In an experiment at the Ecole Polytechnique Federale de Lausanne, researchers have been able to speed up or slow down light transmitted through an optical fiber with precise control. This capability could have application in telecommunications, optical switching and optical computing. The experiment, which uses stimulated Brillouin scattering, verifies a prediction of Arnold Sommerfeld and Leon Brillouin, who early in the 20th century theorized that narrowband amplification at a sharp spectral transition could enable the speed of light to become variable. "We are reporting the first demonstration of a wide optical control of the signal velocity in an optical fiber," said Luc Thevenaz, who leads the group. "The starting and ending points of a pulse carry the information and those still propagate at the normal velocity, but the peak of those same pulses propagates at a variable group velocity that can exceed c [the speed of light in a vacuum]. This is what we experimentally demonstrated and observed." Thevenaz performed the work with EEs Miguel Gonzalez-Herraez at the University of Alcala (Madrid, Spain) and Kwang-Yong Song at the University of Tokyo (Japan).