Abstract

Successful demonstrations of efficient rare-earth ion emission in the mid-IR spectral range have been restricted until now to fluoride glass optical fibers as host materials and only for a few emission wavelengths pertaining essentially to two ions: erbium and holmium. Out of the few laser emission lines available between 2.6 and 4 μm, by far the most efficient and most studied one has been the Er³⁺ ion transition around 2.8 μm [1]. Accordingly, a few tens of watts have been achieved at 2.83 μm from a monolithic erbium-doped fluoride glass fiber laser [2]. In fact, the only demonstrations of laser emission from a rare-earth doped fluoride glass fiber reaching the watt power level were obtained at wavelengths in the neighborhood of 3 μm. Alternatively, due to their broad gain bandwidth, Raman fiber lasers can be designed to operate at virtually any wavelength provided an adequate pump source is available. Now, the main challenge to the development of mid-IR Raman gain FLs is related to the fact that the effective Raman gain in an optical fiber is actually scaling as 1/λ³, and this has a significant impact on power scaling at long wavelengths. Notwithstanding this, Raman fiber lasers relying on both fluoride [3] and chalcogenide [4] low-loss optical fibers were recently demonstrated. Figure 1 illustrates the potential entire coverage of the spectral region comprised between 2.6 and 4 μm by either rare-earth gain or Raman gain fiber lasers.

© 2015 IEEE