Method of fabricating large optical preforms

A process for manufacturing an annular optical preform of a large diameter and of a predetermined height of the type capable of being drawn into an optical fiber, comprising the steps of:

• rotating a high temperature resistant flat base member about its center,
• positioning a first nozzle a predetermined distance above the center of said base member, generating an RF field at the location of said first nozzle for depositing a pyrolysed central core of glass by a vapor oxidation process on said rotating base member via said nozzle,
• positioning a second nozzle adjacent said first and to the right and a third nozzle adjacent said first and to the left, both at said predetermined distance, generating an RF field at the location of said second and third nozzles for depositing by a vapor oxidation process a pyrolysed first annular glass ring about said core on said rotating base member,
• positioning a fourth and a fifth nozzle with said fourth nozzle adjacent and to the right of said second nozzle and said fifth nozzle adjacent and to the left of said third nozzle each at said predetermined distance, generating an RF field at the location of said fourth and fifth nozzles for depositing by a vapor oxidation process a pyrolysed second annular glass ring about said first ring and on said rotating base member,
• advancing said rotating base member away from said nozzle position at a rate determined by the growth of said central core and annular rings to form a preform whose height increases as said base member advances, with the surface of said preform being parallel to the flat surface of said base member and,
• ceasing the steps of rotating, advancing and generating said RF fields, when said preform attains said predetermined height.