Optical fiber base material and manufacturing method thereof

Abstract

There is provided an optical fiber base material having a uniform outer diameter after sintering. Moreover, there is provided a manufacturing method of an optical fiber base material for depositing and sintering soot cladding a surface of a core rod. The method includes: using the core rod of which an outer diameter is changed in a longitudinal direction; depositing the soot on the core rod to manufacture a porous base material for optical fiber; and sintering the base material to vitrify it transparently. Preferably, the method includes: previously increasing an outer diameter of a portion having the reduced outer diameter after sintering; manufacturing a new core rod that is made by previously reducing an outer diameter of a portion having the increased outer diameter after sintering; and depositing the soot on the new core rod.

1 . A method of manufacturing an optical fiber base material for depositing and sintering soot cladding a surface of a core rod, comprising: 
 using the core rod of which an outer diameter is changed in a longitudinal direction;    depositing the soot on the core rod to manufacture a porous base material for optical fiber; and    sintering the base material to vitrify it transparently.    
   
   
       2 . The manufacturing method of an optical fiber base material as claimed in  claim 1 , further comprising: 
 longitudinally measuring a elongating amount of the outer diameter of the porous base material for optical fiber in sintering;    previously increasing an outer diameter of a portion having the reduced outer diameter after sintering;    manufacturing a new core rod that is made by previously reducing an outer diameter of a portion having the increased outer diameter after sintering; and    depositing the soot on the new core rod.    
   
   
       3 . The manufacturing method of an optical fiber base material as claimed in  claim 1 , further comprising: 
 obtaining a ratio of the elongating amount of each of the measured portions to a elongating amount at a reference position; and    using the new core rod of which an outer diameter is longitudinally changed into an outer diameter made by multiplying the outer diameter by an inverse number of the ratio.    
   
   
       4 . The manufacturing method of an optical fiber base material as claimed in  claim 1 , further comprising: 
 longitudinally measuring a elongating amount of the outer diameter of the optical fiber base material that is transparently vitrified using the new core rod;    manufacturing a core rod of which an outer diameter is further corrected based on the measurement; and    depositing a clad on the manufactured core rod.    
   
   
       5 . The manufacturing method of an optical fiber base material as claimed in  claim 1 , further comprising 
 changing a manufacturing condition so that a ratio of a diameter of the core rod to a thickness of an outside sedimentary layer is constant in a longitudinal direction.    
   
   
       6 . The manufacturing method of an optical fiber base material as claimed in  claim 5 , wherein the manufacturing condition to be changed is a raw material amount supplied and moving velocity of a burner.  
   
   
       7 . The manufacturing method of an optical fiber base material as claimed in  claim 1 , further comprising cylindrically grinding a surface of the optical fiber base material after sintering.  
   
   
       8 . An optical fiber base material that is manufactured by a method for depositing soot on a surface of a core rod to manufacture a porous base material for optical fiber and sintering the porous base material to manufacture the optical fiber base material, wherein the optical fiber base material is manufactured by means of the core rod of which an outer diameter is longitudinally changed by adding a predetermined elongating amount during sintering.  
   
   
       9 . The optical fiber base material as claimed in  claim 8 , wherein a elongating amount of an outer diameter of the porous base material for optical fiber during sintering is measured in longitudinal direction, the outer diameter of the core rod at a portion having the reduced diameter after sintering is previously increased, and the outer diameter of the core rod at a portion having the increased diameter after sintering is previously reduced.  
   
   
       10 . The optical fiber base material as claimed in  claim 9 , wherein after obtaining a ratio of the elongating amount of each of the measured portions to a elongating amount at a reference position, the core rod has a longitudinal outer diameter changed into an outer diameter made by multiplying the outer diameter by an inverse number of the ratio.  
   
   
       11 . The optical fiber base material as claimed in  claim 10 , wherein the optical fiber base material is manufactured so that a ratio of the diameter of the core rod to the thickness of an outside sedimentary layer is constant in a longitudinal direction.  
   
   
       12 . The optical fiber base material as claimed in  claim 8 , wherein the optical fiber base material is manufactured by cylindrically grinding a surface of the optical fiber base material after sintering.  
   
   
       13 . A core rod for an optical fiber base material depositing thereon soot cladding a surface of the core rod, wherein a elongating amount of an outer diameter of the optical fiber base material during sintering is measured in longitudinal direction, the outer diameter at a portion having the reduced diameter after sintering is previously increased, and the outer diameter at a portion having the increased diameter after sintering is previously reduced.