Fig. 1. Schematic of sensor structure. (a) Schematic of S-H-S structure; (b) HCF endface diagram

Fig. 2. Schematic of optical transmission in FP resonant cavity

Fig. 3. Transmission and reflection spectra of the sensor. (a) In the air; (b) in the water

Fig. 4. Microscope diagrams of sensors with different lengths of HCF. (a) 50 μm; (b) 380 μm; (c) 520 μm; (d) 580 μm; (e) 780 μm; (f) 990 μm

Fig. 5. Reflection and transmission spectra for sensors with different lengths of HCF. (a) 50 μm; (b) 380 μm; (c) 520 μm; (d) 580 μm; (e) 780 μm; (f) 990 μm

Fig. 6. Reflection and transmission spectra for sensors with different cladding diameters when HCF length is 520 μm. (a) 125 μm; (b) 100 μm; (c) 90 μm; (d) 80 μm; (e) 65 μm; (f) 50 μm

Fig. 7. Micrograph of sensor and diagram of experimental setup. (a) Micrograph of sensor; (b) diagram of experimental setup

Fig. 8. Schematic of the position of descending. (a) dip 1; (b) dip 2 and dip 3

Fig. 9. Wavelength shift of dip 3 and their linear fitting results changed with relative humidity. (a) Wavelength shift before soak-raise; (b) wavelength shift after soak-raise; (c) linear fitting before soak-raise; (d) linear fitting after soak-raise

Fig. 10. Wavelength shift of descending and their linear fitting results changed with the temperature. (a) dip 1; (b) dip 2; (c) dip 3; (d) linear fitting results

Fig. 11. Wavelength shift of descending and their linear fitting results changed with relative humidity. (a) dip 1; (b) dip 2; (c) dip 3; (d) linear fitting results

Fig. 12. Wavelength shift of descending and their linear fitting results changed with the strain. (a) dip 1; (b) dip 2; (c) dip 3; (d) linear fitting results