Interaction between light and highly confined hypersound in a silicon photonic nanowire

TL;DR

This paper demonstrates a strong interaction between near-infrared light and gigahertz hypersound in a silicon nanowire, enabling advanced optomechanical applications on integrated chips.

Contribution

First experimental demonstration of intense light-sound coupling in a silicon nanowire with potential for integrated optomechanics.

Findings

Achieved co-localization of light and hypersound in a silicon wire.

Trapped 10 GHz phonons in a sub-micrometer area.

Paves the way for integrated optomechanical devices like lasers and delay lines.

Abstract

In the past decade, there has been a surge in research at the boundary between photonics and phononics. Most efforts centered on coupling light to motion in a high-quality optical cavity, typically geared towards observing the quantum state of a mechanical oscillator. It was recently predicted that the strength of the light-sound interaction would increase drastically in nanoscale silicon photonic wires. Here we demonstrate, for the first time, such a giant overlap between near-infrared light and gigahertz sound co-localized in a small-core silicon wire. The wire is supported by a tiny pillar to block the path for external phonon leakage, trapping $\mathbf{10} \; \textbf{GHz}$ phonons in an area below $\mathbf{0.1 \; \boldsymbol\mu}\textbf{m}^{\mathbf{2}}$. Since our geometry can be coiled up to form a ring cavity, it paves the way for complete fusion between the worlds of cavity optomechanics and Brillouin scattering. The result bodes well for the realization of low-footprint optically-pumped lasers/sasers and delay lines on a densely integrated silicon chip.