Growth Characterization of Fiber Bragg Gratings Inscribed in Different Rare-earth-doped Fibers by UV and VIS Femtosecond Laser Pulses

Besides well-known applications of fiber Bragg gratings (FBGs) in sensing and telecommunication, current research focuses also on an integration of gratings in actively doped fibers in order to realize high-power monolithic fiber lasers. The inscription of Bragg gratings directly into the active laser material has been achieved successfully, but the influence of the different dopants in rare-earth-doped fibers on the inscription process has usually failed to be considered. In this paper we report on a systematic investigation of Bragg grating growth behavior during inscription with UV and VIS fs pulses in various actively doped fibers. Furthermore we present an analysis of the initial grating growth in active fibers with different rare-earth dopant concentration under different femtosecond laser exposure conditions. A positive influence of cerium doping on grating growth and photosensitivity has been found. Ytterbium doping has been found to decelerate grating growth, meaning decreased photosensitivity to femtosecond pulses. The specific doping type seems to play an important role in the fabrication of high-reflective Bragg gratings in rare-earth-doped fibers.