Halogen co-doped optical fibers

A method of forming an optical fiber, comprising:

• exposing a soot core preform to a dopant gas at a pressure of from about 1.5 atm to about 40 atm, the soot core preform comprising silica, the dopant gas comprising a Cl doping precursor and a second halogen doping precursor, the Cl doping precursor doping the soot core preform with a Cl dopant and the second halogen precursor doping the soot core preform with a second halogen dopant;
• and
• sintering the soot core preform to form a halogen-doped closed-pore body, the halogen-doped closed-pore body having a combined concentration of the Cl dopant and the second halogen dopant of at least 2.0 wt %, wherein the Cl dopant has a halogen co-doping ratio in a range from 20% to 90%.

An optical fiber, comprising:

• a cladding;
• and
• a core positioned within the cladding, the core comprising a Cl dopant and a second halogen dopant, the Cl dopant and the second halogen dopant having a combined concentration in the core in a range from 2.0 wt % to 7.5 wt %, the Cl dopant having a halogen co-doping ratio in a range from 20% to 90% in the core.