Crystal fiber manufacturing method

A method for producing a crystal fiber of cross-sectional light emission center distribution type which concentrates a light emission center on or near the middle in a cross section of the crystal fiber, the method comprising the steps of:

• using, as a preform, the crystal fiber comprising a light emission center that volatilizes from a melted portion upon the melting of a crystal, and heating a portion of the side of the preform or a plurality of portions of the side of the preform positionally equal in the longitudinal direction of the preform, whereby the portion or the plurality of portions of the preform are melted such that only a given amount of the inside of the portion or the plurality of portions of the preform is not melted, to form the melted portion;
• sequentially transferring the melted portion in the longitudinal direction of the preform, and cooling the melted portion, whereby the melted portion is continuously recrystallized to form a first recrystallized region;
• a) heating a site that is the portion of the side of the preform or the plurality of portions of the side of the preform positionally equal in the longitudinal direction of the preform, and is a portion other than the first to n−1th (wherein n represents a positive integer with 2 as an initial value) recrystallized regions thus formed, whereby the portion or the plurality of portions of the preform are melted such that only a given amount of the inside of the portion or the plurality of portions of the preform is not melted, to form the melted portion;
• b) sequentially transferring the melted portion in the longitudinal direction of the preform, and cooling the melted portion, whereby the melted portion is continuously recrystallized to form a nth recrystallized region;
• and
• c) when the maximum value of the n is defined as M (wherein M represents a positive integer of 2 or larger), repeating the steps a) and b) predetermined times by increasing the n one by one until the n becomes predetermined M.