Programmable terahertz wavefront manipulation with graphene-based reflective coding metasurfaces

Dynamic wavefront control has drawn considerable attention in the terahertz (THz) region due to its flexible and tunable spatial shaping. However, existing metasurfaces are difficult to implement dynamic wavefront shaping after fabrication, severely restricting their practical applications. Here, a graphene-patterned reflective coding metasurface (GRCM), composed of a array of the coding meta-atom including a graphene-patterned ribbon, a SiO2-Si-SiO2 dielectric interlayer, and a metal layer, is proposed for dynamic THz wavefront control and reconfiguration. In the coding meta-atom structure, the SiO2-Si-SiO2 space layer can act as an FP resonant cavity to enhance the reflected phase shift, while the graphene-patterned ribbon across the entire coding meta-atom can work as the bottom gates to independently dope the graphene. Additionally, a ionic gel layer and a gold electrode are deposited on the surface of the graphene-patterned ribbon in sequence to form a high capacitance layer and a top gate. By applying a bias voltage to two gates to actively adjusting Fermi energy of the graphene ribbon, thus, the meta-atom can actively reconfigure discrete coding phases in the range of 0-2 pi. As a proof of concept, various series of the gate voltages predefined by a field programmable gate array (FPGA) are respectively imposed on the graphene ribbons to achieve programmable phase profiles, and the GRCM enables programmable THz wavefront manipulations, such as dynamic beam steering, dynamic multi-beam conversion, dynamic focusing beam manipulation, and dynamic Bessel beam modulation, as well as dynamic reconfiguration between these functions. Therefore, the proposed GRCM platform owns the powerful capacity on dynamic wavefront reconfiguration, which shows the potential applications in reconfigurable THz devices and large-capacity THz wireless communication and imaging systems.