Metasurface with graphene and vanadium dioxide for high-order and high-purity OAM vortex beams generation

Generating high-order and high-purity OAM vortex beams and regulating their wavefronts are of great importance in terahertz communication. However, the current methods used to generate OAM vortex beams remain difficulties to generate higher-order vortex beams based on cost savings. More importantly, tuning the electric field intensity of the generated OAM vortex beam is rarely achieved. Herein, the OAM metasurface with topological charge up to l = −10 is realized by careful design of the metasurface, and its purity is up to 0.56, which is the highest topological charge of the terahertz OAM beam known till now. Furthermore, the tuning ability of the metasurface to the electric field intensity is achieved by the hybrid configuration of graphene and vanadium dioxide (VO₂). The double-tuning capability is verified through design and simulation analysis of the metasurfaces with topological charges l = −1, l = −7, and l = −10. By regulating the phase transition temperature of VO₂ and the Fermi level (E_F) of graphene, the double-tuning ability of the electric field intensity of the OAM beam can be realized, that is, not only can the electric field strength be greatly tuned, but also can be fine-tuned.