Graphene-metal hybrid metasurface for broadband terahertz logic encoder induced by Near-field coupling

High-performance terahertz (THz) logic gate devices are crucial components for signal processing and modulation, playing a significant role in the application of THz communication and imaging. Here, we propose a THz broadband NOR logic encoder based on a graphene-metal hybrid metasurface. The unit structure consists of two symmetrical dual-gap metal split-ring resonators (DSRRs) arranged in a staggered configuration, with graphene strips embedded in their gaps. The NOR logic gate metadevice is controlled by the bias voltages independently applied to the two electrodes. Experiments show that when the bias voltages are applied to both electrodes, the metadevice achieves the NOR logic gate within 0.52 THz bandwidth, with an average modulation depth above 80%. The experimental results match well with the theoretical simulations. Additionally, the strong near-field coupling, induced by the staggered DSRRs, causes redshift at both LC resonance and dipole resonance. This phenomenon was demonstrated by coupled mode theory (CMT). Besides, we analyze the surface current distribution at resonances and propose four equivalent circuit models to elucidate the physical mechanisms of modulation under distinct loaded voltage conditions. The results not only advance modulation and logic gate designs for THz communication, but also demonstrate significant potential applications in 6G networks, THz imaging, and radar systems.