Optical transmission system and optical transmission method

Abstract

[Problem] To provide an optical transport device, an optical transport system and an optical transport method that enable the strengths of optical signals to be recovered when the strengths of the optical signals vary due to the aged deteriorations, failures or the like of transmitters, land transport lines or the like. [Solution] This transport device comprises: a wavelength selection switching means that attenuates, in accordance with an attenuation amount, each of a plurality of optical signals outputted from a plurality of optical transmission means and that multiplexes and outputs the attenuated optical signals; and an optical detection means that detects and compares the strength of at least one of the plurality of optical signals with a first threshold value and a second threshold value higher than the first threshold value. On the basis of the result of said comparison, the wavelength selection switching means reduces the attenuation amount for the optical signal the strength of which has been detected when the strength of the optical signal is lower than the first threshold value, while the wavelength selection switching means increases the attenuation amount for the optical signal the strength of which has been detected when the strength of the optical signal is higher than the second threshold value, whereby the wavelength selection switching means controls the attenuation amount such that the optical signal the strength of which has been detected has a strength value between the first threshold value and the second threshold value.

Description

[Technical field]

[0001] The present invention relates to an optical transmission device, an optical transmission system, and an optical transmission method capable of appropriately controlling the intensity of an optical signal. [Background technology]

[0002] In optical communication systems such as submarine cable systems, communication is carried out by transmitting and receiving wavelength division multiplexed optical signals, which are optical signals with different wavelengths, between land terminal stations. At this time, the intensities of the optical signals contained in the wavelength division multiplexed optical signal are adjusted to appropriate signal intensities in accordance with the system design, and then output from the terminal station to the submarine transmission line.

[0003] In recent years, spectrum sharing has been adopted, in which the bandwidth of a wavelength division multiplexed optical signal is assigned to different users. In spectrum sharing, each user manages their optical transmitter so that an optical signal is output with the appropriate signal strength as determined by the system design.

[0004] In this case, the strength of the optical signal may fluctuate due to aging or failure of the optical transmitter that outputs the optical signal and the land transmission line that connects the optical transmitter to the land terminal station, etc. For this reason, techniques for adjusting the strength of the optical signal are used.

[0005] For example, Patent Document 1 discloses that the intensities of optical signals included in a wavelength division multiplexed optical signal are adjusted to be uniform. Patent Document 2 also discloses a related technique. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-038328 A [Patent Document 2] JP 2013-255195 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, when the strength of an optical signal fluctuates, there is no means for restoring the strength of the optical signal to the appropriate signal strength specified in the system design. When the strength of an optical signal transmitted from a terminal station fluctuates from the appropriate signal strength, the strength of optical signals included in the wavelength division multiplexed optical signal other than the optical signal whose strength has fluctuated is also affected due to the gain characteristics of the amplifier installed in the undersea transmission line.

[0008] In particular, in spectrum sharing, as described above, if the intensity of an optical signal in a band allocated to a specific user fluctuates, this affects optical signals in bands allocated to other users, which is problematic.

[0009] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide an optical transmission device, an optical transmission system, and an optical transmission method that are capable of restoring the strength of an optical signal when the strength of the optical signal fluctuates due to deterioration over time or a fault in a transmitter, a terrestrial transmission line, etc. [Means for solving the problem]

[0010] The optical transmission device of the present invention comprises: a wavelength selection switching means for attenuating each of the plurality of optical signals output from the plurality of optical transmission means according to an attenuation amount, and multiplexing and outputting the attenuated optical signals; a light detection means for detecting an intensity of at least one of the plurality of optical signals and comparing the intensity with a first threshold and a second threshold higher than the first threshold; Based on the result of the comparison, the wavelength selection switching means controls the amount of attenuation for the optical signal by decreasing the amount of attenuation for the optical signal when the intensity of the optical signal whose intensity has been detected becomes lower than a first threshold, and by increasing the amount of attenuation for the optical signal when the intensity of the optical signal whose intensity has been detected becomes higher than the second threshold, so that the intensity of the optical signal whose intensity has been detected becomes a value between the first threshold and the second threshold.

[0011] Alternatively, the optical transmission system of the present invention comprises: The optical transmission device as described above; and a plurality of the optical transmitting means.

[0012] Alternatively, the optical transmission method of the present invention includes: Attenuating each of the plurality of optical signals output from the plurality of optical transmitting means according to an attenuation amount; multiplexing and outputting the attenuated optical signals; Detecting an intensity of at least one of the plurality of optical signals and comparing it to a first threshold and a second threshold higher than the first threshold; Based on the result of the comparison, the amount of attenuation for the optical signal is controlled by decreasing the amount of attenuation for the optical signal when the intensity of the optical signal whose intensity has been detected becomes lower than a first threshold, and by increasing the amount of attenuation for the optical signal when the intensity of the optical signal whose intensity has been detected becomes higher than the second threshold, so that the amount of attenuation for the optical signal whose intensity has been detected becomes a value between the first threshold and the second threshold. Effect of the Invention

[0013] According to the present invention, it is possible to provide an optical transmission device, an optical transmission system, and an optical transmission method that are capable of restoring the strength of an optical signal when the strength of the optical signal fluctuates due to deterioration over time or a fault in a transmitter, a terrestrial transmission line, etc. [Brief description of the drawings]

[0014] [Figure 1] 1 is a block diagram showing an example of the configuration of an optical transmission system according to a first embodiment of the present invention. [Diagram 2] FIG. 1 is a diagram for explaining an optical transmission system according to a first embodiment of the present invention. [Diagram 3] FIG. 1 is a diagram for explaining an optical transmission system according to a first embodiment of the present invention. [Figure 4] 4 is a flowchart showing an operation of the optical transmission system in the first embodiment of the present invention. [Diagram 5]4 is a flowchart showing an operation of the optical transmission system in the first embodiment of the present invention. [Figure 6] 4 is a flowchart showing an operation of the optical transmission system in the first embodiment of the present invention. [Figure 7] FIG. 11 is a block diagram showing an example of a configuration of an optical transmission device according to a second embodiment of the present invention. [Figure 8] 10 is a flowchart illustrating an operation of the optical transmission device according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] <First embodiment> An optical transmission system 1 in a first embodiment will be described with reference to Fig. 1, Fig. 2, Fig. 3, and Fig. 4. Fig. 1 is a block diagram showing an example of the configuration of the optical transmission system 1. Figs. 2 and 3 are diagrams for explaining the details of the optical transmission system. Fig. 4 is a flowchart showing an example of the operation of the optical transmission system 1.

[0016] 1, the optical transmission system 1 includes data centers 10A, 10B, and 10C, an optical transmission device 20, terrestrial transmission paths 30A, 30B, and 30C, and a submarine transmission path 40. When it is not necessary to distinguish between the data centers 10A, 10B, and 10C, each of the data centers 10A, 10B, and 10C will be referred to as a data center 10. When it is not necessary to distinguish between the terrestrial transmission paths 30A, 30B, and 30C, each of the terrestrial transmission paths 30A, 30B, and 30C will be referred to as a terrestrial transmission path 30.

[0017] The data center 10 includes an optical transmitter 11 and a control device 12. The optical transmitter 11 corresponds to an optical transmission means. The optical transmitter 11 outputs an optical signal to the optical transmission device 20 via the land transmission line 30. The optical transmitter 11 outputs an optical signal with a preset intensity. The optical transmitter 11 can adjust the intensity of the optical signal in response to an instruction from the control device 12. For example, the optical transmitter 11 is an optical transponder. Note that a plurality of optical transmitters 11 may be provided in the data center 10. In this case, the data center 10 outputs a wavelength division multiplexed optical signal obtained by multiplexing the optical signals output from the plurality of optical transmitters 11 to the optical transmission device 20.

[0018] The control device 12 controls the optical transmitter 11. For example, the control device 12 can instruct the optical transmitter 11 of the intensity received from the user, thereby causing the optical transmitter 11 to output an optical signal of the intensity. The control device 12 can also communicate with the optical transmission device 20, and notifies the user of the optical transmitter 11 of information received from the optical transmission device 20. For example, when the control device 12 receives an alarm indicating an abnormality in the optical signal from an alarm signal generating means 24 described later, it notifies the user of the optical transmitter 11 of the occurrence of the abnormality.

[0019] The optical transmission device 20 includes a wavelength selection switching unit 22, a light detection unit 23, an alarm signal generation unit 24, and a branching unit 25. The optical transmission device 20 is connected to a plurality of data centers 10 via a land transmission line 30.

[0020] The wavelength selection switching means 22 attenuates each of the multiple optical signals output from the multiple optical transmitters 11 according to an attenuation amount, and multiplexes the attenuated optical signals to output a wavelength division multiplexed optical signal. In the optical transmission system 1, the wavelength selection switching means 22 attenuates each of the multiple optical signals output from the optical transmitters 11 in the data centers 10A, 10B, and 10C by a predetermined attenuation amount.

[0021] The wavelength selection switching means 22 is, for example, a WSS (Wavelength Selective Switch). The WSS separates the input optical signal into wavelengths, reflects each of the separated optical signals by a mirror, combines the reflected optical signals, and outputs a wavelength division multiplexed optical signal. The WSS can adjust the attenuation amount for each optical signal by adjusting the angle of the mirror that reflects each of the separated optical signals. The wavelength division multiplexed optical signal output from the wavelength selection switching means 22 is branched by the branching means 25 and output toward the undersea transmission line 40 and the photodetection means 23. The branching means 25 is, for example, an optical coupler.

[0022] The wavelength selection switching means 22 will be described in detail with reference to Fig. 2. In this description, the data center 10A outputs a wavelength division multiplexed optical signal in which optical signal A and optical signal B shown in Fig. 2 are multiplexed to the optical transmission device 20. In addition, the data center 10B outputs an optical signal C to the optical transmission device 20, and the data center 10C outputs an optical signal D to the optical transmission device 20.

[0023] For example, optical signals A, B, C, and D shown in FIG. 2 are input to the wavelength selection switching means 22. In the wavelength selection switching means 22, a plurality of center wavelengths as shown in FIG. 2 and wavelength intervals centered on each center wavelength are set as a plurality of transmission bands. The wavelength selection switching means 22 blocks light outside the transmission bands by maximizing the amount of attenuation in bands other than the transmission bands. Furthermore, the wavelength selection switching means 22 attenuates the intensity of the optical signal in the transmission band to a reference value set for each transmission band. For example, the amount of attenuation of the transmission band in the wavelength selection switching means 22 is the difference between the intensity of the optical signal set in advance and the reference value. Furthermore, a first threshold value and a second threshold value larger than the first threshold value are set for the transmission band.

[0024] The optical detection means 23 detects the intensity of each of the multiple optical signals based on the wavelength division multiplexed optical signal output from the wavelength selection switching means 22. Specifically, the optical detection means 23 receives the wavelength division multiplexed optical signal branched by the branching means 25. The optical detection means 23 detects the intensity of the optical signal in the multiple transmission bands by calculating the intensity for each unit wavelength. The optical detection means 23 includes, for example, an optical spectrum analyzer.

[0025] Further, the photodetector 23 stores a first threshold value and a second threshold value set for each transmission band. For example, as shown in FIG. 3, when the photodetector 23 detects that the intensity of the optical signal A in the transmission band falls below the first threshold value, the photodetector 23 reduces the attenuation amount for the transmission band in the wavelength selection switching means 22. As a result, the wavelength selection switching means 22 increases the intensity of the optical signal A in the wavelength division multiplexed optical signal. On the other hand, when the photodetector 23 detects that the intensity of the optical signal A in the transmission band exceeds the second threshold value, the photodetector 23 increases the attenuation amount for the transmission band in the wavelength selection switching means 22. As a result, the wavelength selection switching means 22 reduces the intensity of the optical signal. As described above, the intensity of the optical signal in the transmission band is maintained between the first threshold value and the second threshold value by the photodetector 23 and the wavelength selection switching means 22.

[0026] Moreover, the alarm signal generating means 24 generates an alarm signal at least when the intensity of the optical signal falls below a first threshold or when the intensity of the optical signal exceeds a second threshold. For example, the alarm signal generating means 24 generates an alarm signal when at least one of the optical signals A, B, C, and D shown in Fig. 2 falls below the first threshold. The alarm signal generating means 24 generates an alarm signal when at least one of the optical signals A, B, C, and D shown in Fig. 2 exceeds the second threshold. When generating an alarm signal, the alarm signal generating means 24 notifies the terminal in which the optical transmission device 20 is installed of an abnormality in the optical signal.

[0027] The alarm signal generating means 24 also stores the address (e.g., a Media Access Control (MAC) address or an Internet Protocol (IP) address) of the control device 12 that controls the optical transmitter 11 that outputs the optical signal. For example, the alarm signal generating means 24 stores the address of the control device 12 in the data center 10A in association with the optical signal A and the optical signal B. The alarm signal generating means 24 also stores the address of the control device 12 in the data center 10B in association with the optical signal C, and stores the address of the control device 12 in the data center 10C in association with the optical signal D.

[0028] When the strength of the optical signal falls below the first threshold or exceeds the second threshold, the alarm signal generating means 24 notifies the address associated with the optical signal of an abnormality in the optical signal, thereby enabling the user of the optical transmitter 11 in the data center 10 to know that an abnormality has occurred in the optical signal.

[0029] Next, the operation of the optical transmission system 1 will be described with reference to Fig. 4, Fig. 5, and Fig. 6. Fig. 4, Fig. 5, and Fig. 6 are flowcharts showing an example of the operation of the optical transmission system 1.

[0030] The optical transmitter 11 outputs an optical signal to the optical transmission device 20 (S101). In this operation example, the two optical transmitters 11 in the data center 10A output an optical signal A and an optical signal B. In addition, the optical transmitter 11 in the data center 10B outputs an optical signal C, and the optical transmitter 11 in the data center 10C outputs an optical signal D.

[0031] The wavelength selection switching means 22 attenuates the optical signal (S102). In this operation example, optical signals A, B, C, and D are input to the wavelength selection switching means 22. The wavelength selection switching means 22 separates each of the optical signals A to D according to wavelength, and applies a predetermined amount of attenuation to each of the optical signals A to D. For example, the wavelength selection switching means 22 attenuates the optical signal by the difference between a preset intensity of the optical signal and a reference value set for the optical signal. As a result, each optical signal attenuated by the wavelength selection switching means 22 has an intensity of the reference value as shown in FIG. 2.

[0032] The wavelength selection switching means 22 multiplexes the attenuated optical signals and outputs a wavelength division multiplexed optical signal (S103). The optical detection means 23 detects the intensity of the optical signal (S104). Specifically, the optical detection means 23 receives the wavelength division multiplexed optical signal branched by the branching means 25 and detects the intensity of the optical signal included in the wavelength division multiplexed optical signal.

[0033] The photodetector 23 selects one of the multiple transmission bands, and identifies an optical signal within the selected transmission band as an optical signal to be adjusted (S105). In this operation example, the photodetector 23 selects at least one of the transmission bands in which each of the optical signals A to D is located, and identifies one of the optical signals A to D as an optical signal to be adjusted. For example, the photodetector 23 identifies the optical signal A, which has the shortest central wavelength, as the optical signal to be adjusted among the optical signals A to D.

[0034] The optical detection means 23 judges whether the intensity of the optical signal is lower than a first threshold value (S106). Specifically, when the optical signal A is specified as the adjustment target in the above-mentioned S105, the optical detection means 23 judges whether the intensity of the optical signal A is lower than a first threshold value set in the transmission band associated with the optical signal A.

[0035] If the intensity of the optical signal is not determined to be lower than the first threshold (No in S106), the optical detection means 23 judges whether the intensity of the optical signal is higher than the second threshold (S107). For example, the optical detection means 23 judges whether the intensity of the optical signal A is higher than the second threshold set in the transmission band associated with the optical signal A. If the intensity of the optical signal is not determined to be higher than the second threshold (No in S107), the optical detection means 23 judges whether all the optical signals are the adjustment targets (S108). Specifically, the optical detection means 23 judges whether all the optical signals A to D included in the wavelength multiplexed optical signal are identified as the adjustment targets in S105. For example, the optical detection means 23 stores the transmission band of the optical signal identified in S105, and compares it with the transmission band set in the wavelength selection switching means 22 to judge whether all the optical signals are identified as the adjustment targets. Moreover, if it is determined that all optical signals have been subjected to adjustment (Yes in S108), the adjustment of the amount of attenuation for the wavelength selection switching means 22 is terminated. Specifically, the operations of S101 to S103 in the optical transmission system 1 are continuously executed, but the operations of S104 to S118 are not executed.

[0036] Furthermore, when it is determined that at least one of the optical signals included in the wavelength multiplexed optical signal has not been identified as an adjustment target (No in S108), the optical detection means 23 performs the process of S105. In the process of S105, the optical detection means 23 identifies an optical signal that has not been identified as an adjustment target as a new adjustment target. For example, when the optical signal A was identified as an adjustment target in the previously executed S105, the optical detection means 23 identifies one of the optical signals B to D as a new adjustment target.

[0037] In the process of S106, when it is determined that the intensity of the optical signal to be adjusted is lower than the first threshold (Yes in S106), the alarm signal generating means 24 generates an alarm signal (S109) as shown in Fig. 5. At this time, the light detecting means 23 notifies the alarm signal generating means 24 of information indicating the optical signal to be adjusted. The alarm signal generating means 24 notifies the terminal station in which the optical transmission device 20 is provided that an abnormality has occurred in the notified optical signal. In addition, the alarm signal generating means 24 generates an alarm signal including information indicating the notified optical signal, and transmits the alarm signal to an address associated with the optical signal. As a result, the control device 12 in the data center 10 can receive the alarm signal, so that the user of the optical transmitter 11 in the data center 10 can know that an abnormality has occurred in the optical signal.

[0038] Next, the light detection means 23 detects the difference between the intensity of the optical signal whose intensity has fallen below the first threshold and the first threshold (S110). The light detection means 23 judges whether the difference between the intensity of the optical signal and the first threshold is greater than the attenuation given to the optical signal (S111). If it is judged that the difference is greater than the attenuation (Yes in S111), the light detection means 23 notifies the wavelength selection switching means 22 and the alarm signal generation means 24 (S112). For example, the light detection means 23 notifies the wavelength selection switching means 22 to set the attenuation for the transmission band of the optical signal to zero. In addition, the light detection means 23 notifies the alarm signal generation means 24 of the difference between the difference between the intensity of the optical signal and the first threshold and the attenuation before setting it to zero, and the transmission band of the optical signal. The alarm signal generation means 24 notifies the address associated with the transmission band of the optical signal to increase the output of the optical transmitter 11 by the difference notified by the light detection means 23. As a result, in the optical transmission system 1, when the intensity of the optical signal falls below the first threshold even when the attenuation amount in the wavelength selection switching means 22 is set to zero, it is possible to notify the user of the optical transmitter 11 to increase the intensity of the optical signal output from the optical transmitter 11. The user of the optical transmitter 11 who receives the notification increases the output of the optical transmitter 11, thereby adjusting the intensity of the optical signal to exceed the first threshold.

[0039] Furthermore, if the optical detection means 23 does not determine that the difference is greater than the amount of attenuation (No in S111), it notifies the wavelength selection switching means 22 of the difference between the intensity of the optical signal whose intensity has fallen below the first threshold and the first threshold, and the transmission band of the optical signal. As a result, the wavelength selection switching means 22 reduces the attenuation in the notified transmission band by the notified difference (S113). Note that the wavelength selection switching means 22 may reduce the amount of attenuation by an amount obtained by adding a predetermined amount to the notified difference. As a result, in the optical transmission system 1, it is possible to increase the intensity of an optical signal whose intensity has fallen below the first threshold.

[0040] After S112 and S113, the light detection means 23 judges whether all the optical signals have become the adjustment targets (S114). Specifically, the light detection means 23 performs the same process as S108. Furthermore, if it is judged that all the optical signals have become the adjustment targets (Yes in S114), the adjustment of the attenuation amount for the wavelength selection switching means 22 ends. Specifically, the operations of S101 to S103 in the optical transmission system 1 continue to be executed, but the operations of S104 to S118 are not executed.

[0041] Furthermore, when it is determined that at least one of the optical signals included in the wavelength multiplexed optical signal is not identified as an optical signal to be adjusted (No in S114), the optical detection means 23 performs the process of S105. In the process of S105, the optical detection means 23 identifies an optical signal that has not been identified as an optical signal to be adjusted as a new optical signal to be adjusted, similar to the process of S105 after the process of S108.

[0042] Also, when the intensity of at least one of the optical signals included in the wavelength division multiplexed signal is higher than the second threshold (Yes in S107), as shown in Fig. 6, the alarm signal generating means 24 generates an alarm signal (S115). At this time, the optical detection means 23 notifies the alarm signal generating means 24 of information indicating the optical signal to be adjusted. The alarm signal generating means 24 notifies the terminal station in which the optical transmission device 20 is provided that an abnormality has occurred in the notified optical signal. The alarm signal generating means 24 also generates an alarm signal including information indicating the notified optical signal, and transmits the alarm signal to an address associated with the optical signal. As a result, the control device 12 in the data center 10 can receive the alarm signal, so that the user of the optical transmitter 11 in the data center 10 can know that an abnormality has occurred in the optical signal.

[0043] Next, the photodetector 23 detects the difference between the intensity of the optical signal whose intensity exceeds the second threshold and the second threshold (S116). At this time, the photodetector 23 notifies the wavelength selection switcher 22 of the detected difference and the transmission band of the optical signal.

[0044] The wavelength selection switching means increases the amount of attenuation (S117). Specifically, the attenuation amount of the optical signal in the transmission band notified by the light detection means 23 is increased by the notified difference. Note that the wavelength selection switching means 22 may increase the amount of attenuation by an amount obtained by adding a predetermined amount to the notified difference. This makes it possible to reduce the intensity of the optical signal, the intensity of which exceeds the second threshold, in the optical transmission system 1.

[0045] After S117, the light detection means 23 judges whether all the optical signals have become the adjustment targets (S118). Specifically, the light detection means 23 performs the same process as S108. Furthermore, if it is judged that all the optical signals have become the adjustment targets (Yes in S118), the adjustment of the attenuation amount for the wavelength selection switching means 22 ends. Specifically, the operations of S101 to S103 in the optical transmission system 1 continue to be executed, but the operations of S104 to S118 are not executed.

[0046] Furthermore, when it is determined that at least one of the optical signals included in the wavelength multiplexed optical signal is not identified as an optical signal to be adjusted (No in S118), the optical detection means 23 performs the process of S105. In the process of S105, the optical detection means 23 identifies an optical signal that has not been identified as an optical signal to be adjusted as a new optical signal to be adjusted, similar to the process of S105 after the process of S108.

[0047] In addition, when the light detection means 23 determines that all optical signals are to be adjusted in the process of S108 shown in FIG. 4 (Yes in S108), when the light detection means 23 determines that all optical signals are to be adjusted in the process of S114 shown in FIG. 5 (Yes in S114), and when the light detection means 23 determines that all optical signals are to be adjusted in S118 shown in FIG. 6 (Yes in S118), the adjustment of the attenuation amount for the wavelength selection switching means 22 is terminated. On the other hand, after each process, the adjustment of the attenuation amount for the wavelength selection switching means 22 may not be terminated and may be executed again from the process of S104. This allows the intensity of the optical signal to be continuously adjusted between the first threshold value and the second threshold value. When the process of S104 is executed again, the light detection means 23 stores that none of the optical signals are specified as the adjustment target.

[0048] As described above, the optical transmission system 1 includes the wavelength selection switching means 22 and the optical detection means 23. The wavelength selection switching means 22 attenuates each of the multiple optical signals output from the multiple optical transmission means (optical transmitters 11) according to the amount of attenuation, and multiplexes and outputs the attenuated optical signals. The optical detection means 23 detects the intensity of each of the multiple optical signals and compares it with a first threshold and a second threshold higher than the first threshold. Furthermore, based on the result of the comparison, the wavelength selection switching means 22 decreases the amount of attenuation for the optical signal when the intensity of the optical signal becomes lower than the first threshold, and increases the amount of attenuation for the optical signal when the intensity of the optical signal becomes higher than the second threshold higher than the first threshold. In this way, the wavelength selection switching means 22 controls the amount of attenuation so that the intensity of the optical signal whose intensity has been detected becomes a value between the first threshold and the second threshold.

[0049] The strength of an optical signal input to the optical transmission device 20 may fluctuate due to aging or failure of an optical transmitter that outputs the optical signal, a land transmission line from the optical transmitter to a land terminal station, etc. In the optical transmission system 1, even if the strength of the optical signal fluctuates, the strength of the optical signal can be returned to a value between the first threshold and the second threshold. <Second embodiment> The optical transmission device 2 in the second embodiment will be described with reference to Fig. 7 and Fig. 8. Fig. 7 is a block diagram showing a configuration example of the optical transmission device 2. Fig. 8 is a flowchart showing an operation example of the optical transmission device 2. As shown in Fig. 7, the optical transmission device 2 includes a wavelength selection switching means 22 and a light detection means 23.

[0050] The wavelength selection switching means 22 attenuates each of the multiple optical signals output from the multiple optical transmission means according to the attenuation amount, and multiplexes and outputs the attenuated optical signals. It is also assumed that a wavelength division multiplexed optical signal is output to the wavelength selection switching means 22 from a data center or the like (not shown). The wavelength selection switching means 22 in the optical transmission device 2 may have the same configuration, function, and connection relationship as the wavelength selection switching means 22 in the optical transmission system 1.

[0051] The photodetector 23 detects the intensity of at least one of the multiple optical signals. The photodetector 23 also compares the detected intensity with a first threshold and a second threshold higher than the first threshold. The photodetector 23 in the optical transmission device 2 may have the same configuration, function, and connection relationship as the photodetector 23 in the optical transmission system 1. The photodetector 23 notifies the wavelength selection switching means 22 of the results of comparing the detected intensity with each of the first and second thresholds.

[0052] Furthermore, the wavelength selection switching means 22 reduces the amount of attenuation for the optical signal when the intensity of the optical signal becomes lower than a first threshold based on the result of comparison by the optical detection means 23. Also, the wavelength selection switching means 22 increases the amount of attenuation for the optical signal when the intensity of the optical signal becomes higher than a second threshold that is higher than the first threshold based on the result of comparison by the optical detection means 23. In this way, the wavelength selection switching means 22 controls the amount of attenuation for the optical signal so that the intensity of the detected optical signal becomes a value between the first threshold and the second threshold.

[0053] The optical transmission device 2 may include a branching unit 25 as shown in Fig. 7. The branching unit 25 is not necessary, for example, when there is no need to output the light from the wavelength selection switching unit 22 to the outside.

[0054] The operation of the optical transmission device 2 will be described with reference to FIG.

[0055] The wavelength selection switching means 22 attenuates an optical signal (S201). The wavelength selection switching means 22 multiplexes and outputs the attenuated optical signal (S202). The optical detection means 23 detects the intensity of at least one optical signal among the multiple optical signals (S203). The optical detection means 23 determines whether the intensity of the detected optical signal is lower than a first threshold (S204).

[0056] When the optical detection means 23 determines that the intensity of any one of the optical signals whose intensity is detected is lower than the first threshold (Yes in S204), the wavelength selection switching means 22 reduces the attenuation amount for the optical signal whose intensity is lower than the first threshold.

[0057] Furthermore, when the light detection means 23 does not determine that the intensity of any of the optical signals whose intensity has been detected is lower than the first threshold value (No in S204), the light detection means 23 determines whether the intensity of at least one of the optical signals whose intensity has been detected is higher than the second threshold value (S206).

[0058] When the optical detection means 23 determines that the intensity of any one of the optical signals whose intensity is detected is higher than the second threshold (Yes in S206), the wavelength selection switching means 22 increases the attenuation amount for the optical signal whose intensity is higher than the second threshold. On the other hand, when the optical detection means 23 does not determine that the intensity of any of the optical signals whose intensity is detected is higher than the second threshold (No in S206), the optical transmission device 2 ends the operation.

[0059] As described above, the optical transmission device 2 includes the wavelength selection switching means 22 and the optical detection means 23. The wavelength selection switching means 22 attenuates each of the multiple optical signals output from the multiple optical transmission means according to the attenuation amount, and multiplexes and outputs the attenuated optical signals. The optical detection means 23 detects the intensity of at least one of the multiple optical signals and compares it with a first threshold and a second threshold higher than the first threshold. Furthermore, based on the result of the comparison, the wavelength selection switching means 22 decreases the attenuation amount for the optical signal when the intensity of the optical signal becomes lower than the first threshold, and increases the attenuation amount for the optical signal when the intensity of the optical signal becomes higher than the second threshold higher than the first threshold. In this way, the wavelength selection switching means 22 controls the attenuation amount so that the intensity of the optical signal becomes a value between the first threshold and the second threshold.

[0060] The strength of the optical signal input to the optical transmission device 2 may fluctuate due to aging or failure of an optical transmitter that outputs the optical signal, a land transmission line from the optical transmitter to a land terminal station, etc. In the optical transmission device 2, even if the strength of the optical signal fluctuates, the strength of the optical signal can be returned to a value between the first threshold and the second threshold.

[0061] Although the present invention has been described above with reference to the embodiment, the present invention is not limited to the above embodiment. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. [Explanation of symbols]

[0062] 1. Optical transmission system 2. Optical transmission equipment 10, 10A, 10B, 10C Data Center 11 Optical transmitter 12 Control device 20 Optical transmission equipment 22 Wavelength selection switching means 23 Light detection means 24 Alarm signal generation means 25 Branching means

Claims

1. A system comprising: a plurality of optical transmitters, each associated with a different user; An optical transmission device, The optical transmitters are connected to the optical transmission device by different terrestrial transmission lines, The optical transmission device includes: a wavelength selection switching means for attenuating each of the optical signals output from the optical transmitters according to an attenuation amount, and outputting the attenuated optical signals by wavelength division multiplexing; a light detection means for detecting an intensity of at least one of the plurality of optical signals and comparing the intensity with a first threshold and a second threshold higher than the first threshold; the wavelength selection switching means controls the amount of attenuation for the optical signal, when the intensity of the optical signal whose intensity has been detected becomes lower than the first threshold, based on a result of the comparison, by decreasing the amount of attenuation for the optical signal, and by increasing the amount of attenuation for the optical signal, when the intensity of the optical signal whose intensity has been detected becomes higher than the second threshold, so that the intensity of the optical signal whose intensity has been detected becomes a value between the first threshold and the second threshold; when the intensity of the optical signal whose intensity has been detected becomes lower than the first threshold and the difference between the intensity of the optical signal whose intensity has been detected and the first threshold is larger than the amount of attenuation, increasing the intensity of the optical signal whose intensity has become lower than the first threshold for the optical transmitter that transmitted the optical signal whose intensity has become lower than the first threshold; Optical transmission system.

2. The optical transmission system of claim 1, further comprising an alarm signal generating means for generating an alarm signal when the intensity of the optical signal becomes lower than the first threshold value or when the intensity of the optical signal becomes higher than the second threshold value.

3. 3. The optical transmission system according to claim 2, wherein said alarm signal generating means transmits said alarm signal to a control device of said optical transmitter which has output said optical signal.

4. the wavelength selection switching means attenuates each of the optical signals input from the optical transmitters, and outputs the wavelength division multiplexed optical signal to a submarine transmission line provided on the seabed.

4. An optical transmission system according to claim 1.

5. 5. The optical transmission system according to claim 1, wherein the wavelength selection switching means adjusts the amount of attenuation for each bandwidth of the optical signal.

6. An optical transmission method used in an optical transmission system in which a plurality of optical transmitters, each associated with a different user, are connected to an optical transmission device by a different terrestrial transmission path, comprising: In the optical transmission device, Attenuating each of the optical signals output from the optical transmitters according to an attenuation amount; outputting the attenuated optical signal by wavelength division multiplexing; Detecting an intensity of at least one of the plurality of optical signals and comparing it to a first threshold and a second threshold higher than the first threshold; based on a result of the comparison, when the intensity of the optical signal whose intensity has been detected becomes lower than the first threshold, the amount of attenuation for the optical signal is decreased, and when the intensity of the optical signal whose intensity has been detected becomes higher than the second threshold, the amount of attenuation for the optical signal is increased, thereby controlling the amount of attenuation so that the intensity of the optical signal whose intensity has been detected becomes a value between the first threshold and the second threshold; when the intensity of the optical signal whose intensity has been detected becomes lower than the first threshold and the difference between the intensity of the optical signal whose intensity has been detected and the first threshold is larger than the amount of attenuation, increasing the intensity of the optical signal whose intensity has become lower than the first threshold for the optical transmitter that transmitted the optical signal whose intensity has become lower than the first threshold; Optical transmission method.

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