Fano resonance in a single coupled resonant cavity and its application in nanosensing

Sensors based on Fano resonance in metal–insulator–metal (MIM) waveguides exhibit extensive applications in diverse fields, including optical switches, filters, and sensing devices. Here, an MIM-based nanosensor incorporating a compact parallelogram-shaped cavity is proposed, which is able to leverage geometric and compositional elements to generate multiple Fano resonances. Using finite element analysis, we elucidate the resonance formation mechanism by analyzing transmission spectra and field distributions. Parametric studies reveal that cavity geometry and refractive index variations enable independent tuning of dual Fano peaks. Simulation results show that the resonance peak has the advantage of easy linear adjustment, and this feature can be used in high-sensitivity plasmonic sensors. The sensitivity achieved by this structure is 1400[Formula: see text]nm/RIU, and the maximum figure of merit (FOM) is about 4200. In addition, by adding symmetrical isosceles triangular silver metal baffles to the original structure, the sensitivity of the sensor can be increased to 1700[Formula: see text]nm/RIU. Furthermore, by cascading the resonant cavity, the maximum FOM can be significantly increased to [Formula: see text], which is about 3400 times the original. This simplified single-resonator architecture demonstrates significant potential for high-performance applications compared to multi-cavity systems, such as THz modulators, slow light transmission, and sensors.