Resolving the DMD-crosstalk trade-off in SDM through graded-index FMF

This paper investigates the detailed impact of all three graded-index-fiber (GIF) parameters on the balance between DMD and crosstalk. We report an optimized 4-LP-mode GIF offering LP₀₁, LP₁₁, LP₂₁, and LP₀₂, with a minimum |Δneff| = 0.6 × 10⁻³, maximum |DMD| = 5.4 ns/km, while minimum |Aeff| = 80 μm2 and bending loss (BL) of the highest order mode is 0.005 dB/turn (much lower than 10 dB/turn) at a 10 mm bend radius, for core-radius a = 7 to 9 μm, Δn = 0.014 to 0.016, and α = 2 to 4. In this study, we successfully addressed the challenge of degeneracy between LP₂₁ and LP₀₂ in FM-GIF, which has been difficult to overcome. To the best of the authors' knowledge, this is the lowest reported DMD value (≈ 5.4 ns/km) achieved in such a weakly-coupled (|Δneff| = 0.6 × 10⁻³) 4-LP-GI-FMF.