Comparison of isochronal and isothermal decays of Bragg gratings written through continuous-wave exposure of an unloaded germanosilicate fiber

We compare the results of thermally induced isochronal and isothermal decay s of fiber Bragg gratings written through cw exposure of an unloaded german osilicate fiber. Ne show that isochronal step decays can be used to predict isothermal decays, provided that some corrections are carried out to take into account a reversible change in grating reflectivity induced by the inc rease of the fiber temperature. The isochronal accelerated-aging method ena bles one to sample most of the initial distribution of trapped site energie s in a fairly short time. Taking advantage of this property of the method, we show that the initial distribution for a weak grating is similar to thos e for stronger gratings. The consequences of this observation are discussed within the framework of the various reaction pathway model. (C) 2000 Optic al Society of America.