Since larger A_eff can achieve smaller |DMD| in the 2-LP-mode operation region (2-LP-MOR), we set target of A_eff of LP₀₁ mode at 110 μm². If W/r₁ changes, the 2-LP-MOR will shift and if W/r₁ is <~0.5, DMD will decrease immediately. According to the above characteristics of core with TA-GIP, we selected three non-identical cores with the same A_eff at different W/r₁ to make sure large Δn_eff of cores, so that the relative small threshold value of bending radius (R_pk) can be ensured.

We investigated the impact of DRS on the cable cutoff wavelength (λ_cc)$\left({\lambda }_{\mathrm{cc}}\right)$ of LP₂₁ mode in the selected cores in order to make sure the 3898134a83c79e44e413" title="Click to view the MathML source">(λ_cc)$\left({\lambda }_{\mathrm{cc}}\right)$ would not be larger than 1530 nm, which is the lowest limit of C+L band. To optimize the core arrangement, we put the core with W/r₁ of <0.5 at the outer layer, where (λ_cc)$\left({\lambda }_{\mathrm{cc}}\right)$ is not much influenced by the trenches.

TA-GIP is more suitable than trench-assisted multi-step-index profile (TA-MSIP) to obtain low |DMD|. Square lattice structure (SLS) and DRS are better than one-ring structure (ORS) to ensure small crosstalk. Additionally, DRS has less confinement degree on mode than SLS if cladding diameter and core pitch are fixed at similar values. Hence, DRS-FM-MCF with TA-GIP is proved as a more appropriate structure to achieve |DMD| of <100 ps/km, reach XT of <−30 dB/100km and guarantee 409b1386e3d64d80518f99" title="Click to view the MathML source">λ_cc${\lambda }_{\mathrm{cc}}$ is ≤1530 nm at the same time.

Finally, we compared the reported FM-MCFs and the proposed DRS-FM-MCF in this work. We found that TA-GIP is more suitable than trench-assisted multi-step-index profile (TA-MSIP) to obtain low |DMD|$\left|\mathrm{DMD}\right|$ for FM-MCF. Square lattice structure (SLS) and DRS are better than one-ring structure (ORS) to ensure small inter-core crosstalk. Furthermore, DRS has less confinement degree on mode than SLS if cladding diameter and core pitch are fixed at similar values. Hence, DRS-FM-MCF with TA-GIP is proved as a more appropriate structure to achieve the lower |DMD|$\left|\mathrm{DMD}\right|$ of $<100\mathrm{ps}/\mathrm{km}$, reach small XT of $<-30\mathrm{dB}/100\mathrm{km}$ and guarantee the maximum λ_cc${\lambda }_{\mathrm{cc}}$ is $\le 1530\mathrm{nm}$ at the same time.