Monday, October 24, 2005

"OPTICS: Photons advance on two fronts"

Photons have electron and molecular properties that could be applied to such areas as sensors and fiber optics, recent experiments show. One group has discovered that solitons — self-sustaining waves of light — can form stable structures resembling molecules. Another team has extended photonic work on the Hall effect to phonons, which are quantized vibrations in a crystal lattice. The first discovery could enable fiber-optic telecommunications lines to double their capacity and eliminate the need for repeaters. The second result might enable Hall-effect sensors to be made from dielectric materials. France's Grenoble High Magnetic Field Laboratory reported observing the Hall effect in phonons. The work builds on a discovery several years ago by Grenoble researcher Geert Rikken that the Hall effect can be realized in photons — a surprising revelation because it had been thought that only charged particles, such as electrons, would respond in such a way to an external magnetic field. Now Rikken and Grenoble colleagues Cornelius Strohm and Peter Wyder have shown that phonons can likewise be harnessed to exhibit the Hall effect. The Hall effect is used widely in semiconductors for sensing and switching. A phonon-based version of the effect could lead to new operating modes for magneto-optical materials and devices that might in turn yield new sensor types.