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Passive homodyne demodulator and sensor system

  • US 4,609,290 A
  • Filed: 06/06/1983
  • Issued: 09/02/1986
  • Est. Priority Date: 06/06/1983
  • Status: Expired due to Term
First Claim
Patent Images

1. A sensor system using light as the sensing medium including:

  • a light source which produces a light beam of predetermined coherence;

    first beamsplitter means which split said light beam of predetermined coherence into a reference light beam and a sensor input light beam;

    means to impress the effect to be sensed on said sensor input light beam in the form of relative phase changes, φ

    , thereof with respect to said reference light beam to generate a sensor output light beam;

    means to produce a relative linear polarization difference of 90°

    between said reference light beam and said sensor input light beam;

    means to mix said reference light beam and said sensor output light beam; and

    means to demodulate said mix of said reference light beam and said sensor output light beam into at least a first demodulated light beam having an amplitude which is a function of sin φ

    , said means to produce a relative linear polarization difference of 90°

    between said reference light beam and said sensor input light beam including;

    means to produce said reference light beam with a polarization defined as vertical and said sensor input light beam with a polarization defined as horizontal, said means to mix said reference light beam and said sensor output light beam including;

    optical coupler means having;

    a reference input connected to receive said reference light beam;

    a sensor input connected to receive said sensor output light beam;

    a first output out through which passes a first mixed beam having a vertical reference light beam component and a horizontal sensor output light beam component; and

    a second output out through which passes a second mixed beam having a vertical reference light beam component and a horizontal sensor output light beam component, and wherein said means to demodulate said mix of said reference light beam and said sensor output light beam into at least a first demodulated light beam having an amplitude which is a function of sin φ

    also include;

    means to demodulate said mix of reference light beam and said sensor output light beam into second, third, and fourth demodulated light beams, said first, second, third, and fourth demodulated light beams, having amplitudes of K+sin φ

    , K-sin φ

    , K+cos φ

    , and K-cos φ

    respectively where K is a constant having a magnitude of at least 1;

    first polarized beamsplitter means which separate said mix of said reference light beam and said sensor output light beam into first and second predetermined component beams thereof;

    second polarized beamsplitter means which separate said first predetermined component beams into third and fourth predetermined component beams;

    means to optically orient said second polarized beamsplitter means at 45°

    with respect to said first polarized beamsplitter means;

    third polarized beamsplitter means which separate said second predetermined component beams into fifth and sixth predetermined component beams, said third predetermined component beams;

    means to optically orient said third polarized beamsplitter means at 45°

    with respect to said first polarized beamsplitter means;

    means to combine said third predetermined component beams into said first demodulated light beam;

    means to combine said fourth predetermined component beams into said second demodulated light beam;

    means to combine said fifth predetermined component beams into said third demodulated light beam; and

    means to combine said sixth predetermined component beams into said fourth demodulated light beam.

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