A tunable ultra-broadband linear-to-circular polarization converter containing the graphene

In this paper, a tunable ultra-broadband linear-to-circular polarization converter (LCPC) in terahertz regime containing the graphene is proposed, which are composed of two I-shaped gold resonators, a strip-shaped graphene sheet, two dielectric layer and a bottom gold reflector. The proposed LCPC can convert the linearly polarized wave into circularly polarized wave in an ultra-broadband frequency range which can be expanded to the lower frequencies by decreasing the Fermi energy (E-f) of the graphene in terahertz region. When E-f = 0.4 eV, 0.6 eV, 0.8 eV and 1.0 eV, the axial ratio band of the proposed LCPC which is less than 3 dB are covered 0.9248 similar to 2.2880 THz, 0.9408 similar to 2.2893 THz, 0.9665 similar to 2.2803 THz, and 0.9746 similar to 2.2780 THz, whose relative bandwidths are 84.86%, 83.49%, 80.93% and 80.15%, respectively. The maximum 3 dB axial ratio band is located at 0.9248 similar to 2.2880 THz and its relative bandwidth is 84.86% at the case of E-f = 0.4 eV. The polarization conversion rate curves, reflection phase curves, surface current and electric field diagrams are analyzed to elucidate the physical characteristics of the presented LCPC. In addition, the effect of parameters a, b and c on the axial ratio band are also discussed, respectively. This design offers an effective way to realize the reconfigurable LCPC, and also has enormous potential value in realizing the THz devices.