Dynamic Tuning of Hexaplex Plasmon-Induced Transparency in Graphene Grating Metasurfaces for High-Performance Sensing

A dynamically tunable terahertz metamaterial based on a graphene grating structure is proposed and numerically investigated to achieve hexaplex plasmon-induced transparency (hexa-PIT) and high-sensitivity refractive index sensing. The key innovation is that hexa-PIT windows are realized through the synergistic coupling of bright-dark mode hybridization and guided-mode resonance, breaking the limits of conventional multi-PIT designs relying only on bright-dark mode coupling. In this architecture, the bottom graphene sheet acts as a reflective boundary and is essential for exciting the guided-mode resonance that participates in the mode coupling. By adjusting the external bias voltage, the Fermi level of graphene can be flexibly modulated, leading to obvious blue shifts of resonant peaks and precise control of transmission spectra. The finite-difference time-domain (FDTD) simulations, supported by a temporal coupled-mode-theory analysis, validate the multi-mode coupling mechanism and the dynamic tunability. Benefiting from strong light–matter interaction, the graphene grating exhibits excellent sensing performance with a maximum sensitivity of 2.102 THz/RIU and a maximum figure of merit of 2.35 RIU-1, which are competitive with the reported graphene-based PIT sensors. The resonant frequency shows good linear dependence on the surrounding refractive index, enabling high-precision detection. This integrated design provides a valuable theoretical basis and practical reference for terahertz multi-channel filters, modulators, biochemical sensors, and integrated optoelectronic systems.