Original URL: http://www.theregister.co.uk/2004/10/19/slow_light_chill/

Boffins moot chilled light for optical comms

Faster isn't always better

By Lucy Sherriff

Posted in Science, 19th October 2004 14:04 GMT

A group of American theoretical physicists have, on paper at least, proven the existence of a new class of soliton that could help simplify high-speed optical communications because it can be slowed down.

In the 1 October issue of Physical Review Letters, the National Institute of Science and Technology (NIST) physicists outline how a pulsed laser could create a soliton capable of travelling through a supercool gas of Rubidium atoms for more than five centimetres without noticeable distortion.

A soliton is a solitary pulselike wave that can travel long distances without becoming distorted, even when it is moving very slowly through a supercold gas. It doesn't obey the superposition principle, nor does it dissipate.

The phenomenon was first identified in 1800s when a naval engineer observed a water wave travel more than a mile within a canal without dissipating, but light, too, can be found in solitons.

These very short, stable, pulses are the subject of much research because in principle they could be used to pack more information into fibre-optic communications systems. In practice, though, light often needs to be slowed down (to around the speed of a jet airliner) so that signals can be correctly routed and synchronised around a network.

However, when light-solitons are slowed, they quickly become distorted or attenuated, causing data loss. This can happen before the packet has travelled even one millimetre, which is a tiny distance anyway, but is even tinier when you consider that light from the Earth can get to the Moon in less than two seconds.

The scientists are now working on the experimental proof of their theory. It should be more practicable than many experiments in the field, which require around 300 kilometres of fibre to delay an optical signal for one thousandth of a second. This new soliton might only need a few centimetres. ®

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