We present KrF excimer laser-induced dynamics of Bragg grating growths in GeO$_2$ doped microstructured optical fibers. The studied fibers all have 6 rings of airholes in a hexagonal lattice and a GeO$_2$ doped region in the center of the microstructure. We compare the growth rates of fiber Bragg gratings in the different microstructured fibers with UV grating inscription. The influence of the doping level, the airhole filling factor, the airhole pitch distance and the fiber orientation are investigated. We expand the range of microstructured optical fibers in which Bragg gratings can be inscribed, achieving reflection strengths that are useable for FBG-based sensing applications, even for doped regions with GeO$_2$ concentrations as low as 1.36 mol% and 0.45 mol%.
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