Patent ID: 8662011

Claim:
An apparatus for plasma chemical vapor deposition, comprising: a resonator having a resonant cavity formed essentially cylindrically symmetrically around a cylindrical axis along which a substrate tube is positioned, wherein the resonant cavity is substantially annular in shape with a cylindrical inner wall and a cylindrical outer wall, and wherein the cylindrical inner wall comprises a slit that extends along at least part of a circle around the cylindrical axis, into which resonant cavity a microwaveguide extends so that microwaves can exit to the cavity enclosed by the cylindrical inner wall via the slit, and wherein the resonator surrounds at least part of the substrate tube and moves back and forth along the longitudinal axis of the substrate tube during deposition; a hollow inner tube positioned in close fit against the cylindrical inner wall of the resonant cavity, wherein the inner tube extends along the cylindrical axis at least part of the length of the resonant cavity and is transparent to microwaves, and wherein the inner tube is connected to the resonator and moves synchronously therewith along the longitudinal axis of the substrate tube; and an inner ring positioned at one end of the inner tube, the inner ring reducing the internal diameter of the inner tube at the location of the inner ring, the inner ring operable for centering the substrate tube within the interior of the inner tube and spacing the substrate tube apart from the interior wall of the inner tube; wherein the length of the inner tube is no more than twice the length of the resonator, and wherein the inner tube includes at least one circumferential opening extending along part of a circle around the wall of the inner tube.