Abstract

Spatial light modulating devices have received much attention recently, primarily for the numerous functions they can perform in parallel optical computing. Various physical principles have been employed in the construction of these spatial light modulators^1-3 (SLMs) e.g., liquid crystal light valves, microchannel SLMs, Si-PLZT SLMs, quantum well devices, ferroelectric liquid crystal devices, membrane SLMs, and photorefractive devices. Conventional optically addressed 2-D spatial light modulators (OSLM) are based on the detection of the spatial light distribution of a writing wave and the generation of an electric field image that is used to drive a device that modulates the reading wave. Most of the conventional OSLMs are fabricated by integrating photosensing devices with electro-optic modulators. Similarly, the devices based on photorefractive effect utilize the photoconductivity and electro-optic effect of the material. In photorefractive devices, the spatial intensity distribution of the interference between input waves generates a spatial charge distribution that is held by the self-induced space charge electric field; via the electro-optic effect, this space charge field modulates the refractive index in the volume of the material; which in turn affects the wave propagation and the spatial light distribution at the output. While the photorefractive devices and the conventional OSLMs based on electro-optic modulators are similar in the physical mechanisms they employ (i.e., photosensitivity and electro-optic effect), they differ in their modulation mechanisms. For example, conventional OSLMs may use amplitude modulation via polarization or phase modulation in thin electro-optic media; photorefractive SLMs, on the other hand, rely on the nonlinear interactions (i.e., mixing) of waves in the volume of thin or thick photorefractive material.

© 1990 Optical Society of America