Systems and methods for resonance switching resonator fiber optic gyroscopes (RFOGs) with feed-forward processing

Patent metadata

Field	Value
Publication number	US-9772189-B2
Application number	US-201514708928-A
Country	US
Kind code	B2
Filing date	May 11, 2015
Priority date	May 11, 2015
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

Abstract

Systems and methods for resonance switching RFOGs with feed-forward processing are provided. In one embodiment, a system comprises: a fiber optic resonator; first and second laser sources coupled to the resonator, wherein the first source launches a first beam into the resonator and the second source launches a second beam into the resonator in an opposite direction; a first servo loop that locks the first beam to a first resonant mode of the resonator during a first state and to a second resonant mode of the resonator during a second state; a second servo loop that locks the second beam to the second resonant mode during the first state and to the first resonant mode during the second state; a feed-forward rate processor coupled to the servo loops that calculates a FSR average across a prior resonance switching cycle of resonant frequency measurements and applies the average to current measurements.

First claim

What is claimed is:

1. A feed-forward rotation rate processing method for a resonating fiber optic gyroscope having an optical resonator, the method comprising:
operating the resonating fiber optic gyroscope, for a first period of time, with a first optical beam locked to a first resonance mode M 1 of the optical resonator, and a second optical beam locked to a second resonance mode M 2 of the optical resonator, the second optical beam propagating around the optical resonator in a direction opposite to the first optical beam;
calculating, for the first period of time, a first resonance frequency measurement average based on the first optical beam output and a second resonance frequency measurement average for based on the second optical beam output;
operating the resonating fiber optic gyroscope, for a second period of time following the first period of time, with the first optical beam locked to the second resonance mode M 2 of the optical resonator, and the second optical beam locked to the first resonance mode M 1 of the optical resonator;
calculating, for the second period of time, a third resonance frequency average for the first optical beam, and a fourth resonance frequency average for the second optical beam;
calculating a free spectral range average over the first period of time and the second period of time as a function of the first resonance frequency average, the second resonance frequency average, third resonance frequency average, and the fourth resonance frequency average;
generating a rotation rate measurement frequency value f Ω sample signal based on a function of a first resonance frequency measurement for the first optical beam captured after the second period of time, a second resonance frequency measurement for the second optical beam captured after the second period of time, and the free spectral range average.

2. The method of claim 1 , wherein the first resonance mode M 1 and the second resonance mode M 2 are separated in frequency by one free spectral range (FSR).

3. The method of claim 1 , wherein the first period of time and the second period of time are of equal time duration.

4. The method of claim 1 , wherein the free spectral range average includes a measure of line shape asymmetry gradient error.

5. The method of claim 1 , further comprising:
generating the first optical beam with a first laser source controlled by a first resonance switching servo loop; and
generating the second optical beam with a second laser source controlled by a second resonance switching servo loop.

6. The method of claim 5 , further comprising:
ramping an output of the first resonance switching servo loop to switch the first optical beam from the first resonance mode M 1 to the second resonance mode M 2 based on the free spectral range average; and
ramping an output of the second resonance switching servo loop to switch the second optical beam from the second resonance mode M 2 to the first resonance mode M 1 based on the free spectral range average.

7. The method of claim 1 , wherein generating the rotation rate measurement f Ω sample signal further comprises calculating a rotation rate measurement f Ω from an equation equivalent to:

-

f
Ω

=

f
1

-

f
2

+

1
2

<

Δ
⁢

⁢

f
Δ

>

where f 1 is a current resonant frequency measurement for the first optical beam, f 2 is a current resonant frequency measurement for the second optical beam, and

1
2

<

Δ
⁢

⁢

f
Δ

>

is equal to the free spectral range average.

8. The method of claim 7 , wherein the term

1
2

<

Δ
⁢

⁢

f
Δ

>

is calculated from:
<Δ f> q−2 =<f 1 > q−2 −<f 2 > q−2

<Δ f> q−1 =<f 1 > q−1 −<f 2 > q−1

<Δ f Δ >=<Δf> q−1 −<Δf> q−2 =<2 f FSR >

where <f 1 > q−2 is equal to the first resonance frequency average for the first optical beam,
where <f 2 > q−2 is equal to the second resonance frequency average for the second optical beam,
where <f 2 > q−1 is equal to the third resonance frequency average for the first optical beam, and
where <f 1 > q−1 is equal to the fourth resonance frequency average for the second optical beam.

9. The method of claim 1 , further comprising:
calculating a statistical curve fit over a pre-specified segment of valid rotation rate measurement frequency value f Ω sample data; and
generating the rotation rate measurement frequency value f Ω sample signal from rotation rate data extrapolated from the statistical curve fit during a switching operation between the first period of time and the second period of time in which the first optical beam is switching between resonance mode M 1 and M 2 , and when the second optical beam is switching between resonance mode M 2 and M 1 .

10. A resonating fiber optic gyroscope system with feed-forward rotation rate processing, the system comprising:
a fiber optic resonator;
a first laser source and a second laser source each coupled to the fiber optic resonator, wherein the first laser source launches a first optical beam into the fiber optic resonator and the second laser source launches a second optical beam into the fiber optic resonator in a direction opposite to the first optical beam;
a first resonance switching servo loop configured to lock the first optical beam to a first resonant mode M 1 of the fiber optic resonator during a first switching state, and lock the first optical beam to a second resonant mode M 2 of the fiber optic resonator during a second switching state;
a second resonance switching servo loop configured to lock the second optical beam to the second resonant mode M 2 during the first switching state, and lock the second optical beam to the first resonant mode M 1 during the second switching state;
a feed-forward rate processor coupled to the first resonance switching servo loop and the second resonance switching servo loop, wherein the feed-forward rate processor calculates a free spectral range average across a prior resonance switching cycle of resonant frequency measurements and applies the free spectral range average to

Assignees

• Honeywell Int Inc

Inventors

• Strandjord Lee K
• Sanders Glen A
• Ho Waymon

Classifications

• G01C19/662 Primary

  signal readout; dither compensators · CPC title

• G02B6/2934

  Fibre ring resonators, e.g. fibre coils · CPC title

• G01C19/727 Primary

  using a passive ring resonator · CPC title