Terahertz graphene metasurfaces for cross-polarized deflection, focusing, and orbital angular momentum.

Abstract

Polarization is an important characteristic of electromagnetic wave. Due to novel optical properties, graphene-based anisotropic structure is widely used to control polarization state of electromagnetic wave. In this work, four graphene-based meta-atoms are designed to regulate polarization state of terahertz wave by changing Fermi energy level of graphene. When Fermi energy level is 0.01 eV, cross-polarized wave is emitted by four meta-atoms with phase difference of 90° at 1.18 THz, and the corresponding polarization conversion ratio reaches ∼90%. When Fermi energy level is adjusted to 0.70 eV, linear phase gradient will disappear, and cross-polarized wave almost disappears. Using four selected elements, three dynamic metasurfaces are designed for controlling wavefront of reflected beam, and they are gradient metasurface, metalens, and vortex beam generator. The designed metasurfaces successfully combine wavefront control and polarization manipulation, and greatly improve the ability to control electromagnetic wave. Our designs may have many potential applications, such as terahertz switching, imaging, and polarization beam splitter.