Fig. 1. (a) Schematic diagram of the sensor FPF; (b) Schematic diagram of beam transmission

Fig. 2. (a) Simulated interference spectra of MZI_x; (b) Simulated interference spectra of MZI_y; (c) Schematic diagram of Vernier effect

Fig. 3. The longitudinal optical field distributions of the SMF_in-FMF-PMF structure paralleling to the fast axis

Fig. 4. (a) The transmission spectra of FPF structure with different L₂; (b) The frequency spectra of FPF structure with different L₂

Fig. 5. The experimental schematic diagram of the refractive index test

Fig. 6. (a) The transmission spectra refractive index responses of FPF sensor; (b) Linear fitting between refractive index and wavelength

Fig. 7. (a) The transmission spectra temperature responses of proposed sensor FPF; (b) Linear fitting between temperature and wavelength

Fig. 8. (a) Repeated experimental results of refractive Index sensing; (b) Repeated experimental results of temperature sensing