Chiral metasurface design with highly efficient and controllable asymmetric transmission and perfect polarization conversion of linearly polarized electromagnetic waves in the THz range

The influences of metasurfaces on the propagation of electromagnetic waves generate several important effects, such as asymmetric transmission and polarization conversion, that are highly useful in optical and microwave communication applications. However, easy method for dynamically controlling the asymmetric transmission of linearly polarized waves with perfect polarization conversion and high efficiency over a wide band in the THz range remain poorly developed. Our work addresses this issue by designing a novel metasurface structure consisting of two outer orthogonal gratings and a central lattice with an optimized chiral graphene monolayer distribution topology sandwiched between dielectric substrates. The frequency-dependent performance of the proposed metasurface is evaluated according to analyses of the asymmetric transmission coefficient, polarization conversion rate, total transmission coefficient, polarization rotation angle, ellipticity, and chirality parameter based on the results of simulations. The results demonstrate that the proposed structure provides highly efficient asymmetric transmission of linearly polarized waves and perfect polarization conversion in the high frequency range from 0.1 to 3.0 THz. The asymmetric transmission and the polarization conversion of the structure are dynamically controllable by changing the Fermi energy of graphene from 0 eV to 1 eV. The results of the analysis reveal that the observed dynamic controllability is a function of the interrelation between the special configuration of the chiral metasurface structure and the special properties of graphene.