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Semiconductor laser is chip off new block.

Semiconductor laser is chip off new block

A newly developed microscopic laser offers eficiency, power and other qualities that provide a big advance over conventional microscopic lasers, researchers report. The laser, made of a semiconductor chip, could have wide applications in telecommunications and optical computing, they say.

The laser, built at Sandia National Laboratories in Albuquerque, N.M., shoots a beam from the top surface of a gallium arsenide chip only 10 microns thick. It is the first highly efficient, surface-emitting semiconductor laser successfully developed, says Paul Gourley, who led the research team. Most semiconductor lasers emit light from the thin side of the chip, and the few existing types of top-surface-emitting lasers are not very efficient, he adds.

One of the advantages of large laser beams is that they spread so little as they travel over long distances. But getting such a focused beam out of a microscopic laser has been difficult, Gourley says. The beam produced by the new laser is special because it spreads very little (as little as 2.5[deg.]), whereas conventional semiconductor lasers tend to put out fuzzy beams that spread from the mouth of the laser as much as 35[deg.].

The new laser's fine focus and circular beam make it perfect for sending light down optical fibers in telecommunications networks, the Sandia team reports. "Conventional semiconductor lasers can only produce an oval beam that wastes a lot of light when coupled to the circular entrance of an optical fiber," Gourley says.

All lasers work by amplifying light as it passes through energized material. Most lasers increase the amplification by bouncing the light back and forth through energized material lying between parallel mirrors, mutiplying the number of photons passing through. The new semiconductor laser consists of one solid cyrstal that has been built layer by layer. Each layer has been modified to form many mirrored surfaces and an energizing region lying between them.

"What's really novel is that this laser is extremely short," Gourley says. The region between the mirrors is about 1 micron long, which is "one-hundredth the length of conventional semiconductor lasers," he says.

The efficiency of the laser is due in part to the characteristics of the mirrors. With high reflectivity, the mirrors make most of the light take multiple trips through the energizing region for maximum amplification. The mirrors also absorb none of the laser light when photons do pass through them, Gourley says.

At this point, the laser has to be "pumped" with protons from another source to get it going, but Gourley thinks that in a year or so his team will generate a laser beam using just an electrical current.

This laser is exactly right for producing the strong laser light needed for an optical computer, Gourley says. It can also serve as a kind of electro-optical switch, allowing one laser to pump a new beam if the current is turned on, and producing nothing if the current is turned off, he adds.

In fact, the crystal growth technology used to make the laser is now being applied to make all the elements of an optical computer, Gourley says. "We have the source of light -- the laser -- a switch of light, a modulator of light and a detector. You can imagine an integrated system that employs these in an optical computer," he says.
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Author:Vaughan, Christopher
Publication:Science News
Date:Dec 17, 1988
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