Reflective-to-absorptive THz switchable bifunctionality through phase transition of vanadium dioxide in a 1D defective photonic crystal microcavity

The terahertz (THz) absorption features are theoretically investigated in a symmetric one-dimensional photonic crystal hybridized with a vanadium dioxide (VO₂) phase change material (PCM). VO₂ is one of the most prominent PCMs whose conductivity increases three orders of magnitude during its phase transition from a semiconducting monoclinic to a metallic tetragonal structure. Here, we utilize this property of VO₂ to engineer a tunable THz optical device. Our results show that when the VO₂ is in the semiconductor state with low conductivity of 200 S/m, the structure is nearly reflective. However, increasing the VO₂ conductivity continuously to the value of 1.5 × 10⁵ S/m increases its metallic level further leading to the perfect absorption of the structure. Further increasing the VO₂ conductivity to the value of 2 × 10⁵ S/m reconfigures it to the fully metallic state so that the absorption peak value remains unit as well. In other words, there is a unit contrast in the absorption levels between two semiconductor and metallic states of VO₂ for the proposed structure, which makes it promising for designing tunable nearly reflective and absorbent bifunctionality and optical switching THz devices.