2010 Vol. 31, No. 1

OE System and Engineering
Development of optoelectronic systems for armed helicopters
JI Ming, XU Pei-zhong, XU Fei-fei
2010, 31(1): 1-7.
The development course of stabilized sight technology in helicopters is summarized. Base on the latest development of optoelectronic technology, DAS, image fusion technology, coarse/fine combination two-level stabilization, high-performance photoelectric sensor and directional infrared countermeasure system are analyzed; furthermore, the feasibility of these technologies applied in the airborne stabilized sight system is demonstrated. Some suggestions are proposed for the development of the stabilized sight system on helicopters and the application of the new technologies.
Experimental study of optical synthetic aperture imaging technology
WANG Chang-wei, JIANG Yue-song, LIU Li, HE Yun-tao
2010, 31(1): 8-12.
Based on the relations between the imaging quality with point spread function and optical transfer function, taking Golay-3 array as an example, the theoretical simulation and experiment for the optical synthetic aperture imaging technique are implemented in spatial and frequency domains. The point spread function and optical transfer function is the basis for optical synthetic aperture design and optimization. The imaging of complex objects can be obtained by the object function convoluting with the point spread function. The point spread function determines the imaging quality. The intensity distribution diagrams of the point spread function were acquired by the digital simulation and simulated experimental. The optical transfer function of optical synthetic aperture system was achieved from the point spread function. The simulation and experimental results are analyzed and compared. The experimental results agree well with the theoretical analysis. It proves the validity of the theoretical analysis.
Design of compact diffractive-refractive hybrid optical system in ultra-light projective helmets
FAN Hai-ying, ZHANG Bao-ying, YANG Jia, ZHENG Zhi-guo
2010, 31(1): 13-18.
The helmet display being an important part of soldier digital equipments is always a hot spot in the field of high-tech military. The selection criterion for the design parameters of the projective helmet display is analyzed. The new 1.55cm OLED display was taken as the image source based on projection objective. The volume and weight of the optical system were reduced with the refractive/diffractive hybrid structure. The ultra-light and compact optical system for the 3-element helmet display was obtained by means of the system optimization with ZEMAX software. The weight of the optical system is only 1.35g and the diameter is 11.32mm. The resolution corresponding to the human eyes is 1.85 under the condition of the spatial frequency. The meridian and sagittal MTFs are all more than 0.2 at the wide FOV. The resolution meets the requirement of SVGA display mode.
Slab imaging performance for negative refractive index deviating from -1 and its improvement
LIANG Bin-ming, YAO Cui-ya, LI Zhuo, ZHUANG Song-lin
2010, 31(1): 19-23.
Based on the Kirchholf diffraction theory, the slab imaging performances are studied for different negative refractive index deviating from -1, and the field patterns are drawn with MATLAB. The results show that when refractive index deviates from -1, the lightintensity distribution around the image point becomes asymmetric along z-axis, the fields are irregular and the satellite peaks occur. In addition, the aplanatic curvature radius r was found. The results show if the object point is put at the aplanatic point corresponding to the radius curved surface, the spherical aberration can be eliminated but the location of the image point is different from that of n=-1.
Design of inner focusing object lens in HUD parallax surveymeter based on multi configuration
LIU Jun, ZUO Xiao-zhou, WU Xiao-ming, LI Hao-zhao
2010, 31(1): 24-28.
According to the requirement of automatic focusing in HUD parallax measuring principles, an inner focusing objective of larger relative aperture and focusing range was designed. In order to eliminate the defects in traditional design, the selected lens groups are assembled into a system and multiconfiguration method is adopted to optimize the length of different object distance. In this way, the problem of uncontrollability of short-distance imaging quality was solved. The newly designed inner focusing lens performed well and stable under different object distance, MTF values are above 0.4 both on the optical axis and off-axis in infinite distance when the spatial frequency is 120lp/mm, 0.3 on the optical axis at 300mm; the off-axial sagittal of arc is 0.3 and meridian is 0.2, and the relative distortion is confined within 1%. All achieved makes the after-treatment of the image more convenient.
Design of a new-style vane
YANG Li-hua, FAN Xue-wu, YU Shun-jing, ZHANG Xiang-ming, ZOU Gang-yi
2010, 31(1): 29-33.
The traditional vane plumbs with the inside surface of a baffle, but the new-style vane designed in this paper inclines toward the inside surface of a baffle. The reflective light from the incident parasitic light and part of the stray light is blocked in the interbedded space of the new-style vanes and inside surface of baffle to be attenuated, and most of the residual light is retro-transmitted to the optic system, so just tiny stray light is able to arrive at the detector. The inclining angle of the new-style vane must keep the distribution that is bigger than which is the included angle of the incident stray light with the baffle. Only by the distribution can the inclining stray light be avoided to arrive at the optic system directly. Taking the Cassegrain space camera as an example, two types of vanes were set up respectively within external baffles of the two cameras, and then the modeling and simulation for the two structures were performed by the aid of Tracepro software. The results show that the space camera with the new vane is 4 grades higher than that with the traditional vane.
Design of mobile phone camera lens based on ZEMAX
SONG Dong-fan, ZHANG Ping, WANG Cheng, ZHANG Ren-jian, REN Zhao-yu, BAI Jin-tao
2010, 31(1): 34-38.
By the aid of optical engineering software ZEMAX, a five mega pixel mobile phone camera lens matched with one CMOS image sensor of 1.75m pixel size was designed, whose FOV is 60, F number is 2.8, half image height is 2.87mm, total length is 6mm and structure is 3P1G. Aspheric plastic was used for the first, third and fourth lenses. Sphere glass was used for the second lens. Transverse aberration of all the FOVs is less than 20m, RMS radius are less than Airy disk, and MTFs of most FOVs at half the Nyquist frequency (285lp/mm)of CMOS are greater than 0.6. This lens assembly has an excellent imaging performance.
Design and performance analysis of standard starlight simulator
FENG Guang-jun, MA Zhen, LI Ying-cai
2010, 31(1): 39-42.
In order to calibrate and test the space object cameras and star trackers, a starlight simulator which can simulate the minimum objects at infinite distance and the light source with weak starlight illuminance is required. In this way,the space object camera and star sensor can be calibrated in the laboratory and the effect of atmospheric variation can be reduced. The starlight simulators are made of the integrating sphere uniform point source and collimator, which can adjust the dynamic range of the light energy with iris diaphragm, raise the simulation star magnitude, detect the illuminance of point sources accurately, and then solve the problem of calibration under the condition of weak light by precisely measuring all the factors which influence the-illuminance of the star magnitude. The performance and accurate of the starlight simulator are analyzed. It meets the requirement of calibration and test for the space object camera and star trackers in the laboratory.
Magnetic design of magnetic constraint magnetron sputtering source
MI Qian, YUAN Jian-qi
2010, 31(1): 43-47.
The magnetic field distribution of magnetron sputtering coating equipment has a serious effect on film coating. In order to improve the utilization ratio of target of magnetron sputtering source, we abandoned the traditional ring forms of magnetic field runway design concept, and put permanent magnets or electromagnet separation sputtering on both sides of the target, which generated magnetic constraints (magnetic mirror) field on the target surface. This design used finite element analysis method for magnetic field simulation calculation, and the reliability of the finite element method was verified by simulation results and measured results of magnetic field. Ansys finite element analysis software was used for magnetic field distribution simulation, calculation was simplified and design cycle was reduced. Experiment indicates that the constraint magnetic field can greatly improve the utilization ratio of target.
Black-matrix effect in digitized optical elements
JING Ru-hong, HUANG Zi-qiang
2010, 31(1): 47-50.
The computer optical elements (COE) are pure-phased elements, which can shape the laser beam to arbitrary shape, but is very complicated in their processing technic. Now some methods to realize the COE by digitized elements turn up, but the interference from the black-matrix effect is nonnegligible when using these methods. The influence of the black-matrix effect on the certain elements was researched by means of the Fourier optics theory, the factors to influence the black-matrix effect were found out and the corresponding simulation was carried out with MATLAB. The result shows that the energy concentrats to the center of the receiving screen when reducing the width of the black-matrix, and then the interference of blackmatrix effect is decreased effectively.
OE Information Acquisition and Processing
Image enhancement algorithm for improving the vision of electro-optical stabilized sight
HAN Mei, LI Guang-liang, ZHANG Zhi-long, HE Hai-feng, LIU Ya-qin, SANG Wei
2010, 31(1): 51-54.
In order to improve the visual sense of electro-optical stabilized sight for the ease of operation and facilitate the automatic tracking of targets, histogram equalization algorithm was combined with Laplace edge sharpening algorithm to enhance image contrast and preserve image edge details. The simulation results indicate that the vision effect of video images is effectively improved by this algorithm.
Radial geometrical distortion correction in image measurement system
WANG Hui-feng
2010, 31(1): 55-59.
Lens distortion in high precision imaging measurement system has to be strictly controlled, though the design and manufacture of this kind of lens are challenging. Thanks to the maturity of digital technical, image processing offers a new solution to correct the nonlinear distortion of lens. A set of simple and effective methods for detecting radial distortion center and calculating polynomial coefficients was proposed based on the analysis of a nonlinear camera model. Unitary linear regression analysis and gradually approach method were used to obtain the distortion center and recursive least squares estimation was used to get the polynomial coefficients, and images were corrected based on these data for fulfilling requirements. Test and simulation show the radial geometrical distortion can be accurately corrected in imaging measurement system by sampling one frame of image. It is simple and cost effective, could be used to calibrate camera distortion.
Identifying bullet holes on paperboard with projection method
NI Jin-ping, ZHANG Wei-fang, ZHOU Ping
2010, 31(1): 60-64.
In order to identify the positions of the holes on paperboard produced by continuously fired bullet with a vertical target test system based on the image processing, a bullet hole recognition technique based on projection principle was put forward. The primary image was processed and divided into a number of segments by rectangular partitioning. The hole was successfully recognized and the center position of the hole was calculated using the formula described in this paper. The live fire experiment shows that this method can accurately calculate bullet coordinates and its measurement error is less than 1.5mm.
Camouflaged target recognition realized by AOTF multispectral imaging system
DING Na, GAO Jiao-bo, WANG Jun, ZHENG Ya-wei, WANG Ji-long, LI Jun-na, SUN Ke-feng, LI Jian-jun, CHENG Juan, GAO Meng
2010, 31(1): 65-69.
The multispectral imaging system taking an acousto-optic tunable filter (AOTF) as the spectrometer is proposed to overcome the weak points of the traditional spectrometers which have some moving parts and can not perform the real-time wavelength selection. The system is composed of lens, AOTF, AOTF driver, CCD camera and image acquisition unit, and can obtain images in the spectral range of 500nm~1000nm. The spectrum is selected at random by controlling the AOTF, thus the wavelengths at different bands that have typical target characteristics are purposefully chosen, and the different images for the same targets are acquired at different wavelengths. Several tests for the recognition of the target characteristics were performed in lab and field environment with camouflage pattern, helmet and plants. Reflectance characteristics of objects were obtained at different spectral bands, and images of the discriminating targets were acquired from their backgrounds. The experiments confirm that the multispectral imaging system based on AOTF can change and select the spectral band quickly in real time, it has the ability of detecting and recognizing camouflaged targets, and can discriminate the camouflaged targets from backgrounds. Moreover, the system has many merits, such as compact and high-speed spectral sensitivity as well as without moving parts.
Algorithm of improving confocal microscope SNR
HU Mao-hai, YANG Xiao-chun
2010, 31(1): 70-72.
A theoretical model for Kalman filtering algorithm is established based on the imaging characteristic of the confocal microscope. The Kalmam filtering algorithm based on the image pixel is proposed and a realtime Kalman filter is realized by means of the introduction of Kalman filtering method into the system. The experimental result shows that the algorithm can effectively improve the signal-noise-ratio (SNR) for the confocal microscopy imaging systems, but it is obtained at the expense of time. Therefore, the perfect method to improve the resolution of the system is to emphatically consider the optimization of the beam path of the imaging system and the detection circuit.
Electronic image stabilization algorithm based on characteristic point tracking
JIANG Wen-tao, CHEN Wei-dong, LI Liang-fu
2010, 31(1): 73-77.
An image stabilization algorithm based on characteristic point tracking is presented, which abstracts a group of characteristic points from the reference images, tracks the characteristic points based on Kalman filtering in the follow-up images, and then matches coordinates of the characteristic points in current images and reference images. The parameters of displacement and rotation are derived by the affine model, the matrix of images is converted reversely and the stable video images are obtained. The result from experiment indicates that the algorithm which is easy to operate and has great ability to resist any disturbance can get good effect of stabilization.
Self-adaptive region growing algorithm to segment images of spectral imaging for TCM assessment
ZHANG Wan-xiang, PANG Qi-chang, ZHAO Jing, LIN Fu-bin
2010, 31(1): 78-82.
The spectral imaging method for assessing the traditional Chinese medicine (TCM) can evaluate the quality of the medicines and identify their authenticity by using their spectral images. It can also make the assessing procedure fast and non-destructive. In order to eliminate the influence of the background noise on the assessing results of TCM spectral images, extraction of ROI (region of interest) of the TCM spectral images is needed. Since the difference inherent in different kinds of TCM spectral images and the available fixedthreshold segmentation method can not meet the demand of selfadaptive segment, a self-adaptive region growing algorithm to extract ROI of the images is proposed based on the characteristic of TCM. This algorithm can automatically choose the seeds and threshold of the region growing process according to the gray-level histograms of the TCM spectral images, the connectivity among the pixels is taken into the consideration during the growing period, and the region-fill technique is applied to modify the cavity in ROI after the growing. It proves that this algorithm can extract ROI of the images automatically and precisely, the deviation of segmentation is less than 8%, its antinoise ability is good, and the nonsensical growing result is not appear.
Optical Metrology and Measurement
Using collimator in testing zoom lens stray light
2010, 31(1): 83-86.
For testing zoom lens stray light, it is necessary to understand the role of every test component and their impact on the measurement results. In the stray light measurement device, collimator is selected according to lens parameter. This paper discusses the collimator's effect on stray light measurements. By analyzing the formation mechanism of stray light, stray light is divided into two types, in field and out field. Different stray light characteristics are explained and the states of these two types of stray light after passing through the collimator are given. Two zoom lenses of different parameters are measured with a collimator or without a collimator and their results are compared. For stray light formed outside the field of view, use of collimator is significant and important, however, for stray light formed by the incident light beam inside field of view, collimator has no significant impact on measurement result. Collimator can be used to judge the source of stray light. The stray light formed by multiple reflections of incident light between collimating objectives are about 1%, which can be eliminated as a systematic error.
Coaxial positioning of optical measuring device in the shaft hole
GAO Tian-yuan, CHENG Xian-dong, CHEN Lin, WANG Jia-ke
2010, 31(1): 87-90.
A new coaxial positioning device was proposed to overcome the disadvantage of existing technology, which realized high precision measurement in the shaft hole of optical measuring device. According to three points centering principle and six points axis locating principle, the point contact between six elastic claws and the mechanical axis of shaft hole is a kind of rigid contact and it can bear higher load, and the optical axis of measuring device and mechanical axis of shaft hole can achieve precise coincidence, which makes high precision positioning and good coaxiality possible. It was proved that the positioning device could enable optical measuring device to position accurately in shaft hole with the precision of 10 in theory and in practice.
Optical axis detection instrument for shipborne photoelectrical devices
WANG Gang, CHENG Gang, LI Guang-liang, YUAN Xiao-min
2010, 31(1): 91-94.
A design scheme of the optical axis detection instrument for shipborne optoelectronic devices is proposed to overcome the difficulties resulted from environmental limitation and ship stagger during the process of photoelectrical multi-sensors boresight parallelism adjustment in the outer testing locate and loading ship. The coupling of laser and visible-light boresights is realized with common-path and spectrum conversion technologies. The instrument's key part-boresight coupling unit is simulated and analyzed by CAD/CAE. The parallelism errors of 13.576332 and 16.397421 between two reflectors were obtained in the range of -10℃~+40℃. The result of environmental test indicates that the accuracy error of the instrument is less than 20 and meets the design index.
he system research for on-line defect inspection of flat glass
WANG Fei, CUI Feng-kui, LIU Jian-ting, ZHANG Feng-shou
2010, 31(1): 95-99.
Based on the principle of optical interference and vision detection technique, a machine vision based glass defect inspection system was developed. The target image was acquired, preprocessed and segmented. Its features were extracted and regional parameters were calculated. The defect information such as tin spots, air bubbles and glass ribs was obtained. The experiment indicates that the algorithm is simple, fast and reliable. The system can detect defects down to 0.3mm with maximum processing cycle less than 400ms.
The research measuring refractive indexof medium based on reflectivity of linear polarized light
WEI Mao-jin, YANG Wei-wei, LIU De-gong
2010, 31(1): 100-104.
The relationship between the amplitude reflectivity of linear polarized light and the refractive index of medium material was studied. A method was presented for measuring refractive index of medium materials. The relationship between the isotropic medium reflectivity of linear polarized light and the refractive index was derived from Fresnel formula. The principle on measuring refractive index of medium basedon reflectivity of linear polarized light was given. The configuration of the experimental installation was introduced. The variation curve was measured for the amplitude reflectivity of linear polarized light of P component and S component with changing angles of incidence. The refractive index of the materials was obtained according to the variation curve. The results show that a good agreement between experimental data of medium materials and the theory predictions is reached. The scheme is proved feasible.
Frequency doubling method for half-wave voltage measurement based on electro-optical modulation
GUO Ming-lei, HAN Xin-feng, ZHANG Mao-lian
2010, 31(1): 105-109.
To study half-wave voltage measurement in the electro-optic modulation experiment, the main relationships including double-frequency characteristics and linear characteristics between output signal and modulation signal are analyzed based on the principle of crystal electro-optic modulation. The influence of the amplitude of modulating signal on the frequency doubling signal is investigated by computer simulation. The analysis shows that the frequency doubling signal waveform is distorted under the impact of high order harmonic wave, which is not in favor of crystal half-wave voltage measurement. Symmetry of Lissajou figure is used to determine the position of the frequency doubling signal and overcome the disturbance of modulating amplitude waveform aberration. Compared to other methods, this method is easy to use and can measure half-wave voltage accurately.
Fiber Sensing and Optical Communication
Soil pressure sensor based on temperature compensation FBG
HU Zhi-xin, WANG Zhen-wu, MA Yun-bin, ZHANG Jun
2010, 31(1): 110-113.
Since the present soil pressure sensors cannot be used to realize long term and real time monitoring, a temperature compensation FBG sensor is designed. Flat diaphragm with hard core is selected as elastic element, and a compact FBG with high sensitivity, wave division multiplexing and sensor network features is adopted as sensing element. Grating free of stress is used to compensate temperature. According to experiments and tests, the sensor has sensitivity of 1.5nm/MPa, linearity error of 0.35%, repetitiveness of 0.06%, delay of 2.19% and static error of 2.21%, which meet the requirements of engineering application.
Calibrating FOG SINS by single axis table
CHEN Yu-zhong, ZHANG Wei, HU Yong-ming
2010, 31(1): 114-117.
A low cost calibration method for fiber optic gyroscope (FOG) strapdown inertial navigation system (SINS) by single axis table was studied with the system installed in a hexahedron. There are three empty surfaces without FOG in the hexahedron, so angle between three surfaces was measured by nonius protractor. A body reference frame was established according to the three surfaces, and the output model of FOG was given. During the calibration, three surfaces of the hexahedron were put on the surface of single axis table in turn. Calculation formula of FOGs scale factor and mounting misalignment was deduced. The accuracy of the calibration was discussed, and test experiment was done. The result shows the system requirement is met.
Optical Element and Fabrication
Active correction technology for thin-mirror surface
LI Hong-zhuang, LIU Xin-yue, WANG Jian-li
2010, 31(1): 118-123.
The surface of a 400mm diameter experiment mirror was corrected by 12 active supports. In the experiment, the surface error was tested by Zygo interferometer. The force actuator of the active support is composed of displacement actuator and load cell. The response functions of each actuator are tested first, the response functions of all the actuators compose the stiffness matrix, and then the active correcting force is calculated through damp least square method. In the experiment, the ability of the active supports for correcting each aberration was analyzed, the mirror surface was corrected to generate a single Zernike polynomial wavefront of 1 (=0.6328m), and seven terms was selected for the correction finally. After 5 times correction, the 1.16 RMS surface shape error of the initial state was corrected to 0.13 RMS, near the surface quality after polishing.
Error compensation for pentagonal prism
LIU Xin, SU Ying, ZHI Xi-ling, YANG Chong-min, LIU Xin-wu, FAN Chun-li
2010, 31(1): 124-127.
The projection angle of two B-edges of pentagonal prism has a great effect on the second optical parallelism; however, it cannot be measured during on line processing, which results in low qualification rate. By analyzing the impact of perpendicular error of the side face and angle error of 45 on the optical parallelism of pentagonal prism, this paper provides a new process for producing pentagonal prism, which modified the angle error of the last face to compensate the angle errors of three processed faces so as to release the strict requirements for process error of these surfaces. By using this process, qualification rate and productivity was raised, the complexity of the process was reduced, and the strict requirements for the machine and measurement equipments were released.
Infrared Technology
Adaptive algorithm for small target detection in infrared searching system
CHENG Gang, ZHU Hui, ZHANG Yong, WANG Qing-quan
2010, 31(1): 128-131.
Aiming at the small object detection in infrared searching system, a novel algorithm of adaptive spatial filtering is proposed on the basis of the model analysis of infrared images. The background residual errors are calculated in the algorithm while the background is estimated, and the filtering parameters are adjusted to adapt to the fluctuation of the background according to the values of the residual errors. The multi-scale morphology operator is used in the algorithm. This method is suitable to the infrared small object detection in clutter background, and can reserve the information of objects totally. The method is run on the platform of FPGA, and used in an infrared searching system. The experiment results presented in this paper show that the signal-to-noise ratio (SNR) of the processed images can reach to 3 even if the scene is complex and SNR is low. It has a good result on real-time processing and is easy to be realized in engineering.
Infrared target tracking base on auxiliary particle filtering algorithm
WANG Hong-you
2010, 31(1): 132-135.
In order to solve the problems of complex calculation in the infrared target tracking, the auxiliary particle filtering algorithm was built by the utilization of Bayesian importance sampling algorithm, the introduction of auxiliary particle variables on the basis of large weight particles, and the redefinition of importance sampling distribution function to prevent the change of the particle probability density after re-sampling. The two-weighted calculation makes the change of the particle weight ratio more stable and the sampling point closest to the true state only by the particle weight obtained from the resampling, in which the probability threshold of particles at different weight values can be taken as the criterion for judging whether the particle filtering has been completed. In the infrared moving target model structured in the two-dimensional plane, the system is zero-mean Gaussian white noise. Simulation data shows that the algorithm is superior to the particle filtering and re-sampling particle filtering algorithms in the mean square error in x and y directions, picture processing, RMSE performance.
Laser Technology
Characteristics on coherent combined beam of one dimensional laser diode array in far field
LI Song-bai, CHEN Jian-guo, DOU Ru-hai
2010, 31(1): 136-141.
The analytical expression of the far-field light intensity of coherent combined beams was acquired by Fourier method. The far-field characteristics of the coherent combined beam from the one-dimensional phase-locking laser diode array were numerically simulated and experimentally researched. The results show that the peak becomes sharp with the increase of combined beam quantity; the luminous energy of the cophasal mode centralizes into the smaller spatial angle and makes the illumination of the coherent combined beams increased; the luminous energy of the out-phase mode becomes dispersed and the intensity at its peak is reduced due to the jitter of the system, so the symmetry of far field and quality of the beam is affected; and the more numbers of the beams is combined, the less influence of the system jitter on far field becomes.
Application of laser suppression weapon and opto-electronic tracking integrative technique in air defense
DUAN Hong-jian, YANG Ai-fen, QU Jian-rong, LIU Jia-ying
2010, 31(1): 142-146.
In order to improve the ability of the ground anti-air weapon to strike aircrafts, the integration of the laser suppression weapon and the optoelectronic tracking system is proposed to suppress and interfere in the optoelectronic systems of the air targets. The accuracy of laser weapon system can be improved and the overall response time can also be reduced by the integration of the laser suppression weapon and the optoelectronic tracking system. The characteristic of the laser suppression weapon is analyzed. The probability to integrate the laser suppression system in the vehicle-borne antiair weapon with an optoelectronic tracking system is investigated emphatically. The key technology to implement the integration is presented.
Experimental research on Cr4+∶YAG passively Q-switched solid state laser based on thermal bonding
LI Ju-fen, YI Xue-bin
2010, 31(1): 147-150.
In order to obtain integrative ns-pulsed solid-state laser, a Cr4+∶YAG passively Q-switched laser was designed, which combined Cr4+∶YAG with Nd∶YAG by the aid of thermal bonding, and whose F-P laser cavity was composed by coating films on its both sides. The quasi-continuous laser pulse output was realized in the experiment by directly pumping the crystal from its end by the fiber coupled laser diode. The pulse width (5.3ns) was obtained by the p6703A photo-detector. A radiator was designed to eliminate the thermal lens effect existing in the experiment. The contrast of the air blowing and the radiator was implemented. The experiments approves that the design is feasible and the laser works well.
Scattered light in laser Doppler velocimeter
2010, 31(1): 151-155.
In order to design a high performance laser Doppler velocimeter (LDV), the relationship between the signal intensity of laser Doppler and the diameter of spot was analyzed using the speckle theory, and the calculation formulas of the Doppler current was given based on functional theory. The polarization characteristic of scattered light and its intensity distribution were investigated. The results of theory and experiment show signal intensity of laser Doppler is proportional to the diameter of the active area in detector, and inverse proportional to the diameter of laser spot. By selecting circular polarization laser beam with smaller spot size and using detector of small active area to signal in specular direction, the signal to noise ratio and the detection capability of the system are improved significantly.
Function projection synchronization control of uncertain single-mode laser Lorenz system
MIAO Sheng, HUA Shi-qun
2010, 31(1): 156-160.
Based on the Lyapunov stability theory, the nonlinear feedback controller and parameter recognizer were designed with the adaptive control method. The uncertain single-mode laser Lorenz system is taken as the drive system and the uncertain Chen system as the response system in the design, which makes all the status variable of the response system to follow the chaotic path of the drive system strictly in function proportion, and recognizes all the uncertain parameters including unknown coefficients of nonlinear terms of the drive and response systems. The result obtained by the four-order RungeKutta simulation indicates the effectiveness and feasibility of the method, and proves that the function projection synchronization control can improve the performance of the secure communication.
Optical Theory
Inhomogeneous spatial distribution of scattering light intensity based on Bragg acousto-optic diffraction field
2010, 31(1): 161-163.
Proceeding from the wave equation, the coupled wave equations for Bragg acousto-optic interaction of the traditional diffraction sources were deduced to ensure the quality of the signal light beam in the synthetic aperture lidar testing,. According to the different requirements of each testing on the beam quality, the spatial three-dimensional distribution of the light intensity in the diffraction field is analyzed by the aid of the finite difference method. It is found that uneven distribution of the acoustic amplitude affects the intensity distribution in the acousto-optic diffraction field and the inhomogeneous intensity distribution results in the difficulty of information source detection in the experiment. By means of the research of the intensity spatial distribution, the effective clear aperture was increased to 3 mm and the problem of the beam diffraction quality of the acousto-optic modulator was solved. The improved beam quality meets the requirement of the experiment. This method is applied to improving the working parameters of acousto-optic devices.
Optical Material
Intensity distribution of Gaussian beam transmitting through medium with nonlinear refraction and absorption
WANG Long, SHEN Xue-ju, HAN Yu-dong, LI Zheng
2010, 31(1): 164-168.
The far-field intensity distribution of Gaussian beam transmitting through medium with both nonlinear refraction and absorption was derived and simulated on the basis of diffraction theory. The simulation results show that both the refractive index change of the medium and the wave-front curvature caused by input Gaussian beam influence the radial modulation phase of the beam emitting from the medium exit surface, and that both the medium with selffocusing effect putting in front of the focal point and the medium with self-defocusing effect putting behind the focal point have the diffraction ability similar to blazed gratings which can form a diffraction pattern having a series of bright rings with dark spots in the center of them. If the nonlinear refraction of the media is great, nonlinear absorption affects both the distribution and the intensity of the rings; but if the nonlinear absorption is great, it only affects the intensity.