Optical fiber preform, method of manufacturing optical fiber preform, and method of manufacturing optical fiber

Abstract

A porous layer is formed by depositing a silica glass particle around a core rod. The porous layer is dehydrated. The dehydrated porous layer is sintered under a decreased pressure until the dehydrated porous layer becomes a translucent glass layer containing a closed pore. The translucent glass layer is vitrified under an ambient atmosphere including an inert gas other than a helium gas.

1 . A method of manufacturing an optical fiber that includes at least one core layer and at least one cladding layer surrounding the core layer, the method comprising:
 first fabricating including fabricating a first preform by forming a porous layer by depositing particles of glass around a core rod made of transparent glass having the core layer in a shape of a rod;   dehydrating and a sintering the first preform until the porous layer becomes a translucent glass layer containing a closed pore;   second fabricating including fabricating a second preform by inserting the dehydrated and sintered first preform into a glass tube; and   drawing the second preform, while heating the second preform, in such a manner that the translucent glass layer and the glass tube are melted and integrated, and that the translucent glass layer becomes the cladding layer of a transparent glass, wherein   the dehydrating and sintering is performed simultaneously under a temperature equal to or higher than 1250 degrees Celsius and equal to or lower than 1350 degrees Celsius in an ambient atmosphere including either one of a combination of an inert gas and a halogen gas and a combination of an inert gas and a halogen-based compound gas.   
     
     
         2 . The method according to  claim 1 , wherein
 the inert gas is a helium gas, the halogen gas is a chlorine gas, and the halogen-based compound is at least either one of a chlorine compound and a fluorine compound.   
     
     
         3 . The method according to  claim 1 , wherein
 the glass tube is formed with a plurality of glass tubes stacked in a concentric manner with respect to a longitudinal axis, the plurality of glass tubes includes a glass tube containing fluorine and a glass tube made of pure silica glass, and at least an outermost layer of the plurality of glass tubes employs the glass tube made of pure silica glass.   
     
     
         4 . The method according to  claim 1 , further comprising:
 irradiating a light beam from a direction intersecting the optical fiber;   detecting a forward scattered-light that scatters from the optical fiber ahead in a traveling direction of the light beam by an image sensor;   obtaining a scattered-light intensity distribution pattern by processing an output of the image sensor at a signal processing unit; and   determining whether there is an air bubble in the optical fiber from the scattered-light intensity distribution pattern.