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US 4,473,596 AGranted
Plasma method for coating the inside surface of a glass tube
AssigneeInternational Standard Electric Corporation
InventorsHans Beerwald, Gunter Bohm, Gunter Glomski, Manfred Wittmann
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Abstract
A method of making optical fibers by plasma chemical vapor deposition (PCVD) is disclosed wherein the pressure in the glass tube is maintained constant by controlling the rate of evacuation. The pressure-dependent controlled variable is preferably the impedance of the plasma-producing device, and the rate of evacuation is controlled in such a way that this impedance remains constant.
Claims5
A method of coating the inside surface of a glass tube by the steps of:
- feeding a gas mixture through the tube at a substantially constant flow rate and maintaining the gas pressure within a range of about 1 to about 100 mbars;
- forming a plasma zone in the tube and moving said zone along the tube in the axial direction thereof;
- controlling the rate of evacuation to maintain the gas density in the plasma zone substantially constant.
Dependencies are inferred from the claim text.