Light faster than light
A team of researchers from the Ecole Polytechnique Federale de Lausanne (EPFL) has successfully demonstrated, for the first time, that it is possible to control the speed of light - both slowing it down and speeding it up - in an optical fiber, using off-the-shelf instrumentation in normal environmental conditions. Their results, to be published in the August 22 issue of Applied Physics Letters, could have implications that range from optical computing to the fiber-optic telecommunications industry.
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 cherished physical assumptions, Einstein needn’t move over - relativity isn’t called into question, because only a portion of the signal is affected.
Abstract: We demonstrate a method to achieve an extremely wide and flexible external control of the group velocity of signals as they propagate along an optical fiber. This control is achieved by means of the gain and loss mechanisms of stimulated Brillouin scattering in the fiber itself. Our experiments show that group velocities below 71 000 km/s on one hand, well exceeding the speed of light in vacuum on the other hand and even negative group velocities can readily be obtained with a simple benchtop experimental setup. We believe that the fact that slow and fast light can be achieved in a standard single-mode fiber, in normal environmental conditions and using off-the-shelf instrumentation, is very promising for a future use in real applications.
Light that travels… faster than light! ScienceBlog.com
Optically controlled slow and fast light in optical fibers using SBS, Miguel Gonzalez-Herraez, Kwang-Yong Song, and Luc Thevenaz