Fig. 1. Schematic diagram of SMF-MMF-TFCF-MMF-SMF sensor structure

Fig. 2. Fabrication process of SMF-MMF-TFCF-MMF-SMF sensor. (a) Fusing the SMF with the MMF; (b) flat cut the MMF end; (c) fusing the MMF with the FCF; (d) flat cut the FCF end; (e) fusing the FCF with the MMF; (f) TFCF is tapered under hydrogen oxygen flame; (g) completed sensor structure

Fig. 3. Micrograph. (a) Cross-section of FCF; (b) cross-section of TFCF

Fig. 4. Spatial distribution of optical field intensity in the fiber with a wavelength of 1550 nm. (a) Internal light field distribution of SMF-MMF-FCF-MMF-SMF structure; (b) internal light field distribution of SMF-MMF-TFCF-MMF-SMF structure

Fig. 5. Transmission spectra before tapering, and with taper diameters of 60 μm and 40 μm

Fig. 6. Experimental device for RI measurement

Fig. 7. Transmission spectra of the sensor

Fig. 8. Linear fitting of dip wavelength with change of RI. (a) Linear fitting of wavelength of dip 1 with change of RI (inset: transmission spectra near wavelength of dip 1); (b) linear fitting of wavelength of dip 2 with change of RI (inset: transmission spectrum near wavelength of dip 2)

Fig. 9. Experimental device for temperature measurement

Fig. 10. Results of temperature sensing. (a) Relationship between temperature and dip wavelength of sensor; (b) standard deviation of the dip wavelength from 30 ℃ to 60 ℃