Honk if you love optical switching

17 Jun 2002

Switching light pulses between different lines is a problem that has plagued telecommunications companies since they began using optical fibers. But researchers at the University of Southampton think they may have cracked the problem by developing a simple and cheap way to change the light's course by reflecting it off sound waves.

Tim Birks and Philip Russell heat and stretch two optical fibers until their light-conducting cores fuse and form a narrow circular waist. Before and after the junction, the fibers remain independent. Light travels down an optical fiber by bouncing from one side of the core to the other. The two fibers in the new device are "tuned" to carry signals travelling with slightly different angles of bounce, so light travelling up one fiber will not usually cross to the other. But by altering the bounce angle of the light, researchers say the switch can make it cross the junction and continue along the other line.

Birks and Russell change the bounce angle by sounding a tiny piezoelectric horn. Honking the horn sends a sound wave travelling up the fiber to the junction. "The wave is a compression of the material that changes the fibers' density," says Russell. As far as the light is concerned, this wavefront is similar to a solid plane.

"The light is effectively getting reflected off a moving object," he says. This reflection changes the bounce angle of the light to that of the other fiber, so it changes line at the junction.

David Cotter, adviser on photonics networks at British Telecom laboratories in Ipswich, says: "It looks like a very elegant invention. But it is probably limited to megahertz speeds, which would be fast enough for circuit switching, but unsuitable for switching at the bit level for very high-speed signals."