Few-Mode Fibers for Mode-Division-Multiplexed Systems

We describe the design trade-offs that are at stake when optimizing few-mode fibers (FMFs) that support a high number (≥ 6) of LP modes. We particularly detail the design of 6-LPmode fibers that allow to multiply the capacity by a tenfold factor (two modes being spatially non-degenerate and four modes being two times spatially degenerate). For low-differential-mode-groupdelay (low-DMGD) FMFs adapted to strongly-coupled modedivision-multiplexed systems, trench-assisted graded-index-core profiles can be optimized to have Max|DMGD| eff , between the LP modes (Min|Δn eff | >1.0 × 10 -3 ) to limit mode coupling and A eff >~100 μm 2 to limit intra-mode non-linearity with good mode robustness. For such weakly-coupled FMFs, sensitivity to process variability is small and main characteristics do not significantly change when variations are within the manufacturing tolerances. We also briefly discuss experimental validations.