Abstract

Optical volume holographic memories provide the potential for high storage capacity, parallel readout of data pages with short access times and high data transfer rates. Multiple image storage in a single region of a photorefractive crystal can be achieved using different addressing techniques as angular, wavelength, or phase-coded multiplexing. In combination with spatial multiplexing, volume holographic memories may achieve the storage of more than 1 Terabyte of information. Among these techniques, orthogonal phase-coded multiplexing [1] offers several advantages over angular and wavelength multiplexing, having the same storage capacity. A holographic data storage system based on phase-coded multiplexing operates with a fixed wavelength and a fixed geometry, avoiding mechanically moving parts. At the same time it provides short readout times and high energy efficiency. The signal-to-noise ratio of phase-coded multiplexing for a given number of holograms is more than two orders of magnitude higher than for angular and wavelength multiplexing [2]. Moreover, it allows to perform arithmetic operations as addition and subtraction of two or more data pages directly during readout of the memory [3]. Image processing operations like comparison of two stored images or image inversion and the logical operations OR, XOR and NOT with digital data pages can be realized in that way. Therefore, using phase-coded optical memories, high capacity data storage and high speed data processing becomes possible simultaneously.

© 1998 IEEE