Distributed Optical Fibre Sensing

• US 20130301037A1
• Filed: 07/11/2013
• Published: 11/14/2013
• Est. Priority Date: 07/23/2009
• Status: Active Grant

• Current Assignee: Viavi Solutions, Inc. (Lumentum Holdings Inc.)
• Original Assignee: Fotech Solutions Limited
• Inventors: Handerek, Vincent Andrei
• Granted Patent: US 8,760,639 B2
• Time in Patent Office: Days
• US Class Current: 356/73.1
• CPC Class Codes: G01D 5/353 influencing the transmission properties of an optical fibre
• CPC Class Codes: G01D 5/35361 using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering
• CPC Class Codes: G01D 5/35364 using inelastic backscattering to detect the measured quantity, e.g. using Brillouin or Raman backscattering
• CPC Class Codes: G01J 3/44 Raman spectrometry; Scattering spectrometry ; Fluorescence spectrometry
• CPC Class Codes: G01V 1/226 Optoseismic systems
• CPC Class Codes: G01V 1/40 specially adapted for well-logging

Abstract

There is disclosed a distributed optical fibre sensing system in which the sensor fibre comprises at least first and second waveguides used for separate sensing operations. The sensor fibre may be, for example, a double clad fibre having a monomade core and a multimode inner cladding.

Claims

1. A distributed optical fibre sensing system comprising:

a sensor fibre comprising first and second waveguides extending together along the fibre, the first waveguide being a single mode waveguide and the second waveguide being a multi mode waveguide; and

an interrogation system coupled to the sensor fibre and arranged to measure one or more physical parameters as a function of position along the sensor fibre by carrying out at least first and second sensing operations to detect properties of probe light backscattered within the first and second waveguides respectively.

2. The system of claim 1 wherein the first and second adjacent waveguides are waveguides of a double clad optical fibre in which the single mode waveguide is a single mode core of the double clad fibre.

3. The system of claim 1 wherein the first sensing operation utilizes Brillouin backscatter or Rayleigh scattering within the first, single mode waveguide to detect properties of probe light backscattered within the first waveguide.

4. The system of claim 3 wherein the first sensing operation utilizes coherent Rayleigh backscatter within the first, single mode waveguide.

5. The system of claim 4 wherein the interrogation system measures vibration using the first sensing operation.

6. The system of claim 1 wherein the second sensing operation utilizes Raman scattering within the second, multimode waveguide to detect properties of probe light backscattered within the second waveguide.

7. The system of claim 1 in which the interrogation system is arranged to carry out the sensing operations each using at least one of Rayleigh scattering, optical time domain reflectometry, coherent or partially coherent optical time domain reflectometry, spontaneous or stimulated Brillouin scattering, and spontaneous or stimulated Raman scattering, to measure said one or more physical parameters as a function of position along the sensor fibre.

8. The system of claim 1 arranged to derive at least one said physical parameter by combining properties of backscattered probe light detected by two or more of the sensing operations.

9. The system of claim 1 wherein the interrogation system is arranged to carry out the first and second sensing operations utilizing light of different wavelengths to thereby avoid interference between the first and second sensing operations arising from leakage between the first and second waveguides.

10. The system of claim 1 wherein the interrogation system is arranged to carry out multiple sensing operations using one of said first and second waveguides, said multiple sensing operations utilizing probe light of different wavelength for each said sensing operation.

11. The system of claim 1 further comprising a pump light source coupled to the second waveguide, and wherein the sensor fibre includes a section remote from the interrogation system configured as an optical amplifier such that probe light in the first waveguide is amplified by the optical amplifier.

12. The system of claim 1 further comprising a pump-signal combiner arranged to optically couple the interrogation system to the first and second waveguides.

13. The system of claim 12 wherein a double-clad fibre section of the sensor fibre is terminated at the pump-signal combiner, and the pump-signal combiner couples the first and second waveguides of the double clad fibre separately to at least first and second interrogation components of the interrogation system.

14. The system of claim 13 wherein said first interrogation unit is coupled by the pump-signal combiner to the first, single mode waveguide of the double clad fibre and is adapted to determine Rayleigh and/or Brillouin backscatter properties of the sensor fibre, and the second interrogation unit is coupled by the pump-signal combiner to the second, multi mode waveguide of the double clad fibre and is adapted to determine Raman backscatter properties of the sensor fibre,

15. A distributed optical fibre sensing system comprising:

a sensor fibre having both single and multimode waveguides extending along at least part of its length;

a pump light source arranged to deliver pump light into the sensor fibre; and

an interrogator system coupled to the sensor fibre to inject probe light into the fibre, and to derive one or more physical parameters as a function of position along the sensor fibre by detecting said probe light following backscatter within the fibre,

the sensor fibre comprising a first section proximal to the interrogator, a second section distal from the interrogator, and an optical amplifier section between the first and second sections,

at least the first section of the sensor fibre comprising double clad optical fibre providing at least a part of said single mode waveguide and at least a part of said multimode waveguide, the interrogator system being coupled to the single mode waveguide to detect probe light which has been backscattered within the single mode waveguide, and the pump light source being coupled to the multi mode waveguide,

the system being arranged such that the optical amplifier section amplifies said probe light using said pump light.

16. The system of claim 15 wherein the optical amplifier comprises an optically active length of double clad fibre.

17. The distributed fibre sensing system of claim 15 wherein the interrogator system is also coupled to the multimode waveguide of the first section of the sensor fibre, to also detect probe light which has been backscattered within the multimode waveguide.

18. The system of claim 17 wherein the interrogator system uses a first sensing technique to detect probe light backscattered within one or more of the single mode waveguide sections of the sensing fibre, and a second sensing technique to detect probe light backscattered within one or more of the multimode waveguide sections of the sensor fibre.

19. The system of claim 15 wherein at least a part of the second section of the sensor fibre comprises a single clad fibre coupled to the single mode core of the first section of the sensor fibre through the single mode core of the optical amplifier section, such that the interrogator system can detect probe light backscattered within the single clad fibre using said probe light injected into said single mode waveguide.

20. The system of claim 15 wherein the interrogator system comprises one or more interrogator units each arranged to carry out a separate sensing operation to determine scattering properties of probe light within the sensor fibre.

21. A distributed fibre sensing system arranged to detect scattering properties along a sensor fibre, the sensor fibre comprising a double clad optical fibre.

22. A method of monitoring an extended environment, comprising:

positioning a sensor optical fibre through the environment, the sensor fibre having first and second co-extending waveguides, the first waveguide being a single mode waveguide of the sensor fibre, the second waveguide being a multimode waveguide of the sensor fibre;

performing separate first and second sensing operations using the first and second waveguides respectively to determine information on the backscattering of probe light within the sensor fibre, as a function of position along the sensor optical fibre; and

determining parameters relating to said extended environment as a function of position along said sensor optical fibre from said determined information.

23. The method of claim 22 further comprising combining backscattering information from said first waveguide with backscattering information from said second waveguide in said step of determining parameters.

24. The method of claim 22 wherein said sensor optical fibre comprises double clad fibre providing said first and second co-extending waveguides.

32. The method of claim 24 wherein the single mode waveguide is a single mode core of the double clad fibre.

33. The method of claim 22 wherein the first sensing operation utilizes Brillouin backscatter or Rayleigh scattering within the first, single mode waveguide to detect properties of probe light backscattered within the first waveguide.

34. The method of claim 33 wherein the first sensing operation utilizes coherent Rayleigh backscatter within the first, single mode waveguide.

35. The method of claim 34 wherein the interrogation system measures vibration using the first sensing operation.

36. The system of claim 22 wherein the second sensing operation utilizes Raman scattering within the second, multimode waveguide to detect properties of probe light backscattered within the second waveguide.

37. The method of claim 22 in which the interrogation system is arranged to carry out the sensing operations each using at least one of Rayleigh scattering, optical time domain reflectometry, coherent or partially coherent optical time domain reflectometry, spontaneous or stimulated Brillouin scattering, and spontaneous or stimulated Raman scattering, to measure said one or more physical parameters as a function of position along the sensor fibre.

38. The method of claim 22 wherein the interrogation system is arranged to carry out the first and second sensing operations utilizing light of different wavelengths to thereby avoid interference between the first and second sensing operations arising from leakage between the first and second waveguides.

39. The method of claim 22 wherein the interrogation system is arranged to carry out multiple sensing operations using one of said first and second waveguides, said multiple sensing operations utilizing probe light of different wavelength for each said sensing operation.

25-31. -31. (canceled)