25W-class continuous-wave holmium-doped fiber amplifier with narrow-linewidth and linear polarization

We present our narrow-linewidth, polarization maintaining, holmium-doped fiber amplifier achieving approx. 25 W output power at a wavelength of 2095 nm, a polarization extinction ratio of approx. 17 dB and no observable ASE for relative power levels down to -65 dB. In comparison to our earlier publications, we use newly developed holmium-doped fibers by Exail. In a co-directional pumping configuration, we achieve significantly higher efficiencies of approx. 60%, compared to our earlier presented efficiencies of 34% using PM holmium-doped fibers with the same diameters of 20/250 µm. This efficiency increase also results in a higher achieved output power. To the best of our knowledge, our presented output power is the highest published for polarization maintaining holmium-doped fiber amplifiers.