Optical parallel-access read/write shared memory based on photorefractive crystals

Abstract

A shared memory computer model comprises a set of processing elements, an interconnection network, and a shared memory that consists of a set of memory modules. In this model, each processing element has random access to any memory module (MM), and by means of memory interleaving several MMs can be addressed at the same time. Thus high bandwidth data transfer to and from memory is provided. We propose a novel optical implementation of a shared memory that uses a single photorefractive crystal and can be used as the set of MMs in a shared memory computer. A complete instruction set for its memory access consists of four operations, i.e., read, write, erase, and refresh. In this implementation, two arrays of coherent but mutually incoherent sources are used and permit incoherent/coherent double angular multiplexing of data in the crystal. For selective erase (utilizing a row-controllable π-phase shift plate) or refresh, both source arrays are used simultaneously and, together with a nonlinear feedback arrangement utilizing a spatial light modulator, permit regeneration of the stored signal levels. These source arrays also permit any of the four instructions to be applied to any MM, independent of (and simultaneously with) instructions to other MMs. Details of the system design and preliminary experimental results are presented.