Coddled crystal slams door on light

A light touch has improved a material designed to manipulate light. The development brings photonic microcircuits, which would use photons instead of electrons, closer to reality, researchers say.

To create microchips for light, many researchers have been attempting to create repetitive, crystal-like structures called photonic crystals. Now, Susuma Noda of Kyoto University in Japan and his colleagues report making photonic crystals that approach perfection. The group builds its crystals by positioning strips of semiconductor compounds in a three-dimensional stack known as a woodpile.

To end up with woodpiles that are more regular, the scientists realized they needed to reduce flaws that show up during fabrication. After examining their previous woodpiles and the methods for making them, the researchers decided on some changes. They lowered the temperature at which they fused the layers and devised a way to etch away unwanted parts of the structure more gently than before.

In the July 28 Science, the materials researchers claim that their new process produces crystals with “perfect structure from the viewpoint of the optical properties.” The ideal photonic crystal totally rejects electromagnetic waves within a band of wavelengths.

Indeed, an eight-layer woodpile created with the new process transmits only about 0.01 percent of the light at an important telecommunications wavelength. In contrast, an opal-like photonic crystal unveiled in May by a Spanish-Canadian team transmits 100 times as much light in the same band (SN: 6/17/00, p. 399: Available to subscribers at Light chips find a place to take root.).

However, the opal-style crystal assembles itself from cheap materials, whereas the Japanese team must directly build its crystal at relatively high cost, notes John D. Joannopoulos of the Massachusetts Institute of Technology. “These are both very good advances for their own reasons,” he concludes.