Method and apparatus for detecting a disturbance in a medium

Patent metadata

Field	Value
Publication number	US-10447388-B2
Application number	US-201715678546-A
Country	US
Kind code	B2
Filing date	Aug 16, 2017
Priority date	Oct 13, 2006
Publication date	Oct 15, 2019
Grant date	Oct 15, 2019

Abstract

An improved technique for acoustic sensing involves, in one embodiment, launching into a medium, a plurality of groups of pulse-modulated electromagnetic-waves. The frequency of electromagnetic waves in a pulse within a group differs from the frequency of the electromagnetic waves in another pulse within the group. The energy scattered by the medium is detected and, in one embodiment, the beat signal may be used to determine a characteristic of the environment of the medium. For example, if the medium is a buried optical fiber into which light pulses have been launched in accordance with the invention, the presence of acoustic waves within the region of the buried fiber can be detected.

First claim

The invention claimed is:

1. A method comprising:
detecting, using a system comprising a processor, a first beat signal in a medium, the first beat signal comprising a plurality of carrier signals;
determining, from the first beat signal using the system, a plurality of complex signals, each of the plurality of complex signals corresponding to one of the plurality of carrier signals for one of a plurality of fixed locations along the medium;
extracting phase information from each of the plurality of complex signals;
weighting the phase information of each particular complex signal of the plurality of complex signals based on a signal to noise ratio of the one of the plurality of carrier signals that corresponds to the particular complex signal to generate weighted phase information; and
for each respective fixed location, combining the weighted phase information of the plurality of complex signals that correspond to each of the plurality of carrier signals for the respective fixed location to detect a disturbance in the medium.

2. The method of claim 1 , wherein the combining the weighted phase information of the plurality of complex signals that correspond to each of the plurality of carrier signals for the respective fixed location to detect a disturbance in the medium comprises:
combining the weighted phase information of the plurality of complex signals that correspond to each of the plurality of carrier signals for the respective fixed location that have an amplitude satisfying a threshold.

3. The method of claim 1 , wherein the first beat signal results from a scattering of a first pair of electromagnetic waves by the medium.

4. The method of claim 3 , wherein a frequency of a first electromagnetic wave of the first pair of electromagnetic waves is different than a frequency of a second electromagnetic wave of the first pair of electromagnetic waves.

5. The method of claim 3 , wherein a frequency of a first electromagnetic wave of the first pair of electromagnetic waves and a frequency of a second electromagnetic wave of the first pair of electromagnetic waves are within an optical spectrum.

6. The method of claim 3 , wherein a first electromagnetic wave and a second electromagnetic wave of the first pair of electromagnetic waves have a common pulse width.

7. The method of claim 6 , further comprising:
detecting a second beat signal associated with a scattering of a second pair of electromagnetic waves in the medium based on a common pulse width of a third electromagnetic wave of the second pair of electromagnetic waves and a fourth electromagnetic wave of the second pair of electromagnetic waves.

8. The method of claim 7 , wherein the first pair of electromagnetic waves and the second pair of electromagnetic waves propagate along the medium at a same time, and a frequency difference between the first electromagnetic wave and the second electromagnetic wave is different from a frequency difference between the third electromagnetic wave and the fourth electromagnetic wave.

9. The method of claim 7 , wherein the first pair of electromagnetic waves and the second pair of electromagnetic waves propagate along the medium at different times, and a frequency difference between the first electromagnetic wave and the second electromagnetic wave is equal to a frequency difference between the third electromagnetic wave and the fourth electromagnetic wave.

10. A system comprising:
a plurality of detectors for detecting a first beat signal in a medium, the first beat signal comprising a plurality of carrier signals;
a demodulator for determining, from the first beat signal, a plurality of complex signals, each of the plurality of complex signals corresponding to one of the plurality of carrier signals for one of a plurality of fixed locations along the medium;
a processor; and
a memory to store computer program instructions, the computer program instructions when executed on the processor cause the processor to perform operations comprising:
extracting phase information from each of the plurality of complex signals;
weighting the phase information of each particular complex signal of the plurality of complex signals based on a signal to noise ratio of the one of the plurality of carrier signals that corresponds to the particular complex signal to generate weighted phase information; and
for each respective fixed location, combining the weighted phase information of the plurality of complex signals that correspond to each of the plurality of carrier signals for the respective fixed location to detect a disturbance in the medium.

11. The system of claim 10 , wherein the combining the weighted phase information of the plurality of complex signals that correspond to each of the plurality of carrier signals for the respective fixed location to detect a disturbance in the medium comprises:
combining the weighted phase information of the plurality of complex signals that correspond to each of the plurality of carrier signals for the respective fixed location that have an amplitude satisfying a threshold.

12. The system of claim 10 , wherein the first beat signal results from a scattering of a first pair of electromagnetic waves by the medium.

13. The system of claim 12 , wherein a frequency of a first electromagnetic wave of the first pair of electromagnetic waves is different than a frequency of a second electromagnetic wave of the first pair of electromagnetic waves.

14. The system of claim 12 , wherein a frequency of a first electromagnetic wave of the first pair of electromagnetic waves and a frequency of a second electromagnetic wave of the first pair of electromagnetic waves are within an optical spectrum.

15. A non-transitory computer readable storage device storing computer program instructions, which, when executed on a processor, cause the processor to perform operations comprising:
detecting a first beat signal in a medium, the first beat signal comprising a plurality of carrier signals;
determining, from the first beat signal, a plurality of complex signals, each of the plurality of complex signals corresponding to one of the plurality of carrier signals for one of a plurality of fixed locations along the medium;
extracting phase information from each of the plurality of complex signals;
weighting the phase information of each particular complex signal of the plurality of complex signals based on a signal to noise ratio of the one of the plurality of carrier signals that corresponds to the particular complex signal to generate weighted phase information; and
for each respective fixed location, combining the weighted phase information of the plurality of complex signals that correspond to each of the plurality of carrier signals for the respective fixed location to detect a disturbance in the medium.

16. The non-transitory computer readable storage device of claim 15 , wherein the combining the weighted phase information of the plurality of complex signals that correspond to each of the plurality of carrier signals for the respective fixed location to detect a disturbance in the medium comprises:
combining the weighted phase information of the plurality of complex signals that correspond to each of the plurality of carrier signals for the respective fixed location that have an amplitude satisfying a threshold.

17. The non-transitory computer readable storage device of claim 15 , wherein the first beat signal results from a scattering of a first pair of electromagnetic waves by the medium, and a first electromagnetic wave and a second electromagnetic wave of the

Assignees

• At & T Ip Ii Lp

Inventors

• Lewis Andrew B
• Russell Stuart

Classifications

• G01H9/004 Primary

  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) · CPC title

• G01D5/35364

  using inelastic backscattering to detect the measured quantity, e.g. using Brillouin or Raman backscattering · CPC title

• G01M11/3172

  Reflectometers detecting the back-scattered light in the frequency-domain, e.g. OFDR, FMCW, heterodyne detection · CPC title

• G01M11/3127

  using multiple or wavelength variable input source · CPC title

• H04B10/071 Primary

  using a reflected signal, e.g. using optical time domain reflectometers [OTDR] · CPC title