Multi-functional terahertz metasurface for a vortex beam, multi-channel focusing, polarization conversion, and broadband absorption based on vanadium dioxide.

Although terahertz metasurface devices have been widely studied, thus far, metasurfaces can rarely manipulate both circularly and linearly polarized incident waves. In this paper, taking advantage of the phase transition characteristics of vanadium dioxide ( ), a multi-functional terahertz metasurface for a vortex beam, multi-channel focusing, polarization conversion, and broadband absorption is proposed. When is in the insulating state, a vortex beam is generated at 1.2 THz when the circularly polarized wave is incident on the metasurface. Meanwhile, the multi-channel focusing is realized at 1.0 THz, and the cross-polarization conversion rate can reach more than 90% at the frequencies of 0.6 THz, 1.1 THz, and 1.6 THz when the -polarized wave is incident vertically. When is in the metallic state, the metasurface achieves close to 95% absorption in the range of 0.8-1.5 THz. The designed metasurface has tunability and multi-functional characteristics, which have potential applications in wireless communication.