Fig. 1. Schematic of conventional FBG sensing measurement system

Fig. 2. Schematic of FBG spectra

Fig. 3. General demodulation process of FBG strain distribution by transfer matrix method and optimization algorithm

Fig. 4. Schematic of non-uniform strain applied on FBG

Fig. 5. Demodulation process of strain distribution based on differential evolution algorithm with improved objective function

Fig. 6. Results in Case1. (a) Reconstruction of reflection spectrum when reflectivity is unknown; (b) demodulation of strain distribution when reflectivity is unknown; (c) reconstruction of reflection spectrum when reflectivity is known; (d) demodulation of strain distribution when reflectivity is known

Fig. 7. Results in Case2. (a) Reconstruction of reflection spectrum when reflectivity is unknown; (b) demodulation of strain distribution when reflectivity is unknown; (c) reconstruction of reflection spectrum when reflectivity is known; (d) demodulation of strain distribution when reflectivity is known

Fig. 8. Results in Case3. (a) Reconstruction of reflection spectrum when reflectivity is unknown; (b) demodulation of strain distribution when reflectivity is unknown; (c) reconstruction of reflection spectrum when reflectivity is known; (d) demodulation of strain distribution when reflectivity is known

Fig. 9. Convergence process of two objective functions ECC and EN2