Thermal decay of fiber Bragg gratings written in boron and germanium codoped silica fiber

Fiber Bragg gratings (FBG's) have been written in silica fiber codoped with boron and germanium, using a continuous-wave (CW) 244-nm laser, The thermal decay of the gratings written with and without hydrogen loading is examined over a period in excess of 5000 h, It is shown that the thermal decay of the nonhydrogen loaded gratings is well explained by the power law model proposed by Erdogan [1], Gratings written in hydrogen loaded fiber, however, do not obey the power law model, A new model is presented based on a log time representation which can be used to predict the decay characteristics of gratings written in hydrogen loaded fiber.