Fig. 1. Structural diagram of optical fiber sensor

Fig. 2. Simulated SPR transmission spectrum

Fig. 3. Rsoft simulation diagrams. (a) Optical path simulation diagram; (b) transmission spectrum simulation diagram

Fig. 4. EMD of simulated interference spectra. (a) EMD process; (b) EMD results

Fig. 5. Sensor fabrication process. (a) Preparation of multimode fiber and hollow core fiber; (b) fusion of multi-mode fiber and hollow core fiber; (c) deposition of silver nanomembranes; (d) preparation of PAA/CS sensitive film; (e) coating of sensitive film on optical fiber surface; (f) finished sensor structure

Fig. 6. Micrographs of sensor. (a) Left side weld; (b) right side weld; (c) region I; (d) region II

Fig. 7. Diagram of sensor test system

Fig. 8. Refractive index response test results of sensor without coating with sensitive material. (a) Transmission spectra; (b) linear fitting graph

Fig. 9. Sensor refractive index response test results. (a) Transmission spectra; (b) linear fitting graph

Fig. 10. Sensor pH response test results. (a) Transmission spectra; (b) linear fitting graph

Fig. 11. Temperature response test results of sensor SPR effect. (a) Transmission spectra; (b) linear fitting graph

Fig. 12. Temperature test response of MZI effect of sensor. (a) Interference spectra at 20‒40 ℃; (b) interference spectra at 20‒80 ℃

Fig. 13. Interference spectrum EMD and linear fitting diagrams. (a) EMD process; (b) EMD results; (c) relationship between interference wavelength and temperature change; (d) relationship between IMF3 and temperature change; (e) relationship between IMF4 and temperature change; (f) linear fitting diagram

Fig. 14. Results of sensor matrix verification. (a) Transmission spectra; (b) interference spectra

Fig. 15. Verification of stability and repeatability of sensor. (a) Linear fitting diagram of SPR-1 resonance wavelength change; (b) linear fitting diagram of SPR-2 resonance wavelength change; (c) linear fitting diagram of MZI interference wavelength change; (d) comparison of sensitivity changes