Broadband terahertz metasurface with three switchable functions based on complementary structure

In this work, we propose a switchable multifunctional metasurface based on complementary VO2-graphene structure. Tuning the state of VO2 and the Fermi level of graphene, the metasurface can act as broadband half-wave plate (HWP), quarter-wave plate (QWP) or absorber in the same frequency range of 0.65–1.27THz, respectively. In the V1G0 state, the metasurface behaves as a broadband HWP to realize linear-to-linear polarization conversion with the polarization conversion ratio >0.9 in the range of 0.64–1.37THz. In the V0G1 state, the metasurface acts as a broadband QWP achieving linear-to-circular polarization conversion with the ellipticity below −0.9 in the range of 0.65–1.27THz. In the V1G1 state, the metasurface is a broadband absorber with the absorption over 0.9 in the 0.63–1.32THz range. In addition, the physical mechanisms of the metasurface in different states are analyzed through the field and current distributions. Such a switchable multi-functional metasurface can simultaneously achieve high efficiency polarization conversion and absorption, which has potential applications in the integrated terahertz devices.