Low-crosstalk homogeneous 7-core 5-LP-mode fiber based on high and low refractive index double-ring

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 −30dB/100km in FM-MCFs. Intermodal XT is mainly measured by the effective refractive index difference (Δneff) between modes, and the Δneff between any two adjacent modes is larger than 2×10−3. 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 LP01 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.