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
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).
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