New optical technology may challenge CD-ROMs and videotape
Browse the shelves of your local video store next year, and you may see something new: movies on CD-size digital videodiscs (DVDs) rather than tapes. Two camps of electronics companies are still battling over what form the discs will take, but they do agree on one point. DVDs will offer only prerecorded fare. Folks who want to digitally videotape their favorite cooking show or create their own multimedia masterpiece are out of luck.
A new data storage technology pioneered by Optex Communications in Rockville, Md., could change all that. Optex is wrapping up seven years of work on a drive that will record 5.2 gigabytes of data--eight times the capacity of a CD-ROM and enough for several hours of compressed video--onto an erasable 5.25-inch disc cartridge. The capacity is nothing special: magneto-optical drives will soon equal it. More important is the promise that Optex's drives will be cheap and fast.
"We can make the discs for under $10," asserts Brian L. Williams, a former Bell Atlantic executive now at Optex. A magnetic disk of equivalent capacity goes for about $2,000, in comparison. "The drives will probably cost about $200 more than a standard CD-ROM drive at first," he says. Speed is equally improved. "Conventional optical-recording technologies, because they require heat to make marks, hit limits at about 40 megabits per second," says Donald B. Carlin, the company's chief scientist. "We start at 50"--about as fast as current magnetic hard disks--"and can quickly go to 120. It's a whole new realm."
Such recording rates are possible because Optex's device, awkwardly dubbed an electron trapping optical memory (ETOM) disc, introduces two innovations to optical storage. The first is a material that reacts to light rather than to heat. Optex makes its discs by sputtering a thin film of a metal sulfide doped with two rare-earth elements, such as europium and samarium, onto a glass plate at high temperature. This material "can be dirt cheap," says Gerard A. Alphonse, an optics expert at the David Sarnoff Research Center in Princeton, N.J., who gives Optex's technology high marks.
An ETOM drive uses two lasers of different colors. Optex's first prototype sports blue and red gas lasers that can cram up to 10 gigabytes on a disc. Its consumer product, scheduled for testing next year, will replace these with cheaper red and infrared diode lasers. To write data, a cubic micron of the disc is zapped with a very brief pulse of blue light that excites the europium electrons. Energized, they jump to a nearby samarium ion. Some miss and fall back to their ground state, conveniently emitting a reddish-orange flash that confirms the data were received. Most, however, are trapped by the samarium ions. There they will stay for months, probably years--even at temperatures up to 150 degrees Celsius. But zap the spot with a red laser, and the trapped electrons are boosted back to their starting position, yielding a pulse of orange light as they fall. Read the pulse, and you recover the data.
Those data can be more than one bit--a second innovation. CDs and their offspring store information in binary form: a mark is either there (1) or not (0). ETOM introduces shades of gray between these extremes. Write a spot with bright light, and many electrons make the jump, so the disc returns bright flashes when read. Faintly written spots yield proportionately faint responses. Herein lies ETOM's key advantage. With four distinct levels, one can write twice as much digital information on a disc and read it out twice as quickly; with eight levels, three times the data in one third the time. Optex's scientists have demonstrated 13-level recording in their materials. Their initial discs will employ six levels, storing 2.5 bits in each spot.
Last year Optex discovered a new variety of ETOM material that responds to the same infrared lasers used in CD-ROM and the coming DVD drives. That bit of luck will help it clear one of the highest hurdles facing any new medium: compatibility with older technologies. The company has already demonstrated a prototype that could use both ETOM and magneto-optical disks. Its consumer drives, Carlin promises, will record on ETOM discs but will also play back CD-ROMs and DVDs.
One hurdle often leads to another, however. The ability to make perfect copies of prerecorded discs has provoked Hollywood before to strangle novel technologies in the crib: witness digital audiotape. So it is no coincidence that Optex hired Raleigh Coffin--former president of CBS/Fox Video, the world's largest distributor of home videos--as its CEO. And it is no surprise that Coffin's eyes light up when he describes a quirk of ETOMs that will add a bit of cost and complexity to his drives.
Because reading a spot on an ETOM disc releases electrons from their traps, it also completely erases the data they encode. As each bit is read by one laser, it must thus be passed to the other laser to be rewritten a microsecond later. In that split second handoff, Coffin spies an opportunity. "We could design the drive to refresh some data only a certain number of times," he points out, so that a copy-protected movie would be automatically obliterated after, say, the second viewing.
Coffin thinks that although such protection will be important to pacify the DVD producers, it will be critical when people start renting digital movies and multimedia software from services on the network rather than from stores on the street. "If everyone wants to watch "Terminator 2" on Friday night, providers will have two options," Williams describes. They could feed the video slowly over millions of two-hour telephone calls. Or they could download the entire movie in less than 90 seconds to a disc as large and fast as an ETOM--if they can trust that it will evaporate well before pirates could make many illegal copies.
Future possibilities are intriguing, but Optex is now focusing on more mundane matters, such as finding drive manufacturers willing to license its technology. If it is successful, the DVD battlefield may have to make room for yet another player.--W. Wayt Gibbs
SCIENTIFIC AMERICAN August 1995 Volume 273 Number 2 Page 31
Scientific American (ISSN 0036-8733), published monthly by Scientific American, Inc., 415 Madison Avenue, New York, N.Y. 10017-1111. Copyright 1995 by Scientific American, Inc. All rights reserved. Except for one-time personal use, no part of any issue may be reproduced by any mechanical, photographic or electronic process, or in the form of a phonographic recording, nor may it be stored in a retrieval system, transmitted or otherwise copied for public or private use without written permission of the publisher. For information regarding back issues, reprints or permissions, E-mail SCAinquiry@aol.com.
