Impact analysis of a dense hole-assisted structure on crosstalk and bending loss in homogeneous few-mode multi-core fibers.

We present a novel dense hole-assisted structure (DHAS) in homogeneous few-mode multi-core fibers (FM-MCFs) for significantly suppressing inter-core crosstalk (XT) and bending loss while realizing a high spatial density in limited cladding diameter. The fabrication methods of DHAS FM-MCFs are illustrated and the equivalent model of DHAS is proposed. To point out the superiority, the XT of a DHAS 7-core 4-LP-mode fiber is investigated by an average power-coupling coefficients analytical expression in DHAS model and the equivalent model, respectively. A simple derived analytical expression for XT estimation in the trench-assisted homogeneous MCFs is introduced to verify the change of XT with fiber parameters in the equivalent model. The results imply that the XT obtained by the equivalent model is in good agreement with the one through DHAS model. Furthermore, the bending loss and chromatic dispersion dependences on DHAS are calculated by the finite element method (FEM). Through numerical simulations, we show that the DHAS has great contribution to meet the XT value requirement of lower than -30 dB/100km and make the bending loss values satisfy the ITU-T recommendations of G. 654 in a 7-core 4-LP-mode fiber with a 125-μm cladding diameter. The designed structure targets applications in space division multiplexing (SDM) fibers with independent transmission channels.