Low Loss Ultra-Small Core Pitch All-Fiber Fan-In/Fan-Out Device For Coupled-Core Multicore Fibers

We designed and fabricated all-fiber fan-in/fan-out (FI/FO) devices using a fused taper technique for square lattice structure coupled-core multicore fiber (CC-MCF). A vanishing core bridge fiber with a diameter of 80 μm was tailor-designed to minimize both the mode field mismatch and the required tapering ratio at the same time. In experiment, we succeeded in fabricating FI/FO devices with a core pitch as small as 17 μm and achieving practically low insertion losses of 1.43 dB and 2.28 dB for fan-in and fan-out devices, respectively. The fabricated FI/FO devices can well multiplex and demultiplex 1550 nm light into and out from the CC-MCF without obvious total power fluctuation even when an external perturbation is intentionally imposed on the CC-MCF. The proposed FI/FO device is very useful for both the study and application of CC-MCFs which usually have ultra-small core pitches.