The perfect slow wave

23 October 2006

Sydney University physicists have invented a device that creates perfect slow light waves. Their discovery, reported today in Nature Physics, brings light-based computing and communications a step closer.

Their device slows light by about 20 percent without losing information. Until now, when light was slowed down information was lost. But the self reinforcing soliton waves made by the device ensure that the shape of the wave is maintained.

This matters because communications depend on buffering - holding and releasing batches of information. In this experiment the team buffered just a few bits. If they can get to 100 bits then the team from CUDOS, a consortium of five universities will have a winner.

These slow waves could help unleash a much faster internet, and replace the millions of energy hungry routers that power the web. "We are planning to work with Australian companies to bring the technology to market," says Professors Ben Eggleton, CUDOS Director. The team comprised PhD student Joe Mok, CUDOS Senior Research Fellow Dr Ian Littler, Professor Martijn de Sterke and Professor Ben Eggleton. They are all based in the School of Physics.

In 1834, a Scottish engineer was observing a boat being pulled along a canal. The boat stopped, and a mass of water built up in front of it. The water then rolled forward, leaving the boat behind, and continued, as a solitary wave, 30 feet long and one to one-and-a-half feet high traveling for miles without breaking up. The shape of the canal was such that it created a 'self-reinforcing single wave'.

Severn Bore A soliton wave

"The net comprises a web of fiber optic cables carrying vast amounts of information as light. But the routers and switchers that direct the traffic are electronic," says Professor Ben Eggleton.

"They're a bottleneck, and they are consuming vast amounts of energy both directly and indirectly through the banks of air conditioners required to keep them cool,"

"The dream of photonics is to replace all that slow electronics with light. So the challenge is to create analogues of all the electronic components - transistors, capacitors, buffers etc. And the ability to slow light is critical for buffering information. But until now, the slow light devices had limited bandwidth - and as the light waves slowed they were also damaged, destroying the information they were carrying," says Ben.

"We found that by passing the light pulses through a glass that reacts more strongly to brighter light, we could get the wave to reinforce itself - making a soliton, a single wave that will travel as far as needed without distortion.
The light is guided through a carefully designed crystal lattice within a five cm piece of optical fiber.

"We anticipate that we will be able use fibers that are tens of centimeters long (but curled up within an integrated device and ultimately part of a photonic integrated circuit -- the photonic chip), allowing us to slow the light to order. We have also shown that we can tune the fiber - controlling the speed of the pulses as they travel through the fiber," says Ben Eggleton.

"We believe we can turn this early fundamental discovery into a practical device that will bring ultra-fast internet - and opportunities for Australian companies to jump on the next wave of the internet revolution," says Ben.

CUDOS is the Center for Ultrahigh Bandwidth Devices for Optical Systems. It is a consortium between five Australian Universities: The University of Sydney, Macquarie University, University of Technology Sydney, Australian National University and Swinburne University of Technology.

Funding comes from the Australian Research Council under the Centers of Excellence program, the five universities and from the NSW State Government.

Source / Credit: University of Sydney