Low-Crosstalk and High-RCMF Heterogeneous 7-Core 5-LP Mode Fibers With Low-Index Ring and Differentiated Air-Hole Array

This paper proposes a novel heterogeneous 7-core 5-Linear Polarization (LP)-mode space-division multiplexing (SDM) fiber based on low-index ring and differentiated air-hole array (LRDA). The core innovation of this structure lies in the synergistic design of low-index ring and air-hole array, which achieves high-density multiplexing while simultaneously ensuring low loss and ultra-low crosstalk characteristics. Numerical simulation results indicate that the fiber's bending loss meets the requirements for stable operation of five LP modes within the C+L bands. At 1550 nm, the effective refractive index difference (Δneff) between any two modes of the fiber is greater than 1.6 × 10−3. The heterogeneous inter-core crosstalk (HE-ICXT) between the central core and any adjacent outer core is less than −80 dB/100 km, and the homogeneous inter-core crosstalk (HO-ICXT) between adjacent outer cores is less than −70 dB/100 km. In addition, the relative core multiplexing factor (RCMF) reaches as high as 99.54. The manufacturing process for the designed fiber with LRDA structure is presented to verify its engineering feasibility. This paper provides an effective approach for achieving high-density independent transmission across multiple channels in SDM system.