WO2006032116A1 - Procede pour evaluer l'effet de la temperature et de la contrainte sur le spectre reflechi par un reseau de bragg en fibre - Google Patents

Procede pour evaluer l'effet de la temperature et de la contrainte sur le spectre reflechi par un reseau de bragg en fibre Download PDF

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Publication number
WO2006032116A1
WO2006032116A1 PCT/BE2005/000144 BE2005000144W WO2006032116A1 WO 2006032116 A1 WO2006032116 A1 WO 2006032116A1 BE 2005000144 W BE2005000144 W BE 2005000144W WO 2006032116 A1 WO2006032116 A1 WO 2006032116A1
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WO
WIPO (PCT)
Prior art keywords
strain
temperature
fbg
reflected
spectrum
Prior art date
Application number
PCT/BE2005/000144
Other languages
English (en)
Inventor
Christophe Caucheteur
Marc Wuilpart
Patrice Megret
Original Assignee
Faculte Polytechnique De Mons
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from EP04447207A external-priority patent/EP1640692A1/fr
Application filed by Faculte Polytechnique De Mons filed Critical Faculte Polytechnique De Mons
Publication of WO2006032116A1 publication Critical patent/WO2006032116A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
    • G01D5/35354—Sensor working in reflection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
    • G01D5/35309—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer
    • G01D5/35316—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer using a Bragg gratings

Definitions

  • the present invention is related to a method for interrogating a fibre Bragg grating sensor.
  • a fibre Bragg grating consists of a short
  • This structure acts as a highly wavelength selective reflection filter with the peak reflectivity wavelength, ⁇ B ⁇ agg ⁇ determined by the phase matching condition :
  • Fibre Bragg grating optical sensing exploits the fact that the measured information is wavelength encoded in the reflected and transmitted spectra
  • the wavelength shift information can then be related to the measurand at that sensor position.
  • the accurate determination of the -often small- wavelength shift has become a great issue since the early stage of FBG sensing work.
  • Many techniques have been proposed for wavelength interrogation. Usually the wavelength measurement is not very straightforward. Indeed, a simple set-up using a broadband source and an optical spectrum analyser presents a limited resolution capability and lacks cost-effectiveness.
  • the general principle is to convert the wavelength shift into an easily measured parameter such as amplitude, frequency or phase.
  • wavelength-frequency conversion which can be achieved using an acoustic-optic tunable filter, must be controlled by a feedback loop. This is also the case when an unbalanced optical fibre Mach-Zehnder interferometer is used as a wavelength discriminator.
  • Another problem is the cross-sensitivity between temperature and strain effects that cannot be resolved with only one grating written into a standard single mode fibre.
  • Various schemes have thus been proposed to discriminate between these effects.
  • One of the simplest ways is the use of a uniform grating written into a polarisation maintaining fibre (Hi-Bi FBG) . Since such a fibre has a different propagation constant for the slow and fast axis, a fibre grating written into a polarisation maintaining fibre has two distinct Bragg reflection wavelengths corresponding to the two eigenmodes. Each Bragg reflection wavelength has different dependence on temperature and strain.
  • WO99/32863 discloses a method for applying an optical fibre as a hydrostatic pressure sensor.
  • an optical fibre is used provided with a core and a cladding including two side- holes.
  • An FBG is written into the core.
  • the side-hole optical fibre is spliced in between standard single mode fibres, so that a change in differential pressure between the surroundings and the side-holes causes a change in the fibre birefringence.
  • Patent application WO86/01286 relates to a distributed, spatially resolving optical fibre strain sensor.
  • the core of the optical fibre is impressed with a plurality of gratings that modify the reflection and transmission of injected light at the grating positions under conditions of local strain or temperature variation.
  • the present invention aims to provide an interrogation technique for fibre Bragg grating sensors that overcomes the problems of the state of the art solutions.
  • the present invention relates to a method for evaluating temperature and/or strain affecting a fibre Bragg grating (FBG) , comprising the steps of determining the spectrum transmitted or reflected by said FBG, when launching light into said FBG, - determining at least two quantities to characterise said transmitted or said reflected spectrum, monitoring the evolution of said at least two characteristic quantities in response to a change in temperature and/or strain, - evaluating temperature and/or strain using information obtained from the previous step.
  • FBG fibre Bragg grating
  • the step of determining the at least two characterising quantities is performed via Stokes parameters corresponding to the transmitted or the reflected spectrum.
  • the at least two quantities comprise the maximum and the minimum of the ratio Si/So of Stokes parameters S 0 and S 1 of the transmitted spectrum.
  • a first quantity is the minimum of the degree of polarisation (DOP) located • between the two main peaks in the reflected spectrum, said DOP being calculated via the Stokes parameters of the reflected spectrum, and a second quantity is the distance between the closest DOP minima at each side of the first quantity.
  • DOP degree of polarisation
  • the transmitted or reflected spectrum is obtained by using a tunable laser source.
  • the invention discloses a method for evaluating temperature and/or strain affecting a cascade of FBGs, wherein the steps of the method as described above are performed for each FBG of said cascade.
  • the strain is axial strain.
  • the invention relates to a method for temperature/strain sensing of a fibre comprising a FBG, comprising the steps of - calibrating said FBG, and performing the steps of the method as previously described,
  • the calibration step comprises a temperature calibration and/or a strain calibration.
  • the angle of the input linear state of polarisation of the light launched into the FBG is 45° .
  • Fig. 2 represents the reflected spectrum and Si, S 2 , S 3 vs. wavelength. Left : theoretical evolution (same parameters as in Fig.l) and right : experimental measurement.
  • Fig. 3 represents the measurement set-up.
  • Fig. 4 represents the reflected spectrum of a 2 mm long PM-FBG.
  • Fig. 5 represents the reflected spectrum of Fig.4 together with the corresponding normalised Stokes parameters for the reflected signal (left) and the transmitted spectrum + corresponding normalised Stokes parameters for the transmitted signal (right) .
  • Fig. 6 represents (a) DOP in transmission vs. wavelength and (b) transmitted spectrum. Left : simulation with parameters as in Fig.l; right : experimental measurement .
  • Fig. 7 represents (a) DOP in reflection vs. wavelength and (b) reflected spectrum.
  • Fig. 8 represents a grating response to a change of strain.
  • Fig. 9 represents the principle of the demodulation algorithm according to the second embodiment .
  • Fig. 10 represents a grating response to a change of temperature.
  • the eigenmodes or modes x and y are referred to as the fast axis.
  • the x mode is sometimes also called the slow axis, whereas the y mode may be referred to as the fast axis.
  • n eff is the effective refractive index of the fibre
  • A is the grating period and An is the fibre birefringence.
  • An is the fibre birefringence.
  • the light launched into the FBG can be represented by the following Jones vector which defines the input State Of Polarisation (SOP) :
  • ⁇ X (y) and p X (y) denote the transmission and reflection coefficients, respectively, of the uniform fibre Bragg grating corresponding to the mode x (mode y) , the expressions of which are derived from the coupled mode theory :
  • v is the contrast of the interference fringes
  • ⁇ n is the index modulation of the FBG
  • ⁇ represents the wavelength
  • L the physical length of the grating.
  • ⁇ B ⁇ X ( y j are as defined in eq.2 and 3.
  • the Stokes parameters S 0 , Si, S 2 and S 3 are real numbers representing the state of polarisation. They can be easily deduced from the Jones vector, e.g. for the reflected signal :
  • the same derivation can be performed for the transmitted signal.
  • Figures 1 and 2 present a comparison between the theoretical and experimental evolutions of the normalised Stokes parameters with the wavelength for the transmitted and reflected signals, respectively.
  • the FBG parameters used to obtain the theoretical evolutions of the Stokes parameters are chosen close to the parameters of the real FBG.
  • the FBG parameters have been numerically evaluated from the experimental reflected spectrum using a simplex algorithm. The experimental measurements shown in Figs.
  • a polarisation controller is used to modify the state of polarisation of a fully polarised tunable laser source (TLS) such that the input linear SOP is at 45° between the modes x and y of the FBG.
  • TLS fully polarised tunable laser source
  • a polarimeter (POL) measures the transmitted Stokes parameters versus wavelength, with a wavelength step of 10 pm to ensure a good compromise of time and accuracy. Due to the optical circulator in the set-up the polarimeter can also be used to characterise the polarisation properties of the reflected signal . In the experiment the TLS has been tuned from 1533 to 1536 nm. The O x and O y axes of the polarimeter are such that they correspond to the FBG eigenmodes. [0039] As shown in Fig.
  • FIG. 4 presents the reflected spectrum of a 2 mm-long uniform polarisation maintaining (PM) FBG written into hydrogen-loaded PANDA fibre through a 1060 nm period phase mask using a frequency-doubled Argon laser.
  • the two resonant peaks overlap and they are represented by dotted curves.
  • the reflected and transmitted Stokes parameters computed using the physical parameters corresponding to this experimental PM-FBG are shown in Fig. 5.
  • the transmitted Si curve presents one maximum and one minimum at wavelengths corresponding to the two resonant peaks of the PM-FBG. In practice, these wavelengths exhibit different temperature and strain sensitivities since they are characterised by different refractive index.
  • DOP Degree of Polarisation
  • Figures 6 and 7 present the simulated and experimental evolution of the DOP with wavelength for the transmitted and reflected signals, respectively.
  • the simulation is carried out with a wavelength step of 10 pm and considering a source FWHM of 8 pm and an integration time of the measurement device of 1 s.
  • the angle of the input linear state of polarisation is fixed to 45° to confer the same relative contribution to the two peaks.
  • the experimental measurement was made with the set-up described above.
  • the accuracy on the measurement of high DOP (more than 90 %) is guaranteed by the manufacturer of the polarimeter to be within ⁇ 0.5 %.
  • the grating is placed inside an oven regulated by a thermoelectric temperature controller. Temperature is accurately set up to 85°C. The fibre is held unstrained during the thermal coefficients measurement. Strain is applied by different loads placed at the end of the fibre containing the FBG. Temperature is kept at a constant value of 25°C during the strain coefficients measurement.
  • the calibrations are performed using a tunable laser source, a wavemeter and an optical power meter. Figures 9 and 10 present the evolutions obtained from the calibration procedure. In response to a temperature change, the two main reflected peaks of the grating exhibit different sensitivities whereas they shift equally in response to a change of strain.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optical Transform (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

La présente invention concerne un procédé pour évaluer la température et/ou la contrainte influant sur un réseau de Bragg en fibre (FBG), lequel procédé consiste à déterminer le spectre émis ou réfléchi par ce FBG lorsqu'une lumière est injectée dans ce FBG, à déterminer au moins deux quantités caractéristiques de ce spectre émis ou réfléchi, à surveiller l'évolution desdites au moins deux quantités caractéristiques en réponse à un changement de température et/ou de contrainte puis à évaluer la température et/ou la contrainte à l'aide d'informations obtenues à l'étape précédente.
PCT/BE2005/000144 2004-09-22 2005-09-22 Procede pour evaluer l'effet de la temperature et de la contrainte sur le spectre reflechi par un reseau de bragg en fibre WO2006032116A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
EP04447207.4 2004-09-22
EP04447207A EP1640692A1 (fr) 2004-09-22 2004-09-22 Méthode d'évaluation de l'influence de la température et de la contrainte sur le spectre réfléchi par un réseau de Bragg sur fibre
US69017905P 2005-06-13 2005-06-13
US60/690,179 2005-06-13

Publications (1)

Publication Number Publication Date
WO2006032116A1 true WO2006032116A1 (fr) 2006-03-30

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007149230A2 (fr) 2006-06-16 2007-12-27 Luna Innovations Incorporated Discrimination de l'effort et de la tempÉrature distribuÉs dans une fibre À maintien de la polarisation
EP2024718A2 (fr) * 2006-05-23 2009-02-18 Itf Laboratories Inc. Procédé de contrôle et de mesure des propriétés optiques d'un dispositif dans des fibres conservant la polarisation à l'aide d'un réseau de bragg à fibres de référence, et composants à fibres fabriqués par ce procédé

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1986001286A1 (fr) * 1984-08-13 1986-02-27 United Technologies Corporation Jauge de contrainte a fibre optique a resolution spatiale pour mesurer des repartitions de contraintes
JPH1164119A (ja) * 1997-08-11 1999-03-05 Fujikura Ltd 光ファイバ温度歪みセンサおよび温度歪み測定装置
WO1999032863A1 (fr) * 1997-12-19 1999-07-01 Optoplan As Procede d'utilisation d'une fibre optique comme capteur de pression hydrostatique
US20040071400A1 (en) * 2000-04-11 2004-04-15 Karim Haroud Fibre laser sensor
US6788418B1 (en) * 1999-06-15 2004-09-07 Optoplan As Method and apparatus for interrogation of birefringent FBG sensors

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1986001286A1 (fr) * 1984-08-13 1986-02-27 United Technologies Corporation Jauge de contrainte a fibre optique a resolution spatiale pour mesurer des repartitions de contraintes
JPH1164119A (ja) * 1997-08-11 1999-03-05 Fujikura Ltd 光ファイバ温度歪みセンサおよび温度歪み測定装置
WO1999032863A1 (fr) * 1997-12-19 1999-07-01 Optoplan As Procede d'utilisation d'une fibre optique comme capteur de pression hydrostatique
US6788418B1 (en) * 1999-06-15 2004-09-07 Optoplan As Method and apparatus for interrogation of birefringent FBG sensors
US20040071400A1 (en) * 2000-04-11 2004-04-15 Karim Haroud Fibre laser sensor

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 1999, no. 08 30 June 1999 (1999-06-30) *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2024718A2 (fr) * 2006-05-23 2009-02-18 Itf Laboratories Inc. Procédé de contrôle et de mesure des propriétés optiques d'un dispositif dans des fibres conservant la polarisation à l'aide d'un réseau de bragg à fibres de référence, et composants à fibres fabriqués par ce procédé
EP2024718A4 (fr) * 2006-05-23 2011-12-14 Itf Lab Inc Procédé de contrôle et de mesure des propriétés optiques d'un dispositif dans des fibres conservant la polarisation à l'aide d'un réseau de bragg à fibres de référence, et composants à fibres fabriqués par ce procédé
WO2007149230A2 (fr) 2006-06-16 2007-12-27 Luna Innovations Incorporated Discrimination de l'effort et de la tempÉrature distribuÉs dans une fibre À maintien de la polarisation
EP2035792A2 (fr) * 2006-06-16 2009-03-18 Luna Innovations Incorporated Discrimination de l'effort et de la temperature distribues dans une fibre a maintien de la polarisation
EP2035792A4 (fr) * 2006-06-16 2013-05-15 Luna Innovations Inc Discrimination de l'effort et de la temperature distribues dans une fibre a maintien de la polarisation

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