Nonreciprocal Transverse Photonic Spin and Magnetization-Induced Electromagnetic Spin-Orbit Coupling

TL;DR

This paper investigates nonreciprocal transverse spin effects and magnetization-induced spin-orbit coupling in magneto-optic waveguides, revealing thickness-dependent transverse spin shifts and magnetic tunability, and proposing a new physical interpretation of magneto-optic gyrotropy.

Contribution

It introduces a novel physical picture of magneto-optic gyrotropy as a nonreciprocal spin-density shift and formulates electromagnetic spin-orbit coupling in magneto-optic media.

Findings

Transverse spin-density shift depends on waveguide thickness.

Magnetization can tune the transverse spin in waveguides.

Magnetization-induced spin-orbit coupling enables spin to orbital angular momentum conversion.

Abstract

A study of nonreciprocal transverse-spin angular-momentum-density shifts for evanescent waves in magneto-optic waveguide media is presented. Their functional relation to electromagnetic spin- and orbital-momenta is presented and analyzed. It is shown that the magneto-optic gyrotropy can be re-interpreted as the nonreciprocal electromagnetic spin-density shift per unit energy flux, thus providing an interesting alternative physical picture for the magneto-optic gyrotropy. The transverse spin-density shift is found to be thickness-dependent in slab optical waveguides. This dependence is traceable to the admixture of minority helicity components in the transverse spin angular momentum. It is also shown that the transverse spin is magnetically tunable. A formulation of electromagnetic spin-orbit coupling in magneto-optic media is presented, and an alternative source of spin-orbit coupling to non-paraxial optics vortices is proposed. It is shown that magnetization-induced electromagnetic spin-orbit coupling is possible, and that it leads to spin to orbital angular momentum conversion in magneto-optic media evanescent waves.