Polarization-insensitive ultra-wideband tunable perfect absorber based on a vanadium dioxide metasurface

Abstract

This paper provides a polarization-insensitive ultra-wideband tunable perfect absorber based on a patterned vanadium dioxide (VO2) metasurface. The absorption bandwidth reaches 18.5 THz, surpassing that of most previous studies, through integrating two distinct region patterns (A and B). The proposed absorber features a three-layer sandwiched structure and a simpler metasurface pattern, demonstrating the advantages of lower manufacturing cost and a simplified photolithography process. In addition, by optimizing geometric parameters and manipulating VO2 conductivity, the absorption spectrum reveals three specific perfect absorption peaks with the absorptance of 99.06%, 99.85%, and 99.85% at 10 THz, 14 THz, and 21.5 THz and shows polarization-insensitive performance due to the C4 rotational symmetry of the metasurface pattern. Furthermore, we illustrate that the intrinsic mechanism of the proposed perfect absorber arises from the lossy localized surface plasmon polarization (LSPP) excited by the incident wave, with the Fabry–Perot (FP) cavity enhancing LSPP absorption. The absorber reveals a good impedance matching with the free space, where the real and imaginary parts are close to 1 and 0, which also explains the perfect absorption from the perspective of the impedance matching theory. The device can transition between perfect absorption mode and total reflection mode, with relative absorptance also adjustable via manipulating the VO2 conductivity. Ultimately, the absorber displays an excellent angle tolerance maintaining absorptance above 90% in the range of 0°–50°. Consequently, the proposed polarization-insensitive ultra-wideband tunable perfect absorber can be applied in optical switching, object cloaking, and wireless communication.