Abstract: A method for producing an optical fiber preform starting with a first-generation target typically comprising pure silica. A plasma torch deposits an annular region of doped silica to form an intermediate structure. The intermediate structure is drawn down to a second-generation target and another annular region of doped silica is deposited. The process is repeated a plurality of times until an Nth generation target is formed. The deposition optionally employs repeated cycles of depositing a plurality of layers of silica at a high traversal rate without sintering, followed by periodic sintering. In a further embodiment, stabilizer bars extending out from the plasma coils improve distribution of the deposition material. Another embodiment injects the source gas into a particular region of the plasma for control of soot deposition.

Abstract: An apparatus and method for producing a tubular member, which is suitable for use as a starter tube or an optical fiber preform, on a rotating cylindrical target mounted on a lathe. The tubular member is made by means of plasma outside vapor deposition. In this process, a source gas comprising SiCl4 and, optionally, a fluorine-laden chemical, is introduced into an air plasma. Both the air and the source gas are dry gases and have low hydroxyl content. The air plasma is created by a high-frequency induction plasma torch which travels along the length of the target on a carriage. The torch is provided with a short U-shaped gutter on either side of its rim directly beneath the target and the growing tubular member. This gutter helps channel reaction products of the source gas and the plasma so as to enhance deposition on the growing tubular member.