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2014
Volume: 41 Issue 8
46 Article(s)
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Research Article
Stereo Matching Algorithm Based on the Inter Color Correlation and Adaptive Support Weight
Gong Wenbiao, Gu Guohua, Qian Weixian, and Ren Jianle
It is crucial to choose a suitable matching cost relationship for area-based stereo matching. Inter color correlation as the inherent characteristics of pixel, can effectively show the small matching differences between pixel. The traditional method of adaptive support weight is improved, and a new matching algorithm tIt is crucial to choose a suitable matching cost relationship for area-based stereo matching. Inter color correlation as the inherent characteristics of pixel, can effectively show the small matching differences between pixel. The traditional method of adaptive support weight is improved, and a new matching algorithm that combines the color similarity, Euclidean distance similarity and inter color correlation similarity is proposed to compute the corresponding support weight. Meanwhile, in order to solve the brightness difference between the stereo image pairs, matching pixel are transformed by rank and calculating the matching cost relationship. Various errors in the disparity results are effectively handled in a three-step refinement process. The experimental results based on Matlab show that its performance is the best among local matching methods, and its robustness is very strong, as well as low false match rate..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 812001 (2014)
Study for Method Polarization Correction on Ultraviolet Atmospheric Spectral Radiation Based on Stokes Vector
Lin Guanyu, Wang Shurong, and Cao Diansheng
By setting polarization measurements channel in ultraviolet (UV) atmospheric constituents probe, the detection input value of UV atmospheric spectral radiance polarization is corrected based on the Stokes vector approach. The method of analytical functions is used to establish a mathematical model for the degree of polBy setting polarization measurements channel in ultraviolet (UV) atmospheric constituents probe, the detection input value of UV atmospheric spectral radiance polarization is corrected based on the Stokes vector approach. The method of analytical functions is used to establish a mathematical model for the degree of polarization when correction error is largest, and the polarization degree maximum error correction is decreased from 6.6% to 1.6% in the working wavelength from 240 nm to 380 nm. The maximum influence on the atmosphere measurements is strongly reduced due to atmospheric scattering of incident light polarization detection, and the accuracy of UV atmospheric measurements is improved, which provides theoretical and experimental basis for aerospace remote sensing instruments to measure UV atmospheric..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 813001 (2014)
Laser Doppler Method for the Detection of Wake Bubbles
Wang Yun, Liu Jifang, Lu Zhenzhong, and Sun Yanling
A method for ship wake detection is proposed, which is based on the characteristics of the laser Doppler shift spectrum of the backscattering light signal. A simulation of the Doppler shift spectrum because of the moving bubbles in wake is performed by Monte Carlo method. The influence of the bubble population and the A method for ship wake detection is proposed, which is based on the characteristics of the laser Doppler shift spectrum of the backscattering light signal. A simulation of the Doppler shift spectrum because of the moving bubbles in wake is performed by Monte Carlo method. The influence of the bubble population and the velocity distribution on the laser Doppler shift spectrum is analyzed. Using the differential Doppler method, the influence of imitated wake on the Doppler shift spectrum is studied experimentally. Experimental results agree with the theoretical analysis basically. The results show that the amplitude and the cutoff frequency of the shift spectrum will increase with the increasing of bubble population and range of velocity distribution. It indicates the effectiveness of the detection method..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 813002 (2014)
Biomedical Photonics and Laser Medicine
Effects of He-Ne Laser and Enhanced UV-B Radiation on the Photosynthesis on Rice Flags
Zhang Meiping, Liang Zhiying, Han Rong, and Shan Yongjie
In order to investigate the influence of photosynthesis on rice flag under enhanced UV-B radiation and He-Ne laser. He-Ne laser (5 mW·mm-2) irradiation and enhanced UV-B (13.08 kJ·m-2·d-1) radiation were used, the chlorophyll content and Rubisco of rice seedling leaves, chlorophyll fluorescence parameterIn order to investigate the influence of photosynthesis on rice flag under enhanced UV-B radiation and He-Ne laser. He-Ne laser (5 mW·mm-2) irradiation and enhanced UV-B (13.08 kJ·m-2·d-1) radiation were used, the chlorophyll content and Rubisco of rice seedling leaves, chlorophyll fluorescence parameters about plant photosystem II (PSII) are measured. The results show that, after UV-B treatment, the chlorophyll content in rice leaves, and fluorescence parameters (other than qN) is lower than the control group (CK) and has significant differences (P<0.05). The fluorescence parameter photochemical quantum yield (Fv/Fm) is the most sensitive to environmental stress reflection. In indicator group treated by He-Ne laser (L), the chlorophyll content and Rubisco in rice leaves are higher than the control group (CK) (P>0.05), fluorescence parameters does not change significantly (P>0.05). Compared with the control group (P<0.05), groups treated with He-Ne laser and UV-B, chlorophyll content, rubisco, and fluorescence parameters (except for qN ) of the rice leaves are higher than UV-B treated group. UV-B radiation on rice seedlings has injury to PSII, and a certain dose of He-Ne laser can improve the photosynthetic efficiency of rice. He-Ne laser can repair damage of enhanced UV-B to rice..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 804001 (2014)
High-Resolution Full-Field Optical Coherence Tomography for Biological Tissue
Zhu Yue, and Gao Wanrong
A novel full-field optical coherence tomography (FFOCT) system with low cost and high resolution is developed for imaging of cells and tissues. Different from other FFOCT systems illuminated with optical fiber bundle, the improved Khler illumination arrangement with a halogen lamp is used in the proposed FFOCT system.A novel full-field optical coherence tomography (FFOCT) system with low cost and high resolution is developed for imaging of cells and tissues. Different from other FFOCT systems illuminated with optical fiber bundle, the improved Khler illumination arrangement with a halogen lamp is used in the proposed FFOCT system. High numerical aperture microscopic objectives are used for imaging and a piezoelectric ceramic transducer (PZT) is used for phase-shifting. En-face tomographic images can be obtained by applying the five-step phase-shifting algorithm to a series of interferometric images which are recorded by a smart charge coupled device (CCD) camera. Three-dimensional images can be generated from these tomographic images. Imaging of the chip of Intel Pentium 4 processor demonstrats the ultrahigh resolution of the system (lateral resolution 0.8 μm), approaching the theoretical resolution 0.7 μm×0.5 μm (lateral×axial). En-face images of cells of onion surface and potted plant leaves cells show the excellent performance of the system for generating en-face images of biological tissues. The system is characterized by its high resolution, low cost and simple arrangement for adjustment, providing a practical method of performing FFOCT imaging..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 804002 (2014)
Holography and Information Processing
Calculation Method of Diffraction Efficiency and Characteristics of Non-Uuniform Mixed Modulation Gratings
He Tianbo, Bayanheshig, Zhang Shanwen, Li Wenhao, and Tang Yuguo
A method for calculating diffraction efficiencies of non-ideal volume phase holographic gratings is presented by introducing a function between modulation profiles and depths of gratings. By applying Kamiya rigorous delamination-calculation method, rigorous coupled-wave equation for the non-ideal conditions, such as miA method for calculating diffraction efficiencies of non-ideal volume phase holographic gratings is presented by introducing a function between modulation profiles and depths of gratings. By applying Kamiya rigorous delamination-calculation method, rigorous coupled-wave equation for the non-ideal conditions, such as mixed modulation and attenuated modulation profiles, is expressed. The diffraction characteristics of the phase gratings, mixed gratings, out-of-phase gratings and attenuated gratings are investigated. The response degree of diffraction efficiency to the numbers of sub-regions that have been divided is discussed. Comparing with Kogelnik theory and Sabol model, the accuracy of the algorithm is further demonstrated. The results show that, the peaks of diffraction efficiency change over average absorption constants, attenuated constants and the spatial dephasing between the absorption and phase gratings; absorption modulation causes a modest increase of the peak, but average absorption constants drag the efficiencies of the whole transmission orders. The effect of the numbers of sub-regions that have been divided on the angle selectivity and angular spectrum widths of the grating is small, but it decides the accuracy of the algorithm. The work have a certain reference value for calculating the efficiencies and analyzing the diffraction characteristics of the non-ideal modulation of volume holographic gratings..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 809001 (2014)
Infrared Image Denoising Algorithm Based on Sub-Band Component Threshold Estimation
Zhang Baohua, and Liu He
Due to the complex sources and serious interferences of the infrared image noise, and the traditional wavelet threshold methods for estimation have large deviations. An infrared image denoising method based on threshold estimation of bidimensional empirical mode decomposition (BEMD) sub-band is proposed. The noisy imagDue to the complex sources and serious interferences of the infrared image noise, and the traditional wavelet threshold methods for estimation have large deviations. An infrared image denoising method based on threshold estimation of bidimensional empirical mode decomposition (BEMD) sub-band is proposed. The noisy image is decomposed by BEMD into bidimensional intrinsic mode function (BIMF) subbands, Gaussian mixture model is used to calculate noise variance of each sub-band. As the noise estimation only considers the noise components, effects of the feature components are reduced, and then the more accurate threshold is obtained. The adaptive threshold is set to filter the noise. Experimental results show that the proposed method avoids the disadvantage of the hard threshold function and the soft threshold function, the image is relatively clear and visual effects are improved. Compared with traditional denoising methods, its mean square error (MSE) is less than the other methods, and the peak signal to noise ratio (PSNR) increases by 0.5 dB～3 dB. The new method has a better denoising effect, and the more noise variance the more advantages can be obtained..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 809002 (2014)
Phase-Contrast Imaging by the Continuous-Wave Terahertz In-Line Digital Holography
Wang Dayong, Huang Haochong, Zhou Xun, Rong Lu, Li Zeyu, Lin Qiaowen, and Wang Yunxin
Terahertz (THz)-wave in-line digital holography imaging is a new imaging technique based on interferometry record of terahertz wave. It exhibits advantages for the THz imaging because it only needs low coherence light source a simple optical structure, and has high resolution imaging and access to quantitative real-timTerahertz (THz)-wave in-line digital holography imaging is a new imaging technique based on interferometry record of terahertz wave. It exhibits advantages for the THz imaging because it only needs low coherence light source a simple optical structure, and has high resolution imaging and access to quantitative real-time complex complitude of light wave. We built a continuous-wave THz in-line digital holographic setup. By preprocessing hologram and phase recovery algorithm, we obtain amplitude and phase contrast images of the sample and effectively inhibit the conjugate image. Further, the feasibility of THz in-line digital holography is explored in biomedical detection..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 809003 (2014)
Laser Manufacturing
Study on Thickening of Laser Bending Zone for Stainless Steel-Carbon Steel Laminated Sheet
Ma Xupeng, Wang Xuyue, Xu Wenji, and Guo Dongming
The bending zone thickening of the metal sheet becomes bigger after laser bending. IPP image processing software is the measure tool of the thickness and the grain size. Then rely on temperature gradient mechanism (TGM) to research the thickening mechanism. The results show that the grain size becomes bigger in the heaThe bending zone thickening of the metal sheet becomes bigger after laser bending. IPP image processing software is the measure tool of the thickness and the grain size. Then rely on temperature gradient mechanism (TGM) to research the thickening mechanism. The results show that the grain size becomes bigger in the heating process which means thermal expansion thickening (TET). In the positive bending process grains are squeezed and extended by the bending stress and forming extrusion thickening (ET). TET and ET are the principal factors of thickening appearance, and TET occupies the main position. The stainless steel layer and the carbon layer become thicker, and the thickened value of the carbon layer at least account for 69%. At last, the relation between the energy parameters (ie. power, scanning speed, scanning frequency and defocusing amount) and the thickened value is studied, which are the basis of theory and experiment for better bending mould and quality..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 803001 (2014)
Comparison of Ring-Form and C-Form Laser Welding for GH99 Superalloy
Liu Chunyan, Ma Rui, Tan Caiwang, Guo Wei, and Li Liqun
The material used in flame tube in an engine is mainly GH99 superalloy. The traditional welding method is resistance spot welding (RSW). In order to improve welding efficiency, reduce machining procedure and weld defect, comparative study of ring-form and C-form laser welding is carried out. The feasibility of laser weThe material used in flame tube in an engine is mainly GH99 superalloy. The traditional welding method is resistance spot welding (RSW). In order to improve welding efficiency, reduce machining procedure and weld defect, comparative study of ring-form and C-form laser welding is carried out. The feasibility of laser welding replacing RSW is revealed from weld appearance, microstructure and mechanical properties. In addition, the residual stress and deformation of local and whole component after welding is analyzed by using finite element method (FEM). The results indicate that good appearances are obtained both using ring-form and C-form welding methods, and their tensile-shear strengths are 15.4% and 22.1% higher than that of RSW, respectively. FEM calculation results show that C-form welding can lead to smaller residual stress and deformation compared to ring-form..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 803002 (2014)
Study on Remanufacturing Repair of Damaged Crank Shaft Journal Surface by Laser Cladding
Feng Hui, Li Jianfeng, and Sun Jie
In order to achieve the laser cladding remanufacturing on engine crankshaft, the iron-based coating on 45# steel has been obtained by laser cladding. Properties of the cladding layers have been investigated. The morphology and microstructure of layers are observed by an optical microscope. The hardness of layers is tesIn order to achieve the laser cladding remanufacturing on engine crankshaft, the iron-based coating on 45# steel has been obtained by laser cladding. Properties of the cladding layers have been investigated. The morphology and microstructure of layers are observed by an optical microscope. The hardness of layers is tested by a Vickers hardness tester. It is observed that the layer and substrate has a good metallurgical bond. Average hardness of the cladding layer is 2~3 times of that of the substrate. In order to realize the laser cladding for the crankshaft rod journal while the crankshaft is rotating around the principal axis, the requirements to obtain the continuous and uniform cladding are proposed. Under the conditions, the trajectory of laser beam and rotating journal and their relative speed during laser cladding are deduced, and the feasibility of the model is verified by the experiment..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 803003 (2014)
Experiment of Laser Machining of Micro-Structures on the Surface of Polycrystalline Diamond
Su Yongsheng, Li Liang, He Ning, and Zhao Wei
Cutting tools with surface micro-structures have positive effects on reducing friction, improving the wear resistance and anti-adhesion. Micro-structures of different shapes are fabricated using a fiber laser on the surface of polycrystalline diamond tool. The effects of various processing parameters on topography and Cutting tools with surface micro-structures have positive effects on reducing friction, improving the wear resistance and anti-adhesion. Micro-structures of different shapes are fabricated using a fiber laser on the surface of polycrystalline diamond tool. The effects of various processing parameters on topography and quality of micro-grooves are analyzed, such as scanning speed, pulse repetition rate, average output power, etc. The experimental results show that the width and depth of micro-grooves have an increasing and a decreasing tendency with the increase of the average output power and the pulse repetition rate respectively. Furthermore, the surface roughness of micro-grooves sidewall and topography quality of micro-grooves can be improved by the higher average output power and the lower scanning speed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 803004 (2014)
Microstructure and Mechanical Properties of Laser Welded Joints for Dissimilar Steel with Different Thicknesses
Jing Cainian, Fan Jichao, Ni Xiaomei, Li Huaixue, Liu Peng, and Zhang Yisheng
Aiming at the welding problem of steel used in automobile, the microstructure and property of joints in laser welded tailored sheets for dissimilar steel with different thicknesses are analyzed by optical microscope (OM), scanning electron microscope (SEM), hardness and tensile test. The results indicate that weld zoneAiming at the welding problem of steel used in automobile, the microstructure and property of joints in laser welded tailored sheets for dissimilar steel with different thicknesses are analyzed by optical microscope (OM), scanning electron microscope (SEM), hardness and tensile test. The results indicate that weld zone are lath martensite, and the laths mixed with retained austenite. Microstructure near the fusion line is more complex, mainly consists of martensite and bainite. Heat affected zone (HAZ) of transformation induced plasticity (TRIP) steel is mainly composed of bainite and ferrite, and the grains are relatively small. There are significant martensite existed in HAZ of dual phase (DP) steel, and the overheated zone is almost non-existent. The hardness in weld zone is more than 1.6 times as the parent metal. Macroscopic fracture of joint occurs in base metal of thinner DP steel sheet..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 803005 (2014)
Study on Microstructure and Performance of a FexCoCrAlCu/Q235 Laser Alloying Coatings
Zhang Song, Wu Chenliang, Yi Junzhen, Wang Chao, Zhang Chunhua, Guan Meng, and Tan Junzhe
FexCoCrAlCu (x=0,0.5,1,2) high entropy alloy coatings are prepared by laser surface alloying on the surface of Q235 steel. The constituent phases, microstructure, chemical composition and microhardness of the laser alloying coatings are analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), energy disFexCoCrAlCu (x=0,0.5,1,2) high entropy alloy coatings are prepared by laser surface alloying on the surface of Q235 steel. The constituent phases, microstructure, chemical composition and microhardness of the laser alloying coatings are analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), energy disperse spectroscopy (EDS) and microhardness tester respectively. The experimental results show that FexCoCrAlCu/Q235 high entropy alloying coatings with different Fe content form single body-centered cubic (BCC) solid solution. The laser alloying coatings have good metallurgical bonding to the substrate. The solidfied microstructure is the typical dendritic structure with component segregation. The microhardness of the laser alloying coatings is much higher than that of the Q235 steel, and the microhardness of the coatings tends to decrease gradually with the increase of Fe content. From the surface of FexCoCrAlCu/Q235 laser high entropy alloying coatings to the substrate, the mixing entropy presents gradient distribution from high entropy, medium entropy to low entropy..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 803006 (2014)
Microstructure and Mechanical Property of 60 mm-Thick 304 Stainless Steel Joint by Ultra-Narrow Gap Fiber Laser Beam Welding
Zhang Guowei, and Xiao Rongshi
304 stainless steel plates of 60 mm thick are welded using IPG YLS-6000 fiber laser and 5 mm wide groove. The microstructure and mechanical property of joint are tested by optical microscope, scanning electron microscope, energy disperse spectroscopy and tensile testing machine at low temperature. The result shows that304 stainless steel plates of 60 mm thick are welded using IPG YLS-6000 fiber laser and 5 mm wide groove. The microstructure and mechanical property of joint are tested by optical microscope, scanning electron microscope, energy disperse spectroscopy and tensile testing machine at low temperature. The result shows that complete defect free butt joints are obtained with ultra-narrow gap laser welding. The width of weld is uniform and is about 3.8 mm. Microstructure of joint are consist of columnar austenitic, the skeletal and the lath ferrite. There is a little ferrite diffuses and grows to the direction of the base metal and no obvious coarse grain in heat affected zone (HAZ). Main alloy elements such as Cr, Ni are even distributed in the weld and HAZ. The microhardness of the HAZ is slightly higher than that of weld metal and base metal. The tensile strength at temperature of 183 K, 213 K, 243 K and 273 K temperature are 86%, 96.7%, 94.5% and 92.6% of base metal, respectively, which increases when temperature decreases and the maximum is up to 1260 MPa. Samples are bended by 180° without any cracks or other defects..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 803007 (2014)
Laser Physics
10 J Diode-Pumped Thin-Disk Laser in Unstable Resonator
An Xiangchao, Tang Chun, Sang Jianli, Yu Yi, and Jiang Jianfeng
Using the method of ABCD transmission matrix to analyze the positive-branch unstable resonator which consists of multi thin disks, appropriate resonator parameters are got. The self-repeat of resonator is used to calculate oscillation beam size in different disks. The basis of ideal resonator′s threshold gives out the Using the method of ABCD transmission matrix to analyze the positive-branch unstable resonator which consists of multi thin disks, appropriate resonator parameters are got. The self-repeat of resonator is used to calculate oscillation beam size in different disks. The basis of ideal resonator′s threshold gives out the max output energy. Experiment has been carried to verify the analyze, finally we get 10.52 J output laser every single pulse, the magnification is 2.0, the frequency is 25 Hz, the oblique efficiency is 22.75%, the experimental results and the theoretical are totally conformed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 802001 (2014)
Passive Mode-Locked Yb3+-Doped Laser Based on Chired Fiber Bragg Grating
Wang Zhaokun, Du Songtao, Wang Ziwei, He Jing, and Zhou Jun
The passively mode-locked all fiber Yb3+-doped linear laser based on the chirped fiber Bragg grating (C-FBG) combined with a semiconductor saturable absorber mirror (SESAM) is achieved. High doping concentration Yb3+-doped fiber is used as the gain medium, which is pumped by a 976 nm diode laser, with a SESAM as one enThe passively mode-locked all fiber Yb3+-doped linear laser based on the chirped fiber Bragg grating (C-FBG) combined with a semiconductor saturable absorber mirror (SESAM) is achieved. High doping concentration Yb3+-doped fiber is used as the gain medium, which is pumped by a 976 nm diode laser, with a SESAM as one end of the reflector. A C-FBG introduces a large anomalous dispersion, and operates as the other end of the reflector. Finally, a stable picosecond pulse sequence output is achieved with pulse duration of 3 ps at repetition rate of 17.07 MHz. The maximum average power is 12 mW with the center wavelength of 1045 nm. The evolution of higher-order mode-locked optical pulse is dicussed. The mode-locked fiber laser can be self-starting and has a long-time stability, and is expected to become seed sources for high-power ultrashort pulse laser..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 802002 (2014)
Prediction of Optimum Deflection Angles and Errors Analysis for KDP Crystals with Large Aperture
Li Ting, Zhang Yang, Xu Xu, and Zhang Bin
By measuring the transmitted wavefront of crystals with orthogonal polarization interferometry(OPI), the model for determining the deflection angle of KDP crystals is established, and the theory is further verified to be correct and efficient by experiments. Under the stable conditions of probe laser and working temperBy measuring the transmitted wavefront of crystals with orthogonal polarization interferometry(OPI), the model for determining the deflection angle of KDP crystals is established, and the theory is further verified to be correct and efficient by experiments. Under the stable conditions of probe laser and working temperature, the variation trend of prediction values is consistent with that of measurement results, and the difference is within 10.0 μrad. Furthermore, the factors affecting the measurement precision are analyzed and the differences between the theory and measurement results are pointed out. The model of the optimum deflection angles of full aperture for KDP crystals is established according to the single point model. In addition, the influence of crystal refractive-index non-uniformity on the optimum deflection angles of full aperture for crystals and conversion efficiency is also simulated numerically. The results obtained in this paper provide theoretic guidances for accurate prediction of KDP crystals in the engineering project..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 802003 (2014)
186 MHz Low Amplitude Noise Erbium-Doped-Fiber Femtosecond Laser
Yan Lulu, Zhang Yanyan, Zhao Wenyu, Meng Sen, Zheng Enrang, Guo Wenge, Jiang Haifeng, and Zhang Shougang
Femtosecond laser is the most important part of an optical frequency comb, whose performance is mainly determined by the laser′s noise level, repetition rate, pulse width, spectrum and other parameters. A home-made erbium-doped-fiber femtosecond laser with ring structure and a repetition rate of 186 MHz is reported. ThFemtosecond laser is the most important part of an optical frequency comb, whose performance is mainly determined by the laser′s noise level, repetition rate, pulse width, spectrum and other parameters. A home-made erbium-doped-fiber femtosecond laser with ring structure and a repetition rate of 186 MHz is reported. This laser is designed for 9.2 GHz ultra-stable photonics microwave generation. The laser has an output power of 120 mW, and its spectrum center wavelength is in the range from 1550 nm to 1600 nm. The double-sideband relative intensity noise of the laser is -118 dBc/Hz at 1 Hz measured with a signal dynamic analyzer. From 10 Hz to 100 kHz, the relative intensity noise level is well below -130 dBc/Hz..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 802004 (2014)
Three-Dimensional Video Imaging Lidar System based on Acousto-Optic Laser Scanning
Luo Yuan, He Yan, Hu Shanjiang, Zang Huaguo, Shang Jianhua, Wan Yuan, and Chen Weibiao
A new three-dimensional video imaging lidar system based on acousto-optic laser scanning is presented, this system solves the problems of low imaging speed, large volume, and large quality which exist in the lidar system based on the traditional scanning method. Using two-dimensional acousto-optic scanning technology, A new three-dimensional video imaging lidar system based on acousto-optic laser scanning is presented, this system solves the problems of low imaging speed, large volume, and large quality which exist in the lidar system based on the traditional scanning method. Using two-dimensional acousto-optic scanning technology, the scanning speed can be improved. At the same time, high precision time detection chip is used to measure the time of laser pulse flight, in order to gain the distance of the target with high precision. So high precision and video-frequency three dimensional images is achieved. The principle of the system, system components, and the experimental results are described in detail. When the image resolution is 63 pixel×63 pixel, the imaging speed is 25 frame/s, and that can satisfy the demand of high imaging speed requirements for some special situation..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 802005 (2014)
Laser Frequency Stabilization Technology Based on Hollow-Core Photonics Crystal Fiber Gas Cell
Huang Chongde, Chen Dijun, Cai Haiwen, Ye Qing, Liu Ye, Qu Ronghui, and Chen Weibiao
A laser frequency stabilization system for the space integrated path differential absorption (IPDA) lidar is developed. The gas cell is made of the hollow-core photonics crystal fiber (PCF) filled with the CO2 and the absorption line around 1.57 μm is used as the laser frequency reference. The frequency modulation specA laser frequency stabilization system for the space integrated path differential absorption (IPDA) lidar is developed. The gas cell is made of the hollow-core photonics crystal fiber (PCF) filled with the CO2 and the absorption line around 1.57 μm is used as the laser frequency reference. The frequency modulation spectroscopy technique is used to stabilize the laser frequency. The impact of the pressure of CO2, the modulation frequency and depth on the error signal′s slope is simulated, and the optimal parameters are given. The computed results are coincident with the measured results. At last, the performance of the laser frequency stabilization is shown, and the suggestion for further improvement is given..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 802006 (2014)
Optimal Design of High Signal to Noise Ratio Petawatt Laser Front-End Device
Liu Haihui, Wang Tao, Dai Yaping, Li Dawei, and Xu Guang
A novel device is designed to replace the commercial 1053 nm femtosecond mode-locked laser oscillator. In this device, optical parametric chirped pulse amplification (OPCPA) is applied to realize energy amplification and wavelength conversion, and 3160 nm mid-infrared laser pulse is produced as the fundamental wave. ThA novel device is designed to replace the commercial 1053 nm femtosecond mode-locked laser oscillator. In this device, optical parametric chirped pulse amplification (OPCPA) is applied to realize energy amplification and wavelength conversion, and 3160 nm mid-infrared laser pulse is produced as the fundamental wave. Then a high signal to noise ratio (SNR) 1053 nm output pulse is got by the third harmonic generation (THG) process. The application of this device is expected to enhance the SNR of petawatt front-end and improve the SNR of the whole petawatt system at the same time..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 802007 (2014)
Continuous-Wave Single-Frequency 1.5 μm Laser Generated by a Singly Resonant Optical Parametric Oscillator
Li Peng, Ma Yayun, Nie Dandan, Feng Jinxia, and Zhang Kuanshou
A continuous-wave (CW) single-frequency 1.5 μm laser source is obtained by a singly resonant optical parametric oscillator (SRO) based on periodically poled lithium niobate. The SRO is pumped by a CW single-frequency NdYVO4 laser at 1.06 μm with the pump threshold of 2.5 W. 3.2 W of CW single-frequency signal laser at A continuous-wave (CW) single-frequency 1.5 μm laser source is obtained by a singly resonant optical parametric oscillator (SRO) based on periodically poled lithium niobate. The SRO is pumped by a CW single-frequency NdYVO4 laser at 1.06 μm with the pump threshold of 2.5 W. 3.2 W of CW single-frequency signal laser at 1.5 μm is achieved at pump power of 8 W with the optical conversion efficient of 40%. When the SRO is actively locked to the centre frequency of a Fabry-Perot cavity, the power stability is better than ±0.5% in 15 minutes and frequency stability is better than 3 MHz in 1 minute. The center wavelength of the laser system is in the wave band of quantum states transmission, so this kind of system can be employed for researches of practical quantum information processing..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 802008 (2014)
Analysis and Optimization of Phase-Matching Configuration in Ultrabroadband Optical Parametric Amplifier
Wang Yanhai, Zhang Fuling, Liu Guocai, and Lü Shuhui
The phase-matching configuration of optical parametric amplification (OPA) is investigated. The general physical model for evaluating the phase-matching scheme capable of generating ultra-broad gain bandwidth is developed. Based on this model, the phase-matching configuration and the corresponding matching signal wavelThe phase-matching configuration of optical parametric amplification (OPA) is investigated. The general physical model for evaluating the phase-matching scheme capable of generating ultra-broad gain bandwidth is developed. Based on this model, the phase-matching configuration and the corresponding matching signal wavelength can be obtained only under the conditions of a given pump wavelength and nonlinear crystal parameters. Numerical simulations, taking β-BaB2O4 (BBO) crystal for example, are performed, and the results show that there is a extreme difference for the acceptance angles between two different non-collinear phase-matching configurations. Analysis and optimization of non-collinear phase matching parameters are also carried out in order to obtain maximum gain bandwidth and excellent crystal acceptance angle. The calculated results of spectral phase-matching range for OPA based on BBO crystal, can also provide a theoretical basis for the designs of multi-beam-pumped or multi-stage OPA systems..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 802010 (2014)
Image Restoration in Laser Active Imaging Based on Directional Filters
Wang Canjin, Sun Tao, and Chen Juan
Since images from laser active imaging system on moving flat are blurred and polluted by kinds of noise, state of the art image deblurring techniques which are sensitive to image noise cannot achieve satisfying results. A new deblurring method for laser active imaging system based on directional filters is proposed. ThSince images from laser active imaging system on moving flat are blurred and polluted by kinds of noise, state of the art image deblurring techniques which are sensitive to image noise cannot achieve satisfying results. A new deblurring method for laser active imaging system based on directional filters is proposed. The key observation is applying a group of directional filters to the blurry and noisy image to reduce the noise level and estimate the blur kernel. For each directional filter, compute the Radon transform of the blur kernel along the orthogonal direction of the filter. Then the two-dimensional (2D) blur kernel can be reconstructed by inverse Radon transform. The last step is to restore the sharp image due to the blur kernel. An active imaging system is built up for experiment and the results indicate that compared with state of the art blind image deblurring techniques, the proposed method not only drastically improves the image quality in term of subjective visual, but also remarkably improves the PSNR..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 802011 (2014)
Materials and Thin Films
Monitoring and Optimizing the Pressured Point of Composite Vacuum Bag Molding Process with Fiber Bragg Grating sensors
Lu Shaowei, Ma Keming, Xiong Xuhai, Wang Xiaoqiang, and Jia Caixia
Fiber Bragg grating (FBG) sensor is sensitive to strain and temperature during composite curing process. A new method is raised to monitor the temperature and strain with double FBG sensors during composite vacuum bag molding process. The gel point and pressured point are obtained and optimized. The experimental resultFiber Bragg grating (FBG) sensor is sensitive to strain and temperature during composite curing process. A new method is raised to monitor the temperature and strain with double FBG sensors during composite vacuum bag molding process. The gel point and pressured point are obtained and optimized. The experimental results show that the gel temperature and time obtained by FBG sensors and dynamic mechanical thermal analysis (DMTA) are very consistency, and the composite manufactured under optimum pressured point has excellent interface performance and no delamination in the middle layer from scanning electron microscopy (SEM). This method can realize monitoring and optimizing of composite vacuum bag molding process..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 806001 (2014)
Measuring the Absorptance of Deep Ultraviolet Fluoride Coatings with Laser Calorimetry
Zhao Ling, Wu Xiaoye, Gu Yongqiang, Shi Guang, Mei Lin, Cai Xikun, and Zhang Lichao
To obtain the relationship between the absorptances of thin-film materials and the incoming ultraviolet laser energy density, it is better to establish a standard measurement method. The principle and measurement process of laser calorimetry is introduced, the dose depending effect, nonlinear absorption, and unrecoveraTo obtain the relationship between the absorptances of thin-film materials and the incoming ultraviolet laser energy density, it is better to establish a standard measurement method. The principle and measurement process of laser calorimetry is introduced, the dose depending effect, nonlinear absorption, and unrecoverable absorption phenomenon that might influence the measurement results are analyzed, a method based on the laser calorimetry is proposed, which is used to measure the absorptance of fluoride coatings that can be used in 193 nm ultraviolet photolithography systems, and experiments. According to the new proposed method, the dose depending effect, the corresponding laser energy density while the unrecoverable absorption phenomenon appears when the fused silica substrates are irradiated by 193 nm laser are measured; the relationship between absorptances of substrates and the laser energy density are calculated. After that, two substrates are coated with LaF3 and MgF2 separately by boat evaporation; the relationships between absorptances of the coated samples and laser energy density are measured. By the comparison of absorptances before and after coating, the relationships of the two thin-film materials between absorptances and laser energy densities are calculated, and the absorptances of LaF3 and MgF2 in actual working condition are figured out, also the relationship between deposited temperature and absorptance, roughness, waviness of LaF3 is obtained. The experimental results confirm the feasibility of the proposed method, which help to improve the imaging quality and prolong the working life of the objective system that can be used in the photolithography system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 807001 (2014)
Measurement and Metrology
Real-Time Linear Measurement of the Temperature Dependence of the Magneto-Optical Film′s Faraday Rotation Angle
Xu Canhua, Xu Qifeng, Ma Jing, and Xie Nan
The real-time linear measurement of the Faraday rotation angle of polarized light based on the crystal wedge is presented. Compared to the traditional methods, the measurement based on crystal wedge is not only insensitive to the light power fluctuation, but also can realize the real-time detection due to no adjustmentThe real-time linear measurement of the Faraday rotation angle of polarized light based on the crystal wedge is presented. Compared to the traditional methods, the measurement based on crystal wedge is not only insensitive to the light power fluctuation, but also can realize the real-time detection due to no adjustment of the optical elements during the experiments. More importantly the linear measurement can be kept for any polarization angle, and the relative accuracy reaches 8.7×10-4. The Verdet constants of the BiYIG magneto-optical film with Tb doping under various temperature are investigated by this method, and the temperature dependence is analyzed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 808001 (2014)
A High-Precision Pulsed Laser Ranging Time Interval Measurement Technology Based on Sine Curves Method
Huang Minshuang, Long Tengyu, Liu Huihui, and Zhang Ze
A high-precision time-of-flight interval measurement technology based-on multi-point average principle method for pulsed laser range finder has been presented. This method refers sine signals as the measurement benchmark, on the basis of pulse counting method, the sine signal time has been high-precision subdivided witA high-precision time-of-flight interval measurement technology based-on multi-point average principle method for pulsed laser range finder has been presented. This method refers sine signals as the measurement benchmark, on the basis of pulse counting method, the sine signal time has been high-precision subdivided with the principle of multi-point average method to eliminate time cumulative error caused by nonlinear sine curves. The high-precision pulsed laser ranging system has been built, pseudorandom sampling for the reference sine signals in a cycle by using linear frequency modulation technique to achieve high-precision time interval measurement. The structure of ranging system is simple and low cost. The single distance measurement accuracy obtained by experiments is stable within ±3 mm..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 808002 (2014)
High Sensitivity Pneumatic Micro-Distance Measurement System for Lithography Autofocus
Liu Tao, Xu Wendong, Zhao Chengqiang, Wang Chuang, Hu Yonglu, and Liu Yang
In order to overcome the shortcoming of the conventional optical focusing method, such as unable to detect on the patterned area, photoetching material′s potential exposure, complicated laser path and low sensitivity, method of using high sensitivity pneumatic micro-distance measurement system for lithography autofocusIn order to overcome the shortcoming of the conventional optical focusing method, such as unable to detect on the patterned area, photoetching material′s potential exposure, complicated laser path and low sensitivity, method of using high sensitivity pneumatic micro-distance measurement system for lithography autofocus is investigated. The principle, design, method and error analysis are introduced. The pneumatic micro-distance sensor can detect the varity of air flow to determine the defocusing amount. The varity of air flow is transfered into voltage for piezoelectric translator, and the piezoelectric ceramics will be drived to move to the focus range. Because the air pressure in nozzle flapper is related with detection distance, and the air flow is more sensitive than pressure, hotwire probe is used to detect the varity of air flow. The result shows that the accuracy of the measurement system can reach 100 nm, frequency response can come to 20 Hz, the measuring range can be 20 μm. Within a certain range, the detection distance has quite good linear relation with the varity of air flow..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 808003 (2014)
Temperature Measurement for Rotating Parts Based on the Fiber-Optic Slip-Ring
Wang Yanxiao, Yu Youlong, Gao Canhui, Duan Yingying, and Wang Xianhu
The fiber-optic slip-ring, consisting of two collimator lenses and realizing the off-axis rotating connection, as a new passive device proposed and connects with the optical fiber Bragg grating sensor is used to detect the temperature on the rotating parts when its axis is occupied or the shaft is hollow. The main inflThe fiber-optic slip-ring, consisting of two collimator lenses and realizing the off-axis rotating connection, as a new passive device proposed and connects with the optical fiber Bragg grating sensor is used to detect the temperature on the rotating parts when its axis is occupied or the shaft is hollow. The main influence factors of the insertion loss of the device are analyzed, theoretically. Simulation results show that the insertion loss is highly sensitive both to the transversal dislocation and the axial angle between two collimator lenses, while it is slightly insensitive to the change of the axial distance. Experiments show that during the rotating parts uniformed, the received signals through fiber-optic slip-ring are the periodic pulse signals, and the duty cycle of which is 0.5%, corresponds with the result of simulation. Using fiber-optic slip-ring coupling for fiber Bragg grating sensing light path, to achieve the change of temperature on the rotating part real-timely during heating the temperature field, the feasibility of this measurement method is verifies..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 808004 (2014)
Optical Communication
Precisely Tuning Technology of Multi-Wavelength Fiber Laser by Radio Frequency Signal Based on Single Side Band Modulator
Hou Yunzhe, Wang Zhaoying, Qin Xuwei, Liu Shiyuan, Luo Sha, Jia Dongfang, and Ge Chunfeng
A method of using radio frequency (RF) control signal to achieve multi-wavelength fiber laser output precisely tuned is proposed. 65 wavelengths simultaneously tuned precisely is achieved by placing a RF controlling single side band (SSB) modulator outside the cavity of multi-wavelength fiber laser. The multi-wavelengtA method of using radio frequency (RF) control signal to achieve multi-wavelength fiber laser output precisely tuned is proposed. 65 wavelengths simultaneously tuned precisely is achieved by placing a RF controlling single side band (SSB) modulator outside the cavity of multi-wavelength fiber laser. The multi-wavelength output can be tuned simultaneously with a tuning step ranging from 150 MHz to 14 GHz when changing the frequency of RF signal, corresponding to 1.2 pm as a minimum tuning step. The tuning resolution is determined by the resolution of the RF wave generator, which can be as low as 1 Hz. The wavelength spacing remains 50 GHz before and after the multi-wavelength tuning. The sideband-mode suppression ratio (SMSR) of each wavelength output can reach 20 dB..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 805001 (2014)
Design of the Sensitivity Enhanced Strain Sensor Based on Fine Transmission Spectrum of FBG
Su Juan, Dong Xiaopeng, and Shi Zhidong
A novel sensitivity enhanced fiber Bragg grating (FBG) strain sensor based on fine transmission spectrum and edge filter interrogator of a non-uniform FBG is proposed. The fine transmission spectrum changes of FBG under axial non-uniform strain and the strain response character based on spectrum changes are studied theA novel sensitivity enhanced fiber Bragg grating (FBG) strain sensor based on fine transmission spectrum and edge filter interrogator of a non-uniform FBG is proposed. The fine transmission spectrum changes of FBG under axial non-uniform strain and the strain response character based on spectrum changes are studied theoretically. The simulation results show that the strain sensitivity of the FBG under non-uniform strain can be enhanced to 4.6 times normal FBG. The sensor structure is designed and made experimentally to enhance the strain sensitivity by changing uniform strain into non-uniform strain. The experimental results are in good accordance with theoretical results. The FBG strain sensitivity and the range of the dynamic strain measurement ability are both enhanced in narrow linewidth laser locked edge filter interrogation system by using this new FBG sensor. Because of its compact size, the new FBG strain senor has great potential for high frequency dynamic strain monitoring..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 805002 (2014)
Acoustic Emission Location Technology Research Based on FBG Sensor Network and Time Reversal Focusing Imaging Method
Sai Yaozhang, Jiang Mingshun, Sui Qingmei, Lu Shizeng, and Jia Lei
For the problems of complicated structure, difficults to networking and low accuracy of traditional acoustic emission localization system, an acoustic emission localization based on fiber Bragg grating (FBG) sensor network and time reversal focusing imaging technology is designed. Based on the analysis of the principleFor the problems of complicated structure, difficults to networking and low accuracy of traditional acoustic emission localization system, an acoustic emission localization based on fiber Bragg grating (FBG) sensor network and time reversal focusing imaging technology is designed. Based on the analysis of the principle of time reversal focusing, positioning system by four FBG sensors is built and narrow band laser edge filter technology is used to realize signal demodulation. Morlet wavelet transform is used to extract specific frequency component signal, and calculate the modulus value and time lag. Through the establishment of time reversal focusing model, acoustic emission location is realized. The localization method is verified in the aluminum alloy plate. The experimental result shows that this method can effectively realize localization and imaging of acoustic emission source, and localization error is less than 20 mm, and time consumption is less than 2 s. A new method is provided for acoustic emission detection and localization..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 805003 (2014)
Link Fault Detection in Passive Optical Networks Based on Correlation Method Combined with an Amplified Spontaneous Emission Source
Liu Yanyang, Yang Lingzhen, Wang Feifei, Chen Xi, Zhang Zhaoxia, Wang Juanfen, and Liu Xianglian
The fault detection technique for the wavelength division multiplexing passive optical network (WDM-PON) is proposed based on an erbium-doped fiber amplified spontaneons emission (ASE) source. It is quite difficult to the link fault detection because of the multi-branch and node density structure of WDM-PON. The technoThe fault detection technique for the wavelength division multiplexing passive optical network (WDM-PON) is proposed based on an erbium-doped fiber amplified spontaneons emission (ASE) source. It is quite difficult to the link fault detection because of the multi-branch and node density structure of WDM-PON. The technology utilizes the broadband characteristics of the erbium-doped fiber ASE source with the double-pass backward configuration and the delta correlation properties of the time-domain output. It can solve the problem in the WDM-PON fault detection of fiber links. In the experiments, the detection of 8 channels WDM-PON can accurately locate the fiber breakpoint, the joint looseness, and multi-fault reflection. The results show that the 23 dB dynamic range and 4 cm spatial resolution which is independent to the measuring distance are realized. The technology is able to achieve the detection of the WDM-PON faults with 32 channels based on the broadband characteristics of the ASE source to realize WDM-PON fiber link fault location with centimeter resolution..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 805004 (2014)
Study on Strain Transfer Mechanism of Surface Fiber Bragg Grating Sensor
Tian Shizhu, Zhang Guoqing, and Wang Dapeng
The mechanic model of surface fiber Bragg grating (FBG) sensor is built to study the strain transfer between the composite beam and the surface FBG sensor. The relationship between the actual strain of composite beam and the strain of surface FBG sensor is deduced. Various factors which influence the average strain traThe mechanic model of surface fiber Bragg grating (FBG) sensor is built to study the strain transfer between the composite beam and the surface FBG sensor. The relationship between the actual strain of composite beam and the strain of surface FBG sensor is deduced. Various factors which influence the average strain transfer rate of surface FBG sensor have been analyzed. Modulus elasticity, width of the cementing layers length of the fiber pate are primary factors to influence the strain transfer rate. A optimum combination of the three factors is determined through an experiment, which proides reference for practical engineering application in future..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 805005 (2014)
Upstream Data Transmission in Passive Optical Networks Based on Orthogonal Waveform Multiplexing Technology
Yao Haitao, Li Wei, Han Jilong, Wang Yimeng, He Zhixue, Yang Qi, and Yu Shaohua
A multiplexing technique named orthogonal waveform (graph) division multiplexing (OGDM) and its application on the upstream data transmission in passive optical access networks (PON) are proposed. N mutually orthogonal electrical waveforms are assigned to N optical network units (ONU). For intensity modulator, ONU′s coA multiplexing technique named orthogonal waveform (graph) division multiplexing (OGDM) and its application on the upstream data transmission in passive optical access networks (PON) are proposed. N mutually orthogonal electrical waveforms are assigned to N optical network units (ONU). For intensity modulator, ONU′s code “1” means orthogonal electrical waveform and code “0” means no waveform. Those electrical orthogonal waveforms are modulated on lasers with the same wavelength and then are combined at optical distribution network (ODN) to be transmitted to optical line terminal (OLT) in a single fiber. At OLT, the mixed signals can be separated by using correlative demodulation method. Stimulation results show that, under external modulation, the transmission distance reaches 20 km with 320 Gb/s data transmission rates in ideal situation..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 805006 (2014)
Simulation System of the Beacon Pointing and Acquisition Process in the Satellite Laser Communication
Yu Xiaonan, Tong Shoufeng, Zhao Xin, Song Yansong, and Zhang Lei
A set of simulation system is developed on LabVIEW platform for the beacon pointing and acquisition process of the satellite laser communication. This system simulates the satellite orbit and attitude dynamics, establishes the binary pointing relationship and simulates the initial alignment of the turntable with two deA set of simulation system is developed on LabVIEW platform for the beacon pointing and acquisition process of the satellite laser communication. This system simulates the satellite orbit and attitude dynamics, establishes the binary pointing relationship and simulates the initial alignment of the turntable with two degrees of freedom. The beacon laser is driven to do the helical scanning according to the size of the uncertain region. The beam angle and the field of the detector determine the simulation acquisition point so as to acquire it. And then equivalent sinusoidal disturbances with Gaussian noise 1°/s maximum speed and 1°/s2 maximum acceleration are used to finish the dynamical acquisition experiment. Finally, the pointing and acquisition simulation of the dynamic binary laser communication between a geostationary earth orbit (GEO) and a low earth orbit (LEO) is accomplished, and the simulation model of the laser communication process based on the virtual instrument is also constructed, which estabishes the foundation for the tracking system simulation and beaconless acquisition simulation..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 805007 (2014)
Add-Drop Filter by Coupling between Micro-Nano Fiber Ring and Side Polished Fiber
Jin Shaoshen, Chen Zhe, Wei Qingsong, He Xiaoli, Yu Jianhui, Zang Zhigang, Lu Huihui, Luo Yunhan, Tang Jieyuan, and Zhang Jun
A novel add-drop filter based on direct coupling between micro-/nano-fiber (MNF) ring and side-polished fiber(SPF) is proposed and demonstrated. Experiment results show that this kind of filter not only can realize interconnected coupling between the MNF optical system with conventional optical system, but also can reaA novel add-drop filter based on direct coupling between micro-/nano-fiber (MNF) ring and side-polished fiber(SPF) is proposed and demonstrated. Experiment results show that this kind of filter not only can realize interconnected coupling between the MNF optical system with conventional optical system, but also can realize a function as add-drop filter between two optical systems. The maximum extinction ratio of drop port can achieve to be 7.5 dB as a drop filter, while maximum extinction of add port can be 4.8 dB as a add filter. Furthermore, the influence of different ring diameters on the coupling between the two optical systems is numerically and experimentally investigated. The conclusion of the investigation is that when the diameter of MNF is fixed at 6 μm and the diameter of MNF ring reaches to be 580 μm, coupling efficiency of the MNF ring and SPF is maximum and the influence of the coupling on the Q value and fineness of the ring reaches minimum simtaneously. This kind of add-drop filter, without assistant of extra optical device to couple light into MNF from standard optical fiber, provides a more elegant solution for interconnection of the MNF optical system and current standard optical fiber system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 805008 (2014)
Terahertz Technology
Design of Contact Grating for High Energy Terahertz Wave Generation by Tilted Pulse Front Pumping
Liang Xiaojing, Li Yanfeng, Hu Xiaokun, Xu Shuaishuai, Chai Lu, and Wang Qingyue
Titled pulse front pumping (TPFP) based on non-collinear phase matching is the most efficient technique to generate ultrafast terahertz (THz) wave by femtosecond laser sources, and the use of a contact grating that can avoid aberrations caused by the imaging system has the potential of further improving the generation Titled pulse front pumping (TPFP) based on non-collinear phase matching is the most efficient technique to generate ultrafast terahertz (THz) wave by femtosecond laser sources, and the use of a contact grating that can avoid aberrations caused by the imaging system has the potential of further improving the generation efficiency. An embedded contact grating fabricated inside the lithium niobate crystal is proposed for the TPFP scheme for the generation of high-energy THz radiation and designed by the simplified modal method. The grating diffraction under the Littrow mounting is simplified to a two-mode interference process, which greatly simplifies the grating design. The grating period is determined and the dependence of the diffraction efficiency on the fill factor and the groove depth of the grating is systematically explored. By reducing the reflection at the grating-crystal interface the embedded grating can achieve a diffraction efficiency larger than 90% for the -1 diffraction order and the grating parameters are given. This systematic design procedure is applicable to the design of contact gratings based on other THz generation crystals..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 811001 (2014)
Fast Imaging System Based on Self-Made Terahertz Detector
Sun Zhenlong, Tu Xuecou, Jiang Yi, Kang Lin, Chen Jian, and Wu Peiheng
An active imaging system has been constructed by using a Cassegrain reflector with the diameter of 30 cm. The system works at room temperature and 0.22 THz. The detectors are self-made Nb5N6 microbolometer THz detector and commercial VDI detector. Images for 5 parallel copper rods with the diameter of 1.4 cm and space An active imaging system has been constructed by using a Cassegrain reflector with the diameter of 30 cm. The system works at room temperature and 0.22 THz. The detectors are self-made Nb5N6 microbolometer THz detector and commercial VDI detector. Images for 5 parallel copper rods with the diameter of 1.4 cm and space of 5 cm are got and analyzed. The imaging time is reduced from 15 s to 7.5 s by changing the reference frequency and scanning velocity. The range of the image is 20 cm×6.5 cm. The special resolution of the images is about 1.41 cm for the two detectors..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 811002 (2014)
Optical Design and Fabrication
Study on the Fabrication of the High Accuracy Optical Aspherical Mirror with Atmospheric Pressure Inductively Coupled Plasma Chemical Etching Technology
Wang Xu
The inductively coupled plasma chemical etching technology operating at atmospheric pressure is used to fabricate the optical mirror whose materials are fused silica, reaction-sintered silicon carbide (RB-SiC), Si. It is focused of the primary study on the removal function of the plasma torch on different samples. The The inductively coupled plasma chemical etching technology operating at atmospheric pressure is used to fabricate the optical mirror whose materials are fused silica, reaction-sintered silicon carbide (RB-SiC), Si. It is focused of the primary study on the removal function of the plasma torch on different samples. The Gaussian fitting full width at half maximum (FWHM) of the removal function is 18 mm. The removal rates are 10.86, 0.82, 1.51 μm/min respectively. A 100 mm caliber SiC mirror substrate is processed by using this technology, the error rate of the real obtained surface shape and virtual processed surface shape is 8.57%, and the error of converge rate is 4.7%. The experimental results show that the new technology has a potential application value on fabricating the large-aperture aspherical optical mirror in astronomy. So the inductively coupled plasma chemical etching technology operating at atmospheric pressure will have a promising foreground in the future..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 816001 (2014)
Design of Compact Middle-Wave Infrared Camera Used on Airborne Platform
Xu Xinhang, Chen Ning, Wang Bing, Gao Yunguo, and Yang Hongbo
In view of the small space of flying cabin, a compact middle-wave infrared camera is designed for optical-electricity tracking and pointing system used on the airborne platform. Firstly, requisite performances of infrared camera is put forward on the basis of applying requirements of airborne platform. Then, optics sysIn view of the small space of flying cabin, a compact middle-wave infrared camera is designed for optical-electricity tracking and pointing system used on the airborne platform. Firstly, requisite performances of infrared camera is put forward on the basis of applying requirements of airborne platform. Then, optics system including two-time imaging and double reflecting is designed and optimized. A fine focusing mechanism is developed for temperature focusing and distance emendation. A trunk supporting base is designed and its structural rigidity is analyzed by finite element method. Finally, focus, visual angle, noise equivalent temperature difference (NETD) and modulation transfer function (MTF) of infrared camera are tested by optical-electricity testing platform after finely manufacturing, assembling and adjusting. The results show that focus and visual angle agree with design parameters, the measurement NETD is 22 mK, MTF is higher than 0.58 in Nyquist frequency of CCD which approaches diffraction limit level. Therefore, the designed infrared camera with high sensitivity and good imaging quality can satisfy application requirements of airborne platform..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 816002 (2014)
Remote Sensing and Sensors
Ship Target Detection for Moving Video Maritime Surveillance
Li Qingzhong, Zang Fengni, and Zhang Yang
In order to monitor some critical maritime areas, a dynamic platform based on charge coupled device (CCD) cameras is used, a novel algorithm for ship target detection based on texture model of sea surface is presented. The sky background and horizon are detected quickly by using an energy feature in discrete cosine traIn order to monitor some critical maritime areas, a dynamic platform based on charge coupled device (CCD) cameras is used, a novel algorithm for ship target detection based on texture model of sea surface is presented. The sky background and horizon are detected quickly by using an energy feature in discrete cosine transform (DCT) domain of image blocks. In order to separate ship targets from the complex sea background below the horizon, the texture feature of sea surface domain under the horizon image blocks in DCT domain is extracted, and a new texture mixture model of sea surface is developed by using adaptive fuzzy c means clustering technique. Ship targets are segmented from sea background by the constructed sea surface texture model. The experimental results show that the proposed algorithm can detect ship targets quickly and steadily, especially suitable for maritime surveillance based on non-stationary monitoring platforms under the large wave sea background..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 814001 (2014)
A Fast Simulation Algorithm of Scanning Laser Radar
Chen Xiao, Shi Zhiguang, Yang Weiping, and Lu Xinping
Modeling and simulation of scan-imaging laser radar is an important research content in the field of signal processing and system design of laser radar. In order to improve the simulation efficiency without affecting the accuracy of the simulation simultaneously, a novel fast simulation algorithm is proposed. An inequaModeling and simulation of scan-imaging laser radar is an important research content in the field of signal processing and system design of laser radar. In order to improve the simulation efficiency without affecting the accuracy of the simulation simultaneously, a novel fast simulation algorithm is proposed. An inequation that can judge the intersection relations between the pixel and bins can be obtained by deriving the projection of their trajectories on the image plane. Then utilizing the time subdivision and approximate treatments to judge the potential intersection relations of pixel and bins. Finally, the goal of reducing the number of intersection operations can be achieved by testing all the potential relations and finding which of them is real intersection. The consequence of performing the new proposed simulation algorithm and the traditional algorithm in simulating 6 targets shows that they yield the same result, whereas the number of intersection operations of former is equivalent to only 1% of the latter..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 814002 (2014)
Spectroscopy
Influence of Non-Collinear Angle and Phase Matching Angle on YCOB-OPCPA Gain Spectra
Ma Lin, Yu Lianghong, Xu Lu, Chu Yuxi, and Liang Xiaoyan
Theoretical and experimental investigations are carried out to determine the influence of the phase matching angle and non-collinear angle on the optical parametric chirped pulse amplification (OPCPA) amplified spectrum of yttrium calcium oxyborate (YCOB) crystal. In theory, through the numerical simulation calculationTheoretical and experimental investigations are carried out to determine the influence of the phase matching angle and non-collinear angle on the optical parametric chirped pulse amplification (OPCPA) amplified spectrum of yttrium calcium oxyborate (YCOB) crystal. In theory, through the numerical simulation calculation, it is found that the amplified spectrum of YCOB-OPCPA is sensitive to the phase matching angle and non-collinear angle. When the phase matching angle or non-collinear angle is changed even in a small range, center wavelength drifting and narrowing phenomenon will occur in the gain spectrum. However, when the non-collinear angle is between 2.80° and 2.91°, there is always a phase matching angle that can match the non-collinear angle to satisfy the OPCPA output of more than 80 nm broadband with high power. With the purpose of getting high efficiency and broadband OPCPA output, a method to measure the non-collinear angle accurately based on high accurate CCD is proposed. With this method, the YCOB-OPCPA gain spectrum characteristics based on different non-collinear angles are researched, and the broadband OPCPA gain spectrum is acquired. The experimental results can provide a reference for single-shot pulse OPCPA experiments..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 41, Issue 8, 815001 (2014)
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