Optical fiber preform production method, optical fiber preform, and optical fiber production method

An optical fiber preform production method comprising:

• inserting a glass rod into a through-hole that penetrates a cladding glass body, wherein the cladding glass body is a cladding of an optical fiber;
• after the inserting of the glass rod, integrating a dummy silica rod by:
• inserting the dummy silica rod into a connecting glass tube welded in advance to a first end of the cladding glass body,
• heating the connecting glass tube to integrate the dummy silica rod and the connecting glass tube, and
• closing a first tip opening end of the connecting glass tube;
• after the inserting of the glass rod and the integrating of the dummy silica rod, closing a second opening of the through-hole that opens in a second end of the cladding glass body by heating and deforming the second end while vacuum suctioning an inside of the through-hole of the cladding glass body from the second end;
• and
• forming a hermetically sealed inner hole by sealing both ends of the through-hole, wherein
• an internal pressure in the hermetically sealed inner hole is negative relative to atmospheric pressure.