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

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 degrees at 1.18 THz, and the corresponding polarization conversion ratio reaches similar to 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. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

Polarization state of terahertz wave is controlled by changing the Fermi energy level of graphene in this study. Four graphene-based meta-atoms are designed to emit cross-polarized wave with a phase difference of 90 degrees and nearly disappear the wave when adjusted to different Fermi energy levels. Additionally, three dynamic metasurfaces are developed using selected elements to control the wavefront of the reflected beam, combining wavefront control and polarization manipulation successfully.