US 8,009,296 B2Granted

Light-phase-noise error reducer

AssigneeHoneywell International Inc.

InventorsGlen A. Sanders, Tiequn Qiu, Lee K. Strandjord

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Abstract

A resonator gyroscope comprises a reference laser generator to produce a reference light; a first slave light source to produce a first slave light locked to the reference light; a second slave light source to produce a second slave light locked to the reference light; a first optical filter cavity coupled to at least one of the first and second slave light sources to filter out high-frequency fluctuations in the respective first and second slave lights; a resonator coupled to said first and second light sources, the resonator having first and second counter-propagating directions and resonance tracking electronics coupled to the resonator to generate a first beat frequency, a second beat frequency, and a third beat frequency; wherein the rotational rate of the resonator gyroscope is a function of the first, second and third beat frequencies.

Claims20

Dependent claims

A resonator gyroscope comprising:

a reference laser generator, the reference laser generator comprising:
a master light source to produce a reference light;
a frequency discriminator to linearly convert frequency fluctuations of the reference light to intensity fluctuations;
a photodetector to convert fluctuations in the intensity of an optical output of the filter discriminator to an electrical voltage;
a differential amplifier to compare the output voltage of the photodetector with a stable reference voltage;
and
servo electronics to provide control signals to the master light source based on an output of the differential amplifier to drive the master light source such that low-frequency fluctuations in the reference light are removed;
the resonator gyroscope further comprising:
a first slave light source having a first modulation frequency to produce a first slave light having a first frequency;
a first phase-lock-loop (PLL) to beat the first slave light with the reference light and to drive the first slave light source such that the first slave light is locked to the reference light;
a second slave light source having a second modulation frequency to produce a second slave light having a second frequency;
a second phase-lock-loop (PLL) to beat the second slave light with the reference light and to drive the second slave light source such that the second slave light is locked to the reference light;
a first optical filter cavity coupled to at least one of the first and second slave light sources to filter out high-frequency fluctuations in the respective first and second slave lights;
a resonator coupled to said first and second light sources, the resonator having first and second counter-propagating directions and comprising an optical fiber coil, wherein the resonator circulates a first circulating light through the optical fiber coil in the first counter-propagating direction, the first circulating light based on a portion of the first slave light;
and circulates a second circulating light through the optical fiber coil in a second counter-propagating direction, the second circulating light based on a portion of the second slave light;
and
resonance tracking electronics coupled to the resonator to generate a first beat frequency based on a first resonance frequency for the first counter-propagating direction, a second beat frequency based on a second resonance frequency for the second counter-propagating direction, and a third beat frequency based on a third resonance frequency for the second counter-propagating direction;
wherein the second resonance frequency is at least one resonance mode lower than the first resonance frequency and the third resonance frequency is at least one resonance mode higher than the first resonance frequency and the rotational rate of the resonator gyroscope is a function of the first, second and third beat frequencies.

15 more elements

A resonator gyroscope comprising:

a plurality of light sources, each having a modulation frequency;
at least one optical filter cavity coupled to an output of at least one of the plurality of light sources to filter out high-frequency fluctuations in the light from the at least one light source;
one or more light stabilization loops, each of the one or more light stabilization loops coupled to one of the plurality of light sources and comprising:
a resonator having a linear portion in its resonance curve, the resonator converting frequency fluctuations of the light from the respective one of the plurality of light sources to intensity fluctuations;
a photodetector coupled to an output of the resonator to convert fluctuations in the intensity of an optical output of the resonator to an electrical voltage;
a differential amplifier to compare the output voltage of the photodetector with a stable reference voltage;
and
servo electronics to provide control signals to the respective one of the plurality of light sources to lock the modulation frequency of the respective light source to a frequency in the linear portion of the resonance curve such that frequency fluctuations are converted linearly to intensity fluctuations, the control signals also driving the respective light source such that low-frequency fluctuations in the light from the respective light source are removed;
the reference resonator further comprising:
a Sagnac resonator coupled to the plurality of light sources, the Sagnac resonator having first and second counter-propagating directions and comprising an optical fiber coil, wherein the Sagnac resonator circulates a first circulating light through the optical fiber coil in the first counter-propagating direction, the first circulating light based on a portion of light from one of the plurality of light sources received via the at least one optical filter cavity;
and circulates a second circulating light through the optical fiber coil in a second counter-propagating direction, the second circulating light based on a portion of the light from another of the plurality of light sources received via the at least one optical filter cavity;
and
resonance tracking electronics coupled to the Sagnac resonator to generate a first beat frequency based on a first resonance frequency for the first counter-propagating direction, a second beat frequency based on a second resonance frequency for the second counter-propagating direction, and a third beat frequency based on a third resonance frequency for the second counter-propagating direction;
wherein the second resonance frequency is at least one resonance mode lower than the first resonance frequency and the third resonance frequency is at least one resonance mode higher than the first resonance frequency and the rotational rate of the resonator gyroscope is a function of the first, second and third beat frequencies.

11 more elements

A method of determining a rotational rate of a resonator gyroscope, the method comprising:

generating a plurality of laser beams;
passing each of the plurality of laser beams through an optical filter cavity to remove high-frequency fluctuations from each of the plurality of laser beams;
locking each of the plurality of laser beams to a frequency of a linear portion of a resonance curve of a reference resonator to remove low-frequency fluctuations from each of the plurality of laser beams;
providing one of the plurality of laser beams to a Sagnac resonator in a first counter-propagating direction;
providing at least one of the plurality of lasers to the Sagnac resonator in a second counter-propagating direction;
determining a first beat frequency based on a first resonance frequency for the first counter-propagating direction;
determining a second beat frequency based on a second resonance frequency for the second counter-propagating direction, the second resonance frequency at least one resonance mode lower than the first resonance frequency;
and
determining a third beat frequency based on a third resonance frequency for the second counter-propagating direction, the third resonance frequency at least one resonance mode higher than the first resonance frequency;
wherein the rotational rate of the resonator gyroscope is a function of the first, second and third beat frequencies.

7 more elements

Dependencies are inferred from the claim text.