Optical fiber production method

Abstract

An optical fiber production method includes: drawing an optical fiber from an optical fiber preform in a drawing furnace; and cooling the optical fiber. The optical fiber is passed through a plurality of annealing furnaces while the optical fiber is cooled. Equation (1) is held in a given period during the cooling, where a time constant of relaxation of a structure of glass forming a core included in the optical fiber is defined as τ(T), a temperature of the optical fiber at a point in time during the cooling is defined as T, a fictive temperature of glass forming the core at the point in time is defined as T f 0 , and a fictive temperature of glass forming the core after a lapse of time Δt from the point in time is defined as T f . 20° C.< T f −T =( T f 0 −T )exp(−Δ t /τ( T ))<100° C.  (1)

1 . An optical fiber production method comprising:
 drawing an optical fiber from an optical fiber preform in a drawing furnace; and   cooling the optical fiber, wherein   the optical fiber is passed through a plurality of annealing furnaces while the optical fiber is cooled; and   Equation (1) is held in a given period during the cooling, where a time constant of relaxation of a structure of glass forming a core included in the optical fiber is defined as τ(T), a temperature of the optical fiber at a point in time during the cooling is defined as T, a fictive temperature of glass forming the core at the point in time is defined as T f   0 , and a fictive temperature of glass forming the core after a lapse of time Δt from the point in time is defined as T f .
   20° C.< T   f   −T =( T   f   0   −T )exp(−Δ t /τ( T ))<100° C.  (1)
 
   
     
     
         2 . The optical fiber production method according to  claim 1 , wherein Equation (2) is held in a given period during the cooling.
   40° C.< T   f   −T =( T   f   0   −T )exp(−Δ t /τ( T ))<60° C.  (2)
   
     
     
         3 . The optical fiber production method according to  claim 1 , wherein
 a relationship of Equation (3) is held, where a preset temperature of an n th  annealing furnace of the plurality of annealing furnaces from an upstream side is defined as T sn  and a fictive temperature of glass forming a core included in the optical fiber at an outlet port of the nth annealing furnace of the plurality of annealing furnaces from the upstream side is T en .
   20° C.< T   en   −T   sn <100° C.  (3)
 
   
     
     
         4 . The optical fiber production method according to  claim 3 , wherein Equation (4) is held.
   40° C.< T   en   −T   sn <60° C.  (4)
   
     
     
         5 . The optical fiber production method according to  claim 1 , wherein
 a temperature difference between a preset temperature and a fictive temperature of glass forming the core at an outlet port is smaller in the annealing furnace provided on a downstream side than in the annealing furnace provided on an upstream side.   
     
     
         6 . The optical fiber production method according to  claim 1 , wherein
 the optical fiber is in any one of the plurality of annealing furnaces during at least certain period for which a temperature of the optical fiber is greater than or equal to 1,300° C. and less than or equal to 1,500° C.