Fabrication and Characterization of a 37 × 1 Fiber Pump Combiner for Multi-Kilowatt Semiconductor-Laser Power Combining

High-port-count fiber pump combiners are important passive components for scalable laser diode (LD) power combining in high-power fiber-laser systems. However, increasing the number of input ports from 19 to 37 narrows the fabrication window because fiber bundle packing, taper uniformity, splice matching, thermal management, and backward-light tolerance must be controlled simultaneously. In this work, a 37 × 1 tapered fiber bundle pump combiner was fabricated by a tubing-based method using thirty-seven 135/155 µm multimode input fibers and an 800/880 µm output fiber. The input fibers were weakly etched to improve bundle compactness, and the glass-tube-assisted fiber bundle was tapered, cleaved, and fusion-spliced with a tapered output fiber. The fabricated combiner was characterized using thirty-seven 915 nm fiber-coupled LDs. At a total injected power of 4.89 kW, the combiner delivered 4.80 kW output power, corresponding to an overall transmission efficiency of 98.16%. The single-port transmission efficiencies were approximately in the range of 97.3–98.1%, indicating good port-to-port uniformity for the dense 37-fiber bundle. During full-power operation, the highest temperature appeared in the tapered fiber bundle region and reached 103.8 °C, while the fusion-splice region reached 76.2 °C. In addition, the device withstood 500 W backward-propagating light without observable damage, indicating its practical tolerance to reverse-power loading. These results show that the proposed 37 × 1 fiber pump combiner provides an effective all-fiber solution for multi-kilowatt LD power combining.