Long-Sought Laser? Standard microchips may gain speedy optical connections

Even with fast personal computers, Internet goodies such as videos and podcasts often download at sluggish speeds. Now, an advance in laser technology promises to eliminate those and other nagging computer delays, its developers say.

LASER LINEUP. Researchers have developed a new kind of tiny laser, more than 30 of which huddle side by side along this silicon bar (gold). The technology may lead to cheap optical connections that could dramatically boost data flows between and within computers. Intel

Engineers have long known how to wipe out such delays: Outfit ordinary computers with circuitry that sends and receives data as modulations of light rather than as electricity. Optical connections—those used for long-distance telecommunications, for instance—carry far more data than the metal wires that form short-range connections between computers, circuit boards, and chips do. Yet no one has built from ordinary silicon all the light-processing, or photonic, components needed to make cheap optical links for short-range uses.

In recent years, engineers have begun to develop some key silicon photonic devices (SN: 10/30/04, p. 275: Available to subscribers at Laser Landmark: Silicon device spans technology gap). Although researchers have invented silicon lasers, they can’t run on electrical power and so require an external laser for energy (SN: 3/19/05, p. 189: Available to subscribers at Silicon chips land a lasting laser).

A new type of laser has now cleared that hurdle, its inventors claim. The laser was unveiled at a Sept. 18 press conference by a team at the University of California, Santa Barbara and Intel Corp. of Santa Clara, Calif. (Intel is the title sponsor of some of the educational programs of Science Service, publisher of Science News.)

Although not made exclusively of silicon, the device runs on electricity and could be mass manufactured in the same factories as silicon microchips are, the researchers say.

“Perhaps most important is its potential to be realized on a silicon photonics chip at low cost,” comments opto-electronics engineer Graham T. Reed of the University of Surrey in England.

Typically, manufacturers create microchip lasers from exotic—and expensive—semiconductor compounds such as gallium arsenide or indium phosphide. Such compounds readily convert electricity to light, whereas silicon tends to generate heat.

On the other hand, silicon performs exceptionally well as a conductor of light at the infrared wavelengths used for telecommunications, says Mario J. Paniccia, head of Intel’s group on the invention team.

Tapping the strengths of both kinds of semiconductors, the researchers etched a silicon wafer to create horizontal, rodlike, light-conducting structures, called waveguides. Then, at a temperature low enough to be compatible with silicon-microchip processing, they bonded atop that wafer a matching wafer composed primarily of indium phosphide, explains John E. Bowers, who led the Santa Barbara engineering group.

Next, the team cut up the wafers to yield laser chips in which an applied voltage makes the indium phosphide layer produce light. In each laser—less than a millimeter long and about a thousandth of a millimeter wide—the light then bounces between the indium phosphide layer and silicon waveguide beneath it, intensifying until it shoots out the end of the waveguide as a laser beam. Such a beam could potentially carry hundreds of times as much information as an electronic signal does. A report of the research appears in the Oct. 2 Optics Express.

The new hybrid design combines “the best of both worlds,” comments laser engineer Alan E. Willner of the University of Southern California in Los Angeles.

Stay tuned, advises physicist Richard A. Soref of the Air Force Research Laboratory at Hanscom Air Force Base in Massachusetts. He notes that the quest for an electrically powered, all-silicon laser is still going strong.

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