JP5618236B2 - Fiber fuse remote sensing device - Google Patents

Description

  The present invention is a detection device for a fiber fuse generated when high intensity light is transmitted through an optical fiber, and in particular, a fiber fuse remote detection based on an optical time domain reflectometry (OTDR). It relates to the device.

  There is a tendency that the optical power propagating through the optical fiber tends to increase even in communication applications due to the extension of the non-relay distance and the increase in the number of multiplexing by the wavelength division multiplexing (WDM) technology, and eventually the average power may reach several W. Conceivable. There are also attempts to transmit power over optical fibers.

When high-intensity light propagates through an optical fiber, it is known that a destruction phenomenon of the optical fiber called a “fiber fuse” occurs due to fine dust in the optical transmission path or the optical connector portion. Specifically, for example, the dust is ignited at the dust portion and the core of the optical fiber is melted, and the melting phenomenon proceeds toward the light source. The average intensity of the reflected light suddenly increases with time. When fiber fuses suddenly occur, cavities are periodically formed in the optical fiber, and these cavities provide intensity modulation to the return light. For example, if the velocity of the fiber fuse is v (m / s) and the pitch of the cavity of the periodic structure generated in the optical fiber is p (m), the time required to advance by one pitch is p / v. Due to the progress of the fiber fuse in the light source direction, the return light that is reflected and propagates in the opposite direction at the location where the fiber fuse occurs is subjected to intensity modulation, and the basic repetition frequency f ₀ of the intensity modulation is f ₀ = v / p.

For example, in a fiber fuse experiment using a single-mode optical fiber SMF-28 manufactured by Corning, Inc. in the United States, when a 2.75 W laser beam is incident, the traveling speed v of the fiber fuse is 0.46 m / s. The pitch is 15 μm, and the basic modulation frequency f ₀ obtained from the above equation is 31 kHz. Such intensity modulation is considered to increase the noise level.

  The destruction by the fiber fuse proceeds unless the optical power density in the core falls below a certain value. The closer to the light source, the greater the optical power. Therefore, if the fiber fuse phenomenon is left unattended, it will eventually reach the light source and damage the light source.

  Abnormalities in the optical fiber transmission line are usually observed with an OTDR device. This is to observe dissipation due to Rayleigh scattering when light propagates through an optical fiber transmission line, and dissipation due to reflected light traveling in the reverse direction in the incident direction due to reflection from the connection surface of the connector. A short optical pulse of nanoseconds is input as an input pulse (Input Pulse) to the optical transmission line and the time distribution of the intensity of the returned light pulse (Reflected Pulse) from the fiber line is detected. The intensity of scattered light and the reflection intensity from the reflection end can be measured. These reflected lights occurring in the transmission line can be easily measured using the OTDR method, and OTDR devices for this purpose are commercially available from many manufacturers.

  FIG. 14 shows a typical block diagram (Block Diagram) of OTDR. Here, an electric pulse from a pulse generator is applied to a semiconductor laser to generate an optical pulse with a width of nanoseconds (ns) to several tens of ns, and the optical pulse is input to a transmission line to be measured by an optical fiber through an optical coupler. It has a structure. Return light from the transmission path is detected by a photodetector. After amplification, the electrical signal output from the photodetector is sampled and converted from an analog signal to a digital signal by a signal from a time base controller. In addition, the intensity of the reflected light obtained from each pulse is averaged over time, and finally displayed on the display.

  FIG. 15 shows a typical example of an OTDR trace in which backward Rayleigh scattered light is logarithmically displayed. In general, it attenuates exponentially according to the distance, but it can be seen that there is strong reflection if there are a connector, a fusion joint, a bent portion, a mechanical splice, etc. on the optical path. It can also be seen that the reflection from the fiber open end usually has the maximum peak and falls sharply to the noise level at that end. Here, if the distance from the OTDR to an arbitrary reflection point is z, and the time from when an optical pulse is input until it is reflected by the reflection point and returning is t, z = t × (c / 2 )

  Such an OTDR apparatus is used for system maintenance such as a PON (Passive Optical Network) in addition to using a reflection distribution in a single fiber transmission line for measurement. As a result, it is possible to detect a case where an abnormality such as a disconnection occurs in the transmission path during optical communication and to take countermeasures.

For example, if there is a change in the OTDR trace measured in the time from T = T _o to T = T _o + Δ (Δ is sufficiently small), it is detected that an abnormality has occurred in that time zone. Become. Normally, when an abnormality occurs due to breakage or cutting in the middle of the transmission line, the location is fixed, and there is no temporal change in the display of OTDR. That is, a constant waveform is continuously displayed.

  Further, since the intensity of the light incident on the optical fiber decreases exponentially as described above, the fiber fuse as described above is usually generated near the light incident end. In the present invention, the occurrence of the fiber fuse phenomenon is detected by using an apparatus having the same configuration as that of the OTDR.

JP 2006-184264 A

  When a fiber fuse is generated in an optical fiber that transmits high-intensity laser light, in order to suppress damage to the optical fiber, it is possible to easily detect the occurrence and take measures such as interrupting laser light transmission as soon as possible. To.

  In general, a fiber fuse is a phenomenon that does not stop at the place of occurrence but proceeds toward the light source while breaking the fiber. Reflection occurs at the broken point, and the tip of the fiber fuse advances toward the light source at a constant speed as described above, so that the position of the reflection end also changes depending on time. The fiber fuse remote detection device of the present invention for suppressing damage caused by such a fiber fuse is a device that detects the occurrence of a fiber fuse phenomenon caused by the optical signal and issues an alarm when transmitting the optical signal through an optical fiber. Therefore, it has the following configuration.

  In other words, when transmitting an optical signal through an optical fiber, a device that detects the occurrence or occurrence of a fiber fuse caused by the optical signal and issues an alarm, the optical pulse generator and the optical pulse from the optical pulse generator Optical coupling means for incident on the optical fiber, branching means for branching the return light of the optical fiber by the generated fiber fuse, wave wave means for selecting the return light of the optical pulse from the return light, and wave wave means Conversion means for photoelectrically converting the output light, measurement means for measuring the output of the conversion means as a function of time, signal processing means for finding a feature point moving in one direction in the output of the measurement means, and the feature point Alarm means for issuing an alarm signal when the message is found. When the above feature points occur, an alarm signal is output. Using this alarm signal, for example, the transmission of the optical signal by the optical fiber is interrupted to suppress the optical fiber from being damaged by the fiber fuse. As the branching means, a directional optical coupler can be used.

  It is desirable that the optical coupling means is incident using a directional optical coupler so that light from the optical pulse generator is propagated in a direction in which the generation of the fiber fuse is monitored.

  The optical coupling means may use a wavelength division multiple coupling element so that the light from the optical pulse generator is incident so as to propagate in the direction in which the generation of the fiber fuse is monitored.

  Further, the signal processing means observes the movement of the peak location of the light reflection intensity at the time immediately before the light intensity suddenly decreases at the output of the measuring means. This is because when the fiber fuse is generated, the transmission optical fiber is cut there, light is reflected at the cut portion, and the reflected light at the point ahead is lost.

  The signal processing means has a function of averaging the output of the converting means over a predetermined time, and the light at the time immediately before the light intensity sharply decreases in the averaged output of the measuring means. It is also possible to observe the broadening of the intensity peak. This is because if the moving peak is averaged over a sufficiently long time, the width of the peak apparently increases.

  Since the tip of the fiber fuse advances toward the light source at a constant speed as described above, for example, when two optical pulses are transmitted, the optical path length is in the case of the optical pulse after the previous optical pulse. short. For this reason, the time interval between the two pulses reflected at the end of the optical fiber where destruction by the fiber fuse is proceeding becomes shorter than the initial one. Therefore, the signal processing means may detect a reduction in pulse interval in the pulse train included in the return light.

  As described above, it is known that the method for detecting the shortening of the pulse interval in the pulse train included in the return light is equivalent to detecting the frequency component of the pulse train. In this case, since the pulse interval becomes short, the frequency component with a higher frequency included in the pulse train included in the return light is detected.

  As in the above example, instead of transmitting two optical pulses, an optical pulse having a sufficiently long pulse length is transmitted, and the above two pulses are substituted at the rising and falling points. be able to. For this reason, the optical pulse generator generates and outputs a predetermined pulse train, and the signal processing means detects a reduction in time length of each pulse in the pulse train included in the return light. May be.

  In this fiber fuse remote detection device, when a fiber fuse is generated, it can be detected instantaneously from a remote location, and the location where it is generated, its movement, and the progress rate of the fiber fuse can be measured.

It is a block diagram which shows the example which applied the fiber fuse remote detection apparatus of this invention to the optical communication system. It is a block diagram which shows the structural example of a fiber fuse remote detection apparatus. During the fiber fuse progress is a schematic diagram showing an example trace of OTDR output measured at time t = t ₁ and t = t _2. FIG. 4 is a schematic diagram showing that the structure of the reflection end becomes wider than that of FIG. 3 by averaging the output of the OTDR longer than in the case of FIG. 3 while the fiber fuse is in progress. FIG. 6 is a diagram illustrating an example of the dependence of an OTDR trace on which a fiber fuse is in progress and the average time of measurement. It is a block diagram which shows the example of an apparatus structure for detecting generation | occurrence | production of a fiber fuse when the light from the light source (represented by a high output laser) which causes a fiber fuse and the optical pulse from OTDR use the same wavelength band. It is a figure which shows the example of an apparatus structure in case the wavelength of the pulsed light of OTDR overlaps with the ASE (Amplified Spontaneous Emission: Spontaneous emission light noise emitted from the optical amplifier) Raman spectrum from the light source (represented by a high output laser) that causes the fiber fuse. is there. 6 shows (a) an OTDR trace obtained when a fiber fuse is generated, and (b) an OTDR trace obtained with the high power laser turned off and the fiber fuse prevented. FIG. It is a figure which shows the OTDR trace obtained when the fuse was generated using the apparatus of FIG. FIG. 8 is a diagram illustrating an example of an OTDR output display when a fiber fuse is generated when the averaging time is set to (a) 10 s, (b) 20 s, and (c) 30 s in the apparatus configuration of FIG. 7. It is a block diagram which shows the example of a fiber fuse remote detection apparatus using the laser pulse light source and pulse interval measuring device which intermittently output two light pulses (double pulse) of a predetermined interval. It is a block diagram which shows the example of a fiber fuse remote detection apparatus using the laser pulse light source and pulse length measuring device which intermittently output the optical pulse with the length for the said double pulse. It is a block diagram which shows the example of a fiber fuse remote detection apparatus using the laser pulse light source and repetition frequency measuring device which intermittently output the optical pulse train which consists of the several (3 or more) optical pulse of predetermined spacing. It is a figure which shows the typical block diagram of OTDR. It is a figure which shows the typical example of the OTDR trace which displayed back Rayleigh scattered light logarithmically.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, devices having the same function or similar functions are denoted by the same reference numerals unless there is a special reason.

  FIG. 1 shows an example in which the fiber fuse remote sensing device 100 of the present invention is applied to an optical communication system. In this example, optical communication is performed between a line terminating unit (OCU) 110 on the exchange side and a line terminating unit (DSU: Digital Service Unit) 120 on the subscriber side. Transmission from the OCU 110 to the DSU 120 is performed by passing the light from the laser diode (LD) 112 of the optical transmitter (OT) 111 through a low-pass filter (long wavelength side transmission filter) 113 to remove the high frequency side component, and then the optical fiber 130. To the DSU 120. Connectors 131 and 132 provided in the middle of the transmission path of the optical fiber 130 are for connecting an optical fiber of an arbitrary length. The DSU 120 detects the transmitted optical signal by the photodiode 122 of the optical receiver 121 after being waved by the low-pass filter 123.

  The light from the fiber fuse remote detection device 100 installed on the OCU 110 side passes through a high-pass filter (short wavelength side transmission filter) 102, and first selects an optical path by a fiber selector 103. In the selected optical path, there is an optical coupler 105 through which the light enters the optical fiber 130. As the optical coupler 105, a directional optical coupler can be used. The light reflected by the occurrence of the fiber fuse on the optical path of the optical fiber 130 becomes return light, returns to the fiber selector 103 through the optical coupler 105, passes through the high pass filter 102, and enters the OTDR 101. The fiber fuse remote detection device 200 is applied to the transmission from the OT of the DSU 120 to the OR of the OCU 110, and has the same configuration as the fiber fuse remote detection device 100.

  As the fiber fuse remote detection device 100, for example, a device having the configuration shown in FIG. 2 can be used. This apparatus outputs light from a laser pulse light source 1 whose oscillation timing is controlled by a pulse generator 8 to an optical coupler 10 through an optical coupler 2. The return light from the optical fiber coupler 10 is separated by the optical coupler 2 and input to the photodetector 3. That is, the optical coupler 2 operates as an optical branching device. The detection light signal that is the output of the light detector 3 is amplified by the amplifier 4 and then input to the time measuring device 5 to measure the time when the detected light reciprocates. In this measurement, a signal from the time base unit (time reference control unit) 7 is used as the launch time. The time base unit receives a signal from the pulse generator 8 and sends a clock signal to the time measuring device 5. The determination unit 6 uses the data from the time measuring device 5 to find the reflection point. In particular, when approaching gradually and a reflection point due to a fiber fuse occurs, an alarm is displayed on the display 9 or an alarm is issued through the signal line 11. Such a determination unit 6 can be easily realized by using a computer that performs processing using a program having a determination criterion. Although not shown in the figure, this alarm is used to take measures to block or bypass the optical communication line.

FIG. 3 shows an example trace of the OTDR output measured at time t = t ₁ and t = t ₂ while the fiber fuse is in progress. As the fiber fuse progresses, the fiber end moves. Here, it was assumed that the average time τ _avg << (t ₂ -t ₁ ). At time t = t _1, the position of the fiber fuse when L _1, the time t = t ₂ in L _2, the speed v of the fiber fuse _{v = (L 1 -L 2)} / (t 2 -t 1 ). Here, the peak width of the reflection structure is determined by the pulse width and resolution of the OTDR device.

Further, when the OTDR is output while the fiber fuse is in progress, if the averaging is performed longer than in the case of FIG. 3, the structure of the reflection end shows a wider width than that of FIG. 3, as shown in FIG. FIG. 4 is a diagram showing an OTDR waveform when measurement is started at time t = t ₁ and averaging is performed during τ _avg . By averaging, a flat structure is seen in the reflected waveform from the fiber end, and the speed of the fiber fuse can be expressed as v = (L ₁ −L ₂ ) / τ _avg . As shown in the figure, the averaged trace is an accumulation of reflection averages from many places on the way.

  FIG. 5 is a diagram illustrating an example of the dependence of the OTDR trace on which the fiber fuse is in progress and the average time of measurement. The vertical axis is in decibels, and the drop caused by dividing by the number of samples when averaging is not very noticeable. It can also be seen that the width of the flat reflective structure from the fiber end on the OTDR trace depends on the reflection time.

  FIG. 6 is a diagram for detecting the occurrence of a fiber fuse when the light from a light source (represented by a high-power laser) that causes the fiber fuse and the light pulse from the OTDR use the same wavelength band (for example, 1.55 μm). It is a block diagram which shows the apparatus structural example. In this case, the light from the high-intensity excitation light source (1.55 μm) and the light having a wavelength of 1.54 μm from the OTDR are combined using an optical coupler and input to the optical fiber. Of the reflected light from the fiber to be measured, only the pulse component for OTDR is extracted using a bandpass filter and returned to the OTDR device. In order to avoid a dead zone due to reflection from the optical fiber connection terminal of the OTDR device, it is desirable to connect an SMF-28 fiber (for example, 650 m), which is a single mode optical fiber having an appropriate length.

  FIG. 7 shows an apparatus in which the wavelength of the pulse light of OTDR overlaps with an ASE (Amplified Spontaneous Emission: spontaneous emission light noise emitted from an optical amplifier) Raman spectrum from a light source (represented by a high-power laser) that causes a fiber fuse. A configuration example is shown. Here, the light source causing the fiber fuse is 1.48 μm, the wavelength of the OTDR pulse is 1.55 μm, and these lights are combined using a WDM (Wave-length Division Multiplexing) coupler, Input to the optical fiber generated by the fiber fuse. Here, it is possible to prevent the 1.48 μm wavelength component of the reflected light from returning to the OTDR by using the WDM coupler wave function. However, since a broadband Raman ASE component is generated in the optical fiber, it is necessary to suppress this component from entering the OTDR. For this purpose, a band pass filter is used.

  FIG. 8A shows an OTDR trace obtained when a fiber fuse is generated using the apparatus shown in FIG. Next, FIG. 8B shows an OTDR trace obtained with the high-power laser turned off and the fiber fuse prevented. In order to generate a fiber fuse as a trial when adjusting the apparatus, for example, the intensity of the excitation light input to the SMF (single mode optical fiber) is increased to about 3 W and a correction liquid is applied to the fiber exit end. be able to.

In these measurements, the averaging time of the OTDR device was set to 30 s. As described above, since the average time is long, a wide flat reflecting structure can be seen in FIG. Since the width (ΔL) of the reflecting structure is about 8.5 m and the average (τ _avg ) time is 30 s, the fuse speed (v = ΔL / τ _avg ) is calculated to be 0.43 m / s. When the determination unit 6 of FIG. 2 is configured by a computer and software, such calculation can be performed using the computer.

Also, OTDR traces obtained when a fuse is generated using the apparatus of FIG. 7 are shown in FIGS. 9 (a) to 9 (d). This figure shows that when a band-pass filter is introduced, (a) pump off (without excitation light), (b) pump on ((with excitation light), (c) during fuse (with fiber fuse), (d) This shows the OTDR waveform in the case of after fuse termination, where a flat reflection structure is seen in the OTDR waveform during the fiber fuse generation, and it is thin after the fiber fuse is stopped (measurement) A reflection structure with a width determined by the resolution of
FIGS. 9E to 9H show pump off (without excitation light), pump on (with excitation light), during fuse (with fiber fuse), after fuse when no bandpass filter is introduced. termination (shows the OTDR waveform after the fiber fuse is finished.
9 (f) and 9 (g), continuous light due to spontaneous Raman scattering is incident on the OTDR, the noise level increases, and the difference between the reflection structure of the fiber fuse and the noise level is increased. It turns out that it has decreased.

  As described above, the noise caused by Raman ASE can be reduced by using the bandpass filter in the apparatus configuration of FIG. 8, and therefore, it is possible to effectively detect the occurrence of the fiber fuse with a high probability. It is clear that it will be possible.

  Regarding the time dependency of averaging, in the apparatus configuration of FIG. 7, when the averaging time is (a) 10 s, (b) 20 s, and (c) 30 s, the OTDR output table when the fiber fuse is generated An example is shown in FIG. It can be easily seen that the width of the reflecting structure increases in proportion to the averaging time.

  In the case of the apparatus shown in FIG. 11, the laser pulse light source 1 intermittently outputs two light pulses (double pulses) at a predetermined interval. This double pulse is reflected at the fiber fuse point in the transmission optical fiber to become return light. This return light is first branched by the optical coupler 10 and then further branched by the optical coupler 2 to the photodetector 3. input. The detected optical signal that is the output of the photodetector 3 is amplified by the amplifier 4 and then input to the pulse interval measuring device 21. The pulse interval measuring device 21 measures the interval between double pulses and the time when the detected light reciprocates. In this measurement, a signal from the time base unit (that is, the time reference control unit) 7 is used as the launch time. The time base unit receives a signal from the pulse generator 8 and sends a clock signal to the pulse interval measuring device 21. In the determination unit 6, it is checked whether or not the data from the pulse interval measuring device 21 has a shortened pulse interval. If there is such a data, an alarm is issued via the signal line 11 and displayed. Display on the instrument 9. The interval between the double pulses is set such that the distance by which the fiber end is moved by the fiber fuse during the interval can be detected with a distance resolution determined by the pulse width.

  In the case of the apparatus shown in FIG. 12, the laser pulse light source 1 intermittently outputs an optical pulse having a length corresponding to the double pulse. This light pulse is reflected at the fiber fuse point in the transmission optical fiber to become return light. This return light is first branched by the optical coupler 10, then further branched by the optical coupler 2, and input to the photodetector 3. To do. The detected optical signal that is the output of the photodetector 3 is amplified by the amplifier 4 and then input to the pulse length measuring device 22. The pulse length measuring device 22 measures the length of the optical pulse and the time that the detected optical pulse reciprocates. In this measurement, a signal from the time base unit (that is, the time reference control unit) 7 is used as the launch time. The time base unit receives a signal from the pulse generator 8 and sends a clock signal to the pulse length measuring device 22. The determination unit 6 checks whether or not there is data whose pulse length is shortened in the data from the pulse interval measuring device 21, and when such data is present, an alarm is issued via the signal line 11 and a display device. 9 is displayed. The length of the optical pulse is set such that the distance that the fiber end moves by the fiber fuse can be detected during the optical pulse length with a distance resolution determined by the rise and fall of the pulse.

  In this case, the optical pulse is set to be long enough to be modulated by the fiber fuse, and by detecting this modulation in conjunction with the shortening of the pulse length, the fiber fuse can be generated more accurately. Can be detected.

  In the case of the apparatus shown in FIG. 13, the laser pulse light source 1 intermittently outputs an optical pulse train composed of a plurality (three or more) of optical pulses or a repetitive pulse train at a predetermined interval. This optical pulse train is reflected at the fiber fuse point in the optical fiber for transmission to become return light. This return light is first branched by the optical coupler 10 and then further branched by the optical coupler 2 to the photodetector 3. input. The detection optical signal that is the output of the photodetector 3 is amplified by the amplifier 4 and then input to the repetition frequency measuring device 23. The repetition frequency measuring device 23 measures the repetition frequency of the optical pulse train and measures the time that the detected optical pulse train reciprocates. In this case, the reflection by the fiber fuse uses the fact that the repetition frequency increases due to the interval between the optical pulse trains being narrowed. In this measurement, a signal from the time base unit (that is, the time reference control unit) 7 is used as the launch time. The time base unit receives a signal from the pulse generator 8 and sends a clock signal to the frequency measuring device 23 repeatedly. In the determination unit 6, the repetition frequency is increased by the data from the repetition frequency measuring device 23 (for the Doppler frequency, = 2 × fiber refractive index × fuse speed / wavelength). Some of the optical pulse trains and pulse intervals are shortened. If there is such an alarm, an alarm is issued via the signal line 11 and displayed on the display 9. The interval between the optical pulse trains is set so that the distance by which the fiber end moves by the fiber fuse during the interval can be detected with a distance resolution determined by the pulse width.

  The advantage of using a double pulse, an optical pulse having a length corresponding to the double pulse, or an optical pulse train as in the fifth, sixth, or seventh embodiment can be set independently. Even when a remote fiber fuse is detected, it is not necessary to relax the resolution in accordance with, for example, the restrictions of the display.

  By applying the present invention, it is possible to detect the occurrence of a fiber fuse even for an optical fiber for power transmission.

DESCRIPTION OF SYMBOLS 1 Laser pulse light source 2 Optical coupler 3 Optical detector 4 Amplifier 5 Time measuring device 6 Judgment part 7 Time base unit 8 Pulse generator 9 Display 10 Optical coupler 11 Signal line 21 Pulse interval measuring device 22 Pulse length measuring device 23 Repeat Frequency measuring instrument 100 Fiber fuse remote sensing device 101 OTDR
DESCRIPTION OF SYMBOLS 102 High pass filter 103 Fiber selector 104 Optical fiber 105 Optical coupler 110 Switch side line termination device 111 Optical transmitter 112 Laser diode 113 Low pass filter 120 Subscriber side line termination device 121 Optical receiver 122 Photo diode 123 Low pass filter 130 Optical fiber 131, 132 connector 200 Fiber fuse remote sensing device

Claims (8)

An apparatus for detecting the occurrence of a fiber fuse phenomenon caused by the optical signal and transmitting an alarm when transmitting the optical signal through an optical fiber,
An optical pulse generator;
Optical coupling means for making the optical pulse from the optical pulse generator incident on the optical fiber;
Branching means for branching the return light of the optical fiber;
A wave filtering means for selecting the return light of the light pulse from the return light;
A light detecting means for photoelectrically converting the light of the output of the wave-generating means;
Measuring means for measuring the output of the converting means as a function of time;
Determination means for determining occurrence of a fiber fuse phenomenon by finding a feature point that moves in one direction in the output of the measurement means;
An alarm means for issuing an alarm signal when the feature point is found;
With
A fiber fuse remote sensing device which emits an alarm signal when the above feature point occurs.   2. The fiber fuse remote sensing device according to claim 1, wherein the optical coupling means is a directional optical coupler.   2. The fiber fuse remote sensing device according to claim 1, wherein the optical coupling means is a wavelength division multiple coupling element.   4. The determination unit according to claim 1, wherein the determination unit is configured to determine a movement of a peak of the light intensity at a time immediately before the light intensity rapidly decreases in the output of the measurement unit. Fiber fuse remote sensing device according to.   The determination unit has a function of averaging the output of the conversion unit over a predetermined time, and the peak of the light intensity at the time immediately before the light intensity rapidly decreases in the averaged output of the measurement unit. The fiber fuse remote sensing device according to any one of claims 1 to 3, wherein an enlargement of the width is determined. The optical pulse generator generates and outputs a predetermined pulse train,
The fiber fuse remote detection device according to any one of claims 1 to 3, wherein the determination unit determines whether the pulse interval in the pulse train included in the return light is shortened. The optical pulse generator generates and outputs a predetermined pulse train,
The determination means compares the pulse train generated for the frequency component with the pulse train included in the return light, and determines whether or not there is a higher frequency component included in the pulse train included in the return light. The fiber fuse remote sensing device according to any one of claims 1, 2, 3 and 6. The optical pulse generator generates and outputs a predetermined pulse train,
4. The fiber fuse remote detection device according to claim 1, wherein the determination unit determines whether the time length of each pulse in the pulse train included in the return light is shortened. 5. .

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