Abstract: The inside of a tube of an electrically insulating material is coated with a layer of electrically insulating material by reactive deposition of the coating material from a gas mixture which is passed through the tube. The tube is heated and the deposition is activated by a plasma produced by microwaves. The plasma reciprocates in the tube. Energy consumption is reduced by heating the tube to the reaction temperature at least partly by the energy supplied by the plasma to the tube wall. Thermal losses of the tube are reflected back to the tube wall by a heat reflecting element.

Abstract: Optical fibres are manufactured by etching the inner wall of a tube. The tube wall is etched by passing a hydrogen-free fluorine compound through the tube while reciprocating a nonisothermal plasma through the tube. After etching, core glass is chemically deposited on the etched surface. The core glass is deposited from the gaseous phase while using a nonisothermal plasma for initiating the reaction. The inner-coated tube is then collapsed and drawn to form an optical fiber.