Optical fiber, apparatus and method for manufacturing optical fiber

Abstract

A method for manufacturing an optical fiber by drawing an optical fiber preform softened by heating, includes cooling the optical fiber at a cooling rate of not more than 4000° C. per second at a temperature of 1200 to 1400° C. of the optical fiber; and cooling the optical fiber at a cooling rate of not more than 8000° C. per second at a temperature of 850 to 1200° C. of the optical fiber. A drawing rate of the optical fiber is not less than 1000 meters per minute.

1 . A method for manufacturing optical fiber by drawing an optical fiber preform softened by heating, comprising: 
 cooling the optical fiber at a cooling rate of not more than 4000° C. per second at 1200 to 1400° C. of the temperature of the optical fiber; and    cooling the optical fiber at a cooling rate of not more than 8000° C. per second at a temperature of 850 to 1200° C. of the optical fiber.    
   
   
       2 . The method according to  claim 1 , wherein a drawing rate of the optical fiber is not less than 1000 meters per minute.  
   
   
       3 . The method according to  claim 1 , wherein the optical fiber comprises 
 a core into which at least germanium is doped; and    a cladding that is substantially made of SiO 2 , and has    a relative refractive index difference of 0.3 to 0.5 percent of the core with the cladding;    a mode field diameter of not less than 8 micrometers at a wavelength of 1310 nanometers; and    a cable cut-off wavelength λ cc  of not more than 1270 nanometers by 22-meters method.    
   
   
       4 . The method according to  claim 1 , wherein in cooling of the optical fiber at a cooling rate of not more than 8000° C. per second, a second slow-cooling unit is used at not more than 700° C.  
   
   
       5 . The method according to  claim 1 , wherein cooling of the optical fiber at a cooling rate of not more than 8000° C. per second includes cooling the optical fiber in argon gas.  
   
   
       6 . The method according to  claim 1 , wherein cooling of the optical fiber at a cooling rate of not more than 8000° C. per second includes cooling the optical fiber in air.  
   
   
       7 . The method according to  claim 1 , wherein in cooling of the optical fiber at a cooling rate of not more than 4000° C. per second, a first slow-cooling unit is used at 800 to 1000° C.  
   
   
       8 . An apparatus for manufacturing an optical fiber by drawing an optical fiber preform softened by heating, comprising: 
 a first slow-cooling unit that cools the optical fiber drawn from the optical fiber preform at a cooling rate of not more than 4000° C. per second at a temperature of a not less than 1200 to 1400° C. of the optical fiber; and    a second slow-cooling unit that cools the optical fiber at a cooling rate of not more than 8000° C. per second at a temperature of 850 to 1200° C. of the optical fiber.    
   
   
       9 . The apparatus according to  claim 8 , wherein the temperature of the second slow-cooling unit is not more than 700° C.  
   
   
       10 . The apparatus according to  claim 8 , wherein the second slow-cooling unit cools the optical fiber in argon gas.  
   
   
       11 . The apparatus according to  claim 8 , wherein the second slow-cooling unit cools the optical fiber in air.  
   
   
       12 . The apparatus according to  claim 8 , wherein the temperature of the first slow-cooling unit is 800 to 1000° C.  
   
   
       13 . The apparatus according to  claim 8 , wherein at least one of the first slow-cooling unit and the second slow-cooling unit has a length of 1.5 meters in a direction of drawing.  
   
   
       14 . An optical fiber, comprising: 
 a core that is doped at least with germanium; and    a cladding that is substantially made of SiO 2 , and having:    a relative refractive index difference of 0.3 to 0.5 percent of the core with the cladding;    a mode field diameter of not less than 8 micrometers at a wavelength of 1310 nanometers;    a cable cut-off wavelength λ cc  of not more than 1270 nanometers by 22-meters method; and    a transmission loss of not more than 0.35 dB/km at a wavelength of 1383 nanometers,    wherein α=A/λ 4 +B is satisfied, where α is the transmission loss, A is not more than 0.905, B is not more than 0.015, and λ is a wavelength.