Hybrid Piezo-Optomechanics with Brillouin Scattering in Bulk Crystals*

The Brillouin effect is a three-wave mixing process mediating phonons and photons in virtually all media.  At cryogenic temperatures, long-lived phonons and high-finesse optical cavities enable strongly coupled Brillouin optomechanical systems.

Here, we further incorporate resonantly-enhanced piezoelectric coupling to demonstrate the first Brillouin-based electro-optomechanical system, enabling new opportunities for spectroscopy and transduction.  The system is built on 3D cavities with modular construction, enabling the exploration of virtually any piezoelectric material without the need for fabrication.

We demonstrate that the hybrid system is able to reach large optical cooperativities, enabling optical detection of microwave-driven motion at the few-phonon level.  This opens the door to materials studies, as we demonstrate with detection of parasitic piezoelectric coupling in CaF2.  This large cooperativity also partially fulfills the requirements of an efficient microwave-to-optical transducer.  We analyze our system in this context, demonstrating piezo-optomechanical transduction efficiency comparable to existing platforms, and illustrating a realistic path toward unity conversion.