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Japanese company Optware will commercialize an optical disc that can store more than 1 terabyte of data, and an associated disc player, later this year, the company said earlier this week.

The disc and player are based on a 5-inch optical disc like existing CDs and DVDs, but the new disc will be able to store about 120 DVD-format movies, according to Atsushi Machida, a spokesman for Optware.

The high capacity--around 20 times the storage available on existing discs--and a data transfer speed of 1 gigabit per second have been achieved by using digital volume holography read/write technology, developed under the Defense Advanced Research Project Agency (DARPA) in the United States, according to Optware's statement.

Laser Splitting

The system first splits a laser source into two beams: signal (data-carrying) and reference beams. The signal beam goes through a spatial light modulator, which has pages of data arranged in a checkerboard pattern. The pattern either blocks or transmits light; therefore the signal beam will encode data via the spatial light modulator. This encoded beam then interferes with the reference beam via an optical lens to record onto a photosensitive volumetric recording medium.

By changing the angle or wavelength of the reference beam, the technology allows many different data pages to be recorded in three dimensions and read out in the same recording medium, allowing for enormous storage capacity.

In this form, though, the technology is costly, unreliable, and not compatible with existing disc media.

"That was the reason why it has been said that an optical disc based on holography is difficult for commercialization," Machida said. Optware claims to have developed a reliable method of storing data in 3D on existing CD/DVD media.

3D Data

Conventional optical disc systems use a single red laser beam to write a dot, containing 1 bit of information, to a disc's surface. Optware's technology, known as polarized collinear holography, splits the signal laser beam into 1 million narrower beams, creates data pages in the same way as the DARPA system, and with the help of a separate reference laser beam, writes the data in 3D to the disc's volumetric recording layer. One million bits of information can be stored for each dot, according to Optware.

The company will start sample shipping of the disc and the replay device in the third quarter of this year. Its first product will be a write-once disc, to be followed by rewritable discs, Machida said.

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