Impact Study of High Temperature Pre-Annealing on the Isothermal Wavelength Drift of Type II FBGs

Isothermal Bragg wavelength-drift affects the stability of Type II FBG sensors at high temperature. While the annealing characteristics of each fiber are unique, generally a relatively rapid red-drift phase is observed followed by a more gradual blue-drift. At lower temperatures (600–800 °C) this process can require a year before transitioning to the more stable blue-drift. To speed this up, we applied a longer high temperature pre-annealing treatment than our previous study, aiming to exhaust the red-drift and improve device stability.