REAL-TIME NON-LINEAR OPTICAL STRAIN GAUGE SYSTEM

• US 20160084640A1
• Filed: 09/22/2014
• Published: 03/24/2016
• Est. Priority Date: 09/22/2014
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Hunt, Jeffrey H., Belk, John H.
• Granted Patent: US 9,631,923 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01B 11/168 by means of polarisation
• CPC Class Codes: G01L 1/246 using integrated gratings, e.g. Bragg gratings

Abstract

A system for measuring strain includes an optical fiber having a central portion secured between two fixed points. A first light source outputs light at a first frequency and a second light source outputs light at a second different frequency. The two light sources are both coupled to a first end of the optical fiber. A back scatter detector is also coupled to the first end to receive a return light signal from the optical fiber and outputs a signal based thereon. A forward scatter detector is coupled to a second end of the optical fiber to receive a forward light signal from the optical fiber and outputs a signal based thereon. A processor receives the signals from the back scatter detector and the forward scatter detector and generates an output signal proportional to the strain between the two fixed points based on the received signals.

Claims

1. A system for measuring strain between two fixed points, comprising:

an optical fiber having a first end, a second end, and a central portion secured between the two fixed points;

a first light source outputting a light signal having predetermined characteristics and a first frequency and coupled to the first end of the optical fiber;

a second light source outputting alight signal having the same predetermined characteristics and a second frequency different from the first frequency and coupled to the first end of the optical fiber;

a back scatter detector coupled to the first end of the optical fiber for receiving a return light signal from the optical fiber and for outputting a signal based thereon;

a forward scatter detector coupled to the second end of the optical fiber for receiving a forward light signal from the optical fiber and for outputting a signal based thereon; and

a processor coupled to receive the signals from the back scatter detector and the forward scatter detector, the processor configured to generate an output signal proportional to the strain between the two fixed points based on the signals from the back scatter detector and the forward scatter detector.

2. The system of claim 1, wherein the first light source, the second light source and the back scatter detector are coupled to the optical fiber via a 3:

1 coupler.

3. The system of claim 1, wherein the back scatter detector includes a frequency control element configured to have a frequency corresponding to a calculated response frequency based on the first frequency and the second frequency, the calculated response frequency different from the first frequency and the second frequency.

4. The system of claim 1, wherein the forward scatter detector includes a frequency control element configured to have a frequency corresponding to a calculated response frequency based on the first frequency and the second frequency, the calculated response frequency different from the first frequency and the second frequency.

5. The system of claim 1, wherein the central portion of the optical fiber includes Bragg gratings configured to reflect light at a frequency corresponding to a calculated response frequency based on the first frequency and the second frequency, the calculated response frequency different from the first frequency and the second frequency.

6. The system of claim 1, wherein the first light source includes an intensity control element configured to have a predetermined intensity, a polarization control element configured to have a predetermined polarization and a frequency control element configured to have a frequency corresponding to the first frequency.

7. The system of claim 1, wherein the second light source includes an intensity control element configured to have a predetermined intensity, a polarization control element configured to have a predetermined polarization and a frequency control element configured to have a frequency corresponding to the second frequency.

8. A system for measuring strain between two fixed points, comprising:

an optical fiber having a first end, a second end, and a central portion secured between the two fixed points;

a first light source outputting a light signal having predetermined characteristics and a first frequency and coupled to the first end of the optical fiber;

a second light source outputting a light signal having the same predetermined characteristics and a second frequency different from the first frequency and coupled to the first end of the optical fiber;

a back scatter detector coupled to the first end of the optical fiber for receiving a return light signal from the optical fiber and for outputting a signal based thereon; and

a processor coupled to receive the signal from the back scatter detector, the processor configured to generate an output signal proportional to the strain between the two fixed points based on the signal from the back scatter detector.

9. The system of claim 8, wherein the first light source, the second light source and the back scatter detector are coupled to the optical fiber via a 3:

1 coupler.

10. The system of claim 8, wherein the back scatter detector includes a frequency control element configured to have a frequency corresponding to a calculated response frequency based on the first frequency and the second frequency, the calculated response frequency different from the first frequency and the second frequency.

11. The system of claim 8, wherein the central portion of the optical fiber includes Bragg gratings configured to reflect light at a frequency corresponding to a calculated response frequency based on the first frequency and the second frequency, the calculated response frequency different from the first frequency and the second frequency.

12. The system of claim 8, wherein the first light source includes an intensity control element configured to have a predetermined intensity, a polarization control element configured to have a predetermined polarization and a frequency control element configured to have a frequency corresponding to the first frequency.

13. The system of claim 8, wherein the second light source includes an intensity control element configured to have a predetermined intensity, a polarization control element configured to have a predetermined polarization and a frequency control element configured to have a frequency corresponding to the second frequency.

14. The system of claim 8, wherein the first light source includes an intensity control element configured to have a first predetermined intensity, a polarization control element configured to have a first predetermined polarization and a frequency control element configured to have a frequency corresponding to the first frequency;

wherein the second light source includes an intensity control element configured to have a second predetermined intensity, a polarization control element configured to have a second predetermined polarization and a frequency control element configured to have a frequency corresponding to the second frequency;

wherein the first predetermined intensity is the same as the second predetermined intensity; and

wherein the first predetermined polarization is the same as the second predetermined polarization.

15. A system for measuring strain between two fixed points, comprising:

an optical fiber having a first end, a second end, and a central portion secured between the two fixed points;

a first light source outputting a light signal having predetermined characteristics and a first frequency and coupled to the first end of the optical fiber;

a second light source outputting a light signal having the same predetermined characteristics and a second frequency different from the first frequency and coupled to the first end of the optical fiber;

a forward scatter detector coupled to the second end of the optical fiber for receiving a forward light signal from the optical fiber and for outputting a signal based thereon, and

a processor coupled to receive the signal from the forward scatter detector, the processor configured to generate an output signal proportional to the strain between the two fixed points based on the signal from the forward scatter detector.

16. The system of claim 15, wherein the forward scatter detector includes a frequency control element configured to have a frequency corresponding to a calculated response frequency based on the first frequency and the second frequency, the calculated response frequency different from the first frequency and the second frequency.

17. The system of claim 15, wherein the central portion of the optical fiber includes Bragg gratings configured to reflect light at a frequency corresponding to a calculated response frequency based on the first frequency and the second frequency, the calculated response frequency different from the first frequency and the second frequency.

18. The system of claim 15, wherein the first light source includes an intensity control element configured to have a predetermined intensity, a polarization control element configured to have a predetermined polarization and a frequency control element configured to have a frequency corresponding to the first frequency.

19. The system of claim 15, wherein the second light source includes an intensity control element configured to have a predetermined intensity, a polarization control element configured to have a predetermined polarization and a frequency control element configured to have a frequency corresponding to the second frequency.

20. The system of claim 15, wherein the first light source includes an intensity control element configured to have a first predetermined intensity, a polarization control element configured to have a first predetermined polarization and a frequency control element configured to have a frequency corresponding to the first frequency;

wherein the second light source includes an intensity control element configured to have a second predetermined intensity, a polarization control element configured to have a second predetermined polarization and a frequency control element configured to have a frequency corresponding to the second frequency;

wherein the first predetermined intensity is the same as the second predetermined intensity; and

wherein the first predetermined polarization is the same as the second predetermined polarization.