Abnormal growth mechanism of fiber Bragg gratings in high Germanium-doped fibers

Until recently, fiber Bragg gratings have been found to exhibit three different growth mechanisms, type I, type II arising from physical damage - and type IIA. Recently, it has been reported a new regime termed type IA. In this contribution we will report the observation of an abnormal growth mechanism of gratings written in high-Germanium-doped fibers, different from the referred types. First, we will identify possible causes for the observed evolution of the induced perturbation's characteristics (mean value and amplitude) as a function of the accumulated UV fluency. Then, we will analyze the thermal behavior (stability and sensitivity) of gratings formed through the refer-red abnormal mechanism and compare it with the obtained for the other well-known types (type I, IA and IIA), discussing the results and possible applications in sensing and optical communications areas.