基于Fuzzy-P控制的半导体激光器功率稳定研究

为了提高光源抑制噪音的能力，提出一种基于模糊控制和比例控制的模数混合控制器，对中心波长为650 nm的半导体激光二极管的输出功率进行高准确度稳恒控制.实验结果表明，施加功率控制后，光源输出功率的静态稳定度达到±0.48‰，动态稳定度优于±1‰.     

基于等效电路的半导体激光器热噪音特性仿真研究

通过引入Langevin噪音项的噪音等效电路研究了半导体激光器的热噪音特性．研究表明，在激光器的工作过程中，由于自加热效应所引来的热噪音是不能够被忽略的．本文基于半导体激光器的噪音等效电路，仿真分析不同频带宽度、不同注入电流情况下，工作温度的变化对激光器结电压噪音谱的影响．     

大功率半导体激光器驱动电源保护电路设计

大功率半导体激光器驱动电源的关键是保护电路的设计。通过双限流电路和浪涌强制吸收或隔离保护电路的设计，解决了大功率半导体激光器驱动电源常见的浪涌冲击和电流恒定的难题。实验结果表明电流输出稳定度达到0．04％，浪涌被很好地抑制。     

多线阵半导体激光器的单光纤耦合输出

设计并研制了一种多线阵半导体激光器的高亮度光纤耦合输出模块.激光器芯片采用了分子束外延方法生长的宽波导、双量子阱结构AlGaAs/GaAs激光器外延材料,激光器模块采用6只准直的线阵半导体激光器,器件腔长为1.2 mm,单个发光单元宽度为100 μm,发光单元周期为500 μm,单线阵器件包括19个发光单元,单线阵器件的连续输出功率为50 W,每只单线阵器件的准直输出光束经过空间合束后再通过光束对称化变换实现了多线阵器件输出的高光束质量功率合成,采用平凸柱透镜实现了合束光束与400 μm芯径、数值孔径0.22石英光纤的高效率耦合,整体耦合效率达到65%,最大耦合输出功率达到195 W,光纤端面功率密度达到1.55×105 W/cm2.     

稳频半导体激光器的温度控制技术

设计了一种用于半导体激光器稳频的恒温控制器,在室温下2h的测试时间中,测试恒温稳定度为5mK,配合稳定度为±2μA的恒流源,半导体激光器自由运行时激光频率波动稳定在100MHz范围内。     

高效率1018nm全光纤激光器实验研究

采用内包层直径为125μm的双包层掺镱光纤,搭建了谐振腔结构全光纤激光器系统,获得了1018 nm的高功率激光输出。通过优化光纤长度和控制抽运源波长,单模激光输出功率为254 W,光光转换效率达到81%,光谱中无自发辐射光和剩余抽运光,信噪比大于35 d B。由于抽运半导体激光器的输出波长随着输出功率变化,光纤激光器的转换效率也将改变,为了提高转换效率,抽运半导体激光器的输出波长需要精确控制;光纤激光器长期稳定性测试结果表明,4 h连续工作的不稳定度小于0.5%。本光纤激光器系统是同带抽运高功率光纤激光器的理想抽运源。     

激光系统中半导体激光器温度稳定系统研究与设计

激光器系统中半导体激光器的功率输出稳定度和工作温度有很大的关系,为了使大功率半导体激光器输出功率稳定,需要对激光器实现高精度、快速温度控制。针对现有的激光系统中激光器温度控制系统存在控制精度不够高、控制速度慢等问题,设计了一种温度稳定系统,采用PT-100热电偶测量激光器温度,并使用最小二乘法对温度数据进行拟合,使得温度测量精度达到0.01 ℃;使用改进粒子群算法优化(PSO)的PID控制器实现温度控制。仿真实验和实际测试表明,所设计的温度稳定系统能够很好地控制激光器温度,达到目标温度所需的调节时间小于11 s,达到稳态后温度波动在±0.02 ℃内。与传统的温度控制方式相比,所设计的系统能够实现参数自整定并自动调节温度,对大功率激光系统中激光器温度具有良好稳定效果。     

激光二极管泵浦预激光调QNd：YAG单纵模激光器研究

用国产连续输出功率为１．５Ｗ的半导体激光泵浦Ｎｄ：ＹＡＧ激光器，获得了预激光调Ｑ单纵模激光输出，调Ｑ脉冲幅度起伏小于±１％，输出单纵模线宽小于２５ＭＨｚ。     

基于像散与理想光源成像原理的高亮度半导体激光器光纤耦合设计方法

运用像散原理和理想光源成像原理,讨论了半导体激光器消像散设计.提出了一种基于消像散的高亮度半导体激光器光纤耦合系统的设计方法.以波长为808 nm,输出功率为10 W的半导体激光器的光纤耦合为例,给出了详细的计算方法和设计步骤.结果表明:采用该方法将半导体激光器光束耦合入数值孔径为0.22,芯径为50 μm的光纤中,耦合后输出功率为9.712 W,耦合效率为97.12%,功率密度为1.1224×10⁶ W/cm².该方法不仅原理简单,而且设计的耦合系统耦合效率高、体积小,具有较强的实用价值.     

高稳定LD泵浦腔内倍频Nd∶YVO4/KTP连续绿光激光器

设计出一种能够较好地补偿激光晶体热效应的激光谐振腔，实现了高稳定LD单端泵浦KTP腔内倍频Nd∶YVO₄连续绿光激光器.当晶体吸收的泵浦功率为24.56 W时，532 nm激光功率达到5.3 W，光-光转换效率达到21.6％，激光模式为TEM00模.在输出功率5W左右时，激光器1 h功率不稳定度优于0.6％     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.