Method for the production of a blank mold for optical fibers

Abstract

In a known method for the production of a blank mold for optical fibers, a fluorine-doped SiO 2 enveloping glass is produced on a core glass cylinder that rotates about its longitudinal axis, wherein a silicon-containing starting substance is fed to a plasma burner, said substance is then oxidized in a plasma flame assigned to the plasma burner to obtain SiO 2 particles, the SiO 2 particles are deposited by layers on the enveloping surface of the cylinder of the core glass cylinder in the presence of fluorine and sintered into the enveloping glass. The invention aims at providing an economical method, which builds upon the above-mentioned method, in order to produce a blank mold from which optical multi-mode fibers ( 52 ) can be obtained. In comparison with fibers ( 51 ) produced according to standard methods, said optical multi-mode fibers are characterized by high initial transmission in the UV wavelength range and good resistance with respect to brief UV radiation, more particularly in the 210-300 nm wavelength range. According to the invention, a plasma flame that irradiates an ultraviolet light having a wavelength of 214 nm with an intensity of at least 0.9 μW—determined on the basis of plasma flame intensity measurement—is used for the formation and deposition of the SiO 2 particles on the core glass.

1 .- 5 . (canceled) 
   
   
       6 . A method for producing a preform for optical fibers said method comprising:
 providing a cladding glass tube of fluorine-doped quartz glass for cladding a core glass cylinder, wherein said cladding glass tube is produced by supplying a silicon-containing starter substance to a plasma burner, said plasma burner having a plasma flame that oxidizes said substance forming SiO 2  particles, said SiO 2  particles being deposited in layers in the presence of fluorine on a cylindrical outer surface of a substrate tube which is rotating about a longitudinal axis thereof and is made from quartz glass, and wherein said particles are sintered,   collapsing said cladding glass tube onto said core glass cylinder, and   removing said substrate tube prior to collapsing said cladding glass tube.   
   
   
       7 . The method according to  claim 6 , wherein said substrate tube is removed by etching. 
   
   
       8 . The method according to  claim 6 , wherein said substrate tube is etched off during production of the cladding glass tube by introducing an etching gas. 
   
   
       9 . The method according to  claim 8 , wherein said etching gas is SF 6 . 
   
   
       10 . The method according to  claim 6 , wherein said substrate tube has a wall thickness ranging from 2 mm to 10 mm.