Acoustic confinement and Stimulated Brillouin Scattering in integrated optical waveguides

TL;DR

This paper investigates how acoustic mode confinement affects Stimulated Brillouin Scattering (SBS) in integrated optical waveguides, revealing three regimes of SBS arising from different acoustic mode behaviors and their dependence on waveguide properties.

Contribution

It provides a comprehensive analysis of acoustic confinement effects on SBS in integrated waveguides, identifying three distinct regimes and their dependence on material and geometric parameters.

Findings

SBS can occur via guided, leaky, or free acoustic modes.

Acoustic confinement influences SBS gain through mode confinement and lifetime.

Different material systems enable various SBS regimes.

Abstract

We examine the effect of acoustic mode confinement on Stimulated Brillouin Scattering in optical waveguides that consist of a guiding core embedded in a solid substrate. We find that SBS can arise due to coupling to acoustic modes in three different regimes. First, the acoustic modes may be guided by total internal reflection; in this case the SBS gain depends directly on the degree of confinement of the acoustic mode in the core, which is in turn determined by the acoustic V-parameter. Second, the acoustic modes may be leaky, but may nevertheless have a sufficiently long lifetime to have a large effect on the SBS gain; the lifetime of acoustic modes in this regime depends not only on the contrast in acoustic properties between the core and the cladding, but is also highly dependent on the waveguide dimensions. Finally SBS may occur due to coupling to free modes, which exist even in the absence of acoustic confinement; we find that the cumulative effect of coupling to these non-confined modes results in significant SBS gain. We show how the different acoustic properties of core and cladding lead to these different regimes, and discuss the feasibility of SBS experiments using different material systems.