November 4, 2005, Yorktown Heights, NY--Using a silicon photonic-crystal waveguide, IBM researchers have slowed light down to less than 1/300th of its usual speed. In addition, the speed of light within the device can be varied over a wide range by varying an electrical voltage applied to the waveguide. These achievements may both greatly benefit the nascent field of silicon photonics, potentially leading to large improvements in the performance of computers and other electronic systems.
Researchers have known for some years how to slow light to a crawl under laboratory conditions (see Laser Focus World, April 1999, p. 16), but actively controlling the light speed on a silicon chip, using standard silicon with standard micro- and nanoelectronic fabrication technology, is a first. The device's small size, use of standard semiconductor materials, and ability to more closely control this "slow light" could make the technology useful for building ultracompact optical-communications circuits that are practical for integration into computer systems.
Scientists have searched for practical ways to use light to speed communication between the components within a computer. But, to be practical, the components to support such an optical network will need to provide excellent control over the light signal, while also being very small and inexpensive to manufacture. The IBM work addresses several pieces of this puzzle.
Heating the IBM photonic-crystal waveguide locally with a small electrical current alters the refractive index, allowing the speed of light to be quickly tuned over a large range with very low applied electric power.
The active area of the IBM device is microscopically small, pointing to the possibility of complex light-based circuits with footprints not much larger than semiconductor circuits. The manufacturing processes used to build the device are available in nearly any semiconductor factory. The capabilities could be applied to create a variety of nanophotonic components such as optical-delay lines, optical buffers, and even optical memory, all of which would be useful in building computer systems knitted together by powerful optical communications networks.
The report on this work, "Active control of slow light on a chip with photonic crystal waveguides" by Yurii Vlasov, Martin O'Boyle, Hendrik Hamann, and Sharee McNab of IBM's T. J. Watson Research Center in Yorktown Heights, N.Y. is published in the November 3 issue of Nature. This work was partially supported by the Defense advanced Research Agency (DARPA) through the Defense Sciences Office program "Slowing, Storing and Processing Light."