Fig. 1. Schematic of the MPSFBG structure

Fig. 2. Spectrum of the MPSFBG. (a) Partial enlarged view of the transmission peak in the MPSFBG transmission spectrum, and the inset is the entire transmission spectrum of the MPSFBG; (b) shape factor of the MPSFBG transmission peak changing with number of phase shift points

Fig. 3. Influence of the phase shift amount error of one phase shift point in the dual-phase-shifted FBG on the filter parameters. (a) Transmission spectra of fiber grating at different one phase shift amount errors;(b) loss of fiber grating at different one phase shift amount errors;(c) bandwidth of fiber grating at different one phase shift amount errors; (d) shape factor of fiber grating at different one phase shift amount errors

Fig. 4. Influence of the phase shift amount error of the two phase shift points in the dual-phase-shifted FBG on the filter parameters. (a) Transmission spectra of fiber grating at different two phase shift amount errors;(b) loss of fiber grating at different two phase shift amount errors;(c) bandwidth of fiber grating at different two phase shift amount errors; (d) shape factor of fiber grating at different two phase shift amount errors

Fig. 5. Influence of the position error of one phase shift point in the dual-phase-shifted FBG on the filter parameters. (a) Transmission spectra of fiber grating at different one phase shift position errors;(b) loss of fiber grating at different one phase shift position errors;(c) bandwidth of fiber grating at different one phase shift position errors;(d) shape factor of fiber grating at different one phase shift position errors

Fig. 6. Influence of the position errors of the two phase shift points in the dual-phase-shifted FBG on the filter parameters. (a) Transmission spectra of fiber grating at different two phase shift position errors;(b) loss of fiber grating at different two phase shift position errors;(c) bandwidth of fiber grating at different two phase shift position errors;(d) shape factor of fiber grating at different two phase shift position errors

Fig. 7. Structure and experimental setup of MPSFBG. (a) Schematic of the experimental setup; (b) theoretical model of FBG introducing multiple phase shifts using local temperature control; (c) local temperature control structure; (d) sectional view of the local temperature control structure

Fig. 8. Transmission spectra of the uniform FBG without heating

Fig. 9. Transmission spectra of the uniform FBG at different temperatures. (a) Experimental results; (b) theoretical simulation results; (c) difference between the experimental results and theoretical simulation results

Fig. 10. Transmission spectra when the uniform FBG is heated at different positions. (a) Experimental results; (b) theoretical simulation results; (c) difference between the experimental results and theoretical simulation results

Fig. 11. Spectra of the dual-phase-shifted FBG (temperature is 21.1 ℃, 21.3 ℃; heating position is 7.5, 15, 7.5 mm)

Fig. 12. Influence of phase shift amount error caused by temperature fluctuation and phase shift position error on the spectral characteristic of the dual-phase-shifted FBG.(a) Phase shift amount error; (b) phase shift position error