Seal structure for optical fiber drawing furnace and optical fiber production method

A seal structure for an optical fiber drawing furnace for plugging a gap between an upper end opening of the optical fiber drawing furnace and an optical fiber glass preform which has a seed rod and a taper portion present in an upper portion thereof, the seal structure comprising:

• a first cap member which engages with the seed rod of the optical fiber glass preform;
• a second cap member which covers the taper portion of the optical fiber glass preform and the first cap member;
• a spacer member which is disposed between the first cap member and the second cap member, and supports the second cap member, adjusts a height position of the second cap member in an axial direction by a position adjustment structure, and causes a lower end of the second cap member to be positioned close to the taper portion;
• and
• a seal member which establishes a seal between the optical fiber glass preform and/or the second cap member, and the upper end opening,
• wherein the position adjustment structure comprises support portions formed on an upper surface of the spacer member in a circumferential direction and having different height positions in the axial direction.