On-chip stimulated Brillouin scattering via surface acoustic waves

Surface acoustic wave devices are ubiquitously used for signal processing and filtering, as well as mechanical, chemical, and biological sensing and show promise as quantum transducers. While surface acoustic waves (SAWs) are primarily excited and driven using electromechanical coupling and interdigital transducers, there is a strong desire for novel methods that enable the coherent excitation and detection of SAWs all-optically interfacing with photonic integrated circuits. In this work, we numerically model and experimentally demonstrate SAW excitation in integrated photonic waveguides made from GeAsSe glass via backward stimulated Brillouin scattering (SBS). We measure a Brillouin gain coefficient of 203 W−1 m−1 for the surface acoustic resonance at 3.81 GHz, with a linewidth narrowed to 20 MHz. Experimental access to this new regime of SBS not only opens up opportunities for novel on-chip sensing applications by harnessing the waveguide surface but also paves the way for strong Brillouin interactions in materials lacking sufficient acoustic guidance in the waveguide core, as well as the excitation of SAWs in non-piezoelectric materials.