The present invention relates to a method of removing a substrate tube from the deposited layer inside of said substrate tube. In other words, the present invention relates to a method for manufacturing a precursor for a primary preform for optical fibers by means of an internal plasma deposition process, which method comprises the steps of providing a hollow substrate tube; creating a first plasma reaction zone having first reaction conditions in the interior of said hollow substrate tube by means of electromagnetic radiation for effecting the deposition of non-vitrified silica layers on the inner surface of said hollow substrate tube, and subsequently creating a second plasma reaction zone having second reaction conditions in the interior of said hollow substrate tube by means of electromagnetic radiation for effecting the deposition of vitrified silica layers on the non-vitrified silica layers deposited in the previous step; and removing the hollow substrate tube from the vitrified silica layers and the non-vitrified silica layers to obtain a deposited tube.

An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index .sub.1MAX, and a inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

A method for manufacturing a precursor for a primary preform for optical fibers by an internal plasma deposition process including the steps of providing a hollow substrate tube, creating a first plasma reaction zone having first reaction conditions and depositing non-vitrified silica layers along at least a portion of the inner surface of the substrate tube, subsequently creating a second plasma reaction zone having second reaction conditions different from the first reaction conditions and depositing vitrified silica layers along at least a portion of the substrate tube, and cooling the substrate tube to produce the precursor for a primary preform.

An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index .sub.1MAX, and a inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

A method for carrying out a plasma deposition process including the steps of providing a substrate tube, supplying dopant-containing glass-forming gases to the substrate including a main gas flow and one or more secondary gas flows, inducing a plasma in the substrate tube, moving a reaction zone back and forth in strokes between a reversal point near the supply side and a reversal point near the discharge side, and interrupting the secondary gas flow during a portion of each stroke, each interruption having a start point and an end point within the same stroke.

The invention relates to an apparatus for performing a plasma chemical vapor deposition process. The apparatus comprises a mainly cylindrical resonator being provided with an outer cylindrical wall enclosing a resonant cavity extending in a circumferential direction around a cylindrical axis. The resonator is further provided with side wall portions bounding the resonant cavity in the cylindrical direction, and with a slit configuration extending in a circumferential direction around the cylindrical axis providing access from the resonant cavity radially inwardly. Further, the slit configuration includes slit sections that are mutually offset in the cylindrical direction.

A method for manufacturing a primary preform for optical fibers via an internal plasma chemical vapor deposition (PCVD) process in a hollow silica substrate tube having a supply side and a discharge side includes depositing doped or non-doped silica layers on the inner surface of the hollow substrate tube by supplying glass-forming gasses to the interior of the hollow substrate tube via the supply side thereof, and by creating a plasma reaction zone in the interior of the hollow substrate tube via microwave radiation having a microwave power, wherein the microwave power is decreased during the depositing.

The invention relates to a method and an apparatus for performing a plasma chemical vapour deposition process. The apparatus comprises a mainly cylindrical resonator being provided with an outer cylindrical wall and an inner coaxial cylindrical wall defining therebetween a resonant cavity that is operable at an operating frequency. The resonant cavity extends in a circumferential direction around a cylindrical axis of the inner and outer cylindrical wall. Further, the outer cylindrical wall includes an input port connectable to an input waveguide. In addition, the inner cylindrical wall includes slit sections extending in a circumferential direction around the cylindrical axis. A greatest dimension defining the aperture of the slit sections is smaller than half the wavelength of the operating frequency.