First Light-Driven Nanomachine

A silicon nanobeam uses optical force to do mechanical work in an integrated circuit.

Since the 1980s, researchers have used lasers to stop molecular vibrations, so that the molecules can be observed in their natural environment. Now researchers at Yale University have used the same kind of nanoscale optical force to control an integrated circuit. Their device could form the basis of fast, low-power optical chips, just as transistors are the building blocks of today's electronic circuits. The new device, a light-driven nanoresonator, could also be used as an extremely sensitive chemical detector. The work is a major landmark in uniting mechanical and optical forces at the nanoscale.

Photon power: This photonic circuit includes a new light-driven nanomechanical resonator. Pictured in the inset scanning-electron-microscope image, this nanoscale silicon beam oscillates when laser light shines on it, modulating the light signal carried through the circuit. Credit: Hong Tang/Yale University

Chips that use light instead of electrons to carry data should be faster and consume less power than traditional integrated circuits. But so far even the fastest optical chips have incorporated electrical elements called modulators. These modulators encode light with data by converting the signal from light into electrons and back again. This extra step makes optical chips complex and drains power. A circuit developed by Yale researchers led by electrical-engineering professor Hong Tang incorporates a modulator that's driven by light, not electrons.

The Yale group began its work by creating a silicon optical chip. To make the modulator, they etched a small portion of the waveguide, the thin silicon road along which the photons travel, into a 500-nanometer-wide bar. This silicon beam, which is suspended from the chip's surface so that it can flex, has two functions. It both carries the optical signal and modulates it. Tang and his colleagues sent a light signal through the integrated circuit, then shone laser light onto the nano-optical modulator, causing it to oscillate up and down. These oscillations modulate the speed of the light traveling through the beam.

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The Yale team is the first to demonstrate the existence of this optical force on an integrated circuit--and the first to exploit it to make a working device. "The light force can be put to real use," says Tang. His group has also demonstrated that it can make arrays of hundreds of working resonators on a single chip.

Optical tweezers have been very useful for manipulating free-floating nanoscale objects in solution, but they're very complex, requiring a high-power laser and an entire benchtop. Although it still requires input from a laser that isn't yet integrated on the chip, the Yale setup is simpler than that required for optical tweezers.