Patent ID: 6849307

Claim:
A method of manufacturing an optical fiber by using an apparatus comprising an elongated microwave guide coupled to a resonant cavity substantially cylindrically symmetric about a cylindrical axis, the resonant cavity having a length L parallel to the cylindrical axis, an inner wall, and an outer cylindrical wall, the inner cylindrical wall comprising a slit having a width W and extending in a full circle around the cylindrical axis, and the guide having a longitudinal axis which is substantially perpendicular to the cylindrical axis and which does not intercept the slit, the elongated microwave guide configured to deliver microwave radiation energy having a vacuum wavelength λ to the resonant cavity, the width W of the slit and the length L of the resonant cavity both measured in a direction parallel to the cylindrical axis to satisfy the relationship: W≦λ/10, the method comprising: locating a substrate tube along the cylindrical axis and within the inner wall of the resonant cavity, the substrate tube having an inner surface and a length, the substrate tube and resonant cavity being substantially coaxial, and the resonant cavity being caused to move back and forth along the length of the substrate tube; using Plasma Chemical Vapor Deposition to deposit layers of doped silica on the inside surface of the substrate tube; thermally collapsing the substrate tube so as to form a preform rod; causing an extremity of the preform rod to become molten; and drawing an optical fiber from the preform rod.