JP2012021921A - Light measurement system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light measurement system with which both the distortion and the temperature can be measured by using an optical fiber and the distortion information which is more precise can be measured, while suppressing the increase in costs.SOLUTION: A light measurement system capable of measuring the temperature and distortion by using an optical fiber, includes temperature detection means which detects measurement light relating to both the temperature and the distortion by using an optical fiber 2 and detects temperature from measurement light based on the state of the optical fiber arranged in a shielding member 3 which is provided on a part of the optical fiber arranged on an object to be measured and shields stress imparted on the optical fiber from the object to be measured, distortion detection means for detecting the distortion from the measurement light based on the state of the optical fiber arranged on other portions than the shielding member and temperature compensating means for compensating the result of the distortion detection means by using the result of the temperature detection means.

Description

  The present invention relates to an optical measurement system, and more particularly to an optical measurement system capable of measuring temperature and strain using an optical fiber.

  Conventionally, an optical fiber is used to measure a physical quantity distribution such as temperature and strain of an environment in which the optical fiber is installed. Such physical quantity measurement methods using optical fibers include: maintenance and management of optical communication paths, maintenance and management of large-scale structures such as dams and dikes, and materials and structures that have self-diagnosis functions for defects and failures (smart It is used for material structure. (See Patent Document 1)

  For example, when an optical fiber is embedded in a structure and a crack or the like is generated in the structure, physical stress is applied to the optical fiber in the vicinity of the crack, causing a refractive index change in the core in the optical fiber. When this refractive index change occurs, a frequency shift occurs in stimulated Brillouin scattering (SBS) generated in the fiber. Since the frequency shift amount and the fiber stress have a linear relationship, the magnitude of the stress, that is, the size of a crack or the like can be known from the magnitude of the frequency shift amount. As a measuring method using the Brillouin scattering, a method as described in Patent Document 2 or 3 is known.

  By the way, the refractive index of the optical fiber also changes depending on the environmental temperature. For this reason, the frequency shift amount due to SBS is also affected by changes in the environmental temperature, and it is difficult to obtain an accurate distortion amount.

  In order to accurately extract distortion information from the frequency shift amount of the SBS, it is necessary to subtract the change due to the environmental temperature from the measured frequency shift amount. The amount of frequency shift assumed by the temperature change has been clarified to some extent (1-2 MHz / ° C.). Therefore, accurate strain information can be obtained by measuring the temperature using an electrical temperature sensor or an optical fiber temperature sensor, calculating the frequency shift amount caused by the temperature change, and subtracting the calculated value from the measured frequency shift amount. Can be extracted.

  However, in the case of using an electric sensor, it is necessary to attach the sensor to a plurality of locations of the structure to be measured and perform measurement at the site where the structure is installed. Further, as shown in Patent Document 4, when an optical fiber temperature sensor is used, it is necessary to lay a temperature measuring fiber in addition to the strain measuring optical fiber, so at least the number of fibers is required. Problems such as an increase in construction costs arise.

  In addition, as shown in Patent Document 5, a method of simultaneously measuring strain and temperature with a single optical fiber has also been proposed, but the structure of the optical fiber itself is complicated, and the optical fiber is expensive. Become.

JP 2002-90233 A Japanese Patent No. 3667132 Japanese Patent No. 3607930 JP 2002-267425 A JP 2006-145465 A

  The problem to be solved by the present invention is to solve the above-mentioned problems, measure both strain and temperature with a single optical fiber, and measure more accurate strain information. It is an object to provide an optical measurement system that suppresses an increase in the light intensity.

  In order to solve the above problems, the invention according to claim 1 is an optical measurement system capable of measuring temperature and strain using an optical fiber, and detects the measurement light related to temperature and strain using a single optical fiber. A shield member that blocks stress applied to the optical fiber from the measurement object is disposed on a part of the optical fiber disposed on the measurement object, and the state of the optical fiber disposed in the shield member is Temperature detection means for detecting the temperature from the measurement light based on it, strain detection means for detecting strain from the measurement light based on the state of the optical fiber arranged other than the shield member, and the result of the strain detection means Temperature compensation means for compensating for the result of the detection means.

  The invention according to claim 2 is the optical measurement system according to claim 1, wherein a part of the optical fiber arranged in the shield member is provided with a fiber Bragg grating. To do.

  According to a third aspect of the present invention, in the optical measurement system according to the first or second aspect, the shield member is installed at a plurality of locations of the optical fiber, and the temperature compensation means includes two shield members. Using the result of the temperature detecting means based on the state of the optical fiber disposed in at least one or both of the two shield members, the result of the strain detecting means based on the state of the optical fiber disposed between It is characterized by compensating.

  According to a fourth aspect of the present invention, in the optical measurement system according to any one of the first to third aspects, the strain detecting means detects the strain by a measurement method using Brillouin scattering.

  The invention according to claim 5 is the optical measurement system according to any one of claims 1 to 4, wherein the temperature detection means is a measurement method using Brillouin scattering or a measurement method using a fiber Bragg grating. One of them is used to detect the temperature.

  According to a sixth aspect of the present invention, in the optical measurement system according to the fifth aspect, the temperature detection means using the measurement method using the fiber Bragg grating is different from the wavelength of the measurement light used for the strain detection means. It is characterized by using measurement light having a wavelength.

  The invention according to claim 7 is the light measurement system according to claim 6, wherein the measurement light used for the temperature detection means uses a light wave obtained by wavelength-converting the measurement light used for the strain detection means. .

  According to the first aspect of the present invention, in the optical measurement system capable of measuring the temperature and strain using the optical fiber, the measurement light related to the temperature and strain is detected using one optical fiber, and is arranged on the measurement object. In addition, a shield member that blocks stress applied to the optical fiber from the object to be measured is disposed in a part of the optical fiber, and the temperature is detected from the measurement light based on the state of the optical fiber disposed in the shield member. Temperature detecting means for detecting, strain detecting means for detecting strain from measurement light based on the state of the optical fiber arranged other than the shield member, and the result of the strain detecting means is compensated by the result of the temperature detecting means. Since it has a temperature compensation means, it is possible to measure both strain and temperature with a single optical fiber and to measure more accurate strain information. In addition, since the shield member that cuts off the stress applied to the optical fiber is locally provided, an increase in cost can be suppressed.

  According to the invention of claim 2, since a fiber Bragg grating is provided in a part of the optical fiber arranged in the shield member, the temperature of the optical fiber in the shield member can be detected efficiently. It becomes possible.

  According to the invention of claim 3, the shield member is installed at a plurality of locations of the optical fiber, and in the temperature compensation unit, the strain detection unit based on the state of the optical fiber disposed between the two shield members is provided. In order to compensate the result by using the result of the temperature detection means based on the state of the optical fiber arranged in at least one or both of the two shield members, the temperature is based on the temperature near the location where the strain is detected. Since the distortion detection result is compensated, more accurate distortion measurement is possible.

  According to the invention of claim 4, since the strain detection means detects strain by a measurement method using Brillouin scattering, it is possible to more easily realize measurement from a remote place.

  According to the invention of claim 5, the temperature detection means detects the temperature using either a measurement method using Brillouin scattering or a measurement method using a fiber Bragg grating. Measurement can be realized more easily.

  In the invention according to claim 6, since the temperature detection means using the measurement method using the fiber Bragg grating uses measurement light having a wavelength different from that of the measurement light used for the strain detection means, It is possible to separately detect different parameters of temperature and strain using a fiber.

  According to the invention of claim 7, since the measurement light used for the temperature detection means uses a light wave obtained by wavelength conversion of the measurement light used for the strain detection means, it is necessary to prepare a light source for supplying the measurement light for each parameter to be measured. Therefore, it is possible to further suppress the cost increase of the optical measurement system.

1 is a schematic view of a light measurement system according to the present invention. It is a figure explaining the shield member used for the optical measurement system of this invention. FIG. 2 is a block diagram for explaining a first embodiment according to the light measurement system of the present invention. It is a block diagram explaining the 2nd Example which concerns on the optical measurement system of this invention. It is a graph explaining the method of detecting temperature by the measuring system using a fiber Bragg grating, and temperature-compensating the distortion detection result. FIG. 5 is a block diagram illustrating a method for detecting temperature and strain by a measurement method using Brillouin scattering, which is a third embodiment according to the light measurement system of the present invention. It is a graph explaining the method of temperature compensation using the optical measurement system of FIG.

Hereinafter, the light measurement system of the present invention will be described in detail.
As shown in FIG. 1, the light measurement system of the present invention detects temperature and strain measurement light using a single optical fiber 2 in a light measurement system capable of measuring temperature and strain using an optical fiber. A shield member 3 for blocking stress applied to the optical fiber from the measurement object is disposed on a part of the optical fiber disposed on the measurement object, and the optical fiber disposed in the shield member The temperature detection means for detecting the temperature from the measurement light based on the state, the strain detection means for detecting the strain from the measurement light based on the state of the optical fiber arranged other than the shield member, and the result of the strain detection means, Temperature compensation means for compensating for the result of the temperature detection means.

  In a portion indicated by reference numeral 1 in FIG. 1, a strain / temperature measuring device 10 having both temperature detecting means and strain detecting means is arranged. In the strain / temperature measuring device 10, the strain is detected by a measurement method using Brillouin scattering, such as Brillouin optical correlation region analysis (BOCDA), as the strain measurement detecting means. Thereby, it is possible to realize measurement from a remote place more easily and with higher accuracy. The data obtained from the temperature detecting means and the strain detecting means is processed by the data processing means 11. In particular, the temperature compensating means for compensating the result of the strain detecting means with the result of the temperature detecting means is the data. It is incorporated in the processing means 11.

  FIG. 2 is a diagram illustrating the shield member 3. The optical fiber 2 is provided with a shield member 3 that covers a part of the optical fiber in order to block the propagation of stress from the measurement object. The shield member is not particularly limited to a material as long as it has mechanical strength that can block stress from the measurement object. However, the temperature from the object to be measured is preferably configured to be transmitted to the optical fiber disposed inside the shield member. For this reason, the shield member may be configured with a material having high heat transfer efficiency. preferable. For this reason, metal materials, such as stainless steel, can be used more suitably.

  A fiber Bragg grating (FBG) 4 can be provided on a part of the optical fiber 2 disposed inside the shield member 3. The FBG 4 can be detected by a method other than BOCDA as a temperature detecting means.

  FIG. 3 shows a first embodiment of the light measurement system of the present invention. The optical fiber 2 is installed inside or on the surface of a concrete structure such as a bridge as a measurement object. An FBG 4 for temperature measurement is formed in a part of the optical fiber 2. A shield member 3 shown in FIG. 2 is disposed around the optical fiber provided with the FBG.

  The strain / temperature measuring device 10 is provided with strain detection means and temperature detection means. In the strain detection means, a measurement method using Brillouin scattering such as BOCDA is used. Although it demonstrates concretely centering around the technique which pulse-forms the pump light disclosed by patent document 3, many kinds of measuring systems using Brillouin scattering like patent document 1 etc. are proposed, naturally. It goes without saying that these measurement methods can also be used in the present invention.

  Specifically, as the measurement light generating means for generating the probe light and the pump light, as shown in FIG. 3, the light wave from the semiconductor laser (LD1) is divided into two for the probe light and the pump light. The light wave for branching is introduced into the SSB modulator (SSBM) for frequency shift. Although not shown in FIG. 3, a modulated signal generated from a signal source is introduced into the SSBM. The pump light is converted into pulsed light by a Mach-Zehnder type modulator (MZ) which is a pulse modulator.

  The pump light converted into pulsed light by the MZ is amplified by the optical amplifier 13 and is incident on the optical fiber connected to the optical fiber 2. The probe light is also incident from the optical fiber connected to the optical fiber 2, and the probe light and the pump light are configured to propagate in opposite directions in the optical fiber 2. The probe light can also be amplified using an optical amplifier (not shown) as necessary.

  Probe light and pump light interact in the optical fiber 2 to generate Brillouin scattering. The Brillouin scattered light is introduced into the light receiving element (PD) by the circulator 2 on the pump light side and converted into an electric signal. The PD signal is input to the lock-in amplifier. With the pulse signal from the pulse generator 12, the drive timing of the Mach-Zehnder type modulator (MZ), which is a pulse modulator, and the lock-in amplifier is adjusted, and the electrical signal related to the measurement light is selected and transmitted at a predetermined timing. Amplified and input to the signal processing and display unit which is the data processing means 11.

  As the temperature detecting means, Brillouin scattering such as BOCDA can be used as will be described later. In addition, it can measure more simply by using fiber Bragg grating (FBG) 4. The FBG does not require a complicated optical system and driving means such as probe light and pump light unlike the BOCDA because the amount of transmitted light of the specific light wave λ1 varies depending on the temperature.

  The light wave λ1 generated from the semiconductor laser (LD2) is introduced into an optical system (optical fiber) connected to the optical fiber 2 by a multiplexing means (mux). The light wave λ <b> 1 that has passed through the FBG changes in the amount of transmitted light depending on the temperature, and is guided to the branching means (demux) side by the circulator 1.

  In the circulator 1, not only the temperature detection light wave but also the strain detection pump light is derived, so that the circulator 1 is configured to separate only the light wave λ 1 of a specific wavelength by a branching unit (demux). Reference numeral 14 denotes a terminator that receives unnecessary light that has passed through the branching means.

  The light wave λ1 separated from the branching means (demux) is compared in intensity with the output light (reference light) of the semiconductor laser (LD2), which is a light source, by a comparator to detect a change in the light amount of the light wave λ1. The result is output to the signal processing / display unit which is the data processing means 11 to detect the temperature. When the light intensity of the light source does not change, it is possible to detect the temperature only from the output light of the branching means (demux). However, since the light intensity of the light source usually changes, as shown in FIG. A comparator is used.

  In the optical measurement system of the present invention, the frequency shift amount of stimulated Brillouin scattering (SBS) caused by the temperature is obtained based on the temperature detected by the temperature detection unit, and the frequency shift amount due to the environmental temperature is calculated from the result of the strain detection unit. The frequency shift amount of the SBS due to subtraction and distortion alone is detected more accurately. Such data processing is performed by temperature compensation means incorporated in the data processing means 11.

  In FIG. 3, only one temperature detection point (FBG) is illustrated, but normally, as shown in FIG. 1, temperature detection points (shield members 3) are provided at a plurality of locations. As described above, when the shield members are installed at a plurality of locations of the optical fiber and the temperature is detected at multiple points, the temperature compensation unit can, for example, use an optical fiber disposed between two shield members (temperature detection points). It is preferable to compensate for the result of the strain detection means based on the state of the above based on the temperature result detected at one or both of the two temperature measurement points. When using both, the method of using the average value of both temperature results, the method of using the weighted average of the temperature results according to the ratio of the distance from each temperature detection point to the strain detection point, etc. Various methods can be employed.

  As shown in FIG. 3, the wavelength of the measurement light of the semiconductor laser (LD1) used for the strain detection means and the wavelength of the measurement light of the semiconductor laser (LD2) used for the temperature detection means are different from each other. Thus, both can be detected simultaneously. There is no trouble such as interference between both measurement lights, and it is also possible to easily separate the temperature detection light and the strain detection pump light at the branching means (demux). It is.

FIG. 4 is a diagram for explaining a second embodiment of the light measurement system of the present invention.
3 will be mainly described. In order to make a plurality of temperature detection points, a plurality of fiber Bragg gratings (FBG1 to 3) are provided, and each FBG changes a specific wavelength (λ1). To 3) are set differently. Thereby, it becomes possible to selectively switch the temperature detection point by selecting the wavelength (λ1 to 3) of the measurement light.

  Since preparing a light source having a variety of wavelengths in this manner causes an increase in cost, in FIG. 4, a specific wavelength light emitted from one semiconductor laser (LD) is converted into a frequency comb generator (comb). ) Is converted into multi-wavelength light and introduced into an optical fiber connected to the optical fiber 2. FIG. 4 shows an embodiment in which the semiconductor laser used for the temperature detecting means and the semiconductor laser used for the strain detecting means are combined. Naturally, it is also possible to use separate light sources. In this case, a semiconductor laser and a frequency comb generator (comb) are inserted into the LD2 portion of FIG.

  Light waves that have passed through the fiber Bragg gratings (FBG 1 to 3) of the optical fiber 2 are led out to the branching means (demux 1) side by the circulator 1 and separated into different optical paths for each wavelength (λ 1 to 3). Each separated light wave (λ1-3) and a light wave (reference light) separated by introducing a part of the multi-wavelength light generated by the frequency comb generator (comb) into the branching means (demux2) Comparison is made with a comparator provided for each, and a change in the amount of transmitted light is detected. The temperature at each point (FBG1 to 3) is detected from the change in the amount of transmitted light.

  Further, in the embodiment of FIG. 4, in order to generate probe light, the signal source 15 that drives the SSB modulator (SSBM) that performs frequency shift and the signal source 15 that drives the frequency comb generator (comb) are combined. is doing. For this reason, strain detection and temperature detection are switched and executed.

  A method for compensating the temperature of the strain measurement result using the optical measurement system of FIG. 4 will be described with reference to FIG. Fig.5 (a) has shown the light intensity corresponding to the temperature detection from FBG1-3 of FIG. The horizontal axis indicates the position of the measurement point, and the locations (measurement positions) where the shield members (FBG1 to 3) are arranged are indicated by reference numerals S1 to S3. The vertical axis indicates the light intensity corresponding to each measurement point, and indicates that the temperature of the optical fiber at the measurement point increases as the light intensity of the light wave transmitted through the FBG decreases.

From the measurement result of the light intensity relating to the temperature in FIG. 5A, the temperature is calculated as shown in FIG. 5B. Further, a frequency shift amount Δf _T due to Brillouin scattering due to the temperature is calculated as shown in FIG.

On the other hand, when strain measurement is performed using Brillouin scattering, not only the measurement positions S1 to S3 where the shield members are arranged, but also the temperature as well as the stress applied to the optical fiber 2, the strain and temperature are affected. The received frequency shift amount Δf _{S + T} is detected as a measurement result as shown in FIG. 5D, for example.

For example, in order to eliminate the influence of temperature from the frequency shift amount Δf _{S + T of} FIG. 5D, it is possible to use the frequency shift amount Δf _T due to temperature as shown in FIG. 5C. As a compensation method, various methods such as a method using a temperature measurement value near a strain measurement point and a method using an average value of measurement values at two adjacent temperature measurement points can be used. For example, as shown in FIG. 5C, by using an approximate curve of the temperature distribution and correcting the measured value in FIG. 5D, the frequency shift amount Δf due to the influence of only the strain as shown in FIG. _S can be calculated, and it is easily observed that distortion occurs at the location indicated by the arrow A.

  Next, a method for measuring temperature using Brillouin scattering is shown in FIG. Since it is exactly the same as the case of measuring strain, the measurement optical system can be configured only with a measurement optical system using Brillouin scattering. Since the individual configurations are also described in FIG. 3 or 4, description thereof is omitted here, but reference numeral 20 indicates that the pump light does not enter the SSB modulator (SSBM) or the semiconductor laser in the reverse direction. An optical component that blocks light waves traveling in the left direction. Moreover, although the shielding member is arrange | positioned at measurement point S1-S3, FBG is not provided in the optical fiber.

FIG. 7 illustrates a method for performing temperature compensation using the optical measurement system of FIG. First, as shown in FIG. 7A, the frequency shift amount Δf _T due to Brillouin scattering at the measurement points S1 to S3 is measured. Since the stress applied to the optical fiber by the shield member is blocked at the measurement points S1 to S3, this frequency shift amount is a shift amount due to temperature.

Then, as shown in FIG. 7B, the measurement result at other points excluding the measurement points S1 to S3 is the frequency shift amount Δf _{S + T in} which both the strain and the temperature are affected. For this reason, when FIG. 7B is corrected (excludes the influence of temperature change) using FIG. 7A, as shown in FIG. 7C, the frequency shift amount Δf _S affected only by the distortion is shown. A graph showing the spatial distribution is obtained, and the location where the distortion is generated can be easily identified.

  As described above, according to the present invention, it is possible to measure both strain and temperature with a single optical fiber, to measure more accurate strain information, and to suppress the increase in cost. A system can be provided.

DESCRIPTION OF SYMBOLS 1 Detection part 2 Optical fiber 3 Shield member 4 Fiber Bragg grating 10 Strain and temperature measuring instrument 11 Data processing means 12, 15 Signal source 13 Optical amplifier 14 Terminator

Claims (7)

In an optical measurement system capable of measuring temperature and strain using an optical fiber,
Detects measurement light related to temperature and strain using a single optical fiber,
A shield member that blocks stress applied to the optical fiber from the measurement object is arranged on a part of the optical fiber arranged on the measurement object,
Temperature detection means for detecting temperature from measurement light based on the state of the optical fiber disposed in the shield member;
Strain detection means for detecting strain from measurement light based on the state of the optical fiber disposed other than the shield member;
An optical measurement system comprising temperature compensation means for compensating the result of the strain detection means with the result of the temperature detection means.   2. The optical measurement system according to claim 1, wherein a part of the optical fiber disposed in the shield member is provided with a fiber Bragg grating.   3. The optical measurement system according to claim 1, wherein the shield member is installed at a plurality of locations of the optical fiber, and in the temperature compensation unit, the optical fiber disposed between the two shield members. The light is compensated for by using the result of the temperature detecting means based on the state of the optical fiber disposed in at least one or both of the two shield members. Measuring system.   4. The optical measurement system according to claim 1, wherein the distortion detection unit detects distortion by a measurement method using Brillouin scattering. 5.   5. The optical measurement system according to claim 1, wherein the temperature detection unit uses either a measurement method using Brillouin scattering or a measurement method using a fiber Bragg grating to measure the temperature. An optical measurement system characterized by detecting the light.   6. The optical measurement system according to claim 5, wherein the temperature detection means using the measurement method using the fiber Bragg grating uses measurement light having a wavelength different from the wavelength of the measurement light used for the strain detection means. Light measurement system characterized by.   7. The optical measurement system according to claim 6, wherein the measurement light used for the temperature detection means uses a light wave obtained by wavelength-converting the measurement light used for the strain detection means.

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