2007 Vol. 28, No. 3

Optoelectronic Engineering
One-dimensional wavelet transformation analysis on specialty of scattered light from ship wakes
ZHANG Jian-sheng, LIN Shu-yu, MIAO Run-cai, YANG Wan-min
2007, 28(3): 245-249.
Ship wakes have special acoustic, electromagnetic and optical characteristics. Onedimensional wavelet transformations, including dispersive wavelet, continuous wavelet, wavelet packet and complex continuous wavelet transformations, are used to analyze the scattered optical specialty of ship wakes (SOSSW). SOSSW under different conditions have distinct autothresholds, different retained energy and zero setting ratio of the wavelet coefficient. The coloration modes, coefficient curves, and local maximal coefficient lines vary distinctly. The onedimensional disperse wavelet transformation reveals that the detailed signal holds particular periodicity. The analysis of the wavelet detailed semaphore demonstrates the way to eliminate or decrease the effects of these factors. Wavelet coefficients, its distributions and maximal lines differentiate obviously under different pressures according to the onedimensional continuous wavelet transformation. The compression signal of the onedimensional wavelet packet transformation retains the major energy of the original signal. The selected coefficients can act as a characteristic coefficient of the wake bubble curtain under different pressures. The relative magnitude of the mode, mode angle and coefficient distribution along time axis differ from each other based on the onedimensional complex continuous wavelet transformation. The common characteristics of the scattered light signal can be extracted and the difference of various scattered light signals can be directly observed through wavelet analysis, which is useful in wake identification.
Application of optimal control for stabilization loop of vehicle inertial platform
LI Hong-guang, YU Yun-qi, SONG Ya-min
2007, 28(3): 251-256.
Based on the analyses of the mathematical model of the inertial platform stabilization loop, an improved linear quadratic Gaussian (LQG )control method for stabilization servo circuits is put forward to overcome the disturbance from the platform. An integral element is introduced into the feedback to eliminate the stabilization error. According to the criterion of the filter convergence, the state is estimated by using Sage-Husa adaptive filtering algorithm and strong tracking Kalman filter respectively to ensure the state estimation accuracy and the tracking capability of unexpected state. The simulation and experiment indicate that improved LQG control method is accurate and capable of anti-jamming, and it relieves the accuracy requirement for the system model and noise statistical characteristics.
Machine-read method for faded 2-D color barcodes using self-adaptive threshold
GUO Hong-rui, TAN Ji-chun, WANG Xiao-feng
2007, 28(3): 257-261.
The fading law of 2-D paper-based color barcodes is analyzed with the ultraviolet aging test. The relation between the accumulative ultraviolet irradiation time and the chromatic aberration of 2-D color barcodes is analyzed based on the CIELAB model. The detection results of four-color printed label show that the fading velocity of fuchsine is faster than cyan, yellow and black. A self-adaptive threshold method, which can correct color aberration effectively and can machine-read the 2-D barcodes correctly, is put forward based on RGB trichromatic histogram and the principle of probability statistics. The experiment indicates that the machineread bit error rate of the self-adaptive threshold method is less then 0.05%, which was acquired from 25h ultraviolet aging test of barcodes. The result provides a criterion for the service period of the color barcodes.
Optical image encryption based on asymmetric abnormal Fourier transform
DENG Xiao-peng
2007, 28(3): 262-264.
To overcome the disadvantage of the symmetry of input and frequency planes in the previous optical image encoding systems, an improved encryption method is proposed. Instead of adding optical elements, the optical image encryption is realized by spherical wave illumination on asymmetric non-normal Fourier transform system and by placing the phase mask on the Fourier transform plane of the system. Due to the asymmetry of this system and the dependence of the Fourier spectrum plane on relevant parameters of the spotlight, it overcomes the hidden trouble resulting from the symmetry of the previous optical image encoding system and increases four fold security keys. Theoretic analysis and computer simulation indicate that this method is feasible and enhances the security greatly.
Heat uniformity analysis and design of filament of area source electron gun
QIU Ya-feng, CHANG Ben-kang, QIAN Yun-sheng, GAO You-tang, TIAN Si
2007, 28(3): 265-268.
To measure the brightness uniformity of an image intensifier, an area source electron gun is needed to emit uniform electrons. In order to design an electron gun, the electron quantity emitted by each point of filament, the electric filed distribution, the electron trail and the uniform electrons vertically striking the fluorescence screen were investigated theoretically and calculated. It is pointed out that the heat uniformity of the area source electron gun in a vacuum system is a prerequisite for equal electron quantity emitted from each point of the filament, and is also the first problem to be solved before designing the shape of the filament. In the vacuum system, the heat radiation is the main factor to affect the temperature of each point of the filament in area source electron gun. A theoretical analysis of the heat radiation uniformity from the filament of an electron gun in vacuum environment is made with reference to some relevant papers. Three filament structures are designed and their heat balances are calculated. In comparison with each other, the spiral filament is the best. This work sets the foundation for the next step of field analysis and electron trail analysis.
Temperature control technology on rugged airborne TFT-LCD
GU Shi-yi
2007, 28(3): 269-274.
Some problems on temperature control technology of the rugged airborne TFT-LCD are discussed and the operation temperature of -43℃~+71℃ for the airborne TFT-LCD is achieved. Based on the characteristic analysis of TFT-LCD, some methods of the circuit heating are designed to heat LCD module with ITO and heat CCFL with heating wire. Thus the airborne TFT-LCD can be started up and operated under low temperature. Based on thermal design methods, the cooling scheme for the airborne TFT-LCD operating under high temperature is also proposed. The operation temperature range of the ruggedized airborne TFT-LCD is increased with the automatic temperature control system.
Finite element analysis of thermal effect of photovoltaic detector irradiated by laser
LIU Quan-xi, QI Wen-zong, HAO Qiu-long, ZHAO Fang-dong
2007, 28(3): 275-279.
A 3-D physical model of temperature rise for a photovoltaic detector irradiated by Gaussian CW laser is established. The 3-D temperature distribution of the detector is calculated with finite element analysis method. The effects of the irradiation time, the thickness and heat conductivity of glue layer on the melting damage threshold and heat recovery time are discussed. The research results show that the melting damage may occur in the InSb photovoltaic detector when it is radiated continuously by intense laser, and the damage takes place first in the light spot center of the radiated surface. The higher the laser power is, the shorter time the damage takes, and the greater the heat conductivity is, the bigger the damage threshold corresponding to the thinnest glue layer will be. However, only when the detector is radiated by the high power laser, will the effect of the thickness and heat conductivity of the glue layer on the melting damage threshold become clear. The results obtained from the research match well with the experiments. It is pointed out that the glue with high heat conductivity should be selected and the thickness of the glue layer should be made as thin as possible to improve the performance of the photovoltaic detector.
Flame color collection and analysis system based on machine vision
MAO Cui-li, MA Wei-hong, MENG Li-zhuang
2007, 28(3): 280-283.
The flame feature is the most important and straight forward factor to reflect the burning properties of priming systems. Several flame collection methods were compared. Due to the short burning time, fast and noncontact characteristics of priming systems, a machine vision system was established based on the digital image processing technology developing rapidly in these years. An advanced high-precision mass-buffer-memory color planar-array CCD camera and a color frame grabber card were adopted for remote sensing. A series of flame images were obtained precisely, and the flame images were analyzed with the digital image processing technology based on the flame color and shape. The technology provides a reference for further image processing and analysis.
Optical Design
Design of a zoom lens system with matrix method
ZHAO Cun-hua
2007, 28(3): 284-287.
The Gaussian optics is traditionally used to calculate the focus of every element and the distances between them in a zoom system. This design method is different from the traditional one. All the parameters of the zoom system are achieved with mathematic software, which solves a nonlinear equation group set up with a ray-transmission matrix of the zoom lens, based on the theory of the matrix optics. At last, the application of matrix optics is demonstrated in designing a zoom system of a general camera lens.
Design of a compact infrared catadioptric system
WANG Ling-jie, ZHANG Xin, YANG Hao-ming, ZHANG Jian-ping
2007, 28(3): 288-291.
The design method of a compact infrared catadioptric system is proposed. In the design, the metal mirrors are adopted for the primary and secondary mirrors in the system, and the IR transmission material is used for the rear set of lenses. The ratio of total length and focus length is 0.55. The temperature effects of the system were analyzed during the design process and an effective measure was taken for the purpose of making the system quasi-athermalized. The parasitic light in the system was also analyzed. A scheme to suppress the parasitic light is given. The analysis result shows that the stray light on the image plane of the system is less than 0.5%, the expansion coefficients of optical material and structural material are proper for their match, and the thermal effect of the system is verified.
Lens design in helmet-mounted LLL night-vision system
SHANG Hua, LIU Jun, GAO Ming, MAO Cui-li, MENG Li-zhuang
2007, 28(3): 292-296.
To improve the imaging quality of the lens used in helmet-mounted low-levellight (LLL) night vision system and make the lens light in weight, small in size, compact in structure, a high order aspheric lens is designed. According to the theoretical calculation of the lens parameters specific to the helmet-mounted LLL night-vision system, lens parameters are designed to meet the demand. With the high order aspheric lens designed, the number of lenses in object lens is reduced from 9 to 6 and the number of lenses in ocular is reduced from 9 to 7. The analysis results show that the configuration of the aspheric surface for helmet-mounted LLL night-vision systems can make its lens configuration simple.
Design of parallel beam-splitting Nicol prism with combination of Iceland spar and glass
REN Shu-feng, XU Xing-lei, ZHANG Yun-hai, WU Fu-quan
2007, 28(3): 297-300.
A new type of parallel beam-splitting Nicol prism made with the combination of iceland crystal and glass is designed so as to save the rare Iceland spar and increase the shear difference of polarized light. The prism is made of ZBaF3 glass and Iceland spar glued with C10H7Br, which has high refractive index. The experiment shows the extinction ratio of o light is better than 10-5, that of e light is better than 10-3 although it is influenced by the optical glass, and the transmittance of the combination is basically the same as that of the pure Iceland spar prism. The theoretical analysis indicates that the influence of the prism structure on the performance can be neglected in some specific cases and it will have a good application potential.
Night Vision
High signal-to-noise ratio MCP for Gen.Ⅲ image intensifier
PAN Jing-sheng, SU De-tan, XU Zhi-qing, LIU Shu-lin
2007, 28(3): 301-304.
A new technique of MCP fabrication is proposed for overcoming the disadvantages of noise factor increase, signal-to-noise ratio decrease and NEA photocathode superiority reduction caused by the ion barrier film coated on MCP during the operation lifetime of image intensifier. With the technique, the glass composition is optimized, the operation temperature of the synthetic glass is increased, the inwall structure of the channel is improved, and the open aperture ratio reaches 65%~70%. The experiment results show that the high performance MCP can improve the secondary emission performance while the ion feedback noise is reduced. This MCP can offer an even lower noise figure performance in comparison with the standard MCP, and significantly improve the signal-to-noise ratio of Gen.Ⅲ image intensifiers. Finally, it is pointed out that the further work on the MCP will make high signal-to-noise ratio and long operation life filmless Gen.Ⅲ image intensifier possible.
Spectral response measurement of UV image intensifier
CHENG Hong-chang, SHENG Liang, SHI Feng, WANG Fen-fen, FENG Liu
2007, 28(3): 305-308.
An ultraviolet spectral response measurement device was designed for measuring the UV image intensifiers fabricated in this laboratory. This system consists of a light source chamber, a grating spectrometer, a DC voltage regulator and a piampere current meter. The radiant power corresponding to every wavelength of the light source was directly read out with the software of the grating spectrometer, the photocurrent generated from a photocathode was directly measured by the piampere current meter when the photocathode was radiated by UV radiation sources, the ratio of the two measurements was then calculated and processed by Microsoft Excel 2003, and relative spectral response curve was obtained. The curve indicates that the spectral response of UV image intensifiers is from 200nm to 340nm and the peak response is near 270nm, which indicates that the UV image intensifier is solar blind. Measurement results show that the uncertainty of the device is less than 10%.
IR imaging seeker with rose scanning technology
GU Xian-hui, BAO Qi-lian
2007, 28(3): 309-312.
The rose scanning technology is utilized for optical system imaging detection to improve the electro-optic countermeasure capability of the IR seeker in precision guidance system. The design of the linear array detector and Cassegrainian optics is the critical part of the work. The calculation of the target position was realized by introduction of the computer processing of image frames. The technical scheme is introduced and several key techniques are analyzed. The prototype was made and tested in the lab. The test data and simulation results show that its antiinterference capability against infrared decoy is improved. The experiment indicates that the seeker can meet the requirements of the precision-guided weapons, such as portable air defense missiles and shipborne terminal-guidance air defense missiles. The design concept is proved feasible.
Measurement of spectral responsivity of an infrared detector
WANG Ji, ZHENG Xiao-bing, ZHANG Lei, LIN Zhi-qiang
2007, 28(3): 313-316.
The calibration technology for absolute spectral responsivity of the nearinfrared radiation power is investigated. An extended infrared-InGaAs (EIRIGA) photodiode was designed. The spectral responsivity of the EIR-IGA detector was measured to allow it to be a standard power-transfer detector working in the wavelength range of 1.2μm~2.5μm. This near-infrared detector was also calibrated by cryogenic radiometers before. The absolute responsivity of the EIR-IGA detector was calibrated in 1260nm, and the continuous relative spectral responsivity was measured with a new IR SCF system based on IR monochromator. The absolute spectral responsivity of the detector is obtained at last with the two steps.
Graphic integration interface design for MODTRAN
LIU Guang-da, JIANG Yue-song
2007, 28(3): 317-320.
MODTRAN is a popular calculation model for atmosphere infrared radiation transmission. The graphic interface for MODTRAN based on the code compiled with FORTRAN is designed for project applications. Since calculation efficiency of FORTRAN language is high, but its graphic function is weak, while the calculation efficiency of Visual Basic (VB) is low, but its graphic function is powerful, their advantages are utilized adequately, and the concept of reusing the resources of FORTRAN calculation program is realized. The method is to change the FORTRAN program into the dynamic link library (DLL) functions, exchange data between VB program and FORTRAN program by transferring function parameters, then shows the calculation results of FORTRAN DLL functions on VB form and draw the graphs. Thus the graph interface of MODTRAN calculation program is added and the results of calculation are visualized. Therefore, the Chinese graphic interface for MODTRAN was designed for the users in China.
Laser Technology
Laser separation of brittle material
ZHOU Sheng-feng, ZENG Xiao-yan
2007, 28(3): 321-327.
The traditional separation techniques of brittle materials can not meet the high precision and high cleanliness requirements in the semiconductor industry because they are susceptible to some flaws, such as residual stress, micro-cracks, chippings on the edge. However, the laser micro-processing technique is becoming a potential precision processing technique for brittle materials because of its advantages, such as non-pollution, non-contact, high processing precision and operational flexibility. The principle of processing, characteristic and research status on the several typical laser micro-processing techniques, such as laser ablation cutting technique, micro-crack propagation control technique by laser-induced tension,laser lift-off technique used to separate brittle materials are reviewed. The main problems existing in the techniques are pointed out and the improvements are briefly discussed. The development prospect of laser separation techniques is also predicted.
Feedback displacement measurement system using dual-frequency He-Ne laser
CUI Liu, ZHANG Shu-lian
2007, 28(3): 328-331.
A novel nanometer displacement measurement system is investigated. A birefringence element is inserted into the resonance cavity of a He-Ne laser to generate the frequency split effect which changes the original single mode laser into an orthogonally polarized dual-frequency laser whose frequency difference of o-ray and e-ray is variable. The reflective surface placed out of the laser cavity moving along the laser axial can modulate the intensity of the laser by reflecting the output beam back into the cavity. These new phenomena can be used to realize the high resolution and non-contract measurement of displacement. A novel subdivision method which can break through the diffraction limit (half wavelength) is also proposed. The ideal resolution of the system is around 79 nm for He-Ne laser with 633nm wavelength. The achievements in the research have set the foundation for the laser feedback interferometer development.
LD side-pumped Nd∶YAG/S-KTP intracavity frequency doubled high power CW red laser at 660nm
XU Hai-ping, XU Hai-yan, ZHANG Peng, REN Zhao-yu, BAI Jin-tao
2007, 28(3): 332-335.
LD side-pumped Nd∶YAG/S-KTP intracavity frequency-doubled high power CW red laser at 660nm is reported. LD pumping module is composed of nine 20W laser diodes, which has maximum pump power of 180W. The resonant cavity parameters are optimized so as to generate fundamental oscillation at 1319nm when the 3mm×65mm Nd∶YAG rod is pumped continuously. With a KTP crystal (type Ⅱ critical phasematching), 6.8W of CW red laser output and the optical-optical conversion efficiency of 4.3% are obtained when pumping current is 22A.
Effect of vibration on intersatellite coherent laser communication
WANG Zhao-hui, ZHAO Chang-zheng, CHEN Wen-xin, JIAO Bin-liang
2007, 28(3): 336-340.
In the intersatellite coherent optical communication, the vibration of a satellite will lead to a pointing error of transmitting and receiving antennas, which will decrease the signal-to-noise ratio and increase the bit error rate (BER). In this paper, the Rayleigh distribution is taken as the pointing error model caused by satellite vibration, and PSK homodyne communication scheme is used as an example to analyze the influence of the satellite vibration on the system instantaneous BER and average BER. The simulation calculation result of BER is given. It is pointed out that the pointing error of receiving antenna will have a great influence on the quality of the intersatellite optical communication, and the system BER will be less than 10-6 while the standard deviation σ of the pointing error is less than 1μrad.
Design of complex testing system for flame spectrum and image
HAN Ming, LIN Xiao-chun, AN Yu-ying
2007, 28(3): 341-344.
A complex testing system was designed for flame spectrum and image detection based on the standard flame and the discrete equipments, i.e.SR-5000 infrared spectrometer, AvaSpec-2048 UV spectrometer and high-speed color CCD telecamera. With the button panel and the operation software, any discrete equipment can be operator independently, or more equipment can be operated simultaneously and the UV infrared image data can be acquired synchronously. The indication of oscilloscope shows that the synchronization delay is shorter than 50ns. As a result, the flame spectrum of the whole waveband and the image corresponding to every flame spectrum data were obtained in the experiments.
High-speed hole inspection system for steel strips based on machine vision
HE Yong-hui, WANG Kang-jian, SHI Gui-fen
2007, 28(3): 345-349.
The high-speed hole detection system for strip steel was developed to meet the urgent needs for detection of hole defects in the strip steel produced by 1420 CDCM mill in Baosteel Co., Ltd. This system, which was designed based on machine vision technology, has been working in the extremely tough conditions for more than 2 years. Configured with transmission illumination and high-speed linear scanning CCD cameras as image sensors, high quality images of steel strip can be obtained in real time, which can be processed at a speed of 30 ms/frame with the detection software. The software transfers the control instructions and hole-detecting results to the server through a C/S network structure that consists of 3 industrial PCs, and a terminal connecting the server computer displays inspection results and sends alarm signals. Due to its stateoftheart design, high-efficiency object detection and edge detection algorithms, the outstanding performance and good reliability of this system have been fully proved in the practice for more than 2 years.
Light velocity measurement by high-precision time-interval measurement technique
WU Gang, LI Chun-lai, ZHU Lei, LIU Yin-nian
2007, 28(3): 350-353.
The high-precision time-interval measurement technique is used to measure the velocity of light in the laboratory environment. The light velocity can be precisely calculated by measuring the propagation delay time of light in the zerodispersion single-mode fiber, whose length and refractive index are already known. By theoretical derivation, the relationship between the fiber length L, the refractive index n and the fiber delay time τ was deduced, and the light velocity can be calculated by L, n and τ. Compared with the traditional measurement methods of astronomy or the measurement methods with precise instruments, the high-precision time-interval measurement technique can improve the time resolution to 125ps. Two or three simple instruments were used only to get the accurate measurement result in the laboratory environment. The measurement result of the light velocity is 299928077m/s, and the measurement error is 30860m/s.
Low-voltage micro-displacement driving circuit and its control method
ZHU Ji-zhong, CHEN Ruo-lei, LU Zhong
2007, 28(3): 354-357.
The application of a low-voltage micro-displacement driving circuit and its control method on an optoelectronic profilometer are discussed. The low-voltage driving circuit is adopted to drive a piezoelectric ceramic phase shifter to shift the phase of the reference beam, so as to make the instrument lighter, smaller and cheaper. In order to eliminate the nonlinear error in the low-voltage region of the piezoelectric ceramic, the value of the voltage applied on the piezoelectric ceramic is controlled by a PC computer, images are taken by a camera for calculating the intervals between the interference fringes. The value of the voltage is adjusted continually by the PC computer until the phase difference of the interference fringes meets the requirement. The method has several advantages, the nonlinear error in the low-voltage region of the piezoelectric ceramic can be eliminated, the advantage of closed loop circuit can be obtained with the open-loop control circuit and the complexity in assembly of mechanical parts can be reduced.
Theoretical Study
Depolarization characteristics of scattered light emitted from aspherical particles
ZHAO Yi-ming, JIANG Yue-song
2007, 28(3): 358-362.
The scattering characteristics of the polarized light incident on the target represent the attributive information of the targets. Based on the Rayleigh scattering theory, the Mueller matrix elements of the aspherical particles were calculated by using the vector transmission equation and scattering mathematic model of the incident polarized light scattered by the single-layer aspherical particles, and the polarization degree of the scattering medium was solved. Under the conditions of different thickness, particle radii and detecting angles, the variation characteristics of the depolarization degree of the light scattered by the aspherical particles are discussed, and the simulation result is given. A new way is provided by this method for characterizing the internal structure, thickness, roughness of a target, and for the object acquisition and identification.
Numerical calculation of Mie theory
XIANG Jian-sheng, HE Jun-hua
2007, 28(3): 363-366.
The Mie scattering theory is used to measure the particle size by light scattering. The calculation speed and precision of Mie scattering series are very important to the measurement results. Mie scattering series are calculated usually by forward recursion, backward recursion and link recursion for the different particle sizes and relative refractive indexes. The improved method based on the above mentioned three methods is reported, in which the initial value of Mie scattering series is calculated by continuous fractions and the others are calculated by backward recursion. The data are saved in the array data type and the program uses the recurrent method while the algorithm is realized in Matlab. The comparison of the results indicates that the calculation time is very short and the results are hard to overflow. Numerical calculation shows that the algorithm is efficient, reliable and robust in extremely wide range of particle size and refractive index.
Analysis of transform from self-defocusing to selffocusing of LN crystal based on coupling theory
KANG Yi-fan, WANG-Chao, HU Man-li, ZHOU Jing-hui, GAO Ping-an, TANG Tian-tong
2007, 28(3): 367-370.
Z-scan experiment for measuring three-order nonlinear refractive coefficient and time-resolved scan experiment for measuring photorefractive nonlinear refractive coefficient were made with lithium niobate crystal doped with Fe and Tb. To explain the characteristics of the time-resolved scan curves, based on the coupling effects of photorefractive and third-order nonlinearity in the nonlinear medium, together with two analogic refractivity-timed expressions, an analysis on the dynamic evolving process of spatial bright soliton is made and eventually the physical mechanism of dynamical evolution from self-defocusing effect to self-focusing one under specific experimental condition is presented, which is completely coincident with the experimental phenomenon. The analysis has also validated the existing possibility of spatial dark soliton in self-focusing photorefractive crystal.
Absorption spectrum analysis of Nd∶KY(WO4)2 and Nd∶KG(WO4)2 crystals
GUO Li-hua, YANG Wen-qin, FENG Shang-yuan
2007, 28(3): 371-375.
Nd∶KY(WO4)2 and Nd∶KG(WO4)2 crystals are proved to be good laser crystals through the analysis of their absorption spectrum at room temperature. According to the absorption spectrum and data derived from Judd-Ofelt theory as well as measured absorption and data obtained from the test, VC++ program was used to calculate the intensity of spectral line, oscillator strength and absorption cross-section of the crystals. Then the values of three crystalfield adjusting parameters Ωλ(λ=2, 4, 6) of Nd3+ ion were obtained by fitting calculation. The spontaneous transition probability, energy level lifetime, fluorescence branch ratio and integrated emission cross-section were calculated theoretically. The calculated fluorescence branch ratio β indicates that the fluorescence branch ratios of both Nd∶KY(WO4)2(β1060nm=0.4380) and Nd∶KG(WO4)2(β1060nm=0.4618) crystals are large. At last, X=Ω4/Ω6 of Nd∶KY(WO4)2 and Nd∶KG(WO4)2 crystals were calculated and compared with those of other laser crystals. It is concluded that Nd∶KY(WO4)2and Nd∶KG(WO4)2crystals can produce 1060nm laser.
Improvement of conventional synthetic discriminant functions
GAN Hou-ji, HUA Wen-shen, WANG Jin-yu
2007, 28(3): 376-379.
To overcome the great correlation peak fluctuation caused by the composite matchedfilter prepared with conventional synthetic discriminant functions, the conversion process of coding from conventional synthetic discriminant functions to the coding matched filter is analyzed. The reason for correlation peak fluctuation was found. A modified scheme, in which the coding arithmetic is considered when the linear combination coefficients of the synthetic discriminant functions are calculated, is proposed. The results of the computer simulation indicate that, compared with the conventional synthetic discriminant functions, this improved method can greatly reduce the correlation peak fluctuation of the composite matchedfilter, simplify the postprocessing and improve the veracity of the automatic identification of the correlation peak.
Effects of cascade nonlinear medium spatial configuration on optical field characteristics
DENG Ya-hong, LUO Bin, PAN Wei
2007, 28(3): 380-383.
The expression of the optical field distribution in arbitrary location after Gaussian beam passes through cascade nonlinear mediums is derived with Fourier transform method and Fresnel diffraction principle. The variation relation of the optical field peak intensity, the peak power location, beam width and modulation factor in the cascade nonlinear mediums is investigated. The result shows that the optical field peak intensity increases gradually, the peak-to-peak amplitude becomes shorter, the beam width becomes narrower, and the modulation factor becomes bigger as the nonlinear effects enhance. The configuration of the nonlinear mediums should be located equidistantly, and kept away from the peak location of the optical beam by all means. The equidistance of the nonlinear mediums has to be optimized to reduce the risk of the optical element damage.