Silicon light switch is electric

June 29/July 6, 2005

One way to make computer chips faster is to replace the metal connections between circuits with optical links.

Researchers from Cornell University have made a relatively small silicon device that uses an electric field to switch a light beam on and off. The device could eventually be used to speed data interchange between chips or among different parts of chips, resulting in faster computer chips.

The researchers' electro-optic modulator is a ring 12-micron-diameter that traps light, and a nearby light channel. An electrical signal changes the way the light in the ring interacts with the light in the channel, effectively turning it on or off. A micron is one thousandth of a millimeter.

When the circumference of the ring is a whole number times the wavelength of the light -- in this case 24 times -- the light resonates in the ring and is blocked from passing through the waveguide. An electric field, however, can change the ring's refractive index, making the wavelengths no longer resonate. This allows the light to flow through the waveguide, turning the switch on. The refractive index indicates the angle that light bends at the border of a material; this phenomenon is responsible for the illusion that a straw bends at a liquid surface.

The researchers tested the electro-optic modulator with 1.5-gigabit-per-second electronic signals. This is close to half the speed of today's fastest desktop computer chips. It should be possible to increase signal rates to more than 5 gigabits per second, according to the researchers.

The researchers' next step is to make the device able to withstand the rigors of practical use, including variations in temperature.

The device could be ready for practical use in five to ten years, according to the researchers. The work appeared in the May 19, 2005 issue of Nature (Micrometer-Scale Silicon Electro-Optic Modulator).

Page One

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