2012 Vol. 33, No. 5

OE System and Engineering
Application of infrared thermal wave technology in fault diagnosis and defect detection for armored equipments
FENG Fu-zhou, ZHANG Chao-sheng, ZHANG Li-xia, MIN Qing-xu
2012, 33(5): 827-831.
In order to reduce the operating complexity of fault diagnosis and improve the defecting efficiency of defect detection in armored equipments, the infrared thermal wave technology is introduced to armored equipments of PLA, which has been used widely in equipment maintenance in other countries. Firstly, this paper briefly depicted the basic principles and characteristics of infrared thermal wave. Then, two main factors including signal to noise ratio (SNR) and thermal excitation influencing the detection results were analyzed in detail. Finally, the experiments for fault diagnosis and defect detection were carried out. Experimental results show the engine power insufficiency can be positioned accurately without disassemble and the armored plate crack can be detected fast within 3.5s by means of this method.
Ultra-thin front projector for laser display system
KANG Yu-si, TIAN Zhi-hui, LIU Wei-qi, FENG Rui, WANG Yu-long
2012, 33(5): 832-836.
In order to solve the problem of larger projection thickness in optic system, an ultra-short-distance and ultra-wide-angle projection display system was designed by using the method of combining the free-form surface mirror with the aspheric surface. The projection distance was less than 20cm.The color gamut transformation and expansion model of laser and phosphor tricolor was built theoretically, and the real-time processing development hardware system for color transformation was set up using the digital micromirror device (DMD) chip as the spatial light modulator. This system can debug algorithms for varied color system transformations, verify the transformed model and provide a platform for developing specific color transform module.
Characteristic of ship target IR image
WANG Xue-wei, WANG Shi-li, LI Ke
2012, 33(5): 837-840.
Aiming at the features of infrared image obtained by imaging anti-ship missiles, this paper researches on the infrared radiation characteristic of the ship target and background of sea and sky, and makes a conclusion that the infrared image of ship target has an important characteristic, sea-horizon, which can locate the target region. To locate the ship target, the paper studied the sea-horizon feature of ship-target infrared image, and an algorithm based on preprocessing and linear fitting to locate the horizontal feature was put forward. The image preprocessing was carried out by applying the edge detection to obtain the gradient image, then the linearization and thinning processing was operated. At last, the Hough algorithm was used to locate the sea-horizon. The experiment result shows that compared with the improved linear fitting method, this method can extract the sea-horizon characteristic in ship-target infrared image precisely under the condition of low contrast and disturbance of cloud.
Implementation and parameter optimization for path length control of ring laser gyro based on DSP
FU Xin, MA Chong-ze, CHEN Lin-feng, HAN Zong-hu, HU Qiang
2012, 33(5): 841-845.
The main characteristics of TMS320F2810 were introduced and its application in path length control (PLC) technology in ring laser gyro (RLG) was discussed, numerically simulated and experimentally implemented. TMS320F2810 is characterized by high integration, good processing capability, low power dissipation and high performance price ratio, which is very convenient for digital integration and compact design of the RLG control system. Alternative current (AC) path length control system was implemented by this digital signal processing (DSP) chip and some associated circuits, and proportionalintegral-derivative (PID) control parameters were optimized based on Simulink simulation. PLC system was implemented and its software and hardware diagrams were presented, some optimized PID parameters (Kp=0.048, Ki=0.059, Kd=0.013) were obtained, and the whole control loop was experimentally verified. The experimental results show that the performance of the RLG is improved obviously, the bias stability is reduced from 0.025/h to 0.014/h after PID parameter optimization, and the anticipated objective is realized by the proposed control loop.
Nanometrology technology in precision measurement
ZENG Zhao-li, ZHANG Shu-lian
2012, 33(5): 846-854.
With the rapid development of nanometer science, there will be much higher standard on nanometrology technology. So far, the uncertainty of measurement can be realized sub-nanometer and even picometer in the range of dozens of micrometers. The current main technologies used in nanometrology have been reviewed, which include the laser interferometer, beat frequency F-P interferometer, X-ray interferometer, optical and X-ray interferometer, frequency measuring system and optical frequency comb technology.
Accurate calibration method for optical system based on zenith observation
ZHANG Lei, WANG An-guo, LI Hui, SHI Yi, ming
2012, 33(5): 855-861.
Aiming at the problem of optical system coordinated with carrier in practical application, the optical system was placed on the plane of horizontal coordinate system and the star image was taken. Coordinates of star image were calculated through image processing. The equatorial coordinates of stars were obtained by automatic celestial body identification and star apparent position calculation. Reference coordinate was established in plane of the sky centered by zenith point. The equatorial coordinates of stars were converted to reference coordinates, and then to topocentric image coordinates according to the relation between zenithal tangent plane and topocentric coordinate. The calibration equation between image coordinates and topocentric coordinates of stars was set up to calculate the deviation parameter of system. The calibration accuracy is arc-second magnitude. The high precision coordinate conversion from star sensor to carrier is realized by this method.
Numerical model of optical parametric oscillator
LI Xiao-lin, ZHONG Jian-jun
2012, 33(5): 862-866.
A mathematical model for optical parametric oscillator (OPO) by using paraxial approximation was proposed. It could simulate the wave mixing process of both nanosencond waves and contiunes waves. This model including the dispersion of different wavelengths of the three mixing waves used the splitFourier method and the spatial and temporal relations between mixing waves to describe the process in OPO. The model could give output waveform, power and threshold in high efficiency OPO under the conditions of different pump pulse energies, pulse widths, transmissivities and reflectivities of cavity mirrors. In the experiment, a periodically poled lithium niobate crystal (PPLN) was used as the nonlinear medium. When the single pulse energy of input pump beam at 1.06 m was 0.4 mJ, we could get the energy of idle wave at 3.8 m more than 0.07 mJ, which was qualitatively fitted by the numerical result of 0.08 mJ.
People-tracking algorithm with improved particle filter based on feedback fusion
ZHANG Ying-ying, WANG Hong-juan, HUANG Yi-ding
2012, 33(5): 867-871.
A new particle filter based on feedback fusion was proposed to solve the problem that the traditional particle filters were easily influenced by the similar background and occlusion. The proposal distribution was fused with the recent observation information,so that the particle could search for the most probable location of the object. According to the change of the relative displacement, the size of the tracking window was changing adaptively, which reduced the computational complexity and kept the diversity of the particles to a certain extent. The experimental results show that the proposed algorithm effectively deals with the occlusion, chaotic and similar background and change of the target size, providing better tracking performance than particle filter.
Elimination of random errors in four-step phase-shifting digital holography
QIN Yi, WANG Zhi-peng, ZHANG Ying-ying, YANG Xing-qiang
2012, 33(5): 872-876.
A novel approach is proposed to eliminate the random phase-shifting errors and CCD noise in four-step phase-shifting digital holography. By carrying out the phase-shifting process repeatedly, a series of holograms for each phase step are obtained. Theoretical analysis indicates that the random phase-shifting errors and CCD noise can be completely removed if we substitute the single hologram with the average of multiple holograms in the reconstruction. The feasibility of this method is demonstrated by computer simulation, and the results show that this method is useful in improving the quality of reconstruction in phase-shifting digital holography.
OE Information Acquisition and Processing
Improved moving object detection method based on Gaussian mixture mode
DONG Xiao-shu, CHEN Gang, BIAN Zhi-guo
2012, 33(5): 877-883.
Gaussian mixture model (GMM) is widely used in moving objects detection in image sequences; however, the existing moving objects detection methods which are based on Gaussian mixture model are not so efficient especially when dealing with noise or illumination mutation. In order to solve the problems above, a new method is proposed. Edge images are not sensitive to noise or illumination mutation, so that the edge Gaussian mixture model (EGMM) which is constructed with edge images can be used to improve the moving objects detection. And neighborhood-based difference method is improved to restrain noise effectively. The proposed method combines the edge Gaussian mixture model with the improved neighborhood-based difference method. Experimental results prove that the proposed method can increase detection rate while reducing false alarm rate and has stronger capacity of restraining noise and dealing with illumination mutation.
Constructing method of calibration feature points used for circle structure light vision sensor
2012, 33(5): 884-888.
Pipe is one of the most important transmission modes in industry and the detection of the in-pipe surface is necessary to ensure the transmission safety. Circle structure light vision sensor is extensively used to measure the three-dimensional size of devices because of its characteristics of high precision, large information and non contact. The calibration of the circle structure light vision sensor is the most important step to realize the measurement. A novel constructing method of calibration feature points for circle structure light vision sensor was proposed based on coplanar reference object. First the calibration points were obtained based on the invariance of cross ratio in different plane position, then via the camera coordinate system, the transfromation between the different plane local coordinate system and the world coordinate system was realized, finally the space calibration feature points were constructed based on the world coordinate system. The proposed method greatly reduces the cost of the calibration equipment and simplifies the calibrating procedure. The calibration precision achieves 0.340 mm which proves the feasibility of the method.
Research and implementation of lighting information obtaining from light-shadow images
HUANG Guan-lang, ZHANG Wei-ping, LUO Ting-jun, XIAO Yu-fei
2012, 33(5): 889-893.
Current methods exist some problems of obtaining the lighting information that whether the ray is direct light and whether its irradiance reaches or exceeds a certain value. In order to solve the problems, an image-processing method based on Matlab was proposed. By processing the light-shadow images, the lighting information was acquired by this method automatically. Relationships between the characteristics of light-shadow images and the lighting information were analyzed. And some grid images under laboratory lighting conditions were taken. Meanwhile, Matlab program was designed and applied to get the corresponding lighting information of the images. The results showed that this method could obtain the characteristic values of light-shadow images and actual lighting information accurately, and the program run stably.
De-noising method for mixed noise based on median filter and lifting wavelet transform
CHANG Liang-liang, WANG Guang-long
2012, 33(5): 894-897.
Aiming at existing de-noising algorithms are often designed for removing single Gaussian noise or impulse noise, an efficient algorithm for mixed noise removal in image was proposed, including space impulse noise removal and wavelet Gaussian noise removal. Firstly, an impulse noise detection algorithm based on median filter was given to filter impulse, and at the same time a lifting wavelet was constructed by lifting original wavelet. Secondly, a threshold method based on lifting wavelet transform for image was applied to de-noising Gaussian noise. At last, simulations were conducted on the presented algorithm, and the simulation result shows that this algorithm can remove mixed Gaussian and impulse noise in image efficiently.
Moving object detection based on image sequences
TU Li-fen, ZHONG Si-dong, PENG Qi
2012, 33(5): 898-903.
According to the problems of numerous noises and incomplete detection of moving object in dynamic environments, a method for moving target detection based on pyramid-style multi-resolution model was proposed. The areas of target were obtained in low resolution and the details were in high resolution. For complex environment, an image difference operation scheme using high/low double-threshold substituted for traditional single threshold was proposed, which could obtain thresholds automatically. The scale transformation of the current and background frames was carried out first and a group of images in different resolutions were obtained. Then the high/low threshold differential images in different scale spaces were got. At last, an image fusion process was done from the high layer to the low layer, and an integrated object image with few noises was obtained. Experimental results show that the proposed method achieves a high accuracy for the moving object extraction, it has obvious advantages especially in complex dynamic environment. The precision is 0.802 for single object and 0.615 for multi object.
Target tracking method based on joint transform correlation
MA Jin, TIAN Tao
2012, 33(5): 904-908.
Correlation tracking technology plays an important role in image tracking. A tracking method based on joint transform correlation was studied. Adjacent frames in image series were sequentially operated, then the position of the correlation peak and the time interval of adjacent frames were obtained. These data enabled us to get the changes of target in position, direction and velocity. Simulation results show that the proposed method solves the problems in traditional algorithms which have accumulated errors and are easy to make targets drift out of the reference template , and can recognize and track the target steadily based on joint transform correlation.
Stereo matching algorithm based on affine invariant region constraint
PENG Qi, ZHONG Si-dong, TU Li-fen, MEI Tian-can
2012, 33(5): 909-914.
Aiming at the exiting stereo matching algorithms which could not meet the speed requirements, a novel quick stereo matching method based on region constraint was presented. Firstly, four pairs of stable feature points were selected as the initial matching points, and each quadrilateral was structured according to the four pairs of matching points in the left and right image respectively. Then the quadrilateral was divided into four triangles and each triangle was an area for matching. Feature points in the area were matched based on affine invariant. After the matching feature points were obtained, a small window was structured centered on those points. At last, the precision testing was implemented using the traditional method based on gray information. Experimental results demonstrate that the proposed algorithm can notably improve the matching speed which meets the requirement of real time.
Optical Metrology and Measurement
Distortion measurement of grating head-up display
LI Qian, LIU Xue-song, GUAN Yun-tian
2012, 33(5): 915-919.
The distortion of grating head-up display seriously affects the observation, measurement, positioning and analysis of object. Therefore its distortion quantitative measurement must be finished during the process of setting and assembling. Combining with the work principle and distortion causes of grating head-up display and utilizing the photoelectric measurement technology, its distortion quantitative measurement was further studied. Firstly, the distortion measurement system was set up to measure the distortion of grating head-up display caused by different reasons, and its CCD detector was calibrated. Secondly, the calibrated CCD detector was used to measure the distortion of grating head-up display, and the uncertainty of distortion measurement was analyzed. Utilizing this distortion measurement system, the experimental results show that the uncertainty of the relative distortion measurement of grating head-up display is 0.5%.
Concentric circles grating-based telecentric 3D profile measurement system
HAN Zhong-qing, YANG Sheng
2012, 33(5): 920-925.
A concentric circles grating-based telecentric 3D profile measurement system was proposed to satisfy the needs for simplification of system models, removal of system constraints and increase of calculation speed. The method utilized a Fresnel lens and a projector to generate paralleled structured light so as to establish a linear projecting model and reduce the calculating complexity. Wrapped phase information was obtained by using Fourier transform method and through concentric circles grating-based calibrating method, unwrapping phase was obtained point by point at the same time. The whole process got rid of traditional phase unwrapping procedure and effectively repressed the diffusion of errors. When a tested object with 20mm maximal height was measured, the maximal error was 0.23mm and the relative error was 1.15%. The validity was verified by experiments and 3D information of an object could be obtained accurately and rapidly.
Performance investigation of blackbody BB3 500 M and temperature measurement
WU Zhi-feng, DAI Cai-hong, YU Jia-lin, HUANG Bo, OUYANG Hui-quan
2012, 33(5): 926-930.
High temperature blackbody BB 3 500 M was used as the primary standard of spectral irradiance at national institute of metrology (NIM). The blackbody BB 3 500 M cavity radiator was consisted of a series of pyrolytic-graphite (PG) rings, capable of operating at temperature up to 3 500 K. Feedback control mode was used to stabilize the temperature of the blackbody. The stability of the radiator and the blackbody uniformity were measured. In transferring the spectral irradiance from the blackbody to the working standard lamp, the temperature of the blackbody may change. In the experiment, temperature drift within an hour was tested. When the blackbody was heated up to around 3 016 K, the temperature uncertainty was less than 0.3 K. In the radiation path, an aperture was used to screen the radiation from the cylindrical part of the radiation cavity. However, the temperature was not the same all over the effective area of the graphite bottom. The uniformity of the bottom of BB 3 500 M was found to be within 0.2 K. Results showed that BB 3 500 M was suitable for the primary radiation source. In the temperature measurement, temperature below 2 473 K could be traceable to the heat division of NIM. Then the temperature could be extended through the comparison of the spectral radiance at fixed wavelength. In the experiment, the temperature extend was first investigated in low temperature region no higher than 2 473 to verify its applicability. Results in high temperature region showed good consistence that the temperature divergence was smaller than 0.5 K at 345 nm~360 nm wavelength.
Curvature radius testing of optical lens based on autofocusing technology
ZHANG Yi-hui, ZHAO Zhi-qiang
2012, 33(5): 931-935.
An autofocusing-technique-based method for rapid and accurate non-contact measurement of radius of curvature (ROC) of optical lens is designed. The autofocusing is performed on the lens vertex and in the center of curvature respectively, and the distance between these two positions is ROC. The autofocusing technology is improved for the application of ROC measurement of optical lens: the connected region extraction is used to label the target image, and the sensitivity of sharpness evaluation function is improved; the searching strategy, i.e. the traditional hill-climbing method, is improved by meancomparison and 3-point method. The experiments validate the autofocusing-technique-based ROC measurement, and the accuracy is better than 0.2%, the repeatability is better than 0.109%. This approach has been applied to a optical lens ROC test station successfully.
Modified formula of environmental conditions in precision measurement of optical glass refractive index
MA Bo-tao, PEI Chun-yan, Li Xiao-chun
2012, 33(5): 936-939.
The article points out the inadaptation and defects of air pressure correction formula which is used currently in the precision measurement of optical glass refractive index. Based on the latest formula of air refractive index, the article also focuses on the research of environmental conditions and puts forward a new correction formula. And the article indicates that different correction formulas should be used in different testing precisions and different test conditions.
Chromatic thermometry used in ceramic sintering process
TAO Wei, WU Guo-jun, GUAN Yun-tian
2012, 33(5): 940-943.
The method of chromatic thermometry was introduced into the on-line thermometry of ceramic sintering. The thermometry system was designed according to Planck law. The calculation methods of key parameters, such as wavelength, emissivity, rate of conversion, were presented. The relation between wavelength and energy/sensitivity was comprehensively analyzed. The prototype was set up and tested according to the characteristics of ceramic sintering process, and the results indicated the metering error was less than 10 K during 1 300 K~2 000 K.
Optical Element and Fabrication
Optical design of arthroscope based on gradient refractive index lens
WU Qiong, XIANG Yang, HOU Li-jie, TAO Xue, SUN Ming-jiao
2012, 33(5): 944-948.
Arthroscope is a kind of optical device which can observe the internal structure of our joints, as an endoscope to make a diagnosis and give treatment to the joint. The gradient refractive index(GRIN) lens has many merits such as light weight,small volume and good image quality, according to which a optical system with simple structure was designed with Zemax for-1/10"CCD arthroscope. The system has 60 field of view and the F number is 6, the working distance is ~5mm. The value of modulation transfer function (MTF) is more than 0.2 at 125 lp/mm, the resolution of the system is up to 4 m, the spot diagrams of all configurations are smaller than Airy disk. The total track is 204mm, the biggest caliber is less than 4.6mm. According to the characteristics of arthroscope,the system meets the requirement.
Opto-mechanical system of single-star simulator with multi-color temperature and multi-magnitude output
2012, 33(5): 949-953.
The working principle of star sensor based on the charged coupled device (CCD) technology was explained, as well as its important role playing in space positioning. The star sensor was needed to be calibrated by the star simulator using the ground calibration technique. According to the two basic parameters of the stellar light source, the simulation methods of the color temperature and the magnitude were proposed respectively. The realization of the star simulator was studied, and the electric light source, waveband light intensity controller, magnitude controller were designed. The entire system was assembled in laboratory, and the controlling and testing platform was set up. The experiments were carried out and the obtained results show that this system has high reliability. In the peak spectral range of 350 nm~950 nm, it can simulate the magnitude in 0~+6.5MI and the equivalent blackbody temperatures of the star: 2 600 K, 3 600 K, 4 300 K, 5 000 K, 5 500 K, 6 000 K, 6 800 K, 7 600 K, 9 800 K, the relative intensity error is better than 0.10.
Ternary bireflective parallel beamsplitting polarization prism
REN Shu-feng, WU Fu-quan
2012, 33(5): 954-957.
In order to save iceland and output two parallel polarized beams, a new type of bireflective parallel beam splitter combined of iceland and glass is designed. The prism is made of ZBaF3 glass, between which is iceland, using bromonaphthalene as the glue. Selecting the suitable structure angles, two polarized beam whose directions of electric vector are orthogonal can escape vertically to the same exit widow after their total reflection on the front cemented surface and the back surface respectively. The experiments indicate that the transmittance of the prism is more than 80%, and the extinction ratio is better than 10-3. Therefore, the prism still has good performance on the premise of saving iceland greatly.
Heat stop optical analysis for Chinese giant solar telescope
XU Xiao-wei, ZHANG Hai-ying
2012, 33(5): 958-963.
Chinese giant solar telescope(CGST) is an on-axis Gregorian telescope, equipped with a 8 m diameter primary mirror and focal ratio of 1. The heat stop is a key component for the 8 m CGST, positioned at the primary focus, able to remove a heat load of 29 kW, while it absorbs a small portion of the heat at the same time. The geometry of the heat stop was designed, and four cases of sun-centered observations, limb observations, extreme coronal observations, out of range observations were emphatically simulated and analyzed with TracePro, calculating the irradiance distribution on elements of the heat stop, which provided data for the design of follow-up cooling system.
Infrared Technology
Infrared small target detection under complex background
LUO Bei-bei, YI Xing-guo, SHEN Yue, KONG Peng, DONG Qi-lin, ZHANG Wei, LI Chen-guang, FU Qiang
2012, 33(5): 964-968.
Small target detection in complex background is a critical technology in the infrared warning system. Aiming at the problems that there is clutter interference in infrared image and the target-s signal-to-noise ratio is low, this paper presents a non-linear spatial filtering detection method. Based on traditional linear spatial filter algorithm, the algorithm calculates the gray value around the four quadrants of the potential target, and adjusts the dynamic threshold properly. The results show that when the background contains more complex factors, the non-linear spatial filtering method can effectively suppress the clutter to achieve the extraction of the weak target. Compared with the results of linear filtering algorithm, this algorithm decreases the number of false alarms by 3/4, and has easy engineering realization.
Near-infrared contrast of star to sky background during daytime
HAN Yan-Li, WANG Duo, GUO Shao-jun, HAN Jian-li
2012, 33(5): 969-973.
The infrared waveband can detect enough stars for navigation. The contrast of star to sky background is an important parameter of star detection during daytime. This paper analyzed the 6 magnitude star contrast changing with the solar zenith angle, detector height and detection azimuth in near-infrared band. Results show that the star to sky background contrast performs approximate exponential growth with the solar zenith angle, and the contrast with 40solar zenith angle is about 2.69 times of 20;above a certain height, the contrast performs approximate exponential growth with the increase of detector height, it is lower than 3 when the height is less than 15km, but increasing quickly to 60 at 80km; the star to sky background contrast nearly increases linearly with the increase of detection azimuth, and the contrast with 30azimuth is 2.38 times of 0.
Laser Technology
Detection of low-frequency underwater acoustic signal by laser
MIAO Run-cai, XU Jia-ting, XIE Tian, WANG Wen-cheng
2012, 33(5): 974-978.
According to the principle of the surface acoustic wave (SAW) effect, a technology has been developed to detect the low-frequency underwater acoustic signal by laser and a detection apparatus is developed. In dozens of Hertz low-frequencies, the surface wave produced by the underwater acoustic was detected. In the measurement process, the diffraction pattern was scanned by using MATLAB to analyze. Then the diffraction pattern pixel of stripe was obtained. According to the analytic formula of the wavelength and stripe space, the low-frequency liquid surface wavelength with millimeter order was obtained. By using computer programming, the regression curve was fitting according to the principle of least square method. Measurement results agree with the theoretical dispersion relationship. The method has the characteristics of real-time and non contact.
Low altitude fog-haze measurements byRaman-Rayleigh-Mie lidar in Nanjing
CAO Nian-wen, YANG Feng-kai, SHI Jian-zhong, WANG Fan, TIAN Li, BU Ling-bing, XIA Jun-rong
2012, 33(5): 979-984.
This paper presented the fog-haze measurements by Raman-Rayleigh-Mie lidar in north suburb of Nanjing, the measurement results were analyzed and compared with the weather forecast. Continuous measurements were carried out on 2/12/2009, it was clear day from 01:00 to 08:00 in the morning, and foghaze was measured from 10:00 in the morning to 19:00 in the evening. The fog-haze measurement results coincided with the weather forecast on that day. The fog-haze lidar measurement results on 2/12/2009 were analyzed and compared with the boundary aerosol measurement results on 10/01/2011, the differential characters of range-corrected-signals between fog-haze and boundary aerosol were discussed. It is shown that fog-haze usually occurs at about 300m height with a depth of 700m and boundary aerosol usually occurs at about 1000m height with a depth of 1300m in Nanjing.
Laser spot center location algorithm based on Gaussian fitting
WANG Li-li, HU Zhong-wen, JI Hang-xin
2012, 33(5): 985-990.
Laser spot center location is a key technique in the field of optical measurement. Based on the analysis of algorithms commonly used, a Gaussian fitting based laser spot center location method was presented. The unsaturated part of laser spot image was used to fit the Gaussian surface, based on which the amplitude of the fitting function could be looked upon as the laser spot center. In order to verify this algorithm, an artificial light spot was used firstly, experimental results showed that the error of this algorithm was much less than 0.1 pixels; and then a measuring system which mainly consisted of high precision motorized translation stage of one dimension, CCD camera and laser was constructed, the acquisition and analysis of laser spot image were accomplished by computer automatically, experimental results showed that the root mean square error between the algorithm and theoretical analysis was only 0.1 pixels, which had high accuracy.
2.12 μm laser pumped by Zig-Zag slab
MENG Dong-dong, TANG Gang-feng, SHEN Zhao-guo, MAO Xin, YANG Yi
2012, 33(5): 991-995.
In order to obtain narrow pulse width and high peak power laser output steadily in 2.12 m, the experiments of optical parametric oscillator (OPO) were devised, which were based on the fundamental beam of 1.06 m produced by side-pumping Nd∶YAG Zig-Zag slab, furthermore, the 1.06 m beam pumped KTP crystals by type II phase matching technology for producing 2.12 m. External OPO and intra-cavity OPO experiments were researched with the electricaloptical conversion efficiency at 1.53%, 2.86% respectively. At the frequency of 20 Hz, the energy of the 2.12 m laser output surpassed 70 mJ in intra-cavity OPO experiment while the pulse width and stabilization of energy were at 7 ns~9 ns, 8% approximately.
Fiber Sensing and Optical Communication
Modulation of annular light distribution by mechanical fiber scrambler
MU Dan-dan, ZHU Yong-tian, ZHANG Kai
2012, 33(5): 996-1001.
The far-field pattern of fiber output beam changes dramatically due to different positions and angles of the input beam on fiber. This paper studies the change of the fiber-s output beam when the axis of input beam is shifted a small angle off the axis of optical fiber through the anlysis of the fiber-s output distribution. Fiber coupling theory indicates that the fiber macrobending leads to mutual coupling of fiber mode, so an improvement of fiber transmission with a mechanical scrambler which gives certain pressure to bend parts of fiber is designed. The collected output spots in different off-axis angles and scrambling degree are taken by median filtering and Gaussian fitting approaches. The scrambling effects are measured mainly through the profile of radial intensity distribution as well as its fitting degree of Gaussian distribution and the change of the energy ratio between different output focal ratio and input.
Objective lens design of image guide fiber bundle with large field and low distortion
FAN Jing-wei, WANG Wei
2012, 33(5): 1002-1005.
In the design of front lens for the large cross-section image guide fiber bundle, the negative-positive structure with telecentric structure in image space, even aspheric surface and crescent thick lens were applied for solving the problems on off-axial aberrations and illumination uniformity on the image plane, as well as keeping the lens compact and small. After theoretical calculation and optimization, the design was developed whose operating wavelength, focal length, angle of view and relative aperture were 660 nm, 1.22 mm, 60 and 1∶3, respectively. The results showed that the MTF value of the lens was higher than 0.8 at the spatial frequency of 40 lp/mm, the relative distortion of the lens in the largest field was less than 0.05% and the field curvature was lower than 50 m. With the fine quality of imaging, the lens could be used for observation and measurement.
Weighted correction for MTF of fiber-optic image inverter
BAI Xiao-feng, SHI Feng, Lv Feng, CHENG Hong-chang, HE Ying-ping, YIN Lei
2012, 33(5): 1006-1010.
As an optical component for transferring image, fiber-optic image inverter has been extensively used in low-light-level image intensifier. The modulation transfer function (MTF) test system, on which slit is used, can be used to test the fiber-optic inverter-s MTF. But there is too much artificial participation during MTF testing, and the repeatability of inverter-s MTF is generally bad. Data sampling, integrating time and eyestrain which affected the repeatability of inverters MTF were respectively analyzed, the solution related to data sampling and integrating time was given, and the weighted correction method for eyestrain was presented. According to the six fiber-optic inverter-s MTF testing results and the comparison between direct correction and weighted correction of them, it is shown that the weighted correction solves the repeatability of inverter-s MTF well, and the maximum deviation for repeatability is less than 7%.