Detecting the temperature of ethanol based on Fano resonance spectra obtained using a metal-insulator-metal waveguide with SiO2 branches

Abstract

Based on the transmission characteristics of surface plasmon polaritons (SPPs) in sub-wavelength structures, this paper proposes a metal-insulator-metal (MIM) waveguide structure composed of a main waveguide with glass (SiO2) branches (WWGB) coupled with an elliptical split-ring resonance cavity (ESRRC). WWGB has a broadband continuous transmission spectrum, while ESRRC has a narrow-band discrete transmission spectrum. The coupling and interference between the two can generate excited dual-Fano resonance, with sensitivities and figures of merits (FOM) of 800 nm/RIU, 1150 nm/RIU, and 9.88, 104.55, respectively. After adding SiO2 branches to both sides of the main waveguide, the FOM are enhanced to 28.57 and 127.78, representing increases of 189% and 22.15%, respectively. This structure can be applied as a temperature sensor. After filling the cavity of the to-be-tested material with 75% ethanol, as the temperature increases, the Fano resonance wavelength to drift, therefore, the corresponding temperature can be calculated by the Fano resonance wavelength. Experiments show that the proposed MIM waveguide has a maximum sensitivity of 1406.25 nm/RIU, an FOM of 156.25, and a temperature sensitivity of 0.45 nm/℃. Ultimately, the results demonstrate that incorporating SiO2 branches enhances the sensing characteristics of the MIM waveguide, after adding ethanol, the MIM can be applied to temperature sensors, with a high sensitivity of 1406.25 nm/RIU, thereby providing a new design strategy for producing high-performance waveguides.