Process for making a glass fiber with a core and two glass cladding layers and glass fiber made thereby

Abstract

The glass fiber for an optical amplifier has a glass core, a first glass cladding, and a second glass cladding. The core has a composition, in mol %, of Bi 2 O 3 , 30-60; SiO 2 , 0.5-40; B 2 O 3 , 0.5-40; Al 2 O 3 , 0-30; Ga 2 O 3 , 0-20; Ge 2 O 3 , 0-25; La 2 O 3 , 0-15; Nb 2 O 5 , 0-10; SnO 2 , 0-30; alkali metal oxides, 0-40; and Er 2 O 3 , 0.05-8. The process for making the glass fiber includes first making a preform consisting of the core and the first glass cladding by drawing from a double crucible. Then the second glass cladding is formed around the preform by a rod-in-tube process. The glass claddings have a composition that includes a transition metal compound as an absorbent.

1 . A process for producing a glass fiber, said glass fiber comprising a core and at least two glass claddings surrounding said core, said core comprising a matrix glass containing at least one heavy metal oxide and at least one rare earth compound, wherein the matrix glass has a refractive index of greater than about 1.85, a refractive index change Δn from a first of the at least two glass claddings to the core is in a range from 0.001 to 0.08, and the refractive index of the first glass cladding is lower than that of the core; said process comprising the steps of:
 a) making a preform, said preform comprising said core and the first glass cladding, by drawing from a double crucible; and   b) forming at least one further glass cladding around the preform by a rod-in-tube process.   
   
   
       2 . The process as defined in  claim 1 , wherein said rod-in-tube process comprises drilling a through-going hole into a second cladding glass rod to form a tube of said second cladding glass, introducing said perform comprising said core and said first glass cladding into said tube of said second cladding glass, and drawing said tube of said second cladding glass to form said glass fiber. 
   
   
       3 . The process as defined in  claim 1 , wherein said at least one heavy metal oxide is at least one oxide of Bi, Te, Se, Sb, Pb, Cd, Ga and/or As, or a mixture thereof. 
   
   
       4 . The process as defined in  claim 1 , wherein the core comprises at least Bi 2 O 3  and/or TeO 2  and/or Sb 2 O 3 . 
   
   
       5 . The process as defined in  claim 1 , wherein the at least one rare earth compound contains at least one element selected from the group consisting of Ce, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, or a mixture thereof. 
   
   
       6 . The process as defined in  claim 1 , wherein the first glass cladding contains said at least one rare earth compound. 
   
   
       7 . The process as defined in  claim 1 , wherein said matrix glass contains an amount of each of said at least one rare earth compound equal to 0.05 to 5 mol %, but the first glass cladding contains only up to one half of said amount of each of said at least one rare earth compound in said matrix glass. 
   
   
       8 . The process as defined in  claim 1 , wherein an outermost cladding of the at least two glass claddings contains from 5 to 5000 ppm of at least one absorbent component. 
   
   
       9 . The process as defined in  claim 8 , wherein said at least one absorbent component is at least one transition metal compound. 
   
   
       10 . The process as defined in  claim 9 , wherein said at least one transition metal compound comprises Co +2 . 
   
   
       11 . The process as defined in  claim 1 , wherein the index of refraction of the outermost cladding of the at least two glass claddings is greater than the index of refraction of the first glass cladding. 
   
   
       12 . The process as defined in  claim 1 , wherein the matrix glass has a composition, in mol % on an oxide basis, of: 
     
       
         
               
               
               
             
                   
                   
               
                   
                 Bi 2 O 3   
                 30-60  
               
                   
                 SiO 2   
                 0.5-40   
               
                   
                 B 2 O 3   
                 0.5-40   
               
                   
                 Al 2 O 3   
                 0-30 
               
                   
                 Ga 2 O 3   
                 0-20 
               
                   
                 Ge 2 O 3   
                 0-25 
               
                   
                 La 2 O 3   
                 0-15 
               
                   
                 Nb 2 O 5   
                 0-10 
               
                   
                 SnO 2   
                 0-30 
               
                   
                 MI 2 O 
                 0-40 
               
                   
                 Rare 
                 0.5-8,  
               
                   
                 earths 
               
                   
                   
               
           
              
             
             
              
              
              
              
              
              
              
              
              
              
              
              
              
             
          
         
       
       wherein MI is at least one of Li, Na, K, Rb and Cs. 
     
   
   
       13 . The process as defined in  claim 1 , wherein the core has a diameter of from 1 to 15 μm. 
   
   
       14 . The process as defined in  claim 1 , wherein the first glass cladding has a thickness d m1  in a range from 5 to 100 μm. 
   
   
       15 . The process as defined in  claim 14 , in which a second glass cladding of the at least two glass claddings has a thickness (d m2 ) in a range from 10 to 300 μm. 
   
   
       16 . The process as defined in  claim 1 , wherein the glass fiber has a total thickness of 125 μm.