Study on reflection spectrum areas of an FBG for strain gradient measurements

This study conducted computations and experiments to demonstrate the relationship between areas of reflection spectra and strain gradient chirps along a fiber grating. Previous studies have shown that strain gradient chirps on an FGB lead to distortions on its reflection spectrum. However, in applications, how to use a practical measurand (obtained directly from an FBG) to deduce the strain gradient chirp has seldom been addressed in previous studies. The current literature have found that the bandwidth and area of a spectrum are two possible parameters to deduce the strain gradient. From an economic and technological perspective, even in the dynamic measurements, the areas of reflection spectra can be measured by an optical power meter. In this article, based on the coupled-mode theory, a series of computations were performed to obtain the calculated relationship. To validate the calculated relationship, related experiments were also conducted. This relationship is not mentioned in the current literature, numerically and experimentally.