EVALUATING THE POSITION OF A DISTURBANCE

• US 20090274456A1
• Filed: 03/30/2007
• Published: 11/05/2009
• Est. Priority Date: 04/03/2006
• Status: Active Grant

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Sikora, Edmund, Healey, Peter
• Granted Patent: US 8,670,662 B2
• Time in Patent Office: Days
• US Class Current: 398/28
• CPC Class Codes: G01D 5/35303 using a reference fibre, e.g. interferometric devices

Abstract

The present invention relates to a method of and apparatus for evaluating the position of a time-varying disturbance on an optical waveguide. The steps include: transmitting sensing signals onto the optical waveguide, which sensing signals have imposed thereon a modulation which is dependent, at least in part, on their time of transmission; receiving returned sensing signals, which signals have been exposed to the disturbance; and, from the previously imposed modulation on the returned sensing signals, evaluating the position of the disturbance. Because the sensing signals have a modulation that is dependent at least in part on their transmission time, the round-trip time for the signals to travel to and from a disturbance can be inferred. From this round trip time, or a value related thereto, it is possible to directly or indirectly evaluate the position of the disturbance.

Claims

1. A method of interferometrically evaluating the position of a time varying disturbance on an optical waveguide, including the steps of:

transmitting sensing signals onto the optical waveguide, which sensing signals have imposed thereon a modulation which is dependent, at least in part, on their time of transmission;

receiving returned sensing signals, which signals have been exposed to the disturbance; and

, from the previously imposed modulation on the returned sensing signals, evaluating the position of the disturbance.

2. A method as claimed in claim 1, wherein the sensing signals are returned by a process of distributed backscattering.

3. A method as claimed in claim 1, wherein the modulation has a component which varies in a cyclic fashion.

4. A method as claimed in claim 1, wherein the imposed modulation is a phase modulation.

5. A method as claimed in claim 4, wherein the phase is modulated with a frequency which varies linearly with increasing time.

6. A method as claimed in claim 1, wherein the sensing signals are modulated with a frequency that increases with time from a lower level to an upper level, and upon reaching the upper level, returns to the lower level.

7. A method as claimed in claim 6, wherein the frequency varies in a saw-tooth like manner.

8. A method as claimed in claim 1, wherein the modulation is an amplitude modulation.

9. A method as claimed in claim 8, wherein the amplitude modulation is a wave-like modulation.

11. A method as claimed in claim 1, wherein the sensing signals introduced into the waveguide are formed as pairs of signals, which signals of a pair are at least in part copies of one another.

12. A method as claimed in claim 11, Wherein the copies of a given pair are introduced into the main line with a temporal offset relative to one another.

13. A method as claimed in claim 12, wherein the relative delay is undone, for received signals returned from the waveguide.

14. A method as claimed in claim 12, wherein the temporal offset is caused at an interferometer arrangement having a first path and a second path, the transit time of the first path being longer than that of the second path, copies of a pair being caused to travel along a different respective path to one another.

15. A method as claimed in claim 1, wherein the waveguide operates as a single mode waveguide.

10. A method as a claimed in 1, wherein the modulation is a pulse-like modulation.

16. Apparatus for interferometrically evaluating the position of a time varying disturbance an optical waveguide, including:

means for transmitting sensing signals onto the optical waveguide, which sensing signals have imposed thereon a modulation which is dependent, at least in part, on their time of transmission;

means for receiving returned sensing signals, which signals have been exposed to the disturbance; and

, means for evaluating the position of the disturbance using the previously imposed modulation on the returned sensing signals.