Large fluoride glass preform fabrication

Abstract

A process for producing long length fluoride glass preforms, by producing a fluoride glass rod of core glass, overcoating the core glass rod with fluoride cladding glass to form a core/clad unit, and overcoating the core/clad unit with an oxide glass overclad.

What is claimed is: 
     
       1. A process for producing a glass preform, comprising: forming a glass core rod;   overcoating said glass core rod with a cladding glass to form a core/clad unit by pouring molten cladding glass into a cladding mold containing said glass core rod;   removing said core/clad unit from said cladding mold; and   overcoating said core/clad unit with a jacketing glass overclad by pouring molten overcladding glass into a jacketing mold containing said core/clad unit, to form said glass preform.   
     
     
       2. The process of claim 1, wherein molten glass is poured into a heated core rod mold to form said glass core rod. 
     
     
       3. The process of claim 2, wherein said core rod mold is rotated about its bore center line axis as said core rod is formed. 
     
     
       4. The process of claim 2, wherein said core rod mold is provided under a vacuum. 
     
     
       5. The process of claim 2, wherein said core rod mold is heated to a temperature of about 50° C. to about 100° C. below a glass transition temperature of said glass of said core rod. 
     
     
       6. The process of claim 2, wherein said core rod mold is held at an angle between and excluding horizontal and vertical, and rotated about its bore center line axis as said core is formed. 
     
     
       7. The process of claim 1, wherein said glass core rod is formed under a vacuum by pouring molten glass into a core rod mold heated to a temperature below the glass transition temperature of said glass, said core rod mold being rotated about its bore center line axis and being held at an angle between and excluding vertical and horizontal. 
     
     
       8. The process of claim 1, wherein said cladding mold is heated when said molten cladding glass is poured into said cladding mold. 
     
     
       9. The process of claim 8, wherein said cladding mold is rotated about its bore center line axis as said core/clad unit is formed. 
     
     
       10. The process of claim 8, wherein said cladding mold is heated to a temperature of about 50° C. to about 100° C. below a glass transition temperature of said cladding glass. 
     
     
       11. The process of claim 8, wherein said cladding mold is held at an angle between and excluding horizontal and vertical, and rotated about its bore center line axis as said core/clad unit is formed. 
     
     
       12. The process of claim 8, wherein said cladding mold is provided under a vacuum. 
     
     
       13. The process of claim 1, wherein said glass core rod is centered in said cladding mold, said cladding mold being provided under a vacuum and heated to a temperature below the glass transition temperature of said cladding glass and being rotated about its bore center line axis at an angle between and excluding vertical and horizontal. 
     
     
       14. The process of claim 1, wherein said molten overcladding glass is an oxide cladding glass, said jacketing mold is heated, and said glass preform is annealed. 
     
     
       15. The process of claim 14, wherein said jacketing mold is rotated about its bore center line axis as said preform is formed. 
     
     
       16. The process of claim 14, wherein said jacketing mold is provided under a vacuum. 
     
     
       17. The process of claim 14, wherein said jacketing mold is heated to a temperature of about 50° C. to about 100° C. below a glass transition temperature of said oxide cladding glass. 
     
     
       18. The process of claim 14, wherein said jacketing mold is held at an angle between and excluding horizontal and vertical, and rotated about its bore center line axis as said preform is formed. 
     
     
       19. The process of claim 1, wherein said jacketing glass overclad is an oxide cladding glass, said jacketing mold is provided under a vacuum and heated to a temperature below the glass transition temperature of said oxide cladding glass, said core/clad unit being supported within said jacketing mold, said jacketing mold being rotated about its bore center line axis and held at an angle between and excluding vertical and horizontal. 
     
     
       20. A glass preform produced by the process according to claim 1. 
     
     
       21. The process of claim 1, wherein said core rod is of fluoride glass, said cladding glass is of fluoride glass, and said jacketing glass overclad is of oxide glass. 
     
     
       22. A process for producing a fluoride glass preform for making an optical fiber comprising: pouring molten fluoride glass under vacuum into a first mold heated to a temperature below a glass transition temperature of said fluoride glass;   forming a fluoride glass core rod from said molten fluoride glass;   centering said fluoride glass core rod in a second mold;   pouring a molten cladding glass under vacuum into said second mold, said second mold being heated to a temperature below a glass transition temperature of said cladding glass, to form a core/clad fluoride unit;   centering said core/clad fluoride glass unit in a third mold;   pouring an oxide cladding glass into said third mold, said third mold being heated to a temperature below a glass transition temperature of the oxide cladding glass, to form said preform; and   annealing the preform.   
     
     
       23. The process of claim 22, wherein said first mold is held at an angle between and excluding horizontal and vertical and is rotated about its bore center line axis as said molten fluoride glass is poured. 
     
     
       24. The process of claim 22, wherein said second mold is held at an angle between and excluding horizontal and vertical and is rotated about its bore centerline axis as said cladding glass is poured. 
     
     
       25. The process of claim 22, wherein said third mold is held at an angle between and excluding horizontal and vertical and is rotated about its bore center line axis as said oxide cladding glass is poured. 
     
     
       26. The process of claim 22, wherein said first mold is heated to a temperature of about 50° C. to about 100° C. below a glass transition temperature of said fluoride glass. 
     
     
       27. The process of claim 22, wherein said second mold is heated to a temperature of about 50° C. to about 100° C. below a glass transition temperature of said cladding glass. 
     
     
       28. The process of claim 22, wherein said third mold is heated to a temperature of about 50° C. to about 100° C. below a glass transition temperature of said oxide glass overclad. 
     
     
       29. A fluoride glass preform produced by the process according to claim 22. 
     
     
       30. A method for producing a preform from which an optical fiber can be drawn, said preform comprising a core and a cladding about said core, said method comprising steps for: pouring molten glass into a first mold to form said core;   placing said core within a second mold having an inner diameter larger than that of the outer diameter of said core;   pouring molten glass into said second mold under a vacuum to form a cladding on said core.   
     
     
       31. The method of claim 30, further comprising: placing said core and said cladding into a third mold having an inner diameter larger than the outer diameter of said core and said cladding;   pouring molten jacketing material into said third mold to form an overlcad on said cladding.   
     
     
       32. A process for producing a glass preform, comprising: forming a glass core rod;   overcoating said glass core rod with a cladding glass to form a core/clad unit by pouring molten cladding glass into a cladding mold containing said glass core rod;   removing said core/clad unit from said cladding mold; and   overcoating said core/clad unit with a jacketing glass overclad by pouring molten overcladding glass into a jacketing mold containing said core/clad unit to form said glass preform.