• A stress birefringence enhanced polarization maintaining ytterbium doped fiber (PMYDF) was successfully fabricated with the polarization extinction ratio (PER) of 18 dB over meter-long fiber lengths, meaningful and practical for SBC and CBC • 1247 W is the highest linearly polarized laser output power forward pumped based on the oscillator structure, which shows that our homemade PMYDF has excellent laser performance with improved polarization maintaining abilities. • For the first time, the complete process of 20/400 µm PMYDF, including fabrication, measurement, and application, are reported, which is very significant for preparing high-performance PMYDF from optical fiber technology in the future. In this work, we demonstrate a homemade 20/400 µm polarization-maintaining ytterbium-doped fiber (PMYDF) with a stress birefringence value of 4.2 × 10−4. The core concentrations of Yb 2 O 3 and Al 2 O 3 were 0.79 wt% and 0.83 wt% respectively. The cladding absorption at 976 nm was measured to be 1.5 dB/m. The PMYDF exhibited a polarization extinction ratio (PER) of 18 dB over meter-long fiber lengths, favoring linearly polarized laser amplification. By applying the PMYDF in the amplifier, an output power of 1247 W was achieved with a 3 dB spectral linewidth of 87 pm under the pumping of 976 nm lasers, corresponding to a slope efficiency of 83.1 %. With a high polarization capability, this 20/400 µm PMYDF exhibits great potential for application in high-power, narrow linewidth, linearly polarized fiber lasers. [ABSTRACT FROM AUTHOR]