This paper proposes a novel refractive index profile design based on few-mode fibers (FMFs) which can support 4 linear polarization (LP) modes. We first present a FMF whose core is dually assisted by a nano-hole (NH) and a high-index-ring (HIR), and then substitute the dual assistance by an innovative graded concave HIR (GC-HIR) assisted structure. Using the finite element method (FEM), the parameters of the NH-HIR and GC-HIR optical fiber are adjusted to investigate their respective minimum effective refractive index difference (minΔ n _eff ), which is 2.012 × 10 ⁻³ for the former, and 2.532 × 10 ⁻³ for the latter. Both optical fibers have a significant improvement on the crosstalk suppression effect, and the GC-HIR optical fiber is even better. The proposed GC-HIR FMF with special refractive index profile has potential application prospects in mode division multiplexing (MDM) optical fiber communication system, and can provide theoretical foundation for the design and analysis of subsequent optical fibers and key components.

中文翻译：

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渐变凹高折射率环的弱耦合少模光纤

本文提出了一种基于少模光纤（FMF）的新颖的折射率分布设计，它可以支持4种线性偏振（LP）模式。我们首先介绍一种FMF，其核心由纳米孔（NH）和高折射率环（HIR）双重辅助，然后用创新的渐变凹面HIR（GC-HIR）辅助结构代替双重辅助。使用有限元方法（FEM），调整NH-HIR和GC-HIR光纤的参数，以研究它们各自的最小有效折射率差（minΔ ñ _eff ），前者为2.012×10 ^-3，后者为2.532×10 ^-3。两种光纤的串扰抑制效果都有显着提高，GC-HIR光纤甚至更好。提出的具有特殊折射率分布的GC-HIR FMF在模分复用（MDM）光纤通信系统中具有潜在的应用前景，并可以为后续光纤和关键部件的设计和分析提供理论基础。