Polarization-maintaining, large-mode-area erbium-ytterbium co-doped fiber amplifier with high beam quality

We report a new polarization-maintaining (PM) erbium-ytterbium (EY) co-doped large mode area (LMA) fiber with LP01 mode effective area (Aeff) ⁓ 433 μm2 providing high beam quality. We achieved 150 W of output signal power at 1550.12 nm in a reverse-pumped amplifier seeded by a 100-kHz linewidth single frequency laser, for a launched pump power of 384 W at 940 nm. The power conversion efficiency relative to absorbed pump power was ⁓ 41%, with high signal gain of 28 dB. The polarization extinction ratio was 23.2 dB ± 2.5 dB. The amplifier output was nearly diffraction limited, with the beam parameter M2 staying below 1.02 up to 42 W of output signal power, thereafter, increasing almost linearly to 1.14 at 150 W. There was no evidence of transverse mode instability. Notably, for another fiber sample with LP01 mode Aeff ⁓ 530 μm2 , the M22 value was 1.22 at 154 W of output signal power in a reverse-pumped amplifier seeded by a 2 nm bandpass filtered super luminescent diode centered at 1565 nm. To the best of our knowledge, this is the first demonstration of PM EY LMA fiber with LP01 mode Aeff > 500 μm2 while also maintaining M2 < 1.25.