Holographic storage: Virtual reality?

WORM
The photopolymer holographic media that will be used by InPhase in the first generation of drives is a WORM media. Because of the high stability of the polymers used these are ideal for archiving applications since, unlike DVD and other optical technology, there is no problem of oxidation of a metal layer. This means that the manufacturers are currently quoting a 50 year archival life of the media and expect to increase this to 100 years plus in the next two years.

A 300GB recordable media holographic disk drive is scheduled to be launched in 2007 by InPhase. "These recordable drives will open up major consumer markets for products using holographic drives. They will also replace tape in backup applications where the fast random access nature of such drives substantially reduces restore time, which is currently reaching critical levels with tape systems," says InPhase's Diaz

Upper storage limit
In the longer term holographic drive capacities will continue to increase and, according to Diaz, "the theoretical upper storage limit of a 12cm holographic disk using our polymer technology is a massive 17TB".

Although InPhase technology drives look set to be the first commercially available holographic storage systems, there are other approaches which show distinct commercial potential. One comes from the Japanese company Optoware — they have demonstrated a holographic data storage drive that uses a technology known as polarised collinear holography.

This uses separately polarised objective and reference beams that are bundled on the same optical axis as if they were one light beam. The technique relies upon the fact that the holographic recording materials they are using are only sensitive to green light. This allows them to use the two lasers on the same optical axis, a red one for the servo, and a green one to read and write the holographic data.

Red laser
This has the distinct advantage in that it makes the optical system as compact as those of DVD and CD disk systems and allows use of the cheap mass produced servo systems used in existing optical disk systems. It also means that the red laser can be used to read data on standard DVD and CD disks.

The Optoware disk is preformatted with address pits and tracking grooves on the reflecting layer at its bottom. The 12cm 200GB disk has a 1.2mm-thick sandwich structure consisting of a 0.5mm glass substrate, a 0.2mm volumetric recording layer and a 0.5-mm glass substrate coated with a reflection layer.

Data is recorded as an interference fringe in the "volumetric" material layer and uses a 30,000 bit page, which in the demonstration system gave 16.25MB per second transfer rate.

Following a recent fundraising exercise the company, which now counts Toshiba amongst its shareholders, has said that it will be launching a 200GB disk drive and a 30GB holographic data card drive in June 2006.

Holographic data storage devices are thus finally on the verge of becoming a commercial product and look well positioned to solve the burgeoning data storage needs of a number of different applications. In the short term simply for data archiving but in the longer term with the arrival of rewritable disks as a replacement for tape in backup applications, according to InPhase's Diaz. "By 2010 I see very little tape being used and holographic disks will really be taking over in the backup space."

The development of high capacity holographic drives also comes at a time when new consumer applications, such as streaming high definition television feeds, online photography and video archiving and retrieval, are starting to emerge. These will become a more practical and economic reality with this technology

Companies mentioned in this article
InPhase
Formed in 2000 to exploit developments at Lucent's Bell Laboratories, it is part owned by Hitachi-Maxell Ltd., has a drive development partnership with Sanyo and a media development partnership with Bayer.

Aprilis
Formed in 1999 as a spinout from Polaroid, the company is shipping its holographic storage media to customers including Sony, Pioneer, Panasonic and Samsung.

Optoware
Japanese company, formed by ex-Sony engineers, has venture capital funding from Toshiba and others. Is aiming to develop a 1TB capacity HDS.