Stimulated brillouin scattering in nanoscale silicon step-index waveguides: A general framework of selection rules and calculating SBS gain

TL;DR

This paper presents a comprehensive framework for calculating Stimulated Brillouin Scattering (SBS) gain in nanoscale silicon waveguides, emphasizing the role of symmetry and mode coupling in determining SBS efficiency.

Contribution

It introduces a general method based on overlap integrals and symmetry considerations to evaluate SBS gain, applicable to various waveguide geometries and inter-modal processes.

Findings

Spatial symmetry governs elastic mode excitation.

Optical force distribution influences SBS gain magnitude.

Inter-modal coupling enables excitation of all elastic mode symmetries.

Abstract

We develop a general framework of evaluating the gain coefficient of Stimulated Brillouin Scattering (SBS) in optical waveguides via the overlap integral between optical and elastic eigen-modes. We show that spatial symmetry of the optical force dictates the selection rules of the excitable elastic modes. By applying this method to a rectangular silicon waveguide, we demonstrate the spatial distributions of optical force and elastic eigen-modes jointly determine the magnitude and scaling of SBS gain coefficient in both forward and backward SBS processes. We further apply this method to inter-modal SBS process, and demonstrate that the coupling between distinct optical modes are necessary to excite elastic modes with all possible symmetries.