Fig. 1. Schematic diagram of femtosecond laser microfabrication system

Fig. 2. Schematic diagram of FPI structure

Fig. 3. Reflection spectra and images under an optical microscope of three FPI structure samples. (a) S1: F-P cavity is 20 μm away from the fiber end face; (b) S2: F-P cavity is 40 μm away from the fiber end face; (c) S3: F-P cavity is 80 μm away from the fiber end face; (d)-(i) The top and side views corresponding to S1-S3 under the optical microscope

Fig. 4. Schematic diagram of fiber FPI structure optical path

Fig. 5. Spectrum of S2 and its corresponding spatial spectrum

Fig. 6. High temperature sensing experimental setup diagram

Fig. 7. Spectral degradation of sensor structure over time at 900 ℃

Fig. 8. (a) Spectral drift image with temperature; (b) The first temperature cycle data point; (c) Data points for the second temperature cycle; (d) Third temperature cycle data points and fitting curve

Fig. 9. Temperature sensing characteristics of three FPI structures with different sizes (a) in the low-temperature range of 200-400 ℃; (b) High temperature zone 400-800 ℃

Fig. 10. Time dependence of the central wavelength of three samples at 800 ℃

Fig. 11. (a) The spectrogram of sample S1; (b)-(d) The spectrograms of three additional samples S11, S12, and S13, respectively, which have the same size parameters as S1

Fig. 12. (a)-(d) are the segmented fitting data curves of samples S1, S11, S12, and S13 at temperatures ranging from 200 to 800 ℃, respectively