Optical parallel-access shared memory system: analysis and experimental demonstration

An optical implementation of a parallel-access shared memory uses a single photorefractive crystal and can realize the set of memory modules in a digital shared memory computer. This implementation uses two arrays of sources that are individually coherent but mutually incoherent from region to region across each array, and it permits incoherent/coherent double angular multiplexing of data in the crystal. A complete instruction set for its memory access consists of four operations, READ, WRITE, SELECTIVE ERASE, and REFRESH, which can be applied to any memory module independent of (and parallel with) instructions to the other memory modules. In addition, a memory module can execute a sequence of READ operations simultaneously with the execution of a WRITE operation to accommodate differences efficiently in optical recording and readout times common to optical volume storage media. An experimental shared memory system demonstrates two memory modules, each consisting of up to two 5-bit data blocks, implemented in a single Fe:LiNbO(3) crystal. The projected performance of the optical parallel-access shared memory system is analyzed and compared with conventional page-addressed volume holographic memories.