}}$\end{document}. The loss reduces the sensitivity and resolution of the signal. The resolution of the parity detection signal is consistently better than that of intensity detection except for the very large loss and very low photon number. Finally, the physical essence of the super-resolution refractive index measurement is analyzed from the detection means itself.

2023, 16(2): 447-457.   doi: 10.37188/CO.EN.2022-0010
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The cavity surface optical film is one of the most crucial components of the fiber bragg grating External Cavity diode Laser (ECL). Although, the Plane Wave Method (PWM) is widely used in the optical film preparation, it is not an ideal design method when applied in ECL preparation. The Finite-Difference Time-Domain (FDTD) method is used to analyze this problem by taking the effect of facet dimensions and structure into account. According to the simulation, PWM suffers from poor reflectivity and deviation of the reflection curve, which significantly affects performance. Therefore, the optical film design is optimized and verified by experiments. Magnetron sputtering is used to fabricate the optical film, which is then applied to ECL. The measurement results show that the reflectivity of Anti-Reflection (AR) film is reduced by 30% after optimization, while the reflectivity of High-Reflection (HR) film increased to 96%. The prepared ECL’s fiber output power exceeds 650 mW. In this paper, the optical film suitable for ECL is designed and fabricated, and provides a reference for optical films in ECLs and other semiconductor optoelectronic devices.

2023, 16(2): 458-465.   doi: 10.37188/CO.EN.2022-0009
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In this paper, we study the coherence of magnetic surface plasmons in one-dimensional metallic nano-slit arrays and propose a double-dip sensing method to improve sensitivity. Different from the conventional way of scanning wavelength at a fixed incident angle, coherence of surface plasmons is investigated by changing the incident angle at a fixed wavelength. Due to the retardation effect, two coherence dips move in opposite directions as the refractive index of the surrounding medium changes. Compared with one dip used for sensing, two oppositely moving dips can efficiently improve the sensitivity. The total sensitivity of two dips can reach 141.6°/RIU while the sensitivities of two single dips are 39.2°/RIU and 102.4°/RIU respectively. Besides, the inconsistency between the refractive index of slit medium and upper medium has few influences on the sensing performance, which will have wide practical applications.

2023, 16(2): 466-478.   doi: 10.37188/CO.EN.2022-0012
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To solve the problems of short illumination distance and narrow spectral range in the current underwater detection technology, an underwater semiconductor white laser imaging system was established. The quality of the images captured by the system under different light sources and different conditions was studied. A white laser with a power of 220 mW and a color temperature of 6469 K synthesized by an RGB semiconductor laser is used as the underwater lighting source, which is respectively compared with three RGB monochromatic lasers and an LED white light source under different conditions. For these images, different algorithms are used to process, analyze and evaluate their quality. The results indicate that when the white laser is used as the underwater light source, the collected image is not only better than that with the LED white light source with respect to information detail and structural integrity, but also better than the monochrome laser in color reproduction of the target and the integrity of the edge feature information. The semiconductor white laser has the advantages of concentrated energy, strong color rendering, and high illuminance, and its light source performance can meet the requirements of underwater low-illumination imaging. With the same imaging system and imaging distance, images with stronger authenticity, better texture and more target feature information can be obtained.

2023, 16(2): 229-242.   doi: 10.37188/CO.2022-0137
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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.

2023, 16(2): 243-257.   doi: 10.37188/CO.2022-0145
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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.

2023, 16(2): 258-282.   doi: 10.37188/CO.2022-0085
Abstract(375) FullText HTML(227) PDF 10445KB(313)
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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.

2023, 16(2): 283-295.   doi: 10.37188/CO.2023-0017
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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.

2023, 16(1): 1-23.   doi: 10.37188/CO.2022-0189
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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.

2023, 16(1): 24-43.   doi: 10.37188/CO.2022-0071
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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.

2023, 16(1): 44-60.   doi: 10.37188/CO.2022-0074
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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.

2023, 16(1): 61-75.   doi: 10.37188/CO.2022-0022
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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.

2023, 16(1): 76-93.   doi: 10.37188/CO.2022-0134
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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.

2022, 15(6): 1105-1166.   doi: 10.37188/CO.2022-0105
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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.

2022, 15(6): 1167-1181.   doi: 10.37188/CO.2022-0086
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Two-photon microscopy’s ability to maintain good spatial resolution in thick biological tissues has led to its application in in-vivo brain imaging studies soon after its conception. As neural networks have cross-scale multidimensional spatio-temporal properties, two-photon microscopy has developed rapidly and significantly in recent years to meet the demand for in-vivo cross-scale imaging of the brain. This paper firstly introduces the working principle of two-photon microscopy, then reviews the progress of two-photon microscopy from five perspectives: imaging field of view, imaging flux, imaging depth, resolution, miniaturization, and analyzes the difficulties and future challenges of cross-scale two-photon in-vivo microscopic imaging technology.

2022, 15(6): 1182-1193.   doi: 10.37188/CO.2022-0070
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Abstract:

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

2022, 15(6): 1194-1210.   doi: 10.37188/CO.2022-0098
Abstract(552) FullText HTML(351) PDF 10167KB(399)
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With the characteristics of real-time, high-resolution and non-invasive, optical microscopy can scale from cells, tissues to whole living organisms, which has greatly expanded our understanding to the nature of life. However, due to the limited Space-Bandwidth Product (SBP), it is hard for a conventional optical microscope to achieve a large field of view with a high resolution. This makes it very difficult for microscopic imaging in large field of view biological imaging applications, such as imaging of neural circuits between the synapse of the brain neural networks. Recently, large field-of-view imaging technology has received increasing attention and experienced rapid development. The SBP has been improved ten times or even a hundred times as compared to a traditional optical microscope and the field-of-view has been expanded without sacrificing resolution, which, in turn, has resolved some major problems in biomedical research. This review introduces the progress, characteristics and corresponding biological applications of several typical trans-scale optical imaging techniques in recent years, and gives an outlook on their future development.

2022, 15(6): 1211-1227.   doi: 10.37188/CO.EN.2022-0011
Abstract(205) FullText HTML(215) PDF 6600KB(324)
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As an early component of modern Super-Resolution (SR) imaging technology, Structured Illumination Microscopy (SIM) has been developed for nearly twenty years. With up to ~60 nm wavelengths and 564 Hz frame rates, it has recently achieved an optimal combination of spatiotemporal resolution in live cells. Despite these advantages, SIM also suffers disadvantages, some of which originated from the intrinsic reconstruction process. Here we review recent technical advances in SIM, including SR reconstruction, performance evaluation, and its integration with other technologies to provide a practical guide for biologists.

2022, 15(6): 1228-1242.   doi: 10.37188/CO.2022-0077
Abstract(384) FullText HTML(269) PDF 9403KB(270)
Abstract:

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

2022, 15(6): 1243-1257.   doi: 10.37188/CO.2022-0088
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Abstract:

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

2022, 15(6): 1258-1274.   doi: 10.37188/CO.2022-0091
Abstract(639) FullText HTML(327) PDF 6335KB(339)
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Digital pathology has brought new opportunities for remote pathological consultation and joint consultation owing to its convenient storage, management, browsing and transmission. However, because of the limited field of view of a microscope, panoramic imaging cannot be achieved while ensuring a high resolution. The proposal of panoramic digital pathology makes up for this defect and achieves panoramic imaging while ensuring high resolution. However, a single slice can only detect a single target, and disease diagnosis needs to observe the expression of multi-target at the same time. In recent years, multi-target panoramic digital pathology technology has developed rapidly. It has attracted much attention because of its great application potential in drug research and development, clinical research and basic research. Owing to its large field of view, wide range of colors and high flux, the system can detect the expression of various biomarkers on a whole tissue section in situ in a short time to identify the phenotype, abundance, state, and relationship of each cell. Firstly, this paper reviews the development process of digital pathology, panoramic digital pathology and multi-target panoramic digital pathology, as well as the update and iteration of technology in the development process, and illustrates the importance of developing multi-target panoramic digital pathology. Then, the multi-target panoramic digital pathology is described in detail from three perspectives: biological sample preparation, multi-color imaging system and image processing. Next, the applications of multi-target panoramic digital pathology in biomedical fields, such as tumor microenvironments and tumor molecular typing are described. Finally, the advantages, challenges and future development of multi-target panoramic digital pathology are summarized.

2022, 15(6): 1275-1286.   doi: 10.37188/CO.2022-0095
Abstract(189) FullText HTML(88) PDF 5916KB(200)
Abstract:

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

2022, 15(6): 1287-1301.   doi: 10.37188/CO.2022-0078
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Abstract:

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

2022, 15(5): 863-877.   doi: 10.37188/CO.2022-0096
Abstract(578) FullText HTML(309) PDF 6933KB(393)
Abstract:

The effective realization of desired optical system performances depends not only on the design results of imaging quality, but also on the realizability of various tolerances such as optical manufacturing tolerances, assembly tolerances, and environmental tolerances. An optical system with low error sensitivity relaxes tolerance requirements, which can better resist image quality degradation disturbed by errors. While reducing manufacturing costs, it effectively improves the realizability of an optical system, thereby reducing error sensitivity. It is an important link that should be considered in optical system design. This paper analyzes and summarizes the research status of optical system error sensitivity, summarizes typical optical system desensitization methods, and summarizes the application of these methods in optical system design. Finally, potential future development directions for low error sensitivity design methods for optical systems are provided.

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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