A multi-core optical fiber apparatus is disclosed. The multi-core optical fiber apparatus includes a cladding comprising quartz and a plurality of cores embedded in the cladding. Each of the cores has a diameter (D) ranging from 1.3 .mu.m to 2.0 .mu.m, a numerical aperture (NA) from 0.35 to 0.45 and a refractive index profile factor (.alpha.) from 2.0 to 4.0. A center of each of the cores has a germanium content of 20 wt % to 30 wt %. An interval between adjacent cores is 3.0 .mu.m or more.