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Optical Storage Goes 3-D

Photonics Spectra
Apr 2003
Brent D. Johnson

Thanks to the spot size of the blue diode laser and the recent advances in spatial light modulators, holographic data storage is finally practical. However, the ability to write and read such information is meaningless without something on which one can write it. Now, an effective recording media in the form of a photopolymer is available.

apps3D1.jpg
A material from Aprilis Inc. has shown positive results as a medium for holographic storage from Optware Co.

Optical data storage has made important breakthroughs in the information revolution. But although two-dimensional media such as CDs and DVDs enhance the accuracy, longevity and capacity of data storage systems, their transfer rates are still slow relative to the speed of the new computer processors. Going 3-D is an attractive solution.

Traditionally, researchers investigating holography have employed lithium niobate as a storage medium, but the material is much too expensive to be a practical solution for the mass market. As an alternative, DuPont and Polaroid Corp. developed an inexpensive photopolymer, but it suffered from shrinkage. Although suitable for creating novelty holograms of Mickey Mouse, the material was unacceptable for storing financial or medical records.

The alternative route still appears viable. Optware Co. of Yokohama, Japan, will release a media tester for holographic storage this year that employs a photopolymer medium from Aprilis Inc. -- which has resolved the problem of shrinkage.

Hideyoshi Horimai, president of Optware and inventor of polarized collinear holography, said that the company had experimented with DuPont's photopolymer as well as Optilink AB's materials, but it settled on HMD120 holographic media from Aprilis. This silicone-based holographic medium uses a polymerization chemistry based on cationic ring openings that undergoes ultralow shrinkage during photochemical recording, and is accurate to within 15 nm.

In the system, light from a blue laser is encoded with digital information as it passes through a Texas Instruments micromirror-based spatial light modulator and is focused onto the recording medium. The result is a high-density recording that can be transferred a page at a time, instead of bit by bit.

Horimai said that the material is robust and can store three to four times more data than competing storage media. The material's sensitivity enables recording rates of hundreds of megabytes per second.

The HMD series offers a capacity of 200 GB and a data transfer rate of 200 MB/s, and it is available in a 120-mm disc format. The HMC series is available in 50-mm2 card format. Both come in standard recording thicknesses of 200 and 300 µm, and they have an expected archival lifetime of more than 10 years.

Optware will release its broadcast driver for archival storage this summer.


GLOSSARY
photopolymer
A polymer produced as a result of photochemical processes.
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