Development of a health monitoring system using thermally stable fiber bragg gratings for fast reactor power plants. Experimental demonstration of strain measurement

A thermally stable fiber Bragg grating (FBG) written by a femtosecond laser is examined to evaluate the performance in strain measurement, compared with a conventional FBG. Each FBG was affixed on a metal beam with a strain gauge, and the reflection spectrum was measured when the metal beam was bent. To determine the Bragg wavelength, we used the weighted mean algorithm in which the intensity of the spectrum was employed as a weighing factor. The sensitivity of the thermally stable FBG to strain was found to be 0.34 pm/με. Despite this low sensitivity, by employing the Bragg wavelength determination algorithm, the thermally stable FBG can measure strain with an accuracy of ±3 με, which is comparable to an accuracy of ±2 με for the conventional FBG. (author)