Optical cable monitoring device and optical cable monitoring method

Abstract

This invention provides an optical cable monitoring device and optical cable monitoring method that can pinpoint the location of abnormalities in optical cables. [Solution] An optical cable monitoring device comprising: a first acquisition unit for acquiring a monitoring target section of an optical cable; a heating unit for heating the monitoring target section of the optical cable by irradiating it with modulated light based on modulation parameters; a detection unit for detecting the temperature of the monitoring target section of the optical cable by photographing it with imaging parameters based on the modulation parameters; and a second acquisition unit for acquiring abnormal locations in the monitoring target section of the optical cable based on the temperature detection results of the monitoring target section of the optical cable.

Description

[[TECHNICAL FIELD]]

[0001] The present invention relates to an optical cable monitoring device and an optical cable monitoring method. [[BACKGROUND ART]]

[0002] Patent Document 1 describes an abnormal location detection method for an optical fiber cable, in which infrared light is incident from one end of the optical fiber cable to an optical fiber accommodated in the optical fiber cable, and infrared light leaking from an abnormal location of the optical fiber is detected. In this method, the optical fiber cable is passed through a cylindrical body having an infrared light detection element attached to the inner surface, the cylindrical body is relatively scanned in the longitudinal direction of the optical fiber cable, and infrared light leaking from the abnormal location of the optical fiber is detected. [[PRIOR ART DOCUMENTS]] [[PATENT DOCUMENTS]]

[0003] [[Patent Document 1]] Japanese Unexamined Patent Application Publication No. 2005-140712 [[SUMMARY OF THE INVENTION]] [[Problem to be Solved by the Invention]]

[0004] However, the abnormal location detection method for an optical fiber cable disclosed in Patent Document 1 cannot pinpoint the abnormal location of the optical fiber cable.

[0005] The present invention has been made in view of the above problem, and an object of the present invention is to provide an optical cable monitoring device and an optical cable monitoring method capable of pinpointing an abnormal location of an optical cable. [[Means for Solving the Problem]]

[0006] The optical cable monitoring device of this embodiment is characterized by comprising: a first acquisition unit that acquires a monitoring target section of an optical cable; a heating unit that heats the monitoring target section of the optical cable by irradiating it with modulated light based on modulation parameters; a detection unit that detects the temperature of the monitoring target section of the optical cable by photographing it with imaging parameters based on the modulation parameters; and a second acquisition unit that acquires abnormal locations in the monitoring target section of the optical cable based on the temperature detection results of the monitoring target section of the optical cable.

[0007] The optical cable monitoring method of this embodiment is characterized by comprising the steps of: acquiring a section of the optical cable to be monitored; heating the section of the optical cable to be monitored by irradiating it with modulated light based on modulation parameters; detecting the temperature of the section of the optical cable to be monitored by photographing it with imaging parameters based on the modulation parameters; and acquiring an abnormal location in the section of the optical cable to be monitored based on the temperature detection result of the section of the optical cable to be monitored. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an optical cable monitoring device and an optical cable monitoring method that can pinpoint the location of abnormalities in an optical cable. [Brief explanation of the drawing]

[0009] [Figure 1] This diagram shows the schematic configuration of an FTTH system. [Figure 2] This is a diagram showing the cross-sectional structure of an optical cable. [Figure 3] This diagram shows the configuration of optical cables when the outer sheath is white or black. [Figure 4] This diagram shows the schematic configuration of an optical cable monitoring device. [Figure 5] This diagram shows how the first acquisition unit acquires data on the monitored section of the optical cable. [Figure 6] This diagram shows how the detection unit detects the temperature of the monitored section of the optical cable. [Figure 7] This diagram conceptually illustrates an example of pinpoint identification of fiber damage using a lock-in thermography system. [Figure 8] This is a conceptual diagram showing an example of analysis results obtained using optical cable monitoring technology. [Figure 9] This is a flowchart showing each processing step in the optical cable monitoring method. [Figure 10] This diagram shows how the detection unit detects the temperature of the monitored section of the optical cable and how the second acquisition unit acquires information about abnormal locations in the monitored section of the optical cable. [Modes for carrying out the invention]

[0010] The optical cable monitoring device and optical cable monitoring method of this embodiment will be described below. The optical cable monitoring device and optical cable monitoring method of this embodiment are used, for example, in maintenance work on optical lines to identify abnormal locations (fault locations, fault locations) in the optical line.

[0011] <Conventional technical challenges> With the widespread adoption of fiber optic internet services for homes (FTTH: Fiber To The Home), efficient maintenance of the communication equipment supporting FTTH services is required. Among the communication equipment, the optical fibers in overhead fiber optic cables laid between utility poles are often damaged by strong winds, contact with trees, etc., and when damage occurs, it is necessary to pinpoint the damaged area in order to repair it.

[0012] In FTTH services, one technique for identifying (estimating) the location of a fault in an optical cable is to attach an OTDR (Optical Time Domain Reflectometer) to the terminal and transmit an optical pulse laser to measure the distance to the fault point and identify (estimate) the fault location. Alternatively, one could attach an optical closure (aerial installation closure) to the optical cable and identify (estimate) the fault location based on the optical power within the optical closure. However, with either of these techniques, it is difficult to pinpoint the exact location of the fault in the optical cable.

[0013] Another approach is to identify (estimate) the location of an anomaly by shining visible light into the optical cable (optical fiber) and observing the light leakage from the cable. However, this method is only applicable when the outer sheath of the optical cable is damaged and the optical fiber bundle is exposed. For example, if the optical fiber bundle inside the optical cable is damaged without damaging the outer sheath due to cable bending or lateral pressure, little or no light leakage from the optical cable will be observed, making it impossible to identify (estimate) the location of the anomaly. As a result, it becomes necessary to strip the outer sheath of the suspected faulty area and check for optical conductivity. Moreover, if no fault is found at the stripped area, the optical cable must be repaired while protecting the exposed optical fiber bundle from damage due to environmental factors such as rain and wind.

[0014] In addition, infrared thermography is known as a non-destructive technique for diagnosing the condition of various objects. For example, by photographing the infrared light emitted from an object with a thermographic camera, the temperature of the object can be measured, and if the temperature of the object changes due to a malfunction, the location of the malfunction can be identified using infrared thermography. Assuming a method for identifying the location of a malfunction in an overhead cable using a thermographic camera, it is conceivable that continuous light would be input into the optical fiber in the faulty optical cable, and the temperature rise at the suspected fault location would be captured by the thermographic camera, thereby identifying the location of the malfunction.

[0015] However, in the method for identifying a faulty location of an aerial cable using a thermography camera, it is necessary to input a relatively large optical power (for example, at least about 3 dBm) into the optical fiber in order to observe a temperature rise. If light is erroneously input to an optical fiber connected to a communication device, the device may be damaged. Therefore, it is desirable to suppress the optical input power required for the optical fiber (for example, 0 dBm or less). In addition, in the method for identifying a faulty location of an aerial cable using a thermography camera, it takes a certain amount of time (for example, about 1 minute) to cause a sufficient temperature rise to identify the faulty location. Therefore, considering work efficiency at the site, it is desirable to be able to shorten the time required to identify the faulty location.

[0016] <Basic technical idea of the present embodiment> The inventor of the present invention has recognized the above problems as important technical issues, solved the problems of conventional thermography methods (high output, long time, sheath damage), and has conceived an optical cable monitoring device and an optical cable monitoring method capable of realizing safer, faster, and higher-accuracy identification of an abnormal location (faulty location, failure location) of an optical cable.

[0017] In the optical cable monitoring device and the optical cable monitoring method of the present embodiment, for example, a lock-in thermography system may be used to non-destructively, simply and pinpoint identify an abnormal location (faulty location, failure location) of an optical cable with high accuracy. In addition, in the optical cable monitoring device and the optical cable monitoring method of the present embodiment, for example, intensity-modulated light may be input to an optical cable (optical fiber), and periodic temperature changes of the sheath caused by modulated light leaking from the abnormal location (faulty location, failure location) may be continuously captured by a thermography camera. Furthermore, a modulation frequency component may be extracted by image analysis such as Fast Fourier Transform (FFT), and the abnormal location (faulty location, failure location) may be identified from the characteristics of amplitude and phase.

[0018] The optical cable monitoring device and optical cable monitoring method of this embodiment can use a thermographic camera to identify abnormal locations (fault locations, interference locations) in optical cables with low optical input power and in a short time, and can reconnect the abnormal locations (fault locations, interference locations) in the optical cables.

[0019] More specifically, in this embodiment, the first acquisition unit (in the first acquisition step) acquires the monitored section of the optical cable. The heating unit (in the heating step) heats the monitored section of the optical cable by irradiating it with modulated light based on the modulation parameters. The detection unit (in the detection step) detects the temperature of the monitored section of the optical cable by photographing it with imaging parameters based on the modulation parameters. The second acquisition unit (in the second acquisition step) acquires abnormal locations in the monitored section of the optical cable based on the temperature detection result of the monitored section of the optical cable.

[0020] The heating unit consists of, for example, a laser light irradiation unit, and in the heating step, the monitored section of the optical cable is periodically heated by irradiating it with modulated light modulated by the intensity modulation frequency as a modulation parameter. The detection unit consists of, for example, a lock-in thermography system, and in the detection step, the temperature of the monitored section of the optical cable is detected by continuously imaging the monitored section of the optical cable at a frame rate higher than the intensity modulation frequency as an imaging parameter (for example, a frame rate that is twice or more the intensity modulation frequency).

[0021] The second acquisition unit (in the second acquisition step) extracts the amplitude and phase components of temperature changes from the continuous images of the monitored section of the optical cable, and acquires abnormal locations in the monitored section of the optical cable based on the extracted amplitude and phase components. More specifically, the second acquisition unit (in the second acquisition step) acquires locations in the monitored section of the optical cable as abnormal locations where the amplitude component (complex amplitude) of temperature changes in the continuous images is greater than or equal to a threshold, and / or where the phase component of temperature changes in the continuous images is within a predetermined range (aligned).

[0022] As described above, the optical cable monitoring device and optical cable monitoring method of this embodiment input intensity-modulated light (light that is periodically switched ON / OFF) into an optical fiber, and periodically heats the cable sheath with light leaking from the damaged area (use of intensity-modulated light). In addition, the amplitude and phase components of temperature changes are extracted from images continuously captured with a thermographic camera at a frame rate of more than twice the modulation frequency (high frame rate shooting and image analysis). Furthermore, areas with high amplitude values ​​and areas with aligned phases are determined to be damaged points, and if necessary, the shooting location is changed and the analysis is performed again to pinpoint the damaged area. As a result, the required optical input power can be reduced and the fault location can be identified in a short time. In addition, it is resistant to temperature unevenness and disturbances, and the advantages of greatly improving on-site work efficiency and safety are obtained.

[0023] <Specific Embodiments> Figure 1 shows a schematic configuration of the FTTH (Fiber To The Home) system 100. The FTTH system 100 includes a terminal 200, a central office 300, and an optical cable 400 connecting the terminal 200 and the central office 300.

[0024] Terminal 200 is a user-side optical outlet installed at a location such as a detached house, apartment building, or office. Central office 300 is the provider's optical line communication center that supplies communication optical power to terminal 200 via optical cable 400. In Figure 1, each terminal 200 is depicted as being connected to central office 300 via optical cable 400, but in reality, multiple (many) terminals 200 are connected to one central office 300 via optical cable 400. Furthermore, Figure 1 exemplifies three relay sections 500A, 500B, and 500C located midway between the terminal 200 and central office 300 to which the optical cable 400 is connected.

[0025] In Figure 1, the sections between terminal 200 and relay unit 500A, between relay unit 500A and relay unit 500B, between relay unit 500B and relay unit 500C, and between relay unit 500C and central office 300 can each be designated as "monitored sections of optical cable 400" acquired by the first acquisition unit 610, which will be described later.

[0026] Figure 2 shows the cross-sectional structure of the optical cable 400. The optical cable 400 contains multiple optical fibers. As shown in Figure 2, the optical cable 400 may be a spacer-type optical cable. In the example in Figure 2, the optical cable 400 has a spacer 410 with multiple spiral slots 420 formed on its outer circumference, and multiple optical fiber bundles (tape-shaped optical fibers) 430, each containing multiple (e.g., four) optical fibers 430a arranged in parallel, are stacked and housed within each slot 420. A tension member 440 is provided at the central axis position of the spacer 410, and a waterproof tape 450 and an outer sheath 460 are sequentially provided around the spacer 410. Note that the optical cable 400 is not limited to a spacer type.

[0027] A portion of the optical fiber 430a of the optical cable 400 includes a monitoring optical fiber 430b, which is optically connected to an OTDR (Optical Time Domain Reflectometer) device and used to acquire (identify, measure, and detect) the monitored section (anomaly estimation section, fault estimation section). In the example in Figure 2, the monitoring optical fiber 430b included in the optical fiber 430a of the optical cable 400 is depicted with a dashed circle. Note that the monitoring optical fiber 430b may also be used for normal communication purposes.

[0028] Thus, the optical cable 400 has an optical fiber bundle 430 and an outer sheath 460 covering the optical fiber bundle 430. The color of the outer sheath 460 of the optical cable 400 may vary depending on various conditions such as the installation location and environment of the optical cable 400. The color of the outer sheath 460 of the optical cable 400 may be uniform along the longitudinal direction (extension direction) of the optical cable 400, or it may differ at each position along the longitudinal direction (extension direction) of the optical cable 400.

[0029] Figures 3A and 3B show the configuration of the optical cable 400 when the outer sheath 460 is white and black, respectively. Regardless of whether the outer sheath 460 is white or black, the configuration of the optical cable 400 is the same in that various types of light consisting of continuous light (for example, light for communication, light for testing, modulated light based on the modulation parameters described later, modulated light modulated by the intensity modulation frequency, and light that is periodically switched ON / OFF) are incident on it.

[0030] As shown in Figure 3A, optical cables 400 with a white outer sheath 460 are commonly used in homes. In optical cables 400 with a white outer sheath 460, if the optical fiber bundle 430 is damaged but the outer sheath 460 is not damaged, a portion of the light leaking from the optical fiber bundle 430 is absorbed by the outer sheath 460, and the remaining portion is emitted from the outer sheath 460. Therefore, only a portion of the energy of the leaking light is converted into heat. Consequently, the outer sheath 460 of the optical cable 400 has the characteristic of not easily rising in temperature.

[0031] As shown in Figure 3B, optical cables 400 with a black outer sheath 460 are often drop cables used outdoors, and black carbon is added to prevent degradation of the outer sheath 460 due to ultraviolet light. In optical cables 400 with a black outer sheath 460, if the optical fiber bundle 430 is damaged but the outer sheath 460 is not damaged, the outer sheath 460 absorbs all the light leaking from the optical fiber bundle 430, so all the energy of the leaked light is converted into heat. Therefore, the outer sheath 460 of the optical cable 400 has the characteristic of easily rising in temperature.

[0032] Figure 4 shows a schematic configuration of the optical cable monitoring device 600. The optical cable monitoring device 600 includes a first acquisition unit 610, a heating unit 620, a detection unit 630, and a second acquisition unit 640.

[0033] The first acquisition unit 610 acquires (identifies, measures, and detects) the monitored section (anomaly-estimated section, fault-estimated section) of the optical cable 400 at an intermediate position between the terminal 200 and the central office 300. There is flexibility in how the first acquisition unit 610 acquires the monitored section of the optical cable 400, and various design changes are possible, but for example, at least one of an OTDR device and an optical closure can be used.

[0034] Figure 5 shows how the first acquisition unit 610 acquires the monitored section of the optical cable 400. As shown in Figure 5, the OTDR device 610A, which serves as the first acquisition unit 610, is attached to the end of the optical cable 400 on the terminal 200 side. The OTDR device 610A injects an optical pulse as monitoring light into the monitoring optical fiber 430b (see Figure 2) of the optical cable 400 and measures the light intensity of the light returned from the monitoring optical fiber 430b (backscattered light and reflected light). Based on the light intensity data of the light returned from the monitoring optical fiber 430b, the OTDR device 610A calculates whether or not there is an abnormal section (a section with abnormally high loss) in the longitudinal direction of the optical cable 400, and if so, the distance of the abnormal section from the terminal 200. This distance information is acquired (identified, measured, and detected) as the monitored section (estimated abnormal section, estimated fault section) of the optical cable 400 at an intermediate position between the terminal 200 and the central office 300. Furthermore, an optical closure 610B, acting as the first acquisition unit 610, is installed near the relay sections 500A and 500B of the optical cable 400, making it possible to identify nearby connection points. Based on the optical power (optical continuity confirmation) within the optical closure 610B, the monitored section (anomaly estimated section, fault estimated section) of the optical cable 400 at an intermediate position between the terminal 200 and the central office 300 is acquired (identified, measured, and detected). In the example shown in Figure 5, the section of the optical cable 400 between the terminal 200 and the relay section 500A is acquired as the monitored section.

[0035] The heating unit 620 heats the monitored section of the optical cable 400 acquired by the first acquisition unit 610. The heating unit 620 has a laser light irradiation unit (modulated light irradiation unit) that irradiates modulated light as heating laser light from one end of the optical cable 400. As shown in Figure 5, if the monitored section is between the terminal 200 and the relay unit 500A, the laser light irradiation unit (modulated light irradiation unit) of the heating unit 620 irradiates the monitored section of the optical cable 400 with heating laser light (modulated light) from either the terminal 200 side or the relay unit 500A side to which the optical closure 610B is attached.

[0036] More specifically, the heating unit 620 heats the monitored section of the optical cable 400 by irradiating it with heating laser light (modulated light) based on modulation parameters. The heating unit 620 periodically heats the monitored section of the optical cable 400 by irradiating it with heating laser light (modulated light) modulated by an intensity modulation frequency as a modulation parameter. The heating laser light (modulated light) modulated by the intensity modulation frequency is, for example, periodically switched ON / OFF or switching between strong and weak intensity (at predetermined intervals). The intensity modulation frequency is used to define the period, intensity, phase, amplitude, etc., involved in the modulation of the heating laser light (modulated light).

[0037] The heating section (laser light irradiation section, modulated light irradiation section) 620 may vary the modulation parameters of the heating laser light (modulated light), or the intensity modulation frequency as a modulation parameter, depending on the color of the outer sheath 460 of the optical cable 400.

[0038] As mentioned above, in the case of a white cable, if the optical fiber bundle 430 is damaged without damage to the outer sheath 460, a portion of the light leaking from the optical fiber bundle 430 is absorbed by the outer sheath 460, and the remaining portion is emitted from the outer sheath 460, so the temperature of the outer sheath 460 of the optical cable 400 does not rise easily. On the other hand, in the case of a black cable, if the optical fiber bundle 430 is damaged without damage to the outer sheath 460, all of the light leaking from the optical fiber bundle 430 is absorbed by the outer sheath 460, so the temperature of the outer sheath 460 of the optical cable 400 rises easily.

[0039] Utilizing the above characteristics, the heating unit (laser light irradiation unit, modulated light irradiation unit) 620 may relatively shorten the period and relatively increase the intensity of the heating laser light (modulated light) when the outer sheath 460 of the optical cable 400 is white, while relatively lengthening the period and relatively decreasing the intensity of the heating laser light (modulated light) when the outer sheath 460 of the optical cable 400 is black. In addition to the color of the outer sheath 460 of the optical cable 400, the heating unit (laser light irradiation unit, modulated light irradiation unit) 620 may also vary the modulation parameters of the heating laser light (modulated light), or the intensity modulation frequency as a modulation parameter, depending on other parameters such as the thickness of the outer sheath 460 of the optical cable 400.

[0040] The laser light irradiation unit (modulated light irradiation unit) of the heating unit 620 may irradiate the monitored section of the optical cable 400 with heating laser light (modulated light) having different characteristics from the light used for communication and / or testing by the optical cable 400.

[0041] The power of the communication light between terminal 200 and central office 300 is determined by a standard, and this power is often insufficient to heat (increase the temperature of) the monitored section of optical cable 400. Therefore, the heating laser light (modulated light) emitted by the heating unit (laser light irradiation unit, modulated light irradiation unit) 620 may be set to a higher power than the communication light between terminal 200 and central office 300.

[0042] In Passive Optical Network (PON), a fiber optic transmission standard used in FTTH, a test wavelength band is defined, and optical filters are often installed to prevent light in this test wavelength band from being input to communication equipment. In this case, even if high-power optical input is applied in the test wavelength band, it will not affect the communication equipment. However, in optical line configurations where such optical filters do not exist, it may be better to avoid, for example, an average optical input of 0 dBm or more to prevent failure of communication equipment. In such cases, if the optical cable 400 is a multi-core cable as shown in Figure 2, and fiber damage occurs at the same location on multiple cores, the temperature of the cable sheath at the fiber damage location can be increased while keeping the optical input power per core below 0 dBm, and the temperature rise can be observed by the detection unit (thermographic camera, lock-in thermography system) 630 described later. The heating laser light (modulated light) irradiated by the heating unit (laser light irradiation unit, modulated light irradiation unit) 620 may be set to a different wavelength band and power than the light in the test wavelength band mentioned above.

[0043] The detection unit 630 detects (acquires and measures) the temperature of the monitored section of the optical cable 400 acquired by the first acquisition unit 610. Figure 6 shows the detection of the temperature of the monitored section of the optical cable 400 by the detection unit 630. The detection unit 630 has a thermographic camera (lock-in thermographic system) 630A that scans along the monitored section of the optical cable 400. The thermographic camera 630A is slidably supported on a guide rail (not shown) arranged along the monitored section of the optical cable 400, and may detect the temperature of the monitored section of the optical cable 400 while moving along the monitored section of the optical cable 400 by a drive mechanism (not shown) including a motor and gears. There is some flexibility in how the scanning mechanism of the detection unit 630 (thermographic camera 630A) is configured, and various design changes are possible (for example, a scanning mechanism using a tripod may be used).

[0044] The term "lock-in thermography system" may be interpreted as "lock-in thermography device." A lock-in thermography system (lock-in thermography device) is defined as a system or device relating to a technology that non-destructively detects defects or anomalies inside materials by combining a thermographic camera with periodic heating. In other words, a thermographic camera can be considered as a component of a lock-in thermography system (lock-in thermography device). However, a thermographic camera and a lock-in thermography system (lock-in thermography device) may be interchangeable (they may be synonymous). For example, when referring to a thermographic camera, it may mean a lock-in thermography system (lock-in thermography device) that includes that thermographic camera, and when referring to a lock-in thermography system (lock-in thermography device), it may mean a thermographic camera included in that lock-in thermography system (lock-in thermography device).

[0045] The detection unit 630 (thermographic camera 630A) detects the temperature of the monitored section of the optical cable 400 by imaging the monitored section of the optical cable 400 using imaging parameters based on the modulation parameters of the heating unit (laser light irradiation unit, modulated light irradiation unit) 620. The detection unit 630 (thermographic camera 630A) detects the temperature of the monitored section of the optical cable 400 by continuously imaging the monitored section of the optical cable 400 at a frame rate higher than the intensity modulation frequency of the heating unit (laser light irradiation unit, modulated light irradiation unit) 620, for example, a frame rate of twice or more the intensity modulation frequency. It is preferable, but not limited to, that the frame rate for continuous imaging by the detection unit 630 (thermographic camera 630A) is higher than the intensity modulation frequency of the heating unit (laser light irradiation unit, modulated light irradiation unit) 620. Furthermore, the frame rate for continuous imaging by the detection unit 630 (thermographic camera 630A) may be higher than the intensity modulation frequency of the heating unit (laser light irradiation unit, modulated light irradiation unit) 620, and less than twice the intensity modulation frequency.

[0046] The detection unit 630 (thermographic camera 630A) may vary the imaging parameters for the monitored section of the optical cable 400, or the frame rate as an imaging parameter, depending on the color of the outer sheath 460 of the optical cable 400. For example, when the outer sheath 460 of the optical cable 400 is white, the frame rate for continuous imaging of the monitored section of the optical cable 400 may be made relatively shorter, while when the outer sheath 460 of the optical cable 400 is black, the frame rate for continuous imaging of the monitored section of the optical cable 400 may be made relatively longer.

[0047] The second acquisition unit 640 is implemented as a functional component of the computer (CPU: Central Processing Unit) or processor of the optical cable monitoring device 600. Based on the temperature detection results of the monitored section of the optical cable 400 by the detection unit 630 (thermographic camera 630A), the second acquisition unit 640 acquires (identifies, calculates, and detects) abnormal locations (fiber damage locations) in the monitored section of the optical cable 400.

[0048] More specifically, the second acquisition unit 640 extracts the amplitude component (complex amplitude) and phase component of temperature change from the continuous images of the monitored section of the optical cable 400 taken by the detection unit 630 (thermographic camera 630A), and acquires abnormal locations in the monitored section of the optical cable 400 based on the amplitude component and the phase component.

[0049] As a first example, the second acquisition unit 640 may acquire locations where the amplitude component of temperature change in the continuously captured images of the monitored section of the optical cable 400 by the detection unit 630 (thermographic camera 630A) exceeds a threshold value, as abnormal locations in the monitored section of the optical cable 400.

[0050] As a second example, the second acquisition unit 640 may acquire locations where the phase component of temperature change in the continuously captured images of the monitored section of the optical cable 400 by the detection unit 630 (thermographic camera 630A) falls within a predetermined range (aligns), as abnormal locations in the monitored section of the optical cable 400.

[0051] As a third example, the second acquisition unit 640 may acquire as an abnormal location in the monitored section of the optical cable 400 locations where the amplitude component of the temperature change in the continuous images of the monitored section of the optical cable 400 taken by the detection unit 630 (thermographic camera 630A) is above a threshold, and the phase component of the temperature change in the continuous images of the monitored section of the optical cable 400 taken by the detection unit 630 (thermographic camera 630A) is within a predetermined range (aligned).

[0052] To summarize the first to third examples, the second acquisition unit 640 may acquire as an abnormal location in the monitored section of the optical cable 400 any location where the amplitude component of the temperature change in the continuous images of the monitored section of the optical cable 400 taken by the detection unit 630 (thermographic camera 630A) is greater than or equal to a threshold, and / or where the phase component of the temperature change in the continuous images of the monitored section of the optical cable 400 taken by the detection unit 630 (thermographic camera 630A) is within a predetermined range (aligned).

[0053] Figure 7 is a conceptual diagram illustrating an example of pinpoint identification of fiber damage using a lock-in thermography system. In Figure 7, an optical cable 400, a heating unit (laser light irradiation unit, modulated light irradiation unit) 620, and a detection unit 630 (thermography camera 630A) are depicted. The block labeled 620 shows an FP LD (Fabry-Perot Laser Diode), which is an example of a heating unit (laser light irradiation unit, modulated light irradiation unit). Figure 7 also shows the waveform of the laser light (modulated light) irradiated by the heating unit (laser light irradiation unit, modulated light irradiation unit) 620 (horizontal axis is time, vertical axis is optical power) and continuous images captured at a predetermined frame rate by the detection unit 630 (thermography camera 630A). Furthermore, Figure 7 shows a parameter setting unit (signal generator) 650 that sets the intensity modulation frequency (modulation parameter) of the laser light (modulated light) emitted by the heating unit (laser light irradiation unit, modulated light irradiation unit) 620, and the frame rate (imaging parameter) for continuous imaging by the detection unit 630 (thermographic camera 630A). The block labeled 650 shows an example of a parameter setting unit (signal generator), which is an AWG (Arbitrary Waveform Generator).

[0054] In this embodiment, the location of fiber damage can be identified by observing the temperature change of the cable sheath 460 using a thermographic camera 630A. First, a periodic signal output from the parameter setting unit (signal generator) 650 is input to the heating unit (laser light irradiation unit, modulated light irradiation unit) 620, causing the heating unit (laser light irradiation unit, modulated light irradiation unit) 620 to output light with modulated intensity. Next, the intensity-modulated light is input to the optical fiber inside the optical cable 400 where a fiber break has occurred, but the cable sheath 460 is not damaged (no light leaks). The intensity-modulated light leaks from the fiber break location and irradiates the cable sheath 460, causing the temperature of the cable sheath 460 to change due to the intensity-modulated light.

[0055] Temperature changes caused by intensity-modulated light are continuously captured using a thermographic camera 630A at a frame rate of more than twice the laser modulation frequency. Subsequently, the complex amplitude at the laser modulation frequency is extracted from the multiple images captured in succession using extraction processing such as Fast Fourier Transform (FFT). Locations with high amplitude values ​​or aligned phases are searched for in the cable sheath 460. If no such locations are found, the imaging location is changed and imaging is performed again. If such locations are found, these locations are determined to be fiber break points. Finally, the cable sheath 460 at the damaged part of the optical fiber is stripped, the optical fiber is reconnected, and the stripped area of ​​the cable sheath 460 is protected.

[0056] Figures 8A and 8B are conceptual diagrams showing an example of analysis results using the optical cable monitoring technology of this embodiment. Figure 8A shows an amplitude image obtained by the lock-in thermography system, and Figure 8B shows a phase image obtained by the lock-in thermography system. In both images, the curved area in the center is the location where the fiber was intentionally broken. In the amplitude image of Figure 8A, it can be seen that the amplitude value is larger at the fiber break point. In the phase image of Figure 8B, while the phase is random everywhere except at the fiber break point, the phase is aligned at the fiber break point, and it can be seen that the phase gradually changes as you move away from the center of the break point. Utilizing these characteristics, in this embodiment, the amplitude and phase components of temperature changes can be extracted from continuous images of the monitored section of the optical cable, and based on the extracted amplitude and phase components, abnormal locations in the monitored section of the optical cable can be obtained.

[0057] Figure 9 is a flowchart showing each processing step of the optical cable monitoring method.

[0058] In step ST1, for example, the first acquisition unit 610 identifies the cable section containing the fiber damage point and the connection point near the damage point. In step ST2, the target optical fiber (e.g., optical cable 400) is connected to an intensity-modulated laser light source (e.g., heating unit 620). In step ST3, the temperature of the damaged area of ​​the optical fiber is changed by intensity-modulated light from the intensity-modulated laser light source (e.g., heating unit 620). In step ST4, the target cable (e.g., optical cable 400) is continuously photographed using a thermographic camera 630A at a frame rate of more than twice the laser modulation frequency. In step ST5, for example, the second acquisition unit 640 performs frequency analysis on the images continuously captured using the thermographic camera 630A to extract the amplitude and phase image of the laser intensity modulation frequency.

[0059] In step ST6, for example, the second acquisition unit 640 determines whether or not the fiber break location has been identified from the amplitude-phase image. If the fiber break location has not been identified from the amplitude-phase image (step ST6: No), the process proceeds to step ST7, where the imaging location by the thermographic camera 630A is changed, and then the process returns to step ST3. If the fiber break location has been identified from the amplitude-phase image (step ST6: Yes), the process proceeds to step ST8, where the cable sheath 640 at the fiber break location is stripped, the fiber (e.g., optical cable 400) is reconnected, and then the stripped area of ​​the cable sheath 640 is protected.

[0060] The following describes further modifications (another embodiment) of the optical cable monitoring technology of this embodiment. In this modification (another embodiment), for example, the location (period) where the intensity of the laser light (modulated light) irradiated by the heating unit (laser light irradiation unit, modulated light irradiation unit) 620 is maximum may be sampled and used.

[0061] The detection unit 630 may, after waiting for the temperature rise saturation time required for heating the monitored section of the optical cable 400, detect the temperature of the monitored section of the optical cable 400 by photographing it with predetermined shooting parameters (frame rate) (scanning with the thermographic camera 630A may also be started). The timing for starting the calculation of the temperature rise saturation time may be, for example, the timing when the heating unit (laser light irradiation unit, modulated light irradiation unit) 620 starts irradiating the optical cable 400 with heating laser light (modulated light).

[0062] The detection unit 630 (thermographic camera 630A) may, as a first temperature detection method, detect the post-heating temperature after the monitored section of the optical cable 400 has been heated by the heating unit (laser light irradiation unit, modulated light irradiation unit) 620 (after the temperature rise saturation time has elapsed).

[0063] The detection unit 630 (thermographic camera 630A) may, as a second temperature detection mode, detect the pre-heating temperature before the monitored section of the optical cable 400 is heated by the heating unit (laser light irradiation unit, modulated light irradiation unit) 620, and the post-heating temperature after the monitored section of the optical cable 400 is heated by the heating unit (laser light irradiation unit, modulated light irradiation unit) 620 (after the temperature rise saturation time has elapsed).

[0064] As mentioned above, in the case of a white cable, if the optical fiber bundle 430 is damaged without damage to the outer sheath 460, a portion of the light leaking from the optical fiber bundle 430 is absorbed by the outer sheath 460, and the remaining portion is emitted from the outer sheath 460, so the temperature of the outer sheath 460 of the optical cable 400 does not rise easily. On the other hand, in the case of a black cable, if the optical fiber bundle 430 is damaged without damage to the outer sheath 460, all of the light leaking from the optical fiber bundle 430 is absorbed by the outer sheath 460, so the temperature of the outer sheath 460 of the optical cable 400 rises easily.

[0065] Utilizing the above characteristics, the detection unit 630 (thermographic camera 630A) may vary the temperature rise saturation time, which is the waiting time from the start of heating of the monitored section of the optical cable 400 to temperature detection, depending on the color of the outer sheath 460 of the optical cable 400. More specifically, in the case of a white cable, the heating effect of the monitored section of the optical cable 400 is less likely to occur early (temperature rise is less likely), so the temperature rise saturation time may be set to be relatively longer (longer than in the case of a black cable). Conversely, in the case of a black cable, the heating effect of the monitored section of the optical cable 400 is more likely to occur early (temperature rise is more likely), so the temperature rise saturation time may be set to be relatively shorter (shorter than in the case of a white cable).

[0066] If the detection unit 630 detects the post-heating temperature of the monitored section of the optical cable 400 (in the case of the first temperature detection method described above), the second acquisition unit 640 may acquire abnormal locations in the monitored section of the optical cable 400 based on the post-heating temperature. More specifically, the second acquisition unit 640 may acquire locations in the monitored section of the optical cable 400 where the post-heating temperature is equal to or greater than a threshold temperature as abnormal locations.

[0067] If the detection unit 630 detects the pre-heating temperature and the post-heating temperature of the monitored section of the optical cable 400 (in the case of the second temperature detection mode described above), the second acquisition unit 640 may acquire abnormal locations in the monitored section of the optical cable 400 based on the difference temperature between the pre-heating temperature and the post-heating temperature. More specifically, the second acquisition unit 640 may acquire as abnormal locations locations within the monitored section of the optical cable 400 where the difference temperature between the pre-heating temperature and the post-heating temperature is equal to or greater than a threshold temperature.

[0068] The second acquisition unit 640 may, utilizing the characteristics of the white and black cables described above, set different threshold temperatures for determining abnormal locations in the monitored section of the optical cable 400, depending on the color of the outer sheath 460 of the optical cable 400. For example, the threshold temperature may be set lower for white cables, which tend to have lower cable temperatures, and higher for black cables, which tend to have higher cable temperatures.

[0069] In addition, if the optical cable 400 is installed outdoors (exposed), temperature variations may occur along the longitudinal direction (extension direction) of the optical cable 400 depending on environmental factors (e.g., weather, temperature, humidity, amount of sunlight, etc.), and these temperature variations may hinder the identification of abnormal locations. Therefore, in order to reduce the impact of temperature variations due to the above environmental factors, parameters such as the temperature rise saturation time and threshold temperature may be varied depending on the location along the longitudinal direction (extension direction) of the optical cable 400.

[0070] Figure 10 shows the detection of the temperature of the monitored section of the optical cable 400 by the detection unit 630 and the acquisition of abnormal locations in the monitored section of the optical cable 400 by the second acquisition unit 640.

[0071] In the example in Figure 10, the monitored section of optical cable 400 is divided into monitored sections 400-1, 400-2, 400-3, 400-4, 400-5, 400-6, ..., 400-N (where N is a natural number), and the detected temperatures (temperature after heating or differential temperature) T1, T2, T3, T4, T5, T6, ..., TN for each of the divided monitored sections are shown. The relationship between the detected temperatures T1 to TN in monitored sections 400-1 to 400-N and the threshold temperature Tth is then determined. Divided monitored sections where the detected temperature is less than the threshold temperature Tth are determined to be normal, and divided monitored sections where the detected temperature is greater than or equal to the threshold temperature Tth are identified as abnormal locations. In the example in Figure 10, divided monitored sections T1, T2, T4 to T6, ..., TN are determined to be normal, and divided monitored section T3 is identified as an abnormal location.

[0072] Temperature detection and identification of abnormal areas in the monitored sections of optical cable 400 may be performed simultaneously over the entire length of the monitored section of optical cable 400, or it may be performed for each segment of the monitored section of optical cable 400. In the former case, temperatures T1 to TN for monitored sections 400-1 to 400-N are detected together, and then the relationship between the detected temperatures T1 to TN and the threshold temperature Tth is compared. In the latter case, when the temperature of a monitored section is detected, the relationship between the detected temperature and the threshold temperature Tth is compared, and then when the temperature of another monitored section is detected, the relationship between the detected temperature and the threshold temperature Tth is compared, and this is performed for all segmented monitored sections.

[0073] As described above, the optical cable monitoring device of this embodiment includes: a first acquisition unit that acquires a monitoring target section of an optical cable; a heating unit that heats the monitoring target section of the optical cable by irradiating it with modulated light based on modulation parameters; a detection unit that detects the temperature of the monitoring target section of the optical cable by photographing it with imaging parameters based on the modulation parameters; and a second acquisition unit that acquires abnormal locations in the monitoring target section of the optical cable based on the temperature detection results of the monitoring target section of the optical cable.

[0074] The optical cable monitoring technology of this embodiment involves inputting intensity-modulated light into the optical fiber within the cable, and periodically heating the cable sheath with light emitted from the damaged area of ​​the optical fiber. Subsequently, the cable is continuously photographed with a thermographic camera at a frame rate of more than twice the modulation frequency of the light. The captured images are analyzed, and if a temperature change is confirmed, the damaged area is reconnected. The specific procedure is as follows. (1) Identify the cable section with fiber damage and the nearby connection points of the optical fiber by OTDR measurement and confirmation of optical continuity within the optical closure (first acquisition step). (2) Intensity-modulated laser light is incident on the optical fiber with fiber damage (heating step). (3) The area suspected of malfunction is continuously photographed with a thermographic camera at a frame rate of more than twice the laser modulation frequency (detection step). (4) Extract the complex amplitude at the optical modulation frequency from the continuously captured images and search for areas on the cable sheath where the amplitude value is high or the phase is aligned (second acquisition step). (5) If the above elements cannot be confirmed in the amplitude and phase images, change the shooting location and repeat (4) above. If the above elements can be confirmed in the amplitude and phase images, perform (6) below (second acquisition step). (6) Areas with high amplitude in the amplitude image, or areas with aligned phases in the phase image, are identified as areas of optical fiber damage (second acquisition step). (7) Strip the outer sheath of the cable from the damaged part of the optical fiber and reconnect the optical fiber. (8) Protect the stripped portion of the cable.

[0075] Although the invention described herein has been explained in detail above, it will be clear to those skilled in the art that the invention described herein is not limited to the embodiments described herein. The invention described herein can be implemented in modified and altered forms without departing from the spirit and scope of the invention as defined by the claims. Therefore, the descriptions herein are for illustrative purposes only and do not imply any limitation on the invention described herein. [Explanation of Symbols]

[0076] 100 FTTH system 200 terminals 300 Interchanges 400 fiber optic cables 410 Spacer 420 slots 430 Optical fiber bundle (tape-shaped optical fiber) 430a optical fiber 430b monitoring optical fiber 440 Tension Members 450 Waterproof Tape 460 Outer shell (sheath) 500A 500B 500C Relay section 600 Optical Cable Monitoring Device 610 First acquisition part 610A OTDR device 610B Optical Closure 620 Heating section (laser light irradiation section, modulated light irradiation section) 630 Detection unit 630A Thermal Imaging Camera (Lock-in Thermal Imaging System, Lock-in Thermal Imaging Device) 640 Second Acquisition Department 650 Parameter setting unit (signal generator)

Claims

1. A first acquisition unit that acquires the monitored section of the optical cable, A heating unit that heats the monitored section of the optical cable by irradiating it with modulated light based on modulation parameters, A detection unit that detects the temperature of the monitored section of the optical cable by photographing the monitored section of the optical cable with imaging parameters based on the modulation parameters, A second acquisition unit acquires abnormal locations in the monitored section of the optical cable based on the temperature detection results of the monitored section of the optical cable, An optical cable monitoring device characterized by having the following features.

2. The heating unit periodically heats the monitored section of the optical cable by irradiating it with modulated light modulated by the intensity modulation frequency as the modulation parameter. The detection unit detects the temperature of the monitored section of the optical cable by continuously photographing the monitored section at a frame rate higher than the intensity modulation frequency as an imaging parameter. The optical cable monitoring device according to feature 1.

3. The heating unit periodically heats the monitored section of the optical cable by irradiating it with modulated light modulated by the intensity modulation frequency as the modulation parameter. The detection unit detects the temperature of the monitored section of the optical cable by continuously photographing the monitored section of the optical cable at a frame rate that is twice or more the intensity modulation frequency as the shooting parameter. The optical cable monitoring device according to feature 1.

4. The second acquisition unit extracts the amplitude and phase components of temperature changes from the continuous images of the monitored section of the optical cable, and acquires abnormal locations in the monitored section of the optical cable based on the amplitude and phase components. The optical cable monitoring device according to claim 2 or 3.

5. The second acquisition unit acquires locations in the monitored section of the optical cable where the amplitude component of the temperature change in the continuous image exceeds a threshold and / or the phase component of the temperature change in the continuous image falls within a predetermined range, as abnormal locations in the monitored section of the optical cable. The optical cable monitoring device according to feature 4.

6. The detection unit waits for the temperature rise saturation time required for the heating of the monitored section of the optical cable, and then detects the temperature of the monitored section of the optical cable by photographing it with the aforementioned shooting parameters. The optical cable monitoring device according to feature 1.

7. The optical cable comprises an optical fiber bundle and an outer sheath covering the optical fiber bundle. The detection unit varies the temperature rise saturation time depending on the color of the outer sheath of the optical cable. The optical cable monitoring device according to feature 6.

8. The detection unit detects the temperature of the optical cable before heating the monitored section and the temperature of the optical cable after heating the monitored section. The second acquisition unit acquires abnormal locations in the monitored section of the optical cable based on the difference temperature between the temperature before heating and the temperature after heating. The optical cable monitoring device according to feature 1.

9. The second acquisition unit acquires the locations within the monitored section of the optical cable where the differential temperature is equal to or greater than the threshold temperature as the abnormal locations. The optical cable monitoring device according to feature 8.

10. The optical cable comprises an optical fiber bundle and an outer sheath covering the optical fiber bundle. The second acquisition unit adjusts the threshold temperature according to the color of the outer sheath of the optical cable. The optical cable monitoring device according to feature 9.

11. The optical cable comprises an optical fiber bundle and an outer sheath covering the optical fiber bundle. The heating unit has a laser light irradiation unit that irradiates the optical cable with the modulated light, The laser beam irradiation unit varies the modulation parameter or the intensity modulation frequency as the modulation parameter depending on the color of the outer sheath of the optical cable. The optical cable monitoring device according to feature 1.

12. The optical cable comprises an optical fiber bundle and an outer sheath covering the optical fiber bundle. The detection unit has a lock-in thermography system that scans along the monitored section of the optical cable, The lock-in thermography system varies the imaging parameters or the frame rate as an imaging parameter depending on the color of the outer sheath of the optical cable. The optical cable monitoring device according to feature 1.

13. Steps to obtain the monitored section of the optical cable, The steps include: heating the monitored section of the optical cable by irradiating it with modulated light based on modulation parameters; The steps include detecting the temperature of the monitored section of the optical cable by photographing the monitored section of the optical cable with imaging parameters based on the modulation parameters, The steps include: obtaining an abnormal location in the monitored section of the optical cable based on the temperature detection result of the monitored section of the optical cable; A method for monitoring optical cables, characterized by having the following features.

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