Spin-orbit interaction of light induced by transverse spin angular momentum engineering

TL;DR

This paper demonstrates a novel interaction between transverse spin angular momentum in evanescent waves and orbital angular momentum in optical vortex beams, enabling new control methods for light's angular momentum at the nanoscale.

Contribution

It introduces the first direct spin-orbit interaction mechanism involving transverse spin in evanescent waves and optical vortices, with experimental and numerical validation.

Findings

Transverse-spin-to-orbital angular momentum conversion observed.

Unidirectional excitation of waveguide modes controlled by spin-orbit states.

Enhanced spin-direction coupling effect demonstrated.

Abstract

We report the first demonstration of a direct interaction between the extraordinary transverse spin angular momentum in evanescent waves and the intrinsic orbital angular momentum in optical vortex beams. By tapping the evanescent wave of whispering gallery modes in a micro-ring-based optical vortex emitter and engineering the transverse spin state carried therein, a transverse-spin-to-orbital conversion of angular momentum is predicted in the emitted vortex beams. Numerical and experimental investigations are presented for the proof-of-principle demonstration of this unconventional interplay between the spin and orbital angular momenta, which could provide new possibilities and restrictions on the optical angular momentum manipulation techniques on the sub-wavelength scale. This phenomenon further gives rise to an enhanced spin-direction coupling effect in which waveguide or surface modes are unidirectional excited by incident optical vortex, with the directionality jointly controlled by spin-orbit states. Our results enrich the spin-orbit interaction phenomena by identifying a previously unknown pathway between the polarization and spatial degrees of freedom of light, and can enable a variety of functionalities employing spin and orbital angular momenta of light in applications such as communications and quantum information processing.