Optical communication system control device and program

Abstract

To suppress the influence of optical noise due to nonlinear optical effects in an optical communication system that transmits a plurality of wavelength-multiplexed signal lights.SOLUTION: A control device includes acquisition means for acquiring the signal-to-noise ratios of a plurality of signal lights determined by an optical receiving device from the optical receiving device, and control means for controlling the amount of attenuation to be provided by an adjuster in each of one or more sections of an optical transmission line, the control means executes a determination process for determining the amount of attenuation to be provided by the adjuster in each of the one or more sections, the determination process includes an adjustment process for determining the amount of attenuation to be provided by the adjuster in the section to be adjusted by increasing the amount of attenuation provided by the adjuster in the section to be adjusted among the one or more sections and monitoring the signal-to-noise ratio of the plurality of signal lights. The section includes an optical amplifier, an adjuster connected downstream of the optical amplifier in the transmission direction of the signal light to adjust the optical power of the signal light, and an optical fiber connected downstream of the adjuster.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a technique for suppressing the influence of optical noise caused by nonlinear optical effects in optical fibers. [Background technology]

[0002] Regarding power saving in optical communication systems, non-patent document 1 discloses that by using O-band, which is the wavelength band of 1260 nm to 1360 nm, part of the signal processing can be omitted, thereby achieving more power saving than the conventionally used wavelength band of 1530 nm to 1565 nm (C-band).

[0003] On the other hand, Non-Patent Document 2 discloses that in the wavelength range near 1310 nm, the influence of optical noise (non-linear optical noise) caused by the non-linear optical effect of optical fibers becomes extremely large, and therefore the O band is not suitable for wavelength division multiplexing transmission. Note that wavelengths near 1310 nm have a chromatic dispersion value of 0 or close to 0. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Seiler,PM,et.al.,Toward coherent O-band data center interconnects.Front.Optoelectron.14,414-425,2021 [Non-Patent Document 2] A.Ferrari,et.al.,"Assessment on the Achievable Throughput of Multi-Band ITU-T G.652.D Fiber Transmission Systems", in Journal of Lightwave Technology,vol.38,no.16,pp.4279-4291,15,August 15, 2020 Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure provides a technique for suppressing the influence of optical noise due to nonlinear optical effects in an optical communication system that transmits a plurality of wavelength-multiplexed signal lights. [Means for solving the problem]

[0006] According to one aspect of the present disclosure, there is provided a control device for an optical communication system in which an optical transmitter transmits a plurality of wavelength-multiplexed signal lights to an optical receiver via an optical transmission path including one or more sections. Each of the one or more sections includes an optical amplifier for amplifying the plurality of signal lights, an adjuster connected downstream of the optical amplifier in a transmission direction of the plurality of signal lights and for adjusting the optical power of the plurality of signal lights, and an optical fiber connected downstream of the adjuster in the transmission direction. The control device includes an acquisition means for acquiring, from the optical receiver, a signal-to-noise ratio of the plurality of signal lights determined by the optical receiver demodulating the plurality of signal lights, and a control means for controlling an attenuation amount to be provided by the adjuster in each of the one or more sections, the control means executing a determination process for determining an attenuation amount to be provided by the adjuster in each of the one or more sections, the determination process including an adjustment process for determining an attenuation amount to be provided by the adjuster in the adjustment target section by monitoring the signal-to-noise ratio of the plurality of signal lights while increasing an attenuation amount to be provided by the adjuster in the adjustment target section among the one or more sections. Effect of the Invention

[0007] According to the present disclosure, it is possible to suppress the influence of optical noise due to nonlinear optical effects in an optical communication system that transmits a plurality of wavelength-multiplexed signal lights. [Brief description of the drawings]

[0008] [Figure 1] 1 is a block diagram of an optical communication system according to some embodiments. [Diagram 2] 13 is a flow chart of a reconciliation process according to some embodiments. [Diagram 3] FIG. [Figure 4] 13 is a flow chart of a reconciliation process according to some embodiments. [Diagram 5] 13 is a flow chart of a reconciliation process according to some embodiments. [Figure 6] FIG. 2 is a block diagram of a control device, according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more features among the multiple features described in the embodiments may be arbitrarily combined. In addition, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0010] Before describing each embodiment, a common configuration among the embodiments will be described below. FIG. 1 is a configuration diagram of an optical communication system according to some embodiments. An optical transmitter 1 transmits wavelength-multiplexed light obtained by wavelength-multiplexing a plurality of signal lights to an optical receiver 2 via an optical transmission line 3. The wavelength range of the wavelength-multiplexed light includes wavelengths at which the absolute value of the chromatic dispersion value is lower than a threshold value in an optical fiber used in the optical transmission line 3, for example, wavelengths at which the absolute value of the chromatic dispersion value is 0. As an example, the chromatic dispersion value becomes 0 at 1310 nm, and the wavelength range of the wavelength-multiplexed light is a wavelength range of 1260 nm to 1360 nm. In other words, the wavelength-multiplexed light is light in the O band.

[0011] The optical receiving device 2 separates the wavelength-multiplexed light from the optical transmitting device 1 and demodulates each signal light. When demodulating each signal light, the optical receiving device 2 determines the signal-to-noise ratio (SNR) of each signal light. As an example, the optical receiving device 2 generates an electrical signal corresponding to the signal light by coherently detecting the signal light, and determines the SNR of each signal light by determining the noise component based on the coordinates in a complex plane of the amplitude and phase of the generated electrical signal and the coordinates of each signal point determined by the modulation method. The optical receiving device 2 repeatedly transmits the SNR of each signal light to the control device 5. In the following description, the signal-to-noise ratio determined from the electrical signal generated based on the signal light is referred to as the SNR of the signal light, and the ratio of the signal light to the noise light is referred to as the OSNR of the signal light.

[0012] The optical transmission line 3 includes optical amplifiers 31-1, 31-2, and 31-3. The optical amplifier 31-1 amplifies the wavelength-multiplexed light from the optical transmission device 1 in a lump. In FIG. 1, the optical amplifier 31-1 is shown as an external device of the optical transmission device 1, but the optical amplifier 31-1 may be an internal device of the optical transmission device 1. The optical amplifier 31-2 amplifies the wavelength-multiplexed light input to the optical reception device 2 in a lump. In FIG. 1, the optical amplifier 31-2 is shown as an external device of the optical reception device 2, but the optical amplifier 31-2 may be an internal device of the optical reception device 2. The optical amplifier 31-3 is an optical amplifier provided in the middle of the optical transmission line 3 to compensate for attenuation of the optical signal in the optical transmission line 3. In the configuration of FIG. 1, the optical transmission line 3 has two optical amplifiers 31-3, but the number of optical amplifiers 31-3 may be one or more depending on the length of the optical transmission line 3. Furthermore, when the length of the optical transmission line 3 is short, the number of optical amplifiers 31-3 may be zero.

[0013] As shown in FIG. 1, the optical transmission line 3 has an optical amplifier 31-1 provided at its starting point, an optical amplifier 31-2 provided at its end point, and one or more optical amplifiers 31-3 provided along the optical transmission line 3 as necessary. As described above, the number of optical amplifiers 31-3 may be zero. In other words, if the optical amplifiers 31-1, 31-2, and 31-3 are referred to as optical amplifiers 31 without distinguishing between them, the optical transmission line 3 is divided into "sections" each consisting of an optical amplifier 31 and an optical fiber connecting the optical amplifier 31 and an optical amplifier 31 downstream of the optical amplifier 31 in the transmission direction of the signal light. In the configuration of FIG. 1, the optical transmission line is divided into three sections, a section 3-1, a section 3-2, and a section 3-3. More generally, when the number of optical amplifiers excluding the optical amplifier 31-2 that amplifies the wavelength-multiplexed light immediately before the optical receiving device 2 is P (P is an integer equal to or greater than 1), the optical transmission line is divided into P sections.

[0014] An adjuster 32 is provided downstream of the optical amplifier 31 in each section and upstream of the optical fiber. In FIG. 1, adjuster 32-1 is provided in section 3-1, adjuster 32-2 is provided in section 3-2, and adjuster 32-3 is provided in section 3-3. Adjuster 32 can be configured to adjust the overall optical power density of the wavelength-multiplexed light collectively, for example. As an example, adjuster 32 can be a variable attenuator that imparts an attenuation of 0 or more to the passing wavelength-multiplexed light. By adjusting the amount of attenuation imparted to the passing wavelength-multiplexed light, adjuster 32 can adjust the overall optical power density of the wavelength-multiplexed light.

[0015] The adjuster 32 may be configured to individually adjust the optical power density of each signal light included in the wavelength-multiplexed light. In this case, the adjuster 32 may be configured with a plurality of optical filters or a programmable optical filter capable of shaping an arbitrary optical waveform. The adjuster 32 can individually adjust the optical power density of each signal light of the wavelength-multiplexed light by providing zero or more attenuation to each signal light passing through the adjuster 32.

[0016] The nonlinear optical effect of an optical fiber occurs strongly at wavelengths with small absolute values ​​of chromatic dispersion, but the occurrence of the nonlinear optical effect can be suppressed by lowering the optical power density of the signal light. In other words, by adjusting the optical power density of the wavelength-multiplexed light output by the optical amplifier 31 at the most upstream side of the section with the adjuster 32, the occurrence of optical noise due to the nonlinear optical effect in the optical fiber of that section can be suppressed, and therefore the deterioration of the SNR can be suppressed. The optical amplifiers 31 of each section can be adjusted in advance so that the optical power of the wavelength-multiplexed light output by the optical amplifiers 31 of each section is the same.

[0017] The control device 5 executes a determination process to determine the amount of attenuation to be applied by the adjuster 32 for each section. In the determination process, each section is grouped into one or more groups based on the length of its optical fiber (hereinafter, section length). For example, a range of non-overlapping section lengths is defined in advance, and grouping is performed based on which range the section length of each section belongs to. For example, each section is grouped into a first group to an Nth group (N is an integer equal to or greater than 1). Note that when N is an integer equal to or greater than 2, the section length of a section belonging to the kth group (k is an integer from 1 to N-1) is shorter than the section length of a section belonging to the (k+1)th group.

[0018] In this case, the control device 5 first determines all sections belonging to all groups as sections to be adjusted. Then, it executes the adjustment process for the sections to be adjusted, which will be described below. When the first adjustment process is completed, the control device 5 executes the second adjustment process, excluding all sections belonging to the Nth group, which is the group with the longest section length, from the sections to be adjusted. In other words, the sections to be adjusted in the nth adjustment process (n is an integer from 1 to N) are all sections belonging to the first group to the (N-n+1)th group. The control device 5 repeatedly executes the adjustment process until there are no more sections to be adjusted. In other words, in the determination process, the adjustment process is repeated N times, which is the same number as the number of groups.

[0019] Next, the adjustment process will be described. The control device 5 increases the attenuation in the adjuster 32 in the section to be adjusted by the adjustment amount (increase amount). As described above, when the attenuation in the adjuster 32 is increased from a state in which optical noise due to nonlinear optical effects is occurring, the optical noise is reduced, and the SNR is improved. However, if the attenuation in the adjuster 32 is increased too much, the influence of the reduction in the level of the signal light becomes stronger than the reduction in the optical noise, and the OSNR deteriorates, and therefore the SNR also deteriorates. Therefore, the control device 5 repeatedly increases the attenuation provided by the adjuster 32 in the section to be adjusted by the adjustment amount and monitors the change in the SNR. Then, the control device 5 determines the attenuation amount at which the SNR becomes appropriate, and sets it in the adjuster 32 in the section to be adjusted.

[0020] In the determination process, since a section in a group with a longer section length is excluded from the section to be adjusted first, the attenuation amount set in the adjuster 32 may be smaller for a section that belongs to a group with a longer section length. This is because the longer the section length, the greater the required optical power.

[0021] The control device 5 may execute the determination process periodically. Alternatively, the control device 5 may execute the determination process in response to an execution command input by an operator. Alternatively, the control device 5 may execute the determination process in response to a change in the number of signal lights transmitted from the optical transmitting device 1 to the optical receiving device 2. The control device 5 may determine a change in the number of signal lights based on the SNR of each signal light reported to the control device 5 by the optical receiving device 2.

[0022] First Embodiment A first embodiment will be described below. In this embodiment, the adjuster 32 is configured to collectively adjust the overall optical power density of the wavelength multiplexed light. Fig. 2 is a flowchart of the adjustment process by the control device 5. As described above, the process in Fig. 2 is executed for an adjustment target section that includes one or more sections, and is repeated until there are no more adjustment target sections. In describing the process in Fig. 2, the adjustment target section will be simply referred to as a "section".

[0023] In S11, the control device 5 obtains the minimum value of the SNR of each signal light, and sets the signal light with the minimum SNR as the reference signal light, and sets the SNR of the reference signal light as the first evaluation value. FIG. 3 shows an example of the SNR of each signal light. As shown in FIG. 3, the SNR of the signal light in a "predetermined range" in which the absolute value of the chromatic dispersion value is smaller than the threshold value is affected by nonlinear optical noise and is worse than the SNR of the signal light outside the predetermined range. The SNR of the signal light with a wavelength within the predetermined range differs depending on the chromatic dispersion value at the wavelength of the signal light. In FIG. 3, the SNR of the signal light with wavelength λ0 is the smallest. Generally, the wavelength λ0 corresponds to the wavelength with the smallest absolute value of the chromatic dispersion value among the wavelengths of the signal light. In the case of FIG. 3, the reference signal light is the signal light with wavelength λ0, and the first evaluation value is the SNR of the signal light with wavelength λ0. Next, in S12, the control device 5 initializes the counter value i to 1. In S13, the control device 5 increases the attenuation provided by the adjuster 32 of each section by the adjustment amount Xi. The adjustment amount Xi may be a predetermined value.

[0024] After increasing the amount of attenuation provided by the adjuster 32 of each section, the control device 5 determines the SNR of the reference signal light in S14 and sets it as a second evaluation value. Next, the control device 5 compares the first evaluation value with the second evaluation value in S15. If the second evaluation value is equal to or greater than the first evaluation value, that is, if the SNR of the reference signal light does not deteriorate due to the increase in the amount of attenuation provided by the adjuster 32 of each section, the control device 5 increments the counter value i by 1 in S16, sets the current second evaluation value as the first evaluation value, and repeats the process from S13. On the other hand, if the second evaluation value deteriorates more than the first evaluation value in S15, that is, if the SNR of the reference signal light deteriorates due to the increase in the amount of attenuation provided by the adjuster 32 of each section, the control device 5 decreases the amount of attenuation provided by the adjuster 32 of each section by the adjustment amount Xi in S17, and ends the process of FIG. 2. In other words, the control device 5 sets the amount of attenuation to be applied by the adjuster 32 in each section so that the SNR of the reference signal light becomes the highest among the measured values.

[0025] In addition, when the attenuation amount given by the adjuster 32 of each section is repeatedly increased by the adjustment amount Xi, the SNR of the signal light within the predetermined range in Fig. 3 is improved due to the strong influence of the decrease in optical noise among the influences of the decrease in optical noise and the decrease in signal light power, and then deteriorates due to the influence of the decrease in signal light power. The process in Fig. 2 corresponds to the process of finding the transition point where the SNR of the reference signal light changes from improvement to deterioration. In addition, the SNR of the signal light outside the predetermined range in Fig. 3 does not change for a while even if the attenuation amount given by the adjuster 32 of each section is repeatedly increased by the adjustment amount Xi, and then deteriorates due to the influence of the decrease in signal light power. The reason why the SNR does not deteriorate for a while even if the attenuation amount given by the adjuster 32 of each section is increased is because if the OSNR is sufficiently high, the SNR is not immediately affected even if the OSNR deteriorates.

[0026] As described above, in this embodiment, the attenuation amount to be applied by the adjuster 32 of each section is increased while monitoring the SNR of the reference signal light, and the attenuation amount to be applied by the adjuster of each section is determined. With this configuration, it is possible to suppress the influence of optical noise due to nonlinear optical effects in an optical communication system that transmits a plurality of wavelength-multiplexed signal lights. In this embodiment, the SNR of each signal light is determined before increasing the attenuation amount of the adjuster 32 of each section in the adjustment process, and the signal light with the smallest SNR is set as the reference signal light. However, the signal light with the wavelength with the lowest chromatic dispersion value or any signal light within a predetermined range in FIG. 3 may be set as the reference signal light. In this case, S11 in FIG. 3 is a process in which the SNR of the reference signal light, which is the predetermined signal light, is set as the first evaluation value.

[0027] Second Embodiment Next, a second embodiment will be described. In this embodiment, the adjuster 32 is configured to adjust the optical power density for each signal light of the wavelength multiplexed light. Fig. 4 is a flowchart of the adjustment process by the control device 5. As described above, the process of Fig. 4 is executed for an adjustment target section that includes one or more sections, and is repeated until there are no more adjustment target sections. In describing the process of Fig. 4, the adjustment target section will be simply referred to as a "section".

[0028] In S21, the control device 5 obtains the average value of the SNR of all the signal lights, and sets this as the first evaluation value. In S22, the control device 5 determines the signal light to be adjusted (hereinafter, the adjustment target light) based on the first evaluation value. The adjustment target light is a signal light having a lower SNR than the first evaluation value among the signal lights having a wavelength with an absolute value of chromatic dispersion lower than a threshold. For example, referring to FIG. 3, the adjustment target light is a signal light having a lower SNR than the first evaluation value among the signal lights within a predetermined range. In S23, the control device 5 initializes the counter value i to 1. In S24, the control device 5 increases the attenuation amount given by the adjuster 32 of each section to each adjustment target light by the adjustment amount Xi. Note that the adjustment amount Xi of the attenuation amount given to the same adjustment target light by the adjuster 32 of each section is the same. The adjustment amount Xi of the attenuation amount given to different adjustment target lights may be the same or different. As an example, the adjustment amount Xi may be the same predetermined value for all adjustment target lights. The adjustment amount Xi may be a value based on the difference between the first evaluation value and the SNR of the light to be adjusted, for example, the larger the difference between the first evaluation value and the SNR of the light to be adjusted, the larger the value. In this case, the adjustment amount Xi may differ depending on the light to be adjusted.

[0029] After increasing the attenuation amount provided by the adjuster 32 for each section, the control device 5 obtains the average value of the SNR of all the signal lights in S25 and sets this as the second evaluation value. Next, the control device 5 compares the first evaluation value with the second evaluation value in S26. If the second evaluation value is equal to or greater than the first evaluation value, that is, if the average value of the SNR of all the signal lights increases due to the adjustment of the attenuation amount, the control device 5 increments the counter value i by 1 in S27, sets the current second evaluation value as the first evaluation value, and repeats the process from S24. On the other hand, if the second evaluation value becomes smaller than the first evaluation value in S26, that is, if the average value of the SNR of all the signal lights decreases due to the adjustment of the attenuation amount, the control device 5 reduces the attenuation amount provided by the adjuster 32 for each section by the adjustment amount Xi for each adjustment target light in S28, and ends the process of FIG. 4. That is, the control device 5 sets the attenuation amount in the adjuster 32 for each section to the value that maximizes the second evaluation value among the measured values.

[0030] As described above, in this embodiment, at the time when the adjustment process is started, that is, before the attenuation in the adjuster 32 of each section is increased for the first time in the adjustment process, one or more signal lights having wavelengths within a wavelength range in which the SNR is lower than the average value of the SNRs of the signal lights and the absolute value of the chromatic dispersion value of the optical fiber is lower than a threshold value are set as adjustment target lights. The adjustment target lights are signal lights that can be determined to be affected by optical noise. Then, the attenuation to be applied to one or more adjustment target lights by the adjuster 32 of each section is increased while the SNR of each signal light is monitored, thereby determining the attenuation to be applied to one or more adjustment target lights by the adjuster 32 of each section. With this configuration, it is possible to suppress the influence of optical noise due to nonlinear optical effects in an optical communication system that transmits multiple wavelength-multiplexed signal lights.

[0031] <Third embodiment> Next, a third embodiment will be described. In this embodiment, the adjuster 32 is configured to adjust the optical power density for each signal light of the wavelength multiplexed light. Fig. 5 is a flowchart of the adjustment process by the control device 5. As described above, the process of Fig. 5 is executed for an adjustment target section including one or more sections, and is repeated until there are no more adjustment target sections. In describing the process of Fig. 5, the adjustment target section will be simply referred to as a "section".

[0032] In S31, the control device 5 determines the signal light to be adjusted (hereinafter, the adjustment target light) based on the SNR of each signal light. The adjustment target light is all signal light other than the signal light having the maximum SNR. In the following description, the signal light having the maximum SNR is referred to as the reference signal light. In S32, the control device 5 initializes the counter value i to 1. In S33, the control device 5 increases the attenuation amount given by the adjuster 32 of each section for each adjustment target light by the adjustment amount Xi. In addition, the adjustment amount Xi of the attenuation amount given to the same adjustment target light by the adjuster 32 of each section is the same. The adjustment amount Xi of the attenuation amount given to different adjustment target lights may be the same or different. As an example, the adjustment amount Xi may be the same predetermined value for all adjustment target lights. In addition, the adjustment amount Xi may be a value based on the difference between the SNR of the reference signal light and the SNR of the adjustment target light, for example, the larger the difference between the SNR of the reference signal light and the SNR of the adjustment target light, the larger the value. In this case, the adjustment amount Xi may differ depending on the light to be adjusted.

[0033] In S34, the control device 5 judges whether the SNR of each adjustment target light has deteriorated due to the increase in the attenuation amount by the adjustment amount Xi in S33. Then, for the adjustment target signal light with deteriorated SNR, the control device 5 reduces the attenuation amount provided by the adjuster 32 of each section by the adjustment amount Xi increased in S33, and excludes it from the adjustment target light. Next, in S35, the control device 5 judges whether the number of adjustment target lights is 0. If the number of adjustment target lights is not 0, the control device 5 increments the counter value i by 1 in S36 and repeats the process from S33. On the other hand, if the number of adjustment target lights is 0 in S35, the control device 5 ends the process of FIG. 5. That is, the control device 5 executes, for each adjustment target light, setting the attenuation provided to the adjustment target light by the adjuster 32 of each section to a value that maximizes the SNR of the adjustment target light among the measured values.

[0034] As described above, in this embodiment, all signal lights except for the signal light with the highest SNR at the time when the adjustment process is started, that is, before the attenuation amount in the adjuster 32 of each section is increased for the first time in the adjustment process, are set as adjustment target lights. Then, for each adjustment target light, the attenuation amount to be applied to the adjustment target light by the adjuster 32 of each section is determined by monitoring the SNR of the adjustment target light while increasing the attenuation amount to be applied to the adjustment target light by the adjuster 32 of each section. With this configuration, it is possible to suppress the influence of optical noise due to nonlinear optical effects in an optical communication system that transmits a plurality of wavelength-multiplexed signal lights.

[0035] 6 shows an example of the configuration of the control device 5. The acquisition unit 51 acquires from the optical receiving device 2 the signal-to-noise ratio of each of the multiple signal lights determined by the optical receiving device 2 demodulating the multiple signal lights. The control unit 52 controls the amount of attenuation provided by the adjuster 32 in each section of the optical transmission line 3. The control unit 52 executes the above-mentioned determination process. That is, the above-mentioned adjustment process is repeated the same number of times as the number of groups of sections. Note that information indicating which section belongs to which group is created in advance and set in the control unit 52.

[0036] The control device 5 may be realized by executing an appropriate program on one or more processors of a device, for example, a computer. The present disclosure also provides a program that, when executed by one or more processors of a device, causes the device to function as the control device 5, and a non-transitory computer-readable storage medium that stores the program.

[0037] The above configuration makes it possible to suppress the effects of optical noise caused by nonlinear optical effects in optical communication systems that transmit multiple wavelength-multiplexed signal light, thereby contributing to Goal 9 of the United Nations Sustainable Development Goals (SDGs) to "build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0038] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention. [Explanation of symbols]

[0039] 51: Acquisition unit, 52: Control unit

Claims

1. A control device for an optical communication system in which an optical transmitter transmits a plurality of wavelength-multiplexed signal lights to an optical receiver via an optical transmission line including one or more sections, comprising: each of the one or more sections includes an optical amplifier that amplifies the plurality of signal light beams, an adjuster that is connected to the downstream side of the optical amplifier in a transmission direction of the plurality of signal light beams and adjusts optical power of the plurality of signal light beams, and an optical fiber that is connected to the downstream side of the adjuster in the transmission direction; The control device includes: an acquisition means for acquiring, from the optical receiving device, a signal-to-noise ratio of the plurality of signal lights determined by the optical receiving device demodulating the plurality of signal lights; a control means for controlling the amount of attenuation provided by the regulator in each of the one or more sections; Equipped with The control means executes a determination process for determining an attenuation amount to be applied by the adjuster for each of the one or more sections, A control device, wherein the determination process includes an adjustment process that determines the amount of attenuation to be provided by the adjuster in the adjustment target section among the one or more sections by monitoring the signal-to-noise ratio of the multiple signal lights while increasing the amount of attenuation provided by the adjuster in the adjustment target section.

2. The one or more sections are grouped into a first group to an Nth group (N is an integer equal to or greater than 1); When N is 2 or more, the length of the optical fiber in a section belonging to the kth group (k is an integer from 1 to N-1) is shorter than the length of the optical fiber in a section belonging to the (k+1)th group; The determination process includes repeating the adjustment process N times; 2. The control device according to claim 1, wherein the adjustment target section in the nth (n is an integer from 1 to N) adjustment process is a section belonging to a first group to an (N-n+1)th group.

3. the adjuster in each of the one or more sections is configured to collectively adjust the optical power of the entirety of the plurality of signal lights, In the adjustment process, the control unit determines an amount of attenuation to be applied by the adjuster in the adjustment target section by monitoring a signal-to-noise ratio of a reference signal light among the plurality of signal lights while increasing an amount of attenuation to be applied by the adjuster in the adjustment target section; 2. The control device according to claim 1, wherein the reference signal light is a signal light having a wavelength within a wavelength range in which an absolute value of the chromatic dispersion value of the optical fiber is lower than a threshold value.

4. 4. The control device according to claim 3, wherein the reference signal light is a signal light having a wavelength that has the smallest absolute value of the chromatic dispersion value among the wavelengths of the plurality of signal lights.

5. 4. The control device according to claim 3, wherein in the adjustment process, the control means monitors the signal-to-noise ratio of the reference signal light while increasing the attenuation amount provided by the adjuster in the adjustment target section, and determines the attenuation amount that results in the highest signal-to-noise ratio of the reference signal light as the attenuation amount to be provided by the adjuster in the adjustment target section.

6. the adjuster in each of the one or more sections is configured to individually adjust the optical power of the plurality of signal lights; In the adjustment process, the control means determines one or more adjustment target lights for which an attenuation amount to be applied by the adjuster in the adjustment target section is to be increased, and determines an attenuation amount to be applied by the adjuster in the adjustment target section to the one or more adjustment target lights by monitoring an average value of the signal-to-noise ratios of the plurality of signal lights while increasing an attenuation amount to be applied by the adjuster in the adjustment target section to the one or more adjustment target lights, 2. The control device according to claim 1, wherein the one or more adjustment target lights are signal lights having a signal-to-noise ratio lower than an average value of the signal-to-noise ratios of the plurality of signal lights at a time point when the adjustment process is started, and a wavelength within a wavelength range in which an absolute value of a chromatic dispersion value of the optical fiber is lower than a threshold value.

7. 7. The control device according to claim 6, wherein in the adjustment process, the control means monitors an average value of the signal-to-noise ratio of the plurality of signal lights while increasing an attenuation amount to be applied to the one or more adjustment target lights by the adjuster in the adjustment target section, and determines the attenuation amount that results in the highest average signal-to-noise ratio of the plurality of signal lights as the attenuation amount to be applied to the one or more adjustment target lights by the adjuster in the adjustment target section.

8. the adjuster in each of the one or more sections is configured to individually adjust the optical power of the plurality of signal lights; In the adjustment process, the control means determines one or more adjustment target lights for which an attenuation amount to be applied by the adjuster in the adjustment target section is to be increased, and for each of the one or more adjustment target lights, determines an attenuation amount to be applied to the adjustment target light by the adjuster in the adjustment target section by monitoring a signal-to-noise ratio of the adjustment target light while increasing an attenuation amount to be applied to the adjustment target light by the adjuster in the adjustment target section; The control device according to claim 1 , wherein the one or more adjustment target lights are signal lights excluding a signal light having a highest signal-to-noise ratio among the plurality of signal lights at a time point when the adjustment process is started.

9. 9. The control device according to claim 8, wherein in the adjustment process, the control means monitors the signal-to-noise ratio of the light to be adjusted while increasing the amount of attenuation applied to the light to be adjusted by the adjuster in the adjustment section, and determines the amount of attenuation that results in the highest signal-to-noise ratio of the light to be adjusted by the adjuster in the adjustment section as the amount of attenuation to be applied to the light to be adjusted by the adjuster in the adjustment section.

10. 2. The control device according to claim 1, wherein the range of wavelengths of the plurality of signal lights includes a wavelength at which a chromatic dispersion value of the optical fiber becomes zero.

11. A program that, when executed by one or more processors of an apparatus having one or more processors, causes the apparatus to function as a control device according to any one of claims 1 to 10.

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