Thermal decay of fibre Bragg gratings of positive and negative index changes formed at 193 nm in a boron-codoped germanosilicate fibre

A complex grating decay process is observed at elevated temperatures as predicted by a recently proposed three-energy-level model. We have also measured thermal stability of fiber gratings of both positive and negative index changes in a boron-codoped germanosilicate fiber in order to characterize the energy levels of the system and to predict grating lifetimes. The negative index gratings are found to be able to operate at 300°C for more than 23 years without significant degradation