Patent ID: 7068901

Claim:
A method for manufacturing an optical fiber preform comprising a central core portion having a maximal value Nc of refractive index in the center, and outside the central core portion, comprising at least a depressed portion having a minimal value Nd of refractive index, a ring portion having a maximal value Nr of refractive index and an outside cladding layer having a maximal value No of refractive index, the optical fiber preform satisfying a relation of Nc≧Nr>No>Nd among the values of refractive index, the method being characterized by comprising following steps: a glass rod fabrication step of fabricating a glass rod by inserting a core rod containing at least the central core portion into a depressed pipe containing at least the depressed portion, and integrating them; a glass pipe fabrication step of fabricating a glass pipe having the ring portion; an integration step of fabricating a vitreous body by integrating the glass rod and the glass pipe after inserting the glass rod into the glass pipe; and measuring a refractive index distribution of the glass rod; and designing a ratio Ra of an outer diameter of the central core portion to an outer diameter of the depressed portion, a ratio Rb of an outer diameter of the depressed portion to an outer diameter of the ring portion, and a relative refractive index difference Δr of the ring portion to the outside cladding layer based on the measurement result.