Research on the optical characteristics of tunable vanadium dioxide terahertz metamaterial absorbers

A tunable wideband terahertz absorber based on vanadium dioxide (VO₂) has been proposed, and its optical characteristics have been studied. The absorber structure is comprised of three layers, which includes a VO₂ metasurface layer, a silicon dioxide (SiO₂) dielectric layer, and a gold substrate. The structure of this VO₂ metasurface consists of symmetrically distributed square perforated VO₂ resonators with circular holes, with a relative dielectric constant δ < 3.8 for the SiO₂ dielectric layer and a conductivity 4.56 10⁵ S/m 5 ≥ for the gold substrate. We studied the optical characteristics of the absorber through simulations and theoretical calculations employing the Finite-Difference Time-Domain (FDTD) technique. It was found that, while the VO2 is in the metallic phase, the absorber demonstrates a superior absorption spectrum, achieving a high absorptivity of 90% across a frequency range from 2.2 THz to 4.0 THz, with the absorption bandwidth reaching up to 1.8 THz. The absorptance for two peaks at 2.7 THz and 3.4 THz reaches 99% and 100%, respectively. When VO2 transitions to its dielectric state, its absorptance can be adjusted in a dynamic manner from 100% to 20%, achieving almost perfect amplitude modulation. The physical mechanism of wideband absorption is elucidated using electric field distribution and tunable absorption is verified using impedance matching theory. Besides, it displays insensitivity to variations in the angle of incident light polarization and maintains absorption stability under oblique incidence. This absorber exhibits excellent absorption performance, and the research and application of terahertz devices have opened up new frontiers.