We report cascaded combiners for a high power continuous wave (CW) fiber laser in this paper. The cascaded combiners are fabricated with an improved lateral splicing process. During the fusing process, there is no stress or tension between the pump fiber and the double-cladding fiber. Thus, the parameters of the combiner are better than those that have been reported. The coupling efficiency is 98.5%, and the signal insertion loss is 1%. The coupling efficiency of the cascaded combiners is 97.5%. The pump lights are individually coupled into the double-cladding fiber via five combiners. The thermal effects cannot cause damage to the combiners and the cascaded combiners can operate stably in high power CW fiber lasers. We also develop a high power CW fiber laser that generates a maximum 780 W of CW signal power at 1080 nm with 71% optical-to-optical conversion efficiency. The fiber laser is pumped via five intra-cavity cascaded combiners and five extra-cavity cascaded combiners with a maximum pump power of 1096 W and a pump wavelength of 975 nm.
The angle-polished side-pump coupler is fabricated by fused splicing angle-polished multimode fibers and 20/400 μm double-clad Yb-doped large mode area fiber together. The coupling efficiency of side-pumped coupler for 975 nm pumping light can reach up to 97%, and the leakage ratio of 1080 nm signal light is less than 2%. We analyze the performance of a single side-pumped coupler and also the influence of the distribution of cascade stage couplers on the efficiency of fiber amplifier. Using self-developed side-pumped couplers, we build a distributed side-pumped, ytterbium-doped double-clad all-fiber master oscillator amplifier, and an continuous and single mode laser of 1080 nm wavelength with a 303 W maximum output power is obtained. Finally, increasing the number of the side couplers to improve pump power, the output power of the amplifier becomes higher.
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