Graphene and Vanadium Dioxide Assisted Terahertz Metasurface for Broadband Absorption, Polarization Conversion, and Wavefront Manipulation

A terahertz (THz) metasurface based on graphene and vanadium dioxide (VO2) is proposed, which integrates broadband absorption, polarization conversion, and wavefront manipulation functions. When VO2 is in the metallic state, the function of the metasurface is a broadband absorber with a relative bandwidth of 76.1%. The dynamic adjustment of the absorption bandwidth is achieved by tuning the Fermi level of graphene, which results in a modulation depth of 54%. When VO2 is in the insulating state, the function of the metasurface transforms into a polarization converter. The relative bandwidth of the polarization conversion rate is 70.3%. For wavefront manipulation, four distinct units are designed by adjusting the geometric dimensions and rotation angles of the metal structure. The phase of the light beam reflected by these structural units can be uniformly distributed within a 2 pi range. Three 1D metalenses with good focusing effects have been developed. Also, vortex beam generators with different topological charges are designed using convolution technology, and a metasurface capable of simultaneously generating four vortex beams are realized. Compared with some previously reported ones, the metasurface in this paper has certain advantages in functional integration, tuning method, and modulation depth.