Precision manufacturing of multicore fibers for superior fiber laser performance

The demand for high-power fiber lasers continues to grow, yet conventional single-mode fibers face physical limitations due to nonlinear effects and thermally induced transverse mode instabilities. Multicore fibers provide a promising approach to overcoming these constraints by enabling compact multi-channel amplification with the potential for coherent beam combination to enhance brightness. However, achieving high combination efficiency requires stringent control over the position and arrangement of individual cores, which becomes increasingly challenging as the number of cores increases. This study investigates two manufacturing techniques for high-core-count multicore fibers: deep-hole drilling and stacking. In the drilling approach, holes are machined into a glass cylinder and filled with doped glass rods. During fiber fabrication, the collapsing process introduces a cushion-shaped distortion, which depends on the gap size between rods and holes, the pitch, and the number of cores. As the core count increases, these distortions become a limiting factor. In contrast, the stacking method, employing an optimized arrangement of large and small rods, preserves the square core structure during fusion, avoiding geometric distortions. Our analysis shows that while drilled fibers allow for high core count integration up to approximately 100 cores, further scaling leads to unacceptable distortions. Stacked preforms, however, maintain geometric integrity, offering a viable alternative for even higher core counts. These findings provide critical insights into the design and fabrication of multicore fibers for coherent beam combination, highlighting the trade-offs between manufacturing feasibility and performance optimization for high-power fiber laser applications.