Dual-mode switchable metasurface for multi-type OAM vortex beam generation and dual-band perfect absorption in terahertz band

Abstract As metasurface technology is developing rapidly in the past decades, multi-operating mode and tunability are evolving into hot spots in its development. In this paper, we present a dual-operating mode metasurface consisting of vanadium dioxide (VO 2 ). At room temperature (25 °C), it operates as a reflection mode. Eight metasurface unit cells with different reflection phases are designed, which can achieve 2 π phase coverage in the frequency band of 0.4 THz-0.5 THz. Furthermore, by bringing encoded convolution and superposition theorems into the design of metasurface arrays, vertically incident circularly polarized (CP) waves can be transformed into single-beam, multi-beam, deflected and superimposed orbital angular momentum (OAM) vortex beams, respectively. On the other hand, at high temperature (68 °C), it operates as a dual-band terahertz absorber. It achieves near-perfect absorption at 1.71 THz and 1.87 THz with 99.9% and 98.9%, and also has polarization insensitivity. Therefore, the metasurface designed in this paper has promising applications in future terahertz communications, high-resolution imaging, and electromagnetic stealth.