Tunable circular conversion dichroism of single-layer twisted graphene-patterned metasurface

Two-dimensional (2D) chirality-induced asymmetric transmission/reflection has great potential for polarization applications. Usually, asymmetric effects resulting from circular conversion dichroism (CCD) occur in chiral metasurfaces. Here, we propose a single-layer twisted graphene-patterned (with tilted elliptical hole arrays) metasurface and theoretically reveal its tunable CCD in the terahertz (THz) region. The unit cell of the metasurface is achiral. Merely by altering the in-plane orientation of holes for structural 2D chirality, a tunable CCD can be achieved at normal incidence. Interestingly, the reflection phase can be consid-ered an intuitive method to show this metasurface's anisotropy, which complements the conventional CCD measurement in characterizing chiral materials. Furthermore, we can achieve active CCD based on the tunability of graphene. Due to the Fabry-Perot resonance, a multiband enhancement of CCD spectrum will happen by changing the dielectric layer thickness. The proposed metasurface provides more flexible opportunities for designing active THz devices for polarization manipulation.

Automated summary

This study proposes a single-layer twisted graphene-patterned metasurface with tilted elliptical hole arrays and theoretically reveals its tunable circular conversion dichroism (CCD) in the terahertz (THz) region. The unit cell of the metasurface is achiral, and by changing the in-plane orientation of holes for structural 2D chirality, a tunable CCD can be achieved at normal incidence. The reflection phase can be considered as an intuitive method to show the metasurface's anisotropy, and active CCD can be achieved based on the tunability of graphene.