Patent ID: 11927491
Assignee: TAIYUAN UNIVERSITY OF TECHNOLOGY
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 1:
2. A temperature demodulation method oriented to a fiber Raman temperature sensing system, the temperature demodulation method comprising:
Step 1: constructing a self-calibration temperature detection device oriented to the fiber Raman temperature sensing system comprising a fiber Raman thermodetector, thermostatic baths, a multi-mode sensing fiber, and a multi-mode fiber reflector;
wherein the fiber Raman thermodetector includes a pulsed laser, a wavelength division multiplexer (WDM), two avalanche photodiodes (APDs), two low-noise amplifiers (LNAs), a data acquisition card, and a computer;
wherein an output end of the pulsed laser is connected to an input end of the WDM; two output ends of the WDM are respectively connected to input ends of a first APD and a second APD; an output end of the first APD is connected to an input end of a first LNA; an output end of the second APD is connected to an input end of a second LNA; output ends of the first LNA and the second LNA are connected with input ends of the data acquisition card; and an output end of the data acquisition card is connected to an input end of the computer;
wherein an input end of the multi-mode sensing fiber is connected to a common end of the WDM, wherein a middle part of the multi-mode sensing fiber is respectively wound with a first reference fiber ring and a second reference fiber ring, and a rear part is used as a sensing fiber to be tested; the first reference fiber ring is placed in a first temperature bath, and the second reference fiber ring is placed in a second temperature bath; and wherein an output end of the sensing fiber to be tested is connected to the multi-mode fiber reflector;
Step 2: performing an interpolation processing on Stokes light for chromatic dispersion compensation by:
setting a temperature value of the first temperature bath as Tc;
setting a temperature value of the second temperature bath as T2;
starting the fiber Raman thermodetector, and transmitting laser pulses emitted by the pulsed laser to the first reference fiber ring, the second reference fiber ring, the sensing fiber to be tested and the multi-mode fiber reflector via the WDM;
conducting spontaneous Raman scattering when the laser pulses propagate in the multi-mode sensing fiber, thereby enabling the Stokes light and anti-Stokes light to be generated at each position of the multi-mode sensing fiber;
wherein backward Stokes light and the anti-Stokes light generated in the multi-mode sensing fiber respectively arrive at the first APD, the first LNA, and the second APD, the second LNA via the WDM;
performing a photoelectric conversion and amplification on the backward Stokes light and the anti-Stokes light;
acquiring data and obtaining positional and light intensity information of the Stokes light and the anti-Stokes light along the multi-mode sensing fiber using the data acquisition card and the computer; and
according to positions in a light intensity curve of the Stokes light and the anti-Stokes light of the first reference fiber ring and the second reference fiber ring, performing the interpolation processing on the Stokes light along the multi-mode sensing fiber to enable times when the Stokes light and the anti-Stokes light generated at a same position of the multi-mode sensing fiber arrive at the data acquisition card are the same;
wherein steps of the interpolation processing are:
setting positions of the Stokes light and the anti-Stokes light generated at a position of the first reference fiber ring detected by the data acquisition card as Ls1 and La1;
setting positions of the Stokes light and the anti-Stokes light generated at a position of the second reference fiber ring as La2 and La2; and
setting φs (L) as, ϕ
        s
      
      ⁡
      
        (
        L
        )
      
    
    =
    
      
        ϕ
        s
      
      ⁡
      
        (
        
          
            
              
                
                  L
                  
                    s
                    ⁢
                    1
                  
                
                -
                
                  L
                  
                    s
                    ⁢
                    2
                  
                
              
              
                
                  L
                  
                    a
                    ⁢
                    1
                  
                
                -
                
                  L
                  
                    a
                    ⁢
                    2
                  
                
              
            
            ⁢
            L
          
          +
          
            L
            
              s
              ⁢
              1
            
          
          -
          
            
              L
              
                a
                ⁢
                2
              
            
            ⁢
            
              
                
                  L
                  
                    s
                    ⁢
                    1
                  
                
                -
                
                  L
                  
                    s
                    ⁢
                    2
                  
                
              
              
                
                  L
                  
                    a
                    ⁢
                    1
                  
                
                -
                
                  L
                  
                    a
                    ⁢
                    2
                  
                
              
            
          
        
        )
      
    
  
  ,

where φs (L) represents a value of light intensity of the Stokes light generated at a position of the multi-mode sensing fiber, and L represents a distance between the position and a front end of the multi-mode sensing fiber;

Step 3: processing signals about the backward Stokes light and the anti-Stokes light by:
obtaining, by the data acquisition card, a backscattering light intensity curve of the anti-Stokes light and the Stokes light, whose light intensity ratio is represented as:, ϕ
              a
            
            
              ϕ
              s
            
          
          =
          
            
              
                
                  K
                  a
                
                ⁢
                
                  V
                  a
                  4
                
              
              
                
                  K
                  s
                
                ⁢
                
                  V
                  s
                  4
                
              
            
            ⁢
            
              F
              T
            
            ⁢
            
              exp
              ⁡
              
                (
                
                  -
                  
                    
                      h
                      ⁢
                      Δ
                      ⁢
                      v
                    
                    
                      k
                      ⁢
                      T
                    
                  
                
                )
              
            
            ⁢
            
              exp
              ⁡
              
                [
                
                  
                    (
                    
                      
                        α
                        s
                      
                      -
                      
                        α
                        a
                      
                    
                    )
                  
                  ⁢
                  l
                
                ]
              
            
          
        
        ,
      
    
    
      
        (
        1
        )
      
    
  

where Ks and Ka are coefficients related to a scattering end cross section of the multi-mode sensing fiber; Vs and Va are frequencies of the Stokes light and the anti-Stokes light; FT is a photoelectric conversion factor of the two APDs; h and K are Planck Constant and Boltzmann Constant respectively; Δv is a Raman frequency offset of the multi-mode sensing fiber, which is 13.2 Terahertz (THz); as and aa are attenuation coefficients of incident Stokes light and incident anti-Stokes light per unit length of the multi-mode sensing fiber, respectively; T represents a temperature value at a position 1 of the sensing fiber to be tested; and 1 represents the distance between the position and the front end of the multi-mode sensing fiber;
wherein a backscattering light intensity ratio of the anti-Stokes light and the Stokes light at the position of the first reference fiber ring is expressed as:, ϕ
              ac
            
            
              ϕ
              sc
            
          
          =
          
            
              
                
                  K
                  a
                
                ⁢
                
                  V
                  a
                  4
                
              
              
                
                  K
                  s
                
                ⁢
                
                  V
                  s
                  4
                
              
            
            ⁢
            
              F
              T
            
            ⁢
            
              exp
              ⁡
              
                (
                
                  -
                  
                    
                      h
                      ⁢
                      Δ
                      ⁢
                      v
                    
                    
                      kT
                      c
                    
                  
                
                )
              
            
            ⁢
            
              exp
              ⁡
              
                [
                
                  
                    (
                    
                      
                        α
                        s
                      
                      -
                      
                        α
                        a
                      
                    
                    )
                  
                  ⁢
                  
                    l
                    c
                  
                
                ]
              
            
          
        
        ,
      
    
    
      
        (
        2
        )
      
    
  

where Tc represents a temperature value at a position lc of the first reference fiber ring; and lc represents the distance between the position and the front end of the multi-mode sensing fiber; and
a ratio of formula (1) and formula (2) is:, A
          =
          
            
              
                
                  ϕ
                  a
                
                /
                
                  ϕ
                  s
                
              
              
                
                  ϕ
                  ac
                
                /
                
                  ϕ
                  sc
                
              
            
            =
            
              
                exp
                ⁡
                
                  [
                  
                    
                      -
                      
                        
                          h
                          ⁢
                          Δ
                          ⁢
                          v
                        
                        k
                      
                    
                    ⁢
                    
                      (
                      
                        
                          1
                          T
                        
                        -
                        
                          1
                          
                            T
                            c
                          
                        
                      
                      )
                    
                  
                  ]
                
              
              ⁢
              
                exp
                ⁡
                
                  [
                  
                    
                      (
                      
                        
                          α
                          s
                        
                        -
                        
                          α
                          a
                        
                      
                      )
                    
                    ⁢
                    
                      (
                      
                        l
                        -
                        
                          l
                          c
                        
                      
                      )
                    
                  
                  ]
                
              
            
          
        
        ;
      
    
    
      
        (
        3
        )
      
    
  

Step 4: processing signals about forward Stokes light and the anti-Stokes light by:
reflecting the forward Stokes light and the anti-Stokes light generated in the multi-mode sensing fiber by the multi-mode reflector and respectively arriving at the first APD, the first LNA, and the second APD, the second LNA again via the WDM;
performing the photoelectric conversion and amplification;
obtaining, using the data acquisition card and the computer, a forward scattering light intensity curve of the anti-Stokes light and the Stokes light, whose light intensity ratio is expressed as:, ϕ
              
                a
                ⁢
                f
              
            
            
              ϕ
              
                s
                ⁢
                f
              
            
          
          =
          
            
              
                
                  K
                  a
                
                ⁢
                
                  V
                  a
                  4
                
              
              
                
                  K
                  s
                
                ⁢
                
                  V
                  s
                  4
                
              
            
            ⁢
            
              F
              T
            
            ⁢
            
              
                R
                a
              
              
                R
                s
              
            
            ⁢
            
              exp
              ⁡
              
                (
                
                  -
                  
                    
                      h
                      ⁢
                      Δ
                      ⁢
                      v
                    
                    
                      k
                      ⁢
                      T
                    
                  
                
                )
              
            
            ⁢
            
              exp
              ⁡
              
                [
                
                  
                    (
                    
                      
                        α
                        s
                      
                      -
                      
                        α
                        a
                      
                    
                    )
                  
                  ⁢
                  
                    (
                    
                      
                        2
                        ⁢
                        L
                      
                      -
                      l
                    
                    )
                  
                
                ]
              
            
          
        
        ,
      
    
    
      
        (
        4
        )
      
    
  

where Ra and Rs are reflectivities of the multi-mode reflector to the anti-Stokes light and the Stokes light, and L is a length of the multi-mode sensing fiber;
wherein a forward scattering light intensity ratio of the anti-Stokes light and the Stokes light at the position of the first reference fiber ring is expressed as:, ϕ
              afc
            
            
              ϕ
              sfc
            
          
          =
          
            
              
                
                  K
                  a
                
                ⁢
                
                  V
                  a
                  4
                
              
              
                
                  K
                  s
                
                ⁢
                
                  V
                  s
                  4
                
              
            
            ⁢
            
              F
              T
            
            ⁢
            
              
                R
                a
              
              
                R
                s
              
            
            ⁢
            
              exp
              ⁡
              
                (
                
                  -
                  
                    
                      h
                      ⁢
                      Δ
                      ⁢
                      v
                    
                    
                      kT
                      c
                    
                  
                
                )
              
            
            ⁢
            
              exp
              ⁡
              
                [
                
                  
                    (
                    
                      
                        α
                        s
                      
                      -
                      
                        α
                        a
                      
                    
                    )
                  
                  ⁢
                  
                    (
                    
                      
                        2
                        ⁢
                        L
                      
                      -
                      
                        l
                        c
                      
                    
                    )
                  
                
                ]
              
            
          
        
        ;
      
    
    
      
        (
        5
        )
      
    
  

 and a ratio of formula (4) and formula (5) is:, B
      =
      
       
        
         
          ϕ
          af
         
         /
         
          ϕ
          sf
         
        
        
         
          ϕ
          afc
         
         /
         
          ϕ
          sfc
         
        
       
       =
       
        
         exp
         [
         
          
           -
           
            
             h
             ⁢
             Δ
             ⁢
             v
            
            k
           
          
          ⁢
          
           (
           
            
             1
             T
            
            -
            
             1
             
              T
              c
             
            
           
           )
          
         
         ]
        
        ⁢
        
         exp
         [
         
          
           (
           
            
             α
             s
            
            -
            
             α
             a
            
           
           )
          
          ⁢
          
           (
           
            
             l
             c
            
            -
            l
           
           )
          
         
         ]
        
       
      
     
     ;
    
   
   
    
     (
     6
     )
    
   
  
 

Step 5: performing a self-calibration temperature demodulation method oriented to the fiber Raman temperature sensing system by:
obtaining a formula as follows after resolving formulas (3) and (6):, B
          =
          
            
              
                
                  ϕ
                  af
                
                /
                
                  ϕ
                  
                    
                      
                    
                    sf
                  
                
              
              
                
                  ϕ
                  afc
                
                /
                
                  ϕ
                  
                    
                      
                    
                    sfc
                  
                
              
            
            =
            
              
                exp
                ⁡
                
                  [
                  
                    
                      -
                      
                        
                          h
                          ⁢
                          Δ
                          ⁢
                          v
                        
                        k
                      
                    
                    ⁢
                    
                      (
                      
                        
                          1
                          T
                        
                        -
                        
                          1
                          
                            T
                            c
                          
                        
                      
                      )
                    
                  
                  ]
                
              
              ⁢
              
                exp
                ⁡
                
                  [
                  
                    
                      (
                      
                        
                          α
                          s
                        
                        -
                        
                          α
                          a
                        
                      
                      )
                    
                    ⁢
                    
                      (
                      
                        
                          l
                          c
                        
                        -
                        l
                      
                      )
                    
                  
                  ]
                
              
            
          
        
        ;
      
    
    
      
        (
        6
        )
      
    
  

after resolving formula (7), obtaining a specific temperature demodulation formula along the multi-mode sensing fiber:, A
              ⁢
              B
            
          
          =
          
            
              
                
                  
                    ϕ
                    a
                  
                  /
                  
                    ϕ
                    s
                  
                
                
                  
                    ϕ
                    ac
                  
                  /
                  
                    ϕ
                    sc
                  
                
              
              ⁢
              
                
                  
                    ϕ
                    af
                  
                  /
                  
                    ϕ
                    sf
                  
                
                
                  
                    ϕ
                    afc
                  
                  /
                  
                    ϕ
                    
                      
                        
                      
                      sfc
                    
                  
                
              
            
            =
            
              exp
              ⁡
              
                [
                
                  
                    -
                    
                      
                        h
                        ⁢
                        Δ
                        ⁢
                        v
                      
                      k
                    
                  
                  ⁢
                  
                    (
                    
                      
                        1
                        T
                      
                      -
                      
                        1
                        
                          T
                          c
                        
                      
                    
                    )
                  
                
                ]
              
            
          
        
        ,
      
    
    
      
        (
        7
        )