Judgment system, judgment method

Abstract

This invention provides a determination system and method that reduce the number of monitoring devices required to monitor optical signals. [Solution] The transmission system S, which functions as a determination system, comprises a first amplifier 10 that amplifies an optical signal, a plurality of switches 20 provided downstream of the first amplifier 10 for selecting the wavelength of the optical signal, a second amplifier 30 provided downstream of the switches for amplifying the optical signal, a monitoring unit 40 provided downstream of the second amplifier 30 for monitoring the in-band signal-to-noise ratio of the optical signal and the out-of-band signal-to-noise ratio of the optical signal, and a control unit 50 that determines that the first amplifier 10 or the second amplifier 30 is abnormal based on a first noise which is the increase in noise in the in-band signal-to-noise ratio caused by an abnormality in the first amplifier 10 or the second amplifier 30, and a second noise which is the increase in noise in the out-of-band signal-to-noise ratio caused by the abnormality.

Description

Technical Field

[0001] The present disclosure relates to a determination system and a determination method.

Background Art

[0002] An optical transmission system that enables large-capacity communication is composed of a large number of devices interconnected via optical lines. The devices include amplifiers that amplify optical signals, switches (wavelength selective switches) that select a desired wavelength from wavelength-multiplexed optical signals, and the like. A method has been proposed for detecting an abnormality in a device by monitoring optical signals transmitted and received between these devices (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When detecting an abnormality in an amplifier, for example, a monitoring device is provided at the subsequent stage of the amplifier. The monitoring device is, for example, an OSNR monitor that monitors the optical signal-to-noise ratio (OSNR). With this configuration, an abnormality in the amplifier can be detected based on the OSNR of the optical signal output from the amplifier. On the other hand, this detection method requires the same number of monitoring devices as the number of amplifiers, leaving room for improvement in terms of cost.

[0005] The present disclosure has been made in view of such circumstances, and an object thereof is to reduce the number of monitoring devices that monitor optical signals.

Means for Solving the Problems

[0006] One aspect of the present disclosure is a determination system comprising: a first amplifier for amplifying an optical signal; a switch provided downstream of the first amplifier for selecting the wavelength of the optical signal; a second amplifier provided downstream of the switch for amplifying the optical signal; a monitoring unit provided downstream of the second amplifier for monitoring the in-band signal-to-noise ratio of the optical signal and the out-of-band signal-to-noise ratio of the optical signal; and a control unit that determines that the first amplifier or the second amplifier is abnormal based on a first noise which is an increase in noise in the in-band signal-to-noise ratio caused by an abnormality in the first amplifier or the second amplifier, and a second noise which is an increase in noise in the out-of-band signal-to-noise ratio caused by the abnormality.

[0007] One aspect of the present disclosure is a determination method performed by a determination system comprising: a first amplifier for amplifying an optical signal; a switch provided downstream of the first amplifier for selecting the wavelength of the optical signal; a second amplifier provided downstream of the switch for amplifying the optical signal; a monitoring unit provided downstream of the second amplifier for monitoring the in-band signal-to-noise ratio and the out-of-band signal-to-noise ratio of the optical signal; and a control unit, wherein the control unit determines that the first amplifier or the second amplifier is abnormal based on a first noise, which is an increase in noise in the in-band signal-to-noise ratio caused by an abnormality in the first amplifier or the second amplifier, and a second noise, which is an increase in noise in the out-of-band signal-to-noise ratio caused by the abnormality. [Effects of the Invention]

[0008] According to this disclosure, the number of monitoring devices that monitor optical signals can be reduced. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows the overall configuration of the optical transmission system. [Figure 2] Figure 2 shows the spectrum of the optical signal after it has passed through the amplifier. [Figure 3] Figure 3 shows the change in the spectrum of the optical signal before and after the wavelength-selective switch (WSS). [Figure 4] Figure 4 shows the spectrum of the optical signal that passed through the WSS. [Figure 5] Figure 5 shows the optical signal spectrum when the amplifier after the WSS is malfunctioning. [Figure 6] Figure 6 shows the optical signal spectrum when the amplifier preceding the WSS is malfunctioning. [Figure 7] Figure 7 is a flowchart for determining an amplifier malfunction in the configuration shown in Figure 1. [Figure 8] Figure 8 shows an example of the Add configuration of the Reconfigurable Optical Add / Drop Multiplexer (ROADM). [Figure 9] Figure 9 shows an example of a ROADM Drop configuration. [Figure 10] Figure 10 is a flowchart for determining an amplifier malfunction in the configuration shown in Figure 8 or Figure 9. [Figure 11] Figure 11 shows a comparative example of an optical transmission system. [Figure 12] Figure 12 shows an example of a hardware configuration. [Modes for carrying out the invention]

[0010] The embodiments of this disclosure will be described below with reference to the drawings.

[0011] (1) Configuration of the optical transmission system The overall configuration of an optical transmission system S will be described with reference to FIG. 1. The optical transmission system S includes a first amplifier 10, a wavelength selective switch (switch) 20, a second amplifier 30, a monitoring unit 40, a control unit 50, a multiplexing / demultiplexing unit 60, and a transponder 70. These components are interconnected by optical lines such as optical fibers. Note that the configuration including the first amplifier 10, the switch 20, and the second amplifier 30 may be referred to as a node. Although two nodes are shown in FIG. 1, the number of nodes is not limited thereto, and may be one or three or more.

[0012] The optical transmission system S functions as the determination system of the embodiment. Specifically, the control unit 50 that controls the optical transmission system S determines an abnormality of the first amplifier 10 or the second amplifier 30 via the monitoring unit 40. That is, the control unit 50 functions as a determination device that determines an abnormality of the first amplifier 10 or the second amplifier 30. Alternatively, it may be understood that the control unit 50 and the monitoring unit 40 function as a determination device that determines an abnormality of the first amplifier 10 or the second amplifier 30.

[0013] The first amplifier 10 is an optical amplifier that amplifies an optical signal input from the preceding stage. The switch 20 is a wavelength selective switch (WSS) that selects a desired wavelength from an optical signal (assumed to be wavelength-multiplexed) input from the preceding stage. Note that the switch 20 is also an optical switch. The second amplifier 30 is an optical amplifier that amplifies an optical signal input from the preceding stage.

[0014] The first amplifier 10 is provided at the preceding stage of the switch 20, and the second amplifier 30 is provided at the subsequent stage of the switch 20. The first amplifier 10 may be referred to as a Pre AMP. The second amplifier 30 may be referred to as a Booster AMP. When the first amplifier 10 and the second amplifier 30 are not distinguished by their relative positional relationship with the switch 20, they may be simply referred to as amplifiers. Although two switches 20 are provided in FIG. 1, the number may be only one.

[0015] With reference to FIG. 2, the spectrum of an optical signal that has passed through an amplifier will be described. The upper part of FIG. 2 shows the spectrum of the optical signal that has passed through the amplifier in a normal state. Amplified spontaneous emission (ASE) noise (hereinafter also simply referred to as noise) is added to the amplified optical signal.

[0016] The lower part of FIG. 2 shows the spectrum of the optical signal that has passed through the amplifier in an abnormal state. In the spectrum of the optical signal that has passed through the amplifier in the abnormal state, the noise is amplified and the optical signal-to-noise ratio (OSNR) is reduced compared to the case of passing through the amplifier in the normal state. Note that the OSNR may also be referred to as the signal-to-noise ratio of the optical signal.

[0017] When the optical signal power is S and the noise power is N, the OSNR is expressed, for example, by the following formula (the unit is decibel). Note that the OSNR may be represented by another well-known formula. OSNR=10log(S / N)

[0018] Note that the abnormality may be a concept including degradation. The abnormality or degradation of the amplifier may be determined based on a comparison with noise added when the optical signal passes through the amplifier in the normal state. This determination is implemented by a control unit 50 to be described later.

[0019] With reference to FIG. 3, the spectrum of the optical signal that has passed through a switch 20 will be described. As shown in FIG. 3, noise outside the optical signal is cut from the optical signal that has passed through the switch 20. On the other hand, noise inside the optical signal is not cut even after passing through the switch 20.

[0020] With reference to FIG. 4, terms related to the spectrum of the optical signal that has passed through the switch 20 will be described. The power of the noise inside the optical signal is called in-band noise power (In-band noise power in the figure). The (logarithmic) ratio between the power of the optical signal and the in-band noise power is called an in-band optical signal-to-noise ratio (In-band OSNR, in-band signal-to-noise ratio of the optical signal).

[0021] The power of noise outside the optical signal is called out-band noise power (Out-band noise power in the diagram). Out-band noise power is smaller than in-band noise power because most of the original noise is cut off by switch 20. The (logarithmic) ratio of the optical signal power to the out-band noise power is called the out-band OSNR (Out-band OSNR).

[0022] The monitoring unit 40 is an OSNR monitor that monitors the optical signal output from the preceding stage (second amplifier 30) (for example, the spectrum of the optical signal) and calculates the OSNR, specifically the In-band OSNR and Out-band OSNR described above. Note that "calculation" may be read as "monitoring".

[0023] The monitoring unit 40 may also calculate the OSNR (In-band OSNR and Out-band OSNR) from monitoring data other than the optical signal spectrum. For example, the monitoring unit 40 may monitor the PreFEC-BER (pre-forward error correction bit error rate) of the optical signal and calculate (estimate) the OSNR (In-band OSNR and Out-band OSNR).

[0024] The monitoring unit 40 is located downstream of the second amplifier 30. In other words, the monitoring unit 40 monitors the optical signal that has passed through the first amplifier 10, the switch 20, and the second amplifier 30. One monitoring unit 40 is provided at each node.

[0025] The control unit 50 is an operation system (OpS) that controls the optical transmission system S. The control unit 50 is connected to the monitoring unit 40. The control unit 50 determines an abnormality in the amplifier based on the In-band OSNR and Out-band OSNR of the optical signal calculated by the monitoring unit 40. Note that the control unit 50 may be a separate determination device provided in addition to the OpS that controls the optical transmission system S in order to determine an abnormality in the amplifier. In other words, the control unit 50 that determines an abnormality in the amplifier is not limited to being included in the OpS, but may be a separate unit from the OpS.

[0026] A method for determining an amplifier malfunction will be described with reference to Figures 5 and 6. Note that if either the first amplifier 10 or the second amplifier 30 is malfunctioning, the OSNR of the optical signal calculated by the monitoring unit 40 (e.g., In-Band OSNR) will decrease, indicating the malfunction. The decrease in OSNR may be determined, for example, by comparison with a predetermined threshold. The predetermined threshold may be, for example, the OSNR of the optical signal output from the second amplifier 30 when both the first amplifier 10 and the second amplifier 30 are functioning normally. Furthermore, since it is rare for both the first amplifier 10 and the second amplifier 30 to be malfunctioning, this scenario will not be considered. Below, a method for determining which amplifier is malfunctioning will be described when the OSNR decreases and it is determined that either the first amplifier 10 or the second amplifier 30 is malfunctioning.

[0027] First, as shown in Figure 5, when the second amplifier 30 is malfunctioning, the noise in the optical signal increases compared to the spectrum of the optical signal when both the first amplifier 10 and the second amplifier 30 are functioning correctly. Here, since the second amplifier 30 is located after the switch 20, the noise generated by the first amplifier 10 is filtered out of the band, and then the increased noise both inside and outside the band compared to the normal state is added. Therefore, the increase in noise caused by the malfunction of the second amplifier 30 is roughly the same inside and outside the band.

[0028] Furthermore, as shown in Figure 6, when the first amplifier 10 is malfunctioning, the noise in the optical signal increases compared to the spectrum of the optical signal when both the first amplifier 10 and the second amplifier 30 are functioning correctly. Here, unlike the case shown in Figure 5, since the first amplifier 10 is located before the switch 20, the noise increased by the first amplifier 10 both inside and outside the band is added together, and then the noise outside the band is cut off. Subsequently, the second amplifier 30 generates (normal) noise both inside and outside the band. Therefore, the increase in noise caused by the malfunction of the first amplifier 10 is greater inside the band than outside the band.

[0029] As described above, the control unit 50 determines whether the first amplifier 10 or the second amplifier 30 is malfunctioning by comparing the increase in noise inside and outside the optical signal band. A threshold value (th), which will be described later, may also be used to compare the increase in noise inside and outside the band.

[0030] The multiplexer / demultiplexer 60 is an optical multiplexer / demultiplexer that multiplexes or separates the wavelengths of an optical signal. The multiplexer / demultiplexer 60 is connected to the switch 20. The transponder 70 is an optical transponder that connects the inside and outside of the optical transmission system S. The transponder 70 is connected to the multiplexer / demultiplexer 60.

[0031] (3) Examples (3.1) Example 1 Referring to Figures 1 and 7, the flow for determining an abnormality in one of the amplifiers will be explained. First, the control unit 50 selects the upstream monitoring unit 40 from among the unchecked monitoring units 40 in the optical transmission system S shown in Figure 1 (step S01).

[0032] Next, the control unit 50 determines from the monitoring data of the selected monitoring unit 40 whether the OSNR (e.g., In-band OSNR) of the optical signal output from the second amplifier 30 has decreased (step S02). The decrease in OSNR is determined by comparing it with the OSNR when both amplifiers (first amplifier 10 and second amplifier 30) are functioning normally, as described above.

[0033] If the OSNR is low (YES in step S02), the control unit 50 compares the noise constituting the OSNR inside and outside the optical signal band (step S03).

[0034] Specifically, the control unit 50 determines that the second amplifier 30, located downstream of the switch 20, is malfunctioning if the difference between the increase in in-band signal noise generated by the first amplifier 10 and the second amplifier 30 due to a malfunction in either amplifier (ΔP_in-band ASE in the figure) and the increase in out-band signal noise generated by the first amplifier 10 and the second amplifier 30 due to a malfunction in either amplifier (ΔP_out-band ASE in the figure) is smaller than a threshold (th) (YES in step S03). The threshold (th) is used as the allowable error range. In other words, the control unit 50 determines that the second amplifier 30 is malfunctioning if ΔP_in-band ASE and ΔP_out-band ASE are almost the same.

[0035] Furthermore, the control unit 50 determines that the first amplifier 10, which is located before the switch 20, is abnormal if the difference between ΔP_in-band ASE and ΔP_out-band ASE is greater than the threshold (th) (NO in step S03) (step S05). As described above, the threshold (th) is used as the allowable range of error. In other words, if ΔP_in-band ASE and ΔP_out-band ASE differ by more than the error (if ΔP_in-band ASE is greater than the error by more than the error), the control unit 50 determines that the first amplifier 10 is abnormal.

[0036] Furthermore, if the control unit 50 determines that the second amplifier 30 is abnormal (step S04), it may simultaneously determine that the first amplifier 10 is normal. Similarly, if the control unit 50 determines that the first amplifier 10 is abnormal (step S05), it may determine that the second amplifier 30 is normal.

[0037] After the control unit 50 determines that any amplifier is abnormal, it repeats the flow from step S01 until it has confirmed all monitoring units 40 provided in the optical transmission system S (NO in step S06). Once all monitoring units 40 have been confirmed (YES in step S06), the flow ends. If it is determined in step S02 that the OSNR has not decreased (NO in step S02), the process proceeds to step S06. Also, if there is only one monitoring unit 40 (if there is only one node to be monitored), steps S01 and S06 may be omitted.

[0038] The above flow may be modified as appropriate, provided there are no inconsistencies. For example, all monitoring units 40 may be checked first, and a decrease in OSNR may be determined for each monitoring unit 40. In this case, the determination in steps S03 to S05 above is performed on the upstream monitoring unit 40 among the monitoring units 40 in which a decrease in OSNR is confirmed. Next, the determination in steps S03 to S05 above is performed on the second upstream monitoring unit 40 among the monitoring units 40 in which a decrease in OSNR is confirmed. This determination is performed on all monitoring units 40 in which a decrease in OSNR is confirmed.

[0039] (3.2) Example 2 Referring to Figures 8 to 10, an example of applying the determination method by the control unit 50 to the Add and Drop configurations of the Reconfigurable Optical Add / Drop Multiplexer (ROADM) will be described. Figure 8 shows the Add configuration, and Figure 9 shows the Drop configuration. Note that the Add configuration shown in Figure 8 and the Drop configuration shown in Figure 9 may be nodes constituting the optical transmission system S.

[0040] In the configuration shown in Figure 8, the control unit 50 can determine whether the first amplifier 10 (or the first amplifier 10 located between the right-side switch 20 (Post WSS) and the multiplexing / demultiplexing unit 60) or the second amplifier 30 located after the right-side switch 20 is malfunctioning. This allows the control unit to determine whether the malfunction is before or after the Add configuration. Note that in Figure 8, the first amplifier 10 located before the left-side switch 20 is assumed to be functioning normally.

[0041] In the configuration shown in Figure 9, the control unit 50 can determine whether the first amplifier 10, which is located before the left switch 20 (Pre WSS), or the second amplifier 30, which is located between the left switch 20 and the multiplexer / demultiplexer 60, is malfunctioning. In the configuration shown in Figure 9, the monitoring unit 40, to which the control unit 50 is connected, is located after the multiplexer / demultiplexer 60, not after the second amplifier 30, which is located after the right switch 20. This allows it to determine whether the malfunction is before or after the Drop configuration.

[0042] Figure 10 is a flowchart for determining amplifier abnormalities in the Add configuration shown in Figure 8 or the Drop configuration shown in Figure 9. Steps S11, S12, S13, and S14 in Figure 10 are the same as steps S02, S03, S04, and S05 explained with reference to Figure 7, respectively, so their explanation is omitted here.

[0043] (4) Effects The determination system of this embodiment includes a first amplifier 10 that amplifies an optical signal, a switch 20 provided downstream of the first amplifier 10 for selecting the wavelength of the optical signal, a second amplifier 30 provided downstream of the switch 20 for amplifying the optical signal, a monitoring unit 40 provided downstream of the second amplifier 30 for monitoring (calculating) the in-band signal-to-noise ratio and the out-of-band signal-to-noise ratio of the optical signal, and a control unit 50 that determines that the first amplifier 10 or the second amplifier 30 is abnormal based on a first noise (ΔP_in-band ASE), which is the increase in noise in the in-band signal-to-noise ratio caused by an abnormality in the first amplifier 10 or the second amplifier 30, and a second noise (ΔP_out-band ASE), which is the increase in noise in the out-of-band signal-to-noise ratio caused by an abnormality.

[0044] In the comparative example shown in Figure 11, it was necessary to provide a monitoring device (OSNR monitor in the figure) for each amplifier to be judged. In contrast, in the judgment system of the embodiment, it is possible to determine which of the two amplifiers (first amplifier 10 and second amplifier 30) is abnormal by providing only one monitoring unit 40 for each of the two amplifiers.

[0045] Specifically, the control unit 50 determines that the first amplifier 10 is abnormal if the difference between the first noise (ΔP_in-band ASE) and the second noise (ΔP_out-band ASE) is smaller than the threshold (th). On the other hand, the control unit 50 determines that the second amplifier 30 is abnormal if the difference between the first noise (ΔP_in-band ASE) and the second noise (ΔP_out-band ASE) is larger than the threshold (th).

[0046] The judgment system described above (for example, the control unit 50) can use a general-purpose computer system, such as the one shown in Figure 12. The illustrated computer system comprises a processor (CPU: Central Processing Unit) 901, memory 902, storage 903 (HDD: Hard Disk Drive, SSD: Solid State Drive), communication device 904, input device 905, and output device 906. The memory 902 and storage 903 are storage devices. In this computer system, each function of the judgment system is realized by the processor 901 executing a predetermined program loaded onto the memory 902.

[0047] Furthermore, the judgment system may be implemented on a single computer or on multiple computers. The judgment system may also be a virtual machine implemented on a computer. The judgment system program can be stored on computer-readable storage media such as HDDs, SSDs, USB (Universal Serial Bus) memory, CDs (Compact Discs), and DVDs (Digital Versatile Discs), or distributed over a network. Computer-readable storage media are, for example, non-transitory storage media.

[0048] This disclosure is not limited to the embodiments described above, and numerous modifications are possible within the scope of its essence. [Explanation of Symbols]

[0049] S Optical transmission system 10 First Amplifier 20 switches 30. Second Amplifier 40 Monitoring Department 50 Control Unit 60 Multiplexing / demultiplexing section 70 transponders

Claims

1. A first amplifier that amplifies the optical signal, A switch is provided downstream of the first amplifier to select the wavelength of the optical signal, A second amplifier is provided downstream of the aforementioned switch to amplify the optical signal, A monitoring unit is provided downstream of the second amplifier to monitor the in-band signal-to-noise ratio of the optical signal and the out-of-band signal-to-noise ratio of the optical signal, A control unit that determines that the first amplifier or the second amplifier is malfunctioning based on a first noise, which is the increase in noise in the in-band signal-to-noise ratio caused by a malfunction in the first amplifier or the second amplifier, and a second noise, which is the increase in noise in the out-of-band signal-to-noise ratio caused by the malfunction. A judgment system equipped with the following features.

2. The control unit determines that the first amplifier is abnormal if the difference between the first noise and the second noise is less than a threshold. The determination system according to claim 1.

3. The control unit determines that the second amplifier is abnormal if the difference between the first noise and the second noise is greater than a threshold. The determination system according to claim 1.

4. A first amplifier that amplifies the optical signal, A switch is provided downstream of the first amplifier to select the wavelength of the optical signal, A second amplifier is provided downstream of the aforementioned switch to amplify the optical signal, A monitoring unit is provided downstream of the second amplifier to monitor the in-band signal-to-noise ratio of the optical signal and the out-of-band signal-to-noise ratio of the optical signal, Control unit and A determination method performed by a determination system comprising: The control unit determines that the first amplifier or the second amplifier is malfunctioning based on a first noise, which is the increase in noise in the in-band signal-to-noise ratio caused by a malfunction in the first amplifier or the second amplifier, and a second noise, which is the increase in noise in the out-of-band signal-to-noise ratio caused by the malfunction. Judgment method.

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