Optical fiber winding bobbin, optical fiber winding method, and bobbin-wound optical fiber

An optical fiber winding bobbin comprising:

• a main winding body portion having an outer circumferential surface around which an optical fiber is wound;
• a main winding flange that is disposed on one end portion of the main winding body portion in an axial direction and that protrudes radially outward;
• and
• a plurality of ribs that protrudes axially outward from an outer surface of the main winding flange and that is disposed on the outer surface facing an axially outer side,
• wherein the main winding flange comprises:
• an inner circumferential edge portion connected to the main winding body portion;
• a central portion;
• an outer circumferential portion having a thin portion and positioned outward from the central portion in a radial direction;
• and
• a slit that extends in the radial direction over an area from the inner circumferential edge portion to an outer circumferential edge of the main winding flange,
• an axial thickness of the thin portion is smaller than an axial thickness of the inner circumferential edge portion,
• the plurality of ribs comprises:
• first ribs disposed radially around the main winding flange at a predetermined interval;
• a second rib that is disposed adjacent to a radially inner end of the slit in a circumferential direction and that prevents deformation of the main winding flange caused by concentration of stress induced by the slit;
• and
• a third rib disposed on a side opposite to the portion adjacent to the radially inner end of the slit in the radial direction, wherein
• a central axis of the main winding flange is interposed between the second and third ribs of the outer surface in the radial direction.