The building-up and suppression of cladding-mode coupling in UV exposure fiber Bragg gratings (FBGs) is investigated experimentally and theoretically. Experimental results reveal that fundamental mode can simultaneously couple to cladding modes from different groups in the un-tilted FBGs as the transmission spectrum takes on multilevel. Theoretical results indicate that due to the non-uniform refractive index profile on the transverse plane of the FBGs, core-guided fundamental mode not only couples to axis-symmetrical cladding modes LP0n, but also transfers to circular-symmetrical cladding modes like LP1n if they distribute in the core region. Based on the symmetry property of the coupled cladding modes, the "ring-by-ring" inscription is theoretically proposed to suppress the cladding mode coupling for the first time, which plays a significant role in high-power fiber lasers research and application.

中文翻译：

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光纤布拉格光栅包层模耦合的建立和抑制

通过实验和理论研究了紫外曝光光纤布拉格光栅 (FBG) 中包层模耦合的形成和抑制。实验结果表明，当传输频谱呈现多级时，基模可以同时耦合到来自未倾斜 FBG 中不同组的包层模式。理论结果表明，由于 FBG 横向平面上的非均匀折射率分布，纤芯引导的基模不仅耦合到轴对称包层模式 LP0n，而且还转移到圆对称包层模式，如 LP1n，如果它们分布在核心区域。基于耦合包层模式的对称性，首次在理论上提出了“逐环”刻字来抑制包层模式耦合，