JP3010429B2 - Optical fiber monitoring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inputting an optical pulse to an optical fiber, receiving the light returning from the optical fiber with a photodetector, and detecting a failure of the optical fiber based on an output signal of the photodetector. In the optical fiber monitoring device to detect,
The present invention relates to a technique for improving the monitoring efficiency.

[0002]

2. Description of the Related Art When detecting a fault in an optical fiber, an operator connects an optical pulse test apparatus to the optical fiber which is considered to have the fault and checks the position of the fault.

FIG. 7 shows a configuration of an optical pulse test apparatus 10 for testing an optical fiber. The optical pulse test apparatus 10 includes an optical pulse generator 11 that outputs pulsed light, a light receiver 12, and an optical pulse output from the optical pulse generator 11. An optical coupler 14 for entering light into the fiber 1 and guiding light (backscattered light or Fresnel reflected light) returning from the optical fiber 1 to the optical connector 13 side to the light receiver 12;
The output signal of the light receiver 12 obtained by the incidence of the light pulse a plurality of times is averaged, and the averaged signal is, for example, as shown in FIG.
Display on the screen on the time axis (distance axis). The operator finds a loss increasing position or a disconnection position of the optical fiber from the waveform displayed on the screen, and carries out the recovery work.

[0004]

However, if the above-described optical pulse test apparatus is used every time a failure occurs, it takes a long time to recover from the failure.

[0005] For this reason, it is conceivable to provide a monitoring system that automatically measures the optical fiber and informs a manager of the measurement result. When such a monitoring system is configured, it is necessary to return from the optical fiber. In order to find a far-end failure point where the output signal level when receiving the incoming light is close to the noise level, the number of times of averaging the output signal of the light receiver must be increased to, for example, several hundred. Therefore, the measurement time per one optical fiber to be monitored becomes very long, and monitoring cannot be performed efficiently.

In order to solve this problem, it is conceivable that the width of the light pulse is widened and the level of the output signal of the photodetector is increased to reduce the number of times of averaging. If a pulse is used, the width of the mouth dead zone also increases, and it becomes impossible to accurately find a fault occurrence position near the mouth of the optical fiber.

[0007] It is an object of the present invention to solve this problem and to provide an optical fiber monitoring device capable of efficiently and accurately monitoring an optical fiber.

[0008]

According to a first aspect of the present invention, there is provided an optical fiber monitoring apparatus for generating an optical pulse, wherein the optical pulse is formed so as to be variable in width. A pulse generator (24), a photodetector (25) for receiving light returning from the optical fiber to be monitored to which the optical pulse of the optical pulse generator is incident, and an optical fiber from the optical pulse generator to the optical fiber to be monitored. Optical fiber measuring means (27) for injecting a plurality of light pulses and averaging the output signal of the light receiver until a predetermined time elapses from the light pulse incident timing of each time to obtain measurement data of the optical fiber to be monitored. , 30), and first initial data in which measurement data of the monitored optical fiber previously measured by the optical fiber measuring means using the wide light pulse is stored in advance as first initial data. Memory (31c-31e) and a second initial data memory which previously stores, as second initial data, measurement data of the optical fiber to be monitored previously measured by the optical fiber measuring means with the narrow optical pulse. (31g-31i); wide pulse designating means (30) for causing the optical fiber measuring means to measure the optical fiber to be monitored by the wide optical pulse for monitoring; and wherein the optical fiber measuring means comprises the wide optical pulse. First comparing means (36, 37) for comparing measurement data obtained when the monitoring target optical fiber is newly measured with the first initial data, according to a comparison result of the first comparing means. A narrow pulse designating means (30) for causing the optical fiber measuring means to measure a mouth portion of the optical fiber to be monitored by the narrow optical pulse; A second comparing means (38) for comparing measurement data obtained when the fiber measuring means newly measures the monitored optical fiber with the narrow optical pulse and the second initial data. .

According to a second aspect of the present invention, there is provided an optical fiber monitoring apparatus for generating an optical pulse, wherein the optical pulse generator is formed so that the width of the optical pulse can be varied. An optical receiver (25) for receiving the light returning from the optical fiber to be monitored, into which the optical pulse of the device has been incident; and an optical pulse from the optical pulse generator to the optical fiber to be monitored a plurality of times. An optical fiber measuring means (27, 30) for averaging the output signal of the light receiver until a predetermined time elapses from the incident timing to obtain measurement data of the monitored optical fiber; A first initial data memory (31c to 31c) in which measurement data of the monitored optical fiber measured in the past by a wide optical pulse is stored in advance as first initial data.
e) and a second initial data memory (31g to 31i) in which the measurement data of the monitored optical fiber previously measured by the optical fiber measuring means with the narrow optical pulse is stored in advance as second initial data. ) And a wide pulse designating means (3) for causing the optical fiber measuring means to measure the monitored optical fiber by the wide optical pulse for monitoring.
0) and first comparison means (36, 36) for comparing measurement data obtained when the optical fiber measurement means newly measures the monitored optical fiber with the wide light pulse and the first initial data. 37), a narrow pulse designating means (30) for causing the optical fiber measuring means to measure the mouth portion of the optical fiber to be monitored by the narrow optical pulse for monitoring, and the optical fiber measuring means comprises: Second comparing means (38) for comparing measurement data obtained when newly measuring the mouth portion of the optical fiber to be monitored with the light pulse of the above and the second initial data, wherein the first comparison It is configured to detect an abnormality of the monitored optical fiber based on the comparison result of the means and the second comparing means.

According to a third aspect of the present invention, there is provided the optical fiber monitoring device according to the first or second aspect, wherein the optical fiber measuring means includes a wide optical pulse designated by the wide pulse designating means. When the measurement is instructed, the averaging process is performed on the output signal corresponding to the specific position of the optical fiber to be monitored among the output signals of the light receiver until a predetermined time elapses from the light pulse incident timing. The processing result is obtained as measurement data of the optical fiber to be monitored.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an optical fiber monitoring device 20 according to one embodiment. This optical fiber monitoring device 20 forms a system for centrally monitoring a large number of optical fibers together with a center device 42 connected via the telephone line 5, and automatically monitors and measures a plurality of optical fibers. Then, the occurrence of a failure such as a disconnection accident or deterioration is detected and sent to the center side.

The optical fiber monitoring device 20 is provided with three connectors 20a, 20b and 20c for connecting the optical fiber 1 to be monitored from outside. Each of the connectors 20a to 20c is connected to one to four optical switches 21. The connectors 20a to 20c are each connected to one of the fibers that are not used for communication, out of one optical cable in which a plurality of optical fibers are bundled, as monitored optical fibers.

The optical switch 21 has four connection terminals 21a.
To 21d and one switching terminal 21e, and the connection terminals 21a to 21d are received by a switching signal from a measurement control unit 30 described later.
One of the switches 21d is optically connected to the switching terminal 21e. The three connection terminals 21a to 21c of the optical switch 21 are fiber-connected to the connectors 20a to 20c, respectively, and the connection terminal 21d has a predetermined length (for example, 50 m) provided in the device with a known attenuation characteristic or the like. One end of the reference optical fiber 22 is connected.

A switching terminal 21 e of the optical switch 21 is connected to an optical pulse generator 24 and a photodetector 25 via an optical coupler 23.
It is connected to the.

The optical coupler 23 converts an optical pulse output from the optical pulse generator 24 into a switching terminal 21 e of the optical switch 21.
And the light returning from the switching terminal 21e to the optical coupler 23 is incident on the light receiver 25.

The light pulse generator 24 controls the width of the light pulse to be, for example, 20 nS under the control of the measurement control unit 30 described later.
It is configured to be variable in the range of ２０20 μS.
The light receiver 25 converts the signal according to the intensity of the received light into an A / D signal.
Output to the converter 26. The A / D converter 26 includes the light receiving device 2
5 is converted into a digital signal and the averaging circuit 2
7 is output.

The averaging circuit 27 outputs a series of output signal data output from the photodetector 25 each time an optical pulse is output to one optical fiber connected to the optical switch 21 a predetermined number of times. Are averaged by the predetermined number M,
The averaged result is output to the measurement controller 30. That is, a series of output signal data output from the A / D converter 26 is stored in an internal memory (not shown) in the order of addresses from when the first light pulse is output until a predetermined time elapses, and the second time. The output signal data of the light receiver corresponding to the light pulse is added to the previous output signal data stored in the internal memory and stored. This operation is performed a predetermined number of times M, and the respective data accumulated and stored in the internal memory are respectively averaged to 1 / M, and the averaged output signal data is output to the measurement control unit 30 as the measurement data of the optical fiber. I do.

The measurement controller 30 forms the first and second optical fiber measuring means of this embodiment together with the averaging circuit 27, controls the switching of the optical switch 21, and controls the optical pulse generator 24.
Of the optical pulse, and the designation of the pulse width and the number of times of averaging by the averaging circuit 27, and periodically measures each optical fiber connected to each connection terminal of the optical switch 21. The output signal data of the light receiver 25 averaged in 27 is stored in the memory 31 as measurement data. This measurement is performed according to, for example, schedule information received from the center device 42.

The memory 31 stores, as initial data R, measurement data of the entire length of the reference optical fiber 22 measured with an optical pulse having a narrow pulse width Ha (for example, 20 nS) at the time of manufacture of the monitoring device. A fiber initial data memory 31a, a reference fiber measurement memory 31b for storing measurement data Fr of the entire length of the reference optical fiber 22 newly measured with a narrow pulse width Ha in order to obtain a drift amount, and each monitored optical fiber 1 Monitoring fiber initial data memory in which the measurement data of each monitored optical fiber 1 measured by the optical pulse having the wide pulse width Hb (for example, 20 μS) at the time of connection (at the time of installation) is stored as initial data Pa, Pb, and Pc, respectively. 31c to 31e, and measurement data of the monitored optical fiber 1 measured with a newly wide pulse width Hb for monitoring. The monitoring fiber measurement memory 31f for storing the data F, and the measured data of each monitored optical fiber 1 measured with the optical pulse having the pulse width Ha when each monitored optical fiber 1 is connected (during installation) are initial data. Monitoring fiber initial data memories 31g to 31i stored as Qa, Qb, and Qc, and a monitoring fiber for storing measurement data F 'of the monitoring target optical fiber 1 newly measured with a narrow pulse width Ha for monitoring. A measurement memory 31j is provided.

The measurement control unit 30 is configured so that an arbitrary optical fiber can be measured and its measurement data can be stored by an operation unit (not shown). The data is stored in each initial data memory by this measurement.

The determining unit 32 includes a first calculating unit 33 and a second calculating unit 33.
Calculation means 34, third calculation means 35, determination means 36,
It comprises a first waveform comparing means 37 and a second waveform comparing means 38, and determines the presence or absence of disconnection or deterioration of each monitored optical fiber based on the data stored in the memory 31.

The first calculating means 33 obtains a level difference α between the measurement data Fr stored in the reference fiber measurement memory 31b and the initial data R stored in the reference fiber initial data memory 31a as a drift amount. This level difference is the difference between the data stored in the two memories 31a and 31b and having the same address and the address corresponding to the position where there is no influence of the connector reflection of the reference optical fiber 22.

The second calculating means 34 stores the measurement data F of the optical fiber 1 to be monitored measured for monitoring and stored in the monitoring fiber measurement memory 31f and the monitoring fiber initial data memories 31c to 31e. The level difference β between the initial data Pa to Pc and the initial data corresponding to the monitored optical fiber 1 is obtained. This level difference is a difference between the initial data of the address corresponding to the far end (or a position near the far end) of each monitored optical fiber 1 and the measured data. Note that the level differences α and β may be not only the level difference of a specific address but also the average value of the level differences of a plurality of addresses.

The third calculating means 35 is provided with the second calculating means 3
From the level difference β obtained by the first calculation means 33
Is subtracted, and the result of the subtraction is output as a true level difference γ.

The determining means 36 determines whether or not the level difference γ obtained by the third calculating means 35 is within an allowable range of ± L. If the level difference γ is within the allowable range, the monitored optical fiber 1 measured is The measurement control unit 30 is informed that there is no abnormality, and if it is outside the allowable range, the first waveform comparison unit 37 is informed that a failure has occurred in the measured optical fiber 1 to be monitored.

The first waveform comparing means 37 determines that a fault has occurred in the measured optical fiber 1 to be monitored.
Is determined, the measurement data F of the monitoring target optical fiber 1 stored in the monitoring fiber measurement memory 31f,
Of the initial data stored in each of the monitoring fiber initial data memories 31c to 31e, the waveform is compared with the initial data corresponding to the monitored optical fiber 1 to detect a fault occurrence position.

That is, the difference between the measurement data F of the monitored optical fiber 1 stored in the monitoring fiber measurement memory 31f and the initial data (any of Pa to Pc) of the monitoring fiber initial data memory is obtained for each address. Then, an address position where the deviation data exceeds the allowable range α ± L is determined, and a fault occurrence position is determined from the address position. If the fault occurrence position is within the dead zone of the mouth and cannot be specified, the information is notified to the measurement control unit 30, and the measurement control unit 30 transmits the vicinity of the mouth with a narrow pulse width Ha to the monitored optical fiber 1. To re-measure.

The second waveform comparing means 38 measures the measured data F 'near the mouth of the monitored optical fiber 1 measured by the narrow pulse width Ha and stored in the monitored fiber measurement data memory 31j, and the monitored light. Monitoring target fiber initial data memory corresponding to fiber 1 (31g to 3g)
1i) is obtained for each address, an address position where the deviation data exceeds the allowable range α ± L is obtained, and a fault occurrence position is obtained from this address position.

On the other hand, the communication control unit 40 sends the judgment result of the judgment unit 32 to the center device 42 via the modem device 41, and sets the schedule information sent from the center device 42 to the measurement control unit 30. I do.

The center device 42 is connected to a plurality of optical fiber monitoring devices 20 by telephone lines, receives fault occurrence position information and the like from the optical fiber monitoring devices 20, and instructs an appropriate organization to perform a recovery process. I do.

FIG. 2 is a flowchart showing an example of a processing procedure of the measurement control unit 30 and the judgment unit 32 of the optical fiber monitoring device 20. Hereinafter, the operation of the optical fiber monitoring device 20 will be described according to this flowchart.

In advance, the reference fiber initial data memory 31
a stores the initial data of R in FIG. 3, and the monitoring fiber initial data memories 31c to 31e store, for example, P in FIG.
It is assumed that initial data from the mouth to the far end obtained by measuring the optical fiber 1 to be monitored with a light pulse having a wide width Hb as shown in FIG. Further, the monitoring fiber initial data memories 31g to 31i include, for example, FIG.
It is assumed that initial data of the mouth portion obtained by measuring the monitoring target optical fiber 1 with a light pulse having a narrow width Ha is stored as in Qa.

First, the optical switch 21 is connected to the reference optical fiber 22, the narrow pulse width Ha is specified for the optical pulse generator 24, and the averaging number Ma is specified for the averaging circuit 27. Then, the total length of the reference optical fiber 22 is measured (S1 to S1).
3). The number of times of averaging Ma (number of times of pulse incidence) is set to a small number (for example, about 25 times) because the length of the reference optical fiber 22 is short and the level of the reflection component is much higher than the noise component. Measurement is completed in a short time.

When the measurement data shown by Fr in FIG. 3 is obtained by this measurement, the measurement data Fr is stored in the reference fiber measurement memory 31b (S4).

Next, the data at the specific address position A of the measurement data Fr and the reference fiber initial data memory 3
The level difference α between the initial data R and the data at the address position A stored in 1a is obtained as the drift amount (S5). The reference optical fiber 2 accommodated in the device
Since the secular change of the characteristic No. 2 is negligibly small, this drift amount is caused by a change in the level of the output light of the optical pulse generator 24, a change in the light receiving sensitivity of the light receiver 25, or a change in the loss of the optical switch 21. And the effect is
This is also included in the measurement result of each monitored optical fiber 1.

After the drift amount of the device is obtained in this manner, the optical switch 21 is connected to the connection terminal 20a, and a wide pulse width Hb is designated for the optical pulse generator 24, and the averaging circuit is used. After the averaging count Mb is designated for 27, the entire length of the monitored optical fiber 1 connected to the connection terminal 20a is measured (S6 to S8).

In this measurement, since the light pulse having the wide pulse width Hb is used, the width of the dead zone at the mouth is widened, but the level of the reflected light of each monitored optical fiber 1 is increased as a whole, so that the average The number of conversions Mb is, for example, about 50, and data from which noise components have been sufficiently removed can be obtained. The number of times Mb can be reduced to about 1/3 of the number of times of averaging with the pulse width normally used in the conventional optical pulse test apparatus, so that the measurement time can be significantly reduced.

When the measurement data shown in FIG. 4F is obtained by this measurement, the measurement data F is stored in the monitoring fiber measurement memory 31f (S9).

Next, the data at the far end address position B of the measurement data F and the reference fiber initial data memory 31
The difference between the initial data R stored at the address a and the data at the address position B is determined as the level difference β, and the level difference α is subtracted from the level difference β to obtain the monitored optical fiber 1.
The true level difference γ due to the characteristic change of itself is calculated (S
10, S11).

Then, it is determined whether or not this level difference γ exceeds the allowable range ± L.
Monitoring target optical fiber 1 connected to connection terminal 20a
It is determined that there is no abnormality, and the measurement returns to the wide pulse width Hb for the next monitored optical fiber 1 (S12 to S1).
4).

If the level difference γ exceeds the allowable range ± L, the difference between the measured data F and the initial data Pa of the monitoring fiber initial data memory 31c for each address is obtained. An address position exceeding the allowable range α ± L is detected (S15 to S17).

For example, as shown in FIG.
If the deviation data D between the data and the initial data P suddenly exceeds the allowable range α ± L at the address C that is far from the address Z corresponding to the end of the lip dead zone, a disconnection accident occurs at the position corresponding to the address C. Is determined to have occurred, and if the data changes slowly and exceeds the allowable range α ± L at the address C ′ as in the case of the deviation data D ′, there is deterioration near the position corresponding to the address C ′. Is determined. When the fault occurrence position is away from the dead zone as described above, the position information is sent to the center device 42 (S
18).

If the address Z corresponding to the end of the dead zone exceeds the allowable range α ± L as in the deviation data D ″, the loss is increased in the dead zone, and the position is specified. After the narrow pulse width Ha is specified for the optical pulse generator 24 and the averaging count Mc is specified for the averaging circuit 27, the vicinity of the mouth of the monitored optical fiber 1 connected to the connection terminal 20a is determined. Is measured, and measurement data F ′ obtained by the measurement is obtained.
(See FIG. 5) is stored in the monitoring fiber measurement data memory 31j (S19 to S21). This averaging count Mc
Since the measurement target is a short range near the mouth and the level of the reflected light is high, sufficiently stable data can be obtained, for example, about 50 times. Since the address range to be averaged is narrow, the averaging operation is completed in a short time.

Then, in the same manner as described above, the difference between each address of the measured data F 'and the initial data Qa of the monitoring fiber initial data memory 31g is obtained, and the address whose deviation data exceeds the allowable range γ ± L is detected. Then, the fault location corresponding to the detected address is sent to the center device 42 (S22, S23).

In addition to the procedure described above, for example, after measuring a reference fiber, measurement of all monitored optical fibers with a wide pulse width and determination of the presence / absence of a fault are performed, and then an abnormal fiber is measured. Or a re-measurement using a narrow pulse may be performed.

As described above, the optical fiber monitoring apparatus 20 of this embodiment shortens the averaging process time by giving a wide light pulse to increase the level of light returning from the far end of the monitored optical fiber. However, the speed of determining the presence / absence of abnormalities in a plurality of optical fibers is increased, and for the monitored optical fibers having abnormalities in the mouth, the data obtained by narrow-width light pulses is compared with the initial data to determine the location of the failure. Since the identification is performed, even if the number of monitored optical fibers is large, monitoring can be performed very efficiently.

In the above-described embodiment, the drift amount is obtained by measuring the reference fiber, and the optical fiber to be monitored is determined based on the measurement data obtained by correcting the drift amount. Even if there is an error, the monitoring target optical fiber can be accurately monitored without erroneously determining that the optical fiber is abnormal.

[0048]

[Other Embodiments] In the above-described embodiment, an abnormality of an optical fiber is determined by comparing data measured with a wide optical pulse with initial data, and a narrow optical pulse is detected only when there is an abnormality in the mouth dead zone. The mouth portion was re-measured at the same time, but the full length measurement using a wide light pulse and the mouth portion measurement using a narrow light pulse were performed each time for one monitored optical fiber, and the measured data and the initial data were compared. An abnormality of the monitored optical fiber may be detected based on the comparison result. In this case, the monitoring efficiency is lower than that of the above-described embodiment, but compared to the case where the entire length of the optical fiber to be monitored is measured with a narrow optical pulse, the monitoring efficiency is sufficiently efficient, and the oversight of the abnormality at the mouth portion is small. I'm done.

In the above embodiment, the optical fiber to be monitored is measured over the entire length by a wide optical pulse. However, the output signal data of a specific position, for example, the optical receiver at only the far end is taken in and averaged. Alternatively, the presence or absence of a failure in the monitored optical fiber may be detected only by comparing the measured data at the far end with the initial data. By doing so, the time for the averaging operation can be greatly reduced, the monitoring efficiency can be further improved, and the data stored in each of the monitored fiber initial memories 31c to 31e is also the data at the specific position. And save a lot of memory space.

Further, the optical fiber monitoring device of the above embodiment is configured to measure the monitoring target optical fiber and determine the abnormality, and to send the result to the center device. However, a display for displaying the monitoring result is provided. The present invention can be similarly applied to a single-use optical fiber monitoring device having a unit.

In the above embodiment, the reference optical fiber is provided independently for the monitored optical fiber, and the measurement for the reference optical fiber and the measurement for the monitored optical fiber are performed at different timings. Connect the fiber to the monitored optical fiber in series,
The measurement of the reference optical fiber and the monitored optical fiber can be performed simultaneously.

[0052]

As described above, the optical fiber monitoring apparatus according to the first aspect of the present invention measures the optical fiber to be monitored with a wide light pulse, and when it is determined that the mouth portion is abnormal in this measurement. The mouth part is measured with a narrow light pulse. The optical fiber monitoring apparatus according to claim 2 of the present invention measures the optical fiber to be monitored with a wide light pulse, and measures the mouth portion with a narrow light pulse. Abnormality of the monitored optical fiber is detected based on the comparison result. As a result, a high-level output signal can be obtained from the photodetector even at the far end, and the number of averaging processes can be significantly reduced. In addition, since only the mouth portion is measured with a narrow optical pulse, it is efficient. Monitoring can be performed.

Further, when the optical fiber measuring means performs measurement using a wide optical pulse, it corresponds to the specific position of the optical fiber to be monitored among the output signals of the optical receiver until a predetermined time elapses from the optical pulse incident timing. Since the averaging process is performed on the output signal to be obtained and the processing result is obtained as the measurement data of the optical fiber to be monitored, the time for the averaging operation can be greatly reduced, and the monitoring efficiency is further improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a processing procedure according to an embodiment;

FIG. 3 is a diagram illustrating an example of a measurement result of a reference optical fiber according to an embodiment.

FIG. 4 is a diagram illustrating a measurement result of an optical fiber to be monitored by a wide optical pulse according to an embodiment;

FIG. 5 is a diagram showing a measurement result of an optical fiber to be monitored by a narrow optical pulse according to one embodiment;

FIG. 6 is a diagram illustrating an example of deviation data according to an embodiment;

FIG. 7 is a diagram showing a configuration of a conventional device.

FIG. 8 is a diagram showing measurement results of a conventional device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 monitored optical fiber 20 optical fiber monitoring device 21 optical switch 22 reference optical fiber 24 optical pulse generator 25 optical receiver 30 measurement control unit 31 memory 33 first arithmetic means 34 second arithmetic means 35 third arithmetic means 36 Determination means 37 first waveform comparison means 38 second waveform comparison means

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeo Hori 5-10-27 Minamiazabu, Minato-ku, Tokyo Inside Anritsu Corporation (56) References JP-A-4-132930 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) H04B 10/00 G01M 11/00 H04B 17/00

Claims (3)

(57) [Claims] An optical pulse generator configured to generate an optical pulse and to be able to change the width of the optical pulse, and an optical fiber to be monitored to which the optical pulse of the optical pulse generator is incident. A photodetector (25) for receiving the returning light; and an optical pulse from the optical pulse generator to the optical fiber to be monitored a plurality of times, until a predetermined time elapses from the timing of each optical pulse incidence. Optical fiber measuring means (27, 30) for averaging the output signal of the optical fiber to obtain measurement data of the optical fiber to be monitored, and the optical fiber to be monitored previously measured by the optical fiber measuring means by the wide light pulse A first initial data memory (31c-31e) in which the measured data of the optical fiber is stored in advance as first initial data; The measured data of the optical fiber to be monitored
A second initial data memory (31g-31i) pre-stored as initial data of a wide pulse specifying means (31g-31i) for causing the optical fiber measuring means to measure the optical fiber to be monitored by the wide optical pulse for monitoring. 30) and first comparing means (36, 36) for comparing measurement data obtained when the optical fiber measuring means newly measures the monitored optical fiber with the wide light pulse and the first initial data. 37) and according to the comparison result of the first comparing means, the narrow pulse designating means (3) which causes the optical fiber measuring means to measure the mouth portion of the monitored optical fiber with the narrow optical pulse.
0), and second comparing means (38) for comparing measurement data obtained when the optical fiber measuring means newly measures the monitored optical fiber with the narrow optical pulse and the second initial data. ) And an optical fiber monitoring device comprising: 2. An optical pulse generator (24) formed to generate an optical pulse and to be able to change the width of the optical pulse, and a monitoring target optical fiber into which the optical pulse of the optical pulse generator is incident. A photodetector (25) for receiving the returning light; and an optical pulse from the optical pulse generator to the optical fiber to be monitored a plurality of times, until a predetermined time elapses from the timing of each optical pulse incidence. Optical fiber measuring means (27, 30) for averaging the output signal of the optical fiber to obtain measurement data of the optical fiber to be monitored, and the optical fiber to be monitored previously measured by the optical fiber measuring means by the wide light pulse A first initial data memory (31c-31e) in which the measured data of the optical fiber is stored in advance as first initial data; The measured data of the optical fiber to be monitored
A second initial data memory (31g-31i) pre-stored as initial data of a wide pulse specifying means (31g-31i) for causing the optical fiber measuring means to measure the optical fiber to be monitored by the wide optical pulse for monitoring. 30) and first comparing means (36, 36) for comparing measurement data obtained when the optical fiber measuring means newly measures the monitored optical fiber with the wide light pulse and the first initial data. 37); a narrow pulse specifying means (30) for causing the optical fiber measuring means to measure the mouth portion of the optical fiber to be monitored by the narrow light pulse for monitoring; and A second comparison of the measurement data obtained when the mouth portion of the optical fiber to be monitored is newly measured by the optical pulse with the second initial data. An optical fiber monitoring device comprising: a comparing unit (38), and detecting an abnormality of the monitored optical fiber based on a comparison result of the first comparing unit and the second comparing unit. 3. The optical fiber measuring means, wherein when the wide pulse designating means instructs measurement using a wide light pulse, the optical fiber measuring means outputs the light receiving device output signal from the light receiver until a predetermined time elapses from the light pulse incident timing. And an averaging process for an output signal corresponding to a specific position of the monitored optical fiber, and obtaining the processing result as measurement data of the monitored optical fiber. Item 3. The optical fiber monitoring device according to Item 2.