Mode-switchable vortex beam generator based on Dirac semimetal and vanadium dioxide

Abstract

The sensitivity of phase-change materials to low-energy photons has enabled the development of tunable terahertz (THz) generators for vortex beams. In this study, a composite unit structure based on Dirac semimetal (DSM), vanadium dioxide (VO2), and polyimide is proposed, with 360° phase coverage achieved by rotating the angle of the DSM structure. In addition, the switching of VO2 between medium and metal is controlled by changing its temperature, resulting in a metasurface orbital angular momentum (OAM) vortex beam to switch between the transmission of a five-layer structure and the reflection of a three-layer structure. The metasurface, operating in a five-layer structured transmission mode, is designed as a vortex beam generator with topological charges of −1 and +2, and realized a tunable vortex beam generator operating frequency by changing the Fermi energy level of the DSM. The metasurface, operating in a three-layer structured reflection mode, is designed as a broadband tunable vortex beam generator with topological charges of −1 and +2. The switchable OAM modes generated by the vortex beam generator are realized by changing the Fermi energy level of the DSM, and selective incidence of left circularly polarized and right circularly polarized waves is realized in the THz band. This switchable vortex beam generator based on DSM and VO2 has potential applications in wireless communication systems in the THz range.