All-fiber lasers offer significant advantages, including excellent beam quality, high integration, and a simple structure, making them a crucial approach for achieving high-power and high-efficiency laser outputs. Fiber splicing is a key technology in the realization of all-fiber laser outputs, as low-loss and high mechanical strength splicing can substantially enhance the optical-to-optical conversion efficiency and the long-term stability of the fiber laser. At present, the output power of quartz fiber lasers has reached the level of ten thousand watts, a development that is closely linked to the advancement of mature fusion technologies for quartz fibers and the fabrication techniques of optical fiber devices. However, due to the limitations of the material transmission window, the output wavelength of quartz fiber lasers is restricted to less than 2.5 μm, preventing the realization of mid-infrared laser output at longer wavelengths. Multi-component fibers, such as heavy metal oxides and fluorides, possess a broad transmission window in the mid-infrared band, and can be utilized for the development of mid-infrared fiber laser devices. At present, the most mature pump sources for such systems are semiconductor lasers or fiber lasers with a quartz fiber-coupled output. Fusion splicing between quartz output tail fibers and multi-component fibers is a critical technology for the integration of all-fiber lasers. To address the aforementioned challenges, this study investigates the fusion splicing between quartz optical fibers and various multi-component optical fibers, including heavy metal oxides, fluorides, and other multi-component optical fibers. By adjusting key parameters such as the main fusion power and the offset distance of the fire head, the effects of splicing loss and mechanical strength in fiber optic connections between single-mode silica fiber (SMF-28e⁺) and various other fibers, namely, bismuthate fiber (PBB), zirconium fluoride-based fiber (ZBYA), and fluorotellurite fiber (TBY), as well as those between PBB and TBY, ZBYA and TBY, and PBB and ZBYA, are investigated. The findings indicate that the effectiveness of fusion splicing between different types of optical fibers is closely related to the transition temperature difference between the respective optical fibers. This study establishes a foundation for further research and development of high-power all-fiber lasers and providing a significant reference for the development of optical fiber fusion splicing technology.

In this study, the asymmetric fusion splicing method is employed due to the differences in the transition temperatures of the various optical fibers. The low fusion loss and reduced mechanical strength of dissimilar optical fibers in this study are attributed to the mismatch in mode field diameter. In the specific welding process, direct fusion following the inherent procedure of the fusion splicer would result in excessively high loss. Therefore, it is necessary to iteratively adjust parameters such as the main fusion light power, main fusion light duration, fiber end-face interval setting, overlap amount, and fiber offset during the experiment to achieve the lowest possible fusion loss while ensuring the highest mechanical strength.

In this study, fiber splicing is conducted on four different types of dissimilar optical fibers, and the splicing results of three types of dissimilar soft glass fibers are demonstrated. Through repeated experiments, it is determined that the primary factors influencing splicing loss and mechanical strength are the welding power and head offset, respectively. In addition to mode field mismatch, the transition temperature of the fiber itself is found to be a critical factor affecting the splicing outcome. During the experiment, the insertion loss at the fusion point is measured using the truncation method (Fig. 3). A 1150 nm laser is coupled into fiber 1, and the fiber splicing loss is calculated by comparing the output powers before and after splicing fiber 2. Overall, when the dissimilar fiber reaches the optimal fusion state, the fiber fusion loss decreases to varying degrees with an increase in the main fusion optical power. However, once the power exceeds a certain threshold, the loss increases sharply, indicating that the fusion point has been burned out (Fig. 4). When quartz fibers are fused with soft glass fibers, the loss is generally low. The lowest loss is observed in the fusion of SMF-28e⁺ and PBB, where the loss is only 0.04 dB when the main fusion optical power is 72 bit. This is because the transition temperature difference between the quartz and soft glass fibers is greater than that of the heterogeneous soft glass fiber fusion splicing, resulting in better core coupling during annealing and cooling. The highest fiber-splicing loss in the experiment is observed between the PBB and ZBYA fibers. As the main fusion power is gradually increased to 70 bit, the loss decreases from 7.7 dB to a minimum of 0.27 dB. However, when the power is further increased to 82 bit, the splicing point burns out, causing the loss to rise sharply to a maximum of 8.2 dB. Based on the transmission characteristics in the optical fiber, it can be concluded that the more ideal the shape of the fusion point, the lower the splicing loss. In the study of fusion splicing between dissimilar optical fibers, it is essential to consider not only the splicing loss but also the mechanical strength to meet application requirements. Prior to reaching the optimal offset of the fire head, a smaller offset results in lower mechanical strength. Once the optimal mechanical strength is achieved, further increases in the offset lead to a gradual decline in mechanical strength (according to the different dissimilar fiber fusion, the offset of the fire head is controlled within a certain range). The fusion point with the lowest mechanical strength is observed in the fusion of SMF-28e⁺ and PBB, where the maximum mechanical strength reaches 148 gf (1 gf=0.0098 N) at a head offset of 125 μm. In contrast, the best performance is achieved in the fusion of PBB and ZBYA, with the maximum mechanical strength reaching 324 gf at the optimal head offset of 20 μm (Figs. 5 and 6).

In this study, when different types of dissimilar optical fibers are spliced, the splicing parameters affecting the splicing loss and mechanical strength of the optical fiber are primarily the main fusion optical power and the offset of the fire head. By controlling these variables and keeping the other splicing parameters fixed, the results for the splicing of SMF-28e⁺ and PBB, SMF-28e⁺ and ZBYA, SMF-28e⁺ and TBY, PBB and TBY, ZBYA and PBB fibers are obtained. The minimum splicing loss between quartz fiber and soft glass fiber is 0.04 dB (PBB and SMF-28e⁺), with a maximum mechanical strength of 148 gf. For dissimilar soft glass fiber fusion splicing, the minimum loss is 0.19 dB (PBB and TBY), with a maximum mechanical strength of 220 gf. These results indicate that the transition temperature difference between dissimilar fibers is a key factor influencing the final fusion splicing outcome. We believe that all-fiber systems will find increasingly broader applications as research on dissimilar fiber splicing extends to the mid-infrared band.