Optical sensor device having creep-resistant optical fiber attachments

• US 20020009252A1
• Filed: 06/01/2001
• Published: 01/24/2002
• Est. Priority Date: 05/06/1998
• Status: Active Grant

• Current Assignee: Weatherford Technology Holdings, LLC (Weatherford International PLC)
• Original Assignee: Cidra Sarl (Nordic Cultural & Educational Foundation)
• Inventors: Maron, Robert J., Fernald, Mark R., Dunphy, James R., Grunbeck, John J., Daigle, Guy A., Engel, Thomas W.
• Granted Patent: US 6,768,825 B2
• Time in Patent Office: Days
• US Class Current: 385/12
• CPC Class Codes: G01L 1/246 using integrated gratings, e.g. Bragg gratings
• CPC Class Codes: G01L 11/025 using a pressure-sensitive optical fibre
• CPC Class Codes: G01L 9/0039 using photoelectric means
• CPC Class Codes: G01L 9/0077 for measuring reflected light
• CPC Class Codes: G02B 6/02052 comprising optical elements other than gratings, e.g. filters comprising gratings G02B6/02057
• CPC Class Codes: G02B 6/2552 reshaping or reforming of light guides for coupling using thermal heating, e.g. tapering, forming of a lens on light guide ends
• CPC Class Codes: G02B 6/3644 the coupling means being through-holes or wall apertures
• CPC Class Codes: G02B 6/3854 Ferrules characterised by materials
• CPC Class Codes: G02B 6/3861 Adhesive bonding adhesives in general C09J

Abstract

A method and device for pressure sensing using an optical fiber having a core, a cladding and a Bragg grating imparted in the core for at least partially reflecting an optical signal at a characteristic wavelength. The cladding has two variation regions located on opposite sides of the Bragg grating to allow attachment mechanisms to be disposed against the optical fiber. The attachment mechanisms are mounted to a pressure sensitive structure so as to allow the characteristic wavelength to change according to pressure in an environment. In particular, the variation region has a diameter different from the cladding diameter, and the attachment mechanism comprises a ferrule including a front portion having a profile substantially corresponding to at least a portion of the diameter of the variation region and a butting mechanism which holds the ferrule against the optical fiber.

Claims

1. An optical pressure sensor responsive to an optical signal which provides an optical sensor signal indicative of pressure in an environment, said pressure sensor comprising:

an optical waveguide having a longitudinal axis, a first mounting location and a second mounting location separated by a separation distance along the longitudinal axis which propagates the optical sensor signal, wherein the waveguide comprises a core and a cladding disposed outside the core, and wherein the cladding has an outside diameter and includes a first and a second variation region each having a modified outside diameter different from the outside diameter, wherein the first and second variation regions are respectively located at the first mounting location and the second mounting location;

a Bragg grating imparted in the waveguide between the first mounting location and the second mounting location which provides the optical sensor signal having a spectral profile centered at a characteristic wavelength along said waveguide;

a first attachment mechanism disposed against at least one portion of the first variation region which prevents relative movement between the first variation region and the first attachment mechanism;

a second attachment mechanism disposed against at least one portion of the second variation region which prevents relative movement between the second variation region and the second attached mechanism; and

a mounting device having a first end which mounts to the first attachment mechanism and a second end which mounts to the second attachment mechanism which defines a separation length between the first and second attachment mechanisms along the longitudinal axis of the waveguide and allowing the separation length to vary according to the pressure of the environment, thereby causing a change in the separation and the characteristic wavelength.

2. The pressure sensor of claim 1, wherein

the first attachment mechanism comprises:

a first ferrule including a front portion having a profile substantially corresponding to the modified outside diameter of the first variation region of the cladding; and

a first butting mechanism butting the first ferrule against the waveguide which presses the front portion of the first ferrule onto at least one portion of the first variation region at the first mounting location which limits relative movement between the first ferrule and the first variation region of the cladding, and

the second attachment mechanism comprises;

a second ferrule including a front portion having a profile substantially corresponding to the modified outside diameter of the second variation region of the cladding; and

a second butting mechanism butting the second ferrule against the waveguide to press the front portion of the second ferrule onto at least one portion of the second variation region at the second mounting location which limits relative movement between the second ferrule and the second variation region of the cladding.

3. The pressure sensor of claim 2, wherein the first butting mechanism provides a pressing force against the front portion of the first ferrule along a first direction substantially parallel to the longitudinal axis, and the second butting mechanism provides a pressing force against the front portion of the second ferrule along a second direction substantially opposite to the first direction.

4. The pressure sensor of claim 1, wherein the mounting device comprises a bellows structure which mounts to the first and second attachment mechanisms at the first and second ends of the mounting device.

5. The pressure sensor of claim 1, further comprising a temperature compensation means responsive to temperature of the environment which provides a temperature compensation optical signal.

6. The pressure sensor of claim 1, wherein the first and second attachment mechanisms have two collars, and each of said collars holds one of the attachment mechanisms against the waveguide.

7. The pressure sensor of claim 1, wherein the first and second variation regions include expanded regions in the cladding such that the modified outside diameter is greater than the outside diameter of the cladding.

8. The pressure sensor of claim 1, wherein the first and second variation regions include recessed regions in the cladding such that the modified outside diameter is smaller than the outside diameter of the cladding.

9. The pressure sensor of claim 2, further having a coating located between the cladding and the first and second ferrules which helps the ferrules to conform with the outside diameter of the respective variation regions to reduce point contact stresses on the waveguide.

10. The pressure sensor of claim 1, wherein the first and second attachment mechanisms overhangs at least one portion of the respective variation regions.

11. The pressure sensor of claim 1, wherein the waveguide further comprises a buffer layer over the cladding which protects the waveguide against the first and second attachment mechanisms and which enhances the attachment of the first and second attachment mechanisms to the waveguide.

12. The pressure sensor of claim 11, wherein the first and second attachment mechanisms are bonded to the buffer layer.

13. The pressure sensor of claim 11, wherein the buffer layer comprises a metal layer.

14. The pressure sensor of claim 13, wherein the metal layer comprises Ni and Au.

15. The pressure sensor of claim 11, wherein the buffer layer comprises a polymer layer.

16. The pressure sensor of claim 2, wherein the first and second ferrules comprise a plurality of pieces substantially surrounding the respective variation regions which attach to the cladding.

17. The pressure sensor of claim 1, wherein the modified outside diameter causes minimal deformation to the core which minimizes optical loss from the core due to the modified outside diameter.

18. The pressure sensor of claim 1, wherein the core of the waveguide is axially continuous near the first and second variation regions.

19. The pressure sensor of claim 1, further comprising a further waveguide segment including a cladding having a second outside diameter substantially equal to the modified outside diameter which splices with the waveguide and provides each of the first and second variation regions.

20. The pressure sensor of claim 1 wherein said change in the separation distance causes a change in tensile strain on the grating.

21. The pressure sensor of claim 1, wherein said change in the separation distance causes a change in compressive strain on the grating.

22. The pressure sensor of claim 1, wherein the modified outside diameter is provided by fusing a tube to the cladding.

23. The pressure sensor of claim 1, wherein the modified outside diameter is provided by heating and stretching the waveguide which changes the outside diameter of the cladding.

24. The pressure sensor of claim 1, wherein the modified outside diameter is provided by etching the outside diameter of the cladding.

25. A method of sensing pressure in an environment with an optical sensor signal, comprising:

providing an optical waveguide having a longitudinal axis which propagates the optical signal and provides a sensor signal indicative of the pressure in the environment in response to the optical signal, wherein the waveguide has a first mounting location and a second mounting location separated by a separation distance along the longitudinal axis, and wherein the waveguide comprises a core and a cladding disposed outside the core, wherein the cladding has an outside diameter and includes a first and a second variation region each having a modified outside diameter different from the outside diameter, and wherein the first and second variation regions are respectively located at the first mounting location and the second mounting location;

providing a grating imparted in the core of the waveguide between the first mounting location and the second mounting location which provides the optical sensor signal having a spectral profile centered at a characteristic wavelength along said waveguide;

providing a first attachment mechanism disposed against at least one portion of the first variation region, which prevents relative movement between the first variation region and the first attachment mechanism;

providing a second attachment mechanism disposed against at least one portion of the second variation region, which prevents relative movement between the second variation region and the second attached mechanism; and

providing a mounting device having a first end, which mounts to the first attachment mechanism and a second end, which mounts to the second attachment mechanism, which defines a separation length between the first and second attachment mechanisms along the longitudinal axis of the waveguide and allowing the separation length to vary according to the pressure of the environment, thereby causing a change in the separation distance between the first and second variation regions and the spacing of the grating.

26. The method of claim 25, wherein

the first attachment mechanism comprises:

a first ferrule including a front portion having a profile substantially corresponding to the modified outside diameter of the first variation region of the cladding; and

a first butting mechanism butting the first ferrule against the waveguide for pressing the front portion of the first ferrule onto at least one portion of the first variation region at the first mounting location which limits relative movement between the first ferrule and the first variation region of the cladding, and

the second attachment mechanism comprises;

a second ferrule including a front portion having a profile substantially corresponding to the modified outside diameter of the second variation region of the cladding; and

a second butting mechanism butting the second ferrule against the waveguide which presses the front portion of the second ferrule onto at least one portion of the second variation region at the second mounting location which limits relative movement between the second ferrule and the second variation region of the cladding.

27. The method of claim 26, wherein the first butting mechanism provides a pressing force against the front portion of the first ferrule along a first direction substantially parallel to the longitudinal axis, and the second butting mechanism provides a pressing force against the front portion of the second ferrule along a second direction substantially opposite to the first direction.

28. The method of claim 25, wherein the mounting device comprises a multi-element bellows structure which mounts the first and second attachment mechanisms at the first and second ends of the mounting device.

29. The method of claim 25, further comprising the step of providing a temperature compensation means responsive to temperature of the environment which provides a temperature compensation optical signal.

30. The method of claim 25, further comprising the step of providing collars to hold the first and second attachment mechanisms against the waveguide.

31. The method of claim 25, wherein the first and second variation regions include expanded regions in the cladding such that the modified outside diameter is greater than the outside diameter of the cladding.

32. The method of claim 25, wherein the first and second variation regions include recessed regions in the cladding such that the modified outside diameter is smaller than the outside diameter of the cladding.

33. The method of claim 26, further comprising the step of providing a coating between the cladding and the first and second ferrules which helps the ferrules to conform with the outside diameter of the respective variation regions and reduces point contact stresses on the waveguide.

34. The method of claim 25, further comprising the step of providing a buffer layer over the cladding to protect the waveguide against the first and second attachment mechanisms and for enhancing attachment of the first and second attachment mechanisms to the waveguide.

35. The method of claim 34, further comprising the step of bonding the buffer layer to the first and second attachment mechanisms.

36. The method of claim 25, wherein the first and second ferrules comprise a plurality of pieces substantially surrounding the respective variation regions to attach to the cladding at each mounting location.

37. The method of claim 25, further comprising the step of splicing a further waveguide segment including a cladding having a second outside diameter substantially equal to the modified outside diameter with the waveguide to form each of the first and second variation regions.

38. The method of claim 25, further comprising the step of fusing a tube to the cladding to form the modified outside diameter of the first and second variation regions.

39. The method of claim 25, further comprising the step of heating and stretching the waveguide to form the modified outside diameter of the first and second variation regions.

40. The method of claim 25, further comprising the step of etching the outside diameter of the cladding to form the modified outside diameter of the first and second variation regions.

41. A distributed pressure sensing system for sensing pressure at a plurality of locations in an environment, comprising:

a light source which provides an optical sensor signal;

an optical waveguide having a longitudinal axis which propagates the optical sensor signal, wherein the waveguide includes a core and a cladding disposed outside the core and the core has an outside diameter and includes a plurality of sensing sections, each having a grating imparted therein, and each grating has a plurality of perturbations defined by a spacing along the longitudinal axis, which provides the optical sensor signal; and

wherein the cladding in each sensing section has a first and a second variation region each having a modified outside diameter different from the outside diameter;

a plurality of pressure sensitive structures, each mounted at one sensing section, each pressure structure comprising;

a first attachment mechanism disposed against at least one portion of the first variation region to prevent relative movement between the first variation region and the first attachment mechanism;

a second attachment mechanism disposed against at least one portion of the second variation region to prevent relative movement between the second variation region and the second attached mechanism; and

a mounting device having a first end which mounts to the first attachment mechanism and a second end which mounts to the second attachment mechanism to define a separation length between the first and second attachment mechanisms along the longitudinal axis of the waveguide and allowing the separation length to vary according to the pressure of the environment, thereby causing a change in the distance between the first and second variation regions and the spacing of the grating.

42. The distributed pressure sensing system of claim 41, wherein

the first attachment mechanism comprises:

a first ferrule including a front portion having a profile substantially corresponding to the modified outside diameter of the first variation region of the cladding; and

a first butting mechanism butting the first ferrule against the waveguide to press the front portion of the first ferrule onto at least one portion of the first variation region at the first mounting location to limit relative movement between the first ferrule and the first variation region of the cladding, and

the second attachment mechanism comprises;

a second ferrule including a front portion having a profile substantially corresponding to the modified outside diameter of the second variation region of the cladding; and

a second butting mechanism butting the second ferrule against the waveguide to press the front portion of the second ferrule onto at least one portion of the second variation region at the second mounting location which limits relative movement between the second ferrule and the second variation region of the cladding.

43. The distributed pressure sensing system of claim 41, wherein the mounting device comprises a multi-element bellows structure to mount the first and second attachment mechanisms at the first and second ends of the mounting device.

44. The distributed pressure sensing system of claim 41, wherein each of the pressure sensitive structures further comprises a temperature compensation means responsive to temperature of the environment for providing a temperature compensation optical signal.

45. The distributed pressure sensing system of claim 42, wherein the first and second variation regions include expanded regions in the cladding such that the modified outside diameter is greater than the outside diameter of the cladding.

46. The distributed pressure sensing system of claim 42, wherein the first and second variation regions include recessed regions in the cladding such that the modified outside diameter is smaller than the outside diameter of the cladding.

47. The distributed pressure sensing system of claim 42, wherein the first and second ferrules each comprises a plurality of pieces substantially surrounding the respective variation region for attaching to the cladding.

48. The distributed pressure sensing system of claim 41, further comprising spectral filters to separate the sensor signal from one grating to the sensor signal from another grating.