KR100666379B1 - Optical fiber Bragg grating structure and apparatus of measuring deformation of structure and method thereof - Google Patents

Abstract

The present invention relates to an optical fiber grating structure and a structure deformation measuring apparatus and method using the same, wherein the optical fiber grating structure is at least one installed on the support such that the support and the portion formed so that a plurality of gratings are spaced apart from each other can be supported in a curved pattern An optical fiber grid is provided. According to the optical fiber grating structure and the structure deformation measuring apparatus and method using the same, the optical fiber grating having a grating formed at equal intervals is structurally bent and supported to detect and change the amount of light corresponding to the deformation degree of the measurement object. It provides the advantage of being able to calculate physical quantities such as bending, stress, temperature, etc. for the object.

Description

Optical fiber Bragg grating structure and apparatus of measuring deformation of structure and method

1 is a view showing an optical fiber grating structure according to an embodiment of the present invention,

FIG. 2 is a graph illustrating a result of measuring a bandwidth change of reflected light with respect to a strain applied to the optical fiber grating structure of FIG. 1,

3 is a view illustrating an example of a structure deformation measuring apparatus to which the optical fiber grating structure of FIG. 1 is applied;

4 is a view showing a structure deformation measuring apparatus of another embodiment to which the optical fiber grating structure of FIG. 1 is applied,

5 is a view showing an optical fiber grating structure according to a second embodiment of the present invention,

6 is a view illustrating an example of a structure deformation measuring apparatus to which the optical fiber grating structure of FIG. 5 is applied;

7 is a view showing an optical fiber grating structure according to a third embodiment of the present invention,

8 is a view showing an optical fiber grating structure according to a fourth embodiment of the present invention,

9 is a diagram illustrating a structure deformation measuring apparatus to which the optical fiber grating structure of FIG. 8 is applied.

<Description of Symbols for Major Parts of Drawings>

11: first support 13: second support

15: bending support guide member 17: optical fiber lattice

The present invention relates to an optical fiber grating structure and a structure deformation measuring apparatus and method using the same, and more particularly, an optical fiber grating structure capable of measuring a physical quantity related to deformation of a structure to be measured, and a structure deformation measuring apparatus using the same, It is about a method.

Optical fiber gratings, which are widely used for optical communication and sensors, are engraved with a plurality of gratings spaced apart from each other along the longitudinal direction of the optical fiber, and the wavelength of light reflected from the grating varies depending on the ambient temperature or the degree of tension.

Since the optical fiber lattice reflects only wavelengths satisfying Bragg conditions according to ambient temperature or tensile strength, and transmits other wavelengths as it is, the refractive index or length of the optical fiber is changed when the lattice's ambient temperature is changed or tension is applied to the lattice. The wavelength of the reflected light is changed and thus changed.

The optical fiber grating sensor using the characteristics of the optical fiber grating has been widely applied to diagnose the safety state by detecting deformation of bridges, dams, buildings, etc., or to diagnose the wing state of an aircraft.

The structure deformation measuring apparatus using the conventional optical fiber grating used an optical spectrum analyzer capable of analyzing the wavelength change of the light reflected from the optical fiber grating. However, the optical spectrum analyzer has the disadvantage of being large and expensive.

In order to solve this problem, a technique of converting a wavelength change signal of a fiber grating into an optical intensity change signal using an optical interferometer such as a Mach-Zehnometer interferometer has been attempted. There is a problem that it is difficult to secure the reliability of the sensor. In addition, a modulator such as a Fabry-Perot Filter and an Acostic-OPtic Filter may convert a wavelength change signal of the light into an electrical intensity signal and measure the measured signal. However, this method also has the disadvantage that the system is complicated by the addition of a modulator and loss of information may occur during signal conversion.

On the other hand, there is a method of measuring the intensity of light instead of the wavelength change by using a chirped fiber bragg grating in which the gaps between the gratings are formed in the optical fiber, but the chirped fiber grating is manufactured by ultra-precision manufacturing technology. Since the manufacturing process is complicated and expensive, it is difficult to commercialize.

 The present invention was devised to improve the above problems, and in detail, the optical fiber grating structure and the structure deformation measuring apparatus and method using the same can be changed in the light intensity in response to changes due to external factors in a simple structure. The purpose is to provide.

In order to achieve the above object, an optical fiber grating structure according to the present invention comprises at least one support; And at least one optical fiber grating installed on the support such that a portion of the plurality of gratings spaced apart from each other may be supported in a curved pattern.

According to an aspect of the invention the support includes a first and a second support for fixing to the measurement object; And a curved support guide member coupled in a curved shape between the first support and the second support, wherein the optical fiber grating is coupled to the curved support guide member to correspond to an extension pattern of the curved support guide member.

According to another aspect of the invention the support is a plate-like support made of a flexible material, the optical fiber grating is fixed in a curved pattern to the plate-like support.

Further, the support has a first optical fiber lattice bent in a first bending pattern and a second optical fiber lattice bent in a second bending pattern different from the first bend pattern of the first optical fiber lattice to calculate a plurality of physical quantities. Installed apart from each other.

In addition, in order to achieve the above object, the structure deformation measuring apparatus according to the present invention is at least one optical fiber and at least one optical fiber installed in the support so that the portion formed so that a plurality of gratings are separated from each other in a curved pattern An optical fiber grating structure having a grating; A light source for emitting light to the optical fiber grating; And a photo detector for detecting the light passing through the optical fiber grating or reflected and outputting the light as an electrical signal.

The light emitted from the light source may be transmitted to the optical fiber grating, and the directional coupler may transmit the light reflected from the optical fiber grating to the photodetector.

In addition, the structural deformation measuring method according to the present invention in order to achieve the above object is at least one optical fiber so that the grating forming portions formed with a plurality of gratings spaced apart from each other on the measurement object can be supported for the measurement object in a curved pattern Installing a grating on the measurement object; Emitting light to the optical fiber grid; And calculating an amount of deformation associated with the object to be measured by detecting the intensity of light passing through or reflected from the optical fiber grating.

Hereinafter, with reference to the accompanying drawings will be described in more detail the optical fiber grating structure and structure deformation measuring apparatus and method using the same according to a preferred embodiment of the present invention.

1 is a view showing an optical fiber grating structure according to an embodiment of the present invention.

Referring to the drawings, the optical fiber grating structure 10 includes first and second support members 11 and 13, a bending support guide member 15, and an optical fiber grid 17.

The first and second supports 11 and 13 support the bent support guide member 15.

The first and second supports are fixed to a measuring object such as a building or a bridge by various known fixing members such as an adhesive such as silicone or epoxy or a bolt.

The curved support guide member 15 is formed in a curved pattern, and both ends thereof are coupled to the first and second support members 11 and 13 spaced a predetermined distance apart.

Preferably, the curved support guide member 15 maintains a curved shape while being supported by the first and second support members 11 and 13, but can be sensitively sensitive to external environmental factors such as temperature and strain. It is desirable to be formed of flexible material.

The first support 11, the second support 13, and the curved support guide member 15 may be integrally formed of the same material.

Unlike the illustrated example, the bending support guide member 15 may be fixed to the measurement object in a directly set bending pattern, and in this case, the bending support guide member 15 becomes a support.

The optical fiber grid 17 is fixedly coupled to the bending support guide member 15 along the bending pattern of the bending support guide member 15.

The fixing method of the bending support guide member 15 of the optical fiber grid 17 can be fixed using a resin such as epoxy or other adhesive.

At least one of both ends 17a and 17b of the optical fiber grid 17 may be provided with a connector to facilitate coupling with other elements optically.

The optical fiber grating 17 may be formed by bending the grating at equal intervals on the linear optical fiber along the bending pattern of the bending support guide member 15 to be fixed by the method described above to have the bending pattern.

In the optical fiber grid structure 10 having such a structure, a nonlinear grating is forcibly formed by a curved pattern.

Accordingly, in the optical fiber grid structure 10, strains different from each other are generated for each position due to strain or temperature applied from the outside, for example, strain or temperature, and thus the reflection bandwidth of the incident light varies. That is, the intensity of light reflected by an external factor that can deform the optical fiber grid 17 is changed.

Experimental results for confirming that the reflection bandwidth is variable when the optical fiber grid 17 of the curved structure is deformed by external factors are shown in FIG. 2.

The experiment was carried out in a state in which the optical fiber grid 17 in which the lattice was engraved at equal intervals was extended so as to extend in a straight line between the first support 11 and the second support 13, as shown in FIG. 1. As described above, the wavelength band of the light reflected from the optical fiber grating was measured with respect to the light incident from the light source having a central wavelength of 1537 nanometers while being moved at different distances in the compression direction to be bent in a sinusoidal shape. The value denoted by the letter d in the figure is a moving distance when the second support 13 is moved finely in the direction to the first support 11 at the initial position where the optical fiber grating 17 is straightened.

As can be seen from FIG. 2, the deflection pattern of the optical fiber grating 17 having a vertical width increases as the distance moved by the second support 13 toward the first support 11 increases. This increases the bandwidth of the reflected light.

Therefore, by measuring the intensity of the reflected light or transmitted light reflected from the curved optical fiber grid 17, the physical quantity to be measured for the measurement object, for example, temperature, strain, bending, vibration and the like can be measured.

The structure deformation measuring apparatus using the optical fiber lattice structure 10 is shown in FIG. 3. Elements having the same function as in the above-described drawings are denoted by the same reference numerals.

Referring to the drawings, the structure deformation measuring apparatus 30 includes a light source 31, a directional optical coupler 32, an optical fiber lattice structure 10, and a photodetector 33.

The light source 31 is preferably one that can emit light of a wide band of wavelengths. As an example, a light emitting diode may be applied to the light source 31.

The directional optical coupler 32 transmits the light emitted from the light source 31 to the optical fiber grid 17 of the optical fiber grid structure 10, and the light reflected from the optical fiber grid 17 is transmitted to the photodetector 33. .

An optical circulator may be applied to the directional optical coupler 32.

The photodetector 33 outputs an electrical signal corresponding to the amount of light incident from the directional optical coupler 32.

Although not shown, a deformation amount calculation unit (not shown) that calculates a physical quantity corresponding to a deformation factor to be measured with respect to the measurement target from the light quantity information output as an electrical signal corresponding to the amount of light incident from the photodetector 33 is connected. It is.

The deformation amount calculation unit uses a calculation formula or a reference equation stored in a look-up table for calculating a physical quantity to be measured from a signal input from the photodetector 33 corresponding to the physical quantity to be calculated, for example, Calculate the strain value or ambient temperature applied to the measurement object.

The structure deformation measuring apparatus 30 fixes the first support 11 and the second support 13 to the measurement target, and is emitted from the light source 31 and then reflected from the optical fiber grid structure 10 to detect the photodetector 33. The amount of deformation, such as strain applied to the measurement object, can be quantitatively calculated using the information on the amount of light detected in step 9).

On the other hand, unlike the illustrated example, as shown in FIG. 4, the light source 41 and the light at both ends of the optical fiber grid structure 10 to measure a desired physical quantity using the light quantity information transmitted through the optical fiber grid structure 10. The detectors 43 can each be coupled in series. In this case, when an external force is applied in a direction in which the first support 11 and the second support 13 are mutually compressed, the amount of light incident on the photodetector 43 is reduced.

5 shows another optical fiber lattice structure.

Referring to the drawings, the optical fiber lattice structure 50 includes a plate-like support 51 and an optical fiber lattice 57 having a lattice forming portion 57a fixed to the plate-like support 51 in a curved pattern.

The plate support 51 is preferably formed of a flexible material.

The method of fixing the optical fiber grating to the plate-like support 51 is a method of fixing the linear optical fiber grating formed at equal intervals to the plate-like support 51 with a fixing member such as epoxy to the plate-shaped support 51 in a state where the external force is flexed. This can be applied.

Alternatively, the receiving groove or the insertion hole may be formed to correspond to the bending pattern of the optical fiber grid 57 to be formed in the plate-shaped support 51, and the optical fiber grid may be accommodated and fixed in the receiving groove or the insertion hole.

The optical fiber lattice structure 50 may be used by fixing the plate-like support 51 to the measurement object using a coupling member.

In addition, the structure deformation measuring apparatus to which the optical fiber lattice structure 50 is applied is used in the optical fiber lattice structure 50 using the light source 61, the photodetector 63, and the directional coupler 62 as shown in FIG. 6. The amount of deformation may be calculated using the light quantity information of the reflected light. In addition, although not shown, as described above, the light source and the light emitter may be coupled in series to the optical fiber grid structure 50 so as to detect the light transmitted from the optical fiber grid structure 50.

The bending pattern of the optical fiber grating structure of the optical fiber grating structure has a structure in which the optical fiber grating 77 having the bend pattern formed in the 'S' shape is fixed to the plate-shaped support 71 in addition to the sinusoidal waveform described above, Of course, various non-linear lattice patterns, such as the structure of the English small letter 'ℓ', can be applied once.

The fiber grating can be stretched by temperature in addition to strain as is known.

Therefore, when the external environment of the object to be measured does not vary in temperature or the strain does not vary, the amount of deformation caused by any one of the physical environmental factors may be measured using one curved fiber grating described above.

In contrast, two independent parameters are required to calculate each physical quantity in an environment in which an optical fiber lattice can be deformed for each of temperature and strain.

Therefore, a plurality of optical fiber gratings having a plurality of bending patterns having different shapes may be used by using a characteristic in which the bandwidth of reflected light to the external environment is different depending on the structure of the bending pattern of the optical fiber grating so that it can be used in such an environment. Of course, the physical quantity can be measured.

An example of such a structure is shown in FIG. 8.

Referring to FIG. 8, the optical fiber grating structure 80 is formed of an 'S' shape on a bottom surface of the first optical fiber grating 83 and the plate support 81 having a sinusoidal first bend pattern formed on an upper surface of the plate support 81. A second optical fiber lattice 85 having a two bend pattern is provided.

Unlike the illustrated example, the first optical fiber lattice 83 and the second optical fiber lattice 85 having different bending patterns on the same surface may be formed to be spaced apart from each other.

The structure deformation measuring apparatus to which the optical fiber lattice structure 80 of this structure is applied is shown in FIG. 8.

Referring to the drawings, the structure deformation measuring apparatus 90 includes a first light source 91, a first directional optical coupler 92, a first photodetector 93, a second light source 96, a second directional optical coupler ( 97), a second photodetector 98 and an optical fiber lattice structure 80.

Since the structure deformation measuring apparatus 90 has a bandwidth of reflected light with respect to incident light of the first optical fiber grating 83 and the second optical fiber grating 85 with respect to the same external environmental factor applied to the plate-shaped support 80, Using the reflected light quantity information of each of the optical fiber gratings 83 and 85 acquired through the first and second photodetectors 93 and 98, respectively, whether or not the cause of deformation is due to temperature or strain, Can be determined and calculated.

In addition, in FIG. 9, the directional optical couplers 92 and 97 are omitted, and the photodetectors 93 and 98 may be connected to detect the transmitted light of each of the optical fiber grids 83 and 85. .

Hereinafter, a structure deformation measuring method using the optical fiber lattice structure will be described.

First, the optical fiber grating having a lattice formed at equal intervals is bent and attached using a fixing material such as an adhesive to have a bend as described above on the measurement object, or described above with reference to FIGS. 1, 5, 7 and 8. The optical fiber grid structures 10, 50, 70 and 80 are fixed to the measurement object. In addition, the light source and the light emitter or the directional optical coupler may be previously coupled to the corresponding terminals of the optical fiber grid structures 10, 50, 70, 80, and then fixed to the measurement target, or the optical fiber grid structure 10 ( 50) (70) (80) may be combined after being fixed to the measurement object.

Next, light is incident on the light incidence ends of the optical fiber lattice 17, 57, 77, 83, 85 of the optical fiber lattice structure 10, 50, 70, 80, and the optical fiber lattice 17 (57) (77) (83), (85) and the light passing through or reflected by the photodetector, and from the detected light quantity information to the deformation of the optical fiber grid (17) (57) (77) (83) (85) The corresponding physical quantity can be calculated.

As described above, the method of calculating the deformation amount from the electrical signal output from the photodetector corresponds to the deformation amount when the reflected light amount changes linearly, and corresponds to the deformation amount when the nonlinearity is changed by the calculation equation. It is good to calculate by using.

As described above, according to the optical fiber grating structure and the structure deformation measuring apparatus and method using the same according to the present invention, the degree of deformation of the measurement object is determined by a method of structurally bending and supporting the optical fiber grating having a grating formed at equal intervals. By detecting a change in the corresponding amount of light, it is possible to calculate a physical quantity such as bending, stress, and temperature for the measurement object.

Claims (10)

At least one support; And at least one optical fiber grating installed on the support such that the plurality of gratings are forcibly bent at equal intervals and the plurality of gratings are nonlinearly arrayed and supported in a curved pattern. The method of claim 1, wherein the support First and second supports for fixing to the measurement object; And a curved support guide member coupled in a curved shape between the first support and the second support. The optical fiber grating structure, characterized in that coupled to the bending support guide member corresponding to the extension pattern of the bending support guide member. The method of claim 1, wherein the support is a plate-like support made of a flexible material, The optical fiber grating structure, characterized in that the optical fiber grid is fixed in a curved pattern to the plate-shaped support. The first optical fiber lattice bent in a first bending pattern and the second optical fiber lattice bent in a second bending pattern are spaced apart from each other. Optical fiber grating structure, characterized in that. At least one support; An optical fiber grating structure having at least one optical fiber grating installed on the support such that a plurality of gratings are forcibly bent at equal intervals and the plurality of gratings are nonlinearly arrayed and supported in a curved pattern; A light source for emitting light to the optical fiber grating; And a photo detector for detecting light passing through the optical fiber grating or reflected and outputting the reflected light as an electrical signal. The method of claim 5, And a directional coupler for transmitting the light emitted from the light source to the optical fiber grating and the light reflected from the optical fiber grating to the photodetector. The apparatus of claim 5, wherein the support comprises: first and second supports for fixing to a measurement object; And a curved support guide member coupled in a curved shape between the first support and the second support. And the optical fiber grating is coupled to the curved support guide member so as to correspond to the extension pattern of the curved support guide member. The apparatus of claim 5, wherein the support is a plate-shaped support made of a flexible material, and the optical fiber grating is fixed to the plate-shaped support in a curved pattern. The method of claim 5, wherein the first optical fiber lattice bent in a first bending pattern and the second optical fiber lattice bent in a second bending pattern different from the first bending pattern of the first optical fiber lattice are installed spaced apart from each other Structure deformation measuring apparatus, characterized in that. Forcibly bending an optical fiber in which a plurality of gratings are equally spaced, and installing at least one optical fiber grating on the measurement object such that the plurality of gratings are nonlinearly arrayed and supported in a curved pattern; Emitting light to the optical fiber grid; And And calculating the amount of deformation associated with the object to be measured by detecting the intensity of light passing through or reflected from the optical fiber grating.

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