液晶光阀的偏光显示特性分析

讨论了液晶光阀的偏光扭曲向列性效应, 分析了液晶光阀中液晶分子在交流电场作用下重新取向后的扭曲, 测量了TB3639型液晶光阀在特定的频率连续改变外加交流电压条件下,液晶分子重新取向后的扭曲角度以及液晶光阀的电光特性。测量结果表明,在外加电压连续改变时,入射线偏振光的透射率呈现连续非线性变化,这种非线性变化可以由液晶分子的扭曲量来改变。同时液晶分子180°的扭曲使得液晶光阀具有较陡的电光特性曲线,这对于多通道矩阵寻址方式的液晶光阀而言在矩阵显示中可有更多的通道寻址线和更高的对比度。     

红外液晶光阀光学调制特性研究

介绍了液晶光阀的结构及其光学调制原理,利用光阀对读出光反射率计算公式,分析了液晶光阀参数对其光学调制特性的影响,通过理论计算,得到整层液晶分子扭曲角和液晶层厚度与液晶光阀调制能力的关系,分析给出了适合对中波和长波红外波段仿真的红外液晶光阀参数。     

利用液晶光阀实现道路光学图象的实时边界提取

本文利用45°水平定向扭曲向列相液晶光阀的非线性输入输出特性,实验研究了道路光学图象的实时边界提取,效果很好.与数字边界提取相比,光阀边界提取的最大优势在于,处理与图象大小无关,时间少于15ms(即光阀的响应时间),可以达到实时操作,而且可以用白光做输入光源.     

垂直定向液晶光阀中液晶电光特性的理论分析

采用 ４×４ 矩阵法模拟计算了垂直定向液晶光阀的电光特性, 从理论上分析了影响液晶光阀电光特性的因素。根据向列液晶的弹性连续体理论及边界力矩平衡方程, 求出了垂直定向向列液晶在液晶界面之间相互作用锚泊能为有限值时的液晶指向矢分布。根据指向矢分布计算了一定外加电场下液晶光阀的电光特性, 并和锚泊能为无限大时的特性进行了比较和分析     

液晶光阀的电光色散特性研究

分析液晶光阀(LCLV)的电光色散特性,重点研究扭曲向列型液晶光阀TB3639的电光色散特性。在温度为27 ℃时, 将TB3639液晶光阀置于频率为1 000 Hz的交流电场中,测出电光特性T-λ曲线,同时得到不同波长的T-V电光特性曲线,确定对比度与光波波长的函数关系k(λ),并得出电光色散特性关系曲线k(λ)～λ。分析结果表明, TB3639液晶光阀在可见光区域,具有相对较高的对比度,其色散较小。波长在450～750 nm区域其对比度均大于0.8;其中波长在550～670 nm区域其对比度变化不大,均大于0.95,其色散最小。     

图像火灾探测中液晶光阀的特性

在实验的基础上,深入研究了TN型液晶光阀的原理和光学特性。发现TN型液晶光阀对红外波段和可见光波段所产生的不同透射和截止效应都取决于光阀的偏振片。分析了液晶光阀的视角和波谱透过率等因素对图像火灾探测的影响,并指出了在利用液晶光阀做光开关的火灾探测系统中应该注意的问题。     

频率驱动液晶光阀的电光特性研究

讨论了液晶光阀频率驱动方式的原理, 并分析了液晶光阀在频率驱动方式下的电光特性。在特定的交流电压下改变外加电场频率, 测量了TB3639型液晶光阀在频率驱动方式下的电光特性关系曲线。测量结果表明,TB3639液晶光阀在可见光区域具有电光显示灰度变化特性,不仅能实现黑白显示,也能实现不同灰度级显示。频率驱动方式在可见光的范围内对不同波长的透射率变化趋势影响大致相同,在应用中可避免出现色差较大的现象。这种新型频率驱动方式对液晶器件的显示有改善作用,将开拓液晶显示器件的新应用, 具有实际应用价值。     

液晶光阀工作特性的测量与分析

用简便易行的方法对液晶光阀（LCLV）的工作特性曲线作了测量，包括光阀在正像、反转像和微分像状态读出光强与写入光强的响应曲线，以及不同写入光照度下液晶层透过率与工作电压的关系曲线。对所得结果的分析揭示了这方面以前未曾深入研究的液晶光阀非线性转换的特性。由此为光阀的很多新用途提供了坚实的实验基础，指出了进一步探索的方向。     

反射式液晶光阀用于激光束空间整形可行性研究

 从理论和实验两方面对一种反射式液晶光阀（LCOS）的调制特性进行了研究。着重研究了在高功率激光系统中,反射式液晶光阀作为空间整形器件面临的一些应用问题,特别是它的各种调制特性、整形能力以及对于光束质量的影响。研究发现,与透射式液晶光阀相比,反射式液晶光阀有着明显的优势,效率达到42%,远远优于透射式液晶光阀10%的效率,从而能够实现系统的大幅度简化,是一种非常有潜力的空间光调制器件。     

自控液晶光阀组式光刻快门研究

通过理论推导,构建了抗蚀剂的感光特性、光源的光效与曝光量之间的数学模型,为液晶光阀代替穿孔带提供了理论依据.结合液晶光阀的工作原理和光刻快门的控制原理,对液晶光阀组的控制进行了研究并给出了其控制电路图.通过实际光刻试验,自控液晶光阀组光刻快门机构可以完成编码图案的控制,通光控制达到了预计要求,刻出的图案清晰,线条陡直.证明液晶光阀组替代穿孔带用作光刻快门是完全可行的.     

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.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

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.     

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.     

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.