Distributed fiber optic sensor with location capability

• US 20070096007A1
• Filed: 08/29/2005
• Published: 05/03/2007
• Est. Priority Date: 08/29/2005
• Status: Active Grant

• Current Assignee: Fiber Sensys, Inc. (OPTEX GROUP Co., Ltd.)
• Original Assignee: CompuDyne Corp. (Integris (United States))
• Inventors: Singh, Shailesh, Anderson, Duwayne
• Granted Patent: US 7,514,670 B2
• Time in Patent Office: Days
• US Class Current: 250/200
• CPC Class Codes: G01D 5/35303 using a reference fibre, e.g. interferometric devices
• CPC Class Codes: G01D 5/35322 using interferometer with one loop with several directions of circulation of the light, e.g. Sagnac interferometer
• CPC Class Codes: G01D 5/35383 using multiple sensor devices using multiplexing techniques
• CPC Class Codes: G08B 13/186 using light guides, e.g. optical fibres
• CPC Class Codes: G08B 13/2497 using transmission lines, e.g. cable

Abstract

A spatially distributed sensor system has an optical transmitter, an optical conduit optically coupled to the optical transmitter at an input position, and a sensing element optically coupled to the optical conduit at a position along the optical conduit spatially separated from the input position. The sensing element is structured to split off a fraction of light from the optical transmitter upon being coupled into the optical conduit and to return light to the optical conduit. The spatially distributed sensor system also has an optical receiver coupled to the optical conduit to receive at least a portion of light from the optical conduit that includes light returned to the optical conduit from the sensing element. An analysis of light received by the optical receiver provides information to determine a position of the sensing element.

Claims

1. A spatially distributed sensor system, comprising:

an optical transmitter;

an optical conduit optically coupled to said optical transmitter at an input position;

a sensing element optically coupled to said optical conduit at a position along said optical conduit spatially separated from said input position, wherein said sensing element is structured to split off a fraction of light from said optical transmitter upon being coupled into said optical conduit and to return light to said optical conduit in an amount responsive to an effect being sensed; and

an optical receiver coupled to said optical conduit to receive at least a portion of light from said optical conduit that includes light returned to said optical conduit from said sensing element,

wherein an analysis of light received by said optical receiver provides information to determine a position of said sensing element.

2. A spatially distributed sensor system according to claim 1, wherein said optical transmitter comprises a laser, said laser being modulated to produce a time varying source of light.

3. A spatially distributed sensor system according to claim 2, wherein said laser is a pulsed laser.

4. A spatially distributed sensor system according to claim 2, wherein said laser is directly modulated to produce a pulsed signal,

wherein a time between transmission and reception of a pulse of light from said pulsed signal provides information to determine said position of coupling of said sensing element to said optical conduit.

5. A spatially distributed sensor system according to claim 2,

wherein said optical transmitter further comprises an external modulator,

wherein said laser is externally modulated to produce a pulsed signal, and

wherein a time between transmission and reception of a pulse of light from said pulsed signal provides information to determine said position of coupling of said sensing element to said optical conduit.

6. A spatially distributed sensor system according to claim 1, wherein said optical transmitter comprises a laser and a depolarizer to provide depolarized light to input into said optical conduit.

7. A spatially distributed sensor system according to claim 1, wherein said optical conduit is an optical fiber, and wherein said sensing element comprises an optical fiber coupled to said optical conduit by a tap coupler.

8. A spatially distributed sensor system according to claim 7, wherein said optical fiber of said sensing element undergoes a change in an optical property in the presense of a fluid to determine at least the presense of a threshold amount of a substance of interest.

9. A spatially distributed sensor system according to claim 7, wherein said sensing element further comprises a reflecting element attached to or disposed within said optical fiber of said sensing element and a polarizer attached to or disposed within said optical fiber of said sensing element between said tap coupler and said reflecting element.

10. A spatially distributed sensor system according to claim 9, wherein said optical fiber of said sensing element is a single-mode optical fiber at a wavelength of operation of the spatially distributed sensor system.

11. A spatially distributed sensor system according to claim 7, wherein said sensing element comprises a second optical fiber having a light coupling end arranged with a space reserved from an output end of the first-mentioned optical fiber of said sensing element,

wherein said second optical fiber has a reflecting element at least attached thereto or disposed therein, and

wherein an amount of optical coupling between the first-mentioned and second optical fibers of said sensing element change upon motion of the first-mentioned with respect to said second optical fiber of said sensing element.

12. A spatially distributed sensor system according to claim 7, wherein said sensing element further comprises a substantially 50/50 coupler coupled to an end of said optical fiber of said sensing element and a second optical fiber having both ends coupled to said substantially 50/50 coupler to form a Sagnac interferometer loop.

13. A spatially distributed sensor system according to claim 7, wherein said tap coupler allows at least 90% of light to pass said sensing element without entering said sensing element.

14. A spatially distributed sensor system according to claim 7, wherein said tap coupler directs between 0.5% and 6% of light in said optical conduit into said sensing element.

15. A spatially distributed sensor system according to claim 1, further comprising a second sensing element optically coupled to said optical conduit at a second position along said optical conduit spatially separated from said input position and the first-mentioned position of coupling of the first-mentioned sensing element,

wherein said second sensing element is structured to split off a second fraction of light from said optical transmitter upon being coupled into said optical conduit and to return light to said optical conduit in a second amount responsive to a second effect being sensed,

wherein said optical receiver is structured to receive at least a portion of light from said optical conduit that includes light returned to said optical conduit from said second sensing element, and

wherein an analysis of light received by said optical receiver provides information to determine a position of said second sensing element.

16. A spatially distributed sensor system according to claim 1, further comprising a plurality of sensing elements each optically coupled to said optical conduit at respective plurality of positions along said optical conduit,

wherein each said sensing element splits off light from said optical conduit and returns light to said optical conduit in respective amounts responsive to respective effects being sensed,

wherein said optical receiver is structured to receive at least a portion of light from said optical conduit that includes light returned to said optical conduit from each said sensing element, and

wherein an analysis of light received by said optical receiver provides information to determine positions of each of said plurality of sensing elements.

17. A spatially distributed sensor assembly, comprising:

an optical conduit; and

a plurality of sensing elements optically connected to said optical conduit;

wherein each sensing element of said plurality of sensing elements is structured to return light to said optical conduit in an amount indicative of an effect being detected.

18. A spatially distributed sensor system according to claim 17, wherein said optical conduit is an optical fiber.

19. A spatially distributed sensor system according to claim 17, wherein a sensing element of said plurality of sensing elements is structured to detect an effect based upon polarization properties of light transmitted therein.

20. A spatially distributed sensor system according to claim 17, wherein a sensing element of said plurality of sensing elements comprises an interferometer.

21. A spatially distributed sensor system according to claim 17, wherein a sensing element of said plurality of sensing elements comprises an optical fiber that changes an optical transmission property upon contact with a substance being detected.

22. A method of sensing a spatially localized effect, comprising:

transmitting a pulse of signal light along an optical conduit;

splitting off a fraction of light from said pulse of signal light at each of a plurality of spatially localized sensors; and

returning light to said optical conduit from each of said plurality of spatially localized sensors in an amount indicative of an effect being detected.