Interaction between light and sound demonstrated on silicon core

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Belgian scientists from Ghent University and nanoelectronics research institute, Imec, have demonstrated the interaction between light and sound in a nanoscale waveguide. Their research, published in Nature Photonics, reveals the physics of light-matter coupling at the nanoscale level, and paves the way for enhanced signal processing on mass-producible silicon photonic chips.

In the last decade, the field of silicon photonics has gained increasing attention as a driver of lab-on-a-chip biosensors and of faster-than-electronics communication between computer chips. The technology builds on nanoscale structures known as silicon photonic wires, which are roughly a hundred times narrower than a typical human hair.

These nanowires carry optical signals from one point to another at the speed of light, and are produced using the same technology to fabricate electronic circuitry. The wires work only because light moves slower in the silicon core than in the surrounding air and glass; therefore the light is trapped inside the wire by the phenomenon of total internal reflection.

The researchers from the Photonics Research Group of Ghent University and Imec have demonstrated a peculiar type of light-matter interaction, managing to confine not only light but also sound to the silicon nanowires. The sound oscillates ten billion times per second, far more rapid than human ears can hear.

Unlike light, sound moves faster in the silicon core than in the surrounding air and glass. Thus, the scientists sculpted the environment of the core to make sure any vibrational wave trying to escape it would actually bounce back. Doing so, they confined both light and sound to the same nanoscale waveguide core.

Trapped in such a small area, the light and vibrations strongly influence each other: light generates sound, and sound shifts the colour of light − a process known as stimulated Brillouin scattering. By exploiting this interaction, the researchers managed to amplify specific colours of light.

It is anticipated that this demonstration could open up new ways to manipulate optical information. For instance, light pulses could be converted into sonic pulses and back into light – thereby implementing much-needed delay lines. Further, the researchers expect that similar techniques can be applied to even smaller entities such as viruses and DNA, as these particles have unique acoustic vibrations that may be used to probe their global structure.

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Further information

Paper in Nature Photonics