Fiber-optic sensing system for distributed detection and localization of alarm conditions

• US 20040067003A1
• Filed: 10/02/2002
• Published: 04/08/2004
• Est. Priority Date: 10/02/2002
• Status: Active Grant

• Current Assignee: Cicese-Centro De Investigacion Cietifica Y De Educacion Superior De Ensenada B.C.
• Original Assignee: Cicese-Centro De Investigacion Cietifica Y De Educacion Superior De Ensenada B.C.
• Inventors: Miridonov, Serguei, Jimenez, Francisco Javier Mendieta, Abenchuchan, Enrique Mitrani, Chliaguine, Mikhail, Spirine, Vassili
• Granted Patent: US 6,876,786 B2
• Time in Patent Office: Days
• US Class Current: 385/13
• CPC Class Codes: G01D 5/35303 using a reference fibre, e.g. interferometric devices
• CPC Class Codes: G01M 11/086 Details about the embedment of the optical fiber within the DUT
• CPC Class Codes: G01M 3/047 with photo-electrical detection means, e.g. using optical fibres
• CPC Class Codes: G02B 6/022 using mechanical stress, e.g. tuning by compression or elongation, special geometrical shapes such as "dog-bone" or taper G02B6/02204 takes precedence; optical modulation using photo-elastic effect G02F1/0131
• CPC Class Codes: G02B 6/2932 comprising a directional router, e.g. directional coupler, circulator

Abstract

An optical fiber sensor system comprising of an optical fiber including plurality of sensitive elements, each sensitive element has characteristic spectral band which in normal undisturbed condition lies in a first wavelength range and, under an influence of some specified condition to be detected, shifts to a second wavelength range; first and second wavelength ranges do not overlap. Means for probing an optical transmission or reflection of the fiber operate within second wavelength range to monitor the changes of the transparency or reflectivity of the fiber caused by the shift of characteristic spectral band into the second wavelength range.

The invention provides means for distributed monitoring of equipment or construction structures and detection of specified conditions and can provide alarm signal when the specified conditions become effective.

Claims

34. ) An optical fiber sensor system comprising:

a) an optical fiber placed into an area to be monitored;

b) a plurality of sensitive elements, wherein said optical fiber is optically and mechanically coupled to said plurality of said sensitive elements, said sensitive elements having a characteristic spectral band occupying a first wavelength range in normal condition, said characteristic spectral band of at least one said sensitive element having the capability of at least partially shifting into a second wavelength range, said shifting into a said second wavelength range being triggered by a predefined event, and wherein said second wavelength range of said sensitive elements does not overlap with said first wavelength range of said sensitive elements;

c) means for probing optical transmission or reflection of said optical fiber, said means for probing said optical transmission or said reflection of said fiber being optically coupled with said fiber and operating within said second wavelength range, said means for probing said optical transmission or said reflection of said optical fiber being a light source and a photosensitive apparatus, such that when said optical transmission or reflection of said fiber exceeds a predetermined threshold value, an alarm condition is indicated.

35. ) The optical fiber sensor system according to claim 34, wherein said sensitive elements are bent segments of said fiber and said characteristic band is a loss band.

36. ) The optical fiber sensor system according to claim 34, wherein said sensitive elements are long period gratings imprinted in said fiber and said characteristic band is a loss band.

43. ) The optical fiber sensor system according to claim 34, wherein said photosensitive apparatus is a photodetector.

44. ) The optical fiber sensor system according to claim 34, wherein said characteristic spectral band is a loss band and said light source is coupled at a first end of said optical fiber and said photosensitive apparatus is coupled at a second end of said optical fiber.

45. ) The optical fiber sensor system according to claim 34, wherein said characteristic spectral band is a reflection band and said light source is coupled at a first end of said optical fiber and said photosensitive apparatus

46. ) The optical fiber sensor system according to claim 34, comprising a first bi-directional coupler, said first bi-directional coupler transmitting light in a forward direction from said light source to said optical fiber and from said optical fiber to said photodetector.

47. ) The optical fiber sensor system according to claim 46, further comprising a reflective member at a second end of said fiber.

48. ) The optical fiber.sensor system according to claim 47, wherein said reflective member is a mirror.

49. ) The optical fiber sensor-system according to claim 47, wherein said reflective member is provided by a reflective coating at a second end of said fiber.

50. ) The optical fiber sensor system according to claim 34, wherein said light source is a broadband source.

51. ) The optical fiber sensor system according to claim 50, wherein said light source is a light emitting diode.

52. ) The optical fiber sensor system according to claim 34, wherein said light source is a narrow band source.

53. ) The optical fiber sensor system according to claim 52, wherein said light source is a diode laser.

54. ) The optical fiber sensor system according to claim 34, wherein said means for probing optical transmission or reflection of said optical fiber further comprises means for localization of a specific said element from said plurality of sensitive elements, wherein said characteristic band of said specific said element has shifted at least partially into said second wavelength range.

55. ) The optical fiber sensor system according to claim 54, further comprising an optical time domain reflectometer, wherein said optical time domain reflectometer operating in said second wavelength range localizes said specific said element from said plurality of sensitive elements.

56. ) The optical fiber sensor system according to claim 46, further comprising a second bi-directional coupler for connection of an optional external means for localization of a specific said element from said plurality of sensitive elements, wherein said band of said specific said element has been at least partially shifted into said second wavelenngth range, and wherein said second bi-directional coupler is connected between said optical fiber and said first bidirectional coupler.

57. ) The optical fiber sensor system according to claim 46, further comprising means for modulation of radiation of said light source by an external electrical signal.

58. ) The optical fiber sensor system according to claim 46, further comprising a means for amplification of an output signal from said photodetector.

37. ) The optical fiber sensor system according to claim 1, wherein said sensitive elements are Bragg gratings imprinted in said fiber and said characteritic band is a reflection band.

38. ) The optical fiber sensor system according to claim 37 further comprising elastic member capable of transforming an external influence into a strain of said optical fiber, wherein said optical fiber is placed with a predetermined tension in a close vicinity of said elastic member and said fiber is fixed to said elastic member in points located between adjacent Bragg gratings.

39. ) The optical fiber sensor system according to claim 38, further comprising clamps, wherein said optical fiber is fixed to said elastic member by means of said clamps.

40. ) The optical fiber sensor system according to claim 38, further comprising an adhesive, wherein said optical fiber is fixed to said elastic member by means of said adhesive.

41. ) The optical fiber sensor system according to claim 38, wherein said elastic member is hollow, and said optical fiber is placed inside said hollow.

42. ) The optical fiber sensor system according to claim 41, wherein said elastic member comprises tubing.

59. ) The optical fiber sensor system according to claim 38, wherein said elastic member is made of material having a high thermal expansion coefficient.

60. ) The optical fiber sensor system according to claim 59, wherein said elastic member is made of stainless steel.

61. ) The optical fiber sensor system according to claim 37, further comprising fixing said optical fiber with a predetermined tension to a structure to be monitored in points located between each of two adjacent said elements of said plurality of sensitive elements, wherein said optical fiber sensor system is used to detect excess strain.

62. ) The optical fiber sensor system according to claim 38, further comprising that said elastic member is made of a material having a low thermal expansion coefficient, and said elastic member is fixed to a structure to be monitored at more than one point, wherein said optical fiber sensor system is used as an excess strain detection system.

63. ) The optical fiber sensor system according to claim 38, wherein said elastic member is comprised of a material capable of swelling when in contact with a fluid.

64. ) The optical fiber sensor system according to claim 63, wherein said fluid is being monitored for leakage.

65. ) The optical fiber sensor system according to claim 63, wherein said elastic member is comprised of butyl rubber.

66. ) The optical fiber sensor system according to claim 63, wherein said elastic member is comprised of silicone rubber.