Terahertz vortex waves, as important carriers of orbital angular momentum (OAM), exhibit potential in multichannel communications, high-dimensional information encoding, and super-resolution imaging. However, conventional coding metasurfaces based on metallic structures still suffer from limitations in dynamic switching of vortex wave modes, precise wide-angle beam steering, and reconfigurability. To overcome these drawbacks, this work proposes a graphene-based reconfigurable coding metasurface. By utilizing the excellent electrical tunability of graphene, flexible control over the phase response of individual coding metasurface elements is achieved. In addition, a genetic algorithm is introduced to intelligently optimize the coding sequences, enabling precise radiation control of terahertz vortex waves over a wide angular range.
Specifically, a reconfigurable coding metasurface element with a four-layer configuration is designed. By applying an external bias voltage to adjust the Fermi level of graphene, dynamic modulation of the reflection phase is realized via the continuously tunable surface conductivity of graphene. Full-wave simulations are performed in CST to obtain the reflection amplitude and phase responses of the coding metasurface elements under different Fermi levels. Based on these results, 3-bit coding metasurface elements with full 0-2π phase coverage are constructed. Furthermore, a 32 × 32 coding metasurface array is designed, and an FPGA is employed to independently apply bias voltages to each coding metasurface element, allowing real-time programmable switching of coding sequences. According to the phase distribution characteristics of vortex waves, single-mode coding sequences with topological charges of l = -1, 1, 2, and 3 are designed. Moreover, based on the principle of field superposition, multimode coding sequences corresponding to l = -1 and 1, as well as l = 1 and 2, are constructed. Finally, a genetic algorithm is introduced to iteratively optimize the coding sequences with the target radiation angle (θ, φ) as the optimization objective. Combined MATLAB-CST co-simulations are conducted to analyze the vortex wave modes and radiation angle characteristics.
The simulation results demonstrate that the proposed coding metasurface elements achieve full 0-2π phase coverage at 1.1 THz, with a phase interval of approximately 45° between adjacent coding metasurface elements, while the reflection amplitude remains above 0.8 over the entire operating band. The coding metasurface based on these coding elements can flexibly generate and dynamically switch among six vortex wave modes, including four single-mode states and two multimode states. With the assistance of the genetic algorithm, the coding metasurface enables precise control of the radiation angle over a wide angular range of 0° ≤ θ ≤ 60° and 0° ≤ φ ≤ 360°. Moreover, after beam deflection, the radiated beams maintain favorable beam profiles and phase continuity, with significant sidelobe suppression and no obvious beam distortion.
In summary, the proposed graphene-based reconfigurable coding metasurface achieves dynamic generation and flexible switching of multimode vortex waves by tuning the Fermi level of graphene via bias voltage control, combined with FPGA-based programmable operation. Meanwhile, precise beam steering over a wide angular range is realized with the aid of a genetic algorithm. This work provides an effective approach and valuable design reference for programmable wavefront manipulation, OAM multiplexing, and high-capacity multichannel communication systems in the terahertz regime.