Methods of and apparatus for vapor delivery control in optical preform manufacture

An apparatus for controlling the delivery of vapor to a deposition site, said apparatus comprising:

• a deposition bubbler which contains a quantity of a liquid and which is in fluid communication with the deposition site;
• a supply bubbler which contains a quantity of the liquid and which is in fluid communication with the deposition bubbler;
• heating means for increasing the temperature of the liquid in the supply bubbler and in the deposition bubbler to vaporize liquid therein;
• means for introducing a carrier gas into the supply bubbler and for flowing the gas from the supply bubbler into the deposition bubbler to cause vapor of the liquid to become entrained in the carrier gas and to flow from the supply bubbler into the deposition bubbler and out of the deposition bubbler to the deposition site;
• and
• control means for maintaining sufficient liquid within said supply bubbler and suitable relative temperatures of the liquid in said supply bubbler and of the liquid in said deposition bubbler to control the vapor mass flow rate into and out of the deposition bubbler to prevent unintended perturbations in the deposition bubbler and cause the concentration level of the delivered vapor which is entrained in the carrier gas to be a predetermined value.