Fusion Splicing Technique for Minimizing Insertion Loss and Back Reflection Between Single-Mode and Hollow-Core Fibers

This paper investigates optimized fusion splicing techniques for connecting single-mode fiber (SMF) and hollow-core fiber (HCF) with the aim of minimizing insertion loss and back-reflection. Several approaches were evaluated, including direct fusion splicing, fiber tapering, angled cleaving prior to fusion, and the insertion of a graded-index (GRIN) fiber. It was observed that conventional automatic fusion settings designed for SMF result in significant end-face deformation and high splice loss. By carefully adjusting arc power, discharge position, and fiber overlap, splice performance was substantially improved. Fiber tapering enhanced mode-field alignment but required precise and repeatable control. Angled cleaving effectively reduced back-reflection, albeit at the expense of increased insertion loss. The use of a GRIN fiber provided the most effective mode-field matching, achieving the lowest insertion loss and back-reflection among the tested methods. The results demonstrate that reliable SMF–HCF splicing is feasible, however, further optimization is required to ensure long-term robustness and reproducibility.