• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The present invention relates to an optical fiber curvature sensor. According to the invention, two longitudinal periodic modulation networks (R1, R2) of the refractive index of the core of the optical fiber are inscribed in the fiber (F) one behind the other or one on the other. These networks are configured to reflect wavelength λ1 and λ2 respectively such that λ1 = λB + ΔλB1 and λ2 = λB + ΔλB2, where λB is the Bragg wavelength of the arrays and ΔλB1 and ΔλB2 are significant offsets. the temperature, deformations and curvature of the optical fiber. According to the invention, the two networks are defined so that the quantities ΔλB1 and ΔλB2 have substantially identical temperature sensitivities and deformations and substantially opposite curvature sensitivities.
    公开号:FR3049342A1
    申请号:FR1652495
    申请日:2016-03-23
    公开日:2017-09-29
    发明作者:Romain Guyard；Yann Lecieux；Dominique Leduc；Cyril Lupi
    申请人:Centre National de la Recherche Scientifique CNRS；Universite de Nantes；
    IPC主号:
    专利说明:

    FIBER OPTIC CURVE SENSOR AND MEASURING DEVICE COMPRISING SAID SENSOR
    Technical area
    The present invention relates to the field of measuring the curvature of a structure by means of an optical fiber. The invention more particularly relates to an optical fiber curvature sensor and a measuring device comprising said sensor. The invention finds particular applications in the field of energy for the measurement of curvature of cables, such as submarine cables, in the field of robotics for the measurement of curvature of robot arms or in the medical field for the measurement of umbilical curvature of endoscopes.
    State of the art
    A number of optical fiber curvature sensors are known. The sensor is placed on the element whose radius of curvature is to be measured so that the optical fiber of the sensor matches the shape of said element. The measurement of the radius of curvature then amounts to measuring the radius of curvature of the optical fiber.
    Some fiber optic sensors are based on the creation of a fault zone in the optical fiber generally obtained by polishing the sheath. This zone induces intensity losses when it is curved, which losses depend on the radius of curvature. The determination of the losses then makes it possible to determine the radius of curvature of the optical fiber.
    Another technique is to measure intermodal interference taking advantage of the sensitivity of the sheath modes to the curvature. This technique, however, requires complex architectures, namely a micro-structured fiber inscribed in a stretched area welded between two optical fibers.
    Finally, other methods are based on the use of fibered index networks such as a Bragg grating or a long period network. These two types of networks are networks registered in the optical fiber. They differ in their step which is of a few hundred nanometers for a Bragg grating and a few tens or even hundreds of micrometers for a long period network.
    A Bragg grating sensor is shown in Figure 1. The Bragg grating R is inscribed in the core of the optical fiber. The Bragg grating reflects a specific frequency, called the Bragg Ag wavelength, and transmits all other frequencies.
    This wavelength of Bragg λg is proportional to the pitch of the grating (Λ) and to the effective index of the core of the fiber (Ueff):
    (1)
    Any modification of any of these parameters proportionally moves the Bragg wavelength. Since the Bragg wavelength depends on the grating pitch (Λ), the fiber index gratings can therefore be fabricated to reflect different wavelengths of Bragg.
    The stress variations applied to the fiber and the temperature variations of the fiber affect both the effective refractive index neff and the pitch A of the fiber index grating, which results in an offset Δλ of the length of the fiber. reflected wave. Strain is understood to mean any type of force applied to the optical fiber, such as a torsion, compression, tension or curvature force.
    The wavelength shift Δλ of the light reflected with respect to the Bragg λg wavelength thus depends on the curvature of the optical fiber but also on the temperature of the fiber and the other stresses applied to the optical fiber. This wavelength shift therefore does not provide a direct measurement of the radius of curvature of the optical fiber. Summary of the invention
    An object of the invention is to overcome all or part of the disadvantages of the aforementioned prior art.
    More particularly, an object of the invention is to provide an optical fiber curvature sensor using the fibrated index network technique but making it possible to directly determine the radius of curvature from wavelengths.
    Another object of the invention is to provide a curvature sensor that is simple to produce and has a small overall size. For this purpose, the invention proposes a curvature sensor comprising: at least one optical fiber comprising a core and at least one first sheath surrounding said core, said core and said at least one first cladding having different refractive indices, said at least one optical fiber further comprising an end for receiving polychromatic light, a first longitudinal periodic modulation network of the refractive index of the core of the optical fiber, called first grating, inscribed in the heart of said at least one an optical fiber and configured to reflect a wavelength of light, said wavelength being shifted by an amount relative to a reference wavelength and the amount being sensitive to temperature, deformations and the curvature of the optical fiber, - a second longitudinal periodic modulation network of the refractive index of the core of the optical fiber, called two xth network, inscribed in the heart of said at least one optical fiber and configured to reflect a wavelength λ 2 of the light, said wavelength λ 2 being shifted by an amount relative to said reference wavelength Δg and the quantity being sensitive to the temperature, the deformations and the curvature of the optical fiber, said first and second networks being defined so that the quantities and Aλg2 have sensitivities to temperature and substantially identical deformations and sensitivities to the curvature substantially opposite.
    The sensor of the invention thus delivers reflected wavelengths = λg + Δλg ^ and A2 = Ag + λgj. The two networks reflecting these wavelengths having identical behaviors with respect to the temperature and to the deformations but opposite with respect to the curvature, when subtracting these two wavelengths, the difference Δλ = -Δ2 = AΔg ^ - Aλgj depends solely on the curvature of the fiber. It is thus possible to directly deduce the curvature of the networks from the difference Δλ.
    According to a particular embodiment, the sensor comprises a single optical fiber and the first and second networks are Bragg gratings inscribed one behind the other in the heart of the optical fiber, said first and second networks having effective indices. different ways.
    According to another particular embodiment, the sensor comprises a single optical fiber and the first and second networks are inscribed on one another, the first network being a Bragg grating and the second network being a long-period grating. In this embodiment, the optical fiber advantageously comprises a second sheath surrounding said first sheath, said second sheath having a refractive index lower than the refractive index of the first sheath.
    According to another embodiment, the sensor comprises a single optical fiber and a plurality of Bragg gratings inscribed one behind the other in the heart of the optical fiber, said plurality of Bragg gratings being arranged in such a way as to behave like the association of a Bragg network and a long-term network. More particularly, the sensor comprises a super-structured Bragg grating, commonly called SFBG for Superstructured Fiber Bragg
    Grating in English language. To realize this super-structured network, one inscribes in the heart of the fiber a hundred short Bragg gratings in series. All Bragg networks are identical (not even, same length, same index modulation). The networks are regularly spaced a distance Llpg · Their length L ^ bg is a fraction of Llpg- The total length of the structure is of the order of a centimeter, like a conventional network. This structure behaves like the association of a Bragg grating of Lfbg step and a long period network of steps.
    According to another particular embodiment, the sensor comprises first and second optical fibers in a resin bar having an axis of symmetry, the first and second networks being respectively inscribed in said first and second optical fibers. In this embodiment, the first and second gratings are advantageously inscribed at substantially identical positions along said axis of symmetry and said first and second optical fibers are placed at equal distances from said axis of symmetry.
    In this embodiment with two optical fibers, said first and second networks may be Bragg gratings. According to a variant, said first and second networks are long-period networks. The invention also relates to a device for measuring the curvature of a longitudinal element, characterized in that it comprises: a curvature sensor as defined above, said at least one optical fiber of the curvature sensor being disposed along said element, a polychromatic light source for emitting light through said at least one optical fiber, and - a circuit for receiving wavelengths
    and determining the curvature of said element from said wavelengths.
    This device makes it possible to deliver in a simple manner a curvature value of the longitudinal element. Other advantages may still appear to those skilled in the art on reading the examples below, illustrated by the appended figures, given for illustrative purposes.
    Brief Description of the Figures - Figure 1 shows a schematic view of a curvature sensor of the prior art; FIG. 2 is a diagram showing the evolution of the Bragg AΔg length shift as a function of the radius of curvature R for 3 average effective network index values; FIG. 3 represents a schematic view of a sensor of curvature according to the invention; FIG. 4 represents a sectional view of an optical fiber of the curvature sensor of the invention; FIG. 5 represents the refractive index profile of the optical fiber of FIG. 4; FIG. 6 is a diagram showing the evolution of the offsets and AΔg 2 of the Bragg lengths of the two networks of the curvature sensor of FIG. 3 as a function of the curvature 1 / R; FIG. 7 is a diagram showing the evolution of the shift Δλ = Δλ ^^^ - ΧΧ ^^ 2 as a function of the curvature 1 / R; FIG. 8 is a schematic view of a curvature measuring device comprising the sensor of FIG. 3.
    DETAILED DESCRIPTION OF THE INVENTION The invention is based on the fact that the variation of the resonant length (or Bragg wavelength λg) of an index grating such as a Bragg grating or a grating. long period is governed by the average effective index ngff of the network.
    When such a network is bent, the resonance wavelength shifts. The offset is given by:
    (2) where Λ is the pitch of the grating, Δη ^^^ is the variation of the effective index n ^^^ of the core of the fiber with the curvature, δη ^^ is the average effective index of the grating and is the variation of the coupling coefficient of the network with the curvature. These two factors depend only on the optical fiber and move in opposite directions: n increases when the radius of curvature decreases while decreases as the radius of curvature decreases. We see in relation (2) that the variation of the coupling coefficient is multiplied by the average effective index δη ^^. Therefore, depending on this parameter, the variation of coupling coefficient Δκ ^^^ can either be negligible compared to the variation of effective index Δη ^^^, or compensate for it or be much larger than this one. It can be deduced from the foregoing that the variation in resonance wavelength Δλβ can be either negative, zero or positive, as illustrated in FIG. 2 for a Bragg grating. By playing on the average effective index 5n ^^ of the network, it is possible to set the wavelength shift Δλβ to a negative, zero or positive value for a given radius of curvature R.
    In the example of FIG. 2, an offset Δλβ is obtained as a function of the radius of curvature R which is: - positive for δη ^^ = δ.ΙΟ ^ "*; - zero for δη ^^ = 1.62.1 · - The idea of the invention is thus to associate two index gratings having the same sensitivity to the deformation and to the temperature but opposite sensitivities as a function of the curvature.
    According to the invention, the proposed sensor therefore comprises two fiber index gratings having the same sensitivity to temperature and deformations but opposite responses as a function of the radius of curvature. A schematic diagram of this sensor is shown in FIG.
    Referring to Figure 3, the sensor comprises two Bragg gratings R1 and R2 arranged in series on an optical fiber F. The two networks are photoinscribed in the heart of the optical fiber. These two networks being made of the same material, they have the same sensitivity to temperature. The two arrays R1 and R2 are also designed to have the same sensitivity to deformations (torsion, compression, tension or stretch) and opposite responses to the curvature.
    Thus, subjected to the same conditions of temperature, deformations and curvature, the two sensors R1 and R2 react in the following manner:
    (3) where is the wavelength variation of the grating R1, is the wavelength variation of the grating R2, T is the temperature of the optical fiber, where j is the sensitivity of the grating to the temperature, ε represents the deformation of the fiber, is the sensitivity to deformation, + f (R) denotes the wavelength shift due to the curvature in the grating R1 and -f (R) denotes the offset of the wavelength due to the curvature in the network R2.
    When the sensor is subjected to a polychromatic light, the network RI reflects a light having a wavelength λg + and the grating R2 reflects a light having a wavelength
    If we subtract the reflected wavelengths and λj, we obtain a magnitude Δλ independent of the temperature and the deformations and which depends only on the radius of curvature R:
    It is thus possible to obtain directly the radius of curvature R from the wavelength shift Δλ.
    The optical fiber F is a monomode and index jump fiber having the following characteristics: - core radius: ai = 4.2 μm; fiber core index: ni / - outer radius of the sheath: a2 = 62.5 μm; - index of the core of the fiber: U2.
    The dimensions and the index profile of the optical fiber are visible in FIGS. 4 and 5. The index of cladding n2 is evaluated from the Sellmeier relation applied to the silica:
    (4) where A, B, C, D and E are the temperature-dependent coefficients of Sellmeier by the relation X = aT + b, with T the temperature expressed in degrees centigrade.
    The coefficients a and b of the Sellmeier A, B, C, D and E of the silica are expressed in the following table:
    The index of the core ni is deduced from the index of the cladding U2 by the relation: ni = 1, 0036 ÎI2.
    The network RI has a length L1 = 8.9 mm, a grating pitch Ai = 541, 1 nm and an average effective index = 1 · 10 *. The grating R2 has a length L2 = 250 μm (micrometers), a grid pitch A2 = 541.4 nm and an average effective index δη ^^ 2 = 3.5 · 10 "^ ·.
    The wavelengths and A2 reflected respectively by the networks R1 and R2 (at rest) are then: = 65, 2 nm and A2 = 1570 nm.
    These resonant wavelengths are sufficiently spaced apart to avoid any overlapping of the resonances or inversion of their position in the curvature range
    As can be seen in FIG. 6, the offset of the wavelength of the grating R1 decreases with the curvature of the fiber while the shift of the wavelength Aλg2 of the grating R2 follows an opposite curve.
    The sensitivity to the axial deformation () of the network
    Ri is identical to that of the network R2 and is evaluated at 1.23 pm / με (where 1 με corresponds to a deformation of 10 ^ m / m). Similarly, the temperature sensitivities () of the two arrays R1 and R2 are substantially identical, of the order of 12.02 pm / ° C ^ ® '^^.
    As a result, the subtraction of the two wavelength signals and λj, Δλ = - Aj = AAg2 - AAg2, is independent of the temperature T and the deformations ε and depends solely on the curvature of the optical fiber. The curve of FIG. 7 illustrates the dependence between wavelength shift ΔΑ and the curvature of the sensor of FIG. 3. The dependence is nonlinear. The simple measurement of the offset ΔΑ makes it possible to obtain the radius of curvature from this curve.
    In the embodiment illustrated above, the networks R1 and R2 are Bragg gratings inscribed one behind the other in the optical fiber F. As indicated above, these two networks differ only in their mean effective indices and δη ^ ^ 2) 'their steps (Λχ and Λ2) and their lengths (Li and L2) so that their dependencies on the curvature are opposite.
    According to an alternative embodiment, the networks R1 and R2 are respectively a Bragg grating and a long period grating inscribed in the core of the optical fiber F on one another. The optical fiber F advantageously comprises two sheaths. The second sheath serves to isolate the light that propagates in the first sheath of the external environment. Its refractive index is lower than that of the first sheath. The two networks advantageously have the same length. The long-period grating is designed to have only a resonance in the measured spectral range. Moreover, the resonant mode is chosen so as to have the same sensitivity to deformation as the Bragg grating. The average effective indices of the two networks are such that the responses of the two networks to curvatures are opposite.
    According to another embodiment, the sensor comprises a single optical fiber and a plurality of Bragg gratings inscribed one behind the other in the core of the optical fiber, the plurality of Bragg gratings being arranged in such a way as to behave like the association of a Bragg network and a long-term network.
    More particularly, the sensor comprises a super-structured Bragg grating, commonly called SFBG for Superstructured Fiber Bragg Grating in English. To realize this super-structured network, one inscribes in the heart of the fiber a hundred short Bragg gratings in series. All Bragg networks are identical (not even, same length, same index modulation). The networks are regularly spaced a distance Llpg. Their Lfbg length is a fraction of Llpg. The total length of the structure is of the order of a centimeter, like a classical network.
    This structure behaves like the association of a Bragg grating of Lfbg step and a long period network of steps.
    According to another alternative embodiment, the sensor comprises two optical fibers arranged in a resin bar having an axis of symmetry. The two fibers are advantageously placed at equal distances from the axis of symmetry of the bar. The IN network is inscribed in the first fiber and the second network is inscribed in the second fiber. They are advantageously registered at substantially identical positions along the axis of symmetry. In this embodiment, the networks R1 and R2 may be Bragg gratings or long-period networks. In the latter case, the optical fibers advantageously comprise two sheaths. As for the other embodiments, the average effective indices of the two networks are selected so that the responses of the two networks to the curvatures are opposite.
    As explained above, the wavelengths and A2 from the sensor make it possible to determine the radius of curvature. These two wavelengths must therefore be received and processed to obtain the radius of curvature. The invention thus relates, more generally, to a device for measuring the curvature of a longitudinal element comprising: a curvature sensor according to one of the embodiments described above, the optical fiber of the curvature sensor being arranged along the element whose radius of curvature is to be measured. a polychromatic light source for emitting light through the optical fiber of the sensor; and - a circuit for receiving the wavelengths = λg + and λ2 = Δg + ΔΔg2 from the curvature sensor and determining the curvature of the sensor. element from said wavelengths.
    Such a device is shown schematically in FIG. 8. It comprises a white or polychromatic light source 10, a curvature sensor 11 as defined above for receiving the light emitted by the source 10 and delivering corresponding wavelengths and λ 2. at the wavelengths reflected by the gratings R1 and R2 of the sensor, a circuit 12 for determining the radius of curvature R of the element from the wavelengths and λ 2. A coupler 13 is used for the transmission of the polychromatic light from the source 10 to the sensor 11 and the transmission of the wavelengths and A2 of the sensor 11 to the circuit 12. The circuit is for example an interferometer equipped with processing means to realize the subtraction to X = - X ^ and to deduce, for example by means of a table of correspondence (or look-up table in English language), the radius of curvature R of the element.
    Of course, it is possible to have several curvature sensors according to the invention along the element, with offset resonant wavelengths, to measure the curvature at several points thereof.
    The sensor and the device presented here have many advantages: - simplicity of manufacture; - Simplicity of implementation, - reduced size of the sensor; obtaining the radius of curvature directly from a difference in wavelength; - Insensitivity to drops in intensity of emitted or reflected light.
    Furthermore, the proposed measurement being independent of temperature and deformation, the invention can be used in many fields, especially in applications where the sensor can be subjected to temperature gradients, for example in marine applications or medical. The invention is described in the foregoing by way of example. It is understood that one skilled in the art is able to realize different embodiments of the invention, for example by combining the various characteristics above taken alone or in combination, without departing from the scope of the invention .
    权利要求:
    Claims (10)
    [1" id="c-fr-0001]
    1) Curvature sensor comprising: - at least one optical fiber (F) having a core and at least a first sheath surrounding said core, said core and said at least one first sheath having different refractive indices, said at least one an optical fiber further comprising an end for receiving polychromatic light, - a first longitudinal periodic modulation network of the refractive index of the core of the optical fiber, called the first grating (RI), inscribed in the core of said minus one optical fiber and configured to reflect a wavelength of light, said wavelength being shifted by an amount relative to a reference wavelength λg and said amount being temperature sensitive, deformed and the curvature of the optical fiber, characterized in that it further comprises at least one second longitudinal periodic modulation network of the index of r fraction of the core of the optical fiber, called second grating (R2), inscribed in the core of said at least one optical fiber and configured to reflect a wavelength λj of light, said wavelength λ 2 being shifted by a quantity relative to said reference wavelength λg and said quantity Aλg2 being sensitive to the temperature, the deformations and the curvature of the optical fiber. said first and second networks being defined so that the quantities Δλβ ^ and have substantially identical temperature and deformation sensitivities and substantially opposite curvature sensitivities.
    [0002]
    2) A sensor according to claim 1, characterized in that it comprises a single optical fiber and in that the first and second networks (R1, R2) are Bragg gratings inscribed one behind the other in the heart of the optical fiber, said first and second networks having average effective indices (, δη ^^ 2 ^ different.
    [0003]
    3) A sensor according to claim 1, characterized in that it comprises a single optical fiber and in that the first and second networks (R1, R2) are inscribed on one another, the first network being a network of Bragg and the second network being a long-lived network.
    [0004]
    4) Sensor according to claim 3, characterized in that the optical fiber comprises a second sheath surrounding said first sheath, said second sheath having a lower refractive index of the refractive index of the first sheath.
    [0005]
    5) Sensor according to claim 1, characterized in that it comprises a single optical fiber and a plurality of Bragg gratings inscribed one behind the other in the heart of the optical fiber, said plurality of Bragg gratings being arranged in order to behave like the association of a Bragg network and a long-lived network.
    [0006]
    6) Sensor according to claim 1, characterized in that it comprises first and second optical fibers in a resin bar having an axis of symmetry, the first and second networks being respectively inscribed in said first and second optical fibers.
    [0007]
    7) A sensor according to claim 6, characterized in that the first and second networks (R1, R2) are arranged at substantially identical positions along said axis of symmetry and said first and second optical fibers are placed at equal distances from said axis of symmetry.
    [0008]
    8) Sensor according to claim 6 or 7, characterized in that said first and second networks (R1, R2) are Bragg gratings.
    [0009]
    9) Sensor according to claim 6 or 7, characterized in that said first and second networks (R1, R2) are long-period networks.
    [0010]
    10) Device for measuring the curvature of a longitudinal element, characterized in that it comprises: a curvature sensor (11) according to any one of claims 1 to 9, said at least one optical fiber of the curvature sensor being disposed along said element, - a polychromatic light source (10) for emitting light through said at least one optical fiber, and a circuit (12) for receiving the wavelengths = λg + and λ2 = λg + AÎg2 and determine the curvature of said element from said wavelengths.
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    EP3433575B1|2020-04-15|
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    FR3049342B1|2016-03-23|2018-04-13|Universite De Nantes|FIBER OPTIC CURVE SENSOR AND MEASURING DEVICE COMPRISING SAID SENSOR|FR3049342B1|2016-03-23|2018-04-13|Universite De Nantes|FIBER OPTIC CURVE SENSOR AND MEASURING DEVICE COMPRISING SAID SENSOR|
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    法律状态:
    2017-03-07| PLFP| Fee payment|Year of fee payment: 2 |
    2017-09-29| PLSC| Publication of the preliminary search report|Effective date: 20170929 |
    2018-03-16| PLFP| Fee payment|Year of fee payment: 3 |
    2020-03-31| PLFP| Fee payment|Year of fee payment: 5 |
    2021-03-30| PLFP| Fee payment|Year of fee payment: 6 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1652495|2016-03-23|
    FR1652495A|FR3049342B1|2016-03-23|2016-03-23|FIBER OPTIC CURVE SENSOR AND MEASURING DEVICE COMPRISING SAID SENSOR|FR1652495A| FR3049342B1|2016-03-23|2016-03-23|FIBER OPTIC CURVE SENSOR AND MEASURING DEVICE COMPRISING SAID SENSOR|
    PCT/FR2017/050685| WO2017162992A1|2016-03-23|2017-03-23|Optical fibre curvature sensor and measurement device comprising said sensor|
    US16/087,290| US11131544B2|2016-03-23|2017-03-23|Optical fibre curvature sensor and measurement device comprising said sensor|
    EP17716579.2A| EP3433575B1|2016-03-23|2017-03-23|Optical fibre curvature sensor and measurement device comprising said sensor|
    DK17716579.2T| DK3433575T3|2016-03-23|2017-03-23|BURNING SENSOR WITH OPTICAL FIBER AND MEASURING DEVICE INCLUDING THE SENSOR|
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