Control device and program for optical communication systems

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 generated by non - linear optical effects in optical fibers.

Background Art

[0002] Regarding power saving in optical communication systems, Non - Patent Document 1 discloses that by using the O - band, which is a wavelength band of 1260 nm to 1360 nm, a part of signal processing can be omitted, and thus power saving can be achieved compared to 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) generated by the non - linear optical effect of an optical fiber becomes extremely large, and thus the O - band is not suitable for wavelength division multiplexing transmission. Note that the wavelength near 1310 nm is a wavelength at which the value of wavelength dispersion is 0 or close to 0.

Prior Art Documents

Non - Patent Documents

[0004]

Non - Patent Document 1

Non - Patent Document 2

Summary of the Invention

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

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

[0007] According to this disclosure, in an optical communication system that transmits multiple wavelength-multiplexed signal lights, the effects of optical noise due to nonlinear optical effects can be suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] Configuration diagrams of optical communication systems according to several embodiments. [Figure 2] Flowcharts of the adjustment process according to several embodiments. [Figure 3] Diagram illustrating the adjustment process. [Figure 4] Flowcharts of the adjustment process according to several embodiments. [Figure 5] Flowcharts of the adjustment process according to several embodiments. [Figure 6] Configuration diagrams of control devices according to several embodiments. [Modes for carrying out the invention]

[0009] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more features from the multiple features described in the embodiments may be combined arbitrarily. Furthermore, identical or similar configurations will be given the same reference numeral, and redundant descriptions will be omitted.

[0010] Before describing each embodiment, the common configuration of each embodiment will be explained below. Figure 1 is a configuration diagram of an optical communication system according to several embodiments. The optical transmitting device 1 transmits wavelength-division multiplexed (WDM) light, obtained by wavelength-division multiplexing multiple signal lights, to the optical receiving device 2 via the optical transmission path 3. The wavelength range of the WDM light includes wavelengths in the optical fiber used in the optical transmission path 3 where the absolute value of the chromatic dispersion is lower than a threshold, for example, wavelengths where the absolute value of the chromatic dispersion is 0. As an example, the chromatic dispersion is 0 at 1310 nm, and the wavelength range of the WDM light is the wavelength range of 1260 nm to 1360 nm. In other words, the WDM light is O-band light.

[0011] The optical receiver 2 separates the wavelength-division multiplexed light from the optical transmitter 1 by wavelength and demodulates each signal light. When demodulating each signal light, the optical receiver 2 determines the signal-to-noise ratio (SNR) of each signal light. As an example, the optical receiver 2 generates an electrical signal corresponding to the signal light by coherent detection of the signal light, and determines the SNR of each signal light by determining the noise component based on the coordinates of the amplitude and phase of the generated electrical signal in the complex plane and the coordinates of each signal point determined by the modulation scheme. The optical receiver 2 repeatedly transmits the SNR of each signal light to the control device 5. In the following explanation, the signal-to-noise ratio determined from the electrical signal generated based on the signal light will be referred to as the SNR of the signal light, and the ratio of the signal light to the noise light will be referred to as the OSNR of the signal light.

[0012] The optical transmission path 3 includes optical amplifiers 31-1, 31-2, and 31-3. Optical amplifier 31-1 amplifies the wavelength-division multiplexed light from the optical transmitter 1 in a single unit. In Figure 1, optical amplifier 31-1 is shown as an external device of the optical transmitter 1, but optical amplifier 31-1 may be an internal device of the optical transmitter 1. Optical amplifier 31-2 also amplifies the wavelength-division multiplexed light input to the optical receiver 2 in a single unit. In Figure 1, optical amplifier 31-2 is shown as an external device of the optical receiver 2, but optical amplifier 31-2 may be an internal device of the optical receiver 2. Optical amplifier 31-3 is an optical amplifier provided in the middle of the optical transmission path 3 to compensate for attenuation of the optical signal in the optical transmission path 3. In the configuration of Figure 1, there are two optical amplifiers 31-3 provided in the optical transmission path 3, but the number of optical amplifiers 31-3 may be one or more depending on the length of the optical transmission path 3. Furthermore, if the length of the optical transmission path 3 is short, the number of optical amplifiers 31-3 may be zero.

[0013] As shown in Figure 1, the optical transmission path 3 has an optical amplifier 31-1 at its starting point, an optical amplifier 31-2 at its ending point, and one or more optical amplifiers 31-3 provided in the middle of the optical transmission path 3 as needed. As mentioned above, the number of optical amplifiers 31-3 may be zero. In other words, if we refer to optical amplifiers 31-1, 31-2, and 31-3 as simply optical amplifier 31 without distinction, the optical transmission path 3 is divided into "sections" consisting of an optical amplifier 31 and an optical fiber connecting the optical amplifier 31 and the optical amplifier 31 downstream of it in the direction of signal light transmission. In the configuration of Figure 1, the optical transmission path is divided into three sections: section 3-1, section 3-2, and section 3-3. More generally, if the number of optical amplifiers excluding the optical amplifier 31-2 that amplifies wavelength-division multiplexed light immediately before the optical receiver 2 is P (where P is an integer of 1 or more), the optical transmission path is divided into P sections.

[0014] A regulator 32 is provided downstream of the optical amplifier 31 in each section and upstream of the optical fiber. In Figure 1, regulator 32-1 is provided in section 3-1, regulator 32-2 is provided in section 3-2, and regulator 32-3 is provided in section 3-3. The regulator 32 can be configured, for example, to adjust the overall optical power density of the wavelength-division multiplexed light collectively. As an example, regulator 32 may be a variable attenuator that applies an attenuation of 0 or more to the passing wavelength-division multiplexed light. By adjusting the amount of attenuation applied to the passing wavelength-division multiplexed light, regulator 32 can adjust the overall optical power density of the wavelength-division multiplexed light.

[0015] Furthermore, the tuner 32 may be configured to individually adjust the optical power density of each signal light included in the wavelength-division multiplexed light. In this case, the tuner 32 may consist of multiple optical filters or programmable optical filters that can be shaped into any optical waveform. The tuner 32 can individually adjust the optical power density of each signal light in the wavelength-division multiplexed light by applying an attenuation of 0 or more to each signal light passing through it.

[0016] The non - linear optical effect of an optical fiber occurs strongly at wavelengths with a small absolute value of the wavelength dispersion value. However, by reducing the optical power density of the signal light, the occurrence of the non - linear optical effect can be suppressed. That is, by adjusting the optical power density of the wavelength - multiplexed light output by the optical amplifier 31 on the most upstream side of the section with the adjuster 32, the generation of optical noise due to the non - linear optical effect in the optical fiber of the section can be suppressed, and thus the deterioration of the SNR can be suppressed. Note that the optical amplifiers 31 in each section can be pre - adjusted so that the optical power of the wavelength - multiplexed light output by the optical amplifiers 31 in each section is the same.

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

[0018] In this case, the control device 5 first sets all sections belonging to all groups as adjustment target sections. Then, it executes an adjustment process for the adjustment target sections described below. When the first adjustment process is completed, the control device 5 excludes all sections belonging to the Nth group, which is the group with the longest section length, from the adjustment target sections and executes the second adjustment process. That is, the adjustment target sections in the nth (n is an integer from 1 to N) adjustment process 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 adjustment target sections. That is, 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 amount in the adjuster 32 in the adjustment target section by the adjustment amount (increase amount). As described above, when the attenuation amount of the adjuster 32 is increased from the state where optical noise is generated by the non-linear optical effect, the optical noise decreases, so the SNR is improved. However, if the attenuation amount of the adjuster 32 is increased too much, the influence of the decrease in the level of the signal light becomes stronger than the decrease in the optical noise, and the OSNR deteriorates, and thus the SNR also deteriorates. Therefore, the control device 5 repeatedly increases the attenuation amount applied by the adjuster 32 in the adjustment target section 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 adjustment target section.

[0020] In the determination process, since the sections in the group with a longer section length are excluded from the adjustment target section earlier, the attenuation amount set in the adjuster 32 can be smaller for the sections belonging to the group with a longer section length. This is because the longer the section length, the larger the required optical power.

[0021] Note that the control device 5 can execute the determination process periodically. Alternatively, the control device 5 can execute the determination process in response to the operator inputting an execution command. Alternatively, the control device 5 can execute the determination process in response to a change in the number of signal lights transmitted from the optical transmission device 1 to the optical reception device 2. Note that the control device 5 can determine the change in the number of signal lights based on the SNR of each signal light reported by the optical reception device 2 to the control device 5.

[0022] <First Embodiment> Hereinafter, the first embodiment will be described. In the present embodiment, the adjuster 32 is configured to adjust the overall optical power density of the wavelength-division multiplexed light in a lump. 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 including one or more sections, and is repeated until there is no adjustment target section. Regarding the description of the process in FIG. 2, the adjustment target section is simply referred to as a "section".

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

[0024] After increasing the attenuation amount provided by the regulator 32 in each section, the control device 5 determines the SNR of the reference signal light in S14 and sets this as the second evaluation value. Subsequently, in S15, the control device 5 compares the first evaluation value with the second evaluation value. If the second evaluation value is greater than or equal to the first evaluation value, that is, if the SNR of the reference signal light did not deteriorate due to increasing the attenuation amount provided by the regulator 32 in each section, the control device 5 increases the counter value i by 1 in S16 and repeats the process from S13, setting the current second evaluation value as the first evaluation value. On the other hand, in S15, if the second evaluation value deteriorates compared to the first evaluation value, that is, if the SNR of the reference signal light deteriorated due to increasing the attenuation amount provided by the regulator 32 in each section, the control device 5 decreases the attenuation amount provided by the regulator 32 in each section by adjustment amount Xi in S17 and terminates the process shown in Figure 2. In other words, the control device 5 sets the amount of attenuation applied by the adjuster 32 in each section so that the SNR of the reference signal light is the highest among those measured.

[0025] Furthermore, when the attenuation amount applied by the regulator 32 in each section is repeatedly increased by the adjustment amount Xi, the SNR of the signal light within the predetermined range in Figure 3 is improved due to the reduction in optical noise and the reduction in signal light power, and then deteriorates due to the reduction in signal light power. The process in Figure 2 corresponds to the process of finding the transition point where the SNR of the reference signal light moves from improvement to deterioration. Furthermore, the SNR of the signal light outside the predetermined range in Figure 3 does not change for a while even when the attenuation amount applied by the regulator 32 in each section is repeatedly increased by the adjustment amount Xi, and then deteriorates due to the reduction in signal light power. The reason why the SNR does not deteriorate for a while even when the attenuation amount applied by the regulator 32 in each section is increased is that if the OSNR is sufficiently high, deterioration of the OSNR does not immediately affect the SNR.

[0026] In this embodiment, the amount of attenuation applied by the tuner 32 in each section is determined by monitoring the SNR of the reference signal light while increasing the attenuation amount applied by the tuner 32 in each section. This configuration makes it 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. In this embodiment, the SNR of each signal light is determined before increasing the attenuation amount of the tuner 32 in each section during the adjustment process, and the signal light with the smallest SNR is set as the reference signal light. However, it is also possible to use the signal light with the lowest wavelength dispersion value or any signal light within the predetermined range in Figure 3 as the reference signal light. In this case, S11 in Figure 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 tuner 32 is configured to adjust the optical power density for each wavelength-division multiplexed light signal. Figure 4 is a flowchart of the adjustment process by the control device 5. As described above, the process in Figure 4 is performed on adjustment target sections that include one or more sections, and is repeated until there are no more adjustment target sections left. For the explanation of the process in Figure 4, adjustment target sections will simply be referred to as "sections".

[0028] In S21, the control device 5 calculates the average value of the SNR of all signal light and sets this as the first evaluation value. In S22, the control device 5 determines the signal light to be adjusted (hereinafter referred to as the "adjustment target light") based on the first evaluation value. The adjustment target light is the signal light with a wavelength whose absolute value of chromatic dispersion is lower than the threshold, and whose SNR is lower than the first evaluation value. For example, as shown in Figure 3, the adjustment target light is the signal light within a predetermined range whose SNR is lower than the first evaluation value. 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 tuner 32 in each section for each adjustment target light by the adjustment amount Xi. The adjustment amount Xi of the attenuation amount given to the same adjustment target light by the tuner 32 in 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. Furthermore, the adjustment amount Xi may be a value based on the difference between the first evaluation value and the SNR of the light being adjusted; for example, the larger the difference between the first evaluation value and the SNR of the light being adjusted, the larger the adjustment amount Xi may be. In this case, the adjustment amount Xi may vary depending on the light being adjusted.

[0029] The control device 5 increases the attenuation amount provided by the regulator 32 in each section, and then in S25 calculates the average value of the SNR of all signal light, which is set as the second evaluation value. Subsequently, in S26, the control device 5 compares the first evaluation value with the second evaluation value. If the second evaluation value is greater than or equal to the first evaluation value, that is, if the average value of the SNR of all signal light has increased due to the adjustment of the attenuation amount, the control device 5 increases the counter value i by 1 in S27 and repeats the process from S24, setting the current second evaluation value as the first evaluation value. On the other hand, in S26, if the second evaluation value is smaller than the first evaluation value, that is, if the average value of the SNR of all signal light has decreased due to the adjustment of the attenuation amount, the control device 5 reduces the attenuation amount provided by the regulator 32 in each section for each light to be adjusted by the adjustment amount Xi in S28, and terminates the process shown in Figure 4. In other words, the control device 5 sets the attenuation amount in the regulator 32 in each section to the value that yielded the highest second evaluation value among those measured.

[0030] In this embodiment, at the start of the adjustment process, that is, before increasing the attenuation amount in the adjuster 32 for each section for the first time during the adjustment process, one or more signal lights with wavelengths within a wavelength range whose SNR is lower than the average value of the SNR of each signal light and whose absolute value of the chromatic dispersion of the optical fiber is lower than the threshold are designated as the light to be adjusted. The light to be adjusted is a signal light that can be determined to be affected by optical noise. Then, by monitoring the SNR of each signal light while increasing the attenuation amount applied to one or more light to be adjusted in the adjuster 32 for each section, the amount of attenuation applied to one or more light to be adjusted in the adjuster 32 for each section is determined. With this configuration, the influence of optical noise due to nonlinear optical effects can be suppressed in an optical communication system that transmits multiple wavelength-division multiplexed signal lights.

[0031] <Third Embodiment> Next, a third embodiment will be described. In this embodiment, the tuner 32 is configured to adjust the optical power density for each wavelength-division multiplexed light signal. Figure 5 is a flowchart of the adjustment process by the control device 5. As described above, the process in Figure 5 is performed on adjustment target sections that include one or more sections, and is repeated until there are no more adjustment target sections left. For the explanation of the process in Figure 5, adjustment target sections will simply be referred to as "sections".

[0032] In S31, the control device 5 determines the signal light to be adjusted (hereinafter referred to as 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 with the maximum SNR. In the following explanation, the signal light with the maximum SNR will be 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 in each section for each adjustment target light by the adjustment amount Xi. The adjustment amount Xi of the attenuation amount given by the adjuster 32 in each section for the same adjustment target light is assumed to be the same. The adjustment amount Xi of the attenuation amount given to different adjustment target lights may be the same or different. For example, the adjustment amount Xi may be the same predetermined value for all adjustment target lights. Also, 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 may be. In this case, the adjustment amount Xi may vary depending on the light being adjusted.

[0033] In S34, the control device 5 determines whether the SNR has deteriorated for each light to be adjusted by increasing the attenuation amount by adjustment amount Xi in S33. Then, for signal lights to be adjusted whose SNR has deteriorated, the control device 5 reduces the attenuation amount applied by the adjuster 32 in each section by the adjustment amount Xi increased in S33 and excludes them from the lights to be adjusted. Next, in S35, the control device 5 determines whether the number of lights to be adjusted is 0. If the number of lights to be adjusted is not 0, the control device 5 increases the counter value i by 1 in S36 and repeats the process from S33. On the other hand, if the number of lights to be adjusted is 0 in S35, the control device 5 terminates the process shown in Figure 5. In other words, the control device 5 sets the attenuation applied to each light to be adjusted by the adjuster 32 in each section to the value that yielded the highest SNR for that light among those measured, for each light to be adjusted.

[0034] In this embodiment, all signal light except for the signal light with the highest SNR at the start of the adjustment process, that is, before increasing the attenuation amount in each section's adjuster 32 for the first time during the adjustment process, is designated as the light to be adjusted. Then, for each light to be adjusted, the attenuation amount applied to that light by each section's adjuster 32 is increased while monitoring the SNR of that light, thereby determining the amount of attenuation applied to that light by each section's adjuster 32. With this configuration, the influence of optical noise due to nonlinear optical effects can be suppressed in an optical communication system that transmits multiple wavelength-multiplexed signal lights.

[0035] Figure 6 shows an example of the configuration of the control device 5. The acquisition unit 51 acquires the signal-to-noise ratio of each of the multiple signal lights, which is determined by the optical receiver 2 demodulating the multiple signal lights, from the optical receiver 2. The control unit 52 controls the amount of attenuation applied by the adjuster 32 in each section of the optical transmission path 3. The control unit 52 executes the determination process described above. In other words, it repeats the adjustment process described above the same number of times as the number of section groups. Information indicating which section belongs to which group is created in advance and set in the control unit 52.

[0036] The control device 5 can be implemented by having one or more processors in a device, for example, a computer, execute an appropriate program on one or more of its processors. Furthermore, according to this disclosure, a program that, when executed on one or more processors of the device, causes the device to function as the control device 5, and a non-temporary computer-readable storage medium for storing the program are provided.

[0037] With the above configuration, the effects of optical noise due to nonlinear optical effects can be suppressed in optical communication systems that transmit multiple wavelength-multiplexed signal lights. Therefore, it becomes possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0038] The invention is not limited to the embodiments described above, and various modifications and changes 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 transmitting device transmits multiple wavelength-multiplexed signal lights to an optical receiving device via an optical transmission path that includes one or more sections, Each of the one or more sections includes an optical amplifier for amplifying the plurality of signal lights, a regulator connected downstream of the optical amplifier in the transmission direction of the plurality of signal lights for adjusting the optical power of the plurality of signal lights, and an optical fiber connected downstream of the regulator in the transmission direction. The control device is An acquisition means for acquiring the signal-to-noise ratio of the plurality of signal lights determined by the optical receiving device demodulating the plurality of signal lights from the optical receiving device, 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 performs a determination process to determine the amount of attenuation to be provided by the regulator for each of the one or more sections. The control device includes an adjustment process that determines the amount of attenuation to be applied by the adjuster in the adjustment target section by monitoring the signal-to-noise ratio of the plurality of signal lights while increasing the amount of attenuation applied by the adjuster in the adjustment target section among the one or more sections.

2. The aforementioned one or more intervals are grouped into groups from the first group to the Nth group (where N is an integer of 1 or more), If N is 2 or greater, the length of the optical fiber in the section belonging to the kth group (where k is an integer from 1 to N-1) is shorter than the length of the optical fiber in the section belonging to the (k+1)th group. The aforementioned decision process includes repeating the aforementioned adjustment process N times. The control device according to claim 1, wherein the adjustment target interval in the nth adjustment process (where n is an integer from 1 to N) is an interval belonging to the first group to the (N-n+1)th group.

3. Each of the one or more sections is configured to adjust the total optical power of the plurality of signal lights in a single unit. In the adjustment process, the control means determines the amount of attenuation applied by the adjuster in the adjustment target section by monitoring the signal-to-noise ratio of the reference signal light among the plurality of signal lights while increasing the amount of attenuation applied by the adjuster in the adjustment target section. The control device according to claim 1, wherein the reference signal light is signal light with a wavelength within a wavelength range where the absolute value of the chromatic dispersion of the optical fiber is lower than a threshold value.

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

5. 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 amount of attenuation applied by the adjuster in the adjustment target section, and determines the amount of attenuation that results in the highest signal-to-noise ratio of the reference signal light to be the amount of attenuation applied by the adjuster in the adjustment target section.

6. 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 light sources to be adjusted in which the attenuation amount applied by the adjuster in the adjustment target section will be increased, and determines the amount of attenuation amount applied by the adjuster in the adjustment target section to the one or more light sources by monitoring the average value of the signal-to-noise ratio of the plurality of signal lights while increasing the attenuation amount applied by the adjuster in the adjustment target section to the one or more light sources to be adjusted, The control device according to claim 1, wherein the one or more light to be adjusted is a signal light with a wavelength within a wavelength range in which, at the time the adjustment process is started, the signal-to-noise ratio is lower than the average value of the signal-to-noise ratios of the plurality of signal lights, and the absolute value of the chromatic dispersion of the optical fiber is lower than a threshold.

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

8. 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 light sources to be adjusted in which the attenuation amount applied by the adjuster in the adjustment target section will be increased, and for each of the one or more light sources to be adjusted, while increasing the attenuation amount applied to the light source by the adjuster in the adjustment target section, monitors the signal-to-noise ratio of the light source to determine the amount of attenuation applied to the light source by the adjuster in the adjustment target section. The control device according to claim 1, wherein the one or more light to be adjusted are signal lights excluding the signal light with the highest signal-to-noise ratio among the plurality of signal lights at the time the adjustment process is started.

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 as the amount of attenuation applied to the light to be adjusted by the adjuster in the adjustment section.

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

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

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