Dynamically adjustable refractive index sensor based on elliptical resonant cavity-enhanced graphene MIM waveguides

Abstract To overcome the limitations of conventional metal-insulator-metal (MIM) waveguide sensors in dynamic tuning, graphene nanotubes have been integrated into elliptical resonant cavities within MIM waveguides. This innovative design aims at achieving an adjustable hybrid graphene-MIM refractive index sensor. Using numerical simulations, including finite element analysis and coupled-mode theory for multi-mode interference, key system characteristics such as transmission, electric, and magnetic field distributions have been thoroughly examined. By dynamically adjusting graphene’s chemical potential, the resonant wavelength and the width of Fano resonances can be flexibly tuned across a broad wavelength range, providing dynamic control over the sensor’s refractive index. Furthermore, specific resonance peaks can be independently modulated through structural optimization. Under optimal structural parameters, the sensor achieves a sensitivity of up to 1600 nm RIU −1 with a quality factor figure of merit (FOM * ) of 199.76. In comparison to conventional MIM-based waveguides, the proposed device offers notable advantages such as structural simplicity, flexible tunability, straightforward fabrication, and a wide operational bandwidth. These results present significant implications for the advancement of dynamically tunable, high-performance nano-photonic integrated sensors.