Fusion splicing of hollow-core to standard single-mode fibers using a gradient-index bridge fiber

High-performance interconnection between hollow-core fiber and conventional solid-core fiber is of great significance for a lot of promising applications of hollow-core fibers. The current problems for high-performance hollow-core fiber/solid-core fiber interconnection mainly involve mode field mismatch of the two fibers and the complex splicing process. Subject of study. We study fusion splicing of anti-resonant hollow-core fiber with low loss (0.52 dB) and conventional single-mode fiber using a convenient graded-index bridge fiber. Purpose of the work. We aim to eliminate the mode field diameter mismatch between anti-resonant hollow-core fiber and single-mode fiber and simplify the mode field diameter adaptation method and process. Method. We employ a convenient graded-index bridge fiber approach, where a gradient index fiber is first spliced with the single-mode fiber, and the mode interference within the graded-index bridge fiber causes periodic enlargement and shrinkage of the mode field diameter. By precise cutting of the graded-index bridge fiber, the mode field diameter can be well controlled and made approximately equal to the mode field diameter of the anti-resonant hollow-core fiber. After mode field diameter adaptation, an optimized arc discharge fusion splicing procedure is applied for the anti-resonant hollow-core fiber/single-mode fiber fusion splicing. Main results. A fusion splicing loss of about 0.52 dB is achieved, which involves nearly 0.42 dB mode-field-diameter-mismatch-induced loss and about 0.1 dB fusion splicing loss that is caused by the deformation of the anti-resonant hollow-core fiber. Practical significance. The developed approach is convenient and cost-effective, which can benefit a lot of applications of anti-resonant hollow-core fibers in future telecommunications, fiber gas lasers as well as fiber-optic sensing.