Holmium-doped ZBLAN fiber lasers at 1.2 μm

Holmium (Ho3+)-doped ZBLAN glasses have been investigated for the purpose of achieving efficient fiber lasers at 1.2 mu m. Because of the long lifetime of the upper laser level and the small phonon energy in Ho3+-doped ZBLAN glasses, strong fluorescence at 1.2 mu m that usually cannot be observed in Ho-doped silica glass has been measured. Fluorescence of 1 mol%, 3 mol%, and 6 mol% Ho3+-doped ZBLAN glasses are reported. The effect of cerium and terbium ions on the emission of Ho3+-doped ZBLAN glass has also been studied. Obstacles to achieving an efficient Ho3+-doped ZBLAN laser are analyzed and discussed. In studies of a commercial Ho3+-doped ZBLAN fiber laser, it was found that the 3 mu m four-energy-level laser can easily overwhelm the 1.2 mu m laser, which is a three-energy-level system having the same upper laser level with the 3 mu m laser. In order to effectively suppress the competiting 3 mu m transition, advanced Ho3+-doped ZBLAN fiber has been designed and fabricated for 1.2 mu m fiber lasers. Fiber lasers at 1.2 mu m using the new Ho3+-doped ZBLAN fiber have been developed. Our experiments demonstrate that the new Ho3+-doped ZBLAN fiber is an efficient gain medium for lasers at 1.2 mu m.