Thermally tunable wideband and bifunctional plasmonic-VO₂ metasurface in THz region

Abstract

In this paper, a thermally tunable plasmonic-VO 2 metasurface with wideband bifunctionality is introduced and studied. This planar structure can be a wideband polarization converter and absorber based on insulator to metal phase change of VO 2 . In room temperature, the introduced metasurface is a linear (LP) to circular (CP) polarization converter for which the ellipticity is more than 95% and its operating bandwidth is 36.55 % in the wavelength range of 1.91 to 2.77 (μm). By increasing temperature up to 358 (K), VO 2 faces phase change to metallic state and then the proposed metasurface acts as an absorber of electromagnetic waves for which the absorbance is more than 80% and its operating bandwidth is ~ 71%, in the wavelength range of 1.68 to 3.5 (μm). For this bifunctional metasurface, its ellipticity for the converter and absorbance for the absorber is almost insensitive to incident angle (θ°) up to 25° and 30° respectively for the both TE and TM modes. The effects of the polarization angle (φ°) is also studied and shown that by increasing polarization angle up to 90° in the absorber case, the working bandwidth of absorber is unaltered.