2018 Vol. 39, No. 5

Oe System and Engineering
Optical imaging system in bionic vision based on liquid lens
Meng Xiaochen, Fan Fan, Zhu Lianqing, Lou Xiaoping
2018, 39(5): 595-599. doi: 10.5768/JAO201839.0501001
With the wide applications of machine vision technology in the fields of advanced manufacturing system, robot system, intelligent monitoring and aerospace military industry, the miniaturization and dexterization of bionic vision system has become one of the important research directions. Aiming at the shortcomings of traditional machine vision system, such as complex zoom structure, easy wear and low life, a bionic optical system with liquid lens was designed and built on the basis of the principle and imaging characteristics of liquid lens. The main technical parameters of the system are as follows: the focal length range is 18.5 mm~22.5 mm, the lens zoom ratio is 1.22, and the field angle is 38 °×24 °. The design results accord with each index, and the image quality can meet the requirements at different focal lengths, which can realize real-time focusing. The size of the whole optical system is 36 mm×55 mm×30 mm, which has a compact structure and strong practicability.
Research on synchronized tracking system based on rotating mirror
Feng Bin, Shi Yuanyuan, Wu Yaoxia, Chen Ruting
2018, 39(5): 600-604. doi: 10.5768/JAO201839.0501002
In order to study the problem of motion attitude of high-speed flying projectiles, a rotating mirror synchronization tracking technique is proposed. A rotating mirror is placed in the direction of the main optical axis of the high speed CCD camera. The motion of the projectile in the ballistic line is reflected to the high speed CCD camera to achieve synchronous tracking. A rotating mirror tracking system based on the midpoint of the field of view of the high-speed CCD camera is designed. In the system, the motion model of projectiles and rotating mirrors is set up, and the curves of time varying with the MATLAB software are obtained. When the parameters are H=300 m and V=100 m/s, the errors existing in the system are analyzed. The results show that the system can achieve synchronous tracking of high-speed projectiles.
Research on dynamic focusing system of laser scanning projection instrument
Hou Maosheng, Yang Fan, Sun Mingli, Li Lijuan, Zhu Yundong, Lin Xuezhu
2018, 39(5): 605-612. doi: 10.5768/JAO201839.0501003
In order to realize the automatic focus of laser projection system, a laser dynamic focusing system was constructed. The system can adjust the mirror group spacing of the focusing system according to the change of the back-reflected light intensity signal, so that the laser scanning projection system can focus the minimum spot on the projection surface at different distances, thereby improving the positioning accuracy of the system. Firstly, according to the principle of laser dynamic self-focusing system, two kinds of dynamic self-focusing schemes, optical lever type and inverted telephoto type, were designed and the corresponding mathematical models were derived; then, through the simulation of ZEMAX, two dynamic focusing systems were compared, and the self-focusing system with faster response speed and more reasonable structure was chosen; finally, a new self-focusing laser scanning projection system was set up, and the performance of dynamic focusing was verified. The experimental results show that the inverted telephoto type self-focusing system is more reasonable, at a projection surface of 4.5 m, the converging spot diameter is optimally up to 0.2 mm, which can improve the positioning accuracy of the laser scanning projector during auxiliary assembly to 0.1 mm. It can meet the precise positioning requirements of components in advanced manufacturing and assembly engineering.
Micro-lens array for integrative transmitting and receiving continuous scanning
Xie Hongbo, Wang Yao, Mao Chensheng, Su Yongpeng, Yang Lei
2018, 39(5): 613-618. doi: 10.5768/JAO201839.0501004
A newly designed micro-lens array, being used integrative transmitting and receiving combined with continuous scanning, was proposed and demonstrated. Based on the typical Kepler telescope structure with a field lens, the micro-lens arrays with three-piece style, conducts the selection of receiving field of view (FOV) and the synchronous deflection of transmitting light with large FOV by laterally slight displacement between the two contiguous micro-lenses. In order to avoid the loss and crosstalk of light energy, the visual magnification of telescope is constrained to be 1 which makes the apertures of micro-elements in incident and emitting ports keep consistent. With the ZEMAX software, the entire optical model is mainly composed of transmitting and receiving parts that are designed independently and joined together later. The micro-lens array's central wavelength is 1 064 nm, with ±1.06° instantaneous FOV and ±10° scanning FOV, the size of each micro-element is 1 mm×1 mm.In addition, the bilateral scanning can be realized with only one moving element.The designed system is characterized by the advantages including compact size, large scanning range and high sensitivity.
Load analysis and structure checking of inertially stabilized platform based on cable differential transmission
Li Daquan, Hong Huajie, Yuan Dongyang, Jiang Xianliang
2018, 39(5): 619-626. doi: 10.5768/JAO201839.0501005
Aiming at the structural design of a new type inertially stabilized platform based on cable differential transmission, the load analysis, frame structure strength and stability checking were studied. According to the load characteristics and working conditions of the platform, the load was divided into inertial load, centroid-offset acceleration load, friction load and environmental load, and then calculated respectively to conduct load synthesis and power estimation. The static and dynamic structural verification was carried out with the azimuth frame taken as an example. The finite element analysis based on the result of load analysis shows that the frame has good static and dynamic characteristics: the deformation during load transferring and frame overload with the carrier are within the allowable range of the system, which meets the design requirements; the first-order inherent frequency of frame structure is 156.04 Hz, much higher than the bandwidth of the servo system. Accordingly the resonance can be avoided and the frame shows high structural dynamic stability.
Spatial rotation multi-axis parallelism adjustment and calibration technology
Zhao Wei, Chang Ming, Liu Hu, Zhao Hongjun, Jiang Feng, Li Yuxi, Zhang Xiangming, Yang Xiaoqiang
2018, 39(5): 627-632. doi: 10.5768/JAO201839.0501006
The optical axis parallelism of the spatial rotating multi-optical axis system affects the pointing accuracy of the system and is difficult and time consuming to calibrate.Based on the optical axis calibration principle of the spatial rotating multi-optical axis system, the calibration theoretical model was obtained. Combined with the experimental research, a high-precision optical axis calibration scheme was established. Taken the mechanical rotation axis as the reference target, the coarse and fine adjustments were combined, the coarse adjustment was performed for the sensor mounting surface and the fine alignment of optical magnitude was implemented by means of double wedges. Firstly, the parallelism between the visible light axis and the mechanical rotary axis was calibrated, then the parallelism between the laser axis and the mechanical rotary axis was guaranteed, and finally the parallelism between the visible light axis and the laser axis was guaranteed. The experimental results show that the calibration scheme is accurate and efficient, the index is better than 0.1 mrad, which can be used for practical engineering.
Design of dual-wavelength M-Z interference system based on prism structure
Li Xiaoxiao, Shen Tao, Zhou Yan
2018, 39(5): 633-637. doi: 10.5768/JAO201839.0501007
In order to facilitate the adjustment of optical path difference, the conventional Mach-Zehnder (M-Z) interference system was improved by using the total reflection prism, and the theoretical model of M-Z measurement system based on the principle of dual-wavelength interference was established. A complete optical system model was built using Zemax, and the entire system was simulated and tested.The results of image quality evaluation show that the energy concentration of the system within the range of 532 nm~632.8 nm is 85%, the distortion value is less than 0.02% and the modulation transfer function is above 0.9 at the cut-off frequency of 10 lp/mm, which meets the system imaging requirements for the tests of transmissive sample. It provides a theoretical basis and technical support for the practical application of high performance interference systems.
Design of compact optical system with large aperture and ultra long focal length
Xu Mengmeng, Xue Donglin, Zeng Xuefeng
2018, 39(5): 638-643. doi: 10.5768/JAO201839.0501008
In order to meet the needs of space remote sensing optical system in compact structure, small size and high resolution, a design idea and method of compact optical system with long focal length was studied. Based on the Gaussian optics and Seidel aberration theory, the initial structure of the coaxial four-mirror system was built, and the secondary obstructions were avoided by means of field-bias. A large aperture and ultra long focal length coaxial four-mirror optical system was optimized. The aperture of the system was 1 800 mm, the effective focal length was 25 000 mm, and the design full field angle was 1°×0.1°.The design results show that the wavefront of the system is better than 1/50λ(λ=632.8 nm), the relative distortion in the whole field is less than 0.4%, and the total length of this system is only 1/10 of effective focal length (EFL). The structure is simple and compact, the image quality is close to the diffraction limit, and it has certain guiding significance for the design of large aperture and ultra long focal length space remote sensing optical system.
Design of large aperture and long focal length zoom optical system
Ba Hubing, Miao Li
2018, 39(5): 644-649. doi: 10.5768/JAO201839.0501009
In order to realize the requirements of large aperture and long focal length zoom optical system in photoelectric tracking equipment and by analyzing and calculating the zoom principle, the suitable initial structure was determined, then the mechanical compensation zoom type was adopted to realize the whole zoom system through analysis and comparison. The entire system needs to be designed to achieve a continuous zoom of 100 mm ~ 600 mm, while ensuring that its F number does not change, and because of the large aperture and long range of focal length change, the design is more difficult.The final result obtained through optimizing design show that the total length of the whole system is 563.956 mm, and the F number remains almost unchanged, which can be used to realize remote imaging in practical applications. When the focal length of the system is medium and short, its modulation transfer function (MTF) value is more than 0.4 at the 30 lp/mm, and its performance decreases slightly in the long focal length, which meets the requirements for practical applications.
Design of embedded system for optical angle measurement based on linear array CCD
Cheng Yao, Zhao Jian, Mi Zengzhen
2018, 39(5): 650-654. doi: 10.5768/JAO201839.0501010
As a photoelectric converter, charge coupled device (CCD) is widely used in the field of measurement because of its low cost, simple structure, fast scanning speed and high frequency response. It was proposed to use a monochrome linear array CCD to encode and debug the angle information in a non-contact optical manner.By collecting this signal and using the data processing module, the demodulation of the image signal was accomplished, and the angle measurement was realized. The system used TSL1401 and LPC2138 as the core to form an embedded measurement system, which used the TSL1401 to collect signals, then transferred them to the LPC2138 for data processing through A/D, and finally obtain the angle values. Through the optical measurement of angle, a new method of non-contact measurement was realized.
Oe Information Acquisition and Processing
Remote sensing image fusion based on deep learning non-subsampled shearlet
Chen Qingjiang, Li Yi, Chai Yuzhou
2018, 39(5): 655-666. doi: 10.5768/JAO201839.0502001
Remote-sensing image fusion refers to the method of selectively and strategically combining image information with different observation characteristics obtained by different sensors to obtain a new image with better observation characteristics. A deep-sensing image fusion algorithm combined with non-subsampled shearlet transform (NSST) was proposed. In this algorithm, the spatial resolution of multi-spectral (MS) image is enhanced by an improved super-resolution reconstruction network. The panchromatic (PAN) image histogram-matched refers to each component of the reconstructed MS image. And the corresponding channel image is subjected to NSST transformation to obtain low-frequency sub-bands and several high-frequency direction sub-bands, respectively. To obtain low-frequency fusion coefficient, the low-frequency region uses an adaptive weighted average rule based on the gradient region, while the high-frequency sub-bands adopt the local spatial frequency maximum rule to obtain the high-frequency fusion coefficient, and finally the fused image can be obtained by inverse NSST transform reconstruction. The MS images City and Inland in different datasets were upsampled by the bicubic interpolation method. With the proposed algorithm, the general image quality index (UIQI) was 0.988 6 and 0.932 1, respectively, and the spectral angle mapping (SAM) was 1.872 1 and 2.143 2, respectively. Experimental results show that the image structure of the fusion algorithm in this paper is more clear, the saved spectral information is more complete, the fusion quality is better than the contrast algorithm, and the fusion image is more conducive to human visual observation.
Research and application of binarization algorithm of QR code image under complex illumination
Gan Zhijian, Fang Junbin, Guan Heyuan, Tang Jieyuan, Luo Yunhan, Yu Jianhui, Lu Huihui, Zhang Jun, Zhong Yongchun, Chen Zhe
2018, 39(5): 667-673. doi: 10.5768/JAO201839.0502002
In complex illumination conditions, the images collected by two dimensional code scanner are prone to general highlighting with shade and part highlighting with shade, which make it difficult to determine the image segmentation threshold. In Sauvola algorithm, the effect of the window size w value and the correction factor k value on the quick response (QR) code image binarization was studied. Aiming at the shortcomings, such as the poor anti-noise ability of the global binarization method and the slow processing speed of the local binarization method, an improved QR code image binarization method was proposed, which combined the Otsu and Sauvola algorithms to improve the algorithm anti-noise ability, and used the integral graph to improve the algorithm operation efficiency. Experiments show that the binarization effect of this method is better than the classical binarization method, and the average running efficiency is 17 times higher than that of the original Sauvola algorithm, which increases the recognition success rate.
Fast adaptive compressed 3D imaging based on wavelet trees and Hadamard matrix
Jiang Xiaoyong, Jiang Yuqi, Dai Huidong
2018, 39(5): 674-682. doi: 10.5768/JAO201839.0502003
Aiming at the problem of slow 3D imaging speed in photon counting system, a method of fast adaptive compressed 3D imaging method based on wavelet trees and Hadamard matrix was proposed. The sampling efficiency was improved by modulating projective patterns with Hadamard matrix, the scene was illuminated with modulated short-pulsed structured light, and the echoes were collected by the single-pixel photon counting detector. The sample area was selected by analyzing the wavelet trees of coarser images. With the patterns projected from the sample area modulated by Hadamard matrix, image details could be sampled. After the multistage sampling, the high-resolution image could be recovered with Hadamard inverse transform. The experimental results indicate that a 3D image at resolution up to 512×512 pixel can be acquired and retrieved with practical time as low as 41 s.
OPtical Metrology and Measurement
Dynamic resolution detection system design of CCD aerial camera
Zhang Xinting, Kang Lei, Yao Qinghua, Wu Qianqian
2018, 39(5): 683-686. doi: 10.5768/JAO201839.0503001
A set of dynamic resolution detection system for CCD aerial camera was designed. The diameter of the entrance pupil is D=200 mm, the focal length is f′=2 000 mm, the angle of the field of view(FOV) is 2ω=5°. The system was simulated by Zemax optical design software, the design results show that, at the Nyquist frequency of 40 lp/mm, the modulation transfer function(MTF) curves are all above 0.5. The secondary spectra introduced by the long focal length were corrected through using the wave-deviation method. At the same time, the concept of resolution ruler was introduced, each separate resolution plate was made into a resolution ruler of 300 mm×24 mm by stitching, and the resolution ruler was driven by the motor to make a uniform linear motion to simulate the dynamic target.The design of the test system can detect the dynamic resolution of the aircraft under simulated flight conditions, the testing accuracy is 1″, and it can be widely used in mapping, military reconnaissance, aerospace and other fields.
Research on focal length measurement based on double Ronchi gratings
Jiang Zhengdong, Zhu Ronggang, Chen Lei, He Yong
2018, 39(5): 687-690. doi: 10.5768/JAO201839.0503002
With the wide application of long focal length optical elements in remote-sensing technology, high-power lasers and astronomical telescope systems, the high-precision measurement of such optical elements' focal length is required. Based on the technique of double-grating interferometry, a new improved algorithm was proposed. This algorithm obtained the focal length calculation formula by the functional relation between the Moiré fringe tilt angle and the focal length of the element to be measured, and optimized the calculation formula by using the ideal state of the Moiré fringe when illuminated by a collimated beam. So the step for determining the Moiré fringe's baseline can be avoided, and the precision of the Moiré fringe tilt angle can be improved. In the experiment, two Ronchi gratings with period of 20 μm were used to build the measuring system. The measurement result of the test lens is 36.690 m, and the repeatability accuracy is up to 0.382‰.
High-precision responsivity calibration system for terahertz detector
Li Xue, Fang Bo, Deng Yuqiang, Li Jianmin, Qi Cenke, Cai Jinhui
2018, 39(5): 691-696. doi: 10.5768/JAO201839.0503003
In order to calibrate the terahertz detector to ensure its accuracy and reliability of measurement, the calibration technology for responsivity of terahertz detector was studied. For commonly used blackbody radiation test technology for terahertz detector, there have been several problems such as high requirements on the environment, equipment and the difficulties in establishment. Taking the thermoelectric terahertz detector developed by the National Institute of Metrology as a standard detector, a calibration scheme was proposed and a responsivity calibration system for terahertz detector was designed and established. To improve the calibration accuracy, the beam quality of the calibration optical system was experimentally tested and the diaphragm aperture was set reasonably to meet the calibration requirements. At 0.1 THz, the responsivity of two field-effect self-mixing terahertz detectors were calibrated. The results show that the relatively extended uncertainty is 6.80% (k=2), verifying the feasibility of the calibration system. In the system, the power responsibility of terahertz detector can be traceable to the National Terahertz Power Standard and ensure the accuracy and reliability of terahertz power measurement.
Optical Metrology and Measurement
No datum point zero calibration method of reconnaissance vehicle
Zhang Xuantao, Guo Cheng, Yu Shuai, Mi Jianjun
2018, 39(5): 697-700. doi: 10.5768/JAO201839.0503004
A method to calibrate the zero position of reconnaissance vehicle in room was proposed. This method uses a dedicated zero calibration instrument and does not require the datum point. The dedicated zero calibration instrument combines the high-precision north finder, the level, and the calibration mirror with a zero accuracy of 0.15 mil. The method can effectively solve the zero calibration problem of reconnaissance vehicle under the conditions that the site or meteorological conditions are not satisfied.
Optical Element and Fabrication
Design of sub-wavelength grating for improving efficiency of OLED substrate
Zhong Kejun, Fu Yanjun, Jiang Guangyu
2018, 39(5): 701-706. doi: 10.5768/JAO201839.0505001
A two-dimensional continuous surface sub-wavelength grating was designed on the organic light-emitting diode(OLED) substrate surface in order to improve the efficiency of OLED. The sub-wavelength grating with approximate continuous surface structure was design by the method of equal height step approximation, according to the theory of equivalent medium and the principle of thin film optics. The grating parameters were designed as follows: the etching depth is 0.29 μm, the period is 0.165 μm, the ratio of the bottom diameter to the period is equal to 1, which can effectively realize high transmittance of wide spectrum and wide angle. The effect of the grating on the light efficiency of the OLED substrate was simulated by the finite-difference time domain method, and the results show that the maximum light output efficiency of 30% can be increased.
Volume holographic mixed-gratings model in photopolymer doped with gold nanoparticles
Wu Shenghan, Cao Liangcai, Hao Jinping, Zhu Chen, Jin Guofan
2018, 39(5): 707-713. doi: 10.5768/JAO201839.0505002
During holographic recording, mixed gratings in photopolymer doped with gold nanoparticles are formed by the primary refractive index grating caused by periodic spatial distribution of photoproduct and the secondary absorption grating induced by spatial distributed nanoparticles because of local surface plasmon resonance. A mixed-grating model based on Kogelnik's coupled wave theory was investigated to analyze the volume holographic characteristics. Results show that both refractive index grating and absorption grating contribute to the improvement of diffraction efficiency; the mixed gratings also exert positive influence on angular selectivity.
Application of sliding mode dynamic surface control in fast steering mirror
Wei Wenjun, Zhao Xuetong
2018, 39(5): 714-721. doi: 10.5768/JAO201839.0505003
A sliding mode dynamic surface control(SMDSC)strategy was proposed in order to solve the uncertain interference problem which may influence the tracking precision and the response time of the fast steering mirror (FSM)system, due to the external environment and the mechanical inertia and electromagnetic inertia of the voice coil actuator in the course of acquisition, tracking and pointing in FSM system. The controller introduces the tracking differentiator (TD) to instead the first-order filter in the traditional dynamic surface control, which improves the problem of unsatisfactory convergence speed and control precision of the first-order inertial link. Besides, the controller which combines sliding mode control with dynamic surface control further improves the anti-interference ability and tracking accuracy of the system. A large number of simulation studies show that, compared with the traditional dynamic surface control and classical proportional-integral-derivative (PID) control, the designed SMDSC increases by 62.5%, 75% respectively in the response time, 72%, 88% respectively in the adjustment time, and 75%, 96% respectively the tracking accuracy.
Theoretical analysis of generating two-stage non-diffracting beam based on axicon method
Yang Guiyang, Ma Guolu, Zeng Guoying
2018, 39(5): 722-728. doi: 10.5768/JAO201839.0505004
In order to further complete the transmission and transformation theory of multilevel non-diffracting beam, the light field distribution of two-stage non-diffracting beam was analyzed detailed based on axicon method and Fresnel diffraction theory. Firstly, the distribution of spatial light intensity and axial light intensity was simulated by numerical simulation software. At the same time, the influence of processing technology on the light distribution of the two-stage axicon with the hyperbolic contours on the vertex of the axicon and the critical point of one/two stage axicon was investigated. Then the influencing factors on the field intensity and the oscillation period of the light field were analyzed. The results show that the diffraction light field generated by the ideal two-stage axicon is composed of 4 regions. In the interference overlap zone, the intensity is the coupling superposition of the diffraction field of the one/two stage axicon, and the other regions still maintain the single-stage non-diffracting light field distribution, while for the two-stage axicon with the hyperbolic contours on the vertex of the axicon and the critical point of one/two stage axicon, the light field distribution is greatly affected by hyperbolic characteristic parameters.Its special light field distribution provides new possibilities for expanding multi-level non-diffracting beam to large-scale space measurement and particle micro-operation.
Method for realizing Tracepro redevelopment based on DDE technology
Zhan Qianjing, Liu Xiaoqin, Hou Zaihong, Wu Yi
2018, 39(5): 729-734. doi: 10.5768/JAO201839.0505005
The Tracepro software was redeveloped using dynamic data exchange (DDE)communication technology.The universal methods for connection, transmission, request, etc. in DDE communication protocols were proposed to be used, in order to realize the functions of transmitting script from redevelopment software for simulation and then retrieving the simulation results and returning to the redevelopment software. In the software, functions such as automatic model generation, automatic parameter configuration, automatic simulation, and optimization analysis can be realized, which can improve the design efficiency. Taking the design of LED cup modeling and simulation software as an example, the interaction with Tracepro was realized in software, and the rapid modeling, design and simulation of LED were completed.
Infrared Technology
Research on methane gas spectroscopy detection method based on mid-infrared DFG laser source
Fang Jiulong, Chang Jianhua, Dai Feng, Liu Zhenxing, Dou Xiaolei, Zhao Yongyi
2018, 39(5): 735-742. doi: 10.5768/JAO201839.0506001
Gas spectroscopy detection based on mid-infrared laser source has been applied in the field of atmospheric monitoring as a new method for measuring and analyzing trace gases.A detection system of methane gas based on mid-infrared difference-frequency generation (DFG) laser source was constructed.The system uses a tunable semiconductor laser with 1 550 nm and 1 060 nm band as the fundamental frequency source, and uses a periodically-poled lithium niobate (PPLN) crystal as the differential frequency nonlinear inverter to achieve a narrow linewidth tunable mid-infrared source output at 3.3 μm. Experimental results show that, when the temperature of the PPLN crystal is fixed at 99.5℃, the maximum idler laser output power of 112 μW, and the nonlinear DFG conversion efficiency is 1.246 mW/W2. The acceptance bandwidth for the pump wavelength and the crystal temperature are 5.3 nm and 4.3℃, respectively. On this basis, the methane gas absorption spectrum and the second harmonic detection signal at 3 028.751 cm-1 were obtained by direct absorption method and harmonic detection method, respectively.
Infrared behavior recognition based on spatio-temporal two-stream convolutional neural networks
Wu Xueping, Sun Shaoyuan, Li Jiahao, Li Dawei
2018, 39(5): 743-750. doi: 10.5768/JAO201839.0506002
Aiming at the recognition of human behavior in infrared video, an infrared human behavior recognition method based on spatio-temporal two-flow convolutional neural network was proposed. In this method, first the entire infrared video is equally segmented, and then the infrared image extracted randomly and the corresponding optical flow image in each video segment are input into the spatial convolutional neural network, and the spatial network can effectively learn which part of the infrared image is actually the action by merging the optical flow information. Next the recognition results of each small segment are merged to get the spatial network results. At the same time, the randomly selected optical stream image sequence in each segment of the video is input into the temporal convolutional neural network, and the result of the temporal network can be obtained by fusing the result of each small segment. Finally, the results of spatial network and the temporal network are weighted and summed to obtain the final video classification results.In the experiment, the action on the infrared video data set containing 23 kinds of infrared behavior action categories was identified by this method, and the correct recognition rate was 92.0%. The results show that the algorithm can effectively identify the infrared video behavior.
Thermal-stress damage of MCT infrared focal plane array detector caused by laser irradiation
Xia Runqiu, Liu Yang, Zhang Yue, Niu Chunhui, Lyu Yong
2018, 39(5): 751-756. doi: 10.5768/JAO201839.0506003
Based on the structure and the thermal-stress properties of materials of mercury cadmium telluride(MCT) infrared focal plane array detector (IRFPA), the damage mechanism of MCT IRFPA caused by laser irradiation was elaborated. Based on the relevant irradiation environment and conditions, a three-dimensional simulation model was established by finite element analysis. Based on COMSOL Multiphysics software, the temperature changes and stress changes of various parts of MCT detector were detected, when irradiated by 10.6 μm laser. The numerical analysis method was used to compare the temperature field changes and stress field changes along the surface radial and internal axial directions of the MCT detector after laser irradiation with different spot power.The numerical analysis method was used to compare the spot area of MCT detectors. Temperature field changes and stress field changes in the radial and internal axial directions of lasers with a constant irradiated area and different constant powers.The simulation results show that the surface temperature and stress of the MCT detector increase rapidly after continuous laser irradiation of 106 W/cm2, causing damage to the detector surface.Meanwhile, the temperature change of the irradiated part of the detector also causes the internal local stress value to change.Through comparing the stress damage threshold and variation trend of the MCT detector with the experimental data in the literature referenced, it is found that the results are basically the same, the feasibility of the model can be verified.
Laser Technology
Transmission performance of 50 Gbit/s high-speed laser communications with QPSK modulation
Liu Xianzhu, Wang Tianshu, Chen Junda, Zhang Xinmeng, Yang Jinhua, Jiang Huilin
2018, 39(5): 757-761. doi: 10.5768/JAO201839.0507001
Advanced multi-level modulation format has shown its great potential in high-speed and high-spectral-efficiency optical communications at sea. The quadrature phase-shift keying (QPSK) modulation format was introduced into the free-space optical (FSO) communications. Experiments demonstrate that the high-speed FSO transmission links of up to 50 Gbit/s can be achieved, and the eye diagrams and constellations of the transmitted QPSK signals can be clearly observed. By comparing the bit error rate (BER) curves before and after transmission, it is found that the receiving sensitivities are both less than -36.7 dBm for the transmissions of the FSO link, and their power penalties are both less than 4.2 dB at the BER of 3.8×10-3.
Dynamic tracking and pointing accuracy measurement method of space laser communication system
Wu Lei, Hao Shujie, Xie Xuanmei, Li Gaoping, Yu Bing, Yu Dongyu, Yin Wanhong
2018, 39(5): 762-766. doi: 10.5768/JAO201839.0507002
Dynamic tracking and pointing accuracy is one of the important parameters of the acquisition, tracking and pointing (ATP) subsystem of space laser communication system, and its accurate measurement is the key to evaluate the performance of the space laser communication at long distance. The tracking and pointing precision measurement method of the ATP subsystem was introduces, and a dynamic aiming parameter measuring device for space laser communication system based on collimator method was designed. Moreover, the factors affecting the uncertainty of dynamic tracking accuracy measurement were analyzed and discussed. Test results show that the measurement accuracy of the ATP subsystem is 1.9 μrad (k=2) under the condition of 100 Hz vibration frequency, which can be used for the tracking parameter detection of space ATP subsystem of laser communication system and the long-range laser communication performance evaluation.