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Fiber optic detection system using a Sagnac interferometer

  • US 5,046,848 A
  • Filed: 09/08/1989
  • Issued: 09/10/1991
  • Est. Priority Date: 09/08/1989
  • Status: Expired due to Term
First Claim
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1. A fiber optic sensor, comprising:

  • optical path means for facilitating the propagation of light, said optical path means having first and second ends;

    light emitting means for producing light energy;

    first beam splitting means, having first, second and third ports, for directionally transporting light energy incident on said first port to said second port, and for directionally transporting light energy incident on said second port to said third port, said first port coupled to said light emitting means;

    second beam splitting means having first, second, and third ports for directionally transporting light energy incident on said first port to said second and third ports, and for directionally transporting light energy incident on said second and third ports to said first port, said first port of said second beam splitting means coupled to said second port of said first beam splitting means said second port of said second beam splitting means being connected to said first end of said optical path means, said third port of said second beam splitting means being connected to said second end of said optical path means;

    third beam splitting means having first, second and third ports, for directionally transporting light energy incident on said first port to said second port, and for directionally transporting light energy incident on said second port to said first and third ports, said first port of said third beam splitting means being coupled to said second port of said second beam splitting means;

    phase modulation means connected along said optical path means and being coupled to said second port of said third beamsplitting means, for impressing a modulation frequency on light propagating in both directions along said optical path means, said phase modulation means being at least slightly offset from the center of said optical path means with respect to said second beam splitting means;

    first phase sensitive detection means, optically connected to said third port of said first beam splitting means, and also connected to said phase modulation means, for detecting light from said first beam splitting means;

    second phase sensitive detection means, optically connected to said third port of said third beam splitting means and to said light emitting means, for detecting light from said third beam splitting means, said second phase sensitive detection means comprising;

    a detector, optically connected to said third port of said third beam splitting means, for detecting light from said third beam splitting means and producing a signal indicative of the characteristics of said second beam of light;

    a phase sensitive detector, electrically connected to said detector, for demodulating said phase modulated frequency impressed upon said light propagating along said optical path means;

    an integrator having an input connected to said phase sensitive detector and an output; and

    variable oscillation means, having an input coupled to said output of said integrator and a first output coupled to said phase sensitive detector of said second phase sensitive detection means, a second output coupled to said light emitting means, and a third output connected to a signal processor means, said processor means being connected to said first and said second phase sensitive detection means for providing a position output and an amplitude output for the location and severity, respectively, of an environmental disturbance along said optical path means.

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