Multifunctional metasurface for broadband absorption, linear and circular polarization conversions

With the development of metasurfaces and the improvement of manufacturing technology, it is important and imperative to design novel metasurfaces that can flexibly manipulate terahertz (THz) waves. In this paper, a multifunctional metasurface (MFMS) based on graphene and photosensitive silicon (Si) is proposed, which integrates three functions: broadband absorption, broadband linear and circular polarization conversions in THz band. For absorption mode, the MFMS can absorb above 90% energy in the frequency band of 1.74-3.52 THz with the relative bandwidth of 67.6%. For both linear-linear and circular-circular polarization conversion modes, the relative bandwidth with over 90% polarization conversion rates (PCRs) reaches 49.3% in the frequency band of 1.54-2.55 THz. The working mechanism of the MFMS is analyzed by the surface current distributions, and its properties of the absorption and polarization conversion under oblique incident angles are investigated, respectively. The proposed metasurface has promising prospects in terahertz devices such as modulators, smart switches and other terahertz devices.