Fiber optic sensor system

• US 20060139652A1
• Filed: 12/21/2005
• Published: 06/29/2006
• Est. Priority Date: 12/21/2004
• Status: Active Grant

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Inventors: Berthold, John W.
• Granted Patent: US 7,864,329 B2
• Time in Patent Office: Days
• US Class Current: 356/478
• CPC Class Codes: G01D 5/35303 using a reference fibre, e.g. interferometric devices
• CPC Class Codes: G01D 5/35354 Sensor working in reflection
• CPC Class Codes: G01D 5/35383 using multiple sensor devices using multiplexing techniques
• CPC Class Codes: G01H 9/004 using fibre optic sensors light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125
• CPC Class Codes: G01P 15/093 by photoelectric pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions

Abstract

A method and apparatus for detecting seismic vibrations using a series of MEMS units, with each MEMS unit including an interferometer is described. The interferometers on the MEMS units receive and modulate light from two differing wavelengths by way of a multiplexing scheme involving the use of Bragg gratings and light circulators, and an optoelectronic processor receives and processes the modulated light to discern vibrational movement of the system, which in turn allows for monitoring and calculation of a specified environmental parameter, such as seismic activity, temperature or pressure.

Claims

1. A multiplexed fiber optic sensor system comprising:

a source of broadband light;

a plurality of interferometers which modulate light received from the source;

a plurality of circulators associated with each interferometer, each of said circulators including at least one Bragg grating;

an optoelectronic processor which receives modulated light and produces a signal indicative of an environmental parameter, said optoelectronic processor having a cross-correlator; and

means for delivering light between the light source, the interferometers, the circulators and the optoelectronic processor.

2. The system according to claim 1, wherein at least one of the interferometers is integrated on a MEMS device.

3. The system according to claim 2, wherein the MEMS device includes a cantilever.

4. A fiber optic sensor system comprising:

a source of light;

at least one MEMS device which modulates light received from the source, said MEMS device having an interferometer and a cantilever;

an optoelectronic processor which receives the modulated light and produces a signal indicative of an environmental parameter; and

means for delivering the light between the light source, the MEMS device and the optoelectronic processor.

5. The system according to claim 4, wherein the cantilever is constructed from silicon or silicon carbide.

6. The system according to claim 4, wherein the cantilever has a shaped selected from the group consisting of:

U, E and Y.

7. The system according to claim 4, wherein the cantilever is framed within a planar silicon wafer.

8. The system according to claim 4, wherein the optoelectronic processor comprises a cross correlator.

9. The system according to claim 8, wherein the cross correlator includes a controllably variable gap.

10. The system according to claim 4, wherein the means for delivering the light comprises at least one Bragg grating.

11. The system according to claim 10, wherein the means for delivering the light comprises a plurality of circulators, at least one of said circulators interposed between the light source and the MEMS device and at least another of said circulators interposed between the MEMS device and the optoelectronic processor.

12. The system according to claim 4, wherein the interferometer is selected from the group consisting of:

a Fabry-Perot interferometer, a two beam interferometer and a multiple beam interferometer.

13. The system according to claim 4, wherein the light has a wavelength band between 1500-1600 nm.

14. The system according to claim 4, wherein the environmental parameter is selected from the group consisting of:

seismic activity, temperature and pressure.

15. A method of monitoring an environmental parameter comprising:

circulating a broadband light source to a plurality of interferometers so that each of said interferometers receives a unique wavelength band from the broadband light source, each of said interferometers modulating the light provided thereto;

providing the modulated light from each of said interferometers to an optoelectronic processor; and

cross-correlating the modulated light to produce a signal indicative of an environmental parameter.

16. The method according to claim 15, further comprising, prior to circulating the light, integrating at least one of the interferometers on a MEMS device.

17. The method according to claim 16, wherein the MEMS device includes a cantilever, said cantilever defining a boundary of the interferometer integrated on the MEMS device.

18. The method according to claim 15, wherein the signal indicative is indicative of seismic activity, temperature or pressure.