Long range optical fiber sensing systems

Patent metadata

Field	Value
Publication number	US-2023221151-A1
Application number	US-202117904599-A
Country	US
Kind code	A1
Filing date	Feb 19, 2021
Priority date	Feb 21, 2020
Publication date	Jul 13, 2023
Grant date	—

Abstract

A long range optical fiber sensor such as a distributed acoustic sensor has a sensing fiber located remotely from the interrogator, with a length of transport fiber path connecting the two. Because no sensing is performed on the transport fiber then the pulse repetition rate from the interrogator can be high enough such that the pulse repetition rate and pulse power are optimised according to the sensing fiber length and hence sensing frequency response and sensitivity are also optimised according to the sensing fiber length.

First claim

1 . A long range optical fiber distributed sensor system, comprising:
an optical source arranged in use to produce optical sensing pulses; a sensing optical fiber deployable in use in an environment to be sensed and arranged in use to receive the optical sensing pulses; and sensing apparatus arranged in use to detect light from the optical sensing pulses reflected and/or backscattered back along the sensing optical fiber and to determine any one or more of an acoustic, vibration, temperature or other parameter that perturbs the path length of the sensing optical fiber in dependence on the reflected and/or backscattered light; the system being characterised by: at least one transport fiber arranged between the sensing optical fiber and the optical source to transport the optical sensing pulses from the optical source to the sensing fiber and to transport backscatter and/or reflections from along the sensing fiber back to the sensing apparatus; at least one optical fiber amplifier arranged in series with the transport fiber, and; an optical fiber amplifier pump source arranged to provide pump light to the optical fiber amplifier, the optical fiber amplifier arranged in use to amplify at least one of: i) the forward optical sensing pulses; or ii) the forward optical sensing pulses and the returning backscatter and/or reflections.

2 . A long-range optical fiber sensor according to claim 1 , wherein the transport fiber comprises a forward transport fiber arranged to convey optical sensing pulses from the optical source to the sensing optical fiber, and a return transport fiber arranged to convey back scatter and/or reflections from the sensing optical fiber back to the interrogator.

3 . A long range optical fiber sensor according to claim 2 , wherein a separate optical fiber amplifier is provided on each of the forward and return transport fibers.

4 . A long range optical fiber sensor according to claim 3 , wherein a respective optical fiber amplifier pump source is provided for the respective optical fiber amplifiers, wherein the pump source for the optical fiber amplifier on the return transport fiber provides a continuous wave pump signal, whereas the pump source for the optical fiber amplifier on the forward transport fiber provides a pulsed pump signal that co-propagates with the forward optical sensing pulses.

5 .- 20 . (canceled)

21 . A long range optical fiber distributed sensor system, comprising:
an optical source arranged in use to produce optical sensing pulses; a sensing optical fiber deployable in use in an environment to be sensed and arranged in use to receive the optical sensing pulses; and sensing apparatus arranged in use to detect light from the optical sensing pulses reflected and/or backscattered back along the sensing optical fiber and to determine any one or more of an acoustic, vibration, temperature or other parameter that perturbs the path length of the sensing optical fiber in dependence on the reflected and/or backscattered light; the system being characterised by: at least one transport fiber arranged between the sensing optical fiber and the optical source to transport the optical sensing pulses from the optical source to the sensing fiber and to transport backscatter and/or reflections from along the sensing fiber back to the sensing apparatus; wherein the transport fiber comprises a forward transport fiber arranged to convey optical sensing pulses from the optical source to the sensing optical fiber, and a return transport fiber arranged to convey back scatter and/or reflections from the sensing optical fiber back to the interrogator; wherein the forward transport fiber comprises at least a first part formed of high power handling fiber and a second part formed of low loss fiber, the first and second parts being arranged in series.

22 . A long range optical fiber sensor according to claim 21 , wherein the respective lengths of the first parts and the second parts are determined in dependence on the respective loss rates of the high power fiber and the low loss fiber.

23 . A long range optical fiber sensor according to claim 22 , wherein the high power handling fiber has a higher loss rate than the low loss fiber, and the length of the first part corresponds to a length of high power fiber that for an input optical sensing pulse of a first power propagates that pulse until it reaches the same power level as would have been achieved had low loss fiber been used for the first part with the input optical sensing pulse being of a second power lower than the first power, the first and second power levels being those power levels such that pulse propagation would occur in the respective fiber types without causing non-linear distortion effects.

24 . A long range optical fiber sensor according to claim 21 , and further comprising an optical fiber amplifier arranged in series with the transport fiber, and an optical fiber amplifier pump source arranged to provide pump light to the optical fiber amplifier, the optical fiber amplifier arranged in use to amplify the forward optical sensing pulses and/or the returning backscatter and/or reflections.

25 . A long range optical fiber sensor according to claim 24 , wherein a separate optical fiber amplifier is provided on each of the forward and return transport fibers.

26 . A long range optical fiber sensor according to claim 25 , wherein a respective optical fiber amplifier pump source is provided for the respective optical fiber amplifiers, wherein the pump source for the optical fiber amplifier on the return transport fiber provides a continuous wave pump signal, whereas the pump source for the optical fiber amplifier on the forward transport fiber provides a pulsed pump signal that co-propagates with the forward optical sensing pulses.

27 .- 41 . (canceled)

42 . A long range optical fiber distributed sensor system, comprising:
an optical source arranged in use to produce optical sensing pulses; a sensing optical fiber deployable in use in an environment to be sensed and arranged in use to receive the optical sensing pulses; and sensing apparatus arranged in use to detect light from the optical sensing pulses reflected and/or backscattered back along the sensing optical fiber and to determine any one or more of an acoustic, vibration, temperature or other parameter that perturbs the path length of the sensing optical fiber in dependence on the reflected and/or backscattered light; the system being characterised by: at least one transport fiber arranged between the sensing optical fiber and the optical source to transport the optical sensing pulses from the optical source to the sensing fiber and to transport backscatter and/or reflections from along the sensing fiber back to the sensing apparatus; and a Raman pump light source arranged to provide Raman pump light into the transport fiber, the Raman pump light being arranged to interact with the optical sensing pulses and/or the reflections and/or backscatter from the sensing optical fiber to increase the power of the optical sensing pulses and/or the reflections and/or backscatter; wherein the transport fiber comprises a forward transport fiber arranged to convey optical sensing pulses from the optical source to the sensing optical fiber, and a return transport fiber arranged to convey back scatter and/or reflections from the sensing optical fiber back to the interrogator; and wherein a separate Raman pump light source is provided for each of the forward and return transport fibers.

43 . A long range optical fiber sensor according to claim 42 , wherein the Raman pump light source for the return t

Assignees

• Silixa Ltd

Inventors

• Farhadiroushan Mahmoud
• Parker Tom
• Shatalin Sergey
• Maxwell Jack

Classifications

• G01K11/32

  using changes in transmittance, scattering or luminescence in optical fibres · CPC title

• E21B47/06 Primary

  Measuring temperature or pressure · CPC title

• G01H9/004

  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

• G01D5/35354

  Sensor working in reflection · CPC title

• E21B47/135

  using light waves, e.g. infrared or ultraviolet waves · CPC title