Fig. 1. Schematic diagram of the near-infrared all-fiber MTP-MZI mode monitor.：（a）flat MTP-MZI； （b）curved MTP-MZI

Fig. 2. Simulation of light field：（a）linear NCF； （b）curved NCF

Fig. 3. （a）Schematic diagram of the preparation of the MTP-MZI coupling region； （b）the microscope image of NCF and SMF side-by-side positioned on the fusion splicer； （c）the microscope image of fusion region of NCF and SMF after discharge

Fig. 4. The experiment setup of the MTP-MZI with curvature changing

Fig. 5. Flow chart of MTP-MZI model monitoring experiment：（a）initial state of the mode monitor； （b）mode characterization experiments with MTP-MZI bending； （c）introduction of higher-order modes； （d）experimental validation of mode monitoring

Fig. 6. （a）The transmission spectra of MTP-MZI with variation curvatures； （b）the corresponding spatial frequency spectrum

Fig. 7. （a）Transmission spectra with curvature range from 0.626 47 m^-1 to 1.042 72 m^-1； （b）the corresponding spatial frequency spectra； （c）transmission spectra with curvature range from 1.842 56 m^-1 to 2.326 41 m^-1； （d）the corresponding spatial frequency spectra

Fig. 8. （a）A comparison of the transmission spectra of the MTP-MZI without and with HCF； （b）the corresponding spatial frequency spectra

Fig. 9. （a）Transmission spectrum of the MTP-MZI with HCF at curvature of 0.574 33 m^-1， 0.834 8 m^-1 and （b）1.094 62 m^-1， 1.868 17 m^-1， respectively； （c）the transmission spectrum of the MTP-MZI with HCF at curvature of 2.225 04 m^-1 and the straight MTP-MZI without HCF； （d）the corresponding spatial spectra

Fig. 10. （a）Initial transmission spectra of the original mode monitor， Repeat1， and Repeat2， respectively； （b）the corresponding spatial frequency spectra； （c）and （e）MTP-MZI transmission spectrum and initial transmission spectrum with HCF with curvature of 2.225 04 m^-1 in Repeatability Experiments 1 and 2； （d）and （f）are the corresponding spatial spectra