JP3924298B2 - Optical fiber sensor and light scattering strain measurement method - Google Patents

Description

  The present invention relates to an optical fiber sensor and a strain measurement method using the same, and more particularly to an optical fiber sensor for measuring and monitoring deformation of a civil engineering structure and a strain measurement method using the same.

  Civil engineering structures such as tunnels need to be known for structural stability by measuring strain. As such a measurement technique, an optical strain measurement sensor that measures strain of an optical fiber is known. Two types of optical strain measurement sensors, BOTDR (Brillouin Optical Time Domain Reflectometer) and FBG (Fiber Bragg Grating), are known as high-precision measurement devices. Changes in the dynamic scattered light spectrum of the Brownian motion of the material due to strain, or optical interference of light passing through the grating is used. In order to detect a slight change in optical properties, it is required to avoid the generation of noise as much as possible.

  As a sensor for measuring the deformation of a soil structure, as shown in Patent Document 1, an optical fiber and a tube having elasticity around it are integrated, and the sensor is folded at its tip. Yes. The optical fiber is used by folding the optical fiber at its tip. If the bending radius of the optical fiber is small at the folded portion, the optical fiber is easily broken. Furthermore, when the bending radius of the optical fiber is small, a part having a different reflection condition in the optical fiber may occur, and the attenuation rate of the transmitted light may increase.

  On the other hand, if the bending radius of the optical fiber is increased, the thickness of the tube that accommodates the optical fiber is largely avoided, and the driving operation when the optical fiber sensor is buried in the ground becomes difficult, or the ground is damaged by driving. There are effects such as deformation.

JP-A-10-176965

  The object of the present invention is to follow the benefits of known high-accuracy detection as it is, to avoid the generation of noise due to distortion of the folded portion, and to be easily embedded in the soil without being affected by the size of the folded portion. It is to provide an optical fiber sensor.

  As for the optical fiber sensor of this invention, the optical fiber (11) is accommodated in the housing | casing. The optical fiber (11) is formed as a folded portion (11t) that is bent to form a folded portion, and a two-wire portion that is formed as two pieces connected to both ends of the folded portion (11t). The housing is formed as a first housing portion (12) that accommodates the folded portion and a second housing portion (13) that accommodates the two-wire portion and is coupled to the first housing portion (12). The first housing portion (12) is tapered to the side opposite to the side that couples to the second housing portion (12). The optimum shape of the tapered shape is a cone.

  Since the second housing (13) that accommodates the folded portion (11t) is formed in a shape that is easy to be driven in, the size of the second housing is large (the cross-sectional area is large on the cross section perpendicular to the driving direction). ) Can be designed, and as a result, distortion due to bending of the folded portion (11t) does not occur. Since the generation of the bending distortion is avoided, the generation of the deviation noise of the frequency spectrum of the scattered / transmitted / interfering light due to the bending distortion can be avoided, and the measurement of the distortion of the civil engineering structure can be made highly accurate. In particular, when the scattered light is Brillouin scattered light, the effect of improving the accuracy is significantly high.

  The two line portions are fixed to the second housing portion at a set length interval. The set length is longer than the pulse width of the measurement light passing through the two lines. By setting such measurement conditions, the improvement in accuracy is dramatically improved.

  Both are fixed to the second housing part, but the folded part is not fixed to the first housing part. Such an embodiment is remarkably reasonable.

  It is practically remarkable that the second housing portion (12) includes a guide pipe (34), the two main wire portions are passed through the guide pipe (34), and the two main wire portions are fixed to the guide pipe (34). It is advantageous for the peak.

  The light scattering strain measurement method according to the present invention is a method for measuring the strain of an optical fiber portion that is strained by the spectral shift of Brillouin scattered light using the above-described optical fiber sensor. After embedding the first housing part and the second housing part in the civil engineering structure, confirming that the Brillouin scattered light is in the vicinity of the measurement target point, and confirming that, the spectral width of the Brilliance scattered light is The multi-step measurement of calculating the Brillouin scattered light spectrum shift after confirming that it is properly minimum and that the spectral width is minimum is noise-free. Under the environment, high-precision measurement is practically realized. By providing the condition of the length of the fixed interval, the high precision performance is further improved.

  The optical fiber sensor and the light scattering strain measurement method according to the present invention facilitate the embedding work in the soil when it is premised on avoidance of noise generation.

  The best mode of implementation of the optical fiber sensor according to the present invention will be described with reference to the drawings. The optical fiber sensor 10 is shown as an FBG type sensor, as shown in FIG. The optical fiber sensor 10 is used entirely or partially embedded in the embankment. The optical fiber sensor 10 measures the deformation (strain) generated in the embankment. The optical fiber sensor 10 includes an optical fiber 11, a tube 12, and a tip cap portion 13. One end portion 11a of the optical fiber 11 is connected to a light receiving device (not shown) that enters light into the optical fiber 11 and receives the reflected light. The other end portion 11b of the optical fiber 11 is inserted through the upper portion of the inner surface of the tube 12 from the proximal end side 12a toward the distal end portion 12b, and is folded at a position where the distal end portion 12b exits the tube 12. The inner surface lower portion of the tube 12 is inserted toward the proximal end side 12a. Thereby, the deformation | transformation which arose in the embankment in the upper position or the lower position of the pipe | tube 12 is measurable.

  The tube 12 is provided with another optical fiber (not shown) in addition to the optical fiber 11 in order to measure the deformation that has occurred in the embankment at the lateral left or right position of the tube 12. ing. One end of the optical fiber is connected to the above-described light receiving device, and the other end is inserted through the left inner surface of the tube 12 from the proximal end 12a toward the distal end 12b, and from the distal end 12b to the tube 12 Then, the tube 12 is inserted at the position where the tube 12 is exposed to the outside, and the right inner portion of the tube 12 is inserted toward the base end portion 12a. With such two optical fibers, it is possible to measure the deformation generated in the embankment in the four directions, up, down, left, and right around the tube 12.

  The optical fiber 11 is fixed to the inner surface of the tube 12 at fixed points 19 at predetermined intervals in the longitudinal direction of the optical fiber 11. An epoxy resin adhesive is used as the fixing means. A plurality of optical filters (not shown) having different refractive indexes are preferably provided at predetermined intervals in the longitudinal direction of the core (not shown) of the optical fiber 11 of the optical fiber sensor 10 of the FBG type. . The plurality of optical filters reflect only light having a specific wavelength out of incident light. When the tube 12 is deformed by the deformation of the embankment and the optical fiber 11 expands and contracts following the deformation of the tube 12, the interval between the lattices of the filter changes, and the wavelength of the reflected light changes with the change. Thereby, the deformation of the embankment can be measured.

  The optical fiber 11 has a configuration in which the optical fiber body is covered. The diameter of the optical fiber main body is 125 μm, and the diameter of the optical fiber 11 including the coating is 200 μm to 2 mm.

  The tube 12 is made of a substance (metal, resin, etc.) that follows the deformation of the object, for example, vinyl chloride. The material of the pipe 12 is selected so as to have a hardness that does not cause the earth pressure to be crushed and to be deformable following the deformation of the measurement object (for example, embankment). For measuring the deformation of the measuring object in the extending direction, the tube 12 is a substance (metal, resin, etc.) having a shape (such as a bellows structure) that follows the deformation of the object, for example, a metal bellows. Can be a tube.

  A tip cap portion 13 that covers a portion of the optical fiber 11 that protrudes from the tip portion 12 b of the tube 12 is provided at the tip portion of the optical fiber sensor 10. The tip cap portion 13 includes a substrate portion 14, a cover main body portion 15 and a circumferential wall portion 16 provided on the substrate portion 14.

  The substrate part 14 is formed in a circular flat plate shape. A hole having a diameter equal to or larger than the inner diameter of the tube 12 is formed in the central portion of the substrate portion 14, and the optical fiber 11 protrudes from the distal end portion 12 b of the tube 12 to the outside through the hole. A circumferential wall portion 16 is erected on the substrate portion 14. The circumferential wall means a wall formed in a cylindrical shape whose circumferential direction is closed (continuous). The inner peripheral portion 16a of the circumferential wall portion 16 is connected to the outer diameter portion 12c of the tube 12 by an adhesive (not shown) over the entire circumference.

  The bending radius r of the portion of the optical fiber 11 that protrudes from the tip 12b of the tube 12 is 30 mm or more. The cover main body 15 is formed to have a size that can accommodate the folded portion 11t of the optical fiber 11 having the bending radius r in a non-contact state with the folded portion 11t. The cover main body 15 is formed in a generally bowl shape, and has a first portion 15a, a second portion 15b, and a third portion 15c. The first portion 15a is formed in a conical shape with an open bottom. The third portion 15c is a circumferential wall portion that is erected on the outermost peripheral portion of the substrate portion 14 and formed so that its diameter gradually decreases. The second portion 15b is formed continuously with the first portion 15a and the third portion 15c so as to connect the first portion 15a and the third portion 15c, and the second portion 15b is formed from the largest diameter portion of the first portion 15a. It is a surrounding wall part formed so that the diameter gradually increases to the smallest diameter part of the three parts 15c.

  According to the present embodiment, since the cover main body portion 15 is used, the folded portion 11t of the optical fiber 11 has a bending radius that causes no problem with respect to the characteristics of the transmission light of the optical fiber 11 and the strength characteristics of the optical fiber 11. (In the present embodiment, it is set to 30 mm or more). Furthermore, since the cover main body portion 15 is formed in a generally bowl shape, it is likely to be driven when the optical fiber sensor 10 is driven into the ground or the like like a pile. On the other hand, since the tube 12 that accommodates the optical fiber 11 can be configured to be sufficiently thin except for the folded portion 11t of the optical fiber sensor 10, it is easy to be driven and the influence of the bumps on the ground due to the driving is minimized. Can be suppressed.

  FIG. 2 shows another embodiment of the optical fiber sensor according to the present invention. The optical fiber sensor 20 of the present embodiment is a BOTDR type here. For example, as shown in FIG. 2, the optical fiber sensor 20 is embedded along the circumferential direction of the circumferential surface SR of the tunnel pit K, and measures deformation (strain) generated in the tunnel.

  As shown in FIG. 3, the optical fiber sensor 20 includes an optical fiber 21, a tube 22, and a tip cap portion 23. One end 21a of the optical fiber 21 is connected to a light receiving device (not shown) that receives light into the optical fiber 21 and receives the reflected light. The other end portion 21b of the optical fiber 21 is inserted through the inside of the tube 22 from the proximal end side 22a toward the distal end portion 22b, and is folded at a position where the distal end portion 22b exits the tube 22, and then the tube 22 The inside of 22 is inserted toward the base end side 22a. The point that the two optical fibers 21 are used is the same as the above-described embodiment. The optical fiber 21 is fixed to the inner surface of the tube 22 at fixed points 29 at fixed intervals DS set to be greater than GL (gauge length) in the longitudinal direction of the optical fiber 21. An epoxy resin adhesive is used as the fixing means. In this case, the optical fiber 21 is fixed in a state where a uniform strain is generated (for example, a state in which a tension of 0.1% is applied) between the fixed points 29 and 29.

  The optical fiber 21 has a configuration in which the optical fiber body is covered. The diameter of the optical fiber main body is 125 μm, and the diameter of the optical fiber 21 including the coating is 200 μm to 2 mm. The tube 22 is made of vinyl chloride. The material of the tube 22 can be considered similarly to the tube 12. The tip cap portion 23 that covers the portion of the optical fiber 21 that protrudes from the tip portion 22a of the tube 22 is provided at the tip portion of the optical fiber sensor 20 in the same manner as described above.

  In the present embodiment, it is essential that the distance DS at which the optical fiber 21 is fixed to the tube 22 is equal to or greater than the GL described above. The light pulse enters the optical fiber 21 from its one end 21a. The incident light pulse propagates in the optical fiber 21 and is scattered in the optical fiber 21. Thereafter, the light receiving device receives the scattered light via the one end 21a. The light receiving device measures the longitudinal characteristics (presence or absence of deformation) of the optical fiber 21 from the relationship between the light reception timing (time) of the received backscattered light and the light intensity. In other words, the intensity of the received light becomes constant as the light receiving time from the incidence to the light reception becomes longer, in other words, as the distance in the longitudinal direction of the optical fiber 21 from the one end 21a increases. If the ratio is smaller, the characteristics in the longitudinal direction of the optical fiber 21 are uniform, and it can be seen that the optical pulse propagates while being attenuated according to the distance in the longitudinal direction of the optical fiber 21.

  In the BOTDR apparatus, attention is paid to Brillouin scattered light in the backscattered light. A value considered to be the center of the light intensity of the received Brillouin scattered light is extracted, and the frequency (center frequency) of the center value is detected. If distortion occurs at a point (measurement section) where the Brillouin scattered light is scattered in the longitudinal direction of the optical fiber 21, it appears as a change in the center frequency. Thereby, the deformation in the tunnel mine can be measured.

  As shown in FIG. 4, the pulse width (pulse duration) of the optical pulse incident from the BOTDR device 61 is 10 nsec. When the optical pulse is incident on the optical fiber 21 and propagates, the optical pulse corresponds to a length of 1 m in the optical fiber 21. In the present embodiment, this 1 m is the GL described above (see FIG. 5). The received Brillouin scattered light includes all of the scattered light generated within 1 m. This 1 m is a measurement section for distortion detection.

  Here, a case is considered in which the optical fiber 21 is fixed to the tube 22 at an interval of 20 cm, which is smaller than 1 m. Furthermore, here, distortion occurs in the portion of the 20 cm optical fiber 21 whose both ends are fixed, and for example, the distortion levels at the three adjacent points are different from each other (see FIG. 6). In this case, the Brillouin scattered light corresponding to the 1 m measurement section including the 20 cm portion includes three spectra having different center frequencies as shown in FIG. In this state, it is very difficult to obtain a single center frequency from the whole including three spectra. Backscattered light is more difficult because it usually contains noise. For this reason, the deformation that occurred locally in the measurement section (GL section) (20 cm with respect to 1 m, that is, in a small area with respect to GL) may not be measured. It should be noted that it is impossible to measure a 1 m measurement section unless the distortion is a uniform level within a range of at least about 50%.

  On the other hand, in the present embodiment, as described above, the optical fiber 21 is fixed to the tube 22 at fixed intervals DS set to be GL or more. Here, the fixed interval DS is 1 m. As in the case described above, it is assumed that three portions each having a length of 2 mm are generated in a portion of the optical fiber 21 and the three strain levels are different from each other. When only both ends of a 1 m (fixed interval DS) section are fixed, the optical fiber 21 can be freely expanded and contracted (without restriction) in the 1 m section between the both ends. Accordingly, in the portion of the 1 m optical fiber 21 whose both ends are fixed, the distortions generated in the 1 m (here, three distortions having different levels) are averaged in the 1 m section. As a result, a single distortion of a certain level is generated in the 1 m section over almost the whole area or most of the section. As a result, Brillouin scattered light having a single center frequency can be obtained from the 1 m measurement section, and stable measurement can be performed even if the deformation is local to the measurement section (GL section). Can do.

  FIG. 8 shows still another embodiment of the optical fiber sensor according to the present invention. The optical fiber sensor 30 is a BOTDR type. As shown in FIG. 8, for example, when the tunnel pit K is viewed from the front, the optical fiber sensor 30 is radially embedded from the peripheral surface SR in the pit toward the ground, and the deformation ( Measure the distortion.

  As shown in FIG. 9, the optical fiber sensor 30 includes an optical fiber 31, a pipe 32, a tip cap portion 33, and a guide pipe 34. The guide pipe 34 has substantially the same length as the length of the pipe 32 in the longitudinal direction. The outer diameter of the guide pipe 34 is smaller than the inner diameter of the tube 32, and the inner diameter of the guide pipe 34 is larger than the outer diameter of the optical fiber 31. Two guide pipes 34 are fixed to the upper and lower portions of the inner surface of the tube 32 in a side view. Each guide pipe 34 is fixed to the inner surface of the pipe 32 with an adhesive 71 (see FIGS. 12 and 13) over the entire area in the longitudinal direction of the guide pipe 34.

  The optical fiber 31 has a configuration in which the optical fiber body is covered. The diameter of the optical fiber main body is 125 μm, and the diameter of the optical fiber 31 including the coating is 200 μm to 2 mm. The tube 32 is made of vinyl chloride. The material of the tube 32 can be considered in the same manner as the tube 12. The guide pipe 34 is a metal or resin pipe. The guide pipe 34 is made of a material that can be deformed following the deformation of the pipe 32. Further, when the guide pipe 34 is deformed, the guide is larger than the outer diameter of the optical fiber 31 so that the optical fiber 31 in the guide pipe 34 is deformed along the deformed guide pipe 34 (as it is deformed). It is necessary that the inner diameter of the pipe 34 is not too large. Further, the inner surface of the guide pipe 34 needs to have a small coefficient of friction (easy to slide) so as not to hinder expansion and contraction of the optical fiber 31.

  One end 31a of the optical fiber 31 is connected to a device (not shown) that receives light in the optical fiber 31 and receives the scattered light. The other end portion 31b of the optical fiber 31 is inserted through the inside of the first guide pipe 34 from the proximal end side 34a toward the distal end portion 34b, and from the distal end portion 34b to the tube 32 (or the first guide pipe 34). The second guide pipe 34 is inserted into the second guide pipe 34 toward the base end side 34a. The point that the two optical fibers 31 are used is the same as the above-described embodiment.

  The optical fibers 31 are fixed to the inner surface of each guide pipe 34 at fixed points 39 at fixed intervals DS set to be GL or more in the longitudinal direction of the optical fiber 31. As the fixing means, an epoxy resin adhesive 72 (see FIG. 13) is used.

  As shown in FIGS. 12 and 13, the guide pipe 34 is fixed to the inner surface of the pipe 32 with an adhesive 71 at a place other than the fixing point 39, and the optical fiber 31 is fixed to the guide pipe 34. Is not fixed. As shown in FIG. 13, at the fixing point 39, the guide pipe 34 is fixed to the inner surface of the pipe 32 with an adhesive 71 and the optical fiber 31 is fixed to the guide pipe 34 with an adhesive 72. Has been.

  At the distal end portion of the optical fiber sensor 30, a distal end cap portion 33 that covers a portion of the optical fiber 31 that protrudes from the distal end portion 32 b (34 b) of the tube 32 (or the guide pipe 34) is provided. The configuration of the tip cap portion 33 is the same as the configuration of the tip cap portion 13 of the above-described form.

  In this embodiment, when the optical fiber 31 is fixed at the fixed point 39 with a fixed interval DS equal to or greater than GL, the optical fiber 31 is not fixed directly to the pipe 32 but to the guide pipe 34. It is important that As shown in FIG. 10, when the optical fiber 31 is directly fixed to the tube 32, when the interval between the adjacent fixing points 39 is large, for example, when the tube 32 is bent upward and convexly deformed. Even so, the optical fiber 31 is not deformed in the upwardly convex deformation of the tube 32 but protrudes in the direction (inside) away from the inner surface 32s of the tube 32, as indicated by the symbol M. is there. In this case, the actual amount of deformation of the optical fiber 31 is smaller than the amount of elongation that the optical fiber 31 originally needs to deform corresponding to the amount of elongation of the tube 32, or the tube 32 is deformed. On the contrary, the optical fiber 31 may be contracted and deformed. As a result, the distortion of the measurement object cannot be accurately measured.

  As shown in FIG. 11, in this embodiment, in order to solve the above problems, the optical fiber 31 is deformed in accordance with the deformation of the tube 32 and the optical fiber 31 is deformed in accordance with the deformation of the tube 32. In addition, a guide pipe 34 for guiding and regulating the optical fiber 31 is employed. The reason why the optical fiber 31 is fixed to the guide pipe 34 at a fixed interval DS equal to or greater than GL is the same as in the second embodiment described above.

  FIG. 14 shows still another embodiment of the optical fiber sensor according to the present invention. In the present embodiment, signal processing is used in a measurement method in which optical fiber measurement values are obtained continuously, such as BOTDR. The optical fiber 41 is fixed to a tube (not shown) at a predetermined fixed interval DS. In the fixed point fixing, the distortion (level) may be different between adjacent fixed points. In that case, when the backscattered light (Brillouin scattered light) is detected in a state where the measurement light that is an optical pulse straddles between the adjacent fixed points, as shown in FIG. As a result, it becomes difficult to obtain the center frequency of the light to be measured. Furthermore, the measurement value differs depending on how the measurement light straddles between the adjacent fixed points.

  Since the measurement light does not enter during the single fixed interval DS, the above problem occurs. As shown in FIG. 15, when two spectra are overlapped, the half-value width D of the spectrum is widened. In the present embodiment, paying attention to the spectrum width D, signal processing is performed by the following method shown in FIG. 18 to solve the above problem.

  As shown in step S1, it is determined whether or not it is in the vicinity of the evaluation point. That is, for example, as shown in FIG. 8, when a long optical fiber is connected to one BOTDR device and measurement values (backscattered light) are continuously obtained, a preset evaluation point (strain measurement) is obtained. In order to measure only the backscattered light at the target point), only the measurement value corresponding to the evaluation point is extracted based on the light reception timing.

  As a result of step S1, if it is determined that it is not in the vicinity of the evaluation point based on the light reception timing (step S1-N), step S1 is repeated again, and step S2 is performed only for the measurement light in the vicinity of the evaluation point. Perform the following steps. As a result of step S1, when it is determined that the position is near the evaluation point (step S1-Y), the half-value width D of the spectrum of the measurement light is calculated (step S2). It is determined whether or not the calculation result is minimum (step S3). In step S3, if it is determined that the value is smaller than a preset value, it can be determined that the value is minimum, or step S1 and step S2 are executed for a plurality of measurement lights, and the plurality of the measurement light beams are determined. It can be determined that the smallest of the is the smallest.

  As a result of step S3, when it is determined that it is not the minimum (step S3-N), the measurement position for extracting the measurement light is shifted (step S4), and the process returns to step S1 again. If it is determined as a result of step S3 that it is minimum (S3-Y), the shift amount of the center frequency is calculated (step S5). As a result of step S3, when the half-value width D of the spectrum of the measurement light is the minimum, as shown in FIGS. 16 and 17, the spectrum is uniform and the measurement light enters between the fixed intervals DS. .

  As shown in FIG. 16, the measurement interval of the signal light is set to be equal to or less than (fixed interval DS of the optical fiber 41−the length GL of the measurement light), and the spectrum half width D of the measured backscattered light is obtained. The center frequency is obtained from the spectrum of the sample point where D becomes narrow, and converted to a distortion value.

  As described above, in the present embodiment, a sensor having a finite GL, such as BOTDR and FBG, which can connect a sensor serially on an optical fiber and can measure axial strain, Four points are set as a part of the point of the said embodiment.

First point:
A sensor that measures the deformation of a pile by attaching an optical fiber to a driven pile (tube). It is. Conventionally, a bending radius of 30 mm or more is required due to the characteristics of the transmitted light and the strength characteristics of the optical fiber, and the shape of the pile itself is large. As a result, it was difficult to drive, and there was an influence such as a bump of the ground by driving.
Second point:
It is the point which made the fixed space | interval in the inside of a pile GL or more. Conventionally, since the entire surface is fixed, local deformation cannot be detected.
Third point:
The optical fiber is inserted into the guide pipe, and the optical fiber fixed at a predetermined interval causes the axial extension to occur while following the deformation of the measurement object.
Fourth point:
When evaluating the measurement value of the section fixed at a fixed point by setting the measurement interval of the signal light to be equal to or less than the (fixed interval−GL) of the optical fiber in the measurement method in which the continuous measurement value of the optical fiber is obtained like BOTDR, This is the point that the characteristics of the signal light are evaluated at the most uniform position. Conventionally, in the case of a method in which measurement values are obtained continuously as in BOTDR, when fixed points are fixed, distortion may differ between adjacent fixed points, and the measurement values may vary. This has a problem in how to obtain the distortion value of the measuring device, and it is difficult to obtain signal light generated by the light when the measurement light falls within one fixed section, and the center frequency of the light to be measured is obtained. This is because signal lights generated in adjacent fixed sections are mixed and measured.

FIG. 1 is a side view showing an optical fiber sensor according to a first embodiment of the present invention. FIG. 2 is a front view showing a state where the optical fiber sensor is used in the second embodiment of the present invention. FIG. 3 is a side view showing an optical fiber sensor according to a second embodiment of the present invention. FIG. 4 is a side view for explaining a state where an optical pulse is incident from the BOTDR device to the optical fiber sensor according to the second embodiment of the present invention. FIG. 5 is a diagram showing the relationship between incident light pulses and GL in the optical fiber sensor according to the second embodiment of the present invention. FIG. 6 is a diagram for explaining a case in which a plurality of distortions having different levels occur in a single measurement section in a conventional general optical fiber sensor. FIG. 7 is a diagram showing three spectra having different frequencies in a conventional general optical fiber sensor. FIG. 8 is a front view showing a state in which the optical fiber sensor according to the third embodiment of the present invention is used. FIG. 9 is a side view showing an optical fiber sensor according to a third embodiment of the present invention. FIG. 10 is a front view showing a state in which the deformation of the optical fiber does not follow the deformation of the tube in the conventional general optical fiber sensor. FIG. 11 is a front view showing a state in which the problem of FIG. 10 is solved in the optical fiber sensor according to the third embodiment of the present invention. 12 is a cross-sectional view taken along line X1-X1 of FIG. 13 is a cross-sectional view taken along line X2-X2 of FIG. FIG. 14 is a side view showing a state in which measurement light straddles between adjacent fixed points with respect to a conventional general optical fiber sensor. FIG. 15 is a diagram showing a state where two spectra overlap in the case of FIG. FIG. 16 is a side view illustrating a state in which measurement light enters between a single fixed point in the fourth embodiment of the present invention. FIG. 17 is a diagram showing a state where there is only a single spectrum in the case of FIG. FIG. 18 is a flowchart showing an operation flow of the fourth embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Optical fiber 11t ... Folding part 12 ... 1st housing | casing part 13 ... 2nd housing | casing part 34 ... Guide pipe

Claims (6)

Optical fiber,
A housing for housing the optical fiber,
The optical fiber is
A folded portion that is bent to form a folded portion;
A two-line portion formed as two connecting to both ends of the folded portion, respectively,
The housing is
A first housing portion that houses the folded portion;
A second housing portion that accommodates the two wire portions and is coupled to the first housing portion;
The first housing portion is tapered to a side opposite to the side coupled to the second housing portion ;
The first housing portion has a conical surface, and the first housing portion is an optical fiber sensor driven into a civil engineering structure . The optical fiber sensor according to claim 1 , wherein the second housing part is driven into the civil engineering structure together with the first housing part. Optical fiber,
A housing for housing the optical fiber,
The optical fiber is
A folded part that is bent to form a folded,
A two-line part formed as two connecting to both ends of the folded part,
The housing is
A first housing portion that houses the folded portion;
A second housing portion that accommodates the two wire portions and is coupled to the first housing portion;
The first housing portion is tapered to a side opposite to the side coupled to the second housing portion;
The two main line is fixed with respect to the second housing portion at an interval of setting the length, the set length is rather longer than the pulse width of the measuring light passing through the two lines portions,
Both the two are fixed to the second casing part, but the folded part is not fixed to the first casing part.
Optical fiber sensor. Said second housing portion comprises a guide pipe, the two main line portions is passed through the guide pipe, the two main line portions light 1 claim selected from claims 1-3 which are fixed to the guide pipe Fiber sensor. A light scattering strain measurement method for measuring strain of an optical fiber portion that is distorted by spectral shift of Brillouin scattered light using the optical fiber sensor according to claim 1,
Multiple steps below:
Embedding the first housing part and the second housing part in a civil engineering structure;
Taking out the measurement light generated in the vicinity of the measurement target point of the optical fiber from the Brillouin scattered light , and confirming that the spectral width of the measurement light is appropriately the minimum value,
A light scattering distortion measurement method comprising: calculating a shift of a spectrum of the measurement light after confirming that the spectrum width is the minimum value. A light scattering strain measurement method for measuring strain of an optical fiber portion that is distorted by spectral shift of Brillouin scattered light using the optical fiber sensor of claim 3 ,
Multiple steps below:
Embedding the first housing part and the second housing part in a civil engineering structure;
Taking out the measurement light generated in the vicinity of the measurement target point of the optical fiber from the Brillouin scattered light , and confirming that the spectral width of the measurement light is appropriately the minimum value,
A light scattering distortion measurement method comprising: calculating a shift of a spectrum of the measurement light after confirming that the spectrum width is the minimum value.

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