Researchers at IBM Corp. have fabricated the world's first optical chip to electrically control the speed of light. Director of physical sciences at the T.J. Watson Research Center (Yorktown Heights, N.Y.) Thomas Theis (pictured above) describes IBM's demonstration of an optical silicon chip that can electrically alter the effective index of refraction of an integrated photonic-crystal waveguide. The experimental component could one day enable tunable optical delay-line chips, optical buffers, high-extinction optical switches and highly efficient wavelength converters, IBM said. Together with other optical components, such devices could also eliminate the telecommunications industry's reliance on bulky and costly optical-to-electrical and electrical-to-optical converters. The optical chip can variably slow light by a factor of 300x, under active control by a low-power (under 2-milliwatt), fast-changing (less than 100-nanosecond) electrical signal. It was constructed using normal silicon-on-insulator CMOS fabrication techniques, the team said. The active element is a 250-micron-long photonic-crystal waveguide formed with a nanoscale version of micromachining that perforated a 223-nm-thick membrane with holes 109 nm in diameter, spaced at a 437-nm pitch. As a result, the waveguide slows light passing through it in a 20-nm bandwidth at the communications wavelength of 1,620 nanometers.