高功率光纤激光器反常模式不稳定效应实验研究  

Experimental Research on Abnormal Transverse Mode Instability in High-Power Fiber Lasers

作　　者：曾令筏 文榆钧 王小林[1,2,3] 王鹏[1,2,3] 奚小明 杨保来 张汉伟[1,2,3] 习锋杰[1,2,3] 韩凯 王泽锋 许晓军[1,2,3] Zeng Lingfa;Wen Yujun;Wang Xiaolin;Wang Peng;Xi Xiaoming;Yang Baolai;Zhang Hanwei;Xi Fengjie;Han Kai;Wang Zefeng;Xu Xiaojun(College of Advanced Interdisciplinary Studies,National University of Defense Technology,Changsha 410073,Hunan,China;Nanhu Laser Laboratory,National University of Defense Technology,Changsha 410073,Hunan,China;Hunan Provincial Key Laboratory of High Energy Laser Technology,National University of Defense Technology,Changsha 410073,Hunan,China)

机构地区：[1]国防科技大学前沿交叉学科学院,湖南长沙410073 [2]国防科技大学南湖之光实验室,湖南长沙410073 [3]国防科技大学高能激光技术湖南省重点实验室,湖南长沙410073

出　　处：《中国激光》2024年第6期1-8,共8页Chinese Journal of Lasers

基　　金：国防基础科研计划、长沙市杰出创新青年培养计划(kq2206006)。

摘　　要：模式不稳定是限制当前高功率光纤激光器功率提升的主要因素。在近单模光纤激光器中,一般采用减小光纤弯曲直径的方法增加高阶模损耗、提升模式不稳定阈值;然而,少模光纤激光器中存在多个高阶模式,会导致动态模式不稳定(TMI)阈值随着弯曲直径减小而降低的反常模式不稳定现象。基于纤芯/包层直径为30/600μm的双包层掺镱光纤以及具有不同直径的光纤水冷柱,设计了一台后向泵浦的高功率光纤放大器,研究了该激光器中的反常模式不稳定现象。结果表明:当采用中心波长为976 nm的稳波长激光二极管(LD)作为泵浦源时,随着增益光纤弯曲直径由13 cm增加至16 cm,激光器的TMI阈值由1650 W提升至3740 W,提升幅度约为1.27倍,输出激光的相对亮度提升了87%。光纤弯曲直径的增加虽然会带来输出激光光束质量的轻微退化,但输出激光的相对亮度能够大幅提升。最终,结合光纤弯曲以及泵浦波长优化,实现了7.1 kW高亮度光纤激光输出,相对亮度为1293。Objective Since its first report in 2010,transverse mode instability(TMI)remains one of the primary limiting factors in the power scaling of high-power fiber lasers.Fiber bending presents a straightforward and effective TMI suppression technique based on mode control.Typically,a negative correlation exists between the TMI threshold and fiber bending diameter.This implies that decreasing the bending diameter increases the TMI threshold.In near-single-mode fiber laser systems,the laser s output power usually increases by reducing the bending diameter to suppress TMI.However,to counteract nonlinear effects exemplified by the SRS and enhance the pumping capacity,fibers with larger mode fields and cladding diameters gain widespread use in high-power fiber lasers.Throughout this transition,an unusual TMI phenomenon is observed where the threshold power increases with the fiber bending diameter s increase.In this scenario,the beam quality of the output laser can be sacrificed to a certain extent in favor of power enhancement,thereby boosting brightness.In this study,an experimental investigation is conducted on the abnormal TMI effect in high-power fiber lasers with respect to varying fiber bending diameters.It is expected that these findings will pave new paths for the evolution of highbrightness fiber lasers.Methods In this study,we designed a high-power fiber laser amplifier based on a double cladding ytterbium doped fiber with a core/cladding diameter of 30/600μm,combined with water-cooled columns with cylindrical fiber grooves of different diameters.The nominal absorption coefficient of this fiber was 0.40 dB/m@915 nm.In the experiment,we used water-cooled columns with diameters of 13,14,15,and 16 cm to compare the output characteristics of the lasers with different fiber bending diameters.First,under the condition of a fiber length of 20 m,the TMI threshold of the laser with different bending diameters was examined using a wavelengthstabilized 976 nm LDs as the pump source,and the abnormal TMI phenomenon was exam

关 键 词：光纤光学 光纤放大器 反常模式不稳定 光纤弯曲 泵浦波长优化 

分 类 号：TN248[电子电信—物理电子学]