Development and analysis of a model based on chirped fiber Bragg gratings employed for cracks characterization in materials

Abstract

In this work a model was developed that allows to understand the behavior of a chirped fiber Bragg grating for the detection and characterization of cracks in materials. In addition to the amplitude response, we show that the group delay of the grating provides useful information for the characterization of the crack. The position of the crack can be determined thanks to the linear chirp of the grating that fixes a correlation between the spatial position and both, the wavelength and the group delay. However, our analysis shows that this simple approach has a source of error, which can be overcome if a controllable external strain can be applied to the embedded grating, additional to the strain generated by the embedding process. Thus, the width of the crack can be also estimated. The effect of the appearance of a crack on the grating generates simple o multiple transmission peaks that are analysed considering the behavior of a Fabry-Perot fiber cavity. This simple model was experimentally tested and preliminary results were in good agreement with the simulations.

FBG Spectrum Regeneration by Ni-Coating and High-Temperature Treatment

“…The former employs the well-known Sinc, Gaussian, Nuttall, and Tanh functions to enhance the grating sensitivity by increasing the spectrum ripple factor, lowering the side lobe levels, decreasing the FWHM, and removing undesirable noise [ 22 ]. In contrast, the latter numerical function is also utilized to increase the sensitivity by increasing the period, which allows the Bragg WL’s position to be linearly modified [ 23 , 24 ].…”