Method for producing deuterium-treated optical fiber, and deuterium-treated optical fiber

Provided are: an alkali metal element-added core optical fiber which has excellent hydrogen resistance characteristics; and a method which enables the production of this alkali metal element-added core optical fiber. A method for producing a deuterium-treated optical fiber of the present invention produces an alkali metal element-added core optical fiber by comprising: a preform formation step wherein a quartz glass-based optical fiber preform having a core to which an alkali metal element is added is formed; a fiber drawing step wherein an optical fiber is formed by fiber-drawing the optical fiber preform; and an exposure step wherein the optical fiber is exposed to a deuterium gas atmosphere. In the exposure step, the optical fiber is exposed to a deuterium gas atmosphere at a temperature of 20 DEG C or more under such a condition that the value of (deuterium gas partial pressure) * (exposure time) is 50 kPa.hour or more.