A broadband absorber with multiple tunable functions for terahertz band based on graphene and vanadium dioxide

A broadband perfect absorber tunable in terahertz band based on vanadium dioxide (VO2) and graphene met-amaterial is proposed. We have carried out numerical simulations using Finite-Difference Time-Domain (FDTD) method. This structure can tune the absorption rate of VO2 by changing its conductivity. Moreover, due to the addition of graphene, the absorption is improved and the bandwidth reaches 3.24 THz. The structure allows spectral shift by varying the Fermi level of graphene, which can achieve >90 % ultrawideband absorption in 3.74 to 6.96 THz range when the Fermi level is 0.8 eV. In the range of 4.338 to 6.332 THz, nearly 100 % absorption can be achieved. The proposed absorber also exhibits good polarization insensitivity and wide angle of incident stability. Our design has potential applications in terahertz spectroscopy and imaging, also can be applied to modulators, sensors, stealth and photoelectric switches.