Arbitrary spin-to–orbital angular momentum conversion of light

TLDR

SAM‑to‑OAM converters based on geometric phase transform left‑ and right‑circular polarizations into vortex beams with opposite orbital angular momentum, and have been employed in classical and quantum optics. The study proposes a method to convert arbitrary spin angular momentum states into total angular momentum states comprising a superposition of independent orbital angular momentum modes. The authors designed a metasurface that maps left‑ and right‑circular polarizations to independent OAM values, and a second device that extends this conversion to elliptically polarized states. The results demonstrate a general material‑mediated link between spin and orbital angular momentum, enabling the generation of complex structured light and potential use in optical communication.

Abstract

Optical elements that convert the spin angular momentum (SAM) of light into vortex beams have found applications in classical and quantum optics. These elements-SAM-to-orbital angular momentum (OAM) converters-are based on the geometric phase and only permit the conversion of left- and right-circular polarizations (spin states) into states with opposite OAM. We present a method for converting arbitrary SAM states into total angular momentum states characterized by a superposition of independent OAM. We designed a metasurface that converts left- and right-circular polarizations into states with independent values of OAM and designed another device that performs this operation for elliptically polarized states. These results illustrate a general material-mediated connection between SAM and OAM of light and may find applications in producing complex structured light and in optical communication.