Tunable terahertz circular polarization convertor based on graphene metamaterial

In this paper, a tunable terahertz circular-polarization (CP) convertor based on graphene metamaterial is proposed and investigated numerically and theoretically. The unit-cell of the CP convertor is composed of a subwavelength metal grating sandwiched with bi-layered complementary-oval-shaped (COS) graphene array sheet separated by a dielectric spacer. The electric property of the COS graphene can be adjusted dynamically by varying the Fermi energy level (Ef) through the external gate voltage. The simulation results indicate that the proposed CP convertor can transform the incident right-circularly polarized (RCP) wave to left-circularly polarized (LCP) waves when Ef = 0.8 eV, and the polarization conversion ratio (PCR) is up to 99.9% at 1.1 THz. The numerical simulation results are consistent well with the theoretical calculation by wave-transfer matrix method. The physical origins behind the enhanced CP conversion are supported by field distributions and Fabry-Pe ' rot interference theory. Furthermore, the conversion properties of the CP convertor can be adjusted continuously by changing the Fermi energy level. Thus, our design can be found potential applications in many areas, such as remote sensors, reflector antennas, and radiometers in terahertz region.