On-Chip Stimulated Brillouin Scattering via Surface Acoustic Waves

TL;DR

This paper demonstrates the first on-chip surface acoustic wave stimulated Brillouin scattering (SAW-SBS) in a photonic waveguide, enabling new integrated sensing and signal processing applications through tailored waveguide design and experimental validation.

Contribution

It introduces the first experimental realization of surface acoustic wave SBS on a chip, using tailored GeAsSe waveguides to achieve strong optical-acoustic interactions without piezoelectric materials.

Findings

Achieved a Brillouin gain coefficient of 225 W$^{-1}$m$^{-1}$.

Demonstrated linewidth narrowing to 40 MHz.

Validated surface acoustic wave excitation in non-piezoelectric materials.

Abstract

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. However, nowadays most SAWs are excited and driven via electromechanical coupling and interdigital transducers (IDTs), limiting operation bandwidth and flexibility. Novel ways to coherently excite and detect SAWs all-optically interfaced with photonic integrated circuits are yet elusive. Backward Stimulated Brillouin scattering (SBS) provides strong coherent interactions between optical and acoustic waves in chip-scale waveguides, however, demonstrations have been limited to single longitudinal waves in the waveguide core. Here, we numerically model and experimentally demonstrate surface acoustic wave stimulated Brillouin scattering (SAW-SBS) on a photonic chip. We designed and fabricated tailored waveguides made out of GeAsSe glass that show good overlap between SAWs at 3.81 GHz and guided optical modes, without requiring a top cladding. We measure a 225 W$^{-1}$m$^{-1}$ Brillouin gain coefficient of the surface acoustic resonance and linewidth narrowing to 40 MHz. 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 that do not provide sufficient acoustic guidance in the waveguide core as well as excitation of surface acoustic waves in non-piezoelectric materials.