Optical relay device, optical relay method, and program

Abstract

The present invention performs frequency flipping processing for at least one optical signal channel in units of channel.

Description

Optical repeater, optical repeater method, and program

[0001] The present invention relates to an optical repeater, an optical repeating method, and a program.

[0002] In recent years, the introduction of 5G wireless communication systems has been progressing, and in the post-5G era, there is a growing demand not only for wireless communication but also for optical communication fields, for high-capacity communication, ultra-high speeds, ultra-low latency, and multiple simultaneous connections. For this reason, research into optical communication systems is progressing, with the expectation that they will be used for a variety of communication services and industrial applications.

[0003] For example, in backbone optical communication systems, a digital coherent system that combines optical phase modulation and polarization multiplexing / demultiplexing technology has been used to achieve a capacity exceeding 100 Gbps (Giga bit per second). Furthermore, research and development is being conducted on transmission systems that improve frequency utilization efficiency and enable multiple simultaneous connections by narrowing the signal bandwidth and using wavelength division multiplexing (WDM). Research and development is also being conducted on distortion compensation technologies that use optical processing or digital signal processing to compensate for signal distortion that occurs during optical transmission, which hinders high-capacity communication due to high baud rates and high-level signal modulation in optical communication systems.

[0004] Related techniques are known, for example, from Patent Documents 1 to 4. Patent Document 1 discloses a wavelength converter that converts the wavelength of an optical signal using a coherent system at a receiving end and a transmitting end.

[0005] Patent Document 2 discloses that a phase conjugate signal is generated between a transmitter and a receiver by digital signal processing, and an optical phase conjugate device that shifts the optical carrier frequency is connected.

[0006] Patent Document 3 discloses connecting a dispersion compensation module between a transmitter and a receiver to compensate for chromatic dispersion in an optical transmission line.

[0007] Patent document 4 discloses that a node in an optical network having multiple spans generates a phase conjugate signal or an inverted optical spectrum of an optical signal in order to improve the transmission efficiency of the optical signal (paragraph 0040, etc.).

[0008] Patent Document 1: JP-T-2017-511036A US Patent Application Publication No. 2012 / 0224855 Specification Patent Document 2: JP-A-2011-035735 Patent Document 3: JP-A-2015-220756

[0009] In the technology related to the optical network system described above, it is required to suppress degradation of signal quality due to nonlinear distortion in optical transmission.

[0010] An object of the present disclosure is to provide an optical network system, a control method, a control program, a control device, and an optical repeater that solve the above-mentioned problems.

[0011] The optical repeater according to the present disclosure includes a digital signal processing unit that performs frequency flip processing on at least one or more channels of an optical signal on a channel-by-channel basis.

[0012] The optical repeating method according to the present disclosure performs frequency flip processing on at least one or more channels of an optical signal on a channel-by-channel basis.

[0013] The program according to the present disclosure causes a computer of an optical repeater device to function as a digital signal processing means that performs frequency flip processing on at least one or more channels of an optical signal on a channel-by-channel basis.

[0014] According to the present disclosure, it is possible to suppress degradation of signal quality due to nonlinear distortion in optical transmission.

[0015] 1 is a configuration diagram showing an example of a configuration of an optical network system according to a basic example. FIG. 1 is a configuration diagram showing an example of a configuration of an optical repeater according to a basic example. FIG. 2 is a configuration diagram showing a configuration of an optical transceiver according to the present disclosure. FIG. 3 is a diagram for explaining a problem of an optical transceiver according to the present disclosure. FIG. 4 is a diagram for explaining a problem of an optical transceiver according to the present disclosure. FIG. 5 is a configuration diagram showing a schematic configuration of a control device according to an embodiment. FIG. 6 is a configuration diagram showing a schematic configuration of an optical repeater according to an embodiment. FIG. 7 is a configuration diagram showing an example of a configuration of an optical network system according to a first embodiment. FIG. 8 is a configuration showing an example of a configuration of each device in the optical network system according to the first embodiment. FIG. 9 is a configuration diagram showing an example of a configuration of a chromatic dispersion compensator according to the first embodiment. FIG. 10 is a flowchart showing an operation example of the optical network system according to the first embodiment. FIG. 11 is a diagram showing a specific example of chromatic dispersion compensation by a control method according to the first embodiment. FIG. 12 is a diagram showing a specific example of chromatic dispersion compensation by a control method according to the first embodiment. FIG. 1 is a diagram showing a specific example of chromatic dispersion compensation by a control method according to embodiment 2. FIG. 2 is a diagram showing a specific example of chromatic dispersion compensation by a control method according to embodiment 3. FIG. 3 is a diagram showing a specific example of chromatic dispersion compensation by a control method according to embodiment 3. FIG. 4 is a diagram showing a minimum configuration of a control device according to an embodiment of the present disclosure. FIG. 5 is a diagram showing a processing flow by a control device with a minimum configuration according to an embodiment of the present disclosure. FIG. 6 is a diagram showing a minimum configuration of an optical repeater according to an embodiment of the present disclosure. FIG. 7 is a diagram showing a processing flow by an optical repeater with a minimum configuration according to an embodiment of the present disclosure. FIG. 8 is a diagram showing another configuration of an optical repeater according to an embodiment of the present disclosure. FIG. 9 is a diagram showing a processing flow by an optical repeater with a different configuration according to an embodiment of the present disclosure. FIG. 10 is a diagram showing a configuration overview of computer hardware according to an embodiment of the present disclosure.

[0016] Hereinafter, embodiments of the optical network system, control method, control program, control device, and optical repeater of the present disclosure will be described with reference to the drawings. In each drawing, the same elements are given the same reference numerals, and duplicated explanations will be omitted as necessary. Note that arrows in the configuration diagrams (block diagrams) are for illustrative purposes only and do not limit the type or direction of signals.

[0017] (Considerations leading to the embodiment) Figure 1 shows the configuration of an optical network system according to a basic example that forms the basis of this embodiment. The optical network system 1 according to the basic example is, for example, a backbone wavelength multiplexing optical transmission system, in which devices that constitute the system perform wavelength multiplexing of optical signals and perform high-level modulation and digital coherent transmission of optical signals of each wavelength, thereby achieving high-capacity communications of over 100 Gbps. High-density wavelength multiplexing makes it possible to improve the efficiency of optical frequency utilization, and can accommodate mobile traffic and wavelength defragmentation.

[0018] The optical network system 1 includes optical repeaters 2 (e.g., 2-1 to 2-10) that can flexibly switch transmission paths (wavelength paths or optical transmission paths) of optical signals as they are in order to switch transmission paths in the event of a failure or to accommodate local traffic demands (e.g., communication traffic demands from data centers 4 and 5, the network of an IT service provider 6, and the networks of event venues 7 and 8). By including the optical repeaters 2 (e.g., 2-1 to 2-10), the optical network system 1 can maintain communications using optical signals as an infrastructure. The optical repeaters 2 are photonic nodes that can relay wavelength-multiplexed optical signals, such as reconfigurable optical add / drop multiplexer (ROADM) devices. Each optical repeater 2 is assigned a wavelength path (also simply referred to as a path), and forwards traffic from the local network or other optical repeaters 2 accommodated therein to a destination network or other communication device via an optical communication cable that transmits optical signals of the assigned wavelength path.

[0019] 2 shows an example of the configuration of an optical repeater 2 according to a basic example. The optical repeater 2 drops / adds an optical wavelength-multiplexed signal and coherently modulates / demodulates the signals of each wavelength that are dropped / added. As shown in FIG. 2, the optical repeater 2 includes an optical switch unit 300 and a transmitter / receiver unit 310.

[0020] The optical switch unit 300 transfers optical signals of a predetermined wavelength path received from an optical repeater 2 in a previous stage in the optical network system 1 to an optical repeater 2 in a subsequent stage, and also drops / adds the received optical signals for each wavelength. For example, the optical switch unit 300 includes a demultiplexer 301, a multiplexer 302, and an add / drop unit 303. The demultiplexer 301 separates an optical signal received from the optical transmission line 3 into optical signals of multiple wavelengths. The multiplexer 302 multiplexes optical signals of multiple wavelengths into a single optical signal and transmits it to the optical transmission line 3. The add / drop unit 303 drops / adds optical signals of each wavelength between the demultiplexer 301 and the multiplexer 302.

[0021] The transceiver unit (transponder) 310 receives optical signals of each wavelength branched from the add / drop unit 303 of the optical switch unit 300 and outputs the coherently demodulated received data to a local device (network). The transceiver unit 310 also inputs transmission data from the local device and transmits (adds) coherently modulated optical signals of each wavelength to the add / drop unit 303 of the optical switch unit 300. The transceiver unit 310 includes a plurality of optical transceivers 311 that transmit and receive optical signals of each wavelength. The optical transceiver 311 receives an optical signal of a predetermined wavelength and further transmits an optical signal of a predetermined wavelength (the same as or different from the received wavelength) to a destination.

[0022] Here, we will consider issues that arise when an optical transceiver is used as the optical transceiver 311. Fig. 3 shows an example configuration of an optical transceiver according to this disclosure. As shown in Fig. 3, the optical transceiver 314 according to this disclosure includes a coherent receiver front-end unit 210, a coherent transmitter front-end unit 220, an acquisition unit 910, and a digital signal processor 901. Digital signal processing enables phase conjugation processing and chromatic dispersion compensation on a channel-by-channel basis.

[0023] The coherent receiver front-end unit 210 coherently detects an optical signal received from the optical repeater 2 at the previous stage using local oscillator light (LO light) of a predetermined wavelength and outputs the detected signal to the digital signal processing unit 901. The coherent transmitter front-end unit 220 optically modulates (coherently modulates) the signal processed by the digital signal processing unit 901 to a predetermined wavelength and transmits the generated optical signal to the optical repeater 2 at the next stage. The digital signal processing unit 901 is a DSP (Digital Signal Processor), converts the signal coherently detected by the coherent receiver front-end unit 210 into a digital signal, outputs signal-processed received data, and recovers input transmission data and outputs a signal converted for optical modulation to the coherent transmitter front-end unit 220. In this disclosure, the digital signal processing unit 901 performs phase conjugation processing and chromatic dispersion compensation on a channel-by-channel basis.

[0024] 4A and 4B show the amount of chromatic dispersion when an optical repeater 90 including an optical transceiver 314 according to this disclosure is used. As shown in Fig. 4A, the optical repeater 90 is connected between a transmitting terminal device (transmitting end) 30 and a receiving terminal device (receiving end) 40 via optical transmission paths 3a and 3b. The optical transmission path 3a has a distance L1, and the optical transmission path 3b has a distance L2, and L1 and L2 may be the same length or different lengths. An optical signal with a wavelength λ1 is transmitted through the optical transmission path 3a, and an optical signal with a wavelength λ2 is transmitted through the optical transmission path 3b.

[0025] 4A, the side of the optical repeater 90 closer to the transmitting terminal device 30 than the optical repeater 90 is sometimes referred to as the front stage of the optical repeater 90 (the receiving side of the optical signal), and the side of the optical repeater 90 closer to the receiving terminal device 40 is sometimes referred to as the rear stage of the optical repeater 90 (the transmitting side of the optical signal). Also, the optical transmission path between the optical repeater 90 and the transmitting terminal device 30 is sometimes referred to as the front stage (first portion) optical transmission path, and the optical transmission path between the optical repeater 90 and the receiving terminal device 40 is sometimes referred to as the rear stage (second portion) optical transmission path.

[0026] As shown in Figure 4B, the amount of chromatic dispersion increases in proportion to the distance of the optical transmission path. Therefore, if an optical repeater relays an optical signal solely by signal amplification, the amount of chromatic dispersion continues to increase with the distance from the transmitting terminal device 30 to the receiving terminal device 40. As a result, as the distance of the optical transmission path increases, the quality of the optical signal received at the receiving terminal device 40 deteriorates significantly. In addition to chromatic dispersion, nonlinear distortion also significantly deteriorates the quality of the optical signal. Nonlinear distortion is a phenomenon in which the refractive index of a material changes in proportion to the optical signal strength as the optical signal propagates through an optical fiber, causing a change in the phase of the light itself. Such nonlinear distortion is a factor that limits the increased capacity and long-distance transmission that can be achieved by increasing the baud rate and multi-value of optical signals.

[0027] In the example disclosed above, phase conjugation processing and chromatic dispersion compensation are performed in the optical repeater 90 connected to the path from the transmitting terminal device 30 to the receiving terminal device 40. In the example disclosed above, by performing phase conjugation processing and chromatic dispersion compensation in the optical repeater 90, nonlinear distortion occurring in the upstream transmission path and nonlinear distortion occurring in the downstream transmission path in the phase conjugate light transmitted from the optical repeater 90 are canceled out, thereby mitigating the influence of nonlinear distortion in the receiving terminal device 40, which is the receiving end.

[0028] The disclosed example herein above mitigates the effects of intra-channel nonlinear distortion in single channel transmission in an optical transmission line.

[0029] In addition to the examples disclosed above, it is desirable to be able to fully achieve the effect of mitigating nonlinear distortion when an optical transmission signal transmitted through an optical fiber has multiple optical channels. This disclosure makes it possible to reduce the nonlinear effect between channels during multi-channel transmission in an optical repeater in a multiple optical transmission network. Furthermore, this disclosure also makes it possible to reduce intra-channel nonlinear distortion by performing optimal chromatic dispersion compensation and phase conjugation in the optical repeater in a multiple optical transmission network.

[0030] An outline of this embodiment is shown. In addition to a repeater configuration using optical phase conjugation and chromatic dispersion compensation for intra-channel nonlinearity reduction, a configuration for inter-channel nonlinearity reduction is shown in this disclosure. As a compensation method for intra-channel nonlinear distortion, compensation may be performed using a digital backpropagation method in a digital signal processing unit at the optical transmitting end or receiving end. Alternatively, although the effect will be smaller, it is also possible to only use a configuration for reducing inter-channel nonlinear distortion without performing intra-channel nonlinear distortion compensation processing.

[0031] (Outline of the embodiment) Fig. 5 shows a schematic configuration of a control device according to the present embodiment. Fig. 6 shows a schematic configuration of an optical repeater according to the present embodiment. A control device 10 and an optical repeater 20 constitute an optical network system. The optical repeater 20 according to the present embodiment constitutes a part of the optical network system, and the control device 10 according to the present embodiment controls the optical repeater 20, which is another component of the optical network system.

[0032] 5, the control device 10 includes a management unit 11, a phase conjugate control unit 12, a chromatic dispersion compensation control unit 13, and a frequency flip control unit 14. The management unit 11 manages wavelength information of optical signals transmitted and received by an optical repeater 20 along a path of an optical network, and transmission line information of an optical transmission line connected to the optical repeater 20. The phase conjugate control unit 12 determines phase conjugation processing in the optical repeater 20 based on the wavelength information and transmission line information managed by the management unit 11. The chromatic dispersion compensation control unit 13 determines the amount of chromatic dispersion compensation to be performed in the optical repeater 20 based on the wavelength information and transmission line information managed by the management unit 11. The frequency flip control unit 14 instructs frequency flip processing to be performed on at least one or more channels of an optical signal on a channel-by-channel basis.

[0033] 6, the optical repeater 20 includes a coherent receiving front end unit 21, a phase conjugation unit 22, a chromatic dispersion compensation unit 23, a coherent transmitting front end unit 24, a phase conjugation acquisition unit 25, a chromatic dispersion compensation acquisition unit 26, a frequency flip instruction acquisition unit 27, and a frequency flip processing unit 28. Although not shown in FIG. 6, the optical repeater 20 transmits and receives multiple optical channels, and performs phase conjugation, chromatic dispersion compensation, and frequency flip processing on the signals of each channel.

[0034] The phase conjugate acquisition unit 25 acquires the phase conjugate processing determined by the phase conjugate control unit 12 from the control device 10. The chromatic dispersion compensation acquisition unit 26 acquires the amount of chromatic dispersion compensation determined by the chromatic dispersion compensation control unit 13 from the control device 10. The frequency flip instruction acquisition unit 27 acquires information on the channel for which frequency flip processing is to be performed. The coherent receiver front end unit 21 coherently detects the received optical signal based on the local oscillation light and outputs the coherently detected electrical signal. The phase conjugate unit 22 performs phase conjugation processing by digital signal processing on the electrical signal output from the coherent receiver front end unit 21 based on the phase conjugate processing setting acquired by the phase conjugate acquisition unit 25. The chromatic dispersion compensation unit 23 performs chromatic dispersion compensation processing by digital signal processing on the electrical signal output from the phase conjugate unit 22 based on the amount of chromatic dispersion compensation acquired by the chromatic dispersion compensation acquisition unit 26. The frequency flip processing unit 28 performs frequency flip processing for at least one or more optical signals on a channel-by-channel basis, using the electrical signal output from the chromatic dispersion compensating unit 23, based on the frequency flip processing information acquired from the frequency flip instruction acquiring unit 27. The frequency flip processing is a process of inverting the frequency components of the optical signal for each frequency, based on a reference frequency set at the center of the frequency band of the channel. The coherent transmission front-end unit 24 coherently modulates the electrical signal that has been phase conjugated by the phase conjugating unit 22 and the electrical signal that has been chromatic dispersion compensated by the chromatic dispersion compensating unit 22, based on the transmitted light, and transmits the coherently modulated optical signal.

[0035] As described above, in the embodiment, the control device 10 determines the phase conjugation process and the amount of chromatic dispersion compensation in the optical repeater 20 based on wavelength information of the optical signals transmitted and received by the optical repeater 20 in the path and transmission line information of the optical transmission line connected to the optical repeater 20. The control device 10 performs the phase conjugation process and chromatic dispersion compensation of the determined amount of chromatic dispersion compensation in the optical repeater 20 to reduce intra-channel nonlinear distortion. The control device 10 also performs frequency flip process on a channel-by-channel basis to suppress nonlinear effects between channels.

[0036] By performing phase conjugation of the optical signal in the optical repeater 20, it is possible to invert the distortion of the optical signal in the optical transmission path upstream of the optical repeater 20. As the signal propagates through the optical transmission path downstream of the optical repeater 20, the distortion is reversed and canceled out at the receiving end. According to the embodiment described below, the optical repeater 20 can perform chromatic dispersion compensation using an appropriate amount of phase conjugation and chromatic dispersion compensation. Therefore, by using phase conjugation and chromatic dispersion compensation in each optical repeater 20 in a multi-span optical network, it is possible to maximize the cancellation effect of nonlinear distortion caused by multi-span optical transmission, and effectively suppress degradation of signal quality due to intra-channel nonlinear distortion at the receiving end of the optical network. Furthermore, since the optical repeater 20 performs frequency flip processing on a channel-by-channel basis, it is possible to suppress nonlinear effects between channels.

[0037] (First Embodiment) Next, a first embodiment will be described with reference to the drawings. Fig. 7 shows an example of the configuration of an optical network system according to this embodiment. As shown in Fig. 7, an optical network system 50 according to this embodiment includes a control device 100, a plurality of optical repeaters 200, a transmitting terminal device 30, and a receiving terminal device 40.

[0038] The plurality of optical repeaters 200, the transmitting terminal device 30, and the receiving terminal device 40 are connected to each other via an optical transmission path 3 so that they can communicate with each other optically. The plurality of optical repeaters 200, the transmitting terminal device 30, and the receiving terminal device 40 are connected to the control device 100 so that they can communicate with each other control signals. The plurality of optical repeaters 200, the transmitting terminal device 30, and the receiving terminal device 40 may be connected to the control device 100 via the optical transmission path 3, or may be connected to each other via any other transmission path including wired or wireless so that they can communicate with each other.

[0039] The multiple optical repeaters 200, the transmitting terminal device 30, and the receiving terminal device 40 are optical transmission devices (optical nodes) that perform optical communication via the optical transmission path 3. The transmitting terminal device 30 and the receiving terminal device 40 constitute the transmitting end and the receiving end of a path formed by connecting the multiple optical transmission paths 3. The transmitting terminal device 30 transmits a multi-channel optical signal wavelength-multiplexed using the wavelengths of the path set by the control device 100 to the receiving terminal device 40 via the optical transmission path 3. The receiving terminal device 40 receives the multi-channel optical signal wavelength-multiplexed using the wavelengths of the path set by the control device 100 from the transmitting terminal device 30 via the optical transmission path 3.

[0040] Similar to the basic example, the multiple optical repeaters 200 are repeaters capable of repeating wavelength-multiplexed multi-channel optical signals. The multiple optical repeaters 200 constitute an optical network 51 for WDM communication. It can also be said that the multiple optical repeaters 200, together with the transmitting terminal device 30 and the receiving terminal device 40, constitute the optical network 51. The optical network 51 is a wavelength-multiplexed optical network, similar to that shown in FIG. 1. The optical network 51 may be a mesh-shaped network, a ring-shaped network, a point-to-point network, or a network of other topologies. Furthermore, the multiple optical repeaters 200 form a path from the transmitting terminal device 30 to the receiving terminal device 40 under the control of the control device 100, and transmit optical signals (data) at wavelengths set on the path route.

[0041] The control device 100 manages and controls an optical network 51 including a plurality of optical repeaters 200. For example, the control device 100 is an NMS (Network Management System) that manages the network.

[0042] The control device 100 manages and controls paths formed by optical repeater devices 200 in the optical network 51. The control device 100 manages the route and wavelength of the path from the transmitting terminal device 30 to the receiving terminal device 40, and sets the route and wavelength of the path for the transmitting terminal device 30, the receiving terminal device 40, and the optical repeater devices 200 on the path.

[0043] 8 shows an example of the configuration of each device in the optical network system according to this embodiment. As shown in Fig. 8, the control device 100 includes a network management unit 110, a network control unit 120, a chromatic dispersion compensation amount calculation unit 130, a phase conjugation determination unit 140, and a frequency flip instruction unit 150.

[0044] The network management unit 110 manages information necessary for network management, such as network configuration information and path configuration information in the optical network 51. For example, the network management unit 110 may be configured as a database that stores information necessary for network management. The network configuration information includes the connection relationships of the optical repeater devices 200, transmitting terminal devices 30, and receiving terminal devices 40 that make up the network, as well as transmission path information of the optical transmission path 3 that connects each device. The transmission path information includes the distance L (transmission path length) of the optical transmission path, and may also include the structure and type of optical fiber, transmission characteristics, etc. The path configuration information includes information on each device that makes up the path, wavelengths that each device can use on the path, and wavelength usage status, etc. This information may be set in advance in a database, or may be set based on information collected from each device, and may also be updated by the network control unit 120, etc.

[0045] The network control unit 120 controls paths in the optical network 51 and the optical repeater devices 200, transmitting terminal devices 30, and receiving terminal devices 40 that constitute the paths. The network control unit 120 references network configuration information and path configuration information in the network management unit 110 to determine the route and wavelength of the path from the transmitting terminal device 30 to the receiving terminal device 40, and sets the determined route and wavelength in the transmitting terminal device 30, the receiving terminal device 40, and the optical repeater devices 200 on the path. The wavelength of light in the path is determined for each optical transmission line in the path. For example, when the route of a path overlaps with the route of another path, different wavelengths are selected between the paths from among available wavelengths in the optical transmission lines in the overlapping sections. The network control unit 120 also outputs information necessary for calculating the amount of chromatic dispersion compensation in the optical repeater devices 200 that constitute the path to the chromatic dispersion compensation amount calculation unit 130. For example, the network control unit 120 outputs reception wavelength information (wavelength information of the received optical signal), transmission wavelength information (wavelength information of the transmitted optical signal), and transmission path information of the previous and next optical transmission paths of the optical repeater 200. The network control unit 120 also outputs phase conjugate determination information in the optical repeater 200 that constitutes the path to the phase conjugate determination unit 140. For example, the network control unit 120 outputs the number of paths and the number of optical repeaters in the optical network 51.

[0046] The chromatic dispersion compensation amount calculation unit 130 calculates the amount of chromatic dispersion compensation required for the optical repeater 200 constituting the path to perform chromatic dispersion compensation. The chromatic dispersion compensation amount calculation unit 130 is a compensation control unit that determines and controls the amount of chromatic dispersion compensation for the optical repeater 200. The chromatic dispersion compensation amount calculation unit 130 determines the optimal amount of chromatic dispersion compensation for the optical repeater 200 based on the receiving wavelength information, transmitting wavelength information, and transmission path information before and after the optical repeater obtained from the network control unit 120. The chromatic dispersion compensation amount calculation unit 130 notifies the corresponding optical repeater 200 of the receiving wavelength information, transmitting wavelength information, and optimal amount of chromatic dispersion compensation for the optical repeater 200.

[0047] The phase conjugate determination unit 140 controls the phase conjugate processing of the optical repeater 200 that constitutes the path. The phase conjugate determination unit 140 determines the optimal phase conjugate processing for the optical repeater 200 based on the number of paths and the number of optical repeaters in the optical network 51 obtained from the network control unit 120. The phase conjugate determination unit 140 notifies the optical repeater 200 of the phase conjugate processing information.

[0048] The frequency flip instruction unit 150 instructs the frequency of a channel on which frequency flip processing is to be performed. The frequency flip instruction unit 150 instructs that frequency flip processing be performed on at least one or more channels on a channel-by-channel basis. The frequency flip instruction unit 150 may instruct that frequency flip processing be performed on all channels of the optical signal on a channel-by-channel basis. The frequency flip instruction unit 150 may sequentially identify channels to be processed and channels not to be processed among multiple channels with different frequency bands that are arranged in order based on the frequency bands, and instruct to perform frequency flip processing on the channels to be processed.

[0049] In the optical network 51, multi-channel optical signals are relayed by a plurality of optical repeaters 200 via the optical transmission line 3. When a plurality of optical repeaters 200 in the optical network 51 perform frequency flip processing for a channel of the optical signal, the control device 100 counts the number of frequency flip processing times for that channel and notifies the receiving end optical device 40. Based on the notified number of frequency flips for that channel, the signal processing unit for that channel in the receiving end optical device determines whether to perform frequency flip processing, and performs signal processing on the received signal.

[0050] 8, the optical repeater 200 according to this embodiment includes an optical transceiver 201 and a node control unit 202. Although not shown in FIG. 8, in order to transmit and receive multiple optical channels, the optical repeater 200 includes an optical switch unit 300 and a transceiver unit 310, and the transceiver unit 310 includes multiple optical transceivers 201, similar to the basic example in FIG. 2. In other words, the node control unit 202 can control the optical switch unit 300 and the transceiver unit 310 (multiple optical transceivers 201).

[0051] The optical transceiver 201 includes a coherent receiving front end unit 210 , a coherent transmitting front end unit 220 , a digital signal processing unit 230 , a receiving light source 240 , a transmitting light source 250 , an ADC 260 , and a DAC 270 .

[0052] The receiving light source 240 generates a local light r1 having a wavelength (frequency) set by the node control unit 202, and outputs the generated local light r1 to the coherent receiving front end unit 210. The transmitting light source 250 generates a transmitting light r2 having a wavelength (frequency) set by the node control unit 202, and outputs the generated transmitting light r2 to the coherent transmitting front end unit 220.

[0053] The frequency (wavelength) of the local light r1 is the frequency (carrier frequency) of the received input optical signal SO1, and the frequency of the transmitted light r2 is the frequency of the transmitted output optical signal SO2. For example, the local light r1 and the transmitted light r2 may have different frequencies or the same frequency. By changing the frequencies of the local light r1 and the transmitted light r2, the wavelength of the optical signal to be relayed can be switched. This allows the input optical signal SO1 to be converted into an output optical signal SO2 with a different wavelength.

[0054] The coherent receiver front-end unit 210 and the coherent transmitter front-end unit 220 have the same configuration as in Fig. 3. The coherent receiver front-end unit 210 is an optical / electrical converter that converts an optical signal into an electrical signal, and a coherent detector that performs coherent detection. The coherent receiver front-end unit 210 coherently detects the input optical signal SO1 (received optical signal) based on the local oscillator light r1, and outputs the generated analog signal SA1 (first analog electrical signal).

[0055] The ADC (Analog / Digital Converter) 260 performs AD conversion on the analog signal SA1 generated by the coherent reception front end unit 210, and outputs the converted digital signal SD1 (first digital electrical signal).

[0056] The DAC (Digital / Analog Converter) 270 performs DA conversion on the digital signal SD2 (second digital electrical signal) that has been signal processed by the digital signal processing unit 230, and outputs the converted analog signal SA2 (second analog electrical signal).

[0057] The coherent transmission front end unit 220 is an electrical / optical converter that converts an electrical signal into an optical signal and a coherent modulator that performs coherent modulation. The coherent transmission front end unit 220 coherently modulates the analog signal SA2 that has been DA converted by the DAC 270 based on the transmitted light r2, and outputs the generated output optical signal SO2 (transmitted optical signal).

[0058] For example, the input optical signal SO1 and the output optical signal SO2 are phase-modulated and polarization-multiplexed optical signals. The analog signals SA1 and SA2 and the digital signals SD1 and SD2 are four-lane (4-channel) signals including an IX signal of the I component (in-phase component) of the X polarization, a QX signal of the Q component (quadrature component) of the X polarization, an IY signal of the I component of the Y polarization, and a QY signal of the Q component of the Y polarization.

[0059] The digital signal processing unit 230 performs digital signal processing on the digital signal SD1 converted by the ADC 260 and outputs a processed digital signal SD2. The digital signal processing unit 230 is a digital circuit that performs predetermined digital signal processing to compensate for signal quality. The digital signal processing unit 230 performs digital signal processing on all or part of the IX signal, QX signal, IY signal, and QY signal (X polarization or Y polarization) of the four lanes.

[0060] The digital signal processing unit 230 performs only specific signal processing, without performing processing that involves a large delay, such as code error correction (data recovery). This makes it possible to compensate for the required signal quality while suppressing signal delay. In this embodiment, the digital signal processing unit 230 includes a chromatic dispersion compensation unit 231 that performs chromatic dispersion processing, a phase conjugate processing unit 232 that performs phase conjugate processing, and a frequency flip processing unit 233 that performs frequency flip processing.

[0061] Chromatic dispersion compensation using digital signal processing can be achieved by convolution processing of the impulse response of the inverse transfer function of the optical transmission line with the received signal. Therefore, for example, the chromatic dispersion compensator 231 may be configured using a transversal filter (FIR filter). Since the characteristics of the optical transmission line can be modeled using an FIR filter, chromatic dispersion can be compensated for using an FIR filter with the inverse characteristics. While an FIR filter performs time domain equalization (TDE) that equalizes the received signal in the time delay domain, the same characteristics can also be achieved using frequency domain equalization (FDE) that equalizes the signal in the frequency domain. Configuring the chromatic dispersion compensator using FDE allows for a smaller circuit size than an FIR filter.

[0062] 9 shows an example of the configuration of the chromatic dispersion compensator 231 configured using FDE processing. The chromatic dispersion compensator 231 in Fig. 9 is an example of the configuration of overlap FDE, and includes an overlap adding unit 411, a fast Fourier transform unit 412, an inverse transfer function multiplying unit 413, an inverse fast Fourier transform unit 414, and an overlap removing unit 415.

[0063] The node control unit 202 sets the amount of chromatic dispersion compensation notified by the control device 100 in the chromatic dispersion compensation unit 231 in the digital signal processing unit 230. When the chromatic dispersion compensation unit 231 is configured with an FDE as shown in FIG. 9 , the node control unit 202 sets the transfer function coefficient of the inverse transfer function multiplication unit 413 in FIG. 9 in accordance with the amount of chromatic dispersion compensation notified by the control device 100.

[0064] The overlap adding unit 411 overlaps a portion of the preceding and following signals with the input signal (digital signal). The fast Fourier transform unit 412 then converts the overlapped signal into a frequency-domain signal using a fast Fourier transform (FFT). The inverse transfer function multiplier unit 413 equalizes the frequency-domain signal by multiplying it by the inverse transfer function of the transmission path. The inverse fast Fourier transform unit 414 then converts the signal into a time-domain signal using an inverse fast Fourier transform (IFFT). The overlap removal unit 415 removes the overlap from the signal restored to the time domain and outputs the signal. When FDE is used, the amount of chromatic dispersion compensation can be adjusted by changing the inverse transfer function. The overlap adding unit 411 and the overlap removal unit 415 may be omitted.

[0065] Frequency flip processing in digital signal processing inverts the frequency response components of an input signal. The input signal is converted into a frequency domain signal using FFT. The frequency components are inverted based on the center frequency of the channel. Then, the signal is converted into a time domain signal using IFFT. Frequency flip processing can be performed together with chromatic dispersion compensation in the same FDE processing unit as chromatic dispersion compensation, or it can be performed in an FDE processing unit independent of chromatic dispersion compensation.

[0066] Phase conjugation processing by digital signal processing finds the complex conjugate of the input digital signal, that is, inverts the sign of the imaginary component Q in the Ix signal, Qx signal, Iy signal, and Qy signal, as shown in the following equation (1).

[0067]

[0068] The node control unit 202 receives control information from the control device 100 and controls each unit of the optical repeater 200 based on the received control information. The node control unit 202 is an acquisition unit that acquires reception wavelength information and transmission wavelength information from the network control unit 120, an optimal chromatic dispersion compensation amount from the chromatic dispersion compensation amount calculation unit 130, phase conjugation processing information from the phase conjugation determination unit 140, and information on the channel to perform frequency flip from the frequency flip instruction unit 150. The node control unit 202 sets the frequency (wavelength) of the local light r1 for the reception light source 240 based on the acquired reception wavelength information, and sets the frequency of the transmission light r2 for the transmission light source 250 based on the acquired transmission wavelength information. The node control unit 202 sets the phase conjugation processing calculation for the phase conjugation processing unit 232 based on control information including an instruction to perform phase conjugation processing acquired from the control device 100. The node control unit 202 sets the chromatic dispersion compensation amount for the chromatic dispersion compensator 231 based on the acquired optimal chromatic dispersion compensation amount. The node control unit 202 sets the channel information acquired from the control device 100 in the frequency flip processing unit 233 .

[0069] 10 shows an example of the operation of the optical network system according to this embodiment. As shown in FIG. 10 , first, the network management unit 110 of the control device 100 determines the wavelength to be used by the optical repeater 200 (S101). The network control unit 120 of the control device 100 determines the route of the path in the optical network 51 and identifies the optical transmission lines and optical repeaters 200 on the route of the path. The network control unit 120 determines the wavelength of each identified optical transmission line, thereby determining the wavelengths of the upstream and downstream stages (before and after conversion) of each optical repeater 200, i.e., the wavelengths of the optical signals transmitted and received by the optical repeater 200. The network control unit 120 outputs the reception wavelength information and transmission wavelength information of the optical repeater 200 according to the determined wavelength to the chromatic dispersion compensation amount calculation unit 130, the phase conjugate determination unit 140, and the frequency flip instruction unit 150, and also outputs transmission path information (distance) of the optical transmission paths upstream and downstream of the optical repeater 200 to the chromatic dispersion compensation amount calculation unit 130 and the phase conjugate determination unit 140. When a path includes multiple optical repeaters 200, the following process is performed for each optical repeater.

[0070] Next, the control device 100 causes the chromatic dispersion compensation amount calculation unit 130 of the optical repeater 200 to calculate the chromatic dispersion characteristics in the upstream and downstream optical transmission paths (S102). The chromatic dispersion compensation amount calculation unit 130 calculates the chromatic dispersion characteristics in the upstream and downstream optical transmission paths of the optical repeater 200 based on the reception wavelength information and transmission wavelength information acquired from the network control unit 120 and the transmission path information (distance) of the upstream and downstream optical transmission paths of the optical repeater 200. Note that if the transmission information includes the structure, type, and transmission characteristics of the optical fiber, the chromatic dispersion characteristics may be determined based on this information.

[0071] For example, the chromatic dispersion characteristic is the slope of the amount of chromatic dispersion accumulated with respect to the distance of the optical transmission path (distance-dependent chromatic dispersion characteristic). Since the slope of this chromatic dispersion amount varies depending on the wavelength, a table that associates wavelengths (or wavelength bands) with the slope of the amount of chromatic dispersion may be stored in advance. The chromatic dispersion compensation amount calculation unit 130 may refer to this table to determine the chromatic dispersion characteristic corresponding to the wavelength.

[0072] Next, the chromatic dispersion compensation amount calculation unit 130 of the control device 100 determines an optimal chromatic dispersion compensation amount for the optical repeater 200 (S103). The chromatic dispersion compensation amount calculation unit 130 determines an optimal chromatic dispersion compensation amount for the optical repeater 200 based on the chromatic dispersion characteristics of the optical transmission paths upstream and downstream of the optical repeater 200 and transmission path information for the optical transmission paths upstream and downstream. The chromatic dispersion compensation amount calculation unit 130 calculates the amount of chromatic dispersion accumulated in the optical transmission path of the upstream stage (receiving side), calculates the amount of chromatic dispersion accumulated in the optical transmission path of the downstream stage (transmitting side), and determines an optimal chromatic dispersion amount based on the chromatic dispersion amounts of the upstream stage and the downstream stage. In particular, the chromatic dispersion compensation amount calculation unit 130 determines the optimal chromatic dispersion amount based on the amount of chromatic dispersion accumulated between the transmitting terminal device 30 and the optical repeater 200 and the amount of chromatic dispersion accumulated between the optical repeater 200 and the receiving terminal device 40. For example, the chromatic dispersion compensation amount calculation unit 130 determines the amount of chromatic dispersion accumulated in the optical transmission path upstream of the optical repeater 200 based on the chromatic dispersion characteristics and transmission path information (distance) of the optical transmission path upstream of the optical repeater 200, and determines the amount of chromatic dispersion accumulated in the optical transmission path downstream of the optical repeater 200 based on the chromatic dispersion characteristics and transmission path information of the optical transmission path downstream of the optical repeater 200. Note that in this example, the chromatic dispersion compensation amount calculation unit 130 determines the amount of chromatic dispersion compensation based on the chromatic dispersion characteristics and transmission path information, but because the chromatic dispersion characteristics correspond to the wavelength information, the chromatic dispersion compensation amount may also be determined based on the wavelength information and transmission path information. In other words, the chromatic dispersion compensation amount calculation unit 130 may determine the amount of chromatic dispersion compensation for multiple optical repeaters 200 that make up the path based on the wavelength information and transmission path information of the path.

[0073] Next, the phase conjugate determination unit 140 of the control device 100 determines the optimal phase conjugate processing in the optical repeater 200 (S104). The phase conjugate determination unit 140 determines the optimal phase conjugate processing in the optical repeater 200 based on the number of optical paths between the transmitting terminal device 30 and the receiving terminal device 40 in the optical network 50 and the number of optical repeaters 200. Next, the control device 100 determines the frequency of the channel on which frequency flip processing is to be performed (step S105).

[0074] Next, the control device 100 notifies the optical repeater 200 of the receiving wavelength information and transmitting wavelength information determined in S101, the optimal phase conjugate processing information determined in S104, the optimal chromatic dispersion compensation amount determined in S103, and the frequency information of the channel for which frequency flip processing is to be performed determined in step S105 (S106).

[0075] Next, the node control unit 202 of the optical repeater 200 sets the wavelength of the wavelength information notified from the control device 100, the phase conjugate processing information, the optimum chromatic dispersion compensation amount, and information on the frequency of the channel for which frequency flip processing is to be performed (S107). The node control unit 202 sets the wavelength of the acquired reception wavelength information to the reception light source 240, sets the wavelength of the acquired transmission wavelength information to the transmission light source 250, sets the acquired phase conjugate processing information to the phase conjugate processing unit 232, sets the acquired optimum chromatic dispersion compensation amount to the chromatic dispersion compensator 231, and sets the acquired frequency of the channel for which flip processing is to be performed to the frequency flip processing unit 233 of the channel.

[0076] Next, the optical repeater 200 performs wavelength conversion, phase conjugation, chromatic dispersion compensation, and frequency flipping (S108). The receiving light source 240 generates local light r1 of a set wavelength (frequency), and the transmitting light source 250 generates transmitting light r2 of a set wavelength, thereby performing wavelength conversion in the optical transceiver 201. The phase conjugation processing unit 232 performs phase conjugation by phase conjugation, and the chromatic dispersion compensation unit 231 performs chromatic dispersion compensation on the signal after phase conjugation by digital signal processing based on a set compensation amount. The frequency flip processing unit 233 also performs frequency flipping to invert the frequency components of the optical signal for each frequency based on a reference frequency set at the center of the specified frequency band.

[0077] 11A and 11B show specific examples of phase conjugation and chromatic dispersion compensation performed by the control method of this embodiment. In this embodiment, the optical repeater 200 performs phase conjugation on the nonlinear distortion accumulated in the upstream optical transmission path of the optical signal received by the optical repeater 200. This allows the nonlinear distortion of the optical signal transmitted from the optical repeater 200 during transmission in the downstream optical transmission path to be canceled out at the receiving end. To achieve this effect, the optical repeater 200 of this embodiment determines an optimal amount of chromatic dispersion compensation that maximizes the nonlinear distortion cancellation effect. The optimal amount of chromatic dispersion compensation in this example is a compensation amount calculated based on the amounts of chromatic dispersion in the upstream and downstream transmission paths of the optical repeater 200.

[0078] As shown in FIG. 11A , in this example, one optical repeater 200 is disposed on the path between the transmitting terminal device 30 and the receiving terminal device 40. The transmitting terminal device 30 and the optical repeater 200 are connected via an optical transmission line 3a (first optical transmission line), and the optical repeater 200 and the receiving terminal device 40 are connected via an optical transmission line 3b (second optical transmission line). For example, the distance L1 of the optical transmission line 3a is different from the distance L2 of the optical transmission line 3b, and the distance L2 of the optical transmission line 3b is longer than the distance L1 of the optical transmission line 3a, but they may also be the same distance. An optical signal with a wavelength λ1 is transmitted through the optical transmission line 3a, and an optical signal with a wavelength λ2 is transmitted through the optical transmission line 3b. For example, the wavelengths λ1 and λ2 may both be in the C-band wavelength band, or may be different, such as the C-band and the L-band wavelength band, or may both be in the L-band wavelength band. The optical repeater 200 converts a received optical signal of wavelength λ1 into an optical signal of wavelength λ2, and transmits the converted optical signal of wavelength λ2.

[0079] 11B , since the wavelength of the optical signal in the upstream optical transmission line 3a is λ1, the chromatic dispersion compensation amount calculation unit 130 of the control device 100 determines the slope DS1 of the chromatic dispersion amount in the optical transmission line 3a in accordance with the wavelength λ1. The slope DS1 of the chromatic dispersion amount in the optical transmission line 3a may be read from a storage unit such as a database. The chromatic dispersion compensation amount calculation unit 130 of the control device 100 uses the slope DS1 of the chromatic dispersion amount and the effective nonlinear distance Leff1 in the optical transmission line 3a to determine the accumulated chromatic dispersion amount M1 (= DS1 × Leff1) at the effective nonlinear distance Leff1 in the upstream optical transmission line 3a. The nonlinear effect is an effect that depends on the optical signal intensity, and the optical intensity in the transmission line decreases according to an exponential function characterized by a propagation loss constant. Therefore, it is sufficient to consider the nonlinear effect only in regions where the optical intensity is high. The effective nonlinear distance Leff is defined as the distance in which the nonlinear effect is taken into consideration, and is given by the following equation (2) using the length L and the propagation loss constant α in the optical fiber.

[0080]

[0081] Furthermore, since the wavelength of the optical signal in the downstream optical transmission path 3b is λ2, the chromatic dispersion compensation amount calculation unit 130 of the control device 100 determines the slope DS2 of the chromatic dispersion amount in the optical transmission path 3b in accordance with the wavelength λ2. The slope DS2 of the chromatic dispersion amount in the optical transmission path 3b may be read from a storage device such as a database. The chromatic dispersion compensation amount calculation unit 130 of the control device 100 calculates the accumulated chromatic dispersion amount M2 at the effective nonlinear distance Leff2 in the downstream optical transmission path 3b as M2 = -M1, under the condition that the accumulated chromatic dispersion amount M2 has the opposite sign to the accumulated chromatic dispersion amount M1 at the effective nonlinear distance Leff1 in the upstream optical transmission path 3a. The chromatic dispersion compensation amount calculation unit 130 then determines the accumulated chromatic dispersion amount M3 in the transmission signal of the optical repeater. M3 can be calculated as M3 = M2 + DS2 × Leff2 = DS1 × Leff1 + DS2 × Leff2.

[0082] The chromatic dispersion compensation amount calculation unit 130 of the control device 100 then calculates the cumulative chromatic dispersion compensation amount M5 for the optical repeater 200 to compensate for chromatic dispersion using phase conjugation, using M5=M4×2.

[0083] The chromatic dispersion compensation amount calculation unit 130 of the control device 100 calculates the difference M6 between the accumulated chromatic dispersion amount M3 and the accumulated chromatic dispersion compensation amount M5, and transmits the difference M6 to the optical repeater 200 as the optimal chromatic dispersion compensation amount. The control device 100 also transmits control information including an instruction to perform phase conjugation processing to the optical repeater 200. As a result, the node control unit 202 of the optical repeater 200 instructs the phase conjugation processing unit 232 to perform phase conjugation processing calculation based on the control information including the instruction to perform the acquired phase conjugation processing, as described with reference to FIGS. 9 and 10 . The phase conjugation processing unit 232 performs the phase conjugation processing calculation. Furthermore, the node control unit 202 of the optical repeater 200 sets the chromatic dispersion compensation amount M6 notified from the control device 100 in the chromatic dispersion compensation unit 231 of the digital signal processing unit 230, as described with reference to FIG. 9 . 9, the node control unit 202 sets the transfer function coefficient of the inverse transfer function multiplier 413 in FIG. 9 according to the chromatic dispersion compensation amount M6 notified by the control device 100. As a result, the optical repeater 200 calculates the accumulated chromatic dispersion M3 (M3=M4-M5-M6) for the downstream optical transmission line 3b after calculating the accumulated chromatic dispersion compensation amount M5 using the phase conjugation processing of the phase conjugation processing unit 232 and performing chromatic dispersion compensation using the chromatic dispersion compensation amount M6 of the chromatic dispersion compensator 231, and outputs an optical signal with this accumulated chromatic dispersion M3 (FIG. 11B). This suppresses the nonlinear effect in the receiving terminal device 40.

[0084] The optical repeater 200 can calculate the accumulated chromatic dispersion M3 without performing phase conjugation by M3 = M2 + DS2 × Leff2 = DS1 × Leff1 + DS2 × Leff2. Therefore, the chromatic dispersion compensator 231 of the optical repeater 200 may calculate the accumulated chromatic dispersion M3 and output an optical signal having the accumulated chromatic dispersion M3 without performing phase conjugation ( FIG. 11B ). For convenience of explanation, the explanations in FIGS. 11A and 11B assume that an optical signal with a wavelength λ1 is transmitted through the optical transmission path 3a and an optical signal with a wavelength λ2 is transmitted through the optical transmission path 3b. However, it is also possible that a multi-channel optical signal with multiple wavelengths λ (frequency bands) is transmitted through the optical transmission path 3a, and a multi-channel optical signal with multiple wavelengths λ (frequency bands) is also transmitted through the optical transmission path 3b.

[0085] FIG. 11C is a diagram showing an overview of phase conjugation processing. As shown in FIG. 11C, in a certain span in the optical network 51 (between the transmitting terminal device 30 and a network device such as the optical repeater device 200 in FIG. 11C), nonlinear distortion of the transmitted signal occurs as signal degradation due to nonlinear effects (1111 in FIG. 11C). Phase conjugation processing (inversion of the optical signal) is performed in the optical repeater device 200. This provides a cancellation effect of nonlinear distortion using phase conjugation in the span downstream of the optical repeater device 200 (between the optical repeater device 200 and the receiving terminal device 40), thereby reducing signal degradation (nonlinear distortion) in the receiving terminal device 40. In addition, chromatic dispersion compensation can be performed to enhance the cancellation effect of intra-channel nonlinear distortion in the receiving terminal device 40.

[0086] The processing in the control device 100 described above is one aspect of processing in which the amount of chromatic dispersion compensation to be performed in the optical repeater 200 is determined based on wavelength information of the optical signals transmitted and received by the optical repeater 200 constituting the optical network in the path of the optical network and transmission line information of the optical transmission line connected to the optical repeater 200, and the phase conjugation processing in the optical repeater 200 is determined based on the wavelength information and the transmission line information.

[0087] In addition, a part of the processing in the control device 100 is one aspect of the processing of sending an instruction to the optical repeater 200 to perform phase conjugate processing to calculate the complex conjugate of the optical signal based on the accumulated chromatic dispersion amount M4 of the optical signal received by the optical repeater 200.

[0088] In addition, a portion of the processing in the control device 100 is one aspect of processing to calculate a first accumulated chromatic dispersion amount M1 in a first effective nonlinear distance (Leff1) based on a transmitting network device in a first optical transmission path (previous path) between the optical repeater 200 and a transmitting network device that transmits an optical signal received by the optical repeater 200, among the optical transmission paths connected to the optical repeater 200.

[0089] Furthermore, a part of the processing in the control device 100 is one aspect of processing to calculate a second accumulated chromatic dispersion amount (M2) of the optical signal in a second effective nonlinear distance (Leff2) based on the optical repeater device itself in a second optical transmission path (later path) between the optical repeater device 200 and a network device on the receiving side of the optical signal transmitted by the optical repeater device 200, among the optical transmission paths connected to the optical repeater device 200, and which has the opposite sign to the first accumulated chromatic dispersion amount (multiplied by minus 1).

[0090] Furthermore, a part of the processing in the control device 100 is one aspect of processing to calculate a chromatic dispersion compensation amount (M6) indicating the difference between the chromatic dispersion amount (M3) at the time of transmission in the optical repeater 200 of the optical signal when the accumulated chromatic dispersion amount of the optical signal becomes the second accumulated chromatic dispersion amount (M2) at the second effective nonlinear distance (Leff2) based on a statistical value (DS2) of the transition of the accumulated chromatic dispersion amount of the optical signal according to the distance in the second optical transmission path, and the chromatic dispersion amount (M5) which is the result of the complex conjugate.

[0091] The processing of the optical repeater 200 described above is one aspect of processing in which chromatic dispersion compensation processing is performed on an electrical signal based on a received optical signal based on the chromatic dispersion compensation amount (M6), and phase conjugate processing is performed on an electrical signal based on a received optical signal based on phase conjugate processing information acquired from the control device 100.

[0092] Furthermore, some of the processing in the optical repeater 200 described above is one aspect of processing for performing phase conjugate processing based on the accumulated chromatic dispersion amount of the optical signal received by the optical repeater 200 itself and an instruction to perform phase conjugate processing for calculating the complex conjugate of the optical signal.

[0093] Furthermore, a part of the processing in the optical repeater 200 described above is one aspect of processing for determining the amount of chromatic dispersion (M3) of the optical signal to be transmitted to the receiving network device, based on the amount of chromatic dispersion (M5) that is the result of complex conjugation after phase conjugation processing and the amount of chromatic dispersion compensation (M6) acquired from the control device 100.

[0094] FIG. 11D is a first diagram showing an overview of frequency flip processing. The frequency flip processing unit 233 of the optical repeater 200 performs frequency flip processing on each channel of the received multi-channel optical signal, on a channel-by-channel basis. Here, as shown in FIG. 11D, it is assumed that the received optical signal is a signal of two frequency bands, channel 1 and channel 2. It is assumed that channel 1 includes signals of frequencies L11 to L1n on the low frequency side of the center frequency, and signals of frequencies R11 to R1n on the high frequency side. It is also assumed that channel 2 includes signals of frequencies L21 to L2n on the low frequency side of the center frequency, and signals of frequencies R21 to R2n on the high frequency side.

[0095] Assume that the frequency flip processing unit 233 of the optical repeater 200 is instructed to perform frequency flip processing for channel 1 and channel 2. In this case, the optical repeater 200 performs frequency flip processing to invert the signal components of the frequencies L11 to L1n on the low frequency side of channel 1 and the signal components of the frequencies R11 to R1n on the high frequency side, based on the center frequency of channel 1. Similarly, the frequency flip processing unit 233 of the optical repeater 200 performs frequency flip processing to invert the signal components of the frequencies L21 to L2n on the low frequency side of channel 2 and the signal components of the frequencies R21 to R2n on the high frequency side, based on the center frequency of channel 2.

[0096] As a result, the optical repeater 200 outputs an optical signal that includes signal components R1n to R11 on the low frequency side relative to the center frequency of channel 1, and signal components L1n to L11 on the high frequency side relative to the center frequency of channel 1. The optical repeater 200 also outputs an optical signal that includes signal components R2n to R21 on the low frequency side relative to the center frequency of channel 2, and signal components L2n to L21 on the high frequency side relative to the center frequency of channel 2. The order of the frequency components in each region is reversed by frequency flip processing.

[0097] According to the above-described frequency flip processing, the frequency region R1 on the channel 2 side in the frequency band of channel 1 is separated from the frequency region L2 on the channel 1 side in the frequency band of channel 2, thereby reducing the correlation between channels and thereby reducing the nonlinear effect between channels. With a high baud rate signal, the transmission band is widened and the regions R1 and L2 can be separated significantly. This makes it possible to reduce the nonlinear effect between channels due to frequency flip.

[0098] Here, the optical repeater 200 may perform frequency flip processing on all channels of the received optical signal on a channel-by-channel basis. Alternatively, the optical repeater 200 may receive multiple channels with different frequency bands, sequentially identify channels to be processed and channels not to be processed among the multiple channels arranged in order based on the frequency bands, and perform frequency flip processing on the channels to be processed. The channels to be processed and channels not to be processed in the frequency flip processing may be identified by the optical repeater 200 itself, or may be identified based on an instruction from the control device 100.

[0099] FIG. 11E is a second diagram illustrating an overview of frequency flip processing. Assume that the optical repeater 200 receives optical signals in the frequency bands of the first channel 1ch, the second channel 2ch, and the third channel 3ch. Based on an instruction from the control device 100 or based on its own decision, the frequency flip processing unit 233 of the optical repeater 200 determines to perform frequency flip processing on the second channel 2ch, which is the second of the three channels. This causes the signal component in the frequency domain on the second channel 2ch side of the first channel 1ch to move away from the signal component in the frequency domain on the first channel 1ch side of the second channel 2ch, thereby reducing the nonlinear effect between the first channel 1ch and the second channel 2ch. Furthermore, the signal component in the frequency domain on the third channel 3ch side of the second channel 2ch to move away from the signal component in the frequency domain on the second channel 2ch side of the third channel 3ch, thereby reducing the nonlinear effect between the second channel 2ch and the third channel 3ch.

[0100] 11F is a third diagram showing an overview of frequency flip processing. Assume that the optical repeater 200 receives optical signals in the frequency bands of the first channel 1ch, the second channel 2ch, and the third channel 3ch. The frequency flip processing unit 233 of the optical repeater 200 determines to perform frequency flip processing on all three channels based on an instruction from the control device 100 or based on its own decision. This allows the nonlinear effect between the first channel 1ch and the second channel 2ch and the nonlinear effect between the second channel 2ch and the third channel 3ch to be reduced in the same way.

[0101] Fig. 12 shows another example of the amount of chromatic dispersion compensation by the control method of this embodiment. Unlike Fig. 11B, in this example, as shown in Fig. 12, the transmitting terminal device 30 transmits an optical signal with an accumulated chromatic dispersion amount M10 to the optical transmission line 3a. Note that when the transmitting terminal device 30 is an optical repeater device 200 or the like in the optical network 51, dispersion such as the accumulated chromatic dispersion amount M10 may occur in the optical signal transmitted by the transmitting terminal device 30.

[0102] 12, since the wavelength of the optical signal is λ1 in the optical transmission line 3a upstream of the optical repeater 200, the control device 100 determines the slope DS1 of the amount of chromatic dispersion in the optical transmission line 3a according to the wavelength λ1. The control device 100 uses the effective nonlinear distance Leff1 to calculate the amount of accumulated chromatic dispersion M11 (=DS1×Leff1+M10) at the effective nonlinear distance Leff1 in the upstream optical transmission line 3a.

[0103] Furthermore, since the wavelength of the optical signal in the subsequent optical transmission line 3b is λ2, the control device 100 determines the slope DS2 of the chromatic dispersion amount in the optical transmission line 3b in accordance with the wavelength λ2. The control device 100 calculates the accumulated chromatic dispersion amount M13 (= DS1 × Leff1 + DS2 × Leff2 + M10) in the transmission signal of the optical repeater, under the condition that the accumulated chromatic dispersion amount M12 at the effective nonlinear distance Leff2 in the subsequent optical transmission line 3b has an opposite sign to the accumulated chromatic dispersion amount M11 at the effective nonlinear distance Leff1 in the preceding optical transmission line 3a. The control device 100 calculates the phase conjugate compensation amount M15 (= M14 × 2) compensated for by phase conjugation in the optical repeater 200.

[0104] The control device 100 calculates the difference M16 between M13 and M15, and sets M6 as the optimum amount of chromatic dispersion compensation in the optical repeater 200. The control device 100 sets the optical repeater 200 to perform phase conjugation processing.

[0105] As described above, in this embodiment, in an optical repeater that performs wavelength conversion on a channel-by-channel basis, an analog signal output from an optical receiving front end is converted into a digital signal by an ADC, and after undergoing digital signal processing, is converted back into an analog signal by a DAC, and is then returned to the optical transmitting front end for relaying. At this time, the digital signal processing unit performs phase conjugation processing, compensation for chromatic dispersion distortion occurring in the optical fiber transmission line according to the transmission line length of the network path (transmission line), and frequency flip processing on a channel-by-channel basis.

[0106] Specifically, the control device 100 calculates the optimal chromatic dispersion compensation amount to be compensated in the optical repeater so that the accumulated chromatic dispersion amount over the effective nonlinear distance in the upstream transmission path and the accumulated chromatic dispersion amount over the effective nonlinear distance in the downstream transmission path have opposite signs, and the optical repeater 200 performs phase conjugation, frequency flipping on a channel-by-channel basis, and chromatic dispersion compensation using the calculated optimal chromatic dispersion compensation amount. This allows the accumulated nonlinear distortion in the upstream optical transmission path at the receiving end of the optical repeater to be offset by the optical transmission in the downstream optical transmission, maximizing the effect of suppressing nonlinear distortion in the receiving terminal. Furthermore, even when the transmitted signal from the transmitting terminal contains excess dispersion, as shown in Figure 12, the optical repeater can set an appropriate chromatic dispersion amount and compensate for nonlinear distortion. Furthermore, frequency flipping on a channel-by-channel basis reduces inter-channel nonlinear distortion.

[0107] (Embodiment 2) Next, embodiment 2 will be described with reference to the drawings. In this embodiment, the configuration and basic operation of the optical network system are the same as those in embodiment 1. Figures 13A and 13B show a specific example of the amount of chromatic dispersion compensation using the control method in this embodiment. In this embodiment, the case where the number of spans in the optical network is an odd number equal to or greater than 3, and in particular, an example where the number of spans is 3, will be described.

[0108] As shown in FIG. 13A , an optical repeater 200a (first optical repeater) and an optical repeater 200b (second optical repeater) are arranged on the path between the transmitting terminal device 30 and the receiving terminal device 40. The transmitting terminal device 30 and the optical repeater 200a are connected via an optical transmission line 3a (first optical transmission line), the optical repeater 200a and the optical repeater 200b are connected via an optical transmission line 3b (second optical transmission line), and the optical repeater 200b and the receiving terminal device 40 are connected via an optical transmission line 3c (third optical transmission line). For example, the distance L1 of the optical transmission line 3a, the distance L2 of the optical transmission line 3b, and the distance L3 of the optical transmission line 3c may be different or the same. An optical signal with a wavelength λ1 is transmitted through the optical transmission line 3a, an optical signal with a wavelength λ2 is transmitted through the optical transmission line 3b, and an optical signal with a wavelength λ3 is transmitted through the optical transmission line 3c. Optical transmission path 3a may transmit multi-channel optical signals of multiple wavelengths λ (frequency bands), optical transmission path 3b may transmit multi-channel optical signals of multiple wavelengths λ (frequency bands), and optical transmission path 3c may transmit multi-channel optical signals of multiple wavelengths λ (frequency bands).

[0109] In the case where the total number of spans is an odd number of three or more, such as three or more in embodiment 2, the control of the control device 100 using the method of embodiment 1 is applied to combinations of two spans, such as optical transmission line 3a and optical transmission line 3b, and for one remaining optical transmission line 3, such as optical transmission line 3c, the control device 100 sets the optimal dispersion compensation amount in the last optical repeater 200 (optical repeater 200b in this embodiment) that constitutes the optical network 51, so that nonlinear distortion can be suppressed when one span is optically transmitted on that optical transmission line 3 (optical transmission line 3c in this embodiment).

[0110] 13B, the optical repeater 200a performs phase conjugation processing and calculates the amount of chromatic dispersion compensation M26 to which the first embodiment is applied, based on the control of the control device 100. The amount of chromatic dispersion M26 after compensation in the optical repeater 200a is determined by the same method as in the first embodiment. The control device 100 sets the amount of dispersion compensation M26 to which the first embodiment is applied in the optical repeater 200a. The control device 100 also sets the optical repeater 200a so as to perform phase conjugation processing.

[0111] Furthermore, under the control of the control device 100, the optical repeater 200b compensates for an optimal amount of chromatic dispersion compensation that minimizes the nonlinear effect in one span of optical transmission on the optical transmission line 3c. The control device 100 determines the slope DS3 of the chromatic dispersion amount on the optical transmission line 3c according to the wavelength λ3. The control device 100 calculates the chromatic dispersion M28 (=DS3×L3′) of the transmission signal from the optical repeater 200b under the condition that the accumulated chromatic dispersion of the transmission signal on the optical transmission line 3c over the effective nonlinear distance L3′ becomes zero. The control device 100 calculates the accumulated chromatic dispersion amount M27 accumulated on the optical transmission line 3b.

[0112] The control device 100 sets the amount of chromatic dispersion to be compensated for by the optical repeater 200c as M27+M28 from the calculated chromatic dispersion amounts M27 and M28 in the optical repeater 200c. The control device 100 also sets the optical repeater 200c so that it does not perform phase conjugation processing.

[0113] When the total number of spans is an odd number N equal to or greater than 5, the control device 100 identifies a combination consisting of one optical repeater and two optical transmission lines that allows the first embodiment to be implemented, as in the case of a total span of 3 shown in the second embodiment. The control device 100 sets the phase conjugation and optimal chromatic dispersion compensation according to the first embodiment for each identified combination of optical repeaters. For one remaining optical transmission line among the N spans, the control device 100 sets the optimal amount of chromatic dispersion compensation in the optical repeater that minimizes nonlinear distortion in transmission over one span.

[0114] In each relay device 200, frequency flip processing may be performed on a specified channel as in the other embodiments described above.

[0115] As described above, in this embodiment, nonlinear distortion at the receiving end is suppressed in the case of multiple spans, particularly in the case of an odd number of spans. Specifically, combinations consisting of one optical repeater and two optical transmission lines are set so that the first embodiment can be implemented, and phase conjugation and chromatic dispersion compensation according to the first embodiment are set for the optical repeater in each combination. For the remaining optical transmission lines, the optimal amount of chromatic dispersion compensation shown in the second embodiment is set so that nonlinear distortion in one span is minimized. Therefore, in an optical network consisting of an odd number of transmission lines, the effect of canceling out nonlinear distortion during optical transmission using chromatic dispersion compensation can be maximized, and signal quality at the receiving end can be improved.

[0116] Third Embodiment Next, a third embodiment will be described with reference to the drawings. In this embodiment, the configuration and basic operation of the optical network system are the same as those in the first embodiment. Figures 14A and 14B show a specific example of the amount of chromatic dispersion compensation by the control method in this embodiment. In this embodiment, an example will be described in which the number of spans in the optical network is four or an even number greater than four, and the number of spans is four.

[0117] 14A, an optical repeater 200a (first optical repeater), an optical repeater 200b (second optical repeater), and an optical repeater 200c are arranged on the path between the transmitting terminal device 30 and the receiving terminal device 40. The transmitting terminal device 30 and the optical repeater 200a are connected via an optical transmission line 3a (first optical transmission line), the optical repeater 200a and the optical repeater 200b are connected via an optical transmission line 3b (second optical transmission line), the optical repeater 200b and the optical repeater 200c are connected via an optical transmission line 3c (third optical transmission line), and the optical repeater 200c and the receiving terminal device 40 are connected via an optical transmission line 3d (fourth optical transmission line). For example, the distance L1 of the optical transmission line 3a, the distance L2 of the optical transmission line 3b, the distance L3 of the optical transmission line 3c, and the distance L4 of the optical transmission line 3d may be different or the same. An optical signal of wavelength λ1 is transmitted through optical transmission path 3a, an optical signal of wavelength λ2 is transmitted through optical transmission path 3b, an optical signal of wavelength λ3 is transmitted through optical transmission path 3c, and an optical signal of wavelength λ4 is transmitted through optical transmission path 3d. Two or more of these optical wavelengths λ1 to λ4 may have the same wavelength λ or may be different. Multi-channel optical signals of multiple wavelengths λ (frequency bands) may be transmitted through optical transmission path 3a, multi-channel optical signals of multiple wavelengths λ (frequency bands) may also be transmitted through optical transmission path 3b, optical signals of channels of multiple wavelengths λ (frequency bands) may also be transmitted through optical transmission path 3c, and optical signals of channels of multiple wavelengths λ (frequency bands) may also be transmitted through optical transmission path 3d.

[0118] As shown in Figure 14B, when the total number of spans in embodiment 3 is 4, for example, the control of the control device 100 according to embodiment 1 is applied to two spans, optical transmission line 3a and optical transmission line 3b, and the control of the control device 100 according to embodiment 1 is also applied to two spans, optical transmission line 3c and optical transmission line 3d.

[0119] The control device 100 sets, in the optical repeater 200a, the amount of dispersion compensation to which the control of the control device 100 according to embodiment 1 has been applied and information for performing phase conjugation processing. That is, the control device 100 sets, in the optical repeater 200a, the optimal amount of chromatic dispersion compensation M36 obtained by applying the control of the control device 100 according to embodiment 1 to the optical repeater 200a. The control device 100 also sets, in the optical repeater 200a, the optical repeater 200a to perform phase conjugation processing in the same manner as in embodiment 1.

[0120] The control device 100 also sets, in the optical repeater 200c, the amount of dispersion compensation to which the control of the control device 100 according to embodiment 1 has been applied and information for performing phase conjugation processing. That is, the control device 100 sets, in the optical repeater 200c, the optimal amount of chromatic dispersion compensation M44 found by applying the control of the control device 100 according to embodiment 1 to the optical repeater 200c. The control device 100 also sets, in the optical repeater 200c, the amount of phase conjugation processing to be performed in the same manner as in embodiment 1.

[0121] The control device 100 determines the gradient DS2 of the chromatic dispersion amount in the optical transmission line 3b in accordance with the wavelength λ2. The control device 100 obtains the cumulative chromatic dispersion amount M37 (=DS2×L2+M33) accumulated in the optical transmission line 3b.

[0122] The control device 100 sets the amount of chromatic dispersion to be compensated for in the optical repeater 200b as M37-M38 from the calculated chromatic dispersion amount M37 and the dispersion amount M38 of the transmission signal on the optical transmission line 3c, which is smaller than M37, in the optical repeater 200b. The control device 100 also sets the optical repeater 200b so that phase conjugation processing is not performed.

[0123] When the total number of spans is an even number equal to or greater than six, the control device 100 sets a combination of one optical repeater and two optical transmission lines that enables implementation of embodiment 1, as in the case where the total number of spans is four as shown in embodiment 3. The control device 100 sets phase conjugation and optimal chromatic dispersion compensation according to embodiment 1 for each combination of optical repeaters.

[0124] In each relay device 200, frequency flip processing may be performed on a specified channel as in the other embodiments described above.

[0125] As described above, in this embodiment, nonlinear distortion at the receiving end is compensated for in a large number of spans, particularly in the case of an even number of spans. Specifically, a combination of one optical repeater and two optical transmission lines is set so that the first embodiment can be implemented, and phase conjugation and chromatic dispersion compensation according to the first embodiment are set for the optical repeater in each combination. Therefore, in an optical network consisting of an even number of transmission lines, the effect of canceling out nonlinear distortion during optical transmission using chromatic dispersion compensation can be maximized, and signal quality at the receiving end can be improved.

[0126] Fig. 15 shows the minimum configuration of the control device. Fig. 16 shows the processing flow by the control device with the minimum configuration. The control device 100 includes at least a chromatic dispersion compensation control means 151 and a phase conjugate processing control means 152. The chromatic dispersion compensation control means 151 determines the amount of chromatic dispersion compensation to be performed in the optical repeater 200 based on wavelength information of optical signals transmitted and received by the optical repeater 200 constituting the optical network path and transmission line information of the optical transmission line connected to the optical repeater 200 (step S161). The phase conjugate processing control means 152 determines the phase conjugate processing to be performed in the optical repeater 200 based on the wavelength information and transmission line information (step S162).

[0127] Fig. 17 shows the minimum configuration of an optical repeater. Fig. 18 shows the processing flow by an optical repeater with the minimum configuration. The optical repeater 200 includes at least a chromatic dispersion compensation means 171 and a phase conjugate processing means 172. The phase conjugate processing means 172 performs phase conjugation processing on an electrical signal based on a received optical signal based on the acquired phase conjugate processing information (step S181). The chromatic dispersion compensation means 171 performs chromatic dispersion compensation processing on an electrical signal based on a received optical signal based on the amount of chromatic dispersion compensation (step S182).

[0128] In other embodiments, the optical repeater 200 may perform part or all of the processing of the control device 100 .

[0129] FIG. 19 illustrates another optical repeater configuration. FIG. 20 illustrates a processing flow for an optical repeater with another configuration. In another embodiment, the optical repeater 200 may further include a chromatic dispersion compensation control unit 191 and a phase conjugate processing control unit 192, as shown in FIG. 19 , in addition to the chromatic dispersion compensation unit 171 and the phase conjugate processing unit 172. The chromatic dispersion compensation control unit 191 determines the amount of chromatic dispersion compensation to be performed in the optical repeater 200 based on wavelength information of the optical signal transmitted and received by the optical repeater 200 (the optical repeater 200) constituting the optical network path and transmission line information of the optical transmission line connected to the optical repeater 200 (step S2001). The phase conjugate processing control unit 192 determines the phase conjugate processing in the optical repeater 200 based on the wavelength information and transmission line information (step S2002). In this case, the chromatic dispersion compensation control unit 191 and the phase conjugate processing control unit 192 may perform processing similar to that of the control device 100 described above. Furthermore, when the optical repeater 200 performs the processing of the chromatic dispersion compensation control means 191 and the phase conjugate processing control means 192, it may obtain from the control device 100 information necessary for the processing, similar to that of the control device 100 described above.

[0130] In another embodiment, the optical repeater 200 may be provided with at least one of a chromatic dispersion compensation control means 191 and a phase conjugate processing control means 192 in addition to the configuration of the chromatic dispersion compensation means 171 and the phase conjugate processing means 172, with the remaining means being provided in the control device 100.

[0131] Fig. 21 is a diagram showing another configuration of an optical repeater. Fig. 22 is a diagram showing a processing flow by an optical repeater with another configuration. In another embodiment, the optical repeater 200 includes a frequency flip processing means 280. The frequency flip processing means 280 performs frequency flip processing on at least one or more channels of an optical signal on a channel-by-channel basis (step S2201).

[0132] The control device, optical repeater, transmitting terminal device, and receiving terminal device in the above-described embodiments may be configured with hardware or software, or both, and may be configured with a single piece of hardware or software, or may be configured with multiple pieces of hardware or software. Each device (control device, etc.) and each function (processing) may be realized by a computer 60 having a processor 61 such as a CPU (Central Processing Unit) and a memory 62 as a storage device, as shown in Figure 23. For example, a program for performing the method (control method, etc.) in the embodiment may be stored in the memory 62, and each function may be realized by the processor 61 executing the program stored in the memory 62.

[0133] These programs include instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The programs may be stored on a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disc (DVD), Blu-ray disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The programs may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals.

[0134] Note that part or all of the above-described embodiments can be described as, but are not limited to, the following supplementary notes.

[0135] an optical repeater that configures an optical network; and a control device that controls the optical repeater, wherein the control device comprises: management means for managing wavelength information of optical signals transmitted and received by the optical repeater in a path of the optical network and transmission line information of an optical transmission line connected to the optical repeater; wavelength dispersion compensation control means for determining an amount of wavelength dispersion compensation to be performed in the optical repeater based on the wavelength information and the transmission line information; and phase conjugate processing control means for determining phase conjugate processing in the optical repeater based on the wavelength information and the transmission line information, wherein the optical repeater comprises: wavelength dispersion compensation amount acquisition means for acquiring the determined amount of wavelength dispersion compensation from the control device; phase conjugate processing acquisition means for acquiring the determined phase conjugate processing information from the control device; phase conjugate processing means for performing phase conjugate processing on an electrical signal based on a received optical signal based on the acquired phase conjugate processing information; and wavelength dispersion compensation means for performing wavelength dispersion compensation on an electrical signal based on a received optical signal based on the acquired amount of wavelength dispersion compensation.

[0136] (Supplementary Note 2) The optical network system described in Supplementary Note 1, wherein the chromatic dispersion compensation control means calculates the amount of accumulated chromatic dispersion over an effective nonlinear distance in the optical transmission path on the receiving side of the optical repeater and the amount of accumulated chromatic dispersion over an effective nonlinear distance in the optical transmission path on the transmitting side of the optical repeater based on the wavelength information and the transmission path information on the receiving side of the optical repeater and the wavelength information and the transmission path information on the transmitting side of the optical repeater.

[0137] (Supplementary Note 3) The optical network system described in Supplementary Note 2, wherein the chromatic dispersion compensation control means determines the amount of chromatic dispersion compensation based on the amount of accumulated chromatic dispersion in an effective nonlinear distance in the optical transmission path on the receiving side of the optical repeater, the amount of accumulated chromatic dispersion in an effective nonlinear distance in the optical transmission path on the transmitting side of the optical repeater, and the amount of chromatic dispersion compensation by phase conjugation processing in the optical repeater.

[0138] (Supplementary Note 4) The optical network system described in any one of Supplementary Note 1 to Supplementary Note 3, wherein the chromatic dispersion compensation control means determines the amount of chromatic dispersion compensation based on an accumulated chromatic dispersion amount included in a transmission signal before optical transmission in an optical transmission path on the receiving side of the optical repeater, the accumulated chromatic dispersion amount over an effective nonlinear distance in the optical transmission path on the receiving side of the optical repeater, the accumulated chromatic dispersion amount over an effective nonlinear distance in the optical transmission path on the transmitting side of the optical repeater, and the amount of chromatic dispersion compensation by phase conjugation processing in the optical repeater.

[0139] (Supplementary Note 5) The optical network system described in any one of Supplementary Note 1 to Supplementary Note 4, wherein the chromatic dispersion compensation amount is a compensation amount calculated under the condition that the accumulated chromatic dispersion amount in the effective nonlinear distance in the optical transmission path on the receiving side of the optical repeater and the accumulated chromatic dispersion amount in the effective nonlinear distance in the optical transmission path on the transmitting side of the optical repeater have opposite signs.

[0140] (Supplementary Note 6) In an optical network system according to claim 1, in which an odd number of paths, three or more, are connected via the optical repeater, the chromatic dispersion compensation control means and the phase conjugate processing control means determine the amount of chromatic dispersion compensation and the phase conjugate processing in the target optical repeater based on the wavelength information and the transmission line information in paths before and after the target optical repeater other than the optical repeater connected to the last path among the plurality of paths.

[0141] (Supplementary Note 7) The chromatic dispersion compensation control means and the phase conjugate processing control means, in the optical repeater, determine a combination of two paths, one in the front stage and one in the rear stage, and one optical repeater that repeats the path, as well as one remaining path, and determine an optical repeater other than the optical repeater connected to the one remaining path as the target optical repeater. (Supplementary Note 1) An optical network system described in any one of Supplementary Note 1 to Supplementary Note 6.

[0142] (Supplementary Note 8) The optical network system according to Supplementary Note 7, wherein the phase conjugate processing control means determines a phase conjugate processing to be performed on the optical repeater in the combination.

[0143] (Supplementary Note 9) The optical network system described in either Supplementary Note 7 or Supplementary Note 8, wherein the chromatic dispersion compensation control means determines the amount of chromatic dispersion compensation in the optical repeater of the combination based on the wavelength information and the transmission line information in the two optical transmission lines of the combination.

[0144] (Supplementary Note 10) The optical network system according to Supplementary Note 7, wherein the chromatic dispersion compensation control means determines an amount of chromatic dispersion compensation in an optical repeater of the one remaining path based on the wavelength information and the transmission path information in the optical transmission path of the one remaining path.

[0145] (Supplementary Note 11) The optical network system according to any one of Supplementary Note 7 to Supplementary Note 10, wherein the chromatic dispersion compensation amount is a compensation amount calculated under the condition that the cumulative chromatic dispersion amount in the effective nonlinear distance in the optical transmission line of the remaining one path becomes zero.

[0146] (Supplementary Note 12) In an optical network system in which an even number of four or more paths are connected via the optical repeater, the chromatic dispersion compensation control means and the phase conjugate processing control means determine the amount of chromatic dispersion compensation and the phase conjugate processing in the optical repeater based on the wavelength information and the transmission line information in the paths before and after each of the optical repeaters in the multiple paths.

[0147] (Supplementary Note 13) The optical network system according to any one of Supplementary Note 1 to Supplementary Note 12, wherein the chromatic dispersion compensation control means and the phase conjugate processing control means determine a combination of two optical transmission lines and one optical repeater in the optical repeater.

[0148] (Supplementary Note 14) The optical network system according to any one of Supplementary Note 7 to Supplementary Note 13, wherein the phase conjugate processing control means determines a phase conjugate processing for the optical repeater in the combination.

[0149] (Supplementary Note 15) The optical network system according to any one of Supplementary Note 7 to Supplementary Note 14, wherein the chromatic dispersion compensation control means determines the amount of chromatic dispersion compensation in the optical repeater of the combination based on the wavelength information and the transmission line information in the two optical transmission lines of the combination.

[0150] (Supplementary Note 16) A control method comprising: managing wavelength information of optical signals transmitted and received by an optical repeater in a path of an optical network, transmission line information of an optical transmission line connected to the optical repeater, and the number of paths of the optical network; and determining an amount of chromatic dispersion compensation and phase conjugation processing to be performed in the optical repeater based on the wavelength information, the transmission line information, and the number of paths of the optical network.

[0151] (Supplementary Note 17) The control method according to Supplementary Note 16, wherein the amount of chromatic dispersion compensation and the phase conjugation process are determined based on the amount of accumulated chromatic dispersion in an effective nonlinear distance in an optical transmission path on the receiving side of each optical repeater in a path of the optical network and the amount of accumulated chromatic dispersion in an effective nonlinear distance in an optical transmission path on the transmitting side of the optical repeater.

[0152] (Supplementary Note 18) A control program for causing a computer to execute a process of managing wavelength information of optical signals transmitted and received by an optical repeater in a path of an optical network, transmission line information of an optical transmission line connected to the optical repeater, and the number of paths of the optical network, and determining the amount of chromatic dispersion compensation and phase conjugation processing to be performed in the optical repeater based on the wavelength information, the transmission line information, and the number of paths of the optical network.

[0153] (Supplementary Note 19) The program according to Supplementary Note 18, which determines the amount of chromatic dispersion compensation and phase conjugation processing based on the amount of accumulated chromatic dispersion in an effective nonlinear distance in an optical transmission path on the receiving side of each optical repeater in a path of the optical network and the amount of accumulated chromatic dispersion in an effective nonlinear distance in an optical transmission path on the transmitting side of the optical repeater.

[0154] (Supplementary Note 20) A control device comprising: a chromatic dispersion compensation control means for determining an amount of chromatic dispersion compensation to be performed in an optical repeater based on wavelength information of an optical signal transmitted and received by an optical repeater constituting an optical network in a path of the optical network and transmission line information of an optical transmission line connected to the optical repeater; and a phase conjugation processing control means for determining a phase conjugation processing in the optical repeater based on the wavelength information and the transmission line information.

[0155] (Supplementary Note 21) The control device according to Supplementary Note 20, wherein the phase conjugate processing control means transmits to the optical repeater an instruction to perform phase conjugate processing for calculating a complex conjugate of the optical signal.

[0156] (Supplementary Note 22) The control device according to Supplementary Note 21, wherein the chromatic dispersion compensation control means calculates a first accumulated chromatic dispersion amount in a first effective nonlinear distance based on the transmitting network device in a first optical transmission path between the optical repeater and a transmitting network device that transmits an optical signal received by the optical repeater, among optical transmission paths connected to the optical repeater; calculates a second accumulated chromatic dispersion amount in a second effective nonlinear distance based on the optical repeater itself in a second optical transmission path between the optical repeater and a receiving network device that receives the optical signal transmitted by the optical repeater, the second accumulated chromatic dispersion amount having an opposite sign to the first accumulated chromatic dispersion amount; and calculates the chromatic dispersion compensation amount indicating a difference between the chromatic dispersion amount of the optical signal at the time of transmission in the optical repeater when the accumulated chromatic dispersion amount of the optical signal becomes the second accumulated chromatic dispersion amount in the second effective nonlinear distance based on a statistical value of transition of the accumulated chromatic dispersion amount of the optical signal according to the distance in the second optical transmission path.

[0157] (Supplementary Note 23) An optical repeater representing a device that is communicatively connected to a control device comprising: chromatic dispersion compensation control means that determines an amount of chromatic dispersion compensation to be performed in the device based on wavelength information of optical signals transmitted and received by the device that constitutes the optical network and transmission line information of an optical transmission line connected to the device; and phase conjugate processing control means that determines phase conjugate processing in the device based on the wavelength information and the transmission line information, wherein the optical repeater comprises: phase conjugate processing means that performs phase conjugate processing on an electrical signal based on an optical signal received, based on phase conjugate processing information acquired from the control device; and chromatic dispersion compensation means that performs chromatic dispersion compensation on an electrical signal based on the optical signal received, based on the amount of chromatic dispersion compensation.

[0158] (Supplementary Note 24) The optical repeater according to Supplementary Note 23, wherein the phase conjugate processing means performs phase conjugate processing based on an instruction to perform phase conjugate processing for calculating a complex conjugate of the optical signal.

[0159] (Supplementary Note 25) Calculating a first accumulated chromatic dispersion amount in a first effective nonlinear distance based on a transmitting network device in a first optical transmission path between the optical repeater and a transmitting network device that transmits an optical signal received by the optical repeater among optical transmission paths connected to the optical repeater; Calculating a second accumulated chromatic dispersion amount in a second effective nonlinear distance based on the optical repeater itself among optical transmission paths connected to the optical repeater and a receiving network device that receives the optical signal transmitted by the optical repeater, the second accumulated chromatic dispersion amount having an opposite sign to the first accumulated chromatic dispersion amount; Communicating with a control that calculates the chromatic dispersion compensation amount indicating the difference between the chromatic dispersion amount of the optical signal at the time of transmission in the optical repeater when the accumulated chromatic dispersion amount of the optical signal becomes the second accumulated chromatic dispersion amount in the second effective nonlinear distance based on a statistical value of the transition of the accumulated chromatic dispersion amount of the optical signal according to the distance in the second optical transmission path, and the chromatic dispersion amount that is a result of the complex conjugation; and a chromatic dispersion compensation unit that determines the amount of chromatic dispersion of the optical signal to be transmitted to the receiving network device based on the amount of chromatic dispersion that is the result of the complex conjugation and the amount of chromatic dispersion compensation acquired from the control device after performing the phase conjugation process.

[0160] (Supplementary Note 26) An optical repeater comprising: a digital signal processing means for performing frequency flip processing on at least one or more channels of an optical signal on a channel-by-channel basis.

[0161] (Supplementary Note 27) The optical repeater according to Supplementary Note 26, wherein the digital signal processing means performs the frequency flip process on all channels of the optical signal on a channel-by-channel basis.

[0162] (Supplementary Note 28) The optical repeater device described in Supplementary Note 26 or Supplementary Note 27, wherein the digital signal processing means sequentially identifies channels to be processed and channels not to be processed among the plurality of channels having different frequency bands, the plurality of channels being arranged in order based on the frequency bands, and performs the frequency flip processing on the channels to be processed.

[0163] (Supplementary Note 29) The optical repeater device according to any one of Supplementary Note 26 to Supplementary Note 28, wherein the digital signal processing means performs the frequency flip process of inverting the frequency components of the optical signal for each frequency based on a reference frequency set at the center of the frequency band.

[0164] (Supplementary Note 30) An optical repeater device according to any one of Supplementary Notes 26 to 29, wherein the digital signal processing means comprises: a phase conjugate processing means for performing a phase conjugate processing on an electrical signal based on the received optical signal; a chromatic dispersion compensation means for performing a chromatic dispersion compensation processing on the electrical signal based on the received optical signal; and a frequency flip processing means for performing the frequency flip processing.

[0165] (Supplementary Note 31) The optical repeater device according to any one of Supplementary Notes 26 to 30, wherein the frequency flip processing means performs the phase conjugation processing and the chromatic dispersion compensation processing for all channels of the optical signal, and performs the frequency flip processing for at least one channel on a channel-by-channel basis.

[0166] DESCRIPTION OF SYMBOLS 1... Optical network system 2... Optical repeater 3... Optical transmission path 5... Data center 6... IT service provider 7, 8... Event venue 10... Control device 11... Management unit 12... Phase conjugate control unit 13... Wavelength dispersion compensation control unit 14... Frequency flip control unit 20... Optical repeater 21... Coherent receiving front end unit 22... Phase conjugate unit 23... Wavelength dispersion compensation unit 24... Coherent transmitting front end unit 25... Phase conjugate acquisition unit 26... Wavelength dispersion compensation acquisition unit 27... Frequency flip instruction acquisition unit 28... Frequency flip processing unit 30... Transmitting terminal device 40... Receiving terminal device 50... Optical network system 51... Optical network 60... Computer 61... Processor 62... Memory 90... Optical repeater 100... Control device 110... Network management unit 120... Network control unit 130... Wavelength dispersion compensation amount calculation unit DESCRIPTION OF SYMBOLS 140 Phase conjugate determination unit 150 Frequency flip instruction unit 200 Optical repeater 201 Optical transceiver 202 Node control unit 210 Coherent receiving front end unit 220 Coherent transmitting front end unit 230 Digital signal processing unit 231 Wavelength dispersion compensation unit 232 Phase conjugate processing unit 233 Frequency flip processing unit 240 Receiving light source 250 Transmitting light source 260 ADC 270 DAC 300 Optical switch unit 301 Demultiplexer 302 Combiner 303 Drop-and-add unit 310 Transmitting / receiving unit 311, 312, 313, 314 Optical transceivers 401 Delay unit 402 Multiplier 403 Adder 411 Overlap addition unit 412 Fast Fourier transform unit 413 Inverse transfer function multiplication unit 414: Inverse fast Fourier transform unit 415: Overlap removal unit 900: Digital signal processing unit 910: Acquisition unit 901: Digital signal processing unit

Claims

1. Digital signal processing means for performing frequency flip processing on at least one or more optical signal channels on a channel-by-channel basis. An optical repeater device comprising:

2. The digital signal processing means performs the frequency flip processing on all channels of the optical signal on a channel-by-channel basis.

2. The optical repeater according to claim 1.

3. The digital signal processing means sequentially identifies processing targets and non-processing targets among the plurality of channels arranged in order based on the frequency bands among the plurality of channels with different frequency bands, and performs the frequency flip processing on the channels identified as processing targets.

3. The optical repeater according to claim 1.

4. The digital signal processing means performs the frequency flip process of inverting the frequency components of the optical signal for each channel based on a reference frequency set at the center of the frequency band.

4. The optical repeater according to claim 3.

5. The digital signal processing means a phase conjugate processing means for performing a phase conjugate process on an electrical signal based on the received optical signal; a wavelength dispersion compensation unit that performs wavelength dispersion compensation processing on an electrical signal based on the received optical signal; a frequency flip processing means for performing the frequency flip processing; The optical repeater according to claim 4 , comprising:

6. The frequency flip processing means performs the phase conjugation processing and the chromatic dispersion compensation processing for all channels of the optical signal, and performs the frequency flip processing for at least one channel on a channel-by-channel basis.

6. The optical repeater according to claim 5.

7. A frequency flip process is performed on at least one or more optical signal channels on a channel-by-channel basis. Optical relay method.

8. The computer of the optical repeater, digital signal processing means for performing frequency flip processing on at least one or more channels of the optical signal on a channel-by-channel basis; A program that functions as a