All-fiber cascaded combiners for high-power adjustable-ring mode laser beam with a flattop central beam.

• We first presented all-fiber cascaded combiners for ARM beam laser with a flattop central beam. The cascaded combiners are consist of a 3×1 combiner and a (6+1)×1 combiner in series. • By selecting appropriate structural parameters of the cascaded combiners, the first 3 × 1 combiner can form a multi-mode laser beam, which is input to the center port of the second (6 + 1) × 1 combiner to obtain an ARM beam with a uniformly distributed central beam. • The cascaded combiners yield an 8.8 kW central output laser with a transmission efficiency of 96.2 % and M2 factor of 5.24, as well as a ring output laser with an average efficiency higher than 98 %. An all-fiber structure that obtains an adjustable-ring mode (ARM) beam with a uniformly distributed central beam is put forward for the first time based on the beam combining technology. This structure is all-fiber cascaded combiners consisting of a 3 × 1 combiner and a (6 + 1) × 1 combiner in series. A multi-mode fiber with core diameter of 50 µm acts as the connective fiber, transmitting the combined laser of the first 3 × 1 combiner into the center guide core of the output fiber by the well-designed (6 + 1) × 1 combiner. Through the independent transmission of the center and ring beams, an 8.8 kW uniformly distributed central output laser with a transmission efficiency of 96.2 % and M2 of 5.24 is obtained by the cascaded combiners. The feasibility of ARM laser beam with a 10 kW-level flattop central beam provides a new approach for high-power laser welding. [ABSTRACT FROM AUTHOR]