Apparatus and method for enhanced beat note detection

Patent metadata

Field	Value
Publication number	US-12516936-B2
Application number	US-202318453610-A
Country	US
Kind code	B2
Filing date	Aug 22, 2023
Priority date	Aug 22, 2023
Publication date	Jan 6, 2026
Grant date	Jan 6, 2026

Abstract

Lower noise and complexity techniques are disclosed for compensating for time varying phase changes in fiber optics in a resonant fiber optic gyroscope (RFOG). Orthogonal components derived from an electrical beat note signal and a difference between clockwise and counterclockwise resonant frequencies of an optical resonator coil of the RFOG are determined. The orthogonal products are converted to a phase which is differentiated with respect to time to obtain a beat note correction signal.

First claim

What is claimed is:

1 . A method for generating a beat note correction signal configured to reduce bias error in a resonant fiber optic gyroscope including an optical source optically coupled to an optical resonator coil, wherein the optical source is configured to generate a clockwise optical signal configured to propagate clockwise around the optical resonator coil and a counterclockwise optical signal configured to propagate counterclockwise around the optical resonator coil, the method comprising:
receiving a resonant frequency in each of a clockwise direction and a counterclockwise direction of the optical resonator coil; receiving a beat note electrical signal derived from a portion of the clockwise optical signal and a portion of the counterclockwise optical signal; determining a difference frequency which is a function of the resonant frequency in the clockwise direction of the optical resonator coil and the resonant frequency in the counterclockwise direction of the optical resonator coil; generating (a) a sine signal which is a function of the difference frequency and (b) a cosine signal which is the function of the difference frequency; digitizing the beat note electrical signal; generating a first low pass filtered signal by mixing the sine signal with a digitized beat note electrical signal and removing first set of mixing products other than a first mixing product closest to zero Hertz; generating a second low pass filtered signal by mixing the cosine signal with the digitized beat note electrical signal and removing a second set of mixing products other than a second mixing product closest to zero Hertz; using the first and the second low pass filtered signals, generating a phase signal using a rectangular to polar coordinates converter; and generating the beat note correction signal by differentiating the phase signal with respect to time.

2 . The method of claim 1 , further comprising, using the difference frequency and the beat note correction signal, determining a rate of rotation around a winding axis of the optical resonator coil.

3 . The method of claim 1 , further comprising low pass filtering the beat note correction signal.

4 . The method of claim 1 , further comprising high pass filtering the digitized beat note electrical signal to remove any direct current component;
wherein the first low pass filtered signal and the second low pass filtered signal are generated using the digitized beat note electrical signal that has been high pass filtered.

5 . The method of claim 1 , further comprising reducing a sampling rate of each of the first low pass filtered signal and the second low pass filtered signal;
wherein the phase signal is generated using the first and the second low pass filtered signals with a reduced sampling rate.

6 . The method of claim 1 , further comprising generating a beat note radius signal that is an indicium of an amplitude of the beat note electrical signal.

7 . A non-transitory machine readable medium storing data that when loaded into a programmable circuit, causes the programmable circuit to instantiate an instantiated circuit configured to generate a beat note correction signal configured to reduce bias error in a resonant fiber optic gyroscope including an optical source optically coupled to an optical resonator coil, wherein the optical source is configured to generate a clockwise optical signal configured to propagate clockwise around the optical resonator coil and a counterclockwise optical signal configured to propagate counterclockwise around the optical resonator coil, wherein the instantiated circuit is configured to:
receive a resonant frequency in each of a clockwise direction and a counterclockwise direction of the optical resonator coil; receive a beat note electrical signal derived from a portion of the clockwise optical signal and a portion of the counterclockwise optical signal; determine a difference frequency which is a function of the resonant frequency in the clockwise direction of the optical resonator coil and the resonant frequency in the counterclockwise direction of the optical resonator coil; generate (a) a sine signal which is a function of the difference frequency and (b) a cosine signal which is the function of the difference frequency; digitize the beat note electrical signal; generate a first low pass filtered signal by mixing the sine signal with a digitized beat note electrical signal and removing a first set of mixing products other than a first mixing product closest to zero Hertz; generate a second low pass filtered signal by mixing the cosine signal with the digitized beat note electrical signal and removing a second set of mixing products other than a second mixing product closest to zero Hertz; using the first and the second low pass filtered signals, generate a phase signal using a rectangular to polar coordinates converter; and generate the beat note correction signal by differentiating the phase signal with respect to time.

8 . The non-transitory machine readable medium storing data of claim 7 , wherein the instantiated circuit is further configured to, using the beat note correction signal and the difference frequency, determine a rate of rotation around a winding axis of the optical resonator coil.

9 . The non-transitory machine readable medium storing data of claim 7 , wherein the instantiated circuit is further configured to low pass filter the beat note correction signal.

10 . The non-transitory machine readable medium storing data of claim 7 , wherein the instantiated circuit is further configured to high pass filter the digitized beat note electrical signal to remove any direct current component;
wherein the first low pass filtered signal and the second low pass filtered signal are generated using the digitized beat note electrical signal that has been high pass filtered.

11 . The non-transitory machine readable medium storing data of claim 7 , wherein the instantiated circuit is further configured to reduce a sampling rate of each of the first low pass filtered signal and the second low pass filtered signal;
wherein the phase signal is generated using the first and the second low pass filtered signals with a reduced sampling rate.

12 . The non-transitory machine readable medium storing data of claim 7 , wherein the instantiated circuit is further configured to generate a beat note radius signal that is an indicium of an amplitude of the beat note electrical signal.

13 . A resonant fiber optic gyroscope (RFOG), comprising:
an optical source comprising at least one laser and configured to generate a clockwise (CW) optical signal and a counterclockwise optical (CCW) signal; a beat note detector configured to receive a first portion of the CW optical signal and a first portion of the CCW optical signal, and to generate a beat note electrical signal using the first portions of the CW and the CCW optical signals; an optical resonator coil; resonator closure optics configured to couple a second portion of the CW optical signal and a second portion of the CW optical signal into the optical resonator coil, and to transmit a third portion of the CW optical signal and a third portion of the CCW optical signal from the optical resonator coil; a CW rate detector configured to convert a portion of the third portion of the CW optical signal to a CW electrical signal; a CCW rate detector configured to convert a portion of the third portion of the CCW optical signal to a CCW electrical signal; a CW resonance tracking loop circuit configured to determine a resonant frequency of the optical resonator coil in a CW direction;

Assignees

• Honeywell Int Inc

Inventors

• Smiciklas Marc
• Croker Chuck
• Tarleton Norman Gerard
• Sanders Glen A

Classifications

• G01C19/723

  Heterodyning fibre optic gyrometers · CPC title

• G01C19/727

  using a passive ring resonator · CPC title

• G01C19/721 Primary

  Details, e.g. optical or electronical details · CPC title

• G01C25/00 Primary

  Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass (testing, calibrating or compensating compasses G01C17/38) · CPC title