Stimulated optomechanical excitation of surface acoustic waves in a microdevice

TL;DR

This paper demonstrates the first experimental excitation of surface acoustic waves in silica microspheres using stimulated Brillouin scattering, expanding optomechanical control in microresonators for sensing and frequency references.

Contribution

It introduces a method to excite high-frequency surface acoustic waves in microresonators via forward Brillouin scattering, overcoming phase matching challenges.

Findings

Mechanical resonances from 49 to 1400 MHz were excited.

Surface-acoustic whispering-gallery modes were observed.

High-order transverse optical modes enabled phase matching.

Abstract

Stimulated Brillouin interaction between sound and light, known to be the strongest optical nonlinearity common to all amorphous and crystalline dielectrics, has been widely studied in fibers and bulk materials but rarely in optical microresonators. The possibility of experimentally extending this principle to excite mechanical resonances in photonic microsystems, for sensing and frequency reference applications, has remained largely unexplored. The challenge lies in the fact that microresonators inherently have large free spectral range, while the phase matching considerations for the Brillouin process require optical modes of nearby frequencies but with different wavevectors. We rely on high-order transverse optical modes to relax this limitation. Here we report on the experimental excitation of mechanical resonances ranging from 49 to 1400 MHz by using forward Brillouin scattering. These natural mechanical resonances are excited in ~100 um silica microspheres, and are of a surface-acoustic whispering-gallery type.