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Fiber optic Michelson sensor and arrays with passive elimination of polarization fading and source feedback isolation

  • US 5,206,924 A
  • Filed: 09/01/1992
  • Issued: 04/27/1993
  • Est. Priority Date: 01/31/1992
  • Status: Expired due to Fees
First Claim
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1. A polarization-independent fiber optic interferometric sensor system comprising:

  • a polarization beamsplitter having first and second input ports and first and second output ports, said polarization beamsplitter being responsive to light applied to said first input port for coupling light of a first polarization state from said first input port to said first output port and light of a second polarization state orthogonal to said first polarization state from said first input port to said second output port and being further responsive to light applied to said first output port of said second polarization state for coupling said light to said second input port;

    optical source means coupled to said polarization beamsplitter for providing light of said first polarization state to said first input port;

    an interferometer including an optical coupler having third and fourth input ports and third and fourth output ports, sensing and reference arms having different associated birefringences and being respectively coupled to said third and fourth output ports, and first and second Faraday rotator mirror assemblies respectively coupled to distal ends of said sensing and reference arms;

    means for conveying said light of said first polarization state from said first output port to said third input port of said optical coupler, said conveying means having a birefringence which changes the polarization of said light of said first polarization state to a first arbitrary polarization state, said output coupler allowing first and second portions of said light of said first arbitrary polarization state to respectively pass into said sensing and reference fiber arms to produce respective second and third arbitrary polarization states at said distal ends of said sensing and reference fibers, said first and second Faraday rotator mirror assemblies respectively converting said first and second portions of light of said second and third arbitrary polarization states into first and second portions of light of fourth and fifth arbitrary polarization states, said sensing and reference arms being responsive to light passing therethrough for developing an interference pattern output, said optical coupler combining said first and second portions of light of said fourth and fifth arbitrary polarization states into a beam of light and passing said beam of light through said conveying means to produce said second polarization state at said first output port of said polarization beam splitter, said beam of light of said second polarization state passing through said polarization beam splitter to substantially only said second input port of said polarization beam splitter; and

    photodetection means responsive to said interference pattern output for developing an electrical signal that has a peak-to-peak amplitude proportional to the visibility of said interference pattern output.

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