'Time telescope' could boost fibre-optic communication

17:48 28 September 2009 by Colin Barras
A "telescope" that can magnify time could dramatically increase the amount of data that can be sent through fibre optic cables, speeding up broadband internet and other long-distance communications.

It isn't possible to speed up the flashes of light that stream through the global network of optical fibres at around 200 million metres per second. But more information can be squeezed into each burst of light, says Mark Foster at Cornell University in Ithaca, New York, using what he and his colleague Alexander Gaeta call a "time telescope" fitted with "time lenses".

Time lenses
"A time lens is essentially like an optical lens," says Foster. An optical lens can deflect a light beam into a much smaller area of space; a time lens deflects a section of a light beam into a smaller chunk of time.

The Cornell team made their time lenses using a silicon waveguide that can channel light. An information-carrying pulse made from a series of small laser bursts signalling digital 1s and 0s travels through an optical fibre and into the waveguide. As it enters, it is combined with another laser pulse from an infrared laser. The infrared pulse vibrates the atoms of the waveguide, which in turn shifts the frequencies of the data-carrying pulse before it exits the waveguide and passes into an optical fibre beyond.

"The front of the [data-carrying] pulse is shifted down in frequency and the end is shifted up in frequency within the silicon waveguide," says Foster. Because the speed of light passing through a medium depends on its frequency, the front of the pulse is slowed down while its rear speeds up. At the time lens's focal point the rear of the pulse catches up with the front, producing a fleeting image with a spectrum encoding the entire light pulse. ... (New Scientist)