JP2004347575A - Fbg sensing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an FBG sensing device having high reliability without a drive part in a light source or a wavelength measurement part, suitable for high-speed measurement such as vibration measurement, having sufficiently large light source output to sufficiently perform remote measurement, having low production cost, and allowing construction of a system simply processing data. <P>SOLUTION: This FBG sensing device has: an FBG (a fiber Bragg grating)reflecting a specific wavelength band, and having a characteristic wherein the reflection wavelength band shifts by receiving strain; the light source outputting light in the FBG reflection wavelength band; and a light receiver detecting light intensity outputted from the light source, and reflected from the FBG. By measuring a change amount of the reflected light intensity caused by the shift of the reflection wavelength band of the FBG, a strain amount of the FBG is detected. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an FBG sensing device that performs strain (pressure) measurement using an FBG made of an optical fiber.
[0002]
[Prior art]
In recent years, structures rapidly constructed during the high growth period have been deteriorating, and governments have been actively researching methods for evaluating the soundness of structures. Conventionally, as a method of measuring the strain of a structure, an electrical method using a resistance wire strain gauge has been the mainstream, but there are problems such as reliability, lightning strike, electromagnetic noise, etc. Measurement (sensing) is drawing attention. Optical fibers have attracted attention because they have a small transmission loss and can be monitored at remote distances.
[0003]
In the field of optical fiber sensing, an FBG (fiber Bragg grating) is used for strain measurement of a structure in combination with a broadband light source or a variable wavelength light source. The FBG reflects light of a specific wavelength determined by the grating interval. When stress is applied to the FBG and the FBG expands and contracts (distortion of the FBG), the grating interval changes, and the reflection wavelength of the FBG changes. The FBG is attached to a measuring point of the structure, a broadband light source or a variable wavelength light source is incident, and the reflection wavelength is measured to measure the FBG distortion, that is, the distortion of the structure. Also, by measuring at high speed, the vibration of the structure can be measured, and it is applied as a seismometer.
[0004]
As a method of measuring the reflection wavelength of the FBG, Patent Document 1 proposes a method using a broadband light source as a light source and using a Fabry-Perot filter (hereinafter, referred to as an FP filter).
[0005]
FIG. 9 is a diagram showing an outline of the configuration shown in Patent Document 1. As shown in FIG.
[0006]
Light derived from the broadband light source 101 passes through the optical splitter 102, passes through the optical fiber 108, and reaches the FBG 103. Light of a specific wavelength is reflected by the FBG 103, passes through the optical fiber 108, passes through the optical splitter 102, passes through the FP filter 109, and reaches the light receiver 104. The light quantity is converted into a current in the light receiver 104.
[0007]
The FP filter 109 is an interferometer using an etalon plate, and drives the distance between two parallel etalon plates by a piezoelectric element to control the interference distance. The light transmitted through the FP filter transmits a specific wavelength depending on the interference distance. By changing the interference distance to an arbitrary length, reflected light in all wavelength bands output from the broadband light source 101 can be detected. Since the driving distance of the piezoelectric element is determined by the voltage, the wavelength can be set for the driving voltage. By detecting the light amount of the light receiver 104 corresponding to the drive voltage, the reflection spectrum from the FBG 103 can be detected, and the reflection peak wavelength can be specified.
[0008]
Further, Patent Document 2 proposes an FBG sensing device using an FP filter as a light source and using the wavelength variable light source. As described in Patent Document 1, the reflection spectrum from the FBG can be detected based on the amount of light received corresponding to the drive voltage of the FP filter, and the reflection peak wavelength can be specified.
[0009]
An apparatus using such an FP filter has a driving unit, and causes a problem in reliability. Further, since it is necessary to detect the light amounts of all the wavelengths according to the spectrum of the measurement area, the number of data becomes enormous, and a high-precision arithmetic processor is required. Use of such an arithmetic processor is inferior in reliability. The FP filter has a wavelength-swapping frequency of about 10 Hz to 100 Hz. According to Non-Patent Document 1, the response speed of wavelength measurement is required to be 100 to 200 Hz assuming vibration measurement during an earthquake. Therefore, when the FP filter is used, it is not suitable for vibration measurement.
[0010]
Patent Document 3 proposes to use two narrow band filters having no drive unit in the wavelength measurement unit.
[0011]
FIG. 10A illustrates a configuration diagram of the FBG sensing device disclosed in Patent Document 3, specifically describing a wavelength measurement unit that measures a wavelength.
[0012]
It is composed of a broadband light source 201, a 2 × 2 coupler 202 for splitting light, an FBG 203 as a distortion sensor, a 2 × 2 coupler 210 for splitting light, a narrow band filter 209 having wavelength dependency, a light receiver 204, and an optical fiber 208. ing.
[0013]
Light output from the broadband light source 201 passes through the 2 × 2 coupler 202, passes through the optical fiber 208, and is guided to the FBG 203. The FBG 203 reflects a specific wavelength, transmits through the optical fiber 208, returns to the 2 × 2 coupler 202, branches and is guided to the 2 × 2 coupler 210, further branches into two of A and B, and narrows the narrow band filter 209. , And is converted into an electric signal by the light receiver 204.
[0014]
The narrow band filter 209 has a wavelength dependency as shown in FIG. 10B, and can detect the reflection wavelength of the FBG 203.
[0015]
Generally, an SLD (super luminescence diode) light source or an ASE (Amplified Spontaneous Emisson) light source is used as a broadband light source.
[0016]
The ASE light source generates a broadband, high-power spontaneous emission light by injecting excitation light of a specific wavelength into an optical fiber doped with erbium. Although an output that is approximately 100 times (20 dB higher) than the SLD light source can be obtained, the use of a higher output light source makes it possible to arrange a measurement point (FBG) for the light source at a more remote location.
[0017]
As described above, the transmission loss of the optical fiber is small, but the loss is about 0.25 dB / km. If the output of the light source is improved by 100 times, that is, by 20 dB, the remote distance can be extended by about 40 km (80 km in round trip: 80 km × 0.25 dB / km = 20 dB).
[0018]
However, the output of the ASE light source is not a sufficiently large value of about -10 dBm / nm. In the configuration shown in FIG. 10, since the narrow band filter 209 has the wavelength dependency as shown in FIG. In general, the attenuation in the narrow band filter 209 is about 20 dB at the maximum (the bottom of the spectrum in FIG. 10B). Since the minimum light receiving sensitivity of the light receiver 204 is about −50 dBm, the allowable range due to the transmission loss of the optical fiber is only about 20 dB in consideration of the output of the light source and the attenuation of the narrow band filter 209. Considering the loss of other components and the margin of the system, the allowable range is further reduced. In other words, it is not possible to measure sufficiently long distances.
[0019]
[Patent Document 1] JP-A-2003-21576
[Patent Document 2] JP-T 2001-511895
[Patent Document 3] JP-A-2000-223761
[Non-Patent Document 1] Akira Mita, Proceedings of the 25th Workshop on Lightwave Sensing Technology, June 2000, LST25-16, PP111-116
[0020]
[Problems to be solved by the invention]
In the above prior art, there is a problem that the drive unit is provided in the light source and the wavelength measurement unit, which has low reliability and is not suitable for high-speed measurement such as vibration measurement. There was a disadvantage that remote measurement could not be performed sufficiently because it was insufficient. In addition, high production costs such as wavelength tunable light sources and broadband light sources, and high production costs are used for the wavelength detection unit, and the production cost is lower than that of the mainstream electric type in the field of structural strain measurement. There was a drawback that would be very high.
[0021]
Here, there is no drive unit in the light source and the wavelength measurement unit, which is highly reliable, suitable for high-speed measurement such as vibration measurement, and has a sufficiently large light source output, sufficient remote measurement, and low manufacturing cost. Another object of the present invention is to provide an FBG sensing device capable of constructing a system with simple data processing.
[0022]
[Means for Solving the Problems]
The present invention has been made to solve these problems, and an FBG (Fiber Bragg Grating) having a characteristic of reflecting light in a specific wavelength band and changing a reflection wavelength band by receiving distortion, and the FBG In an FBG sensing device including a light source that outputs light in a reflection wavelength band and a light receiver that detects the light amount output from the light source and reflected from the FBG, the displacement of the reflected light amount due to a change in the reflection wavelength band of the FBG The amount of FBG distortion is detected by measuring the amount.
[0023]
Further, the present invention is characterized in that an output wavelength band of the light source is narrower than a reflection wavelength band of the FBG.
[0024]
Further, the present invention is characterized in that the output wavelength of the light source is on the shorter wavelength side than the FBG reflection peak wavelength.
[0025]
Further, the invention is characterized in that the output wavelength of the light source is adjusted so that the logarithmic conversion value of the amount of reflected light from the FBG is approximately linear with the amount of distortion.
[0026]
Further, the present invention is characterized in that the FBG is designed such that, for an arbitrary output wavelength of the light source, the logarithmic conversion value of the amount of reflected light from the FBG is approximately linear with the amount of distortion. I do.
[0027]
Further, the present invention is characterized in that the FBG is designed such that, for an arbitrary output wavelength of the light source, the amount of reflected light from the FBG is approximately linear with the amount of distortion.
[0028]
Further, the invention is characterized in that it comprises an optical splitter for splitting the output light of the light source into a plurality of light beams, the above-mentioned FBGs provided at the respective branched ports, and a photodetector paired with the FBGs.
[0029]
Further, the present invention includes a plurality of the FBGs having different reflection wavelength bands, the FBGs are arranged in series, a plurality of light sources outputting light in the FBG reflection wavelength band, and a plurality of light sources output from the light sources and reflected from the FBGs. A plurality of light receivers for detecting the amounts of light emitted from the light sources, and a multiplexer / demultiplexer for multiplexing the outputs of the plurality of light sources.
[0030]
Also, the present invention includes a plurality of the FBGs having different reflection wavelength bands, the FBGs are arranged in parallel, a plurality of light sources outputting light in the FBG reflection wavelength band, and a plurality of light sources output from the light sources and reflected from the FBGs. A plurality of light receivers for detecting the amount of light, a multiplexer / demultiplexer for multiplexing the outputs of the plurality of light sources, and a multiplexer / demultiplexer for demultiplexing the multiplexed output light.
In addition, the present invention includes a plurality of the FBGs having different reflection wavelength bands, the FBGs are arranged in series or in parallel, a plurality of light sources outputting light in the FBG reflection wavelength band, output from the light source, and An FBG sensing device comprising: a plurality of light receivers for detecting the amount of reflected light; and a multiplexer / demultiplexer for multiplexing the outputs of the plurality of light sources and a multiplexer / demultiplexer for demultiplexing the multiplexed output light. In order to compensate for the amount of reflected light that fluctuates due to an external factor applied to an optical fiber or the like disposed between the light source and the FBG, at least one of the FBGs is installed so as not to affect the distortion and the temperature. It is characterized in that it is used as a reference for light quantity fluctuation.
[0031]
In addition, the present invention includes a plurality of the FBGs having different reflection wavelength bands, the FBGs are arranged in series or in parallel, a plurality of light sources outputting light in the FBG reflection wavelength band, output from the light source, and An FBG sensing device comprising: a plurality of light receivers for detecting the amount of reflected light; and a multiplexer / demultiplexer for multiplexing the outputs of the plurality of light sources and a multiplexer / demultiplexer for demultiplexing the multiplexed output light. In order to compensate for the amount of reflected light that fluctuates due to external factors applied to an optical fiber or the like disposed between the light source and the FBG, at least one of the FBGs is installed so as not to affect distortion and temperature, The output of the light source that outputs light in the reflection wavelength band of the FBG is adjusted so that the amount of reflected light incident on the light receiver does not fluctuate, and the output of the light source in another at least one different wavelength band is adjusted. Characterized by comprising a function of integer.
[0032]
Further, the invention is characterized in that the light source is an incoherent light source.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the FBG sensing device according to the present invention will be described.
[0034]
FIG. 1 is a diagram showing a configuration of the FBG sensing device of the present invention.
[0035]
It comprises a light source 1, a light receiver 4, an optical splitter 2, an FBG 3, and an optical fiber 8, and the components are connected by an optical fiber. The optical splitter 2 may be a two-branch coupler or an optical circulator. The light source 1, the light receiver 4, and the optical splitter 2 may be an integrated module that is optically coupled. The optical fiber 8 can be set according to the measurement distance, and may be within 1 m or 10 km or more.
[0036]
FIG. 2 is a diagram illustrating a reflection spectrum of the FBG 3 according to the amount of distortion. The amount of distortion here is generated by extending FBG3. It is known that the amount of distortion changes linearly with respect to the shift amount of the reflection wavelength of the FBG3, and that a wavelength displacement of 1.2 pm generally occurs for a strain of 1 με. Is converted.
[0037]
Light output from the light source 1 passes through the optical splitter 2, passes through the optical fiber 8, and reaches the FBG 3. Light of a specific wavelength is reflected by the FBG 3. As shown in FIG. 2, for example, when the wavelength of the light source 1 is 1556.7 nm ((2) in FIG. 2) and the amount of distortion is 0 με, the reflection loss is 0 dB, but if 100 με of distortion is applied to the FBG3, The reflection band of the FBG 3 shifts, and the reflection loss of the light source 1 at the wavelength of 1556.7 nm changes to -5 dB. Thus, the reflection loss is displaced according to the amount of distortion. The reflected light passes through the optical fiber 8, passes through the optical splitter 2, and reaches the light receiver 4. The light receiver 4 linearly converts the displacement of the amount of reflected light into an electric signal, and detects the amount of distortion applied to the FBG 3.
[0038]
As described above, the amount of distortion applied to the FBG 3 can be measured by the displacement of the amount of reflected light, the data obtained by the light receiver 4 is simple without using a complicated wavelength detector as the light receiver, and high-speed and highly reliable measurement is possible. I can suggest a method.
[0039]
Here, the light source 1 is desirably a light source having a narrow wavelength spectrum.
[0040]
As shown in FIG. 2, the full width at half maximum (−3 dB) of the FBG 3 is about 0.2 nm. The wavelength shifts according to each distortion amount, but no change in reflectance or spectrum is observed. Assuming now that the spectrum of the light source 1 is a 1556.6 nm line spectrum having no wavelength band, the reflection loss at each distortion amount is the intersection of the dotted line of (3) in FIG. 2 with the reflection loss spectrum of each distortion amount. Is shown in the position. On the other hand, it can be easily predicted from FIG. 2 that, when the spectrum of the light source 1 is wide and wider than the reflection wavelength band of the FBG, the displacement of the reflection loss according to the amount of distortion becomes smaller. As described above, it is desirable that the spectrum of the light source 1 be sufficiently narrower than the reflection wavelength band of the FBG 3 in order to perform more accurate measurement.
[0041]
The DFB laser used for the light source for optical communication has a sufficiently narrow band of 1 pm or less in full width at half maximum of the output wavelength and is suitable for the present invention. The output is as high as 5 dBm or more, which is 15 dB or more higher than that of a high-output broadband light source (ASE light source).
[0042]
As described above, in the present invention, a narrow-band light source that easily obtains high output is suitable, and transmission loss due to the optical fiber 8 can be sufficiently compensated for, so that it is also suitable for long-distance measurement. With respect to the reflection wavelength band of the FBG 3, it is found that the use of a reflection wavelength band having a wider full width at half maximum reduces the reflection loss and is suitable for longer distance measurement.
[0043]
It is desirable that the light source 1 can arbitrarily select an output wavelength. Generally, the manufacturing variation of the reflection wavelength of the FBG 3 is about 0.5 nm, and it is difficult to match the case where the output wavelength of the light source 1 is fixed and the reflection wavelength band of the FBG 3 from FIG.
[0044]
The above-mentioned DFB laser can adjust the output wavelength by about 1 nm by controlling the temperature of the laser, and is desirable as the light source of the present invention.
[0045]
Further, it is desirable that the output wavelength of the light source 1 be in a shorter wavelength range than the reflection peak wavelength when there is no distortion of the FBG 3.
[0046]
As shown in FIG. 2, for example, when the output wavelength of the light source 1 is at 1556.8 nm, which is a longer wavelength region than the reflection peak wavelength when there is no distortion of the FBG 3, there is no distortion and there is distortion (FIG. 2: 100 με). At the same time), there is a problem that the distortion amount cannot be measured. If the output wavelength of the light source 1 is in a wavelength region shorter than the reflection peak wavelength when there is no distortion of the FBG 3, the reflection loss is uniquely determined with respect to the distortion amount, and such a problem does not occur.
[0047]
Although the distortion amount in FIG. 2 shows the distortion only in the elongation direction, the distortion in the contraction direction may be any wavelength as long as the output wavelength of the light source 1 is shorter than the reflection peak wavelength when the FBG 3 contracts to the maximum.
[0048]
FIG. 3 is a diagram illustrating the reflection loss of the FBG 3 determined by the output wavelength of the light source 1. (1) to (4) indicate the wavelengths shown in FIG. (1) is the reflection peak wavelength of the FBG 3 when there is no distortion, and in (2) of a wavelength slightly shorter than this wavelength, the logarithmic conversion value of the distortion amount and the reflection loss becomes approximately linear. At this time, if a log amplifier (electric amplifier that performs logarithmic conversion) is used for the electric output of the photodetector 5, the amount of distortion is linearly represented with respect to the amount of electricity, and an extremely simple measurement method can be proposed. By adjusting the output wavelength of the light source 1 such that the logarithmic conversion value of the amount of light reflected from the FBG 3 is approximately linear with the amount of distortion, a simpler system can be proposed.
[0049]
Further, if the FBG 3 is designed so that the logarithmic conversion value of the reflected light amount of the FBG 3 at an arbitrary wavelength, not only at a specific wavelength as shown in (2) of FIG. The construction of can be simplified. That is, in FIG. 2, it is sufficient that the wavelength of the reflection spectrum of the FBG 3 and the reflection loss (logarithmic conversion value) show a linear relationship. Further, if the reflection light amount of the FBG 3 is designed to be approximately linear with the distortion amount at an arbitrary wavelength, that is, if the wavelength of the reflection spectrum of the FBG 3 and the absolute amount of the reflection loss show a linear relationship, Further, the construction of the system can be simplified.
[0050]
Next, a second embodiment of the present invention will be described.
[0051]
FIG. 5 is a configuration diagram of an FBG sensing device according to a second embodiment of the present invention. It is composed of a light source 11, a light receiver 14, optical splitters 12, 15, an FBG 13, and an optical fiber 18, and each component is connected by an optical fiber. The optical splitter 12 may be a two-branch coupler or an optical circulator.
[0052]
The light output from the light source 11 passes through the optical splitter 16. At this time, the light amount is reduced to about １ ／ (−3 dB). The light quantity in the case of four branches is reduced to １ ／ (−6 dB). As described above, the DFB laser, which is a general narrow-band light source, has a sufficiently large output, so that even if the light amount is reduced, an output higher than that of the broad-band light source is obtained, which is suitable for long-distance measurement.
[0053]
After passing through the optical splitter 16, the light passes through the optical splitter 12, passes through the optical fiber 18, and reaches the FBG 13 as in the first embodiment. Light of a specific wavelength is reflected by the FBG 13. As in the first embodiment, the reflection loss changes according to the amount of distortion. The reflected light passes through the optical fiber 18, passes through the optical splitter 12, and reaches the light receiver 14. The light receiver 14 linearly converts the displacement of the amount of reflected light into an electric signal, and detects the amount of distortion applied to the FBG 13.
[0054]
By branching the output of the light source 11 in this manner, it is possible to detect the amount of distortion at a plurality of locations with one light source.
[0055]
Next, a third embodiment of the present invention will be described.
[0056]
FIG. 6 is a configuration diagram of an FBG sensing device according to a third embodiment of the present invention. It comprises light sources 21a, 21b, light receiver 24, optical splitter 22, FBGs 23a, 23b, optical wavelength multiplexer / demultiplexer 26, and optical fiber 28, and each component is connected by an optical fiber. The optical splitter 22 may be a two-branch coupler or an optical circulator. Further, the light source 21, the light receiver 25, and the optical splitter 22 may be an integrated module optically coupled.
[0057]
The lights output from the light sources 21a and 21b pass through the optical splitter 22, pass through the optical wavelength multiplexer / demultiplexer 26, and are multiplexed. Each of the light sources 21a and 21b outputs light of a different wavelength, and is adjusted to be within the reflection wavelength band of each of the FBGs 23a and 23b. The multiplexed light passes through the optical fiber 28, reaches the FBGs 23a and 23b, and is reflected. Since the FBG 23 transmits light outside the reflection wavelength band, the FBG 23 is not affected by each other. As in the first embodiment, the reflection loss of the FBG 23 changes in accordance with the amount of distortion. The reflected light passes through an optical fiber 28, is split by a wavelength multiplexer / demultiplexer 26, passes through each optical splitter 22, reaches each light receiver 24, and is converted into an electric signal. As in the first embodiment, the amount of distortion in the FBGs 23a and 23b is detected from the amount of received light converted into an electric signal. As described above, if the optical wavelength multiplexer / demultiplexer 26 is used, a plurality of distortion amounts can be detected by one optical fiber 18.
[0058]
Next, a fourth embodiment of the present invention will be described.
[0059]
FIG. 7 is a configuration diagram of an FBG sensing device according to a fourth embodiment of the present invention. It comprises a light source 31, a light receiver 34, an optical splitter 32, an FBG 33, and optical wavelength multiplexer / demultiplexers 36 and 37, and each component is connected by an optical fiber. The optical splitter 32 may be a two-branch coupler or an optical circulator.
[0060]
The lights output from the light sources 31a and 31b pass through the optical splitter 32, pass through the optical wavelength multiplexer / demultiplexer 36, and are multiplexed. Each of the light sources 31a and 31b outputs light of a different wavelength, and is adjusted to be within the reflection wavelength band of each of the FBGs 33a and 33b. The multiplexed light passes through the optical fiber 38, is demultiplexed by the optical wavelength multiplexer / demultiplexer 37, reaches the FBGs 33a and 33b, and is reflected. As in the first embodiment, the reflection loss of the FBG 33 changes in accordance with the amount of distortion. The reflected light is multiplexed by an optical wavelength multiplexer / demultiplexer 37, passes through an optical fiber 38, is demultiplexed by a wavelength multiplexer / demultiplexer 36, passes through each optical splitter 32, and receives each optical receiver 34, and is converted into an electric signal. As in the first embodiment, the amount of distortion in the FBGs 33a and 33b is detected from the amount of received light converted into an electric signal. As described above, if the optical wavelength multiplexers / demultiplexers 36 and 37 are used, a plurality of distortion amounts can be detected by one optical fiber 38. Further, even if a failure such as disconnection of the optical fiber occurs between the FBG 33a (or the FBG 33b) and the optical wavelength multiplexer / demultiplexer 37, the FBG 33b (or the FBG 33a) is not affected by the failure, so that a more reliable system is provided. Can be proposed.
[0061]
Next, a fifth embodiment of the present invention will be described.
[0062]
According to a fifth embodiment of the present invention, in the FBG sensing device having the configuration shown in FIG. 6, one FBG 23a is installed at a position where it is not subjected to distortion, and a Peltier element or a heater is provided so as not to be affected by temperature. The temperature is controlled by such means. Since these controls require electrical control and supply power, it is more desirable to implement control such that the temperature characteristics are canceled by applying shrinkage to the FBG by mounting it on an invar or the like having a negative linear thermal expansion coefficient.
[0063]
The lights output from the light sources 21a and 21b pass through the optical splitter 22, pass through the optical wavelength multiplexer / demultiplexer 26, and are multiplexed. Each of the light sources 21a and 21b outputs light of a different wavelength, and is adjusted to be within the reflection wavelength band of each of the FBGs 23a and 23b. The multiplexed light passes through the optical fiber 28, reaches the FBGs 23a and 23b, and is reflected. Since the FBG 23 transmits light outside the reflection wavelength band, the FBG 23 is not affected by each other. As in the first embodiment, the reflection loss of the FBG 23b is changed according to the amount of distortion, but the reflection loss does not change because the FBG 23a is installed so as not to receive distortion. The reflected light passes through an optical fiber 28, is split by a wavelength multiplexer / demultiplexer 26, passes through each optical splitter 22, reaches each light receiver 24, and is converted into an electric signal. As in the first embodiment, the amount of distortion in the FBGs 23a and 23b is detected from the amount of received light converted into an electric signal.
[0064]
Here, consider a case where a physical load is applied to the optical fiber 28 and the transmission loss of the optical fiber 28 changes.
[0065]
The amount of reflected light entering the light receiver 24 from each of the FBGs 23a and 23b changes, and the amount of distortion of the FBG 23b cannot be accurately detected. However, the change in the amount of light reflected by the optical fiber 28 between the FBG 23a and the FBG 23b is equivalent, so that the amount of change in the amount of light reflected by the FBG 23a is given to the amount of light reflected by the FBG 23b so that the amount of distortion applied to the FBG 23b can be compensated and accurately detected.
[0066]
By installing the FBG 23a that does not affect the amount of strain (and temperature) in this way, the amount of strain can be accurately detected regardless of the load applied to the optical fiber 18.
[0067]
In the embodiment of the present invention, the same effect can be obtained by installing the FBG 33a so as not to be affected by strain and temperature in the FBG sensing device having the configuration shown in FIG.
[0068]
Next, a sixth embodiment of the present invention will be described.
[0069]
FIG. 8 is a diagram showing a configuration of the FBG sensing device of the present invention.
[0070]
According to the present invention, in the FBG sensing device having the configuration shown in FIG. 8 as in the fifth embodiment, the FBG 43a is installed at a position where it is not subjected to distortion, and is controlled so as not to be affected by temperature.
[0071]
The lights output from the light sources 41a and 41b pass through the optical splitter 42, pass through the optical wavelength multiplexer / demultiplexer 46, and are multiplexed. Each of the light sources 41a and 41b outputs light of a different wavelength, and is adjusted to be within the reflection wavelength band of each of the FBGs 43a and 43b. The multiplexed light passes through the optical fiber 48, reaches the FBGs 43a and 43b, and is reflected. Since the FBG 43 transmits light outside the reflection wavelength band, the FBGs 43 are not affected by each other. As in the first embodiment, the reflection loss of the FBG 43b is displaced according to the amount of distortion, but the reflection loss does not change because the FBG 43a is installed so as not to receive distortion. The reflected light passes through an optical fiber 48, is split by a wavelength multiplexer / demultiplexer 46, passes through each optical splitter 42, reaches each light receiver 44, and is converted into an electric signal. As in the first embodiment, the amount of distortion in the FBGs 43a and 43b is detected from the amount of received light converted into an electric signal.
[0072]
Here, when a physical load is applied to the optical fiber 48 to cause a change in the transmission loss of the optical fiber 48 and the amount of reflected light entering the photodetectors 44a and 44b from the respective FBGs 43a and 43b changes, the distortion amount of the FBG 43b is accurately calculated. Cannot be detected.
[0073]
In the present invention, the output of the light source 41a is controlled by the light source output control circuit 49 and the output of the light source 41b is controlled so that the amount of reflected light from the FBG 43a received by the light receiver 44a is always constant, so that the amount of reflected light from the FBG 43a is controlled. Is always constant, and since the light source 41b is simultaneously controlled, the amount of distortion of the FBG 43b can be accurately detected. When the light sources 41a and 41b are DFB lasers, the output of the light source shows a substantially proportional relationship with the laser current. Therefore, the variation (ratio) of the laser current generated in the light source 41a may be given to the light source 42b.
[0074]
By installing the FBG 43a that does not affect the amount of distortion (and temperature) and controlling the light sources 41a and 41b so that the amount of reflected light from the FBG 43a is constant, the amount of distortion is independent of the load applied to the optical fiber 18. Can be accurately detected.
[0075]
FIG. 8 is a diagram in which the control function of the light source is added to FIG. 6. Similarly, even in the configuration in which the control function of the light source is added to FIG. 7, the distortion amount is accurately detected regardless of the load applied to the optical fiber 18. You can do it.
[0076]
Although a DFB laser is taken as an example of the light source in the above embodiment, a low output laser such as a ring laser using EDF can provide a stable output due to the influence of temperature fluctuation of the optical fiber.
[0077]
【Example】
An FBG sensing device according to the first embodiment of the present invention was created.
[0078]
The light source 1 used was a DFB laser generally used in optical communication. The maximum output is about 3 mW and the output wavelength is around 1556 nm. The full width at half maximum of the wavelength spectrum is 1 pm. It also has a temperature control function, and the peak of the output wavelength can be adjusted by about 1 nm by setting the control temperature to 15 ° C. to 35 ° C. In this experiment, it was adjusted to 1556.70 nm.
[0079]
The photodetector 4 also used a pin photodiode generally used in optical communication. The light receiving sensitivity is -50 dBm, and the wavelength band is 1000 nm to 1600 nm, and flat characteristics are obtained. The relationship between the amount of received light and the current is linear from -50 dBm to 0 dBm.
[0080]
A circulator having a transmission loss of about 0.5 dB and a wavelength characteristic of the transmission loss of less than 0.1 dB was used for the optical branching device 2.
[0081]
The FBG3 used had a reflectance of 95% or more, a full width at half maximum of reflection spectrum of 0.25 nm or less, and a reflection peak wavelength of 1556.72 nm.
[0082]
FIG. 4 shows the results of this example.
[0083]
A result almost equal to (2) shown in FIG. 2 was obtained. It was confirmed that the error from the approximation curve almost coincided with the distortion amount at 10 με or less.
[0084]
Similarly, in the third, fourth, fifth, and sixth embodiments of the present invention, an FBG sensing device was manufactured, and the same result as the experiment based on the first embodiment was obtained.
[0085]
The same FBG23a or FBG33a as FBG3 was used, and the FBG23b or FBG33b having a reflection peak wavelength of 1533.52 nm was used. For the optical wavelength multiplexing / demultiplexing 26, 36, and 37, a multiplexer / demultiplexer that multiplexes / demultiplexes light at 1545 nm or more and 1545 nm or less was used. The transmission characteristics in each wavelength range have a wavelength dependency of 0.1 dB or less at 20 nm.
[0086]
【The invention's effect】
As described above, according to the present invention, an FBG (fiber Bragg grating) having a characteristic of reflecting a specific wavelength band and changing a reflection wavelength band by receiving distortion, and a light source for outputting light in the FBG reflection wavelength band And an FBG sensing device provided with a light receiver that detects the amount of light output from the light source and reflected from the FBG, by measuring the amount of displacement of the amount of reflected light due to a shift in the reflection wavelength band of the FBG. Since the amount of distortion is detected, there is no drive unit in the light source and wavelength measurement unit, so it is highly reliable, suitable for high-speed measurement such as vibration measurement, and has a sufficiently large light source output and sufficient remote measurement. It is possible to provide an FBG sensing device which can be constructed at a low cost, can be manufactured at low cost, and can construct a system with simple data processing.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an FBG sensing device of the present invention.
FIG. 2 is a diagram showing a reflection spectrum of an FBG according to a distortion amount.
FIG. 3 is a diagram showing the relationship between FBG distortion determined by the output wavelength of a light source and reflection loss.
FIG. 4 is a diagram illustrating a relationship between distortion and return loss of the FBG according to the embodiment of the present invention.
FIG. 5 is a configuration diagram of an FBG sensing device according to a second embodiment of the present invention.
FIG. 6 is a configuration diagram of an FBG sensing device according to a third embodiment of the present invention.
FIG. 7 is a configuration diagram of an FBG sensing device according to a fourth embodiment of the present invention.
FIG. 8 is a diagram showing a configuration of an FBG sensing device of the present invention.
FIG. 9 is a diagram showing a schematic configuration of a conventional example.
10A is a diagram illustrating a schematic configuration of a conventional example, and FIG. 10B is a diagram illustrating transmission characteristics of a filter.
[Explanation of symbols]
1: Light source
2: Optical splitter
3: FBG
4: Light receiver
8: Optical fiber
11: Light source
12, 15: Optical splitter
13: FBG
14: Receiver
18: Optical fiber
21a, 21b: light source
22: Optical splitter
23a, 23b: FBG
24: light receiver
26: Optical wavelength multiplexer / demultiplexer
28: Optical fiber
31a, 31b: light source
32: Optical branching device
33a, 33b: FBG
34: Receiver
36, 37: Optical wavelength multiplexer / demultiplexer
38: Optical fiber
41a, 41b: light source
42: Optical splitter
43a, 43b: FBG
44a, 44b: light receiver
46, 47: Optical wavelength multiplexer / demultiplexer
48: Optical fiber
49: Light source output control circuit
101: Broadband light source
102: Optical splitter
103: FBG
104: Receiver
108: Optical fiber
109: FP filter
201: Broadband light source
202, 210: 2 × 2 coupler
203: FBG
204: Receiver
208: Optical fiber
209: narrow band filter

Claims (12)

An FBG (fiber Bragg grating) having a characteristic of reflecting light in a specific wavelength band and changing a reflection wavelength band by receiving distortion, a light source for outputting light in the reflection wavelength band of the FBG, and a light source In the FBG sensing device provided with a light receiver for detecting the amount of light output and reflected from the FBG, the amount of distortion of the FBG is detected by measuring the amount of displacement of the amount of reflected light due to the shift of the reflection wavelength band of the FBG. An FBG sensing device, characterized in that: The FBG sensing device according to claim 1, wherein an output wavelength band of the light source is narrower than a reflection wavelength band of the FBG. The FBG sensing device according to claim 1, wherein an output wavelength of the light source is on a shorter wavelength side than a reflection peak wavelength of the FBG. The FBG sensing device according to claim 1, wherein an output wavelength of the light source is adjusted such that a logarithmic conversion value of the amount of reflected light from the FBG is approximately linear with a distortion amount of the FBG. The FBG is designed such that, for an arbitrary output wavelength of the light source, the logarithmic conversion value of the amount of reflected light from the FBG is approximately linear with the amount of distortion of the FBG. 2. The FBG sensing device according to 1. 2. The FBG according to claim 1, wherein the FBG is designed such that, for an arbitrary output wavelength of the light source, the amount of light reflected from the FBG is approximately linear with the amount of distortion of the FBG. 3. Sensing device. 7. An optical splitter for splitting the output light of the light source into a plurality of light beams, the FBGs provided at respective branched ports, and a photodetector paired with the FBGs is provided. An FBG sensing device according to any one of claims 1 to 3. A plurality of the FBGs having different reflection wavelength bands are arranged in series, a plurality of light sources for outputting light in the reflection wavelength band of each FBG, a multiplexer / demultiplexer for multiplexing the outputs of these light sources, and The FBG sensing device according to any one of claims 1 to 6, further comprising a plurality of light receivers for detecting the amount of light output and reflected by each FBG. A plurality of the FBGs having different reflection wavelength bands are arranged in parallel, a plurality of light sources for outputting light in the reflection wavelength band of each FBG, a multiplexer / demultiplexer for multiplexing the outputs of these light sources, and The FBG sensing device according to any one of claims 1 to 6, further comprising a plurality of light receivers for detecting the amount of light output and reflected by each FBG. A plurality of the FBGs having different reflection wavelength bands are provided, the FBGs are arranged in series or in parallel, a plurality of light sources outputting light in the FBG reflection wavelength band, and a light amount output from the light sources and reflected from the FBGs. An FBG sensing device comprising: a plurality of photodetectors for detection; and a FBG sensing device including a multiplexer / demultiplexer for multiplexing the outputs of the plurality of light sources and a multiplexer / demultiplexer for demultiplexing the multiplexed output light. In order to compensate for the amount of reflected light that fluctuates due to external factors applied to an optical fiber or the like disposed between the FBGs, at least one of the FBGs is installed so as not to affect distortion and temperature, and The FBG sensing device according to any one of claims 1 to 6, wherein: A plurality of the FBGs having different reflection wavelength bands are provided, the FBGs are arranged in series or in parallel, a plurality of light sources outputting light in the FBG reflection wavelength band, and a light amount output from the light sources and reflected from the FBGs. An FBG sensing device comprising: a plurality of photodetectors for detection; and a FBG sensing device including a multiplexer / demultiplexer for multiplexing the outputs of the plurality of light sources and a multiplexer / demultiplexer for demultiplexing the multiplexed output light. In order to compensate for the amount of reflected light that fluctuates due to an external factor applied to an optical fiber or the like disposed between FBGs, at least one of the FBGs is installed so as not to affect distortion and temperature, and is incident on the light receiver. The function of adjusting the output of the light source that outputs light in the reflection wavelength band of the FBG so as to eliminate the change in the amount of reflected light, and adjusting the output of the light source in at least one other different wavelength band. FBG sensing apparatus according to any one of 6 claim 1, characterized in that there was e. 12. The FBG sensing device according to claim 1, wherein the light source is an incoherent light source.

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