Few-Mode Multicore Fiber With 36 Spatial Modes (Three Modes (LP$_{\bf 01}$ , LP$_{\bf 11a}$, LP $_{\bf 11b}$) × 12 Cores)

The design and characteristics of a novel three-mode 12-core fiber are demonstrated. This fiber has low intercore crosstalk (IC-XT) and low differential mode group delay (DMD). In order to produce such a fiber, three new techniques are introduced to few-mode multicore fiber. A heterogeneous core arrangement with two types of cores, is used to minimize IC-XT; a multistep index, which can control DMD without sacrificing intermode crosstalk, is adopted as a core profile to reduce DMD; and a square lattice structure allows for the inclusion of 12 cores within a cladding diameter of 230 μm. Optimum design of the fiber using these techniques is determined from calculations. Finally, detailed characteristics of a three-mode 12-core fiber based on the design are reported. A fabricated 40-km fiber is confirmed to have a DMD of less than |530| ps/km over the C + L band and an estimated worst-case IC-XT of less than -55 dB/100 km at 1550 nm. This low IC-XT allows for the transmission of 32 QAM signals.