Optical fiber characteristic measurement device and optical fiber characteristic measurement method

Abstract

The invention relates to an optical fiber characteristic measuring device and an optical fiber characteristic measuring method. An optical fiber characteristic measurement device (10) is provided with a calculation unit (54) that extracts a plurality of peak values included in a Brillouin gain spectrum of Brillouin scattered light (LS) generated within an optical fiber to be measured (80), and measures the characteristics of the optical fiber to be measured (80).

Description

Technical Field

[0001] The present invention relates to an optical fiber characteristic measuring device and an optical fiber characteristic measuring method. Background Art

[0002] Conventionally, there is known a method for measuring the characteristics of an optical fiber by obtaining the Brillouin frequency shift (BFS) of Brillouin scattering generated in the optical fiber (see, for example, Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Publication No. 2020-41843

[0004] When calculating BFS as the frequency of one peak detected in the Brillouin gain spectrum (BGS), it is necessary to set the spatial resolution of measuring BGS to be smaller than the abnormal part of the optical fiber. Here, the smaller the spatial resolution, the more the number of target sections for detecting BGS in a manner that the entire length direction of the optical fiber can be measured without omission. The more the number of target sections for detecting BGS increases, the longer it takes to detect BGS for the entire measurement object with respect to the optical fiber characteristics. As a result, the measurement time of the optical fiber characteristics is prolonged. Summary of the invention

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an optical fiber characteristic measuring device and an optical fiber characteristic measuring method capable of shortening the time for measuring optical fiber characteristics.

[0006] (1) Some embodiments of the optical fiber characteristic measurement device include a computing unit that extracts a plurality of peaks included in a Brillouin gain spectrum of Brillouin scattered light generated in a measured optical fiber and measures the characteristics of the measured optical fiber. The optical fiber characteristic measurement device extracts each of the plurality of peaks included in the Brillouin gain spectrum, thereby making it less likely to miss an abnormality included in a part of the measurement interval even if the measurement interval is set to be longer. The measurement interval can be set to be longer, and as a result, the measurement time of the optical fiber characteristics can be shortened.

[0007] (2) Based on the optical fiber characteristic measuring device described in (1) above, the operation unit may be configured such that the measurement interval for measuring the characteristic of the optical fiber to be measured is set at at least one position in the optical fiber to be measured, the Brillouin gain spectrum of the measurement interval set at each position is measured, the characteristic of the interval in which the Brillouin gain spectrum containing the abnormal peak but not the normal peak is measured is determined to be abnormal, the interval in which the Brillouin gain spectrum containing both the normal peak and the abnormal peak is measured is subdivided, the Brillouin gain spectrum is measured in each of the subdivided intervals, and it is determined whether each of the subdivided intervals is abnormal. By subdividing the measurement interval containing the abnormality and repeatedly measuring it, the range in which the measurement interval is set shorter is limited. By setting the measurement interval shorter only for a portion of the optical fiber to be measured, the measurement time of the optical fiber characteristic can be shortened.

[0008] (3) The optical fiber characteristic measuring device described in (2) above may also have a light source that emits modulated light injected into the optical fiber to be measured. The light source may be configured so that the operation unit can control the amplitude of the modulated light that determines the length of the measurement interval and the modulation frequency of the modulated light that determines the position of the measurement interval. The position and length of the measurement interval can be determined by controlling the modulation frequency and amplitude of the modulated light, thereby enabling the measurement position and the spatial resolution of the measurement to be switched instantly. That is, random access can be achieved. In addition, the length of the measurement interval can be determined by controlling the modulation frequency and amplitude of the modulated light, thereby enabling the spatial resolution of the measurement to be switched instantly. As a result, it is easy to achieve subdivision of the measurement interval.

[0009] (4) The optical fiber characteristic measuring device described in (3) above may further include a storage unit that stores the measured Brillouin gain spectrum and information identifying a section in which the Brillouin gain spectrum is measured in association with each other. The calculation unit may control the amplitude and modulation frequency of the modulated light based on the information stored in the storage unit.

[0010] (5) Some embodiments of the optical fiber characteristic measurement method include the step of extracting a plurality of peaks included in a Brillouin gain spectrum of Brillouin scattered light generated in an optical fiber to be measured, and measuring the characteristics of the optical fiber to be measured.

[0011] Effects of the Invention

[0012] According to the optical fiber characteristics measuring device and the optical fiber characteristics measuring method according to the present invention, it is possible to shorten the time required to measure optical fiber characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a diagram showing the measurement interval widely set in the device according to the comparative example.

[0014] Figure 2A Graph showing the Brillouin gain spectrum of the measurement section not including the abnormal part.

[0015] Figure 2B Graph showing the Brillouin gain spectrum of the measurement section including the abnormal portion.

[0016] Figure 3 It is a diagram showing a narrow measurement interval set in the device according to the comparative example.

[0017] Figure 4 It is a graph of the Brillouin gain spectrum of the measurement interval including the entire abnormal portion.

[0018] Figure 5 It is a block diagram showing a configuration example of an optical fiber characteristic measuring device according to the present invention.

[0019] Figure 6 This is a diagram showing an example of a measurement interval set in the device according to the present invention.

[0020] Figure 7 Yes means Figure 6 A diagram showing an example of subdivision of the measurement interval.

[0021] Figure 8 This is a flowchart showing an example of the process of the optical fiber characteristic measuring method according to the present invention. DETAILED DESCRIPTION

[0022] In order to measure the characteristics of the optical fiber such as temperature or strain at each position in the longitudinal direction, a method of detecting scattered light or reflected light generated inside the optical fiber in response to the light incident on the optical fiber is considered. As one of the methods for measuring the characteristics of the optical fiber, the Brillouin Optical Correlation Domain Reflectometry (BOCDR) method can be cited.

[0023] BOCDR method includes the following steps: injecting pump light branched from frequency modulated modulated light into an optical fiber; and detecting interference light caused by interfering reference light branched from the modulated light with Brillouin scattered light generated inside the optical fiber. Brillouin scattered light is backscattered light generated by Brillouin scattering caused by pump light injected into the optical fiber, and returns to the end where the pump light was injected.

[0024] The BOCDR method further includes a step of acquiring a spectrum of Brillouin scattered light from a signal of detected interference light. The spectrum of Brillouin scattered light is also called Brillouin gain spectrum (BGS). In the BOCDR method of the present invention, the frequency of the reference light is shifted to perform spectral analysis of the interference light that interferes with the Brillouin scattered light, thereby detecting the BGS.

[0025] The peak frequency of BGS is defined by the characteristics of the optical fiber in which the Brillouin scattered light is measured. Therefore, the characteristics of the optical fiber are measured by calculating the peak frequency of BGS. The peak frequency of BGS is also called the Brillouin frequency shift (BFS).

[0026] In the BOCDR method, Brillouin scattered light and reference light are interfered to selectively extract Brillouin scattered light in a specific interval where a correlation peak appears in the optical fiber. The correlation peak is a peak that appears in the interference light due to the mutual reinforcement of Brillouin scattered light and reference light. The specific interval where the correlation peak appears is an interval where Brillouin scattered light with a correlation peak of interference light appears due to mutual reinforcement with the reference light in the optical fiber. In the BOCDR method, the fiber characteristics such as temperature or strain at the position where the correlation peak appears are measured by finding the BFS of the position where the correlation peak appears. The specific interval where the correlation peak appears is also called the measurement interval for measuring the characteristics of the optical fiber.

[0027] The measurement interval is set at at least one position in the optical fiber. The position of the measurement interval is determined by the modulation frequency of the pump light and the reference light. That is, the position of the measurement interval is set at an arbitrary position in the optical fiber by controlling the modulation frequency of the pump light and the reference light.

[0028] The peaks appearing in the interference light are periodically located in the length direction of the optical fiber. Therefore, the measurement intervals are periodically located in the length direction of the optical fiber. That is, a plurality of measurement intervals are located in the length direction of the optical fiber. The Brillouin scattered light generated in each measurement interval returns to the end with a time difference corresponding to the distance difference. Therefore, the BGS of each measurement interval is distinguished based on the time difference of the Brillouin scattered light returning from each measurement interval.

[0029] In the BOCDR method, the measurement interval is moved and the BFS is calculated from the BGS of each measurement interval, thereby detecting changes in characteristics such as temperature or strain at each position in the longitudinal direction of the optical fiber. As a result, characteristic distributions such as temperature distribution or strain distribution in the longitudinal direction of the optical fiber are measured.

[0030] The length of the measurement interval is determined by the amplitude of the pump light. Specifically, the smaller the amplitude of the pump light, the shorter the measurement interval. The shorter the measurement interval, the higher the resolution of the fiber characteristics in the length direction. On the other hand, in order to measure without omission in the length direction of the fiber, the shorter the measurement interval, the shorter the interval of the scanning modulation frequency needs to be set. The shorter the interval of the scanning modulation frequency, the more the number of changes in the modulation frequency required to set the entire length direction of the fiber as the measurement interval increases. As a result, the time required for measuring in the entire length direction of the fiber increases. That is, a dilemma arises between the resolution of the fiber characteristics in the length direction and the time required for measuring in the entire length direction of the fiber. In other words, the smaller the spatial resolution of measuring BGS, the more the number of target intervals for detecting BGS in order to measure without omission in the entire length direction of the fiber increases. The more the number of target intervals for detecting BGS increases, the longer it takes to detect BGS for all measurement objects with respect to the fiber characteristics.

[0031] (Comparative Example)

[0032] like Figure 1 As shown, the optical fiber characteristic measuring device 90 according to the comparative example allows pump light to be injected into the measured optical fiber 980 to measure the characteristics of the measured optical fiber 980. The optical fiber characteristic measuring device 90 controls the modulation frequency and amplitude of the pump light so that the BGS of each of the first measurement interval indicated by MS91 and the second measurement interval indicated by MS92 can be measured. The measured optical fiber 980 has an abnormal portion 982 in which the characteristics such as temperature or strain become abnormal. The abnormal portion 982 is located in the second measurement interval.

[0033] exist Figure 2A The BGS measurement results of the first measurement interval are shown in FIG. Figure 2B The BGS measurement results of the second measurement interval are shown in FIG. Figure 2A and Figure 2B In the graph, the horizontal axis represents frequency and the vertical axis represents the power of each frequency component. Figure 2A The BGS in the first measurement interval shown in the graph of has one peak. The frequency of this peak is BFS1. Figure 2B The BGS of the second measurement interval shown in the graph of has two peaks. The frequencies of the respective peaks are BFS1 and BFS2. BFS1 is the frequency of the peak that appears when there is no abnormality in the characteristics of the measured optical fiber 980. On the other hand, BFS2 is the frequency of the peak that appears when there is an abnormality in the characteristics of the measured optical fiber 980.

[0034] In other words, if Figure 2A As shown in FIG. 1 , when BGS includes BFS1 but does not include BFS2, the section where BGS is measured does not include the abnormal portion 982 of the measured optical fiber 980. Figure 2BAs shown, when the BGS includes both the BFS1 and the BFS2 , the section where the BGS is measured includes the abnormal portion 982 of the measured optical fiber 980 .

[0035] Here, the optical fiber characteristic measuring device 90 according to the comparative example detects only one peak from BGS and calculates only one BFS. Figure 2A The BGS shown in FIG. 1 detects BFS1, thereby recognizing that the first measurement interval does not include the abnormal portion 982 and determining the first measurement interval to be normal. Figure 2B The BGS shown detects only BFS1, and thus cannot recognize that the second measurement section includes the abnormal portion 982, and cannot determine that the second measurement section is abnormal.

[0036] Therefore, in the optical fiber characteristic measurement device 90 according to the comparative example, when only one peak is detected from the BGS and the abnormal portion 982 is included in only a part of the measurement section, the abnormality in the measurement section may be missed.

[0037] In order not to miss the abnormal portion 982, the optical fiber characteristic measuring device 90 of the comparative example sometimes shortens the measuring interval to improve the resolution of the optical fiber characteristic in the longitudinal direction. Figure 3 As shown, the optical fiber characteristic measuring device 90 controls the modulation frequency and amplitude of the pump light in such a manner that the BGS of each of the first measuring interval represented by MS81 or the nth measuring interval represented by MS8n can be measured. Here, the optical fiber characteristic measuring device 90 sets the measuring interval in such a manner that the entirety of at least one measuring interval is included in the abnormal portion 982. Figure 3 , the entire nth measurement interval is included in the abnormal portion 982 .

[0038] exist Figure 4 The measurement results of BGS in the nth measurement interval are shown in FIG. Figure 4 In FIG. 1 , the horizontal axis represents frequency. The vertical axis represents the power of each frequency component. The BGS of the nth measurement interval has one peak. The frequency of the peak is BFS2. The optical fiber characteristic measurement device 90 involved in the comparative example can determine the nth measurement interval as abnormal.

[0039] However, as described above, the time required for measurement is extended by increasing the resolution of the length direction of the optical fiber characteristics. In addition, when the length of the abnormal portion 982 included in the measured optical fiber 980 is unknown, it is unknown to what extent the resolution can be increased. Therefore, the optical fiber characteristics measurement device 90 involved in the comparative example sometimes increases the resolution excessively.

[0040] Therefore, the present invention provides an optical fiber characteristic measuring device 10 (see FIG. 1 ) which is not likely to miss an abnormality of an optical fiber even at a relatively low resolution. Figure 5 ) for explanation.

[0041] (Configuration Example of Optical Fiber Characteristics Measurement Device 10 According to the Present Invention)

[0042] Below, refer to Figure 5 An embodiment of an optical fiber characteristic measuring device 10 for measuring the characteristics of an optical fiber is described. An optical fiber characteristic measuring device 10 according to one embodiment of the present invention measures the characteristics of an optical fiber under test (FUT: Fiber Under Test) 80 using the BOCDR method. The characteristics of the optical fiber under test 80 include, for example, the temperature distribution or strain distribution in the longitudinal direction of the optical fiber under test 80, the vibration of the optical fiber under test 80, or other characteristics of the optical fiber under test 80. The characteristics such as the frequency, amplitude or spectrum of the scattered light or reflected light generated in the optical fiber under test 80 change according to the physical quantities such as the temperature or strain that affect the optical fiber under test 80. Therefore, in the optical fiber characteristic measuring device 10, the optical fiber under test 80 itself is used as a sensor.

[0043] like Figure 5 As shown, an optical fiber characteristic measuring device 10 according to an embodiment of the present invention includes a light source 11 , an optical branching unit 20 , a combining unit 40 , a photodetector 41 , an amplifier 42 , an ESA (Electric Spectrum Analyzer) 43 , and a computing device 50 .

[0044] The light source 11 emits frequency modulated light. The light source 11 may be configured to include a semiconductor laser element such as a distributed feedback laser diode (DFB-LD). The optical fiber characteristic measuring device 10 further includes a driving power source 12. The driving power source 12 is based on a modulation frequency (f m ) is used to drive the light source 11. The light source 11 is driven based on the modulation frequency (f m ) and emits the frequency modulated light.

[0045] The light branching unit 20 branches the input light in two or more directions. In the present embodiment, the light branching unit 20 branches the light input from the light source 11 into the pump light LP and the reference light LR. The light branching unit 20 may be configured to include an optical coupler, for example.

[0046] The optical fiber characteristics measurement device 10 further includes a switch 21 , a delay fiber 22 , a polarization scrambler (PS) 23 , and a circulator 24 between the optical branching unit 20 and the optical fiber to be measured 80 .

[0047] The switch 21 converts the pump light LP into a pulse light P by chopping it. The pulse light P travels toward the measured optical fiber 80 through the delay optical fiber 22, the polarization scrambler 23, and the circulator 24. The delay optical fiber 22 delays the travel of the pulse light P by a predetermined time. The delay optical fiber 22 may include, for example, an optical fiber of a predetermined length. The polarization scrambler 23 controls the state of the polarization wave so that the components of the polarization wave included in the pulse light P are uniformly close in each direction of the polarization wave.

[0048] The circulator 24 allows the pulse light P traveling from the optical branching section 20 to travel toward the optical fiber 80 to be measured. In addition, the circulator 24 allows the Brillouin scattered light LS returning from the optical fiber 80 to be measured to travel toward the combining section 40, not toward the optical branching section 20. The Brillouin scattered light LS is light generated by Brillouin scattering in the optical fiber 80 to be measured. Brillouin scattering is a phenomenon that occurs in the optical fiber 80 to be measured when the pulse light P is incident on the optical fiber 80 to be measured.

[0049] The circulator 24 may be replaced by an optical coupler. The optical branching unit 20 is also referred to as a first optical branching unit. The circulator 24 is also referred to as a second optical branching unit.

[0050] The combiner 40 combines two or more input lights into one light beam and outputs it. In this embodiment, the combiner 40 combines the reference light LR and the Brillouin scattered light LS into one light beam and outputs it to the photodetector 41. The combiner 40 may include an optical coupler, for example.

[0051] The photodetector 41 detects the intensity of input light and outputs an electrical signal corresponding to the intensity of the detected light. The photodetector 41 may be configured to include, for example, a photodiode (PD) or a phototransistor.

[0052] The amplifier 42 amplifies the electric signal. The amplifier 42 may be configured to include an amplifier, for example. In the present embodiment, the amplifier 42 is configured to amplify the signal in an RF (Radio Frequency) band including a peak frequency of BGS, which is a spectrum of the Brillouin scattered light LS.

[0053] The ESA 43 performs spectrum analysis on the signal amplified by the amplifier 42. In the present embodiment, the ESA 43 performs spectrum analysis in the RF band.

[0054] The computing device 50 includes an acquisition unit 52 , a computing unit 54 , and a storage unit 56 .

[0055] The acquisition unit 52 may include a communication interface for communicating with the ESA 43 or the driving power source 12 by wire or wirelessly. The communication interface may be configured to communicate based on a communication standard such as a LAN (Local Area Network). The communication standard is not limited to a LAN, and may be other various standards.

[0056] The calculation unit 54 may be configured to include, for example, a processor such as a CPU (Central Processing Unit) or a dedicated circuit such as an FPGA (Field Programmable Gate Array). The calculation unit 54 may be configured to execute a program that realizes the functions of the calculation device 50 .

[0057] The storage unit 56 can store various information used for the operation of the computing device 50 or programs for realizing the functions of the computing device 50. The storage unit 56 can function as a working memory of the computing unit 54. The storage unit 56 can be composed of, for example, a semiconductor memory. The storage unit 56 can be integrally formed with the computing unit 54 or separately formed.

[0058] The computing device 50 or the optical fiber characteristic measuring device 10 may include an input device for receiving input from a user. The input device may include, for example, a keyboard or physical keys, or may include a touch panel or touch sensor or a pointing device such as a mouse.

[0059] The computing device 50 or the optical fiber characteristic measuring device 10 may have a display device. The display device may include various displays such as a liquid crystal display. The computing device 50 or the optical fiber characteristic measuring device 10 may have an interface for outputting displayed information to an external display device. The computing device 50 or the optical fiber characteristic measuring device 10 may have a voice output device such as a speaker. The computing device 50 or the optical fiber characteristic measuring device 10 may have an interface for outputting voice information to an external speaker.

[0060] (Operation Example of Optical Fiber Characteristics Measurement Device 10 According to the Present Invention)

[0061] In the optical fiber characteristic measuring device 10, the light source 11 controls the driving power source 12 to generate a signal based on the modulation frequency (f m ) is frequency modulated (FM) light emission.

[0062] The light emitted from the light source 11 is branched into the pump light LP and the reference light LR by the light branching unit 20 . The reference light LR travels toward the multiplexing unit 40 .

[0063] After the pump light LP is branched at the optical branching unit 20, it passes through the switch 21, the delay fiber 22, and the polarization scrambler 23 and travels toward the circulator 24. The delay fiber 22 can adjust the delay time of the pulse light P by changing the length of the fiber. The delay fiber 22 is used to adjust the delay time of the pulse light P even when the modulation frequency (f m ) is also used in the case where the 0th-order correlation peak that has not moved is arranged outside the measured optical fiber 80.

[0064] The circulator 24 allows the pulse light P that has traveled from the optical branching section 20 to travel toward the optical fiber 80 to be measured. In addition, the circulator 24 allows the Brillouin scattered light LS that has returned from the measuring optical fiber 80 to travel toward the combining section 40, not toward the optical branching section 20. The Brillouin scattered light LS is light generated by Brillouin scattering in the optical fiber 80 to be measured. Brillouin scattering is a phenomenon that occurs in the optical fiber 80 to be measured when the pulse light P is incident on the optical fiber 80 to be measured.

[0065] The operation of the optical branching section 20, also referred to as the first optical branching section, and the circulator 24, also referred to as the second optical branching section, can be expressed in the following manner. The first optical branching section branches the modulated light after frequency modulation into the pump light LP and the reference light LR, and causes the pump light LP to travel toward the second optical branching section, and causes the reference light LR to travel toward the combiner 40. The second optical branching section causes the pump light LP to travel toward the optical fiber 80 to be measured in a manner of being injected from one end of the optical fiber 80 to be measured. In addition, the second optical branching section causes the Brillouin scattered light LS generated in the optical fiber 80 to be measured and returned to travel toward the combiner 40. That is, the second optical branching section causes the pump light to be injected from one end of the optical fiber 80 to be measured, and extracts the Brillouin scattered light LS generated in the optical fiber 80 to be measured.

[0066] The optical fiber characteristic measuring device 10 generates interference light in which the reference light LR and the Brillouin scattered light LS after the frequency shift interfere with each other at the combining unit 40, detects the interference light by the photodetector 41, amplifies the detection signal by the amplifier 42, and performs spectrum analysis of the amplified signal by the ESA 43. The ESA 43 outputs the spectrum analysis result of the signal in which the interference light is detected to the computing device 50.

[0067] like Figure 6 As shown, the optical fiber characteristic measuring device 10 according to the present invention allows pump light LP to be injected into the optical fiber 80 to be measured and measures the Brillouin gain spectrum. The optical fiber characteristic measuring device 10 determines the characteristics of the optical fiber 80 to be measured based on the measurement result of the Brillouin gain spectrum, thereby measuring the characteristics of the optical fiber 80 to be measured.

[0068] In the optical fiber characteristic measuring device 10, the operation device 50 sets at least one measurement interval for the measured optical fiber 80, and determines whether the characteristics of each measurement interval are abnormal. For example, the operation device 50 can set a first measurement interval represented by MS1 and a second measurement interval represented by MS2 in the measured optical fiber 80. The first measurement interval and the second measurement interval can be set so that the length of the first measurement interval is the same as the length of the second measurement interval, or can be set so that the length of the first measurement interval is different from the length of the second measurement interval. In the present embodiment, the first measurement interval and the second measurement interval are set so that the length of the first measurement interval is the same as the length of the second measurement interval.

[0069] The operation device 50 controls the modulation frequency and amplitude of the modulated light branched into the pump light LP so that the BGS of each of the first measurement interval and the second measurement interval can be measured. In other words, the light source 11 is configured so that the operation unit 54 can control the amplitude of the modulated light that determines the length of the measurement interval and the modulation frequency of the modulated light that determines the position of the measurement interval. The operation device 50 can obtain the BGS of each measurement interval by controlling the modulation frequency and amplitude of the modulated light. In other words, the operation device 50 can move the measurement interval to each position or change the length of the measurement interval by controlling the modulation frequency and amplitude of the modulated light.

[0070] In the optical fiber characteristic measurement device 10 according to the present embodiment, the modulation frequency and amplitude of the modulated light can be controlled to determine the position and length of the measurement interval, thereby instantaneously switching the measurement position and spatial resolution. That is, random access can be achieved.

[0071] The computing unit 54 of the computing device 50 may associate the BGS obtained from the ESA 43 with the information that specifies the measurement interval in which the BGS is measured and store them in the storage unit 56. The information that specifies the measurement interval may include the distance from the end of the measured optical fiber 80 to the measurement interval. That is, the information that specifies the measurement interval may include the position where the correlation peak appears in the measured optical fiber 80. The information that specifies the measurement interval may include the length of the measurement interval. The information that specifies the measurement interval may include the modulation frequency and amplitude of the pump light LP. The information that specifies the measurement interval may include the time from when the pump light LP is injected into the measured optical fiber 80 until the Brillouin scattered light LS returns.

[0072] The calculation unit 54 can control the amplitude and modulation frequency of the modulated light based on the information stored in the storage unit 56 .

[0073] Here, the optical fiber 80 to be measured has an abnormal portion 82 in which the characteristics such as temperature and strain are abnormal. The abnormal portion 82 is located in the second measurement section.

[0074] The BGS of the first measurement interval not including the abnormal portion 82 is different from the above Figure 2A The result shown in FIG. 1 also has one peak. The frequency of this peak is BFS1. The BGS of the second measurement interval including the abnormal portion 82 is the same as the above-mentioned Figure 2B The result shown also has two peaks. The frequencies of the respective peaks are BFS1 and BFS2. BFS1 is the frequency of the peak that appears when there is no abnormality in the characteristics of the measured optical fiber 80. The peak that appears when there is no abnormality in the characteristics of the measured optical fiber 80 is also referred to as a normal peak. On the other hand, BFS2 is the frequency of the peak that appears when there is an abnormality in the characteristics of the measured optical fiber 80. The peak that appears when there is an abnormality in the characteristics of the measured optical fiber 80 is also referred to as an abnormal peak.

[0075] The computing unit 54 of the computing device 50 according to the present invention detects each peak value and calculates multiple BFS when the BGS includes multiple peak values. The computing unit 54 can detect multiple peak values ​​by performing a peak search on the BGS, for example. The computing unit 54 can detect a peak value having a power greater than or equal to twice the power of noise in the BGS. This makes it less likely that noise will be mistakenly detected as a peak value.

[0076] exist Figure 6 In the measurement example of the optical fiber 80 to be measured shown in FIG. Figure 2B The BGS of the second measurement interval shown in FIG. 1 detects two peaks and calculates BFS1 and BFS2. That is, the calculation unit 54 detects a normal peak and an abnormal peak from the BGS of the second measurement interval. In this case, the calculation unit 54 determines that a part of the second measurement interval includes the abnormal portion 82.

[0077] When it is determined that part of the measurement interval includes the abnormal portion 82, the calculation unit 54 divides the measurement interval into subdivided areas, and performs BGS measurement and peak detection for each of the subdivided areas. When it is determined that part of the second measurement interval includes the abnormal portion 82, the calculation unit 54 performs, for example, Figure 7 The second measurement interval is subdivided as shown. Figure 7 In the example of , the abnormal portion 82 includes the entire interval represented by MS2n.

[0078] When an abnormal peak can be detected from the BGS of at least one of the segmented segments but a normal peak cannot be detected, the calculation unit 54 can determine that the entire segment is included in the abnormal portion 82. When the entire segment is included in the abnormal portion 82, the position of the abnormal portion 82 is measured as the position of the segment.

[0079] If the segmented interval in which an abnormal peak is detected from BGS but a normal peak is not detected cannot be found, the calculation unit 54 may further repeatedly perform segmentation. The calculation unit 54 may repeatedly perform segmentation until a segment in which an abnormal peak is detected from BGS but a normal peak is not detected is found. The calculation unit 54 may further segment the segmented interval, or may shorten the length of the segmented measurement interval and perform segmentation again.

[0080] The optical fiber characteristic measurement device 10 according to the present embodiment can control the modulation frequency and amplitude of the modulated light to determine the length of the measurement interval, thereby instantaneously switching the spatial resolution of the measurement. As a result, it is easy to subdivide the measurement interval.

[0081] <Example of a flowchart of the optical fiber characteristics measurement method>

[0082] The computing device 50 of the optical fiber characteristic measuring device 10 according to the present invention can execute the Figure 8 The optical fiber characteristic measuring method including the flow chart shown in the figure measures the characteristics of the measured optical fiber 80. At least a part of the optical fiber characteristic measuring method can be implemented as an optical fiber characteristic measuring program executed by the computing unit 54 of the computing device 50. The optical fiber characteristic measuring program can be stored in a non-transitory computer-readable medium.

[0083] The computing device 50 sets a measurement interval of the measured optical fiber 80 (step S1). The computing device 50 causes the light source 11 to emit modulated light having a modulation frequency and amplitude corresponding to the set measurement interval and causes pump light LP to be injected into the measured optical fiber 80, thereby acquiring BGS of each measurement interval (step S2).

[0084] The computing device 50 performs a peak search of the BGS in each measurement interval (step S3). The computing device 50 determines whether the BGS contains an abnormal peak for each measurement interval (step S4). If the BGS does not contain an abnormal peak (step S4: NO), the computing device 50 proceeds to the flow of step S7.

[0085] When the BGS includes an abnormal peak (step S4: YES), the computing device 50 determines whether the BGS includes a normal peak (step S5). When the BGS does not include a normal peak (step S5: NO), the computing device 50 determines that the measurement section of the BGS including only the abnormal peak is abnormal (step S6).

[0086] After determining that the BGS does not include an abnormal peak in the process of step S4, or after determining that the measurement interval is abnormal in the process of step S6, the computing device 50 determines whether the peak search of the BGS of all measurement intervals is completed (step S7). If the peak search of the BGS of all measurement intervals is not completed (step S7: NO), the computing device 50 returns to the process of step S3 and performs the peak search of the BGS of the measurement intervals in which the peak search is not completed. If the peak search of the BGS of all measurement intervals is completed (step S7: YES), the computing device 50 ends. Figure 8 Execution of the process of the flowchart.

[0087] When it is determined in the process of step S5 that the BGS includes a normal peak (step S5: YES), the computing device 50 subdivides the measurement interval in which the BGS including both the normal peak and the abnormal peak is measured (step S8). After executing the process of step S8, the computing device 50 returns to the process of step S2 and performs BGS acquisition and peak search for the subdivided interval. As described above, the computing device 50 may repeatedly perform subdivision until an interval in which an abnormal peak is detected from the BGS but a normal peak is not detected is found.

[0088] (Summarize)

[0089] As described above, the optical fiber characteristic measurement device 10 according to the present invention detects a plurality of peaks from the BGS measured in each measurement section of the measured optical fiber 80, and can detect abnormal peaks even when the abnormal portion 82 exists only in a part of the measurement section. As a result, even when the measurement section is set widely, the presence of the abnormal portion 82 included in the measured optical fiber 80 is unlikely to be missed. In addition, the measurement section can be set widely to shorten the measurement time.

[0090] Furthermore, when the abnormal portion 82 exists in a part of the measurement section, only the measurement section is divided and measured, thereby shortening the measurement time compared to the case where the entire optical fiber 80 to be measured is measured in a small measurement section.

[0091] Although the embodiment of the present invention has been described above with reference to the drawings, the specific configuration is not limited to the embodiment and various modifications are included within the scope not departing from the gist of the present invention.

[0092] The optical fiber characteristic measurement apparatus 10 according to the above embodiment has been described as measuring BGS by the BOCDR method. The optical fiber characteristic measurement apparatus 10 may be configured to measure BGS by the BOCDA (Brillouin Optical Correlation Domain Analysis) method.

[0093] Description of the label

[0094] 10 ... optical fiber characteristic measuring device (11: light source, 12: driving power supply, 20: optical branching unit, 21: switch, 22: delay fiber, 23: polarization scrambler, 24: circulator, 40: combining unit, 41: photodetector, 42: amplifier, 43: ESA, 50: computing device, 52: acquisition unit, 54: computing unit, 56: storage unit)

[0095] 80 ... optical fiber to be measured (82: abnormal part)

[0096] LP…Pump Light

[0097] LR…reference light

[0098] LS…Brillouin scattered light

[0099] P...Pulse Light

Claims

1. An optical fiber characteristic measuring device (10), wherein: The optical fiber characteristic measuring device (10) comprises a calculation unit (54) for extracting a plurality of peaks included in a Brillouin gain spectrum of Brillouin scattered light (LS) generated in a measured optical fiber (80) to measure the characteristics of the measured optical fiber (80).

2. The optical fiber characteristic measuring device (10) according to claim 1, wherein: The calculation unit (54) sets a measurement interval for measuring the characteristics of the measured optical fiber (80) at at least one position in the measured optical fiber (80). The Brillouin gain spectrum of the measurement interval set at each position is measured, The characteristic of the section in which the Brillouin gain spectrum including the abnormal peak but not the normal peak is measured is determined to be abnormal. The interval in which the Brillouin gain spectrum including both the normal peak and the abnormal peak is measured is subdivided. The Brillouin gain spectrum is measured in each subdivided interval. Determine whether each segmented interval is abnormal.

3. The optical fiber characteristic measuring device (10) according to claim 2, wherein: The optical fiber characteristic measuring device (10) further comprises a light source (11) for emitting modulated light incident on the optical fiber (80) to be measured. The light source (11) is configured so that the calculation unit (54) can control the amplitude of the modulated light that determines the length of the measurement interval and the modulation frequency of the modulated light that determines the position of the measurement interval.

4. The optical fiber characteristic measuring device (10) according to claim 3, wherein: The optical fiber characteristic measuring device (10) further comprises a storage unit (56) which stores the measured Brillouin gain spectrum and information identifying a section in which the Brillouin gain spectrum is measured in association with each other. The calculation unit (54) controls the amplitude and modulation frequency of the modulated light based on the information stored in the storage unit (56).

5. A method for measuring optical fiber characteristics, wherein: The optical fiber characteristic measurement method comprises the steps of extracting a plurality of peaks included in a Brillouin gain spectrum of Brillouin scattered light (LS) generated in a measured optical fiber (80) to measure the characteristics of the measured optical fiber (80).

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