A >20-W, linearly polarized single-frequency continuous-wave all-fiber laser at ∼1540 nm

•First demonstration of an all-polarization-maintaining continuous-wave fiber master oscillator power amplifier (MOPA) system at ∼1540 nm.•Experimental results closely followed simulation results based on Erbium-Ytterbium co-doped fiber (EYDF) design.•Achieved >20 W output power, ∼1.4 kHz linewidth, excellent power stability (20 W without compromising the laser intensity noise (−110 dBc/Hz@ relaxation oscillation peak) at the specific wavelength of ∼1540 nm. The experimental results agree well with the simulated results. To the best of our knowledge, this is the first demonstration of a ∼1540-nm single-frequency all fiber laser and reaching such a high-power level. The amplified laser features a narrow linewidth of ∼1.4 kHz and a spectral side-mode-suppression ratio of >38 dB, even as the laser wavelength is tuned from 1538.216 nm to 1540.616 nm. It is believed to be the narrowest laser linewidth realized in the 22 dB and power root mean square fluctuations of