Spin-orbit interaction in nanofiber-based Brillouin scattering

TL;DR

This paper explores the spin-orbit interaction in nanofiber-based Brillouin scattering, demonstrating how circularly polarized light interacts with vortex acoustic waves, leading to polarization changes governed by angular momentum conservation.

Contribution

It provides a combined theoretical and experimental analysis of spin-orbit interactions in nanofiber Brillouin scattering, highlighting polarization regimes and angular momentum effects.

Findings

Backscattered Brillouin signal can be depolarized or circularly polarized.

Circularly polarized pump causes handedness reversal in backscattered light.

Conservation of angular momentum governs the polarization behavior.

Abstract

Angular momentum is an important physical property that plays a key role in light-matter interactions such as spin-orbit interaction. Here, we investigate theoretically and experimentally the spin-orbit interaction between a circularly polarized optical (spin) and a transverse vortex acoustic wave (orbital) using Brillouin backscattering in a silica optical nanofiber. We specifically explore the state of polarization of Brillouin backscattering induced by the TR21 torso-radial vortex acoustic mode that carries an orbital angular momentum. Using a full-vectorial theoretical model, we predict and observe two operating regimes for which the backscattered Brillouin signal is either depolarized or circularly polarized depending on the input pump polarization. We demonstrate that when the pump is circularly polarized and thus carries a spin angular momentum, the backscattered signal undergoes a handedness reversal of circular polarization due to optoacoustic spin-orbit interaction and the conservation of overall angular momentum.