Optical fiber and method for manufacturing same

摘要

Provided is an optical fiber having a large relative refractive index difference and a reduced transmission loss, as well as a manufacturing method therefor. An optical fiber preform (100), which is made of silica glass as the main element and which includes a core region having a relative refractive index difference of 2.0% or more and less than 3.0% on the basis of the refractive index of pure silica glass and a first cladding region provided around the core region and having a relative refractive index difference of -0.8% or more and less than -0.3% on the basis of the refractive index of pure silica glass, is drawn into a glass fiber. The glass fiber thus drawn is passed through an annealing furnace (21) installed below a drawing furnace (11), whereby the cooling rate of the glass fiber is restrained as compared with the case where it is cooled by air.