Crystal Puts a Kink in Light

E-mail and other telecommunications zip across the globe via satellite as microwaves or through optical fibers as infrared light. But there's a logjam at either end of such transmissions: The messages slow down considerably when they are converted into electrical signals and passed through electronic circuits. In tomorrow's issue of Science, researchers describe a crucial element of future optical circuits that might process the infrared or microwave signals with lightning speed.

The heart of such circuits might be an artificial structure called a photonic crystal, which can transmit light of specific frequencies with minimal loss. Photonic crystals contain a repeating pattern of reflective elements, spaced at roughly the wavelength of the light or other electromagnetic waves to be manipulated. Because the light bounces around within the crystal, it interferes with itself, filtering out unwanted frequencies. To be useful, however, the crystal has to bend the light as well.

The experimenters, led by Shawn-Yu Lin of Sandia National Laboratories in Albuquerque, New Mexico, made a photonic crystal from columns of aluminum oxide each a half-millimeter in diameter, set in a grid. Their spacing, about a millimeter apart, enabled the array to manipulate electromagnetic waves of millimeter wavelength, somewhere between the microwave and infrared parts of the spectrum. When the researchers removed a row of columns, they could pass millimeter waves along the missing row with virtually no loss. And when the researchers chiseled out a second corridor at right angles to the first, the waves turned the corner in a distance roughly equal to their wavelength.

Reproduced at higher frequencies, this bending would mean that infrared waves--of interest to the telecommunications world--could turn through 90 degrees in about a micrometer, 1000 times tighter than anything possible using optical fibers. The challenge, however, is manufacturing such chips, because the pillars of an infrared photonic crystal have to be fashioned accurately on a scale of micrometers.

"This experiment models the future wiring" of tomorrow's optical microcircuits, says photonic crystal pioneer Eli Yablonovitch of the University of California, Los Angeles. "I think it could really revolutionize the way that we are making optical circuits," adds Katie Hall of Lincoln Laboratory in Lexington, Massachusetts.