Fig. 1. Schematic diagram of experimental device

Fig. 2. Interference spectra of sensors with different lengths

Fig. 3. Schematic diagram of the FFT spectrum of the sensing structure

Fig. 4. Stability of the sensor in water

Fig. 5. (a) Spectral shift diagram of refractive index of sensor; (b) Refractive-index linearity

Fig. 6. Temperature sensitivity