JP4286382B2 - Fiber tension sensor for temperature tension measurement - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sensor used to measure local temperature and tension of a structure such as a building, a ship, or an airplane. The present invention relates to the temperature dependence and tension dependence of a reflected light peak or transmission loss peak of a fiber grating. The present invention relates to a temperature tension measurement fiber grating sensor that can measure temperature and tension with a single fiber grating.
[0002]
[Prior art]
The fiber grating has a grating portion in which perturbations such as a periodic change in the refractive index of the core and the core diameter are formed in the length direction of the optical fiber. And by designating the period (grating pitch) of this periodic change comparatively narrow, the characteristic in which the light of a specific wavelength band is reflected among the lights transmitted to the core of an optical fiber is acquired. As a result, in the wavelength spectrum of the reflected light, a peak of reflected light in a specific wavelength band (hereinafter referred to as a reflected light peak) occurs. In the wavelength spectrum of transmitted light, a transmission loss peak (hereinafter referred to as a transmission loss peak) is obtained in a wavelength band corresponding to the reflected light peak.
[0003]
In this type of fiber grating, since the effective refractive index of the core of the grating portion changes according to the temperature change, the center wavelength of the reflected light peak or transmission loss peak (hereinafter, unless otherwise noted, the peak wavelength is collectively It can be used as a temperature sensor by utilizing the fact that the center wavelength is changed.
The center wavelength usually refers to the wavelength at the center of a wavelength range that gives a half value of the maximum value of the peak.
In addition, since stress (tension) is applied to the fiber grating and the length of the optical fiber changes, the grating pitch changes. Therefore, it can be used as a tension sensor by utilizing the change in the center wavelength. Can do.
[0004]
For example, by embedding a fiber grating sensor using a fiber grating in various buildings and structures and detecting the center wavelength of the peak of the wavelength spectrum, the temperature and strain at the measurement point where the grating part is located can be optically measured. It is possible to construct a measurement system for remote measurement.
[0005]
In other sensing technologies, if the number of measurement points increases, it is necessary to increase the number of measuring instruments according to the number of increases, which increases the cost, but fiber grating sensors use time division technology or wavelength division technology to measure Even if the expensive ones are not increased, the temperature and tension at a plurality of measurement points can be measured by increasing the number of relatively inexpensive fiber gratings, which is very advantageous from the viewpoint of cost.
[0006]
[Problems to be solved by the invention]
However, in the conventional fiber grating sensor, it has been difficult to separately detect whether the change in the center wavelength of the peak as described above is due to a temperature change or a tension change. Therefore, what can measure both temperature and tension with high accuracy has been demanded.
[0007]
This invention is made | formed in view of the said situation, and makes it a subject to provide the fiber grating sensor which can isolate | separate and measure temperature and tension | tensile_strength.
It is another object of the present invention to provide a single fiber grating sensor that can measure both temperature and tension with high accuracy.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention proposes solving means as follows. The first aspect of the present invention is a grating portion in which a core of a bare optical fiber exposed by removing a part of a coating layer of one optical fiber, and the refractive index of the core periodically changing in the length direction. A synthetic resin layer is integrally provided on the outer periphery of the bare optical fiber in which the plurality of grating portions are formed, and when the tension is applied to the optical fiber, the length of the synthetic resin layer is formed. Depending on the position of the direction Because the magnitude of the tension applied to the grating part is different, The amount of change in the grating pitch of the plurality of grating portions is different from each other. And a reinforcing material is integrated on the outer surface of the synthetic resin layer. A fiber tension sensor for measuring temperature tension, which is characterized in that:
According to a second aspect of the present invention, there is provided a grating portion in which a core of a bare optical fiber exposed by removing a part of a coating layer of one optical fiber, the refractive index of the core periodically changing in the length direction. A synthetic resin layer having a thickness of 0.5 mm or more is provided on at least one grating portion on the outer periphery of the bare optical fiber formed with the plurality of grating portions, and tension is applied to the optical fiber. Is applied, the amount of change in the grating pitch of the plurality of grating portions becomes different from each other. And a reinforcing material is integrated on the outer surface of the synthetic resin layer. A fiber tension sensor for measuring temperature tension, which is characterized in that:
3rd invention is the fiber grating sensor of 1st or 2nd invention, The reinforcing material is From materials with negative linear expansion coefficient Ru This is a temperature tension measuring fiber grating sensor.
In the present invention, the term “optical fiber” includes an optical fiber or an optical fiber having a coating layer on a bare optical fiber.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an explanatory view showing an example of a fiber grating. In FIG. 1, reference numeral 1 denotes a single mode bare optical fiber. The bare optical fiber 1 includes a high refractive index core 1a and a low refractive index cladding 1b concentrically provided around the core 1a. A grating portion 4 in which the refractive index of the core 1a locally changes periodically in the length direction is provided in a part of the core 1a (optical fiber) in the length direction.
[0010]
The core 1a is made of germanium-added quartz glass, and the clad 1b is made of pure quartz glass or fluorine-added quartz glass.
The grating portion 4 can be manufactured by utilizing a so-called photorefractive effect that increases the refractive index of the germanium-added quartz glass when irradiated with ultraviolet light in a specific wavelength band, for example, as follows.
[0011]
First, an optical fiber strand having a coating layer made of an ultraviolet curable resin or the like provided on the outer periphery of the bare optical fiber 1 is prepared, and a part of the coating layer is removed to expose the bare optical fiber 1.
On the other hand, a phase mask made of a material that transmits light, such as quartz glass, and having a plurality of gratings formed on one side with a predetermined period is prepared, and the side on which the grating is formed faces the side of the bare optical fiber 1. Arrange to do. When ultraviolet light having a wavelength of about 240 nm is irradiated through this phase mask, interference fringes are generated by the grating of the phase mask, and an ultraviolet light intensity pattern is formed. As a result, the refractive index of the core 1a in the part where the interference fringes are generated changes, and the grating part 4 in which the refractive index of the core periodically changes in a period corresponding to the period of the interference part is obtained.
[0012]
2 (a) and 2 (b) show a first embodiment of a temperature tension measuring fiber grating sensor (hereinafter referred to as an FG sensor) of the present invention. FIG. FIG. 2B is a cross-sectional view taken along line AA shown in FIG. 2B, and FIG.
In this FG sensor, the bare light exposed by removing the coating layer 5 in the middle of the optical fiber (optical fiber) in which the coating layer 5 made of an ultraviolet curable resin or the like is provided on the bare optical fiber 1. A fiber grating provided with two reflection-type grating portions 4A and 4B is used for the fiber 1.
[0013]
In the length direction of the bare optical fiber 1, the grating portion 4 </ b> A is provided near the center of the exposed bare optical fiber 1, and the grating portion 4 </ b> B is provided near the end of one coating layer 5.
Moreover, the grating pitches of the grating portions 4A and 4B are different so that the center wavelengths of the peaks obtained in the grating portions 4A and 4B are different. FIG. 3 shows the wavelength spectrum of the reflected light of the FG sensor. The peak a is the reflected light peak of the grating portion 4A, and the peak b is the reflected light peak of the grating portion 4B.
[0014]
The exposed bare optical fiber 1 and the portion including the ends of the covering layer 5 on both sides of the bare optical fiber 1 are formed into a cylindrical synthetic resin tube (collective covering layer) together with a columnar reinforcing material 7 having a semicircular cross section. It is contained within 9.
The curved surface portion 7 a on the side surface of the reinforcing material 7 is in contact with the inner wall of the synthetic resin tube 9, and the fiber grating is a space surrounded by the flat surface portion 7 b on the side surface of the reinforcing material 7 and the inner wall of the synthetic resin tube 9. It is arranged near the center. A synthetic resin layer 11 is filled between the outer surface of the bare optical fiber 1 and the outer surface of the coating layer 5, and the flat portion 7 a and the inner wall of the synthetic resin tube 9, thereby forming a reinforcing structure 12. In other words, the reinforcing material 7 is integrated with the outer surface of the synthetic resin layer 11.
[0015]
The synthetic resin tube 9 is provided in order to integrate the synthetic resin layer 11 and the reinforcing material 7. When a heat shrinkable tube made of polyethylene or the like is used, the operability at the time of manufacturing the FG sensor is good. And it is hard to form a gap in the tube 9 made of synthetic resin, which is preferable. In this example, the reinforcing material 7 uses Miraclone PH-33 (manufactured by NGK).
[0016]
The outer diameter of the synthetic resin tube 9 is preferably 1 to 10 mm, more preferably 1.5 to 3 mm, from the viewpoint of space efficiency.
The thickness of the synthetic resin tube 9 is not particularly limited, but is usually 0.1 to 0.6 mm. If it is less than 0.1 mm, the effect of providing the synthetic resin tube 9 cannot be obtained, and if it exceeds 0.6 mm, the action of the synthetic resin layer 11 on the grating portions 4A and 4B may be affected. In this example, the inner diameter of the synthetic resin tube 9 is 4.3 mm, the outer diameter is 4.8 mm, and the thickness of the synthetic resin tube 9 is 0.25 mm.
[0017]
The length of the synthetic resin tube 9 (synthetic resin layer 11) (hereinafter simply referred to as the length in the length direction of the bare optical fiber 1) is 3 to 500 mm, preferably 5 to 50 mm. is there. If it is less than 3 mm, the difference in the magnitude of the tension applied to the grating portions 4A and 4B becomes small, and the sensitivity may decrease. If it exceeds 500 mm, the space efficiency is lowered, which is inconvenient. In this example, the length of the synthetic resin tube 9 is 40 mm.
[0018]
In this example, the outer diameter of the bare optical fiber 1 is about 125 μm, and the outer diameter including the coating layer 5 is about 250 μm.
The length of the bare optical fiber 1 from which the covering layer 5 in the synthetic resin tube 9 is removed is 30 mm, and the length of the covering layers 5 and 5 in the synthetic resin tube 9 on both sides of the bare optical fiber 1 is Each is 5 mm.
[0019]
The lengths (grating lengths) of the grating portions 4A and 4B are preferably 0.5 to 10 mm, respectively, but are appropriately adjusted depending on the characteristics of the grating portions 4A and 4B. In this example, the grating length of the grating portion 4A is 2 mm, and the grating length of the grating portion 4B is 2 mm.
The grating pitches of the grating portions 4A and 4B are set to 1 μm or less, preferably 0.34 to 0.58 μm in order to obtain a reflection type characteristic, but the grating pitch of the grating portions 4A and 4B is as described above. They are different from each other.
[0020]
The distance between the grating portions 4A and 4B is 4 to 400 mm, preferably 8 to 30 mm. If it is less than 8 mm, the difference in the amount of tension applied between the grating portions 4A and 4B becomes small, which may be inconvenient. If it exceeds 30 mm, the temperature difference cannot be ignored, and the temperatures of the grating portions 4A and 4B are not uniform, which may be inconvenient.
The distance from the end of the synthetic resin tube 9 on the side of the grating portion 4B to the grating portion 4B is 10 mm in this example. This distance is appropriately adjusted according to the difference in the change amount of the grating pitch due to the tension applied to the grating portions 4A and 4B.
[0021]
As the synthetic resin layer 11, polyethylene or the like is used.
Further, when the synthetic resin layer 11 is made of a material having a Young's modulus larger than the Young's modulus of the material to be measured in which the FG sensor is embedded, the grating portions 4A and 4B are hardly affected by distortion at measurement points other than the tension. ,preferable.
Since there are a wide variety of materials for the object to be measured, it is difficult to limit the range of the Young's modulus of the synthetic resin layer 11, but it is usually 1 MPa or more, and substantially 10 to 100 MPa.
[0022]
Also, when installing the FG sensor in the object to be measured, only the optical fiber coating layer 5 is embedded in the object to be measured so that the synthetic resin tube 9 and the synthetic resin layer 11 do not contact the object to be measured. If the cavity can be installed in the object to be measured, it is preferable that the grating portions 4A and 4B are similarly less susceptible to distortion at measurement points other than tension. In this case, it is not necessary to determine the Young's modulus of the synthetic resin layer 11 in consideration of the Young's modulus of the object to be measured. For example, the Young's modulus of the synthetic resin layer 11 is 0.1 MPa or more, substantially 1 to 1000 MPa. The
In this example, the synthetic resin layer 11 is made of polyethylene, and its Young's modulus is 55 MPa.
[0023]
The thickness of the synthetic resin layer 11 on the outer periphery of the bare optical fiber 1 is appropriately adjusted depending on the material, the characteristics of the FG sensor, and the like, but is at least 0.1 mm or more, preferably 0.2 to 1.0 mm.
In this example, the synthetic resin layer 11 has a minimum thickness of 0.4 mm and a maximum value of 0.6 mm.
[0024]
Ceramics or the like are used as the reinforcing material 7. Moreover, it is preferable that the linear expansion coefficient of the reinforcing material 7 is negative because the linear expansion coefficient when integrated with the synthetic resin layer 11 is close to that of the quartz glass constituting the bare optical fiber 1.
That is, since the linear expansion coefficient of the synthetic resin is larger than that of quartz glass, the center wavelength of the peaks of the grating portions 4A and 4B is not only the change of the effective refractive index of the core 1a but also the synthetic resin layer 11 due to the temperature change. Changes under the influence of expansion and contraction. This influence can be corrected by measuring in advance.
However, in this example, the linear expansion coefficient when the synthetic resin layer 11 and the reinforcing material 7 are integrated by canceling out the linear expansion coefficient of the synthetic resin layer 11 and the linear expansion coefficient of the reinforcing material 7. Is substantially equal to the linear expansion coefficient of the material of the bare optical fiber 1. Therefore, it is not necessary to correct the expansion and contraction accompanying the temperature change of the synthetic resin layer 11, and the measurement accuracy can be further improved.
[0025]
The linear expansion coefficient of quartz glass is 5 × 10 ^-7 ~ 6 × 10 ^-7 The coefficient of linear expansion of a synthetic resin such as polyethylene is, for example, 1 × 10 ^-Four ~ 4x10 ^-Four Therefore, the coefficient of linear expansion of the material of the reinforcing material 7 is −20 × 10 ^-Five ~ -4x10 ^-Five Is preferable.
In this example, the linear expansion coefficient of the synthetic resin layer 11 is 4 × 10. ^-Four The reinforcing material 7 is ceramic, and its linear expansion coefficient is −5 × 10 ^-Five It is.
Although the reinforcing material 7 is not an essential configuration, it is preferable to provide the reinforcing material 7 because the linear expansion coefficient of the synthetic resin layer 11 can be adjusted as described above and the mechanical strength of the FG sensor is improved.
[0026]
This FG sensor can be manufactured as follows.
First, the reinforcing material 7 is put in the synthetic resin tube 9 before heating. On the other hand, the ends of the bare optical fiber 1 of the fiber grating and the covering layer 5 on both sides thereof are placed in a tube constituting the synthetic resin layer 11, and this tube is further placed in a synthetic resin tube 9.
Next, when the synthetic resin tube 9 is heated from the outside, the synthetic resin tube 9 contracts, and the tube constituting the synthetic resin layer 11 melts and fills the gap in the synthetic resin tube 9. 11 As the synthetic resin hardens, the reinforcing material 7, the synthetic resin layer 11, the fiber grating, and the synthetic resin tube 9 are integrated to obtain the reinforcing structure 12.
[0027]
In this FG sensor, the synthetic resin layer 11 is integrally provided on the outer periphery of the bare optical fiber 1 in which the grating portions 4A and 4B are formed, and the bare optical fiber 1 in the synthetic resin layer 11 is composed of the synthetic resin layer. 11 is held with a uniform holding force.
Therefore, when a tension is applied to the optical fiber drawn from the reinforcing structure 12 due to the strain at the measurement point, the tension is gradually attenuated in the synthetic resin layer 11. As a result, in the vicinity of the center of the synthetic resin layer 11 in the length direction, the tension applied to the bare optical fiber 1 is reduced and the tension applied to the end of the synthetic resin layer 11 is increased. Is formed.
[0028]
Since the grating portions 4A and 4B are provided near the center and near the end in the length direction of the synthetic resin layer 11, the magnitudes of tension applied to the grating portions 4A and 4B are different. As a result, the amount of change in the grating pitch of the grating portions 4 and 4B is different, and the amount of change in the center wavelength of the peak in the wavelength spectrum is different from each other.
[0029]
On the other hand, the grating portions 4A and 4B are close to the temperature change, and show the same amount of change in the center wavelength due to the same refractive index change.
Therefore, when the wavelength spectrum of the reflected light or the wavelength spectrum of the transmitted light in the grating sections 4A and 4B is monitored, if the amount of change in the center wavelength of each peak is different, tension is applied, and the amount of change is If they are the same, a temperature change has occurred.
[0030]
When temperature change and strain occur at the measurement point at the same time, measure the tension from the difference in the center wavelength of each peak, and measure the temperature from the change in the center wavelength after subtracting the tension change. Tension can be measured simultaneously.
In this example, the number of grating portions is two, but there is no particular limitation as long as there are a plurality of grating portions, the amount of change in the center wavelength with respect to temperature is substantially equal, and the change in center wavelength with respect to tension is different from each other. .
[0031]
Thus, in this FG sensor, it is possible to determine whether the change in the center wavelength of the peak of the wavelength spectrum is due to temperature or tension. Therefore, temperature and tension can be measured separately, and the measurement accuracy is improved. Moreover, since temperature and tension can be measured with one FG sensor, it is advantageous in terms of cost and space efficiency.
Further, since the reinforcing structure 12 constituting the FG sensor is a compact configuration including the synthetic resin layer 11, the reinforcing material 7, and the synthetic resin tube 9, the applicable location is wide regardless of the installation location. In addition, the configuration is simple and the cost is low.
[0032]
FIG. 4 is a side sectional view showing a second embodiment of the FG sensor of the present invention.
In this FG sensor, a bare optical fiber 1, which is exposed by removing two coating layers in the middle of an optical fiber in which a coating layer 5 made of an ultraviolet curable resin or the like is provided on the bare optical fiber 1, is exposed. 1, a fiber grating provided with reflective grating portions 4C and 4D is used.
[0033]
A reinforcing structure 12C having the same configuration as the reinforcing structure 12 of the first embodiment is provided on the outer periphery of the bare optical fiber 1 in which the grating portion 4C is formed. The grating portion 4C is located near the center in the length direction of the synthetic resin tube 9 (synthetic resin layer 11).
[0034]
In this example, the inner diameter and outer diameter of the synthetic resin tube 9 are the same as those in the first embodiment.
Moreover, the preferable range about the length of the synthetic resin tube 9 (synthetic resin layer 11) is the same as that of the first embodiment.
Further, the length of the bare optical fiber 1 from which the coating layer 5 in the synthetic resin tube 9 is removed, and the length of the coating layer 5 in the synthetic resin tube 9 on both sides of the bare optical fiber 1 are the first embodiment. Similar to the example.
[0035]
The grating lengths, grating pitches, and distances between the grating portions 4C and 4D are the same as those of the grating portions 4A and 4B in the first embodiment.
Conditions such as the thickness and Young's modulus of the synthetic resin layer 11 are the same as those in the first embodiment.
[0036]
On the other hand, on the bare optical fiber 1 on which the grating portion 4D is formed, a re-coating layer 5A formed of the same ultraviolet curable resin as the material of the coating layer 5 is provided. The outer diameter of the re-coating layer 5A is substantially equal to the outer diameter of the covering layer 5, and in this example is about 250 μm. For example, after forming the grating portion 4D on the bare optical fiber 1, the re-coating layer 5A is coated with an uncured ultraviolet curable resin on the bare optical fiber 1 and then cured by irradiating with ultraviolet light. Is formed.
[0037]
In this fiber grating, since the relatively thick synthetic resin layer 11 constituting the reinforcing structure 12C is provided on the grating portion 4C, the tension applied to the grating portion 4C with respect to the strain at the measurement point is small. Since a thin re-coating layer 5A similar to the coating layer 5 of the optical fiber is provided on the part 4D, the tension applied to the grating part 4D increases with respect to the strain at the measurement point. As a result, the amount of change in the grating pitch in the grating portions 4C and 4D can be made different.
The magnitude of the tension applied to the grating portion 4C can be adjusted by changing the Young's modulus of the material of the synthetic resin layer 11, the thickness and length of the synthetic resin layer 11, and the like.
[0038]
Further, the amount of change in the center wavelength of the peak of the wavelength spectrum of the grating parts 4C and 4D with respect to the temperature change at the measurement point is that provided on the outer periphery of the bare optical fiber 1 is the synthetic resin layer 11 and the re-coating layer 5A. Yes, because they are different, they are not equal. However, the influence by the synthetic resin layer 11 is not so great, and it can be corrected by investigating the influence of the synthetic resin layer 11 and the re-coating layer 5A on the grating portions 4C and 4D in advance with respect to the temperature change.
Therefore, also in this configuration, temperature and tension can be measured separately, and the same effect as in the first embodiment can be obtained.
[0039]
FIG. 5 shows a third embodiment of the present invention. The difference from the second embodiment is that the Young's modulus of the synthetic resin layer 11 is formed on both of the two grating portions 4E and 4F. Except for the difference, the reinforcing structures 12E and 12F having the same configuration as the reinforcing structure 12C are provided.
The grating portions 4E and F are located near the center in the length direction of the synthetic resin tubes 9 and 9 (synthetic resin layers 11 and 11), respectively.
The grating parts 4E and 4F are the same as the grating parts 4C and 4D of the second embodiment.
[0040]
In this example, the size of the members constituting the two reinforcing structures 12E and 12F is equal to the reinforcing structure 12C of the second embodiment. However, the materials of the two synthetic resin layers 11 and 11 are made of, for example, polyethylene and are the same, but their Young's moduli are different. In this example, the Young's modulus of the synthetic resin layer 11 constituting the reinforcing structure 12E is 10 MPa, and the Young's modulus of the synthetic resin layer 11 constituting the reinforcing structure 12F is 100 MPa. The difference in Young's modulus between these synthetic resin layers 11 and 11 can be adjusted as appropriate depending on the characteristics of the FG sensor, but is usually 20 to 200 MPa.
[0041]
In this fiber grating, since the Young's modulus of the synthetic resin layers 11 and 11 provided on the outer circumferences of the grating portions 4E and 4F is different, the tension applied to the grating portions 4E and 4F with respect to the strain at the measurement point is different. It will be different. That is, the greater the Young's modulus, the smaller the tension applied to the grating portion, and the greater the Young's modulus, the greater the tension applied to the grating portion. Therefore, the amount of change in the grating pitch in the grating sections 4E and 4F differs with respect to the distortion at the measurement point, and the amount of change in the center wavelength of the wavelength spectrum differs from one another.
On the other hand, since the amount of change in the center wavelength of the wavelength spectrum of the grating portions 4E and 4F with respect to temperature change is substantially equal, temperature and tension can be measured separately as in the first embodiment.
[0042]
Further, in this FG sensor, the synthetic resin layer 11 constituting the reinforcing structures 12E and 12F is formed from a material having the same Young's modulus, and the lengths of the synthetic resin layers 11 and 11 are different from each other. Similar effects can be obtained.
That is, as the grating portion is positioned near the center in the length direction of the synthetic resin layer 11 as described above, the magnitude of the tension applied to the grating portion with respect to the distortion at the measurement point becomes smaller. Therefore, by increasing the length of one side and arranging the grating portion near the center thereof, the amount of change in the grating pitch with respect to the distortion at the measurement point is made smaller than the grating portion in the other synthetic resin layer 11, and A difference can be provided in the amount of change in the center wavelength of the peak of the wavelength spectrum of the grating portion. The difference in length between the synthetic resin layers 11 and 11 can be adjusted as appropriate depending on the characteristics of the FG sensor, but is usually 5 to 300 mm.
[0043]
FIG. 6 is a schematic diagram showing an example of a measurement system using the FG sensor of the present invention.
This measurement system measures temperature and tension at the first measurement point to the fourth measurement point. The reinforcing structure shown in FIG. 2 extends along one optical fiber 13 along its length. FG sensors having 12 are formed at intervals of four.
[0044]
Grating portions 4G and 4H are formed in the reinforcing structure 12 at the first measurement point, and grating portions 4I and 4J are formed in the reinforcing structure 12 at the second measurement point. The grating portions 4K and 4L are formed, and the grating portions 4M and 4N are formed in the reinforcing structure 12 at the fourth measurement point. The center wavelengths of the reflected light peaks of these grating portions 4G,..., 4N are set to be different from each other by a predetermined wavelength.
Further, the end of the optical fiber 13 on the fourth measurement point side is a non-reflective terminal by a conventional method. On the other hand, the end of the optical fiber 13 on the first measurement point side is connected to a light source and a spectrum analyzer via a 3 dB coupler.
[0045]
Then, when light having a relatively wide wavelength band is incident on the optical fiber 13 from the light source and the wavelength spectrum of the reflected light is detected by the spectrum analyzer, as shown in FIG. 7, the grating portions 4G,. Each corresponding peak g,..., N is obtained.
And the temperature and tension | tensile_strength of a 1st measurement point can be measured by measuring the change of the center wavelength of the peaks g and h. Similarly, the temperature and tension at the second measurement point to the fourth measurement point can be measured by measuring the change in the center wavelength of the peaks i,..., N.
[0046]
Therefore, a measurement system capable of measuring at a plurality of measurement points can be configured with one light source and a spectrum analyzer, and the cost is low.
In this measurement system, the wavelength spectrum of the reflected light was detected, but the spectrum analyzer was connected to the end of the optical fiber 13 on the fourth measurement point side, and the wavelength spectrum of the transmitted light of the grating portions 4G,. The temperature and tension can be measured in the same manner by measuring the change in the center wavelength of the transmission loss peak.
[0047]
【The invention's effect】
As described above, in the FG sensor of the present invention, it can be determined whether the change in the center wavelength of the peak of the wavelength spectrum is due to temperature or tension. Therefore, temperature and tension can be measured separately, and the measurement accuracy is improved. Moreover, since temperature and tension can be measured with one FG sensor, it is advantageous in terms of cost and space efficiency.
Moreover, since it is a compact structure, an applicable location becomes a wide range regardless of an installation location. In addition, the configuration is simple and the cost is low.
Further, the reinforcing material made of a material having a negative linear expansion coefficient is integrated on the outer surface of the synthetic resin layer, so that the linear expansion coefficient when the synthetic resin layer and the reinforcing material are integrated constitutes a bare optical fiber. Since it is close to quartz glass, it is not necessary to correct the expansion and contraction accompanying the temperature change of the synthetic resin layer, and the measurement accuracy can be further improved.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an example of a fiber grating.
FIG. 2 shows a first embodiment of a temperature tension measuring fiber grating sensor of the present invention. FIG. 2 (a) is a cross-sectional view taken along line AA in FIG. 2 (b), and FIG. b) is a sectional side view.
FIG. 3 is a graph showing a wavelength spectrum of reflected light of an FG sensor.
FIG. 4 is a side sectional view showing a second embodiment of the FG sensor of the present invention.
FIG. 5 is a side sectional view showing a third embodiment of the FG sensor of the present invention.
FIG. 6 is a schematic diagram showing an example of a measurement system using the FG sensor of the present invention.
7 is a graph showing an example of a wavelength spectrum of reflected light obtained in the measurement system shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Bare optical fiber, 1a ... Core, 1b ... Cladding,
4A, 4B, 4C, 4D, 4E, 4F ... grating part, 5 ... coating layer,
11 ... Synthetic resin layer, 12, 12C, 12E, 12F ... Reinforcing structure,
13: An optical fiber (optical fiber).

Claims (3)

A bare optical fiber core exposed by removing a part of the coating layer of one optical fiber is formed with a plurality of grating portions in which the refractive index of the core periodically changes in the length direction. ,
Periphery on the synthetic resin layer of the plurality of grating sections formed was bare optical fiber is provided integrally, when the tension in the optical fiber is applied, the grating portion by the position of the length direction of the synthetic resin layer Since the magnitude of the applied tension is different, the amount of change in the grating pitch of the plurality of grating portions is different from each other, and the reinforcing material is integrated on the outer surface of the synthetic resin layer. Features a fiber tension sensor that measures temperature tension. A bare optical fiber core exposed by removing a part of the coating layer of one optical fiber is formed with a plurality of grating portions in which the refractive index of the core periodically changes in the length direction. ,
A synthetic resin layer having a thickness of 0.5 mm or more is provided on at least one grating portion on the outer periphery of the bare optical fiber in which the plurality of grating portions are formed, and when a tension is applied to the optical fiber, A temperature tension measuring fiber grating sensor , wherein the change amounts of the grating pitches of the plurality of grating portions are different from each other, and a reinforcing material is integrated with an outer surface of the synthetic resin layer . In the fiber grating sensor according to claim 1 or 2, wherein the reinforcing material, the temperature tension measuring fiber grating sensor, wherein ing of a material having a negative coefficient of linear expansion.

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