JP2010004356A - Monitoring device and monitoring circuit installed in optical communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a slave station to check its own abnormal continuous transmission by monitoring whether the slave station itself dims in a discovery period or not by using a state that a newly subscribed slave station responds to a master station but the other slave stations make no response in the discovery period which is a period for inquiring whether a slave station is newly subscribed to an optical communication system or not from the master station in a broadcasting mode. <P>SOLUTION: When a monitoring part 23 for detecting whether an optical signal is transmitted from an optical transmitter 21 does not detect a point of time that an optical signal is not transmitted in a repeated period of a discovery period, the monitoring part determines abnormal light is emitted in the slave station and stops the light emission. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a monitoring device installed in a slave station of an optical communication system connecting between a master station and a plurality of slave stations, and capable of monitoring a continuous light emission failure of the own station in the slave station, and a monitoring device thereof The present invention relates to a suitably used monitoring circuit.

A PON (Passive Optical Network) system in which a single trunk optical fiber is shared by a plurality of slave stations in an optical communication system that performs bidirectional communication between the master station and a plurality of slave stations using an optical data communication network Has been proposed. The trunk optical fiber and each slave station are connected with each branch optical fiber via an optical branching unit.
In this PON system, packets are distributed in broadcast form from a master station to a slave station. Since the upstream packet from the slave station collides unless some sort of traffic control is performed, the upstream optical signal from the slave station is transmitted in a time division manner.

However, the optical transmitter of the slave station may break down and be always on. Since the management of the slave station is usually performed by the master station administrator rather than the terminal user, it is necessary for the master station administrator to identify the slave station that is lit and repair or replace the slave station. is there.
However, if the master station is always lit, it is difficult to identify the slave station that is lit because the upstream packet from the slave station cannot be identified. Therefore, it is desired that the slave station monitors the failure of the own station.

In Patent Document 1 below, an optical signal continuously transmitted from a slave station at the time of an abnormality continues for a longer period than an existing period of an optical packet (this is referred to as a “burst optical signal”) transmitted by each slave station at a normal time. Paying attention, the invention discloses an invention in which when the slave station detects abnormal continuous transmission of its own station, the power supply of its own optical transmission module is cut off and the slave station is disconnected from the network.
Japanese Utility Model Publication No. 5-65146

In Patent Document 1, an integrator having a time constant is installed to detect an optical transmission current, and if the detected optical transmission current exceeds a threshold for a set time, it is determined that light is emitted for a long time. Therefore, it is determined that abnormal continuous light emission occurs.
However, one slave station may send a plurality of burst optical signals continuously (best effort). At this time, there is only a short no-signal section between other adjacent burst optical signals. Therefore, in the method using the conventional integrator, the no-signal interval is shorter than the time constant, and it is regarded as abnormal continuous light emission, and it may be determined to be abnormal although it is normal.

  In addition, since the number of slave stations connected to the optical communication system changes dynamically, it is necessary to set a relatively long setting time for determining an abnormality. For example, when there is only one slave station, there is a case where the slave station normally transmits for a long time, and a longer time must be set as the set time for abnormality detection. For this reason, normal communication of the optical network is hindered until abnormal continuous light emission is stopped.

  Therefore, an object of the present invention is to realize a monitoring device and a monitoring circuit that can easily detect the extinction failure state of the local station even when transmitting a continuous optical signal.

  The inventor of the present application paid attention to the discovery period provided in the optical communication system. The “discovery period” is a period for inquiring in broadcasting format from the parent station side whether or not a child station has newly joined. During this period, the new subscriber station responds to the master station, but the other slave stations remain silent. Therefore, the slave station can confirm the abnormal continuous transmission of the local station by monitoring whether the local station is extinguished during this period.

  The monitoring device of the present invention is a monitoring device installed in any slave station of an optical communication system that connects a master station and a plurality of slave stations with an optical communication line and transmits an optical signal from each slave station to the master station. A monitoring unit for detecting whether an optical signal is transmitted from the optical transmitter, the monitoring unit being equal to or longer than a repetition period of a discovery period provided for searching for a slave station newly joining the optical communication system If a time point when no optical signal is transmitted is not detected in the predetermined period, it is determined that the slave station is emitting abnormal light and light emission is stopped.

According to this configuration, the slave station should not emit light at least during the discovery period. Therefore, if the extinction is confirmed even once within a predetermined period equal to or greater than the discovery period, it can be determined that the light emission state of the own station is normal. On the contrary, if the light is not extinguished within the predetermined period, it is determined that the optical transmitter has a quenching failure.
Since the new subscriber station emits light during the discovery period, the present invention cannot be applied, but the present invention can be applied if the discovery period is after the subscription.

  In order to detect whether an optical signal is transmitted from the optical transmitter, the monitoring unit detects a drive current that drives the optical transmitter, and in a predetermined cycle that is equal to or greater than a repetition cycle of the discovery period, If the drive current value does not fall below a predetermined threshold value, it may be determined that the slave station is emitting abnormal light. Since no light can be emitted when the drive current is zero, it is possible to reliably know whether or not the optical signal is extinguished by detecting the drive current that drives the optical transmitter.

  The monitoring unit may monitor whether the drive current value is less than a predetermined threshold during a period when the burst enable signal is disabled. In many cases, a burst enable signal is input to the optical transmitter of the slave station, and this determines whether the optical transmitter is turned off or turned on for communication. Therefore, if the output of the current detection unit is monitored when the burst enable signal is disabled, it can be confirmed whether or not the extinction state is correctly set according to the disabled state of the burst enable signal.

  In order to detect whether or not an optical signal is transmitted from the optical transmitter, the monitoring unit is in a state of a burst enable signal that transits between an enable state in which light is emitted from the optical transmitter and a disable state in which the optical transmitter is extinguished. A signal presence / absence determination unit that determines whether the burst enable signal does not become disabled in a predetermined period equal to or greater than the repetition period of the discovery period. It may be determined that the light emission is stopped. With this configuration, when the burst enable signal is disabled, the optical transmitter is regarded as extinguished and performs supervisory control. Actually, there may be a failure in which the burst enable signal is disabled but continues to emit light, but such a failure is considered to be very small. Abnormal light emission of the slave station can be detected.

As a means for stopping the light emission, by providing a switch in a drive line supplied from the power source to the optical transmitter, when it is determined that there is a failure, the switch is turned off to stop the power supply to the optical transmitter. Is possible. Accordingly, it is possible to prevent the failure of constant light emission by the optical transmitter from affecting the normal communication of other stations in the network.
The “predetermined period equal to or greater than the repetition period of the discovery period” may be any period as long as it includes the discovery period. However, the longer the abnormality detection time is, the longer it is. Therefore, the “predetermined period” may be set to the repetition period itself.

  The monitoring circuit of the present invention has an input terminal that receives detection information of a drive current that drives the optical transmitter, and a control output terminal that controls a switch that turns on and off the power of the optical transmitter, The current value input from the input terminal is compared with a predetermined threshold value, and if the current value does not become lower than the predetermined threshold value in a predetermined cycle, a switch-off output signal is supplied to the control output terminal. It is characterized by putting out. If this monitoring circuit is installed in any slave station of an optical communication system that transmits an optical signal from each slave station to the master station, the slave station determines that the slave station is emitting abnormal light and stops the light emission of the optical transmitter. be able to.

  The monitoring circuit of the present invention has an input terminal for receiving detection information of the burst enable signal and a control output terminal for controlling a switch for turning on / off the power of the optical transmitter, and is input from the input terminal. The presence or absence of the burst enable signal may be detected, and if the burst enable signal is not disabled in a predetermined cycle, a switch-off output signal may be output to the control output terminal. A failure that always emits light can be detected by the burst enable signal.

  As described above, according to the present invention, there is a discovery period in a predetermined cycle, and an extinction state always occurs in that cycle. It can be detected as a failure. In addition, the monitoring unit can determine that there is an abnormality in the case where the light emitting device is always in a light emitting state due to a failure of the optical transmitter, or any failure in which light is always emitted by the given burst enable signal.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a configuration diagram of a PON (Passive Optical Network) optical communication system as an example of an optical communication system to which the present invention is applied.
A PON optical communication system includes a master station (hereinafter referred to as “station side apparatus OLT”) provided in a station building and a slave station (hereinafter referred to as “home side apparatus ONU”) provided in a plurality of subscribers, an optical fiber SMF and They are connected via an optical coupler OC.

The home-side apparatus ONU includes a network interface for connecting a terminal for enjoying an optical network service, such as a personal computer installed in a subscriber's home.
The optical coupler OC is composed of a star coupler that does not require any external power supply and passively branches and multiplexes signals from input signals.

  The optical fibers connected to the station-side device OLT, the optical coupler OC, the optical coupler OC, and the home-side device ONU are single mode fibers each composed of one optical fiber SMF. That is, one station side device OLT is connected to one optical coupler OC through one trunk optical fiber SMF. The optical coupler OC is connected to N home-side devices ONU (N is a number of 32 or less in this example) by branch optical fibers SMF. Therefore, a signal transmitted and received by one station-side device OLT is distributed to a maximum of N home-side devices ONU by one optical coupler OC. Note that the number of optical couplers OC and the number of home-side devices ONU are merely examples.

The communication system according to the embodiment of the present invention incorporates the technology of Gigabit Ethernet (Ethernet is a registered trademark) into the PON optical communication system, and GE-PON (Gigabit Ethernet-Passive Optical Network). The method is adopted.
According to the GE-PON system, communication between the station side device OLT and the home side device ONU is performed in units of variable length frames.

  First, a downlink frame that enters the station side apparatus OLT from the higher level network is subjected to a predetermined bridge process in the station side apparatus OLT, and a logical link to be relayed is specified. Then, it is transmitted from the station side device OLT to the optical fiber SMF as an optical signal. The optical signal transmitted to the optical fiber SMF is branched by the optical coupler OC and transmitted to the home-side device ONU connected to the optical coupler OC. Only the home-side device ONU constituting the logical link receives a predetermined optical signal. Capture and relay frame to home network interface.

  On the other hand, the upstream optical signal includes an upstream frame from each home-side apparatus ONU. The upstream optical signal needs to be transmitted so that the optical signals from the respective home devices ONU do not compete with each other in time. For this purpose, the station side device OLT allocates a window (hereinafter simply referred to as a window) during which an upstream optical signal may be transmitted to each home side device ONU, and notifies it as a control frame. The home apparatus ONU to which the window is assigned transmits an optical signal including a series of frame signals to the assigned window. This upstream optical signal is referred to as a “burst optical signal”. The burst optical signal is a finite-time optical signal sequence in which the light emission state is changed to 0 or 1 by a baseband signal.

  Therefore, the competition of the upstream optical signal between each home-side apparatus ONU is avoided. Each home-side apparatus ONU may transmit a single burst optical signal or a plurality of burst optical signals as long as a certain window is given, so long as it fits in that window (thus, a burst optical signal). The length of is variable). When transmitting a plurality of burst optical signals, the time between adjacent burst optical signals can be very short (described later with reference to FIGS. 6 and 10).

The station side device OLT can receive the burst optical signal from each home side device ONU.
FIG. 2 is a functional block diagram showing the configuration of the home device ONU.
The home-side device ONU receives the data from the optical multiplexer / demultiplexer 11 that separates the optical transmission signal and the reception signal at the wavelength of the light, and the station-side device OLT, and separates the data addressed to itself from the PON system. An optical receiver 12 that delivers to the user interface 15 that is an interface with the home network and acquires information about the transmission time designated from the station side device OLT, and an optical burst according to the transmission scheduler 13 that receives data from the upper interface 15 An optical transmission unit 14 for transmission and a transmission scheduler 13 for scheduling transmission at a time designated by the station-side apparatus OLT are provided.

  The home apparatus ONU includes an internal clock (not shown) that is updated with reference to time information sent from the station apparatus OLT. With this configuration, the transmission scheduler 13 and the monitoring unit (described later) synchronize with the station side device OLT and transmit an optical burst signal at the timing indicated by the station side device OLT, or monitor the light emission state of the home side device ONU. You can do it.

FIG. 3 is a block configuration diagram showing details of the optical transmitter 14.
The optical transmitter 14 is installed between the optical transmitter 21 that transmits an optical signal, the current detector 22 that detects the drive current supplied to the optical transmitter 21, and the power source and the optical transmitter 21. And a monitoring unit 23 that monitors the detection current of the current detection unit 22.
The optical transmitter 21 incorporates a light source L such as a laser diode and a driver circuit D. When a drive current flows through the light source L, the light source L emits light. The driver circuit D receives a burst enable signal from the transmission scheduler 13 and a data signal from the user interface 15. The driver circuit D allows the drive current to flow only while the burst enable signal is enabled. Then, the light source L is optically modulated based on the data signal.

The current detection unit 22 supplies, for example, a voltage corresponding to a detection current generated based on an electromotive force of a coil surrounding a conductor through which a drive current flows, to the monitoring unit 23. When the monitoring unit 23 determines that the optical transmitter 21 is always in a failure state of light emission, the switch SW is opened by an operation from the monitoring unit 23, thereby stopping light emission.
The monitoring unit 23 is configured by a circuit realized by an IC (Integrated Circuit) or the like, and monitors the presence / absence of the detection current of the current detection unit 22 by comparing with a predetermined threshold value Ith, and uses the following procedure. It is determined whether or not the optical transmitter 21 is always in a failure state of light emission (note that in the optical transmitter 14 in FIG. 3, the monitoring unit 23 does not input a burst enable signal, but a configuration in which a burst enable signal is input is also possible. (There will be a description later with reference to FIGS. 9 and 12).

  FIG. 4 is a functional block diagram of the monitoring unit 23. The monitoring unit 23 includes an input terminal T1 that receives detection information of a drive current that drives the optical transmitter 21, and a control output terminal T2 that controls a switch SW that turns on and off the power of the optical transmitter 21. , An A / D converter 31 for A / D converting the detection current of the current detection unit 22, a sampling circuit 32 for acquiring an A / D conversion value at each sampling time t, and the magnitude of the sampled value (detection current) And a determination circuit 34. The comparison circuit 33 compares the threshold value Ith with the determination circuit 34. The A / D converter 31 may be omitted and the analog values may be directly compared.

FIG. 5 is a flowchart for explaining the determination procedure of the monitoring unit 23. First, the sampling circuit 32 supplies the A / D converted current value to the comparison circuit 33 at every sampling time t (step S1). The comparison circuit 33 reads this sample value (step S2), and compares the magnitude with the threshold value Ith (step S3).
Here, FIG. 6 is a waveform diagram showing an example of the detected current of the current detector 22. In this graph, the time of each sampling, the time between adjacent burst optical signals described above (referred to as an optical burst signal break R), and discovery provided for searching for a home-side apparatus ONU newly joining the optical communication system. A period W is shown.

At the break R of the optical burst signal, the current value is slightly reduced. However, since the break R of the optical burst signal is short in time, the current value cannot be sufficiently reduced, and in the next burst period. In. In such a period, it is difficult to find a decrease in current using the threshold value Ith.
The discovery period W is determined to be longer than the sum of the round trip time of the optical transmission path from the station side device OLT to the home side device ONU at the longest distance and the response time of the new subscriber home side device ONU. Yes. If the round-trip distance of the optical transmission path is 40 km, it is determined to be 200 μsec, for example.

In such a relatively long discovery period W, the current value is sufficiently lowered, so that it is possible to find a decrease in current using the threshold value Ith. In other words, the threshold value Ith is set to such a value that a decrease in current value can be detected in the discovery period W.


A description will be given below with numerical examples. Inside the optical transmitter 21, when the burst enable signal is in the enabled state, the driver circuit D turns on / off the drive current of the light source L based on the data signal and modulates the optical signal. The current detection 22 detects the average current with a response that is not affected by the on / off of the drive current due to the modulation. The time constant of the response is “τ”. In the case of GE-PON, since the same logical code continues for a maximum of 5 bits (4 ns), for example, it is preferable to set τ> 5 × 4 ns. On the other hand, the driver circuit D turns off the drive current of the light source L when the burst enable signal is disabled. The output of the current detection 22 decreases with a time constant τ. The time constant τ is preferably set to τ <W, for example, so that the output of the current detection 22 sufficiently decreases in the discovery period W. If τ <W, the drive current drops below 1 / e (e is the base of natural logarithm) at the end of the discovery period W. Therefore, the threshold Ith is set to 1 / e of the drive current when the light source L is on. If this is set, a decrease in drive current can be detected.

  When the threshold value Ith is set to a high value, the drive current may fluctuate and fall below the threshold value Ith even though the driver circuit D does not turn off the drive current. In order to prevent such erroneous detection, a lower threshold value Ith is desirable. Therefore, it is more preferable to set the time constant τ <(W / 2) of the response of the driver circuit D. In this way, the threshold value Ith can be set lower than 1 / e.

  In FIG. 6, “Discovery period T” is shown. The discovery period T is the time from the discovery period to the next discovery period. That is, the station-side apparatus OLT performs a discovery procedure for the newly-added home-side apparatus ONU once in the discovery cycle T. This discovery cycle T is a value set in the system, and is, for example, 1 second. By providing the discovery cycle T, abnormal light emission can always be determined within the time of the discovery cycle T even if the discovery cycle T is long.

  When the sample value read by the comparison circuit 33 is smaller than the threshold value Ith in step S3 of FIG. 5, the determination circuit 34 is in the extinguished state, so that the optical transmitter 21 is always emitting light. Judge that there is no fault condition. When it is larger than the threshold value Ith, the discovery period T starts to be counted. During this counting, steps S1 to S4 are repeated. The repeated cycle is the sampling time t. The upper limit of the sampling time t must naturally be W in order to detect the extinction state within the discovery period W.

  If the discovery cycle T elapses while repeating the procedures of steps S1 to S4 (step S5), the quenching of the optical transmitter 21 has not been detected despite the discovery period W. The optical transmitter 21 is in a quenching failure state and is determined to be abnormal, and the monitoring unit 23 turns off the switch SW (step S6). The count of the discovery period T is reset when the sample value read by the comparison circuit 33 is smaller than the threshold value Ith (step S7).

As a result, the home-side device ONU is provided with a switch SW that operates under the control of the monitoring unit 23 between the power source and the optical transmitter 21, and stops transmission by turning off the switch SW in the case of a failure in the constant light emission state. Then, the own station in the extinction failure state can be withdrawn from the system. Therefore, adverse effects on other devices of the system can be prevented.
FIG. 7 is a functional block diagram illustrating another configuration example of the monitoring unit 23. In this example, the monitoring unit 23 includes an A / D converter 31 that performs A / D conversion on the detected current value of the current detection unit 22, a comparison circuit 33 that compares the A / D conversion value and the threshold value Ith, and a comparison circuit. When the comparison result of 33 indicates A / D conversion value <threshold value Ith, a latch circuit 32a for latching the state and a determination circuit 34a are provided. The A / D converter 31 may be omitted and the analog values may be directly compared.

  FIG. 8 is a flowchart for explaining the determination procedure of the monitoring unit 23. The latch circuit 32a latches the comparison result (A / D conversion value <threshold value Ith) of the comparison circuit 33 (step U1). The determination circuit 34a counts the discovery cycle T (step U2). Then, when this discovery cycle T has elapsed (step U3), the latched value is read (step U4), and it is determined whether the comparison result of A / D conversion value <threshold value Ith is latched (step S4). Step U5). When the comparison result of A / D conversion value <threshold value Ith is latched, the determination circuit 34a may have turned off the optical transmitter 21 during the discovery period T. It is determined that 21 is not in a constant light emission failure state. At this time, the determination circuit 34a resets the latch state of the latch circuit 32a (step U6), and returns to step U1. If it is larger than the threshold value Ith, it means that the quenching of the optical transmitter 21 has not been detected despite the discovery period W, and the optical transmitter 21 is in a quenching failure state and is determined to be abnormal. Then, the switch SW is turned off (step U7).

Next, a configuration in which the monitoring unit 23 uses the burst enable signal as an auxiliary will be described.
In this configuration, a procedure for confirming the extinction of the optical transmitter 21 based on the drive current detection value when the burst enable signal is disabled is adopted.
FIG. 9 is a configuration diagram of the optical transmitter 14. Explaining only the difference from FIG. 3, the burst enable signal is also input to the monitoring unit 23.

  FIG. 10 is a waveform diagram showing an example of the waveform of the burst enable signal and the waveform of the current detected by the current detector 22. In this graph, R, which is a break of the optical burst signal, and the discovery period W are shown. During any period, the burst enable signal is disabled. In response to the presence or absence of the burst enable signal, the driver circuit D turns on / off the drive current of the light source L, and sets the time constant detected by the current detection circuit 22 to “τ”. The time constant τ is preferably set to τ <W, and more preferably τ <(W / 2), so that the drive current sufficiently decreases in the discovery period W.

FIG. 11 is a circuit diagram showing still another circuit configuration of the monitoring unit 23. The monitoring unit 23 directly compares the analog values.
The monitoring unit 23 includes an input terminal T1 that receives detection information of a driving current that drives the optical transmitter 21, a control output terminal T2 that controls a switch SW that turns on and off the power of the optical transmitter 21, and a burst enable. A comparison circuit 35 that has an input terminal T3 that receives signal detection information, compares the detection current of the current detection unit 22 with a threshold value Ith, and outputs a high-level signal when the threshold value is smaller than the threshold value Ith; A logical product circuit 36 for inputting the burst enable signal and the output signal of the comparison circuit 35, a latch circuit 37 that holds the output of the logical product circuit 36 and is reset every discovery period W, and a determination circuit 38 are provided. .

According to this circuit configuration, the AND circuit 36 passes the output of the comparison circuit 35 during the period when the burst enable signal is disabled. When the detection current in the comparison circuit 35 becomes smaller than the threshold value Ith, a signal indicating that is held in the latch circuit 37. The latch circuit 37 is reset when the discovery period W elapses.
The determination circuit 38 takes in the output signal of the latch circuit 37 to determine whether or not the optical transmitter 21 has been turned off during the discovery period W. If the optical transmitter 21 has been turned off, it is determined that the optical transmitter 21 is not always in a failure state of light emission. If the optical transmitter 21 has never been turned off, the optical transmitter 21 is in a poor extinction state and is determined to be abnormal, and the switch SW is turned off.

Next, a circuit configuration for determining the state of the optical transmitter 21 using only the burst enable signal will be described.
FIG. 12 is a block configuration diagram showing details of the optical transmission unit 14. The difference from the configuration of FIG. 3 is that the current detection unit 22 that detects the drive current supplied to the optical transmitter 21 is omitted. That is, only the burst enable signal is input to the monitoring unit 23.

  FIG. 13 is a functional block diagram of the monitoring unit 23. The monitoring unit 23 has a control output terminal T2 for controlling the switch SW for turning on / off the power of the optical transmitter 21, and an input terminal T3 for receiving detection information of the burst enable signal, and also samples the burst enable signal. A sampling circuit 41 to be converted, a signal presence / absence determination circuit 42 that compares the magnitude of the sampled value (presence / absence of a burst enable signal) with a threshold value Sth and determines whether the burst enable signal is enabled or disabled, It has.

  FIG. 14 is a flowchart for explaining the signal presence / absence determination procedure of the monitoring unit 23. First, the sampling circuit 41 supplies the A / D converted voltage value to the comparison circuit 35 at every sampling time t (step V1). The comparison circuit 35 reads this sample value and compares the magnitude with the threshold value Sth (step V2). If the signal presence / absence determination circuit 42 is lower than the threshold value Sth, the burst enable signal is in a disabled state, and therefore it is determined that the optical transmitter 21 is not in the “always light emission failure state”. If it is greater than the threshold value Sth, it is determined that the burst enable signal is in an enabled state, and the discovery period T is counted (step V3). During this counting, steps V1 to V3 are repeated. The repeated cycle is the sampling time t. If the discovery cycle T elapses during the repetition (step V4), it is determined that the burst enable signal has not been disabled despite the discovery period W, and the optical transmitter 21 is in a quenching failure state. Therefore, it is determined that there is an abnormality, and the switch SW is turned off (step V5). Note that the count is reset when the sample value is lower than the threshold value Sth (step V6).

  In this embodiment, the monitoring unit 23 monitors only the burst enable signal without detecting the drive current, and considers that the optical transmitter 21 has been extinguished if the burst enable signal is disabled. Although a failure in which the optical transmitter 21 continues to be lit even when the burst enable signal is interrupted can be assumed, such a failure is an extremely rare case, and thus the optical transmitter 21 has sufficient reliability in this embodiment. Can be detected.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above embodiments. For example, instead of detecting the drive current, a photodiode that monitors the light from the light source L may be installed near the light source L, and the photocurrent flowing through the photodiode may be detected. Further, although extinction is detected every discovery period T, it is not necessary to strictly limit to the discovery period T. It is also possible to detect extinction by setting a predetermined period equal to or greater than the discovery period T. This is also because the discovery period W always exists within a predetermined period. In addition, various modifications can be made within the scope of the present invention.

1 is a configuration diagram of a PON (Passive Optical Network) optical communication system as an example of an optical communication system to which the present invention is applied. FIG. It is a functional block diagram which shows the structure of the home side apparatus ONU. FIG. 3 is a block configuration diagram showing details of an optical transmitter 14. 3 is a functional block diagram of a monitoring unit 23. FIG. 5 is a flowchart for explaining a determination procedure of a monitoring unit 23. 4 is a waveform diagram illustrating an example of a detection current of a current detection unit 22. FIG. 6 is a functional block diagram illustrating another configuration example of the monitoring unit 23. FIG. 5 is a flowchart for explaining a determination procedure of a monitoring unit 23. 2 is a configuration diagram of an optical transmission unit 14. FIG. It is a wave form diagram which shows an example of the waveform of a burst enable signal, and the waveform of the detection electric current of the electric current detection part 22. FIG. 3 is a circuit diagram showing a circuit configuration of a monitoring unit 23. FIG. FIG. 3 is a block configuration diagram showing details of an optical transmitter 14 3 is a functional block diagram of a monitoring unit 23. FIG. 5 is a flowchart for explaining a determination procedure of a monitoring unit 23.

Explanation of symbols

11 Optical multiplexer / demultiplexer 12 Optical receiver 13 Transmission scheduler 14 Optical transmitter 15 User interface 21 Optical transmitter 22 Current detector 23 Monitoring unit 31 A / D converters 32 and 41 Sampling circuits 33 and 35 Comparison circuits 34 and 38 Determination Circuit 36 AND circuit 37 latch circuit 42 signal presence / absence determination circuit

Claims (7)

A monitoring device installed in any slave station of an optical communication system for connecting an optical communication line between a master station and a plurality of slave stations and transmitting an optical signal from each slave station to the master station,
A monitoring unit for detecting whether an optical signal is transmitted from the optical transmitter;
If the monitoring unit does not detect a time point when an optical signal is not transmitted in a predetermined period equal to or greater than a repetition period of a discovery period provided for searching for a slave station to newly join an optical communication system, A monitoring device characterized in that the slave station determines that it is emitting abnormal light and stops light emission. The monitoring unit includes a current detection unit that detects a drive current that drives the optical transmitter, and a comparison unit that compares a current value detected by the current detection unit with a predetermined threshold value.
The monitoring unit determines that the slave station is emitting abnormal light when the drive current value does not become less than a predetermined threshold in a predetermined period equal to or longer than the repetition period of the discovery period. The monitoring device according to claim 1, wherein the monitoring device is stopped. A burst enable signal is input to the monitoring unit,
The monitoring apparatus according to claim 2, wherein the monitoring unit monitors whether the drive current value becomes less than a predetermined threshold value during a period in which the burst enable signal is disabled. The monitoring unit includes a signal presence / absence determining unit that determines a state of a burst enable signal that transitions between an enable state in which light is emitted from an optical transmitter and a disabled state in which the optical transmitter is quenched.
If the burst enable signal is not disabled in a predetermined period equal to or longer than the discovery period repetition period, the monitoring unit determines that the slave station is emitting abnormal light and stops light emission. The monitoring apparatus according to any one of claims 1 to 3.   The monitoring apparatus according to claim 2, further comprising a switch that is controlled by the monitoring unit and that turns on and off a driving current to the optical transmitter. An input terminal for receiving detection information of a driving current for driving the optical transmitter;
A control output terminal for controlling a switch for turning on and off the power of the optical transmitter;
The current value input from the input terminal is compared with a predetermined threshold value, and if the current value does not become lower than the predetermined threshold value in a predetermined cycle, a switch-off output is output to the control output terminal. A monitoring circuit characterized by outputting a signal. An input terminal for receiving detection information of a burst enable signal;
A control output terminal for controlling a switch for turning on and off the power of the optical transmitter;
The presence or absence of a burst enable signal input from the input terminal is detected, and if the burst enable signal is not disabled in a predetermined cycle, a switch-off output signal is output to the control output terminal. Characteristic monitoring circuit.

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