Chemical powder deposition method for the manufacture of optical fiber preforms and optical fibers

Abstract

The specification describes the production of optical fibers and optical fiber preforms using Chemical Powder Deposition (CPD). In this process a slurry of silica powders and dopant powders in a liquid carrier is prepared and the inside surface of a silica glass starter tube is coated with the slurry, then dried. The coating is then consolidated and the tube collapsed as in the conventional MCVD process. Multiple coatings, and coatings with varying compositions, can be used to produce any desired profile. In an alternative embodiment, doped silica glass of the desired final composition is prepared, and then pulverized to form the powder for the slurry. In both embodiments, the use of powders of known composition in the slurry allows direct control over the final glass composition, as compared with conventional processes in which the composition in the final glass is indirectly controlled by control of the thermodynamics of a vapor phase reaction.

1 . Method 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 preform is prepared by steps comprising:    (i) forming a slurry comprising glass powder and a carrier liquid,    (ii) coating a glass substrate with the slurry,    (iii) drying the slurry to form a first dried coating,    (iv) at least partially consolidating the first dried coating.    
     
     
         2 . The method of  claim 1  wherein step (iii) is performed at a temperature in the range 20-80° C.  
     
     
         3 . The method of  claim 2  wherein step (iii) is performed for a period in excess of 30 minutes.  
     
     
         4 . The method of  claim 1  including the additional steps of 
 (v) coating the consolidated coating with a slurry,  
 (vi) drying the slurry to form a second dried coating,  
 (vii) at least partially consolidating the second dried coating.  
 
     
     
         5 . The method of  claim 1  wherein the slurry in step (v) comprises powder with a composition different than the powder in the slurry in step (ii).  
     
     
         6 . The method of  claim 1  wherein the slurry comprises greater than 25% solids.  
     
     
         7 . The method of  claim 1  wherein the slurry is formed by mixing the glass powders to form a mixed glass powder, then mixing the mixed glass powder with the carrier liquid.  
     
     
         8 . The method of  claim 1  wherein the slurry is formed by mixing the glass powders while in the carrier liquid.  
     
     
         9 . The method of  claim 1  wherein the consolidation step (iv) produces a body with at least 50% of the density of the body in the fully dense vitreous state.  
     
     
         10 . The method of  claim 1  wherein the carrier liquid comprises an organic alcohol with a molecular weight of 60 or greater.  
     
     
         11 . The method of  claim 1  wherein the carrier liquid is an alkyl alcohol.  
     
     
         12 . The method of  claim 11  wherein the carrier liquid is butanol.  
     
     
         13 . The method of  claim 1  wherein the substrate is the inside surface of a glass tube.  
     
     
         14 . The method of  claim 1  wherein the substrate is a glass rod.  
     
     
         15 . The method of  claim 1  wherein the substrate comprises partially consolidated soot.  
     
     
         16 . The method of  claim 15  wherein the substrate is a rod.  
     
     
         17 . The method of  claim 15  wherein the substrate is a tube.  
     
     
         18 . The method of  claim 1  wherein the glass powder comprises a mixture of powdered silica and one or more powdered dopant compounds.  
     
     
         19 . The method of  claim 1  wherein the one or more powdered dopant compounds are selected from the group consisting of oxides, nitrates, and sulfates.  
     
     
         20 . The method of  claim 1  wherein the one or more powdered dopant compounds are compounds of elements selected from the group consisting of La, Ce, Pr, Pm, Gd, Tb, Dy, Ho, Tm, Lu, Er, Nd, Yb, Sm, Al, Ga, Li, Rb, Na, K, Cs, Cr, Fe, Ni, Zn, Ca, Ba, Sr, Sn, Pb, As, Sb, and Bi.  
     
     
         21 . The method of  claim 1  wherein the glass powder comprises a powder of doped silica particles.  
     
     
         22 . The method of  claim 13  wherein the drying step (iii) includes flowing nitrogen through the tube.  
     
     
         23 . The method of  claim 1  wherein the heating step (iv) is carried out by heating the substrate to a temperature above 1900° C.  
     
     
         24 . Method 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 preform is prepared by steps comprising:    (i) forming a first slurry comprising glass powder and a carrier liquid,    (ii) coating a glass substrate with a slurry coating, the coating step performed by: 
 (1) suspending a glass tube vertically from a support member,  
 (2) lowering the support member and the glass tube into a bath comprising the slurry,  
 (3) raising the support member and the glass tube from the bath, leaving a slurry coating on the tube,  
 (4) allowing the slurry coating thickness to reach equilibrium,  
   (iii) drying the slurry coating to form a dried coating, and    (iv) heating the dried coating to form a vitreous glass layer.    
     
     
         25 . The method of  claim 24  wherein the tube is mounted within another tube with concentric plugs sealing the space between the tubes.  
     
     
         26 . Method for the manufacture of an optical fiber preform comprising: 
 (a) forming a slurry comprising glass powder and a carrier liquid,    (b) coating a glass substrate with the slurry,    (c) drying the slurry to form a dried coating,    (d) at least partially consolidating the dried coating.