US 7,372,574 B2Granted

System and method for stabilizing light sources in resonator gyro

AssigneeHoneywell International Inc.

InventorsGlen A. Sanders, Lee K. Strandjord

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Abstract

Methods and apparatus are provided for stabilizing laser light sources of a resonator gyro. A resonator gyro comprises a first light source configured to produce a first input light, a second light source configured to produce a second input light, a resonator coupled to the first and second light sources, a resonance detection circuit coupled to the resonator, and a controller coupled to the resonance detection circuit and the first and second light sources. The resonance detection circuit detects a resonance frequency for each of the counter-propagating directions of the resonator. The controller tunes the first input light to a clockwise resonance frequency, and tunes the second input light to a counter-clockwise resonance frequency. A difference between the resonance frequencies is proportional to a rotational rate of the resonator gyro.

Claims17

Dependent claims

A resonator gyro comprising:

a first light source configured to produce a first input light having a first frequency;
a second light source configured to produce a second input light having a second frequency;
a resonator coupled to said first and second light sources, said resonator having first and second counter-propagating directions and comprising an optical fiber coil having a hollow core, said resonator configured to:
circulate a first circulating light through said hollow core in said first counter-propagating direction, said first circulating light based on a portion of said first input light;
and
circulate a second circulating light through said hollow core in a second counter-propagating direction, said second circulating light based on a portion of said second input light;
a resonance detection circuit coupled to said resonator and comprising:
a first photodetector configured to sample light from said first circulating light;
a second photodetector configured to sample light from said second circulating light;
a first resonance detection circuit coupled to said first photodetector and configured to detect a resonance center of said first counter-propagating direction;
and
a second resonance detection circuit coupled to said second photodetector and configured to detect a resonance center of said second counter-propagating direction;
a controller coupled to said resonance detection circuit and said first and second light sources, said controller comprising:
a first servo having an input coupled to said first resonance detection circuit and having an output coupled to said first light source;
and
a second servo having an input coupled to said second resonance detection circuit and having an output coupled to said second light source;
wherein said controller is configured to:
tune said first frequency to said resonance frequency of said first counter-propagating direction;
and
tune said second frequency to said resonance frequency of said second counter-propagating direction, a difference between said resonance frequencies of said first and second counter-propagating directions proportional to a rotational rate of the resonator gyro;
wherein said first input light has a first modulation frequency and said second input light has a second modulation frequency, and wherein the resonator gyro further comprises:
a first tracking loop based on said first light source, said resonator, said first photodetector, said first resonance detection circuit, and said first servo, said first tracking loop having a first unity gain frequency, said first modulation frequency at least four times greater than said first unity gain frequency;
and
a second tracking loop based on said second light source, said resonator, said second photodetector, said second resonance detection circuit, and said second servo, said second tracking loop having a second unity gain frequency, said second modulation frequency at least four times greater than said second unity gain frequency.

21 more elements

A resonator gyro comprising:

a first light source configured to produce a first input light having a first frequency;
a second light source configured to produce a second input light having a second frequency;
a third light source configured to produce a third input light having a third frequency;
a resonator coupled to said first, second, and third light sources, said resonator having first and second counter-propagating directions, said resonator configured to:
circulate a first circulating light based on said first input light in said first counter-propagating direction;
circulate a second circulating light based on said second input light in said second counter-propagating direction;
and
circulate a third circulating light based on said third input light in said second counter-propagating direction;
a tracking circuit coupled to said resonator and configured to detect a first resonance frequency (f1) of said first counter-propagating direction, a second resonance frequency (f2) of said second counter-propagating direction, and a third resonance frequency (f3) of said second counter-propagating direction, said second resonance frequency (f2) one longitudinal mode lower than said first resonance frequency (f1), said third resonance frequency (f3) at least one longitudinal mode higher than said first resonance frequency (f1), wherein said tracking circuit comprises:
a photodetector configured to sample light based on said second and third circulating light;
a demodulator coupled to said photodetector and configured to produce a first demodulated signal based on said second circulating light and a second demodulated signal based on said third circulating light;
an accumulator coupled to said demodulator and configured to produce a first accumulated signal from said first demodulated signal and a second accumulated signal from said second demodulated signal, said first accumulated signal indicating a first control value to lock said second light source to said second resonance frequency, said second accumulated signal indicating a second control value to lock said third light source to said third resonance frequency;
a first adder having a first input coupled to said accumulator and having a second input configured to receive a predetermined constant offset, said first adder configured to produce a first summed signal from said predetermined constant offset and said first accumulated signal and further configured to produce a second summed signal from said constant offset and said second accumulated signal;
a wave generator configured to produce first and second sine waves;
a second adder having a first input coupled to said wave generator, a second input coupled to said first adder, and an output coupled to said controller, said second adder configured to produce a first control signal from said first summed signal and said first sine wave;
a third adder having a first input coupled to said wave generator, a second input coupled to said first adder, and an output coupled to said controller, said third adder configured to produce a second signal from said second summed signal and said second sine wave;
and
a subtracter coupled to said first adder and configured to produce a digital rate output of the resonator gyro from a difference of said first and second summed signals, said digital rate output proportional to said rotational rate of the resonator gyro;
and
a controller coupled to said tracking circuit and said first, second, and third light sources, said controller configured to:
tune said first frequency to said first resonance frequency (f1);
tune said second frequency to said second resonance frequency (f2);
and
tune said third frequency to said third resonance frequency (f3), wherein (f3 −f1)−(f1−f2)=2 Δf, and Δf is a frequency difference proportional to a rotational rate of the resonator gyro.

21 more elements

A method for determining a rotation rate of a resonator gyro, the method comprising the steps of:

locking a first input light beam to a clockwise resonance frequency of the resonator gyro, the clockwise resonance frequency on a first longitudinal resonance mode;
locking a second input light beam to a first counter-clockwise resonance frequency of the resonator gyro, the first counter-clockwise resonance frequency on a second longitudinal resonance mode away from the first longitudinal resonance mode;
determining a frequency difference between the first and second input light beams, the frequency difference proportional to the rotation rate;
and
modulating the first and second input light beams at a frequency greater than at least four times a loop unity gain frequency of the resonator gyro prior to said determining step.

2 more elements

A resonator gyro comprising:

a first light source configured to produce a first input light having a first frequency;
a second light source configured to produce a second input light having a second frequency;
a resonator coupled to said first and second light sources, said resonator having first and second counter-propagating directions and comprising an optical fiber coil having a hollow core, said resonator configured to:
circulate a first circulating light through said hollow core in said first counter-propagating direction, said first circulating light based on a portion of said first input light;
and
circulate a second circulating light through said hollow core in a second counter-propagating direction, said second circulating light based on a portion of said second input light;
a resonance detection circuit coupled to said resonator and comprising:
a first photodetector configured to sample light from said first circulating light;
a second photodetector configured to sample light from said second circulating light;
a first resonance detection circuit coupled to said first photodetector and configured to detect a resonance center of said first counter-propagating direction;
and
a second resonance detection circuit coupled to said second photodetector and configured to detect a resonance center of said second counter-propagating direction;
a controller coupled to said resonance detection circuit and said first and second light sources, said controller comprising:
a first servo having an input coupled to said first resonance detection circuit and having an output coupled to said first light source;
and
a second servo having an input coupled to said second resonance detection circuit and having an output coupled to said second light source;
wherein said controller is configured to:
tune said first frequency to said resonance frequency of said first counter-propagating direction;
and
tune said second frequency to said resonance frequency of said second counter-propagating direction, a difference between said resonance frequencies of said first and second counter-propagating directions proportional to a rotational rate of the resonator gyro;
a first tracking loop based on said first light source, said resonator, said first photodetector, and said first resonance detection circuit, said first tracking loop having a first unity gain frequency, each of said first light source, said first photodetector, said first resonance detection circuit, and said first servo having a control signal bandwidth greater than said first unity gain frequency;
and
a second tracking loop based on said second light source, said resonator, said second photodetector, and said second resonance detection circuit, said second tracking loop having a second unity gain frequency, each of said second light source, said second photodetector, said second resonance detection circuit, and said second servo having a control signal bandwidth greater than said second unity gain frequency.

20 more elements

A resonator gyro comprising:

a first light source configured to produce a first input light having a first frequency;
a second light source configured to produce a second input light having a second frequency;
a resonator coupled to said first and second light sources, said resonator having first and second counter-propagating directions and comprising an optical fiber coil having a hollow core, said resonator configured to:
circulate a first circulating light through said hollow core in said first counter-propagating direction, said first circulating light based on a portion of said first input light;
and
circulate a second circulating light through said hollow core in a second counter-propagating direction, said second circulating light based on a portion of said second input light;
a resonance detection circuit coupled to said resonator and comprising:
a first photodetector configured to sample light from said first circulating light;
a second photodetector configured to sample light from said second circulating light;
a first resonance detection circuit coupled to said first photodetector and configured to detect a resonance center of said first counter-propagating direction;
and
a second resonance detection circuit coupled to said second photodetector and configured to detect a resonance center of said second counter-propagating direction, said second resonance detection circuit comprising:
an analog-to-digital (A/D) converter coupled to second photodetector and configured to produce a digitized signal from said sampled light of said second photodetector;
a demodulator coupled to said A/D converter and configured to produce a demodulated signal based on said digitized signal;
an accumulator coupled to said demodulator and configured to produce an accumulated signal from said demodulated signal;
a first adder having a first input coupled to said accumulator and a second input configured to receive a value determining said resonance frequency of said second counter-propagating direction, said first adder configured to produce a control signal from said accumulated signal and said value;
a wave generator configured to produce a sine wave;
and
a second adder having a first input coupled to said wave generator and a second input coupled to said first adder, said second adder configured to produce a second summed signal from said control signal and said sine wave, said second summed signal indicating said difference between said resonance frequencies of said first and second counter-propagating directions, said second summed signal having a sine wave portion for modulating said second input light;
and
a controller coupled to said resonance detection circuit and said first and second light sources, said controller configured to:
tune said first frequency to said resonance frequency of said first counter-propagating direction;
and
tune said second frequency to said resonance frequency of said second counter-propagating direction, a difference between said resonance frequencies of said first and second counter-propagating directions proportional to a rotational rate of the resonator gyro.

21 more elements

A resonator gyro comprising:

a first light source configured to produce a first input light having a first frequency;
a second light source configured to produce a second input light having a second frequency;
a resonator coupled to said first and second light sources, said resonator having first and second counter-propagating directions and comprising an optical fiber coil having a hollow core, said resonator configured to circulate light based on said first and second input light through said hollow core in said first and second counter-propagating directions;
a resonance detection circuit coupled to said resonator and configured to detect a resonance frequency for each of said first and second counter-propagating directions;
and
a controller coupled to said resonance detection circuit and said first and second light sources, said controller configured to:
tune said first frequency to said resonance frequency of said first counter-propagating direction;
and
tune said second frequency to said resonance frequency of said second counter-propagating direction, a difference between said resonance frequencies of said first and second counter-propagating directions proportional to a rotational rate of the resonator gyro;
wherein said controller comprises:
a first current drive having an input configured to receive a control signal from said resonance detection circuit and an output coupled to said first light source, said first current drive configured to tune and modulate said first light source based on first control signal;
a photodetector configured to detect a signal having a beat frequency based on said first and second input light;
a direct digital synthesizer configured to receive a control value from said resonance detection circuit and further configured to produce an oscillation signal in response to said control value;
a mixer having a first input coupled to said photodetector, a second input coupled to said direct digital synthesizer, and an output, said mixer configured to produce a mixed signal from said control value and said beat frequency;
an integrator coupled to said output of said mixer;
and
a second current drive having an input coupled to said integrator and an output coupled to said second light source, said second current drive configured to tune and modulate said second light source based on said control value.

14 more elements

Dependencies are inferred from the claim text.