Patent ID: 11906387
Assignee: NIPPON TELEGRAPH AND TELEPHONE CORPORATION
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 2:
3. A mode field diameter test device comprising:
test light incidence means for selectively causing test light to be incident in a mode subject to measurement, on one end of an optical fiber under test;
far-field pattern measurement means for measuring a far-field pattern of the mode subject to measurement, with respect to a divergence angle θ at the other end of the optical fiber under test, by a far-field scanning technique; and
mode field diameter calculation means for calculating, using a first equation, a mode field diameter from information about incident mode orders in the optical fiber under test by the test light incidence means and the far-field pattern measured by the far-field pattern measurement procedure, or mode field diameter calculation means for calculating an electric field distribution in a near field from the far-field pattern and further calculating a mode field diameter using a second or third equation;
wherein the second equation is Equation (C6),, [
  
   
    Math
    .
       
    C
   
   ⁢
   6
  
  ]
 

 
  
   
    
     MFD
     =
     
      2
      ⁢
      
       
        
         
          2
          ⁢
          
           (
           
            
             2
             ⁢
             μ
            
            -
            1
           
           )
          
         
        
        [
        
         
          
           ∫
           0
           ∞
          
          
           
            
             E
             
              v
              ⁢
              μ
             
             2
            
            (
            r
            )
           
           ⁢
           rdr
          
         
         
          
           ∫
           0
           ∞
          
          
           
            
             {
             
              
               
                dE
                
                 v
                 ⁢
                 μ
                
               
               (
               r
               )
              
              dr
             
             }
            
            2
           
           ⁢
           rdr
          
         
        
        ]
       
       
        1
        /
        2
       
      
     
    
   
   
    
     (
     C6
     ), where ν is the order in a circumferential direction, μ is the order in a radial direction, r is a radial coordinate in a cross section of the optical fiber, and Eνμ(r) is the electric field distribution of an LPνμ mode in the near field.