Ultra-Low Crosstalk 125-μm-Cladding Four-Hole Four-Core Fibers Fabricated by the Over-Cladding Bundled Rods Method

We realized a four-core fiber with 125 μm-cladding and four-holes using a novel fabrication technique, namely the over-cladding bundled rods (OBR) method. Four air holes were successfully introduced by using the OBR method without the need for a drilling process, and this enabled a 10 dB/km improvement in the crosstalk characteristic. As a result, we realized four-core fibers with a 125 μm cladding diameter and operating in both the single mode and 2 linear polarized (LP) modes in the C + L band were realized while maintaining an inter-core crosstalk of less than -30 dB/100 km. The OBR method is a promising technique for effectively realizing a multi-core fiber with ultra-low crosstalk and a high spatial density.