Topological spin transport of photons: "magnetic monopole" gauge field in Maxwell equations and polarization splitting of rays in periodically inhomogeneous media

TL;DR

This paper explores the topological spin transport of photons in inhomogeneous media, revealing how magnetic monopole-like gauge fields influence ray trajectories and polarization splitting, with implications for optical physics.

Contribution

It introduces a gauge-theoretic framework for photon spin transport in inhomogeneous media, deriving new semiclassical ray equations that incorporate magnetic monopole effects.

Findings

Rays experience topological deflections and splitting due to gauge fields.

The derived equations predict polarization-dependent ray trajectories.

Inhomogeneity parameters influence the magnitude of ray deflections.

Abstract

Topological spin transport of electromagnetic waves (photons) in stationary smoothly inhomogeneous isotropic medium is studied. By diagonalizing photon kinetic energy in Maxwell equations we derive the non-Abelian pure gauge potential in the momentum space, which in adiabatic approximation for transverse waves takes the form of two Abelian U(1) potentials corresponding to magnetic monopole-type fields. These fields act on circularly polarized waves resulting in the topological spin transport of photons. We deduce general semiclassical (geometrical optics) ray equations that take into account a Lorentz-type force of the magnetic-monopole-like gauge field. Detailed analysis of rays in 3D medium with 2D periodic inhomogeneity is presented. It is shown that rays located initially in the inhomogeneity plane experience topological deflections or splitting that move them out from this plane. The dependence of the rays' deflection on the parameters of the medium and on the direction of propagation is studied.