Cleaning step to remove metals or metal oxides from porous glass body

A method of manufacturing comprising:

• a first vapor deposition step comprising vapor depositing a first porous glass body of a glass former and a doping constituent onto a substrate;
• a cleaning step after the first vapor deposition step, the cleaning step comprising exposing the first porous glass body to a cleaning gas at a cleaning temperature for a cleaning period of time, the cleaning gas (i) removing a metal or metal oxide from the first porous glass body, (ii) changing an oxidation state of a metal or metal oxide within the first porous glass body, or (iii) a combination of (i) and (ii);
• and
• a second vapor deposition step after the cleaning step, the second vapor deposition step comprising vapor depositing a second porous glass body of the glass former onto the first porous glass body resulting in a porous preform for an optical fiber;
• wherein the first vapor deposition step, the cleaning step, and the second vapor deposition step each occur in a different furnace.