Abstract
In this paper, we investigate the design of few-mode fibers (FMFs) guiding 2 to 12 linearly
polarized (LP) modes with low differential mode delay (DMD) over the C-band, suitable for
long-haul transmission. Two different types of refractive index profile have been considered: a
graded-core with a cladding trench (GCCT) profile and a multi-step-index (MSI) profile. The
profiles parameters are optimized in order to achieve: the lowest possible DMD and macro-bend
losses (MBL) lower than the ITU-T standard recommendation. The optimization results show that the
MSI profiles present lower DMD than the minimum achieved with a GCCT profile. Moreover, it is
shown that the optimum DMD and the MBL scale with the number of modes for both profiles. The
optimum DMD obtained for 12 LP modes is lower than 3 ps/km using a GCCT profile and lower than
2.5 ps/km using a MSI profile. The optimization results reveal that the most preponderant
parameter of the GCCT profile is the refractive index relative difference at the core center,
${\Delta}n_{co}$
. Reducing
${\Delta}n_{co}$
, the DMD is reduced at the expense of increasing the MBL. Regarding the MSI
profiles, it is shown that 64 steps are required to obtain a DMD improvement considering 12 LP
modes. Finally, the impact of the fabrication margins on the optimum DMD is analyzed. The
probability of having a manufactured FMF with 12 LP modes and DMD lower than 12 ps/km is
approximately 68% using a GCCT profile and 16% using a MSI profile.
© 2013 IEEE
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