Temperature-induced reversible changes in the spectral characteristics of fiber Bragg gratings

It is reported that reversible changes in the reflectivity of Bragg grating s can be induced by a change in the temperature of the grating (77 K < T < 573 K). The changes have proved to be greater in highly doped Ge fibers tha n in standard fibers, whereas they could hardly be detected in hydrogenated fibers. The sign of the change for type I gratings was opposite that for t ype IIA gratings. The changes are likely due to a temperature-induced incre ase (or a decrease) in the amplitude of the refractive-index modulation. Po ssible mechanisms for these changes in modulation are discussed. Interestin gly for the purpose of correcting data of isothermal accelerated aging expe riments, a numerical relation that accounts for the temperature-induced cha nges in type I grating reflectivity is given. (C) 2001 Optical Society of A merica.