Krämer, R.G.R.G.KrämerMöller, F.F.MöllerMatzdorf, C.C.MatzdorfGoebel, T.A.T.A.GoebelStrecker, M.M.StreckerHeck, M.M.HeckRichter, D.D.RichterPlötner, M.M.PlötnerSchreiber, T.T.SchreiberTünnermann, A.A.TünnermannNolte, S.S.Nolte2022-03-062022-03-062020https://publica.fraunhofer.de/handle/publica/26220910.1364/OL.389427We present highly robust fiber Bragg gratings (FBGs) in passive large-mode-area fibers for kilowatt fiber laser systems. The gratings were inscribed directly through the fiber coating using near-infrared femtosecond laser pulses and then implemented in an all-fiber ytterbium-doped single-mode oscillator setup reaching up to 5 kW signal output power. The untreated cooled FBGs showed thermal coefficients as low as 1 K kW−1, proving excellent qualification for the implementation into robust high-power fiber laser setups.enfiber Bragg gratingfiber laserinfrared devicelaser pulseYtterbium620535journal article