Optical accelerometers for use in navigation grade environments

Patent metadata

Field	Value
Publication number	US-10830787-B2
Application number	US-201815968668-A
Country	US
Kind code	B2
Filing date	May 1, 2018
Priority date	Feb 20, 2018
Publication date	Nov 10, 2020
Grant date	Nov 10, 2020

Abstract

An accelerometer includes a membrane, an energy source producing a laser beam which is directed at the membrane causing it to vibrate, and a transparent cap disposed at one end of the energy source. The accelerometer includes a first controller for adjusting an output power of the energy source in a first feedback loop, a second controller for controlling the wavelength of the laser beam in a second feedback loop, and a detector sensing a reflected portion of the laser beam. An acceleration signal is based in part on the frequency of the reflected portion of the laser beam.

First claim

What is claimed is:

1. An accelerometer comprising:
a membrane;
an energy source, the energy source producing a laser beam, the laser beam directed at the membrane causing it to vibrate;
a transparent cap, the transparent cap disposed at one end of the energy source;
a first controller for adjusting an output power of the energy source in a first feedback loop;
a second controller for controlling the wavelength of the laser beam in a second feedback loop; and
a detector sensing a reflected portion of the laser beam,
wherein an acceleration signal is based in part on the frequency of the reflected portion of the laser beam.

2. The accelerometer of claim 1 further comprising a vacuum gap positioned between the transparent cap and the membrane.

3. The accelerometer of claim 2 , wherein the transparent cap comprises a first thickness,
wherein the vacuum gap comprises a second thickness, and
wherein the first thickness is in a range of about 10 to about 100 times greater than the second thickness.

4. The accelerometer of claim 1 , further comprising an amplifier communicatively coupled to the detector,
wherein the detector passes at least one electronic signal representative of the reflected portion of the laser beam to the amplifier, and
wherein the amplifier maintains or increases the amplitude of at least one characteristic of the at least one electronic signal.

5. The accelerometer of claim 4 further comprising:
at least one automatic gain controller communicatively coupled to the amplifier; and
at least one proportional integral differential (PID) controller communicatively coupled to the amplifier.

6. The accelerometer of claim 5 , wherein the at least one automatic gain controller is communicatively coupled to the first controller, and
wherein the at least one automatic gain controller is part of the first feedback loop.

7. The accelerometer of claim 5 , wherein the at least one PID controller is communicatively coupled to the second controller, and
wherein the second feedback loop comprises the at least one PID controller.

8. The accelerometer of claim 7 further comprising a low pass electronic filter,
wherein the low pass electronic filter is communicatively coupled to the at least one PID controller upstream of the at least one PID controller.

9. The accelerometer of claim 8 , the transparent cap further comprising:
a first surface, the first surface adjacent the energy source;
a second surface, the second surface proximate the membrane; and
an index matching fluid, the index matching fluid disposed on the first surface.

10. The accelerometer of claim 1 further comprising at least one optical fiber, the at least one optical fiber transporting energy from the energy source to the transparent cap;
the transparent cap further comprising:
a first surface, the first surface adjacent the energy source;
a second surface, the second surface proximate the membrane; and
an index matching fluid, the index matching fluid disposed between the at least one optical fiber and the first surface,
wherein the index-matching fluid has substantially the same refractive index as the at least one optical fiber.

11. The accelerometer of claim 1 , wherein the membrane at least partially comprises at least one of tungsten, titanium, nickel, chromium, a nickel-chromium alloy, and a titanium-tungsten alloy.

12. The accelerometer of claim 1 further comprising at least one temperature sensor, the at least one temperature sensor disposed on the transparent cap for sensing a temperature of the transparent cap.

13. The accelerometer of claim 12 further comprising a computing device, wherein the computing device receives at least one signal representative of a temperature of the transparent cap from the at least one temperature sensor, and
wherein the computing device digitally closes the first and second feedback loops based at least in part on the temperature of the transparent cap.

14. The accelerometer of claim 13 , wherein the computing device is communicatively coupled to both the second controller and the first controller.

15. The accelerometer of claim 1 , wherein a wavelength of the laser beam modulates as the second controller adjusts a temperature of the energy source.

16. The accelerometer of claim 1 , wherein an amplitude of the laser beam modulates as the first controller adjusts the output power of the energy source.

17. A method of measuring acceleration, the method comprising:
providing a membrane within a laser beam;
oscillating the membrane with energy from the laser beam;
adjusting the temperature of a source of the laser beam, causing a wavelength of the laser beam to modulate;
adjusting a power output of the source of the laser beam, causing an amplitude of the laser beam to modulate;
detecting at least one variation in the oscillating membrane; and
providing at least one signal representative of an oscillation of the membrane to both a first feedback loop and a second feedback loop,
wherein adjusting the temperature of a source of the laser beam uses at least one input from the first feedback loop,
wherein adjusting a power output of the source of the laser beam uses at least one input from the second feedback loop, and
wherein an acceleration signal is based in part on the frequency of an amplitude modulation of a reflected portion of the laser beam.

18. An optical accelerometer comprising:
an energy source, the energy source producing a laser beam;
a membrane, the membrane at least partially disposed within the laser beam;
a laser power controller for adjusting an output power of the energy source causing an amplitude of the laser beam to modulate;
a temperature controller for adjusting the temperature of the energy source causing a wavelength of the laser beam to modulate; and
a detection device, the detection device sensing at least one oscillation of the membrane,
wherein the laser power controller and the temperature controller are both arranged in a feedback loop with the detection device to maintain the at least one oscillation of the membrane, and
wherein an acceleration signal is based in part on the frequency of an amplitude modulation of a reflected portion of the laser beam.

19. The optical accelerometer of claim 18 , further comprising a lock-in amplifier communicatively coupled to the detection device for maintaining or increasing an amplitude of at least one characteristic of the laser beam.

20. The optical accelerometer of claim 18 , further comprising an optical circulator,
wherein the optical circulator comprises three ports, each port of the three ports coupled in optical communication with one of the energy source, the membrane, and the detection device.

Assignees

• Gen Electric

Inventors

• Challener William Albert
• Wang Mengli

Classifications

• G01P15/093 Primary

  by photoelectric pick-up · CPC title

• B81B7/02

  containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS] (B81B7/04 takes precedence) · CPC title

• G01P2015/0862

  being provided with particular means being integrated into a MEMS accelerometer structure for providing particular additional functionalities to those of a spring mass system · CPC title

• G01P15/131

  with electrostatic counterbalancing means · CPC title

• G01P15/097

  by vibratory elements · CPC title