Abstract

Spatial light modulators are crucial and often the limiting elements in optical information processing and computing architectures. Recent advancements have shown that parallel readout of optical memory disks may be a competitive alternative for spatial light modulation.¹ Two main recording techniques have evolved: the direct imaging mode,¹ in which the serially written bits are area encoded to give rise to grey scale images, and the holographic approach,² in which the written bits generate a binary encoded hologram. A differential interferometric readout configuration¹ has been shown to be a promising readout technique for the direct imaging mode. In this configuration, a birefringent plate is introduced to produce two orthogonally polarized readout beams offset by one-half of the interbit spacing, which are then interfered to generate a readout signal only where bits have been written. Such a technique produces a high contrast ratio by eliminating the background reflection of the disk. The signal-to-noise ratio (SNR) and efficiency obtainable in practice for this technique, taking into account the performance characteristics of a variety of currently available disk media, are discussed and compared to the corresponding values for the holographic mode. Furthermore, we have recently achieved several improvements of this technique. A total specific birefringence of the shear plate in the differential interferometric readout configuration can be obtained, for a given shear, by choosing the thickness and optic axis tilt angle appropriately, thus eliminating the need for a compensator. Manufacturing tolerances necessary to obtain sufficient SNR in the output image for this modified configuration are shown to be realizable.

© 1989 Optical Society of America