1. Field of the Invention
The present invention relates to a multi-core optical fiber having a plurality of core portions.
2. Description of the Related Art
As means for remarkably increasing communication capacity, multi-core optical fibers, each having a plurality of core portions, have been disclosed.
As one type of the multi-core optical fibers, a multi-core holey fiber is disclosed (see Japanese National Publication of International Patent Application No. 2008-534995). This holey fiber is an optical fiber that has core portions and a cladding portion positioned around the core portions and having a plurality of holes arranged around the core portions. In the holey fiber, an average refractive index of the cladding portion is reduced by the holes, and the principle of total reflection of light is utilized to confine the light to the core portions and to propagate the light (see International Publication Pamphlet No. WO2008/093870). Because the refractive index is controlled by the holes, the holey fiber is able to realize endlessly single mode (ESM) characteristics realizing single mode transmission at all wavelengths and unique properties such as anomalous dispersion at shorter wavelengths. A multi-core holey fiber is a holey fiber having a plurality of core portions, and is thought of as being possible to realize SDM transmission in addition to the ESM characteristics.