Narrowband-to-broadband switchable and polarization-insensitive terahertz metasurface absorber enabled by phase-change material

Abstract

Abstract A terahertz absorber with controllable and switchable bandwidth that is insensitive to polarization is of great interest. Here, we propose and demonstrate a metasurface absorber with switchable bandwidth based on a phase-change material of vanadium dioxide (VO2) and verify its performance by finite element method simulations. The metasurface absorber is composed of a hybrid cross fractal as a resonator separated from a gold ground plane by a polyimide spacer. Switching from narrowband to broadband absorber is achieved via connecting VO2 patches to the gold first-order cross fractal converting the resonator to a third-order cross fractal. In the insulator phase of VO2, the main narrowband absorption occurs at the frequency of 6.05 THz with a 0.99 absorption and a full-width half-maximum (FWHM) of 0.35 THz. Upon insulator-to-metal transition of VO2, the metasurface achieves a broadband absorption with FWHM of 6.17 THz. The simulations indicate that by controlling the partial phase transition of VO2, we can tune the bandwidth and absorption level of the absorber. Moreover, the designed absorber is insensitive to polarization due to symmetry and works well for a very wide range of incident angles. In the metallic state of VO2, the absorber has an absorption exceeding 0.5 in the 3.57–8.45 THz frequency range with incident angles up to 65°.