Patent ID: 9199877
Filing Date: 2015-12-01
Classification: C03B,C03C,G02B,Y10T

Abstract:
1. An optical fiber preform manufacturing method comprising: a thermal diffusion process for oxidizing and thermally diffusing an alkali metal element into the inner side of a silica glass pipe, the glass pipe being heated with a heat source performing relative movement in the longitudinal direction of the glass pipe, while vapors of alkali metal salt generated by heating an alkali metal salt is supplied with a carrier gas to the inside of the glass pipe from an end thereof, the thermal diffusion process including: heating up the glass pipe to a temperature of 1500° C. or more and 2200° C. or less while heating the alkali metal salt at a temperature for making the vapor pressure of the alkali metal salt to be 0.1 kPa or less, and raising up the heating temperature of the alkali metal salt to a temperature for making the vapor pressure of the alkali metal salt to be larger than 0.1 kPa, while maintaining the heating temperature of the glass pipe at 1500° C. or more and 2200° C. or less; a collapsing process for forming a core rod by collapsing the glass pipe after the thermal diffusion process; and a cladding process for adding a cladding part around the circumference of the core rod.