Methods for modifying ovality of optical fiber preforms

Abstract

Methods for modifying preform core ovality during and subsequent to the formation of an optical fiber preform. After MCVD deposition forms the core rod, but prior to overcladding of the core rod, the code rod may be etched to change its ovality. In order to etch the core rod, the core rod may be mounted to lathe, rotated by at least two rotors, and subjected to a heat source. Additionally, one of the at least two rotors may be phase-shifted from another one of the at least two rotors after the core rod is mounted on the lathe.

1 . A method of modifying an ovality of an optical preform, comprising: 
 providing a core rod, wherein said core rod comprises a core and a cladding layer, and wherein said cladding layer has a non-uniform thickness;    mounting said core rod on a lathe having at least two rotors;    rotating said core rod using said at least two rotors; and    etching said core rod to alter the geometry of the cladding layer such that optical preform ovality is modified;    wherein one of said at least two rotors is phase-shifted from another one of said at least two rotors after said core rod is mounted on said lathe.    
   
   
       2 . The method of  claim 1 , wherein the etching of said core rod comprises etching said core rod using heating means.  
   
   
       3 . The method of  claim 2 , wherein said heating means comprises a plasma torch.  
   
   
       4 . The method of  claim 3 , wherein etching said core rod comprises heating the cladding layer of said core rod with the plasma torch; and 
 wherein an amount of glass removed from a portion of said cladding layer is based at least in part on an amount of time that said portion is heated by said plasma torch.    
   
   
       5 . The method of  claim 1 , wherein etching said core rod comprises etching said core rod where the cladding layer is substantially oval in cross-section.  
   
   
       6 . The method of  claim 1 , wherein etching said core rod produces a core rod having less than 5% core ovality.  
   
   
       7 . The method of  claim 1 , wherein etching said core rod produces a core rod suitable for producing optical fiber having less than 0.1 ps/sqrt (km) of polarization mode dispersion.  
   
   
       8 . The method of  claim 1 , further comprising scanning the core rod prior to etching said core rod to measure the ovality of said core rod.  
   
   
       9 . The method of  claim 8 , wherein scanning the core rod comprises scanning the cladding layer to measure the ovality of said cladding layer.  
   
   
       10 . The method of  claim 8  wherein scanning said core rod comprises an off-line scanning of said core rod.  
   
   
       11 . The method of  claim 8 , wherein scanning said core rod comprises an on-line scanning of said core rod.  
   
   
       12 . The method of  claim 1 , wherein rotating said core rod comprises rotating said core rod as said core rod is etched.  
   
   
       13 . The method of  claim 1 , wherein rotating said core rod comprises rotating said core rod in clockwise and counterclockwise directions.  
   
   
       14 . The method of  claim 13 , wherein the phase-shift between said at least two rotors is alternated between clockwise and counterclockwise directions.  
   
   
       15 . The method of  claim 1 , wherein the angular velocity of said rotors is synchronized.  
   
   
       16 . The method of  claim 1 , wherein the phase-shift between said at least two rotors is based at least in part on the ovality of the optical preform.  
   
   
       17 . The method of  claim 16 , wherein the phase-shift between said at least two rotors is calculated according to the equation ΔΘ=K*O v *sin(Ωt), where ΔΘ is the amount of phase shift in degrees, O v  is the ovality measured as a percentage as a function of position, K is a conversion constant, and Ω is a frequency at which the core rod is rotating.  
   
   
       18 . A method of modifying an ovality of an optical preform, comprising: 
 providing a core rod, wherein said core rod comprises a core and a cladding layer, and wherein said cladding layer has a non-uniform thickness;    mounting said core rod on a lathe having at least two rotors;    rotating said core rod using said at least two rotors; and    etching said core rod to alter the geometry of the cladding layer such that optical preform ovality is modified;    wherein one of said at least two rotors is phase-shifted from another one of said at least two rotors after said core rod is mounted on said lathe; and    wherein the phase-shift between said at least two rotors is based at least in part on the ovality of the optical preform.    
   
   
       19 . The method of  claim 18 , wherein the phase-shift between said at least two rotors is calculated according to the equation ΔΘ=K*O v *sin(Ωt), where ΔΘ is the amount of phase shift in degrees, O v  is the ovality measured as a percentage as a function of position, K is a conversion constant, and Ω is a frequency at which the core rod is rotating.  
   
   
       20 . A method of modifying an ovality of an optical preform, comprising: 
 providing a core rod, wherein said core rod comprises a core and a cladding layer, and wherein said cladding layer has a non-uniform thickness;    mounting said core rod on a lathe having at least two rotors;    rotating said core rod using said at least two rotors; and    etching said core rod to alter the geometry of the cladding layer such that optical preform ovality is modified;    wherein one of said at least two rotors is phase-shifted from another one of said at least two rotors after said core rod is mounted on said lathe; and    wherein the phase shift between said at least two rotors is calculated according to the equation ΔΘ=K*O v *sin(Ωt), where ΔΘ is the amount of phase shift in degrees, O v  is the ovality measured as a percentage as a function of position, K is a conversion constant, and Ω is a frequency at which the core rod is rotating.