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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Status of 3D memory storage materials

Gajendra D. Savant, Tomasz P. Jannson, Winston Ho

Published Apr 27, 1993• 0 citations
Publisher

Abstract

The speed of modern supercomputers is primarily limited by the relatively slow speed of memory. Research over the past years has focused on developing optical memory systems that, by nature of optics, promise to achieve high speed and high memory capacity. Three- dimensional optical memory systems are well known for their storage capacity and achievable short access time. But the early attempts to exploit 3-dimensional media were limited to photorefractive crystals such as lithium niobate, due to the unavailability of any other suitable medium (alternative media are precluded by their diffraction limited storage densities and non- erasable characteristics). Although volume phase holograms can be recorded in photorefractive crystals, these materials have many obvious flaws such as strong scattering, phase distortion, self diffraction, fast decay, and low refractive index modulation. There have also been continuous efforts to develop new 3-D media (such as photon echo, photorefractive polymers, bacteriorhodusphin, memory access cache, etc., but none can be applied in real world 3-D device because these materials are still in the early stage of development.

DOI
10.1117/12.144068

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The speed of modern supercomputers is primarily limited by the relatively slow speed of memory. Research over the past years has focused on developing optical memory systems that, by nature of optics, promise to achieve high speed and high memory capacity. Three- dimensional optical memory systems are well known for their storage capacity and achievable short access time. But the early attempts to exploit 3-dimensional media were limited to photorefractive crystals such as lithium niobate, due to the unavailability of any other suitable medium (alternative media are precluded by their diffraction limited storage densities and non- erasable characteristics). Although volume phase holograms can be recorded in photorefractive crystals, these materials have many obvious flaws such as strong scattering, phase distortion, self diffraction, fast decay, and low refractive index modulation. There have also been continuous efforts to develop new 3-D media (such as photon echo, photorefractive polymers, bacteriorhodusphin, memory access cache, etc., but none can be applied in real world 3-D device because these materials are still in the early stage of development.
We are developing a high density, high speed optical memory, using rare-earth doped hole- burning materials. These materials are theoretically capable of achieving storage densities of 1000 Gigabits/cm3 at input/output (I/O) rates of several gigabits/sec. One remarkable attribute of this storage concept is that both the temporal and spatial information encoded on a laser beam can be stored. Because both the temporal and spatial information can be stored, digital data can be recorded serially as a data or packet stream as well as holographically using the page format. During the past year we have achieved a breakthrough in demonstrating random access holographic data storage at high frame rates. Five hundred holograms were stored and retrieved with very good fidelity at 30 Hz (video rate). Each holographic image with 512 multiplied by 488 pixels could be randomly accessed during the storage and retrieval process. This frame rate is the highest demonstrated frame rate for any optical technique. This breakthrough was achieved through the invention of a memory architecture that allows multiple holographic frames to be stored without any mechanical beam scanning. In this new architecture multiplexing of 500 holograms was achieved by stepping the laser frequency over a range covered by high speed acousto-optic modulators (AOM).
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