Fluid diffusion resistant glass-encased fiber optic sensor

• US 6,626,043 B1
• Filed: 01/31/2000
• Issued: 09/30/2003
• Est. Priority Date: 01/31/2000
• Status: Expired due to Term

• Current Assignee: Weatherford Technology Holdings, LLC (Weatherford International PLC)
• Original Assignee: Weatherford/Lamb Incorporated (Weatherford International PLC)
• Inventors: Kersey, Alan D., Fernald, Mark R., Bailey, Timothy J., Putnam, Martin A., MacDougall, Trevor W.
• Primary Examiner(s): PATEL, HARSHAD R
• Application Number:
  US09/494,417
• Time in Patent Office: 1,338 Days
• Field of Search: 737/05, 737/44, 737/08, 250/227.2, 250/227.14, 250/227.19, 250/227.27, 250/227.23, 385/101, 385/107, 385/109
• US Class Current: 73/705
• 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 9/0077 for measuring reflected light

Abstract

A fluid diffusion resistant tube-encased fiber grating pressure sensor includes an optical fiber 10 having a Bragg grating 12 impressed therein which is encased within a sensing element, such as a glass capillary shell 20. A fluid blocking coating 30 is disposed on the outside surface of the capillary shell to prevent the diffusion of fluids, such as water molecules from diffusing into the shell. The fluid diffusion resistant fiber optic sensor reduces errors caused by the diffusion of water into the shell when the sensor is exposed to harsh conditions.

Claims

1. A pressure sensor for detecting an external pressure, comprising:

an optical fiber comprising a cladding and a core, wherein the core includes an optical pressure sensor,

a unitary quartz shell encasing the optical fiber and for transmitting the external pressure to the optical pressure sensor; and

a non-polymeric coating formed on at least an external surface of the shell to prevent moisture ingress from affecting the pressure sensor.

2. The pressure sensor of claim 1, wherein the shell is coupled to at least a portion of the optical fiber.

3. The pressure sensor of claim 1, wherein the shell comprises a tube.

4. The pressure sensor of claim 1, wherein the coating comprises at least one layer.

5. The pressure sensor of claim 1, wherein the coating is selected from the group consisting of gold, chrome, silver, carbon or silicon nitride.

6. The pressure sensor of claim 1, wherein the coating is capable of preventing the diffusion of water molecules into the shell.

7. The pressure sensor of claim 1, wherein said coating comprises:

a first layer comprising chrome formed on the external surface of the shell; and

a second layer comprising gold formed on the first layer.

8. The pressure sensor of claim 7, wherein the first layer has a thickness of about 250 Å

and wherein the second layer has a thickness of about 20,000 Å

.

9. The pressure sensor of claim 1, wherein the optical pressure sensor is a Fiber Bragg Grating.

10. The pressure sensor of claim 1, wherein the optical fiber further comprises an optical temperature sensor.

11. The pressure sensor of claim 10, wherein the optical temperature sensor and the optical pressure sensor are connected along the optical fiber in series.

12. The pressure sensor of claim 1, further including a capillary tube positioned between the shell and the optical fiber.

13. The pressure sensor of claim 12, wherein the capillary tube contains a narrowed portion, and wherein the optical pressure sensor is located in the narrowed portion.

14. The pressure sensor of claim 1, wherein the shell is comprised of a glass.

15. The pressure sensor of claim 1, wherein the shell has an outside diameter of 0.3 mm.

16. The pressure sensor of claim 15, wherein the shell and the optical fiber are contiguous and are made of the same material.

17. The pressure sensor of claim 1, wherein the shell is capable of being strained due a change in the external pressure, such strain causing a change in an optical characteristic of the optical pressure sensor indicative of the external pressure.

18. The pressure sensor of claim 17, further comprising a temperature sensor in the optical cable, wherein the temperature sensor is positioned so that it is not substantially affected by the change in the external pressure.

19. The pressure sensor of claim 1, wherein the shell is fused to the optical fiber.

20. A method for forming a pressure sensor for detecting an external pressure, comprising:

providing an optical fiber with a core and a cladding, wherein the core includes an optical pressure sensor;

encasing the optical fiber in a unitary quartz shell, wherein the shell is capable of transmitting the external pressure to the optical pressure sensor; and

forming a non-polymeric coating on at least an external surface of the shell to prevent moisture ingress from affecting the pressure sensor.

21. The method of claim 20, further comprising coupling the shell to at least a portion of the optical fiber prior to the coating step.

22. The method of claim 20, wherein the shell comprises a tube.

23. The method of claim 20, wherein the coating comprises at least one layer.

24. The method of claim 20, wherein the coating is selected from the group consisting of gold, chrome, silver, carbon or silicon nitride.

25. The method of claim 20, wherein the coating is capable of preventing diffusion of water molecules into the shell.

26. The method of claim 20, wherein forming the coating comprises:

forming a first layer comprising chrome on the external surface of the shell; and

forming a second layer comprising gold on the first layer.

27. The method of claim 26, wherein the first layer is formed to a thickness of about 250 Å

and wherein the second layer is formed to a thickness of about 20,000 Å

.

28. The method of claim 20, wherein the optical pressure sensor is a Fiber Bragg Grating.

29. The method of claim 20, wherein the optical fiber further comprises an optical temperature sensor.

30. The method of claim 29, wherein the optical temperature sensor and the optical pressure sensor are connected along the optical fiber in series.

31. The method of claim 20, further comprising forming a capillary tube between the shell and the optical fiber.

32. The method of claim 31, wherein the capillary tube contains a narrowed portion, and wherein the optical pressure sensor is located in the narrowed portion.

33. The method of claim 20, wherein the shell is comprised of a glass.

34. The method of claim 20, wherein the shell has an outside diameter of 0.3 mm.

35. The method of claim 34, wherein the shell and the optical fiber are contiguous and are made of the same material.

36. The method of claim 20, wherein the shell is capable of being strained due a change in the external pressure, such strain causing a change in an optical characteristic of the optical pressure sensor indicative of the external pressure.

37. The method of claim 20, wherein forming the coating comprises a sputtering process.

38. The method of claim 20, further comprising preparing said external surface prior to forming the coating.

39. The method of claim 38, wherein said preparing comprises degreasing the external surface, or etching the external surface, or both.

40. The method of claim 39, wherein etching comprises an ion etching process.

41. The method of claim 20, wherein encasing the optical fiber in a shell comprises fusing the shell to the optical fiber.