A switchable and tunable multifunctional terahertz polarization converter based on a graphene metasurface

We propose a switchable and tunable terahertz metasurface polarization converter based on graphene. The metasurface is composed of a bottom gold film, a lower SiO2 layer, an intermediate N-type graphene layer, an upper SiO2 layer, and a top layer of square graphene resonant rings. By using the CST Microwave Studio, we studied their polarization conversion properties. The results show that the metasurface enables a versatile range of functions, including x-to-y linear polarization conversion within the frequency range of 4.23-7 THz, the transformation of linearly polarized waves into right-hand circularly polarized and left-hand circularly polarized waves. Moreover, at 3.873 THz, the metasurface can exhibit circular dichroism (CD) with a high CD value of 0.7. Based on the effect, a strategy to detect three representative avian influenza viruses was proposed and tested, which implies that the metasurface can be applied in biosensing. The proposed metasurfaces, enabling polarization conversion and circular dichroism, offer potential for application in waveplate designs and biosensing implementations.