2020 Vol. 41, No. 5

2020, 41(5): 1-6.
Alignment design of assembly optical system for laser active detection
LI Huizhen, LIU Zhangfei, WANG Guocong, ZHANG Yong’an, CUI Jie, LI Xudong, MI Jianjun, Song Yamin
2020, 41(5): 879-884. doi: 10.5768/JAO202041.0501001
The detection and receiving system with field of view(FOV) no less than 15°×6° was introduced, which was composed of two groups of optical systems with 8°×6° FOV in the horizontal direction. In order to ensure the splicing quality and angular positioning accuracy of the FOV within the whole of the detection and receiving system, the installation and adjustment methods as well as procedures of the detection and receiving system were designed in detail, and the accuracy indexes of each installation and adjustment step were allocated. Focusing on the optical axis parallelism, resolution, FOV splicing installation and its key points were described. Through strict control of the accuracy for each installation and adjustment step, the final test results of the detection and receiving system are as follows: the focus f ′ is 52.7 mm, the FOV is 15.2°×6.2°, which meet the requirements of the design indexes.
Structure design and analysis of tracking frame for horizontal telescope
ZHANG Yan, CHEN Baogang, LI Hongwen, CAO Yuyan
2020, 41(5): 885-890. doi: 10.5768/JAO202041.0501002
The structure design scheme of U-type tracking frame was put forward for a 700 mm aperture horizontal telescope. The double row dense ball bearings were used for azimuth shafting, and the bearing was designed as double row of axial thrust steel balls and double row of radial steel balls. The dense of the ball could ensure the high rotation accuracy of the shafting. First, the pitching shafting was designed as a structure with one end fixed and one end floating to compensate the effect of mechanical error and thermal deformation on the rotation accuracy. Then, the finite element model of tracking frame was established, and the first order resonance frequency could reach to 47.6 Hz, which showed that it had good modal characteristics. Finally, the electronic level and digital autocollimator were used to measure the pitch axis and azimuth axis respectively. The shaking of azimuth axis shafting was better than 1.3″, and the shaking of pitching axis shafting was better than 1.8″. The test results show that the designed telescope tracking frame structure has high stiffness and high rotation accuracy, which provides some reference value for the structure design of similar tracking frames.
Design of optical system based on DMD for simulator with large field of view and long exit pupil distance
DAI Yu, CHENG Xin, ZHANG Wenming, LI Jie, LYU Shenglin
2020, 41(5): 891-897. doi: 10.5768/JAO202041.0501003
In order to meet the requirements of the high dynamic star simulator, a set of projection optical system and illumination optical system suitable for digital micromirror device (DMD) was designed. The secondary imaging method was adopted by the projection optical system, which solved the problem that it was difficult to achieve long working distance and system aberrations alignment in the case of large field of view and long exit pupil distance. The compound eye lens array was used to design the corresponding illumination optical system, and the approximately coaxial arrangement of the illumination system and projection system was realized by using a total reflection prism. The design results show that the optical system has a 60 mm exit pupil distance and a 28.6° field of view, the distortion is less than 0.045% and the 80% of the energy is concentrated in the circle with a diameter of 8 μm, the illumination uniformity of the illumination system is greater than 94%, which meet the design index requirements, and is suitable for the optical system of DMD dynamic star simulator with large field of view and long exit pupil distance.
Design of weak optical signal detection system for measuring eye axial length
ZHANG Yuning, LI Piding, WANG Cheng, XIANG Huazhong
2020, 41(5): 898-903. doi: 10.5768/JAO202041.0501004
Since the reflectivity of two reflective surfaces of the corneal surface and the retinal pigment cortex is greatly different when measuring the axial length of eye, the intensity of the reflected optical signal belonges to the weak signal category under the premise of the incident light safety in the eye. In order to remove the noise and quickly extract the peak value of the signal for the calculation of the starting and ending point of the eye axial length, a weak optical signal detection system was designed. This system used PIN photodiode to receive weak optical signal and a weak light signal detection system was built coordinated with the I-V conversion circuit, automatic gain control circuit as well as the post-processing circuit. The experiment used ZIESS simulation eye to test. The results show that the designed detection system can detect the weak optical signal of about 0.77 nW at least, the maximum photoelectric conversion capacity can reach 4.5×108 V/W, the signal-to-noise ratio is more than 9 dB, and the maximum error between the measured eye length and the actual value can reach 0.05%. This system is characterized by low noise, high gain and large dynamic range, which provides an effective solution for accurate measurement of the eye axial length.
Calculating MTF of Kirkpatrick-Baez system by wave aberration theory
YU Chenghao, LYU Lijun
2020, 41(5): 904-910. doi: 10.5768/JAO202041.0501005
The modulation transfer function(MTF) can objectively evaluate the imaging performance of optical system. Based on the theory of wave aberration of plane symmetric optical system, the wave aberration expression of main aberration of Kirkpatrick-Baez(KB) microscope optical system was given. By using the autocorrelation method, the MTF curve of the KB system was obtained by the Gauss-Legendre numerical integration, and then compared with the MTF curve of the optical analysis software. The results show that calculating the MTF by wave aberration theory can not only quantificationally and intuitively analyze the imaging performance of KB system, but further analyze the single aberration distribution of optical system. The application of this theory can provide a more effective targeted optimization scheme for KB system.
Horizontal alignment technology of coaxial three-mirror optical system
WANG Haichao, CHEN Jiayi, HUO Tengfei, LI Bin, LIU Junhang
2020, 41(5): 911-915. doi: 10.5768/JAO202041.0501006
Coaxial three-mirror optical system is a popular optical system design form in space optical remote sensor. Taking the alignment of high-resolution camera of the GF-1 sensing satellite as an example, the computer-aided alignment technology of coaxial three-mirror optical system was researched. The primary mirror optical axis was set as the benchmark. By adjusting the alignment methods of three-mirror control system field of view and secondary mirror control system aberration, the changes in the relationship between the misalignment rate of secondary mirror and three-mirror and Zernike coefficient were analyzed. The system sensitivity matrix was obtained by the optical design software to guide the system alignment, which improved the accuracy of alignment and shortened the period of alignment. Test results show that the Zernike coefficient of each field of view in optical system is better than 0.05λ, and the RMS value of system wave aberration is better than 0.06 λ. The system passes the on-orbit imaging test with clear and multilayer images.
Analysis of polarization characteristics for cat’s eye target echo scattering based on microfacet theory
QIN Xuzhi, NIU Chunhui, CHEN Shijie, LYU Yong
2020, 41(5): 916-923. doi: 10.5768/JAO202041.0501007
In order to study the scattering polarization characteristics of cat's eye target echo, a polarized bidirectional reflection distribution function model was established based on the microfacet theory. The degree of polarization of the cat's eye target echo for linearly polarized light was related to target surface roughness, complex refractive index, incident angle and observation angle. The influence of the surface roughness of cat's eye target on the degree of polarization of its echo was studied. The relationship between the degree of polarization of cat's eye target echo and the target surface roughness parameter was obtained by Matlab simulation. The silicon wafers polished by different sandpapers were selected as the cat's eye target. When the root-mean-square heights of silicon wafers is 0.067 µm, 0.554 µm, 0.726 µm, 1.651 µm and 1.893 µm respectively, the degree of polarization of surface echo scattering is 98.83%, 98.16%, 96.08%, 94.91% and 94.6%, respectively. The degree of polarization of cat's eye target echo decreases with the increase of its surface roughness.
Low distortion wide working distance machine vision optical lens design
LIU Xiaona, WANG Shaobo, OUYANG Mingzhao, HAN Xuefeng
2020, 41(5): 924-928. doi: 10.5768/JAO202041.0501008
The optical parameter requirements for machine vision lens are different from the other areas. In order to guarantee the measurement precision, the lens distortion is required to be small or even close to zero, and some workplaces also require a wide working distance, etc. This design was about a kind of optical lens based on machine vision cameras which used eight pieces of glass lenses. By fixing rear group and moving front group to realize the working distance from infinity to super close-up 0.1 m at the spatial frequency 120 lp/mm, the lens distortion was controlled within 0.1% and the MTF of full field of view was greater than 0.4. This optical system used two pieces of lens as its rear group, which was different from other structures with only one lens. It was not only good for improving optical performance, but also good for the balance and stability of the system. There was no aspherical lens or special glasses with high refractive index and high abbe number, it used common crown and flint glasses to reduce the lens cost, and the good rate of the mass production was more than 90% within the tolerance range of lens processing and assembly. This optical lens system can be widely used in machine vision especially in intelligent machine vision industry.
Obtaining water-to-air panoramic images by inverse ray tracing method
HE Dahua, LI Su, LI Yapeng
2020, 41(5): 929-937. doi: 10.5768/JAO202041.0502001
The water-to-air images of sea surface and air targets through wavy surface will be distorted. In order to quantitatively analyze the effect of sea surface waveform on image distortion, an ideal water-to-air imaging model was established so as to obtain the panoramic image through the waveform. Firstly, based on the given imaging model, the main-ray inverse tracing method was used to calculate the direction vector of overwater refracted ray corresponding to the underwater incident ray by Snell’s law, and the corresponding relation of objective image between the target point on the celestial sphere and the single pixel point on the imaging target surface was obtained. Then, all the pixel points on the imaging target surface were traversed, and a water-to-air panoramic image was formed. Finally, based on the four kinds of special waveform, the water-to-air panoramic image of sky circular target and background was calculated in MATLAB environment. The calculation results show that the water-to-air panoramic image can be effectively calculated by the inverse ray tracing method and can be quantitatively analyzed the image distortion degree by adjusting the waveform parameters. The main-ray inverse tracing method is suitable for analyzing the distortion characteristics of the water-to-air panoramic image with first-order guided waves, which lays a foundation for studying the distortion characteristics of water-to-air image under more complex waves.
Study on calibration method of grating projection 3D measuring system
ZHU Yongjian, HUANG Zhen, MA Junfei, QIN Guofeng, QIN Yunbai
2020, 41(5): 938-946. doi: 10.5768/JAO202041.0502002
The calibration of both camera and projector becomes the key element to decide the accuracy of 3D fringe projection measurement, and accuracy of parameter calibration directly affects accuracy of the measurement. By analyzing the imaging degradation model of mark points, a sub-pixel edge detection method was proposed to obtain the high-precision edges based on the combination of Gaussian curve fitting and edge partial area effect, and thus to improve the accuracy of mark point detection. A quick sort matching method of mark points was presented based on the image rectification technic by way of perspective transformation, and the high-precision camera calibration was finished rapidly. Furthermore, by analyzing the phase error in projector calibration, a linear interpolation method was proposed based on radial basis function in order to improve the phase accuracy of circle center of mark points. Then the experimental results show that the edge residual error of mark points is 0.087 1. Compared to the Gaussian curve fitting method, its accuracy is improved by 41%, the average re-projection errors of camera calibration is 0.052 4 pixels, and the re-projection error of projector is 0.120 3 pixels. Compared to the bi-linear interpolation method, its calibration accuracy is increased by 23.9%.
Image dehazing based on side window box filtering and transmittance correction
CHEN Guangfeng, WANG Junzhou
2020, 41(5): 947-955. doi: 10.5768/JAO202041.0502003
Aiming at the problems of color oversaturation phenomenon and inaccurate image initial transmittance estimation in the haze line prior dehazing algorithm, an image dehazing algorithm based on side window box filtering and transmittance correction was proposed. In order to solve the problem of missing edge detailed information caused by inaccurate initial transmittance estimation, firstly the method of the non-local total generalized variation (TGV) regularization was used to estimate the initial transmittance, and the second-order non-local TGV regularized device was used as the regular term to ensure the outliers caused by the noise and ambiguity between image color and depth had robustness. Then, the initial transmittance was optimized by using the edge window filtering algorithm, in this way the texture information and edge information in the image were preserved. Finally, the original image without haze was restored by using the atmospheric scattering model and the multi-angle optimized transmittance. The experimental results show that the proposed algorithm can solve the color oversaturation of the image and the edge detailed texture information loss, and there is no hue shift and halo effect. In the qualitative evaluation, the restored image has a good visual effect, and in the quantitative evaluation, the evaluation indexes of the image after dehazing based on the proposed algorithm are higher than that based on the haze line prior algorithm.
Image denoising algorithm based on dual-branch modified codec
QI Faguo, ZHANG Haiyang, LIU Chun, ZHAO Changming, ZHANG Zilong
2020, 41(5): 956-964. doi: 10.5768/JAO202041.0502004
Aiming at the problems of the traditional image denoising algorithm such as difficult multi-noise removal, complex deep convolutional neural network denoising model network and long training time, a dual-branch modified codec(DMC) network based on auto-encoder structure was proposed to achieve the high-efficient image denoising. One of the dual branch structure used the down-up sampling to eliminate the point noise, the other focused on the macroscopical image restoration and artifacts removal, and the residual structure was used to integrate at the end to realize the mixed noise denoising of the digital image. The experimental results show that for the image test set of the mixed noise containing Gaussian noise with standard deviation of 15 and mean value of 0, salt and pepper noise as well as shot noise with noise density of 5%, compared with the peak signal-to-noise ratio of the input mixed noise image, the experimental denoising effect is improved by 5.3% on average. Compared with the 12-layer full convolutional neural network, the denoising effect is equivalent and the training speed is increased by about 25.4%, which embodies the advantages of its lightweight. The experimental conclusions indicate that compared with the deep convolution neural network, this method has the advantages of fast training speed and simple network; compared with the traditional image denoising algorithm, it has better noise removal effect. This algorithm can be applied to the end denoising of lightweight vision platform.
Reconstruction and localization of radioactive area fusing images from Kinect and γ camera
WANG Gang, XIAO Yufeng, ZHENG Youneng, TIAN Xinghao
2020, 41(5): 965-972. doi: 10.5768/JAO202041.0502005
Aiming at the visualization requirements of radioactive distribution information during the decommissioning of nuclear facilities and nuclear emergency disposal, a reconstruction and localization method of radioactive area fusing the image information from Kinect and γ camera was proposed. First, a combined imaging model of Kinect and γ camera was constructed and its joint calibration was implemented based on the special imaging method of γ camera. Second, based on the visual map construction method, a dense point cloud map of the radioactive environment was established and the pose of Kinect was obtained. Then, the radioactive distribution information was extracted from the γ camera images, and the point cloud of the radioactive area in the map was calculated according to the camera combination model. Finally, the 3D localization of the central area for γ camera imaging was performed based on the minimum bounding box. In the experiment, by synchronizing the Kinect and γ camera data with spatial alignment, the fusion of 3D distribution reconstruction model and radioactive scene map of the single point source was realized in the case of a few γ camera images. The root-mean-square error of the point source localization is 0.11 m in a laboratory environment of 8 × 12 m2 , which verifies the effectiveness of the proposed method.
Image encryption lossless recovery method based on QR code and arithmetic coding
BAI Xing, WANG Jing, WANG Jinchao, ZHOU Xin
2020, 41(5): 973-977. doi: 10.5768/JAO202041.0502006
The QR code is introduced into the optical image encryption system as a data container, which can remove the speckle noise generated by the optical system when the image decryption is carried out, so that the decrypted image can be restored without loss. It is a very ideal and practical method for removing the noise. However, due to the limited storage capacity of QR code, only a few letters, short sentences or a very small(32×32 pixel) grayscale image can be stored, which seriously restricts the further application of this technology. In order to store a larger grayscale image into the QR code, an image lossless compression method based on arithmetic coding was proposed. First, the grayscale image was read as the binary data in the form of a file. Then, converted it to decimal data and compressed it into the binary data by using the arithmetic coding. Finally, converted it to decimal data again. The experimental results show that this method has high compression efficiency, which can store a 64×64 pixel image with rich grayscale values into a 31-version QR code for encryption and decryption successfully.
Phase unwrapping errors correction for phase-encoding based on fringe projection profilometry
LIU Lu, PAN Yanjuan, XI Dongdong, WANG Yuwei, TANG Qixing
2020, 41(5): 978-983. doi: 10.5768/JAO202041.0502007
Phase-encoding method is a phase unwrapping method commonly used in the fringe projection technology. However, due to the influence of the random noises, image sampling and system defocusing, it is prone to break the corresponding relation between the fringe order and the wrapped phase, which may cause the phase unwrapping errors. According to its distribution characteristics, a phase unwrapping errors correction method with an additional binary fringe was proposed. The half-period dislocation was existed between the codewords of the binary fringe and the phase-encoding fringe, which made the calculated two groups of fringe order values complementary, and the phase unwrapping errors could be effectively eliminated by using the complementary. Both simulation and experimental results show that the proposed method can accurately recover the absolute phase of the measured objects, which has higher reliability.
Surface scratch detection of mobile phone screen based on machine vision
ZHANG Jianguo, LI Ying, QI Jiakun, JI Tiantian, LIU Jun
2020, 41(5): 984-989. doi: 10.5768/JAO202041.0502008
Aiming at the problem of irregular shape and low contrast of the scratches in the image of mobile phone screen, a method based on machine vision was proposed to detect the surface scratches of mobile phone screen. Firstly, the PatMax algorithm and affine transformation were adopted to preprocess the screen images of mobile phone. Then the shear transformation was used to decompose the image into two parts: low frequency and high frequency, the element shapes in four directions of 0°, 45°, 90° and 135° were constructed to perform gray-scale closing operation on the low frequency part, and the N × M median filter denoising operation was performed on the high frequency part, the enhanced image was generated by the inverse shear transformation. Finally, the improved Otsu double threshold method was used to extract the target. 450 pieces of mobile phone screen images were randomly selected for experiments, and the highest detection rate is 98.7%. The results show that this method can effectively enhance the detail information of the images, which greatly guarantees the integrity of the scratch defects.
Study on simulation method of intercept probability for ultra-low-altitude targets by antiaircraft gun TV tracking system
SHI Hailong, LIAO Xubo, WANG Jingjing, WU Yanlin
2020, 41(5): 990-996. doi: 10.5768/JAO202041.0502009
In view of the problem that the antiaircraft gun TV tracking system can not assess the intercept probability of ultra-low-altitude targets by the actual assembling method, the factors affecting the intercept probability were analyzed, such as the ground image and the target were simultaneously in the field of view of the photoelectric system and affected the image processing of the photoelectric system. By constructing the software and hardware environment, a simulation test method based on the three-dimensional virtual test field was proposed. The typical test case was constructed and used in the test of the antiaircraft gun TV tracking system. Firstly, the video was captured by the simulation system, and then the image was input into the video tracker for processing. By observing whether the tracking state was stable in the output video or not, it was qualitatively or quantitatively determined whether the target could be intercepted. This method was applied to the test of a certain wheeled missile-gun combined with air defense weapon system, and the validity of the method was verified.
Research on spatial observation data fusion method based on array photoelectric system
ZHAO Juncheng, LIU Jianping, YUAN Liang
2020, 41(5): 997-1004. doi: 10.5768/JAO202041.0502010
Since the array-type network has the advantages of large coverage area, high reliability and strong adaptability of the environment, the coordinate conversion and data fusion method based on the observation data of the array photoelectric system was proposed according to the information of azimuth and pitch angle of the target changing continuously with time obtained by the reconnaissance equipment in the network. The m×n arrays station arrangement network system was used by the reconnaissance station. When the target entered into the surveillance coverage area, each reconnaissance station observed in all directions. The obtained target angular position information and the time data were sent to the central station in real-time for coordinate transformation and data fusion processing, which achieved the fast detection and coordinate positioning of the spacial target. Meanwhile, the related algorithm software was designed in the outfield experiment, and the reconnaissance observation of the airspace target was completed under the 1×3 reconnaissance array. According to the data processing results of the central station, the 3D tracks of the measured target were set up in real-time. The experimental results show that the proposed coordinate conversion and data fusion method can effectively improve the practical application ability of the array photoelectric system.
Misalignment analysis of cylindrical outer surfaces in interferometric measurement
XU Shuai, HAN Sen, WU Quanying, ZHANG Linghua, WANG Quanzhao, CHEN Qiubai, WANG Yan
2020, 41(5): 1005-1013. doi: 10.5768/JAO202041.0503001
A special round reflector can be used in the Fizeau interfermeter system to achieve the one-time measurement of the cylindrical outer surfaces roughness. However, the relative spatial position of the reflector and the cylinder to be tested is difficult to accurately determine, so the measurement misalignment error will be introduced, which will affect the accuracy of the measurement results. In order to eliminate the errors, the types of errors and causes should be concretely analyzed. The light propagation path was studied, and the mathematical model was established. In cylindrical coordinate system, the relations of offset misalignment error, rotation misalignment error, processing angle error and measurement of the optical path difference were obtained. The Matlab software was used for simulation, and the interference fringes corresponding to the three kinds of misalignment errors were plotted. The interference fringes with errors introduced were analyzed, and the experimental results were compared to reduce the effect of error on measurement results. Finally, the morphology information of the cylindrical outer surfaces was obtained.
Research on influence of surface microstructure on plane blackbody reflectance
MA Yuxuan, FENG Guojin, LIU Zilong, ZHANG Qiaoxiang, ZHENG Chundi, WU Houping, GAN Haiyong, LIANG Fengchen, LI Yuxiao
2020, 41(5): 1014-1019. doi: 10.5768/JAO202041.0503002
In order to study the influence of different microstructures on the plane blackbody reflectance, 40 kinds of plane blackbody samples with surface microstructures composed of different cone gear types (square cone and circular cone), height and density were designed. The same process was adopted on the samples surface, and the same type of surface absorption coating was sprayed to reduce the surface reflection. The reflectance of the samples in the visible and near-infrared bands was measured by the spectrometer. The measurement results show that the microstructure can reduce the reflectance from 1.4% in the plane state to nearly 0.4%. When other conditions are consistent, the higher the height of the cone gear and the denser the cone gear, the lower the reflectance of the plane blackbody; different cone gear types have no significant effect on the reflectance; compared with the simulation value obtained by the Tracepro, the higher the height of the cone gear, the denser the cone gear surface, the greater the relative error, and the relative error is in the range of 10% ~ 65%.
Profile measurement of red blood cells based on simultaneous phase-shifting microscopic interference
XU Junyi, YUAN Qun, GAO Zhishan, XU Yao
2020, 41(5): 1020-1025. doi: 10.5768/JAO202041.0503003
The profile of red blood cells is an important index for the prevention and diagnosis of various diseases in the medical field. A simultaneous phase-shifting microscopic interference method was proposed to realize the dynamic measurement of the profile of red blood cells. A transmission-type microscopic interference imaging system was set up to measure the red blood cells of New Zealand rabbit with a diameter of 7 μm~8 μm, and a maximum height of 2 μm in a simulated microvessel with an inner diameter of 100 μm. Aiming at the microvesse environment in which the red blood cells were located, a method of extracting the profile of red blood cells based on the phase subtraction of microvessels and a correction method of imaging magnification were proposed. The average diameter and maximum height of the red blood cells in the simulated microvessels are obtained by experiments, which are 7.757 μm and 2.022 μm, respectively. The potential of this method in vivo measurement of RBC profile has been verified.
Research on high precision MRTD testing and calibration technology
WANG Xuexin, YANG Hongru, WU Lipeng, YAN Xiaoyu, GUO Yu, LI Siwei
2020, 41(5): 1026-1031. doi: 10.5768/JAO202041.0503004
The testing of the imaging parameter minimum resolvable temperature difference (MRTD) for infrared thermal imager was studied. Firstly, the testing method and device of the MRTD as well as the working principle of the evaluation system for infrared thermal imager were introduced. Then, in the process of MRTD testing, the influence of the testing position, differential blackbody temperature difference, differential blackbody emissivity and optical system geometrical aberration of infrared thermal imager on the testing results was analyzed in detail. Aiming at these problems, a method of calibrating the temperature difference of the infrared thermal imager evaluation system by using the infrared scanning radiometer was proposed. This method was used to test the MRTD of the infrared thermal imager at a certain spatial frequency, and the testing results were given to provide a reference for the MRTD parameters accurate testing of the infrared thermal imager.
Distortion consistency correction technique for ultra-wide field of view off-axis optical system
ZHAO Xiting, ZHANG Chao, JI Yi, LIU Hui, JIAO Wenchun, HUANG Yang, LI Chongyang, ZHANG Zhifei
2020, 41(5): 1032-1036. doi: 10.5768/JAO202041.0503005
In order to meet the requirements of ultra-wide field of view and high resolution dynamic monitoring in coastal zone, high resolution and wide coverage has become an important development trend of spatial optical remote sensors. The combination of two cameras was adopted by the HY-1C/D satellite coastal zone imager to realize the large width. The single camera is an 32° off-axis optical system with an ultra-wide field, and the camera has a large arc distortion. The distortion consistency correction technique for ultra-wide field of view off-axis optical system was mainly studied. The adjustment method of multivariate simulation-high precision measurements-interactive iteration was proposed, and the multivariable full-link simulation calculation with image quality, visual axis and distortion was carried out. Through the high precision distortion measurement system, the interactive iteration adjustment of the distortion compensation was realized, the problem of uncontrollable distortion in lens adjustment stage was solved, and the double camera distortion consistency control precision was better than 0.1%, which completely meet the test technical requirements. The results show that this method is reasonable and feasible.
Simulation and verification of longitudinal chromatic aberration for optical system
ZHUANG Jincheng, ZHANG Qiyuan, WANG Fang, WU Peng, WANG Haoyu, WANG Quanzhao, WU Quanying, HAN Sen
2020, 41(5): 1037-1046. doi: 10.5768/JAO202041.0503006
In ordinary focal length measurement, the measurement accuracy is usually affected by the longitudinal chromatic aberration because of the different design wavelengths between the optical system and the testing equipment. In order to solve this problem, the variation rule of longitudinal chromatic aberration for optical system was established, and the Conrady formula and apochromatic characteristic formula used to express the functional relationship of longitudinal chromatic aberration in the 400 nm~1 000 nm wavelength were determined. According to the linear relationship characteristic of the optical system between defocus amount of near-focus and position, the focal length position at 5 different wavelengths was measured by using Fizeau interferometer to obtain the longitudinal chromatic aberration curve of the single lens and the double cemented lens. Experimental results show that the longitudinal chromatic aberration function relationship of the monochromatic system complies with the Conrady formula, and the longitudinal chromatic aberration function relationship of the achromatic system matches the achromatic characteristic formula in the 400 nm~1 000 nm wavelength. The research provides new ways and references for the theoretical calculation and accurate detection of focal length.
Study of measurement technique on military LCD under strong light
YUAN Linguang, LI Zhengqi, ZHAN Chunlian, LU Fei, LI Yan, WU Lipeng, YOU Yue, CHEN Juan, DONG Zaitian
2020, 41(5): 1047-1052. doi: 10.5768/JAO202041.0503007
In order to meet the requirements of evaluating the quality and reliability objectively and accurately for military LCD, a kind of detection device for military LCD under strong light which illuminance can up to 105 lx was developed. First, the design of the key components such as strong light source、response time detection module and big triaxial detecting platform were described. The critical detection methods about response time、brightness uniformity and display normally at high temperature were then studied. Finally, a rugged LCD was detected, the test result of experiment proves that the measurement accuracy of response time is better than 3%.
Effect of double-layer phosphor coating on LED light output of COB encapsulation
FU Zhihong, WU Ningjie, TIAN Youqiang, GUO Pengcheng, WANG Hong
2020, 41(5): 1053-1059. doi: 10.5768/JAO202041.0505001
In order to improve the output of LED light, a double-layer phosphor coating structure was designed based on the traditional phosphor coating. By studying the concentration of the upper-lower coating layer and the upper coating amount, the effect of the double-layer coating structure on the LED light output of the chips on board (COB) encapsulation was explored. The results show that when the current is 440 mA, a white light LED with a COB encapsulation structure of 15 W is finally realized in the experiment: 1) When only yellow phosphor is coated, the upper-lower rubber powder ratio is 14.2~28, and the volume of the upper coating layer is 0.8 times than that of the lower layer, the LED luminous flux of the COB encapsulation is 2 179 lm, the luminous efficiency can reach to 145.3 lm / W, the color rendering index is 63, and the maximum increase in light output is 7.82%. 2) The phosphor is adjusted to the combination of yellow-green phosphor and red phosphor, and the final color temperature, light efficiency and color rendering index are 4 854 K, 129.7 lm/W and 82.1, respectively. Therefore, the double-layer phosphor coating structure can improve the optical performance of the COB-encapsulated LED, which has certain application value for the actual production.
Fisheye lens design based on small-sized projector with 4k resolution
LIU Xiaochan, CHEN Chen, SHAN Hong, LIU Hongjun, GAO Song, SONG Tao, LI Weishan, ZHANG Yu
2020, 41(5): 1060-1066. doi: 10.5768/JAO202041.0505002
Based on a small-sized projector with 4k resolution, an easy processing fisheye lens with low cost, small diameter and high resolution was designed. Through rational selection of structure, focal power distribution, aperture position setting, lens shape adjustment, materials optimization and match, the image aberration was fully corrected. The lens only consist of nine glasses, with the field angle of 175°, F# of 2.2, back focal length of 39.8 mm. At the Nyquist frequency of 131 lp/mm, the MTF of 1.0 field is 0.3, the MTF of other fields are all above 0.43. All the technique parameters meet the requirements of using the projector. The Monte Carlo analysis results show that all the tolerance is in the normal range that is feasible to process, hence the lens is fit for batch production and assembly.
Design of infrared target system for outfield
XIA Tianyuan, SHUAI Hongjin, QIU Yafeng
2020, 41(5): 1067-1073. doi: 10.5768/JAO202041.0506001
In order to realize the minimum resolvable temperature difference(MRTD) test of infrared detector in outfield, the principle and process of MRTD were described. Combined with the technical means in the past, a set of infrared target system for outfield was designed. By using the blackbody as the target source, the difficulty of control was reduced; by using the rotating target wheel to switch different spatial frequencies, the size of the blackbody was reduced; by using the 2D regulating mechanism, the azimuth and pitch angle of the target could be adjusted manually. The infrared target system can change the temperature from 5 ℃ to 100 ℃, and the target surface temperature inhomogeneity is less than 1 ℃. It can provide 12 groups of MRTD test targets with different spatial frequencies. After the finite element analysis, it is proved that the whole system has good stability and can meet the needs of outfield MRTD test.
Nonuniformity analysis and correction of DMD imaging in infrared target simulation system
SU Yuyang, WANG Zhile, LU Min, ZOU Wei
2020, 41(5): 1074-1081. doi: 10.5768/JAO202041.0506002
The infrared target simulation system based on the digital micromirror device (DMD) has the advantages of high resolution, high frame rate and large temperature range, which can detect and evaluate the working performance of the infrared detection system economically and effectively. In order to study the influence of the structure design for illumination system on the imaging uniformity and reduce the illumination uniformity of the image surface in the infrared target simulation system based on the DMD, a method to eliminate the imaging nonuniformity was proposed. In which the structure parameters of the DMD illumination system were analyzed and designed, the ratio of the imaging beam cross-sectional area was taken as the relative illumination index, the mathematical model was established with the software for numerical simulation, and the structure parameters which could eliminate the illuminance nonuniformity caused by the vignetting was obtained. The relative illuminance distribution of each point on the image plane was ranged from 8.75%~1; the results of the theoretical analysis were verified by the TracePro, and the relative illuminance distribution of each point on the image plane was ranged from 90.91%~1, which was consistent with the theoretical analysis results. It was proved that in the case of the rational design of the structure parameters for DMD illumination system, the image plane illuminance nonuniformity caused by the vignetting could be reduced effectively, which provided a reference for the design of structural parameters for infrared target simulation system and image plane illuminance analysis.
Effect of incidence angle on fluorescence properties of colloidal infrared quantum dots thin film
ZHAO Kang, GENG Rui, YANG Mingqing, CHEN Qingshan
2020, 41(5): 1082-1088. doi: 10.5768/JAO202041.0506003
The excellent optical properties of colloidal infrared quantum dots make their fluorescence characteristics have a wide application prospect. In practical applications, the colloidal infrared quantum dots usually need to be packaged into the form of thin film to maintain the stable fluorescence characteristics. However, the change of the dispersed form of quantum dots may lead to reduction of the fluorescence efficiency and change of the fluorescence angle characteristics. Thus, the detection system for infrared quantum dots fluorescence intensity was established to study the fluorescence distribution of colloidal infrared quantum dots thin film under excitation light incident in different angles. The experimental results show that when the angle between the excitation light and the sample surface is within a large range of 10°~170°, the fluorescence emergence with fluorescence peak intensity of 70%~80% can be detected in both reflected and transmitted fluorescence regions. The intensity difference between reflected fluorescence and transmitted fluorescence in this range, as well as the change law of fluorescence intensity varies with the excitation light incident angle are related to the concentration and distribution form of quantum dots in the samples, respectively. In addition, with the enhancement of the incident laser energy, the flat range of the sample emergence fluorescence intensity to the change of incident angle is further expanded.
Infrared weak small target detection algorithm based on embedded GPU
FAN Pengcheng, ZHANG Weiguo, LIU Wangang, ZHANG Wei, HUANG Weidong, LIU Guodong, XU Xiaofeng
2020, 41(5): 1089-1095. doi: 10.5768/JAO202041.0506004
The infrared weak small targets have few target pixels, low target contrast, high imaging frame rate, large amount of image data, and strong real-time detection. Aiming at the characteristic that the infrared weak small targets detection algorithm was suitable for the GPU parallel computing, the parallel optimization was implemented on the Jetson TX2 of the embedded GPU platform, and the optimized design was mainly reflected in the following three aspects: detection algorithm design, memory access, and debugging optimization. The experimental results show that for the infrared videos with a resolution of 640×480 pixels, the target detection algorithm after parallel optimization can complete the calculation in 10 ms, which meets the requirements of real-time processing.
Simulation and experimental study of LDA Zigzag side-pumped polygonal thin-disk laser amplifier
BIAN Shengwei, QIU Jisi, TANG Xiongxin, CHEN Qiao, GE Wenqi, LIU Hao, WANG Haocheng, LIU Yueliang, CHEN Yanzhong, FAN Zhongwei
2020, 41(5): 1096-1107. doi: 10.5768/JAO202041.0507001
A laser diode array (LDA) zigzag side-pumped polygonal thin-disk laser amplifier configuration was introduced. The three-dimensional ray tracing method was used for the detailed simulation, and the pump coupling structure of this amplifier system was optimized and designed. The effects of the doping ion concentration of polygonal gain medium and the side cutting angle on the pump light distribution in medium were mainly studied. Under the condition that the crystal thickness is 1.5 mm and the end face diameter is 16 mm, when the side cutting angle in the range of 35° to 65° and the Nd3+ doping concentration in the range of 0.20 at.% to 0.30 at.%, the Nd:YAG polygonal thin-disk has relatively uniform distribution of the pump light in simulation, and the pump light distribution uniformity is better than 0.1. The flat-topped distribution of fluorescence and gain distribution are also obtained in the experiment. The uniform flat-topped distribution of energy storage in medium is conducive to the realization of high power and high beam quality laser output, which provides many important references for the design and experiments of the zigzag side-pumped polygonal thin-disk laser system.
Correlation analysis of gray scale and geometric features of femtosecond laser spot
WANG Fubin, SUN Zhilin, WANG Shangzheng
2020, 41(5): 1108-1116. doi: 10.5768/JAO202041.0507002
During the processing of femtosecond laser ablation of monocrystalline silicon, the effective gray area in the spot image collected by the charge coupled-device (CCD) camera was difficult to distinguish with the background. In order to solve this problem, a method combining the principal component analysis with the adaptive histogram equalization of limited contrast was proposed to enhance the spot image, and then a detrending cross-correlation analysis method was proposed, which analyzed the long-range correlation of gray features and geometric features for the spot sequence images. The results show that the gray features of the spot sequence images have a strong long-range correlation with the spot texture contrast and the spot area, and they show a strong inverse correlation with the texture homogeneity. The correlation relationships are used to predict the gray features in the subsequent micro-groove processing.
Particle size detection of coffee powder based on laser induced voltage technology
LIU Xuecong, MIAO Xinyang, ZHAN Honglei, ZHU Mingda, ZHANG Shanzhe, ZHAO Kun
2020, 41(5): 1117-1121. doi: 10.5768/JAO202041.0507003
The size of the coffee particles directly affects the quality of the finished coffee, therefore, efficiently identifying the size of the coffee powder particle size is particularly important for the identification of coffee quality. In the range of 89 μm ~140 μm, the laser-induced voltage (LIV) technology was used to detect the Yunnan small-grain coffee powder with different particle sizes. The coffee powder with different particle sizes exhibited different LIV responses, and its signal amplitude, response time, half-width, and other parameters were significantly different. As the particle size of the coffee powder gradually increased, the LIV signal decreased first and then increased to a minimum of 104 μm~107 μm. The response time and half-width of the signals also varied with the particle size, with positive and negative correlation, respectively. The results show that the laser induced voltage technology is more sensitive to changes in the particle size of the coffee powder, which is expected to be an effective detection method for the particle size of the coffee powder.
Research on curvature model and transmission characteristics of hollow micro-bottle resonator
HOU Fengyu, WANG Zijie, YU Yang, SUN Hang, YANG Yong, ZHANG Xiaobei
2020, 41(5): 1122-1128. doi: 10.5768/JAO202041.0508001
The curvature change model of the hollowed micro-bottle resonator was proposed and the influence of curvature on its transmission characteristics was studied. Firstly, the distribution of the whispering-gallery mode in the micro-bottle resonator was analyzed by the simulation. The restriction to the whispering-gallery mode by the micro-bottle resonator became stronger with the increase of curvature, which resulted in the higher energy of the internal light field. Then, the hollowed micro-bottle resonators with different curvature were fabricated by controlling the discharge times of the fusing splicer. And according to the equation of ideal gas state, the curvature model in the fabrication process was derived and the variation trend of the curvature for hollowed micro-bottle resonator with the discharge times was studied. The experimental results show that the quality factor can be enhanced with the increase of curvature, which can reach to 7.26×105. This conclusion has important value in improving the quality factor of the resonator.
Simulation of Fabry-Perot strain sensor based on tapered fiber Bragg grating
HAO Zijian, PU Shengli, LI Yongxi, LI Dihui, HAN Zhongxue
2020, 41(5): 1129-1136. doi: 10.5768/JAO202041.0508002
In order to solve the problems of small free spectrum range or low interference fringe fineness, a strain sensing structure and its improved scheme of Fabry-Perot cavity based on single tapered fiber Bragg grating was proposed. By utilizing the characteristic of reflecting different wavelengths at different positions of the chirped fiber Bragg grating, the Fabry-Perot cavity was formed with a continuous variation of cavity length with wavelength, and the infinitely-great free spectrum range as well as the high resonance valley fineness was obtained. Numerical results show that the strain sensing sensitivity is positively related with the lumbar region diameter and grating region length of tapered fiber. In the range of 0~300 με, the strain sensing sensitivity is obtained to be 7.05 pm/με when the lumbar region diameter is 3/25 of the fiber diameter and the grating region length is 30 mm. The results have some reference value for the design of other interferometric sensing structures.