Conclusions This work demonstrates a highpower allfiber MOPA at 2.05 μm based on a commercial singlemode thuliumdoped silica fiber. A rate equation model is developed to optimize the incident signal power and thuliumdoped fiber length of the poweramplifier. In an experiment, a maximum output power of 57 W at 2048.7 nm is obtained under a 793 nm diode pump power of 102.6 W, corresponding to a slope efficiency of 52.6%. The linewidth and OSNR are measured as 0.08 nm and 58.8 dB, respectively.