| 摘要 |
A photonic bandgap fiber includes a core and a cladding that surrounds the core. In this photonic bandgap fiber, high refractive index portions which have the refractive index higher than that of a medium of the cladding are provided in the cladding so as to form a triangular lattice structure with a lattice constant A, and the refractive index of the core is higher than the refractive index of the medium of the cladding and lower than the refractive index of the high refractive index portion. At this time, the coupling length between the core and the high refractive index portion that is closest to the core is longer than the coupling length between adjacent high refractive index portions, or a periodic structure formed by the high refractive index portions is not provided around the entirely of the area along the circumference of the core.
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