3.42 μm lasing in heavily-erbium-doped fluoride fibers

In this paper, we investigate laser emission at 3.4 mu m in heavily-erbium-doped fluoride fibers using dual-wavelength pumping. To this extent, a monolithic 7 mol% erbium-doped fluoride fiber laser bounded by intracore fiber Bragg gratings at 3.42 mu m is used to demonstrate a record efficiency of 38.6 % with respect to the 1976 nm pump. Through numerical modeling, we show that similar laser performances at 3.4 mu m can be expected in fluoride fibers with erbium concentrations ranging between 1 - 7 mol%, although power scaling should rely on lightly-doped fibers to mitigate the heat load. Moreover, this work studies transverse mode-beating of the 1976 nm core pump and its role in the generation of a periodic luminescent grating and in the trapping of excitation in the metastable energy levels of the erbium system. Finally, we also report on the bistability of the 3.42 mu m output power of the 7 mol% erbium-doped fluoride fiber laser. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement