Spin- and orbital-Hall effect in cyclic group symmetric metasurface

TL;DR

This paper demonstrates a cyclic group symmetric metasurface that generates vortex beams with spin-dependent transverse shifts, enabling control of spatial beam profiling through spin- and orbital-Hall effects for advanced optical applications.

Contribution

Introduction of a novel cyclic group symmetric metasurface that induces spin- and orbital-Hall effects, enabling spin-controlled transverse shifts in vortex beams.

Findings

Achieved spin-dependent transverse shift in vortex beams.

Controlled spatial beam profiling via spin- and orbital-Hall effects.

Potential applications in optical communication and vortex beam manipulation.

Abstract

Light possesses both spin and orbital angular momentum (AM). While spin AM is determined by helicity of circular-polarization, orbital AM is characterized by topological charge of vortex beam. Interaction of AM with optical beam orbit leads to optical spin Hall or orbital Hall effect, exhibited as spin-dependent or topological charge-dependent transverse shift of optical beam. Conservation of AM enables spin-to-orbital AM conversion, where circular-polarized Gaussian beam is converted to opposite-helicity circular-polarized vortex beam with topological charge $\pm 2$, an example of controlling spatial beam profiling by spin flip. However, the resultant vortex beam has the beam center of gravity unchanged, the same as that of incident Gaussian beam, meaning a null transverse shift. Here we introduce a cyclic group symmetric metasurface to demonstrate generation of vortex beam exhibiting spin-dependent transverse shift, namely, spin- and orbital-Hall effect, attributed to an alteration of dynamical phase of scattered beam according to the order $n$ of cyclic group while keeping geometric phase constant. Capability of spin-controlled spatial beam profiling with a transverse shift via spin- and orbital-Hall effect has important implications for spatial demultiplexing in optical communication utilizing orbital AM mode division multiplexing as well as for optical vortex tweezer and signal processing involving vortex beams.