Tunable beam splitter using bilayer geometric metasurfaces in the visible spectrum

Metasurfaces have been widely investigated tbr their capabilities of manipulating wavefront versatilely and miniaturizing traditional optical elements into ultrathin devices. In this study, a nanoscale tunable beam splitter utilizing a bilayer of geometric metasurfaces in the visible spectrum is proposed and numerically examined. Inspired by the diffractive Alvarez lens and multilayer geometric metasurfaces, opposite quadratic phase distributions are imparted on both layers, and a varying linear phase gradient will arise through relatively lateral displacement between two layers, generating tunable angles of deflection. In addition, such geometric metasurfaces offer opposite directions of phase gradients for orthogonal circularly polarized incidences, leading to effective polarization beam splitting. Results prove that the splitting angles can be tuned precisely, and the energy split ratio can be effectively changed according to the ellipticity of the polarized incidence. This design could find significant applications in optical communication, measurement, display, and so on. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement