Optical fiber with low fictive temperature

Abstract

Optical fibers having low fictive temperature and methods of making such fibers are described. Management of the cooling rate of an optical fiber during fiber draw permits control over the fictive temperature of the fiber. Non-monotonic cooling rates are shown to promote reductions in fiber fictive temperature. The non-monotonic cooling includes slower cooling rates in upstream portions of the process pathway and faster cooling rates in downstream portions of the process pathway. Reduction in fiber fictive temperature is achieved by controlling the ambient temperature of the fiber to slow the cooling rate of the fiber in upstream portions of the process pathway that correspond to the fiber temperature regime in which the fiber viscosity is sufficiently low to permit efficient structural relaxation. Increases in cooling rate in downstream portions of the process pathway permit adjustment of fiber temperature as needed to meet entrance temperature requirements of downstream processing units. Lower fiber fictive temperature and lower fiber attenuation are achieved at faster draw speeds through non-monotonic cooling of fiber temperature.

What is claimed is: 
     
         1 . An apparatus for processing an optical fiber comprising:
 a slow cooling device, said slow cooling device having an entrance for receiving an optical fiber, an exit for delivering an optical fiber, and a controlled cooling region between said entrance and said exit, said controlled cooling including two or more zones for processing an optical fiber, said two or more zones including a first zone maintained at a first average ambient temperature and a second zone maintained at a second average ambient temperature, said first zone being upstream of said second zone, said second average ambient temperature being at least 500° C., said first average ambient temperature being greater than said second average ambient temperature by at least 100° C.   
     
     
         2 . The apparatus of  claim 1 , wherein said first average ambient temperature is at least 1100° C. 
     
     
         3 . The apparatus of  claim 1 , wherein said second average ambient temperature is at least 900° C. 
     
     
         4 . The apparatus of  claim 1 , wherein said first average ambient temperature is greater than said second average ambient temperature by at least 500° C. 
     
     
         5 . The apparatus of  claim 1 , further comprising a third zone, said second zone being upstream of said third zone, said third zone having a third average ambient temperature, said third average ambient temperature being at least 100° C. greater than said second average ambient temperature.