Electro-optic metasurface-based free-space modulators.

Research in optical metasurfaces has explosively grown in recent years, primarily due to their ability of exercising complete control over the transmitted and reflected fields. Application prospects in many emerging technologies require this control to become dynamic, so that the metasurface response could be tuned with external stimuli. In this work, electrically tunable optical metasurfaces operating in reflection as optical free-space modulators are demonstrated. The intensity modulation is achieved by exploiting the electro-optic Pockels effect and tuning the Fabry-Perot resonance in a 320 nm-thick lithium niobate (LN) film sandwiched between a continuous thick gold film and an array of gold nanostripes, serving also as control electrodes. The proposed compact (<1000 μm) modulators operate in the wavelength range of 900-1000 nm, featuring a maximum intensity modulation depth of ∼20% at the driving voltage of ± 10 V within the bandwidth of 8.0 MHz (with the potential bandwidth of ∼25 GHz). By arranging a 2 × 2 array of individually addressable modulators, space-variant control of light reflection is demonstrated, therefore opening a way towards the realization of inertia-free, ultrafast, and robust spatial light modulators based on tunable LN flat optics components.