Fig. 1. Schematic of the Sagnac interferometer temperature sensor

Fig. 2. Cross section of optical fiber

Fig. 3. PCF mode field distribution

Fig. 4. Effect of b₁ on effective refractive index and birefringence

Fig. 5. Variation of birefringence with temperature

Fig. 6. Effect of d₁ on birefringence and fiber birefringence temperature sensitivity

Fig. 7. Variation of birefringence with wavelength before and after filling with ethanol

Fig. 8. Liquid filling method

Fig. 9. Variation of birefringence with temperature corresponding to different filling methods

Fig. 10. Variation of birefringence corresponding to filling different temperature sensitive liquids with temperature

Fig. 11. Different combinations of structural parameters correspond to birefringence

Fig. 12. Variation of birefringence with temperature for fibers with different structural parameters under different filling methods

Fig. 13. The transmission spectrum with different temperature

Fig. 14. Relationship between concave point wavelength and temperature