Triple-Cladding Ytterbium Doped Fiber for 12 kW Single Module

High power continuous-wave ytterbium-doped fiber lasers have unique advantages such as high electro-optical efficiency, excellent beam quality and good thermal management, and are widely used in industrial materials processing and scientific research. However, multi-kW $(\geqslant$ 10kW) high-power fiber lasers has encountered numerous technology challenges in double-cladding fibers. In this work, we designed and fabricated a triple-cladding ytterbium doped fiber with large core diameter by using Modified Chemical Vapor Deposition (MCVD) combined with all-gas-phase doping method. An excellent laser performance could be demonstrated for such a fiber with an output power of more than 10 kW and a slope efficiency of 82%, no Transverse Mode instability (TMI) is observed. Long-term laser stability at 12 kW-level was carried out in a master oscillator power amplifier (MOPA) laser system for 500 hours with power degradation less than 1%, meanwhile a stimulated Raman scattering (SRS) suppression ratio that is larger than 45dB was obtained.