2014 Vol. 35, No. 2

OE System and Engineering
Demonstration and design of optoelectronic tracking system
QU Jian-rong, WANG Xiao-qi, DUAN Hong-jian
2014, 35(2): 173-178.
Aiming at the photoelectronic tracking system marched weapon systems, we expounded the considerations for its demonstration and design, discussed the selection principle for the detector of the optoelectronic tracking system as well as the advantages/disadvantages of the T-model and U-model structures from the actual situations.Moreover we analyzed the main factors determining the critical indicators such as tracking distance,tracking precision,response speed and working scope. Corresponding to the critical indicators, we also determined the factors influencing the indicators of EO system inside. Furthermore we proposed some related techniques, including guiding interception function,relationship among optical axes,and so on.
Application of Risley prism on optical reconnaissance
HONG Hua-jie, ZHOU Yuan, TAO Zhong, FAN Da-peng, FAN Shi-shun
2014, 35(2): 179-187.
In recent years, the application of Risley prism on the military reconnoiter came to wide attention. The basic configuration and working principle were demonstrated individually, and the troubles on engineering implementation were analyzed. The products at home and abroad were described. The maximal refraction angle of light beam is 10 on Risley prism prototype developed by university of defense technology. Some experiments results show it has realized the scanning imaging function and light beam scanning function preliminarly.
Static testing system of fire control performance parameters
SUN Hao, WANG Chun-Yan
2014, 35(2): 188-192.
To improve static performance indicators of weapon fire control system, a static testing system was developed to test loosened quantity of cannon barrel, transition process quality, rigidity, drift velocity, and maximum moving speed and other parameters. An optical measuring head was used to capture the images of muzzle relative motion on the coordinate by a relatively method, the parameters were calculated accordingly. Elastic sleeve was used to achieve reliable installation and easy removal of the static measuring head. Results show that: In -30℃~+50℃ environment, the modulation transfer function (MTF) value of the optical system is more than 0.6, which is closing to the diffraction limit; When 2=9.15,f=50 mm, the static angular accuracy 0.2 mil, which meets the technical requirements. The mechanical fixture is suitable for fixed connection with 100 mm,105 mm and 125 mm artilleries. The system can not only measure some parameters of XX model tank barrel, but also be widely used in anti-aircraft artillery, armored vehicles, shipboard fire control systems, tanks and other weapons.
Optimal design of free-form-surface optical component in helmet mounted display
ZHANG Bo, WANG Ling, CHANG Wei-jun, CHEN Jiao, JIAO Ming-yin
2014, 35(2): 193-197.
According to the requirement of system, the incipient structure of the off-axis optical system without freeform surface was computed. Choosing the Zernike polynomials surface as freeform surface, using the relationship of aberration and the Zernike polynomials, the aberration of surface parameters correction system was adjust, and the system was optimized by using CODE V. The different examples of direct optimization method and step-by-step optimization method were compared, and result shows the step by step optimization method is more suitable for the system design. Simulation results show that in the entire field of view, the diameter root mean square(RMS) of spot diagram dispersion circle is less than 27 m, MTF value at 30 lp/mm is more than 0.197 and the maximum grid distortion is -7.15%.
Integral sliding mode control for armored vehicles steady sighting system based on extended state observer
SUN Hao-ze, CHANG Tian-qing, CHEN Jun-wei, XIE Jie
2014, 35(2): 198-204.
To solve problems of system performance degradation caused by nonlinearity such as friction and parameter drift,an integral sliding mode controller for armored vehicles steady sighting system based on extended state observer(ESO) was designed. An error integral compensation term was introduced into the sliding surface based on the state variables in order to reduce the steady state error and break the restrictions that the derivative of the tracking signal must be known. The ESO was introduced to estimate and compensate the inner and outer disturbances of the system, which could help to reduce the required value of switching gain for sliding mode control method and weaken the chattering phenomenon of the system.The simulation and experiment result shows that the tracking accuracy keeps within 0.5% and the max system steady error is less than 0.1 mrad, which implies that the method can restrain the influences caused by the diversified nonlinearity and improve the system performance effectively.
Stray light analysis for multi-target compounding hardware-in-loop system
FAN Zhi-gang, HU Hai-li, CHEN Shou-qian, ZUO Bao-jun, NI Chen
2014, 35(2): 205-209.
Stray light analysis is one of the key technologies for the optical system design. Based on the Monte-Carlo method, the analysis of stray light level for multitarget compounding hardware-in-loop (HWIL) system in software Tracepro was present. Simulation results showed that two critical parts of stray lights of HWIL system were derived: one part was the unused expanded beam, which hit on the boundary of main concave mirror; another part was self-thermal stray light, which was caused by self-thermal radiation of key elements when system was under room temperature. The dependence of stray light coefficient on the cooling temperature of key element was analyzed, and the stray light coefficient was less 2% for cooling temperature of 200K. The simulation results are beneficial to the design of multi-target compounding HWIL system for the missile.
Design and application of spectral polarization imaging detection system
HE Zi-jian, WANG Ke-wei, MA Li-fang, WANG Jia-chun, ZHAO Da-peng, WANG Qi-chao
2014, 35(2): 210-214.
In order to acquire the polarization information of target and background and improve the accuracy of detection for ground target, a spectral polarization imaging detection system was proposed, which could modulate the polarization state through revolving the polarizer and select spectra through revolving the filter so as to achieve spectral polarization imaging detection. An experiment was designed to validate the result of the polarization degree acquired from the system. The result shows that the system can reach the detection accuracy up to 4%. Additional, the detection experiment about the camouflage coating target which was under typical woodland background was conducted by the system. The result of image processing indicates that the target is prominent in the background, the polarization-s difference is up to 0.292 between target and soil,while 0.283 between target and grass.
Calibration design of ultraviolet and visible dual-band variable focus device
LIU Jun, YANG Shu-ning, GAO Ming
2014, 35(2): 215-220.
A focusing optical system used for calibration of ultraviolet and visible light optical axis parallelism was designed with the focusing range of 70 m~. Aiming at most calibration systems- problems that can not focus at present, a method was put forward, which can calibrate the ultraviolet and visible light optical axis parallelism, and focus the ultraviolet part. We used the off-axis Cassegrain system as the initial structure to design, and added the focus group and compensation group into the traditional Cassegrain system so as to implement the focusing and aberration compensation. The designed system can effectively solve the calibration problems of the ultraviolet and visible light double-axis parallelism and improve the calibration efficiency. Also, the modulation transfer function (MTF) values and spot diagram both close to the diffraction limit under different object distances, moreover, the energy concentration reaches 90%, the view image quality of the entire field is even and image surface is clear, which are good for the follow-up image processing.
Design of laser and mid-wave infrared optical system
YAN Xiu-qi, FU Yue-gang
2014, 35(2): 221-225.
According to the system requirement, the laser and mid-wave infrared composite guidance optical system was designed. The infrared working wavelength of the system was 3m~5m, the laser wavelength was 1.064 m, the receiving diameter of the system was 250 mm, F number was 1.4, the value of MTF was greater than 0.4 at 33 lp/mm, the optical transmittance was greater than 60%, the infrared focal plane array was 640512 pixels, and each pixel was 15 m15 m.The secondary imaging with refractive and reflective structure was used to deal with the athermalization and compact problem.
Application of light star sensor with small field in stellar measurement during daytime
HE Lei, ZHANG Ping, LIU Xiao-dong, ZHANG Bu-sheng, CHEN Wei
2014, 35(2): 226-229.
The feasibility of the stellar detection within the atmosphere in daytime by using light star sensor with small field was analyzed from the sky background, the spectral properties of star, and the structure characteristic of star sensor. Using the method of spectral filtering and reasonable choice of system parameters, a light star sensor was developed. Moreover, star detect experiment in daytime was carried out in high altitude area. With the observing altitude of 3 km, the atmosphere visibility of 10 km and the field of view of 21.5, the maximum detectable stellar magnitude limit was 3.8 when the avoiding angle of the sun was out of 30. The theory analysis and experiment result both indicate that light star sensor with small field can detect star in daytime.
Design of sunlight direct-enhanced illumination system in highway tunnel
YAO Jun-xia, NING Duo
2014, 35(2): 230-236.
In order to eliminate the black-hole effect and white-hole effect efficiently by taking use of green energy, based on the research of sunlight conveyor, a new system for enhanced illumination is developed by using enhanced parallel sunlight on the import and export zone of the highway tunnel. High efficient and long distant sunlight transporting is achieved under the condition of no-optical-fiber-like medium through optical path transformation and reflection. The technical requirement of self-adaptation with the natural sunlight in tunnel enhanced illumination is solved automatically by taking the disadvantage of sunlight intensity changing. According to the fixed photo-receptor system, a polar axis type automatic tracking system is designed, which realizes the realtime tracking for the sunlight. The experiment result shows that the system not only improves the transmission efficiency by about 40% without using optical fiber or light pipe, but also develops a new way for the popularization and application of direct sunlight lighting in the tunnel and other underground engineering in the future.
OE Information Acquisition and
Phase correction and matching based on multi-frequency heterodyne method
HUANG Ya-nan, LOU Xiao-ping
2014, 35(2): 237-241.
A phase unwrapping method based on multi-frequency heterodyne principle by projecting four different frequency fringes was deduced. Meanwhile, In order to reduce the phase unwrapping errors, a phase correction method was proposed, and the effect on matching result was compared before and after phase correction. In order to improve the accuracy of the matching, the revised absolute phase value was used as the basis for matching. Besides, the subpixel matching algorithm was utilized based on phase linear interpolation.Finally, the 3D reconstruction technology was used to obtain the three-dimensional point cloud. Results show that the matching rate of plane measurement is increased by 4.97%, with the measurement accuracy of 0.189 5 mm .
3D microscopic imaging based on wide-field optical coherence tomography
FENG Sheng-tong, FEN Yin-qi, ZHANG Min, HAO Jun-jun
2014, 35(2): 242-247.
Wide-field optical coherence tomography(WFOCT) has a promising application for its high scanning rate and resolution. The principle of widefield optical coherence tomography was described, and 2D images of glassware were reconstructed using eight-step phase-shifting method. Besides, the axial resolution and depth detection were studied, and the depth detection could reach 3.3 mm in view of glass material. After obtaining several 2D images, by using VC6.0 and OpenGL programming, the 3D microscopic imaging was realized based on the marching cube(MC) algorithm. The experimental results show that the WFOCT system can be applied in the biological tissues detection as well as the 3D morphology microscopic imaging and depth detection for the objects of high reflectivity.
New algorithm for monitoring optical thin-film thickness
MI Qian, ZHAO Lei
2014, 35(2): 248-253.
The optical properties of optical thin-film are related to each-layer thickness closely,in order to acquire the optical thin-film product satisfying the requirement,the thickness must be monitored during the course of deposition. The monitoring accuracy of the optical thin-film determines the accuracy of deposited film thickness. Aiming at the defects that the electro-optical extremum method is difficult to monitor the extreme points and the non-normalized coating system accurately, we presented a new algorithm for optical thin-film thickness monitoring.Though the mathematical calculation, the relationship between film thickness and transmittance turns to be linear, and this new algorithm can eliminate the bad effects of optical source fluctuation and transmission noise. The accuracy of this new algorithm is less than 2%.
Wavelet transform digital image watermarking algorithms based on HVS
WU Feng-bo, WANG Feng
2014, 35(2): 254-259.
In order to realize the image watermarking as a function of data authentication, access control and copyright protection, a wavelet transform digital image watermarking algorithm which gave a full consideration to the human eye visual perception characteristics was proposed. First, Arnold transform and the stacking method were performed on the binary image watermarking, which was converted into the one-dimensional sequence; second, the kind of modulation was adopted when embedding the watermark information determined by the positive and negative values of key generation gaussian sequence; and then, the original image was processed with 3-level discrete wavelet transform(DWT) decomposition, on the second floor of the wavelet image intermediate frequency sub-band, combining with the human visual characteristics, the positive or negative modulation of watermarking was superimposed on wavelet coefficients with the host image greater than the just noticeable difference(JND) value. The experimental results show that, the algorithm can resist JPEG compression, plus-noise, shearing and other attacks, and has good transparency, robustness and security.
Optical Metrology and Measurement
Illuminance uniformity of image plane in photoelectronic imagetesting system
2014, 35(2): 260-263.
Non-uniform light source and wide field angle were two causes for illumination non-uniformity of image plane in photoelectronic image testing system. To study the influence, the relationship model between spacing of LED light source and image plane illumination was built. The influence of different LED intervals on image plane illumination was simulated and analyzed. The relationship model between opening angle of object plane of optical coupling system and image plane illumination was established, and the influence of opening angle of object plane on illuminance uniformity of image plane was simulated and studied. The experiment results show that non-uniform light source and wide field angle are two main causes for non-uniformity illumination of image plane, which provides the theoretical basis for designing better corresponding correction algorithm.
High-sensitive trace detection of NO2 with broadband cavity-enhanced spectroscopy
DONG Mei-li, XU Xue-zhe, ZHAO Wei-xiong, GU Xue-jun, HU Chang-jin, GAI Yan-bo, GAO Xiao-ming, HUANG Wei, ZHANG Wei-jun
2014, 35(2): 264-269.
A blue light emitting diode (LED) based incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instrument was set up for high sensitive detection of NO2 molecule. A detection sensitivity of 3.210-9 cm-1 (1, 300 ms integrating time, and 10 times average) was demonstrated on the basis of absorption spectroscopy of NO2, corresponding to a minimum detection concentration of about 187 pmol/mol for NO2. The measurement sensitivity and optimum acquisition time of the IBBCEAS system were evaluated using Allan variance analysis. The detection limit of 44 pmol/mol for NO2 was achieved with an optimum acquisition time of 30 s. The IBBCEAS measured NO2 data in ambient air were compared to the values measured with an online NOx analyzer (Thermo 42i). Result shows a good agreement between the NOx analyzer and the IBBCEAS.
Influences of surface roughness of Li2O-Al2O3-SiO2glass-ceramic on nanoindentation test
XIANG Yong, REN Jie, BAI Man-she, CHEN Yong, CHEN Jing, ZHANG Jin-kuan
2014, 35(2): 270-274.
The basic theory of nanoindentation testing technique and the Oliver-Pharr method as one of the most useful calculation method were introduced. The hardness, elastic modulus and depth-load curve with different surface roughnesses of glass-ceramic in the Li2O-Al2O3-SiO2 system were measured by nano-indentation test respectively. The test results show that the stability, accuracy and reliability are reduced by the surface roughness: the smoother the sample surface is, the smaller the fluctuation of hardness and elastic modulus is and the higher the coincidence degree of the depth-load curve is. The elastic modulus is decreased with the increasing of the maximum load, which is caused by the plastic deformation of material. Testing results of the nanohardness and elastic modulus of glass-ceramic in the Li2O-Al2O3-SiO2 system are 8.8 GPa and 7.79 GPa respectively on the ultra-smooth surface of the sample(Ra=0.9 nm). The coincidence degree of results of the nanoindentation test is significant to express the super smooth surface integrity.
Research and measurement of material surface-s strain field based onphotoelastic coating
LI Xiao-mao, WANG Xiang, GUO Xian, ZHU Bao-liang, LI Yan-jie
2014, 35(2): 275-280.
Strain gauge can measure the strain of one point, but it cannot measure the strain field of material surface. To solve this problem, photoelastic coatings were adopted to measure the material surface-s strain field. Photoelastic coatings were casted, and the strain fringe constant of the photoelastic coatings was calibrated. Experiments loading photoelastic coatings with special shapes were carried out, and the strain fringe interpretation method was studied. Photoelastic coatings were applied to measure the strain field of simply supported beam. Comparing with strain gauge, the strain value on weak spots obtained by photoelastic coatings is less than 5% on the high side. In experiments that concrete specimens were under loading of 4.4 MPa to 39.6 MPa, the variation of strain fringe in the process, of which the surface crack of the concrete specimen appeared, propagated and finally was fractured, was obtained. It is proved that photoelastic coatings can measure the variation of surface-s strain field of metal and concrete visually and credibly.
High-precision roll angle measuring method based on collimated beams
HAO Wen-xia, LVYong, LI Xiao-ying, CHEN Qing-shan, , GENG Rui, ZHANG Ming-zhu
2014, 35(2): 281-285.
For the problems of low accuracy and difficult measurement in roll angle measurement,a roll angle measuring method based on spot position changes of collimated beams was presented. The positions of the two light spots on the CCD change with the movement of measured object, so does the slope of the line determined by the two light spots. The change of the slope is caused by yawing, pitching and rolling movements. In the measuring system, the pitch angle and yaw angle were measured based on the principle of self-collimation. After the affection of the pitch and yaw were eliminated, the roll angle was accurately measured. A mathematical model of the system was built,and Zemax software was used to establish a system model to simulate roll angle. Simulation results were calculated by the solving model of roll angle. Within the range of 0~1 800 the results of the mathematical model were exactly consistent with the value of Zemax, so that the feasibility and correctness of measuring method were validated.
Analysis of external influence factors in camera calibration
ZHI Jian-hui, DONG Xin-min, KONG Xing-wei, WANG Xu-feng
2014, 35(2): 286-291.
As camera calibration results can be influenced by external factors easily, to improve the accuracy of calibration results, the pin-hole camera imaging model was utilized, and the adaptive corner detection method was adopted to pick up the feature points in calibration images, then the mean value of re-projection error in the coordinates was introduced as the performance index, a series of experiments were designed correspondingly for the three external factors including the number of image, the luminance of light and the size of square in calibration board. The experiments results indicate that choosing brighter light source can improve the calibration accuracy above 38%; given 156 points feature, only 18~22 calibration pictures are needed, and also, smaller square size can increase the results- accuracy about 50%. All mentioned above show the importance of light source, number of pictures and square size in camera calibration accuracy-improving.
Measurement for bulk and surface absorptances of K9 substrates with laser calorimeter
LIU Hao, PAN Feng, CHEN Song-lin, WANG Zhen, MA Ping, OUYANG Sheng, WEI Yao-wei
2014, 35(2): 292-296.
Absorption might be increased due to the impurities introduced by polishing. To differentiate the surface absorptance and bulk absorptance of K9 substrates is of great importance. It is significant for the research of laser resistance, and helpful for the improvement of producing and polishing technique of K9. In this paper, the principle of laser calorimetry was analyzed, and a laser calorimeter according to ISO 11551 was applied to measure K9 substrates. The weak absorptance of K9 substrates with same polishing technique and different thicknesses was characterized. It is found that the absorptance increases nearly linearly with the increasing of thickness. The equation to calculate the surface and bulk absorptances was analyzed, and the surface absorptance in this experiment was 1.2110-5, while the bulk absorptance coefficient was 1.7210-3/cm which was much greater than the former . The conclusion is made that the K9 absorption is mainly caused by the material itself, and improving polishing technique cannot do much to decrease its absorption.
Projection lithographic objective lens with sub-ten micrometerline-width and its MTF experimental measurements
LEI Liang, LI Lang-lin, YUAN Wei, LIU Xin, ZHOU Jin-yun
2014, 35(2): 311-315.
We introduced the design method of a 2 reduction projection lithographic objective with double-telecentric structure by Zemax optical design software, which uses the 405nm laser diode (LD) as the light source and has 6 lenses. Its number aperture is NA=0.06, the resolution approaches to 5 m. In the field of view of 12 mm12 mm, its wave-front aberration is less than a quarter of wavelength and the distortion ratio is no more than 0.005%. We also measured the accurate optical transfer function (MTF) value by experiments after the projection objective was fabricated. Through analyzing the noise disturbance law in MTF tests we got the conclusion that the projection objective has sub-ten micrometer resolution.
Optical Element and Fabrication
Two-mirror five-reflection optical system design
2014, 35(2): 297-299.
Reflective optical system has characteristics of wide spectrum, no chromatic aberration and small vertical dimension, based on these a two-mirror fivereflection optical system is proposed, which has a wide spectrum of 0.4 m~12 m, long focal length of 1.6 m, overall length of less than 85 mm. High order aspheric surface is introduced into the two reflecting mirrors, and through the aberration balance, the image quality satifies requirement. A new photoelectric conversion material is also used to make the reticle in this system, if the laser beam focus on it, laser energy will excite visible light-long wave infrared spectroscopy, which offers simulated infinity goals for optical axis adjustment of optoelectronic products.
Mapping encoding method of matched filters
GAN Hou-ji, CHENG Si-wei, YE Ling-jun
2014, 35(2): 300-306.
The matched filter made in advance is the key for good correlation recognition results in Vander Lugt correlator. The data utilization ratio of detour phase encoding method which is always used is low, and its correlation results need to be improved. Mapping encoding method based on the minimum Euclidean distance principle was studied, the filters were encoded by amplitude and phase modulation characteristic of the spatial light modulator, then the effect on the correlation results of the amplitude factors for matched filtering function was analyzed by emulating experiments, and finally the correlation results of two methods were contrasted. Simulation results indicate that the more the amplitude factor is, the higher the correlation peak is; while the amplitude factor reaches 103, the correlation peak reaches its maximal value; and at the time the correlation peak is nearly two times as much as that of detour phase encoding method. Consequently the mapping encoding method is more propitious for the differentiation of correlation peaks than detour phase encoding method.
Design and study of Lyot monochromatic light depolarizer
REN Shu-feng, WU Fu-quan
2014, 35(2): 307-310.
Based on the Lyot depolarizer, a new type of depolarizer for monochromatic light was designed. This depolarizer consisted of two quarter-wave plates with slow-axis angle of 45. By analyzing the superimposition of transmitted light, it was found that the incident linearly polarized light of arbitrary azimuth angle of vibration could be converted to circularly polarized light with stable intensity, and the formula of depolarization degree was derived. For the waveband of 633 nm, two quarter-wave plates were selected purposely to make the sample whose depolarization degree was tested. Experiment results indicate that the depolarization degree was over 94% and it is over 97% as the incident angle is adjusted slightly.
Infrared Technology
Method of correction optical axis offset in infrared continuous zoom system
CHEN Zhi-bin, SONG Yan, ZHANG Chao
2014, 35(2): 316-320.
In order to reduce the optical axis drift of the mechanical compensating continuous zoom thermal imager during zooming, on the basis of the researches on the structure and principle of the continuous zoom infrared thermal imager, we optimized the initial system parameters to ensure the smoothness of the compensation group moving curve, and designed the cam curves of the zoom group and compensation group to be non-linear, which could ensure the uniformity of the focal length and reduce the optical axis drift caused by the rotation of the cam. For systematic errors, we fitted the axis drift curve by using trigonometric functions and polynomials, and took advantage of dynamic software compensation techniques to compensate the optical axis drift. The results show that the optical axis drift can be controlled within about a charged couple device (CCD) pixel size in this method. This way has strong robustness ,which can provide a certain reference value for similar zoom lens design.
Polarization image fusion algorithm based on wavelet transform
YUE Zhen, LI Fan-ming
2014, 35(2): 321-326.
Based on the characteristics that the infrared polarization image can restrain background noise greatly, and can be more sensitive to target edge information, a polarization image fusion algorithm based on wavelet transform is proposed. It is mainly used in image fusion between the infrared radiation intensity image and the polarization degree image in order to increase the amount of information of the image. First, wavelet transform can make different wavelet scaling decomposition in each involved image respectively, and get the wavelet coefficients of each scale. Second, it uses the method of neighborhood average gradient on each scaling wavelet coefficients to get each scaling wavelet fusion coefficients. Last, it makes image reconstruction based on wavelet transform to get fused image. The comparison between the images and fused images shows that this method can keep image clarity of the radiation intensity image, as well as highlight the edge and contour information. Compared to the radiation intensity image, the average gradient of fused images increases by 112%, while compared to the polarization degree image, the standard deviation of fused images increases by 151% ,and the information entropy of fused images increases by 38%.
Real-time non-uniformity correction algorithm for infraredsearch and track system
KONG Peng, HOU Min, LUO Bei-bei, YANG Dong, YI Xing-guo, LIU Wan-gang, ZHANG Wei
2014, 35(2): 327-331.
Aiming at the problem that the current two-point non-uniformity correction method was difficult to track the non-uniformity of infrared image drift with time in infrared search and track system(IRST) real-timely, a novel real-time joint correction algorithm based on the improved two-points correction method and scenes was proposed. This algorithm uses the two-point method to get the basic correcting parameter, then analyzes mass real-time image data to find the values related to the system non-uniformity changing with time. The degradation of infrared image caused by two-point non-uniformity correction is solved and intensive tests validate that the relative non-uniformity decreases from 5% to 2% after using the joint correction method, it has good time stability and better correction effect.
Laser Technology
1 W Nd-YAG single-longitudinal-mode ring laser usingacousto-optic modulator
LIAN Tian-hong, WANG Shi-yu, LIU Guo-rong, WANG Yi-bin, CAI De-fang, LI Bing-bin, GUO Zhen
2014, 35(2): 332-335.
Using unidirectional ring resonator is the most promising way to get high power single-longitudinal-mode (SLM) laser output. To enforce the singlelongitudinal-mode ring cavity to operate unidirectionally, a component which can introduce loss difference between the counter-propagating beams in the cavity is necessary. A diode-pumped Nd∶YAG SLM four-mirror rectangle ring laser was experimentally demonstrated. The stability of the cavity was ensured by the thermal of the gain medium, and an intra-cavity acousto-optic modulator was used as the optical diode, which provided different losses on the counterpropagating beams. The beam with larger loss died out in their competition for the gain and hence the unidirectional operation was demonstrated. An SLM output power of 1 W at 1.06 m with a beam quality factor M2 of 1.21 was obtained. The considerable increased output power and compact architecture are especially important for future practical application.
Secchi disk imaging model and its application in performanceevaluation of underwater laser imaging systems
SHEN Yue, ZHENG Wei, YU Bing, WU Lei, LI Gao-ping, YANG Hong-ru
2014, 35(2): 336-341.
The performance of an active underwater laser imaging system is not only determined by the parameters of the imaging system, but also affected by the optical properties of the water. In order to evaluate the performance of the active underwater laser imaging system, the relation among the Secchi depth and the optical properties (such as absorbing coefficient, scattering coefficient, and diffuse attenuation coefficient) of the water were investigated based on the Secchi depth imaging model. Moreover, the expression for the maximum detection depth of the underwater laser imaging system as a function of the Secchi depth was deduced. Experimental results show that the relative error between the theoretical value and the measured value of the maximum detection depth of the intensified charge-coupled device(ICCD) range gated underwater laser imaging system is less than 20%. The Secchi depth imaging model is useful for performance evaluation of the underwater laser imaging systems because that it can reflect the relationship of the detection capability of the active laser imaging system and the optical properties of the water.
Cat-s-eye effect based on active laser detection
LI Xu-dong, MI Jian-jun, RU Zhi-bing, ZHANG An-feng, HU Zheng-liang, ZHOU Xin-ni, LI Bao-jun, ZHANG Wan-lin, LIU Bing
2014, 35(2): 342-347.
Aiming at the extensive application of the active laser detecting based on cat-s-eye effect in electro-optic counterreconnaissance, we built the mathematic model of the optic-echo index for the head-on sight electro-optic equipment and the mathematic model for detecting range combined with the detecting components, simulated the numerical value relation between the optic-echo index and the internal characteristic parameter, and the one between the detecting range and the primary parameter for the head-on sight electro-optic equipment- In order to verify the mathematic model-s correctness,taking the 2.5 mm,5.5 mm aperture cat-s-eye retroreflectors and the 25 mm,35 mm,56 mm aperture sight electro-optic equipments as the targets, and the active laser detection equipment as the detecting system, we conducted maximum detecting distance simulation and verification tests, the analogue detecting ranges were 1 290 m,1 656 m, 866 m, 1 919 m and 1 266 m, respectively, the maximal detecting ranges were 1 100 m,1 500 m, 800 m, 1 800 m and 1 200 m, respectively. The result demonstrates that the analog numerical values are accordant with the test numerical values for the maximal detecting ranges.
Effect of laser irradiation energy on opticalproperties and morphology of SiO2 films
GUO Fang, XU Jun-qi, SU Jun-hong, DANG Shao-kun, GOLOSOV D A
2014, 35(2): 348-352.
To recognize the variation of SiO2 films irradiated by the laser, SiO2 films were prepared by electron beam evaporating on K9 substrates in the same experimental conditions with the exception that the irradiating laser energy was different in order to investigate the effects on the film-s transmittance, refractive index, extinction coefficient, film thickness, surface morphology and laser-induced damage threshold (LIDT) .The result shows that irradiating laser can decrease the SiO2 films- thickness , and improve the surface roughness of films. Finally, the result means that irradiation can increase the LIDT of films from 16.96 J/cm2 to 18.8 J/cm2.
Fiber Sensing and Optical Communication
Gain-flattened Raman fiber amplifier based on highly nonlinear fiber
GONG Jia-min, ZHAO Yun, LENG Bin
2014, 35(2): 353-358.
In order to realize the flat inline amplification of all dense wavelength division multiplexing(DWDM) transmission channels in optical fiber communication systems, it was proposed to get gain-flattened Raman fiber amplifier based on cascading highly nonlinear fiber. An approximate value of output signal power at the output port was finally obtained considering different signal light losses, when the linear method was used for obtaining the Raman gain spectrum. Moreover, the average gain and gain flatness were 20.45 dB and 0.15 dB, respectively. Then, the factors for the output characteristics of Raman fiber amplifier were analyzed. Simulation results demonstrate that the designed Raman fiber amplifier has advantages of high gain, smaller gain flatness as well as simple configuration.
Near-field optical tweezers based on micron tapered fiber
ZHAO Yu, YANG De-chao, CHEN Hao, ZHANG An-fu, ZHANG Wen-dong, XUE Chen-yang, YAN Shu-bin
2014, 35(2): 359-363.
The evanescent field intensity distribution of the fiber was analyzed both theoretically and experimentally(z=10 nm, 100 nm, 500 nm,1 000 nm), and the manipulation of micron fiber optical tweezers for microspheres was studied in experiment. In the experiment, a single-mode optical fiber with a diameter of 125 m was transformed into a tapered fiber with a 2 m diameter at the minimum waist. When the laser light was launched into the fiber, due to the evanescent field of the tapered fiber, the polystyrene microspheres with a diameter of 3 m could keep balanced state, and the nearby microspheres were attracted onto the fiber surface and rolled at the speed of 5.3 m/s in the direction of light propagation. This experiment traps the microspheres and verifies the mechanical effect of the fiber optical tweezers. The non-contact, non-destructive manipulation of fiber optical tweezers for microspheres has potential applications in the field of biosensors.