Low-Loss, Low-Back-Reflection Fusion Splicing of Large-Mode-Area Fibers With Nested Hollow-Core Antiresonant Fibers for All-Fiber High-Power, Single-Frequency Fiber Laser Transmission

The all-fiber integration of hollow-core fibers (HCF) with high-power fiber laser systems remains a significant technical challenge, hindering their scale-up in laser applications. In this study, we demonstrate a low-loss, low-back-reflection, high-power fusion between a nested hollow-core antiresonant fiber (Nested HC-ARF) and a large-mode-area fiber (LMA) using fiber up-taper and angle splicing technology. A minimum fusion loss of 0.29 dB was achieved at a 0° angle when the two types of fibers were mode-field matched. Based on this, we investigated the relationship between back-reflection suppression and fusion loss for Nested HC-ARF and LMA, achieving a balance between them. The best performance was achieved at an angle-cleave of approximately 2°, where the back reflection was suppressed to below −30 dB, and the fusion splice loss was 0.44 dB. Finally, utilizing this fusion splicing technology, we have, for the first time, achieved all-fiber single-frequency pulsed fiber laser transmission using Nested HCFs, with a maximum input power of 62.92 W and a fiber splice point temperature maintained at 28 °C over a 20 m length of Nested HC-ARF. The time-frequency characteristics of single-frequency pulsed lasers remain well-preserved before and after transmission. Our approach enables efficient all-fiber integration between HCFs and high-power fiber laser systems, facilitating HCFs for a wide range of applications in laser processing, and gas sensing.