Method for producing optical fiber preform, and optical fiber preform

A method for manufacturing an optical fiber preform, the method comprising:

• doping at least one element selected from an alkali metal group consisting of an alkali metal element and an alkaline earth metal element into an inner surface of a first glass pipe formed of silica-based glass;
• collapsing the first glass pipe after the doping by heating, thereby obtaining a glass rod;
• and
• performing at least one rod-in-collapse, the at least one rod-in-collapse including insertion of a rod including the glass rod into a second glass pipe and integration of the rod and the second glass pipe by heating,
• wherein the collapsing and the performing the at least one rod-in-collapse are performed while traversing an external heat source in a first direction from a first end toward a second end of the glass rod or in a second direction from the second end toward the first end, and
• wherein, in the collapsing and the performing the at least one rod-in-collapse, a difference between the number of times of the traversing in the first direction and the number of times of the traversing in the second direction is 1 or less.