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Abstract

An optical fiber manufacturing method includes a drawing step and a slow cooling step. In the slow cooling step, an optical fiber passes through a heating furnace having a temperature which is set such that in at least 70% of a region from a first position at which a glass outer diameter of the optical fiber becomes less than 500% of a final outer diameter to a second position at which a temperature T of the optical fiber becomes 1400° C., an actual temperature of the optical fiber is within ±100° C. of a target temperature Tt(n) for each position n. The target temperature Tt(n) is a temperature at which a fictive temperature Tf(n+1) of a core at a position n+1 determined by calculation using the recurrence formula “Tf(n+1)=T(n)+(Tf(n)−T(n))exp(−Δt(T(n)))” starting from a fictive temperature Tf(0) of the optical fiber at the first position n=0 is lowest.

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First Claim