Claims
- 1. A method for determining a pressure and a temperature comprising the steps of:
applying light to a first core of an optical fiber such that the light is guided by the core; creating a long period optical grating in the optical fiber by stressing the fiber such that a plurality of localized changes in an index of refraction in the first core are created, the optical grating causing at least some of the light guided by the first core to be coupled to a mode not guided by a fundamental mode of the first core; determining a wavelength at which is coupled to a mode not guided by the fundamental mode of the first core; calculating a temperature based at least in part on the wavelength; measuring an amount of light coupled to a mode not guided by the first core; and calculating a pressure based on the amount of light coupled to a mode not guided by the fundamental mode of the first core.
- 2. The method of claim 1, further comprising the steps of:
disposing a portion of the optical fiber in a tube; and bonding the tube to the fiber at a plurality of locations such that the long period optical grating is formed when a force is exerted on the tube.
- 3. The method of claim 2, wherein the tube is bonded to the fiber in a plurality of circumferential bonds such that the first core is compressed in areas corresponding to the circumferential bonds when the force is exerted on the tube.
- 4. The method of claim 2, wherein the tube is bonded to the fiber in a plurality of locations on a top of the fiber and a plurality of locations on a bottom of the fiber such that a plurality of microbends are formed in the fiber when the force is exerted on the tube.
- 5. The method of claim 2, wherein the tube is glass.
- 6. The method of claim 2, wherein the tube is metal.
- 7. The method of claim 1, further comprising the steps of:
disposing a portion of the optical fiber in a tube, an inside surface of the tube having a plurality of ridges formed thereon, the ridges being spaced apart; and exposing the tube to a force such that the ridges create the long period grating.
- 8. The method of claim 1, further comprising the steps of:
placing at least one plate adjacent to the fiber, the plate having a plurality of spaced apart ridges formed thereon; and exposing the plate to a force such that the ridges create the long period grating.
- 9. The method of claim 8, wherein the ridges compress areas of the first core corresponding to the ridges.
- 10. The method of claim 8, wherein the ridges cause a plurality of microbends in the optical fiber.
- 11. The method of claim 1, wherein the mode not guided by the fundamental mode of the first core is a cladding mode.
- 12. The method of claim 1, wherein at least a portion of the first core is surrounded by a concentric second core, and wherein the mode not guided by the fundamental mode of the first core is a mode guided by the concentric second core.
- 13. The method of claim 1, further comprising the step of providing a spaced apart second core in close proximity to the first core, wherein the mode not guided by the fundamental mode of the first core is a mode guided by the spaced apart second core.
- 14. The method of claim 13, wherein the second core is surrounded by a second cladding, the second cladding being separate from a first cladding surrounding the first core.
- 15. The method of claim 13, wherein the second core and the first core are surrounded by a single cladding.
- 16. The method of claim 1, wherein the amount of light is determined by comparing an amplitude of light at a wavelength at which is coupled to a mode not guided by the fundamental mode of the first core to an amplitude of light at a wavelength at which no coupling occurs.
- 17. The method of claim 12, wherein the amount is measured by measuring light coupled to the concentric second core.
- 18. The method of claim 13, wherein the amount is measured by measuring light coupled to the spaced apart second core.
- 19. A optical fiber sensor comprising:
an optical fiber, the optical fiber having a first core and a cladding; a light source connected to an end of the optical fiber; a tube surrounding a portion of the optical fiber, the tube having an interior surface and an exterior surface, the interior surface of the tube being bonded to the optical fiber at a plurality of spaced-apart bonding locations, wherein a long period grating is produced in a portion of the first core surrounded by the tube when a pressure is applied to the exterior surface of the tube; and a processor connected to the optical fiber, the processor being configured to determine an amount of attenuation of the light source by the long period grating.
- 20. The optical fiber sensor of claim 19, wherein an entire circumference of the optical fiber is bonded to the tube at each bonding location.
- 21. The optical fiber sensor of claim 20, wherein the circumference is perpendicular to the core such that opposing balanced forces are exerted on a core of the fiber at each bonding location, the balanced forces creating changes in the refractive index of the core at each bonding location.
- 22. The optical fiber sensor of claim 19, wherein the bonding locations are periodically spaced.
- 23. The optical fiber sensor of claim 19, wherein the bonding locations are chirped.
- 24. The optical fiber sensor of claim 19, wherein light guided by the first core is coupled to a non-guided mode in the cladding by the long period grating.
- 25. The optical fiber sensor of claim 19, wherein the optical fiber further comprises a second core and wherein light in the first core is coupled to a guided mode in the second core.
- 26. The optical fiber sensor of claim 25, wherein the first and second cores are concentric.
- 27. An optical fiber sensor comprising:
a first core; and a cladding surrounding the first core, the cladding having an exterior surface, the exterior surface having a portion including a plurality of spaced-apart circumferential grooves formed therein.
- 28. The optical fiber sensor of claim 27, wherein each of the grooves has a direction perpendicular to the core, whereby a change in an index of refraction of the first core is created in areas of the core corresponding to areas of the cladding between the grooves when the portion is exposed to a pressurized fluid.
- 29. The optical fiber sensor of claim 27, wherein each of the grooves has a direction that forms an acute angle with a direction of the first core, whereby a series of microbends is formed in the first core when the portion is exposed to a pressurized fluid.
- 30. The optical fiber sensor of claim 29, wherein the groove has a first wall, a second wall and a bottom surface and the first wall is perpendicular to the bottom surface.
- 31. The optical fiber sensor of claim 27, further comprising a second core, the second core being positioned such that light guided by the first core is coupled to the second core when the portion is exposed to the pressurized fluid.
- 32. The optical fiber sensor of claim 31, wherein the second core is surrounded by the cladding.
- 33. The optical fiber sensor of claim 31, further comprising a second cladding surrounding the second core.
- 34. An optical fiber sensor comprising:
an optical fiber, the fiber having at least a first core and a first cladding, the first cladding; a first plate, the first plate having a first plurality of ridges formed thereon and pressed against the optical fiber; and a second plate, the second plate having a second plurality of ridges formed thereon and pressed against the optical fiber; wherein the first plurality of ridges and the second plurality of ridges are offset such that a series of microbends in the core is created when the first plate and the second plate are exerting forces on the fiber, the microbends causing light guided by the first core to be coupled to a second mode not guided by the first core.
- 35. The sensor of claim 34, wherein the second mode is a cladding mode.
- 36. The sensor of claim 34, wherein the optical fiber further comprises a second core and the second mode is a mode guided by the second core.
- 37. The sensor of claim 36, wherein the second core surrounds the first core.
- 38. The sensor of claim 36, wherein the second core is spaced apart from the first core.
- 39. The sensor of claim 38, wherein the second core is surrounded by a second cladding.
- 40. The sensor of claim 38, wherein the second core is surrounded by the first cladding.
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional Application Serial No. 60/378,351, filed May 8, 2002, the contents of which are hereby incorporated by reference herein.
Provisional Applications (1)
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Number |
Date |
Country |
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60378351 |
May 2002 |
US |