We propose a novel model to explain the physical process of the thermally induced core laser leakage (TICLL) effect in a high power co-pumped ytterbium doped fiber (YDF) amplifier. This model considers the thermally induced mode bending loss decrease and the thermally induced mode instability (TMI) in the coiled YDF, and is further used to reproduce the TICLL effect in the high power co-pumped step-index $20/400$ fiber amplifier. Besides, the TICLL effect in the co-pumping scheme and counter-pumping scheme is compared. The result proves that the TICLL effect is caused by the combined effect of the thermally induced mode bending loss decrease and the TMI, and could be mitigated by adopting the counter-pumping scheme. To our best knowledge, this is the first theoretical explanation of the TICLL effect in high power fiber amplifier.

中文翻译：

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高功率共泵掺镱光纤放大器中热致纤芯激光泄漏的数值模拟

我们提出了一种新模型来解释高功率共泵掺镱光纤 (YDF) 放大器中热致纤芯激光泄漏 (TICLL) 效应的物理过程。该模型考虑了卷曲 YDF 中的热致模弯曲损耗降低和热致模不稳定性 (TMI)，并进一步用于再现高功率共泵阶跃指数中的 TICLL 效应$20/400$光纤放大器。此外，比较了共泵方案和反泵方案中的TICLL效应。结果证明TICLL效应是由热致模弯曲损耗降低和TMI共同作用引起的，可以通过采用反泵方案来缓解。据我们所知，这是对大功率光纤放大器中 TICLL 效应的第一个理论解释。