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Computing at the Speed of Light






Mr. Huang, a researcher at AT& T Bell Laboratories in Holmdel, New Jersey, is trying to develop an optical computer. Instead of electrons doing the calculating, it would use photons of light. An optical computer could run thousands of times faster than its quickest electronic forebear.

For some, the idea is impractical to the point of foolishness. “You get shot on sight for talking about optical computing in this building, ” snarls Hyatt Gibbs, director of the Optical Sciences Center at the University of Arizona in Tucson, a program backed by the National Science Foundation. He says the discipline is “a dead issue, at least for this generation.”

International Business Machines Corporation (IBM) and several prominent scientists say optics may be good for some things, like carrying phone messages, but doing complex digital computations isn’t among them.

In January 1990, though, Bell Laboratories announced a notable step toward optical computing. It unveiled a digital optical processor, apparently the world’s first.

The gizmo is a collection of lasers, lenses, prisms, and microscopic “photonic” devices that takes up about 4 square feet on a lab bench and looks suspiciously like an undergraduate physics experiment. But when it is running, infrared laser beams turn its switches on and off a million times a second and process 32 channels of information at once.

So it can now be said that Mr. Huang has proved that it is possible to make an optical computer. He worries, however, that America may not be the first to make one.

For one thing, Japan’s Mitsubishi Electric Company and NEC Corporation have already unveiled optical switching devices, though they haven’t put them together into processors as Bell Labs now has. Mitsubishi has also announced a technology that could make it possible to etch a million optical switches on a 1-centimeter-square wafer.

Thirteen large Japanese electronics companies have teamed with Japan’s Ministry of International Trade and Industry (MITI) in a research effort slated to last ten years. Funding is small so far, but 200 researchers meet monthly at Tokyo University to share progress.

Mr. Huang hopes his research will convince people that optical computing isn’t so difficult that it should be ignored. If it could be perfected, believers point out, it would have powerful advantages over electricity.

The first is speed. Light moves faster than electrons or anything else. A computer that could tap into the speed of a photon – a packet of light energy – would operate at the limit of physics.

Also, because photons don’t interact with one another, light beams can cross without interference, permitting almost unlimited wireless connections between computing elements. The computer technique known as parallel processing – splitting a problem up and sending parts to different processors – would be much easier, notes Demetri Psaltis, professor of electrical engineering at California Institute of Technology (Caltech).

Finally, light can carry a lot more information than can electricity. Bell Labs calculates that one small lens could convey the phone conversations of the world’s entire population, even if everyone were speaking simultaneously.

Yet one of light’s chief strengths is also its big drawback. A digital computer, the only kind most people consider useful, is basically a collection of switches. Since light beams don’t interact, it is hard to make them turn one another on and off.

Mr. Huang claims that this problem was solved in 1986, when Bell Labs announced its optical switching device, called a SEED (it stands for self electro=optic effect device). In the processor demonstrated in 1990, pairs of SEED devices act like the transistors in ordinary computers. One laser beam focused on a SEED determines whether another beam will be reflected by the neighboring SEED or absorbed by it. Since photons can’t switch each other without help, a small amount of electricity is used to change the refractive nature of the materials; but the process is controlled optically.

When each device is switched, its output serves as input to another device, allowing basic logic to be performed. On a nearby television screen, the effect is seen as an array of blinking lights.

Asked about the size of the processor, its main architect, a Scot named Michael Prise, explains somewhat defensively that things are about to get much smaller. Right now, he says, he could build the same machine in a quarter of the space. The next-generation model will take up only 2 cubic inches – and will have many more switching devices and is likely to run much faster.

But this machine is significant for what it does, not how big it is. Although it runs relatively slowly and is only about as smart as a dishwasher control unit, that is a big leap forward for optical computing. Previously, no one had ever assembled a digital processor that could do more than pass light around in a circle.

The heart of AT& T Bell Laboratories’ optical computer is a switch that is activated by a beam of light. By linking several such switches together, researchers have created a device that can perform mathematical operations.

The switch works in two stages:

1. The laser beams are directed at different halves of the switch. One beam is stronger in intensity than the other, representing a message in computer code. As the two beams hit the switch, an electric charge is generated that causes a physical change in the material; one half becomes opaque while the other becomes translucent.

2. These beams are then followed by two more powerful light beams of equal strength. The beam hitting the opaque half of the switch is only weakly reflected by the mirror behind it, while the other beam is strongly reflected. The result is a new pair of light beams that are used to trigger the next switch in the device, and so on.

 

Ответьте на вопросы к тексту:

1. What does an optical computer use instead of electrons?

2. When was the world’s first digital optical processor developed?

3. What has Mr. Huang proved?

4. Why is one of light’s chief strengths also its big drawback?

5. What is the essence of parallel processing?

6. What is the speed of the gizmo?

7. What is SEED?


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