Distributed Optical Fibre Sensor

• US 20130222811A1
• Filed: 11/09/2010
• Published: 08/29/2013
• 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
• Granted Patent: US 9,304,017 B2
• Time in Patent Office: Days
• US Class Current: 356/477
• 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 fibre sensor for detecting one or more physical parameters indicative of an environmental influence on a sensor optical fibre, as a function of position along the sensor fibre. 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 light of each of said different wavelengths; and

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

wherein the sensor is arranged to adjust one or more of said plurality of different wavelengths to control the relative phase bias or biases between interferometric signals in the backscattered probe light arising from respective probe light pulses of said different wavelengths.

2. 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 backscattered probe light of all of said wavelengths.

3. The distributed optical fibre sensor of claim 1 wherein the sensor is arranged to control the relative phase bias between interferometric signals in the backscattered light arising from two or more of said probe light pulses to be within π

/4 radians, or more preferably within π

/8 radians, of zero or π

radians.

4. The distributed optical fibre sensor of claim 1 wherein the sensor is arranged to control the relative phase bias between interferometric signals in the backscattered light arising from two of said probe light pulses to be within π

/4 radians of π

/2 radians, or more preferably within π

/8 radians of π

/2 radians.

5. The distributed optical fibre sensor of claim 1 wherein the analyser is arranged to determine said parameter using data derived from the detected backscatter of said probe light pulses of adjusted wavelength.

6. The distributed optical fibre sensor of claim 4 wherein the analyser is arranged to combine data derived from the detected backscatter of said two probe light pulses vectorially, and to determine said physical parameter from said vectorially combined data.

7. The distributed optical fibre sensor of claim 1 wherein the sensor is arranged to control the relative wavelength differences between three or more of said probe light pulses of different wavelength to introduce pre-determined phase biases in the respective interferometric signals, to combine data derived from the selected backscatter of said three or more light pulses vectorially, and to determine said physical parameter from said combined data.

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

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 coexisting 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.

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

29. The distributed optical fibre sensor of claim 28 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.

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

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

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

33. The distributed optical fibre sensor of claim 1 wherein the sensor is an interferometric sensor arranged to:

launch said probe light pulses such that interference signals from each wavelength can be separately detected in the backscattered light;

detect said interference signals in the backscattered light of each optical wavelength, and;

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

34. The distributed optical fibre sensor of claim 33 where the sensor is arranged such that the detector detects 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.

13. 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 pulse lengths to each other;

a detector arranged to detect probe light backscattered in said sensing fibre, including separately detecting light of each of said different pulse lengths; and

an analyser arranged to determine said parameter as a function of position along the sensing fibre from said detected backscattered probe light of one or more of said different pulse lengths.

14. The distributed optical fibre sensor of claim 13 wherein the analyzer is arranged to determine said parameter as a function of position along the sensing fibre from said detected backscattered probe light of all of said pulse lengths.

15. The distributed optical fibre sensor of claim 13 wherein data derived from the detected backscatter of pulses exhibits response characteristics to detectable changes in the sensing fibre, and the sensor is arranged to derive one or more properties of the response characteristics for pulses of at least one of the different lengths from results of a comparison between data derived from the detected backscatter of probe light pulses of different pulse lengths.

16. The distributed optical fibre sensor of claim 15 wherein the one or more properties comprise a measure of linearity or non-linearity of the response characteristics.

17. The distributed optical fibre sensor of claim 15 wherein the one or more properties are functions of position along the sensing fibre.

18. The distributed optical fibre sensor of claim 15 wherein the analyser is arranged to determine said parameter using data derived from the detected backscatter of probe light pulses, by weighting or selecting the use of the data from different pulse lengths according to said one or more properties of the response characteristics.

19. The distributed optical fibre sensor of claim 15 wherein the sensor is arranged to control the lengths of one or more launched probe light pulses according to said one or more properties of the response characteristics.

20. The distributed optical fibre sensor of claim 19 wherein the analyser is arranged to determine said physical parameter using detected backscattered probe light from probe light pulses of said controlled length.

21. The distributed optical fibre sensor of claim 13 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.

22. The distributed optical fibre sensor of claim 21 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.

23. The distributed optical fibre sensor of claim 13 wherein each probe light pulse of different length in a group also has a different wavelength to the other pulses in the group.

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

52. The distributed optical fibre sensor of claim 13 wherein the parameter is a measure of vibration.

24. 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 and being launched such that backscattered light from all the pulses of each group coexists within the sensing fibre;

a detector arranged to detect probe light backscattered in said sensing fibre, including separately and simultaneously detecting light of each of said different wavelengths; and

an analyser arranged to determine said parameter as a function of position along the sensing fibre from said detected backscattered probe light.

25. The distributed optical fibre sensor of claim 24 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.

26. The distributed optical fibre sensor of claim 24 wherein the probe light source is arranged to interleave launching of the probe light pulses of different wavelengths, and the analyser is arranged to construct, for a plurality of positions along the sensing fibre, time series of said parameter by interleaving data derived from the detected backscatter of probe light for each of said different wavelengths.

27. The distributed optical fibre sensor of claim 26 wherein the sensor is an acoustic sensor arranged to detect acoustic vibration as a function of position along the sensing fibre from the constructed time series, the said interleaving providing an enhancement of the acoustic range of the sensor.

51. The distributed optical fibre sensor of claim 24 wherein all the probe light pulses of each group coexist within the sensor fibre.

53. The distributed optical fibre sensor of claim 24 wherein the parameter is a measure of vibration.

35. 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:

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 light of each of said different wavelengths; and

determining said parameter as a function of position along the sensing fibre from said detected backscattered probe light of one or more of said wavelengths.

36. The method of claim 35 wherein the step of launching comprises launching the probe light pulses such that backscattered light from all the pulses of each group coexists within the sensing fibre, and the step of detecting comprises separately and simultaneously detecting light of each of said different wavelengths.

37. The method of claim 35, further comprising automatically adjusting one or more of said plurality of different wavelengths to control the relative phase bias between the interferometric backscatter of said different wavelengths.

38. The method of claim 37 further comprising combining vectorially data derived from the detected backscatter of at least two of said different wavelengths, and determining said parameter from said vectorially combined data.

44. The method of claim 35 further comprising interleaving launching of the probe light pulses of different wavelengths, and constructing, for a plurality of positions along the sensing fibre, time series of said physical parameter by interleaving data derived from the detected backscatter of probe light for each of said different wavelengths.

45. A method of enhancing the acoustic range of a distributed optical fibre sensor arranged to detect acoustic vibration as a function of position along a sensing fibre, comprising the steps of claim 44.

46. The method of claim 35 wherein the parameter is indicative of an environmental influence to which the sensor fibre is responsive.

47. The method of claim 46 wherein the parameter is determined from its effect on the backscattering of said probe light giving rise to changes in interference signals detected in the backscattered probe light.

39. 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:

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 pulse lengths to each other;

detecting probe light backscattered in said sensing fibre, including separately detecting light of each of said different pulse lengths; and

determining said parameter as a function of position along the sensing fibre from said detected backscattered probe light of one or more of said pulse lengths.

40. The method of claim 39 further comprising launching at least two probe light pulses of a group with different pulse lengths to each other.

41. The method of claim 40 wherein data derived from the detected backscatter of pulses exhibits response characteristics to detectable changes in the sensing fibre, the method comprising deriving one or more properties of the response characteristics for pulses of at least one of the different lengths from results of a comparison between data derived from the detected backscatter of probe light pulses of different pulse lengths.

42. The method of claim 41 further comprising determining said physical parameter using data derived from the detected backscatter of probe light pulses, by weighting or selecting the use of the data from different pulse lengths according to said one or more properties of the response characteristics.

43. The method of claim 41 further comprising controlling the lengths of one or more of said launched probe light pulses according to said one or more properties of the response characteristics.

48. A method of operating a distributed optical fibre sensor comprising a sensing fibre, by interrogating the sensing fibre with more than one optical wavelength, with the reflectometric parameters adjusted differently for each wavelength.

49. The method of claim 48 wherein the adjusted reflectometric parameters comprise one or more of optical pulse length and wavelength or coherence for adjustment of interferometric signal quality.