Method for producing multicore optical fiber and multicore optical fiber

A method for producing a multicore optical fiber including a plurality of cores extending in a longitudinal direction of the multicore optical fiber and a common cladding that covers each of the plurality of cores, the method comprising:

• a glass rod drilling step of forming a plurality of core rod insertion holes extending in the longitudinal direction in a glass rod having a circular cross-sectional shape and forming a concave portion formation hole at a position different from positions of the plurality of core rod insertion holes to form a common cladding tube;
• a core rod inserting step of inserting core rods that are to become the plurality of cores into the respective plurality of core rod insertion holes;
• an integrating step of heating the common cladding tube and the core rods and integrating the common cladding tube with the core rods and collapsing the concave portion formation hole to form a core-cladding composite body having a noncircular cross-sectional shape and including the plurality of cores and the common cladding;
• an outline detecting step of detecting an outline of the core-cladding composite body;
• an optical fiber preform forming step of machining an outer circumferential surface of the core-cladding composite body using results obtained in the outline detecting step to form an optical fiber preform having a flat surface;
• and
• a drawing step of drawing one end of the optical fiber preform under heating to obtain the multicore optical fiber.