Characterization of thermal (in)stability and temperature-dependence of type-I and type-IIA Bragg gratings written in B-Ge co-doped fiber

The temperature-dependence and the thermal stability of UV-exposed type-I and type-IIA fiber Bragg gratings written in boron-germanium co-doped silica fiber were examined, in terms of their refractive-index modulations and the change in the Bragg wavelengths. The decay in the reflectivity of the gratings with time at different temperatures was studied and modelled according to a power-law and a master aging curve approach. The distribution of the activation energy, for these types of gratings, was evaluated to describe their thermal stability and then the comparison of their stabilities has been made. Temperature-induced reversible and irreversible changes in the grating characteristics were observed. The temperature-induced reversible spectral characteristics of type-I and type-IIA gratings were found to be different in nature. All these results were discussed within the framework of the current theoretical approaches for predicting the stability and operational lifetime of these types of gratings.