A Tiny Chaotic Laser

Physicists have created a microscopic laser that uses chaos to help it emit light a thousand times more powerful than previous lasers of its kind. The new laser, described in today's Science, could be a cheap way to transmit long-distance phone calls over fiber-optic cables, to detect pollution, or to experiment with chaos in close quarters.

Lasers amplify light and usually release it in a narrow beam. Most lasers amplify light by reflecting it between parallel mirrors. A microdisk laser works differently: In it, light bounces around the inner edge of a semiconductor disk, stimulating the emission of more synchronized light each time it makes a loop. These micrometer-sized racetracks, developed in 1991 by Sam McCall and colleagues at Bell Laboratories in Murray Hill, New Jersey, are very good at trapping light. Too good, in fact: Stymieing the use of microdisk lasers has been the difficulty in getting them to give up their light.

An international team led by Claire Gmachl of Bell Labs thought that fiddling around with the shape of the microdisk might help. They deformed a disk so it looked more like a slightly rounded football stadium, hoping that the light would shoot out at the sharp bends at the stadium's ends. More light came out of the lasers, but closer to where the goal line would be. Theorists had a surprising explanation why: The shape makes the light bounce around chaotically, unless it settles into a bow-tie-shaped path. Where the bow-tie hits the edge of the cavity, beams of mid-infrared laser light emerged. And they packed quite a punch--about 40 milliwatts, a thousand times more output than had been achieved with previous microdisks.

"It's very good exploratory research," says physicist Dennis Deppe of the University of Texas, Austin. But the chaotic lasers will have to compete with the standard edge-emitting lasers that currently dominate the commercial market. The new lasers may have some advantages, however--they are very compact and emit better-focused beams than typical edge-emitters, which could reduce the need for additional lenses. The technique could also be used to make near-infrared or visible light lasers, Gmalch says.