Photonic crystals promise to shrink the optical devices used in
telecommunications by confining light more compactly than
current designs do. But getting light in and out of them has
been a challenge: once light leaves a photonic crystal it sprays
out in all directions, and much of it is lost. Two independent
reports, in the 15 March Physical Review B and the 19 March PRL,
describe using the surface of the photonic crystal as a kind of
antenna to beam the emitted light in a single direction, like a
flashlight. Improvements on this technique may help photonic
crystal devices to efficiently swap light signals with
conventional fiber optic devices. One type of photonic crystal
consists of a two-dimensional array of microscopic cylinders.
Light within a forbidden range of wavelengths can’t propagate
through the array, so if a row of cylinders is omitted, the
light will be trapped in the missing row. The resultant
waveguide can be less than a wavelength wide, much narrower than
traditional structures. Researchers