Abstract: A butting step S1 of butting end surfaces of multi-core fibers against each other by aligning central axes CA of clads 20 of the multi-core fibers to cause each core 11 of one multi-core fiber 1a and each core 11 of the other multi-core fiber 1b to face each other, and a fusing step S2 of fusing the multi-core fibers to each other by carrying out discharge by a pair of discharge electrodes 50a and 50b that sandwich a butted position of the multi-core fibers and face each other are provided. The fusing step S2 causes tips 51a and 51b of the discharge electrodes to perform reciprocating motion such that a straight line SL that connects the tips 51a and 51b of the discharge electrodes moves while describing a surface perpendicular to the central axes CA.

Abstract: A multi-core fiber includes a plurality of cores, a marker which is disposed to be parallel to the cores, and a clad which surrounds outer peripheral surfaces of the cores and the marker. The marker may propagate light having a wavelength which is the same as a wavelength of light which propagates in the core as single mode light.

Abstract: A multi-core fiber includes a plurality of cores, a marker which is disposed to be parallel to the cores, and a clad which surrounds outer peripheral surfaces of the cores and the marker. The marker may propagate light having a wavelength which is the same as a wavelength of light which propagates in the core as single mode light.