Methods and apparatus of tracking/locking resonator free spectral range and its application in resonator fiber optic gyroscope
First Claim
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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Abstract
A resonator fiber optic gyroscope is provided. The resonator fiber optic gyroscope includes a gyroscope resonator, a laser; a clockwise modulator; a clockwise circulator; a clockwise reflection detector; a first-lock-in-amplifier, 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; and a third-lock-in-amplifier. The first and second lock-in-amplifiers demodulate at the first harmonic of the modulation frequency. The second-lock-in-amplifier demodulates at the second harmonic of the modulation frequency. Either 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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Citations
20 Claims
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1. A resonator fiber optic gyroscope system, comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of locking a free spectral range (FSR) of a gyroscope resonator in a resonator fiber optic gyroscope system and a laser modulation frequency of an optical beam coupled to an input port of the gyroscope resonator to each other, the method comprising:
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modulating a clockwise optical beam emitted from a laser with a laser modulation frequency of (n+0.5) times the FSR, where n is zero or a positive integer; coupling the modulated clockwise optical beam into a clockwise input port of the gyroscope resonator; receiving a signal from a clockwise reflection detector; demodulating a first harmonic of the signal received from the clockwise reflection detector at a first-lock-in-amplifier; receiving a demodulated first-harmonic signal from the first-lock-in-amplifier at a clockwise-resonance-tracking servo; providing feedback to the laser from the clockwise-resonance-tracking servo in order to lock the laser to the gyroscope resonator; receiving a signal from a clockwise transmission detector; demodulating a second harmonic of the signal received from the clockwise transmission detector at a second-lock-in-amplifier; providing feedback from the second-lock-in-amplifier to a second servo; demodulating a first harmonic of the signal received from the clockwise transmission detector at a third-lock-in-amplifier; and providing feedback from the third-lock-in-amplifier to the clockwise-resonance-tracking servo to correct errors in a clockwise resonance tracking loop. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17)
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18. A resonator fiber optic gyroscope system, comprising:
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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 first 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 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 first laser to lock the first 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; 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, a second laser configured to couple a counter-clockwise optical beam into to the counter-clockwise input port; a counter-clockwise modulator to impose a modulation frequency equivalent to (p+0.5) times the FSR on the counter-clockwise optical beam before the counter-clockwise optical beam is coupled into the counter-clockwise input port, where p is zero or a positive integer and where p does not equal n; a counter-clockwise circulator; a counter-clockwise reflection detector to detect the counter-clockwise optical beam output from a counter-clockwise reflection port; a fourth-lock-in-amplifier to receive a signal from the counter-clockwise reflection detector, wherein the fourth-lock-in-amplifier demodulates at the first harmonic of the modulation frequency of the counter-clockwise optical beam; a counter-clockwise-resonance-tracking servo to receive output from the fourth-lock-in-amplifier and to provide feedback to the second laser to lock the second laser to the gyroscope resonator; a counter-clockwise transmission detector to detect an optical beam output from the clockwise input port; and the fifth-lock-in-amplifier to receive a signal from the counter-clockwise transmission detector, wherein the fifth-lock-in-amplifier demodulates at the first harmonic of the modulation frequency of the counter-clockwise optical beam and provides feedback to the counter-clockwise-resonance-tracking servo to correct errors in a counter-clockwise resonance tracking loop, wherein one of;
the modulation frequency of the clockwise optical beam is locked to the (n+0.5)FSR through the second servo;
or the FSR is locked to 1/(n+0.5) times the modulation frequency of the clockwise optical beam through the second servo. - View Dependent Claims (19, 20)
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Specification