Optical fiber and method of making it from a preform

摘要

An optical fiber comprising a core region 100 doped with Cl which raises the refractive index; and a cladding region 200, provided at the outer periphery of the core region 100, having a cladding layer 201 doped with F which lowers the refractive index is formed. The cladding region 201 to become the outermost cladding layer is configured such that the doping amount of F successively decreases within an outer peripheral part 205 including the outer periphery thereof to a predetermined doping amount which is the minimum doping amount of F within the cladding layer 201. Therefore, the stress within the optical fiber is dispersed into the outer peripheral part 205 having an enhanced viscosity, whereby the stress concentration into the core is suppressed. Since the favorable tension range at the time of drawing the optical fiber becomes wider at this time, tension control is facilitated.