Single-peak fitting based on wavelength recognition in FBGs spectra under quadratic strain distribution.

The stress concentration appears in the form of a quadratic or higher-order strain distribution, which affects the measurement accuracy of fiber Bragg grating (FBG). The FBG spectrum presents asymmetric deterioration when the stress concentration exceeds a specific limit, making the symmetric Gaussian fitting algorithm no longer suitable for seeking its peak wavelength. In this paper, the degree of stress concentration is defined by the quadratic coefficient of the strain field. The bearing capacity of different length FBGs to the Gaussian fitting algorithm is investigated under the quadratic strain distribution. The experimental results show that the FBG with shorter length had a higher tolerance to the Gaussian peak-seeking algorithm. The Extreme fitting algorithm based on a single peak has been proposed to adapt to the asymmetric changes of FBGs spectra. The exceptional adaptability of the Extreme peak-seeking algorithm compared with Gaussian fitting has been proved, which provides a reliable reference for the accurate peak seeking of FBG reflect spectrum in a nonuniform strain field. [ABSTRACT FROM AUTHOR]