Switchable and tunable terahertz metamaterial absorber based on graphene and vanadium dioxide

Metamaterial possess great application prospects for optical reconfigurable devices with high performance. So far, developing switchable and tunable metamaterial absorber in terahertz band is still urgent. In this paper, by designing a multi-layer structure and combining two typical active materials, graphene and vanadium dioxide (VO2), we propose a polarization-insensitive terahertz metamaterial absorber with tunable and switchable properties between triple-band and ultra-wideband. The absorber consists of two layers of graphene, one is square pattern and the other is square-ring pattern, which induced resonance response at different frequencies. And the VO2 layer plays a controlling role between two graphene layers. When VO2 is in the dielectric state, the absorber is triple-band absorption, and the center frequencies and absorption of the three absorption bands are 1.29 THz and 94.2%, 3.94 THz and 99.9%, and 6.56 THz and 95.3%, respectively. When VO2 is in the metallic state, the absorber is ultra-wideband absorption, and the bandwidth of the absorption exceeding 90% is 1.56 THz. Meanwhile, by changing the Fermi energies of graphene, the absorptions can be tunable in the both absorption modes. The absorber also shows a high tolerance for manufacturing errors through exploring the relationships between the absorption and structure parameters. The metamaterial absorber proposed in this work has many advantages simultaneously, including multiple-band absorption, ultra-wideband absorption, switchable absorption mode, high absorption, tunable absorption and polarization insensitivity, which benefits the integration and application of terahertz devices.