Multi-core holey fiber and optical transmission system

An optical transmission system comprising:

• an optical transmission unit, which outputs at least one optical signal having a wavelength included in a used transmission wavelength band;
• an optical multiplexing unit that multiplexes optical signals output from the optical transmitting unit;
• a multi-core holey fiber comprising:
• a plurality of cores arranged separately from each other;
• and
• a cladding surrounding the plurality of cores, wherein the cladding has plurality of holes arranged in a triangular lattice shape and to create hole layers around the plurality of cores;
• wherein a ratio d/Λ is less than 0.5, where Λ [μm] is lattice constant of the triangular lattice, d [μm] is diameter of each of the holes;
• a distance between adjacent cores is equivalent to not less than six hole layers;
• the core arranged farthest from the center of the multi-core holey fiber is surrounded by not less three hole layers;
• and the sum of coupling coefficients between the adjacent cores is not more than 1.6×10−5/m;
• an optical demultiplexing unit that demultiplexes the optical signals transmitted through the multi-core holey fiber;
• and
• an optical receiving unit that receives the optical signals demultiplexed by the optical demultiplexing unit;
• wherein the length of the multi-core holey fiber is not more than 1/100 of an effective coupling length based on the sum of coupling coefficients.