Drilling into the infrared.

The effort to construct a photonic crystal, which treats photons or light waves in the same way that a semiconductor treats electrons, has moved from engineered structures that exclude microwave radiation of certain wavelengths to those that forbid the passage of infrared light. Last year, Eli Yablonovitch and his co-workers at Bellcore in Red Bank, N.J., drilled crisscrossing holes into a solid slab of an electrically insulating material to produce an array of cavities that prevent microwaves of a certain narrow frequency range from penetrating the structure (SN: 11/2/91, p. 227). The same team has now used ion beams to drill an identical pattern of much narrower, more closely spaced holes into gallium arsenide. Preliminary measurements show that this array has a band gap -- a band of forbidden frequencies -- in the infrared region of the electromagnetic spectrum.

Yablonovitch sees no reason why such arrays can't be engineered to exclude electromagnetic waves of any specific, narrow band of wavelengths, from the microwave region to the ultraviolet. Furthermore, by introducing suitable defects in the otherwise perfectly regular pattern of drilled holes, it's possible to construct the equivalent of doped semiconductors to obtain the components necessary for making a particularly efficient light-emitting diode or laser.