Holmium-doped ZBLAN fiber lasers at 1.2 μm

Abstract

Holmium (Ho 3+ )-doped ZBLAN glasses have been investigated for the purpose of achieving efficient fiber lasers at 1.2 μm. Because of the long lifetime of the upper laser level and the small phonon energy in Ho 3+ -doped ZBLAN glasses, strong fluorescence at 1.2 μm that usually cannot be observed in Ho-doped silica glass has been measured. Fluorescence of 1 mol%, 3 mol%, and 6 mol% Ho 3+ -doped ZBLAN glasses are reported. The effect of cerium and terbium ions on the emission of Ho 3+ -doped ZBLAN glass has also been studied. Obstacles to achieving an efficient Ho 3+ -doped ZBLAN laser are analyzed and discussed. In studies of a commercial Ho 3+ -doped ZBLAN fiber laser, it was found that the 3 μm four-energy-level laser can easily overwhelm the 1.2 μm laser, which is a three-energy-level system having the same upper laser level with the 3 μm laser. In order to effectively suppress the competiting 3 μm transition, advanced Ho 3+ -doped ZBLAN fiber has been designed and fabricated for 1.2 μm fiber lasers. Fiber lasers at 1.2 μm using the new Ho 3+ -doped ZBLAN fiber have been developed. Our experiments demonstrate that the new Ho 3+ -doped ZBLAN fiber is an efficient gain medium for lasers at 1.2 μm.