Optical connection structure

An optical connection structure comprising:

• a multi-core fiber including a plurality of first cores each extending in a longitudinal direction, a first cladding surrounding the plurality of first cores, and a first fiber tip surface including tips of the plurality of first cores and a tip of the first cladding;
• a first ferrule having a first inner hole and a first ferrule end surface, wherein the first inner hole houses a tip part of the multi-core fiber and the first fiber tip surface is exposed in the inner part of the first ferrule end surface, the first ferrule fixing the tip part of the multi-core fiber in the first inner hole;
• a plurality of optical fibers optically connected to the multi-core fiber, each of the optical fiber including a second core extending in the longitudinal direction, a second cladding surrounding the second core, and a second fiber tip surface including a tip of the second core and a tip of the second cladding;
• and
• a second ferrule having a second inner hole and a second ferrule end surface, wherein the second inner hole houses tip parts of the plurality of optical fibers and the second fiber tip surface of each of the plurality of optical fibers is exposed in the inner part of the second ferrule end surface, the second ferrule fixing the tip parts of the plurality of optical fibers in the second inner hole with an adhesive,
• wherein the adhesive is packed in the second inner hole such that a surface of the adhesive facing the first fiber tip surface is recessed from the second ferrule end surface into the second inner hole, and
• wherein a refractive-index matching material is applied in a space defined by the first ferrule end surface the second inner hole, the surface of the adhesive that is recessed from the second ferrule end surface into the second inner hole, and the second fiber tip surface that is exposed in the inner part of the second ferrule end surface.