Method and apparatus for optical sensing

Patent metadata

Field	Value
Publication number	US-12287235-B2
Application number	US-202318370963-A
Country	US
Kind code	B2
Filing date	Sep 21, 2023
Priority date	May 27, 2009
Publication date	Apr 29, 2025
Grant date	Apr 29, 2025

Abstract

The present invention provides novel apparatus and methods for fast quantitative measurement of perturbation of optical fields transmitted, reflected and/or scattered along a length of an optical fibre. The present invention can be used for point sensors as well as distributed sensors or the combination of both. In particular this technique can be applied to distributed sensors while extending dramatically the speed and sensitivity to allow the detection of acoustic perturbations anywhere along a length of an optical fibre while achieving fine spatial resolution. The present invention offers unique advantages in a broad range of acoustic sensing and imaging applications. Typical uses are for monitoring oil and gas wells such as for distributed flow metering and/or imaging, seismic imaging, monitoring long cables and pipelines, imaging within large vessel as well as for security applications.

First claim

The invention claimed is:

1. An optical sensing system comprising:
a pulsed light source arranged in use to generate a pulsed optical signal;
an interferometer arranged in use to receive the pulsed optical signal, the interferometer comprising at least two optical paths and at least one frequency shifter arranged in use to introduce a frequency shift between the optical paths in dependence on an RF signal generated by an RF source so as to generate respective pulses having a frequency shift there between;
a sensing fiber arranged in use to receive the respective pulses;
a photodetector arranged in use to receive light backscattered and/or reflected from along the sensing fiber as the respective pulses travel there along and to convert the received light into at least one electrical signal;
means for splitting the at least one electrical signal into a plurality of electrical signals;
a plurality of mixers arranged to receive respectively the plurality of electrical signals, the mixers respectively mixing the plurality of electrical signals with the RF signal at respective different phase angles to down-convert the plurality of electrical signals into a plurality of respective baseband signals; and
a processor arranged to digitize the plurality of respective baseband signals and to determine the relative optical phase modulation at at least one section of the sensing fiber therefrom.

2. A system according to claim 1 , further comprising:
a delay arranged in use to match the path lengths of the interferometer, and a coupler; the delay and the coupler being arranged in use so as to superimpose the respective pulses to generate an interference signal, wherein the coupler is further arranged to introduce relative phase shifts to the interference signal; and
means for monitoring the interference signal at the relative phase shifts.

3. A system according to claim 1 , wherein the sensing fiber is a single mode fiber, polarization maintaining fiber, a single polarization fiber, multimode fiber or a ribbon fiber.

4. A system of according to claim 1 , wherein the system is a distributed acoustic sensor system.

5. A method of fiber optic sensing, comprising:
generating a pulsed optical signal using a pulsed light source;
receiving the pulsed optical signal at an interferometer having at least two optical paths;
introducing a relative frequency shift between the at least two optical paths using at least one frequency shifter in dependence on an RF signal to generate respective pulses having a frequency shift there between;
inputting the respective pulses into a sensing fiber;
receiving light backscattered and/or reflected from along the sensing fiber as the respective pulses travel there along;
converting the received light into at least one electrical signal;
splitting the at least one electrical signal into a plurality of electrical signals;
mixing the plurality of electrical signals with the RF signal at respective different phase angles to down-convert the plurality of electrical signals into a plurality of respective baseband signals;
digitizing the plurality of respective baseband signals; and
determining the relative optical phase modulation at at least one section of the sensing fiber therefrom.

6. A method according to claim 5 , further comprising:
superimposing the respective pulses to generate an interference signal;
introducing a relative phase shift to the interference signal; and
monitoring the interference signal at relative phase shifts.

7. A method according to claim 5 , wherein the method is a method of distributed acoustic sensing.

Assignees

• Silixa Ltd

Inventors

• Farhadiroushan Mahmoud
• Parker Tom Richard
• Shatalin Sergey

Classifications

• G01D5/35358

  using backscattering to detect the measured quantity · CPC title

• G01D5/35377

  Means for amplifying or modifying the measured quantity · CPC title

• G01V1/40

  specially adapted for well-logging · CPC title

• G01F1/66

  by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters · CPC title

• G01F1/661

  using light · CPC title