Patent ID: 11860028
Assignee: NIPPON TELEGRAPH AND TELEPHONE CORPORATION
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 6:
7. A signal processing device comprising:
receiver for receiving in-phase components and quadrature components of scattered light generated by a light pulse that has entered a measurement target optical fiber, and acquiring reference vectors and measurement vectors, the reference vectors constituted by, among the in-phase components and the quadrature components of the scattered light, in-phase components and quadrature components at both ends of a given target segment of the measurement target optical fiber in a reference state, and the measurement vectors constituted by in-phase components and quadrature components at both ends of the target segment of the measurement target optical fiber at a given time; and
detector for determining that physical vibration has been applied to the target segment of the measurement target optical fiber when a triangular shape formed by a vector on a near end side and a vector on a far end side of the target segment of the measurement target optical fiber is envisioned for each of the reference vectors and the measurement vectors and shape change in a triangular shape formed by the measurement vectors with respect to a triangular shape formed by the reference vectors is a predetermined value or more;
wherein the detector uses a value Dmin obtained using formula (C1) as the shape change, where r1 is the size of the vector on the far end side of the target segment of the measurement target optical fiber among the reference vectors, and θ1 is the angle of the vector with respect to an axis of an in-phase component, r2 is the size of the vector on the near end side of the target segment of the measurement target optical fiber among the reference vectors, and θ2 is the angle of the vector with respect to an axis of an in-phase component, r3 is the size of the vector on the far end side of the target segment of the measurement target optical fiber among the measurement vectors, and θ3 is the angle of the vector with respect to an axis of an in-phase component, and r4 is the size of the vector on the near end side of the target segment of the measurement target optical fiber among the measurement vectors, and θ4 is the angle of the vector with respect to an axis of an in-phase component., D
            min
          
          =
          
            
              
                r
                1
                2
              
              +
              
                r
                2
                2
              
              +
              
                r
                3
                2
              
              +
              
                r
                4
                2
              
              -
              W
            
          
        
        ⁢
        
          

        
        ⁢
        
          W
          =
          
            2
            ⁢
            
              
                
                  
                    r
                    1
                    2
                  
                  ⁢
                  
                    r
                    3
                    2
                  
                
                +
                
                  
                    r
                    2
                    2
                  
                  ⁢
                  
                    r
                    4
                    2
                  
                
                +
                
                  2
                  ⁢
                  
                    r
                    1
                  
                  ⁢
                  
                    r
                    2
                  
                  ⁢
                  
                    r
                    3
                  
                  ⁢
                  
                    r
                    4
                  
                  ⁢
                  
                    cos
                    ⁡
                    
                      [
                      
                        
                          (
                          
                            
                              θ
                              1
                            
                            -
                            
                              θ
                              2
                            
                          
                          )
                        
                        -
                        
                          (
                          
                            
                              θ
                              3
                            
                            -
                            
                              θ
                              4
                            
                          
                          )
                        
                      
                      ]
                    
                  
                
              
            
          
        
      
    
    
      
        (
        C1
        )