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2013
Volume: 40 Issue 4
41 Article(s)
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Research Article
Unified Method for Anisoplanatism of Adaptive Optical Systems
Chen Jingyuan, Zhou Yu, Chang Xiang, and Xiong Yaoheng
The general formularies to study the anisoplanatism of adaptive optical systems are constructed by the transverse spectral filtering method. At some peculiar situation, these formularies can be expressed to explicit form, and the classical scalar law and the relevant characteristic scale can be obtained and generalizedThe general formularies to study the anisoplanatism of adaptive optical systems are constructed by the transverse spectral filtering method. At some peculiar situation, these formularies can be expressed to explicit form, and the classical scalar law and the relevant characteristic scale can be obtained and generalized. While in general, only numerical values can be obtained. As an example, the lunar laser ranging system with an adaptive optics (AO) to correct the uplink beam is used to explain the use of these formularies to study the anisoplanatism of AO systems..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 413001 (2013)
Change of Propagation Quality Factor of Partially Coherence Hermite-Gaussian Beams Traveling through Oceanic Turbulence
Chen Feinan, Chen Yanru, Zhao Qi, Chen Jingjing, and Xin Yu
The spatial power spectrum function of oceanic turbulence is used to calculated the variations of turbulence perturbation item with turbulence parameters in extended Huygens-Fresnel integral by numerical methods. Then, the change of propagation quality factor of partically coherence Hermite-Gaussian (PCHG) beam traveliThe spatial power spectrum function of oceanic turbulence is used to calculated the variations of turbulence perturbation item with turbulence parameters in extended Huygens-Fresnel integral by numerical methods. Then, the change of propagation quality factor of partically coherence Hermite-Gaussian (PCHG) beam traveling in oceanic turbulence is calculated by Wigner distribution function and the second moment definition of the beam. The affection of beam parameters on M2 factor is also analyzed. At last, the matrix of M2 factor is used to calculate the track of M2 factor of nonsymmetrical two-dimensional PCHG beam. It is found that the track plots of two dimensional PCHG beams′ spots on the receive plane are different from each other because of different models on x direction and y direction, but the difference decreases with the increase of propagation distance, and finally tends to same circular track..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 413002 (2013)
Beam Transmission and Control
Inner-Port Connectivity Aware Dynamic Routing Schemes in Optical Wavelength Division Multiplex Networks
Chen Yue, Hua Nan, and Zheng Xiaoping
As the scales of the optical networks grows continuously, the multi-dimensional reconfigurable optical add-drop multiplexer (ROADM) becomes the key node technology in the next generation communication networks. However, because of the high cost of the non-blocking high-degree optical switching fabric, the asymmetric swAs the scales of the optical networks grows continuously, the multi-dimensional reconfigurable optical add-drop multiplexer (ROADM) becomes the key node technology in the next generation communication networks. However, because of the high cost of the non-blocking high-degree optical switching fabric, the asymmetric switching fabric (i.e. there are unconnected ports in an optical node) can be widely used. To solve the inner-port connectivity aware (IPCA) routing and wavelength allocation problem, an integer linear programming (ILP) model is first formulated. Then three IPCA routing schemes are proposed, including the IPCA based on K-shortest pathe (IPCA-KSP) scheme, the IPCA-Dijkstra scheme and entire path searching (EPS) scheme. Simulation results show that, the EPS scheme can find the shortest path by enumeration, but its factorial computational complexity is not tolerable. The IPCA-KSP scheme cannot guarantee to find the shortest path, which only works effectively in small-scale networks. By modifying the path search process of the classical Dijkstra′s algorithm, the IPCA-Dijkstra scheme can find the shortest path with low complexity..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 405005 (2013)
Holography and Information Processing
Research of Color Digital Holography in Image Space
Lou Yuli, Li Junchang, Gui Jinbin, Song Qinghe, Li Chongguang, and Fan Zebin
In order to obtain sufficient information about object-wave fields when there are large differences between the size of the object and CCD array, it is a common way to transform object light with lens system in the detection research of color digital holography. Based on the similar characteristics of object and image,In order to obtain sufficient information about object-wave fields when there are large differences between the size of the object and CCD array, it is a common way to transform object light with lens system in the detection research of color digital holography. Based on the similar characteristics of object and image, the image of object is often viewed as object fields in image space and the reconstructed color digital image. It is a problem that must be solved to determine imaging plane of object when illuminated by lights with different wavelengths and to reconstruct these image fields with the same size. A new simple method of determining image plane of different-color lights without knowing lens parameters of optical system is presented. Further more, based on focal-depth research of digital holographic reconstructed image,the color image of object is reconstructed well in image space..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 409001 (2013)
Speckle Noise Suppression of Reconstructed Image Based on Dual-Tree Complex Wavelet and Anisotropic Diffusion
Wu Yiquan, Ye Zhilong, and Wan Hong
In order to suppress the speckle noise of reconstructed image in digital holography effectively and to further improve the quality of reconstructed image, a speckle noise suppression method of reconstructed image in digital holography based on dual-tree complex wavelet transform (DT-CWT) and anisotropic diffusion is prIn order to suppress the speckle noise of reconstructed image in digital holography effectively and to further improve the quality of reconstructed image, a speckle noise suppression method of reconstructed image in digital holography based on dual-tree complex wavelet transform (DT-CWT) and anisotropic diffusion is proposed. The reconstructed image is decomposed through DT-CWT. Then, the low-frequency components and the high-frequency components in six directions are processed through P_Laplace diffusion and Laplacian pyramid-based nonlinear diffusion (LPND), respectively. The new reconstructed image is synthesized through inverse dual-tree complex wavelet transform (IDT-CWT). The experimental results are given, and a subjective visual comparison is made with the method of wavelet threshold shrinkage and total variation (TV) diffusion, the method of LPND, and the method combining contourlet transform with TV and adaptive contrast diffusion. While the results are evaluated quantitatively according to peak signal to noise ratio (PSNR), correlation coefficient (COR) and running time. Experimental results show that the proposed method has a better performance in speckle noise suppression and preserves the detail and textural features of original reconstructed image more efficiently..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 409002 (2013)
Laser Manufacturing
[in Chinese]
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Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 402009 (2013)
Mitigation of Ultraviolet Laser Damage on Fused Silica Surface with Femtosecond Laser System
Fang Zhou, Zhao Yuan′an, Chen Shunli, Hu Guohang, Liu Wenwen, Chen Weixiao, Li Dawei, and Shao Jianda
Growth of laser induced damage on the surface of fused silica plays a major role in determining optics lifetime in high power laser systems. In this paper, a femtosecond laser system is applied to create benign mitigation pits to replace growing damage sites; the mitigation mechanism is also explored. The electric fileGrowth of laser induced damage on the surface of fused silica plays a major role in determining optics lifetime in high power laser systems. In this paper, a femtosecond laser system is applied to create benign mitigation pits to replace growing damage sites; the mitigation mechanism is also explored. The electric filed distribution around mitigation pit is modeled with the finite difference time domain (FDTD) method to determine the optimal mitigation geometry. The shape、size and depth of mitigation pit are controlled by varying energy of femtosecond laser, changing the movement mode of sample stage, in order to achieve the optimal mitigation geometry. The results of laser damage growth test indicate that the rectangular mitigation structure can reduce the light intensity distribution and the damage threshold of mitigation pits is much higher than damaged sites. Furthermore, Energy dispersive spectrometers (EDS) microanalysis technique is used to detect the chemical composition of mitigation pits, and results shows that ultraviolet absorbing defects are removed after mitigation. Reduces of the ultraviolet absorbing defects as well as the local light intensity are key factors to succeed in mitigating growing damage sites..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 403001 (2013)
Microstructure and Mechanical Properties of X80 Pipeline Steel Backing Welded Joint by Fiber Laser-MAG Hybrid Welding
Lei Zhenglong, Tan Caiwang, Chen Yanbin, Liu Dejian, Hu Xiyuan, Hu Peipei, and Zeng Huilin
Fiber laser-metal active-gas welding (MAG) hybrid welding on 6-mm-thick root of X80 pipeline steel is carried out to attain one side welding both sides formation. Mechanical properties of welded joint in optimal parameters such as microhardness, tensile strength, impact toughness, bending strength are studied. Based onFiber laser-metal active-gas welding (MAG) hybrid welding on 6-mm-thick root of X80 pipeline steel is carried out to attain one side welding both sides formation. Mechanical properties of welded joint in optimal parameters such as microhardness, tensile strength, impact toughness, bending strength are studied. Based on this, the effect of thermal cycle caused by hybrid welding on welded joint is investigated. The results indicate that good appearance, defect free joint can be achieved in the optimized parameters, and the cross-section of welded joint exhibits feature of “goblet”, which can be divided into two parts: arc zone and laser zone. The microhardness in arc zone is higher than that in laser zone. Fracture of tensile test occurs in the base metal. The microstructures of weld in arc zone mainly consist of acicular ferrite and a small amount of proeutectoid ferrite. Whereas, The microstructures of weld in laser zone mainly compose of acicular ferrite and bainite-like (upper bainite and granular bainite). The difference in microstructure of heat affected zone (HAZ) between arc zone and laser zone is small, but the coarse zone in arc zone is obviously wider than that in laser zone..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 403002 (2013)
Study of Weld Metal Solidification Characteristics and Relationship between Microstructure and Microhardness in Pulsed Laser Welding
Ji Yaoyao, Hong Yongchang, and Zhang Wu
The welding test of DP500 dual-phase steel sheet of 0.65 mm is implemented by the Nd:YAG solid pulsed laser welder. The pulsed laser weld surface and cross-section morphology are analyzed, and the paper focuses on the weld solidification characteristics under different pulse laser frequencies and the relationship betweThe welding test of DP500 dual-phase steel sheet of 0.65 mm is implemented by the Nd:YAG solid pulsed laser welder. The pulsed laser weld surface and cross-section morphology are analyzed, and the paper focuses on the weld solidification characteristics under different pulse laser frequencies and the relationship between microstructure grain and microhardness. The result shows that each of the welding spots forming the weld seam can be divided into two parts: welding spot overlap region and unoverlap region. With the change of the pulse laser frequency, the morphology of weld and the welding spot overlapping ratio both change, and the microstructure grain exhibits heterogeneity. Meanwhile, microhardness distribution appears to be fluctuant, the minimum microhardness value appears in the welding spot overlap region while, the maximum microhardness value appears in the unoverlap region. With the pulse laser frequency increasing, the difference of microstructure grain decreases and the fluctuation of the microhardness distribution along the longitudinal section of the weld center is also gradually reduced..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 403003 (2013)
Functionally Graded YSZ/NiCrAlY Coating Prepared by Laser Induction Hybrid Rapid Cladding
Zhou Shengfeng, Dai Xiaoqin, Xiong Zheng, and Zhang Tianyou
To eliminate cracks and thermally grown oxide (TGO) in thermal barrier coatings (TBCs), the functionally graded yttria-stabilized-zirconia (YSZ)/NiCrAlY coating by laser induction hybrid rapid cladding (LIHRC) is investigated. The results show that the crack-free YSZ/NiCrAlY coating with good profile and gradual microhTo eliminate cracks and thermally grown oxide (TGO) in thermal barrier coatings (TBCs), the functionally graded yttria-stabilized-zirconia (YSZ)/NiCrAlY coating by laser induction hybrid rapid cladding (LIHRC) is investigated. The results show that the crack-free YSZ/NiCrAlY coating with good profile and gradual microhardness can be obtained when laser scanning speed and powder feeding rate increase to 3200 mm/min and 90.63 g/min during LIHRC, respectively. The c-ZrO2, m-ZrO2 and t-ZrO2 phases in primary YSZ powder are all completely transformed into the metastable t′-ZrO2 phase. The fine, dense and dual-phase microstructure composed of columnar dendrites is characterized by the gradual increase of YSZ content in the coating. Moreover, the interface of consecutive layer disappears, which is different from ceramic layer-bond layer (i.e., double-layer) constituent of TBCs formed during the individual laser cladding. After the isothermal oxidation, the metastable t′-ZrO2 phase in the LIHRC-formed functionally graded YSZ/NiCrAlY coating transforms into t-ZrO2, which can increase the oxidation resistance of superalloy GH4169..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 403004 (2013)
Phase-Field Method Simulation of Microstructure Evolution at the Bottom of Melt Pool in Coaxial Laser Cladding
Sun Daojin, Liu Jichang, and Li Qindong
Two-dimensional macroscopic temperature field of the work-piece and evolution of the microstructure which is located at the bottom of the melt pool in coaxial laser cladding are calculated. Formation of the clad bead due to powder feeding is simulated. Macroscopic temperature field is computed. Then, one macroscopic ceTwo-dimensional macroscopic temperature field of the work-piece and evolution of the microstructure which is located at the bottom of the melt pool in coaxial laser cladding are calculated. Formation of the clad bead due to powder feeding is simulated. Macroscopic temperature field is computed. Then, one macroscopic cell at the bottom of the melt pool is re-meshed for calculation of the microstructure evolution. Initial temperature conditions are calculated with interpolation method among the temperatures of its nearest neighbor macroscopic cells. Its four boundary temperatures can be considered as the same as its four neighbors′ temperatures. Crystal nucleus is set in the lower boundary of microscopic domain. Finally, phase field and temperature field are calculated using phase-field method. The calculation results agree with the experimental results, which proves the validity of the macro and micro coupling model..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 403005 (2013)
Effect of Laser Shock Processing Times on Microstructure and Microhardness of High Carbon Pearlitic Steel
Xiong Yi, He Hongyu, Luo Kaiyu, Guo Zhiqiang, Lu Yanjun, and Zhang Lingfeng
High carbon pearlitic steel is processed by laser shocking processing (LSP). The microstructure and hardness of high carbon pearlitic steel are examined using scanning electron microscope (SEM) and transmission electron microscope (TEM) and microhardness tester. The results show that the cementite lamellae is bent, fraHigh carbon pearlitic steel is processed by laser shocking processing (LSP). The microstructure and hardness of high carbon pearlitic steel are examined using scanning electron microscope (SEM) and transmission electron microscope (TEM) and microhardness tester. The results show that the cementite lamellae is bent, fractured and spheroidized after multiple LSP impacts. With increase of LSP times, the spheroidization of the cementite lamellae is aggravating at the center of the laser spot, and the dissolution of the cementite is increased, supersaturated carbon atoms are dissolved in ferrite, leading to the increase of the lattice parameters. Moreover, the microhardness increases with increase of LSP times. After multiple LSP impacts, the microhardness at the center of the laser spot increases from 300 HV to 333 HV (2 LSP impacts), 353 HV(6 LSP impacts)..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 403006 (2013)
Controllability Research on Dilution Ratio of Nickel-Based Superalloy by Laser Cladding Reparation
Pan Hu, Zhao Jianfeng, Liu Yunlei, Wang Kai, Xiao Meng, and Gao Xuesong
In order to improve the stability of laser cladding reparation property, several single-factor tests are carried out for GH4169 nickel-based superalloy by controlling the dilution ratio. The result shows that within certain parameter range, the dilution ratio increases with the increase of laser power or the decrease oIn order to improve the stability of laser cladding reparation property, several single-factor tests are carried out for GH4169 nickel-based superalloy by controlling the dilution ratio. The result shows that within certain parameter range, the dilution ratio increases with the increase of laser power or the decrease of feeding speed, and the scanning speed may have little influence. In order to simplify the study process of dilution ratio, this paper puts forward the concept of powder-heat-absorption density, which means the laser energy absorbed by a unit mass of powder during the process of laser cladding, establishes the positive correlation between the powder heat absorption and dilution ratio with the combination between laser power and power feeding speed. By using the regression thoughts and with the data analysis about the test results by SPSS software, the relation model between powder heat absorption and dilution ratio is established and the accuracy is verified, which provides the theoretical references and test support about the study of stability of laser cladding reparation property of nickel-based superalloy..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 403007 (2013)
Laser Physics
Optimization of Pump Pulses in a Vertical-External-Cavity Surface-Emitting Laser
Zhang Peng, Dai Teli, Liang Yiping, Fan Siqiang, Jiang Maohua, and Zhang Yu
It has been demonstrated experimentally that pulsed pumping can significantly improve the thermal management in an optically-pumped vertical-external-cavity surface-emitting laser and upgrade the output power. In this paper, the transient heat conduction equation is solved by use of finite element method, and the maximIt has been demonstrated experimentally that pulsed pumping can significantly improve the thermal management in an optically-pumped vertical-external-cavity surface-emitting laser and upgrade the output power. In this paper, the transient heat conduction equation is solved by use of finite element method, and the maximum temperature rise in the multiple quantum wells active region of laser is focused. Based on the influences of repetition rate and pulse width of pump pulses on the maximum temperature rise, the repetition rate and pulse width of pump pulses are optimized. It can be concluded from the numerical results that, for a substrate-removed InGaAs quantum well vertical-external-cavity surface-emitting laser, the optimized pulse width is between 1 μs and 10 μs, and the optimized pulse repetition rate is no more than 50 kHz..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 402001 (2013)
Intracavity Losses Measurement of the TiSapphire Laser with Relaxation Resonant Oscillation Frequency and Output Power
Lu Huadong
A simple method to measure the intracavity losses of the single frequency laser utilizing the resonant relaxation oscillation (RRO) frequency and output power is presented. By analyzing the dependence of the RRO frequency on the output power, the theoretical function of the intracavity losses is presented. SubstitutingA simple method to measure the intracavity losses of the single frequency laser utilizing the resonant relaxation oscillation (RRO) frequency and output power is presented. By analyzing the dependence of the RRO frequency on the output power, the theoretical function of the intracavity losses is presented. Substituting the measured output power and RRO of the single frequency Ti:sapphire laser into the theoretical function, its intracavity losses is obtained..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 402002 (2013)
Tunable Large-Mode-Area Fiber Lasers Based on Multimode Interference Effect
Pan Yuzhai, Liu Xiaoli, Su Xiaohui, and Huang Xuejiao
A widely tunable linear-cavity double-cladding Ytterbium-doped fiber laser based on multimode interference (MMI) effect is reported. The laser cavity consists mainly of MMI fiber reflecting elements, which is composed of single-mode fiber, multi-mode fiber and broadband metal reflecting mirror, double-cladding YtterbiuA widely tunable linear-cavity double-cladding Ytterbium-doped fiber laser based on multimode interference (MMI) effect is reported. The laser cavity consists mainly of MMI fiber reflecting elements, which is composed of single-mode fiber, multi-mode fiber and broadband metal reflecting mirror, double-cladding Ytterbium-doped large-mode-area (LMA) fiber, broadband dielectric total reflecting mirror and 3 dB output coupler. The wavelength tuning of fiber lasers is realized by moving the mirror in MMI fiber reflecting elements, which is changing the reflection peak wavelength. A wavelength tuning range of about 32 nm ranging from 1038.82 nm to 1071.06 nm is experimentally demonstrated by utilizing the optical spectral analyzer, with the 3 dB linewidth of 0.2 nm and the signal-to-noise ratio of roughly 40 dB. The average output optical power of 430 mW is obtained with 1.5 W of the launched pump power at 974 nm, and the slope efficiency is about 31%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 402003 (2013)
Multi-Pass Traveling-Wave NdGlass Amplification with a Duct for Coupling
Zhao Tianzhuo, Yu Jin, Huang Ke, Ma Yunfeng, Zhang Xue, and Fan Zhongwei
A multi-pass traveling-wave Ndglass amplifier with a duct for coupling is introduced. Based on the analysis results of the relations between structural parameters and coupling efficiency of dust, a pumping structure contains 8 laser diode arrays is designed, and it′s output status is simulated. The pumping structure coA multi-pass traveling-wave Ndglass amplifier with a duct for coupling is introduced. Based on the analysis results of the relations between structural parameters and coupling efficiency of dust, a pumping structure contains 8 laser diode arrays is designed, and it′s output status is simulated. The pumping structure converges pumping energy generated from 168 bars on the area of 8 mm×8 mm, and about 7.3 J output energy is obtained. According to the output characters of the pumping structure, a rotated multi-pass traveling-wave amplification structure is designed, which based on the working material of Ndglass, and 15 mJ output energy is obtained with a 300 μJ injected signal laser..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 402004 (2013)
Attenuation Characters of Laser Used for Guided Weapons in Fine Water Sprays
Du Yongcheng, and Yang Li
The round-trip attenuating process of laser used for guiding by artificial water sprays is studied with the Monte-Carlo method. A new way for confirming the directions of scattered photons is established. The method is based on calculating the cumulative probability distribution function (CPDF) of polydisperse mists anThe round-trip attenuating process of laser used for guiding by artificial water sprays is studied with the Monte-Carlo method. A new way for confirming the directions of scattered photons is established. The method is based on calculating the cumulative probability distribution function (CPDF) of polydisperse mists and user-defined function (UDF) fitting by Matlab. Software efficiencies of two kinds of Monte-Carlo methods for photons tracking are analyzed and compared. A conclusion comes to that the wight method is evidently more efficient than the event method. The radii of frequently-used water mists are usually in the range of 101～102 μm which are suited to attenuate the 10.6 μm laser and can be used for laser stealth. But the effect is worse for 1.06 μm laser, under the condition of dense water sprays, for the single scattering albedo is close to 1..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 402005 (2013)
Analysis of Optical-Axis Perturbation in Non-Planar Ring Oscillator
Feng Tao, Zhang Xuejie, Zhang Yan, Liu Fang, Ren Zhiyuan, and Zhu Jianqiang
In order to analyze the self-consistence characteristics of optical-axis perturbation due to the manufacturing error of monolithic crystal, mathematical model for the mirror tilt of the non-planar ring cavity has been developed and optical-axis perturbation is discussed by utilizing the augmented ray matrix formulationIn order to analyze the self-consistence characteristics of optical-axis perturbation due to the manufacturing error of monolithic crystal, mathematical model for the mirror tilt of the non-planar ring cavity has been developed and optical-axis perturbation is discussed by utilizing the augmented ray matrix formulation. The results show that: self-consistence of the optical-axis is not sensitive to distance deviation and it can be realized by designing the input-output coupling mirror to be a curved surface. Static analysis indicates that the optical-axis is still self-consistent for the plane input-output coupling mirror when the angles of two symmetric totally reflective planes satisfy the certain relationship. Besides, if the certain condition of the angles cannot be satisfied, steps to reduce the deviation of coupling point position are considered from aspects of making manufacturing error symmetrical and decreasing error. At last, dynamic analysis provides a much more reasonable method to explore the manufacturing tolerance, offering a theoretical guide for the experiment..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 402006 (2013)
Experimental Research on Gain Characteristic in Large Aperture Active Mirror Slab Amplifiers
Liu Jing, Shi Xiangchun, Li Lei, Cheng Xiaojin, Yang Zhongguo, and Wang Jianlei
The structure of large aperture active mirror slab amplifier is presented, which is pumped by Xe-lamps. The application of active mirror in Nd: glass laser amplifier is explored. The size of Nd:glass is 890 mm×450 mm×50 mm . Doping density is 1.2% of mass fraction. The small signal gain coefficient and energyThe structure of large aperture active mirror slab amplifier is presented, which is pumped by Xe-lamps. The application of active mirror in Nd: glass laser amplifier is explored. The size of Nd:glass is 890 mm×450 mm×50 mm . Doping density is 1.2% of mass fraction. The small signal gain coefficient and energy storage efficiency of different voltages are measured at the best delay time. The energy storage efficiency is 1.94% and the small signal gain coefficient is 0.0371 cm-1 when the charging voltage is 22 kV and the Xe-lamp′s discharging pulse width is 0.51 ms. Experiments are designed to research the effect of lateral amplified spontaneous emission (ASE) and luminous fefficiency of Xe-lamp on the small signal gain coefficient..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 402007 (2013)
Application Study on Fused Silica Prisms in Excimer Laser Spectrum Control
Shan Yaoying, Zhao Jiangshan, Li Hui, Wang Qian, Sha Pengfei, Zhou Yi, Zhou Jun, Yuan Zhijun, Zhang Haibo, and Lou Qihong
Due to the application of excimer lasers, it is necessary to control the output spectrum of excimer laser. Control spectrum contain narrowing bandwidth and stable output of center wavelength. The familiar mean of line-narrowing is using combination of beam expander prisms and grating to narrow the bandwidth of laser. WDue to the application of excimer lasers, it is necessary to control the output spectrum of excimer laser. Control spectrum contain narrowing bandwidth and stable output of center wavelength. The familiar mean of line-narrowing is using combination of beam expander prisms and grating to narrow the bandwidth of laser. With the combination of fused silica prisms and grating controlling the ArF excimer laser, the line-narrowed excimer laser of the output spectrum of light source is 0.957 pm. Theory analysis and experiments indicate that with a high transmission in ultraviolet (UV), fused silica prisms can reach the same effect in line-narrowing with the CaF2 which is often used now. At the same time, the cutting way of isoceles triangle prisms can be made more exactly, less costing and should be applied more widely..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 402008 (2013)
Optical Sampling of Chaotic Laser Based on Four-Wave Mixing in Highly Nonlinear Fiber
Liang Junqiang, Wang Juanfen, Li Pu, and Wang Yuncai
Based on four-wave mixing in highly nonlinear fiber, a scheme to chaotic laser sampling independent of polarization is proposed due to poor coherence of chaotic laser, and random fluctuations of polarization state. And the chaotic laser with wavelength of 1550 nm and power range from 0~10 mW is sampled by numerical metBased on four-wave mixing in highly nonlinear fiber, a scheme to chaotic laser sampling independent of polarization is proposed due to poor coherence of chaotic laser, and random fluctuations of polarization state. And the chaotic laser with wavelength of 1550 nm and power range from 0~10 mW is sampled by numerical method. It can be found that the four-wave mixing sampling can be optimal for the pump light with wavelength of 1557 nm and power of 2 W when the fiber length is 60 m. Using the above parameters, polarization insensitive sampling for chaotic laser is implemented with sample rate of 5 GHz. The peak power of the chaotic pulse is amplified. The gain coefficient is approximately 10.8 dB. The results can provide a theoretical basis for the further experiment..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 402009 (2013)
All-Normal-Dispersion Passively Mode-Locked Yb-Doped Fiber Laser with Multimode Interference Effect
Tan Fangzhou, Liu Jiang, Sun Ruoyu, and Wang Pu
An all-fiber dissipative-soliton passively mode-locked fiber laser is reported. A filter based on multimode interference is used, which consists of two seqments of single-mode fiber (SMF) and a segment of multimode fiber (MMF). By proper selection of the MMF length, a band-pass filter with central wavelength of 1067 nmAn all-fiber dissipative-soliton passively mode-locked fiber laser is reported. A filter based on multimode interference is used, which consists of two seqments of single-mode fiber (SMF) and a segment of multimode fiber (MMF). By proper selection of the MMF length, a band-pass filter with central wavelength of 1067 nm and band width of 7.5 nm is fabricated. The filter for spectral filtering in an all-normal dispersion mode-locked ytterbium-doped fiber laser is used. A semiconductor saturable absorber mirror (SESAM) is used as a saturable absorber in the laser cavity. With the pump power of 865 mW, stable pulse train which is highly chirped with average repetition rate of 18.5 MHz and pulse width of 21 ps is obtained. The average output power is 8 mW, so the single pulse energy is 0.43 nJ. The full width at half maximum (FWHM) of output pulse is 4.32 nm. The spectrum has a steep edge..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 402010 (2013)
High Brightness Diode Laser Source Based on Three-Wavelength Multiplexing
Zhang Jun, Peng Hangyu, Liu Yun, Qin Li, Shan Xiaonan, and Wang Lijun
Because of the prominent advantages, diode lasers have a significant prospect of application. But limited by the beam quality, it is difficult to be a direct source applied in the fields demanding for power, beam quality and brightness at the same time. The technologies of beam shaping of 45° tilted cylindrical leBecause of the prominent advantages, diode lasers have a significant prospect of application. But limited by the beam quality, it is difficult to be a direct source applied in the fields demanding for power, beam quality and brightness at the same time. The technologies of beam shaping of 45° tilted cylindrical lens, self-polarization multiplexing and three-wavelength multiplexing are employed to couple 8 bars with three wavelengths into a laser beam, and a diode laser source is developed with continuous wave (CW) power of 500 W, electro-optical conversion efficiency of 39.5%, holistic beam quality of 12.44 mm·mrad and brightness of 42.8 MW/(cm2·sr), which can be applied directly in the fields of materials processing and defense..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 402011 (2013)
Materials and Thin Films
Friction Properties Between Phosphate Laser Glass and Optical Polishing Pitch
Shan Haiyang, Xu Xueke, He Hongbo, Zhang Baoan, Yi Kui, Shao Jianda, and Fan Zhengxiu
The coefficient of friction is an important parameter for the characterization of optical glass polishing properties. The average coefficient of friction determines the polishing rate, and its variation range affects the surface accuracy and surface roughness of optical glass. In this work, the orthogonal experiments aThe coefficient of friction is an important parameter for the characterization of optical glass polishing properties. The average coefficient of friction determines the polishing rate, and its variation range affects the surface accuracy and surface roughness of optical glass. In this work, the orthogonal experiments are designed to study the influence of the experimental parameters on the friction properties between phosphate laser glass and optical polishing pitch in the polishing process. The degree that experimental parameters influence the average value and variation range of coefficient of friction is similar. The influence of the applied load is larger while that of polishing pitch type is smaller. A large average frictions coefficient corresponds to a large variation range of frictions coefficient in the experiment. Furthermore, the reasons for the change of frictions coefficient with time are discussed from the aspects of stick-slip friction, adhesion, abrasive grinding and polishing liquid thickness..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 406001 (2013)
Semi-Polar Faceted InGaN/GaN Quantum Wells in Self-Organized GaN Islands for White Light Emission
Yang Xiaodong
The controllable growth of self-organized 3D semi-polar faceted GaN islands is reported, which performs as an ideal template for the fabrication of semi-polar InGaN/GaN light-emitting quantum wells on the sidewalls. Special transmission electron microscope (TEM) sample preparation is employed to analyse the microstructThe controllable growth of self-organized 3D semi-polar faceted GaN islands is reported, which performs as an ideal template for the fabrication of semi-polar InGaN/GaN light-emitting quantum wells on the sidewalls. Special transmission electron microscope (TEM) sample preparation is employed to analyse the microstructure and growth mechanism of the multi quantum wells on the sidewall facets. Together with cathodoluminescence, the results show that the mixed white light (blue, green and red) emission in a single island can be achieved and the semi-polar faceted InGaN/GaN quantum wells act as the main region for the bright multi-color light emitting. Further optimization of the facet structure will improve the flexibility of light emission and provide a new method for the next generation of white lighting..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 406002 (2013)
Measurement and Metrology
Measurement of the Critical Intense Cavitation Pressure Based on the Acousto-Optical Refraction Effect in Liquid
Lü Peng, Zhou Yuan, Song Ke, Wang Hua, and Shen Yong
To measure the critical pressure when intense cavitation occurred in liquid, a method to detect the critical intense cavitation pressure which based on the acousto-optical refraction effect is proposed. According to the distribution of the far-field spot which changes with time to determine the occurrence of intense caTo measure the critical pressure when intense cavitation occurred in liquid, a method to detect the critical intense cavitation pressure which based on the acousto-optical refraction effect is proposed. According to the distribution of the far-field spot which changes with time to determine the occurrence of intense cavitation, it can detect the value of the critical intense cavitation pressure non-invasively by the relation between the maximum deflection distance of the ray and the change of the focus acoustic pressure with a high repeatability. By analysing the distribution of the cavitation bubbles in liquid , and the cavitation threshold pressure changing with the external environmental pressure to calibrate the results, it′s proved that the feasibility of this way to detect the critical intense cavitation pressure..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 408001 (2013)
Laser Methane Remote Sensing Technology Based on Digital Feedback Frequency Stabilization
Sun Yanguang, Dong Zuoren, Chen Dijun, Ye Qing, Cai Haiwen, Qu Ronghui, and Gong Shangqing
A portable methane remote sensor based on digital feedback frequency stabilization is developed. Current and temperature dual-feedback strategy suppresses the laser′s long-term wavelength drift; meanwhile it ensures the long-term stability of optical power. Experimental results show that the wavelength drift is less thA portable methane remote sensor based on digital feedback frequency stabilization is developed. Current and temperature dual-feedback strategy suppresses the laser′s long-term wavelength drift; meanwhile it ensures the long-term stability of optical power. Experimental results show that the wavelength drift is less than 1.2 pm in 9 h, and the optical power also remains stable, which ensures the long-term continuous measurement stability of the concentration. Repeatability of concentration measurement value is stable in different detection distances, with a 5% fluctuation. Experimental results indicate that the instrument can be used in practical environment, such as natural gas tube leakage and coal mine..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 408002 (2013)
Study on Measuring Carbon Particles from Coal Combustion in Hydrogen Flame Using Laser-Induced Radiation Method
Pan Zhenyan, Chen Linghong, Wu Yingchun, Zuo Lei, Wu Xuecheng, and Cen Kefa
A rapid measurement of micro-nano carbon particles within complicate combustion media is investigated. Carbon particles from pulverized coal combustion in the pure hydrogen flame are heated by a high-power pulsed laser beam. The size distribution of carbon particles is obtained using a multistage exponential function mA rapid measurement of micro-nano carbon particles within complicate combustion media is investigated. Carbon particles from pulverized coal combustion in the pure hydrogen flame are heated by a high-power pulsed laser beam. The size distribution of carbon particles is obtained using a multistage exponential function method to fit time-resolved radiation emitted by the laser-heated particles, where the flow zone is determined by Kn. The results show that three sizes of carbon particles exist and the average diameters are 7 nm, 25 nm, 3 μm, respectively, which correspond to the newly-born soot, mature soot, and char or unburned coal particles. The variations of each kind of carbon particles during coal combustion are investigated according to the size and relative concentration of each particles component versus the flame height. The above method can be used as a tool for rapid detecting size distribution of multi-scale carbon particulates under the high-temperature environment..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 408003 (2013)
Mueller Matrix Ellipsometer Based on Nonlinear Least Squares Fitting Method
Hou Junfeng, Wang Dongguang, Deng Yuanyong, Sun Yingzi, and Zhang Zhiyong
A Mueller matrix measuring method is brought forward based on nonlinear least squares fitting. Stokes parameters of output polarization state are measured, and functions between output polarization states, the system unknown parameters and sample′s Mueller matrix are built. Nonlinear least squares fitting method is useA Mueller matrix measuring method is brought forward based on nonlinear least squares fitting. Stokes parameters of output polarization state are measured, and functions between output polarization states, the system unknown parameters and sample′s Mueller matrix are built. Nonlinear least squares fitting method is used to calculate sample′s Mueller matrix. Then a Mueller matrix ellipsometer measuring system based on ferroelectric liquid crystal retarders and rotating waveplate and rotating polarizer is established, the Labview software is applied to realize the intelligent. Error analysis and measurement are done. It is found that the Mueller matrix measuring precision of the system is within 0.01 and repeatability is 0.005 in wavelength range 600~900 nm。The measuring system avoids the complex calibration of Mueller matrix ellipsometer as before, simplifying measuring procedures and realizing the self-calibration measurement..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 408004 (2013)
Focal Length Testing Method of Long Focal Length Laser Optical System
Duan Yaxuan, Chen Yongquan, Zhao Jianke, Li Kun, Tian Liude, and Zhang Jie
In order to measure the focal length of long focal length laser optical system, a method based on the principle of autocollimation, using fiber laser, beam splitter, flat mirror, precision angular instrument, charge couple device (CCD) and wavefront sensor is proposed. The fiber pinhole is placed at the focal point of In order to measure the focal length of long focal length laser optical system, a method based on the principle of autocollimation, using fiber laser, beam splitter, flat mirror, precision angular instrument, charge couple device (CCD) and wavefront sensor is proposed. The fiber pinhole is placed at the focal point of laser optical system by testing the transmission wavefront of laser optical system with the Shack-Hartmann wavefront. Then, the CCD is placed at the best image surface by the scanning focus algorithm. The synchronization acquisition of the angular instrument and CCD is made. The focal length of laser optical system is calculated with the angle got by precision angular instrument and the deviation of pinhole image calculated by the centroid algorithm. The long focal length laser optical system of which the focal length is 7171 mm has been tested by this method. The uncertainty of test result is 13.48 mm (k=2). The test results show that this method is practical to the focal length testing of long focal length laser optical system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 408005 (2013)
Method of Improving Measurement Accuracy of Stokes Parameters
Tang Feilong, Li Zhongliang, Bu Yang, Wang Xiangzhao, Fan Lili, and Cao Shaoqian
The retardation error is the main error of Stokes parameters measurement based on rotating quarter-wave method. The principle of Stokes parameters measurement based on conventional rotating quarter-wave method is analyzed theoretically. The relation between the retardation error and the measurement error is discussed. The retardation error is the main error of Stokes parameters measurement based on rotating quarter-wave method. The principle of Stokes parameters measurement based on conventional rotating quarter-wave method is analyzed theoretically. The relation between the retardation error and the measurement error is discussed. An improved rotating quarter-wave method is proposed for improving the measurement accuracy of Stokes parameters. In this method, the angle between the axis of polarizer and the polarization direction of the light is adjusted to a certain value (90° or 45°), and the influence of the retardation error on the measurement accuracy of Stokes parameters is reduced obviously. The effectiveness of the proposed method is investigated by comparing to the conventional rotating quarter-wave method through experiments. Experimental results show that the measurement error of Stokes parameters is reduced by the proposed method from 4.31% to 0.33%, under the condition that the retardation error is lower than 1.2°..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 408006 (2013)
Mobile CARS Temperature Measurements at Exhaust of Supersonic Combustor
Zhang Lirong, Hu Zhiyun, Ye Jingfeng, Shao Jun, Zhang Zhenrong, and Liu Jingru
The environment of engine test is usually companied with strong vibration and intense noise. The laboratorial laser combustion diagnostic systems can not be directly used in the harsh environment of engine test. Through modularization and anti-vibrating engineering designs, an integrated mobile coherent anti-Stokes RamThe environment of engine test is usually companied with strong vibration and intense noise. The laboratorial laser combustion diagnostic systems can not be directly used in the harsh environment of engine test. Through modularization and anti-vibrating engineering designs, an integrated mobile coherent anti-Stokes Raman scattering (CARS) system is developed, which can be used in the engine test. To analyze the sources and characteristics of vibrations, the vibrations in the engine test are measured. Some de-vibrating techniques are utilized accordingly, and vibrations on the mobile CARS system decrease effectively. Employing the mobile CARS system, single pulse CARS measurements and temperature evolution on a model supersonic engine combustor are obtained. According to the results, temperature range of unstable combustion is higher than that of stable combustion, but the mean temperature is lower, indicating that the efficiency of unstable combustion is lower..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 408007 (2013)
Detection of Micro-Crack by Ultrasonic Approach of One-Sided Pitch-Catch Method Based on Laser Assisted Heating
Li Jia, Ni Chenyin, Zhang Hongchao, Dong Liming, and Shen Zhonghua
Due to the geometry irregularities of specimens and the inhomogeneous of materials, micro-crack is usually generated by abrupt change of local stress. Traditional detecting techniques using ultrasound, such as pitch-catch method, are difficult to distinguish the micro-crack effectively, because the size of the cracks aDue to the geometry irregularities of specimens and the inhomogeneous of materials, micro-crack is usually generated by abrupt change of local stress. Traditional detecting techniques using ultrasound, such as pitch-catch method, are difficult to distinguish the micro-crack effectively, because the size of the cracks are so small that they are often hidden from ultrasonic detection by a stronger scattering from the very same structural imperfection, such as surface protuberance, surface grooves, corrosion pits, etc. The laser ultrasonic detecting system is built to detect the surface irregularities based on one-sided pitch-catch method. The laser line source is used to excite ultrasound and the optical deflection beam method is used to detect ultrasound. The traditional pitch-catch method, scanning laser source method and the scanning heating laser source method are used to detect the surface irregularities of specimen which contains a surface protuberance and a surface breaking micro-crack. The pitch-catch method requires high signal to noise ratio of signals and the reliability is poor. The scanning laser source method can detect both one but can not distinguish the crack from them. Based on the characteristics that the micro-crack can get closed partially after illuminated by heating laser, the scanning heating laser method can recognize it efficiently. The finite element method (FEM) is used to calculate the transmitted surface acoustic waves (SAW) which are influenced by different sizes of surface breaking cracks..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 408008 (2013)
Micro and Nano Optics
Improve Axial Resolution of Fluorescent Microscopy Using Cylindrical Vector Beams Modulated by Diffractive Optical Elements
Cao Guowei, Li Yongping, and Bi Guoqiang
A novel method to improve the axial resolution of fluorescent microscopy using photo-switching characteristics of fluorescent protein is proposed. For microscopy with different numerical apertures, a 100-nm axially-selective-activation is achieved by using cylindrical vector beams with vortex phase as activation and deA novel method to improve the axial resolution of fluorescent microscopy using photo-switching characteristics of fluorescent protein is proposed. For microscopy with different numerical apertures, a 100-nm axially-selective-activation is achieved by using cylindrical vector beams with vortex phase as activation and deactivation beams which are modulated by designed diffractive optical elements. Furthermore, adjusting the power ratio R of the activation beam and deactivation beam will make the maximum activation probability of fluorescent protein suitable for single-molecule microscopy. The numerical calculation based on Cy5 demonstrates that along the z axis the activation probability has a single peak with full-width at half-maximum (FWHM) of only 25.7 nm and about 90% of activated molecules are located in a 30-nm-thick layer around zero point (for R=500)..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 410001 (2013)
Optical Communication
Temperature Characteristic of Stimulated Brillouin Scattering in Single-Mode Fiber
Huang Wenfa, Wang Xiaochao, Wang Jiangfeng, Li Xuechun, Fan Wei, and Lu Xinghua
Stimulated Brillouin scattering (SBS) threshold and frequency shift of single-mode fiber are studied under different temperatures. Based on the theory of SBS, the relation of SBS threshold and frequency shift with temperature is analyzed. Experimental system is designed and built, and SBS spectrum and threshold of 2 kmStimulated Brillouin scattering (SBS) threshold and frequency shift of single-mode fiber are studied under different temperatures. Based on the theory of SBS, the relation of SBS threshold and frequency shift with temperature is analyzed. Experimental system is designed and built, and SBS spectrum and threshold of 2 km single-mode fiber are measured under different temperatures. The experiments indicate that the Brillouin frequency shift increases linearly with the increasing temperature. Low temperature can suppress Stokes lights. The lower the temperature is, the higher SBS threshold is. Temperature has a direct effect on the SBS of fiber..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 405001 (2013)
Research on the Micro and High-Precision Fiber Bragg Grating Soil Pressure Sensor
Jiang Shanchao, Cao Yuqiang, Sui Qingmei, Wang Jing, Wang Ning, and Wang Zhengfang
A micro and high-precision fiber Bragg grating soil pressure sensor based on the characteristics of stainless steel patch is developed. Through stainless steel patch and mechanical transfer element, this sensor transfers soil pressure into axial direction tension of the fiber grating and improves its sensitivity greatlA micro and high-precision fiber Bragg grating soil pressure sensor based on the characteristics of stainless steel patch is developed. Through stainless steel patch and mechanical transfer element, this sensor transfers soil pressure into axial direction tension of the fiber grating and improves its sensitivity greatly. Because of such design, this sensor reduces its volume largely and avoids the chirp effect caused by grating axial stress effectively. The theoretical calculation pressure sensitive coefficient value of this sensor is 29.6557 nm/MPa，which is 9885 times of the bare grating. The performance test proves that the linearity of this sensor is very well and measured pressure sensitive coefficient is 27.5 nm/MPa and slightly less than the theoretical calculation value, which is mainly caused by strain transfer efficiency lower than 1. In order to improve the experimental measurement precision, Haar wavelet transform is used to reduce the instrument error caused by wavelength dithering brought by the limitation of the sample rate and conversion precision of the demodulating equipment. The experiment data show that the dithering amplitudes of grating central wavelength reduce to 50% of the origin data after Haar wavelet transformation..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 405002 (2013)
Supercontinuum Generation from a Tapered Photonic Crystal Fiber Pumped with a High-Power Nanosecond Fiber Laser
Guo Chunyu, Ouyang Deqin, Ruan Shuangchen, Yan Peiguang, Wei Huifeng, Lin Huaiqin, Wu Yiming, and Yang Jinhui
By modulating the laser diode, a nanosecond laser with center wavelength of 1064.14 nm, spectral width of 0.63 nm, repetition frequency of 1.55 MHz and pulse width of 11 ns is realized. This seed laser is then amplified to a high-power, high-repetition rate nanosecond fiber laser with an average output power of 18.2 W By modulating the laser diode, a nanosecond laser with center wavelength of 1064.14 nm, spectral width of 0.63 nm, repetition frequency of 1.55 MHz and pulse width of 11 ns is realized. This seed laser is then amplified to a high-power, high-repetition rate nanosecond fiber laser with an average output power of 18.2 W using a tri-stage master oscillator power amplifier (MOPA) configuration. This nanosecond fiber laser is used to pump a 145 m long tapered photonic crystal fiber with a self-made mode field adaptor (MFA), and a 2.2 W all-fiber white light supercontinuum source is realized with a 15 dB spectral flatness in the detected spectral range from 440 nm to 1700 nm. The spectral edge also corresponds well with the theoretical value..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 405003 (2013)
Study on the Repetition Space-Time Codes for Multiple-Input Multiple-Output Free-Space Optical Systems
Li Ming, Cao Yang, Li Shuming, and Yand Shaowen
The multiple-input-multiple-output (MIMO) technique is one of the effective means to mitigate the effects of atmospheric scintillation and reduce the symbol error rate (SER) for free-space optical communications. Considering the combinatin of Alamouti space-time code and time topping ultra-wide band (TH-UWB) communicatThe multiple-input-multiple-output (MIMO) technique is one of the effective means to mitigate the effects of atmospheric scintillation and reduce the symbol error rate (SER) for free-space optical communications. Considering the combinatin of Alamouti space-time code and time topping ultra-wide band (TH-UWB) communications, a novel repetition space-time codes (RSTC) method for 2×2 free-space optical communications with pulse position modulation (PPM) is developed. In particular, two decoding methods of equal gain combining (EGC) maximum likelihood detection (MLD) and correlation matrix detection (CMD) are derived. When a quasi-static fading and weak turbulence channel model is considered, simulation is conducted. Simulation results show that whether the channel state information (CSI) is known or unknown, the coding system demonstrates more significant performance of the SER than the uncoding. In other words, transmitting diversity can be achieved while conveying the information only through the time delays of the modulated signals transmitted from the different antennas. CMD has almost the same effect of signal combing with maximal ratio combining (MRC). However, when the channel correlation increases, SER performance of the coding 2×2 system degrades significantly..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 405004 (2013)
High-Speed High-Multiplexing Distributed Temperature Sensor Network Based on Weak-Reflection Fiber Gratings
Zhang Yanjun, Xie Xiaopeng, and Bi Weihong
High-speed high-multiplexing distributed temperature sensor network based on weak-reflection fiber gratings is proposed. In order to solve problems such as long monitoring time and poor real-time performance of the system, a multiple-wavelength light source is used instead of tunable laser. Three fiber Bragg gratings (High-speed high-multiplexing distributed temperature sensor network based on weak-reflection fiber gratings is proposed. In order to solve problems such as long monitoring time and poor real-time performance of the system, a multiple-wavelength light source is used instead of tunable laser. Three fiber Bragg gratings (FBG) with high reflectivity and low bandwidth are carved on a single fiber and their central wavelengths are 1529.488, 1545.202 and 1557.100 nm, respectively. Another three groups of nine FBG whose central wavelengths are 1529.488, 1545.202 and 1557.100 nm with 3% reflectivity are carved equidistantly on the same fiber. Light from the high-reflection FBG is used as the light source of the system and the weak gratings are used as the monitoring gratings. The experimental results show that, in the temperature range of 5 ℃~80 ℃, the central wavelength of each weak-reflection FBG changes linearly as the temperature changes, and the error of temperature measurement is ±0.5 ℃ and spatial resolving power is 10 m..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 405006 (2013)
Optical Design and Fabrication
Precise Alignment of Separated Sagnac Interferometer
Zhang Xuemin, Wei Ruyi, Yan Su, Duan Jiayou, Li Hua, and Yang Jianfeng
A separated Sagnac interferometer with optical diameter of 60 mm and spectral channel of 65 is introduced based on its working principle. Ideal interference fringes and interference fringes are simulated when reflector has an angle deviation, and the effect of alignment error to the interference fringes is analyzed. ThA separated Sagnac interferometer with optical diameter of 60 mm and spectral channel of 65 is introduced based on its working principle. Ideal interference fringes and interference fringes are simulated when reflector has an angle deviation, and the effect of alignment error to the interference fringes is analyzed. The position accuracy and angle accuracy of alignment are induced based on the optical design parameters. The method of precision alignment is introduced in detail, which includes the installation of primary alignment plane, the precise location of splitting prism, the precise adjustment of long-arm and short-arm reflectors. Through the installation of alignment refrence and the masterly refrence transformation, the precise alignment of separated Sagnac interferometer is achieved based on the principle of auto-collimation, whose position accuracy is better than 0.01 mm, angle accuracy is better than 1″, super possition accuracy of primary working plane is better than 1″..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 40, Issue 4, 416001 (2013)
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