Photon–phonon spin–orbit interaction in optical fibers

Abstract

Spin–orbit interaction (SOI) is a striking physical phenomenon in which spin and orbital features of a particle or a wave field affect each other. Recently, there has been significant interest in the SOI of light as it accompanies a number of fundamental light–matter interaction processes, enabling intriguing applications. We demonstrate the spin-orbit coupling between photons and phonons, in contrast to recently reported studies dealing with a “single-field” SOI. We show that the spin angular momentum of phonons can be transformed into the orbital angular momentum of photons, and vice versa, during the fiber acousto-optic interaction. This results in the acoustic-spin-dependent, dynamically tunable generation of topologically charged optical vortex beams directly from a Gauss-like mode. This type of optical mode conversion can be useful in such vortex-based photonics applications as micromechanics, classical and quantum information technologies, and simulation of quantum computing. This particular example of a “two-field SOI” shows that the concept of spin-orbit coupling can be generalized to describe the interaction between elementary excitations of different physical nature. Our findings indicate that SOI-assisted effects might be found in physical systems with photon–phonon, magnon–phonon, electron–phonon, and other interactions, enabling tailored topologically charged multiparticle states in photonics, spintronics, plasmonics, etc.