Halogen-doped silica for optical fiber preforms

A method of producing halogen-doped silica comprising:

• doping a silica soot body with a gas-phase doping precursor to form a doped silica soot body, the doped silica soot body having a density in the range from 0.25 g/cm3 and 1.00 g/cm3, the gas-phase doping precursor comprising a halogen and having a partial pressure of at least 2.0 atm;
• and
• sintering the doped silica soot body to a closed-pore state, the sintering comprising:
• a first sintering treatment, the first sintering treatment transforming the doped silica soot body to a partially consolidated silica soot body in the presence of the gas-phase doping precursor, the gas-phase doping precursor having a partial pressure of at least 2.0 atm during the first sintering treatment, the partially consolidated silica soot body having a density less than 1.90 g/cm3 and at least 0.15 g/cm3 greater than the density of the doped silica soot body;
• and
• a second sintering treatment, the second sintering treatment transforming the partially consolidated silica soot body to a closed-pore silica body, the closed-pore silica body having a density of at least 1.90 g/cm3 and at least 0.05 g/cm3 greater than the density of the partially consolidated silica soot body, the second sintering treatment occurring in a gas environment having a total pressure less than 1.0 atm.