Patent ID: 6966201

Claim:
A method for fabricating a preform comprising: (a) doping a soot body by using an acid-base reaction to precipitate a dopant into the soot body, step (a) including: (a1) soaking the soot body in a metal chloride aqueous solution containing a dopant precursor; (a2) allowing the dopant precursor to permeate the soot body; and (a3) immersing the soot body in a solution containing ammonium hydroxide to cause dopant from the dopant precursor to precipitate into the soot body; (b) loading the doped soot body into a substrate tube; (c) stabilizing the body's position in the substrate tube; (d) rotating the substrate tube around its longitudinal axis; (e) applying heat from a heat source to the substrate tube at a first end of the body to cause the first end of the soot body to begin to sinter, and to cause the substrate tube to begin to at least partially collapse around the first end of the soot body; and (f) advancing the heat source along the substrate tube and the body to cause a progressive sintering of the body, and to cause a progressive, at least partial, collapse of the substrate tube around the body, the progressive sintering of the body leading the progressive collapse of the substrate tube.