Broadband multi-functional terahertz polarization converter based on graphene metasurface

Based on graphene metasurface, this paper proposes a broadband multifunctional reflective polarization converter in the terahertz regime. This converter was formed of periodic unit cells, and each cell comprises two gold resonant ribbons, two-layer graphene sheets, a dielectric spacer, and a ground plane. The results demonstrated that the converter presented dynamical multiple polarization-manipulating functions, such as linear-to-circular conversion and linear-to-linear conversion, by varying the Fermi energy of the graphene. For example, in the frequency range from 0.92 to 1.47 THz, the ultra-broadband cross-polarization conversion was obtained with a Fermi energy of 0 eV, and in the range from 0.55 to 1.26 THz, the ultra-broadband linear-to-circular polarization conversion was achieved by varying the Fermi energy with a tunable relative bandwidth of 78.5%. Finally, the physical mechanisms were determined by analyzing the equivalent circuits and current distributions. This polarization converter has the potential for future applications in electronic measurements, photonic design, and other optoelectronic systems.