Abstract

Optically addressed spatial light modulators (OASLMs) that incorporate nematic liquid crystal (NLC) light modulating layers find many applications in optical information processing due to their gray-scale capability. These devices are usually driven with sine or square-wave voltages at frequencies of 1-10 kHz that are beyond those to which the NLC can respond. The NLC responds to the rms value of the applied voltage across it. Some NLC OASLMs incorporate photosensors of hydrogenated amorphous silicon (a-Si:H) that offer high resolution and high sensitivity[1-6]. We have made some NLC OASLMs with intrinsic a-Si:H for phase-modulation applications. The observed behavior from these devices cannot be explaining using a resistor-capacitor circuit model in which the a-Si:H is treated as a photoconductor. Instead, a metal-insulator-semiconductor (MIS) model is found to fit the experimental data very well. The indium-tin oxide (ITO) electrode and the NLC layer in the OASLM form the respective metal and insulator layers. This MIS model can be used to optimize the thicknesses of the NLC and a-Si:H layers in an OASLM to obtain large phase or amplitude modulation.

© 1995 Optical Society of America