Kilowatt-level 4×1 Fiber Combiner of Low Brightness Loss with a Square Core Output Fiber

We present the design and fabrication of a 4 × 1 fiber combiner with low brightness loss. The effective area ratio (AR) of light transmission was first introduced to estimate the brightness loss. A square core fiber was used as the output fiber of the fiber combiner to achieve a high AR. The adiabatic criterion for tapering multimode fibers was investigated to obtain the structure parameters required for the fabrication. We used an auxiliary fiber of appropriate size to achieve a regular squared fiber bundle and improve bundle cutting and splicing quality. The fiber combiner yielded a high average power transmission efficiency of 97.8% when the brightness ratio was 1.05. In addition, the output power of 1030 W was obtained by combining two LDs. This type of fiber combiner can produce multi-kilowatts laser by combining high power LDs or fiber lasers. And it can be flexibly applied in laser welding, laser cladding, and laser cleaning.