Optical storage of information offers great potential for high capacity and speed. A very promising approach to the embodiment of an optical memory is based on volume storage in the form of phase holograms. Attractive storage materials for such a system are electrooptic crystals. The storage mechanism in these materials is based on light induced permanent changes of the refractive index-the photorefractive effect. In this article the physical processes underlying photorefractive hologram recording are outlined, and some of the advantages and limitations of this method are discussed.

Photorefractive effects for reversible holographic storage of information

Holography, the three‐dimensional imaging technology, was portrayed widely as a paradigm of progress during its decade of explosive expansion 1964–73, and during its subsequent consolidation for commercial and artistic uses up to the mid 1980s. An unusually seductive and prolific subject, holography successively spawned scientific insights, putative applications and new constituencies of practitioners and consumers. Waves of forecasts, associated with different sponsors and user communities, cast holography as a field on the verge of success—but with the dimensions of success repeatedly refashioned. This retargeting of the subject represented a degree of cynical marketeering, but was underpinned by implicit confidence in philosophical positivism and faith in technological progressivism. Each of its communities defined success in terms of expansion, and anticipated continual progressive increase. This paper discusses the contrasting definitions of progress in holography, and how they were fashioned in chan...

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Attributing scientific and technological progress: The case of holography

The principle of beam-addressed holographic memories are outlined and existing data memories are considered in relation to future holographic memories. The next objective is to expand the capacity to the gigabyte region while maintaining read—write access times of about 100 μs. In view of the limitations imposed by conventional storage techniques, two basic approaches to fast gigabyte memories are discussed. On reasonable approach is to design modular systems comprising a number of storage modules of variable capacity. The other is to reach the gigabyte region by using multiple exposure techniques. Besides block-organized memories, bit-organized and byte-organized holographic memories with transported storage media are considered as possible alternatives to conventional memories with magnetic tapes, discs, and drums.

H. Eschler

Papers

Gigabyte capacities for holographic memories