Polarization-multiplexing graphene-based coding metasurface for flexible terahertz wavefront control

In terahertz wireless communication systems, flexible wavefront control devices based on various structure metasurfaces have attracted enormous attention for next-generation communication. In general, tunable terahertz metasurfaces integrated with active materials or MEMS technologies are used for dynamic wavefront control. However, most existing metasurfaces suffer from various limitations, including intrinsic properties of active materials, low reliability of MEMS technologies, and single polarization mode of incident waves, which hinders their development and application. To address these challenges, herein, we design two types of reflective graphene-based coding metasurfaces for active wavefront control. The metasurface coding meta-atom is composed of a graphene split-ring resonator, a dielectric layer, and a metal ground plane. By simply rotating the coding meta-atom, independent 2 pi phase coverage for circularly polarized (CP) or linearly polarized (LP) illumination can be achieved, enabling polarization multiplexing. Thus, a metasurface (MS-1) is constructed based on the vortex phase profile to generate different wavefronts. Moreover, these wavefronts can be actively switched between a vortex beam, a multi-beam, and a specular reflection beam by altering the polarization mode of the incident waves and the Fermi level of the graphene coding regions Additionally, another metasurface (MS-2) is developed according to the parabolic phase profile to create a tunable metalens that allows active control over focal intensity and depth by adjusting the Fermi level of graphene. Such wavefront-controlled metasurfaces have high capacity and integration, making them very promising for potential applications in terahertz communication and imaging systems.