Optical fiber characteristic measuring device and optical fiber characteristic measuring method

Abstract

To provide an optical fiber characteristic measuring device and an optical fiber characteristic measuring method that can reduce the time for measuring optical fiber characteristics.SOLUTION: An optical fiber characteristic measuring device 10 comprises an operation unit 54 that extracts a plurality of peaks included in the Brillouin gain spectrum of Brillouin scattered light LS generated inside an optical fiber 80 to be measured to measure the characteristics of the optical fiber 80 to be measured.SELECTED DRAWING: Figure 2B

Description

[Technical field]

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

[0002] 2. Description of the Related Art Conventionally, there has been known a method for measuring the characteristics of an optical fiber by determining the Brillouin frequency shift (BFS) of Brillouin scattering occurring within the optical fiber (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-41843 A Summary of the Invention [Problem to be solved by the invention]

[0004] When the BFS is calculated as the frequency of one peak detected in the Brillouin gain spectrum (BGS), the spatial resolution for measuring the BGS must be set shorter than the abnormal part of the optical fiber. Here, the shorter the spatial resolution, the greater the number of sections for which the BGS is detected so that the entire length of the optical fiber can be measured without missing anything. The greater the number of sections for which the BGS is detected, the longer it takes to detect the BGS over the entire area of ​​the optical fiber characteristics being measured. As a result, the measurement time for the optical fiber characteristics becomes longer.

[0005] The present disclosure has been made in consideration of the above-mentioned points, and has an object to provide an optical fiber characteristic measuring device and an optical fiber characteristic measuring method that can shorten the measurement time of optical fiber characteristics. [Means for solving the problem]

[0006] (1) An optical fiber characteristic measuring device according to some embodiments includes a calculation unit that extracts multiple peaks contained in the Brillouin gain spectrum of Brillouin scattered light generated in an optical fiber under test and measures the characteristics of the optical fiber under test. By extracting each of the multiple peaks contained in the Brillouin gain spectrum, the optical fiber characteristic measuring device is less likely to overlook an abnormality contained in a part of the measurement section even if the measurement section is set long. As a result of being able to set a long measurement time, the measurement time for the optical fiber characteristics is shortened.

[0007] (2) In the optical fiber characteristic measuring device described in (1) above, the calculation unit may set a measurement section in which the characteristics of the measured optical fiber are measured at at least one position in the measured optical fiber, measure the Brillouin gain spectrum in the measurement section set at each position, determine that the characteristics of a section in which a Brillouin gain spectrum including an abnormal peak but not a normal peak is measured is abnormal, subdivide the section in which a Brillouin gain spectrum including both a normal peak and an abnormal peak is measured, measure the Brillouin gain spectrum in each subdivided section, and determine whether each subdivided section is abnormal. By subdividing the measurement section including an abnormality and repeating the measurement, the range in which the measurement section is set short is limited. By setting the measurement section short only in a part of the measured optical fiber, the measurement time for the optical fiber characteristics is reduced.

[0008] (3) The optical fiber characteristic measuring device described in (2) above may further include a light source that emits modulated light to be incident on the measured optical fiber. The light source may be configured so that the calculation unit can control the amplitude of the modulated light that determines the length of the measurement section and the modulation frequency of the modulated light that determines the position of the measurement section. By being able to determine the position and length of the measurement section by controlling the modulation frequency and amplitude of the modulated light, the measurement position and the spatial resolution of the measurement can be instantly switched. In other words, random accessibility is realized. In addition, by being able to determine the length of the measurement section by controlling the modulation frequency and amplitude of the modulated light, the spatial resolution of the measurement can be instantly switched. As a result, subdivision of the measurement section can be easily realized.

[0009] (4) The optical fiber characteristic measuring device described in (3) above may further include a memory unit that stores the measured Brillouin gain spectrum and information specifying the section in which the Brillouin gain spectrum was 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 memory unit.

[0010] (5) An optical fiber characteristic measuring method according to some embodiments includes a step of measuring the characteristics of an optical fiber under test by extracting a plurality of peaks contained in a Brillouin gain spectrum of Brillouin scattered light generated in the optical fiber under test. Effect of the Invention

[0011] According to the optical fiber characteristic measuring device and the optical fiber characteristic measuring method of the present disclosure, the measurement time of the optical fiber characteristics is shortened. [Brief description of the drawings]

[0012] [Figure 1] FIG. 13 is a diagram showing a measurement section that is set wide in an apparatus according to a comparative example. [Figure 2A] 1 is a graph of the Brillouin gain spectrum in a measurement section that does not include an abnormal portion. [Figure 2B] 1 is a graph of the Brillouin gain spectrum of a measurement section including an abnormal portion. [Diagram 3] FIG. 13 is a diagram showing a measurement section that is set narrower in an apparatus according to a comparative example. [Figure 4] 1 is a graph of the Brillouin gain spectrum of a measurement section that entirely includes an abnormal portion. [Diagram 5] 1 is a block diagram showing an example of the configuration of an optical fiber characteristic measuring device according to the present disclosure. [Figure 6] FIG. 13 is a diagram showing an example of a measurement section set by the device according to the present disclosure. [Figure 7] FIG. 7 is a diagram showing an example of subdivision of the measurement section of FIG. 6. [Figure 8]4 is a flowchart illustrating an example of a procedure for an optical fiber characteristic measuring method according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In order to measure characteristics such as temperature or strain at each position along the length of an optical fiber, a method of detecting scattered or reflected light generated inside the optical fiber in response to light incident on the optical fiber can be considered. One method of measuring the characteristics of an optical fiber is Brillouin Optical Correlation Domain Reflectometry (BOCDR). The BOCDR method includes injecting pump light branched from frequency-modulated light into an optical fiber, and detecting interference light between a reference light branched from the modulated light and Brillouin scattered light generated inside the optical fiber. Brillouin scattered light is backscattered light generated by Brillouin scattering due to pump light incident on the optical fiber, and returns to the end where the pump light was incident.

[0014] The BOCDR method further includes obtaining a spectrum of the Brillouin scattered light from the signal obtained by detecting the interference light. The spectrum of the Brillouin scattered light is also called the Brillouin gain spectrum (BGS). In the BOCDR method according to the present disclosure, the BGS is detected by performing a spectrum analysis of the interference light obtained by offsetting the frequency of the reference light and causing it to interfere with the Brillouin scattered light.

[0015] The BGS peak frequency is determined according to 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 BGS peak frequency. The BGS peak frequency is also called the Brillouin frequency shift (BFS).

[0016] In the BOCDR method, the Brillouin scattered light is selectively extracted from a specific section in which a correlation peak appears in the optical fiber by interfering with the Brillouin scattered light and the reference light. The correlation peak is a peak that appears in the interference light due to the constructive interaction between the Brillouin scattered light and the reference light. The specific section in which the correlation peak appears is a section in the optical fiber in which the Brillouin scattered light that constructively interacts with the reference light to cause the correlation peak of the interference light to appear. In the BOCDR method, the BFS at the position where the correlation peak appears is obtained to measure the characteristics of the optical fiber, such as the temperature or strain at that position. The specific section in which the correlation peak appears is also called a measurement section in which the characteristics of the optical fiber are measured.

[0017] The measurement section is set at at least one position in the optical fiber. The position of the measurement section is determined according to the modulation frequencies of the pump light and the reference light. That is, the position of the measurement section can be set at any position in the optical fiber by controlling the modulation frequencies of the pump light and the reference light.

[0018] The peaks that appear in the interference light are periodically positioned along the length of the optical fiber. Therefore, the measurement sections are periodically positioned along the length of the optical fiber. In other words, multiple measurement sections are positioned along the length of the optical fiber. The Brillouin scattered light generated in each measurement section returns to the end with a time difference that depends on the difference in distance. Therefore, the BGS of each measurement section is distinguished by the difference in the time it takes for the Brillouin scattered light to return from each measurement section.

[0019] In the BOCDR method, the change in characteristics such as temperature or strain at each position in the length direction of the optical fiber is detected by moving the measurement section and calculating the BFS from the BGS of each measurement section, and as a result, the characteristic distribution such as temperature distribution or strain distribution in the length direction of the optical fiber is measured.

[0020] The length of the measurement section is determined according to the amplitude of the pump light. Specifically, the smaller the amplitude of the pump light, the shorter the measurement section. The shorter the measurement section, the higher the resolution in the length direction of the optical fiber characteristics. On the other hand, in order to measure the length direction of the optical fiber without leaking anything, the shorter the measurement section, the shorter the interval for sweeping the modulation frequency must be. The shorter the interval for sweeping the modulation frequency, the more times the modulation frequency needs to be changed in order to make the entire length direction of the optical fiber the measurement section. As a result, the time required to measure the entire length direction of the optical fiber increases. In other words, there is a trade-off between the resolution in the length direction of the optical fiber characteristics and the time required to measure the entire length direction of the optical fiber. In other words, the shorter the spatial resolution for measuring the BGS, the more the number of sections for which the BGS is detected so that the entire length direction of the optical fiber can be measured without leaking anything. The more the number of sections for which the BGS is detected, the longer it takes to detect the BGS in the entire measurement target of the optical fiber characteristics.

[0021] (Comparative Example) As shown in Fig. 1, an optical fiber characteristic measuring device 90 according to the comparative example measures the characteristics of a measured optical fiber 980 by injecting pump light into the measured optical fiber 980. The optical fiber characteristic measuring device 90 controls the modulation frequency and amplitude of the pump light so as to measure the BGS of each of a first measurement section represented by MS91 and a second measurement section represented by MS92. The measured optical fiber 980 has an abnormal portion 982 in which a characteristic such as temperature or strain is abnormal. The abnormal portion 982 is located within the second measurement section.

[0022] FIG. 2A shows the BGS measurement results for the first measurement section. FIG. 2B shows the BGS measurement results for the second measurement section. In FIGS. 2A and 2B, the horizontal axis represents frequency. The vertical axis represents the power of each frequency component. The BGS for the first measurement section shown in the graph of FIG. 2A has one peak. The frequency of that peak is BFS1. The BGS for the second measurement section shown in the graph of FIG. 2B has two peaks. The frequencies of each peak 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.

[0023] 2A, when the BGS includes BFS1 but not BFS2, the section where the BGS is measured does not include the abnormal portion 982 of the measured optical fiber 980. When the BGS includes both BFS1 and BFS2 as shown in FIG. 2B, the section where the BGS is measured includes the abnormal portion 982 of the measured optical fiber 980.

[0024] Here, the optical fiber characteristic measuring device 90 according to the comparative example detects only one peak from the BGS and calculates only one BFS. Then, by detecting BFS1 from the BGS shown in Fig. 2A, the optical fiber characteristic measuring device 90 recognizes that the first measurement section does not include an abnormal portion 982 and determines that the first measurement section is normal. On the other hand, by detecting only BFS1 from the BGS shown in Fig. 2B, the optical fiber characteristic measuring device 90 cannot recognize that the second measurement section includes an abnormal portion 982 and cannot determine that the second measurement section is abnormal.

[0025] Therefore, the optical fiber characteristic measuring device 90 of the comparative example detects only one peak from the BGS, and therefore may overlook the fact that the measurement section is abnormal if the abnormal portion 982 is only included in a portion of the measurement section.

[0026] The optical fiber characteristic measuring device 90 according to the comparative example may shorten the measurement section to increase the resolution of the optical fiber characteristics in the longitudinal direction so as not to miss the abnormal portion 982. As shown in Fig. 3, the optical fiber characteristic measuring device 90 controls the modulation frequency and amplitude of the pump light so as to measure the BGS of each of the first measurement section represented by MS81 or the nth measurement section represented by MS8n. Here, the optical fiber characteristic measuring device 90 sets the measurement sections so that at least one measurement section is entirely included in the abnormal portion 982. In Fig. 3, the nth measurement section is entirely included in the abnormal portion 982.

[0027] FIG 4 shows the measurement results of the BGS in the nth measurement section. In FIG 4, the horizontal axis represents frequency, and the vertical axis represents the power of each frequency component. The BGS in the nth measurement section has one peak. The frequency of that peak is BFS2. The optical fiber characteristic measuring apparatus 90 according to the comparative example can determine that the nth measurement section is abnormal.

[0028] However, as described above, increasing the resolution in the length direction of the optical fiber characteristic increases the time required for measurement. In addition, if the length of the abnormal part 982 included in the measured optical fiber 980 is unknown, it is not clear how much the resolution should be increased. Therefore, the optical fiber characteristic measuring device 90 according to the comparative example may increase the resolution more than necessary.

[0029] Therefore, the present disclosure describes an optical fiber characteristic measuring device 10 (see FIG. 5) that is unlikely to overlook an abnormality in an optical fiber even with low resolution.

[0030] (Example of configuration of optical fiber characteristic measuring device 10 according to the present disclosure) Hereinafter, an embodiment of an optical fiber characteristic measuring device 10 for measuring characteristics of an optical fiber will be described with reference to Fig. 5. The optical fiber characteristic measuring device 10 according to an embodiment of the present disclosure measures characteristics of a test optical fiber (FUT: Fiber Under Test) 80 by using the BOCDR method. The characteristics of the test optical fiber 80 include, for example, temperature distribution or strain distribution in the length direction of the test optical fiber 80, vibration of the test optical fiber 80, or other characteristics of the test optical fiber 80. Characteristics such as frequency, amplitude, or spectrum of scattered light or reflected light generated in the test optical fiber 80 change depending on physical quantities such as temperature or strain that affect the test optical fiber 80. Therefore, in the optical fiber characteristic measuring device 10, the test optical fiber 80 itself is used as a sensor.

[0031] As shown in FIG. 5, an optical fiber characteristic measuring device 10 according to one embodiment of the present disclosure includes a light source 11, an optical branching section 20, a multiplexing section 40, a photodetector 41, an amplifier 42, an ESA (Electric Spectrum Analyzer) 43, and a calculation device 50.

[0032] 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 supply 12. The driving power supply 12 is configured to supply a modulation frequency (f m The light source 11 is driven based on a modulation signal having a modulation frequency (f m ) and emits frequency-modulated light based on the

[0033] The optical branching unit 20 branches the input light into two or more directions. In this embodiment, the optical branching unit 20 branches the light input from the light source 11 into a pump light LP and a reference light LR. The optical branching unit 20 may be configured to include, for example, an optical coupler.

[0034] The optical fiber characteristic measuring apparatus 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 80 to be measured.

[0035] The switch 21 converts the pump light LP into pulsed light P by chopping it. The pulsed light P passes through a delay fiber 22, a polarization scrambler 23, and a circulator 24 and travels to the optical fiber 80 under test. The delay fiber 22 delays the travel of the pulsed light P by a predetermined time. The delay fiber 22 may include, for example, an optical fiber of a predetermined length. The polarization scrambler 23 controls the state of polarization so that the polarization components contained in the pulsed light P become nearly uniform in each direction of polarization.

[0036] The circulator 24 causes the pulsed light P traveling from the optical branching unit 20 to travel toward the measured optical fiber 80. The circulator 24 also causes the Brillouin scattered light LS returning from the measured optical fiber 80 to travel toward the multiplexing unit 40, rather than toward the optical branching unit 20. The Brillouin scattered light LS is light generated by Brillouin scattering in the measured optical fiber 80. Brillouin scattering is a phenomenon that occurs in the measured optical fiber 80 when the pulsed light P is incident on the measured optical fiber 80.

[0037] The circulator 24 may be replaced with an optical coupler. The optical branching unit 20 is also called a first optical branching unit. The circulator 24 is also called a second optical branching unit.

[0038] The multiplexing section 40 combines two or more input light beams into one light beam and outputs the combined light beam. In this embodiment, the multiplexing section 40 combines the reference light LR and the Brillouin scattered light LS into one light beam and outputs the combined light beam to the photodetector 41. The multiplexing section 40 may be configured to include, for example, an optical coupler.

[0039] The photodetector 41 detects the intensity of the input light and outputs an electrical signal corresponding to the intensity of the detected light. The photodetector 41 may include, for example, a photodiode (PD) or a phototransistor.

[0040] The amplifier 42 amplifies the electrical signal. The amplifier 42 may be configured to include, for example, an amplifier. In this embodiment, the amplifier 42 is configured to amplify a signal in an RF (Radio Frequency) band that includes the peak frequency of BGS, which is the spectrum of the Brillouin scattered light LS.

[0041] The ESA 43 performs a spectral analysis of the signal amplified by the amplifier 42. In this embodiment, the ESA 43 performs a spectral analysis of the RF band.

[0042] The calculation device 50 includes an acquisition unit 52, a calculation unit 54, and a storage unit 56.

[0043] The acquisition unit 52 may include a communication interface that communicates, for example, with the ESA 43 or the driving power source 12 by wire or wirelessly. The communication interface may be configured to be capable of communicating based on a communication standard such as a LAN (Local Area Network). The communication standard is not limited to the LAN and may be various other standards.

[0044] The calculation unit 54 may be configured to include 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.

[0045] The storage unit 56 may store various information used in the operation of the arithmetic unit 50, or programs and the like that realize the functions of the arithmetic unit 50. The storage unit 56 may function as a work memory for the arithmetic unit 54. The storage unit 56 may be configured as, for example, a semiconductor memory or the like. The storage unit 56 may be configured integrally with the arithmetic unit 54 or may be configured separately.

[0046] The arithmetic unit 50 or the optical fiber characteristic measuring device 10 may include an input device that accepts input from a user. The input device may include, for example, a keyboard or physical keys, or may include a touch panel or a touch sensor, or a pointing device such as a mouse.

[0047] The arithmetic unit 50 or the optical fiber characteristic measuring device 10 may be provided with a display device. The display device may include various displays such as a liquid crystal display. The arithmetic unit 50 or the optical fiber characteristic measuring device 10 may be provided with an interface that outputs the information to be displayed to an external display device. The arithmetic unit 50 or the optical fiber characteristic measuring device 10 may be provided with an audio output device such as a speaker. The arithmetic unit 50 or the optical fiber characteristic measuring device 10 may be provided with an interface that outputs audio information to an external speaker or the like.

[0048] (Example of operation of the optical fiber characteristic measuring device 10 according to the present disclosure) In the optical fiber characteristic measuring device 10, the light source 11 is controlled by the driving power supply 12 to have a modulation frequency (f m ) and emits frequency modulated (FM) light.

[0049] Light emitted from the light source 11 is split into pump light LP and reference light LR by the optical splitter 20. The reference light LR travels to the multiplexer .

[0050] The pump light LP is branched by the optical branching unit 20, and then travels through a switch 21, a delay fiber 22, and a polarization scrambler 23 toward a circulator 24. The delay fiber 22 can adjust the delay time of the pulse light P by changing the length of the optical fiber. The delay fiber 22 is a fiber that is connected to a modulation frequency (f m ) is swept, the zeroth order correlation peak is located outside the optical fiber 80 under test.

[0051] The circulator 24 causes the pulsed light P traveling from the optical branching unit 20 to travel toward the measured optical fiber 80. The circulator 24 also causes the Brillouin scattered light LS returning from the measured optical fiber 80 to travel toward the multiplexing unit 40, rather than toward the optical branching unit 20. The Brillouin scattered light LS is light generated by Brillouin scattering in the measured optical fiber 80. Brillouin scattering is a phenomenon that occurs in the measured optical fiber 80 when the pulsed light P is incident on the measured optical fiber 80.

[0052] The operation of the optical branching unit 20, also called the first optical branching unit, and the circulator 24, also called the second optical branching unit, can be restated as follows. The first optical branching unit branches the frequency-modulated light into pump light LP and reference light LR, and advances the pump light LP to the second optical branching unit and the reference light LR to the multiplexing unit 40. The second optical branching unit advances the pump light LP toward the measured optical fiber 80 so as to be incident on one end of the measured optical fiber 80. The second optical branching unit also advances the Brillouin scattered light LS generated in the measured optical fiber 80 and returned to the multiplexing unit 40. In other words, the second optical branching unit inputs the pump light from one end of the measured optical fiber 80 and extracts the Brillouin scattered light LS generated in the measured optical fiber 80.

[0053] In the optical fiber characteristic measuring apparatus 10, interference light is generated in a multiplexing section 40 by interference between frequency-offset reference light LR and Brillouin scattered light LS, the interference light is detected by a photodetector 41, the detection signal is amplified by an amplifier 42, and the amplified signal is subjected to spectral analysis by an ESA 43. The ESA 43 outputs the result of the spectral analysis of the signal detecting the interference light to a calculation device 50.

[0054] 6, an optical fiber characteristic measuring apparatus 10 according to the present disclosure measures the Brillouin gain spectrum by injecting pump light LP into a test optical fiber 80. The optical fiber characteristic measuring apparatus 10 measures the characteristics of the test optical fiber 80 by determining the characteristics of the test optical fiber 80 based on the measurement result of the Brillouin gain spectrum.

[0055] In the optical fiber characteristic measuring apparatus 10, the calculation device 50 sets at least one measurement section in the measured optical fiber 80 and determines whether the characteristics of each measurement section are abnormal. For example, the calculation device 50 may set a first measurement section represented by MS1 and a second measurement section represented by MS2 in the measured optical fiber 80. The first measurement section and the second measurement section may be set so that the length of the first measurement section is the same as the length of the second measurement section, or may be set so that the length of the first measurement section is different from the length of the second measurement section. In this embodiment, it is assumed that the first measurement section and the second measurement section are set so that the length of the first measurement section is the same as the length of the second measurement section.

[0056] The arithmetic device 80 controls the modulation frequency and amplitude of the modulated light branched off to the pump light LP so that the BGS can be measured in each of the first and second measurement sections. In other words, the light source 11 is configured so that the arithmetic unit 54 can control the amplitude of the modulated light that determines the length of the measurement section and the modulation frequency of the modulated light that determines the position of the measurement section. The arithmetic device 50 can obtain the BGS of each measurement section by controlling the modulation frequency and amplitude of the modulated light. In other words, the arithmetic device 50 can move the measurement section to each position or change the length of the measurement section by controlling the modulation frequency and amplitude of the modulated light.

[0057] In the optical fiber characteristic measuring device 10 according to the present embodiment, the position and length of the measurement section can be determined by controlling the modulation frequency and amplitude of the modulated light, so that the measurement position and spatial resolution can be instantly switched, i.e., random accessibility is realized.

[0058] The calculation unit 54 of the calculation device 50 may store in the memory unit 56 the BGS acquired from the ESA 43 in association with information identifying the measurement section in which the BGS was measured. The information identifying the measurement section may include the distance from the end of the measured optical fiber 80 to the measurement section. In other words, the information identifying the measurement section may include the position where a correlation peak appears in the measured optical fiber 80. The information identifying the measurement section may include the length of the measurement section. The information identifying the measurement section may include the modulation frequency and amplitude of the pump light LP. The information identifying the measurement section may include the time from when the pump light LP is incident on the measured optical fiber 80 until the Brillouin scattered light LS returns.

[0059] The calculation section 54 may control the amplitude and modulation frequency of the modulated light based on the information stored in the storage section 56 .

[0060] Here, the measured optical fiber 80 has an abnormal portion 82 in which the characteristics such as temperature or strain are abnormal. The abnormal portion 82 is located within the second measurement section.

[0061] The BGS of the first measurement section not including the abnormal portion 82 is similar to the result shown in FIG. 2A described above, and has one peak. The frequency of that peak is BFS1. The BGS of the second measurement section including the abnormal portion 82 is similar to the result shown in FIG. 2B described above, and has two peaks. The frequencies of each peak are BFS1 and BFS2. BFS1 is the frequency of a peak that appears when there is no abnormality in the characteristics of the measured optical fiber 80. A peak that appears when there is no abnormality in the characteristics of the measured optical fiber 80 is also called a normal peak. On the other hand, BFS2 is the frequency of a peak that appears when there is an abnormality in the characteristics of the measured optical fiber 80. A peak that appears when there is an abnormality in the characteristics of the measured optical fiber 80 is also called an abnormal peak.

[0062] When the BGS includes multiple peaks, the calculation unit 54 of the calculation device 50 according to the present disclosure detects each peak and calculates multiple BFSs. The calculation unit 54 may detect multiple peaks by, for example, performing a peak search on the BGS. The calculation unit 54 may detect peaks in the BGS that have a power that is at least twice the noise power. In this way, noise is less likely to be erroneously detected as a peak.

[0063] In the measurement example of the measured optical fiber 80 shown in Fig. 6, the calculation unit 54 detects two peaks from the BGS of the second measurement section shown in Fig. 2B 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 section. In this case, the calculation unit 54 determines that an abnormal portion 82 is included in a part of the second measurement section.

[0064] When the calculation unit 54 determines that the measurement section includes an abnormal section 82 in part, it subdivides the measurement section and performs BGS measurement and peak detection for each subdivided section. When the calculation unit 54 determines that the second measurement section includes an abnormal section 82 in part, it subdivides the second measurement section, for example, as shown in Fig. 7. In the example of Fig. 7, the entire section represented by MS2n is included in the abnormal section 82.

[0065] When the calculation unit 54 detects an abnormal peak without detecting a normal peak from the BGS of at least one of the subdivided sections, it can determine that the entire section is included in the abnormal portion 82. When the entire section is included in the abnormal portion 82, the position of the abnormal portion 82 is measured as the position of that section.

[0066] If the calculation unit 54 cannot find a section in which an abnormal peak is detected without detecting a normal peak from the BGS from the subdivided section, the calculation unit 54 may repeat further subdivision. The calculation unit 54 may repeat subdivision until it finds a section in which an abnormal peak is detected without detecting a normal peak from the BGS. The calculation unit 54 may further subdivide the subdivided section, or may shorten the length to which the measurement section is subdivided and repeat the subdivision.

[0067] In the optical fiber characteristic measuring device 10 according to the present embodiment, the length of the measurement section can be determined by controlling the modulation frequency and amplitude of the modulated light, so that the spatial resolution of the measurement can be instantly switched. As a result, the measurement section can be easily subdivided.

[0068] <Example of a flow chart for measuring optical fiber characteristics> The calculation device 50 of the optical fiber characteristic measuring device 10 according to the present disclosure may measure the characteristics of the measured optical fiber 80 by executing an optical fiber characteristic measuring method including the steps of the flowchart shown in Fig. 8. At least a part of the optical fiber characteristic measuring method may be realized as an optical fiber characteristic measuring program executed by the calculation unit 54 or the like of the calculation device 50. The optical fiber characteristic measuring program may be stored in a non-transitory computer-readable medium.

[0069] The arithmetic device 50 sets a measurement section of the measured optical fiber 80 (step S1). The arithmetic device 50 causes the light source 11 to emit modulated light having a modulation frequency and amplitude corresponding to the set measurement section, and causes the pump light LP to be incident on the measured optical fiber 80, thereby acquiring the BGS of each measurement section (step S2).

[0070] The calculation device 50 executes a peak search of the BGS for each measurement section (step S3). The calculation device 50 determines whether the BGS for each measurement section includes an abnormal peak (step S4). If the BGS does not include an abnormal peak (step S4: NO), the calculation device 50 proceeds to step S7.

[0071] If the BGS contains an abnormal peak (step S4: YES), the calculation device 50 determines whether the BGS contains a normal peak (step S5). If the BGS does not contain a normal peak (step S5: NO), the calculation device 50 determines that the measurement section in which the BGS containing only abnormal peaks is measured is abnormal (step S6).

[0072] After determining in step S4 that the BGS does not contain an abnormal peak, or after determining that the measurement section is abnormal in step S6, the calculation device 50 determines whether the BGS peak search for the entire measurement section has been completed (step S7). If the BGS peak search for the entire measurement section has not been completed (step S7: NO), the calculation device 50 returns to the procedure of step S3 and executes a BGS peak search for the measurement section for which the peak search has not been completed. If the BGS peak search for the entire measurement section has been completed (step S7: YES), the calculation device 50 ends the execution of the procedure of the flowchart in FIG. 8.

[0073] If the calculation device 50 determines in the procedure of step S5 that the BGS contains a normal peak (step S5: YES), it subdivides the measurement section in which the BGS containing both normal and abnormal peaks was measured (step S8). After executing the procedure of step S8, the calculation device 50 returns to the procedure of step S2, and acquires a BGS and executes a peak search for the subdivided section. As described above, the calculation device 50 may repeat the subdivision until it finds a section in which no normal peak is detected from the BGS but an abnormal peak is detected.

[0074] (summary) As described above, the optical fiber characteristic measuring device 10 according to the present disclosure detects multiple peaks from the BGS measured in each measurement section of the measured optical fiber 80, and can detect an abnormal peak even if the abnormal part 82 exists only in a part of the measurement section. As a result, even if the measurement section is set wide, the presence of the abnormal part 82 in the measured optical fiber 80 is less likely to be overlooked. Furthermore, the ability to set the measurement section wide reduces the measurement time.

[0075] Furthermore, if an abnormal portion 82 exists in part of the measurement section, by dividing and measuring only that measurement section, the measurement time can be reduced compared to measuring the entire measured optical fiber 80 in a small measurement section.

[0076] Although an embodiment of the present disclosure has been described above with reference to the drawings, the specific configuration is not limited to this embodiment, and various modifications are also included within the scope that does not deviate from the spirit of the present disclosure.

[0077] The optical fiber characteristic measuring apparatus 10 according to the embodiment described above has been described as measuring the BGS by the BOCDR method. The optical fiber characteristic measuring apparatus 10 may be configured to measure the BGS by the Brillouin Optical Correlation Domain Analysis (BOCDA) method. [Explanation of symbols]

[0078] 10 Optical fiber characteristic measuring device (11: light source, 12: driving power supply, 20: optical branching section, 21: switch, 22: delay fiber, 23: polarization scrambler, 24: circulator, 40: multiplexing section, 41: photodetector, 42: amplifier, 43: ESA, 50: calculation device, 52: acquisition section, 54: calculation section, 56: memory section) 80 Optical fiber to be measured (82: Abnormal part) LP pump light LR reference light LS Brillouin scattered light P Pulsed Light

Claims

1. An optical fiber characteristic measuring device comprising: a calculation unit that extracts a plurality of peaks contained in a Brillouin gain spectrum of Brillouin scattered light generated in a measured optical fiber, and measures the characteristics of the measured optical fiber.

2. The calculation unit is A measurement section for measuring the characteristics of the test optical fiber is set at at least one position in the test optical fiber; Measure the Brillouin gain spectrum in the measurement section set at each position, determining that the characteristics of a section of the Brillouin gain spectrum that includes an anomalous peak but does not include a normal peak are anomalous; A section in which the Brillouin gain spectrum including both normal and abnormal peaks is measured is subdivided; Measure the Brillouin gain spectrum in each divided section. determining whether each subdivision is abnormal; 2. The optical fiber characteristic measuring device according to claim 1.

3. a light source for emitting modulated light to be incident on the optical fiber to be measured; 3. The optical fiber characteristic measuring device according to claim 2, wherein the light source is configured so that the calculation unit can control the amplitude of the modulated light, which determines the length of the measurement section, and the modulation frequency of the modulated light, which determines the position of the measurement section.

4. a storage unit that stores the measured Brillouin gain spectrum and information that specifies the section in which the Brillouin gain spectrum is measured in association with each other; 4. The optical fiber characteristic measuring device according to claim 3, wherein the calculation unit controls the amplitude and modulation frequency of the modulated light based on the information stored in the storage unit.

5. An optical fiber characteristic measuring method comprising the step of measuring characteristics of an optical fiber under test by extracting a plurality of peaks contained in a Brillouin gain spectrum of Brillouin scattered light generated in the optical fiber under test.

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