Based on the coupling mode theory and numerical simulation, intramode-group coupling in orbital angular momentum (OAM) fibers with elliptical deformation is analyzed in depth. The elliptical deformation not only introduces a time delay difference between even and odd modes of the same high-order vector mode but also destroys the structure of the high-order vector modes; the structural damage depends on the strength of the elliptical deformation. When the elliptical deformation is relatively small, the structural damage of high-order vector modes can be ignored and coupling can be thought as occurring only between two OAM modes composed of the same high-order vector mode. While the elliptical deformation becomes larger, the structural damage cannot be ignored, coupling appears among four OAM modes in the same OAM mode group, and the coupling between two OAM modes composed of the same high-order vector mode is more serious. The results will pave the way for the establishment of accurate propagation models and the optimization of the OAM fiber design.

中文翻译：

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轨道角动量光纤椭圆变形引起的模内群耦合效应


基于耦合模理论和数值模拟，对椭圆变形轨道角动量（OAM）光纤中的模群内耦合进行了深入分析。椭圆变形不仅引入了同一高阶矢量模的偶模和奇模之间的时延差，而且破坏了高阶矢量模的结构；结构损伤取决于椭圆变形的强度。当椭圆变形较小时，高阶矢量模态的结构损伤可以忽略不计，耦合可以认为只发生在由同一高阶矢量模态组成的两个OAM模态之间。当椭圆变形变大时，结构损伤不容忽视，同一OAM模态组中的4个OAM模态之间出现耦合，且由同一高阶矢量模态组成的两个OAM模态之间的耦合更为严重。研究结果将为准确传播模型的建立和OAM光纤设计的优化铺平道路。