In order to support the transmission of orbital angular momentum (OAM) modes effectively, the ring-core fiber has received a lot of attention due to the similar structure of the electric field distribution with the intensity profile of OAM mode. Both photonic crystal fibers and other micro-structured fibers almost contain a ring-core structure to support the transmission of more OAM modes. However, the middle of the ring-core fiber is usually a large air hole, and such a structure makes it difficult to manufacture the ring-core perfectly. Concave damage may occur in the ring-core. The effects of concave damage on the transmission of OAM modes are analyzed. The concave damage leads to a large effective refractive index difference between the odd and even modes of vector mode, and a method for proper compensation is proposed. The lining is added to the inner side of the ring-core, which is made of the same material as the cladding, and slightly increasing the refractive index of the lining material promotes the performance of the compensation. After numerical simulation, the walk-off distance can be increased by a factor of 2–20 after compensation.

中文翻译：

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通过在环芯光纤中添加衬里层来改善轨道角动量模式的传播来减轻凹损伤的影响

为了有效支持轨道角动量（OAM）模式的传输，环芯光纤由于其电场分布结构与OAM模式的强度分布相似而受到广泛关注。光子晶体光纤和其他微结构光纤几乎都含有环芯结构，以支持更多OAM模式的传输。然而，环芯光纤的中间通常是一个较大的气孔，这样的结构使得环芯的制造很难完美。环芯可能会出现凹形损坏。分析了凹损伤对OAM模式传输的影响。凹形损伤导致矢量模奇偶模有效折射率差异较大，提出了适当补偿的方法。环芯内侧添加衬里，其材质与包层相同，稍微提高衬里材料的折射率，可以提高补偿性能。经过数值模拟，补偿后走离距离可增加2-20倍。