Irregular layout sharpens light

Photonic crystal is semiconductor material with regularly spaced rods or holes that is designed to guide certain wavelengths of light.

University of Southern California researchers have found that the broken symmetry of aperiodic photonic crystal, or crystal that does not contain repeating patterns, can be better than ordinary photonic crystals at functions like filtering light. The researchers have developed a computer program that can be used to find aperiodic photonic crystal designs that behave a certain way.

Aperiodic photonic crystal could improve devices that shape, detect and filter light, including communications devices like photodetectors, demultiplexers, which sort wavelengths of light, and channel drop filters, which filter out different wavelengths. The material could also be tapped to transfer light beams from optical fibers to regular photonic crystals.

The researchers' program simulates a photonic crystal and randomly moves one of its rods. If this makes the crystal better able to filter light according to a set goal, it is kept. The program runs through many steps until the goal is met.

The researchers' simulation took 9,700 steps to produce a configuration that bent light at a 45-degree angle and kept the beam's intensity tightly focused into a top-hat shape. This shape in the intensity profile of the beam is nearly impossible to achieve using regular photonic crystal, according to the researchers.

Aperiodic photonic crystals could be used in practical applications in five years, according to the researchers The work appeared in the February 1, 2004 issue of the Journal of Applied Physics.