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Low-Loss and Low-DMD 6-Mode 19-Core Fiber With Cladding Diameter of Less Than 250 μm

We investigate a few-mode multicore fiber structure suitable for realizing a high spatial density while maintaining a feasible cladding diameter. First, we discuss the impact of cladding diameter on mechanical reliability, and set a target cladding diameter of less than 250 μm to maintain a comparable reliability to conventional fiber. We then optimize the 6-mode core profile to obtain a low differential mode delay (DMD) characteristic and reveal that a hexagonally arranged 19-core structure can realize more than 100 spatial channels with a cladding diameter of less than 250 μm. Finally, we fabricate 6-mode 19-core fiber with a 246 μm cladding diameter and realize a relative core multiplicity factor of more than 60 with a low loss and a DMD of less than 0.24 dB/km and 0.33 ns/km, respectively.