Objective This study systematically analyzed the impact and mechanism of various parameters on the efficacy of fusion splicing and explored an efficient and widely applicable fusion splicing technology between fluoride fiber and silica fiber. By investigating the optimal splicing parameters between single-mode indium fluoride fiber and single-mode silica fiber, we introduced the large-package-small structure concept, which establishes a reliable fusion point based on the significant difference in thermal expansion performance. We quantitatively analyzed key splicing parameters such as heating time, power, offset, and hot push that greatly influence the splicing outcome. The relationships between heating time, splicing loss, tensile strength, power, offset, and hot push were established by comparing splicing outcomes under different parameters. This research successfully achieved high-quality fusion splicing between single-mode indium fluoride fiber and single-mode silica fiber, with a minimal splicing loss of 0.04 dB and a tensile strength exceeding 150 MPa. Furthermore, the fusion point's temperature remained below 40 ℃ when subjected to a 9.6 W pumping test with a mid-infrared supercontinuum source, demonstrating high damage threshold and long-term stability. Additionally, high-quality fusion splicing was accomplished between silica fiber, fluorotellurite fiber, and ZBLAN fiber, resulting in a splicing loss of less than 0.1 dB, thereby confirming the broad applicability of the technology. These findings serve as a solid foundation for the advancement of mid-infrared high-power all-fiber lasers.

Methods The study analyzed the principle of the offset thermal splicing method and identified its inability to yield a stable splicing point. As an alternative, the large-package-small structure concept was proposed, leveraging the thermal expansion coefficient difference between fluoride fiber and silica fiber to create a stable splicing point. Building upon this concept, the study elucidated the action mechanism of each parameter in the fusion splicing process and determined the splicing loss and tensile strength trends with each parameter through quantitative analysis of heating time, power, offset, and hot push. A laboratory fusion splicing process was developed based on this technology, and its reliability was validated through fusion splicing experiments involving silica fiber with ZBLAN and silica fiber with fluorotellurite fiber.

Results and Discussions Under the optimal fusion splicing parameters for single-mode indium fluoride fiber and single-mode silica fiber, a splicing loss as low as 0.04 dB and a tensile strength exceeding 150 MPa were achieved at lower power levels. Moreover, the temperature of the fusion-splicing point remained below 40 ℃ during testing with a 9.6 W mid-infrared supercontinuum source, indicating high damage threshold and long-term stability. Fusion splicing between silica fiber and fluorotellurite fiber, as well as silica fiber and ZBLAN fiber, resulted in splicing losses of less than 0.1 dB and satisfactory tensile strength, affirming the technology's reliability.

Conclusions  This study highlights the effectiveness of the offset thermal fusion splicing method through the fusion of single-mode indium fluoride fiber and single-mode silica fiber. By establishing a mature laboratory fusion splicing technology, the research achieved a high-quality fusion-splicing point with ultra-low loss, high tensile strength, high damage threshold, and long-term stability. The technology's reliability was confirmed through fusion splicing experiments involving silica fiber with fluorotellurite fiber and silica fiber with ZBLAN fiber, underscoring its significant potential in the realm of high-power all-fiber mid-infrared fiber lasers.