NCSA NEWS

Picture this: Light -- photons -- racing through a miniaturized city. Some photons zoom along thoroughfares. Others navigate the city's streets, making hard right and left turns. The buildings lining the streets house still other photons that, like a fleet of taxis, are fueled and ready to be called into service.

Physicist John Joannopoulos occasionally entertains such fanciful visions; mostly, though, he spends his time bringing them to fruition. Joannopoulos's team at the Massachusetts Institute of Technology (MIT) is using an SGI CRAY Origin2000 at the Alliance's leading-edge site -- NCSA -- to simulate photonic crystals -- structures that, like imaginary cities of light, guide photons along minuscule "streets" (waveguides), store it in tiny "buildings" (microcavities), and control its symmetry and frequency. This line of research, says Joannopoulos, who is also a member of the Alliance's User Advisory Board, "will eventually enable [scientists] to do things with light that we haven't been able to do before." At the very least, he says, these crystals will lead to much-improved designs of optical devices such as light filters, lasers, and light-emitting diodes, which send out the pulses of light that are used widely in communication networks.

Already materials fabricated with the photonic crystals simulated by Joannopoulos's group are reducing the amount of light lost when it is squeezed into a small space or when a cable makes a 90-degree turn. In most existing fiberoptic cable, for example, only about 30 percent of a light wave successfully navigates sharp bends -- the remainder scatters off the corner. In the material being tested by Joannopoulos's collaborators, light is transmitting around these corners with 98 percent efficiency. This tighter control, says Joannopoulos, is what could make structures like those he is simulating mainstays of the miniature optical devices of the future.