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A gain-enhanced 10/125 μm polarization-maintaining Yb-doped fiber (PMYDF), with the cladding absorption of 7.5 dB/m at 976 nm, for narrow linewidth linearly polarized fiber oscillator or amplifiers is presented. By utilizing the gain-enhanced PMYDF in an all-fiber laser oscillator, an output power of 123 W is achieved with applying appropriate bending strategies and thermal management, corresponding to the slope efficiency of 86.7%. By applying the gain-enhanced PMYDF in seed, an increase of 34% in the longitudinal mode interval is effectively achieved compared to the commercial PMYDF, while the number of longitudinal modes is only 75%. According to the main oscillation power amplification (MOPA) system, the total amount of spectral broadening applying the seed with the gain-enhanced PMYDF are only 67%, 64% and 54% of applying the seed with the commercial PMYDF, corresponding to co-pumping, bi-pumping and counter-pumping schemes, respectively.