Power scaling based on traditional ytterbium-doped fibers (YDFs) is limited by optical nonlinear effects and transverse mode instability (TMI) in high-power fiber lasers. Here, we propose a novel long tapered fiber with a constant cladding and tapered core (CCTC) along its axis direction. The tapered-core region of the fiber is designed to enhance the stimulated Raman scattering (SRS) threshold and suppress higher-order mode resonance in the laser cavity. The CCTC YDF was fabricated successfully with a modified chemical vapor deposition (MCVD) method combined with solution doping technology, which has a cladding diameter of 400 μm and a varying core with a diameter of ~24 μm at both ends and ~31 μm in the middle. To test the performance of the CCTC fiber during high-power operation, an all-fiber laser oscillator based on a CCTC YDF was investigated experimentally. As a result, a maximum output power of 3.42 kW was achieved with an optical-to-optical efficiency of 55.2%, although the TMI effect was observed at an output power of ~3.12 kW. The measured beam quality (M2 factor) was ~1.7, and no sign of the Raman component was observed in the spectrum. We believe that CCTC YDF has great potential to simultaneously mitigate the SRS and TMI effects, and further power scaling is promising by optimizing the structure of the YDF.

中文翻译：

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用于大功率光纤激光振荡器的新型恒定包层锥芯掺镱光纤

基于传统掺镱光纤 (YDF) 的功率缩放受到高功率光纤激光器中的光学非线性效应和横模不稳定性 (TMI) 的限制。在这里，我们提出了一种沿其轴向具有恒定包层和锥形纤芯 (CCTC) 的新型长锥形光纤。光纤的锥形纤芯区域旨在提高受激拉曼散射 (SRS) 阈值并抑制激光腔中的高阶模式共振。CCTC YDF采用改进的化学气相沉积（MCVD）方法结合溶液掺杂技术成功制造，其包层直径为400μm，两端直径为~24μm，中部直径为~31μm。中间。为了测试CCTC光纤在大功率运行时的性能，实验研究了基于CCTC YDF的全光纤激光振荡器。结果，尽管在约 3.12 kW 的输出功率下观察到 TMI 效应，但在光对光效率为 55.2% 的情况下实现了 3.42 kW 的最大输出功率。测量的光束质量（米2因子）为~1.7，并且在光谱中没有观察到拉曼分量的迹象。我们认为 CCTC YDF 具有同时减轻 SRS 和 TMI 效应的巨大潜力，并且通过优化 YDF 的结构进一步扩展功率是有希望的。