Patent ID: 8532454

Claim:
A multi-core optical fiber comprising: a plurality of core portions; and a cladding portion that is positioned so as to surround outside of the core portions and has a refractive index that is lower than a refractive index of each of the core portions, wherein a diameter of each of the core portions is equal to or smaller than 12 micrometers, a relative refractive-index difference of each of the core portions with respect to the cladding portion is equal to or larger than 0.2%, a cut-off wavelength is equal to or shorter than 1.53 micrometers, a bending loss caused by winding around a diameter of 20 millimeters at a wavelength of 1.55 micrometers is equal to or smaller than 10 dB/m, an effective core area of each of the core portions at a wavelength of 1.55 micrometers is equal to or larger than 30 μm 2 , and an interval distance between each of the core portions and another one of the core portions positioned adjacent thereto is set so that cross-talk of light between these core portions for a total length is equal to or smaller than −35 decibels at a wavelength of 1.55 micrometers.