| abstract |
The invention relates to the manufacturing of a preform having at least one fluorine doped region. One method of the invention for producing the fluorinated preform includes heat treating a porous soot preform, the preform substantially devoid of any sintered glass layer, to a temperature of greater than about 1200° C. The method further includes exposing the preform to an atmosphere comprising a fluorine containing compound, wherein the time and the temperature of said exposing step is controlled so that Φ comprises≧about 1 wherein Φ is defined as R max /(D/k) ½ , wherein R max is the outer radius of the preform, D is the diffusion coefficient of the fluorine containing compound into the preform, and k is the reaction rate constant of the reaction between the fluorine and the soot, thereby controlling the radial penetration of fluorine into the preform. A second method includes depositing fluorine doped silica soot on a starting member to form a soot preform having at least one fluorine doped soot region and heating the soot preform at a rate of more than about 10° C./min to a temperature of more than about 1300° C. A third method includes heating a preform having at least one region of fluorine doped soot at a rate of more than about 10° C./min to a temperature of more than about 1400° C. |