Self-calibrating nuclear magnetic resonance (NMR) gyroscope system

Patent metadata

Field	Value
Publication number	US-9618362-B2
Application number	US-201414295091-A
Country	US
Kind code	B2
Filing date	Jun 3, 2014
Priority date	Jun 3, 2014
Publication date	Apr 11, 2017
Grant date	Apr 11, 2017

Abstract

One embodiment includes a nuclear magnetic resonance (NMR) gyroscope system. The system includes a vapor cell comprising an alkali metal and a plurality of gyromagnetic isotopes and a pump laser configured to generate an optical pump beam configured to spin-polarize the alkali metal. The system also includes a probe laser that generates an optical probe beam and a detection system configured to monitor the optical probe beam and to calculate a rotation of the NMR gyroscope system about a sensitive axis based on a modulation of the optical probe beam in response to precession of the plurality of gyromagnetic isotopes resulting from the spin-polarization of the alkali metal. The system further includes a calibration controller that modulates a characteristic of the optical pump beam to substantially mitigate bias errors associated with the gyromagnetic isotopes in the calculation of the rotation of the NMR gyroscope system about the sensitive axis.

First claim

What is claimed is:

1. A nuclear magnetic resonance (NMR) gyroscope system comprising:
a vapor cell comprising an alkali metal and a plurality of gyromagnetic isotopes;
a pump laser configured to generate an optical pump beam configured to spin-polarize the alkali metal;
a probe laser configured to generate an optical probe beam;
a detection system configured to monitor the optical probe beam and to calculate a rotation of the NMR gyroscope system about a sensitive axis based on a modulation of the optical probe beam in response to precession of the plurality of gyromagnetic isotopes resulting from the spin-polarization of the alkali metal; and
a calibration controller configured to modulate a characteristic of the optical pump beam to substantially mitigate bias errors associated with the gyromagnetic isotopes in the calculation of the rotation of the NMR gyroscope system about the sensitive axis.

2. The system of claim 1 , wherein the calibration controller is configured to modulate a circular-polarization of the optical pump beam to substantially mitigate the bias errors associated with the gyromagnetic isotopes in the calculation of the rotation of the NMR gyroscope system about the sensitive axis.

3. The system of claim 1 , further comprising a magnetic field generator configured to generate a magnetic field that is substantially aligned with the sensitive axis, the magnetic field comprising a DC component and an AC component.

4. The system of claim 3 , wherein the calibration controller is further configured to modulate the DC component of the magnetic field to substantially mitigate bias errors associated with the gyromagnetic isotopes in the calculation of the rotation of the NMR gyroscope system about the sensitive axis.

5. The system of claim 4 , wherein the calibration controller is configured to time-align the modulation of the optical pump beam and the DC component of the magnetic field.

6. The system of claim 1 , wherein the pump laser is configured to generate the optical pump beam in a first linear-polarization, wherein the calibration controller comprises:
a polarization controller configured to modulate the optical pump beam between the first linear-polarization and a second linear-polarization that is orthogonal with respect to the first linear-polarization based on a time modulation signal; and
a quarter-wave plate configured to convert the first linear-polarization to a first circular-polarization and to convert the second linear-polarization to a second circular-polarization opposite the first circular-polarization.

7. The system of claim 6 , wherein the pump laser is a first pump laser configured to generate a first optical pump beam having the first linear-polarization, the system further comprising a second pump laser configured to generate a second optical pump beam having the second linear-polarization, wherein the polarization controller is configured to alternately provide the first and second optical pump beams along a common optical path to an input of the quarter-wave plate based on the time modulation signal.

8. The system of claim 6 , wherein the polarization controller is configured to stimulate the pump laser to modulate the optical pump beam generated by the pump laser between the first and second linear-polarizations based on the time modulation signal.

9. The system of claim 6 , wherein the polarization controller comprises optics that alternately switch the optical pump beam between the first and second linear-polarizations based on the time modulation signal.

10. The system of claim 6 , wherein the polarization controller is configured to alternately rotate the quarter-wave plate by approximately 90° based on the time modulation signal to modulate the circular-polarization between the first and second circular-polarizations.

11. A method for self-calibration of a nuclear magnetic resonance (NMR) gyroscope system, the method comprising:
generating an optical pump beam via a pump laser;
providing the optical pump beam through a vapor cell comprising an alkali metal and a plurality of gyromagnetic isotopes, the optical pump beam being provided along a sensitive axis of the NMR gyroscope system to spin-polarize the alkali metal;
generating an optical probe beam via a probe laser;
providing the optical probe beam through the vapor cell orthogonally with respect to the optical pump beam to provide a detection beam exiting the vapor cell;
modulating a characteristic of the optical pump beam to render bias error corresponding to at least one of isotope shift and quadrupole shift associated with the plurality of gyromagnetic isotopes observable based on a difference in precession of the plurality of gyromagnetic isotopes as provided by the detection beam; and
removing the bias error from a calculation of rotation of the NMR gyroscope system about the sensitive axis.

12. The method of claim 11 , wherein modulating the characteristic of the optical pump beam comprises modulating a circular-polarization direction of the optical pump beam.

13. The method of claim 12 , wherein generating the optical pump beam comprises generating a first optical pump beam having a first linear-polarization via a first pump laser and generating a second optical pump beam having a second linear-polarization via a second pump laser, wherein modulating the circular-polarization direction of the optical pump beam comprises alternately providing the first and second optical pump beams along a common optical path to an input of a quarter-wave plate based on a time modulation signal.

14. The method of claim 11 , further comprising:
generating a magnetic field that is substantially aligned with the sensitive axis, the magnetic field comprising a DC component and an AC component; and
modulating the DC component of the magnetic field to render bias error associated with the isotope shift associated with the plurality of gyromagnetic isotopes observable.

15. The method of claim 14 , further comprising time-aligning the modulation of the optical pump beam and the DC component of the magnetic field.

16. A nuclear magnetic resonance (NMR) gyroscope system comprising:
a vapor cell comprising an alkali metal and a plurality of gyromagnetic isotopes;
a pump laser configured to generate an optical pump beam having a first linear-polarization;
a calibration controller comprising:
a polarization controller configured to modulate the optical pump beam between the first linear-polarization and a second linear-polarization that is orthogonal with respect to the first linear-polarization based on a time modulation signal; and
a quarter-wave plate configured to convert the first linear-polarization to a first circular-polarization and to convert the second linear-polarization to a second circular-polarization opposite the first circular-polarization, the modulated circularly-polarized optical pump beam being provided through the vapor cell along a sensitive axis;

a probe laser configured to generate an optical probe beam; and
a detection system configured to monitor the optical probe beam, to observe bias errors associated with precession of the plurality of gyromagnetic isotopes based on the modulated circularly-polarized optical pump beam, and to calculate a rotation of the NMR gyroscope system about a sensitive axis based on a modulation of the optical probe beam in response to the precession of the plurality of gyromagnetic isotopes and based on the observed bias errors.

17. The system of claim 16 , wherein the pump laser is a first pump laser configured to generate a f

Assignees

• Bulatowicz Michael D
• Larsen Michael S
• Northrop Grumman Systems Corp

Inventors

• Bulatowicz Michael D
• Larsen Michael S

Classifications

• 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

• G01C25/005

  initial alignment, calibration or starting-up of inertial devices · CPC title

• G01C19/62 Primary

  with optical pumping · CPC title