Patent ID: 8544299

Claim:
A method for making a quartz glass tube as a semifinished product configured for making optical fibers, said tube having an inner fluorine-doped quartz glass layer and an outer quartz glass layer, said method comprising: producing the quartz glass of the inner fluorine-doped quartz glass layer in a first plasma deposition process so as to form on a carrier tube of quartz glass an inner layer having a wall thickness of at least 1.5 mm, with the quartz glass having a fluorine content of at least 1.5% by wt., and producing the quartz glass of the outer quartz glass layer in a second plasma deposition process depositing an outer layer thereof directly or indirectly on the inner layer so as to form a composite tube, said quartz glass of the outer layer having a viscosity and being doped with a substance that increases said viscosity relative to undoped quartz glass, said outer quartz glass layer not being doped with fluorine, or being doped with a fluorine content lower than the fluorine content of the inner quartz glass layer, and removing the carrier tube, and elongating the composite tube into the quartz glass tube.