2014 Vol. 35, No. 6

OE System and Engineering
Engineering analysis method of strap-down inertial navigation system error
Guo Shuan-yun, Ma Zhong-xiao, Xu Kai-luan, Kang Zhen, He Jun-feng
2014, 35(6): 927-932.
For choosing right gyro and accelerometer to design a good strapdown inertial navigation system(SINS) according to its precision need,a new error analysis method combining theory with engineer design experience was proposed. The functions of inertial sensor-error,velocity-position error and attitude error under difference working conditions of SINS were set up.One method that for designing a SINS with the position-error less than 100 m during 2 min was suggested.
Adjustment technique for multi-spectral optic axis parallelism of suppression sighting system
Sun Yu-kai, Liu Zhao-qing, Wang Jing, Wang Xiao-yi
2014, 35(6): 933-937.
The parallelism of optical axis of suppression sighting system is an index to achieve accurate suppression, the characteristics of which can guarantee the parallelism of the rotary mechanical axis, visible axis and laser axis.An adjustment method for optic axis parallelism of suppression sighting system utilizing the dual-optical wedge was put forward,which could make the optic axis deflect through rotating the dual-optic wedge so as to realize the parallelism calibration of every axis. The characteristics organization of the system was analyzed, the principle and method of the dual-optical wedge were introduced on focus, and the mathematics model was established.The simulation for the model was done by Matlab, the experimental setup based on the proposed method was built and tested.Result shows that the triaxial parallelism precision is all less than 0.1 mrad by using the dual-optic wedge method.
Analysis and design of optical system of laser semi-active proportional seeker
Li Fu-wei, Zhang Yun-qiang, Pan Guo-qing
2014, 35(6): 938-942.
According to the analysis of the working principle of laser semi-active proportional seeker, the characteristics of the optical system were summarized. Based on the overall design requests, an optical system of laser semi-active proportional seeker,with 1.064 m waveband,38 mm focal length,3 instantaneous field of view (IFOV) and 1 linear zone, was designed. The wavefront with large lateral spherical aberrations was simulated by Zernike polynomial and superposed on the incident wave surface, then the system was optimized.By changing the lateral spherical aberrations ,the size and uniformity of image facula could be regulated, and the diameter of facula was determined as 1.5 mm.
Image stabilization based on optical correlator
Tang Wu-sheng, Sui Jing-gao, Zhang Xiao-ya, Zhang Sheng-hui, Chen Yi-xiu, Jia Hui, Yang Jian-kun
2014, 35(6): 943-948.
Compared to conventional electronic and mechanical image stabilization techniques, the image stabilization technology based on optical correlator could process data rapidly and ensure high accuracy. With optical joint transform correlation, the displacement difference of two adjacent frames would be obtained. Through extracting the relevant peak position, translational and rotational stabilization could be implemented, and with the experimental analysis, the accuracy of translational stabilization could be achieved 0.1 pixels (after improvements of compensation algorithm, it could be up to 0.04 pixels), and the accuracy of rotational stabilization could be up to 0.1 .
Optical system design of large-diameter off-axis reflection-type star simulator
Zhang Wen-ying, Zhang Guo-yu, Zhang Lei
2014, 35(6): 949-954.
Star simulator,as the ground calibration system of star sensor, can be used to simulate the star involving its size, magnitude,spectrum,color temperature,position and the angular distance between stars,etc.With the continuous development of space technology,the requirement of the star simulator itself has become higher, and then the design of collimation optical system for star simulator important component has become the key factor. Based on the characteristics of off-axis reflective optical system which has no chromatic aberration,small volume,high light efficiency and the center without blocking, an off-axis parabolic collimation optical system was proposed,and the assembly and calibration process was discussed. The system consists of an off-axis parabolic mirror and a plane mirror,which has a clear aperture of 300 mm,focal length of 3 000 mm,and viewing angle of 30.The image quality analysis shows when the distortion in field of view is 0.006 2%(0.01%), the modulation transfer function (MTF)reaches the diffraction limit and the wave aberration is 0.071 6 .This design of the optical system can meet the requirements.
Optical design of visible and IR spectral catadioptric system
Chen Jiao, Luan Ya-dong, Hu Bo, Wang Ling, Teng Guo-qi, Zhang Bo, Lin Xiao-juan
2014, 35(6): 955-959.
Based on the requirements of miniaturization and light weight for airborne optic systems, IR and TV system were designed with the common light path. For the 640480 uncooled focal plane array,an infrared long wave system was presented with a focal length of 185mm, field of view (FOV)of 5.8, F number of 1.3. For the 1/3 charge coupled device (CCD)(4.8 mm 3.6 mm,759 596pixels), a visible(TV) system ,which had 86mm focal length, 4 FOV and 4.5 F number, was completed.
Transient high temperature sensor design based on black-body radiation thermal film
Wang Jun-feng, Li Jin-ying
2014, 35(6): 960-965.
Against the difficult problem of the transient temperature measurement, by using the radiation thermometry technology and contact thermometry technology combined method, we designed a transient high temperature measuring device which consisted of the blackbody radiation temperature sensitive body, the cylindrical metal housing of high strength and the signal conditioning circuit in the housing. Though the proper selection of thermal sensing thin film special material and the rational design of the overall structure, as well as using ANSYS software, we analyzed the transient high temperature heat conduction of the blackbody temperature thin film. Analysis shows that when temperature load of 2 000 ℃, 2 500 ℃, 3 000 ℃ applied, the temperature sensor response time was 487.001 s,545.001 s,590.001 s,respectively.This device can overcome the traditional transient temperature sensor shortcoming of bulky, slow response, inconvenience to install and susceptibility to harsh environment factors and so on. It has a good application value in the field of thermometry technology.
Application and optical design case analysis of LED used in air craft navigation lamp
Su Dan
2014, 35(6): 966-970.
To show the advantages and prospects of LED applicated in the field of aviation ,we introduced the LED light source used in aircraft navigation lights, which has the merit of small volume, light weight, easy design and maintenance, etc, and elaborated on the requirements of high security, high reliability and high optical quality for applying LED in aircraft navigation lights . Through the analysis on the optical distribution demands of navigation lights, we designed an optical lens which was consisting of total internal reflect (TIR) system and prism system according to the selected LED source. The optical simulation result shows that, the center optical intensity is more than 40 cd when the power consuming is less than 1W , indicating the LED navigation lamp has good optical performance.
Device for photoelectric auto-correction of artillery based on PSD
Chen Ran, Wang Chang-jiang, Liu Guang-hua
2014, 35(6): 971-975.
Artillery auto-correction technique is important for realizing the automation and intellectualization of tank cannon artillery correction process as well as enhancing the accuracy of firing. A device for photoelectric auto-correction of artillery based on position sensitive detector (PSD) was introduced. By adopting PSD as the photoelectric detector and utilizing the photoelectric conversion and signal processing technology, this device could gain the real-time barrel bending deformation automatically and give the correction of the howitzer, so as to realize the error correction and the automatic correction in the artillery. At different initial positions and shooting angles, the device could achieve the correction precision of 0.1 mil (mil :unit of angle for artillery measuring distance, 1 mil=0.060.001 rad)
Design of optical system for trapped 199Hg+ in linear ion trap
He Yue-hong, She Lei, Chen Yi-he, Li Jiao-mei
2014, 35(6): 976-980.
An optical system for trapped 199Hg+ in linear ion trap was designed by the Zemax software. The optical system consists of two parts which are optical excitation system and fluorescence collection system. The optical excitation system is composed of 202Hg electrodeless lamp and excitation lens system. The diameter of 15 mm surface light which is produced by 202Hg electrodeless lamp is transformed into rectangular light of 23 mm4 mm by the excitation lens system. The rectangular light excites 199Hg+ atomic transition and then the 199Hg+ radiates fluorescence. The fluorescence is collected by the fluorescence collection system which is composed of collection lens system, filter and photomultiplier tube (PMT). The design results show that the fluorescence emitting surface is imaged well in the PMT whose diameter is 23 mm by the collection lens system. So the fluorescence collection is quite efficient and the collection efficiency is about 3%. Experimental results show that the optical system is completely satisfied for present experiment and it has a high signal to noise ratio (SNR) which is about 20. It makes necessary preparation for application of highperformance 199Hg+ microwave frequency standard.
Design of micro spectrometer for steel detecting
Li Teng-fei, Li Song, Wang Ya-pei, Li Qiang, Wang Liang-xun
2014, 35(6): 981-986.
In consideration of inadequate research on photoelectric direct reading spectrometer used for steel detecting,we presented the Czerny-Turner system design method, discussed the optimization method and verifying method, as well as developed the spectrometer. It adopted cubic polynomial to fit calibration wavelength, and the tested resolution reached 0.225 nm in 436 nm~608 nm all band and 0.135 nm in mid band which could meet the demands of steel detecting. Furthermore, the qualitative analysis method based on multi-frame judgment guaranteed a 1.5% detective limit of 7 kinds of elements. The half quantitative analysis based on fitting spectrum database could offer 2% detective precision of the 25 kinds of samples. They could provide an important reference for the recognition of steel mark.
Surface vertical alignment effect on performance of holographic polymer dispersed liquid crystal gratings
Li Wen-cui, Shu Xin-jian, Yang Yi, Huang Wen-bin
2014, 35(6): 987-990.
In order to get the holographic polymer dispersed liquid crystal (HPDLC) grating with high diffraction efficiency and perfect morphology, the effect of surface vertical alignment on the properties of HPDLC grating was investigated. Firstly, the effect of the vertical surface treatment on the orientation of liquid crystal molecules was studied. It is found that the vertical anchor effect of liquid crystal decreases with the increase of cell gap and the orientation depth is about 3 m ~ 5 m. Secondary, the characterization experiment of separation was done.And results show that as the cell gap increases, the surface effect on the bulk LC droplets reduces due to the longer distance. For the thinner cell, almost all the LC droplets are confined on the inner surfaces of the substrates which cannot flow and coalesce with the neighboring droplets, so the phase separate is not good. However, if the cell is too thick, the effect of vertical alignment on the LC droplets in the middle of the cell is very small and the bulk droplets are less ordered so that the morphology is similar to those of conventional (without vertical alignment) HPDLC cells. Experimental results indicate that only in the condition of certain surface vertical alignment strength(cell gap is 12 m), the HPDLC with high diffraction efficiency and low scattering loss can be realized.
OE Information Acquisition and
Corner point detection in interested boundary tracking
Tian Jun-wei, Wang Qin, Zhao Peng, Wang Gang-gang
2014, 35(6): 991-995.
Aiming at the problem for losing boundary information within the region near the corner point during boundary tracking,the method for judging and searching corner point was studied. On the basis of analyzing the relationship between the radius of extended neighborhood and the location of the corner, the corner point judging rule was proposed and the range in which corner point existed was deduced. The region searching algorithm was proposed to detect the corner point in the deduced range. From the relationship of 5 known boundary points, the algorithm estimated the neighborhood in which the corner point was included, and made the neighborhood contracted to the corner point by selecting appropriate radius. Examinations were performed at test images and side face image. Results show that the boundary points increase form 13 to 21 for test image and from 19 to 37 for side face image, the new method can detect the corner point accurately and can also detect right seeds so that the boundary tracking algorithm can include all contour information.
Multi-plane holographic display and its noise elimination
Zhou Peng-cheng, Bi Yong, Sun Min-yuan, Qi Yan, Zhang Ren-li
2014, 35(6): 996-1002.
The computer-generated hologram of multi-plane three dimensional object was produced based on chromatography and the Gerchberg-Saxton algorithm. And a three dimensional display with full parallax was obtained by writing the hologram into spatial light modulator. According to this method,the gray image was displayed and high image quality could be got.The cube composed of 100 planes was set up and its 3D image could be obtained.In addition, the phase translation function was added into the computer-generated hologram ,the noise of multi-order diffraction images, which arose from the grid-structure of spatial light modulator, was eliminated substantially,then the energy utilization efficiency was as much as 379% of before. Thus a 3D holographic display of high diffraction efficiency, high image-quality and full parallax can be realized.
Off-axis holography based on Burch coding
Chen Lin, Xu Zhong-bao, Wu Wen-jun, Zhou Sheng-fei, Wang Xin-yi
2014, 35(6): 1003-1008.
A method for separating the original image and the conjugate image in the reconstruction of Fourier computer generated hologram (CGH) was studied. According to the analysis on the process of CGH reconstruction by Fourier transform, the method which put the original sampling points into a larger null matrix was used to separate the original image and conjugate image. After the fast Fourier transform with the new matrix, CGH was obtained by Burch coding, then a high pass filter was used to eliminate the influences of interference of background light on the visual impression when image was reconstructed. The degree of separation of the original image and the conjugate image of CGH produced by this method can be controlled with the size of the null matrix, the larger the null matrix, the greater the degree of separation. The experimental results show that the original image and conjugate image of CGH can separate when the null matrix is 4 times of the original size. But in order to filter the zero order light spot easily, the null matrix should be more than 4 times of the original size slightly.
Endoscopic image segmentation method combined region growing and Hough transformation
Geng Chun-ming, Fang Fei
2014, 35(6): 1009-1015.
An image segmentation method for effective detection area based on region growing and Hough transformation was proposed in view of the features of actual endoscopic image. Firstly, region growth was used to segment the region of interest (ROI) roughly, there might be missed edge or false edges. Then the image was smoothed to remove noise by morphological processing. Next, the Canny operator was used to detect the edge and suppress the noise at the same time . In the end, Hough transformation, which was applied to detect circles, was conducted to determine the image position of the effective regions. The simulations of 90 groups of actual endoscopic images with Visual C++ 6.0 were done.The experimental result shows that the method can segment the strong light interference and extract the effective detection regions accurately of 88 groups;only 2 of them were not accurate enough.
Optical Metrology and Measurement
Improved method for nighttime visibility measurement based on digital photography
Xiao Shao-rong, Zhou Jia, Wu Qun-yong, Xu Meng, Shang Guo-qing, Shi Liu-feng
2014, 35(6): 1016-1022.
In order to reduce the uncertainty caused by background light noise when measuring nighttime visibility using digital photogrammetric method, the system based on double light sources was improved. An effective method was adopted to limit CCD field angle by using the shading cylinder. For obtaining the grayscales of the double LED backlights at different distances taken by CCD, computerized image processing was applied for captured images. Then the visibility was derived from extinction coefficient acquired by Allard-s law. The contrast test was done to analyze the gray information in three conditions: in dark background, with or without shading cylinder in light background. Taken the visibility measured in dark background as the standard value,compared with the results from using shading cylinder ,the correlation coefficient and average relative errors are 0.911 3 and 6.87%, while they are 0.322 7 and 23.38% without shading cylinder.It can be seen that, the ability of restraining interference from background noise is enhanced by using shading cylinder, thus more accurate results can be got with measuring nighttime visibility.
Laser differential confocal curvature measurement system with grating length
Xu Peng, Zhao Wei-qian, Wang Fang-biao, Xiao Yang, Zhou Tao-geng
2014, 35(6): 1023-1028.
In order to enhance the environmental anti-interference capability for the radius of curvature (ROC) measurement and meet the requirements of use on the production spot, a laser differential confocal curvature measurement system with grating was developed, which used the property, that the zero point of a differential confocal intensity curve corresponds to the focus of objective, to precisely identify the cat-eye and confocal positions of the tested lens, and then used the grating to measure the distance between these two positions, thereby the highprecision measurement of ROC was achieved. Experimental results show that the system has an accuracy of better than 510-6. So it can meet the demand of high-precision measurement of ROC.
Adjustment and calibration of dual-CCD-s mirroring overlapping position in digital holography
Pan Yun, Pan Wei-qing
2014, 35(6): 1029-1034.
The development and application of digital holography has been greatly limited by the insufficient pixel numbers and dynamic range of charge coupled device (CCD). To solve this problem, an arrangement scheme of dual-CCD-s mirroring overlapping position was put forward, based on the information fusion technology. Firstly, the interference image of two spherical waves was used to adjust the dual-CCD-s mirroring overlapping position, and the feasibility of this method was proved. Then in the experiment, the dual-CCD-s position was adjusted in real time by using the off-axis interferometry of spherical wave and plane wave, and the digital interference technology. Finally, the calibration parameters of the dual-CCD-s mirroring overlapping position were given by using the computer digital image processing technology. The experimental results show that, the dual-CCD-s mirroring overlapping position can be precisely adjusted and calibrated by this method, and the error is only 14 m.
Centering alignment technology of high-precision standard lens
Zuo Xiao-zhou, Jiang Feng, Zhang Yan, Hui Yang-gang, Liu Xin
2014, 35(6): 1035-1039.
A new high-precision assembly technique by combining traditional turnery technique with computer assisted assembly, in an attempt to meet the strict requirements on centering errors of high-precision standard lens, was introduced. First, the tilt-errors of optical axes were managed by turning centering initially, and then with the assistance of high-precision centering errors measurement,shift-error alignment for each lens was conducted. Last,through simulating the optical axis space state by computer,the ration abrade for circle was done precisely at given angle so as to control the tilt-error between each lens.The result indicates that by using this technology, the tilt-error of the lens is less than 5 and the shift-error is within 3 m, thus the design objectives are met.
Surface roughness measurement based on digital holography
Chen Gang, Zhou Wen-jing, Hu Zhen, Zhou Qing, Peng Ke-qin, Zhang Wei
2014, 35(6): 1040-1047.
Surface roughness measurement based on digital holography was carried out. The tested surface roughness parameters were calculated from the surface profile which was mapped from the reconstructed phase distribution of digital hologram. Firstly, the standard calibration plate and high-resolution panel were taken as the tested samples to reconstruct errors and test the repeatability of the digital holography measurement system,involving the lateral size error and the height error. The reconstruction error and repeatability error for lateral size were 1.11%, 0.61%, respectively. And the errors for height were 11%, 1.8%, respectively. Then an ordinary coated reflector was taken as a sample, and its surface roughness values along 3 segments of evaluation length were 0.010 37 m, 0.010 33 m, and 0.009 67 m, respectively(15 sampling lengths).
Measurement errors of flash parameters in visual electrophysiology
Ding Xiang, Dong Wei, Liu Wen-li, Li Jiao, Chen Yan
2014, 35(6): 1048-1053.
The accuracy of flash parameters is critical to visual electrophysiological examination. An equivalent circuit model of the flash measurement system was established according to the characteristics of visual electrophysiological flashes. The influence of parameters of the flash measurement system on measurement error of flash waveform, intensity and duration was analyzed theoretically and experimentally. Xeon lamp and LED flash sources were tested. Experiments were carried out to investigate how measurement errors varied with parameters of the measurement system. The method for reducing the measurement errors respect to different application requirements was proposed, as well as the method to eliminate the theoretical errors when measuring the flash duration of LED and the flash intensity, which were demonstrated by experiments. The intensity and duration of LED flash were measured at different system parameters by using the proposed methods. Results demonstrated that the standard deviation of the flash intensity is 0.17% and that of the duration is 0.07%, which can be regarded as constants, showing good consistence with theoretical analysis.
Optical Element and Fabrication
Effect of photocathode sealing solder melting layer defect on gas tightness for ultraviolet imaging device
Xu Jiang-tao, Yang Xiao-jun, Zhang Tai-min, Han Kun-ye
2014, 35(6): 1054-1057.
To solve the problem of ultraviolet imaging device sealing leakage between the photocathode and the tube body, we deeply analyzed the quality problem of the tube body InSn alloy in melting process,and found out the solder melting layer defect came mainly from the incompletely solder degassing, the basal surface oxidation and the equipment contaminated with oil.Through optimizing the process parameters, we improved the process quality and changed the indium equipment of the tube body aside solder melting into casting molten,to make the qualified rate of the tube body solder melting reache 100% and the qualified rate of gas tightness between photocathode and tube body sealing yield to 98%.
Diamond turning compensation techniques of diffractive optical elements
Zhang Feng, Wang Zhi-bin, Zhang Yun-long, Guo Xiao-gang, Su Ying, Guo Rui
2014, 35(6): 1058-1062.
The ultra-precision diamond turning is a significant way to manufacture high- precision diffractive optical elements (DOE); however, this way is unable to achieve compensation machine currently that results in lower machining accuracy. Based on the study on the process of diamond turning and the compensation of surface shape error, and on the analysis of actual measurement data by the surface profile, the normal residual error was calculated between the actual turning curve and the ideal curve to get new machining trace of diamond turning in this paper. The compensation test on DOE of 78 with the diamond turning machine was done, and finally the value of peak value (PV) converges rapidly from 10.4 m to 4.3 m.
Optical stimulation and application of multi-chip COB LED packaging with minitype lens array
Lin Cheng
2014, 35(6): 1063-1068.
Recently, high power multi-chip chip on board (COB) LED has become the industrial trends, duo to its advantages, such as higher packaging density, higher thermal stability, wider irritation angle and etc. However, low light extraction efficiency of COB LED restricts its application and development. In order to improve the light extraction efficiency of LED, the models of COB LED packaged by cone arrays, half-ellipsoid arrays, rectangular pyramid arrays and hemisphere array were established and investigated by applying stimulation software. The stimulation result showed that under optimal conditions, the luminous flux of COB LED with 0.9 mm height and 0.5 mm diameter cone array lens increased from 67 lm to 84.3 lm, that is, light extraction efficiency increased by 25.8%. Finally, LED samples with RGB multi-chips were packaged by 1 mm diameter hemisphere array, and the light extraction efficiency increased by 18.8%.
Experiment on defect-free edge polishing of LiNbO3 chips
Li Pan, Bai Man-she, Xing Yun-yun, Yan Ji-zhong
2014, 35(6): 1069-1074.
To meet the requirements for defect-free edge polishing of high-precision fiber optic gyroscope integrated optic modulator LiNbO3 chips, a new polishing process based on pad polishing was developed. According to the analysis on the causes for edge damage during the edge polishing, three solutions were presented:controlling the big particles in polishing material, choosing the low sub-face damage polishing and making the particles size close to or less than double of the critical cutting depth. With the new process, the defect-free edge polishing of LiNbO3 chips could be achieved and the results show that the edges under 1 500 microscope have no visible defect, the chip end face roughness Ra is less than 0.8 nm and the surface flatness reaches better than /2.Additional,this polishing process has great application value.
Extended depth of field in microscopy
Zhang Ping, Wu Jia-min, Lin Jing-yu, Liu Ye-bin
2014, 35(6): 1075-1082.
Due to the urgent needs in life sciences, the extended depth of field (EDOF) in microscopy is becoming a focus. In order to study the microscopy depth of filed, the EDOF was studied and summarized. Based on the dramatic enhancement of EDOF, the optical scanning, spatial light modulation, wavefront coding and light filed microscopy were introduced and compared synthetically. Their theory, method and capacities for EDOF were summarized, and the technology defect and future development were analyzed. With the enhancement of technologies, the depth of filed in microscopy can be enhanced about 1 or 2 orders of magnitude compared with traditional microscopy.
Infrared Technology
Car-s night-vision system based on infrared detection technique
Zhang Zhi-feng, Yang Gui-shuan, Shen Shuai-feng, Mao Wen-jing, Qiao Lin, Du Yin-xiao
2014, 35(6): 1083-1087.
In order to ensure the driving safety and enhance the discrimination accuracy, a car-s night-vision system was put forward based on active near infrared detection technique. The system included the infrared emitting unit, infrared imaging unit, and image display unit. The loss rate of the system in field test was 1.3%. The experimental results imply that most infrared components in traditional automotive light are useless for night illumination, and the visible light energy efficiency is lower. The car-s night-vision system based on infrared detection technique can ensure effectively driving security.
Position analysis method of infrared image point based on energy distribution
Li Bin, Liu Gang, Hu Qiu-ping, Liu Zhao
2014, 35(6): 1088-1093.
In order to solve the problem of infrared image point position analysis,a method based on energy distribution was proposed.The image point position and accuracy were analyzed by the digital image processing techniques. The position analysis model and method flow were studied according to the image characteristics of infrared target;secondly,based on the analysis of position error factors, the accuracy evaluation was completed;finally,a typical application example was tested and verified through calculation.Compared with the traditional method,it is shown that the method based on energy distribution can be employed in position analysis of infrared image point with visual representation and high precision:the accuracy is better than 1/6 pixel usually or even better than 1/10 pixel for larger image.The method is significant in the research on IR detecting instrument and position analysis.
Spatial NETD measurement of thermal imager
Hu Tie-li, Ma Shi-bang, Guo Yu, Xin Zhou, Li Si-wei, Xie Qi, Liu Rui-xing, Fan Ji-hong, Zhang Mei, Xie Yi, Liu Jun-ning
2014, 35(6): 1094-1098.
The spatial noise on staring array thermal imager restricts its capability in detecting, distinguishing and tracking the long distance targets. To solve the problem in measuring the thermal imager spatial noise, its measuring theory was analyzed and the mathematical model for measuring the spatial noise based on signal transfer function (SiTF) was presented. After removing the temporal noise equivalent temperature difference (NETD) from the noise of a certain group or district or the whole pixels in thermal imager, the spatial NETD model was calculated through analyzing statistically the noise of those pixels. In measuring the SiTF and spatial NETD of cooled MCT320256 thermal imager, when the temperature of the background blackbody is 5 ℃, the SiTF of central district in field of view(FOV) is 27.29 mV/℃, and the spatial NETD is 0.128 ℃. When the temperature of the background blackbody is 20 ℃, the SiTF of central district in FOV is 29.03 mV/℃, and the spatial NETD is 0.121 ℃。The measuring results show that the measuring method can evaluate the influence of spatial noise on the performance of thermal imager.
Laser Technology
Surface characteristics study of laser-induced thin film damagebased on similarity measure algorithm
Yang Li-hong, Xie Hui, Su Jun-hong
2014, 35(6): 1099-1103.
The determination method of laser damage of thin film and the evaluation method of damage threshold are indispensable for enhancing anti-laser ability of infrared system observation window and its operating performance. The damage characteristics and mechanism of film by pulse laser induced damage were researched. The experiments used by YAG pulsed laser for TiO2 thin film were offered for 1-on-1 way of laser induced. By using the two images taken from charge coupled device (CCD) before and after laser illumination, the matching of the damaged image and the undamaged image was realized, and the difference image measure algorithm was established. The experiments conclude that the different energy measures of TiO2 thin film samples can identify the damage situation:the measure value M0.1, no damage; 0.1M 0.2, mild injuries;0.2M0.5, moderate damage; M0.5, serious injuries. The roughness of thin film samples irradiated by the laser with the energy density of 0.5 J/cm2 increases obviously. The results show that the method of image matching test before and after laser irradiation can realize discrimination of laser-induced film damage.
Influence of fused side-pump coupler fiber angle on coupling efficiency
Tan Qi-rui, Ge Ting-wu, Wang Zhi-yong
2014, 35(6): 1104-1108.
Pump coupler is the key passive optical device of the high-power fiber laser. Its producing process is the side-fusing of the pump fiber and the main fiber. This producing process can keep the insertion loss of the main fiber low, but the angle between the pump fiber and the main fiber has a great influence on the coupling efficiency. In order to solve this problem, the theoretical model was established according to the structural characteristics of the fused sidepump coupler. The equations of the power and the fiber angle were derived. The simulation results were obtained and were demonstrated by the experiments. The conclusions are as follows: the pump coupling efficiency gradually increases with the decrease of the fiber angle between the pump fiber and the main fiber, but the critical fiber angle exists. When the numerical aperture (NA) of the pump fiber is smaller, the couple efficiency and the critical angle are larger. The critical fiber angle is 9.7 and the maximum coupling efficiency is 96.9% when the pump fiber NA is 0.22. The critical fiber angle is 11.5 and the maximum coupling efficiency is 97.8% when the pump fiber NA is 0.15. The conclusions are instructive for the designs and the productions of the highpower fiber coupler.