2012 Vol. 33, No. 1

OE System and Engineering
Panoramic lens for full view monitoring
JIANG Lun, HUANG Wei, XU Wei-Cai
2012, 33(1): 1-4.
A panoramic lens for full view monitoring was designed with ZEMAX.The system consists of a concave and convex mirror group and a relay lens. The mirror group enable the lens to obtain a large field of view, and the relay lens projects the virtual image formed by the mirror group onto the detector. The effective focal length is 0.97mm,the relative aperture is 1∶1.5, field of view is 65~95in vertical direction and 360in horizontal, the wavelength spectrum is 475nm~750nm and the total optical length is 69.7mm.The result shows that the maximum f- distortion is less than 5% and the modulation transformation function at 60lp/mm is greater than 0.58, which proves that the image quality of the optical system is good. The system has large filed of view and it is simple in structure and small in volume, which meets the requirements of full view monitoring lens systems.
Optimal scheme of AOTF imaging spectrometer optical system
CHANG Ling-ying, ZHAO Bao-chang, QIU Yue-hong, WEN De-sheng
2012, 33(1): 5-8.
Compared with the traditional spectral imaging instruments, an acousto-optic tunable filter is a new type of imaging spectrometer, which can obtain target polarization spectrometer and two-dimensional spatial information. However, AOTF can only receive the beam with angle less than 5~6 in the practical application. Because of the limited receiving angle, AOTF spectral imager optical system can not achieve the large aperture and large field of view at the same time. We developed the AOTF imaging spectrometer field of view to meet the requirements of 128128 pixels and the TeO2 crystal size of 10mm10mm. Based on the features of the acousto-optic tunable filter imaging spectrometer optical system, an optimal system design was determined, the aperture stop was placed in the crystal, aperture stop size was limited by TeO2 crystal size, and the system field of view was determined by the crystal. The energy utilization ratio is improved and the signal to noise ratio of the image is increased.
Application of FSM in high accuracy line-of-sight stabilization system
XU Fei-fei, JI Ming, XIE Jing, NIU Jing, GAO Yu, XU Qing-qing
2012, 33(1): 9-13.
Fast-steering mirror (FSM) is a device used for controlling the direction of a light beam precisely. This article proposed a method to compensate the residual error of a coarse stabilized platform with FSM driven by PZT to improve line-of-sight stabilization accuracy greatly. The high precision line-of sight (LOS) stabilization system was simulated. The results of simulation showed that the stability error of coarse stabilized platform is 110rad, and the stability error after FSM compensation is less than 8 rad. This method can improve the stabilization accuracy at least one order of magnitude.
Design and simulation of confocal detection system utilizing tunable-focus liquid lens
ZHANG Yun-bo, HOU Wen-mei, ZHENG Ji-hong
2012, 33(1): 14-18.
The technology of confocal microscope is widely applied in the three-dimensional profile metrology of the micro-electro-mechanical system and semiconductor device. This paper presents a novel confocal microscpe system based tunable-focus lens. By utilizing the changeable focal length of this lens instead of the traditional scanning methods in axial displacement, the system can realize scanning in axial direction without mechanical movement and eliminate the vibration caused by the axial scan movement. It can decrease the system complexity, and reduce the cost. A displacement stage based confocal system and a tunable-focus lens based confocal system were designed, and experiments were carried out for the two systems. Experimental results show that the confocal images of in-focus and out-of-focus of the two systems are similar, furthermore, the light intensity distribution along axial direction is basically the same, and that shows this new scan method is feasible.
xPC based hardware-in-the-loop simulation of electro-optical platform systems
HUANG Xian-lin, BAO Wen-liang, LU Hong-qian, LI Ming-ming
2012, 33(1): 19-24.
In order to design and debug the stabilizing and tracking control arithmetic of an electro-optical platform system conveniently and efficiently, a hardware-inthe-loop simulation system was designed and implemented based on Matlab xPC target environment. The overall design of the system was presented, and the implementation of software and hardware was described. Through hardware-in-the-loop simulation, the model structure and parameter of the plant were identified, furthermore, proportional integral controller, correction controller, and synthesis controller were designed and tested. Vibration experiments were carried out for every control system designed to evaluate the line-of-sight stabilization accuracy. Experimental results show that the correction controller, which has the maxium gain value in the low frequency band, makes the system achieve the highest stabilization accuracy. According to experimental results, the controller which has optimal disturbance attenuation is selected.
Optical design of hyperspectral imager
JI Zhuo-xin, LIU Zhi-ying, FU Yue-gang
2012, 33(1): 25-29.
Hyperspectral imaging detection technology involves optics, spectroscopy, machinery, microelectronics, computer and other disciplines. The design of imaging spectrometer should be compact and apochromatic. Based on the aberration theory, theoretical formula of secondary spectrum was derived according to the dispersion characteristics of typical glass materials in 400 nm~1 000 nm. For a system with FOV of 7.63, F/# =5, f= 60 mm, its secondary spectrum was corrected in design with ZEMAX software. The results indicate the MTF of the imaging system is greater than 0.5 at 60 lp/mm in visible and infrared band, other aberration requirements are met as well.
Study on uv coverage of optical synthetic aperture imaging technology and optimization of aperture
LIN Xie-jia, WU Zhen
2012, 33(1): 30-36.
Based on the horizon coordinate system and angle coordinate system, the formula between interferometric array and uv coverage of optical synthetic aperture imaging was derived using coordinate rotation. An Y-type in Nanjing was taken as an example to make the observation in a specific sky area, and the Monte Carlo method was used to optimize two objective functions, and the optimization results were compared to find more suitable objective function.
Imaging spectrometer optical design based on prism-grating-prism dispersing device
WU Cong-jun, YAN Chang-xiang
2012, 33(1): 37-43.
In order to make the imaging spectrometer compact and to be directly viewed, an optical system incoporating prism-grating-prism(PGP) component was designed.The system includes PGP device, collimating lens, imaging lens and receiving device. The system uses volume hologram bragg diffraction grating(VHDG) instead of ordinary ruled grating, which have high diffraction efficiency. Symmetric structure that can eliminate lateral abberations automatically is applied to this system. The requirements of design specification are given, which include 512512 pixels CCD with pixel size of 20 m20 m, 148 spectrum channels,slit size of 10 mm0.02 mm,object NA of 0.15, and operation wavelength ranging from 400 nm to 800 nm. System concept and features, diffraction efficiency, paraments relationship are discussed. According to analysis, diffraction efficiency is higher than 0.6 in the whole spectrum range. Using ZEMAX optical optimization software, the MTF of the sysytem is better than 0.7 at the Nyquist frequency, the spectural resolution is better than 3 nm, and the length of the sysytem is 90 mm.
Focalization character of Gaussian beam passing through optical system with misaligned lens
TANG Rui, SHEN Xue-ju
2012, 33(1): 44-50.
To analyze focalization character of Gaussian beams passing through optical system with misaligned lens,an approximate expanded formula of misaligned circular aperture function and an generalized diffraction formula were used. The dependence of field distribution of output beam maximum value on the landscape orientation displacement and angle displacement were given. Result shows that various misaligned components have effects on the field distribution of reflection beam. Based on a specific lens system, the impact of maladjustment factors on output beams maximum value field distribution was analyzed quantitatively. The results show that the transverse-displacement has more impact than the angle-displacement on the focalization character when the parameter is small.
Optimization for compound parabolic concentrator in UV communication
LI Xiao-ming, HUA Wen-shen, MA Zuo-hong, ZHANG Yue
2012, 33(1): 51-56.
In order to enhance detectors- sensitivity and efficiency in UV communication system, an optical antenna was designed to strengthen the ability of collecting weak light signal in atmosphere. Based on the practical engineering background of UV optical communication system, a compound parabolic concentrator (CPC) for optical detection was optimized using rotation, translation, cutting of top and cutting of bottom respectively. Calculation, simulation and emulation of CPC were conducted. The parameters, such as maximum incident angle, flux efficiency and relationship between incident angle and the collection rate in different optimized methods for the compound parabolic concentrator for light detection were calculated and analyzed. Then different engineering conditions where different optimized methods worked were deduced. Namely, the negative direct rotation method can be used for line of sight distance communication. Cutting of bottom method can be served for the non-line-of-sight scattering short-range communications, and cutting of top CPC can be used to replace the standard one to save material cost.
Characteristics of ferroelectric liquid crystal optical addressed spatial light modulator
WANG Jiang-tao, CHEN Xiang-ning
2012, 33(1): 57-63.
According to the equivalent circuit model of an optical addressed spatial modulator whose main structure is a-Si:H/Al/FLC, the resolution, response velocity, contrast ratio and gray scale response characteristics were analyzed by Pspice and Matlab. The results indicate that in the condition of certain FLC cell thickness, the resolution of FLC-OASLM can be increased by decreasing the thickness of a-Si:H, but it makes the dynamic range decrease and manufacture more difficult at the same time; the max MTF value is 1 only when the spatial frequency is 0. The output light is very weak when no write light; when write light intensity is from 0.08 mW/cm2 to 10 mW/cm2, the delay time decreases 110 s and the rise time decreases 154 s; when write light intensity is 1 mW/cm2 and erase light intensity is from 0 to 1 mW/cm2, the delay time increases 41 s and rise time only increases 3 s; so the response velocity of FLC-OASLM can be increased by increasing the intensity of write light or decreasing the intensity of erase light in the conditions of certain other parameters. The contrast ratio of FLC-OASLM increases slowly at a low control light intensity, but it increases quickly with the further increasing control light intensity, and finally it is close to a steady value which is 21:1 in this paper. In the conditions of certain other parameters, the response of output light falls step by step with the increasing intensity of erase light; and after erase light intensity arrives at 3 mW/cm2, the changes of erase light intensity have nearly no effects on the rise time; while the fall time keeps on decreasing with the increasing erase light intensity; more than ten gray scales can be obtained by designing the drive source signal reasonably; so these indicate erase light can realize gray scale function of FLC-OASLM. Simulation results agree with the tested results from others-essays well. The excellent performances make FLC-OASLM have a wide application in the fields of optical information processing and optical imaging.
OE Information Acquisition and
Dual-band target tracking based on color transfer technique
HE Yong-qiang, ZHOU Yun-chuan, REN Hong-yan, SHI Li-qing
2012, 33(1): 64-70.
Since Camshift algorithm is easy to lose tracked object in complex background, this paper puts forward a tracking method based on Camshift algorithm, before which a color transfer technique is used between color reference image and fused image in YCBCR space. During color transfer, the proposed method used information of dual-band image effectively, and the target not only had the excellence of high contrast, but also enhanced the drawing of color probability distribution, the proposed method improved the efficiency of Camshift. The comparison of the visual image, color transferred infrared image and the traditional color transferred image was made using the same tracking method, a group of experimental results demonstrate that the distance between the center of tracking window and target centroid is just 3 pixels in the pictures based on proposed method, tracking precision outperforms the results of contrast experiment pictures. At the same time, the tracking time of the proposed method is 20.6 ms, which meets the real time requirement.
Application of compressed sensing in optical imaging
XIAO Long-long, LIU Kun, HAN Da-peng, LIU Ji-ying
2012, 33(1): 71-77.
Compressed sensing is a new sampling theory, which captures and encodes signals at a rate significantly below Nyquist rate provided that these signals are sparse or compressible. This paper reviews the theoretical framework of compressed sensing. It first employs non-adaptive linear projections to preserve the structure of the signal, and then the signal recovery is conducted accurately or in all probability by using an optimal reconstructed algorithm from these projections. Its related applications in optical imaging systems are introduced, such as single-pixel camera, super thin imagers, coded aperture imagers, multiplexing intelligent imagers, spectral imagers, and CMOS imagers. Some prospects and suggestions about further works on this theory are also presented.
Tracking algorithm of dual template adaptive updating based on multiple features
LIU Zhen-tao, WANG Zhao-ying, LIU Wei-qun
2012, 33(1): 78-84.
To solve the problem of single color feature and the lack of necessary template updating method in mean shift algorithm, an adaptive tracking algorithm of dual template adaptive updating based on multiple features is proposed. The difference of gray mean in the neighborhood of pixel point and the layered space information are introduced to enhance feature differentiation. By analyzing the similarity coefficient of dual template in target and background region, the origin of disturbance factor is estimated truly, and the target template in target region of current frame is updated by similarity coefficient. The speed of template updating is adapted to the transformation of target feature, and at the same time excessive template updating is restrained, which solves the problem of the occasion and speed of template updating. The robustness of the proposed algorithm is demonstrated by simulations in different tracking scenarios.
Image filtering algorithm for video-based vehicle monitoring systems
ZHANG Quan-fa, FEI Guang-yan, WANG Qing-feng, REN Chao-dong
2012, 33(1): 85-89.
In video-based vehicle monitoring systems, image noises seriously influenced the results of vehicle recognition, background learning, and so on. The existing filtering algorithms could not meet both the speed and filtering effect requirements of these systems. After comparing the effect and speed of vehicle recognition without filtering and with median filtering or mean filtering, the mean value filtering was selected for further study. By appropriately reducing the amount of calculation, the speed of the new filtering algorithm was increased through improving the processes of data accessing and calculating, and the algorithm was realized with Visual C++ 6.0. Experiment results show that the speed of the new algorithm is 55% faster than box filtering.
New algorithm for real-time outlier removal data in data processing of exterior trajectory
XU Li-na, CHEN Jun-biao, MU Gao-chao
2012, 33(1): 90-95.
A new algorithm was studied to satisfy exterior trajectory data pre-treatment. The algorithm not only provided an effective method to real-time data processing but also had low computational cost. It was an adaptive outlier removal algorithm, which had good adaptability for radar data and photoelectric theodolite data. The standard deviation of the five successive test data was multiplied by three and the product was taken as threshold. The new method of calculating the dynamic threshold could complete real-time outlier removal of exterior trajectory data. Matlab simulation and measured data analysis proved that the proposed algorithm could completely removed isolated outlier. It is suitable for real-time exterior trajectory data processing.
Application of color fusion technology in military applications
XU Hui, YUAN Yi-hui, ZHANG Jun-ju, TIAN Si, CHANG Ben-kang
2012, 33(1): 96-100.
The real-time infrared and visible color fusion is realized by employing color transfer theory in l space. The structure and workflow of an infrared and LLL color fusion system were designed. Two applications of color fusion in military application were described, including detection of sniper in nighttime and detection of camouflage vehicles. The experimental images were shown. A subjective evaluation of target detectability in image was designed to assess target detectability of experimental images. Experimental results show that color fusion technology could increase military target detectability significantly.
Optical Metrology and Measurement
New reference sources for radiometric calibration
ZHENG Xiao-bing, YUAN Yin-lin, XU Qiu-yun, WU Hao-yu, ZHANG Wei, ZOU Peng, LI Jian-jun
2012, 33(1): 101-107.
Reference light sources are key devices in a radiometric calibration system. To meet the calibration requirements of recently developed opto-electronic sensors with various spectral resolutions and operation modes, reference light sources are required to possess new functions such as spectral match, large dynamic adjustment range, fine scanning in wide spectrum, as well as the basic features such as high stability and uniformity. This paper gives a brief introduction of the design features, main performances and initial applications of a spectrally adjustable light source based on LED modules and a wide spectrum tunable monochromatic planar light source based on tunable lasers. Incorporated with detector-based transfer standards, these new reference light sources can meet specific calibration requirements and improve absolute calibration accuracy.
Automatic side shape measurement system for steel billet based on machine vision
HE Ping-an, ZHANG Ming-jian, GUO Ding-yi, WAN Lai-yi, GONG Hui, LIN Jie-bang
2012, 33(1): 108-114.
The measurement system based on machine vision is composed of an array CCD, a laser transmitter, a laser receiver and an industrial computer. An array CCD is used to grab the images of side shape of steel billet. After digital images are processed, the height and thickness of the side edge of steel billet are calculated and analyzed by special software. In order to implement the control of the steel billet, abnormal images are saved and sent to external control system.
On-line monitoring technique for trace gases in atmosphere based on differential optical absorption spectroscopy
SUN Li-qun, CHEN Ke-xin, YANG Huai-dong, HE Qing-sheng
2012, 33(1): 115-119.
Differential optical absorption spectroscopy (DOAS) is a widely used method to measure trace gases in the atmosphere. The concentrations of trace gases can be retrieved by fitting differential absorption spectra with standard differential absorption cross-section using the linear least-square method. The basic principle of DOAS is introduced. The construction of DOAS on-line monitoring system was designed and the retrieval method of trace gases concentration based on the principle of least squares was discussed. The properties of DOAS system were tested by experiments. The advantages of DOAS system used in atmosphere quality monitoring are proven.
Three-dimensional profilometry improvement based on grating projection
FU Yan-jun, LUO Qian
2012, 33(1): 120-123.
Grating projected method was used to measure the three-dimensional profile of smooth mouse. The traditional Fourier transform profilometry was improved. The signals were directly filtered without frequency shift after Fourier transform, then inverse Fourier transform was performed and the phase difference relative to the height was obtained. Compared with the traditional Fourier transform profilometry, the method removes three frequency shifts, greatly reduces calculation complexity and improves filtering accuracy. It takes 0.1 second to measure three-dimensional profile with the accuracy of 0.2 mm. The result indicates that the method could be used for smooth object measurement with good accuracy and efficiency.
Measurement of convex aspheric mirror by non-null testing
WANG Xiao-kun
2012, 33(1): 124-128.
Conventional testing methods for convex aspheric surfaces were briefly reviewed, and two novel methods for testing convex asphere by partial compensation method and sub-aperture stitching interferometry (SSI) were proposed. The basic principle and theory of the two methods were investigated. The partial compensator was designed and customized, the system error of the partial compensator was calibrated, and the synthetical optimization stitching model and the effective stitching algorithm were established based on homogeneous coordinate transformation and simultaneous least-squares fitting. The prototype and setup for testing of convex asphere by the non-null testing were developed. A convex SiC asphere with the aperture of 130 mm was tested by the two methods respectively. The results show that the difference of PV and RMS error between SSI and partial compensation is 0.010 and 0.002 respectively, the full aperture surface maps of the two methods are consistent and it provides two non-null testing methods for measuring convex aspheric surfaces.
Visual detection of regular hexagon
ZHOU Zhi-feng
2012, 33(1): 129-133.
A vision detection method based on geometric characteristics to detect regular hexagon is proposed. Hough transform and the regular hexagon characteristics are briefly introduced, and the detection of regular hexagon is decomposed into the line detection,the circle detection, the calculation of the lengths of line segments and the angles between adjacent lines. Based on the detected line segments, the line equations are constructed in the image plane. The intersection points of adjacent lines and the angles between two adjacent lines are calculated by the constructed line equations. The length of every side of regular hexagon is obtained by computing the distance between the two adjacent intersection points. The circle detection method based on Hough transform is employed to inspect whether all intersection points locate at the same circumference. The detection experiment of hexagon bolt is carried out to illustrate the performance of the presented method. The measurement errors of angles and side lengths of regular hexagon are 0.38% and 0.85% respectively. The result shows that the method is valid and can detect regular hexagon in the image precisely.
Application of Shack-Hartmann wavefront sensor in optical testing
LI Hong-zhuang, WANG Zhi-chen, LIU Xin-yue, WEI Pei-feng, MING Ming, MENG Hao-ran
2012, 33(1): 134-138.
Shack-Hartmann (S-H) wavefront sensors were developed for optical test and the corresponding experiment results are introduced. In the laboratory, the test results were compared with Zygo interferometer, which showed that the accuracy of the S-H sensor was better than /50 RMS. And using star as light source, the wavefront error of the telescope with 1m diameter and 11m focal length was tested through the S-H sensor. The results show that the wavefront error of the telescope is about 0.39~ 0.46 RMS, and the error inceases as the elevation angle of the telescope increases. The dominating wave-front error is 3rd astigmatism.
Novel method for measuring refractive index of liquid
MIAO Run-cai, HAN Peng-bin, LI Neng-neng, GAO Mei-ling
2012, 33(1): 139-143.
A new method for measuring the refractive index of the liquid was proposed and a device was developed by using liquid film shading effect principle. Distilled water, anhydrous alcohol and 1.2-trimethylene glycol were chosen as samples to be measured. The refractive indices of these liquids were measured by the new experiment device. In the measurement process, the experimental graphs were analyzed by two methods. One used the reading microscope to measure and analyze the results directly, the other used the CCD to record and intelligently analyzed the CCD records by computer. Experimental errors were analyzed. Automatic real-time measurement was realized. Measurement results agree with the theoretical calculation. This device is simple, accurate, and easy to operate.
Resolution measurement of third generation LLL image intensifier
SHI Ji-fang, SUN Yu-nan, XIE Qi, LI Hong-guang, WU Li-peng, HAN Zhan-suo, WANG Sheng-yun, YANG Bing
2012, 33(1): 144-147.
Traditional resolution measurement of image intensifier is based on the observation of human eyes, but this method is dependent on individual observer and its veracity is not very high. In order to improve this situation, an automatic resolution method for 3rd image intensifier was devised. A scientific class CCD was used in the system, and the observation system is composed of the CCD and a computer. Resolution target image on the image intensifier fluorescence screen was acquired and sent to the computer to carry out image processing and software analysis. Then the resolution of 3rd image intensifier is obtained, and the result is compared with traditional one.
Non-contact measurement of refractive index based on parallel surface plate
XIONG Fen, HU Zhong-wen, JIANG Ming-da
2012, 33(1): 148-152.
Since conventional refractive index measurement methods such as least deviation angular test method, auto-collimation method and critical angle method require a sample prism specially made for such measurement, they are time-consuming and complicated. on-contact measurement of refractive index based on parallel surface plate was used to ensure the integrity of the material to be measured and achieve automatic measurement.The results show that the method is easy to realize automatic measurement and its accuracy could be achieved by choosing apropriate measurement angles. The obtained rotation angle accuracy is a=0.003(10), the guide precision is L=0.000 8 mm and the measurement accuracy of parallel surface plate thickness is d=0.001 mm .
Optical Element and Fabrication
New PBS multilayer design for LCOS projector
YU Zhen, HAO Huai-qing
2012, 33(1): 153-158.
A new optical multilayer design for 45 incidence angle on PBS mirror is introduced. Compared with the traditional method of three stocks periodic multilayer design on PBS mirror, the new method is different in basic principles, which is called as non-periodic gradient multilayer method. It is based on the concept of changing the layers from period to non-period orderly. The purpose is to influence Brewster angle sensitivity effect on PBS mirror. Only two kinds of coating metrical were used on the substrate of SF75 prism glass deposition multilayer. P-polarization transition was over 70% and S-polarization reflection was less than 0.4% when incidence angle changed from 39 gradually to 51. The bandwidth of the polarization cutoff was expanded to 400 nm~700 nm. The new design for LCOS display system improves optical performance, simplifies process and reduces coating time and production cost.
VOx films prepared by RF magnetron sputtering
MA Wei-hong, CAI Chang-long
2012, 33(1): 159-163.
Vanadium oxide (VOx) film is a film material extensively used in the infrared thermal imaging detector, so it is important to study its deposition process and obtain the VOx films having high temperature coefficient of resistance (TCR). VOx films were deposited using RF magnetron sputtering with a high purity vanadium metal target (99.99%) at the room temperature. The influence of Ar/O2 ratio and sputtering power on TCR was researched, and the optimized technique parameters were obtained. The resistance properties of VOx films deposited by RF magnetron sputtering under the different process conditions were tested using the avometer and the film composition was tested using X-ray photoelectron spectroscopy (XPS). Results showed the TCR of VOx films was better than 1.8%.
Ion beam polishing with scanning mode of rectangular coordinates in polar coordinates system
GUO Wei-yuan, CHENG Xian-kai
2012, 33(1): 164-169.
In the developing process of ion beam polishing equipment, the choice of scanning mode of ion source is very important. Traditional scanning process has two different ways. One is the mode of rectangular coordinates and the other is the mode of polar coordinates. According to the features of rectangular coordinate system and polar coordinate system, ion beam polishing with scanning mode of rectangular coordinates can be implemented in polar coordinates system. This method takes dwell time algorithm in rectangular scanning mode, which is much more simple. And in the same circumstances, its machinable round mirror caliber in polar scanning mode is bigger than that in rectangular scanning mode. Movable area of ion source in the way of polar coordinates is a line. Its rest place can be put other things, so dimensional utilization rate is higher. According to the simulation analysis of this new method, its feasibility has been proved.
Application of diamond grinding wheel in optics process
WANG Yang-yang, YAN De-quan
2012, 33(1): 170-174.
In the precision optics process, diamond grinding wheel is widely used for precision grinding of various hard and brittle materials. In order to improve the surface quality and sub-surface damage of the optical parts, great efforts were made in improving the manufacture of diamond grinding wheel and the grinding process of various brittle optical materials. The structure, fixing mode, combined material and main body of diamond grinding wheels were summarized. The static balancing and dynamic balancing of diamond grinding wheel were analyzed. Ultra precision grinding element with Rt1 m, Ra<0.3 m was manufactured with this method. It is proved that this method can significantly improve the efficiency of following process.
Infrared Technology
Athermalisation of infrared Cassegrain optical system in missile
LIU Jun, WU Xiao-chen
2012, 33(1): 175-180.
In order to eliminate the ambient temperature effect on the performance of infrared optical system in missile, an athermal infrared Cassegrain optical system was designed for 3.7 m~4.8 m band. The ANSYS software was used to analyze the effect of heated dome deformation on imaging quality of infrared system. Optical passive athermalisation technique was a proper choice, which could achieve the compensation for ambient temperature in the range of -40 ℃~+65 ℃. The results showed that the off-axis of MTF was greater than 0.41 at 20 lp/mm, the dispersion spot diameter was less than one pixel in different views and the structure of optical system was simple. This design ensured the stability of the optical system imaging plane and effectively improved the ability of detecting and recognizing targets for fire control system.
Athermalization of middle infrared optical system
BAI Yu, XING Ting-wen, LIN Wu-mei, XIE Wei-min
2012, 33(1): 181-185.
The effect of temperature variation on infrared optical system and athermalization technique were introduced. An athermal middle infrared refractive optical system was designed by CODE-V optical design software,which used Ge, Al and ZnSe material. The image quality of the system approached diffraction limit in the temperature range of -40℃~65℃. The exit pupil and stop of the optical system was coincided. The optical system has many advantages,such as simple structure,small volume,light weight and low cost.It can be applied to space infrared optical system.
Removal of stray radiation from warm shields in cooled infrared optical systems
LIU Yang, AN Xiao-qiang, DENG Jian
2012, 33(1): 186-190.
Stray radiation may be introduced after warm shields are mounted in cooled infrared systems. The stray radiation consists of radiation and reflection from the warm shields. Since it degrades the SNR, dynamic range and image quality of the system, it shall be avoided by design. The stray radiation was analyzed based on the theory of radiation and heat transfer, and NETD was calculated. The scheme to avoid stray light effects was proposed and verified by ray tracing. The stray radiation of flat shields and spherical reflective shields was analyzed and compared in LIGHT TOOLS. Stray radiation effects were avoided if spherical reflective warm shields with proper radius are properly positioned. A spherical reflective warm shield with radius 30.3mm was used to replace the original flat one, and the stray radiation dropped by more than 99%.
Laser Technology
Driving technology for pulsed laser simulator with adjustable frequency and duty cycle
CHEN Zhi-bin, LIU Bao-hua, XUE Ming-xi, LIU Yu-xiang, HOU Zhang-ya
2012, 33(1): 191-196.
In laser equipment test, a laser receiver is tested by receiving laser pulses at specific wavelength transmitted by a signal simulator and observing its response. It is an effective way to evaluate the performance of the laser equipment. Based on the analysis of emitting mechanism of LED, we proposed a method to simulate 1.06 m guided laser pulse with LED, and designed the driving circuit of LED laser signal simulator with easy-to-adjust frequency and duty cycle. Experimental results show that the driving circuit has good adjustability of frequency and duty cycle.
Laser simulation of DIRCM system
TIAN Xiao-fei, MA Li-hua, ZHAO Shang-hong, DONG Yi, MENG Wen
2012, 33(1): 197-202.
Aiming at the effective simulation of the DIRCM in the hardware-in-the-loop simulation, the calculated radiation energy for the laser source is 8 times of the absolute value of the aircraft radiation intensity in the band range of 3 m~5 m based on the analysis of the laser source in DIRCM and real battlefield scenario. Combined with the change of atmospheric transmission transmittance in 4 m, the change rule of radiance on the IR seeker is obtained with the change of distance between the aircraft and the missile. The simulation scheme of DIRCM in the hardware-in-the-loop simulation is designed based on the principle of realistic simulation, the energy change of the laser source is calculated with the change of distance between the aircraft and the missile, the energy of IR interference radiation energy in 1 km is set as the energy of the simulation laser source, and the energies in other distances are controlled through the attenuation slice. At last, for the purpose of improving the versatility and intelligence in DIRCM simulation, the closed loop control of simulation laser is designed, and the method of closed loop control for interference wavelength and modulation mode is studied.
Parameter optimization based on FFT algorithm in numerical simulation of laser propagation in turbulent atmosphere
WANG Long, SHEN Xue-ju, ZHANG Wei-an, DONG Hong-jun, HE Yong-qiang
2012, 33(1): 203-209.
To correctly simulate laser propagation in turbulence with phase screen method, based on the turbulent atmosphere-s property, the sampling principle and the grid intervals- relation between two adjacent screens determined by FFT, a formula to calculate the optimal value for grid number based on step distance and grid intervals is derived, and laser propagation in free space and turbulent atmosphere is simulated. It is shown that the simulation result for laser propagation in free space coincides with the theory result when grid number-s value is 848 calculated by the given formula. Specifying grid number a smaller or lager value such as 836 or 860, it is equivalent to that light ray is converged or diverged by a convex lens arrays or a concave lens arrays when passing through even screens, which weaken or exaggerate turbulence-s effect on propagation beam and generate erroneous simulation result.
Analysis and calculation of second-order statistics of transmitted beam in airborne laser communication system
HAN Zhi-gang, XU Dong-hua, LU Hong-qiang
2012, 33(1): 210-215.
In order to predict and estimate the effects of the atmosphere turbulence on airborne laser communication system, the second-order statistics of transmitted beam are deduced and calculated, which include beam diameter, beam wander, spatial coherence radius and the angle of arrival. The results show that the effects of atmosphere turbulence on airborne laser communication will be mitigated significantly as the altitude of airborne platform increases. Due to the larger atmosphere refractive index structure constant in lower altitude, the beam diameter and beam wander in uplink are larger than those in downlink. The angle of arrival in downlink is on the order of several rad, which is larger than that in uplink. Based on the methods and the results, the effects caused by atmosphere turbulence on airborne laser communication systems can be predicted and estimated accurately.
Fiber Sensing and Optical Communication
Impact of polarizer on reflecting fiber-optic current transducer
LI Rui-chun, ZHAO Jing, LI De-chang
2012, 33(1): 216-219.
Polarizer is one of the important polarized components of reflecting fiber-optic current transducer, but the impact of its imperfection has not been presented so far. This paper studied the polarizer independently provided that the rest devices were ideal. Then Jones matrix was employed to establish the matrix expression of every device and the expression of interference results of the imperfect polarizer was derived. The influence of extinction ratio and the pigtail splice point of the polarizer on reflecting fiber-optic current transducer was analyzed and the simulation was carried out. The result indicated that in the closed-loop process, the polarizer with an appropriate parameter and a fine fusion splicing of the pigtail could reduce the impact of the imperfection of polarizer on the whole system. This study can be used for the analysis of light path error and the improvement of transducer structure.
Effect of nonlinear phase noise on performance of DQPSK modulation system
DONG Yi, NI Yan-hui, HONG Hua, ZHAO Shang-hong, TIAN Xiao-fei
2012, 33(1): 220-223.
In order to study the effect of nonlinear phase noise on the performance of DQPSK modulation system, based on the analysis of mathematical model of nonlinear phase noise, the property of bit error rate (BER) varying with the change of signal to noise ratio at transmitter was simulated in a 40 Gb/s DQPSK modulation system by keeping the signal to noise ratio at transmitter invariable. Compared with DPSK modulation, DQPSK modulation is much more sensitive to the effect of nonlinear phase noise, and the BER will obviously increase when the nonlinearity is big enough, by which communication quality of the system will be seriously influenced. As a result, the effect of nonlinear phase noise on the system must be taken into consideration when DQPSK modulation is used.
Error analysis for optical alignment of beam splitters in optical communication
ZHANG Lei, HE Wen-jun, ZHENG Jian-ping, WANG Jia-ke
2012, 33(1): 224-228.
In collimating beam optical path, the error or minor movement of optical elements in optical system could be taken as minor rotation about a fixed point. The imaging relationship could be summarized as iterations of conjugating relationship between object and image in turn. The mathematical model of optical alignment and error analysis is built from the dynamic imaging method. The effect of beam splitter alignment error on optical communication system is analyzed with this model. The mechanical alignment of beam splitter system is theoretically supported with dynamic coordinate of every mirror. The axes parallelism between laser transmitting system and beacon receiving system reaches 5 after alignment.
Ground station-s space diversity technology for satellite-to-ground optical communication
JIANG Xiao-feng, ZHAO Shang-hong, LI Yong-jun, HOU Rui, WANG Xiang
2012, 33(1): 229-232.
The choice of station-s address, interval and number of stations in ground station-s space diversity technology is investigated by modeling optical link for satellite-to-ground optical communication. The result of research shows, reasonable choice of station-s address can improve the availability of satellite-toground optical communication link; the interval of stations should ensure the weathers at different stations are uncorrelated but not too long; the attenuation resulted from zenith angle is more than 10 dB when the ratio of interval and altitude of satellite is larger than 1; the necessary amount of stations is smaller if the availability of single ground station is higher; only 3 stations are needed with equivalent availability of microwave link when the availability of single station is 0.6.