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Methods and apparatus of tracking/locking resonator free spectral range and its application in resonator fiber optic gyroscope

  • US 9,001,336 B1
  • Filed: 10/07/2013
  • Issued: 04/07/2015
  • Est. Priority Date: 10/07/2013
  • Status: Active Grant
First Claim
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1. A resonator fiber optic gyroscope system, comprising:

  • a gyroscope resonator having a clockwise input port and a counter-clockwise input port and a free spectral range (FSR) corresponding to the resonator round trip length;

    a laser configured to couple a clockwise optical beam into to the clockwise input port;

    a clockwise modulator to impose a modulation frequency equivalent to (n+0.5) times the FSR on the clockwise optical beam before the clockwise optical beam is coupled into the clockwise input port, where n is zero or a positive integer;

    a clockwise circulator;

    a clockwise reflection detector to detect the clockwise optical beam output from a clockwise reflection port;

    a first-lock-in-amplifier to receive a signal from the clockwise reflection detector, wherein the first-lock-in-amplifier demodulates at the first harmonic of the modulation frequency of the clockwise optical beam;

    a clockwise-resonance-tracking servo to receive output from the first-lock-in-amplifier and to provide feedback to the laser to lock the laser to the gyroscope resonator;

    a clockwise transmission detector to detect an optical beam output from the counter-clockwise input port;

    a second servo;

    a second-lock-in-amplifier to receive a signal from the clockwise transmission detector, wherein the second-lock-in-amplifier demodulates at the second harmonic of the modulation frequency of the clockwise optical beam and provides feedback to the second servo; and

    a third-lock-in-amplifier to receive a signal from the clockwise transmission detector, wherein the third-lock-in-amplifier demodulates at the first harmonic of the modulation frequency of the clockwise optical beam and provides feedback to the clockwise-resonance-tracking servo to correct errors in a clockwise resonance tracking loop,wherein one of;

    the modulation frequency of the clockwise optical beam is locked to (n+0.5) times the FSR through the second servo, where n is zero or a positive integer;

    or the FSR is locked to 1/(n+0.5) times the modulation frequency of the clockwise optical beam through the second servo.

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