All-glass fiber amplifier pumped by ultrahigh brightness pump

We investigate high brightness pumping of multi-kW fiber amplifier in a bi-directional pumping configuration. Each pump outputs 2 kW in a 200 μm, 0.2 NA multi-mode fiber. Specialty gain fibers, with 17 μm MFD and 5-dB/meter pump absorption, have been developed. The maximum fiber amplifier output power is 2550 W, limited by multi-mode instability, with 90% O-O efficiency and M 2 < 1.15. The fiber amplifier linewidth is <12 GHz. We also present kW fiber amplifier results using gain fiber with metalized fiber coating.