▎ 摘　　要

We present a dynamically switchable broadband dual-mode polarization conversion metasurface in the terahertz (THz) regime, which consists of double-layer graphene grating, metal resonator, and gold-vanadium dioxide (VO2) alternating grating and silicon dioxide (SiO2) dielectric spacer. The phase transition capability of VO2 is utilized to realize the switching of polarization conversion between transmission mode and reflection mode, and the design of double-layer graphene grating can enhance the transmittance in transmission mode. When VO(2 )is in the insulating state, by increasing the Fermi level of the double-layer graphene, linear polarization conversion in transmission mode can be achieved in 0.52~1.74 THz with the relative bandwidth of about 107.9%; when VO2 is in the metallic state and the Fermi level of graphene is 0 eV, the metasurface works in reflection mode, achieving the reflective linear polarization conversion in the range of 0.62~1.70 THz with relative bandwidth of up to 93.1%. The PCR in the two modes can be dynamically adjusted by changing the Fermi level of graphene and the conductivity of VO2. The proposed dual-mode metasurface is a potential in the design of optical polarization control devices for spectroscopy, imaging etc.