A multi-parameter Bragg grating fiber optic sensor and triaxial strain measurement

The principle of operation of a multi-parameter dual Bragg grating fiber optic sensor formed in a polarization maintaining fiber is described. The response of the sensor to separately applied longitudinal loading, transverse loading and temperature change is presented in terms of wavelength shifts of the Bragg peaks. Results of those tests are used as sensor calibration data. A model to predict the longitudinal and two orthogonal transverse strain components from measured wavelength shifts of the Bragg peaks observed in combined loading tests is described. The model is based on an assumed linear behavior between wavelength shifts and sensor loadings and uses the calibration data as input. Predictions of transverse strain are compared with applied strains in the combined loading tests and found to be inadequate for transverse strain components. A model for predicting strains is then developed to account for non-linearities between transverse loading and wavelength shifts observed in sensor calibration data. Predictions of longitudinal strain and both transverse strain components from measured wavelength shifts in combined loading are seen to be in excellent agreement with applied test strains.