Optical fiber bundle structure, optical fiber connection structure, and optical fiber bundle structure manufacturing method

An optical fiber bundle structure manufacturing method comprising:

• inserting a glass fiber portion of an optical fiber core wire into a capillary, the optical fiber core wire including the glass fiber portion including a core and a clad and a resin coated portion;
• melting and drawing the capillary and the glass fiber portion inserted in the capillary such that d2/d1 is equal to or larger than 0.57 and smaller than 1, where d1 is a diameter of the core of the glass fiber portion in a rear end portion of the capillary and d2 is a diameter of the core of the glass fiber portion in a distal end portion of the capillary;
• and
• cutting a portion that is drawn by the melting and drawing such that a cross section crossing an axial direction of the capillary is exposed,
• wherein the capillary has a hollow shape and includes a large-diameter portion, a tapered portion, and a small-diameter portion, and
• wherein t≤3.1Λ, where t is a thickness of the small-diameter portion of the capillary, and Λ is a distance between the cores of the plurality of optical fiber core wires located in the small-diameter portion.