Abstract

The different topics of this thesis include temperature sensors based on the hydrogen-loaded fiber Bragg gratings, and the thermal stability of hydrogen loaded fiber Bragg gratings in the high temperature range. The aim of this thesis is to investigate a new type of high temperature fiber Bragg grating. We have fabricated the hydrogen loaded fiber Bragg gratings for high temperature sensor applications. These gratings differ from other types of fiber Bragg gratings, because their refractive index structure is attributed to the change in the hydroxyl groups and germanium oxygen-deficient centers. An annealed hydrogen loaded fiber Bragg grating has shown to survive at temperatures in excess of 936{493}C. The gratings of the sensors retained their reflectivity up to 70%, when they were kept at 700{493}C for 90 minutes. The annealed fiber Bragg grating can be stabilized at temperatures in excess 700{493}C for sensor applications. The main results of this thesis provide a better understanding of the thermal response of the hydrogen-loaded fiber Bragg gratings and their decay behavior at elevated temperatures. It is demonstrated that temperature annealing treatment of these fiber Bragg gratings is able to enhance effectively the grating's thermal stability. Finally, photosensitivity of pure silica and germanium-doped optical fibers at the presence of hydroxyl groups was also studied.