Broadband multifunctional polarization converter based on graphene and vanadium dioxide metasurfaces along with analytical methods

In this paper, a tunable broadband multifunctional polarization converter based on graphene and vanadium dioxide (VO₂) is designed. When VO₂ is in the metallic state, the structure has the functions of three-band linear to linear and two-band linear to circular polarization conversion. In the broadband frequency range of 15.05 to 16.66 THz, the ellipticity is more than 0.9. Moreover, the structure has circular to linear and two-band circular to circular polarization conversion functions. For the insulating state of VO₂, the structure has the performance of two-band linear to linear and three-band linear to circular polarization conversion. The surface current distribution of the polarization converter is studied to better understanding the physical mechanism of the structure. In addition, the effects of incident and polarization angles and geometrical parameters on the polarization conversion performance are investigated. By changing the chemical potential of graphene, the structure can switch between different polarization conversion functions. It is shown that the performance of the converter is independent of the incident angle up to about 40°. To verify the simulation results, theoretical analyses of multiple interference theory and equivalent circuit model are presented. The proposed structure with features such as adjustability, multiple polarization conversion functions, broad bandwidth, stability over wide incident angle, and ease of construction has potential applications in radar detection, stealth technology, imaging systems, and sensing.