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

Claim 0:
1. 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 first equation is Equation (C4),, [
  
   
    Math
    .
       
    C
   
   ⁢
   4
  
  ]
 

 
  
   
    
     
      MFD
      =
      
       
        
         v
         +
         
          2
          ⁢
          μ
         
         -
         1
        
       
       ⁢
       
        λ
        π
       
       ⁢
       
        
         2
         ⁢
         
          
           
            ∫
            0
            
             π
             /
             2
            
           
           
            
             
              
               ❘
               "\[LeftBracketingBar]"
              
              
               
                F
                
                 v
                 ⁢
                 μ
                
               
               (
               θ
               )
              
              
               ❘
               "\[RightBracketingBar]"
              
             
             2
            
            ⁢
            sin
            ⁢
            θ
            ⁢
            cos
            ⁢
            θ
            ⁢
            d
            ⁢
            θ
           
          
          
           
            ∫
            0
            
             π
             /
             2
            
           
           
            
             
              
               ❘
               "\[LeftBracketingBar]"
              
              
               
                F
                
                 v
                 ⁢
                 μ
                
               
               (
               θ
               )
              
              
               ❘
               "\[RightBracketingBar]"
              
             
             2
            
            ⁢
            
             sin
             3
            
            ⁢
            θcos
            ⁢
            θ
            ⁢
            d
            ⁢
            θ
           
          
         
        
       
      
     
    
   
   
    
     (
     C4
     ), where ν is the order in a circumferential direction, μ is the order in a radial direction, λ represents a wavelength of the test light, θ is the divergence angle, Fνμ(θ) is an electric field distribution in a far field, and |Fνμ(θ)|2 represents the far-field pattern.