Actively tunable multi-band terahertz perfect absorber due to the hybrid strong coupling in the multilayer structure

In this work, we propose a multi-band terahertz perfect absorber employing the topological photonic crystal combined with VO₂ and graphene. The hybrid strong coupling among the topological photonic state, the Tamm plasmon polaritons excited around the interfaces of VO₂ and graphene results in the three perfect absorption bands. Benefiting from the reversible insulator-metal phase transition of VO₂ and the tunable Fermi level of graphene, it can actively switch among no absorption, single-band, dual-band and multi-band absorptions around 1THz, with the absorption frequencies tunable as well. Besides, the absorption bands are sensitive to the incident angle in almost the same dispersion rate, with high absorptions in a large angle range. Moreover, the splitting frequencies between the adjacent absorption peaks strongly depend on the pair number of the alternating multilayers. Apart from the three absorption bands, there are still many absorption peaks in the large frequency range resulting from the standing waves, including other 7 peaks above 0.9 between 0.83THz and 1.55THz. Such a tunable multi-band absorber with multiple modulation methods may find extended applications in active integrated terahertz devices.