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A 2 kW pump-light-stripper-free all-fiber distributed-pumping oscillator fabricated with the distributed side-coupled cladding-pumped Yb-doped fiber is demonstrated for the first time, to the best of our knowledge. An output power of 1969 W with a slope efficiency of 72.2% is obtained. By utilizing the final-section counter-pumping scheme, pure output spectra free from residual pump light are obtained without using any pump light stripper, which demonstrates that the pump light stripper is not indispensable for this configuration. Besides, no stimulated Raman scattering component is observed in the output spectra. The laser has the M2 factor ranging from 2.0 to 2.6. We believe that the pertinent results are helpful and valuable for designing high-power fiber laser systems.

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The characteristics of a single-mode continuous-wave thermally guiding very-large-modearea fiber amplifier are investigated numerically using the rate-equation model while taking thermal transfer into account. It is revealed that the seed power should play an important role in the fiber amplifier and should be large enough to ensure high output efficiency. The effects of three pumping schemes (i.e. the co-, counter-and bi-directional pumping schemes) and the initial refraction index difference are also studied. It is revealed that the optimum fiber length changes with the pumping scheme, and the initial refraction index difference should be lower than 10 −4 in order to ensure the linear increment of the output signal power with the pump power. Furthermore, a brief comparison between the thermally induced waveguides in the fiber amplifiers for three pumping schemes is also made.

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