Vanadium-dioxide-assisted digital optical metasurfaces for dynamic wavefront engineering

Abstract

We propose a novel reconfigurable digital optical metasurface to dynamically control the wavefront of reflected near-infrared (NIR) light at a subwavelength scale. Whereas reconfigurable metasurfaces have been previously demonstrated with complex active elements in the microwave regime (such as biased diodes or transistors), we hereby utilize vanadium dioxide to attain reconfigurability in the optical regime. In contrast to traditional passive metasurfaces, in which local reflection phases are required to cover the full range of 360° to arbitrarily engineer the wavefronts, our tunable digital metasurface utilizes either 0° or 180°. We design a unit cell with vanadium dioxide such that its normalized local reflection coefficient switches from −1 to +1 upon change in the state of the vanadium dioxide. Hence, we realize a surface for which various digital patterns of either −1 or +1 can be arbitrarily programmed. Based on the theory of binary holography, we numerically demonstrate the dynamic control of a NIR wavefront by programming the proposed digital optical metasurface as a reconfigurable beam splitter and as a scannable optical reflectarray.