Surface acoustic wave Brillouin scattering in a photonic integrated circuit

Surface acoustic wave (SAW) devices are ubiquitously used for signal processing and filtering, as well as mechanical, chemical and biological sensing, and show promise as quantum transducers. Yet, ways to coherently excite and detect SAWs all-optically and interfaced with photonic integrated circuits are yet elusive. Here, we experimentally show, for the first time, optically excited and detected SAWs in a photonic integrated circuit. Coupling between the surface acoustic and optical wave is achieved via stimulated Brillouin scattering in GeAsSe glass waveguides tailored to show strong overlap between SAWs at 3.81GHz and guided optical modes, without requiring a top cladding. We measure a 225W^-1m^-1 gain coefficient for the SAW and 40MHz linewidth. Experimentally accessing this new regime of stimulated Brillouin scattering opens the door for novel on-chip sensing and signal processing applications, strong Brillouin interactions in materials without acoustic guidance in the waveguide core, and excitation of SAWs in non-piezoelectric materials.