An in-band pumped wavelength-tunable high-power narrow-linewidth Er/Yb co-doped fiber amplifier

We report a narrow-linewidth Er/Yb co-doped fiber (EYDF) amplifier tunable from 1570 to 1610 nm with an output power exceeding 330 W and a 3 dB linewidth below 150 pm. It is the highest, to the best of our knowledge, output power for the 1.5 μm-band tunable fiber lasers to date. The maximum output power reached 450 W with the optical efficiency of 35.3% when operating at 1570 nm. The main amplifier was in-band pumped by 1535 nm fiber lasers to avoid 1 μm-band amplified spontaneous emission (ASE). A piece of EYDF was inserted before the main amplifier to filter out the 1.5 μm-band ASE that originated from the pre-amplifiers, which permitted a powerful amplification for all tunable wavelengths without ASE damage. We demonstrated a robust approach for achieving high-power, tunable, narrow-linewidth 1.5 μm-band fiber lasers with high ASE suppression ratios.