Manipulating the Speed of Light

Photo: A long cable that consists of optical fibre

This is not the first time that scientists have tweaked the speed of a light signal. They 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.

The telecommunications industry transmits vast quantities of data via fiber optics. Light signals race down the information superhighway 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. If the light signal could be controlled by light, it would be possible to route and process optical data without the costly electrical conversion.

This is exactly what Luc Thévenaz and his fellow researchers in the Nanophotonics and Metrology laboratory at École Polytechnique Fédérale de Lausanne (EPFL) have demonstrated. Using their Stimulated Brillouin Scattering (SBS) method, the group was able to slow a light signal down by a factor of 3.6, creating a sort of temporary “optical memory.” They were also able to create extreme conditions in which the light signal travelled faster than 300 million meters a second. And even though this seems to violate all sorts of physical assumptions, Einstein needn’t move over – relativity isn’t called into question, because only a portion of the signal is affected.

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

COMPAMED.de; Source: École Polytechnique Fédérale de Lausanne (EPFL)