Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/02—Optical fibres with cladding with or without a coating
  • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
  • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
  • G02B6/0208—Refractive index modulation gratings, e.g. Bragg gratings characterised by their structure, wavelength response
  • G02B6/021—Refractive index modulation gratings, e.g. Bragg gratings characterised by their structure, wavelength response characterised by the core or cladding or coating, e.g. materials, radial refractive index profiles, cladding shape
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/02—Optical fibres with cladding with or without a coating
  • G02B6/02295—Microstructured optical fibre
  • G02B6/02309—Structures extending perpendicularly or at a large angle to the longitudinal axis of the fibre, e.g. photonic band gap along fibre axis
• • 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
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
  • G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
  • G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
  • G01K11/3206—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres at discrete locations in the fibre, e.g. using Bragg scattering
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L1/00—Measuring force or stress, in general
  • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
  • G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
  • G01L1/246—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using integrated gratings, e.g. Bragg gratings
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
  • G01M11/08—Testing mechanical properties
  • G01M11/081—Testing mechanical properties by using a contact-less detection method, i.e. with a camera
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
  • G01M11/08—Testing mechanical properties
  • G01M11/083—Testing mechanical properties by using an optical fiber in contact with the device under test [DUT]
  • G01M11/085—Testing mechanical properties by using an optical fiber in contact with the device under test [DUT] the optical fiber being on or near the surface of the DUT
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
  • G01M5/0091—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings by using electromagnetic excitation or detection
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/02—Optical fibres with cladding with or without a coating
  • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
  • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
  • G02B6/02123—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
  • G01J2005/0077—Imaging

Definitions

• the invention relates to the field of integrated health monitoring using fiber optic Bragg grating sensors. It relates to such a sensor as well as methods of locating and installing this sensor on a support.
• the invention applies in particular to the installation or to the verification of the positioning of a Bragg grating optical fiber sensor on a surface of a structure made of composite material, or even within this structure.
• Composite materials are widely used today to replace metallic materials in many applications including aeronautics. They offer the advantage of allowing a significant reduction in the weight of the structures while having similar mechanical properties. However, the aging of composite materials and the associated evolution of their mechanical properties are still poorly understood. Thus, in applications requiring a high level of security, such as aeronautics, the use of these materials is often associated with the integration of different sensors on or in the structure in order to follow this development.
• integrated health control or "structural health monitoring” in English.
• fiber optic sensors with Bragg gratings represent a particularly suitable technology.
• the same Bragg gratings with a fiber optic sensor can comprise several Bragg gratings acting in different wavelength bands and thus providing as many sensitive elements for the same optical fiber: this is called spectral multiplexing of the Bragg gratings.
• the Bragg gratings can also be differentiated in the time domain, or in both the frequency domain and the time domain: we then speak respectively of temporal multiplexing and spectral and temporal multiplexing.
• Bragg gratings with fiber optics can be integrated on the surface of structures or at the very heart of the material, for example in the folds of the composite material, during its manufacture. In all cases, precise positioning of the Bragg gratings on given areas of interest is generally necessary when installing the fiber optic sensors. However, this positioning is made difficult by the lack of visibility of the Bragg network or networks registered in the optical fiber.
• Optical fibers generally have a relatively small diameter, the outside diameter of the protective coating being typically between 150 ⁇ m (micrometers) and 250 ⁇ m and the diameter of the core being typically of the order of ten nanometers in the case of so-called optical fibers. single-mode or even a few tens of micrometers in the case of so-called multimode optical fibers.
• Bragg gratings being inscribed in the core of optical fibers, they also have very small dimensions, usually making them barely visible or barely visible.
• One solution is to mark the optical fiber at the Bragg gratings to allow an indirect location.
• the marking consists for example of depositing an adhesive tape or a layer of paint around the optical fiber.
• the marks remain difficult to spot because the outside diameter of the fiber is small.
• the material on the surface of which the sensor is to be installed is generally dark, which makes it even more difficult to see the marks.
• this surface marking may disappear under the action of products chemical, for example cleaning the surface of the optical fiber with ethanol before bonding it to the surface of a structure.
• the location of the Bragg gratings may still prove useful after the installation of fiber optic sensors on the instrumented structure. This location makes it possible to verify the correct positioning of the measurement points or to find these measurement points, for example during maintenance phases of the structure.
• the location of the Bragg gratings suffers from the same difficulties as during their installation.
• the task can be complicated by adding, after installation of the Bragg grating sensors, a film of adhesive or a protective coating on the surface of the structure. It is then possible that the Bragg gratings are no longer visually identifiable at all. The same is true when fiber optic Bragg grating sensors are embedded in the composite material.
• One solution for locating the Bragg gratings of a fiber optic sensor installed on a structure consists in requesting them locally and individually while injecting a measurement signal into the optical fiber and by monitoring their spectral response.
• the positions for which a variation in the Bragg wavelength is observed correspond to the positions of the Bragg gratings.
• This approach makes it possible to locate Bragg gratings on the surface or embedded in the material.
• scanning can be long and tedious in the case of large areas.
• the heat source must be kept close enough to the surface to ensure sufficient variation in the response of the Bragg gratings and sufficiently distant to avoid damage to the structure. For non-planar surfaces, specific tools would be required to perform the sweep.
• the invention aims to provide a simple solution to allow the localization of the different Bragg gratings of a Bragg grating fiber optic sensor integrated into a structure, both during installation of this sensor and after installation.
• the invention is based on the property of elastic diffusion of microstructures present in an optical fiber.
• a light beam has a wavelength of the same order of magnitude as the dimensions of the microstructures, this light beam is scattered by each of these microstructures. Part of the light beam is thus diffused towards the outside of the optical fiber at the level of each microstructure and can be viewed directly or indirectly.
• the microstructures can correspond to the patterns forming a Bragg grating or be formed specifically in addition to the Bragg grids.
• the first object of the invention is a method of locating a Bragg grating optical fiber sensor on a support, the sensor comprising an optical fiber in which at least one set of microstructures is inscribed, each microstructure being suitable diffusing part of a light beam in a predetermined scattering wavelength range.
• the method comprises a step of injecting, into the optical fiber, a light beam the spectrum of which includes said range of predetermined scattering wavelengths so that each microstructure diffuses part of the beam luminous.
• the second object of the invention is a method of installing a Bragg grating fiber optic sensor on a support.
• the method comprises locating the Bragg grating optical fiber sensor according to the method described above and a step of positioning the optical fiber on the support as a function of the scattered part of the light beam.
• the term “support” designates any mechanical part capable of accommodating on its surface or within it at least one section of optical fiber of a Bragg grating optical fiber optical sensor.
• the support can in particular be made of composite material. It forms, for example, a panel of a nacelle of a turbojet engine or a panel of the fuselage of an aircraft.
• microstructure designates any pattern formed in the optical fiber by a local variation of the optical index.
• Each microstructure has a shape and dimensions allowing a diffusion phenomenon, in particular a diffusion of Mie. It can thus be designated by the term "diffusing microstructure".
• Each microstructure typically has dimensions of the same order of magnitude as the wavelength of the light beam injected into the optical fiber. The dimensions of each microstructure are for example between l / 10 and 10l, where l denotes the wavelength of the light beam or the central wavelength of the spectrum of the light beam.
• each microstructure diffuses part of the light beam injected into the optical fiber. Diffusion implies that part of the light beam escapes radially from the optical fiber, allowing its detection with the naked eye or with the aid of an instrument.
• the position of the microstructures along the optical fiber can thus be identified by the radiation emitted radially by the optical fiber.
• the installation method further comprises a step of projecting a light target onto the support.
• the light target indicates each location where a Bragg grating is to be positioned on the support.
• the light target is for example formed by projection of a light beam whose spectrum includes a range of wavelengths in the visible spectrum.
• the light target comprises for example a set of light points.
• the microstructures and the spectrum of the light beam can be determined so that the microstructures scatter the light beam in part of the visible spectrum. In other words, the microstructures can have dimensions of between 380 nm (nanometers) and 780 nm. The position of the microstructures along the optical fiber can then be seen with the naked eye.
• the microstructures and spectrum can also be determined based on a range of absorption wavelengths of the support material, called the "absorption range".
• the microstructures and the spectrum can be determined so that the microstructures diffuse the light beam in a wavelength range allowing the conversion of the electromagnetic energy of the light beam into heat.
• This embodiment is particularly suitable for locating a Bragg grating optical fiber sensor integrated within the support.
• the localization or installation process may also include a step of acquiring an image of the support in the infrared spectrum. This step can be carried out using an infrared image sensor, commonly called a “thermal camera”. It makes it possible to identify hot spots generated on or in the support by the local diffusion of the light beam by means of microstructures.
• the microstructures of each assembly are arranged so as to form a Bragg grating in the optical fiber.
• the microstructures are arranged so as to diffuse the light beam injected into the optical fiber, but also so as to reflect it.
• the reflection phenomenon is obtained by arranging the microstructures periodically along the longitudinal axis of the optical fiber.
• the microstructures are formed in the core of the optical fiber or at the interface between the core and the sheath of the optical fiber.
• each microstructure has a spherical shape.
• a Bragg grating is then presented in the form of a periodic chain of microbubbles.
• the microbubbles have for example a diameter between l / 10 and 10l, where l denotes the wavelength of the light beam or the central wavelength of the spectrum of the light beam.
• the microstructures can take other forms, for example an ellipsoid or an ellipsoid of revolution.
• a shape that is not perfectly spherical can in particular be useful in order to scatter the light beam anisotropically.
• microstructures can also be in the form of corrugations at the interface between the core and the sheath of the optical fiber.
• the optical fiber comprises, on the one hand, microstructures generating a diffusion phenomenon and, on the other hand, patterns generating a reflection phenomenon.
• each set of microstructures is positioned in the vicinity of a Bragg grating.
• the scattering of part of the light beam occurs near the Bragg grating, making its position visible along the optical fiber.
• the microstructures can be arranged in the core of the optical fiber, for example upstream and / or downstream of the Bragg grating.
• the microstructures can be arranged in the optical fiber sheath. They can in particular be arranged in the sheath in the vicinity of the interface between the core and the optical sheath. They can be arranged upstream, downstream and / or parallel to the Bragg network.
• the arrangement of microstructures in the optical fiber cladding is suitable when the diffusion and reflection phenomena occur in distinct wavelength ranges. A light beam having a wavelength range outside the guide wavelength range of the optical fiber can then propagate in the sheath and be scattered by the microstructures.
• the arrangement of the microstructures in the sheath of the optical fiber has the advantage of not impacting the propagation of the light beam in the useful wavelength range of the Bragg grating.
• the invention also relates to a Bragg grating optical fiber sensor comprising an optical fiber in which is inscribed at least one set of patterns forming a Bragg grating.
• the optical fiber further comprises a set of microstructures in the vicinity of each Bragg grating, the microstructures being distinct from the patterns forming the Bragg grating, each microstructure being capable of diffusing part of a light beam within a predetermined scattering wavelength range.
• the optical fiber comprises a core and an optical sheath and the microstructures are arranged in the optical sheath.
• the microstructures are arranged in the vicinity of the heart, that is to say closer to the internal peripheral surface of the optical sheath than to the external peripheral surface of the optical sheath.
• microstructures could also be placed in the core of the optical fiber or at the interface between the core and the optical sheath.
• the microstructures are for example in the form of spheres or ellipsoids of revolution. They can also be in the form of corrugations at the interface between the heart and the optical sheath.
• each Bragg grating is arranged to reflect a light beam in a wavelength range of Predetermined Bragg, distinct from the predetermined scattering wavelength range.
• the Bragg wavelength range and the scattering wavelength range may partially overlap or be disjoint.
• diffusion and reflection phenomena occur in different wavelength ranges.
• the microstructures of each assembly form a Bragg grating
• the microstructures are distinct from the patterns of the Bragg grating, this implies that the microstructures have dimensions that are distinct from the period of the patterns of the Bragg grating.
• each Bragg grating is arranged to reflect a light beam in a range of predetermined Bragg wavelengths, included in the range of predetermined scattering wavelength.
• the two wavelength ranges can be identical.
• FIG. 1 shows a first example of a Bragg grating optical fiber sensor that can be used in the implementation of the location or installation method according to the invention
• FIG. 2 shows a second example of a Bragg grating optical fiber sensor that can be used in the implementation of the location or installation method according to the invention
• FIG. 3 shows a third example of a Bragg grating optical fiber sensor that can be used in the implementation of the location or installation method according to the invention
• FIG. 4 shows an example of a method of locating a Bragg grating optical fiber sensor according to the invention
• FIG. 5 shows an example of a method of installing a Bragg grating fiber optic sensor according to the invention
• FIG. 1 represents a first example of a Bragg grating optical fiber sensor which can be used in the implementation of the localization or installation method according to the invention.
• the optical fiber sensor 10 comprises an optical fiber 11 comprising a heart 111 and an optical sheath 112 surrounding the heart 111.
• the heart 111 and the optical sheath 112 extend longitudinally along an axis X.
• the optical fiber sensor 10 further comprises a set of microbubbles 12 formed in the heart 111 of the optical fiber 11.
• the microbubbles 12 are arranged on the longitudinal axis X of the optical fiber 11. They have a refractive index different from that of the heart 111 of optical fiber 11.
• Each microbubble 12 is in the form of a sphere whose diameter is between 10 nm (nanometers) and 1 mm (millimeter). The diameter can in particular be between 380 nm and 780 nm, in order to correspond to the wavelengths of the visible spectrum, or between 780 nm and 1 mm, in order to correspond to the infrared spectrum. It is for example 400 nm.
• the microbubbles 12 provide a first function of diffusion of a light beam conveyed by the optical fiber 11. In other words, they form a diffusing structure. The diameter of the spheres must therefore correspond substantially to the wavelength of the light beam for which diffusion is sought.
• the microbubbles 12 are distributed periodically along the X axis with a pitch of between 10 nm and 1 mm.
• the pitch can in particular be between 380 nm and 780 nm or between 780 nm and 1 mm. It is determined by the distance separating the centers of two adjacent microbubbles 12.
• the microbubbles 12 provide a second function for reflecting the light beam conveyed by the optical fiber. They form patterns of a Bragg grating.
• the pitch must correspond to the wavelength for which a reflection is sought. This wavelength is called the "Bragg wavelength”. It should be noted that the Bragg wavelength may differ from the scattering wavelength.
• the optical fiber 11 may comprise a plurality of sets of microbubbles 12 distributed along the optical fiber 11 in order to form as many Bragg gratings and diffusing structures.
• the microbubbles may have dimensions and / or steps which differ depending on the set to which they belong. Thus, the diffusion and reflection phenomena appear for different wavelengths.
• the microbubbles have identical dimensions in the different sets but different steps between the different sets.
• Bragg gratings can be located using a light beam having a single wavelength or a relatively narrow range of wavelengths.
• Bragg gratings respond to mechanical constraints and temperature changes at different wavelengths and thus constitute individual sensors.
• FIG. 2 represents a first example of a Bragg grating optical fiber sensor according to the invention and a second example of such a sensor that can be used in the implementation of the location or installation method according to the invention.
• the optical fiber sensor 20 comprises an optical fiber 21 comprising a heart 211 and an optical sheath 212 surrounding the heart 211, the heart 211 and the optical sheath 212 extending longitudinally and concentrically along an axis X.
• the sensor fiber optic 20 further comprises a set of microbubbles 22 and a set of patterns 23 formed in the core 211 of the optical fiber 21.
• the microbubbles 22 and the patterns 23 have a refractive index different from that of the core 211 of the fiber optics 21.
• the microbubbles 22 are for example photo-registered by femtosecond laser. They are arranged on the longitudinal axis X of the optical fiber 21, on either side of the patterns 23. The diameter of the microbubbles is determined as a function of the wavelength at which the diffusion phenomenon is desired.
• the patterns 23 having a cylindrical shape whose axis corresponds to the axis X of the optical fiber 21. They extend radially over the entire section of the core 211 of the optical fiber 21.
• the patterns 23 are distributed periodically over the along the X axis of the optical fiber 21. They thus form a Bragg grating whose Bragg wavelength depends on the pitch separating the patterns and on the refractive index of the heart 211.
• microbubbles could also be used as patterns for the Bragg grating.
• the microbubbles 22 are arranged on either side of the Bragg grating, that is to say upstream and downstream of the Bragg grating. They do not directly indicate the position of the Bragg grating but they allow its precise location by framing it. In other embodiments, the microbubbles could be arranged only on one side of the Bragg grating.
• FIG. 3 represents a second example of a Bragg grating optical fiber sensor according to the invention and a third example of such a sensor that can be used in the implementation of the location or installation method according to the invention.
• the optical fiber sensor 30 comprises an optical fiber 31 comprising a heart 311 and an optical sheath 312 surrounding the heart 311, the heart 311 and the sheath optics 312 extend longitudinally and concentrically along an X axis.
• the optical fiber sensor 30 further comprises a set of microbubbles 32 formed in the optical sheath 312 and a set of patterns 33 formed in the heart 311.
• the microbubbles 32 and the patterns 33 have a refractive index different from that of the core 311.
• the patterns 33 are identical to the patterns 23 of the optical fiber sensor 20 shown in FIG. 2.
• the optical fiber sensor 30 differs from the optical fiber 20 of FIG. 2 in that the microbubbles 32 are arranged in the optical sheath 312, in the vicinity of the patterns 33 of the Bragg grating.
• the microbubbles 32 can be arranged in a single plane passing through the longitudinal axis X of the optical fiber 31 or in several planes passing through the axis X.
• the microbubbles 32 are preferably positioned in the vicinity of the interface between the core 311 and the optical sheath 312.
• the diffusing structure is always produced by microbubbles.
• any other type of microstructure capable of diffusing a light beam at least partially guided in the optical fiber could be used.
• the microstructures could have an ellipsoid shape.
• the optical fiber could include a protective coating enveloping the optical sheath. This protective coating can potentially partially pass the scattered light beam.
• FIG. 4 represents an example of steps of a method for locating a Bragg grating optical fiber sensor according to the invention.
• the optical fiber sensor is inserted within a structure or mounted on a surface of this structure.
• the Bragg grating fiber optic sensor can in particular be one of the sensors described above.
• the location method 40 includes a step 41 of injecting a light beam into the optical fiber of the optical fiber sensor.
• the light beam has a spectrum determined as a function of a range of absorption wavelengths of the material of the structure. In other words, the spectrum is determined so that the local scattering of the light beam causes the structure to heat up.
• the power of the light beam is also determined so as to cause a local temperature variation sufficient for the structure.
• a step 42 an infrared image of the structure is acquired.
• an image acquisition of the structure is carried out in the infrared spectrum.
• This step 42 can be carried out in parallel with step 41, for example after a predetermined duration, allowing local heating of the structure, or after step 41.
• the infrared image is converted into the spectrum visible to allow an operator to locate hot spots on the image indicating the presence of a diffusing structure and therefore of a Bragg grating.
• the light beam may have a spectrum spreading at least partly in the infrared domain.
• the scattered light beam can be directly detected by the infrared sensor without requiring the structure to heat up.
• FIG. 5 represents an example of steps of a method of installing a Bragg grating optical fiber sensor according to the invention.
• the Bragg grating fiber optic sensor can in particular be one of the sensors described above.
• the installation method 50 comprises a step 51 of injecting a light beam into the optical fiber of the sensor, a step 52 of projecting a light target onto a support, a step 53 of positioning the Bragg gratings and a step 54 of fixing the fiber optic sensor.
• the light beam injected into the optical fiber preferably comprises a range of wavelengths in the visible spectrum. The scattered part of this light beam can thus be observed directly by an operator.
• the light target comprises a set of light points each defining a location on the support intended to accommodate a Bragg grating.
• Step 53 of positioning the Bragg gratings consists in making each section of optical fiber diffusing the light beam coincide with a light point on the target.
• Stage 54 of fixing the fiber optic sensor consists in fixing the fiber optic sensor on the support so as to maintain the Bragg gratings on the desired locations.
• the optical fiber sensor can in particular be bonded to the support or coated in the support by depositing a layer of material.
• the step 52 of projection of the light target is carried out in parallel with the step 51 of injection of the light beam and of the step 53 of positioning of the Bragg gratings. Step 52 can also be continued during and after step 54 of fixing the sensor.
• FIG. 6 illustrates the method of installing a Bragg grating optical fiber sensor on a support according to the invention.
• the optical fiber sensor 60 comprises an optical fiber 61 in which are integrated twelve Bragg gratings individually identifiable by diffusing structures 62.
• a light beam is injected into the optical fiber 61 and is partly scattered by each diffusing structure 62.
• a light target is projected onto a support 64 in order to form twelve light points 65 indicating a desired location for a Bragg grating.
• the optical fiber 61 is positioned so as to extend by snaking on a support 64 by making the diffusing structures 62 correspond with the light points 65.

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• 2018
  • 2018-06-21 FR FR1855475A patent/FR3082954B1/fr active Active
• 2019
  • 2019-06-19 WO PCT/FR2019/051504 patent/WO2019243745A1/fr active Application Filing
  • 2019-06-19 US US17/253,983 patent/US11733450B2/en active Active
  • 2019-06-19 CN CN201980041856.4A patent/CN112534319B/zh active Active
  • 2019-06-19 EP EP19742870.9A patent/EP3811130A1/de active Pending

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