Design and Analysis of Z-Trench-Assisted 9-LP-Mode Fiber With Low Differential Modal Group Delay and High Spatial Density

We present a novel Z-trench-assisted (Z-TA) graded index 9-LP-mode fiber that significantly suppresses the maximum absolute differential modal group delay (Max
$\vert $
DMGD
$\vert$
) while obtaining a high normalized spatial density (NSD). The finite element method (FEM) is applied for numerical simulations, and the results show that the Max
$\vert $
DMGD
$\vert $
is 18.9-ps/km at 1550-nm. To the best of our knowledge, it is improved by more than 30% compared to that of the theoretical optimal value in TA structure so far. Furthermore, the NSD of the proposed fiber can reach 44.64 at 1550-nm. Over the
$C$
band, the Z-TA 9-LP-mode fiber exhibits Max
$\vert $
DMGD
$\vert < 32.6$
-ps/km, mode field area (
$A_{eff}) > 100~\mu \text{m}^{2}$
and low bending loss. In addition, the Z-TA structure is able to maintain relatively low degradation of DMGD characteristics when strict manufacturing variabilities are considered.