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Efficient holmium fiber lasers have been studied as attractive laser sources operating around 2.1 μm. We report on holmium-doped silica fibers prepared by the modified chemical vapor deposition in combination with either a solution-doping method or a nanoparticle-doping method. A set of 15 fibers with various compositions was characterized and compared with respect to their fluorescence lifetime, laser slope efficiency and laser threshold. This set of fibers in wide concentration ranges allowed us to assess reliably the influence of material composition and the influence of doping method. The best-performance fibers exhibited slope efficiency 83.1%, laser threshold 155 mW and a record value of upper laser level lifetime of 1.35 ms. These results were achieved in fibers with holmium concentration lower than 800 molar ppm and Al/Ho molar ratio greater than 70. Significant differences between fibers prepared by solution doping and nanoparticle doping were not observed. The behavior of Al 2 O 3 nanoparticles during fiber preparation is discussed in details.

Laser sources emitting in the infrared range at around 2 µm are attracting great interest for a variety of applications like processing of transparent thermoplastic polymers in industry as well as plenty of applications in medicine, spectroscopy, gas sensing, nonlinear frequency conversion to the mid-infrared, to mention a few. Of late, fiber lasers compared to other kinds of lasers benefit from their all-fiber design, leading to a compact, robust, and well thermally manageable device. Particularly, thulium- and holmium-doped fiber lasers are the first choice in fiber lasers emitting light around 2 µm. In this paper, we give an overview of our recent results in the research on thulium- and holmium-doped optical fibers, fiber lasers, and related research topics in the 2-µm spectral range. In particular, we present, to our knowledge, the first results of improvement of pump absorption in double-clad fibers thanks to the fiber twist frozen during drawing. Finally, a brief demonstration of material processing by thulium all-fiber laser operating at 2 µm is presented.

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