MEASURING A CHARACTERISTIC OF A MULTIMODE OPTICAL FIBER

• US 20090097015A1
• Filed: 09/30/2008
• Published: 04/16/2009
• Est. Priority Date: 10/15/2007
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (SLB)
• Original Assignee: Schlumberger Technology Corporation (SLB)
• Inventors: Lees, Gareth P., Davies, Dylan, Hilton, Graeme, Hartog, Arthur H.
• Granted Patent: US 8,077,314 B2
• Time in Patent Office: Days
• US Class Current: 356/73.1
• CPC Class Codes: G01D 5/35364 using inelastic backscattering to detect the measured quantity, e.g. using Brillouin or Raman backscattering
• CPC Class Codes: G01K 11/32 using changes in transmittance, scattering or luminescence in optical fibres
• CPC Class Codes: G01M 11/319 Reflectometers using stimulated back-scatter, e.g. Raman or fibre amplifiers

Abstract

To measure a characteristic of a multimode optical fiber, a light pulse source produces a light pulse for transmission into the multimode optical fiber. A spatial filter passes a portion of Brillouin backscattered light from the multimode optical fiber that is responsive to the light pulse. Optical detection equipment detects the portion of the Brillouin backscattered light passed by the spatial filter.

Claims

1. An apparatus to measure a characteristic of a multimode optical fiber, comprising:

a light pulse source to produce a light pulse for transmission into the multimode optical fiber;

a spatial filter to pass a portion of Brillouin backscattered light from the multimode optical fiber that is responsive to the light pulse; and

optical detection equipment to detect the portion of the Brillouin backscattered light passed by the spatial filter.

2. The apparatus of claim 1, wherein the spatial filter includes an aperture to pass a portion of a speckle pattern generated by the multimode optical fiber.

3. The apparatus of claim 1, wherein the spatial filter includes a single-mode optical fiber.

4. The apparatus of claim 1, wherein the spatial filter includes an opaque layer with a hole in the opaque layer.

5. The apparatus of claim 1, wherein the spatial filter is a near-field spatial filter connected to a proximal end of the multimode optical fiber.

6. The apparatus of claim 1, wherein the spatial filter is a far-field spatial filter that is spaced apart from the proximal end of the multimode optical fiber.

7. The apparatus of claim 1, wherein the spatial filter has plural apertures to select plural respective speckles from the Brillouin backscattered light.

8. The apparatus of claim 1, further comprising:

an optical filter to receive the Brillouin backscattered light; and

an optical detector to receive an output of the optical filter,

wherein the optical filter and optical detector are part of the optical detection equipment.

9. The apparatus of claim 1, further comprising:

an optical local oscillator that produces light; and

a beam combiner to combine the light from the optical local oscillator and the Brillouin backscattered light portion into a combined light for further processing.

10. The apparatus of claim 1, further comprising Raman detection equipment to process Raman backscattered light from the multimode optical fiber.

11. The apparatus of claim 1, wherein the spatial filter is positioned between the multimode optical fiber and the optical detection equipment.

12. The apparatus of claim 11, further comprising an optical coupling device to:

direct the light pulse from the light pulse source to the multimode optical fiber; and

direct the portion of the Brillouin backscattered light passed by the spatial filter to the optical detection equipment.

13. The apparatus of claim 1, wherein the optical detection equipment includes a signal processing device to determine the characteristic of the multimode optical fiber.

14. The apparatus of claim 13, wherein the determined characteristic includes at least one characteristic selected from among temperature and strain of the multimode optical fiber.

15. A method of measuring a characteristic of a multimode optical fiber, comprising:

transmitting a light pulse into the multimode optical fiber;

passing Brillouin backscattered light from the multimode optical fiber that is responsive to the light pulse through a spatial filter, wherein a portion of the Brillouin backscattered light is passed through the spatial filter;

directing the portion of the Brillouin backscattered light to optical detection equipment for processing.

16. The method of claim 15, wherein passing the Brillouin backscattered light through the spatial filter comprises passing the Brillouin backscattered light through an aperture that passes a portion of a speckle pattern generated by the multimode optical fiber.

17. The method of claim 15, wherein passing the Brillouin backscattered light through the spatial filter comprises passing the Brillouin backscattered light through a single-mode optical fiber.

18. The method of claim 15, wherein passing the Brillouin backscattered light through the spatial filter comprises passes the Brillouin backscattered light through an opening of an opaque layer attached to an end of the multimode optical fiber.

19. The method of claim 15, further comprising deploying the multimode optical fiber in a well.

20. The method of claim 15, further comprising deploying the multimode optical fiber along an electrical cable.

21. A system comprising:

a multimode optical fiber;

a light pulse source to produce a light pulse for transmission into the multimode optical fiber;

a spatial filter to pass a portion of Brillouin backscattered light from the multimode optical fiber that is responsive to the light pulse; and

optical detection equipment to detect the portion of the Brillouin backscattered light passed by the spatial filter.

22. The system of claim 21, wherein the spatial filter includes a single-mode optical fiber that is connected to the multimode optical fiber, wherein the single-mode optical fiber is positioned between the multimode optical fiber and the optical detection equipment.

23. The system of claim 21, wherein the spatial filter includes an opaque layer with a hole in the opaque layer, wherein the opaque layer is attached to an end of the multimode optical fiber.