Electrooptic Reflective Metasurfaces for Discrete Beam Deflection

Abstract

Dynamic, electrically controlled optical metasurfaces are essential flat-optics components that are intensively being developed for realizing compact beam steering, optical modulation, and programmable wavefront control. In this work, we propose a novel metasurface concept enabling dynamic optical beam deflection in reflection by electrically controlled diffraction-order switching. The device configuration considered consists of a lithium niobate (LN) electro-optic (EO) layer sandwiched between a gold back reflector and a grating of gold nanoridges that can be individually addressed, functioning as control electrodes. Applying a set of control voltages changes locally, immediately below the gold ridges, the LN refractive index through the Pockels effect and reconfigures the EO induced diffraction grating configuration. By selectively biasing neighboring ridge electrodes, different EO grating periods can be induced, generating thereby diffraction orders that are absent in the unbiased electrode configuration. Numerical optimization of the cavity formed by gold ridges and the back reflector identifies cavity-enhanced operating conditions at telecom wavelengths, which result in efficient redistribution of reflected radiation into electro-optically induced diffraction channels. Using realistic system parameters, we numerically demonstrate the possibility for fast EO switching between four discrete first-order diffraction angles in the 3–9° range at ∼0.1% efficiency level. We discuss further optimization directions that would allow one to expand the accessible angular diffraction space and increase the operation efficiency, highlighting potential of the proposed platform for EO beam steering, free-space modulation, and reconfigurable flat optics.