Provided is a photonic crystal fiber capable of fusion-splicing with an ordinary optical fiber at low splicing loss and having a core region and a cladding region that surrounds the core region, wherein the cladding region is structured such that high refractive index sub-regions are periodically arranged in a two-dimensional periodic structure in the low refractive index background sub-region at a cross-section perpendicular to the fiber axis, and wherein the refractive index of the core region is higher than the refractive index of the low refractive index background sub-region. The refractive index profile of the photonic crystal fiber is uniform along the fiber axis. The effective refractive index of the core guided mode may be higher than the refractive index of the low refractive index background sub-region.
