Slow cooling of optical fibers having halogen doped cores

A method of processing an optical fiber comprising:

• determining, for an optical fiber preform comprising at least one halogen-doped core comprising a concentration of at least one halogen, an annealing temperature based on the concentration of the at least one halogen in the at least one halogen-doped core;
• determining, based on the annealing temperature, a fiber entrance temperature and a fiber exit temperature;
• heating in a draw furnace the optical fiber preform to a temperature above a softening point of the optical fiber preform;
• drawing the optical fiber from the optical fiber preform along a draw pathway;
• and
• cooling the optical fiber in a treatment region disposed along the draw pathway at a draw speed, the optical fiber entering the treatment region at the fiber entrance temperature and exiting the treatment region at the fiber exit temperature, wherein the annealing temperature is between the fiber entrance temperature and the fiber exit temperature.

An optical fiber made by a process comprising:

• drawing the optical fiber from an optical fiber preform within a draw furnace, wherein the optical fiber extends from the draw furnace along a process pathway, and wherein the optical fiber comprises at least one halogen-doped core comprising a halogen concentration of greater than or equal to 0.5 wt %;
• and
• drawing the optical fiber through at least one slow cooling device positioned downstream from the draw furnace at a draw speed, wherein
• the at least one slow cooling device exposes the optical fiber to a slow cooling device process temperature greater than or equal to 800° C. and less than or equal to 1600° C.;
• the draw speed is such that the optical fiber has a residence time of at least 0.1 s in the at least one slow cooling device;
• and
• the optical fiber after the drawing through the at least one slow cooling device has a fictive temperature of greater than or equal to 1300° C. and less than or equal to 1485° C.