JP7846069B2 - Control device and program for optical communication systems - Google Patents

Description

Applicable to Article 30, Paragraph 2 of the Patent Law ▲1▼Date: March 9, 2023 Name of meeting, place of meeting: Optical Fiber Communication Conference (OFC) 2023, San Diego, CA, USA Presenters: Daniel Elson, Yuta Wakayama, Vitali Mikhailov, Jawei Luo, Noboru Yoshikane, Darryl Innis, and Tsurutani Takehiro

This disclosure relates to a technique for suppressing the effects of optical noise caused by nonlinear optical effects in optical fibers.

Regarding power saving in optical communication systems, Non-Patent Document 1 discloses that by using the O-band, which is the wavelength band of 1260 nm to 1360 nm, some signal processing can be omitted, thus achieving power savings compared to the conventionally used 1530 nm to 1565 nm wavelength band (C-band).

On the other hand, Non-Patent Document 2 discloses that in the wavelength range near 1310 nm, the influence of optical noise (nonlinear optical noise) caused by the nonlinear optical effect of optical fibers becomes extremely large, and therefore, the O-band is unsuitable for wavelength division multiplexing transmission. Note that wavelengths near 1310 nm have a wavelength dispersion value of 0 or close to 0.

Seiler, P. M. , etc. al. , Toward coherent O-band data center interconnects. Front. Optoelectron. 14,414-425,2021 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

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 light signals.

According to one aspect of this 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, and control means for controlling the amount of attenuation provided by the regulator in each of the one or more sections. 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.

According to this disclosure, in an optical communication system that transmits multiple wavelength-multiplexed signal light signals, the effects of optical noise due to nonlinear optical effects can be suppressed.

Configuration diagrams of optical communication systems according to several embodiments. Flowcharts of the adjustment process according to several embodiments. Diagram illustrating the adjustment process. Flowcharts of the adjustment process according to several embodiments. Flowcharts of the adjustment process according to several embodiments. Configuration diagrams of control devices according to several embodiments.

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 arbitrarily combined. Furthermore, identical or similar configurations will be given the same reference numeral, and redundant descriptions will be omitted.

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 zero. As an example, the chromatic dispersion is zero 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.

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. For example, the optical receiver 2 generates an electrical signal corresponding to the signal light by coherent detection of the signal light. 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 determines the SNR of each signal light by determining the noise component. 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 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.

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.

As shown in Figure 1, the optical transmission path 3 has an optical amplifier 31-1 provided at its starting point, an optical amplifier 31-2 provided 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 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 (P is an integer of 1 or more), the optical transmission path is divided into P sections.

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 in section 3-2, and regulator 32-3 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.

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 desired 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 zero or greater to each signal light passing through it.

The nonlinear optical effect in optical fibers is strong at wavelengths with small absolute values of chromatic dispersion. However, this effect can be suppressed by reducing the optical power density of the signal light. Specifically, by adjusting the optical power density of the wavelength-division multiplexed light output by the optical amplifier 31 located at the upstream end of the section using the adjuster 32, the occurrence of optical noise due to the nonlinear optical effect in that section of optical fiber can be suppressed, thus reducing the degradation of the signal-to-noise ratio (SNR). The optical amplifiers 31 in each section can be pre-adjusted so that the optical power of the wavelength-division multiplexed light output by each section is the same.

The control device 5 performs a determination process to determine the attenuation amount to be applied by the regulator 32 for each section. In this determination process, each section is grouped into one or more groups based on the length of its optical fiber (hereinafter referred to as section length). For example, a range of non-overlapping section lengths is defined in advance, and grouping is performed based on which range each section's section length belongs to. For example, each section is grouped into the first group to the Nth group (N is an integer greater than or equal to 1). If N is an integer greater than or equal to 2, 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.

In this case, the control device 5 first designates all intervals belonging to all groups as intervals to be adjusted. Then, it performs the adjustment process on these intervals, as described below. Once the first adjustment process is complete, the control device 5 excludes all intervals belonging to the Nth group (the group with the longest interval length) from the intervals to be adjusted and performs the second adjustment process. That is, in the nth adjustment process (where n is an integer from 1 to N), the intervals to be adjusted are all intervals belonging to groups 1 through (N-n+1). The control device 5 repeatedly performs the adjustment process until there are no more intervals to be adjusted. In other words, in the determination process, the adjustment process is repeated N times, the same number as the number of groups.

Next, the adjustment process will be explained. The control device 5 increases the attenuation amount in the regulator 32 of the adjustment target section by the adjustment amount (increase amount). As described above, increasing the attenuation amount of the regulator 32 from a state where optical noise due to nonlinear optical effects is present reduces the optical noise, thus improving the SNR. However, if the attenuation amount of the regulator 32 is increased too much, the effect of the decrease in the signal light level becomes stronger than the reduction in optical noise, degrading the OSNR, and therefore the SNR also deteriorates. Therefore, the control device 5 repeatedly increases the attenuation amount provided by the regulator 32 of the adjustment target section by the adjustment amount and monitors the change in SNR. Then, the control device 5 determines the attenuation amount that results in an appropriate SNR and sets it in the regulator 32 of the adjustment target section.

Furthermore, in the determination process, sections belonging to longer section groups are excluded from the adjustment target section first. Therefore, the attenuation amount set in the adjuster 32 may be smaller for sections belonging to longer section groups. This is because the longer the section length, the greater the required optical power.

Furthermore, the control device 5 may perform the decision process periodically. Alternatively, the control device 5 may perform the decision process in response to an execution command input by the operator. Alternatively, the control device 5 may perform the decision process in response to a change in the number of signal lights transmitted by the optical transmitter 1 to the optical receiver 2. The control device 5 may determine the change in the number of signal lights based on the SNR of each signal light reported to the control device 5 by the optical receiver 2.

<First Embodiment>
The first embodiment will be described below. In this embodiment, the tuner 32 is configured to adjust the overall optical power density of the wavelength-division multiplexed light all at once. Figure 2 is a flowchart of the adjustment process by the control device 5. As described above, the process in Figure 2 is performed on adjustment target sections that include one or more sections, and is repeated until there are no more adjustment target sections left. In the explanation of the process in Figure 2, adjustment target sections will simply be referred to as "sections".

In S11, the control device 5 determines the minimum SNR of each signal light, 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. 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 regulator 32 in each section by an adjustment amount Xi. The adjustment amount Xi may be a predetermined value.

The control device 5 increases the attenuation amount provided by the regulator 32 in each section, and then in S14 determines the SNR of the reference signal light and sets it 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 attenuation amount applied by the adjuster 32 in each section so that the SNR of the reference signal light is the highest among those measured.

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 shown in Figure 3 improves due to the reduction in optical noise and the decrease in signal light power, and then deteriorates due to the decrease 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 shifts from improvement to deterioration. Note that the SNR of the signal light outside the predetermined range shown 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 decrease 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.

In this embodiment, the amount of attenuation applied by the adjuster 32 in each section is determined by monitoring the SNR of the reference signal light while increasing the attenuation amount applied by the adjuster 32 in each section. This configuration allows for the suppression of optical noise due to nonlinear optical effects in an optical communication system transmitting multiple wavelength-multiplexed signal lights. In this embodiment, the SNR of each signal light is determined before increasing the attenuation amount of the adjuster 32 in each section during the adjustment process, and the signal light with the minimum SNR is used 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 shown in Figure 3 as the reference signal light. In this case, S11 in Figure 3 becomes a process where the SNR of the predetermined signal light, the reference signal light, is set as the first evaluation value.

<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".

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 regulator 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 regulator 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.

The control device 5 increases the attenuation amount applied 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. Next, 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 increased 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 in S26 the second evaluation value becomes smaller than the first evaluation value, that is, if the average value of the SNR of all signal light decreased due to the adjustment of the attenuation amount, the control device 5 in S28 reduces the attenuation amount applied by the regulator 32 in each section for each light to be adjusted by the adjustment amount Xi, 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 the measured values.

In this embodiment, 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, one or more signal lights with wavelengths within a wavelength range where the SNR is lower than the average value of the SNR of each signal light, and the absolute value of the chromatic dispersion of the optical fiber is lower than the threshold, are designated as the target light for adjustment. The target light for adjustment 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 target lights in each section's adjuster 32, the amount of attenuation applied to one or more target lights in each section's adjuster 32 is determined. This configuration makes it possible to suppress the effects of optical noise due to nonlinear optical effects in an optical communication system that transmits multiple wavelength-division multiplexed signal lights.

<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".

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 that is different from 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 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.

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 whose SNR has deteriorated, the control device 5 reduces the attenuation amount applied by the regulator 32 in each section by the adjustment amount Xi increased in S33, and excludes them from the range of light to be adjusted. Next, in S35, the control device 5 determines if the number of light to be adjusted is 0. If the number of light to be adjusted 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 light 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 regulator 32 in each section to the value that yielded the highest SNR among the measured light to be adjusted, for each light to be adjusted.

In this embodiment, all signal light except the one 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 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. This configuration makes it possible to suppress the effects of optical noise due to nonlinear optical effects in an optical communication system that transmits multiple wavelength-multiplexed signal lights.

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, determined by the optical receiver 2 demodulating the multiple signal lights, from the optical receiver 2. The control unit 52 controls the attenuation amount applied by the adjuster 32 in each section of the optical transmission path 3. The control unit 52 executes the determination process described above. That is, the adjustment process described above is repeated 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.

Furthermore, the control device 5 can be implemented by having one or more processors in a device, such as a computer, execute an appropriate program on one or more of those processors. 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.

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 light signals. 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."

The invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the invention's essence.

51: Acquisition unit, 52: Control unit

Claims (11)

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. 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. 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. The control device according to claim 3, wherein the reference signal light is the signal light with the smallest absolute value of the chromatic dispersion among the wavelengths of the plurality of signal lights. 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 applied by the adjuster in the adjustment target section, and determines the attenuation amount at which the signal-to-noise ratio of the reference signal light becomes highest as the attenuation amount applied by the adjuster in the adjustment target section. 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. 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 attenuation amount applied to one or more target lights in the adjustment section by the adjuster, and determines the attenuation amount that results in the highest average value of the signal-to-noise ratio of the plurality of signal lights as the attenuation amount applied to one or more target lights in the adjustment section by the adjuster. 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. 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 attenuation amount applied to the light to be adjusted by the adjuster in the adjustment section, and determines the attenuation amount at which the signal-to-noise ratio of the light to be adjusted becomes the attenuation amount applied to the light to be adjusted by the adjuster in the adjustment section. 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. A program, 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.