Optical System

• US 20080018908A1
• Filed: 12/16/2005
• Published: 01/24/2008
• Est. Priority Date: 12/17/2004
• 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 7,656,535 B2
• Time in Patent Office: Days
• US Class Current: 356/483
• CPC Class Codes: G01D 5/35303 using a reference fibre, e.g. interferometric devices

Abstract

The present invention relates to an disturbance sensing system, in particular an optical system in which a disturbance can be inferred. The system includes: a first waveguide portion and a second waveguide portion disposed in a side to side arrangement relative to one another; launch means for launching a first signal and a second signal onto the first waveguide portion and the second waveguide portion respectively, the first and second waveguide portions being optically coupled such that each of the transmitted first and second signals travels along each of the first and second waveguides; and, combining means for combining the transmitted first and second signals so as to produce a combination signal, the first and second signals being related to one another such that a disturbance in either one of the first and the second waveguide portions can be inferred from the combination signal. The noise or other signal resulting from a disturbance applied to both waveguide portions will be at least partially suppressed.

Claims

1. An optical system for sensing a disturbance, the system including:

a first waveguide portion and a second waveguide portion disposed in a side to side arrangement relative to one another;

launch means for launching a first signal and a second signal onto the first waveguide portion and the second waveguide portion respectively, the first and second waveguide portions being optically coupled such that each of the first and second signals travels along each of the first and second waveguides; and

,

combining means for optically combining the transmitted first and second signals so as to produce a combination signal, the first and second signals being related to one another such that a disturbance in the first or the second waveguide portions can be inferred from the combination signal.

2. An optical system as claimed in claim 1, wherein the first and second signals each have an irregular component, the first and second signals being related such that the irregular component is common to the first and second signal.

3. An optical system as claimed in claim 2, wherein the first and second signals each have a waveform, the irregular component being an irregular phase of the respective waveforms.

4. An optical system as claimed in claim 1, wherein the first and second signals are copies of one another.

5. An optical system as claimed in claim 1, wherein there is provided a delay stage arranged to impose a relative time delay between the first and second transmitted signals.

6. An optical system as claimed in claim 5, wherein the first and second signals have a phase coherence time associated therewith, and wherein the relative time delay is greater than the phase coherence time of the signals.

7. An optical system as claimed in claim 6, wherein the relative time delay is greater than the phase coherence time of the signals by at least a factor of five.

8. An optical system as claimed in claim 7, wherein the relative time delay is greater than the phase coherence time of the signals by at least a factor of ten.

9. An optical system as claimed in claim 5, wherein the delay is imposed at least in part by a further waveguide portion integrally formed with the first waveguide portion or the second waveguide portion.

10. An optical system as claimed in claim 1, wherein the optical system is arranged to channel the first and second signal along a common path, such that the first and second signals travel in opposite senses to one another along the common path.

11. An optical system as claimed in claim 10, wherein the common path is a closed path.

12. An optical system as claimed in any proceeding claim claim 1, wherein the first and second waveguide portions are each formed from respective portions of optical fibre.

13. An optical system as claimed in any proceeding claim claim 1, wherein the launching means includes a optical coupler arrangement for coupling an input signal from an optical source to the first and second waveguides, the first and second signals being formed from the input signal.

14. An optical system as claimed in claim 13, wherein the launching means includes launch waveguide portions extending between the coupler arrangement and the respective first and second waveguides.

15. An optical system as claimed in claim 14, wherein the launch waveguide portions are formed integrally with the respective first and second waveguide portions.

16. An optical system as claimed in claim 12, wherein the system is configured such that, in use, the optical coupler arrangement serves to combine the first and second signals transmitted over the first and second waveguides respectively.

17. An optical system as claimed in claim 1, wherein a reflector arrangement is provided for returning light to the combining means.

18. An optical system as claimed in claim 1, wherein a common channel is provided along which the waveguides extend.

19. An optical system as claimed in claim 18, wherein the channel is formed by a common sleeve.

20. An optical system as claimed in claim 19, wherein the channel is formed by a common conduit.

21. Sensing apparatus for sensing a disturbance in a first waveguide portion or a second waveguide portion of a transmission link, the transmission link being arranged to provide a return path to the sensing system, the sensing system including:

launch means for launching a first signal and a second signal onto the first waveguide portion and the second waveguide portion respectively, which first and second signals are related to one another; and

, combining means for optically combining the returned first and second signals so as to produce a combination signal, the first and second signals being related to one another such that a disturbance the first or the second waveguide portions can be inferred from the combination signal.

22. Sensing apparatus as claimed in claim 21, wherein the link is an optical cable, or a conduit housing a plurality of optical fibres.

23. A method of sensing a disturbance in a first waveguide portion or a second waveguide portion of a transmission link, which first and second waveguide portions are arranged in a side to side arrangement, the method including the steps of:

introducing a first signal and a second signal onto the first waveguide portion and the second waveguide portion respectively, which first and second signals are related to one another;

channeling the first and second signals such that each of the first and second signals travels along each of the first and second waveguide portions;

combining the first an second signals so as to produce a combination signal; and

, inferring from the combination signal the presence of a disturbance.

24. A method of sensing a disturbance as claimed in claim 23, including the step of introducing a temporal offset between the first and second signals such that the first and second signals are offset as the signals travel along the waveguide portions, and wherein the disturbance varies on a time scale that is greater than the temporal offset.

25. A method of sensing a disturbance as claimed in claim 23, wherein the disturbance is an acoustic disturbance.

26. A method of determining whether a first waveguide is disturbed relative to a second waveguide, the method including the steps of:

generating pairs of signal copies, each pair having including first signal and a second signal;

channeling the first signals along a first path;

channeling the second signals along a second path, wherein the first and second paths each extend in part along each of the first and second waveguides; and

combining the first and second signals of each pair that have traveled along the first and second paths.

27. A differential sensing system for sensing a disturbance in a first waveguide relative to a disturbance in a second waveguide, the system having:

means for generating a first signal and a second signal, which first and second signals are copies of one another;

directional means for directing the first signals along a first path and for directing the second signals along a second path, the first and second paths each extending in part along each of the first and second waveguides; and

, combining means for combining the first and second signals that have traveled along the first and second paths.

28. A differential sensing system as claimed in claim 27 wherein the directional means and the combining means include in common a coupler arrangement.

29. A differential sensing system as claimed in claim 28 wherein the directional means include a reflector arrangement, the first and second waveguides each extending between the reflector arrangement and the coupler arrangement.