The bifunctional tunable metasurface based on bilayer graphene

In this study, a bifunctional tunable metasurface based on graphene is designed to realize circular dichroism and linear-to-circular polarization conversion. The bifunctional tunable metasurface shows significant spin-selective absorption with the incidence of circularly polarized waves, resulting in a huge circular dichroism. Then, with the incidence of linearly polarized waves, the circularly polarized waves are reflected, realizing the linear-to-circular polarization conversion (LTC-PC) function. The switch between “off” and “on” states of the circular dichroism as well as the switch between “off” and “on” states of the polarization conversion can be achieved by altering the Fermi levels of graphene. Furthermore, when circularly polarized waves (linearly polarized waves) are incident at a wide angle on the metasurface in the “on” state, the metasurface maintains consistent circular dichroism (polarization conversion) properties. This design can be applied to active spin detectors, terahertz waveplates, signal processing and many other fields.