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.
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