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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