Little lenses for little lasers.

Little lenses for little lasers

High-tech lens grinders have made crystalline flakes twice the length and thrice the width of this "s," yet hosting more than 1000 teensy lenses, each about 2 hair-widths, or 130 microns, across. The thousand-eye chips could fill niches in hybrid optical/electronic computers, sensors and communications devices for civilian uses and important components of the Strategic Defense Initiative, according to the scientists who devised them.

Composed of the semiconductor material gallium phosphide, the lenses are transparent to light of visible wave-lengths. This makes them well-suited for collimating light beams emitted by solid-state lasers based on gallium arsenide, a related material remarkable for its ability to transform electronic excitations into laser beams and vice versa. Such collimation is important for chip-to-chip communication in forthcoming opto-electronic technologies.

In the July 10 APPLIED PHYSICS LETTERS, four researchers at the Massachusetts Institute of Technologyhs Lincoln Laboratory in Lexington led by Zong-Long Liau report making the first arrays of gallium phosphide lenslets. Starting with commercially available wafers of ultraflat gallium phosphide, the researchers use photolithographic and chemical etching techniques to pattern the wafer with six-step circular structures, which resemble three-dimensional dart-boards with the bull's-eyes on top and the outer rings sequentially lower. Finally, an 80-hour treatment with a 1,000 [deg.]C, phosphine-spiked hydrogen wind causes the gallium phosphide in the circular steps to redistribute into smoothly curved lenslets. Phosphorus atoms from the hot phosphine fill pocks that form in the lens during processing.