Apparatus for enhanced beat note detection

Patent metadata

Field	Value
Publication number	US-10837779-B2
Application number	US-201816041205-A
Country	US
Kind code	B2
Filing date	Jul 20, 2018
Priority date	Jul 20, 2018
Publication date	Nov 17, 2020
Grant date	Nov 17, 2020

Abstract

A method comprises receiving a first optical signal and a second optical signal at or near an optical resonator, where the first optical signal includes a clockwise (CW) optical signal and the second optical signal includes a counter clockwise optical signal; injecting the first optical signal and the second optical signal into a resonator loop closure optics system of the optical resonator; sampling a portion of the first optical signal and a portion of the second optical signal; combining the portion of the first optical signal and the second optical signal; converting the combined optical signals to an analog electrical signal; digitizing the analog electrical signal; storing an estimated frequency of a beat signal created by a combination of the CW optical signal and the CCW optical signal; and using the stored estimated beat signal frequency, digitally phase lock to a frequency of the beat signal.

First claim

What is claimed is:

1. A resonant fiber optic gyroscope (RFOG), comprising:
a coherent light source system comprising at least two optical sources;
an optical processing system coupled to the coherent light source system;
an optical resonator coil, having a first port and a second port, configured to be coupled to the optical processing system;
wherein the optical resonator coil is configured to receive a clockwise (CW) optical signal and a counter clockwise (CCW) optical signal generated by the coherent light source system;
wherein the optical processing system comprises a resonator loop closure optics system and a beat note pickoff system;
wherein the beat note pickoff system comprises a first optical divider, a second optical divider, and an optical combiner, and is configured to couple the CW optical signal through the first optical divider and the CCW optical signal through the second optical divider into the resonator loop closure optics and to provide the CW optical signal and the CCW optical signal at an output of the optical combiner;
wherein the resonator loop closure optics system comprises a first beam splitter and a second beam splitter, and is configured to couple the CW optical signal through the first beam splitter and the CW optical signal through the second beam splitter into the optical resonator coil, and where the first beam splitter and the second beam splitter facilitate circulation of the CW optical signal and the CW optical signal through the resonator loop closure optics system and the optical resonator coil;
wherein the optical resonator coil is optically coupled to the resonator loop closure optics system;
a first photodetector having an input coupled to the optical processing system and an output coupled to the coherent light source system;
a second photodetector having an input coupled to the optical processing system and an output coupled to the coherent light source system;
a third photodetector having an input coupled to the optical processing system and an output coupled to the coherent light source system;
a fourth photodetector having an input coupled to the beat note pickoff system, and an output, where the fourth photodetector is configured to receive the CW optical signal and the CCW optical signal, from the output of the optical combiner, at the input of the fourth photodiode; and
a beat note detector circuit comprising phase lock loop circuitry, where the beat note detector circuit is coupled to the output of the fourth photo detector and is configured to receive an estimated beat note frequency from a circuit configured to generate an estimated beat note frequency, to receive an electrical beat note pickoff signal from the output of the fourth photo detector, and to generate a signal representing a beat note frequency based upon the estimated beat note frequency and the electrical beat note pickoff signal;
wherein the beat note detector circuit is configured to be coupled to processing circuitry configured to determine a rate of rotation using the beat note frequency.

2. The RFOG of claim 1 , wherein the beat note detector circuit is coupled to the coherent light source system.

3. The RFOG of claim 1 , wherein the coherent light source system comprises:
a master optical source;
a CW slave optical source;
a CCW slave optical source;
a CW optical phase lock loop configured to be coupled to the CW slave optical source and the master optical source;
a CCW optical phase lock loop configured to be coupled to the CCW slave optical source and the master optical source;
a CW resonance tracking servo system coupled to the CW optical phase lock loop and the output of the third photodiode;
a CCW resonance tracking servo system coupled to the CCW optical phase lock loop and the output of the second photodiode;
a Pound Dreyer Hall (PDH) servo system coupled to the master optical source and the output of the first photodiode; and
an optical combiner coupled to the CW slave optical source, the master optical source, and the optical processing system with a beat note pickoff system.

4. The RFOG of claim 1 , wherein the phase locked loop circuitry comprises:
an analog to digital converter including an output;
a digital mixer including a first input, a second input, and an output, wherein the first input is coupled to the output of the analog to digital converter;
a loop filter, including an input and an output, wherein the input is coupled to the output of the digital mixer;
an adder, including a first input, a second input, and an output, wherein the output of the loop filter is coupled to the first input of the adder;
a register including an output coupled to the second input of the adder;
wherein the register is configured to receive the estimated beat note frequency; and
a numerically controlled oscillator including an input and an output, wherein the input is coupled to the output of the adder and the output is coupled to the second input of the digital mixer.

5. The RFOG of claim 1 , wherein the beat note detector circuit further comprises a transimpedance amplifier coupled between the fourth photodiode and the phase locked loop circuitry.

6. The RFOG of claim 1 , wherein the beat note pickoff system comprises:
a CW optical divider having an input configured to receive a CW optical signal and an output;
a CCW optical divider having an input configured to receive a CCW optical signal and an output; and
an optical combiner having a first input coupled to the output of the CW optical divider, a second input coupled to the output of the CCW optical combiner, and an output coupled to the fourth photodiode.

7. The RFOG of claim 1 , wherein the beat note pickoff system comprises:
a first beam splitter;
a second beam splitter;
a third beam splitter optically coupled to the second beam splitter;
a first mirror optically coupled to the first beam splitter and the third beam splitter; and
a port optically coupled to the third beam splitter and the input of the fourth photodiode.

8. The RFOG of claim 1 , wherein the resonator loop closure optics system comprises:
a first beam splitter;
a second beam splitter optically coupled to the first beam splitter;
a first coupling optics optically coupled to the first beam splitter;
a second coupling optics optically coupled to the second beam splitter;
a first optical waveguide optically coupled to the first coupling optics and the optical resonator coil; and
a second optical waveguide optically coupled to the second coupling optics and the optical resonator coil.

Assignees

• Honeywell Int Inc

Inventors

• Strandjord Lee K
• Ayotte Simon
• Sanders Glen A

Classifications

• G01C19/72 Primary

  with counter-rotating light beams in a passive ring, e.g. fibre laser gyrometers · CPC title

• G01C19/721

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

• G01C19/727 Primary

  using a passive ring resonator · CPC title