| 摘要 |
A method for manufacturing a primary preform for optical fibres by means of an internal plasma chemical vapour deposition (PCVD) process, which method comprises the steps of: providing a hollow glass substrate tube having a supply side and a discharge side; supplying a gas flow in the interior of said hollow substrate tube via the supply side thereof, said gas flow comprising a main gas flow comprising at least one glass-forming gas and at least one secondary gas flow comprising at least one dopant; creating a plasma reaction zone in the interior of said hollow substrate tube by means of microwave radiation for effecting the deposition of glass layers on the inner surface of said hollow substrate tube, said reaction zone being moved back and forth along the longitudinal axis of said hollow substrate tube between a reversal point located near the supply side and a reversal point located near the discharge side of said hollow substrate tube, to obtain a substrate tube having glass layers deposited on its inner surface; and optionally subjecting the substrate tube having glass layers deposited on its inner surface obtained in step iii) to a collapsing treatment so as to form a solid primary preform, wherein the supply of the at least one secondary gas flow is interrupted during step iii) when the plasma reaction zone is located near or at the reversal point located near the supply side and/or the reversal point located near the discharge side. |
