Drawing dielectric optical waveguides

• US 4,040,807 A
• Filed: 06/30/1975
• Issued: 08/09/1977
• Est. Priority Date: 07/10/1974
• Status: Expired due to Term

• Current Assignee: British Telecommunications (BT Group Plc) (BT Group PLC)
• Original Assignee: Post Office Limited (International Distributions Services plc)
• Inventors: Day, Clive Richard, Midwinter, John Edwin
• Primary Examiner(s): Bashore, S. Leon
• Assistant Examiner(s): Miga, Frank W.
• Application Number:
  US05/591,958
• Time in Patent Office: 771 Days
• Field of Search: 65/3 A, 65/32, 65/121, 65/146, 65/335, 65/DIG. 7, 65/157
• US Class Current: 65/405
• CPC Class Codes: C03B 37/023 Fibres composed of different sorts of glass, e.g. glass optical fibres, made by the double crucible technique
• CPC Class Codes: C03B 37/085 Feeding devices therefor
• CPC Class Codes: C03B 5/225 Refining C03B5/18 takes precedence ; Refining agents C03C1/004
• CPC Class Codes: C03B 5/2252 under reduced pressure, e.g. with vacuum refiners

Abstract

The attenuation in a dielectric optical waveguide can be reduced by the following techniques:

1. Surrounding the double crucible during the drawing operation by a non-oxidizing atmosphere.

2. Feeding glass rod into the melt at a slow rate.

3. Guiding glass rod into the melt so that movement of the glass rod transverse to the melt surface is inhibited.

4. Melting the glass in the double crucible under vacuum.

Claims

1. A method of manufacturing a bubble-free dielectric optical waveguide comprising:

loading preformed core and cladding glasses in rod form into the inner and outer compartments respectively of a metallic double crucible, having concentric adjacent outlet orifices, cladding glass being loaded in said outer and core glass in said inner compartment

melting the glasses in said crucible;

completely surrounding the double crucible containing melted glasses with a nonoxidising atmosphere;

drawing from said orifices core and cladding glasses to form a clad dielectric optical waveguide; and

continuously replenishing said inner and outer compartments of the double crucible by feeding preformed core and cladding glass rods having a diameter between 3 and 10 millimeters into the glass melt at a rate less than 30 millimeters per minute thereby avoiding pulling gas into the glass melt.

2. A method as claimed in claim 1 wherein the non-oxidising atmosphere includes carbon-dioxide.

3. A method as claimed in claim 2 wherein the non-oxidising atmosphere includes carbon-monoxide.

4. A method as claimed in claim 2 wherein said non-oxidising atmosphere includes between 5% and 90% by volume of carbon-monoxide.

5. A method as claimed in claim 2 wherein said non-oxidising atmosphere includes between 5% and 20% by volume of carbon-monoxide.

6. A method as claimed in claim 2 wherein said non-oxidising atmosphere is dried prior to use.

7. A method as claimed in claim 2 wherein said non-oxidising atmosphere is heated to remove carbonyls prior to use.

8. A method as claimed in claim 1 wherein the non-oxidising atmosphere includes nitrogen.

9. A method as claimed in claim 8 wherein the non-oxidizing atmosphere includes carbon monoxide.

10. A method as claimed in claim 8 wherein said non-oxidizing atmosphere includes between 5 percent and 90 percent by volume of carbon monoxide.

11. A method as claimed in claim 8 wherein said non-oxidizing atmosphere includes between 5 percent and 20 percent by volume of carbon monoxide.

12. A method as claimed in claim 8 wherein said non-oxidizing atmosphere is dried prior to use.

13. A method as claimed in claim 8 wherein said non-oxidizing atmosphere is heated to remove carbonyls prior to use.

14. A method as claimed in claim 1 wherein said rod has a diameter of between 6 and 8 mm.

15. A method as claimed in claim 14 wherein said feed rate is greater than 15 and less than 30 mm per minute.

16. A method of loading glass into a heated double crucible as claimed in claim 15 wherein prior to feeding said glass rod into said double crucible, said glass rod is stored in a silica tube in a dry inert atmosphere.