Fig. 1. The structure schematic of two slits MIM SPPs waveguides with a regular octagon ring resonator: (a) 3D model; (b) 2D model.

Fig. 2. (a) The real part of as functions of wavelength and d when T = 20 ℃; (b) the real part of as functions of wavelength and T when d = 50 nm.

Fig. 3. (a) Comparison of the simulation and the theoretical results of transmittance of the temperature sensor; (b) the magnetic field of peak I at ; (c) the magnetic field of peak II at ; (d) the magnetic field of peak III at ; (e) the magnetic field of peak IV at ; (f) the magnetic field of peak V at .

Fig. 4. The transmission spectra of the temperature sensor under different T: (a) Peak I, Peak II and Peak III in the wavelength range of 690 nm to 1100 nm; (b) peak IV and Peak V in the wavelength range of 1000 nm to 2500 nm.

Fig. 5. The relationship between the resonance wavelength and T of the five transmission peaks.

Fig. 6. The transmission spectra of the structure under different H: (a) In the wavelength range of 690 nm to 1100 nm; (b) in the wavelength range of 1000 nm to 2500 nm. (c) the transmission spectra of the structure under different L in the wavelength range of 1000 nm to 3000 nm; (d) the relationship between sensitivity of Peak V and Peak IV and parameter H; (e) the relationship between sensitivity of Peak V and Peak IV and parameter L.

Fig. 7. (a) The transmission spectra of the structure under different w; (b) when the temperature changes from 20 ℃ to –20 ℃, the displacement of Peak IV at w = 5 nm and w = 10 nm; (c) the transmission spectra of the structure with different wavelength and w; (d) when the temperature changes from 20 ℃ to –20 ℃, the displacement of Peak V at w = 5 nm and w = 10 nm.

Fig. 8. (a) When the system is used as a temperature sensor, the transmission spectra at T = 20 ℃ and T = –20 ℃; (b) when the system is used as a refractive index sensor, the transmission spectra at n = 1 and n = 1.01.