Abstract

Spatially multiplexed subholograms have potential uses in fiber-optic interconnects and optical computing. However, because of the low dark conductivity of photorefractive materials such as bismuth silicon oxide (Bi₁₂SiO₂₀), charges build up around the edges of the subhologram and effectively screen out the applied dc electric field. This leads to low holographic diffraction efficiencies. Using ac fields instead of dc fields is effective in reducing the amount of charge screening, and we have observed an increase in diffraction efficiency of 2 orders of magnitude with ac fields. We have characterized the properties of spatially multiplexed subholograms in Bi₁₂SiO₂₀ with ac fields and investigated the effects of several different manifestations of charge screening. Our experiments show that when the write and read beams are simultaneously on and the photorefractive grating is in saturation, the diffracted intensity of the read beam is proportional to exp(−al) for I > I_s, where I is the total intensity of the write beams and I_s is the saturation write intensity. This permits direct modulation of the diffracted beam through modulation of the write beams and can be explained by both macroscopic and microscopic charge screening effects.

© 1988 Optical Society of America