Fig. 1. Refractive index profile of the FMF

Fig. 2. Function chart of f(neff). (a) m=0; (b) m=1

Fig. 3. Mode distribution. (a) LP01 mode; (b) LP11 mode

Fig. 4. Configuration of the sensor

Fig. 5. Experimental setup used in the temperature sensing measurement

Fig. 6. Transmission spectra of the sensor under different temperatures

Fig. 7. Interference valley wavelength versus temperature

Fig. 8. FFT frequency spectra of transmission spectra under different temperatures

Fig. 9. Effective refractive index difference between LP01 and LP11 versus temperature

Fig. 10. (a)Transmission spectra of the 12-mm-long sensor under different temperatures; (b) interference valley wavelength versus temperature

Fig. 11. (a)Transmission spectra of the 24-mm-long sensor under different temperatures; (b)interference valley wavelength versus temperature

Fig. 12. (a)FFT frequency spectrum of the 12-mm-long sensor; (b)FFT frequency spectrum of the 24-mm-long sensor

Fig. 13. Transmission spectrum of the sensor at the temperature of 130 ℃