Switchable dual-functional optical vortex manipulation via cylindrical phase-change metagratings

Abstract

Subwavelength artificial engineering microstructures, such as metasurfaces and metagratings, can realize superior optical properties that many natural materials cannot finish. However, most functionalities achieved are mostly single and fixed. The appearance of phase-change materials makes it possible to extend the functions of metagratings. Here, we propose and demonstrate a structural design of cylindrical phase-change metagratings (CPMs) based on VO2, which can achieve switchable dual-functional optical vortex manipulation in the terahertz range. Specifically, by excitation of the temperature-sensitive metallic and insulating states of VO2, the simple two-dimensional cylindrical gear-like structure can achieve dual-functionality for vortex waves with orbital angular momentum (OAM), namely efficient retroreflection and near-perfect absorption. In addition, we also discussed the influence of the gear-like structure dimensions on the transmissivity and absorptivity of dual-function vortex wave manipulation. This work provides a simple and effective approach for the tunable and multifunctional control of vortex waves in subwavelength artificial devices, with potential applications in automated device design and terahertz (THz) communications.