大模场双包层光纤熔接的功率对准技术研究

Study on optical power alignment technique during the splice of large mode area double-cladding fiber

为了提高高功率光纤激光器中大模场双包层光纤的熔接质量,采用NUFERN 20/400μm双包层光纤搭建了光功率对准系统,对大模场双包层光纤中存在包层光以及纤芯中只有基模和存在高阶模时光纤径向偏移与耦合效率的关系进行了理论分析和实验验证。结果表明,大模场双包层光纤中包层光和纤芯中高阶模的存在使耦合效率对径向偏移变化的敏感度降低,滤除包层光和高阶模后耦合效率随光纤径向偏移量呈高斯型变化;使用光功率对准系统搭建千瓦级双端抽运激光系统,最大输出功率约1170W,光光转换效率约73%,光束质量约1.22,实现了千瓦级准单模输出。光功率对准技术能够实现待熔光纤的精确对准,对高功率光纤激光器输出性能的提升有重要意义。

In order to improve the splicing quality of large mode area double-cladding fiber,an optical power alignment system was designed by using NUFERN 20/400μm double-cladding fiber. The cladding light in the cladding layer and the basicmode light in the core were verified. The relationship between core dislocation and coupling efficiency was analyzed theoretically and verified experimentally. The existence of the cladding light or the higher-order mode in the core reduced the sensitivity of coupling efficiency to core dislocation. After stripping the cladding light and the higher-order mode,the coupling efficiency varies with core dislocation as Gaussian shape. A double-ended pumping fiber laser system with k W level output power was built by using the optical power alignment system,with the maximum output power of 1170 W,optical-to-optical conversion efficiency of about 73% and beam quality factor of around 1. 22. Quasi-single-mode output of k W level was gotten. The results show that accurate alignment of double-caldding fiber can be achieved with optical power alignment technique. The study is important for the improvement of output performance of high power fiber lasers.