Optical connection structure, ferrule, and optical connector

An optical connection structure comprising:

• a plurality of optical fibers;
• a ferrule holding the plurality of optical fibers;
• and
• a tubular adapter where the ferrule is inserted and fitted such that the ferrule and another ferrule face each other in the tubular shape, wherein
• the ferrule has a first side surface and a second side surface facing each other,
• the first side surface is provided with a first recess portion or a first protrusion portion extending along a first direction in which the ferrule is inserted into the adapter,
• the second side surface is provided with a second recess portion or a second protrusion portion extending along the first direction, and
• an inner surface of the adapter is provided with a third protrusion portion or a third recess portion fittable with the first recess portion or the first protrusion portion and a fourth protrusion portion or a fourth recess portion fittable with the second recess portion or the second protrusion portion.