Interference light correction device, PON system, and interference light correction method

Abstract

To provide a disturbance light correction device, a PON system, and a disturbance light correction method that are capable of enabling communication between an OLT and a normal ONU even when there is a faulty ONU that emits disturbance light.SOLUTION: A disturbance light correction device includes: a first measuring device that measures disturbance light emitted from a faulty ONU (Optical Network Unit) in a PON (Passive Optical Network) system; a control device that analyzes the disturbance light measured by the first measuring device and calculates optical power of correction light that corrects the disturbance light; and a light-emitting device that emits the correction light having the optical power calculated by the control device. The control device calculates the optical power of the correction light so that when the correction light and the disturbance light are aggregated, optical power of the disturbance light corrected by the aggregation becomes constant.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a disturbance light correction device used in a PON (Passive Optical Network) system, a PON system, and a disturbance light correction method. [Background technology]

[0002] Conventionally, a PON (Passive Optical Network) system is known that is composed of an OLT (Optical Line Terminal) which is an optical terminal device on the central office side, and ONUs (Optical Network Units) which are optical terminal devices on the subscriber side. In a PON system, an optical transmission line is shared by multiple ONUs, so when a fault occurs in an ONU and it transmits interference light, the OLT cannot distinguish an optical signal from a normal ONU. Therefore, Patent Document 1 proposes a method for identifying the faulty ONU that generates interference light.

[0003] In Patent Document 1, when the occurrence of a faulty ONU in a PON system is detected, first, the optical power of the interfering light is measured by an optical power meter. Then, each ONU is designated in order to establish a logical link. When the logical link is established, each ONU is made to output an upstream optical signal in the upstream band, and the optical power of the upstream light at that time is measured by the optical power meter. Then, if the measured optical power of the upstream light is equal to or less than a value obtained by adding a predetermined threshold to the optical power of the interfering light, that ONU is determined as a faulty ONU candidate, and among the faulty ONU candidates, the faulty ONU candidate that is optically closest to the OLT is identified as the faulty ONU. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-87121 A Summary of the Invention [Problem to be solved by the invention]

[0005] Here, in the method of identifying a faulty ONU in Patent Document 1, it is necessary to specify a normal ONU using a discovery procedure in a PON system and establish a logical link. However, if the faulty ONU emits interference light that completely blocks the connection between the normal ONU and the OLT, the discovery procedure cannot be executed, and communication between the OLT and the normal ONU becomes impossible. As a result, it becomes impossible to identify the faulty ONU.

[0006] The present invention has been made in light of the above-mentioned problems, and aims to provide an interference light correction device, a PON system, and an interference light correction method that enable communication between an OLT and a normal ONU even in the presence of a faulty ONU that emits interference light. [Means for solving the problem]

[0007] The interference light correction device of the present invention comprises a first measuring device that measures interference light emitted from a faulty ONU (Optical Network Unit) in a PON (Passive Optical Network) system, a control device that analyzes the interference light measured by the first measuring device and calculates the optical power of correction light that corrects the interference light, and a light emitting device that emits correction light having the optical power calculated by the control device, and when the correction light and the interference light are aggregated, the control device calculates the optical power of the correction light so that the optical power of the interference light corrected by aggregation is constant. A PON system according to the present invention includes a plurality of ONUs, an OLT, and the above-mentioned interference light compensation device, and the interference light compensation device is connected between the plurality of ONUs and the OLT. The interference light correction method of the present invention includes the steps of measuring interference light emitted from a faulty ONU in a PON system, analyzing the measured interference light and calculating the optical power of correction light for correcting the interference light, and emitting correction light having the calculated optical power. The calculation step calculates the optical power of the correction light so that when the correction light and the interference light are aggregated, the optical power of the interference light corrected by aggregation becomes constant. Effect of the Invention

[0008] According to the interference light correction device, PON system, and interference light correction method of the present invention, by correcting the interference light with correction light that keeps the optical power of the interference light constant, it is possible to establish communication between the OLT and a normal ONU even when a faulty ONU is present. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of a PON system according to a first embodiment. [Diagram 2] 4 is a functional block diagram of a control device of the disturbance light correction device according to the first embodiment. FIG. [Diagram 3] 13 is an example of waveform data of interference light. [Figure 4] 11 is a graph showing the relationship between optical power and time in one period of a light emission pattern of interfering light. [Diagram 5] This is data on the optical power of the interfering light for each time period stored in the memory unit. [Figure 6] 11 is a graph for explaining calculation of the optical power of the correction light. [Figure 7] This is data on the optical power of the correction light for each time period stored in the storage unit. [Figure 8] 13 is waveform data of the correction light in one cycle of the light emission pattern. [Figure 9] 11 shows waveform data of the corrected interference light. [Figure 10] 4 is a flowchart of a disturbance light correcting method according to the first embodiment. [Figure 11]This is the waveform data of the communication light input to the OLT after the interference light has been corrected. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Embodiment 1 1 is a schematic diagram of a PON system 100 according to embodiment 1. The PON system 100 in this embodiment includes ONUs 1 which are a plurality of subscriber optical terminal devices, an OLT 2 which is a central office optical terminal device, a branching coupler 3, and a disturbance light compensation device 4.

[0011] As shown in Fig. 1, ONU1 includes a faulty ONU11 and N normal ONUs 12-1 to 12-N. The faulty ONU11 periodically emits interference light due to some fault, which makes the normal ONUs 12-1 to 12-N unable to communicate with the OLT 2, regardless of control from the OLT 2. The normal ONUs 12-1 to 12-N operate normally and communicate with the OLT 2 via the optical transmission path.

[0012] The OLT 2 operates normally and communicates with normal ONUs 12-1 to 12-N via the optical transmission path. The OLT 2 can record the registration information and alarm log of the ONU 1. The OLT 2 monitors the upstream light from the ONU 1, and when the upstream light is present during a period when it should not be present, or when the upstream light is stronger than the expected range, the OLT 2 records an alarm log indicating that a fault has occurred, that is, that a faulty ONU 11 exists. The OLT 2 also notifies the disturbance light compensation device 4 of the occurrence of a fault in the PON system 100.

[0013] The branching coupler 3 branches and aggregates communication light between the ONU 1 and the OLT 2. In this embodiment, the branching coupler 3 is connected between the ONU 1 and the interference light correction device 4.

[0014] The interference light correction device 4 is a device connected between the ONU 1 and the OLT 2, and corrects interference light from the faulty ONU 11. More specifically, the interference light correction device 4 is connected between the branch coupler 3 and the OLT 2. The interference light correction device 4 includes WDM (Wavelength Division Multiplex) couplers 41a and 41b, a cutoff device 42, a first coupler 43a, a second coupler 43b, a third coupler 43c, a first measuring device 44a, a second measuring device 44b, a light emitting device 45, and a control device 46.

[0015] The WDM couplers 41a and 41b are wavelength division multiplexing couplers that split the communication light into upstream light from the ONU1 to the OLT2 and downstream light from the OLT2 to the ONU1. The WDM coupler 41a is connected to the branching coupler 3, and the WDM coupler 41b is connected to the OLT2.

[0016] The cutoff device 42 is an optical switch connected between the WDM coupler 41a and the WDM coupler 41b and cuts off the communication light. The cutoff device 42 is turned on by the control device 46 when the OLT 2 detects the occurrence of a fault in the PON system 100, and is turned off when the correction by the interference light correction device 4 is completed. When the cutoff device 42 is on, the communication light from the WDM 41b, i.e., the communication light from the OLT 2 to the ONU 1 is cut off. This stops the discovery communication from the normal ONUs 12-1 to 12-N. At this time, the faulty ONU 11 emits interference light regardless of the control of the OLT 2, so only the interference light from the faulty ONU 11 is input to the interference light correction device 4.

[0017] When the cutoff device 42 is off, the cutoff of the communication light from the WDM 41b, i.e., the communication light from the OLT 2 to the ONU 1, is released. This enables communication between the normal ONUs 12-1 to 12-N and the OLT 2. In the following description, the period during which the cutoff device 42 is on, i.e., the period from when the OLT 2 detects the occurrence of a fault in the PON system 100 until the disturbance light is corrected by the disturbance light correction device 4, is referred to as "when a fault occurs."

[0018] The first coupler 43a is a two-way branching coupler, and branches the upstream light from the WDM coupler 41a to the first measuring device 44a and the second coupler 43b. When a fault occurs, the upstream light from the WDM coupler 41a contains only the interference light from the faulty ONU 11.

[0019] The second coupler 43b is a two-way branching coupler that combines the upstream light from the first coupler 43a and the upstream light from the light emitting device 45 into one and outputs it to the third coupler 43c. When a fault occurs, the upstream light from the first coupler 43a is interference light from the faulty ONU 11, and the upstream light from the light emitting device 45 is correction light, which will be described later. That is, in the second coupler 43b, the interference light from the faulty ONU 11 and the correction light from the light emitting device 45 are combined, and the interference light corrected by the correction light is output.

[0020] The third coupler 43c is a two-way branching coupler, and branches the upstream light from the second coupler 43b to the WDM coupler 41b and the second measuring device 44b. When a fault occurs, the upstream light from the second coupler 43b is corrected interference light.

[0021] The first measuring device 44a is an optical oscilloscope, and when a fault occurs, measures interference light output from the faulty ONU 11. Specifically, the first measuring device 44a measures interference light input from the faulty ONU 11 via the branching coupler 3, the WDM coupler 41a, and the first coupler 43a, and outputs waveform data of the interference light to the control device 46.

[0022] The light emitting device 45 outputs light for correcting the disturbance light output from the faulty ONU 11. In the following description, the light for correcting the disturbance light is referred to as "correction light." The light emitting device 45 is composed of a condenser lens and a light emitting element such as a laser diode. The correction light output from the light emitting device 45 is output to the second coupler 43b.

[0023] The second measuring device 44b is an optical oscilloscope, and measures the corrected interference light. Specifically, the second measuring device 44b measures the corrected interference light collected in the second coupler 43b and input via the third coupler 43c, and outputs waveform data of the corrected interference light to the control device 46.

[0024] The control device 46 controls the blocking device 42, the first measuring device 44a, the second measuring device 44b, and the light emitting device 45, stores the waveform data acquired from the first measuring device 44a and the second measuring device 44b, and performs calculations necessary for correcting interference light. The control device 46 includes a processor such as a CPU, and a memory such as a RAM, a ROM, or a flash memory.

[0025] 2 is a functional block diagram of the control device 46 of the interference light correction device 4 according to the first embodiment. The control device 46 has a blocking control unit 461, an interference light analysis unit 462, a correction light calculation unit 463, an emission control unit 464, and a storage unit 465. The blocking control unit 461, the interference light analysis unit 462, the correction light calculation unit 463, and the emission control unit 464 are functional units that are realized by a processor executing software (programs) or by a dedicated circuit such as an ASIC.

[0026] The cutoff control unit 461 controls the cutoff device 42 according to the state of the PON system 100. Specifically, when the cutoff control unit 461 receives a notification of the occurrence of a fault in the PON system 100 from the OLT 2, it turns on the cutoff device 42 to cut off the communication light from the OLT 2 to the ONU 1. Furthermore, when the cutoff control unit 461 receives a notification of the completion of correction from the correction light calculation unit 463 after the fault occurs, it turns off the cutoff device 42 to release the cutoff of the communication light from the OLT 2 to the ONU 1. The cutoff control unit 461 may monitor the upstream light from the ONU 1 to detect the occurrence of a fault. In this case, a notification from the OLT 2 is not required.

[0027] The interfering light analysis unit 462 analyzes the interfering light based on the waveform data of the interfering light measured by the first measuring device 44a. FIG. 3 is an example of the waveform data of the interfering light. The interfering light analysis unit 462 first analyzes the period of the emission pattern of the interfering light. Then, the interfering light analysis unit 462 obtains the relationship between the optical power (dBm) and time (s) in one period of the emission pattern of the interfering light, and stores it in the memory unit 465. FIG. 4 is a graph showing the relationship between the optical power and time in one period of the emission pattern of the interfering light, and FIG. 5 is data of the optical power of the interfering light for each time stored in the memory unit 465.

[0028] The interfering light analysis unit 462 divides the optical power of the interfering light and one period of the interfering light into multiple parts. In the example of Fig. 4 and Fig. 5, the optical power of the interfering light is divided into seven stages from the minimum value P1 to the maximum value Pmax, and one period of the interfering light is divided into 11 stages from T0 to T10. Then, the optical power at each time T0 to T10 is calculated from the waveform data of the interfering light, and stored in the storage unit 465.

[0029] The correction light calculation unit 463 calculates the optical power of the correction light for correcting the interference light. Here, in order to enable communication between the normal ONUs 12-1 to 12-N and the OLT 2, it is sufficient to eliminate the fluctuation in the optical power of the interference light and make the optical power of the interference light constant regardless of time. FIG. 6 is a graph for explaining the calculation of the optical power of the correction light. As shown in FIG. 6, in order to make the optical power of the interference light constant at Pmax, it is sufficient to set the optical power of the correction light to the difference ΔP between Pmax and the optical power at each time.

[0030] The correction light calculation unit 463 calculates ΔP at each time T0 to T10 and stores it in the memory unit 465. FIG. 7 shows data on the optical power of the correction light for each time stored in the memory unit 465. As shown in FIG. 7, at times T0 to T2 and T10, the optical power of the interference light is Pmax, so the optical power of the correction light is 0. At times T3 to T9, the value (ΔP) obtained by subtracting the optical power at each time from Pmax is set as the optical power of the correction light. FIG. 8 shows waveform data of the correction light in one cycle of the emission pattern. The cycle of the emission pattern of the correction light is the same as the cycle of the emission pattern of the interference light.

[0031] The light emission control unit 464 controls the light emitting device 45 so that the light emitting device 45 periodically outputs correction light based on the data stored in the memory unit 465. Fig. 9 shows waveform data of the corrected interference light. In Fig. 9, the interference light before correction is shown by a dashed line, and the interference light after correction is shown by a solid line. As shown in Fig. 9, the interference light is corrected by the correction light, so that the optical power of the interference light becomes constant at Pmax.

[0032] Furthermore, the correction light calculation unit 463 corrects the optical power of the correction light based on the waveform data of the corrected interference light measured by the second measurement device 44b. If the optical power of the interference light after correction measured by the second measurement device 44b is not constant at Pmax, the correction light calculation unit 463 corrects the optical power of the correction light stored in the storage unit 465 based on the difference ΔP from Pmax. Then, if the correction light calculation unit 463 determines that the optical power of the interference light after correction measured by the second measurement device 44b has become constant at Pmax, it notifies the cutoff control unit 461 of the completion of the correction. After the correction is completed, the correction light based on the data stored in the storage unit 465 is output from the light emitting device 45 until the occurrence of a new fault is detected.

[0033] Here, in the above description, the optical power of the correction light is calculated so that the optical power of the interference light is constant at Pmax, but "constant" is not limited to being strictly constant, and there may be an error range that is not detected by the OLT 2. The allowable error range is Pmax±1.2 (dBm). The allowable range is determined as a range in which the waveform of the interference light is not included inside the eye pattern mask of the PON system defined by the international standard IEEE802.3ah.

[0034] The storage unit 465 is a non-volatile or volatile memory such as a RAM, a ROM, or a flash memory. The storage unit 465 stores waveform data of the interference light, optical power of the interference light at each time, optical power of the correction light at each time, waveform data of the correction light, and waveform data of the corrected interference light.

[0035] Fig. 10 is a flowchart of the interference light correction method according to the first embodiment. Each process in Fig. 10 is executed by the control device 46 of the interference light correction device 4. This method is started when the control device 46 receives a notification of the occurrence of a fault in the PON system 100 from the OLT 2. First, the cutoff control unit 461 turns on the cutoff device 42 (S1). As a result, the downstream light from the OLT 2 is cut off, and only the interference light is input as the upstream light.

[0036] Then, the first measuring device 44a measures the interference light (S2). The waveform data of the interference light measured by the first measuring device 44a is output to the control device 46. Then, the interference light is analyzed by the interference light analysis unit 462 based on the waveform data of the interference light (S3). Here, the optical power for each time period in one cycle of the emission pattern of the interference light is calculated and stored in the memory unit 465.

[0037] Next, the optical power of the correction light is calculated by the correction light calculation unit 463 (S4). Here, the difference ΔP between the maximum optical power Pmax in one period of the interference light and the optical power for each time is calculated as the optical power for each time of the correction light, and is stored in the storage unit 465. Then, the correction light having the optical power calculated by the correction light calculation unit 463 is output from the light emitting device 45 (S5).

[0038] Next, the corrected interference light is measured by the second measuring device 44b, and the correction light calculation unit 463 determines whether the optical power of the corrected interference light is constant at Pmax (S6). If the optical power of the corrected interference light is not constant at Pmax (S6: NO), the correction light is modified so that the optical power of the corrected interference light is constant at Pmax (S7), and the process returns to step S6. On the other hand, if the corrected interference light is constant at Pmax (S6: YES), the correction of the interference light is deemed to be completed, and the cutoff device 42 is turned off by the cutoff control unit 461 (S8).

[0039] When the cutoff device 42 is turned off, communication between the normal ONUs 12-1 to 12-N and the OLT 2 is resumed. FIG. 11 shows waveform data of the communication light input to the OLT 2 after the interference light is corrected. The solid line in FIG. 11 indicates the communication light from the normal ONUs 12-1 to 12-N input to the OLT 2. Also, in FIG. 11, for reference, the interference light before correction is indicated by a dashed line, and the interference light after correction is indicated by a two-dot chain line. As shown in FIG. 11, by correcting the interference light from the faulty ONU 11 so that Pmax is constant, the LOW level of the communication light received by the OLT 2 becomes constant at Pmax. This makes it possible for the OLT 2 to identify the upstream light output from the normal ONUs 12-1 to 12-N. As a result, even if there is a faulty ONU 11 in the PON system 100 that periodically emits interfering light that prevents the normal ONUs 12-1 to 12-N from communicating with the OLT 2, communication between the normal ONUs 12-1 to 12-N and the OLT 2 can be enabled.

[0040] In addition, by enabling communication between the normal ONUs 12-1 to 12-N and the OLT 2, it is possible to check the alarm log of the OLT 2 and the operating status of the ONUs 1 after communication is restored, and to check which ONUs 1 are still not operating before and after the correction of the interfering light. As a result, it is possible to quickly find out which ONUs 11 are faulty ONUs 11.

[0041] Although the embodiment of the present invention has been described above, the present invention is not limited to the configuration of the above embodiment, and various modifications or combinations are possible within the scope of the technical idea. For example, the correction light calculation unit 463 calculates the optical power of the correction light for each time so that the optical power of the interference light is constant at Pmax, but it is sufficient that the optical power of the interference light is constant, and it may be constant at an optical power greater than Pmax.

[0042] In the above embodiment, the PON system 100 is configured to include the disturbance light compensation device 4 regardless of the occurrence of a fault, but the present invention is not limited to this. For example, the PON system 100 may be configured not to include the disturbance light compensation device 4, and the disturbance light compensation device 4 may be incorporated when a fault occurs. In this case, an administrator who detects the occurrence of a fault by a notification from the OLT 2 may connect the disturbance light compensation device 4 between the ONU 1 and the OLT 2 and turn on the cutoff device 42 of the disturbance light compensation device 4. Alternatively, the cutoff device 42 of the disturbance light compensation device 4 may be turned on in the initial state. The operation of the disturbance light compensation device 4 thereafter is the same as that of the first embodiment. In this case, the cutoff control unit 461 of the disturbance light compensation device 4 does not need to receive a notification of the occurrence of a fault in the PON system 100 from the OLT 2. [Explanation of symbols]

[0043] 1 ONU, 2 OLT, 3 branching coupler, 4 interference light correction device, 11 faulty ONU, 12-1 to 12-N normal ONU, 41a WDM coupler, 41b WDM coupler, 42 cutoff device, 43a first coupler, 43b second coupler, 43c third coupler, 44a first measuring device, 44b second measuring device, 45 light emitting device, 46 control device, 100 PON system, 461 cutoff control unit, 462 interference light analysis unit, 463 correction light calculation unit, 464 light emission control unit, 465 memory unit.

Claims

1. A first measuring device for measuring interference light emitted from a faulty ONU (Optical Network Unit) in a Passive Optical Network (PON) system; a control device that analyzes the interference light measured by the first measurement device and calculates an optical power of a correction light that corrects the interference light; a light emitting device that emits the correction light having the optical power calculated by the control device, The control device is a disturbance light correction device that calculates the optical power of the correction light so that, when the correction light and the disturbance light are aggregated, the optical power of the disturbance light corrected by aggregation becomes constant.

2. The control device includes: Identifying a period of the emission pattern of the interference light; Dividing one period of the interference light into a plurality of periods; The interference light correction device according to claim 1 , wherein the difference between the maximum optical power of the interference light and the optical power of the interference light for each time is set as the optical power of the correction light for each time.

3. Further comprising a cut-off device for cutting off a signal from an OLT (Optical Line Terminal), The interference light correction device according to claim 1 or 2, wherein the interference light is measured by the first measuring device by blocking a signal from the OLT by the blocking device.

4. A second measuring device for measuring the disturbance light corrected by the correction light, The interference light correction device according to any one of claims 1 to 3, wherein the control device corrects the optical power of the correction light when the optical power of the interference light measured by the second measuring device is not constant.

5. A plurality of ONUs; With OLT, The interference light correction device according to any one of claims 1 to 4, The interference light compensation device is a PON system connected between the plurality of ONUs and the OLT.

6. Measuring interference light emitted from a faulty ONU in the PON system; A step of analyzing the measured interference light and calculating an optical power of a correction light for correcting the interference light; and emitting the correction light having the calculated optical power, The calculating step is a method for correcting interference light, which calculates the optical power of the correction light so that, when the correction light and the interference light are aggregated, the optical power of the interference light corrected by aggregation becomes constant.

Images