Single-frequency into dual-frequency absorption switch based on a one-dimensional photonic crystal containing graphene and vanadium dioxide layers

A terahertz absorber based on a one-dimensional photonic crystal (1DPC) containing VO2 and graphene sheet that connects single-frequency into dual-frequency absorption by temperature control is proposed in this paper. The structure consists of a graphene sheet on the Si layer, a Bragg reflector, and a VO2 layer at the end. At 300 K, the VO2 layer is in its insulator phase, and the structure behaves as a single-frequency absorber with 95% absorptivity at 0.472 THz (f1 mode). When temperature varies to 350 K, the VO2 transfer to the metallic phase and the proposed structure can be utilized as a dual-frequency absorber with 98% and 99% absorptivity at 0.472 THz and 0.523 THz (f2 mode), respectively. The physical reason for the absorption modes is explained by the electric field distribution and impedance-matching technique. The frequency position of the absorption modes, and their absorptivity can be tuned by adjusting the Fermi energy of graphene and the period numbers of 1DPC. Also, the first mode absorption shows high absorptivity over a wide incident angle range for TE and TM polarization at both temperatures; in contrast, the second mode absorption at 350 K vanishes over 25˚ of incidence angle. The proposed optical absorber would have potential applications in THz biosensors, filters, and emitters.