Silicon chip puts the brakes on light
Nov 3, 2005
Scientists at IBM have built a silicon chip that uses the combination of built-in miniature heaters and photonic crystal technology to control the speed of light pulses. The silicon waveguide circuit operates at a wavelength of 1.5 microns, which is widely used for telecommunications, and can reduce the "group velocity" of light by a factor of up to 300 (Nature 438 65).
Over the past decade, physicists have used exotic media such as ultracold atomic gases and various crystals to make "slow" or "fast" light. Some groups have managed to stop and store light, while others have demonstrated group velocities greater than the speed of light in vacuum. However, if the speed of light could be controlled with a silicon chip, it might be possible to include such devices in conventional microelectronic circuits.
Yurii Vlasov and colleagues at the IBM T J Watson Research Center in New York have now taken a step in this direction by using a photonic crystal waveguide made of silicon to produce slow light. The waveguide, which is 250 microns long, is etched with a pattern of tiny holes, each 109 nanometres wide, that give the silicon a very high refractive index. An electrical contact acts as a miniature heater.
When a current flows through the heater, it heats up the waveguide, which changes the refractive index and therefore the speed of light in the structure. Applying just 2 milliwatts of electrical power can change the group velocity by a factor of three within 100 nanoseconds.
The IBM work follows a spate of recent work on manipulating the speed of light with optical fibres and various semiconductor structures.