Generations of cross-polarized focusing and vortex beam for terahertz wave based on graphene metasurfaces

Abstract

As a novel material, graphene has been widely applied in the field of metasurface to dynamically control wavefront and polarization of electromagnetic wave in recent years. In this work, four graphene-based meta-atoms are designed for polarization manipulation. Using a hybrid structure of patterned graphene and patched metal, reflective phase of meta-atom can be tuned by Fermi level. When Fermi level is 0.01 eV, cross-polarized waves with phase difference of 90° are generated by meta-atoms with polarization conversion ratio 87% at 2 THz. As Fermi level is adjusted to 0.70 eV, phase difference between four meta-atoms is cancelled with the corresponding polarization conversion ratio only 5%. Then, four metasurfaces are designed for wavefront control and polarization manipulation, and they are focusing metalenses and vortex beam generators. Simulations indicate that the proposed metasurfaces are able to achieve the combination of wavefront control and polarization manipulation, greatly enhancing the ability to control electromagnetic wave. The proposed approach may be applied in the fields of terahertz focusing and communication.