Efficient pump module coupling > 1kW from a compact detachable fiber

In the most developed fiber amplifiers, optical pump power is introduced into the similar to 400 mu m-diameter, 0.46NA first cladding of the double-clad, Yb- doped, gain fiber, using a (6+1):1 multi-mode fiber combiner. For this configuration, the core diameter and numerical aperture of the pump delivery fibers have maximum values of similar to 225 mu m and similar to 0.22, respectively. This paper presents the first fiber-coupled laser-diode pump module emitting more than 1kW of cladding-mode-stripped power from a detachable 225 mu m, 0.22NA delivery fiber at 976nm. The electrical-to-optical power conversion efficiency at 1kW is similar to 50%. The FWHM spectral width at 1kW output is similar to 4nm and has an excellent overlap with the narrow absorption spectrum of ytterbium in glass. Six of these pump modules attached to a (6+1): 1 multimode combiner enable a 5-6kW, single-mode, Yb-doped fiber amplifier.