R2-D2 would be so proud

Holographs: Technology catches up to a storage concept once found only in science fiction.

March 26, 2001|By Ian Austen | Ian Austen,NEW YORK TIMES NEWS SERVICE

For all of their digital sophistication, CD-ROMs, hard drives, DVDs and all other computer storage media share one trait with the tin-foil cylinder that Thomas Edison first used to capture his recitation of "Mary Had a Little Lamb."

Those devices all use only their surfaces to record information.

So it's not surprising that holography, with its ability to create and store images in three dimensions, has long been seen as a way to create high-capacity, but physically compact, systems for digital storage.

A system that could store information throughout a disk, from top to bottom and side to side, could - in theory, at least - hold huge amounts of data.

"It's a very old idea indeed," says Kevin Curtis, a former hologram researcher at Bell Laboratories who is now the chief technology officer at InPhase Technologies, which is developing commercial products based on the technology.

Turning holographic data storage into a product has been a struggle. Decades of research, much of it in the United States and Japan, created systems that lived only in laboratories because they were too costly or too unreliable for the real world.

But Curtis' company, which is partly backed by Lucent Technologies and Imation, a manufacturer of storage media like diskettes and CD-Rs, hopes that technologies partly developed by Bell Labs will change that.

And it might not be alone. Two other research groups that include International Business Machines, Kodak, Lucent Technologies and other companies, along with several colleges, might also be close to conquering the problems of holographic storage.

If Curtis' company succeeds, it will fulfill some bold promises. He predicts that a plastic disc the size of a DVD or CD-ROM, created with his system, will initially be able to hold roughly 400 gigabytes, enough to store 100 full-length feature films. (Most CD-ROMs hold 700 megabytes of information.)

That capacity could be increased to trillions of bytes (or terabytes) over time. "If you think of a CD as a two-bedroom apartment, a terabyte disk would be the entire Empire State Building," Curtis said.

Perhaps the most familiar holograms are the shiny security images on credit cards or the representation of Princess Leia that was shown by R2-D2 in the original "Star Wars" movie.

To create a hologram of an object, light from a single laser is split into two beams. (Laser light is used because of its uniform wavelength and phase.) One beam goes straight to the target - often photographic film, but in this case, a disc. That is the reference beam. The other, known as the signal beam, is usually reflected off the object that is to be transformed into a holographic photograph.

Because pieces of computer data have no physical form that can be photographed, turning them into a hologram requires a preliminary step. The ones and zeroes of the data bits must be turned into black and white squares, using a type of liquid crystal display. That LCD, called a spatial light modulator, displays black-and-white images of the bits that need to be recorded. The signal beam passes through that display on its way to the disc.

Whether the hologram is being used to record data or an image, the signal beam is modified by what it encounters.

When it reaches its target, the modified signal beam collides with the reference beam, causing an interference pattern that is recorded to produce the hologram. To store data, the interference pattern is recorded within a disc containing chemicals that change form in response to light. Before writing the next chunk of data, the system waits for the disk to rotate slightly.

One of the biggest problems surrounding early attempts at holographic storage, Curtis said, had more to do with materials than physics or computer science. Many of those systems, he explained, used crystals that reacted to light to create and store data as holograms, but such crystals proved expensive and difficult to use.

Finding a substitute was not easy. To avoid data errors, the medium had to have a very high optical quality and, above all, be close to perfectly flat. To make things even more difficult, the Bell Labs team was looking for something that could allow discs to be manufactured for about the same cost as a blank DVD.

Eventually, the group produced a plastic composed of two polymers. One creates the transparent and flat base. Suspended within it is a second polymer that reacts to specific colors of laser light.

Of course, the discs are just a small part of the problem. While the materials scientists fiddled with polymers, others working on the project worked on faster ways to transfer data.

Other data discs, such as DVDs, CDs and hard drives, transfer data to computers literally bit by bit. Those drives generally accelerate the process of moving the ones and zeroes of digital information one at a time by spinning more quickly. "Some hard disks now run at just under the speed of sound," Curtis said.

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