Taming Brillouin Optomechanics Using Supermode Microresonators

Abstract

Electrostrictive Brillouin scattering provides a ubiquitous mechanism to optically excite high-frequency (>10 GHz), bulk acoustic phonons that are robust to surface-induced losses. Resonantly enhancing such photon-phonon interactions in high-Q microresonators has spawned diverse applications spanning microwave to optical domains. However, tuning both the pump and scattered waves into resonance usually comes with the cost of photon confinement or modal overlap, leading to limited optomechanical coupling. Here, we introduce Bragg scattering to realize strong bulk optomechanical coupling in the same spatial modes of a micron-sized supermode microresonator. A single-photon optomechanical coupling rate up to 12.5 kHz is demonstrated, showing more than 10 times improvement than other devices. Low-threshold phonon lasing and optomechanical strong coupling are also observed for the 10.2-GHz mechanical mode. Our work establishes a compact and efficient paradigm to optically control bulk acoustic phonons, paving the way toward optomechanical coupling at the single-photon level and providing a powerful engine for large-scale integration of quantum networks in which quantum states are massively transferred and stored.