SENSING A DISTURBANCE

• US 20090135428A1
• Filed: 02/01/2007
• Published: 05/28/2009
• Est. Priority Date: 02/24/2006
• Status: Active Grant

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: HEALEY, Peter
• Granted Patent: US 7,961,331 B2
• Time in Patent Office: Days
• US Class Current: 356/477
• 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

Abstract

The present invention relates to a system for sensing a disturbance in a sensing region along an optical path. The sensing system includes: a source of optical radiation; an upstream junction for channelling light along a first path and along a second path, the first and second paths each extending through the sensing region in an acoustically coupled relationship, such that, in use, a disturbance experienced at one of the first and second paths is experienced at the other of the first and second paths; and, a downstream junction for combining light from the first path with light from the second path so as to provide an interferometric signal from which the presence of a disturbance can be inferred.

Claims

1. A sensing system for sensing a disturbance in a sensing region, the sensing system including:

a source of optical radiation;

an upstream junction for channelling light along a first path and along a second path, the first and second paths each extending through the sensing region in an acoustically coupled relationship, such that, in use, a disturbance experienced at one of the first and second paths is experienced at the other of the first and second paths; and

, a downstream junction for combining light from the first path with light from the second path so as to provide an interferometric signal from which the presence of a disturbance can be inferred.

2. A sensing system as claimed in claim 1, wherein the first and second paths are arranged to extend through the sensing region in a side-by-side fashion.

3. A sensing system as claimed in claim 2, wherein the first and second paths extend along a common sleeve.

4. A sensing system as claimed in claim 1, wherein there is provided a first delay stage and a second delay stage along the first and second paths respectively for imposing a temporal delay to signals travelling along each path, the first delay stage being situated at an upstream location relative to the sensing region, and the second delay stage being located at a downstream location relative to the sensing region.

5. A sensing system as claimed in claim 4, wherein each delay stage is provided by a respective coiled portion of optical fibre.

6. A sensing system as claimed in claim 4 or claim 5, wherein the respective delay provided by the first and second delay stages is equal to within the coherence time of the source.

7. A sensing system as claimed in claim 1, wherein the optical source has a coherence time associated therewith that is less or equal to 10 nano seconds.

8. A sensing system as claimed in claim 1, wherein the source is a continuous wave source.

9. A method of sensing system for sensing a disturbance in a sensing region, including the steps of:

at an upstream junction, channelling optical radiation along a first path and along a second path, the first and second paths each extending through the sensing region in an acoustically coupled relationship, such that, in use, a disturbance experienced at one of the first and second paths is experienced at the other of the first and second paths; and

, at a downstream junctions interferometrically combining light from the first path with light from the second path so as to provide an interferometric signal from which the presence of a disturbance can be inferred.

10. A method as claimed in claim 9, wherein the light travelling along the first and second path is carried in single mode fashion.