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Optical fiber evaluation method and system

  • US RE34,972 E
  • Filed: 03/03/1993
  • Issued: 06/20/1995
  • Est. Priority Date: 06/24/1988
  • Status: Expired due to Term
First Claim
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1. A method for evaluating properties of an optical fiber, comprising the steps of:

  • making incident a first signal light in the form of modulated light from a first light source upon an optical fiber to be measured;

    propagating a second signal light from a second light source in said optical fiber to be measured in the direction opposite to that of the first signal light;

    controlling the frequency of at least one of said first and second light sources;

    setting the frequency difference Δ

    f between said first signal light and said second signal light at a predetermined value;

    producing an optical nonlinear interaction between said first signal light and said second signal light;

    detecting said second signal light after it undergoes said optical nonlinear interaction;

    determining the time dependent signal power W of the detected second signal light; and

    evaluating the properties of said optical fiber to be measured on the basis of said time dependent signal power W,wherein said optical nonlinear interaction is Brillouin light amplification, andwherein the loss α

    (dB/km) of a given section <

    a, b>

    of said optical fiber is evaluated from the equation
    
    
    space="preserve" listing-type="equation">α

    =1000×

    10 log.sub.10 (W.sub.a /W.sub.b)/(vt.sub.ab /2) (dB/km), where v represents the velocity of light in said optical fiber (m/s), Wa and Wb represent the detected time-dependent signal power of said second signal light at the respective ends a and b of said section of said optical fiber to be measured, and tab represents the time required for the first or second signal light to go back and forth between said section <

    a, b>

    .

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