COMPACT FIBER OPTIC SENSORS AND METHOD OF MAKING SAME

• US 20100061678A1
• Filed: 09/08/2009
• Published: 03/11/2010
• Est. Priority Date: 09/10/2008
• Status: Active Grant

• Current Assignee: Kyton, LLC
• Original Assignee: Lake Shore Cryotronics, Inc.
• Inventors: Maklad, Mokhtar M., Swinehart, Philip R.
• Granted Patent: US 9,248,615 B2
• Time in Patent Office: Days
• US Class Current: 385/12
• CPC Class Codes: B29D 11/00663 Production of light guides
• CPC Class Codes: G01K 11/3206 at discrete locations in the fibre, e.g. using Bragg scattering
• CPC Class Codes: G02B 6/0218 using mounting means, e.g. by using a combination of materials having different thermal expansion coefficients
• CPC Class Codes: G02B 6/02209 Mounting means, e.g. adhesives, casings G02B6/02171 and G02B6/02195 take precedence

Abstract

A compact, optically double-ended sensor probes with at least one 180° bend provided in the optical fiber in close proximity to a fiber Bragg grating temperature sensor suspends the optical fiber within a casing in such a way that the expansion and contract of the probe casing will not materially influence the temperature reading of the fiber Bragg grating by adding time varying or temperature varying stress components.

Claims

1. A compact optical fiber sensor comprising:

an optical fiber having a numerical aperture of at least 0.15, said optical fiber including a bend on the order of 180 degrees with a radius of curvature not in excess of 10 mm;

a fiber Bragg grating defined on or in said optical fiber in proximity to or within said bend; and

a casing that at least partially encases said fiber including said fiber Bragg grating and said bend to isolate the fiber and fiber Bragg grating from expansion and contraction.

2. The sensor of claim 1 wherein mechanical stress placed upon the casing has substantially no effect on temperature calibration of the fiber Bragg grating.

3. The sensor of claim 1 wherein said radius of curvature of said bend is in the range of from 0.10 mm to 5 mm.

4. The sensor of claim 1 wherein said optical fiber includes first and second portions that can emerge from the package at any angle to each other by the continuation of the bend angle to greater than said substantially 180 degrees.

5. The sensor of claim 1 wherein the fibers could emerge from the package parallel from the same side or end, parallel at the opposite side or end, or at 90 degree to each other.

6. The sensor of claim 1 wherein said optical fiber includes first and second fiber portions that emerge from said casing substantially orthogonally to one another.

7. The sensor of claim 1 wherein said optical fiber includes first and second fiber portions that emerge from said casing substantially parallel to each other.

8. The sensor of claim 1 wherein said casing contains an atmosphere.

9. The sensor of claim 1 wherein said casing is environmentally sealed.

10. The sensor of claim 9 wherein said environmental sealing comprises an adhesive.

11. The sensor of claim 10 wherein said adhesive is comprises epoxy.

12. The sensor of claim 1 wherein said casing is hermetically sealed.

13. The optical fiber temperature sensor of claim 12 wherein the hermetic sealing is chosen from one of the group consisting of a weld, a metal alloy solder or sealing glass composition

14. The optical fiber temperature sensor of claim 12 wherein the optical fiber in an area of the hermetic sealing is provided with at least one of or a combination of a metal coating, a solderable metal coating, an organic buffer coating or no coating.

15. The optical fiber temperature sensor of claim 12 wherein the hermetic sealing comprises at least one rare earth element metal alloy solder.

16. The optical fiber temperature sensor of claim 1 wherein the fiber Bragg grating is contained within a 360°

bend of said fiber.

17. The optical fiber temperature sensor of claim 16 wherein the 360°

bend is substantially circular and the diameter of said circle of fiber is fixed by at least one support at the point of closure of said circle of the fiber and which further forces the input and output fibers to emerge substantially tangentially to and near the plane of said circle.

18. The optical fiber temperature sensor of claim 1 wherein at least the portion of the fiber defining the fiber Bragg grating has no coating or protection other than the casing.

19. The optical fiber temperature sensor of claim 1 further including at least one support protecting the fiber Bragg grating, the support having at least one projection running substantially parallel to the fiber Bragg grating and weighing between 10 ng and 10 g.

20. The optical fiber temperature sensor of claim 19 wherein said support comprises a tube unattached to the fiber that encompasses the fiber Bragg grating.

21. The optical fiber temperature sensor of claim 20 wherein said tube is attached to the fiber or other portion of the support on only one end thereof, and the fiber is free to expand and contract independently of said tube.

22. The optical fiber temperature sensor of claim 20 wherein the tube comprises one or more of a metal, metal alloy, glass, ceramic, composite and polymer.

23. The optical fiber temperature sensor of claim 1 wherein the casing contains one or more of helium gas and neon gas that enhances thermal conduction between the casing and the fiber Bragg grating.

24. The optical fiber temperature sensor of claim 1 wherein the optical fiber comprises holey fiber, nanostructured or photonic crystal fiber.

25. The sensor of claim 1 wherein the at least one fiber Bragg grating is disposed on a straight section of said fiber within a predetermined distance from said bend.

26. The optical fiber temperature sensor of claim 1 wherein the at least one fiber Bragg grating is contained in a straight section of fiber within the distance of from 0.01 mm to 100 mm from one end of the bend.

27. The optical fiber temperature sensor of claim 1 wherein the fiber Bragg grating is at least partially contained within the bend.

28. The optical fiber temperature sensor of claim 27 wherein the fiber Bragg grating is fabricated in un-stripped fiber.

29. The optical fiber temperature sensor of claim 1 wherein the bend is formed by at least one method chosen from the group of mechanical bending, thermal bending and tapered bending.

30. The optical fiber temperature sensor of claim 29 wherein the bend is first formed and then coated with additional protective materials.

31. The optical fiber temperature sensor of claim 29 wherein the bend is formed by bending the fiber in an inert gas such that the bend is left coated with an adherent coating of carbon, requiring no further recoating.

32. The optical fiber temperature sensor of claim 1 wherein the bend contains at least one length of longitudinally tapered index of refraction, exclusive of the fiber Bragg grating.

33. The optical fiber temperature sensor of claim 1 further comprising at least one rigid band across approximately the diameter of the bend and weighing between 100 ng and 10 g, said band confining and supporting the bend such that the weight of the at least one band is supported entirely by the fiber, free of contact with the casing, and the at least one band moves freely with the fiber within the casing without adding variable stress to the fiber Bragg grating.

34. The optical fiber temperature sensor of claim 1 wherein the casing is made entirely of dielectric materials.

35. An optical fiber comprising:

at least one unbent fiber portion; and

180-degree bend optically coupled to said fiber portion wherein optical intensity losses are reduced by increasing the index of refraction of the fiber core within only the bend by exposing to ultraviolet radiation at least over a portion of the length of the bend.

36. A bend in an optical fiber of claim 35 wherein a portion of the optical fiber within the bend is exposed to ultraviolet radiation in order to increase its numerical aperture, including radiating with any combination of constant and varying intensity over the length of the bend.

37. A method manufacturing an optical fiber having a bend therein, said method comprising:

providing an optical fiber having a core;

bending said optical fiber to provide a substantially 180-degree bend therein; and

increasing the index of refraction of said fiber core within said bend by exposing at least a portion of said bend to ultraviolet radiation.

38. A compact optical fiber sensor comprising:

an optical fiber having a numerical aperture of at least 0.15, said optical fiber forming at least one near 180-degree loop having a radius of curvature in the range of 0.1 mm to 5 mm;

a fiber Bragg grating defined on or in said optical fiber in proximity to or within said loop; and

a casing at least partially encasing said loop,

wherein the fiber is cantilevered so the loop does not touch the casing and the loop is sufficiently light so that the fiber supports the loop against touching the casing.

39. A compact optical fiber sensor comprising:

an optical fiber having a numerical aperture of at least 0.15, said optical fiber including a bend on the order of 180 degrees with a radius of curvature not in excess of 10 mm;

a fiber Bragg grating defined on or in said optical fiber in proximity to or within said bend; and

a casing that at least partially encases said fiber,

wherein the bend is formed by at least one of mechanical bending, thermal bending and tapered bending.