Optical fiber sensing system, measurement device, and event detection method

Abstract

To provide an optical fiber sensing system, a measurement device, and an event detection method that have a simpler configuration and higher sensitivity.SOLUTION: An optical fiber sensing system includes a multi-core fiber having a plurality of core regions within a cladding region, and having optical inter-core crosstalk of -40 dB / km or more at a predetermined wavelength, an excitation light generating unit that inputs pulsed excitation light having the predetermined wavelength from a first end side of the multi-core fiber to a first core region of the plurality of core regions, and a light receiving unit that receives backscattered light generated by the excitation light and output at the first end side from a second core region that is a core region other than the first core region of the plurality of core regions.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical fiber sensing system, a measurement device, and an event detection method. [Background technology]

[0002] As a method for measuring acoustic and vibration using optical fibers, a technique has been developed in which changes in vibration along the length of an optical fiber are observed by observing Brillouin backscattered light and Rayleigh backscattered light generated in the optical fiber by light propagating through the optical fiber (Non-Patent Documents 1 to 4).

[0003] Furthermore, a method using an FBG (Fiber Bragg Grating) has also been proposed as a method for measuring strain and vibration using optical fibers (Non-Patent Document 5).

[0004] Furthermore, in order to expand the communication capacity of optical fiber communication networks, multi-core fibers that have multiple core regions within the cladding region of a single optical fiber, unlike conventional single-core optical fibers, have been developed (Non-Patent Document 6). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] H. Ohno, H. Naruse, M. Kihara, and A. Shimada, “Industrial Applications of the BOTDR Optical Fiber Strain Sensor”Optical Fiber Technology 7, 45-64 2001. [Non-Patent Document 2] Y. Mizuno, W. Zou, Z. He,and K. Hotate, “Proposal of Brillouin optical correlation-domain reflectometry (BOCDR)” OPTICS EXPRESS Vol. 16, No. 16 12148-12153 2008. [Non-Patent Document 3] K. Hotate, T. Hasegawa, “Measurement of Brillouin Gain Spectrum Distribution along an Optical Fiber Using a Correlation-Based Technique-Proposal, Experiment and Simulation”, IEICE TRANS. ELECTRON., Vol.,E83-C, No.3 405-412 2000. [Non-Patent Document 4] K. Nishiguchi “Phase unwrapping for fiber-optic distributed acoustic sensing” Proceedings of the 47th ISCIE International Symposium on Stochastic Systems Theory and Its Applications Honolulu, Dec. 5-8, 2015 [Non-Patent Document 5] Takanori Saito, Kenichi Nakamura, Masaru Koshihara, Hiroshi Furukawa, "High-performance FBG sensor monitor", Institute of Electronics, Information and Communication Engineers, Technical Report of IEICE OFT2011-42 (2011-10) [Non-Patent Document 6] Masanori Koshiba, "Types of multi-core optical fibers and their design guidelines," Optics, Vol. 40, No. 6 (2011) 264, 8-12 Summary of the Invention [Problem to be solved by the invention]

[0006] The devices used in the acoustic and vibration measurement method using optical fibers may require a complex device configuration. For example, devices that detect Brillouin scattered light (such as Brillouin OTDR (BOTDR)) detect Brillouin scattered light whose wavelength is about 10 GHz away from the wavelength of the optical pulse transmitted from the device. For this purpose, the light receiving section needs a high-speed photodiode with a bandwidth of 10 GHz or more and a high-frequency circuit to process the signal. As a result, such devices are expensive and are mostly applied to large systems (e.g., long-distance optical lines of tens of kilometers) where cost-effectiveness is expected, and there are few cases of their introduction into short-distance, small-scale systems of less than 1 km.

[0007] Therefore, there is a demand for a more sensitive optical fiber sensing technology with a simpler configuration.

[0008] The present invention has been made in view of the above, and an object of the present invention is to provide an optical fiber sensing system, a measurement device, and an event detection method that have a simpler configuration and higher sensitivity. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems and achieve the object, one aspect of the present invention is an optical fiber sensing system including: a multicore fiber having a plurality of core regions in a cladding region, and having optical inter-core crosstalk of -40 dB / km or more at a predetermined wavelength; an excitation light generating unit that inputs pulsed excitation light having the predetermined wavelength from a first end side of the multicore fiber to a first core region of the plurality of core regions; and a light receiving unit that receives backscattered light generated by the excitation light and output at the first end side from a second core region that is a core region other than the first core region of the plurality of core regions.

[0010] The excitation light may have a spectral linewidth of 1 MHz or less.

[0011] The core pitch of the plurality of core regions may be 15 μm or more and 25 μm or less.

[0012] The optical fiber sensing system may further include a determination unit that detects a deformation occurring in the multicore fiber, or determines a position where the deformation occurs or a change over time, based on a feature of the backscattered light received by the light receiving unit.

[0013] The determination unit may detect the deformation or determine an occurrence position or a change over time of the deformation based on light intensity, which is one of the characteristic quantities of the received backscattered light.

[0014] The determination unit may determine a position where the deformation has occurred or a change over time based on a time differential value of the light intensity.

[0015] The optical fiber sensing system may further include a probe light source that inputs probe light having a wavelength the same as that of the backscattered light into the second core region from a second end side of the multi-core fiber opposite to the first end side.

[0016] The multi-core fiber may have a plurality of the second core regions, and may include a plurality of the light receiving sections each receiving the backscattered light from each of the second core regions.

[0017] The multicore fiber may have an inter-core crosstalk of -30 dB / km or more.

[0018] One aspect of the present invention is a measurement device including: a light-receiving unit that receives backscattered light generated by the excitation light output from a second core region, which is a core region other than the first core region among the multiple core regions, at a first end side of the multi-core fiber provided near a measurement object, the multi-core fiber having a plurality of core regions in a cladding region, and having optical inter-core crosstalk at a predetermined wavelength of -40 dB / km or more; and a determination unit that detects an event that has occurred in the measurement object and causes deformation of the multi-core fiber, or determines an occurrence position or a change over time of the event, based on a feature amount of the backscattered light received by the light-receiving unit.

[0019] The measurement device may further include a discrimination unit that discriminates the type of the event.

[0020] The multicore fiber may have an inter-core crosstalk of -30 dB / km or more.

[0021] One aspect of the present invention is an event detection method which includes: inputting pulsed excitation light having a predetermined wavelength into a first core region among the plurality of core regions from a first end side of the multicore fiber, the multicore fiber being provided near an object to be measured, the multicore fiber having a plurality of core regions in a cladding region, and having optical inter-core crosstalk at a predetermined wavelength of -40 dB / km or more; receiving backscattered light generated by the excitation light and output at the first end side from a second core region that is a core region other than the first core region among the plurality of core regions; and detecting an event which has occurred in the object to be measured and which causes deformation of the multicore fiber, or determining a position at which the event has occurred or a change over time of the event, based on a feature amount of the received backscattered light.

[0022] The event detection method may further comprise determining a type of the event.

[0023] The multicore fiber may have an inter-core crosstalk of -30 dB / km or more. Effect of the Invention

[0024] According to the present invention, it is possible to realize an optical fiber sensing system, a measurement device, and an event detection method that have a simpler configuration and higher sensitivity. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic configuration diagram of an optical fiber sensing system according to the first embodiment. [Diagram 2] FIG. 2 is a schematic diagram of the measurement device shown in FIG. [Diagram 3] FIG. 3 is a diagram illustrating an example of the characteristics of the multi-core fiber illustrated in FIG. [Figure 4] FIG. 4 is a diagram showing an example of waveform data obtained by data processing in the data processing unit. [Diagram 5] FIG. 5 is a diagram showing waveform data obtained by time-differentiating the waveform shown in FIG. [Figure 6] FIG. 6 is a diagram showing an example of data obtained in the measurement device shown in FIG. [Figure 7] FIG. 7 is a schematic configuration diagram of an optical fiber sensing system according to the second embodiment. [Figure 8] FIG. 8 is a schematic configuration diagram of an optical fiber sensing system according to the third embodiment. [Figure 9] FIG. 9 is a schematic configuration diagram of an optical fiber sensing system according to the fourth embodiment. [Figure 10] FIG. 10 is a schematic diagram of the measurement device shown in FIG. [Figure 11] FIG. 11 is a schematic cross-sectional view showing an embodiment of a multi-core fiber. [Figure 12] FIG. 12 is a schematic cross-sectional view showing an embodiment of a multi-core fiber. [Figure 13]FIG. 13 is a schematic configuration diagram of a first application mode of the optical fiber sensing system. [Figure 14] FIG. 14 is a schematic configuration diagram of a second application mode of the optical fiber sensing system. [Figure 15] FIG. 15 is a schematic configuration diagram of a third application mode of the optical fiber sensing system. [Figure 16] FIG. 16 is a schematic configuration diagram of a fourth application mode of the optical fiber sensing system. [Figure 17] FIG. 17 is a schematic configuration diagram of a fifth application mode of the optical fiber sensing system. [Figure 18] FIG. 18 is a schematic configuration diagram of an optical fiber sensing system according to the fifth embodiment. [Figure 19] FIG. 19 is a flowchart illustrating an example of a processing procedure executed by the control unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment will be described with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, in the description of the drawings, the same or corresponding elements are appropriately given the same reference numerals, and duplicated explanations are appropriately omitted. It should be noted that the drawings are schematic, and the dimensional relationship of each element, the ratio of each element, etc. may differ from reality. There may also be parts in which the dimensional relationship and ratio differ between the drawings.

[0027] (Embodiment 1) [Configuration of optical fiber sensing system] 1 is a schematic configuration diagram of an optical fiber sensing system according to embodiment 1. The optical fiber sensing system 1000 includes an optical fiber unit 100, a connection cable 200, and a measuring device 300.

[0028] The optical fiber section 100 includes a multi-core fiber 10, an optical coupling section 20, and four single-core optical fibers 30. The multi-core fiber 10 has four core regions 12 including core regions 12a and 12b in a cladding region 11. The four core regions 12 are an example of a plurality of core regions.

[0029] The multi-core fiber 10 is a coupled multi-core fiber. The coupled multi-core fiber is an optical fiber with a relatively high inter-core crosstalk, i.e., the inter-core crosstalk at a predetermined wavelength is −40 dB / km or more, preferably −30 dB / km or more. In such a multi-core fiber 10, when light is input from the first end 13 side to one of the four core regions 12, a part of the light is coupled to the other core region by crosstalk and propagates through the other core region toward the second end 14. Note that the predetermined wavelength is, for example, a wavelength used in optical communications such as the 1.55 μm band, but is not particularly limited. Here, the inter-core crosstalk between a certain core region and another core region is an amount defined as the ratio of the second intensity to the first intensity when light of a first optical intensity is input from a first end of a certain core region and light of a second intensity is output from the other core region at the other end.

[0030] Although there are no particular limitations on the core diameter of the core region 12 and the relative refractive index to the cladding region 11, they are preferably set so as to propagate a predetermined wavelength in a single mode. Also, the core pitch (the center-to-center distance between adjacent core regions) of the core region 12 is set so that the inter-core crosstalk at the predetermined wavelength is equal to or greater than a desired value, for example, 15 μm to 25 μm.

[0031] The single-core optical fiber 30 is, for example, a standard single-mode optical fiber used in optical communications, and has one core region in the cladding region. The optical coupling unit 20 is disposed between the first end 13 of the multi-core fiber 10 and the single-core optical fiber 30. The optical coupling unit 20 optically couples the core regions of the four single-core optical fibers 30 to the four core regions 12 of the multi-core fiber 10. For example, the optical coupling unit 20 optically couples the single-core optical fiber 31a of the single-core optical fiber 30 to the core region 12a of the multi-core fiber 10, and optically couples the single-core optical fiber 31b to the core region 12b.

[0032] The optical coupling section 20 can be constructed, for example, by bundling together the same number of single-core optical fibers as the number of core regions 12 that the multi-core fiber 10 has, and connecting them to the multi-core fiber 10 with an adhesive (for example, Watanabe Kengo, Saito Tsunetoshi, Shiino Masato, “Development of Fiber Bundle-Type Fan-Out for 19-Core MCF,” Institute of Electronics, Information and Communication Engineers, IEICE Technical Report OCS2014-35(2014-08)). Furthermore, the optical coupling unit 20 may be of a spatial coupling type configuration in which, for example, light output from single-core optical fibers, the number of which is the same as the number of core regions 12 that the multi-core fiber 10 has, is collected by a lens and coupled to each core region 12 of the multi-core fiber 10 (for example, Tetsuya Kobayashi, Yusaku Tottori, Hiroshi Tsuboya, Yosuke Minagawa, and Kei Hatsukano, “Spatial Optical System Multi-Core Fiber Coupling Device and Its Scalability,” Institute of Electronics, Information and Communication Engineers, IEICE Technical Report OCS2013-104, OFT2013-61, OPE2013-211(2014-02)).

[0033] The connection cable 200 has two single-core optical fibers 201 and 202. The single-core optical fiber 201 optically connects the single-core optical fiber 31a and an optical input / output unit 301 of the measurement device 300. The single-core optical fiber 202 optically connects the single-core optical fiber 31b and an optical input / output unit 302 of the measurement device 300. The single-core optical fibers 201 and 202 are, for example, standard single-mode optical fibers used in optical communications.

[0034] Fig. 2 is a schematic diagram of the measurement device 300 shown in Fig. 1. The measurement device 300 includes light input / output units 301 and 302, a measurement unit 310, and a control unit 320.

[0035] The measuring unit 310 includes a light source 311, a pulse signal generator 312, a photodetector 313, and an A / D converter 314. The light source 311 and the pulse signal generator 312 configure an excitation light generating unit 315. The light source 311 includes, for example, a semiconductor laser device or a fiber laser device. Based on a pulsed electric signal output from the pulse signal generator 312, the light source 311 periodically outputs excitation light, which is a pulsed laser light, at a timing synchronized with the electric signal. The excitation light is output from the light input / output unit 301 to the outside of the measuring device 300.

[0036] The light source 311 may be configured to output pulsed excitation light by a so-called direct modulation method in which the driving power of the laser device is pulsed. The light source 311 may also be configured by a so-called external modulation method in which the light source 311 includes a laser device and an optical modulator, and converts the continuous wave laser light output by the laser device into pulsed laser light by the optical modulator to which a pulsed electric signal (modulation signal) is applied, and then outputs the pulsed laser light. The optical modulator is, for example, a LiNbO3 modulator, an AO modulator, an EA modulator, or the like, and is not particularly limited.

[0037] Photodetector 313 includes, for example, a photodiode. Photodetector 313 receives light input from optical input / output unit 301 of measuring device 300, and outputs a current signal corresponding to the intensity of the light. A / D converter 314 receives the current signal output as an analog signal by photodetector 313, converts it into a digital signal, and outputs it to control unit 320. Photodetector 313 is an example of a light receiving unit.

[0038] The control unit 320 includes hardware such as a processor, a memory, and peripheral devices such as an input / output interface. The processor is, for example, a central processing unit (CPU), a digital signal processor (DSP), or a graphics processing unit (GPU), and performs various arithmetic processing for the functions realized by the control unit 320. The memory includes a portion configured, for example, of a read only memory (ROM), and a portion configured, for example, of a random access memory (RAM). The ROM stores various programs and data used by the processor to perform arithmetic processing. The RAM is used to store a working space when the processor performs arithmetic processing, results of the processor's arithmetic processing, and the like. The control unit 320 may include a computer-readable recording medium. The functions of the control unit 320 are realized by the cooperation of hardware and software, for example, by the processor executing a program read from the memory. The control unit 320 may also include an FPGA (field programmable gate array).

[0039] The control unit 320 includes, as functional units, a receiving unit 321, a data processing unit 322, and a determination unit 323. The receiving unit 321 receives a trigger signal from the pulse signal generator 312. This trigger signal is synchronized with the pulsed electric signal output to the light source 311, and is used for synchronization of data processing in the data processing unit 322. The data processing unit 322 receives a digital signal from the A / D converter 314, and processes the information data included in the digital signal. As will be described later in detail, the determination unit 323 detects deformation occurring in the multi-core fiber 10, or determines the position of occurrence or the change over time of the deformation, based on the data processing result of the data processing unit 322. Note that the time of occurrence of the deformation can also be determined by determining the change over time of the deformation.

[0040] [Operation of optical fiber sensing system] Next, a description will be given of the operation of the optical fiber sensing system 1000. First, in the excitation light generating unit 315, the pulse signal generator 312 outputs a pulsed electric signal to the light source 311. Based on the electric signal output from the pulse signal generator 312, the light source 311 outputs pulsed excitation light having a predetermined wavelength at a timing synchronized with the electric signal.

[0041] The pumping light passes through the optical input / output unit 301, the single-core optical fiber 201, the single-core optical fiber 31a, and the optical coupling unit 20, and is input to the core region 12a from the first end 13 side of the multi-core fiber 10. That is, the pumping light generating unit 315 inputs the pumping light to the core region 12a from the first end 13 side. The core region 12a is an example of a first core region.

[0042] While propagating through the multi-core fiber 10, a part of the pumping light is coupled to another core region 12 other than the core region 12a due to crosstalk, and propagates through the other core regions 12 toward the second end 14.

[0043] The excitation light generates backscattered light such as Rayleigh scattered light at each position in the longitudinal direction within the core region 12. The backscattered light generated within the core region 12 propagates from the second end 14 side to the first end 13 side. Note that part of such backscattered light also couples with other core regions 12 due to crosstalk while propagating through the multi-core fiber 10.

[0044] A part of the backscattered light is output from the core region 12b on the first end 13 side. The core region 12b is an example of a second core region that is a core region other than the first core region. The output backscattered light is input to the measuring device 300 via the optical coupling unit 20, the single-core optical fiber 31b, the single-core optical fiber 202, and the optical input / output unit 302. Furthermore, the photodetector 313 receives the input backscattered light, and outputs a current signal corresponding to the intensity of the backscattered light. The A / D converter 314 receives the current signal as an analog signal output by the photodetector 313, converts it into a digital signal, and outputs it to the control unit 320.

[0045] In the control unit 320, the data processing unit 322 receives the digital signal from the A / D converter 314 and processes the data of the information included in the digital signal. For example, the data processing unit 322 generates two-dimensional data by associating the light intensity of the backscattered light as information included in the digital signal with the acquisition time of the digital signal. The light intensity is an example of a feature quantity that characterizes the backscattered light. Furthermore, based on the time difference between the acquisition time of the digital signal and a reference time, the data processing unit 322 converts the acquisition time into a position (distance from the first end 13 of the multicore fiber 10) where the backscattered light corresponding to the digital signal was generated in the multicore fiber 10. In this way, the data processing unit 322 generates two-dimensional data in which the generation position (distance) of the backscattered light received by the measurement unit 310 in the multicore fiber 10 is associated with the light intensity of the backscattered light generated there. That is, the measurement device 300 operates in the same manner as an OTDR (Optical Time Domain Reflectometer). The data processing unit 322 stores the generated two-dimensional data as a temporal data sequence of the two-dimensional data.

[0046] The pump light is synchronized with the pulsed electric signal output from the pulse signal generator 312, and the electric signal has a repetition period according to the length of the multi-core fiber 10. Specifically, the repetition period is set to be longer than the time from when the pump light is output from the pump light generating unit 315 to when it reaches the second end 14 of the multi-core fiber 10 and then when the backscattered light generated at the second end 14 reaches the photodetector 313. By setting it in this way, it is possible to receive the backscattered light generated by one pump light in a state where only one pump light is propagating in the multi-core fiber 10, rather than in a state where a plurality of pump light are propagating in the multi-core fiber 10.

[0047] Furthermore, the data processing unit 322 performs data processing at a timing synchronized with the pulsed electric signal output from the pulse signal generator 312, in response to a trigger signal from the pulse signal generator 312. This allows the data processing unit 322 to repeatedly process a digital signal sequence that is continuous in time according to the length of the multi-core fiber 10, at the period of the trigger signal.

[0048] Here, when the multi-core fiber 10 is deformed, the degree of crosstalk changes, and therefore the strength of coupling of the excitation light to other core regions also changes. The deformation of the multi-core fiber 10 includes, for example, deformation or vibration caused by an external force acting on the multi-core fiber 10, minute vibration caused by the propagation of an acoustic wave in the multi-core fiber 10, or expansion or contraction caused by a temperature change of the multi-core fiber 10.

[0049] FIG. 3 is a diagram showing an example of the characteristics of the multi-core fiber 10 shown in FIG. 1. FIG. 3 shows a change in light intensity over time when test light is input from the first end 13 side of the multi-core fiber 10 to the core region 12a and the test light output from each core region 12 is received at the second end 14 side. The test light source is a single longitudinal mode oscillation semiconductor laser, and the spectral linewidth of the test light is 1 MHz or less. In addition, "Core2" in the legend of FIG. 3 indicates the test light output from the core region 12a, and "Core1", "Core3", and "Core4" indicate the test light output from the core regions 12 other than the core region 12a. In addition, "SUM" indicates the sum of the test light output from all the core regions 12 including the core region 12a.

[0050] FIG. 3(a) shows a case where the multi-core fiber 10 is placed in a state where no external force is applied to it, and FIG. 3(b) shows a case where the multi-core fiber 10 is touched with a finger and vibrated. As shown in FIG. 3(a) and (b), none of the light intensities change over time when no external force is applied to the multi-core fiber 10. On the other hand, it can be seen that when the multi-core fiber 10 is vibrating, all of "Core1", "Core2", "Core3", and "Core4" vary over time, but "SUM" hardly varies over time. FIG. 3(a) and (b) show that when the multi-core fiber 10 is vibrating, the coupling state of light from the core region where the test light is input to other core regions changes at the place where the vibration occurs, and the inter-core crosstalk changes. A coupled multi-core fiber such as the multi-core fiber 10 can be said to be an optical fiber that sensitively responds to deformation such as vibration.

[0051] 4 is a diagram showing an example of waveform data obtained by data processing by the data processing unit 322. This waveform data shows the time change of the backscattered light from the multi-core fiber 10. That is, the time change shows the distribution of the backscattered light from each point in the longitudinal direction of the multi-core fiber 10. The vertical axis shows the distance to the second end 14 with the first end 13 as the reference. The vertical axis shows the light intensity of the backscattered light.

[0052] Fig. 4(a) shows a case where the multi-core fiber 10 is placed in a state where no external force is acting on the multi-core fiber 10, and Fig. 4(b) shows a case where the multi-core fiber 10 is vibrated by touching it with a finger at a position about 260 m away from the first end 13. Furthermore, Fig. 4(c) is a view in which a part of Fig. 4(b) is enlarged in the vertical axis direction. Note that "Core1" in the legend of Fig. 4 indicates a case where backscattered light output from core region 12b is received, and "Core3" and "Core4" indicate a case where backscattered light output from core region 12 other than core regions 12a and 12b is received.

[0053] As shown in FIG. 4, the light intensity of the backscattered light changes suddenly at the vibration generation position, and the light intensity fluctuates away from that position.

[0054] Therefore, the determination unit 323 detects the deformation generated in the multi-core fiber 10, or determines the position of occurrence or the change over time of the deformation, based on the data processing result of the data processing unit 322 as exemplified in FIG. 4. The determination unit 323 detects the occurrence of vibration, for example, when the light intensity changes suddenly. The determination unit 323 also determines the position where the light intensity changes suddenly over time as the position where the vibration occurred. The determination unit 323 may also determine the change over time of the vibration from the change over time of the amount of change in the light intensity, for example, and further determine the time when the vibration occurred. The determination unit 323 is an example of a determination unit that detects the deformation generated in the multi-core fiber 10, or determines the position of occurrence or the change over time of the deformation, based on the light intensity among the feature quantities of the backscattered light. The determination unit 323 may store the result of the determination, or, if the control unit 320 has a display function or a communication function with an external device, may display the result of the determination or transmit it to an external device.

[0055] The optical fiber sensing system 1000 configured as above utilizes the inter-core crosstalk characteristic of the coupled multi-core fiber, and therefore can measure deformation of the multi-core fiber 10, such as vibration, with high sensitivity. Moreover, in the optical fiber sensing system 1000, the arrival time of the backscattered light to the photodetector 313 is proportional to the position (distance from the first end 13) in the multi-core fiber 10, and therefore the distribution of deformation in the longitudinal direction of the multi-core fiber 10 can be easily measured. Moreover, in the optical fiber sensing system 1000, the core region 12a to which the excitation light is input and the core region 12b to which the received backscattered light is output are separate, and therefore no optical components (optical circulator or optical switch) are required to separate the excitation light and the backscattered light. Therefore, the optical fiber sensing system 1000 can be configured simply.

[0056] In addition, when pulsed excitation light is periodically output, ideally no backscattered light occurs when the excitation light is OFF (when the light intensity of the excitation light is zero), but in reality, even when the excitation light is OFF, weak background light exists continuously over time. In this case, it is known that the backscattered light due to the background light becomes noise and deteriorates the signal-to-noise ratio (SNR) at the light receiving unit. However, in the optical fiber sensing system 1000, the core region 12a to which the excitation light is input and the core region 12b to which the received backscattered light is output are separate, so that the backscattered light due to the background light is prevented from being superimposed on the backscattered light due to the excitation light and input to the light receiving unit. Therefore, the optical fiber sensing system 1000 suppresses deterioration of the SNR.

[0057] According to the inventor's intensive study, it was confirmed that when the spectral linewidth of the test light or the excitation light is as wide as 1 nm or more, the intensity fluctuation of the backscattered light as shown in Figs. 3 and 4 does not occur significantly. From this, it was found that the coherence of the excitation light is significantly affected by the change in the inter-core crosstalk when the multi-core fiber 10 is deformed, and that the sensitivity of deformation detection can be improved by using excitation light having high coherence (narrow spectral linewidth). For this reason, it is preferable that the spectral linewidth of the excitation light is, for example, 1 MHz or less. As the light source 311, for example, a distributed feedback (DFB) semiconductor laser or a fiber laser capable of single longitudinal mode oscillation operation is preferable.

[0058] Furthermore, the data processing unit 322 may perform data processing to obtain a differential value with respect to a time change in the light intensity of the backscattered light. Fig. 5 is a diagram showing waveform data obtained by differentiating the waveform shown in Fig. 4 with respect to the distance direction (horizontal axis). As shown in Fig. 5, in the waveform data of the differential with respect to the distance direction of the light intensity of the backscattered light, the position where the vibration occurs appears as a peak. The differentiation with respect to the distance direction corresponds to the differentiation with respect to the time change. Therefore, if the determination unit 323 identifies the position where the deformation has occurred based on the differential value with respect to the distance direction of the light intensity of the backscattered light, it can identify the position where the deformation has occurred or the time change with higher accuracy.

[0059] Fig. 6 is a diagram showing an example of data obtained by the measurement device 300 shown in Fig. 1. Fig. 6 shows the results of continuously and repeatedly measuring data for a length of 1100 m of the multicore fiber 10, the distance from the first end 13 of which ranges from 1085 m to 1095 m, for 500 seconds.

[0060] Fig. 6(a) shows the case where the multi-core fiber 10 is placed in a state where no external force is applied, and the color shading indicates the light intensity of the backscattered light. In the case of Fig. 6(a), it is found that the light intensity is uniform in the shown position range and time range, and no deformation occurs in the multi-core fiber 10.

[0061] Figure 6(b) shows the case where a position at a distance of about 1090 m from the first end 13 is touched with a finger, and the shade of color indicates the light intensity of the backscattered light. In the case of Figure 6(b), from the position of about 110 seconds on the horizontal axis, a portion where the color becomes lighter farther away from the distance of about 1090 m appears. This indicates that vibration is occurring in the multi-core fiber 10 at a distance of about 1090 m.

[0062] Figure 6(c) shows the derivative of the two-dimensional data in Figure 6(c) along the time axis (horizontal axis), and the shade of color indicates the magnitude of the derivative coefficient. In the case of Figure 6(c), it can be more clearly identified that the vibration began at 110 seconds.

[0063] (Embodiment 2) Fig. 7 is a schematic configuration diagram of an optical fiber sensing system according to embodiment 2. This optical fiber sensing system 1000A has a configuration in which the optical fiber unit 100 of the optical fiber sensing system 1000 shown in Fig. 1 is replaced with an optical fiber unit 100A, and a probe light source 400 and a connection cable 500 are added.

[0064] The optical fiber unit 100A has a configuration in which an optical coupling unit 40 and four single-core optical fibers 50 are added to the optical fiber unit 100. The single-core optical fiber 50 is, for example, a standard single-mode optical fiber used in optical communication, and has one core region in the cladding region. The optical coupling unit 40 is disposed between the second end 14 of the multi-core fiber 10 and the single-core optical fiber 50. The optical coupling unit 40 optically couples the core regions of the four single-core optical fibers 50 to the four core regions 12 of the multi-core fiber 10. Specifically, the optical coupling unit 40 optically couples the single-core optical fiber 51a of the single-core optical fiber 50 to the core region 12b of the multi-core fiber 10. The optical coupling unit 40 can be configured, for example, by bundling single-core optical fibers or using a lens, similarly to the optical coupling unit 20.

[0065] The probe light source 400 outputs a continuous wave probe light having the same wavelength as the backscattered light (for example, the same wavelength as the excitation light). The connection cable 500 is, for example, a standard single mode optical fiber used in optical communication, and optically connects the single-core optical fiber 51a and the probe light source 400. Thus, the probe light source 400 inputs a probe light having the same wavelength as the backscattered light from the second end 14 side opposite to the first end 13 side of the multi-core fiber 10 to the core region 12b, which is the second core region. The intensity of the probe light is preferably such that no unnecessary nonlinear optical phenomenon occurs in the optical fiber section 100. The intensity of the probe light is, for example, about 0 dBm to -10 dBm.

[0066] The probe light input to the core region 12b propagates in the same direction as the backscattered light, i.e., from the second end 14 side to the first end 13 side, and optically amplifies the backscattered light. This increases the optical intensity of the backscattered light received by the photodetector 313 of the measurement device 300.

[0067] The optical fiber sensing system 1000A configured as described above has a simple configuration similar to that of the optical fiber sensing system 1000 of embodiment 1, and is capable of receiving backscattered light with higher light intensity, thereby enabling it to measure deformations such as vibrations with higher sensitivity.

[0068] (Embodiment 3) Fig. 8 is a schematic configuration diagram of an optical fiber sensing system according to embodiment 3. This optical fiber sensing system 1000B has a configuration in which the measuring device 300 of the optical fiber sensing system 1000 shown in Fig. 1 is replaced with a measuring device 300B. Note that the optical fiber unit 100 and the connection cable 200 are omitted from Fig. 8.

[0069] The measuring device 300B has a configuration in which the measuring section 310 of the measuring device 300 is replaced with a measuring section 310B. The measuring section 310B has a configuration in which the light source 311 of the measuring section 310 is replaced with a light source 311B, and optical couplers 316 and 317 and an optical modulator 318 are added. The light source 311B, the pulse signal generator 312, and the optical modulator 318 constitute an excitation light generating section 315B.

[0070] The light source 311 includes, for example, a semiconductor laser device or a fiber laser device, and outputs a continuous wave laser light. The optical coupler 316 splits the laser light output from the light source 311 into two, and outputs each of the two laser lights to the optical modulator 318 and the optical coupler 317. The optical modulator 318 generates pumping light, which is a pulsed laser light, from the input continuous wave laser light based on the pulsed electric signal output from the pulse signal generator 312 at a timing synchronized with the electric signal, and outputs the pumping light periodically. The pumping light is output from the optical input / output unit 301 to the outside of the measurement device 300B, and is output to the core region 12a of the multi-core fiber 10.

[0071] On the other hand, the backscattered light output from the core region 12b of the multicore fiber 10 and input from the optical input / output unit 302 to the measuring device 300B is input to the optical coupler 317. The optical coupler 317 outputs light (combined light) obtained by combining this backscattered light with the laser light (also called local light) input from the optical coupler 316 to the photodetector 313. The photodetector 313 outputs a current signal corresponding to the intensity of the input combined light. The A / D converter 314 receives the current signal output by the photodetector 313 as an analog signal, converts it into a digital signal, and outputs it to the control unit 320.

[0072] In the control unit 320, the data processing unit 322 receives the digital signal from the A / D converter 314 and processes the information data included in the digital signal. For example, the data processing unit 322 generates two-dimensional data by two-dimensionally rearranging a continuous digital signal representing the optical intensity of the combined light at a fixed time interval (i.e., a fixed amount of data) that coincides with the repetition period of the excitation pulse light, in synchronization with a synchronization signal from the pulse signal generator 312. The optical intensity of the combined light includes information on the optical intensity of the backscattered light and information on the phase difference between the backscattered light and the local light. The information on the optical intensity of the backscattered light and the information on the phase difference between the backscattered light and the local light are examples of features that characterize the backscattered light. Furthermore, the data processing unit 322 converts the acquisition time of the data into the position (distance from the first end 13 of the multicore fiber 10) at which the backscattered light corresponding to the digital signal was generated in the multicore fiber 10, using the generation timing of the synchronization signal from the pulse signal generator 312 as the origin. As a result, the data processing unit 322 generates two-dimensional data in which the generation position (distance) in the multi-core fiber 10 of the backscattered light received by the measuring unit 310 is associated with the light intensity of the backscattered light generated there. That is, the measuring device 300 operates in the same manner as a coherent OTDR. Then, the determining unit 323 detects deformation generated in the multi-core fiber 10, or determines the generation position or time change, based on the data processing result of the data processing unit 322.

[0073] The optical fiber sensing system 1000B configured as described above has a simple configuration similar to that of the optical fiber sensing system 1000 of embodiment 1, and can measure deformations such as vibrations with higher sensitivity by using the phase information of the backscattered light.

[0074] (Embodiment 4) Fig. 9 is a schematic configuration diagram of an optical fiber sensing system according to embodiment 4. This optical fiber sensing system 1000C has a configuration in which the connection cable 200 of the optical fiber sensing system 1000 shown in Fig. 1 is replaced with a connection cable 200C, and the measurement device 300 is replaced with a measurement device 300C.

[0075] The connection cable 200C has two single-core optical fibers 203 and 204 in addition to the two single-core optical fibers 201 and 202 that the connection cable 200 has. The single-core optical fiber 203 optically connects the single-core optical fiber 31c of the single-core optical fiber 30 to the optical input / output unit 303 of the measurement device 300C. The single-core optical fiber 31c is optically connected to the core region 12c of the core region 12 of the multi-core fiber 10 by the optical coupling unit 20. The single-core optical fiber 204 optically connects the single-core optical fiber 31d of the single-core optical fiber 30 to the optical input / output unit 304 of the measurement device 300C. The single-core optical fiber 31d is optically connected to the core region 12d of the core region 12 of the multi-core fiber 10 by the optical coupling unit 20. The core regions 12c and 12d are examples of second core regions. That is, the multi-core fiber 10 has core regions 12b, 12c, and 12d as a plurality of second core regions.

[0076] Fig. 10 is a schematic diagram of the measurement device 300C shown in Fig. 9. Measurement device 300C has a configuration in which measurement unit 310 of measurement device 300 is replaced with measurement unit 310C, and optical input / output units 303 and 304 are added. Measurement unit 310C has a configuration in which photodetectors 313a and 313b and A / D converters 314a and 314b are added to measurement unit 310.

[0077] The photodetector 313a receives the backscattered light output from the core region 12c at the first end 13 side, input from the optical input / output unit 303, and outputs a current signal corresponding to the optical intensity. The A / D converter 314a receives the current signal output from the photodetector 313a as an analog signal, converts it to a digital signal, and outputs it to the control unit 320. The photodetector 313b receives the backscattered light input from the optical input / output unit 304 and output from the core region 12d at the first end 13 side, and outputs a current signal corresponding to the optical intensity of the backscattered light. The A / D converter 314b receives the current signal output from the photodetector 313b as an analog signal, converts it to a digital signal, and outputs it to the control unit 320. The photodetectors 313, 313a, and 313b are examples of a plurality of light receiving units.

[0078] In the control unit 320, the data processing unit 322 receives each digital signal from the A / D converters 314, 314a, and 314b, and processes the data of the information included in each digital signal. For example, the data processing unit 322 calculates the sum of squares of the light intensity of each backscattered light as information included in each digital signal, and generates two-dimensional data by associating the sum of squares with the acquisition time of the digital signal. Furthermore, based on the time difference between the acquisition time of the digital signal and a reference time, the data processing unit 322 converts the acquisition time into the position (distance from the first end 13 of the multi-core fiber 10) at which the backscattered light corresponding to the digital signal was generated in the multi-core fiber 10. In this way, the data processing unit 322 generates two-dimensional data in which the generation position (distance) in the multi-core fiber 10 of the backscattered light received by the measurement unit 310C is associated with the sum of squares based on the light intensity of the backscattered light generated there.

[0079] The determination unit 323 detects the deformation occurring in the multi-core fiber 10, or identifies the position of occurrence or time change of the deformation, based on the data processing result of the data processing unit 322. In this case, the sum of squares changes more sensitively to the deformation occurring in the multi-core fiber 10 than the individual light intensities of the backscattered lights. As a result, the optical fiber sensing system 1000C can measure deformation such as vibration with higher sensitivity with a simple configuration.

[0080] In this embodiment, the data processing unit 322 calculates the sum of squares of the light intensity of each backscattered light, but instead of the sum of squares, a variance value or a standard deviation may be calculated. These statistical values ​​such as the sum of squares, variance value, and standard deviation are also examples of feature quantities that characterize the backscattered light.

[0081] (Aspects of multi-core fiber) 11 and 12 are schematic cross-sectional views showing aspects of a multi-core fiber used in an optical fiber sensing system. In the above embodiment, it has been described that the multi-core fiber 10 includes the cladding region 11 and the core region 12. However, the multi-core fiber 10 may be provided with a coating 15 having a tight buffer structure so as to surround the periphery of the cladding region 11 as shown in FIG. 11(a). Also, as shown in FIG. 11(b), the multi-core fiber 10 may constitute an optical fiber cable 600A. The optical fiber cable 600A has a configuration in which a plurality of multi-core fibers 10 are arranged so as to surround the periphery of a tension member 601 made of resin or the like, and a coating 602 is further provided so as to surround the periphery of the plurality of multi-core fibers 10. For example, at least one of the plurality of multi-core fibers 10 is used as a multi-core fiber of the optical fiber sensing system. Note that one or more of the plurality of multi-core fibers 10 may be replaced with an optical fiber other than the multi-core fiber 10.

[0082] 12(a), the multi-core fiber 10 may constitute a composite cable 600B. The composite cable 600B has a configuration in which an inner coating 605 is provided so as to surround two multi-core fibers 10, three power lines 603, and one earth wire 604. Furthermore, in the composite cable 600B, a plurality of tension members 606 are arranged so as to surround the inner coating 605, and a braid 607 is provided so as to surround the plurality of tension members 606. For example, at least one of the two multi-core fibers 10 is used as a multi-core fiber of an optical fiber sensing system. Note that one of the two multi-core fibers 10 may be replaced with an optical fiber other than the multi-core fiber 10.

[0083] 12(b), the multi-core fiber 10 may constitute an optical fiber cable 600C. The optical fiber cable 600C has a configuration in which a plurality of optical fiber ribbons 608 are accommodated in slots 610 provided in a slot material 609. In the optical fiber cable 600C, a tension member 611 is provided at the center of the slot material 609, and external coatings 612 and 613 are provided so as to surround the slot material 609. For example, at least one multi-core fiber 10 constituting the optical fiber ribbon 608 is used as a multi-core fiber of an optical fiber sensing system.

[0084] (Applications of optical fiber sensing systems) Next, an application form of the optical fiber sensing system will be described. In the application form described below, the measurement device 300 includes a light receiving unit (photodetector 313) that receives backscattered light output from the core region 12b to the first end 13 side when pulsed excitation light is input to the core region 12a from the first end 13 side of the multi-core fiber 10 provided near the measurement object, and a determination unit that detects an event that occurs in the measurement object and causes deformation of the multi-core fiber 10 based on a feature amount of the backscattered light received by the light receiving unit, or determines the occurrence position or time change of the event, and functions as a measurement device that executes an event detection method.

[0085] FIG. 13 is a schematic configuration diagram of a first application form of the optical fiber sensing system. In the first application form, the multi-core fiber 10 of the optical fiber unit 100 of the optical fiber sensing system 1000 is laid along a track 10001 such as a railway. The optical fiber sensing system 1000 thus applied can detect vibrations occurring around the track 10001, and determine the location of vibration occurrence and time change. The optical fiber sensing system 1000 can also detect vibrations caused by a train passing over the track 10001, vibrations caused by a person or animal (such as a deer or wild boar) invading the track 10001, and vibrations caused by falling rocks or earth and sand flowing into the track 10001 from around the track 10001 due to a collapse or the like, and can determine the location of vibration occurrence and time change. The track 10001 is an example of a measurement target in the vicinity of which the multi-core fiber 10 is provided. Furthermore, the vibration occurring in the line 10001 is an example of an event that causes deformation of the multi-core fiber 10.

[0086] Fig. 14 is a schematic configuration diagram of a second application form of the optical fiber sensing system. In the second application form, the optical fiber sensing system 1000 is applied to a road 10003 along which automobiles and the like pass, which is provided on the ground 10002, as shown in Fig. 14(a). The road 10003 extends in a direction perpendicular to the plane of the drawing. A protective body 2000 made of resin or the like and extending along the road 10003 is buried in the ground 10002.

[0087] As shown in FIG. 14(b), the multi-core fiber 10 of the optical fiber unit 100 of the optical fiber sensing system 1000 is housed in the protective body 2000 along the longitudinal direction. FIG. 14(c) shows a cross-sectional view of the AA line in FIG. 14(b). The protective body 2000 has a main body 2010, a lid 2020, a spacer 2030, a connecting member 2040, a supporting member 2050, and an attachment member 2060. The main body 2010 has a bottom wall 2011 extending in the longitudinal direction of the protective body 2000, which is a direction perpendicular to the drawing, and two side walls 2012 extending upward in the height direction, which is a vertical direction, from both ends of the bottom wall 2011 in the width direction, which is the left-right direction, in the drawing. The main body 2010 opens in the upward direction of the drawing with respect to the bottom wall 2011. The lid 2020 extends in the vertical direction of the drawing and covers the opening of the main body 2010. The spacer 2030 extends in a direction perpendicular to the plane of the drawing, and is interposed between the main body 2010 and the lid 2020. The connection member 2040 is provided on the side wall 2012 so as to extend in a direction perpendicular to the plane of the drawing, and supports the lid 2020 and the spacer 2030. The support member 2050 is provided on the side wall 2012 so as to extend in a direction perpendicular to the plane of the drawing, and supports the multi-core fiber 10. The attachment member 2060 fixes the multi-core fiber 10 to the support member 2050. Note that the protector 2000 may house a communication cable or a power cable in addition to the multi-core fiber 10.

[0088] The optical fiber sensing system 1000 thus applied can detect vibrations that occur when an automobile passes over the road 10003, and determine the location of the vibrations and their change over time. Specifically, when an automobile passes over the road 10003 and the road 10003 vibrates, the vibrations propagate through the ground 10002 and further propagate to the multi-core fiber 10 via the protective body 2000. The optical fiber sensing system 1000 detects the propagated vibrations and determines the location of the vibrations and their change over time. The optical fiber sensing system 1000 can also detect vibrations that occur when a person or animal enters the road 10003, vibrations that occur due to falling rocks or earth and sand that flow into the road 10003 from the periphery of the road 10003 due to collapse, and vibrations that occur due to construction work on the road 10003 or around the road 10003, and determine the location of the vibrations and their change over time. The road 10003 is an example of a measurement object in the vicinity of which the multi-core fiber 10 is provided. Furthermore, vibrations occurring on the road 10003 are an example of an event that causes deformation of the multi-core fiber 10.

[0089] FIG. 15 is a schematic configuration diagram of a third application form of the optical fiber sensing system. In the third application form, the multi-core fiber 10 of the optical fiber unit 100 of the optical fiber sensing system 1000 is housed in a protective body 3000 laid on the seabed 10005 in the sea 10004. The protective body 3000 is configured to be watertight so that seawater 10006 does not enter inside. For example, when an underwater acoustic wave is generated by the movement of a ship or marine life, the underwater acoustic wave propagates in the sea and vibrates the protective body 3000. The protective body 3000 further propagates to the multi-core fiber 10 of the optical fiber unit 100. Therefore, according to the optical fiber sensing system 1000 applied in this way, it is possible to detect the movement of the ship or marine life and to determine the position where the movement occurs. Furthermore, according to the optical fiber sensing system 1000, it is possible to detect a seismic wave that has propagated underground and reached the seabed 1005 and to determine the time change of the seismic wave. The sea 10004 and the seabed 10005 are examples of measurement objects near which the multi-core fiber 10 is provided. In addition, the movement of ships and marine life, and seismic waves are examples of events that cause deformation of the multi-core fiber 10.

[0090] FIG. 16 is a schematic configuration diagram of a fourth application form of the optical fiber sensing system. In the fourth application form, the multi-core fiber 10 of the optical fiber unit 100 of the optical fiber sensing system 1000 is stretched between utility poles 10007. The optical fiber unit 100 may be included in an overhead cable such as a communication cable. The optical fiber sensing system 1000 thus applied can detect wind that vibrates the optical fiber unit 100, and vibrations occurring around the utility pole 10007, and can determine the location of occurrence and time change of these. The utility pole 10007 and the surrounding area of ​​the utility pole 10007 are examples of measurement objects in the vicinity of which the multi-core fiber 10 is provided. Moreover, wind and vibrations are examples of events that cause deformation of the multi-core fiber 10.

[0091] FIG. 17 is a schematic configuration diagram of a fifth application form of the optical fiber sensing system. In the fifth application form, the multi-core fiber 10 of the optical fiber unit 100 of the optical fiber sensing system 1000 is provided along the main beam of a bridge 10008. The optical fiber sensing system 1000 thus applied can detect vibrations occurring in the bridge 10008 and determine the location of the vibrations and their change over time. The vibrations occurring in the bridge 10008 are generated by a moving body such as a vehicle or a pedestrian passing over the bridge 10008 or by natural phenomena such as wind or an earthquake. The bridge 10008 is an example of a measurement target in the vicinity of which the multi-core fiber 10 is provided. The vibrations are also an example of an event that causes deformation of the multi-core fiber 10.

[0092] (Embodiment 5) An optical fiber sensing system according to an embodiment of the present invention may be configured to have a function of detecting an event that occurs in a measurement object near which a multicore fiber is provided and that causes deformation of the multicore fiber, or a function of determining the occurrence position or time change of the event, as well as a function of discriminating the type of the event.

[0093] Fig. 18 is a schematic configuration diagram of a measurement device in an optical fiber sensing system according to embodiment 5. This optical fiber sensing system 1000D has a configuration in which the measurement device 300 of the optical fiber sensing system 1000 shown in Fig. 1 is replaced with a measurement device 300D. Note that the optical fiber unit 100 and the connection cable 200 are omitted from Fig. 18.

[0094] The measuring device 300D has a configuration in which the control unit 320 of the measuring device 300 is replaced with a control unit 320D. The control unit 320D has a configuration in which a discrimination unit 324 is added to the control unit 320. The discrimination unit 324 discriminates, for example, by using a discrimination means stored in a memory, from data generated by the data processing unit 322, a type of event that occurs in the measurement object near which the multi-core fiber 10 is provided and causes deformation of the multi-core fiber 10.

[0095] The discrimination means can be configured to use various classification methods that can associate data generated by the data processing unit 322 with events corresponding to the data. For example, the discrimination means is configured to include a trained model using training data. In this case, the training data is, for example, a data set in which a known event as a label is linked to data (data including a feature amount of the backscattered light) generated by the data processing unit 322 based on the backscattered light generated by the event. In addition, the trained model can be created by various methods. For example, the trained model can be created by using an image recognition method such as a deep learning method represented by a convolutional neural network, with the data constituting the data set being image data as shown in FIG. 6.

[0096] In the optical fiber sensing system according to the embodiment of the present invention, the control unit may have a learning function. Fig. 19 is a flowchart showing an example of a processing procedure executed by the control unit 320D in the fifth embodiment when the control unit has a learning function.

[0097] First, the data processing unit 322 generates data (step S1). Next, the discrimination unit 324 performs event discrimination (step S2). A data set in which the discriminated events and data are linked is stored as a database in a memory or a recording medium. Next, the discrimination unit 324 performs machine learning based on the database (step S3). Next, the discrimination unit 324 updates or accumulates the trained model based on the results of the machine learning (step S4). Note that the update is a process of deleting a part of past data corresponding to new data, and the accumulation is a process of adding new data without deleting past data.

[0098] The present invention is not limited by the above-mentioned embodiments. The present invention also includes a configuration in which the above-mentioned components are appropriately combined. For example, any of the optical fiber sensing systems of the first to fifth embodiments can be applied to the above-mentioned first to fifth application forms. In addition, two or more of the configuration including a probe light source as in the second embodiment, the configuration using phase information of backscattered light as in the third embodiment, and the configuration receiving backscattered light from a plurality of core regions as in the fourth embodiment may be appropriately combined. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-mentioned embodiments, and various modifications are possible. [Explanation of symbols]

[0099] 10: Multi-core fiber 11: Cladding region 12, 12a, 12b, 12c, 12d: Core region 13 :1st end 14: 2nd end 15, 602: Covering 20, 40: Optical coupling part 30, 31a, 31b, 31c, 31d, 50, 51a, 201, 202, 203, 204: Single-core optical fiber 100, 100A: Optical fiber section 200, 200C, 500: Connection cable 300, 300B, 300C, 300D: Measuring device 301, 302, 303, 304: Optical input / output section 310, 310B, 310C: Measuring section 311, 311B: Light source 312: Pulse signal generator 313, 313a, 313b: Photodetector 314, 314a, 314b: A / D converter 315, 315B: Excitation light generating unit 316, 317: Optical coupler 318: Optical modulator 320, 320D: Control unit 321: Receiving unit 322: Data processing section 323: Judgment section 324: Discrimination part 400: Probe light source 600A, 600C: Fiber optic cable 600B: Composite cable 601, 606, 611: Tension members 603: Power lines 604: Earth wire 605: Internal coating 607: Blade 608: Optical fiber ribbon 609: Slot material 610: Slots 612, 613: Outer sheath 1000, 1000A, 1000B, 1000C, 1000D: Fiber Optic Sensing Systems 2000, 3000: Protective body 2010: Main unit 2011: Bottom wall 2012 :Side wall 2020 :Lid 2030: Spacer 2040: Connection parts 2050: Support member 2060: Mounting material 10001 :Railway 10002: Ground 10003 :Road 10004: Sea 10005 :Undersea 10006 :Seawater 10007 : Electric pole 10008: Bridge

Claims

1. a multi-core fiber having a plurality of core regions in a cladding region, and having an inter-core crosstalk of −40 dB / km or more for light at a predetermined wavelength; an excitation light generating unit that inputs pulsed excitation light having the predetermined wavelength into a first core region of the plurality of core regions from a first end side of the multicore fiber; a light receiving unit configured to receive backscattered light generated by the excitation light and outputted at the first end side from a second core region that is a core region other than the first core region among the plurality of core regions; An optical fiber sensing system comprising:

2. The spectral line width of the excitation light is 1 MHz or less. The optical fiber sensing system of claim 1 .

3. The core pitch of the plurality of core regions is 15 μm or more and 25 μm or less. The optical fiber sensing system of claim 1 .

4. The optical fiber further includes a determination unit that detects a deformation generated in the multi-core fiber or determines a position where the deformation occurs or a change over time based on a feature amount of the backscattered light received by the light receiving unit. The optical fiber sensing system of claim 1 .

5. The determination unit detects the deformation or determines an occurrence position or a time change of the deformation based on a light intensity among characteristic quantities of the received backscattered light. The optical fiber sensing system of claim 4 .

6. The determination unit determines the occurrence position or the time change of the deformation based on a differential value with respect to the time change of the light intensity. The optical fiber sensing system of claim 5 .

7. a probe light source that inputs probe light having a wavelength equal to that of the backscattered light into the second core region from a second end side of the multicore fiber opposite to the first end side. The optical fiber sensing system of claim 1 .

8. the multicore fiber has a plurality of the second core regions, a plurality of light receiving sections each receiving the backscattered light from each of the plurality of second core regions; The optical fiber sensing system of claim 1 .

9. The multicore fiber has an inter-core crosstalk of −30 dB / km or more. The optical fiber sensing system of claim 1 .

10. a light receiving unit that receives backscattered light generated by the excitation light output from a second core region, which is a core region other than the first core region among the plurality of core regions, at a first end side of the multi-core fiber provided near an object to be measured and has a plurality of core regions in a cladding region, the multi-core fiber having an optical inter-core crosstalk at a predetermined wavelength of -40 dB / km or more; when pulsed excitation light having the predetermined wavelength is input to a first core region among the plurality of core regions from a first end side of the multi-core fiber; a determination unit that detects an event that occurs in the object to be measured and causes deformation of the multi-core fiber based on a feature amount of the backscattered light received by the light receiving unit, or determines an occurrence position or a time change of the event; A measuring device comprising:

11. Further, a discrimination unit for discriminating the type of the event is provided.

11. The measuring device according to claim 10.

12. The multicore fiber has an inter-core crosstalk of −30 dB / km or more.

11. The measuring device according to claim 10.

13. A multi-core fiber is provided near an object to be measured, the multi-core fiber has a plurality of core regions in a cladding region, and has a core-to-core crosstalk of light at a predetermined wavelength of −40 dB / km or more. A pulsed excitation light having the predetermined wavelength is input from a first end side of the multi-core fiber to a first core region among the plurality of core regions; receiving backscattered light generated by the excitation light and outputted at the first end side from a second core region that is a core region other than the first core region among the plurality of core regions; Detecting an event that occurs in the object to be measured and causes deformation of the multi-core fiber, or determining the occurrence position or time-dependent change of the event, based on a feature amount of the received backscattered light. Event detection methods.

14. Furthermore, the type of the event is determined. The event detection method according to claim 13.

15. The multicore fiber has an inter-core crosstalk of −30 dB / km or more. The event detection method according to claim 13.

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