Optical accelerometer systems and method

Patent metadata

Field	Value
Publication number	US-9417260-B2
Application number	US-201314103595-A
Country	US
Kind code	B2
Filing date	Dec 11, 2013
Priority date	Dec 11, 2013
Publication date	Aug 16, 2016
Grant date	Aug 16, 2016

Abstract

An example optical accelerometer system is provided. An optical beam is provided having a predefined center frequency and is frequency-modulated about the predefined center frequency. An optical cavity includes a first mirror at a first end and a second mirror at a second end of the optical cavity. The second mirror is movable along the axial length of the optical cavity in response to an external acceleration, and the optical cavity receives the optical beam and emits a resonated optical beam. An acceleration detection system measures an intensity of the resonated optical beam and calculates a magnitude of the external acceleration along the axial length of the optical cavity based on the intensity of the resonated optical beam resulting from motion of the second mirror. A stabilization system stabilizes the predefined center frequency of the optical beam independently of the external acceleration based on the modulation of the optical beam.

First claim

What is claimed is:

1. An accelerometer system comprising:
an optical beam source configured to generate an optical beam having a predefined center frequency and which is frequency-modulated about the predefined center frequency;
an optical cavity comprising:
a first mirror at a first end of an axial length of the optical cavity;
a second mirror at a second end of the axial length of the optical cavity, the second mirror being movable along the axial length of the optical cavity in response to an external acceleration, the optical cavity being configured to receive the optical beam and to emit a resonated optical beam; and
a plurality of force rebalance electrodes configured to apply a force to the second mirror in response to a change of the intensity of the resonated optical beam corresponding to an external acceleration along the axial length of the optical cavity, the magnitude of the force corresponding to the magnitude of the external acceleration; and

an acceleration detection system configured to measure an intensity of the resonated optical beam and to calculate a magnitude of the external acceleration along the axial length of the optical cavity based on the intensity of the resonated optical beam resulting from motion of the second mirror; and
a stabilization system configured to stabilize the predefined center frequency of the optical beam independently of the external acceleration based on the frequency modulation signal of the optical beam.

2. The accelerometer system of claim 1 , wherein the stabilization system comprises an atomic vapor cell comprising an atomic vapor through which a portion of the optical beam is provided, wherein the accelerometer system further comprises a modulation system configured to set the predefined center frequency of the optical beam approximately equal to an atomic transition frequency of the atomic vapor in response to a feedback signal generated by the stabilization system based on an intensity of the portion of the optical beam provided through the atomic vapor cell.

3. The accelerometer system of claim 2 , wherein the intensity of the portion of the optical beam is demodulated at a frequency that is approximately equal to a frequency of the frequency modulation of the optical beam.

4. The accelerometer system of claim 1 , wherein the plurality of force rebalance electrodes are further configured to apply the force to provide an oscillatory motion of the second mirror about a neutral position corresponding to an integer multiple of a wavelength of the predefined center frequency to increase a signal-to-noise ratio (SNR) of the resonated optical beam.

5. The accelerometer system of claim 4 , wherein the intensity of the resonated optical beam is demodulated at a frequency that is approximately equal to a frequency of the oscillatory motion of the second mirror to calculate the magnitude of the external acceleration.

6. The accelerometer system of claim 4 , wherein the plurality of force rebalance electrodes are configured to provide the oscillatory motion of the second mirror about the neutral position based on feedback associated with a peak intensity of the resonated optical beam at the neutral position.

7. The accelerometer system of claim 5 , wherein the plurality of force rebalance electrodes are configured to apply the force to provide the oscillatory motion of the second mirror in one of:
a time-based control algorithm to provide the force oppositely with respect to the second mirror in each of predetermined time durations that are based on the calculated magnitude of the external acceleration;
an AC control algorithm to provide the force via a DC signal component of a force rebalance signal corresponding to the force and modulating an AC component on the DC signal component, a magnitude of the DC signal component of the force rebalance signal being adjusted based on the calculated magnitude of the external acceleration; and
a detection control algorithm corresponding to providing the AC component on a DC signal corresponding to the intensity of the resonated optical beam at a peak intensity of the resonated optical beam to provide a modulated DC signal, and converting the modulated DC signal to the force rebalance signal.

8. The accelerometer system of claim 1 , wherein the optical cavity is a first optical cavity, the system further comprising a second optical cavity and a third optical cavity, each of the second optical cavity and the third optical cavity comprising a first mirror at a first end of an axial length of the respective second and third optical cavities and a second mirror at a second end of the axial length of the respective second and third optical cavities, the second mirror being movable along the axial length of the respective second and third optical cavities, each of the respective second and third optical cavities being configured to receive a respective portion of the optical beam and to emit a respective resonated optical beam, wherein the first, second, and third optical cavities being arranged orthogonally with respect to each other to provide the accelerometer system as a three-axis accelerometer system.

9. A combination nuclear magnetic resonance (NMR) gyroscope and atomic transition locked acceleration sensor (ATLAS) system comprising the accelerometer system of claim 1 , the combination NMR gyroscope and ATLAS acceleration detection system further comprising an NMR gyroscope system configured to determine a rotation about a sensitive axis based on the optical beam, and wherein the stabilization system is configured to stabilize the predefined center wavelength of the optical beam based on the NMR gyroscope system.

10. The combination NMR gyroscope and ATLAS system of claim 9 , comprising:
an atomic vapor cell comprising an atomic vapor through which the optical beam is provided, such that the optical beam is further configured to facilitate precession of the atomic vapor, wherein the stabilization system is configured to stabilize the predefined center frequency of the optical beam approximately equal to an atomic transition frequency of the atomic vapor based on an intensity of the optical beam provided through the atomic vapor cell; and
a probe laser configured to generate an optical probe beam that is provided through the atomic vapor cell to determine a rotation of the NMR gyroscope system about a sensitive axis.

11. A method for determining an external acceleration, the method comprising:
generating an optical beam having a predefined center frequency;
providing the optical beam into an optical cavity comprising a first mirror at a first end of an axial length of the optical cavity and a second mirror at a second end of the axial length of the optical cavity, the second mirror being movable along the axial length of the optical cavity;
providing a baseline version of a force rebalance signal to a plurality of electrodes to apply a force to the second mirror to provide an oscillatory motion of the second mirror about a neutral position corresponding to an integer multiple of a wavelength of the predefined center frequency;
measuring an intensity of a resonated optical beam corresponding to the optical beam being emitted from the optical cavity by demodulating the resonated optical beam at a frequency that is approximately equal to a frequency of the oscillatory motion of the second mirror;
setting a magnitude of the force rebalance signal to maintain the oscillatory motion of the second mirror about the neutral position based on the measured intensity of the resonated optical beam; and
determining a magnitude of an external acceleration along the axial length of the optical cavity based on a difference

Assignees

• Bulatowicz Michael D
• Northrop Grumman Systems Corp

Inventors

• Bulatowicz Michael D

Classifications

• G01P15/13

  by measuring the force required to restore a proofmass subjected to inertial forces to a null position · CPC title

• G01P15/093 Primary

  by photoelectric pick-up · CPC title

• G01C19/60

  Electronic or nuclear magnetic resonance gyrometers · CPC title