Method of producing internally coated glass tubes for the drawing of fibre optic light conductors

Abstract

In the reactive deposition of the core material from a gas which is passed through the tube onto the inner wall of the tube by means of a plasma zone, while a relative motion is effected in the axial direction between the tube and a plasma-producing device, the rate of precipitation is increased without impairing the quality of the core material coat, the reactive deposition being effected at a pressure of from 1 to 100 Torr and a temperature zone being superimposed on the plasma zone.

What is claimed is: 
     
       1. A method of producing internally coated glass tubes for drawing fiber optic light conductors which consists of a core and a jacket of glasses which have a mutually different refractive index, comprising the steps of introducing into a glass tube surrounded by a resonator a reactive gas mixture consisting of SiCl 4  and oxygen at a pressure of about 1 to 100 Torr, adding GeCl 4  to the gas mixture moving the tube relative to the resonator to form .[.a.]. non-isothermal plasma zone within the tube, and heating the tube to a temperature between 800° C.-1200° C. to form a coating free of soot-like particles and consisting of a plurality of layers of SiO 2  doped with an increasing content of GeO 2 . 
     
     
       2. A method as claimed in claim 1 wherein the gas mixture consists of about 96% by volume of oxygen and 4% by volume of SiCl 4 . 
     
     
       3. A method as claimed in claim 2 wherein up to 0.4% by volume of germanium tetrachloride (GeCl 4 ) is added to the reactive gas mixture. .Iadd. 
     
     
       4.  A method of producing internally coated glass tubes, for drawing fibre-optic light conductors which consist of a core and a jacket of glasses which have a mutually different refractive index, comprising the steps of introducing into a glass tube surrounded by a resonator a reactive gas mixture comprising SiCl 4  and oxygen at a pressure of about 1 to 100 Torr, moving the tube relative to the resonator 2 and heating the tube to a temperature between 800° C.-1200° C. while activating the resonator to form a nonisothermal plasma zone within the tube, whereby a coating free of soot-like particles and consisting of a plurality of layers of SiO 2  is formed. .Iaddend. .Iadd.5. A method of producing internally coated glass tubes, as claimed in claim 4, further comprising the step of adding a dopant-forming compound to the gas mixture. .Iaddend. .Iadd.6. A method of producing internally coated glass tubes, as claimed in claim 5, wherein the dopant-forming compound is one or more compounds from the group consisting of TiCl 4  AlCl 3 , and GeCl 4 . .Iaddend. .Iadd.7. A method of producing internally coated glass tubes, as claimed in claim 5 or 6 wherein the dopant-forming compound is added to the gas mixture at a constant rate. .Iaddend. 
     
     
        .Iadd.    A method of producing internally coated glass tubes, as claimed in claim 9, wherein the dopant-forming compound is added to the gas 
     
     
        mixture at an increasing rate. .Iaddend. .Iadd.9.  A method of producing internally coated glass tubes, as claimed in claim 5 or 6 wherein the dopant-forming compound is added to the gas mixture at a varying rate. .Iaddend. .Iadd.10. A method of producing internally coated glass tubes, as claimed in claim 9, wherein the dopant-forming compound is added to the 
     
     
        gas mixture at a decreasing rate. .Iaddend. .Iadd.11.  A method of producing internally coated glass tubes, as claimed in claim 9, wherein the dopant-forming compound is added to the gas mixture at a rate which will produce a coating whose index of refraction increases toward a central axis of the tube. .Iaddend. .Iadd.12. A method of producing coatings on walls of glass comprising the steps of: contacting at least a portion of the wall of the glass with a mixture of a gaseous glass-forming compound and gaseous oxygen at a pressure of about 1 to 100 Torr;   forming a plasma zone in the gas mixture in contact with the glass wall portion;   heating the glass wall portion, to a temperature which is above the temperature necessary to produce substantially stress-free coating layers on the heated tube wall portion but which is below the temperature at which there is substantial reaction of the mixture in the gas phase, to produce a nonisothermal plasma zone; and   thereby causing a heterogeneous reaction to occur on the glass wall resulting in the deposit on the glass wall of a glass coating. .Iaddend.   
     
     
        .Iadd.13.  A method as claimed in claim 12, characterized in that the glass wall is in the form of a tube and further comprising the step of causing relative movement between the plasma zone and the tube. .Iaddend. .Iadd.14. A method as claimed in claim 13, characterized in that the coating and the gas mixture are on the inside of the tube, and the glass-forming compound is a silicon tetrahalide. .Iaddend. .Iadd.15. A method as claimed in claim 14, characterized in that the tube is heated to a temperature which is not greater than 1200° C. and not below 800° C. .Iaddend. .Iadd.16. A method as claimed in claim 15, characterized in that the plasma is formed by means of a high frequency field or a microware resonator. .Iaddend. .Iadd.17. A method as claimed in claim 16, characterized in that a dopant-forming compound is added to the gas mixture. .Iaddend. .Iadd.18. A method of producing a fiber-optic light conductor comprising the steps of: producing an internally coated glass tube as claimed in claim 17; and   drawing the internally coated glass tube to form a a fiber-optic light conductor. .Iaddend.