Euro boffins increase speed of light

A team of European researchers has demonstrated for the first time that it is possible to control the speed of light. The scientists, from the Ecole Polytechnique Fédérale de Lausanne (EPFL), has successfully slowed light down and speeded it up within an optical fibre, using off-the-shelf instrumentation in normal environmental conditions.

The breakthrough is predicted to have commercial applications in a variety of areas including optical computing and fibre-optic telecommunications.

Luc Thévenaz and his fellow researchers in the Nanophotonics and Metrology laboratory at EPFL said they were able not only to slow light down by a factor of three from its usual speed of 300 million metres per second in a vacuum, but they have also accomplished the considerable feat of speeding it up – effectively making light go faster than the speed of light.

The experiments are not the first time that scientists have tweaked the speed of a light signal. Even light passing through a window or water is slowed down a fraction as it travels through the medium. In fact, in the right conditions, scientists have been able to slow light down to the speed of a bicycle, or even stop it altogether. In 2003, a group from the University of Rochester made an important advance by slowing down a light signal in a room-temperature solid.

But all these methods depend on special media such as cold gases or crystalline solids, and they only work at certain well-defined wavelengths. With the publication of their method, the EPFL team, made up of Luc Thévenaz, Miguel Gonzaléz Herraez and Kwang-Yong Song, has demonstrated the first all-optical technique to slow light in off-the-shelf optical fibres.

"This has the enormous advantage of being a simple, inexpensive procedure that works at any wavelength, notably at wavelengths used in telecommunications, " explains Thévenaz.

The telecommunications industry transmits vast quantities of data via fibre optics with light signals travelling at about 186,000 miles per second. But information cannot be processed at this speed, because with current technology light signals cannot be stored, routed or processed without first being transformed into electrical signals, which work much more slowly.

Thévenaz notes that, if the light signal could be controlled by light, it would be possible to route and process optical data without the costly electrical conversion, opening up the possibility of processing information at the speed of light.

The EPFL team’s stimulated Brillouin Scattering (SBS) method can slow a light signal down by a factor of 3.6, creating a sort of temporary 'optical memory'. The researchers were also able to create extreme conditions in which the light signal travelled faster than 300 million meters a second.

Slowing down light is considered to be a critical step in our ability to process information optically. The US Defense Advanced Research Projects Agency (DARPA) considers it so important that it has been funnelling millions of dollars into projects such as applications of slow light in optical fibres and research on all-optical routers. To succeed commercially, a device that slows down light must be able to work across a range of wavelengths, be capable of working at high bit-rates and be reasonably compact and inexpensive.