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Science Blog Light A team of researchers from the Ecole Polytechnique Fdrale de Laus anne (EPFL) has successfully demonstrated, for the first time, that it i s possible to control the speed of light both slowing it down and speedi ng it up in an optical fiber, using off-the-shelf instrumentation in nor mal environmental conditions. Their results, to be published in the Augu st 22 issue of Applied Physics Letters, could have implications that ran ge from optical computing to the fiber-optic telecommunications industry . On the screen, a small pulse shifts back and forth just a little bit. But this seemingly unremarkable phenomenon could have profound technologica l consequences. It represents the success of Luc Thvenaz and his fellow researchers in the Nanophotonics and Metrology laboratory at EPFL in co ntrolling the speed of light in a simple optical fiber. They were able n ot only to slow light down by a factor of three from its well establishe d speed c of 300 million meters per second in a vacuum, but they've also accomplished the considerable feat of speeding it up making light go fa ster than the speed of light. This is not the first time that scientists have tweaked the speed of a li ght 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 condi tions, scientists have been able to slow light down to the speed of a bi cycle, 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 new method, the EPFL team, made up of Luc Thvenaz, Miguel Gonzalz Herraez and Kwang-Y ong Song, has raised the bar higher still. Their all-optical technique t o slow light works in off-the-shelf optical fibers, without requiring co stly experimental set-ups or special media. They can easily tune the spe ed of the light signal, thus achieving a wide range of delays. "This has the enormous advantage of being a simple, inexpensive procedure that works at any wavelength, notably at wavelengths used in telecommun ications," explains Thvenaz. The telecommunications industry transmits vast quantities of data via fib er optics. Light signals race down the information superhighway at about 186,000 miles per second. But information cannot be processed at this s peed, because with current technology light signals cannot be stored, ro uted or processed without first being transformed into electrical signal s, 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, opening up the possibility of process ing information at the speed of light. Using their Stimulat ed Brillouin Scattering (SBS) method, the group was able to slow a light signal down by a factor of 36, creating a sort of temporary "optical m emory." They were also able to create extreme conditions in which the li ght signal travelled faster than 300 million meters a second. And even t hough this seems to violate all sorts of cherished physical assumptions, Einstein needn't move over relativity isn't called into question, becau se only a portion of the signal is affected. 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 mi llions of dollars into projects such as "Applications of Slow Light in O ptical Fibers" and research on all-optical routers. To succeed commercia lly, 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 reasonabl y compact and inexpensive. The EPFL team has brought applications of slow light an important step cl oser to this reality. And Thvenaz points out that this technology could take us far beyond just improving on current telecom applications. He s uggests that their method could be used to generate high-performance mic rowave signals that could be used in next-generation wireless communicat ion networks, or used to improve transmissions between satellites.
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