System forms light necklace

The 1s and 0s of computer information are generally represented on computer chips by electrical signals. Using light signals instead promises to speed computing and more tightly integrate computers with optical communications lines.

Researchers from the University of Vermont, San Francisco State University, the University of Massachusetts at Amherst, Tel Aviv University in Israel, the University of Athens in Greece, and Nankai University in China who are working with soliton clusters have come a step closer to all-optical computing. A soliton is a sphere- or disk-shaped wave that does not spread out as it travels. The researchers have showed that it is possible to contain a lightwave as a soliton necklace -- a standing wave of light arranged as a ring of bright spots.

This type of lightwave control could eventually be used in micro-scale lightwave interference patterns, or photonic lattices, to carry out all-optical data processing, according to the researchers. In particular, the technique could be used to route light signals in all-optical communications devices and optoelectronic devices. The necklace soliton is also potentially useful as laser tweezers because it might have angular momentum that can be transferred to microparticles like cells.

To form a stable silicon necklace, the researchers shone a laser through a mask to produce an optical lattice with bright spots spaced 40 microns apart. A micron is one thousandth of a millimeter. They positioned the lattice within a photorefractive crystal and shone a second beam with a vortex shape into the crystal so that it overlapped eight spots of the lattice. This caused solitons to form in a ring, like pearls on the necklace. Key to the method is the combination of optical lattice and vortex beams, according to the researchers.

The challenges that need to be solved in order to use soliton necklaces in practical applications include finding ways to make solitons change directions as they propagate through a network, and finding ways to monitor and control angular momentum.

Practical photonic lattice applications are likely to emerge in the next five to ten years, according to the researchers. The work appeared in the March 25, 2005 issue of Physical Review Letters.