721 W narrow-linewidth Er/Yb co-doped fiber amplifier enabled by dual-wavelength pumping.

We report a dual-wavelength pumped narrow-linewidth Er/Yb co-doped fiber (EYDF) amplifier with a record output power of 721 W at 1568 nm. The main amplifier was pumped by 1018 nm and 1535 nm fiber lasers. At the maximum output power, the 3-dB linewidth was 107 pm, and the optical efficiency was 30.2%. No slope-efficiency roll-off was observed at the highest power level, indicating that further power scaling is feasible. This work demonstrates an effective pumping scheme for power scaling of EYDF amplifiers.