实现LED准直照明的优化设计

为了有效地利用光源能量,满足LED远场照明系统要求,提出了一种实现LED大视场角准直照明的自由曲面透镜设计方法.运用ZEMAX软件序列模式下的多重组态建立透镜结构,在ZEMAX的二次开发环境下,采用宏语言编写自定义优化函数,实现对光学系统的自动优化.通过得到的自由曲面面型数据,借助光学仿真软件进行模拟,模拟光源采用圆面发光的LED朗伯体,视角为180°,透镜材料为PMMA,点光源模拟得到的发散半角在±0.1°以内,能量利用率在87%以上,实现了较高的能量利用率.     

实现近场均匀照明的双自由曲面大角度透镜设计

针对LED单自由曲面透镜近场大角度照明均匀性不足和出光效率低等问题,基于边缘光线理论和网格划分法,设计了内曲面为椭圆型,外曲面为自由曲面的LED双自由曲面大角度透镜.透镜内曲面对LED入射光线进行发散,外曲面对出射光线方向进行控制,实现大角度均匀照明,并减少全反射损失,提高出光效率.采用扩展光源文件对透镜模型进行光学仿真,并利用反馈优化法对外曲面进行优化,提高近场的照度均匀性.研究表明:在相同近场距离条件下,出光角度为143°、151.8°时,单自由曲面透镜照度均匀性为0.55和0.40,出光效率为92.0%和80%,而所设计的双自由曲面透镜照度均匀性为0.84和0.85,出光效率为98.8%和95.0%,照明效果明显改善.     

用于固态照明的自由曲面微透镜设计

针对LED照明应用中,现有二次光学设计过程对LED初始光强空间角分布的依赖性,讨论了用于LED照明的自由曲面微透镜器件的设计方法.根据斯涅尔定律和边缘光学理论,研究了自由曲面微透镜的面形构造算法,建立了自由曲面微透镜器件的光学模型,并用光学模拟软件对其照明性能进行了模拟实验.结果显示,该微透镜器件能够在目标面上获得满足预期要求的照度分布,照明均匀度在92%以上,且其结构有效解决了LED初始光强空间角分布复杂化的现状和现有二次光学设计对光源初始光强空间角分布依赖性的矛盾.     

基于微分方程数值解的自由曲面透镜的设计

为满足目标面上均匀照明的需求,设计了一款自由曲面透镜。根据LED光源的发光特点,结合光学成像的特性,非成像光学原理和能量守恒定理,推导出实现光能量在目标面上均匀分布的自由曲面面形的微分方程,采用matlab的ode算法求出面形上的离散坐标点,对离散坐标点拟合后得到透镜模型,通过光学模拟仿真软件对透镜模型进行光线追迹。结果表明,配光角度为80°的透镜,透镜的口径与光源发光面宽度之比大于等于9时,目标面上的照度均匀性大于0.9,光能利用率约为85%。该设计方法可以快速精确地设计出所需的透镜,而且透镜结构紧凑,单颗就能实现均匀照明,有利于LED光源照明系统的小型化。     

实现LED照明的自由曲面透镜设计

为在特定平面上实现所需照明,从而满足各类LED照明系统的要求,通过透镜的第一面球面和第二面自由曲面的两次折射实现LED的配光设计.根据给出的LED辐射特性和所需实现的照明面上的能量分布,并预先定义透镜球面的结构参量,可得到一组一阶偏微分方程,数值差分求解直接求得透镜的自由曲面.光源采用发光面积1×1 mm2朗伯体发光的LED,视角180°,由自由曲面透镜得到的各种形状照明面的模拟均匀性皆接近90%,且能量利用率高于98%,编程解一阶偏微分方程组的计算时间少于20 s.     

基于双自由曲面的LED大角度光学透镜设计

针对直下式LED背光源的均匀照明系统,采用双自由曲面组合,设计了一种大角度光学透镜结构。通过近光源面的自由曲面将光发散成的c/cos3(θ)型光场分布,再利用远光源面实现目标面的均匀分布。这样可以在短距离条件下实现大面积的均匀照明,相对于传统的单自由曲面设计,有效地避免了全反射的发生,提高了照明区域的面积。采用光线追迹软件对所设计的结构进行仿真,通过对模拟结果的分析,在灯箱厚度为15mm时,单透镜均匀照明面积可以达到60mm。采用正三角阵列分布,整个目标面均匀度达到87.5%。相对于传统的大功率器件的直下式光源方式,提高了照明的均匀度,同时大大减少了箱体的厚度。     

实现LED矩形均匀照明的透镜设计

 随着大功率LED发射光强的不断提高,采用单粒LED为光源的照明系统已得到普遍应用。设计一种以LED为光源实现矩形均匀照明的透镜,根据微分几何的理论建立透镜面型所满足的微分方程,然后根据能量映射关系和能量守恒定律建立面型与目标面坐标点之间的关系,并通过四阶龙格-库塔法求解微分方程得到面型数据,利用所得的面型数据在三维建模软件Rhinoceros中构建出所求透镜面型,并将透镜导入ASAP进行模拟。模拟结果表明：该光学系统效率达到94.01%,目标面照度均匀性优于92.73%。最后分析了自由曲面的连续性,指出能量映射关系决定着自由曲面的连续性。     

LED路灯的自由曲面二次透镜设计

配光是LED路灯应用的主要技术问题之一。道路照明要求LED路灯在路面为均匀性良好的矩形光斑,在道路外无污染,无眩光。采用Snell定律和光源扩展度守恒原理确定自由曲面的解析方程,借助Matlab工具,采用差分法求解建立的偏微分方程,得到自由曲面的数据组,用作图软件Pro/Engineer为自由曲面透镜建模,通过计算机仿真软件TracePro进行光路仿真检验设计结果,并对所得结果进行分析。设计一款内表面为椭球面,外表面为自由曲面的LED路灯透镜,实现了路面光照总均匀度0.75,纵向均匀度0.85的效果。     

针对LED扩展光源照明的自由曲面透镜设计

针对LED扩展光源,采用双向反馈网格法设计了自由曲面透镜.划分光源和目标面的能量网格,通过对每一条迭代曲线建立反馈系数,对网格点进行修正并建立新的映射关系,设计了两个目标面中心无光照度的自由曲面透镜.将设计的自由曲面透镜用蒙特卡罗方法对不同尺寸的LED扩展光源进行了模拟仿真.结果表明,对于尺寸在4mm×4mm以下的LE...     

基于BreedPSO算法及交叠法的紧凑型大角度双自由曲面透镜设计

为了获得LED扩展光源大角度均匀照明,采用双自由曲面,设计了大角度紧凑型透镜。利用角度扩大函数使内自由曲面对光线发散,根据矢量Snell定律确定点源透镜的外自由曲面。采用交叠法优化双自由曲面扩展光源透镜模型,通过BreedPSO算法进一步优化。对于h/d=2.5的紧凑型系统,均匀度和光效分别为88.12%和84.54%,照明均匀度明显提高。照明系统横向安装位移误差在[0,0.3mm]内,均匀度及光效分别在85%及84%以上,纵向安装位移误差在[-0.04mm,0.05mm],均匀度及光效均在82%以上。     

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.     

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.     

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.     

Fiber Modal Index Measurements Based on Fiber Gratings

A novel method based on fiber gratings for measuring the effective indices of fiber modes is proposed. The effective index difference between the core mode and a cladding mode was obtained by analyzing the interference fringe of a pair of cascaded long-period fiber gratings. In order to extract the core mode index from the measured index difference, an index matching oil immersion method is proposed. By analyzing the interaction between the cladding mode and the oil applied on the cladding surface, the mode order and the effective index of the involved cladding mode might be calculated. Experimental results about the interference fringe shifts induced by the oil index and the oil-applied length are also presented.     

Optical Pulse Compression Schemes That Use Nonlinear Bragg Gratings

Nonlinear optical pulse compression of picosecond pulses typically requires long lengths of optical fiber and multiple components. Periodic structures, such as fiber Bragg gratings, are highly dispersive at wavelengths outside of the photonic bandgap. This implies that such gratings can be used as very short all-fiber compressors. In this paper a number of such compression schemes are reviewed involving uniform and nonuniform fiber Bragg gratings, relying on both soliton and nonsoliton compression principles. Experimental results supporting the corresponding underlying theory are also presented. Finally, an extension of one of the compression schemes is shown, which allows the generation of adjustable high-repetition rate soliton trains.