High-gain single-frequency Tm³⁺-doped ZBLAN fiber amplifier at 2.33 μm

We report here, to the best of our knowledge, the first high-gain, single-frequency Tm³⁺-doped fiber amplifier operating at the 2.3-μm band with conventional ground-state pumping transition (³H₆→³H₄) at 793 nm. The gain fiber is an 8.5-m-long ZBLAN fiber with a Tm³⁺ doping concentration of 3 mol.%, and the seed is a single-frequency distributed feedback diode laser operated at 2331.9 nm. A gain up to 24.1 dB is generated for ∼14 W of launched pump power with the maximum output power of 246 mW. The competitive ³F₄ →³H₆ laser transition at ∼2 µm is also investigated, and the prospects for further power scaling are discussed.