JP2006033442A - System and method for monitoring fracture of optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system and method for monitoring fracture of optical fiber, capable of surely discriminating whether its cause is failure of a transmission device or rupture of an optical fiber, if a failure has occured in the transmission system that uses the optical fiber with no effect on main signals, even if failures have occured in a monitoring part. <P>SOLUTION: The monitor light is transmitted in both directions, an uplink-side optical fiber f6 and a downlink-side optical fiber f5, and a folding-back part 15 is used to fold back the monitor light. The reception level of the acquired monitor light is monitored with one transmission device 12, independently of a monitor light transmitter/receiver 13. Since, the signal light which is a main signal is separated from the monitor light and has no correlation, the uplink-side/downlink-side optical fibers f5 and f6 are monitored for rupture at one end of the optical fibers f5 and f6 with no effect from the state of both transmission devices 12 and 16. If abnormality occurs on the transmission system, it is discriminated whether the cause is failure of the transmission device or rupture of the optical fibers f5 and f6. The monitor light transmitter/receiver 13 can be repaired/replaced, even if a failure occurs with it without affecting the main signal system which is in normal state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical fiber break monitoring system and an optical fiber break monitoring method.

A conventional example of an optical fiber breakage monitoring system using an optical fiber will be described with reference to FIG.
The optical fiber breakage monitoring system shown in FIG. 1 includes a downstream optical fiber fa that transmits signal light from one transmission device 22 to the other transmission device 23 and a signal that travels from the other transmission device B23 to the one transmission device A22. The breakage of the upstream optical fiber fb that transmits light is monitored by the monitoring terminal 20 connected to the transmission device 22 via the monitoring network 21.

In the same optical fiber breakage monitoring system, when the downstream optical fiber fb between the transmission device 22 and the transmission device 23 is broken, the transmission device 23 is cut off from light input and an alarm 24 is generated.
Further, when the upstream optical fiber fa between the transmission device 23 and the transmission device is broken, the transmission device is disconnected from the light input and an alarm 24 is issued.
However, in the conventional optical fiber breakage monitoring system, when the alarm 24 of the transmission device 23 cannot be captured, it is determined whether the cause of the signal failure is a failure of the transmission device 23 or a breakage of the optical fiber fb in the downward direction. It cannot be carved.
In addition, since a similar alarm is issued from the transmission device 22 when a device failure (light output unit failure) or power failure of the transmission device 23 or a power failure of the station building at the point B occurs, the cause of signal interruption It is impossible to determine whether the transmission device 23 is in failure or whether the optical fiber fb in the upward direction is broken.
Therefore, there is an optical fiber cable breakage detection device that detects whether or not the optical fiber fb is broken by turning back the signal from the transmission device 22 on the transmission device 23 side.
This apparatus is configured to detect breakage of an optical fiber cable by multiplexing optical signals for monitoring different wavelengths for monitoring breakage of the fiber cable on the optical fiber cable (see, for example, Patent Document 1).
JP-A-60-177238

However, in the above-described prior art, the main signal system circuit, the control system circuit, and the monitoring unit are integrated, so that the main signal is interrupted when replacement is performed due to failure of the monitoring unit.
Therefore, the object of the present invention is to ensure that when a failure occurs in a transmission system using an optical fiber, the cause can be determined whether the transmission device is broken or the optical fiber is broken. An object of the present invention is to provide an optical fiber breakage monitoring system and an optical fiber breakage monitoring method that do not affect the main signal even if they occur.

In order to solve the above problems, the invention according to claim 1 is directed to a downstream optical fiber that transmits signal light from one transmission device to the other transmission device, and signal light from the other transmission device to the one transmission device. In an optical fiber breakage monitoring system that monitors a breakage of an upstream optical fiber that transmits an optical fiber with a monitoring terminal connected to one transmission device via a monitoring network, the optical fiber breakage is inserted between one transmission device and both optical fibers. A superposition / separation unit that superimposes / separates the signal light and the monitoring light having a wavelength different from that of the signal light, and is inserted between the supervision terminal and the superposition / separation unit, and is independent of the one transmission device. And configured to be inserted between a monitoring light transmitting / receiving unit that emits an alarm signal when the reception level of the monitoring light falls below a threshold value, both optical fibers and the other transmission device, and sends the upstream monitoring light to the signal Minutes from light And, characterized in that a folded portion folding only the monitor light to one of the transmission device side by superimposing the down side of the signal light.
According to the first aspect of the present invention, the monitoring light is transmitted in both directions of the upstream optical fiber and the downstream optical fiber, the monitoring light is folded using the folding unit, and the reception level of the obtained monitoring light is monitored. One transmission device and the monitoring light transmission / reception unit are independent. For this reason, the signal light, which is the main signal, and the monitoring light are separated and have no correlation, so that the upstream / downstream optical fiber is monitored for breakage at one end of the optical fiber without being affected by the state of both transmission devices. If an error occurs in the transmission system, it can be determined whether the transmission device is faulty or the optical fiber is broken. Replacement and repair can be performed without affecting a certain main signal system.

  According to a second aspect of the present invention, in the first aspect of the invention, the monitoring light transmitting / receiving unit has an output end connected to the input end of the superimposing / separating unit, and a light emitting unit that outputs the monitoring light, and an input end Connected to the output terminal of the superimposing / separating unit, converting the monitoring light input from the superimposing / separating unit into an electric signal and comparing it with a threshold value, and connecting the input terminal to the output terminal of the light receiving unit And an output unit connected to the monitoring network, and an alarm unit for outputting a contact output and an SNMP trap to the monitoring network when the light receiving level of the monitoring light is below a threshold value.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the superimposing / separating unit has one input terminal connected to the output terminal of one transmission device, and the other input terminal transmitting and receiving the monitoring light. The output end is connected to the downstream optical fiber, and the signal light from one transmission device and the monitoring light from the monitoring light transmitting / receiving unit are superimposed and output to the downstream optical fiber The superposition side multiplexer, the input end is connected to the upstream optical fiber, one output end is connected to the input end of one transmission device, and the other output end is the input end of the monitoring light transmitting / receiving unit A separation-side branching filter that separates the monitoring light and the signal light from the upstream optical fiber, outputs the signal light to one transmission device, and outputs the monitoring light to the monitoring light transmitting and receiving unit. It is characterized by having.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the folded portion is connected to the downstream optical fiber at an input end, and to the other transmission at one output end. An input end of the apparatus is connected, a return side duplexer that separates the signal light and the monitoring light input from the downstream optical fiber, and one input end is connected to the other output end of the duplexer Connected, the output end of the other transmission device is connected to the other input end, the upstream optical fiber is connected to the output end, and the signal light input from the other transmission device and the return side duplexer And a return-side multiplexer that multiplexes the monitoring light input from.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein when the monitoring light input / output unit issues an alarm signal, the monitoring light transmitting / receiving unit is removed from the superimposing / separating unit. Instead, the breakpoint is specified by connecting an OTDR.

  The invention according to claim 6 is a downstream optical fiber that transmits signal light directed from one transmission device to the other transmission device, and an upstream light that transmits signal light directed from the other transmission device to the one transmission device. In an optical fiber breakage monitoring method for monitoring a fiber breakage with a monitoring terminal connected to one transmission device via a monitoring network, the monitoring light having a different wavelength from the signal light from the monitoring light transmitting / receiving unit and the one transmission device The signal light is superposed by the superimposing / separating unit and transmitted to the other transmission device side by the downstream optical fiber, and the monitoring light is transmitted by the folding unit inserted between the other transmission device and both optical fibers. And the signal light are folded and transmitted to the superimposing / separating unit by the upstream optical fiber, the monitoring light and the signal light are separated by the superimposing / separating unit, and the monitoring light is transmitted to the monitoring light transmitting / receiving unit Specially received by To.

  According to a seventh aspect of the invention, in the sixth aspect of the invention, the monitoring light transmission / reception unit outputs a monitoring light to the superimposing / separating unit by a light emitting unit and is input from the superimposing / separating unit by a light receiving unit. Light is converted into an electrical signal, compared with a threshold value, and a contact output and an SNMP trap are output to the monitoring network when the light receiving level of the monitoring light is below the threshold value by an alarm unit .

  The invention according to claim 8 is the invention according to claim 6 or 7, wherein the superimposing / separating unit includes a signal light from one transmission device and a monitoring light from the monitoring light transmitting / receiving unit by a superposition side multiplexer. Is output to the downstream optical fiber, the monitoring light and the signal light from the upstream optical fiber are separated by the separation-side demultiplexer, the signal light is output to one transmission device, and the monitoring light transmission / reception unit And outputting the monitoring light.

  According to a ninth aspect of the present invention, in the invention according to any one of the sixth to eighth aspects, the folding unit includes the signal light and the monitoring light input from the downstream optical fiber by a folding side duplexer. And the signal light input from the other transmission device and the monitoring light input from the return side duplexer are multiplexed by the return side multiplexer.

  The invention according to claim 10 is the invention according to any one of claims 6 to 9, wherein when the monitoring light input / output unit issues an alarm signal, the monitoring light transmitting / receiving unit is removed from the superimposing / separating unit, Instead, the break point is specified by connecting the OTDR.

  The monitoring light is transmitted in both directions of the upstream optical fiber and the downstream optical fiber, the monitoring light is folded back using the folding unit, the received monitoring light is monitored, and one transmission device and the monitoring light transmitting / receiving unit Are independent. For this reason, the signal light, which is the main signal, and the monitoring light are separated and have no correlation, so that the upstream / downstream optical fiber is monitored for breakage at one end of the optical fiber without being affected by the state of both transmission devices. If an error occurs in the transmission system, it can be determined whether the transmission device is faulty or the optical fiber is broken. Replacement and repair can be performed without affecting a certain main signal system.

The present invention is characterized in that in a point-to-point transmission system using an optical fiber, it is possible to always monitor the breakage of a pair of optical fibers (both upstream and downstream) at one point.
In FIG. 1, the monitoring light transmission / reception unit 13 performs output of monitoring light having a wavelength different from that of the main signal (signal light) and detection of the reception level of the monitoring light, and the reception level of the monitoring light falls below a threshold value. In the event of an alarm, an alarm is output.
The superimposing / separating unit 14 superimposes the monitoring light on the main signal (signal light) by a WDM (Wavelength Division Multiplexing) coupler and separates the monitoring light from the main signal.
The folding unit 15 separates the monitoring light in the downstream direction from the main signal and folds only the monitoring light by superimposing it on the main signal in the upstream direction.
In this way, according to the present invention, the monitoring light is passed in both the upstream and downstream directions, and the reception level of the monitoring light is monitored. Therefore, it is possible to monitor the breaking in the upstream / downward direction at one point.
Since the superimposing / separating unit 14 and the folding unit 15 are composed of passive elements, and the main signal system device and the monitoring light transmission / reception unit 13 are completely separated, even when a failure occurs in the monitoring light transmission / reception unit 12 Does not affect the main signal.

Further, even when the transmission system is down, it is possible to reliably determine whether the transmission device 12 or the transmission device 16 has failed or whether the optical fibers fa and fb are broken. Even if a failure occurs in the monitoring light transmitter / receiver 13, the monitoring light transmitter / receiver 13 and the transmission device 12 are independent from each other, so that the monitoring light transmitter / receiver 13 is replaced or repaired without affecting the main signal system. be able to.
If the wavelength is the same as that of the monitoring light, a measuring instrument such as an OTDR (Optical Time Domain Reflectometery) can be connected and the breaking point can be measured without changing the connection of the main signal optical fibers f5 and f6.

FIG. 1 shows a block diagram of an embodiment of an optical fiber breakage monitoring system to which the optical fiber breakage monitoring method of the present invention is applied.
In this embodiment, a transmission device 12 as one transmission device and a monitoring network 11 are installed at a point A, and a superposition / separation unit 14 and a monitoring light transmission / reception unit 13 are installed at the input / output end of the transmission device 12. ing. The transmission device 12 and the superimposing / separating unit 14 are connected by optical fibers f1 and f2, and the monitoring light transmitting / receiving unit 13 and the superposing / separating unit 14 are connected by optical fibers f3 and f4.
The monitoring network 11 and the monitoring light input / output unit 13 are connected by an electric cable or optical fiber, and the monitoring network 11 and the monitoring terminal 10 are connected by an electric cable or optical fiber.
A transmission device 16 as the other transmission device is installed at the point B, and a turn-back portion 15 is installed at the input / output end of the transmission device 16. The superimposing / separating unit 14 and the folding unit 15 are connected by optical fibers f5 and f6, and the folding unit 15 and the transmission device 16 are connected by optical fibers f7 and f8.

FIG. 3 shows details of the monitoring light transmission / reception unit used in the optical fiber breakage monitoring system shown in FIG.
In FIG. 3, for example, a laser diode is used as the light emitting unit 30 of the monitoring light transmission / reception unit 13, and outputs the monitoring light to the optical fiber f <b> 3. The light receiving unit 31 converts the level of the monitoring light input from the optical fiber f4 into an electric signal level and compares it with a threshold value. The alarm unit 32 connected to the light receiving unit 31 outputs a contact output to the monitoring network 11 (see FIG. 1), SNMP (Simple Network Management Protocol: TCP) when the light receiving level (monitoring light level) is below the threshold value. / Protocol used to manage computers, hubs, routers, and other devices in an IP network) trap.

FIG. 4 shows a detailed configuration of the superposition / separation unit used in the optical fiber breakage monitoring system shown in FIG.
In FIG. 4, a superposition WDM (Wavelength Division Multiplexing) coupler 40 as a multiplexer of the superposition / separation unit 14 includes monitoring light (via the optical fiber f <b> 3) (see FIG. 1). Wavelength B) and the main signal (wavelength A) input from the transmission device 12 via the optical fiber f1 are combined and output to the downstream side of the transmission line (optical fiber f5).
The separation WDM coupler 41 as a demultiplexer demultiplexes the monitoring light and the main signal input from the upstream side of the transmission path (optical fiber f6) into wavelengths A and B, and the main signal (wavelength A) is a transmission device. The monitoring light (wavelength B) is output to the monitoring light transmission / reception unit 13 via the optical fiber f4.
In the figure, the monitoring light has been described as passing through the optical fiber f3, the superimposing WDM coupler 40, the optical fiber f5, (omitted), the optical fiber f6, the separating WDM coupler 41, and the optical fiber f4. The present invention is not limited to this, and the monitoring light passes through the optical fiber f4, the separation WDM coupler 41, the optical fiber f6 (omitted), the superposition WDM coupler 40, and the optical fiber f3 in the direction opposite to the arrow. It may be configured.

FIG. 5 shows a detailed configuration of the folded portion used in the optical fiber breakage monitoring system shown in FIG.
In FIG. 5, a separation WDM coupler 50 as a return side demultiplexer of the return unit 15 separates the monitoring light and the main signal input from the downstream side transmission line (optical fiber f5), and the main signal (wavelength) A) is output to the transmission device 16 via the optical fiber f7, and the monitoring light (wavelength B) is output to the superposition WDM coupler 51 as the return side multiplexer via the optical fiber f10 (which may be a waveguide). .
The superimposing WDM coupler 51 includes a main signal (wavelength A) input from the transmission device 16 via the optical fiber f8, and monitoring light (wavelength B) input from the separation WDM coupler 50 via the optical fiber f10. Are combined (wavelength A + B) and output to the upstream side of the transmission line (optical fiber f6).
Although the configuration of the embodiment has been described in detail above, the transmission apparatuses 12 and 16, the transmission paths (optical fibers) f5 and f6, the monitoring network 11, and the monitoring terminal 10 shown in FIG. 1 are well known to those skilled in the art. Further, since it is not directly related to the present invention, the detailed configuration thereof is omitted.

(Description of operation of the embodiment)
Next, the operation at the time of monitoring of the optical fiber breakage monitoring system shown in FIG. 1 will be described.
In FIG. 1, an optical signal (wavelength A) output from a transmission device 12 installed at a point A and an optical signal (wavelength B) output from a monitoring light transmitting / receiving unit 13 are transmitted via optical fibers f1 and f3. The signals are multiplexed by the superimposing / separating unit 14 and output to the downstream side of the transmission path (optical fiber f5) to reach the point B.
At point B, the signal from the downstream side of the transmission line (optical fiber f5) includes a main signal (wavelength A) output from the transmission device A12 by the turnback unit 15 and an optical signal (wavelength output from the monitoring device transmission / reception unit 13). B). The separated main signal (wavelength A) is input to the transmission apparatus B16 via the optical fiber f7, and communication between the transmission apparatus 15 and the transmission apparatus 16 is performed.

On the other hand, the monitoring light (wavelength B) is combined with the main signal (wavelength A) output from the transmission device 16 via the optical fiber f8 (wavelength A + B), and again toward the point A on the transmission line upstream side (optical fiber). f6).
The upstream side of the transmission line (optical fiber f6) is separated into the main signal (wavelength A) and the monitoring light (wavelength B) by the superposition / separation unit 14 at point A, and the main signal (wavelength A) passes through the optical fiber f2. The data is input to the transmission device 12 through the communication.
The monitoring light (wavelength B) is input to the monitoring light transmitting / receiving unit 13 through the optical fiber f4. That is, the monitoring light is transmitted from the monitoring light transmitting / receiving unit 13 to the optical fiber f3, the superimposing / separating unit 14, the optical fiber f5, the turning unit 15, the optical fiber f6, the optical fiber f4, and the monitoring light transmitting / receiving unit 13 as indicated by the broken line. They are transmitted in order. The optical signal input to the monitoring light sparse receiver 13 is converted into an electrical signal, and the level of the electrical signal is compared with a threshold value.
When the comparison result in the monitoring light transmission / reception unit 13 falls below the threshold value, the monitoring light transmission / reception unit 13 determines that a break has occurred in the optical fibers f5 and f6 of the transmission path, and outputs a contact alarm, and An SMMP trap is output to the monitoring terminal 10 via the connected monitoring network 11.

(Explanation of effect)
As described above, in the present invention, the monitoring light is passed through the transmission paths (optical fibers f5 and f6) in both the upstream and downstream directions, and the reception level of the monitoring light is monitored. The optical fibers f5 and f6 can be monitored for breakage, and the breakage of the optical fibers f5 and f6 as transmission lines can be monitored without affecting the state of the transmission device 12 and transmission device 16, and an abnormality in the transmission system occurs. Thus, it is possible to determine whether the transmission device 12 or 16 is caused by a failure or the optical fibers f5 and f6 are broken.

  As another embodiment of the present invention, the basic configuration is as described above. In FIG. 1, the superimposing / separating unit 14 and the folding unit 15 are configured only by passive elements and are different from the main signal (wavelength A). Since it is possible to return only the signal (monitoring light) of the wavelength (wavelength B), it is possible to perform a line characteristic test by OTDR or the like without affecting the main signal.

FIG. 6 shows a block diagram of another embodiment of an optical fiber breakage monitoring system to which the optical fiber breakage monitoring method of the present invention is applied.
In this figure, in this embodiment, a transmission device 12 as one transmission device and a monitoring network 11 are installed at a point A, and a superposition / separation unit 14 is installed at the input / output end of the transmission device 12. The monitoring light transmission / reception unit 13 is separated from the superimposition / separation unit 14. The transmission device 12 and the superimposing / separating unit 14 are connected by optical fibers f1 and f2.
A transmission device 16 as the other transmission device is installed at the point B, and a turn-back portion 15 is installed at the input / output end of the transmission device 16. The superimposing / separating unit 14 and the folding unit 15 are connected by optical fibers f5 and f6, and the folding unit 15 and the transmission device 16 are connected by optical fibers f7 and f8. The figure shows a state in which the monitoring light transmission / reception unit 13 outputs an alarm, the monitoring light transmission / reception unit 13 is removed, and the OTDR 60 is connected to the superposition / separation unit 14 instead of the monitoring light transmission / reception unit 13.
The monitoring light of the wavelength B from the OTDR 60 includes an optical fiber f11, a superimposing / separating unit 14, an optical fiber f5, a folding unit 15, an optical fiber f6, a break point X, an optical fiber f6, a folding unit 15, and light as indicated by a broken line. The signal is input to the OTDR 60 via the fiber f5, the superimposing / separating unit 14, and the optical fiber f11.
By connecting in this way, the break point X of the optical fiber f6 (or the optical fiber f5) can be specified by the OTDR 60.

It is a block diagram which shows one Example of the optical fiber fracture monitoring system to which the optical fiber fracture monitoring method of this invention is applied. It is a block diagram which shows the prior art example of the optical fiber fracture monitoring system using an optical fiber. It is a figure which shows the detail of the monitoring light transmission / reception part used for the optical fiber breakage monitoring system shown in FIG. It is a figure which shows the detailed structure of the superimposition / separation part used for the optical fiber fracture monitoring system shown in FIG. It is a figure which shows the detailed structure of the folding | turning part used for the optical fiber fracture monitoring system shown in FIG. It is a block diagram which shows the other Example of the optical fiber fracture monitoring system to which the optical fiber fracture monitoring method of this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Monitoring terminal 11 Monitoring network 12, 16 Transmission apparatus 13 Monitoring light transmission / reception part 14 Superimposition / separation part 15 Folding part fa, fb, f1-f10 Optical fiber

Claims (10)

One transmission device breaks down a downstream optical fiber that transmits signal light from one transmission device to the other transmission device and an upstream optical fiber that transmits signal light from the other transmission device to one transmission device. In an optical fiber breakage monitoring system for monitoring with a monitoring terminal connected to the network via a monitoring network,
A superposition / separation unit that is inserted between one transmission device and both optical fibers and superimposes / separates the signal light and the monitoring light having a wavelength different from that of the signal light;
A monitoring light transmitting / receiving unit that is inserted between the monitoring terminal and the superimposing / separating unit and is configured independently of the one transmission device, and that issues an alarm signal when the reception level of the monitoring light falls below a threshold value When,
Inserted between both optical fibers and the other transmission device, separates the upstream monitoring light from the signal light, and superimposes it on the downstream signal light so that only the monitoring light is folded back to the one transmission device side. An optical fiber breakage monitoring system comprising a turn-up portion. The monitoring light transmission / reception unit includes:
A light-emitting unit whose output end is connected to the input end of the superimposing / separating unit and outputs monitoring light;
A light receiving unit that has an input terminal connected to the output terminal of the superimposing / separating unit, converts the monitoring light input from the superimposing / separating unit into an electrical signal, and compares it with a threshold value;
When the input end is connected to the output end of the light receiving unit, the output end is connected to the monitoring network, and the light receiving level of the monitoring light is below a threshold value, a contact output and an SNMP trap are output to the monitoring network. The optical fiber breakage monitoring system according to claim 1, further comprising an alarm unit. The superimposing / separating unit includes:
One input terminal is connected to the output terminal of one transmission apparatus, the other input terminal is connected to the output terminal of the monitoring light transmitting / receiving unit, the output terminal is connected to the downstream optical fiber, and one transmission apparatus A superposition-side multiplexer that superimposes the signal light from and the monitoring light from the monitoring light transmission / reception unit and outputs it to the downstream optical fiber;
The input end is connected to the upstream optical fiber, one output end is connected to the input end of one transmission device, the other output end is connected to the input end of the monitoring light transmitting / receiving unit, A separation-side duplexer that separates the monitoring light and the signal light from the fiber, outputs the signal light to one transmission device, and outputs the monitoring light to the monitoring light transmission / reception unit. The optical fiber breakage monitoring system according to 1 or 2. The folded portion is
The downstream optical fiber is connected to the input end, and the input end of the other transmission device is connected to one output end, and the signal light and the monitoring light input from the downstream optical fiber are separated. A return side duplexer;
One input end is connected to the other output end of the duplexer, the other input end is connected to the output end of the other transmission device, the output end is connected to the upstream optical fiber, and the other end is connected to the other end. 4. The apparatus according to claim 1, further comprising: a return-side multiplexer that combines the signal light input from the transmission apparatus and the monitoring light input from the return-side duplexer. 5. Optical fiber break monitoring system.   When the monitoring light input / output unit issues an alarm signal, the monitoring light transmitting / receiving unit is removed from the superimposing / separating unit, and the OTDR is connected instead to specify the break point. The optical fiber breakage monitoring system according to any one of claims 1 to 4. One transmission device breaks down a downstream optical fiber that transmits signal light from one transmission device to the other transmission device and an upstream optical fiber that transmits signal light from the other transmission device to one transmission device. In the optical fiber breakage monitoring method for monitoring with a monitoring terminal connected to the network via a monitoring network,
The signal light from the monitoring light transmission / reception unit and the monitoring light having a different wavelength and the signal light from one transmission device are superimposed by the superposition / separation unit and transmitted to the other transmission device side by the downstream optical fiber,
The monitoring light and the signal light are folded back at the folded portion inserted between the other transmission device and both optical fibers, and transmitted to the superimposing / separating portion by the upstream optical fiber,
The superimposing / separating unit separates the monitoring light and the signal light,
An optical fiber breakage monitoring method, wherein the monitoring light is received by a monitoring light transmission / reception unit. The monitoring light transmission / reception unit includes:
Monitoring light is output to the superimposing / separating unit by the light emitting unit;
The monitoring light input from the superimposing / separating unit by the light receiving unit is converted into an electric signal, and compared with a threshold value.
7. The optical fiber break monitoring method according to claim 6, wherein a contact output and an SNMP trap are output to the monitoring network when the light receiving level of the monitoring light is below a threshold value by an alarm unit. The superimposing / separating unit includes:
The signal light from one transmission device and the monitoring light from the monitoring light transmitting / receiving unit are superimposed and output to the downstream optical fiber by the superposition side multiplexer,
The monitoring light and the signal light from the upstream optical fiber are separated by the separation side demultiplexer, the signal light is output to one transmission device, and the monitoring light is output to the monitoring light transmitting / receiving unit. The optical fiber breakage monitoring method according to claim 6 or 7. The folded portion is
Separating the signal light and the monitoring light input from the downstream optical fiber by a return side duplexer;
9. The signal light input from the other transmission device and the monitoring light input from the return-side duplexer are multiplexed by a return-side multiplexer. Optical fiber breakage monitoring method.   7. When the monitoring light input / output unit issues an alarm signal, the monitoring light transmitting / receiving unit is removed from the superimposing / separating unit, and the OTDR is connected instead to identify the break point. The optical fiber breakage monitoring method according to any one of 1 to 9.

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