Solid-state lasers: upward to a focus.

The tiny laser in a compact disk player or a laser printer generates light from the excitation of electrons in an active layer of a sandwich of semiconducting materials. Such a laser typically feeds a ribbon of light sideways out of the active layer. An external lens then focuses this light.

Now, researchers at AT&T Bell Laboratories in Murray Hill, N.J., have developed a new type of semiconductor laser that automatically focuses light emerging from the top rather than from the edge of the semiconductor sandwich. This is the first laser that can focus itself, Bell Labs researchers say.

A compact source of focused light such as this could facilitate the passage of light from a laser into an optical fiber or between optical components on a single integrated-circuit chip or on separate circuit boards. "For these applications and others requiring coupling to fibers, a laser source with a converging output would be preferable to any laser in commercial use today," says Daryoosh Vakhshoori, who invented the device.

Known as a zone laser, this experimental device consists of several layers -- each 70 angstroms thick -- of indium gallium arsenide, gallium arsenide, and aluminum gallium arsenide. About 120 micrometers in diameter, this experimental laser produces infrared light. A pattern of concentric grooves -- each 1 micrometer wide and about 0.35 micrometer deep -- cut into the laser's top surface focuses the light to a spot 8 micrometers wide.

The researchers will describe their self-focusing laser at next month's International Electronic Devices meeting in Washington, D.C.