Switchable ultra-broadband absorption and polarization conversion terahertz metasurface

Abstract

Metasurfaces can achieve flexible modulation of electromagnetic waves at the dimension of wavelength level. However, the functions of the reported metasurfaces are usually fixed and cannot be changed, once their structural design is completed. The designed metasurface cannot meet the requirements for flexible regulation of terahertz waves. We found that the phase change materials of vanadium dioxide can achieve a transition from insulating state to metallic state through thermal, electrical, or light excitation, and the phase transition of this material is reversible. Therefore, using vanadium dioxide to form a composite metasurface can achieve dynamic modulation of terahertz waves. In this article, we propose a terahertz metasurface with switchable broadband absorption and polarization conversion. The proposed metasurface is composed of a 9-layer structure stacked from bottom to top with a combination pattern of different dielectric layers. By adjusting the conductivity of vanadium dioxide, the designed metasurface can achieve flexible switching between terahertz wave absorption and polarization conversion functions. When the vanadium dioxide is in the metal state, the designed metasurface behaves as a broadband absorber with an absorption rate of more than 90% in the range of 6.32 THz ~ 18.06 THz and a relative bandwidth of 96.3%. When the vanadium dioxide is in the insulated state, the designed structure exhibits as a polarization converter in the frequency ranges of 2.41 THz ~ 3.42 THz, 4.78THz ~ 7.48 THz, and 9.53 THz ~ 9.73 THz, with a polarization conversion rate of over 90%. We believe that this metasurface structure will have good applications in the field of terahertz wave detection, terahertz switches, terahertz filtering, terahertz communication, and terahertz sensing.