Abstract
The recent progress of high-power fiber lasers is remarkable. Advantages of a fiber laser in characteristics such as ultra-low loss, high-damage threshold, and waveguide structure enable the outstanding high-power operation with excellent beam quality. In this paper, with the overview of the progressive advances of fiber lasers, our work on high-power fiber lasers is reported. The power limitation of double-clad fiber laser is discussed, which clarifies the importance of scaling the launching capability of pump power. A concept of a fiber-disk laser with a side-pumping geometry was developed and more than 1 kW output power was demonstrated, which is the highest power from a single fiber laser. For further power and brightness scaling, coherent beam combining of many fiber lasers is also investigated. N fiber lasers simply coupled by fused fiber couplers generate power-summed output from one of N fiber ports with high addition efficiencies of more than 85% for N≤8 due to selective excitation of constructive interference modes.
