Sensor with high-sensitivity optical fiber having a holographic detector comprising a liquid crystal light valve

Patent metadata

Field	Value
Publication number	US-9791302-B2
Application number	US-201415033424-A
Country	US
Kind code	B2
Filing date	Nov 14, 2014
Priority date	Nov 18, 2013
Publication date	Oct 17, 2017
Grant date	Oct 17, 2017

Abstract

An optical fiber sensor for locating an excitation in proximity to an optical fiber assembly comprises: a laser assembly configured to emit N laser beams indexed i with N>1, of respective emission wavelength λi, an optical fiber assembly comprising N successive sections indexed i, an optical system configured to: inject the laser beams, receive N signal beams indexed i respectively of wavelengths λi, generate N reference beams indexed i respectively of wavelengths λi, produce N interference areas indexed i, a holographic detector comprising: a liquid crystal light valve that at least partially covers the interference areas, and is configured to produce N holograms indexed i from, respectively, N interference areas, at least one optical detector configured to detect N output optical signals indexed I, a processing unit adapted to identify the section of the fiber assembly situated in proximity to the excitation to be located.

First claim

The invention claimed is:

1. An optical fiber sensor for locating an excitation in proximity to an optical fiber assembly, said excitation inducing a modulation of the phase of an optical signal propagating in said optical fiber assembly, said sensor comprising:
a laser assembly of at least one laser, said laser assembly being configured to emit N laser beams indexed i with N>1, of respective emission wavelength λi,
an optical fiber assembly comprising N successive sections indexed i, each section comprising a selective reflection device for an associated emission wavelength λi, the indexes being fixed relative to an end of said fiber assembly,
an optical system configured to:
inject, through said end, said laser beams
receive, through said end, N signal beams indexed i respectively of wavelengths λi, each signal beam being derived from the reflection, on the reflection device associated with the wavelength Δi, of the laser beam of wavelength λi injected then propagated in said fiber assembly,
generate N reference beams indexed i respectively of wavelengths λi, from the laser beam of emission wavelength λi,
produce N interference areas indexed i, each area corresponding to the interference between a reference beam and a signal beam of the same emission wavelength λi,

a holographic detector comprising:
a liquid crystal light valve comprising a liquid crystal layer arranged between two substrates, one of the substrates comprising a photoconductive material for said N emission wavelengths, said valve being arranged such that it at least partially covers said interference areas, said valve being configured to produce N holograms indexed i respectively from said N interference areas,
at least one optical detector configured to detect N output optical signals indexed i diffracted respectively by said N holograms,
a processing unit adapted to identify the section of said fiber assembly situated in proximity to said excitation to be located, from the N output optical signals detected.

2. The sensor as claimed in claim 1 , wherein said processing unit is adapted to identify said section by determining, from the N output optical signals detected, the output optical signal of lowest index exhibiting said phase modulation, said section to be identified corresponding to the section having said lowest index.

3. The sensor as claimed in claim 1 , wherein said phase modulation of said output optical signal corresponds to a temporal modulation of an intensity of said output optical signal detected.

4. The sensor as claimed in claim 1 , wherein the reflection device comprises a dichroic mirror and said optical fiber assembly comprises N optical fibers, each fiber and the associated dichroic mirror corresponding to a section.

5. The sensor as claimed in claim 1 , wherein said optical fiber assembly is formed by a single fiber and each reflection device comprises a Bragg reflector incorporated in said fiber.

6. The sensor as claimed in claim 1 , wherein said laser assembly consists of a single laser sequentially emitting said emission wavelengths.

7. The sensor as claimed in claim 1 , wherein said laser assembly comprises a plurality of N lasers, each laser respectively emitting an emission wavelength.

8. The sensor as claimed in claim 1 , comprising N optical detectors indexed i, each detector being adapted to respectively detect an output optical signal of emission wavelength λi, the detection taking place simultaneously for all the detectors.

9. The sensor as claimed in claim 1 , comprising a single optical detector adapted to sequentially detect said output optical signals.

10. The sensor as claimed in claim 1 , wherein said optical fiber assembly is multimode.

11. The sensor as claimed in claim 1 , wherein said optical fiber assembly is single-mode and polarization maintaining.

12. The sensor as claimed in claim 1 , wherein said optical fiber assembly is submerged and said excitation to be located is an underwater acoustic wave.

13. A method for locating an excitation in proximity to an optical fiber assembly, said excitation inducing a modulation of the phase of an optical signal propagating in said optical fiber assembly, comprising the steps of:
emitting N laser beams indexed i with N>1, of respective emission wavelength λi,
injecting said N laser beams into an optical fiber assembly, through an end of said assembly, said optical fiber assembly comprising N successive sections, indexed i, each section comprising a selective reflection device for an associated emission wavelength λi, the indexes being fixed relative to said end of said fiber,
receiving, through said end, N signal beams indexed i respectively of wavelengths λi, each signal beam being derived from the reflection, on the selective reflection devices associated with the wavelength λi, of the laser beam of wavelength λi injected then propagating in said fiber assembly,
generating N reference beams of index i respectively of wavelengths Δi, from the laser beam of emission wavelength λi,
producing N interference areas indexed i, each area corresponding to the interference between a reference beam and a signal beam of the same emission wavelength λi,
producing N holograms indexed i from said N interference areas with a liquid crystal light valve comprising a liquid crystal layer arranged between two substrates, one of the substrates comprising a photoconductive material for said N emission wavelengths, said valve being arranged such that it at least partially covers said interference areas,
detecting N output optical signals indexed i diffracted respectively by said N holograms,
identifying the section of said optical fiber assembly situated in proximity to said excitation to be located, from said N output optical signals detected.

14. The method as claimed in claim 13 , wherein the identification step comprises a step consisting in determining, from the N output optical signals detected, the output optical signal of lowest index exhibiting said phase modulation, said section to be identified corresponding to the section having said lowest index.

15. The method as claimed in claim 14 , wherein the step of determination of the output optical signal of lowest index exhibiting said phase modulation comprises a step consisting in analyzing, for the N output optical signals, respectively a temporal modulation of the intensity detected.

Assignees

• Thales Sa
• Centre Nat Rech Scient
• Centre Nat De La Rech Scient (Cnrs)

Inventors

• Bortolozzo Umberto
• Huignard Jean-Pierre
• Residori Stefania
• Molin Stéphanie
• Dolfi Daniel

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

• G01B9/02049

  characterised by particular mechanical design details · CPC title

• G01D5/35306 Primary

  using an interferometer arrangement · CPC title