Ytterbium (Yb3+)-doped high power fiber lasers are attractive because of high efficiency, high power and good beam
quality, which have many potential applications in telecommunication, machining and national defense. Most of the high
power Yb3+-doped double-clad (DC) fiber lasers use end pump technology, which is the conventional method to couple
pump lights into the inner cladding. However, this pump method is limited by the single laser diode's power and
brightness. While multimode fused fiber bundle combiner could combine multiplex individual laser diodes and it is
convenient for fabrication compared with side pumped technology. We reported a ytterbium-doped double-clad fiber
laser, one-end pumped by six 915 nm laser diodes combined by a multimode fused fiber bundle combiner. The combiner
fused splicing six fiber pigtails from diodes exhibited low-loss and high efficiency handling of 91%. We demonstrated that the fiber laser generates up to 20.5 W of continuous-wave (CW) output power at 1106 nm with a 22m long D-shape inner cladding ytterbium-doped fiber. The slope efficiency was about 75% and the quantum efficiency was up to 91%. We also demonstrated a high power fiber laser at 300W level pumped by a single 976nm laser diode, and the slope efficiency was nearly 80%.