Numerical demonstration of a switchable binary-state metasurface for the spin hall effect of circularly polarized light.

The spin Hall effect of light, a transverse and spin-dependent splitting at an optical interface, generally depends on the interface properties. By contrast, the spin Hall effect of circularly polarized light is interface-independent, which aids precise nanoscale displacement control. However, the spin Hall-shifted beam generally exhibits low efficiency near normal incidence, where the shift is large. The static nature of metasurfaces with in-plane anisotropy that have been proposed to address this limitation renders them unsuitable for dynamic or reconfigurable applications. In this study, we numerically demonstrated an electrically tunable metasurface that enabled binary-state switching between spin-Hall-shifted and suppressed reflection efficiencies. The metasurface comprised a grating structure and an indium tin oxide layer, whose permittivity was dynamically modulated via an electrical bias, resulting in changes in the reflection amplitude and phase, and thus, in the spin Hall efficiency. Without an applied voltage, the metasurface exhibited suppressed reflection in the spin-Hall-shifted component. By contrast, the dominance switched to spin Hall-shifted reflection upon voltage application. This approach enables the selective control of the spin-dependent reflection intensity without altering the beam displacement, thereby facilitating reconfigurable spin-optical photonic systems.