| 摘要 |
In the present invention, a plurality of cores (51) is disposed around the center axis of a first cladding (52) in the state in which a center axis distance is equal between cores adjacent to each other. The first cladding (52) has a two-layer structure formed of a solid inner layer (52A) passed through the center axis of the first cladding (52) and an outer layer (52B) enclosing the inner layer (52A) and the plurality of cores (51) with no gap. A refractive index n1 of the core (51) is provided higher than refractive indexes (n 2A ) and (n 2B ) of the inner layer (52A) and the outer layer (52B), the refractive indexes (n2A) and (n2B) of the inner layer (52A) and the outer layer (52B) are provided higher than a refractive index n3 of the second cladding 53, and the refractive index (n 2A ) of the inner layer (52A) is provided lower than the refractive index (n 2B ) of the outer layer (52B). |
