A dynamically tunable optical sensor based on a metal–insulator-metal–graphene hybrid structure utilizing Fano resonance

To address the problem that traditional metal-insulator-metal (MIM) waveguide-based sensors cannot be dynamically tuned, a graphene strip is introduced into the square resonant cavity of the MIM waveguide in this work, resulting in the design of a dynamically tunable MIM–graphene hybrid optical sensor. The transmission characteristics, electric field distribution, and magnetic field distribution of the system are numerically investigated using the finite element method (FEM), and further validated through the multi-mode interference coupled-mode theory (MICMT). The results indicate that the introduction of graphene can induce new Fano resonance peaks, where a double-graphene structure is found to generate two distinct Fano resonances. These resonances originate from the coherent coupling between the TM[Formula: see text] cavity mode and the graphene plasmonic resonance mode. By adjusting the chemical potential of graphene, the resonant wavelength of the Fano resonance can be dynamically tuned, thereby enabling real-time modulation of the refractive index sensor. The incorporation of graphene is shown to enhance the system’s sensitivity as both a refractive index sensor and optical pressure sensor, with improvements of 30% and 122.5% being obtained, respectively, compared to graphene-free configurations. The maximum refractive index sensitivity is achieved at 1300[Formula: see text]nm/RIU and the pressure sensitivity reaches 0.89[Formula: see text]nm/MPa. External pressure can cause redshift and blueshift of different resonance peaks, thereby making the modes more distinct. The proposed device demonstrates several advantages, including a simple structure, dynamic tunability, ease of fabrication, and a broad operational bandwidth, making it highly suitable for the development of multifunctional dynamically tunable nanophotonic devices.