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Light can carry information at blazing speed, but processing that information in an optical network may require the light to hold still for a moment. Approaching that goal, a team writing in Physical Review Letters proposes a method they say could decelerate light pulses down to 20 meters per second in a practical nanoscale structure. This “stopped light” would occur inside a waveguide made of a long strip of silicon sandwiched between layers of another material. The pulse would die away after a short time, but it could potentially last long enough for uses such as fast optical switches, nanolasers, or highly efficient solar cells.

The first successful stopping of light occurred in a gas in which researchers used electromagnetically induced transparency, or EIT, a process where the light propagation through a material is influenced by a second light beam. Although EIT methods can slow light to zero velocity, they do so only in a very narrow range of frequencies. And the stopped light is not actually light—it gets transformed into spin states of the material’s electrons (see 15 July 2013 Viewpoint). “For many photonic applications we would like to retain the photons even at the zero-velocity point,” says Kosmas Tsakmakidis of the University of California, Berkeley. Researchers are developing other slow light methods that retain photons and that use small, practical devices, but most of them have only slowed light’s velocity by about 100 times.

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