SENSING A DISTURBANCE

• US 20090097844A1
• Filed: 02/01/2007
• Published: 04/16/2009
• 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 7,817,279 B2
• Time in Patent Office: Days
• US Class Current: 398/16
• CPC Class Codes: G01M 11/3109 Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
• CPC Class Codes: G01M 11/3172 Reflectometers detecting the back-scattered light in the frequency-domain, e.g. OFDR, FMCW, heterodyne detection
• CPC Class Codes: H04B 10/00 Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication

Abstract

The present invention relates to a method of sensing a disturbance along an optical link including the steps of: using a first interferometer arrangement connected to an optical source so as to generate pairs of signal copies, which signal copies of a given pair are temporally delayed relative to one another; transmitting the time-displaced signal copies from the first interferometer arrangement onto the optical link; receiving the time-displaced signal copies transmitted over the optical link; and, using a second interferometer arrangement to temporally recombine the received signal copies from a given pair so as to generate an interferometer signal, which interferometer signal is representative of environmental effects on the optical link.

Claims

1. A method of sensing an environmental effect on an optical links including the steps of:

using a first interferometer arrangement connected to an optical source so as to generate pairs of signal copies, which signal copies of a given pair are temporally delayed relative to one another;

transmitting the time-displaced signal copies from the first interferometer arrangement onto the optical link;

receiving the time-displaced signal copies transmitted over the optical link; and

,

using a second interferometer arrangement to temporally recombine the received signal copies from a given pair so as to generate an interferometer signal, which interferometer signal is representative of an environmental effect on the optical link.

2. A method as claimed in claim 1, wherein the optical source has a coherence time associated therewith, the temporal displacement of the signals copies of a given pair being greater than the coherence time of the source.

3. A method as claimed in claim 2, wherein the temporal displacement is greater than the coherence time of the source by at least a factor of ten.

4. A method as claimed in claim 1, wherein the coherence time of the source is less than 10 pico seconds.

5. A method as claimed in claim 1, wherein each interferometer is arranged to channel radiation such that it is shared between a first path and a second path and to recombine the radiation from the first and second paths, the first and second paths of each interferometer having a respective differential delay associated therewith.

6. A method as claimed in claim 5, wherein the temporal displacement of the signal copies of a given pair is provided by the differential delay of the first interferometer.

7. A method as claimed in claim 1, wherein the signal copies of a given pair are transmitted over a common waveguide of the optical link.

8. A method as claimed in claim 7, wherein the optical signals are carried by the waveguide in a single mode fashion.

9. A method as claimed in claim 1, wherein the source is a continuous wave source.

10. A method as claimed in claim 1, wherein the optical link is a communications link carrying communications traffic.

11. Apparatus for sensing an environmental effect on an optical link, the apparatus including:

an optical source;

a first interferometer arrangement connected to the optical source so as to generate pairs of signal copies, which signal copies of a given pair are temporally delayed relative to one another, the first interferometer arrangement having an output coupler for transmitting the time-displaced signal copies onto the optical link; and

, a second interferometer arrangement, the second interferometer arrangement having an input coupler for receiving the time-displaced signal copies transmitted over the optical link, the second interferometer arrangement being configured to temporally recombine the received signal copies from a given pair so as to generate an interferometer signal, which interferometer signal is representative of environmental effects, if any, on the optical link.