Index profile of alteration of GeO sub 2 doped silica soot bodies by dehydration/consolidation.

An attractive preform fabrication technique would involve overcladding a consolidated, doped silica core rod with soot, gel or other cost effective techniques. Process induced lightguide losses are reduced if the core rod includes a thin cladding layer. To achieve zero-dispersion and minimize losses at 1.55microns associated with step-index structures, it is desirable for the core to have a triangular, parabolic or Gaussian index profile. A process is described where GeO sub 2 doped silica soot bodies with a nominally step index profile are altered during dehydration/consolidation in a chlorine containing atmosphere. Conditions can be tailored so that the GeO sub 2 is removed from the periphery of the soot body leaving a core with a Gaussian index profile surrounded by a thin cladding layer.