Identifying or Locating Waveguides

• US 20070264012A1
• Filed: 09/20/2005
• Published: 11/15/2007
• Est. Priority Date: 09/30/2004
• Status: Active Grant

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Healey, Peter, Heatley, David, Sikora, Edmund, Shackleton, Mark
• Granted Patent: US 7,848,645 B2
• Time in Patent Office: Days
• US Class Current: 398/13
• CPC Class Codes: H04B 10/071 using a reflected signal, e.g. using optical time domain reflectometers [OTDR]
• CPC Class Codes: H04B 10/079 using measurements of the data signal
• CPC Class Codes: H04B 10/85 Protection from unauthorised access, e.g. eavesdrop protection

Abstract

The present invention relates to the location or identification of a waveguide, in particular where a disturbance is applied to the optical waveguide. This is achieved by: (a) monitoring the waveguide at a first location to sense a disturbance along the waveguide; (b) causing a disturbance to the waveguide at a second location; (c) transmitting a sensor signal to the second location; and, (d) inferring, from the sensor signal, the presence or identity of the waveguide at the second location.

Claims

1. A method of locating or identifying a waveguide, the method including the steps of:

(a) monitoring the waveguide at a first position to sense a disturbance along the waveguide;

(b) causing a disturbance to the waveguide at a second position;

(c) transmitting a sensor signal from the first position; and

, (d) inferring, from the sensor signal, the presence or identity of the waveguide at the second position, the inference being made at the second position.

2. A method as claimed in claim 1, wherein the waveguide is monitored by transmitting sensing signals onto the waveguide, which sensing signals are in the form of pairs of signal copies.

3. A method as claimed in claim 2, wherein signal copies of a pair are introduced onto the waveguide with a time delay relative to one another.

4. A method as claimed in claim 1, wherein at least some of the sensing signals that have traveled at least to the second position are caused to return to the first position.

5. A method as claimed in claim 4, wherein returned signal copies of respective pairs are temporally re-aligned.

6. A method as claimed in claim 4, wherein interferometer means having a path difference associated therewith are used to cause the relative time delay between signal copies of a pair.

7. A method as claimed in claim 6, wherein the interferometer means is used to temporally re-align the returned signal copies of a pair.

8. A method as claimed in claim 2, wherein signal copies of a pair are introduced in the same sense along the waveguide.

9. A method as claimed in claim 2, wherein signal copies of a pair are introduced at a common point along the waveguide.

10. A method as claimed in claim 1, wherein the sensor signal is an audio signal, the audio signal being a microphonic representation of the generated disturbance.

11. A method as claimed in claim 10, wherein the audio signal is used to generate an audible signal representative of the disturbance.

12. A method as claimed in claim 1, wherein sensing signals are returned by reflector means and/or a process of distributed backscattering in a portion of the waveguide.

13. A method as claimed in claim 1, wherein a disturbance is applied to each of a plurality of waveguides, at least one of the waveguides being sensed for a disturbance, the identity of the sensed waveguide being inferred from the received sensor signal.

14. A method as claimed in claim 1, wherein the first and second positions are located at respective first and second locations, which locations are geographically separate, the sensor signal being transmitted from the first location to the second location by wireless means.

15. A method as claimed in claim 1 including the further steps of determining the path length of the fibre between the first location and the second location.

16. A method as claimed in claim 15 including the further steps of causing a disturbance to the fibre at a third location;

evaluating the difference in the path length of the fibre between the second and third locations; and

, if a difference in path length exceeds the geographical distance between the second and third locations, generating an alert signal.

17. A method as claimed in claim 15, wherein the path length is determined by:

copying, at least in part, an output signal from a source, such that there is a pair of signal copies;

transmitting the signal copies onto the waveguide;

receiving from the transmission link at least partially returned signal copies previously transmitted thereon;

combining the received signal copies of a transmitted pair so as to produce a combination signal; and

, using a temporal characteristic in the combination signal to evaluate the position of the disturbance on the transmission link.

18. A method as claimed in claim 17, wherein the temporal characteristic includes the time at which a disturbance feature occurs in the combination signal.

19. A method as claimed in claim 1, wherein the disturbance is generated by transmitting acoustic vibrations through a fluid medium.

20. A method as claimed in claim 19, wherein the fluid medium is a liquid.

21. A method as claimed in claim 20, wherein the acoustic vibrations transmitted from a flotation structure.

22. A method as claimed in claim 21, wherein the flotation structure is a ship.

23. A method as claimed in claim 19, wherein the waveguide is a subsea waveguide and the acoustic vibrations are sonar vibrations.

24. A method as claimed in claim 2, wherein the waveguide is configured to carry the sensing signals in a single mode fashion.

25. A method as claimed in claim 1, wherein the sensor signal is received at the second location, such that the determination of the presence of the waveguide can be made at the second location.

26. A method as claimed in claim 1, wherein the waveguide is an optical fibre.

27. Apparatus for locating or identifying an optical fibre, the apparatus including:

a monitoring station for monitoring the waveguide at a first position so as to sense a disturbance along the waveguide, the monitoring station being arranged to transmit a sensor signal indicative of the sensed disturbance; and

, a receiver station for receiving the transmitted audio signal at a second position, such that the presence of the waveguide can be inferred at the second position from the received sensor signal.

28. Apparatus as claimed in claim 27, wherein the sensor signal is an audio signal, the audio signal being a microphonic representation of the generated disturbance.

29. Apparatus as claimed in claim 28, wherein the receiver station includes an audio output device for converting the audio signal into an audible sound representative of the audio signal.

30. Apparatus as claimed in claim 27, wherein the monitoring station and the receiver station respectively include wireless transmitter and receiver means such that the audio signal can be wirelessly transmitted from the monitoring station to the receiver station.

31. Apparatus as claimed in claim 27, wherein the monitoring station includes a transmission stage for transmitting, onto the waveguide, pairs of signal copies such that the signal copies of a given pair have a time offset relative to one another.

32. Apparatus as claimed in claim 31, wherein the monitoring station includes a receiving stage for receiving signal copies previously transmitted onto the link, the receiving stage being arranged, for received pairs, to cause one signal copy of a pair to mix with the other signal copy of that pair.

33. A microphone system as claimed in claim 32, wherein the transmission stage and the receiving stage are formed in common by an interferometer stage.

34. A method of locating or identifying a waveguide, the method including the steps of:

(a) monitoring the waveguide at a first position to sense a disturbance along the waveguide;

(b) causing a disturbance to the waveguide at a second position;

(c) emitting a sensor signal from the first position; and

, (d) inferring, from the sensor signal, the presence or identity of the waveguide at the second position.