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Wednesday, January 20, 1999 Published at 19:27 GMT


Sci/Tech

Holograms to store terabyte

Traditional two-dimensional data storage is reaching its limit

Squeezing a terabyte of data, the equivalent of 1,600 compact discs, on to a single CD-sized hologram may soon be possible.

It is also believed it will be possible to read the data at one gigabit per second - 100 times faster than a DVD drive.

The advance, reported in New Scientist, has been made possible by a new kind of polymer, developed at the Bayer Institute in Leverkusen, Germany. The scientists expect to make the technology work within five years.

Holography is attractive because, in the next few years, traditional two-dimensional storage in hard drives and DVDs is likely to reach its data density limit. However, the problem has been to find a way to read the information stored in the hologram without erasing it.

Bayer's new photo-addressable polymer (PAP) has chain-like molecules which become aligned when polarised laser light passes through and stay like that even after the beam has been turned off. The alignment can then be read by an unpolarised laser beam without affecting the data.

Easier mass production


[ image: One holographic disk would hold the equivalent of 200 CDs]
One holographic disk would hold the equivalent of 200 CDs
Hans Coufal, a holographer at IBM's Almaden Research Center in San Jose, California, believes another advantage of using polymers is that they can be shaped more readily than crystals, making them easier to mass-produce.

"But up to now, polymer materials are not available in the thickness needed to store sufficient amounts of data," says Coufal.

Bayer's Thomas Bieringer agrees this aspect needs addressing: "We do have one polymer which stores holograms in one millisecond, but the polymer has the problem of being too thin and in holographic data storage you need thick samples to maximise the number of images stored."

The Bayer team has narrowed its choice of PAP down to just five out of 300 that it has tested. The ideal, he says, is to combine all the desirable features of these five substances into a single polymer.

Bieringer's aim is to store a thousand data images, each 1024 by 1024 pixels, on a single cubic millimetre of the polymer, and to be able to read each image in a millisecond.



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