Optical fiber manufacturing method using relative bulk densities

An optical fiber manufacturing method for manufacturing an optical fiber that includes a core portion made of glass and a cladding portion made of glass and formed on outer periphery of the core portion, the optical fiber manufacturing method comprising:

• setting such that a first holding member and a core rod are placed inside a glass pipe constituting the cladding portion, the first holding member being one of a pair of holding members that are made of glass and have a plurality of holes formed thereon, the core rod including a core forming portion serving as the core portion and including a cladding forming portion serving as a portion adjacent to the core portion across outer periphery of the core portion, in such a way that the core rod is supported by the first holding member;
• filling glass particles in a gap between the core rod and an inner wall of the glass pipe;
• holding the core rod such that a second holding member of the pair of holding members is placed inside the glass pipe, in such a way that the core rod is held in a sandwiched manner in between the first holding member and the second holding member, and the core rod and the filled glass particles are housed in an area enclosed by the inner wall of the glass pipe, the first holding member, and the second holding member, and
• sealing one end portion of the glass pipe and manufacturing an intermediate object;
• and
• manufacturing an optical fiber using the intermediate object, wherein
• a bulk density of the first holding member and the second holding member is set to be within a predetermined range with reference to bulk density of a filling portion filled with the glass particles, and
• the predetermined range is determined according to a permissible variation range for a core diameter in longitudinal direction of the optical fiber.