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In this study, an all-dielectric metamaterial absorber consisting of a ring nanocavity array, a spacer layer, and a metallic substrate is designed and investigated. The simulation results show that the two perfect absorption peaks (99.91% and 99.96%) are achieved at 539 nm and 673 nm. The two resonance modes caused by the different electric and magnetic field distributions of the ring nanocavity structure lead to different absorption and sensing properties. In addition, the influence of the structural parameters, such as the width of the nanocavity, on the sensing characteristics was studied and is presented here. A high sensitivity and narrow band result in a huge figure of merit when the proposed absorber is operated as a refractive index sensor.

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In this paper, a terahertz (THz) polarization device that achieves four polarization conversion modes with high relative bandwidth and high performance by varying the phase transition properties of vanadium dioxide (VO2) is investigated. In particular, when the device behaves as an orthogonal linear polarization converter, it has a polarization conversion ratio greater than 0.9, an operating bandwidth of 2.14 THz, and a relative bandwidth of 99.5%. In addition, the relationship between different polarization conversion modes of this polarization converter can be analyzed by the Jones matrix. The proposed VO2-based switchable THz polarization converter has important potential for applications in fields such as THz communication encryption and bio-detection.