The part of the cross-sectional area of an optical fiber within which the refractive index is everywhere greater than that of the innermost homogeneous cladding, by a specified fraction of the difference between the maximum refractive index of the core and the refractive index of the innermost cladding. Note 1: Artifacts of the manufacturing process, such as refractive index dip, are ignored in computing the points (refractive indices) of demarcation. Note 2: The core area is the cross-sectional area within which the refractive index is given by where n1 is the maximum refractive index of the core, n2 is the refractive index of the homogeneous cladding adjacent to the core, n3 is the defining refractive index, and m is a fraction, usually not greater than 0. 05.