We report the performance of an LMA Yb-doped fiber, designed for increasing the transverse mode instability threshold and minimizing nonlinear effects in multi-kilowatt class fiber lasers, by reducing the thermo-optic coefficient of the fiber core, compared with that of standard aluminophosphosilicate Yb-doped fibers. A TMI-free 5.2 kW single-mode output power from a Yb 20/400 fiber with a 17.5 μm mode-field diameter was achieved in a broad bandwidth, co-pumped amplifier with 78% optical-to-optical efficiency, while a 4 kW signal output was attained in a 26 GHz linewidth amplifier. Negligible photodarkening loss was observed during 150 hour laser operation at 2 kW.
We report the performance of new LMA Yb fibers with increased cladding absorption for pumping in the 915 nm absorption band. A 0.5 dB/m cladding-absorption Yb20/400 fiber showed negligible photodarkening loss in 400-hour laser operation at 3 kW, with 77% optical-to-optical efficiency. Low-SRS and TMI-free operation at 3.5 kW signal power was achieved with a 0.65 dB/m cladding-absorption and 20.2 μm mode-field diameter Yb fiber, tested in a co-pumped amplifier. The Raman peak was 31 dB below the signal peak at the maximum power.
We report a new Yb-doped gain fiber with 20 µm core and 400 µm cladding, designed for improving the long-term operation of commercial fiber lasers powered by cost-effective pump diodes, centered near 976 nm wavelength. The fiber was tested in a co-pumped amplifier, reaching 3.8 kW signal power with 89% optical-to-optical efficiency. Negligible photodarkening loss was observed in over 200-hour laser operation at 2 kW. The signal power was limited to 3.8 kW by TMI and can be further increased by optimizing the pumping configuration. The fiber is compatible with available 20/400 commercial fibers and components allowing fast system integration.
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