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

Fiber Bragg gratings (FBGs) 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. 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.