Dynamically tunable terahertz triple plasmon-induced transparency in a patterned graphene metamaterial

In this study, we achieve polarization-insensitive triple plasmon-induced transparency (triple-PIT) at terahertz frequencies using a novel graphene metamaterial comprising a graphene block, four graphene squares, and four graphene strips. The insensitivity of this structure to changes in the incident light’s polarization angle is attributed to its high symmetry. The expressions of nth-order coupled mode theory are derived accurately, and its theoretical predictions closely align with the findings of numerical finite-difference time-domain simulations for a triple-PIT system with n = 4. Our results reveal that two synergistic single-PIT phenomena lead to a distinct and tunable triple-PIT effect in the designed metamaterial. This observation is further validated through field distribution studies. Additionally, given the continuous nature of graphene used in the metamaterial, its Fermi level and carrier mobility are easily and dynamically tunable under an applied voltage bias. Notably, the group index of the designed triple-PIT system varies between 603 and 817 as graphene’s Fermi level rises from 0.8 eV to 1.2 eV. In contrast, the group index ranges between 778 and 1216 as graphene’s carrier mobility increases from 2.5 m^2/(V·s) to 4.5 m^2/(V·s). Moreover, the maximum group index reaches 1216 at 4.5 m^2/(V·s), demonstrating the potential of the system in slow-light applications. Thus, the proposed patterned graphene metamaterial and its related findings provide valuable insights for advancing optical switches, dynamically tunable modulators, multichannel filters, and high-performance slow-light devices.