▎ 摘　　要

A switchable and tunable reflective terahertz (THz) polarization converter based on graphene metamaterial is designed and analyzed. By changing the Fermi energy level of graphene, the converter can achieve broadband linear polarization conversion (LPC) and linear-to-circular polarization conversion (LTC-PC). At relatively low Fermi energy level, the converter can achieve dual-band (0.1-0.3 eV) and single-band (0.4-0.6 eV) LPC, respectively, with a broadband frequency range of 2.34-3.54 THz, 3.77-4.22 THz, and 3.75-4.43 THz, and maximum polarization conversion rate (PCR) exceeding 99%. At high Fermi energy level, in addition to the LPC function, the converter can also achieve LTC-PC in the frequency range of 3.34-3.59 THz and 2.89-3.34 THz by adjusting the Fermi energy level. The physical mechanisms are elucidated from the point of the surface current distribution diagram. The structure shows great potential in switchable and tunable broadband THz converters and related applications.