Nonlocal Electro-Optic Metasurfaces for Free-Space Light Modulation

Abstract

Dynamic optical metasurfaces with ultrafast temporal response, i.e., spatiotemporal optical metasurfaces, provide attractive solutions and open fascinating perspectives for modern highly integrated optics and photonics. In this work, electro-optically controlled optical metasurfaces operating in reflection and utilizing resonant waveguide mode excitation are demonstrated from the viewpoint of free-space propagating light modulation. The modulation of reflected light power with superior characteristics in comparison with prior research is achieved by identifying a suitable low-loss waveguide mode and exploiting its resonant excitation. The electro-optic Pockels effect in a 300-nm-thick lithium niobate (LN) film sandwiched between a continuous thick gold film and an array of gold nanostripes, serving also as control electrodes, is exploited to realize fast and efficient light modulation. The fabricated compact (active area <1000 $\mu$m) modulators operate in the wavelength range of 850-950 nm, featuring a maximum intensity modulation depth of $\sim\!$ 42 % at the driving voltage of $\pm$10 V within the bandwidth of 13.5 MHz (with the potential bandwidth of 6.5 GHz). The introduced nonlocal electro-optic metasurface configuration opens new avenues towards the realization of ultrafast, efficient and robust free-space light modulators based on an LN flat optics approach.