OPTICAL FIBER AND ITS MANUFACTURING METHOD

摘要

PROBLEM TO BE SOLVED: To provide an optical fiber capable of surely reducing a transmission loss caused by a Rayleigh scattering loss or the like and its manufacturing method. SOLUTION: An optical fiber preform 2 in which the ratio of viscosity Rη=η0/ηt of the core average viscosity η0 to the whole average viscosity ηt becomes 2.5 or less is manufactured and is drawn in a line drawing furnace 11 to form the optical fiber 3. Thereafter, the optical fiber 3 is heated at a temperature within a prescribed range in a heating furnace 21 provided in the post stage and the optical fiber 3 is gradually cooled. At this time, a virtual temperature Tf within the optical fiber is lowered and the Rayleigh scattering loss is reduced. Simultaneously, the concentration of stress on the core is controlled by the condition Rη<=2.5 of the ratio of viscosity and the occurrence of a structural irregular loss or the like is reduced. Thus, the optical fiber and its manufacturing method by which the transmission loss as a whole is surely reduced are obtained.