Stimulated rate optical power measurement in a fiber optic gyroscope

• US 20050270540A1
• Filed: 06/02/2004
• Published: 12/08/2005
• Est. Priority Date: 06/02/2004
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Litton Systems Incorporated
• Inventors: Bowser, Mark P.
• Granted Patent: US 7,274,460 B2
• Time in Patent Office: Days
• US Class Current: 356/460
• CPC Class Codes: G01C 19/72 with counter-rotating light beams in a passive ring, e.g. fibre laser gyrometers

Abstract

Fiber optic gyroscopes having integrated power measurement capabilities and related methods and apparatus. More particularly, fiber optic gyroscopes having an integrated method for determining the optical power by applying an electronic stimulated rate internal to the closed loop digital electronics of the gyroscopes and monitoring the counts out per second (COPS) using each gyroscope'"'"'s counts output signal. Knowing a COPS value, the optical power can be determined by dividing a constant K by the COPS value, i.e. Optical Power=K/COPS. The value of K is specific to each gyroscope, and can be calculated or measured.

Claims

1. A method of calculating the optical power of a fiber optic gyroscope comprising:

simulating movement of the gyroscope;

monitoring an output of the gyroscope during said simulation;

using the monitored output to calculate an optical power value for the gyroscope.

2. The method of claim 1 wherein the monitored output is a value proportional to an angular velocity of the gyroscope.

3. The method of claim 2 wherein simulating movement of the gyroscope comprises providing a rate value to the gyroscope that causes the gyroscope to output an angular velocity value equivalent to the value it would output if the gyroscope were physically rotating at the provided rate.

4. The method of claim 3 wherein the provided rate value is added to a value corresponding to a phase difference between two counterpropagating light beams.

5. The method of claim 4 wherein using the monitored output to calculate an optical power value comprises dividing the value of the monitored output by a predetermined constant.

6. The method of claim 1 comprising:

determining a counts output per second value for the gyroscope;

determining the optical power of the gyroscope, at least in part, from the counts output per second value.

7. The method of claim 6 further comprising determining a value K for the gyroscope, and determining the optical power of the gyroscope, at least in part, from both K and the counts output per second value.

8. The method of claim 7 wherein determining the optical power of the gyroscope comprises determining the value of K divided by the counts output per second value.

9. The method of claim 8 wherein determining the value of K comprises calculating the value from a plurality of factors that include one or more of the following:

modulation amplitude, optical receiver transimpedance, preamplifier gains, filter gains, A/D converter least significant bit, and the size of the stimulated rate bit.

10. The method of claim 8 wherein determining the value of K comprises obtaining an optical power value and a corresponding counts output per second value and using the ratio of the optical power value to the counts output per second value as K.

11. An optical gyroscope comprising a mechanism for modifying a value determined internally in the gyroscope.

12. The gyroscope of claim 11 wherein the value is related to an angular velocity of the gyroscope.

13. The gyroscope of claim 12 wherein the value is a phase difference between two counterpropogating light beams.

14. The gyroscope of claim 13 wherein modifying a value comprises adding a rate value to the phase difference to produced a resultant sum.

15. The gyroscope of claim 14 wherein the resultant sum causes the gyroscope to adjust the phase difference between the two counterpropogating light beams.

16. The gyroscope of claim 15 wherein the rate value is added to a demodulator output value, and the resultant sum is provided as an input to a ramp generator

17. The gyroscope of claim 16 wherein the gyroscope is a closed loop interferometer fiber optic gyroscope.

18. A closed loop interferometer fiber optic gyroscope comprising a mechanism for specifying a rate such that a specified rate causes the gyroscope, while stationary, to produce the same counts output that it would generate if it were physically rotating at the specified rate.

19. The gyroscope of claim 18 wherein the gyroscope is adapted to provide an output value equal to the optical power of the gyroscope in response to an external request, to internally specify the rate and use the resultant counts value to compute the optical power output value.

20. The gyroscope of claim 19 wherein the gyroscope comprises a mechanism for storing a rate and a constant value to be used in response to an external request for the optical power value.