高亮度布拉格反射波导激光器

设计并制备了808 nm波长布拉格反射波导激光器,在垂直方向采用光子带隙效应进行光场限制,实现了超大光模式体积和单横模激射。所制备的10μm条宽、未镀腔面膜的器件在室温、准连续条件下的总输出功率可超过650 mW,最高功率受热扰动限制。激光器垂直方向和水平方向的远场发散角半高全宽分别为8.3°和8.1°,这种近圆形的光束输出可以有效地提高激光器的耦合效率。     

单频窄线宽分布布拉格反射光纤激光器研究

分析了单频窄线宽分布布拉格反射（DBR）光纤激光器的单模工作条件,在此基础上算出单模工作区域,制作了一个单频窄线宽分布布拉格反射光纤激光器。该激光器在波长为975.5nm的半导体激光器抽动下,在1556.91nm波长处。当抽运功率为55.35mW时输出功率可达1.43mW,频宽小于1.2MHz(受测量仪器分辨率限制）。经测量,该输出激光是稳定的单纵模输出。     

布拉格反射波导半导体激光器的研究

高功率半导体激光器在固体或光纤激光器泵浦、材料加工、医疗、传感、空间通讯和国防上有着极其重要的应用,但传统半导体激光器面临垂直发散角大、椭圆光斑的难题,限制了其直接应用。为了降低激光器的垂直发散角,本项目采用布拉格反射波导结构,利用光子带隙导引替代传统的全反射进行光场限制,优化设计了多种布拉格反射波导激光器结构,并制备了高性能的激光器器件。首先,采用传输矩阵理论和布洛赫波近似的方法计算了布拉格反射波导的模式色散关系,发现通过控制腔模光场分布,可实现不同远场的激光输出。接着,针对布拉格波导光子带隙导引机制,深入研究了四分之一波长布拉格反射波导激光器、单边布拉格反射波导激光器的光场特性,弄清了影响此类激光器远场的本质因素,最终设计并验证了一种布拉格反射波导双光束激光器,激光器在垂直方向可输出两个对称的、近圆形光束,单光束垂直和侧向发散角半高全宽分别低至7.2°和5.4°。另外,通过调控光缺陷层,使激光器工作在受抑隧穿光子带隙导引机制下,实现了超窄的单光束激光输出,激光器单管连续输出功率超过4.6 W,垂直发散角最低降至4.9°(半高全宽)和9.8°(95%功率)。这种高功率、窄的圆形光束输出可以大幅降低半导体激光器的应用成本,提高泵浦或光纤耦合效率,具有广阔的应用前景。     

2μm GaSb基低垂直发散角布拉格反射波导激光器优化设计

为实现2 μm低发散角激光,提出在GaSb基半导体激光器中引入布拉格反射波导,利用光子带隙效应替代传统的全反射进行光场限制。研究了分布反馈反射镜(DBR)的厚度、对数、高低折射率DBR厚度比以及中心腔厚度等参数对激光器垂直远场发散角和光限制因子的影响。结果表明:垂直远场发散角随单对DBR厚度的增加而减小;光限制因子与远场发散角都随拉格反射镜对数的增加而减小,随高低折射率DBR厚度比的减小而增大;随着中心层厚度的增大,光限制因子减小而远场发散角增大。最终在理论上优化设计出了一种双边布拉格反射波导结构的超低垂直发散角2 μm GaSb基边发射半导体激光器,其垂直远场发散角可降低到10°以下。     

基于开槽型DBR光纤激光器拍频的折射率探测

提出一种包层开槽型分布布拉格反射光纤激光器,用于光纤激光折射率探测.该激光器以单纵模双偏振分布布拉格反射光纤激光器为核心传感单元,以结构双折射产生的拍频信号为传感信号对折射率进行探测.实验中应用频率编码,灵敏度高且易于解调.利用二氧化碳激光器的热效应对分布布拉格反射光纤激光器的谐振腔加工开槽,通过控制其扫描范围和功率来制备不同宽度和深度的开槽结构,并研究了不同结构参量对灵敏度特性的影响.实验测得最优灵敏度达-240 MHz/RI-unit.此外,还对该结构的温度传感特性做了测试,相较于未刻槽结构,温度灵敏度提高了21%,达1.73 MHz/℃.该装置结构紧凑、稳定性高、制备简单且成本低廉,可用于进一步研究分布布拉格反射光纤激光器的传感和复用特性.     

高度方向性多光束有机激光（英文）

采用DFB分布反馈结构的有机激光由于其自身优点备受关注,而利用高阶布拉格反馈的多光束有机激光及其原理鲜有报道。不同于以往的低阶布拉格反馈形成单波导或单光束激光,本文通过在平面有机半导体波导引入高阶布拉格反馈分别制备了红色和蓝色多束有机激光器。利用四阶布拉格反馈和PVK∶DCJTI薄膜实现三光束红光激光器,出射角度为±53°和0.5°。利用五阶布拉格反馈和PS∶DSA-ph薄膜实现四光束蓝光激光器,出射角度为±18°和±75°。融合平面波导与光栅耦合的机理,研究了高阶布拉格光栅反馈与器件特性之间的关系。结果表明,理论计算的光束耦合角度和实际测试相符,结果在一定程度上为多光束有机激光器件的设计提供了参考。     

1137 nm长波掺镱光纤激光器的出光实验

分别使用976 nm半导体激光器和1040 nm光纤激光器作为泵浦源,实现了1137 nm长波光纤激光器的出光,输出功率均超过百mW。激光器采用相同的线性腔结构,高反光栅和低反光栅的反射率分别为99.6%和39.7%,增益介质是一段8 m长的掺镱光纤,纤芯直径5 m。当976 nm半导体泵浦功率为912 mW时,1137 nm激光输出功率为182 mW,对应的斜率效率为28.5%;当1040 nm激光功率为1.59 W时,输出的1137 nm激光功率为278 mW,斜率效率约为25%。在此基础上对两种泵浦方式进行了对比分析。     

半导体垂直腔面发射激光器的微腔效应

应用腔量子电动力学和半导体物理学讨论了半导体垂直腔面发射激光器的微腔效应,得到了实际腔结构和注入载流子下的半导体生趣腔面发射激光器的自发发射谱,计算结果表明,半导体分布布拉格反射垂直腔激光器的单方向自发发射可以境强约２００倍。     

1550nm高功率基横模半导体激光器及温度特性

通过引入渐变Al组分和脊型波导的设计,制备了1550 nm高功率AlGaInAs/InP基横模半导体激光器,室温连续工作模式下器件的斜率效率达到0.35 mW/mA,在500 mA的工作电流下,输出功率为138 mW,垂直和水平方向的远场发散角分别为32.9°和11.1°,证明器件具有良好的基横模输出特性。同时,建立高阶模截止条件温度模型,研究了器件在不同温度下功率-电流（P-I）曲线中kink效应与远场发散角steering效应的产生原因,阐述了温度对基横模和高阶模增益的影响机制。通过比较不同腔长器件发生kink效应的电流大小,证明长腔长结构可以有效防止kink效应的发生。     

低远场发散角976 nm基横模脊形半导体激光器

采用非对称大光腔外延结构设计制备出976 nm InGaAs/GaAsP应变补偿量子阱脊形半导体激光器,通过对外延结构的设计优化,以实现器件低远场发散角、低功耗的基横模稳定输出。所制备基横模脊形半导体激光器的脊宽为5μm、腔长为1500μm,在25℃测试温度下,可获得422 mW最大连续输出功率,峰值波长为973.3 nm,光谱线宽（FWHM）为1.4 nm。当注入电流为500 mA时,垂直和水平远场发散角（FWHM）分别为24.15°和3.90°。在15～35℃测试温度范围内对脊形半导体激光器的水平远场发散角进行测试分析,发现随着测试温度的升高,器件远场分布变化较小,水平远场发散角基本维持在3.9°左右。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.