A study of light stimulus propagation phenomena in optical information processing media, liquid crystals

(A)从理论和实验上研究了均匀向列相样品在外加电压下产生垂直入射光生电流瞬变的机制。利用由Freedericksz跃迁引起的非线性光学Pockel效应，导出了光伏电动势的显式表达式。基于等效电路，通过直流场诱导离子漂移对电极的影响来解释电流的暂态。实验结果完全由本理论解释。(B)测量了不同电压和温度下向列相液晶的放电电流瞬变。首次在向列相和各向同性相中观察到了放电瞬变过程中一个明显的峰。为了探索这种异常峰的来源，还进行了基于随机游走方法的计算机模拟。这一反常峰的产生归因于外加电场引起的空间电荷不均匀分布的弛豫。(C)报道了在向列相液晶中用非线性光学整流的新效应模拟视觉激发(SVE)。结果表明，这种光电结构自然类似于真实的视觉神经元器件。作为例子，提出了一种基于支持向量机的模式识别光学并行处理装置结构。

(a) The mechanism of normally incident photoinduced current transients in homogeneous nematic samples in an applied voltage has been studied theoretically and experimentally. Explicit expressions for the photovoltaic emf are derived using the nonlinear optical Pockel's effect induced by the Freedericksz transition. The current transient is elucidated by the effect of dc field-induced ion drift to electrodes based on an equivalent circuit. The experimental results are completely explained by the present theory.(b) Measurements of discharging current transients in nematic liquid crystals have been made at various applied voltages and temperatures. A well-marked peak in the discharging transient is observed in both nematic and isotropic phase for the first time. Computer simulation based upon a random walk method has been also carried out in order to explore the origin of such an anomalous peak. It is concluded that the occurrence of the anomalous peak is ascribed to a relaxation of an applied-electric-field-induced non-uniform distribution of space charges due to impurity ions incorporated in the liquid crystals.(c) The simulation of visual excitation (SVE) by new effect of nonlinear optical rectification in nematic liquid crystals has been reported. It is shown that this opto-electric structure is naturally similar to the real visual neurotic element. As an example, an optical parallel processing device structure using SVE is proposed for pattern recognition.