Holey fiber and method of producing the same

A method of producing a holey fiber by using a stack-and-draw method, the holey fiber comprising:

• a core portion;
• an inner-cladding portion positioned at an outer periphery of the core portion, the inner-cladding portion having a plurality of inner holes formed in a layered structure around the core portion;
• and
• an outer-cladding portion positioned at an outer periphery of the inner-cladding portion, the outer-cladding portion having a plurality of outer holes formed in a layered structure around the inner-cladding portion, wherein
• the inner holes are disposed to form a triangular lattice of which lattice constant Λ1 is equal to or smaller than 2.0 μm and to form equal to or greater than two layers, the outer holes are disposed to form a triangular lattice of which lattice constant Λ2 is greater than the Λ1 and equal to or larger than 3.0 μm and to form equal to or greater than two layers, and
• the overlap index is equal to or greater than 2.0%.