Abstract

We describe the design trade-offs that are at stake when optimizing few-mode fibers (FMFs) that support a high number ( $\ge$ 6) of LP modes. We particularly detail the design of 6-LP-mode 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-group-delay (low-DMGD) FMFs adapted to strongly-coupled mode-division-multiplexed systems, trench-assisted graded-index-core profiles can be optimized to have Max $\vert$ DMGD $\vert$ <10 ps/km and undesired leaky LP modes appropriately cut off, while all guided LP modes show good robustness (Bend Losses <10 dB/turn at 10 mm bend radius). Such low-DMGD FMFs being sensitive to process variability, we show how fiber concatenations can efficiently compensate for this issue and that values <25 ps/km can realistically be reached. For weakly-coupled FMFs adapted to weakly-coupled mode-division-multiplexed systems, step-index-core profiles can be optimized to have large effective index differences, $\Delta n_{\rm eff}$ , between the LP modes (Min $\vert$ $\Delta n_{\rm eff}$ $\vert$ >1.0 × 10 $^{-3}$ ) to limit mode coupling and $A_{\rm eff}$ >∼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.

© 2014 IEEE

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