2019 Vol. 40, No. 5

Oe System and Engineering
Design of underwater bionic polarization imaging optical system
LIU Qingqing, JU Caihua, MING Mei
2019, 40(5): 717-722.
Under the influence of the optical properties of water, in order to detect underwater targets in real time, by studying the principle of visual polarization imaging of mantis shrimp, mimicking its unique compound eye structure, and using the amplitude and aperture-based segmentation techniques, a new underwater real-time polarization imaging system was designed. The combination of a four-channel array structure and a two-channel array enabled the real-time imaging of underwater targets using circular polarization and linear polarization techniques. The design of the system was realized by ZEMAX software, and the focal length is 35 mm, the F number is 4, the working wavelength is 436 nm~656 nm, and the half angle of view is ±2.5°. The designed results indicates that MTF> 0.7(@ 60 lp/mm), system dispersed spot < 9 μm, distortion is less than 0.5%, which can meet the target requirements.
Modeling and simulation analysis of PIN photodetector
ZHANG Hui, KE Chenghu, LIU Zhaohui
2019, 40(5): 723-730. doi: 10.5768/JAO201940.0501002
In order to optimize the response characteristics of PIN photodetectors to incident light signals, according to the carrier rate equation and considering the parasitic parameters of the chip and the parasitic parameters of the package, the equivalent circuit model of the photodetector was derived. In addition, the effects of reverse bias voltage, I-zone width, photosensitive surface, chip parasitic resistance and capacitance, package parasitic resistance, capacitance and inductance on the pulse response characteristics and frequency response characteristics of photodetectors were simulated. The results show that by increasing the reverse bias voltage, reducing the photosensitive surface and parasitic parameters (chip parasitic capacitance and resistance, package parasitic capacitance and resistance), selecting the appropriate I-zone width, , using the resonance effect of the lead inductance, it can suppress the waveform response to generate waveform distortion as well as improve the frequency response bandwidth.
Gas sensor based on corner cube prisms
XIAO Shaorong, HUA Dong
2019, 40(5): 731-737. doi: 10.5768/JAO201940.0501003
A gas sensor absorption cell was introduced which was made of two corner cube prisms. The stability and sensitivity of the cell were improved using the reflectivity character and the senseless to tilting of light beam. The transmission characteristics of light beam were analyzed with geometric optics. Moreover, the transmission equation of probing light and the measurement equation of the system at both single-wavelength and dual-wavelength were put forward, and a gas concentration detection system was constructed. It is concluded that the times N of probing light traveling back and forth in the cell is determined by the distance between axes of the two corner cube prisms, the sensitivity for differential optical absorption spectroscopy(DOAS) is proportional to the times N. The sensor was used to detect concentration of methane.The results show that the inspection threshold of the cell approaches 50 ppm for methane at N is 3.
Research on controllable preparation and optical properties of gold catalysed silicon nanowires
WANG Shanshan, YIN Shujing, LIANG Haifeng, HAN Jun
2019, 40(5): 738-745. doi: 10.5768/JAO201940.0501004
Silicon nanowires are the typical representative of new one-dimensional semiconductor nanomaterials. The ultrathin anodic aluminium oxide membrane was employed as the template for reproducing ordered ultrathin gold nanomeshes array. The silicon nanowires arrays with controllable size and shape distribution were prepared by wet etching of monocrystalline silicon under the catalysis of gold film, and their optical properties were studied. The results show that the chemical properties of gold instead of silver as a catalystare more stable than that of silver, which can effectively avoid the secondary etching and overcome the structural damage of silver film at higher temperature or longer etching time, and the silicon nanowires arrays with regular shape and controllable size can be obtained. The reflectivity and transmissivity of the arrays in the band of 400 nm~1200 nm were tested, and the similarities and differences of mechanism between the gold film catalysis and the conventional method were compared. The test results indicate that, compared with conventional metal-assisted chemical etching, the size and distribution of silicon nanowires arrays prepared by the gold film catalytic method proposed are more uniform and controllable, and the anti-reflective properties are effectively improved in broadband spectrum.
Visible light indoor parking lot positioning navigation system based on LED lighting
LI Jin, MO Juming, FANG Junjian, LIN Puxi, CHEN Zhaojie, LV Quanchao, LIANG Funian, ZHENG Huadan, ZHONG Yongchun, FANG Junbin, CHEN Zhe
2019, 40(5): 746-750. doi: 10.5768/JAO201940.0501005
Indoor parking lot is an important part of static traffic; however, because of the lack of effective indoor positioning technology, there are currently problems in parking navigation and reverse car finding. This paper proposes a visible light positioning and navigation system for indoor parking lot based on LED lighting, which realizes parking navigation for vehicle and reverse car finding for pedestrian. It has the advantages of fast positioning speed, high positioning accuracy and "lighting and positioning dual use". The experimental results testing on the spot shows that the highest positioning accuracy of system can reach 7.5 cm and the system can support positioning and navigation at speed up to 17 km/h for vehicles or pedestrians.
Design of underwater imaging optical system
ZHANG Xinting, KANG Lei, WU Qianqian
2019, 40(5): 751-755. doi: 10.5768/JAO201940.0501006
After investigating the current status of underwater imaging system, the main factors affecting underwater imaging distance and quality were analyzed, namely backscattering.It breaks through the traditional imaging mode of underwater imaging system with multi-detector and multi-field of view.An underwater imaging optical system with large relative aperture and large field of view was designed by using optical design software Zemax.The system uses only one photoelectric detector with a wavelength of 486 nm~656 nm, a relative aperture of 1/1.8, a field of view angle of 1 200, 9 lenses and no aspheric surface, which simplifies the lens processing process and cost.The size of the Airyspot in the central field of view is 3.When Nyquist frequency is 60 lp/mm, the modulation transfer function (MTF) curves of each field of view are higher than 0.7. At the same time, the high distortion caused by the large field of view system was corrected, results show that the distortion is less than 5%, and the image quality is very good.It can be widely used in underwater exploration, marine development, seabed resources exploration, underwater anti-terrorism and other fields.
Design of athermal MWIR/LWIR optical system with double-layer diffractive optical elements
YANG Liangliang, ZHAO Yongbing, CHEN Feng, YUAN Deyin
2019, 40(5): 756-762. doi: 10.5768/JAO201940.0501007
The analysis model of comprehensive polychromatic integral diffraction efficiency (PIDE) of multilayer diffractive optical elements (MLDOEs) working within a range of incident angle was established. Based on the special characteristics of achromatism and athermalization of MLDOEs, an infrared dual-band optical system with double-layer DOEs working in the 3.7 μm~4.8 μm and 7.7 μm~9.5 μm wavebands was designed. The effective focal length of the optical system is 200 mm, and F # is 2. The cooled focal plane array is 320×256 and the pixel pitch is 30 μm. The MTF is higher than 0.66 and 0.54 at the frequency of 17 lp/mm for mid-wave infrared (MWIR) and long-wave infrared (LWIR), respectively. The maximal root-mean-square(RMS) radius is less than 11.702 μm, the wavefront error is smaller than 0.191 7λ and the maximal defocus is less than the focus depth, the designed optical system realizes athermalization over the temperature range from -55℃ to 71℃. The incident angle upon the diffractive surface is within the range of 0°~5.19°, the comprehensive PIDE of the double-layer DOEs are 99.81% and 97.36% for the MWIR and LWIR waveband, respectively. The structure of the designed infrared dual-band optical system with double-layer DOEs is simple with good image quality, can be used in military detection system.
Laser white light source of its optical system analysis
KANG Jian, ZHANG Le, SHAN Yingshuang, CHEN Hao
2019, 40(5): 763-773. doi: 10.5768/JAO201940.0501008
To further promote the application of laser white light source in the fields of automobile headlights, projection and backlight, the synthesis methods of laser white light source were introduced. Besides, its key components were detailedly analyzed from three aspects: pump source, light conversion material and optical system. Through the theoretical analysis, the highest theoretical value of light conversion efficiency in the laser illumination system was 498 lm/W. However, some technical and process problems resulted in that its final efficiency was only 17%. Then, a rod-shaped (length > 10 mm) YAG ceramic (Ce < 0.1 at %) was innovatively proposed to accommodate the high lumen blue light based the summary of the light-conversion materials for high-lumen-density laser lighting system. In addition, from the viewpoint of optical design, a new lens type structure of light-conversion materials was employed to totally enhance the efficiency. Finally, after considering the distribution of related patents, the prospects and applications of laser lighting system were forecasted in the fields of laser display, visible-light communication and so on.
Study of arbitrary dispersion periodic structure using FDTD method
MA Lixian, LI Yanru, CHEN Shuai, FAN Zhenhong
2019, 40(5): 774-778. doi: 10.5768/JAO201940.0501009
The electromagnetic wave propagation problem of multilayer arbitrary dispersion periodic model was solved by using auxiliary differential equation-finite-difference time-domain (ADE-FDTD) method. The complex-conjugate pole-residue pairs were utilized to fit the parameters of any dispersive medium, and the model's dielectric constant was expressed as a formula. Furthermore, the ADE was introduced into the FDTD iteration to deduce a general formula applied on the muti-layer arbitrary dispersion model. In addition, the electromagnetic characteristic simulation of Debye, Drude and solar cell structure were respectively solved. Simulation results show that the numerical calculation results are basically consistent with the CST commercial software simulation results, which proves the validity and universality of our method.
Optical system design for on-line defects detection of optical components
ZHANG Wenxue, WANG Jihong, REN Ge
2019, 40(5): 779-785. doi: 10.5768/JAO201940.0501010
In order to realize the on-line detection of the surface defects of optical elements in the telescope system, a zoom imaging optical system for the detection of the surface defects of optical elements was introduced. Firstly, some key parameters of the zoom system were calculated according to the technical requirements of the telescope system. Then, the final result was obtained after design and optimization with Zemax software. Thewhole zoom system achieves a 6-fold continuous zoom with a focal length of 90 mm~540 mm. During the zoom process, the F number and image surface position of the system remain unchanged, and the design results show that the total length of the zoom system is 553.1mm.Finally, we analyzed the imaging quality of the system from modulation transfer function (MTF) and point sequence diagram.The MTF value of the system at each focal length is greater than 0.3 in 100 lp/mm, and the object resolution is better than 0.055 mm. The root mean square value of the diffusion spot radius of the system at different focal lengths is controlled within the airy spot radius. In addition, we also analyzed the environmental adaptability of the system, studiedthe imaging quality of the system in the temperature range of -10℃~40℃, and gave the temperature compensation scheme. The imaging quality of the whole system is good and can meet the actual demandafter compensation.
Oe Information Acquisition and Processing
Aerial image de-roping based on U-net model
HONG Hanyu, SUN Jianguo, LUAN Ling, WANG Shuo, ZHENG Xinbo
2019, 40(5): 786-794. doi: 10.5768/JAO201940.0502001
The Kuang-chi cloud platform is used to pull the airbag with a cable rope. Since the aerial photography system is suspended under the airbag, the captured image inevitably contains the rope information, which affects the image quality and needs to eliminated in the scene analysis and object detection. A rope detection algorithm based on U-net model was proposed, which introduced the separable convolution to improve the detection speed and adopted a weighted cross entropy as a loss function to solve the problem of convergence instability caused by category imbalance. The final model was able to quickly and accurately detect the rope with fewer data in less time, and then the rope image waseliminated using the fast marching method algorithm (FMM). The test results show that the mean intersection over union(mIOU) of the algorithm reaches 62.8% and has obtained good results.
Fusion detection mechanism of robust correlation filtering visual tracking algorithm
HOU Zhingqiang, WANG Shuai, YU Wangsheng, LI Youmou, MA Sugang
2019, 40(5): 795-804. doi: 10.5768/JAO201940.0502002
In order to solve the tracking drift problem caused by the correlation filtering visual tracking algorithm in complex scenes, a correlation filtering tracking framework fused with detection mechanism was proposed.A space-time regularization filter was used as a tracker, and a linear kernel correlation filter was used as a detector.When the response diagram obtained by correlating the tracker with the target was a plurality of peaks, the detector was activated to perform correlation matching on multiple peaks to obtain a retest result; meanwhile, a filter model update strategy using average peak correlation energy was used to obtain a more reliable detector, so as to improve the tracking accuracy and algorithm robustness.The experimental results on the OTB2015, Temple color 128 and VOT2016 data platforms show that compared with the tracking algorithms of better performance proposed in recent years, the proposed algorithm has better robustness and accuracy in complex scenes such as target motion blur, similar background interference and illumination changing, and both of the tracking accuracy and the success rate are improved.
Super-resolution simplification network based on densely connected structure
GAO Fei, LEI Tao, LIU Xianyuan, CHEN Lianghong, JIANG Ping
2019, 40(5): 805-811. doi: 10.5768/JAO201940.0502003
In recent years, with the development of deep neural networks(DNNs) and their application in the field of super-resolution, the effect of image super-resolution reconstruction has been significantly improved.However, the pervious works mainly focus on good performance of model, ignoring enormous parameters and huge number of computations, which seriously restricts the practical application range of deep learning methods in image super-resolution reconstruction. Aiming at this issue, we designed a novel network based on Dense Net, and our work mainly lied in 3 aspects for improvement: 1) proposing a new architecture based on densely connected structure; 2) adding 1×1 convolutional layers as a feature selector to reduce the computations; 3) exploring the relationship among the number of channels, the reconstruction precision and the calculation amount. Experiment's results indicate that our model get comparable reconstruction precision results with other convolutional neural networks model, and our model takes only half of super-resolution time compared with fast super resolution convolutional neural network(FSRCNN).
Research and implementation of real-time fog and haze video image restoration system based on FPGA
YE Mao, HUANG Pingao, LYU Yang, TANG Ning, LIU Jianwei
2019, 40(5): 812-817. doi: 10.5768/JAO201940.0502004
Aiming at the need of video surveillance and other outdoor video equipment for real-time restoration of video image under severe weather conditions such as fog and fog, an field-programmable gate array(FPGA) implementation method for fast image restoration algorithm was proposed. By appropriately reducing the complexity of the algorithm, the purpose of reducing time cost and hardware implementation complexity could be achieved.In this algorithm, a frame of video is decomposed into 3×3 small windows for operation, and a frame of video pixel calculation is replaced by a pipeline calculation of the center pixel of the window, so that each pixel's all operations are processed in 3 clock cycles, ensuring that the system can be restored in real time, and the hardware cost of the recovery module can be reduced.Experimental results show that the results of FPGA processing coincide with the results of MATLAB processing, the real-time processing resolution is 640×480, and the video can be displayed smoothly at 29 frames /s under the premise of ensuring the defogging effect.
Algorithm of crack extraction based on accumulated gradient
WEI Yongjie, GE Tingting, ZHANG Zhongqi, MA Baoqiang, CHE Jinchao
2019, 40(5): 818-822. doi: 10.5768/JAO201940.0502005
Edge extraction algorithms in digital image processing are often noise sensitive in detecting building cracks due to un-uniform illumination and the surounding affects. An accumulated gradient algorithm was presented to calculate the crack boundary. An adaptive binarization algorithm and morphology operations were adopted to obtain an image mask firstly. The mask image was acted on the original image to obtain the expanded image of the crack area. Then the image was iteratively expanded, and the gray value of the image was added to obtain the cumulative gray value.The accumulated gray between two successive images before and after expansion were subtracted, and the maximum difference was the cumulative gradient, the image before expansion was considered as the extracted crack. Experimental results show the crack can be extracted by this algorithm in complex backgrounds.
Light bar center extraction algorithm for automotive weld sealant strips
2019, 40(5): 823-828. doi: 10.5768/JAO201940.0502006
Automotive weld gluing can improve the body seal level, and it is necessary to detect the strip and obtain three-dimensional information. Laser triangulation is a widely used detection method. One of its key technologies is to accurately extract the center of the strip. However, for the black detection colloid, the strip center extraction is poorly robust, so an algorithm based on strip segmentation for Hessian matrix positioning and Gaussian curve fitting is proposed. Firstly, the overall image contrast is improved, and the noise is removed by the denoising algorithm. Then the extreme value method is used to locate the light strip, and the Hessian matrix is used to locate the center of the laser strip. Finally, the center of the laser strip is accurately fitted by the Gaussian curve.Experimental studies show that after adding white noise with a noise amplitude of 100 to the light bar image, the precision can be also controlled at the sub-pixel level, and the stability of the light bar of the black detected object can be improved.
Fog image reconstruction using target and atmospheric polarization information
ZHANG Qiang, GAO Jun, FAN Zhiguo, WANG Zhenwu, YAN Yu
2019, 40(5): 829-837. doi: 10.5768/JAO201940.0502007
Combining the difference between target polarization information and atmospheric polarization information, an image reconstruction method based on the polarization information of target and atmosphere was proposed. Int this method, firstly, the atmospheric light image and target light image are separated from the light intensity image, the atmospheric light polarization information and target light polarization information are analyzed respectively, and the polarization defogging model is constructed. Secondly, the Gaussian filtering method fused with image gradient information is used to estimate the atmospheric light intensity and target light intensity, the atmospheric light polarization degree and target light polarization degree are calculated respectively.Then, the threshold segmentation method of 3σ rule is used to estimate the atmospheric light intensity at the infinite distance in the atmospheric light image space and finally the target image can be reconstructed. Field experiments were carried out under different weather conditions.The experimental results show that the method proposed can recover the target information well in fog, rain and snow weathers, and the entropy of reconstructed image increases by about 40%, the standard deviation of gray level increases by about 90% and the average gradient and edge strength increase by 3 times.
Optical Metrology and Measurement
Algorithm of global image motion detection based on remote images and engineering parameters
LIU Haiqiu, GAO Yanwei, YAN Dejie
2019, 40(5): 838-846. doi: 10.5768/JAO201940.0503001
Identical scenes in images taken by two adjacent imaging sensors' splicing areas are essential for detecting image motion. However, images with identical scenes are not always present throughout an imaging mission, and it is still a question to detect the image motion for the period with images without identical scenes. In this study, an algorithm based on remote images and engineering parameters is proposed to detect image motion throughout an imaging mission, including the period with images without identical scenes. According to the imaging characteristics of the splicing areas, an imaging mission is divided into two periods: the period with images without identical scenes and that with identical scenes. For the first period, low-frequency image motion is first calculated by using engineering parameters, and an objective function based on the low-frequency image motion and images from slicing areas is then established to measure the deviation between image motion curve and the low-frequency component during the period without identical scenes. Steepest descent method is adopted to find the minimal solution which is taken as the optimal estimation of the image motion for the period without identical scenes. A formula is derived to calculate the image motion for the period with identical scenes by the use of the estimated image motion of the period without identical scenes. Experiments performed on XX-1 space optical remote sensor show that an image motion of about 7 pixels at 0.133 Hz is captured, and its value during the initial 226 ms, the period with images without identical scene, is detectable. Besides, the deviation at blind frequencies is reduced significantly, proving that the proposed algorithm can effectively measure the global image motion, including that during the period with images without identical scenes.
Apply of digital speckle projection in measurement of paper sheet thickness
WU Fan, WU Sijin, LI Weixian, ZHANG Yumeng, ZHU Junyi, SHA Di, DONG Mingli
2019, 40(5): 847-852. doi: 10.5768/JAO201940.0503002
Traditional measurement methods of paper sheet thickness can only measure the thickness of paper sheet at a certain single point, leading to the measurement error due to the uneven distribution of the paper sheet thickness. A new approach of paper sheet thickness measurement using digital speckle projection was proposed to address the problem of single-point measurement. The thickness and contour of paper sheet could be determined by executing the three-dimensional digital image correlation algorithm, after the speckle pattern was projected to the tested paper sheet and a speckle projection experimental system was built. The experimental result is 0.177 mm for measuring the paper which nominal value of thickness is 0.180 mm, and the repetitive experimental results show that the relative difference is less than 4%. Moreover, the full-field distribution of the paper sheet thickness is shown intuitively. In addition, the proposed method of paper sheet thickness measurement has the advantages of simple structure, non-contact full-field measurement, etc., which make the proposed means a promising approach for the measurement of paper sheet thickness during the paper production.
Laser triangulation measurement model based on least square polynomial fitting method
LU Zhigong, HE Peng, ZHI Lianjie, CHEN Wenjian
2019, 40(5): 853-858. doi: 10.5768/JAO201940.0503003
The laser triangulation method has been widely applied due to its advantages in non-contact measurement, large measurement range, high accuracy in measurement, simple structure, high adaptability, etc. However, the theoretical formula of laser triangulation is nonlinear and the parameters (a, b, θ) of optic structure in practical engineering is immeasurable. Therefore, we investigated the construction approach of the mathematical model in triangulation, and adopted the polynomial expansion approach to build the model. Under the application of least square fitting polynomial method of the solution to the model coefficient, we proposed a evaluation method according to the requirements of the maximum relative fitting residual combined with the relative coefficients for controlling the fitting polynomial order. The feasibility of the method was verified by the practical optical system, with the relative error of 0.01%. The method of least square fitting polynomial has practical guiding significance for the calibration of laser triangular displacement sensor and the elimination of systematic error.
Focal length measurement for thin convex lens based on parallel tube method
LI Xiaolei
2019, 40(5): 859-862. doi: 10.5768/JAO201940.0503004
Thin convex lenses are the most important and basic components of optical instruments. It plays an important role in many fields such as astronomy, military and medicine. The focal length is the most important characteristic parameter of optical systems such as thin lens and mirrors. Hence, it is particularly important to accurately measure the focal length of the thin lens. The methods for measuring focal length of thin convex lens are the object/image distance method, self-collimation method, optical-electrical method and parallel tube method in laboratory. Aiming at the problem of low accuracy of measuring the lens focal length by the first three methods, the parallel tube method was adopted to measure the focal length of thin convex lens and the experimental error was analyzed simply. Experimental result shows that, the method can measure the focal length of thin convex lens with high precision, the relative error is only 0.138 %. Therefore, the method for measuring focal length of thin convex lens by parallel tube method is effective and feasible.
Aspheric optimization design of fisheye lens optical system
ZHANG Xiao, LYU Lijun
2019, 40(5): 863-870. doi: 10.5768/JAO201940.0505001
Using aspheric surface to improve the imaging quality of optical system is a common means of lens design.Based on the wave aberration theory of planar symmetric optical system, the wavefront aberration contribution of the fisheye lens was analyzed. According to the variation trend of wavefront aberration with aspheric coefficient, the optical surface with outstanding wave aberration contribution was selected as the candidate for aspheric application, and then the fisheye lens system was optimized by using the optimization algorithm and the evaluation function based on the definition of the distribution of light spot diagram. By optimizing the aspheric surface of a fisheye lens example, the spot diagram range is reduced from 200 μm for the global optimization design to 100 μm, and the evaluation function value is reduced by 1 order of magnitude, which proves that the method can significantly improve the imaging quality of the lens. It can be used as a reference for how to effectively apply the aspheric surface to optimize the optical system of the fisheye lens.
New design of flexible light distribution film
WU Lin, MA Jianshe, SU Ping
2019, 40(5): 871-875. doi: 10.5768/JAO201940.0505002
A new design method of flexible display film was proposed. Because of the use of light-emitting diodes (LED) chips to make display screens, it can improve the shortcomings of conventional display screens, such as seamless splicing, low refresh frequency and relatively narrow application.If the substrate material of the display film is polycarbonate (PI) film, the printed circuit board (PCB) behind the film is also flexible, so the display screen can be flexible and can be applied to more occasions. One of the core designs of the display screen is the design of the display film. In the designed and manufactured flexible display film, the pixel spacing is 1 mm and the bending radius is less than 10 cm, We need to set up isolation layer and phosphor layer, that is on the top and the other side. Finally, the simulation analysis was carried out by using the professional software of lighttools, and a series of specific simulation analysis and experiments were carried out, the bending radius of the sample with 1 mm pixel spacing is 3.1 cm. It can be seen thatthe experimental results are in good agreement with the simulation analysis, proving the design is feasible.
Design and tolerance analysis of converging lens in immersion lithography illumination system
LI Meixuan, DONG Lianhe
2019, 40(5): 876-881. doi: 10.5768/JAO201940.0505003
In order to achieve uniform illumination of the mask surface, the converging lens of an immersion lithography illumination system was designed, and the error sources of the system telecentricity were analyzed. The uniformity deviation of the designed numerical aperture of the converging lens is within 0.2%, and the image telecentricity is less than 0.2 mrad. Taking the system's telecentricity variation of 0.1 mrad, the numerical aperture uniformity variation of 0.1%, the point spread function variation of 20 μm and the focal length variation of 0.1mm as the tolerance basis values, the thickness tolerance of the converging lens is calculated to be ±0.02 mm to ± 0.05 mm and the surface inclination within 10" to 20". It is concluded that the design of the converging lens for the immersion lithographic illumination system is reasonable and the tolerance is practical to meet the non-uniformity lighting requirement on the wafer surface less than 3%.
Design and simulation of optical system for novel LED solar simulator
ZHANG Xinqiang, ZHANG Qingmao, GUO Liang, ZHANG Zhiqing, XU Yiqin
2019, 40(5): 882-886, 928. doi: 10.5768/JAO201940.0505004
In order to solve the difficult problems of collimation, irradiance uniformity and spectral matching of existing LED solar simulators, a simple, efficient and high-power optical system design method of LED solar simulator was proposed based on photoelectric integrated secondary optical design. The small angle collimating lens and the parabolic mirror were utilized to integrate the light source, and the mixing light rod and microstructure were used to homogenize the light, finally the collimating output of light was realized by the parabolic mirror. Based on the design idea of coaxial collimation, the design of the LED solar simulator was completed.In addition, the optical software LightTools was used to simulate and optimize the optical system of LED solar simulator. The experimental results show that the irradiation inhomogeneity is 2.5% and the collimation angle is 1.5° on the effective irradiation surface with a diameter of 260 mm.
Design and preparation of brightness enhancement thin film for MiniLED backlight module
WANG Yong, FENG Qibin, GUO Min, WANG Zi, LYU Guoqiang
2019, 40(5): 887-893. doi: 10.5768/JAO201940.0505005
As the fact that the traditional two-layer prism films can not enhance the brightness of the MiniLED backlight obviously, a thin film with microstructure was designed to substitute for two-layer prism films.Firstly, based on the luminous distribution and the size of the MiniLED die, the microstructure was designed into two parts. For the region as wide as MiniLED die, the microstructure was designed as the prism with 90°vertex. For the region between the two MiniLed dies, the MiniLED die was taken as an extended source and the light emitted from the two endpoints of the MiniLED die reached a certain point of the microstructure and formed an angle. The light along the bisector was collimated to the axial direction. The microstructural profile was calculated combining the Snell's law. After that, a single microstructure and array were modeled and simulated by LightTools. The simulated results show that the on-axis brightness increases by 31.3% compared with the two-layer prism films. Finally, the microstructure was fabricated by the maskless lithography device and tested by cofocal microscope. The experimental results show that the on-axis brightness increases by 25.7% compared with two-layer prism films. The thin film can help enhance brightness of MiniLED backlight module.
Optical structure design of automotive head-up display with long-distance imaging
HUANG Xingzhou, HU Shijie, TANG Guomao, YANG Ping, XU Bing, ZHANG Gaina
2019, 40(5): 894-900. doi: 10.5768/JAO201940.0505006
Aiming at the demand of automobile augmented reality-head up display (AR-HUD) with farther visual distance and bigger field of view(FOV) angle for virtual images, a virtual image display optical path was designed by using the free-form surface off-axis reflection optical path structure with a focal length of -309 mm, a visual range of 7.5 mand a virtual image FOV angle of 9.8°×5.5° for the virtual image. According to the typical human eye resolution angle of 1′, the source image display module adopted the backprojection digital light processing (DLP) micro-projection system with resolution of 854 ×480 pixel to ensure the virtual image clarity observed by the driver.The optical path of human eye and virtual image display was designed as a whole. The Eyebox(aperture stopmigration range)was used to simulate the driver's eye movement range. Results show that, for different aperture stop positions, the modulation transfer function (MTF) of the virtual image plane of the optical system is more than 0.6 at Nyquist spatial frequency of 0.33 lp/mm, and the MTF of the whole field of view is more than 0.3. In addition, Monte Carlo method was used to analyze the tolerance of the system. The MTF value of 90% of the system is greater than 0.49, which shows that the system has better tolerance ability.
Design of space optical backbone network simulation platform based on OPNET and STK
ZHANG Taijiang, LI Yongjun, ZHAO Shanghong, WANG Xingyu, WANG Weilong
2019, 40(5): 901-909. doi: 10.5768/JAO201940.0508001
The space optical backbone network is the core of China's spacial information network. In order to verify the feasibility of the network protocol, the network architecture and the key technologies in the space optical backbone network, a space optical backbone network simulation platform based on OPNET and satellite tool kit(STK) was designed.A space-based backbone network consisting of 4 geostationary earth orbit (GEO) satellites and a space-based access network consisting of 10 low earth orbit (LEO) satellites were designed.And the optical network protocol simulation model from the physical layer to the application layer and the 3 node process models of LEO, GEO and ground stations were developed, moreover, the optical backbone network was simulated and tested. The simulation results show that the maximum delay of the space optical backbone network is 5.48 s, the minimum is 0.35 s, and the global average network delay is 1.06 s. The maximum real-time throughput of the ground station is 0.88 Gbps with a minimum of 0.3 Gbps. The research results indicate that the platform can accurately simulate the function of spatial optical backbone network, meet the needs of efficient transmission of space services, and provide simulation platform support for spatial optical backbone network performance verification.
Research on theoretical model of high sensitivity fiber Bragg grating accelerometer
LIU Qinpeng, HE Xue, JIA Zhen'an, FU Haiwei, GAO Hong, YU Dakuan
2019, 40(5): 910-917. doi: 10.5768/JAO201940.0508002
A general model of fiber Bragg grating (FBG) acceleration detector was established for the two-point package model. The sensitivity and the resonance frequency's analytical expressions of the acceleration detector were deduced theoretically, the influence factors which affecting the sensitivity and resonance frequency were researched deeply, and the acceleration detector's response characteristics were discussed, which would be affected by the ratio, that the package fiber stiffness to the structure stiffness. Based on this, the restrictive relation between theacceleration sensitivity and the resonance frequency with the increasing of the equivalent mass (0~100g) was analyzed, respectively for the stiffness ratio in the range of 0~1 and 0~100. And the resonance frequency's change rules within the scope of 0~500Hz (low-medium frequency) and 0~1200Hz (medium-high frequency) were also studied. Furthermore, the package fibers were chosen 10 mm and 60 mm as the examples to analyze the influence on the above two mentioned, the sensitivity of each simulation could reach up to ~1 000pm/G, and the quality factor was introduced. This study plays a significant role in the design and comprehensive performance evaluation of the acceleration detector, and can provide theoretical references for the optimization of structural parameters.
Research on resolution test system of LLL and infrared fusion equipment
JING Weiguo, SUN Mingzhao, WANG Jiaxiao, WANG Hongpei
2019, 40(5): 918-922. doi: 10.5768/JAO201940.0509001
Based on the analysis of the resolution test system for low-light level(LLL) vision equipment and the multi-resolution time domain (MRTD) test system for infrared equipment, the conception of resolution test scheme for LLL and infrared image fusion equipment was proposed. The exiting equipment of infrared MRTD test system was utilized, the resolution test system of the LLL and infrared fusion image was established by modifying light source, incident light path and target plate, and the analysis on the scheme was conducted.Results indicate that the modified test system can both realize infrared reflection and low-light projection. The measurement accuracy of infrared temperature difference is close to 0.01 K, and the measurement accuracy of low-light illumination can reach 1 lx. The test of fusion image resolution meets the requirement of multiple decrement(1/62≈0.891).
Modeling and analysis of infrared radiation characteristics of transport aircraft skin
JIN Liang, ZHANG Haochun, LI Sen, MA Zhuang
2019, 40(5): 923-928. doi: 10.5768/JAO201940.0509002
In order to study the infrared radiation characters of C-17 transport aircraft, the body of aircraft was modeled and meshed based on the principle of infrared radiation, the structure and material of transport aircraft. The temperature distribution of skin was obtained through simulation of the flow field. Combined with the multiple occlusion algorithm of the surface, the total radiation intensity of aircraft in the infrared band(8 μm~12 μm) was calculated with different Mach numbers in different directions of sight. The result shows that when the azimuth is 0° and the speed of aircraft is 1 Mach number, the radiation intensity can increase by 32% compared with the speed of aircraft is 0.5 Mach numbers. In this view, the Mach number has a great effect on the infrared radiation intensity whose increasing main source is pneumatic heating. When detecting from the front or the back, the infrared radiation intensity peak is approximately symmetrically distributed with the zenith angle. When detecting from the side, the infrared radiation intensity distribution is relatively average. In addition, the zenith angle has little effect on the intensity of infrared radiation.
2019, 40(5)