Nanoscale Refractive Index Sensor Based on an MIM Waveguide Coupled to U-Shaped Ring Resonator with Three Stubs for Alcohol Solution Concentration Detection

In this paper, a nano refractive index sensor consisting of a metal–insulator-metal (MIM) waveguide and a U-shaped ring resonator with three stubs (URRS) resonator is proposed. The transmittance performance of the sensor was theoretically analyzed using the finite element method (FEM). The effects of refractive index and different structural geometrical parameters on the sensor performance were evaluated. The optimal sensitivity of the designed refractive index sensor structure is 2900 nm/RIU, and the figure of merit (FOM) is 55.76. The suggested sensor shows promising potential for utilization in the study of alcohol solution concentration detection. In addition, we applied this sensor structure in the field of alcohol solution concentration detection, and its test results were good with a sensitivity up to 112.