Spin-orbit-coupled fluids of light in bulk nonlinear media

Abstract

We show that nonparaxial polarized light beams propagating in a bulk nonlinear Kerr medium naturally exhibit a coupling between the motional and the polarization degrees of freedom, realizing a spin-orbit-coupled mixture of fluids of light. We investigate the impact of this mechanism on the Bogoliubov modes of the fluid, using a suitable density-phase formalism built upon a linearization of the exact Helmholtz equation. The Bogoliubov spectrum is found to be anisotropic, and features both low-frequency gapless branches and high-frequency gapped ones. We compute the amplitudes of these modes and propose a couple of experimental protocols to study their excitation mechanisms. This allows us to highlight a phenomenon of hybridization between density and spin modes, which is absent in the paraxial description and represents a typical fingerprint of spin-orbit coupling.