Anti-resonant acoustic waveguides enabled tailorable Brillouin scattering on chip

TL;DR

This paper introduces suspended anti-resonant acoustic waveguides (SARAWs) that enable low-loss, tailorable, and easily fabricated on-chip stimulated Brillouin scattering with record-breaking gain and frequency shifts.

Contribution

The paper presents a novel SARAW structure inspired by optical anti-resonance, supporting both forward and backward SBS with superior confinement and selectivity, simplifying design and fabrication.

Findings

Net gain exceeding 6.4 dB in forward SBS

Unprecedented Brillouin frequency shift of 27.6 GHz

Mechanical Q factor up to 1,960

Abstract

Empowering independent control of optical and acoustic modes and enhancing the photon-phonon interaction, integrated photonics boosts the advancements of on-chip stimulated Brillouin scattering (SBS). However, achieving acoustic waveguides with low loss, tailorability, and easy fabrication remains a challenge. Here, inspired by the optical anti-resonance in hollow-core fibers, we propose suspended anti-resonant acoustic waveguides (SARAWs) with superior confinement and high selectivity of acoustic modes, supporting both forward and backward SBS on chip. Furthermore, this structure streamlines the design and fabrication processes. Leveraging the advantages of SARAWs, we have showcased a series of record-breaking results for SBS within a compact footprint on the silicon-on-insulator platform. For forward SBS, a centimeter-scale SARAW supports a large net gain exceeding 6.4 dB. For backward SBS, we have observed an unprecedented Brillouin frequency shift of 27.6 GHz and a mechanical quality factor of up to 1,960 in silicon waveguides. This paradigm of acoustic waveguide propels SBS into a new era, unlocking new opportunities in the fields of optomechanics, phononic circuits, and hybrid quantum systems.