Broadband Tunable and Angularly Stable Circular Polarization Conversion in THz-Gap using Graphene Metasurface

A compact $(\sim \lambda / 10.91)$ transmittive-type graphene metasurface with a thickness of $\sim \lambda / 6.59$ has been explored in this paper. Two thin identical shaped graphene patterns have been deposited on the two opposite sides of a polyimide substrate in such a way that the incident linearly polarized (LP) electromagnetic wave (EM) gets converted to its circularly polarized (CP) form while passing through it. The device has achieved a considerable 3-dB axial ratio (AR) bandwidth of 0.51 THz from 2.79 THz to 3.3 THz. The circular polarization state of the transmitted electromagnetic wave has been validated by calculating the Stoke’s parameters as well as from the study of electric field profile. The device offers broadband tunable characteristics under proper biasing conditions. It can also provide a stable 3-dB axial ratio (AR) performance under different oblique incidences of the EM wave till 60°.