Wolf Alexey A, Skvortsov Mikhail I, Lobach Ivan A, Dostovalov Alexandr V, Babin Sergey A
Opt Express. 2022 Feb 28;30(5):7580-7590. doi: 10.1364/OE.445156.
An all-fiber 4-core Yb-doped laser with a cavity formed by fiber Bragg gratings directly inscribed in each core with femtosecond laser pulses and 4% Fresnel reflection from the output fiber end face is demonstrated. It has been shown that the diameter of the active fiber winding significantly affects the power distribution between the cores, since it affects both the pump power distribution and the cross-coupling between the cores. In particular, with an active fiber winding diameter of 21 cm, the cores behave independently, and the power is distributed almost evenly over all cores. With a winding diameter of 6.5 cm, the lasing is achieved almost exclusively from one core, and a mechanism of that radiation concentration based on bending induced stress in an active multicore fiber is proposed which explains the experimental data. By analyzing the optical and radio-frequency spectra of the output laser radiation, additional details of the 4-core fiber lasing are revealed. In particular, a narrowband (several longitudinal modes) lasing with periodic linear sweeping of central wavelength in time is observed and characterized in the multicore fiber laser, for the first time to our knowledge. It is shown that crosstalk of longitudinal modes arising from different cores is greatly enhanced in the case of a strongly bent fiber.
展示了一种全光纤四芯掺镱激光器，其腔由飞秒激光脉冲直接写入每个芯中的光纤布拉格光栅形成，且输出光纤端面有4%的菲涅尔反射。研究表明，有源光纤绕组的直径会显著影响芯之间的功率分布，因为它既影响泵浦功率分布，也影响芯之间的交叉耦合。特别是，当有源光纤绕组直径为21厘米时，各芯独立工作，功率几乎均匀分布在所有芯上。当绕组直径为6.5厘米时，几乎仅从一个芯实现激光发射，并提出了一种基于有源多芯光纤中弯曲诱导应力的辐射集中机制，该机制解释了实验数据。通过分析输出激光辐射的光学和射频光谱，揭示了四芯光纤激光发射的更多细节。特别是，据我们所知，首次在多芯光纤激光器中观察到并表征了中心波长随时间呈周期性线性扫描的窄带（几个纵向模式）激光发射。结果表明，在光纤强烈弯曲的情况下，不同芯产生的纵向模式串扰会大大增强。
