Strength, Annealing, and Lifetime of Gratings 1 g(E)/N(0), (1/eV) 0.8 0.6 0.4 0.2 0 0 1 2 E(eV) 3 4 5 D1 D2 435 Figure 9.31 The distribution of the energy states of two DIDs in hydrogen-loaded fibers [84]. One defect is centered at 1.35 eV and has a narrow distribution, whereas the second, at 2.67 eV, has a much broader distribution. 9.4.3 Accelerated Aging of Gratings Annealing a grating at an elevated temperature for a short time removes the fast decay, so that at lower temperatures, the decay rate slows down. This is the principle of accelerated aging [77,85]. The relationship between the anneal- ing temperature T 2 and the lifetime of a grating operated at temperature T 1 is given by the simple relationship