Communication device, communication system, and communication method

Abstract

Provided is a communication device that performs wavelength division multiplexing communication with a counterpart device that is a communication partner. The communication device comprises: a wavelength arrangement determination unit that determines a plurality of wavelengths to be used for communication with the counterpart device on the basis of a wavelength arrangement determined so as not to overlap a frequency position of idler light generated by four-wave mixing and an estimate value of the zero dispersion wavelength of a communication path connected to the counterpart device; a plurality of transmitters that transmit the light of the plurality of wavelengths determined by the wavelength arrangement determination unit; and a multiplexing unit that wavelength-multiplexes and outputs the light of the plurality of wavelengths outputted from each of the plurality of transmitters.　

Description

Communication device, communication system, and communication method

[0001] The present invention relates to a communication device, a communication system, and a communication method.

[0002] In an optical communication system that transmits optical signals using optical fiber, if the wavelength deviates from the zero-dispersion wavelength of the optical fiber, the effect of dispersion becomes greater, resulting in an increase in the penalty amount, making long-distance transmission difficult. Therefore, in order to achieve long-distance transmission, it is necessary to set the wavelength used between communication devices of communicating users so that it approaches the zero-dispersion wavelength.

[0003] However, since the zero-dispersion wavelength of optical fibers fluctuates between 1300 and 1324 nm, if the value of the zero-dispersion wavelength for each optical fiber used is not known, it is not possible to set the wavelength.

[0004] Therefore, a method of setting the wavelength using an OTDR (Optical Time Domain Reflectometer) has been proposed. In this method, light emitted from the OTDR of device A is transmitted to device B, and the light is returned to the OTDR of device A by a mirror in device B, thereby measuring the zero-dispersion value and switching the path between the transmitter and receiver. However, this method requires additional equipment, which makes the system more complicated.

[0005] To address this issue, a technique for estimating the value of the zero-dispersion wavelength has been proposed as follows (see, for example, Non-Patent Documents 1 and 2): First, a communication device that performs communication estimates the notch frequency f at which the first notch appears at a frequency other than a multiple (1x, 2x, etc.) of the frequency of the transmission signal based on data on the frequency spectrum of the received optical signal. ０ Next, the communication device calculates the dispersion D using the oscillation wavelength λ, the speed of light c, the chirp parameter α, and the distance L between the communication devices, and estimates the value of the zero-dispersion wavelength by measuring the amount of deviation from the position of the zero-dispersion wavelength in the optical fiber by dividing the dispersion D by the value of the dispersion slope. Here, the oscillation wavelength is calculated based on the operating state of the transmitter, such as the temperature, and the distance L between the communication devices can be calculated based on a timestamp from a low-speed signal or the like.

[0006] As described above, in the past, every time a connection was made between user communication devices, the value of the zero-dispersion wavelength between the users was estimated, and the oscillation wavelength of each communication device was adjusted to match the estimated value of the zero-dispersion wavelength, thereby suppressing waveform degradation due to chromatic dispersion and realizing long-distance transmission. This configuration eliminates the need for additional devices.

[0007] Yasunari Tanaka et al., “Penalty-free 100-km Transmission of 53-Gbps / λ IM-DD Signal Enabled by a Novel Zero-dispersion Wavelength Estimation and Optimization Method”, 2023 Opto-Electronics and Communications Conference (OECC).Yasunari Tanaka et al., “Zero-Dispersion Wavelength Estimation and Optimization Method for Penalty-Free and Equalizer-Free 53-Gbps / λ IM-DD Transmission Over 100 Km”, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 42, NO. 6, MARCH 15, 2024.

[0008] The methods described in Non-Patent Documents 1 and 2 can reduce chromatic dispersion, a major factor limiting transmission distance in high-speed transmission using Intensity Modulation Direct Detection (IMDD). However, they are difficult to apply to wavelength division multiplexing (WDM) transmission, which bundles multiple wavelengths. As mentioned above, the zero-dispersion value of SMF (Single Mode Fiber), a common optical fiber, is a single value within the range of 1300 to 1324 nm, and multiple wavelengths cannot have the same value. Therefore, WDM transmission is significantly affected by chromatic dispersion. Furthermore, WDM transmission within this range generates idler light due to four-wave mixing, a nonlinear optical effect. Therefore, in addition to chromatic dispersion, transmission characteristics are further degraded by inter-channel crosstalk caused by nonlinear waveform distortion.

[0009] It is known that the efficiency of idler light due to four-wave mixing is highest at the zero-dispersion value of the optical fiber. Therefore, if the zero-dispersion value of the optical fiber is estimated using the methods described in Non-Patent Documents 1 and 2 and a specific wavelength for WDM transmission is set near the zero-dispersion value, there is a problem that the transmission distance is significantly limited due to nonlinear waveform distortion caused by four-wave mixing.

[0010] In view of the above circumstances, an object of the present invention is to provide a technique that can extend the transmission distance in a system that performs wavelength division multiplexing transmission.

[0011] One aspect of the present invention is a communication device that communicates with a communication partner, an opposing device, using wavelength division multiplexing, and includes: a wavelength allocation determination unit that determines multiple wavelengths to be used for communication with the opposing device based on a wavelength allocation determined so as not to overlap with the frequency position of idler light generated by four-wave mixing and an estimated value of the zero-dispersion wavelength of a communication path connecting to the opposing device; a plurality of transmitters that transmit light of the multiple wavelengths determined by the wavelength allocation determination unit; and a multiplexing unit that wavelength-multiplexes and outputs the light of the multiple wavelengths output from each of the plurality of transmitters.

[0012] One aspect of the present invention is an optical communication system comprising a first communication device and a second communication device, wherein the first communication device and the second communication device communicate using wavelength division multiplexing, wherein the first communication device is a communication device that communicates using wavelength division multiplexing with an opposing device as a communication partner, and comprises a wavelength allocation determination unit that determines multiple wavelengths to be used for communication with the opposing device based on a wavelength allocation determined so as not to overlap with the frequency position of idler light generated by four-wave mixing and an estimated value of the zero-dispersion wavelength of a communication path connecting to the opposing device, a plurality of transmitters that transmit light of the multiple wavelengths determined by the wavelength allocation determination unit, and a multiplexing unit that wavelength-multiplexes and outputs the light of the multiple wavelengths output from each of the plurality of transmitters, and the second communication device is an optical communication system comprising: a signal processing unit that estimates the zero-dispersion wavelength of the communication path, and a transmitter unit that transmits the estimated value of the zero-dispersion wavelength of the communication path estimated by the signal processing unit to the first communication device.

[0013] One aspect of the present invention is a communication method performed by a communication device that communicates with a communication partner, an opposing device, using wavelength division multiplexing, in which multiple wavelengths to be used for communication with the opposing device are determined based on a wavelength allocation determined so as not to overlap with the frequency position of idler light generated by four-wave mixing and an estimated value of the zero-dispersion wavelength of a communication path connecting to the opposing device, and the light of the multiple wavelengths output from each of multiple transmitters that transmit light of the determined multiple wavelengths is wavelength-multiplexed and output.

[0014] According to the present invention, it becomes possible to extend the transmission distance in a system that performs wavelength division multiplexing transmission.

[0015] Fig. 1 is a diagram showing an example of the configuration of an optical communication system 100 in an embodiment; Fig. 2 is a diagram showing the arrangement relationship between a wavelength-multiplexed signal of three wavelengths and idler light; Fig. 3 is a diagram showing the arrangement relationship between an estimated value of a zero-dispersion wavelength and a wavelength-multiplexed signal of three wavelengths; Fig. 4 is a diagram showing the arrangement relationship between a wavelength-multiplexed signal of four wavelengths and idler light; Fig. 5 is a sequence diagram showing the flow of processing performed by an optical communication system in an embodiment.

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] FIG. 1 is a diagram illustrating an example configuration of an optical communication system 100 according to an embodiment. The optical communication system 100 includes a communication device 10 and a communication device 20. The communication device 10 and the communication device 20 are connected via an optical transmission path. The optical transmission path is configured with an optical fiber. Note that the optical transmission path may be provided with one or more optical amplifiers that amplify optical signals and optical multiplexers / demultiplexers such as couplers. In the example illustrated in FIG. 1, the communication device 10 and the communication device 20 communicate via two-core transmission using two optical transmission paths.

[0018] In the following explanation, for convenience of explanation, the optical transmission path that transmits the optical signal transmitted from communication device 10 to communication device 20 may be referred to as the first transmission path, and the optical transmission path that transmits the optical signal transmitted from communication device 20 to communication device 10 may be referred to as the second transmission path.

[0019] The communication device 10 is a device that communicates with the communication device 20. The communication device 10 communicates with the communication device 20 by, for example, wavelength division multiplexing transmission (hereinafter referred to as "WDM transmission") using a plurality of wavelengths. In WDM transmission, idler light is generated by four wave mixing (FWM), which is one of the nonlinear optical effects. In FWM, an idler light is generated when the frequency of light ω ｉ , ω ｊ , ω ｋ (j ≠ k) for frequency ω ｉｊｋ =ω ｉ +ω ｊ -ω ｋ It is known that idler light occurs at the position of the frequency ω ｉｊｋ The wavelengths are allocated so as not to overlap with the positions of the wavelengths. The specific method of wavelength allocation will be described later.

[0020] The communication device 10 determines a plurality of wavelengths to be used in WDM transmission based on the wavelength allocation result and an estimated value of the zero-dispersion wavelength of the first optical transmission line (hereinafter referred to as the "first estimated value"). For example, the communication device 10 can suppress the influence of chromatic dispersion by determining wavelengths near the zero-dispersion wavelength as the plurality of wavelengths to be used in WDM transmission.

[0021] The first estimated value is estimated in the communication device 20. For example, the communication device 10 transmits an optical signal of a specific wavelength to the communication device 20, and the communication device 20 estimates the first estimated value based on the optical signal of the specific wavelength. The specific wavelength is a wavelength used to estimate the zero-dispersion wavelength and may be determined in advance. An existing method is used as a method for estimating the zero-dispersion wavelength. For example, the method described in Non-Patent Document 1 or 2 may be used as a method for estimating the zero-dispersion wavelength, or another method may be used.

[0022] Furthermore, the communication device 10 estimates the zero-dispersion wavelength of the second optical transmission line based on an optical signal of a specific wavelength transmitted from the communication device 20. The communication device 10 transmits the estimated value of the zero-dispersion wavelength of the second optical transmission line (hereinafter referred to as the "second estimated value") to the communication device 20 via the first optical transmission line. The specific wavelengths used to estimate the zero-dispersion wavelengths of the communication devices 10 and 20 may be the same or different.

[0023] The communication device 20 is a device that communicates with the communication device 10. The communication device 20 communicates with the communication device 10, for example, by WDM transmission. The communication device 20 estimates the zero-dispersion wavelength of the first optical transmission line based on an optical signal of a specific wavelength transmitted from the communication device 10. The communication device 20 transmits the estimated value of the zero-dispersion wavelength of the first optical transmission line (hereinafter referred to as the "first estimated value") to the communication device 10 via the second optical transmission line.

[0024] Furthermore, the communication device 20, during WDM transmission, ｉｊｋ The communication device 20 determines a plurality of wavelengths to be used in WDM transmission based on the wavelength allocation result and the second estimated value. For example, the communication device 20 can suppress the influence of chromatic dispersion by determining wavelengths near the zero-dispersion wavelength as the plurality of wavelengths to be used in WDM transmission.

[0025] (Configuration Example of Communication Device 10) The communication device 10 includes a wavelength setting unit 11, a transmitting unit 12, a multiplexing unit 13, a demultiplexing unit 14, a receiving unit 15, a signal processing unit 16, and a wavelength allocation determining unit 18. As described above, the communication device 10 and the communication device 20 shown in Fig. 1 perform two-core transmission, and therefore the multiplexing unit 13 and the demultiplexing unit 14 are connected to different optical transmission paths.

[0026] The wavelength setting unit 11 sets one or more wavelengths to be used during transmission by the transmitter 12. For example, when estimating a zero-dispersion wavelength, the wavelength setting unit 11 sets a specific wavelength to the transmitter 12. When performing WDM transmission, the wavelength setting unit 11 sets multiple wavelengths determined by the wavelength allocation determination unit 18 to the transmitter 12.

[0027] (Processing of Wavelength Setting Unit 11) For example, when the wavelength setting unit 11 controls the wavelength used for communication based on temperature, the wavelength setting unit 11 holds correspondence information indicating the correspondence relationship between wavelength and temperature. For example, the correspondence information includes information indicating the temperature of the laser corresponding to each wavelength, which is associated with each wavelength. That is, the correspondence information includes information indicating the temperature of the laser corresponding to each wavelength, such as wavelength λ １ Corresponding to the temperature T1 and wavelength λ ２ The temperature setting unit 11 includes information such as temperature T2 associated with the wavelength to be set. Note that this is just an example, and the temperature value is determined within a predetermined range. The wavelength setting unit 11 acquires temperature information corresponding to the wavelength to be set by referring to the correspondence information, and adjusts the temperature of each optical transmitter 121 included in the sending unit 12 so that the temperature becomes the temperature indicated by the acquired temperature information. For example, if each optical transmitter 121 included in the sending unit 12 is caused to output light of a different wavelength, the wavelength setting unit 11 adjusts the temperature of each optical transmitter 121 so that the temperature becomes the temperature corresponding to the wavelength to be output from each optical transmitter 121. In this way, the wavelength setting unit 11 sets the wavelength of the optical signal used by the sending unit 12 for communication.

[0028] (Another example of wavelength setting unit 11) The wavelength setting unit 11 may set the wavelength of the optical signal used by the transmitter 12 for communication using a method other than temperature. For example, the wavelength setting unit 11 may set the wavelength of the optical signal used by the transmitter 12 for communication based on a current. When configured in this way, the wavelength setting unit 11 holds correspondence information indicating the correspondence relationship between wavelength and current. This correspondence information may, for example, be associated with each wavelength and information indicating the current to be applied to the corresponding laser for each wavelength. That is, the correspondence information may include a wavelength λ １ Corresponding to the current C １ , wavelength λ ２ Corresponding to the current C ２The information includes the following. Note that this is just an example, and the value of the current is determined within a predetermined range. The wavelength setting unit 11 acquires current information corresponding to the wavelength to be set by referring to the correspondence information, and applies the current indicated by the acquired current information to each of the optical transmitters 121 included in the transmitting unit 12. For example, if each of the optical transmitters 121 included in the transmitting unit 12 is to output light of a different wavelength, the wavelength setting unit 11 applies to each of the optical transmitters 121 a current corresponding to the wavelength to be output from each optical transmitter 121. In this way, the wavelength setting unit 11 sets the wavelength of the optical signal used by the transmitting unit 12 for communication.

[0029] As described above, any method for changing the wavelength may be used. This embodiment is applicable as long as the zero-dispersion wavelength of the optical fiber and the range of the transmission wavelength overlap (not limited to wavelengths of 1300 to 1324 nm).

[0030] The transmitting unit 12 transmits optical signals of one or more wavelengths set by the wavelength setting unit 11. The transmitting unit 12 includes n (n is an integer of 2 or more) optical transmitters 121. Each optical transmitter 121 transmits an optical signal of a different wavelength. The optical transmitter 121 may be a single-wavelength light source capable of outputting light of a single wavelength, or may be a wavelength-tunable light source capable of outputting light of multiple wavelengths.

[0031] The multiplexing unit 13 wavelength-multiplexes optical signals of one or more wavelengths output from each optical transmitter 121. The multiplexing unit 13 is, for example, an optical coupler or an AWG (Arrayed Waveguide Grating). Note that the multiplexing unit 13 is not limited to the above, and may be any device that can wavelength-multiplex optical signals of one or more wavelengths.

[0032] The demultiplexing unit 14 demultiplexes optical signals of one or more wavelengths transmitted from the communication device 20. Light of a specific wavelength or a multiplexed signal transmitted from the communication device 20 is input to the demultiplexing unit 14. Therefore, the demultiplexing unit 14 demultiplexes the input light of the specific wavelength or the multiplexed signal. The demultiplexing unit 14 is, for example, an AWG or an optical splitter. An AWG is a wavelength multiplexing / demultiplexing device that can demultiplex optical signals by wavelength. An optical splitter is a multiplexing / demultiplexing device that demultiplexes optical signals regardless of wavelength. Note that when the demultiplexing unit 14 is an optical splitter, light of different wavelengths is simultaneously input to each of the multiple optical receivers 151 included in the receiving unit 15. Therefore, in order for each optical receiver 151 to receive a signal of a specific wavelength, a wavelength filter that can extract only the signal of the specific wavelength is required. Therefore, when the demultiplexing unit 14 is an optical splitter, a wavelength filter must be provided in the receiving unit 15.

[0033] The receiving unit 15 receives optical signals of one or more wavelengths demultiplexed by the demultiplexing unit 14. The receiving unit 15 includes n optical receivers 151. Each optical receiver 151 receives an optical signal of a different wavelength demultiplexed by the demultiplexing unit 14. If the demultiplexing unit 14 is an AWG, each optical receiver 151 is connected to an output port of the AWG corresponding to a different wavelength to receive an optical signal of a different wavelength. Note that each optical receiver 151 does not have to be directly connected to the demultiplexing unit 14. For example, an optical switch or the like may be provided between each optical receiver 151 and the demultiplexing unit 14 to connect each optical receiver 151 to the demultiplexing unit 14; the connection method is not particularly limited.

[0034] When the demultiplexing unit 14 is an optical splitter, each optical receiver 151 is provided with a wavelength filter that transmits optical signals of a specific wavelength, thereby receiving an optical signal of a specific wavelength. Each optical receiver 151 converts the received optical signal into an electrical signal and outputs it to the signal processing unit 16. Here, the wavelength filter may be a tunable filter, and may be configured to transmit a wavelength that is set to, for example, the estimated zero-dispersion wavelength value and the wavelength value set by the wavelength allocation determination method.

[0035] The signal processing unit 16 performs signal processing on the electrical signals output from each optical receiver 151. As a result, the signal processing unit 16 acquires a first estimated value estimated by, for example, the communication device 20. The signal processing unit 16 outputs the acquired first estimated value to the wavelength allocation determination unit 18.

[0036] Furthermore, when estimating the zero-dispersion wavelength, the signal processing unit 16 estimates a second estimated value using an electrical signal based on light of a specific wavelength transmitted from the communication device 20. The signal processing unit 16 outputs the estimated second estimated value to the wavelength setting unit 11. When the second estimated value is obtained from the signal processing unit 16, the wavelength setting unit 11 controls the optical transmitter 121 to transmit information indicating the obtained second estimated value to the communication device 20. For example, the wavelength setting unit 11 sets a transmission wavelength for one of the optical transmitters 121 and causes the optical transmitter 121 to transmit information indicating the second estimated value to the communication device 20.

[0037] Here, a specific example of a method for notifying information indicating an estimated value of the zero-dispersion wavelength (for example, a second estimated value) is shown below. Note that this method is not limited to notifying information indicating the second estimated value, but can also be applied to notifying information indicating the first estimated value from the communication device 20 to the communication device 10. Examples of methods for notifying information indicating an estimated value of the zero-dispersion wavelength include (1) a method using an estimated value of the zero-dispersion wavelength obtained in advance, (2) a method using a wavelength set for initial connection, and (3) a method using a low-speed signal. Each of (1) to (3) will be described in detail below.

[0038] (1) The wavelength setting unit 11 sets the value of the first estimated value acquired in advance to one of the optical transmitters 121. In this way, the wavelength setting unit 11 uses the value of the first estimated value acquired in advance as a wavelength for notifying information indicating the second estimated value.

[0039] (2) The wavelength setting unit 11 sets the wavelength set for the initial connection between the communication device 10 and the communication device 20 to one of the optical transmitters 121. In this way, the wavelength setting unit 11 uses the wavelength set for the initial connection as the wavelength for notifying information indicating the second estimated value. In this case, the communication device 20 may set the demultiplexing unit 21 (for example, an AWG port or a wavelength filter) to pass the wavelength for the initial connection.

[0040] (3) Even when a wavelength different from the zero-dispersion wavelength is used, for example, if a transmission signal having information indicating the second estimated value is a low-speed signal, the transmission is possible because the influence of waveform degradation due to chromatic dispersion is small. Alternatively, the communication device 10 can transmit information indicating the second estimated value by including it in the AMCC signal using a method of superimposing a low-speed control signal, such as an AMCC (Auxiliary Management Control Channel) signal, on the main signal, and then obtain the information indicating the second estimated value by extracting only the AMCC signal using a low-pass filter on the receiver side of the communication device 20. By using the methods described above in (1) to (3), the second estimated value can be notified to the communication device 20.

[0041] The wavelength allocation determination unit 18 identifies the frequency positions of idler light generated according to the number of wavelengths used for communication with the communication device 20, and allocates wavelengths to frequency positions that do not overlap with the identified frequency positions of the idler light. The wavelength allocation determination unit 18 determines the multiple wavelengths to be used for communication with the communication device 20 based on the obtained wavelength allocation result and the first estimate value.

[0042] (Configuration Example of Communication Device 20) The communication device 20 includes a demultiplexing unit 21, a receiving unit 22, a signal processing unit 23, a MAC processing unit 24, a wavelength allocation determining unit 26, a wavelength setting unit 27, a transmitting unit 28, and a multiplexing unit 29. As described above, the communication device 10 and the communication device 20 shown in Fig. 1 perform two-core transmission, and therefore the demultiplexing unit 21 and the multiplexing unit 29 are connected to different optical transmission paths.

[0043] The demultiplexing unit 21 demultiplexes optical signals of one or more wavelengths transmitted from the communication device 10. Light of a specific wavelength or a multiplexed signal transmitted from the communication device 10 is input to the demultiplexing unit 21. Therefore, the demultiplexing unit 21 demultiplexes the input light of the specific wavelength or the multiplexed signal. The demultiplexing unit 21 is, for example, an AWG or an optical splitter. Note that if the demultiplexing unit 21 is an optical splitter, light of different wavelengths is simultaneously input to each of the multiple optical receivers 221 provided in the receiving unit 22. Therefore, in order for each optical receiver 221 to receive a signal of a specific wavelength, a wavelength filter capable of extracting only the signal of the specific wavelength is required. Therefore, if the demultiplexing unit 21 is an optical splitter, the receiving unit 22 needs to be provided with a wavelength filter.

[0044] The receiving unit 22 receives optical signals of one or more wavelengths demultiplexed by the demultiplexing unit 21. The receiving unit 22 includes n optical receivers 221. Each optical receiver 221 receives an optical signal of a different wavelength demultiplexed by the demultiplexing unit 21. If the demultiplexing unit 21 is an AWG, each optical receiver 221 is connected to an output port of the AWG corresponding to a different wavelength to receive an optical signal of a different wavelength. Note that each optical receiver 221 does not have to be directly connected to the demultiplexing unit 21. For example, an optical switch or the like may be provided between each optical receiver 221 and the demultiplexing unit 21 to connect the optical receivers 221 to the demultiplexing unit 21; the connection method is not particularly limited.

[0045] When the demultiplexing unit 21 is an optical splitter, each optical receiver 221 is provided with a wavelength filter that transmits optical signals of a specific wavelength, thereby suppressing interference and receiving optical signals of different wavelengths. Each optical receiver 221 converts the received optical signal into an electrical signal and outputs it to the signal processing unit 23. Here, the wavelength filter may be a tunable filter, and may be configured to transmit wavelengths that are set to the estimated zero-dispersion wavelength value and the wavelength value set by the wavelength allocation determination method, for example.

[0046] The signal processing unit 23 performs signal processing on the electrical signals output from each optical receiver 221. As a result, the signal processing unit 23 acquires, for example, a second estimated value estimated by the communication device 10. The signal processing unit 23 outputs the acquired second estimated value to the wavelength allocation determination unit 26.

[0047] Furthermore, when estimating the zero-dispersion wavelength, the signal processing unit 23 estimates a first estimated value using an electrical signal based on light of a specific wavelength transmitted from the communication device 10. The signal processing unit 23 outputs the estimated first estimated value to the wavelength setting unit 27. Furthermore, when transmission data is obtained, the signal processing unit 23 outputs the obtained transmission data to the MAC processing unit 24.

[0048] The MAC processing unit 24 performs predetermined MAC (Medium Access Control) layer processing on the transmission data output from the signal processing unit 23 and outputs the data to a predetermined destination. When transmission data addressed to the communication device 10 is input from another device, the MAC processing unit 24 performs predetermined MAC layer processing on the input transmission data and outputs the data to the wavelength setting unit 27.

[0049] The wavelength allocation determination unit 26 identifies the frequency positions of idler light generated according to the number of wavelengths used for communication with the communication device 10, and allocates wavelengths to frequency positions that do not overlap with the identified frequency positions of the idler light. The wavelength allocation determination unit 26 determines the multiple wavelengths to be used for communication with the communication device 10 based on the obtained wavelength allocation result and the second estimate value.

[0050] The wavelength setting unit 27 sets one or more wavelengths to be used by the transmitter 28 during transmission. For example, when estimating a zero-dispersion wavelength, the wavelength setting unit 27 sets a specific wavelength to the transmitter 28. During WDM transmission, the wavelength setting unit 27 sets a plurality of wavelengths determined by the wavelength allocation determination unit 26 to the transmitter 28. Furthermore, when a first estimated value is obtained from the signal processing unit 23, the wavelength setting unit 27 sets a specific wavelength to the optical transmitter 281, thereby causing the first estimated value to be transmitted to the communication device 20. This makes it possible to notify the communication device 10 of the first estimated value. Similar to the wavelength setting unit 11, the wavelength setting unit 27 sets the wavelength of the optical signal to be used by the transmitter 28 for communication using temperature or a method other than temperature.

[0051] The transmitting unit 28 transmits optical signals of one or more wavelengths set by the wavelength setting unit 27. The transmitting unit 28 includes n optical transmitters 281. Each optical transmitter 281 transmits an optical signal of a different wavelength. The optical transmitter 281 may be a single-wavelength light source capable of outputting light of a single wavelength, or may be a wavelength-tunable light source capable of outputting light of multiple wavelengths.

[0052] The multiplexing unit 29 wavelength-multiplexes optical signals of one or more wavelengths output from each optical transmitter 281. The multiplexing unit 29 is, for example, an optical coupler or an AWG. Note that the multiplexing unit 29 is not limited to the above, as long as it is a device that can wavelength-multiplex optical signals of one or more wavelengths.

[0053] Next, the process performed by the wavelength setting unit in the embodiment will be described in detail.

[0054] (When the number of wavelengths is three) First, a case where three wavelengths (number of wavelengths = 3) are used for communication between the communication device 10 and the communication device 20 will be described. Fig. 2 is a diagram showing the arrangement relationship between a wavelength multiplexed signal of three wavelengths and idler light. As described above, in four-wave mixing, the optical frequency ω ｉ , ω ｊ , ω ｋ (j ≠ k) for frequency ω ｉｊｋ =ω ｉ +ω ｊ -ω ｋ As shown in Figure 2, the idler light is generated at the position of the optical frequency ω １ is placed at the position of number "0" which is the wavelength reference point, and the optical frequency ω ２ When the wavelength of the idler light is generated at the position of the number "1", the wavelength positions at which the idler light is generated are as follows: Here, the numbers "0" to "6" in Fig. 2 are numbers assigned to make the wavelength arrangement easier to understand, and "a" in Fig. 2 represents the frequency interval (frequency difference).

[0055] (i,j,k)=(1,1,2):ω ｉｊｋ =0+0-1=-1 (2,2,1):ω ｉｊｋ =1+1-0=+2

[0056] As described above, the idler light appears at the positions numbered "-1" and "+2". In this way, the wavelength allocation determination units 18 and 26 identify the frequency positions of the idler light generated according to the number of wavelengths used for communication with the opposite device (for example, the communication device 10 or the communication device 20). Since the idler light appears at the positions numbered "-1" and "+2", the optical frequency ω ３ It is not desirable to wavelength allocate the optical frequency ω ３ For example, the wavelength allocation determination units 18 and 26 allocate the wavelengths of the optical frequencies ω ３ is placed at the position numbered "3".

[0057] This allows the three wavelengths in the wavelength allocation to be allocated at positions different from the position where the idler light is generated. Therefore, the influence of the idler light can be suppressed. As a result, WDM transmission using three wavelengths while avoiding four-wave mixing becomes possible. Note that here, the wavelength allocation determination units 18 and 26 determine the optical frequency ω １ is placed at the position of number "0", and the optical frequency ω ２ As an example of suppressing the influence of idler light when the light frequency ω ３ is placed at the position of number "3". ３ may be placed at any position, regardless of positive or negative, other than the positions of numbers "-1" and "+2" where idler light is generated. ３ may be placed at the position numbered "-2".

[0058] In Fig. 2, a configuration is shown in which a plurality of wavelengths used for communication with the opposite device are arranged at a position different from the position where the idler light is generated. The numbers shown in Fig. 2 represent the optical frequency ω １ Since the first estimated value or the second estimated value is a relative position where the wavelength reference point is set to 0, WDM transmission can be performed with a wavelength allocation close to the zero-dispersion wavelength by shifting the coordinate axis (wavelength reference point) with respect to the first estimated value or the second estimated value. The following description will be given taking the first estimated value estimated by the communication device 20 as an example.

[0059] For example, if the first estimated value is 228.85 THz, the wavelength allocation determination unit 18 sets the coordinate axis so that the first estimated value corresponds to the position of number "2." This example is shown in Fig. 3. As shown in Fig. 3, the frequency ω of the light wavelength-allocated in Fig. 2 is １ ~ω ３ While maintaining the arrangement intervals of the three wavelengths, the wavelength arrangement determination unit 18 sets the coordinate axis so that the first estimated value corresponds to the position of number "2." This changes the value of the optical frequency, so in FIG. 3, the optical frequency ω １ ~ω ３ is the frequency of light ω １ ´~ω ３ In this way, by setting the coordinate axes at positions according to the estimated value of the zero-dispersion wavelength, WDM transmission becomes possible with a wavelength allocation close to the zero-dispersion wavelength.

[0060] In the above example, the coordinate axes are set so that the first estimated value corresponds to the position of number "2," but it does not matter which port number the estimated first estimated value corresponds to, or whether it is determined to be at an intermediate position between port numbers. For example, by placing the position of number "3" at the first estimated value, it is also possible to set it to a wavelength with the same value as the zero-dispersion wavelength and a wavelength that is pulse-compressed by negative dispersion.

[0061] Also, the frequency of light ω ２ and the frequency of light ω １ Since the difference between the optical frequencies ω and ω is a relative position, the difference between these values ​​on the frequency axis can be freely set. For example, if the value of a is 100 GHz and the frequency of number "2" is 228.85 THz, the frequency of number "1" is 228.75 THz, the frequency of number "0" is 228.65 THz, and the frequency of number "3" is 228.95 THz. Therefore, the wavelength allocation determination unit 18 calculates the optical frequency ω １ is placed at 228.65 THz, and the optical frequency ω ２ is placed at 228.75 THz, and the optical frequency ω ３ will be arranged at a wavelength of 228.95 THz. Note that although an example of 100 GHz spacing has been described here, there is no particular limitation to this either. The above is just an example, and there is no particular limitation to the method of avoiding four-wave mixing, and it may be the same as the conventional method.

[0062] The wavelength allocation determination unit 18 sets the coordinate axes at positions corresponding to the estimated value of the zero-dispersion wavelength, and then calculates the optical frequency ω １ ´~ω ３ The wavelengths corresponding to the respective frequency positions are determined as a plurality of wavelengths to be used for WDM transmission with the communication device 20. For example, the wavelength allocation determination unit 18 determines the wavelengths corresponding to the respective frequency positions as a plurality of wavelengths to be used for WDM transmission with the communication device 20. １ The first wavelength (λ １ = c / ω １ ´) and the frequency of light ω ２ The second wavelength (λ ２ = c / ω ２ ´) and the frequency of light ω ３ The third wavelength (λ ３ = c / ω ３ The wavelength allocation determination unit 18 then determines the first wavelengths λ ′ as the wavelengths to be used for WDM transmission with the communication device 20. １ , second wavelength λ ２ and the third wavelength λ ３ Identification information indicating each wavelength is output to the wavelength setting unit 11 to notify the set wavelength.

[0063] (When the number of wavelengths is four) Next, a case where four wavelengths (number of wavelengths=4) are used for communication between the communication device 10 and the communication device 20 will be described. Fig. 4 is a diagram showing the arrangement relationship between a wavelength multiplexed signal of four wavelengths and idler light. As shown in Fig. 4, when the frequency of light ω １ is placed at the position of number "0" which is the wavelength reference point, and the optical frequency ω ２ is placed at the position of number "1", and the optical frequency ω ３ When the wavelength of the idler light is generated at the position of number "3", the wavelength of the idler light is as follows:

[0064] (i,j,k)=(1,1,2):ω ｉｊｋ =0+0-1=-1 (1,1,3):ω ｉｊｋ =0+0-3=-3 (1,2,3):ω ｉｊｋ =0+1-3=-2 (1,3,2):ω ｉｊｋ =0+3-1=+2 (2,1,3):ω ｉｊｋ =1+0-3=-2 (2,2,1):ω ｉｊｋ=1+1-0=+2 (2,2,3):ω ｉｊｋ =1+2-3=-1 (2,3,1):ω ｉｊｋ =1+3-0=+4 (3,1,2):ω ｉｊｋ =3+0-1=+2 (3,2,1):ω ｉｊｋ =3+1-0=+4 (3,3,1):ω ｉｊｋ =3+3-0=+6 (3,3,2):ω ｉｊｋ =3+3-1=+5

[0065] As described above, the idler light appears at positions numbered "-3", "-2", "-1", "+2", "+4", "+5", and "+6". In this way, the wavelength allocation determination units 18 and 26 identify the frequency positions of the idler light generated according to the number of wavelengths used for communication with the opposite device (for example, the communication device 10 or the communication device 20). Since the idler light appears at positions numbered "-3", "-2", "-1", "+2", "+4", "+5", and "+6", the optical frequency ω ４ It is not preferable to allocate the wavelengths at the positions of numbers "-3", "-2", "-1", "+2", "+4", "+5", and "+6". Therefore, the wavelength allocation determination units 18 and 26 allocate the wavelengths at the positions of numbers "-3", "-2", "-1", "+2", "+4", "+5", and "+6". ４ For example, the wavelength allocation determination units 18 and 26 allocate the wavelengths of the optical frequencies ω ４ is placed at the position numbered "7".

[0066] This allows the four wavelengths in the wavelength allocation to be allocated at positions different from the positions where idler light is generated. Therefore, the influence of idler light can be suppressed. As a result, WDM transmission using four wavelengths while avoiding four-wave mixing becomes possible. Note that here, the wavelength allocation determination units 18 and 26 determine the optical frequency ω １ is placed at the position of number "0", and the optical frequency ω ２ is placed at the position of number "1", and the optical frequency ω ３ As an example of suppressing the influence of idler light when the light frequency ω ４ is placed at the position of number "7". ４may be placed at any position, regardless of positive or negative, other than the positions of numbers "-3", "-2", "-1", "+2", "+4", "+5", and "+6" where idler light is generated. For example, the wavelength allocation determination units 18 and 26 may ４ may be placed at the position of number "-4". ３ When the light frequency ω is placed at the position of number "-2", the same calculation is performed. ４ can be set to a wavelength arrangement that suppresses the influence of idler light.

[0067] Thereafter, the wavelength allocation determination units 18 and 26 set coordinate axes (wavelength reference points) for the first estimated value or the second estimated value, as described with reference to Fig. 3, and determine the wavelengths to be used for WDM transmission. Note that although the cases where the number of wavelengths is three and four have been described here, similar processing may be performed when the number of wavelengths is five or more.

[0068] (System Operation Example) Next, an operation example of the optical communication system 100 will be described. Fig. 5 is a sequence diagram showing the flow of processing performed by the optical communication system 100 in the embodiment. Note that Fig. 5 describes an example in which an estimated value (e.g., a second estimated value) of the zero-dispersion wavelength is estimated in the communication device 20.

[0069] At the start of communication, the wavelength setting unit 11 of the communication device 10 sets a specific wavelength for one or more of the n optical transmitters 121 (for example, the optical transmitter 121-1, etc.). The optical transmitter 121-1 transmits an optical signal of the specific wavelength set by the wavelength setting unit 11 (step S101). The optical signal of the specific wavelength transmitted from the optical transmitter 121-1 is input to the multiplexing unit 13. Only the optical signal of the specific wavelength transmitted from the optical transmitter 121-1 is input to the multiplexing unit 13. Therefore, the multiplexing unit 13 transmits the optical signal of the specific wavelength transmitted from the optical transmitter 121-1 to the optical transmission path (step S102).

[0070] An optical signal of a specific wavelength transmitted via an optical transmission path is input to the demultiplexing unit 21 of the communication device 20. The demultiplexing unit 21 demultiplexes the input optical signal of the specific wavelength according to the wavelength. For example, if the demultiplexing unit 21 is an AWG, the AWG outputs the optical signal from an output port according to the wavelength of the input optical signal. As a result, the optical signal output from the demultiplexing unit 21 is input to one optical receiver 221 (for example, optical receiver 221-1). The optical receiver 221-1 receives the input optical signal (step S103). The optical receiver 221-1 converts the received optical signal into an electrical signal and outputs it to the signal processing unit 23.

[0071] The signal processing unit 23 estimates the zero-dispersion wavelength based on the electrical signal output from the optical receiver 221-1 (step S104). The signal processing unit 23 outputs a first estimated value, which is an estimated value of the zero-dispersion wavelength, to the wavelength setting unit 27. The wavelength setting unit 27 sets a wavelength for one of the multiple optical transmitters 281 included in the transmitting unit 28 (for example, the optical transmitter 281-1), thereby causing the first estimated value output from the signal processing unit 23 to be transmitted. The wavelength setting unit 27 may set a specific wavelength for the optical transmitter 281-1, for example.

[0072] The optical transmitter 281-1 transmits an optical signal having the wavelength set by the wavelength setting unit 27 (step S105). The optical signal transmitted by the optical transmitter 281-1 includes the first estimated value. The optical signal transmitted from the optical transmitter 281-1 is input to the multiplexing unit 29. Only the optical signal transmitted from the optical transmitter 281-1 is input to the multiplexing unit 29. Therefore, the multiplexing unit 29 transmits the optical signal transmitted from the optical transmitter 281-1 to the optical transmission path (step S106).

[0073] An optical signal transmitted via an optical transmission path is input to the demultiplexing unit 14 of the communication device 10. The demultiplexing unit 14 demultiplexes the input optical signal according to its wavelength. For example, if the demultiplexing unit 14 is an AWG, the AWG outputs the optical signal from an output port according to the wavelength of the input optical signal. As a result, the optical signal output from the demultiplexing unit 14 is input to one optical receiver 151 (for example, optical receiver 151-1). The optical receiver 151-1 receives the input optical signal (step S107). The optical receiver 151-1 converts the received optical signal into an electrical signal and outputs it to the signal processing unit 16.

[0074] The signal processing unit 16 acquires a first estimated value included in the electrical signal output from the optical receiver 151-1. The signal processing unit 16 outputs the acquired first estimated value to the wavelength allocation determination unit 18. During WDM transmission, the wavelength allocation determination unit 18 determines multiple wavelengths to be used for communication with the communication device 20 based on the first estimated value output from the signal processing unit 16 and the number of wavelengths to be used for WDM transmission (step S108). At this time, the wavelength allocation determination unit 18 determines the multiple wavelengths to be used for communication with the communication device 20 by performing wavelength allocation based on the relationship between the wavelengths to be used for WDM transmission and the idler light, as described with reference to FIGS. 2 to 4 .

[0075] The wavelength allocation determination unit 18 outputs identification information corresponding to each of the determined wavelengths to the wavelength setting unit 11. The wavelength setting unit 11 identifies the wavelength to be set in each optical transmitter 121 based on the identification information of each wavelength output from the wavelength allocation determination unit 18. Then, the wavelength setting unit 11 sets each identified wavelength to a different optical transmitter 121 (step S109). For example, if the number of wavelengths is three, the wavelength setting unit 11 sets different wavelengths to three of the multiple optical transmitters 121.

[0076] The optical transmitters 121, each having a preset wavelength, transmit optical signals corresponding to the preset wavelengths. The optical signals of the multiple wavelengths transmitted from the optical transmitters 121 are input to the multiplexing unit 13. The multiplexing unit 13 multiplexes the optical signals of the multiple wavelengths transmitted from the optical transmitters 121 to generate a multiplexed signal (step S110). The multiplexing unit 13 transmits the generated multiplexed signal to the optical transmission path (step S111). This allows WDM transmission from the communication device 10 to the communication device 20.

[0077] 5 has been described taking WDM transmission from the communication device 10 to the communication device 20 as an example. Here, in the processing of step S107, the signal processing unit 16 may estimate the zero-dispersion wavelength based on the electrical signal output from the optical receiver 151-1. Then, the signal processing unit 16 outputs a second estimated value, which is an estimated value of the estimated zero-dispersion wavelength, to the wavelength setting unit 11. The wavelength setting unit 11 may set a wavelength for one of the multiple optical transmitters 121 included in the transmitting unit 12 (for example, optical transmitter 121-1), thereby causing the second estimated value output from the signal processing unit 16 to be transmitted. This allows the communication device 20 to acquire the second estimated value. Therefore, by performing the same processing as that of the communication device 10, WDM transmission can be performed from the communication device 20 to the communication device 10.

[0078] According to the optical communication system 100 configured as described above, WDM transmission that reduces the effects of chromatic dispersion and four-wave mixing is possible by estimating the zero-dispersion wavelength in at least one of the communication device 10 and the communication device 20, and performing wavelength allocation that avoids four-wave mixing while using the estimated value of the zero-dispersion wavelength. Specifically, the communication device 10 includes a wavelength allocation determiner 18 that determines multiple wavelengths to be used for communication with the communication device 20 based on a wavelength allocation determined so as not to overlap with the frequency position of the idler light and an estimated value of the zero-dispersion wavelength of the optical transmission line connecting the communication device 20, a plurality of optical transmitters 121 that transmit light of the multiple wavelengths determined by the wavelength allocation determiner 18, and a multiplexer 13 that wavelength-multiplexes and outputs light of the multiple wavelengths output from each of the plurality of optical transmitters 121.

[0079] In this way, the communication device 10 reduces nonlinear waveform distortion caused by four-wave mixing by allocating wavelengths at positions different from the positions where idler light is generated. Furthermore, the communication device 10 reduces the influence of chromatic dispersion by bringing the value of the transmission wavelength closer to the estimated value of the zero-dispersion wavelength. This makes it possible to extend the transmission distance in a WDM transmission system.

[0080] (Variation 1) The number of optical transmitters 121 included in the communication device 10 does not need to be the same as the number of optical transmitters 281 included in the communication device 20. On the other hand, it is desirable that the number of optical transmitters 121 included in the communication device 10 is the same as the number of optical receivers 221 included in the communication device 20, and the number of optical transmitters 281 included in the communication device 20 is the same as the number of optical receivers 151 included in the communication device 10.

[0081] (Variation 2) In the above embodiment, a configuration was shown in which nonlinear waveform distortion due to four-wave mixing was reduced by allocating wavelengths at a position different from the position of the idler light. In contrast, it is also possible to reduce nonlinear waveform distortion due to four-wave mixing by removing the idler light using, for example, a band pass filter (BPF) or an AWG. For example, since the wavelength and spacing of an AWG are determined for each port number, it is possible to remove the idler light by setting it to a port that is the same as or close to the zero-dispersion wavelength. In this case, port selection can be made using, for example, an optical switch. This configuration makes it possible to extend the transmission distance of WDM signals.

[0082] (Variation 3) In the above-described embodiment, the communication device 10 and the communication device 20 are configured to perform two-core transmission, but the communication device 10 and the communication device 20 may be configured to perform single-core bidirectional transmission. In such a configuration, the communication device 10 and the communication device 20 each include a multiplexing / demultiplexing device. The multiplexing / demultiplexing device included in the communication device 10 and the multiplexing / demultiplexing device included in the communication device 20 are connected via a single optical transmission path. Examples of the multiplexing / demultiplexing device include a circulator and a multiplexing / demultiplexing coupler. It is desirable for the multiplexing / demultiplexing device to be wavelength-independent.

[0083] In single-core bidirectional communication, the same path is used for transmission and reception, so the zero-dispersion wavelength is assumed to be the same. Therefore, it is sufficient if either communication device 10 or communication device 20 has the function of estimating the zero-dispersion wavelength.

[0084] The multiplexing unit 13 included in the communication device 10 outputs a multiplexed signal to the multiplexing / demultiplexing device. The demultiplexing unit 14 included in the communication device 10 receives the multiplexed signal from the multiplexing / demultiplexing device. Similarly, the demultiplexing unit 21 included in the communication device 20 receives the multiplexed signal from the multiplexing / demultiplexing device. The multiplexing unit 29 included in the communication device 20 outputs the multiplexed signal to the multiplexing / demultiplexing device.

[0085] In the case of a single-core bidirectional transmission, the wavelength set by communication device 10 and the multiple wavelengths set by communication device 20 are wavelength division multiplexed for communication from communication device 10 to communication device 20 and for communication from communication device 20 to communication device 10, but by using a method similar to the processing flow shown in the embodiment, it is possible to reduce nonlinear waveform distortion due to four-wave mixing, measure an estimated value of the zero-dispersion wavelength of the optical transmission path, and bring the value of the transmission wavelength closer to the estimated value of the zero-dispersion wavelength of the optical transmission path, thereby extending the transmission distance of wavelength division multiplexing transmission.

[0086] The communication devices 10 and 20 in the above-described embodiments may be partially or entirely implemented by a computer. In this case, a program for implementing the functions may be recorded on a computer-readable recording medium, and the program may be read and executed by a computer system. Note that the term "computer system" here includes hardware such as an operating system (OS) and peripheral devices.

[0087] Furthermore, the term "computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Furthermore, the term "computer-readable recording medium" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs over networks like the Internet or communication lines like telephone lines, and devices that store programs for a fixed period of time, such as volatile memory within the computer systems that serve as servers or clients in such cases. The above programs may also be recorded on computer-readable recording media. Examples of computer-readable recording media include portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, and semiconductor storage devices (e.g., solid-state drives (SSDs)), as well as storage devices such as hard disks and semiconductor storage devices built into computer systems. The above programs may also be transmitted via telecommunications lines.

[0088] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0089] The present invention can be applied to a system that performs wavelength division multiplexing transmission.

[0090] 10, 20... communication device, 11, 27... wavelength setting unit, 12, 28... transmitter, 13, 29... multiplexer, 14, 21... demultiplexer, 15, 22... receiver, 16, 23... signal processor, 18, 26... wavelength allocation determination unit, 24... MAC processor, 121, 121-1 to 121-n, 281, 281-1 to 281-n... optical transmitter, 151, 151-1 to 151-n, 221, 221-1 to 221-n... optical receiver

Claims

1. A communications device that communicates with a counterpart device using wavelength division multiplexing, comprising: a wavelength allocation determination unit that determines multiple wavelengths to be used for communications with the counterpart device based on a wavelength allocation determined so as not to overlap with the frequency position of idler light generated by four-wave mixing and an estimated value of the zero-dispersion wavelength of a communication path connecting to the counterpart device; multiple transmitters that transmit light of the multiple wavelengths determined by the wavelength allocation determination unit; and a multiplexing unit that wavelength-multiplexes and outputs the light of the multiple wavelengths output from each of the multiple transmitters.

2. The communication device described in claim 1, wherein the wavelength allocation determination unit identifies the frequency position of the idler light generated according to the number of wavelengths used for communication with the opposing device, and allocates wavelengths to frequency positions that do not overlap with the identified frequency position of the idler light.

3. The communication device according to claim 1 or 2, wherein the wavelength allocation determination unit determines a plurality of wavelengths identified by the wavelength allocation based on an estimated value of the zero-dispersion wavelength of the communication path as a plurality of wavelengths to be used for communication with the opposing device.

4. A communication device as described in claim 1 or 2, wherein any one of the plurality of transmitters further transmits light of a specific wavelength to the opposing device via the communication path, and the wavelength allocation determination unit obtains an estimate of the zero-dispersion wavelength of the communication path estimated by the opposing device based on the light of the specific wavelength.

5. An optical communication system comprising a first communication device and a second communication device, wherein the first communication device and the second communication device communicate using wavelength division multiplexing, wherein the first communication device is a communication device that communicates using wavelength division multiplexing with an opposite device that is a communication partner, and comprises: a wavelength allocation determination unit that determines multiple wavelengths to be used for communication with the opposite device based on a wavelength allocation determined so as not to overlap with the frequency position of idler light generated by four-wave mixing and an estimated value of the zero-dispersion wavelength of a communication path connecting to the opposite device; a plurality of transmitters that transmit light of the multiple wavelengths determined by the wavelength allocation determination unit; and a multiplexing unit that wavelength-multiplexes and outputs the light of the multiple wavelengths output from each of the plurality of transmitters; and the second communication device is an optical communication system comprising: a signal processing unit that estimates the zero-dispersion wavelength of the communication path; and a transmitting unit that transmits the estimated value of the zero-dispersion wavelength of the communication path estimated by the signal processing unit to the first communication device.

6. A communication method performed by a communication device that communicates with a communication partner, an opposite device, using wavelength division multiplexing, in which multiple wavelengths to be used for communication with the opposite device are determined based on a wavelength allocation determined so as not to overlap with the frequency position of idler light generated by four-wave mixing and an estimated value of the zero-dispersion wavelength of the communication path connecting to the opposite device, and the light of the multiple wavelengths output from each of multiple transmitters that transmit light of the determined multiple wavelengths is wavelength-multiplexed and output.

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