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Nano Antenna

Gold nanospheres show a path to all-optical computing.

Vast amounts of data zip across the Internet each day in the form of light waves conveyed by optical fibers. But our computers still rely on electrical signals traveling through metal wires, which have much lower bandwidth.

Optical interconnects that could guide light through the labyrinth of a circuit board would increase computing speed and save power, but so far they haven’t made it out of the lab.

New research, however, may enable engineers to build nanoscale antennae that turn light into a different sort of wave that can move through metal; the result could be data transmission speeds that are orders of magnitude higher than today’s.

The key to the approach is a gold sphere just 50 nanometers in diameter. A Rice University team led by Peter Nordlander and Naomi Halas has shown that such a sphere, when positioned within a few nanometers of a thin gold film, will behave like a tiny antenna that can transmit or receive light. Light of specific wavelengths excites particles called plasmons inside the nanosphere. This in turn induces a “plasmon wave” in the gold film, which could be converted back into light when it reaches another nanosphere.

Variations on the gold nanosphere might make it possible to exploit materials already used in computer chips, such as copper and aluminum, as superfast optical interconnects, says Mark Brongersma, a materials scientist at Stanford University. A light wave encoding data would hit a metal nanosphere, generating a plasmon wave that would travel through a metal strip or wire, carrying the data with it.

A huge benefit of the approach, Brongersma says, is how much easier the spheres are to make than other specialized antennae whose manufacture requires complex and expensive optical-lithography techniques. “The beautiful thing is you can make them in large quantities,” Brongersma says.

The Rice team’s next step: using hollow gold “nanoshells” rather than solid spheres to expand the range of wavelengths of light they can use. And to further examine the practicality of using the systems as optical interconnects in computer chips, they have begun a series of experiments with nanoparticles and thin wires rather than thin films.

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