Patent ID: 8826698

Claim:
A method for manufacturing a primary preform for an optical fibre, using a plasma chemical internal vapor deposition process, wherein doped or undoped glass-forming precursors are supplied to the interior of a hollow glass substrate tube, a reaction zone in the form of a plasma is moved back and forth along the length of the hollow glass substrate tube between a point of reversal near the supply side and a point of reversal near the discharge side of the hollow substrate tube, wherein the substrate tube is positioned in a furnace and wherein such conditions are created in the reaction zone that one or more glass layer packages made up of at least two separate glass layers are deposited on the interior of the substrate tube, the method comprising the following steps: i) defining deposition conditions for the deposition of a number of glass layers to be deposited adjacent to each other and forming a glass layer package under the deposition conditions, ii) defining deposition conditions subsequent to step i) for the deposition of a successive number of glass layers to be deposited adjacent to each other and forming a subsequent glass layer package under the deposition conditions subsequent to step i), wherein the deposition conditions defined for steps i) and ii) differ from each other, and iii) optionally repeating steps i) and ii); wherein the deposition conditions defined for step iii) may be identical to the process conditions defined under steps i) and ii), wherein: the number of glass layers of each of the glass layer packages is set so that the following condition is met: N ≤ 0 , 1 * λ * Q final d * Q fibre where N=the number of glass layers in a glass layer package [-] λ=the minimum wavelength used of the optical fibre [μm] d=the thickness of a glass layer in a glass layer package of a primary preform [μm] Q final =the diameter of the final preform produced on the basis of the primary preform [mm] Q fibre =the diameter of the optical fibre [mm].