Optical fiber preform producing method, optical fiber production method, and optical fiber

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 becoming the central core portion;
• a glass pipe fabrication step of fabricating a glass pipe by depositing a glass layer having at least one or more refractive indexes inside a starting pipe;
• and
• 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, wherein
• an ellipticity of each of the glass rod and the glass pipe in an inner diameter or outer diameter is 1% or less.

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 becoming the central core portion;
• a glass pipe fabrication step of fabricating a glass pipe by depositing a glass layer having at least one or more refractive indexes inside a starting pipe;
• and
• 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, wherein
• an MCVD method is employed to deposit the glass layer inside the starting pipe, in which a deposition rate of glass layer is 0.4 g/min or more.