Switchable and tunable broadband terahertz absorption, linear polarization conversion and linear to circular polarization based on graphene–vanadium dioxide metamaterials

In this paper, we propose a switchable and tunable broadband terahertz (THz) absorption, linear polarization conversion (LPC) and linear to circular polarization (LTCP) device based on graphene and vanadium dioxide (VO2). When VO2 is in a metallic state and graphene at EF=0.9eV, absorptance is greater than 90% at 1.38 to 3.16 THz with a relative bandwidth of 78.4%. The impedance matching and Coupled mode theory (CMT) verified the simulated results. While VO2 is in a dielectric state, the polarization conversion ratio (PCR) of LPC exceeds 90% at graphene EF=0.1eV with a relative bandwidth of 79.7% at 1.38 to 3.21 THz, and at 3.76 to 4.01 THz, ellipticity of LTCP exceeds 0.999, axial ratio (AR) is less than 0.17 dB and relative bandwidth is 6.4%. For graphene at EF=0.2eV, PCR of LPC is greater than 90% at 1.33 to 3.24 THz with a relative bandwidth of 83.5%, and at 4.10 to 4.29 THz, ellipticity of LTCP exceeds 0.998, AR is less than 0.17 dB and relative bandwidth is 4.5%. Simulated results were verified by U–V plane decomposition. The designed switchable multifunctional metamaterials are promising for a wide range of applications in encoding and wireless communication.