A method of processing an optical fiber includes drawing the optical fiber from an optical fiber preform within a draw furnace, the optical fiber extending from the draw furnace along a process pathway, the optical fiber comprising at least one halogen-doped core; and drawing the optical fiber through at least one slow cooling device positioned downstream from the draw furnace at a draw speed. 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. An optical fiber made by such a process is also disclosed.

An optical fiber drawing furnace heating element includes a heat generator including: a tubular resistance heating element in which at least a part of an optical fiber preform is disposed in a through-hole; a first portion extending, from a first end portion, over a predetermined section along a longitudinal direction; and a second portion disposed closer to a second end portion than the first portion. The second portion has a wall thickness on a side of the first end portion being equal to or larger than a wall thickness of the first portion. The wall thickness of the second portion increases toward a side of the second end portion from the side of the first end portion.

A method of making optical fibers that includes controlled cooling to produce fibers having a low concentration of non-bridging oxygen defects and low sensitivity to hydrogen. The method may include heating a fiber preform above its softening point, drawing a fiber from the heated preform and passing the fiber through two treatment stages. The fiber may enter the first treatment stage at a temperature between 1500 C. and 1700 C., may exit the first treatment stage at a temperature between 1200 C. and 1400 C., and may experience a cooling rate less than 5000 C./s in the first treatment stage. The fiber may enter the second treatment stage downstream from the first treatment stage at a temperature between 1200 C. and 1400 C., may exit the second treatment stage at a temperature between 1000 C. and 1150 C., and may experience a cooling rate between 5000 C./s and 12,000 C./s in the second treatment stage. The method may also include redirecting the fiber with a fluid bearing device or an air-turn device.