Genetic Algorithm for the Reconstruction of Bragg Grating Sensor Strain Distribution

Optical fiber Bragg gratings are unique among embedded strain sensors due to their potential to measure strain distributions with a spatial resolution of a few nanometers over gage lengths of a few centimeters. This article presents a genetic algorithm for the interrogation of optical fiber Bragg grating strain sensors. The method calculates the period distribution along the Bragg grating which can then be directly related to the axial strain distribution. The period distribution is determined from the output intensity spectrum of the grating via a T-matrix approach. The genetic algorithm inversion method presented requires only intensity information and reconstructs non-linear and discontinuous distributions well, including regions with significant gradients. The method is demonstrated through example reconstructions of Bragg grating sensor simulated data. The development of this algorithm will permit the use of Bragg grating sensors for damage identification in regions close to localized damages where strong strain non-linearities occur.