Thermal Brillouin noise observed in silicon optomechanical waveguide

TL;DR

This paper reports the first observation of thermally-driven photon-phonon conversion in silicon waveguides, revealing thermal Brillouin noise and mechanical resonances around 8 GHz, advancing understanding of thermal noise in nanoscale optomechanical systems.

Contribution

It demonstrates thermal Brillouin noise in silicon waveguides and provides a theoretical and experimental framework for understanding thermal noise in nanoscale optomechanical devices.

Findings

Mechanical resonances around 8 GHz observed

Scattering efficiency of 10^{-5} m^{-1} measured

Signal-to-noise ratio of 2 achieved

Abstract

Stimulated Brillouin scattering was recently observed in nanoscale silicon waveguides. Surprisingly, thermally-driven photon-phonon conversion in these structures had not yet been reported. Here, we inject an optical probe in a suspended silicon waveguide and measure its phase fluctuations at the output. We observe mechanical resonances around 8 GHz with a scattering efficiency of $10^{-5} \, \text{m}^{-1}$ and a signal-to-noise ratio of 2. The observations are in agreement with a theory of noise in these waveguides as well as with stimulated measurements. Our scheme may simplify measurements of mechanical signatures in nanoscale waveguides and is a step towards a better grasp of thermal noise in these new continuum optomechanical systems.