Breaking the bandwidth barrier: Graphene-driven programmable transmissive metasurfaces enable ultra-wideband terahertz beam steering

The breakthrough of metasurfaces in recent years has offered a new paradigm for beam manipulation. However, as the working frequency moves to the terahertz (THz) range, the intrinsic properties of tunable devices constrain the bandwidth expansion of THz metasurfaces. This study tackles the bandwidth bottleneck of metasurface technology in THz beam steering by leveraging the ultra-wideband electromagnetic response characteristics enabled by the linear energy-momentum relation of graphene. For the first time, a graphene-driven transmissive programmable metasurface is experimentally validated. Leveraging graphene’s intrinsic broadband properties, three key technical challenges are addressed: First, a dual-resonance structure is designed using coupled-mode theory to enhance the transmission efficiency of graphene-integrated metasurfaces. Second, a graphene-insulator-graphene (GIG) structure is adopted to replace ion gel-based modulation schemes, circumventing the time-dependent performance degradation of ion gel and offering a viable solution for practical implementations of graphene metasurfaces. Third, a broadband 1-bit phase coding theoretical model is established through a mirror current operation mode, effectively alleviating the constraints of non-uniformity in CVD-grown graphene on beam steering bandwidth. The implemented programmable transmissive metasurface, comprising 4,608 unit cells, demonstrates ±45° beam scanning across 187 to 250 GHz (28.8% relative bandwidth), achieving the highest relative bandwidth reported to date. Our work not only provides a reconfigurable hardware platform for the upcoming 6G communications, but also extends the broadband control mechanism to multidimensional parameter manipulation, including amplitude, polarization, and orbital angular momentum.