Fig. 1. Sensing structure based on MIM waveguide. (a) Three-dimensional structure diagram; (b) two-dimensional structure diagram

Fig. 2. Transmission spectra under different waveguide structures

Fig. 3. Normalized electromagnetic field distribution on the waveguide surface when the cavity resonates. (a) Magnetic field distribution of FR 1; (b) magnetic field distribution of FR 2; (c) electric field distribution of FR 1; (d) electric field distribution of FR 2

Fig. 4. Waveguide sensing performance. (a) Transmission spectra under different medium refractive indices; (b) resonance wavelength of FR 1 and FR 2 varies with medium refractive index

Fig. 5. Influence of radius on resonant wavelength and sensitivity. (a) Transmission spectra at different R₁; (b) sensitivity change of the lower resonator; (c) transmission spectra at different R₂; (d) sensitivity change of the upper resonator

Fig. 6. Influence of opening angle on resonant wavelength and sensitivity. (a) Transmission spectra at different θ₁; (b) transmission spectra at different θ₂; (c) sensitivity change of the lower resonator; (d) sensitivity change of the upper resonator