Anti-resonant reflecting acoustic rib waveguides for strong opto-acoustic interaction

TL;DR

This paper introduces Anti-Resonant Reflecting Acoustic Waveguides (ARRAWs), a novel approach to confine elastic and optical fields in standard waveguides, enabling strong opto-acoustic interactions like Stimulated Brillouin Scattering.

Contribution

It proposes and numerically demonstrates ARRAWs as a new method to achieve strong opto-acoustic coupling in conventional silicon waveguides.

Findings

ARRAWs can confine elastic fields via anti-resonance in standard waveguides.

ARRAWs enable Brillouin gains comparable to exotic geometries.

Numerical analysis shows effective mode dispersion in silicon-on-insulator waveguides.

Abstract

Few known material systems can simultaneously guide optical and elastic fields through total internal reflection. This natural limit has restricted the realization of strong optoacoustic effects to highly-specialised and purpose-built platforms which employ either exotic materials, or complex waveguide designs. Here we apply the concept of Anti-Resonant Reflecting Acoustic Waveguides (ARRAWs) as a potential solution to this issue. ARRAWs confine the elastic field to a high-elastic-velocity core via the anti-resonances of a cladding layer of lower elastic velocity. We numerically study the appearance and dispersion of ARRAW-guided modes in a conventional silicon-on-insulator rib waveguide geometry. Applying the technique to the problem of efficient backwards Stimulated Brillouin Scattering (SBS), we predict that ARRAW guidance, in conjunction with conventional optical confinement, can produce Brillouin gains comparable to those of more exotic geometries.