Optical fiber manufacture

Abstract

The specification describes methods for the manufacture of very large optical fiber preforms wherein the core material is produced by MCVD. Previous limitations on preform size inherent in having the MCVD starting tube as part of the preform process are eliminated by removing the MCVD starting tube material from the collapsed MCVD rod by etching or mechanical grinding. Doped overcladding tubes are used to provide the outer segments of the refractive index profile thus making most effective use of the MCVD produced glass and allowing the production of significantly larger MCVD preforms than previously possible.

1 . Process for the manufacture of optical fiber comprising: 
 (a) preparing an optical fiber preform,    (b) heating the preform to the softening temperature, and    (c) drawing an optical fiber from the preform,    the invention characterized in that the optical fiber preform is prepared by steps comprising:    (i) forming by MCVD a first glass layer on the inside of a MCVD starting tube and a second glass layer on the first glass layer, the MCVD starting tube comprising a first glass material, and where the first glass layer is a core layer having a first refractive index and the second glass layer is a first cladding layer having a second refractive index lower than the first refractive index,    (ii) collapsing the MCVD tube to produce a first solid glass cylindrical body,    (iii) removing at least a portion of the first glass material leaving a second solid glass cylindrical body of the MCVD glass material, and    (iv) applying a cladding to the second solid glass cylindrical body of MCVD glass material by inserting the second solid glass cylindrical body of MCVD glass into a cladding tube and collapsing the cladding tube around the second solid glass cylindrical body of MCVD glass material.    
   
   
       2 . The process of  claim 1  wherein the MCVD starting tube has an outside diameter OD, and an inside diameter ID and the portion of the first glass material of the MCVD starting tube cross sectional area that is removed is:  
       (( OD   2 ) 2   −ID   2 )/(( OD   1 ) 2   −ID   2 )<0−0.25  where OD 2  is the outside diameter of the second solid glass cylindrical body.    
   
   
       3 . The process of  claim 2  wherein all of the first glass material is removed.  
   
   
       4 . The process of  claim 1  wherein the step of applying a cladding involves mounting the solid glass cylindrical body within the overclad tube leaving an ambient space between the solid glass cylindrical body and the overlad tube, and controlling the ambient space by flowing gas through the ambient space.  
   
   
       5 . The process of  claim 1  wherein the overclad tube comprises glass with a hydroxyl ion content less than 50 ppB by weight.  
   
   
       6 . The process of  claim 1  wherein said overclad tube is up-doped with germanium.  
   
   
       7 . The process of  claim 1  wherein said overclad tube is downdoped with fluorine.  
   
   
       8 . The process of  claim 1  where the solid glass cylindrical body has a diameter of at least 12 mm.  
   
   
       9 . The process of  claim 1  wherein the first glass material is removed by mechanical grinding.  
   
   
       10 . The process of  claim 1  wherein the first glass material is removed by plasma etching.  
   
   
       11 . The process of  claim 1  wherein the first glass material is removed by chemical etching.  
   
   
       12 . The process of  claim 1  wherein the first glass material is removed by a combination of methods including mechanical grinding, plasma etching and chemical etching.  
   
   
       13 . Process for the manufacture of an optical fiber preform comprising: 
 (a) forming by MCVD a first glass layer on the inside of a MCVD starting tube and a second glass layer on the first glass layer, the MCVD starting tube comprising a first glass material, and where the first glass layer is a core layer having a first refractive index and the second glass layer is a first cladding layer having a second refractive index lower than the first refractive index,    (b) collapsing the MCVD tube to produce a first solid glass cylindrical body,    (c) removing at least a portion of the first glass material leaving a second solid glass cylindrical body of the MCVD glass material, and    (d) applying a cladding to the second solid glass cylindrical body of MCVD glass material by inserting the second solid glass cylindrical body of MCVD glass into a cladding tube and collapsing the cladding tube around the second solid glass cylindrical body.    
   
   
       14 . The process of  claim 13  wherein the MCVD starting tube has an outside diameter OD, and an inside diameter ID and the portion of the first glass material of the MCVD starting tube cross sectional area that is removed is: ((OD 2 ) 2 −ID 2 )/((OD 1 ) 2 −ID 2 )<0−0.25 where OD 2  is the outside diameter of the second solid glass cylindrical body.  
   
   
       15 . The process of  claim 13  wherein all of the first glass material is removed.  
   
   
       16 . The process of  claim 13  wherein the step of applying a cladding involves mounting the second solid glass cylindrical body within the overclad tube leaving an ambient space between the solid glass cylindrical body and the overclad tube, and controlling the ambient space by flowing gas through the ambient space.  
   
   
       17 . The process of  claim 16  wherein the overclad tube comprises glass with a hydroxyl ion content less than 50 ppB by weight.  
   
   
       18 . The process of  claim 13  wherein the first glass material is removed by a combination of methods including mechanical grinding, plasma etching and chemical etching.