Method for manufacturing optical fiber bundle, optical fiber bundle, optical connection structure, and determination method

A method for manufacturing an optical fiber bundle for optically coupling a plurality of optical fibers to a multicore optical fiber, the method comprising:

• preparing a ferrule extending along a first direction, the ferrule having a front end in the first direction, a rear end opposite to the front end in the first direction, and a first fiber accommodating hole as a hole including a first portion that is located at the front end, a second portion that is located at the rear end and has a larger inner diameter than an inner diameter of the first portion, and an inner diameter transition portion that connects the first portion and the second portion to each other;
• preparing a holding portion having a second fiber accommodating hole as a hole extending along the first direction and communicating with the first fiber accommodating hole at the rear end of the ferrule;
• preparing a plurality of optical fibers each having a glass fiber and a coating portion, the glass fiber including a first diameter portion, a second diameter portion having a larger diameter than a diameter of the first diameter portion, a tapered portion connecting the first diameter portion and the second diameter portion, a tip surface located at a tip end of the first diameter portion, and a terminal end surface opposite to the tip surface, at least the first diameter portion, the tapered portion, and the second diameter portion extending along the first direction, and the coating portion being formed by covering a glass fiber continuous with the second diameter portion with a coating;
• inserting the first diameter portion of each of the plurality of optical fibers, the tapered portion of each of the plurality of optical fibers, and a boundary between the second diameter portion of each of the plurality of optical fibers and the coating portion of each of the plurality of optical fibers into the first portion of the first fiber accommodating hole, the second portion of the first fiber accommodating hole, and the second fiber accommodating hole, respectively;
• confirming an arrangement of the plurality of optical fibers at the front end of the ferrule by conducting light from the terminal end surface of each of the plurality of optical fibers and observing the tip surface of each of the plurality of optical fibers;
• determining whether one or both of crossing and deviation occur, the crossing being a crossing within the ferrule between the first diameter portion of one optical fiber among the plurality of optical fibers and the first diameter portion of an other optical fiber among the plurality of optical fibers, the deviation being a deviation between an arrangement of the plurality of optical fibers at the front end of the ferrule and an arrangement of the plurality of optical fibers at the second fiber accommodating hole and being a deviation of a predetermined angle or more along a circumferential direction around a central axis of the first fiber accommodating hole and the second fiber accommodating hole;
• and
• fixing the plurality of optical fibers to the ferrule with an adhesive, wherein
• in the preparing the plurality of optical fibers, the coating of each of the plurality of optical fibers includes a different appearance for each optical fiber and is fixed to the coating of at least one optical fiber among other optical fibers, and
• in a case where one or both of the crossing and the deviation occur in the determining, the inserting, the confirming and the determining are performed again before the fixing.