Method of manufacturing optical fiber base material

A method of manufacturing an optical fiber base including a core, a first cladding, and a second cladding, the manufacturing method comprising:

• preparing a starting base that includes the core and the first cladding covering the core;
• thereafter, forming a porous glass base by supplying glass raw material and oxygen to an induction thermal plasma torch including a gas induction portion with a multiple coaxial tube structure and depositing glass fine particles synthesized by the induction thermal plasma torch on a surface of the starting base;
• and
• thereafter, vitrifying the deposited glass fine particles in an atmosphere containing fluorine by heating the porous glass base in the atmosphere containing fluorine, thereby forming a glass base that includes a second cladding containing fluorine and covering the first cladding, wherein
• said preparing the starting base includes:
• extending the starting base to adjust an outer diameter of the starting base by heating the starting base;
• and
• removing a surface adjacent to a surface of the extended starting base, said removing the surface including performing one or more processes selected from the group consisting of machine polishing and wet etching with hydrofluoric acid.