We propose a what we believe is a novel, to the best of our knowledge, high and low refractive index double-ring (HL-DR) structure in few-mode multicore fibers (FM-MCFs) to simultaneously suppress intercore cross talk (XT) and intermodal cross talk. The fabrication methods of HL-DR seven-core fiber are introduced. A series of intercore XT values are calculated by the average power coupling coefficient, which shows that the HL-DR structure has a great contribution to meet the intercore XT target of less than ${-}{{30}}\;{\rm{dB/100}}\;{\rm{km}}$ in FM-MCFs. Intermodal XT is mainly measured by the effective refractive index difference ($\Delta {n_{{\rm{eff}}}}$) between modes, and the $\Delta {n_{{\rm{eff}}}}$ between any two adjacent modes is larger than ${{2}} \times {{1}}{{{0}}^{- 3}}$. Other main fiber properties, including bending loss and dispersion, are also simulated by the finite-element method. The results imply that the bending loss can satisfy the requirement of five-LP mode operation over the C ${+}$ L band. In addition, the dispersion comparison of ${{\rm{LP}}_{01}}$ mode illustrates that the fiber dispersion performance is not significantly influenced by the addition of the HL-DR structure. Through numerical analyses, an optimal HL-DR seven-core five-LP mode fiber with low XT is obtained, and it has a relative core multiplicity factor (RCMF) of 62.17. The proposed structure targets the design and application of space division multiplexing fibers with high capacity and independent channels.

中文翻译：

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基于高低折射率双环的低串扰同质七芯五LP模光纤

我们提出了一种我们认为是新颖的，据我们所知，在少模多芯光纤 (FM-MCF) 中的高低折射率双环 (HL-DR) 结构，以同时抑制芯间串扰 (XT ) 和多式联运串扰。介绍了HL-DR七芯光纤的制作方法。通过平均功率耦合系数计算出一系列核间XT值，可见HL-DR结构对满足小于${-}{{30}}\;{\rm的核间XT目标有很大贡献{dB/100}}\;{\rm{km}}$在 FM-MCF 中。Intermodal XT 主要通过模式之间的有效折射率差（$\Delta {n_{{\rm{eff}}}}$）来衡量，而$\Delta {n_{{\rm{eff}}}}$任意两个相邻模式之间大于${{2}} \times {{1}}{{{{0}}^{- 3}}$ . 其他主要光纤特性，包括弯曲损耗和色散，也可以通过有限元方法进行模拟。结果表明，弯曲损耗可以满足 C ${+}$ L 波段上五 LP 模式操作的要求。此外，${{\rm{LP}}_{01}}$模式的色散对比表明，加入HL-DR结构对光纤色散性能没有显着影响。通过数值分析，得到了一条低XT最优HL-DR七芯五LP模光纤，其相对纤芯复数因子（RCMF）为62.17。所提出的结构针对具有高容量和独立信道的空分复用光纤的设计和应用。