CN113446962B - Temperature-insensitive curvature sensor based on strong-coupling multi-core fiber, curvature measuring device and method - Google Patents
Temperature-insensitive curvature sensor based on strong-coupling multi-core fiber, curvature measuring device and method Download PDFInfo
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Abstract
The invention discloses a temperature insensitive curvature sensor based on a strong coupling multi-core optical fiber, a curvature measuring device and a method, wherein the curvature sensor comprises: the strong coupling multi-core optical fiber comprises a central fiber core and six peripheral fiber cores which are arranged at the periphery of the central fiber core in a regular hexagon shape, wherein the outlines of the central fiber core and the peripheral fiber cores are regular hexagons; seven FBGs with the same central wavelength are respectively written into the same positions of the central fiber core and the six peripheral fiber cores; and the first single-mode fiber and the second single-mode fiber are respectively aligned and welded with two ends of the central fiber core. When the strongly coupled multi-core optical fiber is bent, the reflection spectrum of the strongly coupled multi-core optical fiber does not have obvious wavelength shift; along with the bending of the optical fiber, the mode distribution of two supermodes can be changed, and the effective refractive index difference can be changed; the size of the curvature radius determines the accumulated phase difference variable quantity between the two supermodes participating in interference; so that the two supermodes interfere to cause a change in the depth of the notch, while the temperature is hardly affected.
Description
Technical Field
The invention relates to the field of curvature detection, in particular to a temperature insensitive curvature sensor based on a strong coupling multi-core optical fiber, a curvature measuring device and a method.
Background
Curvature is an important parameter for describing the shape of an object, and curvature (curvature) of a curve is the rotation rate of a tangential direction angle to an arc length at a certain point on the curve, and is defined by differentiation, and indicates the degree of deviation of the curve from a straight line. The numerical value of the degree of curve bending at a certain point is mathematically expressed. The larger the curvature, the more curved the curve is. The change trend of the object shape can be known through the measurement of the curvature. The curvature sensor has wide application prospects in the aspects of structural body health monitoring, aerospace, robotics, surface shape measurement and the like, wherein the curvature sensor based on the fiber grating has the advantages of small volume, light weight, strong anti-electromagnetic interference capability, quasi-distributed measurement and the like, and is favored by domestic and foreign scholars.
Fiber gratings are one of the most rapidly growing passive devices of optical fibers in recent years. Due to the unique advantages, the fiber-optic fiber has wide application prospect in the fields of fiber-optic communication, fiber-optic sensing and the like, and is considered as a great breakthrough of the development of fiber-optic technology after the erbium-doped fiber amplifier (EDFA) technology. With the continuous improvement of the fiber grating manufacturing technology, the application results are increased, so that the fiber grating becomes one of the most representative fiber passive devices with the most development prospect at present. The application range of the optical fiber technology is greatly widened due to the appearance of the optical fiber grating. As a very important sensing element, a Fiber Bragg Grating (FBG) is also widely used in many fields of optical fiber sensing.
One proposed cascade-based Long Period Fiber Grating (LPG) Curvature Sensor, proposed by Y.P.Wang, et al, has the LPG written by UV exposure only affected by Curvature, while two carbon dioxide lasers are used to demodulate the bending Direction (Y.P.Wang, Y.J.Rao. "A Novel Long Fine Fiber Grating Sensor Measuring and Measuring Bend-Direction-orientation simulation," IEEE Sensors Journal,2005,5 (5): 839-843.). Moreover, j.kong et al propose a two-dimensional bending sensor based on orthogonal cascaded core-shifted fiber bragg gratings, which demodulates curvature and bending direction by comparing the central wavelength shifts of two core-shifted fibers. (J.Kong, A.Zhou, C.Cheng, et al, "Two-Axis casting Sensor Based on clamped Eccentric Core Fiber Bragg Gratings," IEEE Photonics technologies Letters,2016,28 (11): 1237-1240.).
In practice, however, curvature sensors often measure curvature while simultaneously changing the temperature. The sensing signal collected by the sensor is the result of the combined action of the bending curvature and the temperature change. The existing curvature sensor demodulation scheme cannot distinguish curvature from temperature, so that errors exist in curvature demodulation.
In order to solve the problems in the existing scheme, a sensor based on a strong coupling multi-core fiber Bragg grating is provided, a curvature sensor which is insensitive to temperature can be realized, and the sensor belongs to the problems to be solved urgently in the field.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a temperature insensitive curvature sensor based on a strong coupling multi-core optical fiber, a curvature measuring device and a method, and solves the problem that errors exist in curvature demodulation due to the fact that bending curvature and temperature change cannot be distinguished in the prior art.
The purpose of the invention is realized by the following technical scheme:
in a first aspect of the present invention, a temperature-insensitive curvature sensor based on a strongly-coupled multi-core fiber is provided, which includes:
the strong-coupling multi-core optical fiber comprises a central fiber core and six peripheral fiber cores which are positioned at the periphery of the central fiber core and arranged in a regular hexagon shape, wherein the outlines of the central fiber core and the peripheral fiber cores are regular hexagons;
seven FBGs with the same central wavelength are respectively written into the same positions of the central fiber core and the six peripheral fiber cores;
and the first single-mode fiber and the second single-mode fiber are respectively aligned and welded with two ends of the central fiber core.
Further, six sides of the central core are aligned with one of the six peripheral cores.
Furthermore, the writing mode of the FBG includes a phase mask method, a femtosecond laser direct writing method or an arc discharge preparation method.
Further, the FBGs are located at the middle positions of the central core and the six peripheral cores.
The invention provides a preparation method of a temperature-insensitive curvature sensor based on a strong-coupling multi-core optical fiber, which comprises the following steps:
respectively aligning and welding a first single-mode fiber and a second single-mode fiber at two ends of a strong-coupling multi-core fiber with a central fiber core; the periphery of the central fiber core of the strong coupling multi-core optical fiber comprises peripheral fiber cores arranged in a regular hexagon shape, and the outlines of the central fiber core and the peripheral fiber cores are both regular hexagons;
seven FBGs with the same central wavelength are respectively written in the same positions of the central fiber core and the six peripheral fiber cores.
In a third aspect of the invention, there is provided a curvature measuring device based on a temperature insensitive curvature sensor, the device comprising:
the curvature sensor;
the light source is connected with the input end of the curvature sensor;
the spectrum analyzer is connected with the output end of the curvature sensor and is used for calculating to obtain a spectrum according to the output of the curvature sensor;
and the curvature calculation device is connected with the spectrum analyzer and used for calculating a curvature value according to the depth of a gap between two resonance peaks in the spectrum.
Further, the calculating a curvature value according to a notch depth between two resonance peaks in the spectrum comprises: and calculating to obtain an actual curvature value by using the depth-curvature curve and the depth of a gap between two resonance peaks in the spectrum.
Further, the curvature measuring device further includes:
the experiment fixing device is used for fixing the curvature sensor at different experiment curvatures; the spectrum analyzer is also used for calculating and obtaining experimental spectra under different curvatures fixed by the experimental fixing device;
the curvature calculating device is also used for obtaining an experiment curvature value according to the experiment fixing device and obtaining an experiment notch depth by using the experiment spectrum; the curvature calculating device is also used for calculating the experimental notch depth under different experimental curvature values to obtain a depth-curvature curve.
The fourth aspect of the invention provides a curvature measuring method based on a temperature insensitive curvature sensor, which adopts the output data of the curvature sensor; the method comprises the following steps:
acquiring a spectrum converted from output data of a curvature sensor to be measured;
and calculating according to the depth of a gap between two resonance peaks in the spectrum to obtain a curvature value.
Further, the calculating a curvature value according to a notch depth between two resonance peaks in the spectrum includes:
and calculating to obtain an actual curvature value by using the depth-curvature curve and the depth of a gap between two resonance peaks in the spectrum.
Further, the obtaining manner of the depth-curvature curve includes:
acquiring experimental spectra of the curvature sensor under different experimental curvatures;
calculating the depth of an experimental notch of each experimental spectrum;
and calculating the depth of the experimental notch under different experimental curvature values to obtain a depth-curvature curve.
In a fifth aspect of the present invention, based on the implementation of the curvature measuring method, a storage medium is further provided, on which computer instructions are stored, and the computer instructions execute the curvature measuring method based on the temperature-insensitive curvature sensor when running.
In a sixth aspect of the present invention, based on the implementation of the curvature measuring method, there is also provided a terminal (i.e., a curvature calculating apparatus) including a memory and a processor, where the memory stores computer instructions executable on the processor, and the processor executes the computer instructions to perform the curvature measuring method based on the temperature-insensitive curvature sensor.
The invention has the beneficial effects that:
(1) In an exemplary embodiment of the invention, the single-mode fiber and the specialty fiber (strongly coupled multicore fiber) of the curvature sensor have a central core with a large fraction of the light intensity due to the excitation conditions when bent. Therefore, such FBGs in the central core contribute more to the reflection spectrum than FBGs written in the peripheral core. Therefore, when the strongly coupled multi-core fiber 1 is bent, the reflection spectrum has no obvious wavelength shift. In addition, as the fiber is bent, the mode distributions of the two supermodes change, and thus the effective refractive index difference changes. The size of the radius of curvature determines the amount of cumulative phase difference change between the two supermodes participating in the interference. So that the two supermodes interfere to cause a change in the depth of the notch, while the temperature is hardly affected. Thus, the bend radius (i.e., curvature) can be determined by monitoring the notch depth of the reflectance spectrum. Compared with the conventional wavelength reading method, the curvature sensor in the exemplary embodiment can effectively eliminate the problem of cross sensitivity caused by temperature, and simultaneously reduces the requirement on the resolution of an Optical Spectrum Analyzer (OSA). Meanwhile, the sensor of the invention also has the advantages of compact structure, simple demodulation, low cross sensitivity and the like. In addition, the preparation method of the temperature-insensitive curvature sensor based on the strong-coupling multi-core fiber also has the same advantages.
(2) In a further exemplary embodiment of the present invention, the curvature measuring device has a relationship between the notch depth and the curvature, and therefore the curvature calculating device calculates the curvature value from the notch depth between two formants in the spectrum using the spectrum output from the spectrum analyzer. In addition, the curvature measurement method, the stored interpretation and the terminal have the same advantages.
(3) In another exemplary embodiment of the present invention, the curvature measuring device calculates an actual curvature value by using the depth-curvature curve and the notch depth between two formants in the spectrum, which are obtained by experiments, so that the actual curvature value can be directly calculated when the notch depth is known; in addition, the curvature measurement method, the stored interpretation and the terminal have the same advantages.
(4) In yet another exemplary embodiment of the present invention, a specific structure of an experimental fixture is disclosed, facilitating the acquisition of multi-curvature data parameters.
Drawings
FIG. 1 is a schematic illustration of a temperature insensitive curvature sensor configuration according to an exemplary disclosed embodiment of the invention;
FIG. 2 is a schematic illustration of one of the disclosed spectra according to an exemplary embodiment of the present invention;
FIG. 3 is a schematic diagram of a curvature measuring device according to an exemplary embodiment of the disclosure;
FIG. 4 is a schematic structural diagram of an experimental fixture disclosed in an exemplary embodiment of the present invention;
FIG. 5 shows a curvature sensor at 0m for an exemplary embodiment of the present invention -1 、0.29m -1 、0.51m -1 、0.70m -1 、0.87m -1 、1.02m -1 、1.15m -1 A graph of spectral data under curvature;
FIG. 6 is a schematic diagram of a depth-curvature curve calculated from experimental notch depths at different experimental curvature values according to an exemplary embodiment of the disclosure;
in the figure, 1-strong coupling multi-core fiber, 101-central fiber core, 102-peripheral fiber core, 103-FBG, 201-first single-mode fiber, 202-second single-mode fiber, 301-curvature sensor input end fixing device, 302-curvature adjusting table, 303-curvature sensor output end fixing device, 304-curvature adjusting steel belt, 305-load.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it is to be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
In the description of the present invention, it should be noted that directions or positional relationships indicated by "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", and the like are directions or positional relationships described based on the drawings, and are only for convenience of description and simplification of description, and do not indicate or imply that the device or element referred to must have a specific orientation, be configured and operated in a specific orientation, and thus, should not be construed as limiting the present invention.
In the description of the present invention, it should be noted that, unless otherwise explicitly stated or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.
It is to be understood that although the terms first, second, third, etc. may be used herein to describe various information, such information should not be limited to these terms. These terms are only used to distinguish one type of information from another. For example, first information may also be referred to as second information, and similarly, second information may also be referred to as first information, without departing from the scope of the present application. The word "if," as used herein, may be interpreted as "at … …" or "at … …" or "in response to a determination," depending on the context. Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
In the prior art, the curvature sensor is used for measuring the curvature and is often accompanied by the change of temperature, and the sensing signal collected by the sensor is the result of the combined action of the bending curvature and the temperature change, because the FBG is sensitive to both temperature and strain and shows the shift of wavelength. The existing curvature sensor demodulation scheme cannot distinguish curvature from temperature, so that errors exist in curvature demodulation.
Referring to fig. 1, fig. 1 shows a temperature-insensitive curvature sensor based on a strongly-coupled multi-core optical fiber according to an exemplary embodiment of the present invention, which includes:
a Strongly-coupled multi-core fiber 1 (SCMCF) including a central core 101 and six peripheral cores 102 arranged in a regular hexagonal shape at the periphery of the central core 101, wherein the central core 101 and the peripheral cores 102 have regular hexagonal profiles;
seven FBGs 103 with the same central wavelength are written into the same positions of the central core 101 and the six peripheral cores 102, respectively;
a first Single mode fiber 201 and a second Single mode fiber 202 (SMF) are fusion-spliced in alignment with both ends of the central core 101, respectively.
In the present exemplary embodiment, the first single-mode fiber 201 and the second single-mode fiber 202 serve as an input end and an output end of the entire curvature sensor, respectively. The following description will be made by taking the first single-mode fiber 201 as an input end and the second single-mode fiber 202 as an output end, and the corresponding functions can be realized by exchanging the two.
Specifically, an external light source enters the strongly-coupled multi-core fiber 1 through the first single-mode fiber 201 via a first fusion point (a fusion point between the first single-mode fiber 201 and the strongly-coupled multi-core fiber 1), and since seven cores of the strongly-coupled multi-core fiber 1 are all regular hexagons, two types of supermodes are generated in the transmission process of the strongly-coupled multi-core fiber 1. And when two supermodes are transmitted to the FBG 103, two reflected signals related to the two supermodes are re-coupled into the second single mode fiber 202 through the second fusion point (the fusion point between the second single mode fiber 202 and the strongly coupled multi-core fiber), and interference occurs due to the phase difference between the two reflected spectra. Therefore, in the spectrum formed by the reflection of the FBG 103 (as shown in fig. 2, the abscissa Wavelength of fig. 2 represents the Wavelength, and the ordinate Amplitude represents the Amplitude, i.e., the Notch depth), two formants (peak 1 and peak 2) and one Notch depth (Notch) therebetween can be observed. At this time, when the sensor is affected by both bending and temperature, the depth of the notch is made to vary only with bending, and hardly with temperature. The curvature is thus determined in the present exemplary embodiment by demodulating the depth of the notch, so that a temperature-insensitive curvature sensor is realized.
Therefore, when the ordinary single-mode fiber and the special fiber (the strongly-coupled multi-core fiber 1) of the present exemplary embodiment are bent, the central core 101 of the strongly-coupled multi-core fiber 1 has most of the light intensity due to the excitation condition. Therefore, the FBG 103 in such a central core 101 contributes more to the reflection spectrum than the FBG 103 written in the peripheral core 102. Therefore, when the strongly coupled multi-core fiber 1 is bent, the reflection spectrum has no obvious wavelength shift. In addition, as the fiber is bent, the mode distributions of the two supermodes change, and thus the effective refractive index difference changes. The size of the radius of curvature determines the amount of cumulative phase difference change between the two supermodes participating in the interference. So that the two supermodes interfere to cause a change in the depth of the notch, while the temperature is hardly affected. Thus, the bend radius (i.e., curvature) can be determined by monitoring the notch depth of the reflectance spectrum.
Compared with the conventional wavelength reading method, the curvature sensor in the exemplary embodiment can effectively eliminate the problem of cross sensitivity caused by temperature, and simultaneously reduces the requirement on the resolution of an Optical Spectrum Analyzer (OSA). Meanwhile, the sensor of the invention also has the advantages of compact structure, simple demodulation, low cross sensitivity and the like.
For the illustration of the formants (peak 1 and peak 2) in fig. 2, the two peaks with the largest amplitude (i.e. notch depth) in the spectrum are the formants (peak 1 and peak 2) here.
It should be noted that the first single-mode fiber 201 and the second single-mode fiber 202, i.e., SMF, are standard single-mode fibers, and the fiber cores are circular; the strong coupling multi-core optical fiber 1, namely seven fiber cores of the SCMCF are all hexagonal and are necessary characteristics, so that optical signals generate two specific supermodes in the transmission process; and the spacing between each core in the strongly coupled multicore fiber 1 must be close enough to be strongly coupled. Although the single-mode fibers (the first single-mode fiber 201 and the second single-mode fiber 202) and the strongly-coupled multi-core fiber 1 have different shapes, the two fibers may be fusion-spliced; while in a preferred exemplary embodiment, the centers of the two fibers are aligned. Two supermodes generated by the strong coupling multi-core optical fiber 1 have difference, so that two reflection peaks which are equivalently formed when the optical fiber is bent are not overlapped, interference is generated, and a deeper notch is formed.
In addition, the position of the strong-coupling multi-core fiber 1 written with the FBG 103 and the length between the single-mode fibers (the first single-mode fiber 201 and the first single-mode fiber 20) and the fusion point of the strong-coupling multi-core fiber 1 should meet the sensing requirement, and two reflection peaks equivalently formed by two supermodes can interfere to generate a deep enough gap. On this basis, the length of the single-mode fiber is as short as possible to ensure the same curvature at the two fusion splices.
Meanwhile, the numerical apertures of the strong-coupling multi-core fiber 1 and the single-mode fiber are matched, so that the coupling loss is minimum when the strong-coupling multi-core fiber 1 and the single-mode fiber are spliced.
In a specific exemplary embodiment, the diameters of the first single-mode fiber 201 and the first single-mode fiber 202 are both 8.5um, and the cladding diameter is 125um; the diameter of the fiber core of the selected strong-coupling multi-core fiber 1 is 9.2um, the distance between the fiber cores is 11um, the numerical aperture is 1.4, and the length of the strong-coupling multi-core fiber section is 13mm (the lengths of the first single-mode fiber 201 and the first single-mode fiber 202 are selected according to actual requirements); the FBG 103 written in each core of the strong coupling multi-core optical fiber 1 is 2mm in length, the length between the FBG and the fusion point is 6.5mm, and the FBG is positioned in the middle of the strong coupling multi-core optical fiber 1.
More preferably, in an exemplary embodiment, as shown in FIG. 1, six sides of the central core 101 are aligned with one of the six peripheral cores 102. (similar to honeycomb structure)
Preferably, in an exemplary embodiment, the writing manner of the FBG 103 includes a phase mask method, a femtosecond laser direct writing method or an arc discharge preparation method. Among them, the phase mask method is preferable.
More preferably, in an exemplary embodiment, the FBG 103 is located at a position intermediate the central core 101 and the six peripheral cores 102.
In addition, another exemplary embodiment provides a method for manufacturing a temperature-insensitive curvature sensor based on a strongly-coupled multi-core optical fiber, which includes the following steps:
respectively aligning and welding a first single-mode fiber 201 and a second single-mode fiber 202 at two ends of a strong-coupling multi-core fiber 1 with a central fiber core 101; the periphery of the central fiber core 101 of the strong coupling multi-core optical fiber 1 comprises peripheral fiber cores 102 arranged in a regular hexagon shape, and the outlines of the central fiber core 101 and the peripheral fiber cores 102 are both regular hexagons;
seven FBGs 103 of the same center wavelength are written at the same positions of the central core 101 and the six peripheral cores 102, respectively.
Since the method has the same inventive concept as the curvature sensor in the above exemplary embodiment, the contents of advantages and principles are not described herein again.
In addition, the order of the two steps may be changed and arranged according to the actual requirement and the order of the production line.
More preferably, in an exemplary embodiment, as shown in FIG. 1, six sides of the central core 101 are aligned with one of the six peripheral cores 102. (similar to honeycomb structure)
Preferably, in an exemplary embodiment, the writing manner of the FBG 103 includes a phase mask method, a femtosecond laser direct writing method or an arc discharge preparation method. Among them, the phase mask method is preferable.
More preferably, in an exemplary embodiment, the FBGs 103 are located at the middle of the central core 101 and the six peripheral cores 102.
Referring to fig. 3, fig. 3 shows that yet another exemplary embodiment of the present invention provides a curvature measuring device based on a temperature-insensitive curvature sensor, the device comprising:
a curvature sensor as described in any of the above exemplary embodiments;
the light source is connected with the input end of the curvature sensor;
the spectrum analyzer is connected with the output end of the curvature sensor and is used for calculating to obtain a spectrum according to the output of the curvature sensor;
and the curvature calculation device is connected with the spectrum analyzer and used for calculating a curvature value according to the depth of a gap between two resonance peaks in the spectrum.
Specifically, in this exemplary embodiment, the light source enters the strongly-coupled multi-core fiber 1 through the first fusion point (the fusion point between the first single-mode fiber 201 and the strongly-coupled multi-core fiber 1) via the first single-mode fiber 201 of the curvature sensor, and since seven cores of the strongly-coupled multi-core fiber 1 are all regular hexagons, two types of supermodes are generated during the transmission of the strongly-coupled multi-core fiber 1. When the two supermodes are transmitted to the FBG 103, the two reflected signals associated with the two supermodes are re-coupled into the second single-mode fiber 202 through the second fusion point (the fusion point between the second single-mode fiber 202 and the strong-coupling multi-core fiber), and interference occurs due to the phase difference between the two reflected spectra. At this time, the spectrum analyzer receives the output of the curvature sensor and calculates a spectrum, so that in the spectrum formed by the reflection of the FBG 103 (as shown in fig. 2, the abscissa Wavelength of fig. 2 represents the Wavelength, and the ordinate Amplitude represents the magnitude of the Amplitude (i.e., the Notch depth)), two formants (peak 1 and peak 2) and a Notch depth (Notch) therebetween can be observed. At this time, when the sensor is affected by both bending and temperature, the depth of the notch is made to vary only with bending, and hardly with temperature. Because the notch depth has a certain relation with the curvature, the curvature calculating device uses the spectrum output by the spectrum analyzer to calculate the curvature value according to the notch depth between two resonance peaks in the spectrum.
It should be noted that the curvature calculating device may be a PC or other computing device.
More preferably, in an exemplary embodiment, the calculating a curvature value according to a notch depth between two formants in the spectrum includes: and calculating to obtain an actual curvature value by using the depth-curvature curve and the depth of a gap between two resonance peaks in the spectrum.
In particular, in the exemplary embodiment, since the notch depth has a certain relationship with the curvature, the relationship may be expressed in the form of a depth-curvature curve, so that the actual curvature value can be directly calculated when the notch depth is known.
Preferably, in an exemplary embodiment, the apparatus further comprises:
the experiment fixing device is used for fixing the curvature sensor at different experiment curvatures; the spectrum analyzer is also used for calculating and obtaining experimental spectra under different curvatures fixed by the experimental fixing device;
the curvature calculating device is also used for obtaining an experiment curvature value according to the experiment fixing device and obtaining an experiment notch depth by using the experiment spectrum; the curvature calculating device is also used for calculating the experimental notch depth under different experimental curvature values to obtain a depth-curvature curve.
In the exemplary embodiment, the depth-curvature curve is calculated from experimental data. Specifically, referring to fig. 4, fig. 4 shows a curvature sensor under the influence of an experimental fixture comprising: the device comprises a curvature sensor input end fixing device 301, a curvature sensor output end fixing device 303 and a curvature adjusting platform 302, wherein the curvature adjusting platform 302 is located between the curvature sensor input end fixing device 301 and the curvature sensor output end fixing device 303, and a curvature adjusting steel belt 304 is connected between the curvature adjusting platform 302 and the curvature sensor input end fixing device 301.
When experimental measurement is needed, firstly, the curvature of the curvature adjusting steel belt 304 is adjusted (passed) through the curvature adjusting table 302, and then the position of the curvature adjusting table 302 is fixed; then, the part of the curvature sensor with the strong coupling multi-core optical fiber 1 is placed on a curvature adjusting steel belt, the first single-mode optical fiber 201 is fixed by the curvature sensor input end fixing device 301, and the second single-mode optical fiber 202 is fixed; the measurement can then be performed.
Note that, in one exemplary embodiment, when the curvature adjusting table 302 is moved toward the curvature sensor input end fixing device 301 while being in the initial position (i.e., the curvature adjusting steel belt 304 is in a straightened state), the curvature adjusting steel belt 304 is bent upward (from the center of the curvature adjusting steel belt 304).
The spectral data under different curvatures are shown in fig. 5, and fig. 5 (the abscissa Wavelength represents the Wavelength, and the ordinate Amplitude represents the Amplitude (i.e. the depth of the notch)) shows that a certain curvature sensor is respectively at 0m -1 、0.29m -1 、0.51m -1 、0.70m -1 、0.87m -1 、1.02m -1 、1.15m -1 Spectral data under curvature.
Wherein the curvature C may be measured according to: the formula sin (LC/2) = (1/2) = (L-dL) × C the different curvature values C can be calculated. Where L represents a linear distance between the curvature sensor input end fixing device 301 and the curvature adjusting stage 302 when the curvature adjusting steel belt 304 is in a linear state, and dL represents a shortened distance when the curvature adjusting steel belt 304 is in a curved state.
Referring to fig. 6, fig. 6 shows a specific calculation process of the curvature calculation device for calculating the experimental notch depth at different experimental curvature values to obtain the depth-curvature curve: firstly, the abscissa Curvature of FIG. 6 represents Curvature, the left ordinate Amplitude represents Amplitude, and the square points represent the values of the Amplitude (namely, notch depth) under different curvatures obtained in FIG. 5; all values are then connected by a curve (i.e., a depth-curvature curve) and a corresponding depth-curvature formula is fitted to obtain a depth-curvature curve represented by the depth-curvature formula. In the exemplary embodiment shown in fig. 6, the curve corresponds to the formula a = -4.46 × c 2 +15.9 × C-4.62 (a indicates notch depth and C indicates curvature).
It should be additionally noted that the right ordinate wavelength variation in fig. 6 represents the wavelength variation, and it can be seen from the figure that the wavelength variation using the present exemplary embodiment is very small, and is only 16pm at the maximum; and the conventional temperature sensor in the prior art can even reach more than 1000 pm.
After the depth-curvature curve is obtained, when the curvature sensor is used for measurement, spectral data are obtained only through a spectrum analyzer, then the depth of a gap between two resonance peaks in a spectrum is obtained, and the depth of the gap is filled into a value A in a depth-curvature formula, so that the curvature value C is obtained through calculation.
It should be noted that different curvature sensors have different profiles and therefore require different experiments/calibrations.
Preferably, as shown in fig. 4, the experiment fixing device further comprises a weight 305, the weight 305 is located between the curvature adjusting table 302 and the curvature sensor output end fixing device 303, and the weight 305 is used for further fixing the curvature sensor to be tightly attached to the curvature adjusting steel belt 304, so that the bending degree of the curvature sensor is the same as that of the curvature adjusting steel belt 304, and the data accuracy of the whole experiment is improved.
The weight 305 can be placed between the steps of fixing the first single mode fiber 201 with the 301-curvature sensor input end fixing device and fixing with the second single mode fiber 202. In one exemplary embodiment, the top of the weight 305 has a hook, which can be hooked on the second single mode fiber 202; and to avoid inaccurate experimental data due to weight asymmetry, the weight 305 needs to maintain a uniform shape and a uniform weight.
The curvature measuring device has the same inventive concept as the curvature measuring device in the exemplary embodiment, and provides a curvature measuring method based on a temperature insensitive curvature sensor, which adopts the output data of the curvature sensor; the method comprises the following steps:
acquiring a spectrum converted from output data of a curvature sensor to be measured;
and calculating according to the depth of a gap between two resonance peaks in the spectrum to obtain a curvature value.
It should be noted that the method of this exemplary embodiment is applied to a curvature calculation apparatus, that is, the curvature calculation is performed by using the advantage of insensitivity of the curvature sensor in any of the foregoing exemplary embodiments: firstly, stable spectrum data are obtained, and then a curvature value is calculated according to the depth of a gap between two resonance peaks in the spectrum.
More preferably, in an exemplary embodiment, the calculating a curvature value according to a notch depth between two formants in the spectrum includes:
and calculating to obtain an actual curvature value by using the depth-curvature curve and the depth of a gap between two resonance peaks in the spectrum.
Preferably, in an exemplary embodiment, the obtaining of the depth-curvature curve includes:
acquiring experimental spectra of the curvature sensor under different experimental curvatures;
calculating the depth of an experimental notch of each experimental spectrum;
and calculating the depth of the experimental notch under different experimental curvature values to obtain a depth-curvature curve.
Based on the implementation of the curvature measuring method according to any exemplary embodiment, the present exemplary embodiment further provides a storage medium having stored thereon computer instructions, which when executed perform the curvature measuring method based on the temperature-insensitive curvature sensor.
Meanwhile, based on the implementation of the curvature measuring method according to any one of the exemplary embodiments, the present exemplary embodiment further provides a terminal (i.e., a curvature calculating device) including a memory and a processor, where the memory stores computer instructions executable on the processor, and the processor executes the computer instructions to perform the curvature measuring method based on a temperature-insensitive curvature sensor.
Based on such understanding, the technical solution of the present embodiment or parts of the technical solution may be essentially implemented in the form of a software product stored in a storage medium and including instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: various media capable of storing program codes, such as a usb disk, a removable hard disk, a Read-only memory (ROM), a Random Access Memory (RAM), a magnetic disk, or an optical disk.
In all embodiments provided by the present invention, it should be understood that the disclosed apparatus and method may be implemented in other ways. The above-described apparatus embodiments are merely illustrative, and for example, the division of the units/modules is only one logical division, and there may be other divisions in actual implementation, and for example, a plurality of units or modules may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed coupling or direct coupling or communication connection between each other may be through some communication interfaces, indirect coupling or communication connection between devices or units, and may be in an electrical, mechanical or other form.
It is to be understood that the above-described embodiments are illustrative only and not restrictive of the broad invention, and that various other modifications and changes in light thereof will be suggested to persons skilled in the art based upon the above teachings. This need not be, nor should it be exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the spirit or scope of the invention.
Claims (10)
1. A temperature insensitive curvature sensor based on a strong coupling multi-core fiber is characterized in that: the method comprises the following steps:
the strong-coupling multi-core optical fiber comprises a central fiber core and six peripheral fiber cores which are positioned at the periphery of the central fiber core and arranged in a regular hexagon shape, wherein the outlines of the central fiber core and the peripheral fiber cores are regular hexagons;
seven FBGs with the same central wavelength are respectively written into the same positions of the central fiber core and the six peripheral fiber cores;
the first single-mode fiber and the second single-mode fiber are respectively aligned and welded with two ends of the central fiber core;
obtaining two resonance peaks and a gap depth between the two resonance peaks in a spectrum formed by the FBG; determining the curvature by demodulating the depth of the notch; wherein, the two wave peaks with the largest notch depth in the spectrum are resonance peaks.
2. The temperature-insensitive curvature sensor based on the strongly-coupled multi-core optical fiber as claimed in claim 1, wherein: six sides of the central core are aligned with one of the six peripheral cores.
3. The temperature-insensitive curvature sensor based on the strongly-coupled multi-core optical fiber as claimed in claim 1, wherein: the writing mode of the FBG comprises a phase mask method, a femtosecond laser direct writing method or an arc discharge preparation method.
4. The temperature-insensitive curvature sensor based on the strongly-coupled multi-core optical fiber as claimed in claim 1, wherein: the FBGs are located at the middle of the central core and the six peripheral cores.
5. A curvature measuring device based on a temperature insensitive curvature sensor is characterized in that: the device comprises:
the curvature sensor of any one of claims 1~4;
the light source is connected with the input end of the curvature sensor;
the spectrum analyzer is connected with the output end of the curvature sensor and used for calculating to obtain a spectrum according to the output of the curvature sensor;
and the curvature calculation device is connected with the spectrum analyzer and used for calculating a curvature value according to the depth of a gap between two resonance peaks in the spectrum.
6. A curvature measuring device based on a temperature insensitive curvature sensor as claimed in claim 5, characterized in that: the step of calculating a curvature value according to the depth of a gap between two resonance peaks in the spectrum comprises: and calculating to obtain an actual curvature value by using the depth-curvature curve and the depth of a gap between two resonance peaks in the spectrum.
7. A curvature measuring device based on a temperature insensitive curvature sensor as claimed in claim 6, characterized in that: further comprising:
the experiment fixing device is used for fixing the curvature sensor at different experiment curvatures; the spectrum analyzer is also used for calculating and obtaining experimental spectra under different curvatures fixed by the experimental fixing device;
the curvature calculating device is also used for obtaining an experiment curvature value according to the experiment fixing device and obtaining an experiment notch depth by using the experiment spectrum; the curvature calculating device is also used for calculating the experimental notch depth under different experimental curvature values to obtain a depth-curvature curve.
8. A curvature measuring method based on a temperature insensitive curvature sensor is characterized in that: using the output data of the curvature sensor of any of claims 1~4; the method comprises the following steps:
acquiring a spectrum converted from output data of a curvature sensor to be measured;
and calculating according to the depth of a gap between two resonance peaks in the spectrum to obtain a curvature value.
9. A curvature measurement method based on a temperature insensitive curvature sensor as claimed in claim 8, characterized in that: the calculating according to the notch depth between two resonance peaks in the spectrum to obtain the curvature value comprises the following steps:
and calculating to obtain an actual curvature value by using the depth-curvature curve and the depth of a gap between two resonance peaks in the spectrum.
10. A method of curvature measurement based on a temperature insensitive curvature sensor as claimed in claim 9, characterized in that: the acquisition mode of the depth-curvature curve comprises the following steps:
acquiring experimental spectra of the curvature sensor under different experimental curvatures;
calculating the depth of an experimental notch of each experimental spectrum;
and calculating the depth of the experimental notch under different experimental curvature values to obtain a depth-curvature curve.
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