Distributed optical fibre sensor

• US 9,574,970 B2
• Filed: 02/16/2016
• Issued: 02/21/2017
• Est. Priority Date: 11/11/2010
• Status: Active Grant

• Current Assignee: Viavi Solutions, Inc. (Lumentum Holdings Inc.)
• Original Assignee: Fotech Solutions Limited
• Inventors: Handerek, Vincent
• Primary Examiner(s): NGUYEN, SANG H
• Application Number:
  US15/044,588
• Publication Number:
  US 20160161296A1
• Time in Patent Office: 371 Days
• Field of Search: 356/73.1, 356/511, 356/477, 356/479, 356/460, 356/465, 356/483
• US Class Current: 1/1
• CPC Class Codes: G01D 5/35303 using a reference fibre, e.g. interferometric devices
• CPC Class Codes: G01D 5/35306 using an interferometer arrangement
• CPC Class Codes: G01D 5/35358 using backscattering to detect the measured quantity
• CPC Class Codes: G01H 9/004 using fibre optic sensors light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125
• CPC Class Codes: G01L 11/025 using a pressure-sensitive optical fibre
• CPC Class Codes: G01M 11/3127 using multiple or wavelength variable input source
• CPC Class Codes: G01M 11/3145 Details of the optoelectronics or data analysis

Abstract

There is described a distributed optical fiber sensor for detecting one or more physical parameters indicative of an environmental influence on a sensor optical fiber, as a function of position along the sensor fiber. The sensor uses probe light pulses of different wavelengths. At least some of the probe light pulses may also be of different pulse lengths. The relative phase bias between interferometric signals in backscattered probe light of different wavelength pulses may also be controlled.

Claims

1. A distributed optical fibre sensor for determining at least one physical parameter as a function of position along a sensing fibre from properties of probe light backscattered within the sensing fibre, the sensor comprising:

a probe light source arranged to launch probe light pulses into the sensing fibre, the probe light pulses including successive groups each of two or more probe light pulses having different optical wavelengths to each other;

a detector arranged to detect probe light backscattered in said sensing fibre, including separately detecting interference signals in the backscattered probe light arising from respective probe light pulses of said different wavelengths; and

an analyser arranged to determine said parameter as a function of position along the sensing fibre from the detected interference signals of one or more of said wavelengths,

wherein the probe light source is arranged such that the two or more different optical wavelengths of probe light pulses in a group provide one or more predetermined relative phase bias misalignments between the interference signals arising from the different wavelengths.

2. The distributed optical fibre sensor of claim 1 wherein the one or more predetermined relative phase bias misalignments between the interference signals from the different wavelengths correspond to one or more approximately constant phase spacings along the length of the sensing fibre.

3. The distributed optical fibre sensor of claim 2 wherein the one or more predetermined relative phase bias misalignments between the interference signals from the different wavelengths correspond to one or more phase spacings which are constant to within π

/4 along the length of the sensing fibre.

4. The distributed optical fibre sensor of claim 1 wherein the analyser is arranged to determine said parameter as a function of position along the sensing fibre from said detected interference signals of all of said wavelengths.

5. The distributed optical fibre sensor of claim 1 wherein the probe light source is arranged such that the one or more predetermined relative phase bias misalignments between the interference signals in the backscattered light are each within π

/4 radians, or more preferably within π

/8 radians, of zero or π

radians.

6. The distributed optical fibre sensor of claim 1 wherein the probe light source is arranged such that the one or more predetermined relative phase bias misalignments between the interference signals are within π

/4 radians of π

/2 radians, or more preferably within π

/8 radians of π

/2 radians.

7. The distributed optical fibre sensor of claim 1 wherein the analyser is arranged to vectorially combine data derived from the interference signals of said two or more probe light pulses having different optical wavelengths to each other, and to determine said physical parameter from said vectorially combined data.

8. The distributed optical fibre sensor of claim 1 wherein the probe light source is arranged to adjust said one or more of the plurality of different wavelengths in response to detected interference signals.

9. The distributed optical fibre sensor of claim 8 wherein the detected properties are properties corresponding to a reference section of said sensing fibre.

10. The distributed optical fibre sensor of claim 9 further comprising a relative phase bias calibrator arranged to exert an oscillatory forcing on said reference section of optical fibre into which the probe light pulses are launched, and the sensor is arranged to adjust said one or more of the plurality of different wavelengths using signals derived from the detected backscattered light corresponding to said oscillatory forcing.

11. The distributed optical fibre sensor of claim 1 wherein the probe light source is arranged such that backscattered light from all the pulses of each group coexists within the sensing fibre, and the detector is arranged to separately and simultaneously detect light of each of said different wavelengths.

12. The distributed optical fibre sensor of claim 11 wherein the detector comprises a plurality of photodetector elements, and the sensor is arranged such that each photodetector element detects light of a different one of the probe light pulses in each group.

13. The distributed optical fibre sensor of claim 1 wherein all the probe light pulses of each group coexist within the sensor fibre.

14. The distributed optical fibre sensor of claim 13 wherein all the probe light pulses of each group overlap within the sensor fibre, or are launched by the probe light source at the same time, or are launched within 2 microseconds of each other.

15. The distributed optical fibre sensor of claim 1 wherein the different optical wavelengths of the probe light pulses in a group lie within a wavelength band of 1 nanometer width.

16. The distributed optical fibre sensor of claim 1 wherein the parameter is a measure of vibration.

17. The distributed optical fibre sensor of claim 1 wherein the parameter is indicative of an environmental influence to which the sensor fibre is responsive.

18. The distributed optical fibre sensor of claim 1 where the sensor is arranged such that the interference signals comprise coherent Rayleigh noise at each of said different wavelengths, and the analyser determines said parameter from properties of said coherent Rayleigh noise of one or more of said wavelengths.

19. A method of operating a distributed optical fibre sensor to determine at least one parameter as a function of position along a sensing fibre from properties of probe light backscattered within the sensing fibre, the method comprising:

generating and launching probe light pulses into the sensing fibre, the probe light pulses including successive groups each of two or more probe light pulses having different optical wavelengths to each other;

detecting probe light backscattered in said sensing fibre, including separately detecting interference signals in the backscattered probe light arising from respective probe light pulses of said different wavelengths; and

determining said parameter as a function of position along the sensing fibre from said detected interference signals of one or more of said wavelengths,

wherein the probe light pulses are generated such that the two or more different wavelengths of probe light pulses in a group provide one or more predetermined relative phase bias misalignments between the interference signals arising from the different wavelengths.

20. The method of claim 19 wherein the one or more predetermined relative phase bias misalignments between the interference signals from the different wavelengths correspond to one or more approximately constant phase spacings along the length of the sensing fibre.

21. The method of claim 20 wherein the one or more predetermined relative phase bias misalignments between the interference signals from the different wavelengths correspond to one or more phase spacings which are constant to within π

/4 along the length of the sensing fibre.

22. The method of claim 19 further comprising determining said parameter as a function of position along the sensing fibre from said detected interference signals of all of said wavelengths.

23. The method of claim 19 wherein said one or more of said plurality of different wavelengths provide one or more predetermined relative phase biases between the interference signals which are within π

/4 radians, or more preferably within π

/8 radians, of zero or π

radians.

24. The method of claim 19 wherein one or more of said plurality of different wavelengths is automatically adjusted to maintain the one or more predetermined relative phase biases between interference signals to be within π

/4 radians of π

/2 radians, or more preferably within π

/8 radians of π

/2 radians.

25. The method of claim 19 further comprising combining data derived from the detected interference signals of said two or more probe light pulses vectorially, and determining said physical parameter from said combined data.

26. The method of claim 19 further comprising adjusting said one or more of the plurality of different wavelengths in response to said detected interference signals.

27. The method of claim 26 wherein the detected properties are properties corresponding to a reference section of said sensing fibre.

28. The method of claim 27 further comprising using a relative phase bias calibrator to exert an oscillatory forcing on said reference section of optical fibre into which the probe light pulses are launched, and adjusting said one or more of the plurality of different wavelengths using signals derived from the detected backscattered light corresponding to said oscillatory forcing.

29. The method of claim 19 wherein the probe light pulses are generated and launched such that backscattered light from all the pulses of each group coexists within the sensing fibre, and the detection is carried out by a detector arranged to separately and simultaneously detect light of each of said different wavelengths.

30. The method of claim 29 wherein the detector comprises a plurality of photodetector elements, and the method comprises each photodetector element detecting light of a different one of the probe light pulses in each group.

31. The method of claim 19 wherein all the probe light pulses of each group coexist within the sensor fibre.

32. The method of claim 31 wherein all the probe light pulses of each group overlap within the sensor fibre, or are launched into the sensing fibre at the same time, or are launched into the sensing fibre within 2 microseconds of each other.

33. The method of claim 19 wherein the different optical wavelengths of the probe light pulses in a group lie within a wavelength band of 1 nanometer width.

34. The method of claim 19 wherein the parameter is a measure of vibration.

35. The method of claim 19 wherein the detected interference signals are coherent Rayleigh noise at each of said different wavelengths, and the parameter is determined from properties of said coherent Rayleigh noise of one or more of said wavelengths.