Reception device, transmission device, optical communication system, zero dispersion wavelength estimation method, and wavelength determination method

Abstract

Provided is a reception device comprising: a reception unit that receives a plurality of optical signals having different wavelengths and transmitted from one or more opposing devices connected via an optical transmission path; and a signal processing unit that calculates, for each of the received optical signals on the basis of the frequency spectrum thereof, a notch frequency at which a notch appears in the frequency domain excluding harmonics of the frequency of the received optical signal, and uses the plurality of calculated notch frequencies and chirp values corresponding to the wavelengths of the respective plurality of optical signals to estimate one or more zero dispersion wavelengths in the optical transmission path.　

Description

Receiver, transmitter, optical communication system, zero-dispersion wavelength estimation method, and wavelength determination method

[0001] The present invention relates to a receiving device, a transmitting device, an optical communication system, a zero-dispersion wavelength estimation method, and a wavelength determination method.This application claims priority to PCT / JP2023 / 047199, filed in Japan on December 28, 2023, the contents of which are incorporated herein by reference.

[0002] In communication systems that transmit signals using optical fiber, if the wavelength deviates from the zero-dispersion wavelength of the optical fiber, the effect of dispersion becomes greater and the penalty amount increases, making long-distance transmission difficult. Therefore, in order to transmit long-distance signals, it is necessary to set the wavelength so that it approaches the zero-dispersion wavelength.

[0003] However, since the zero-dispersion wavelength of an optical fiber 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, in the past, based on the frequency spectrum data of the received signal, the notch frequency f at which the first notch appeared was determined to be a frequency other than a multiple (1x, 2x, etc.) of the frequency of the transmitted signal. ０ The value of the zero-dispersion wavelength is estimated by calculating 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 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 (see, for example, Non-Patent Document 1). Here, the oscillation wavelength is calculated based on the operating state such as the temperature of the transmitter, and the distance L between the communication devices can be calculated based on a timestamp from a low-speed signal or the like.

[0005] Yasunari Tanaka, “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).

[0006] However, in conventional methods, only general values ​​(e.g., statistical values ​​such as minimum, maximum, and average values ​​specified in standardization) can be used as the dispersion slope value. Therefore, if the accurate value of the dispersion slope is not known, it is conceivable that the estimated value of the zero-dispersion wavelength will be inaccurate. Furthermore, in conventional methods, if the value of the optical fiber length is not known, the value of the zero-dispersion wavelength cannot be estimated.

[0007] In view of the above circumstances, an object of the present invention is to provide a technique that can estimate the value of the zero-dispersion wavelength without using the value of the dispersion slope and the value of the optical fiber length.

[0008] One aspect of the present invention is a receiving device comprising: a receiving unit that receives a plurality of optical signals of different wavelengths transmitted from one or more opposing devices connected via an optical transmission path; and a signal processing unit that calculates, for each received optical signal, a notch frequency at which a notch appears at a frequency excluding multiples of the frequency of the received optical signal, based on the frequency spectrum of each of the received optical signals, and estimates one or more zero-dispersion wavelengths in the optical transmission path using the calculated notch frequencies and chirp values ​​corresponding to the wavelengths of each of the plurality of optical signals.

[0009] One aspect of the present invention is a transmitting device in an optical communication system including a transmitting device and a receiving device, the transmitting device comprising: a transmitting unit that transmits a plurality of optical signals of different wavelengths to the receiving device via an optical transmission path; and a signal processing unit that controls the transmission wavelengths used by the transmitting unit in accordance with values ​​related to one or more zero-dispersion wavelengths in the optical transmission path calculated based on a plurality of notch frequencies at which notches appear at frequencies excluding multiples of the frequencies of each of the plurality of optical signals based on the frequency spectra of each of the plurality of optical signals, and chirp values ​​corresponding to the wavelengths of each of the plurality of optical signals.

[0010] One aspect of the present invention is a transmitting device in an optical communication system including a transmitting device and a receiving device, the transmitting device comprising: a transmitting unit that transmits a plurality of optical signals of different wavelengths to the receiving device via an optical transmission path; and a signal processing unit that controls the transmission wavelength used by the transmitting unit using information regarding one or more zero-dispersion wavelengths in the optical transmission path calculated based on a plurality of notch frequencies at which notches appear at frequencies excluding multiples of the frequencies of each of the plurality of optical signals based on the frequency spectra of each of the plurality of optical signals, and chirp values ​​corresponding to the wavelengths of each of the plurality of optical signals, and information regarding the transmission wavelength used by the transmitting unit determined based on the amount of chromatic dispersion allowed in the system.

[0011] One aspect of the present invention is an optical communication system comprising one or more first communication devices and a second communication device connected via an optical transmission path, wherein the one or more first communication devices comprise a transmitter that transmits a plurality of optical signals having different wavelengths to the second communication device via the optical transmission path, a receiver that receives setting information from the second communication device including values ​​related to one or more zero-dispersion wavelengths in the optical transmission path, and a signal processor that controls a transmission wavelength used by the transmitter in accordance with a value based on the one or more zero-dispersion wavelengths indicated in the setting information received by the receiver, and the second communication device comprises one or more a signal processing unit that calculates, for each received optical signal, a notch frequency at which a notch appears at a frequency excluding multiples of the frequency of the received optical signal, based on the frequency spectrum of each of the received optical signals, and estimates the one or more zero-dispersion wavelengths using the calculated notch frequencies and chirp values ​​corresponding to the wavelengths of each of the plurality of optical signals; and a transmitting unit that transmits setting information including values ​​related to the calculated one or more zero-dispersion wavelengths to the one or more first communication devices.

[0012] One aspect of the present invention is an optical communication system including a first communication device and a second communication device, wherein the first communication device comprises a first receiver that receives an optical signal having one or more wavelengths that are candidates for zero-dispersion wavelengths transmitted from the second communication device, and a first transmitter that transmits a plurality of optical signals having different wavelengths to the second communication device, or transmits an optical signal to the second communication device when the first receiver receives an optical signal having one or more wavelengths that are candidates for zero-dispersion wavelengths, and the second communication device comprises a second receiver that receives a plurality of optical signals having different wavelengths from the first communication device, and a first transmitter that transmits each of the received optical signals to the second communication device. a second signal processing unit that calculates, for each received optical signal, notch frequencies at which notches appear at frequencies excluding multiples of the frequency of the received optical signal based on the frequency spectrum, estimates one or more zero-dispersion wavelength candidates in the optical transmission path using the calculated notch frequencies and chirp values ​​corresponding to the wavelengths of each of the plurality of optical signals, and sets the estimated wavelengths to be the one or more zero-dispersion wavelength candidates; and a second transmitting unit that transmits optical signals of the wavelengths to be the one or more zero-dispersion wavelength candidates set by the second signal processing unit to the first communication device.

[0013] One aspect of the present invention is an optical communication system comprising one or more first communication devices and a second communication device connected via an optical transmission line, wherein the one or more first communication devices comprise a transmitter that transmits a plurality of optical signals having different wavelengths to the second communication device via the optical transmission line, and a signal processing unit that controls the transmission wavelength used by the transmitter using information about the transmission wavelength used by the transmitter, the information being determined based on one or more zero-dispersion wavelengths in the optical transmission line and an amount of chromatic dispersion allowed in the system, and the second communication device comprises a receiver that receives the plurality of optical signals having different wavelengths transmitted from the one or more first communication devices, and a signal processing unit that controls the transmission wavelength used by the transmitter using information about the transmission wavelength used by the transmitter, the information being determined based on one or more zero-dispersion wavelengths in the optical transmission line and an amount of chromatic dispersion allowed in the system, and and a signal processing unit that determines information regarding a transmission wavelength to be used by a transmitting unit provided in at least one of the opposing devices based on a frequency spectrum of each of the plurality of optical signals received by the one or more first communication devices, the one or more zero-dispersion wavelengths being estimated based on a plurality of notch frequencies at which notches appear at frequencies excluding multiples of the frequencies of each of the plurality of optical signals obtained based on the frequency spectrum of each of the plurality of optical signals received by the one or more first communication devices, and chirp values ​​corresponding to the wavelengths of each of the plurality of optical signals, the one or more zero-dispersion wavelengths being estimated based on the one or more zero-dispersion wavelengths and an amount of chromatic dispersion allowed in the system, and a transmitting unit that transmits information regarding the transmission wavelength to the one or more first communication devices.

[0014] One aspect of the present invention is a zero-dispersion wavelength estimation method that receives a plurality of optical signals with different wavelengths transmitted from one or more opposing devices connected via an optical transmission path, calculates, for each received optical signal, a notch frequency at which a notch appears at a frequency excluding multiples of the frequency of the received optical signal based on the frequency spectrum of each of the received optical signals, and estimates one or more zero-dispersion wavelengths in the optical transmission path using the calculated notch frequencies and chirp values ​​corresponding to the wavelengths of each of the plurality of optical signals.

[0015] One aspect of the present invention is a wavelength determination method that receives a plurality of optical signals of different wavelengths transmitted from one or more opposing devices connected via an optical transmission path, calculates, for each received optical signal, a notch frequency at which a notch appears at a frequency excluding multiples of the frequency of the received optical signal based on the frequency spectrum of each of the received optical signals, estimates one or more zero-dispersion wavelengths in the optical transmission path using the calculated plurality of notch frequencies and chirp values ​​corresponding to the wavelengths of each of the plurality of optical signals, and determines information regarding a transmission wavelength to be used by a transmitter provided in at least the one or more opposing devices based on the estimated one or more zero-dispersion wavelengths and an amount of chromatic dispersion allowed in the system.

[0016] According to the present invention, it is possible to estimate the value of the zero-dispersion wavelength without using the values ​​of the dispersion slope and the optical fiber length.

[0017] FIG. 1 is a diagram illustrating an example of the configuration of an optical communication system according to a first embodiment. FIG. 2 is an explanatory diagram regarding a notch frequency used in the first embodiment. FIG. 3 is an explanatory diagram for deriving formula (1) and formula (2) shown in the first embodiment. FIG. 4 is a sequence diagram illustrating a processing flow in the optical communication system according to the first embodiment. FIG. 5 is a sequence diagram illustrating a processing flow in the optical communication system according to the first embodiment. FIG. 6 is a diagram illustrating an example of the configuration of an optical communication system according to a second embodiment. FIG. 7 is a diagram illustrating an example of the configuration of an optical communication system according to a third embodiment. FIG. 8 is an explanatory diagram for deriving formula (1). FIG. 9 is a diagram illustrating an example of penalty due to chromatic dispersion. FIG. 10 is a diagram illustrating an example of penalty due to chromatic dispersion. FIG. 11 is a diagram illustrating an example of penalty due to chromatic dispersion. FIG. 12 is a diagram illustrating an example of a wavelength range. FIG. 13 is a diagram illustrating a first example of the configuration for changing the transmission wavelength of a communication device. FIG. 14 is a diagram illustrating a second example of the configuration for changing the transmission wavelength of a communication device.

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] First Embodiment FIG. 1 is a diagram showing an example of the configuration of an optical communication system 10 according to a first embodiment. The optical communication system 10 includes a communication device 100A and a communication device 100B. The communication devices 100A and 100B perform optical communication via an optical transmission path. The optical transmission path is formed of an optical fiber. Note that the optical transmission path may be provided with one or more optical amplifiers that amplify optical signals. In this embodiment, the communication device 100A is an example of a transmitting device or a first communication device. The communication device 100B is an example of a receiving device or a second communication device.

[0020] The communication device 100A includes a signal processing unit 110A, a temperature controller 120A, a transmitting unit 130A, and a receiving unit 140A.

[0021] The receiver 140A receives the optical signal transmitted from the communication device 100B.

[0022] The signal processing unit 110A performs various signal processing on the optical signal received by the receiving unit 140A. Furthermore, the signal processing unit 110A sets the wavelength of the optical signal to be transmitted to the communication device 100B by the transmitting unit 130A. The signal processing unit 110A 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, in association with each wavelength. That is, the correspondence information includes information indicating the temperature of the laser corresponding to each wavelength, such as the wavelength λ １ Corresponding to the temperature T1 and wavelength λ ２ The temperature information includes information such as temperature T2 associated with the temperature T1. Note that this is just an example, and the temperature value is determined within a predetermined range.

[0023] Therefore, the signal processing unit 110A refers to the correspondence information to acquire temperature information corresponding to the wavelength used for communication, and sets the temperature controller 120A to the temperature indicated by the acquired temperature information. For example, when the signal processing unit 110A acquires information indicating a zero-dispersion wavelength from the communication device 100B, the signal processing unit 110A refers to the correspondence information to acquire temperature information corresponding to the wavelength specified by the acquired information indicating the zero-dispersion wavelength, and sets the temperature controller 120A to the temperature indicated by the acquired temperature information. In this way, the signal processing unit 110A sets the wavelength of the optical signal to be transmitted to the communication device 100B in the transmitting unit 130A.

[0024] The temperature controller 120A adjusts the temperature of the transmitting section 130A to the temperature set by the signal processing section 110A.

[0025] The transmitter 130A is, for example, a wavelength-tunable laser, and transmits an optical signal having a wavelength corresponding to the temperature adjusted by the temperature controller 120A. ａ and wavelength λ ｂ ) optical signal.

[0026] The communication device 100B includes a signal processing unit 110B, a temperature controller 120B, a transmitting unit 130B, and a receiving unit 140B.

[0027] The receiving unit 140B receives the optical signal transmitted from the communication device 100A. For example, the receiving unit 140B receives the optical signal of a different wavelength transmitted from the communication device 100A.

[0028] The signal processing unit 110B performs various signal processing on the optical signal received by the receiving unit 140B. Furthermore, the signal processing unit 110B estimates the zero-dispersion wavelength based on the received optical signals of different wavelengths. Specifically, the signal processing unit 110B calculates notch frequencies at which notches appear at frequencies other than multiples of the optical signal based on the frequency spectra of each of the received optical signals of different wavelengths. The notch frequencies are points at which the slope of the mean line of the frequency spectrum changes from negative to positive and are other than multiples of the frequency of the transmission signal from the opposing device (e.g., communication device 100A).

[0029] The received optical signals of different wavelengths each have a wavelength λ ａ and wavelength λ ｂ When the optical signal is of wavelength λ ａ Notch frequency f where a notch appears at a frequency other than double the frequency of the optical signal based on the frequency spectrum of the optical signal ｎ,ａ Furthermore, the signal processing unit 110B calculates the received wavelength λ ｂ Notch frequency f where a notch appears at a frequency other than double the frequency of the optical signal based on the frequency spectrum of the optical signal ｍ,ｂ where n and m are integers equal to or greater than 0. Notch frequency f ｎ,ａ That is, the wavelength λ ａ This refers to the (n+1)th notch frequency from the low frequency side in the frequency spectrum of the optical signal.

[0030] 2A and 2B are explanatory diagrams relating to the notch frequency used in the first embodiment. In Fig. 2, the horizontal axis represents frequency and the vertical axis represents power. In Fig. 2A, the wavelength λ ａ The notch frequency f calculated based on the optical signal ｎ,ａ In FIG. 2B, the wavelength λ ｂ The notch frequency f calculated based on the optical signal ｍ,ｂ is shown.

[0031] The signal processing unit 110B has a plurality of notch frequencies f ｎ,ａ and f ｍ,ｂ When calculating the frequency f, the spectrum data when the transmission signal is sent back-to-back (BtB) is stored in advance, and the difference with the spectrum after the optical transmission path (for example, the frequency spectrum of the received optical signal) is calculated to find the minimum value, thereby more accurately calculating the frequency f ｎ,ａ and f ｍ,ｂ The signal processing unit 110B may calculate the minimum value by taking the difference through the above process, and calculate a plurality of notch frequencies f ｎ,ａ and f ｍ,ｂThe above difference means the difference between dB, since the unit of the vertical axis is Power spectral density (dB / Hz). In addition, the signal processing unit 110B may calculate the first minimum value by dividing the first minimum value by a plurality of notch frequencies f ｎ,ａ and f ｍ,ｂ In this way, the signal processing unit 110B may estimate the frequency of the plurality of notch frequencies f ｎ,ａ and f ｍ,ｂ It is possible to estimate the notch frequency. As another method for determining the notch frequency, the signal processing unit 110B may, for example, calculate the average line of the frequency spectrum, determine the point where the slope changes from negative to positive, and determine the point where the slope becomes minimal at a frequency other than multiples of the frequency of the transmission signal as the notch frequency. Note that the method for determining the notch frequency is merely an example, and is not restrictive.

[0032] Furthermore, if the difference between the spectrum at BtB and the spectrum after fiber transmission is calculated in the reverse way (for example, BtB spectrum - spectrum after fiber transmission), a maximum value will be obtained. In the following explanation, it is assumed that the notch frequency is obtained at a minimum value (spectrum after transmission - BtB spectrum).

[0033] Furthermore, multiple notch frequencies f ｎ,ａ and f ｍ,ｂ As another method for obtaining the notch frequency f, the signal processing unit 110B may, for example, calculate the mean line of the frequency spectrum, find one or more points where the calculated slope changes from negative to positive, and, from among the one or more points found, identify frequency positions excluding multiples of the frequency of the transmission signal as a plurality of notch frequencies f ｎ,ａ and f ｍ,ｂ In this way, the signal processing unit 110B can calculate the multiple notch frequencies f ｎ,ａ and f ｍ,ｂ can be calculated.

[0034] The signal processing unit 110B calculates the plurality of notch frequencies f ｎ,ａ , f ｍ,ｂ and the multiple chirp values ​​α a , α b and a plurality of wavelengths λ based on the following equations (1) and (2), respectively.０ Calculate multiple wavelengths λ ０ is a wavelength that is a candidate for the zero-dispersion wavelength. ０ Among these, any wavelength λ ０ is the zero dispersion wavelength. The chirp value α a is the wavelength of the optical signal λ ａ The chirp value α is calculated in advance. ｂ is the wavelength of the optical signal λ ｂ The chirp value in the case of the wavelength λ between the communication device 100A and the communication device 100B is calculated in advance. ０ It is assumed that the different wavelengths used to calculate λ are determined. ａ and λ ｂ represents the wavelength of the transmission signal transmitted by the communication device 100A.

[0035]

[0036]

[0037] "A" and "B" shown in equations (1) and (2) are expressed as in equation (3) below.

[0038]

[0039] According to the above formulas (1) and (2), a maximum of two wavelengths λ ０ The signal processing unit 110B calculates the wavelength λ calculated by each of the formulas (1) and (2). ０ If the value of is outside the range of the zero dispersion wavelength of the optical fiber being used, the wavelength λ that is outside the range of the standard zero dispersion wavelength of the optical fiber being used ０ That is, the signal processing unit 110B excludes the wavelength λ 1 , which is outside the range of the zero-dispersion wavelength of the optical fiber being used, from the candidates of the wavelength to be used for communication. ０ Do not use the value of

[0040] The signal processing unit 110B calculates the wavelength λ based on, for example, equation (1). ０ The value of is wavelength λ ａ and wavelength λ ｂor the wavelength λ calculated based on equation (1) ０ The value of is wavelength λ ａ and wavelength λ ｂ If it is not greater than (e.g., (λ ａ >λ ０ and λ ｂ >λ ０ ) or (λ ａ <λ ０ and λ ｂ <λ ０ ) otherwise excluded).

[0041] Furthermore, the signal processing unit 110B calculates the wavelength λ based on, for example, equation (2). ０ The value of is wavelength λ ａ and the wavelength λ ｂ or the wavelength λ calculated based on equation (2) ０ The value of is wavelength λ ａ and the wavelength λ ｂ If it is not smaller than (e.g., (λ ａ >λ ０ and λ ｂ <λ ０ ) or (λ ａ <λ ０ and λ ｂ >λ ０ ) otherwise excluded).

[0042] When the optical fiber used is a standard single mode fiber, the signal processing unit 110B receives the signal at a wavelength λ ０ If the value of is outside the wavelength range of 1300 to 1324 nm, it will be excluded.

[0043] As described above, the wavelength λ calculated by each of the formulas (1) and (2) ０ If the value of does not satisfy the condition, the wavelength λ ０ In order to exclude the value of one wavelength λ ０ In the following explanation, the two wavelengths λ calculated by the formula (1) and the formula (2) are ０ In order to distinguish the values ​​of the first wavelength λ ０,１ , second wavelength λ ０,２ It may also be written as follows.

[0044] A detailed explanation for deriving the above-mentioned formulas (1) and (2) is shown in Fig. 3. As shown in Fig. 3, in the present invention, the distance L between the communication device 100A and the communication device 100B and the dispersion slope value S ０ is deleted as shown in equation (C) and is not used. By transforming equation (C) into equation (D), and transforming equation (D) into equation (E), equations (1) and (2) can finally be derived based on 1) to 4) shown on the right side of Figure 3. In this way, in the present invention, when estimating the value of the zero-dispersion wavelength, it is not necessary to use the value of the dispersion slope and the value of the optical fiber length.

[0045] The signal processing unit 110B transmits the calculated wavelength λ via the temperature controller 120B and the transmitting unit 130B. ０ The signal processing unit 110B causes the communication device 100A to transmit information indicating the value of the wavelength λ. ０ If there are two candidates for wavelength λ, ０ The communication device 100A transmits information indicating the value of .

[0046] Here, based on the above formulas (1) and (2), two candidates for zero dispersion wavelength (for example, the first wavelength λ ０,１ and the second wavelength λ ０,２ ) to one, the communication device 100B may narrow down the candidates for the zero-dispersion wavelength to one by the following method. ０,１ transmits information indicating the value of the first wavelength λ ０,１ The signal processing unit 110B receives an optical signal of the first wavelength λ from the communication device 100A. ０,１ From the frequency spectrum data of the optical signal f ｎ,ａ More specifically, the signal processing unit 110B checks whether a notch appears at the frequency of the first wavelength λ ０,１ In the frequency spectrum data of the optical signal, the n+1th notch frequency f ｎ,（０,１） is the wavelength λ ａ The n+1th notch frequency f in the spectrum data acquired (=first acquired) at ｎ,ａIs it not present at a lower frequency value or the first wavelength λ ０,１ In the frequency spectrum data of the optical signal, the notch is at wavelength λ ａ f obtained at (=first obtained) ０,ａ Check whether the lower frequency value is being output. ｎ,ａ If no notch appears at the frequency below λ , the signal processing unit 110B controls the transmitting unit 130B to transmit information indicating that the wavelength setting is correct (for example, notch appearance information (none)) to the communication device 100A as a low-speed signal. By receiving information indicating that the wavelength setting is correct (for example, notch appearance information (none)), the communication device 100A determines that the zero-dispersion wavelength is the first wavelength λ ０,１ It can be determined that this is the case.

[0047] On the other hand, f ｎ,ａ If a notch appears at the frequency below this, the signal processing unit 110B controls the transmitting unit 130B to transmit information that the wavelength setting is incorrect (for example, notch appearance information (present)) and information that the second wavelength λ ０,２ , and transmits information indicating that the zero-dispersion wavelength is the second wavelength λ ０,２ It can be determined that this is the case.

[0048] Like the signal processing unit 110A, the signal processing unit 110B holds correspondence information indicating the correspondence relationship between wavelength and temperature. By referring to the correspondence information, the signal processing unit 110B acquires temperature information corresponding to the wavelength used for communication, and sets the temperature controller 120B to the temperature indicated by the acquired temperature information.

[0049] The temperature controller 120B adjusts the temperature of the transmitting unit 130B to a set temperature.

[0050] The transmitter 130B is, for example, a wavelength-tunable laser, and transmits an optical signal with a wavelength corresponding to the temperature adjusted by the temperature controller 120B.

[0051] In the following description, the communication device 100A is the transmitting communication device, and the communication device 100B is the receiving communication device. As described above, the receiving communication device has not only a wavelength setting function but also a zero-dispersion wavelength estimation function in the signal processing unit. Note that the communication devices 100A and 100B have the same configuration, so the communication device 100A also has not only a wavelength setting function but also a zero-dispersion wavelength estimation function. Therefore, the communication device 100A can also estimate the zero-dispersion wavelength.

[0052] The communication device 100A receives the wavelength λ ０ The signal processing unit 110A receives information indicating the value of the wavelength λ 1 transmitted from the communication device 100B. ０ For example, the wavelength λ ０ as the first wavelength λ ０,１ When the signal processing unit 110A receives information indicating the first wavelength λ ０,１ and sets the temperature controller 120A so that the temperature is the temperature indicated by the temperature information, thereby changing the transmission wavelength of the optical signal transmitted by the transmitter 130A to the first wavelength λ ０,１ Change it to.

[0053] First wavelength λ ０,１ If no notch appears when the wavelength is changed to the first wavelength λ ０,１ The first wavelength λ ０,１ If a notch appears even when the wavelength is changed to ０ as the second wavelength λ ０,２ When the signal processing unit 110A receives information indicating the second wavelength λ ０,２ and sets the temperature controller 120A so that the temperature is the temperature indicated by the temperature information acquired, thereby changing the transmission wavelength of the optical signal transmitted by the transmitter 130A to the second wavelength λ ０,２ That is, the signal processing unit 110A changes the transmission wavelength of the optical signal to the first wavelength λ 2 transmitted from the communication device 100B. ０,１ and the second wavelength λ ０,２Either one of (for example, the first wavelength λ ０,１ ), if a notch appears, it is necessary to further change the other wavelength (for example, the second wavelength λ ０,２ ) to the transmission wavelength.

[0054] Next, a description will be given of the flow of processing in the optical communication system 10. Fig. 4 is a sequence diagram showing the flow of processing in the optical communication system 10 of the first embodiment.

[0055] The communication device 100A has a wavelength λ ａ Specifically, the signal processing unit 110A of the communication device 100A first determines the wavelength λ by referring to the correspondence information. ａ The signal processing unit 110A sets the temperature controller 120A so that the temperature is the temperature indicated by the temperature information. The temperature controller 120A adjusts the temperature of the transmitting unit 130A so that the temperature is the set temperature. As a result, the transmitting unit 130A transmits a signal having a wavelength λ ａ transmits an optical signal.

[0056] The data pattern on the transmitting side is not particularly limited, and may be, for example, a 01 signal or a PRBS (Pseudo-Random Binary Sequence) signal. The modulation method is also not particularly limited, and may be, for example, a NRZ (Non Return to Zero) signal or a PAM4 (Pulse Amplitude Modulation 4) signal. ａ The optical signal propagates through the optical transmission line and reaches the communication device 100B. The receiving unit 140B of the communication device 100B receives the optical signal propagating through the optical transmission line (step S102). The receiving unit 140B outputs the received optical signal to the signal processing unit 110B. The signal processing unit 110B calculates the notch frequency f based on the optical signal output from the receiving unit 140B. ｎ,ａ is calculated (step S103).

[0057] Thereafter, the communication device 100A receives a signal of wavelength λ ｂ Specifically, the signal processing unit 110A of the communication device 100A first determines the wavelength λ by referring to the correspondence information.ｂ The signal processing unit 110A sets the temperature controller 120A so that the temperature is the temperature indicated by the temperature information. The temperature controller 120A adjusts the temperature of the transmitting unit 130A so that the temperature is the set temperature. As a result, the transmitting unit 130A transmits a signal having a wavelength λ ｂ The process of step S104 may be performed at a time interval known to each of the communication devices 100A and 100B, such as when a predetermined time (e.g., 10 seconds) has elapsed since the start time of the process of step S101. Alternatively, communication may be performed by providing a low-speed control channel, a separate wavelength, or a separate line control that is different from the main signal. This can be achieved by the communication devices 100A and 100B having a function for reading high-speed, low-speed, or waveforms. The start timing and execution method of the process of step S104 described above are merely examples, and other start timings and execution methods may also be used.

[0058] The wavelengths used by the communication device 100A in the processes of steps S101 and S104 may be set in advance, and for example, two wavelengths may be selected from a plurality of wavelengths that can be output by the transmitter 130A. For the sake of simplicity, Fig. 4 shows a configuration in which the communication device 100A transmits optical signals of different wavelengths at different times, but the communication device 100A may also transmit optical signals of two wavelengths simultaneously.

[0059] The wavelength λ transmitted from the communication device 100A ｂ The optical signal propagates through the optical transmission line and reaches the communication device 100B. The receiving unit 140B of the communication device 100B receives the optical signal propagating through the optical transmission line (step S105). The receiving unit 140B outputs the received optical signal to the signal processing unit 110B. The signal processing unit 110B calculates the notch frequency f based on the optical signal output from the receiving unit 140B. ｍ,ｂ is calculated (step S106).

[0060] The signal processing unit 110B calculates the notch frequency f ｎ,ａ and notch frequency f ｍ,ｂ and multiple chirp values ​​α a , α band the wavelength λ is calculated based on the above equations (1) and (2). ０ (Step S107). Here, the wavelength λ calculated based on the above formula (1) is calculated. ０ The first wavelength λ ０,１ and the wavelength λ calculated based on the above formula (2) ０ The second wavelength λ ０,２ Let's say.

[0061] The signal processing unit 110B receives the first wavelength λ ０,１ and the second wavelength λ ０,２ It is determined whether each of the first wavelengths λ is within the range of the zero dispersion wavelength of the optical fiber used for transmission from the communication device 100A to the communication device 100B (step S108). ０,１ and the second wavelength λ ０,２ Let both be in range.

[0062] In this case, the signal processing unit 110B controls the transmitting unit 130B to transmit the first wavelength λ ０,１ or the second wavelength λ ０,２ First, the signal processing unit 110B controls the transmitting unit 130B to transmit information indicating either the first wavelength λ ０,１ The transmitter 130B causes the communication device 100A to transmit information indicating the first wavelength λ ０,１ The communication device 100A transmits information indicating the above (step S109).

[0063] The receiving unit 140A of the communication device 100A receives the first wavelength λ ０,１ The receiving unit 140A receives information indicating the received first wavelength λ ０,１ The signal processing unit 110A references the correspondence information and outputs information indicating the first wavelength λ output from the receiving unit 140A. ０,１ The first wavelength λ is specified by information indicating ０,１ The signal processing unit 110A sets the temperature controller 120A so that the temperature is the temperature indicated by the temperature information. As a result, the signal processing unit 110A sets the transmission wavelength to the first wavelength λ ０,１ (Step S111). After that, the transmitter 130A of the communication device 100A changes the first wavelength λ０,１ The optical signal is transmitted (step S112).

[0064] The receiving unit 140B of the communication device 100B receives the first wavelength λ ０,１ The receiving unit 140B receives the optical signal of the first wavelength λ (step S113). ０,１ The signal processing unit 110B outputs the optical signal of the first wavelength λ output from the receiving unit 140B to the signal processing unit 110B. ０,１ It is determined whether or not a notch has appeared based on the optical signal (step S114).

[0065] A case where it is determined in the process of step S114 that no notch has appeared will be described with reference to Fig. 5. Fig. 5 is a sequence diagram showing the flow of processes in the optical communication system 10 of the first embodiment.

[0066] If it is determined in the process of step S114 that a notch has not appeared, the signal processing unit 110B causes the transmitting unit 130B to transmit notch appearance information (none). The transmitting unit 130B transmits the notch appearance information (none) to the communication device 100A in response to an instruction from the signal processing unit 110B (step S201). The receiving unit 140A of the communication device 100A receives the notch appearance information (none) transmitted from the communication device 100B (step S202). In this case, the communication device 100A sets the transmission wavelength to the first wavelength λ ０,１ After that, the communication device 100A does not change the first wavelength λ ０,１ The optical signal is transmitted to the communication device 100B to perform communication with the communication device 100B (step S203).

[0067] A case where it is determined in the process of step S114 that a notch has appeared will be described with reference to Fig. 6. Fig. 6 is a sequence diagram showing the flow of processes in the optical communication system 10 of the first embodiment.

[0068] If it is determined in the process of step S114 that a notch has appeared, the signal processing unit 110B controls the transmitting unit 130B to transmit notch appearance information (present) and the second wavelength λ ０,２The notch appearance information (present) indicates that a notch has appeared. On the other hand, the notch appearance information (absent) indicates that a notch has not appeared. In response to an instruction from the signal processing unit 110B, the transmission unit 130B transmits the notch appearance information (present) and the second wavelength λ ０,２ The receiving unit 140A of the communication device 100A receives the notch appearance information (present) and the second wavelength λ transmitted from the communication device 100B and transmits the information indicating the notch appearance information (present) and the second wavelength λ transmitted from the communication device 100B to the communication device 100A (step S301). ０,２ The information indicating this is received (step S302).

[0069] The receiving unit 140A receives the notch appearance information (present) and the second wavelength λ ０,２ The signal processing unit 110B outputs information indicating the first wavelength λ ０,１ When it is determined that a notch has appeared in the second wavelength λ ０,２ The second wavelength λ specified by the information shown ０,２ The signal processing unit 110A sets the temperature controller 120A so that the temperature is the temperature indicated by the temperature information. As a result, the signal processing unit 110A sets the transmission wavelength to the second wavelength λ ０,２ (Step S303). After that, the transmitter 130A of the communication device 100A changes the second wavelength λ ０,２ The optical signal is transmitted (step S304).

[0070] The receiving section 140B of the communication device 100B receives the second wavelength λ ０,２ The receiving unit 140B receives the optical signal of the second wavelength λ (step S305). ０,２ The signal processing unit 110B outputs the optical signal of the second wavelength λ output from the receiving unit 140B to the signal processing unit 110B. ０,２ It is determined whether or not a notch has appeared based on the optical signal (step S306).

[0071] If it is determined in the process of step S306 that a notch has not appeared, the signal processing unit 110B causes the transmitting unit 130B to transmit notch appearance information (none). The transmitting unit 130B transmits the notch appearance information (none) to the communication device 100A in response to an instruction from the signal processing unit 110B (step S307). The receiving unit 140A of the communication device 100A receives the notch appearance information (none) transmitted from the communication device 100B (step S308). In this case, the communication device 100A sets the transmission wavelength to the second wavelength λ ０,２ After that, the communication device 100A does not change the second wavelength λ ０,２ The optical signal is transmitted to the communication device 100B to perform communication with the communication device 100B (step S309).

[0072] In the process of step S302 shown in FIG. 6, the communication device 100A receives notch appearance information (present) and the second wavelength λ ０,２ Since there are two candidates for the zero-dispersion wavelength, one of the wavelengths (for example, the first wavelength λ ０,１ ) if a notch appears (not the zero dispersion wavelength), the second wavelength λ indicated by the received information along with the notch appearance information (present) ０,２ is determined to be the correct value (zero dispersion wavelength). Therefore, the processes from step S305 onwards do not need to be performed.

[0073] In the above-described FIGS. 4 to 6, the communication device 100A transmits signals at different wavelengths λ ａ ,λ ｂ and the communication device 100B receives the optical signals of wavelength λ ａ ,λ ｂ Based on each optical signal of wavelength λ ０ However, the reverse configuration is also possible. That is, when the communication device 100B calculates a different wavelength λ ａ ,λ ｂ and the communication device 100A receives the optical signals of wavelength λ ａ ,λ ｂ Based on each optical signal of wavelength λ ０ In this case, the communication device 100A shown in FIGS. 4 to 6 may be replaced with the communication device 100B, and the communication device 100B may be replaced with the communication device 100A.

[0074] In the above-described FIGS. 4 to 6, the first wavelength λ ０,１ and the second wavelength λ ０,２ The case where both of the calculated first wavelength λ are within the range has been described as an example. ０,１ and the second wavelength λ ０,２ Depending on the value of , either one of the values ​​may be outside the range of the zero-dispersion wavelength of the optical fiber used for transmission from the communication device 100A to the communication device 100B. In such a case, the signal processing unit 110B detects the wavelength λ that is outside the range of the zero-dispersion wavelength of the optical fiber used for transmission from the communication device 100A to the communication device 100B. ０ is excluded from the candidates.

[0075] For example, in the process of step 108 of FIG. 4, the first wavelength λ ０,１ is within the range and the second wavelength λ ０,２ In this case, the signal processing unit 110B determines whether the second wavelength λ is outside the range. ０,２ After that, the signal processing unit 110B controls the transmitting unit 130B to exclude the first wavelength λ ０,１ The transmitter 130B causes the communication device 100A to transmit information indicating the first wavelength λ ０,１ In this case, the communication device 100A transmits information indicating the zero-dispersion wavelength to the first wavelength λ ０,１ Therefore, communication device 100B does not need to determine whether a notch has appeared, and communication is started between communication device 100A and communication device 100B.

[0076] According to the optical communication system 10 configured as described above, the communication devices 100A and 100B include a receiver 140A (140B) that receives multiple optical signals with different wavelengths from a counterpart device (communication device 100A or 100B) connected via an optical transmission line, and a signal processor 110A (110B) that calculates, for each of the multiple received optical signals, notch frequencies at which notches appear at frequencies excluding multiples of the frequency of the received optical signal based on the frequency spectrum of each of the multiple received optical signals, and calculates one or more zero-dispersion wavelengths in the optical transmission line using the calculated multiple notch frequencies and chirp values ​​corresponding to the wavelengths of each of the multiple optical signals. In this way, when calculating the zero-dispersion wavelength, the communication devices 100A and 100B do not use general dispersion slope values ​​(statistical values ​​such as minimum, maximum, and average values ​​specified in standardization) or fiber length values ​​for the dispersion slope. Therefore, it is possible to estimate the zero-dispersion wavelength of an optical fiber with a simple configuration. The communication devices 100A and 100B can then control the value of the transmission wavelength of their own device to approach the value of the zero-dispersion wavelength estimated by the opposing device, thereby making it possible to extend the transmission distance of the main signal.

[0077] Second Embodiment In the first embodiment, the case where the optical fiber connecting the communication devices has two cores has been described. In the second embodiment, the case where the optical fiber connecting the communication devices has one core will be described.

[0078] 7 is a diagram showing an example of the configuration of an optical communication system 20 according to the second embodiment. The optical communication system 20 includes a communication device 200A and a communication device 200B. The communication device 200A and the communication device 200B perform optical communication via an optical transmission path. In this embodiment, the communication device 200A is an example of a transmitting device or a first communication device. The communication device 200B is an example of a receiving device or a second communication device.

[0079] The communication devices 200A and 200B are equipped with a multiplexing / demultiplexing device that multiplexes or demultiplexes wavelengths, as shown in Fig. 7. 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.

[0080] The communication device 200A includes a signal processing unit 110A, a temperature controller 120A, a transmitting unit 130A, a receiving unit 140A, and a multiplexing / demultiplexing device 150A. The communication device 200B includes a signal processing unit 110B, a temperature controller 120B, a transmitting unit 130B, a receiving unit 140B, and a multiplexing / demultiplexing device 150B. By including the multiplexing / demultiplexing device 150A in the communication device 200A and the multiplexing / demultiplexing device 150B in the communication device 200B, a single-core, bidirectional configuration can be achieved.

[0081] The multiplexing / demultiplexing device 150A outputs the optical signal output from the transmitting section 130A to the optical transmission line, and outputs the optical signal transmitted from the optical transmission line to the receiving section 140A.

[0082] The multiplexing / demultiplexing device 150B outputs the optical signal output from the transmitting section 130B to the optical transmission line, and outputs the optical signal transmitted from the optical transmission line to the receiving section 140B.

[0083] In the following description, the communication device 200A is the transmitting communication device, and the communication device 200B is the receiving communication device. As described above, the receiving communication device has not only a wavelength setting function but also a zero-dispersion wavelength estimation function in the signal processing unit. Since the communication devices 200A and 200B have the same configuration, the communication device 200A also has not only a wavelength setting function but also a zero-dispersion wavelength estimation function. Therefore, the communication device 200A can also estimate the zero-dispersion wavelength.

[0084] Next, the processing performed by the optical communication system 20 differs from the optical communication system 10 in that processing by the multiplexing / demultiplexing device 150A and the multiplexing / demultiplexing device 150B is added to the communication between the communication devices 200A and 200B. For example, an optical signal transmitted from the transmitting unit 130A of the communication device 200A is output to the communication device 200B by the multiplexing / demultiplexing device 150A, and then output to the receiving unit 140B by the multiplexing / demultiplexing device 150B of the communication device 200B. Also, an optical signal transmitted from the transmitting unit 130B of the communication device 200B is transmitted to the communication device 200A by the multiplexing / demultiplexing device 150B, and then output to the receiving unit 140A by the multiplexing / demultiplexing device 150A of the communication device 200A.

[0085] According to the optical communication system 20 configured as above, the same effects as those of the first embodiment can be obtained even in a single-core bidirectional configuration.

[0086] (Variation 1) In the above-described embodiment, the communication device 200A and the communication device 200B have the same configuration, and therefore the signal processing unit 110A included in the communication device 200A and the signal processing unit 110B included in the communication device 200B both have both a function of setting a wavelength and a function of estimating a zero-dispersion wavelength. Here, the function of setting a wavelength is a function of controlling the temperature controller 120 to control the transmission wavelength of the transmitter 130. The function of estimating a zero-dispersion wavelength is a function of estimating the deviation Δλ from the zero-dispersion wavelength or the zero-dispersion wavelength.

[0087] When connected by a single optical fiber, the same path is used for transmission and reception, and the zero-dispersion wavelength is assumed to be the same. Therefore, it is sufficient for either the signal processing unit 110A or the signal processing unit 110B to have the function of estimating the zero-dispersion wavelength. For example, the signal processing unit 110B may have both the function of setting the wavelength and the function of estimating the zero-dispersion wavelength, and the signal processing unit 110A may have only the function of setting the wavelength (without the function of estimating the zero-dispersion wavelength). Conversely, the signal processing unit 110A may have both the function of setting the wavelength and the function of estimating the zero-dispersion wavelength, and the signal processing unit 110B may have only the function of setting the wavelength (without the function of estimating the zero-dispersion wavelength). In this configuration, the signal processing unit 110A or 110B may use the estimated zero-dispersion wavelength value to control the wavelengths of both the transmitter 130B included in its own device (communication device 200B) and the transmitter 130A included in the communication device 200A.

[0088] Here, an operation of the signal processing unit 110B controlling the wavelengths of both the transmitting unit 130B included in its own device (communication device 200B) and the transmitting unit 130A included in the communication device 200A will be described. The signal processing unit 110B, for example, controls the transmitting unit 130A to transmit information indicating the estimated zero-dispersion wavelength to the communication device 200A. As a result, the information indicating the zero-dispersion wavelength is transmitted to the communication device 200A. As a result, the wavelength of the transmitting unit 130A included in the communication device 200A can be controlled. Furthermore, the signal processing unit 110B references the correspondence information and acquires temperature information corresponding to the estimated zero-dispersion wavelength. The signal processing unit 110B sets the temperature controller 120B so that the temperature is the temperature indicated by the acquired temperature information. The temperature controller 120B adjusts the temperature of the transmitting unit 130B so that the temperature is the set temperature. This allows the signal processing unit 110A to control the transmission wavelength of the transmitting unit 130B included in its own device.

[0089] As another example, the signal processing unit 110B may have only the function of estimating the zero-dispersion wavelength (without the function of setting the wavelength), and the signal processing unit 110A may have only the function of setting the wavelength (without the function of estimating the zero-dispersion wavelength). Conversely, the signal processing unit 110B may have only the function of setting the wavelength (without the function of estimating the zero-dispersion wavelength), and the signal processing unit 110A may have only the function of estimating the zero-dispersion wavelength (without the function of setting the wavelength). In such a configuration, the signal processing unit 110A uses the value of the estimated zero-dispersion wavelength to control the wavelength of the transmitting unit 130B provided in the communication device 1100B, and the signal processing unit 110B uses the value of the estimated zero-dispersion wavelength to control the wavelength of the transmitting unit 130A provided in the communication device 1100A. As an example, in such a case, it is conceivable that the communication device 200A is transmitting a signal that is easily affected by chromatic dispersion, such as a high-speed signal, while the communication device 200B is transmitting a low-speed signal that is less affected by chromatic dispersion, or a high-speed signal that has been made less affected by chromatic dispersion by pre-compensation or multi-value conversion, etc.

[0090] As another example, the signal processing unit 110B may have both the function of setting a wavelength and the function of estimating a zero-dispersion wavelength, and the signal processing unit 110A may have neither the function of estimating a zero-dispersion wavelength nor the function of setting a wavelength (neither the function of setting a wavelength nor the function of estimating a zero-dispersion wavelength). Conversely, the signal processing unit 110B may have neither the function of estimating a zero-dispersion wavelength nor the function of setting a wavelength (neither the function of setting a wavelength nor the function of estimating a zero-dispersion wavelength), and the signal processing unit 110A may have both the function of setting a wavelength and the function of estimating a zero-dispersion wavelength. In such a configuration, the signal processing unit 110A or 110B controls the wavelength of the transmitter 130B provided in its own device using the value of the estimated zero-dispersion wavelength. As an example, in such a case, it is conceivable that the communication device 200A side transmits a relatively slow signal that is not easily affected by chromatic dispersion (a slow signal at which a notch appears), or a high-speed signal that has been made less susceptible to the effects of chromatic dispersion by pre-compensation or multi-value conversion, etc., and the communication device 200B side transmits a high-speed signal that can reduce the effects of chromatic dispersion by setting the wavelength.

[0091] Here, an example will be described in which the signal processing unit 110B of the communication device 200B has both the function of setting a wavelength and the function of estimating a zero-dispersion wavelength, and the signal processing unit 110A of the communication device 200A has neither the function of estimating a zero-dispersion wavelength nor the function of setting a wavelength (no function of setting a wavelength or estimating a zero-dispersion wavelength). The signal processing unit 110B controls the wavelength of the transmitting unit 130B provided in its own device using one of the values ​​of the zero-dispersion wavelength candidates (maximum of two candidates) estimated by the method described in the embodiment. The signal processing unit 110B first selects one of the wavelengths that are candidates for the zero-dispersion wavelength (for example, a first wavelength λ ０,１ The signal processing unit 110B selects the selected first wavelength λ ０,１ and transmits a first wavelength λ ０,１ The communication device 200A transmits an optical signal having the specified information to the communication device 200B. When the receiving unit 140A of the communication device 200A is able to receive the optical signal transmitted from the communication device 200B, the communication device 200A starts communication with the communication device 200B. Here, the case of successful reception refers to, for example, the case where the communication device 200A notifies the communication device 200B to transmit an optical signal with specific information within a specific time period in which a series of operations is possible, in which the communication device 200A transmits an optical signal to the communication device 200B, the communication device 200B estimates the zero-dispersion wavelength, the communication device 200B sets the estimated zero-dispersion wavelength in the transmitting unit 130B and oscillates, and the communication device 200A receives the optical signal, and the communication device 200B notifies the communication device 200A of the optical signal with the specified information within that specific time period. In this case, the communication device 200A transmits a low-speed signal or a high-speed signal that has been made less susceptible to the effects of chromatic dispersion by pre-compensation, multi-value conversion, or the like.

[0092] On the other hand, if the receiving unit 140A of the communication device 200A fails to receive the optical signal transmitted from the communication device 200B, the communication device 200A notifies the communication device 200B that it was unable to receive the signal. Here, a case where it was unable to receive the signal means, for example, a case where the communication device 200A notifies the communication device 200B to transmit an optical signal with certain information within a specific time period in which a series of operations is possible, in which the communication device 200A sends an optical signal to the communication device 200B, the communication device 200B estimates the zero-dispersion wavelength, the communication device 200B sets the estimated zero-dispersion wavelength in the transmitting unit 130B and oscillates, and the communication device 200A receives the signal, and the communication device 200A does not transmit an optical signal with the certain information from the communication device 1100B within that specific time period. In response to the notification that it was unable to receive the signal from the communication device 200A, the communication device 200B selects another candidate, the first wavelength λ ０,２ The optical signal is oscillated with the signal. After that, communication begins between communication device 200A and communication device 200B. The determination of whether or not reception is possible shown here is just an example, and the determination of whether or not reception is possible may be made by other methods, and the method is not important.

[0093] With this configuration, it is not necessary for both communication devices 200A and 200B to have the function of estimating the zero-dispersion wavelength. Therefore, it is possible to reduce the cost of communication devices 200 that do not have the function of estimating the zero-dispersion wavelength. Furthermore, it is possible to estimate the zero-dispersion wavelength in one communication device 200 (e.g., communication device 200B), and to control the wavelength used for communication by the transmitter 130 (e.g., transmitter 130B) included in the opposing communication device 200 (e.g., communication device 200A) and the transmitter 130 (e.g., transmitter 130A) included in the own device. This enables efficient communication.

[0094] Furthermore, as described above, the present invention can be applied even if one of the communication devices 200 does not have either the function of estimating the zero-dispersion wavelength or the function of setting the wavelength (it does not have either the function of setting the wavelength or the function of estimating the zero-dispersion wavelength).

[0095] (Modification 2) When one of the communication devices 200 (for example, the communication device 200B) controls the transmission wavelength of the communication device (for example, the communication device 200A) opposite to the own device (for example, the communication device 200B), it is desirable that the wavelength setting of the transmitter 130B included in the own device and the transmitter 130A included in the communication device 200A are slightly different. Therefore, the signal processing unit 110B controls the zero-dispersion wavelength λ ０ , and controls the transmission wavelength of the opposite communication device by transmitting information indicating the value of λ . Furthermore, the signal processing unit 110B refers to the correspondence information and calculates the zero-dispersion wavelength λ ０ Alternatively, the temperature controller 120B may be configured to control the transmission wavelength of the transmitter 130B by acquiring temperature information corresponding to a wavelength value obtained by adding a small value (for example, Δλ1) to the zero-dispersion wavelength λ. ０ The small value (for example, Δλ1) added to the zero dispersion wavelength λ may be a positive value or a negative value. ０ The wavelength value obtained by adding a small value (for example, Δλ1) to the wavelength is an example of information about the zero-dispersion wavelength.

[0096] Alternatively, the signal processing unit 110B controls the transmitting unit 130B to transmit the zero-dispersion wavelength λ ０ The signal processing unit 110B controls the transmission wavelength of the communication device 200A by transmitting information indicating a wavelength value obtained by adding a small value (for example, Δλ1) to the zero-dispersion wavelength λ ０ The temperature controller 120B may be configured to control the transmission wavelength of the transmitter 130B by acquiring temperature information corresponding to the temperature.

[0097] Note that the wavelength settings of the transmitter 130B included in the communication device 200B and the transmitter 130A included in the communication device 200A only need to be slightly different, so the following configuration may be used. Specifically, the signal processing unit 110B controls the transmitter 130B to set the zero-dispersion wavelength λ ０ The signal processing unit 110B controls the transmission wavelength of the opposing communication device by transmitting, to the communication device 200A, information indicating the wavelength value obtained by adding a small value (for example, Δλ1) to the zero-dispersion wavelength λ. ０Alternatively, the temperature controller 120B may be configured to control the transmission wavelength of the transmitter 130B by acquiring temperature information corresponding to a wavelength obtained by adding a small value (for example, Δλ2 (where Δλ1≠Δλ2)) to the zero-dispersion wavelength λ. ０ The small value (for example, Δλ2 (where Δλ1≠Δλ2)) added to may be a positive value or a negative value. The wavelength value obtained by adding a small value (for example, Δλ2) to the zero-dispersion wavelength is an example of information related to the zero-dispersion wavelength.

[0098] This configuration allows the communication devices 200A and 200B to use different wavelengths. As a result, even when simultaneous communications are performed over a single optical transmission line, the wavelengths are not mixed together, enabling efficient communications.

[0099] Third Embodiment In the second embodiment, communication devices are connected one-to-one (point-to-point). In the third embodiment, a configuration in which communication devices are connected one-to-multiple will be described.

[0100] 8 is a diagram showing an example of the configuration of an optical communication system 30 according to the third embodiment. The optical communication system 30 includes a communication device 200A, a communication device 200B, a communication device 200C, and an optical multiplexer / demultiplexer 300. The communication devices 200A, 200B, and 200C perform optical communication via an optical transmission path and the optical multiplexer / demultiplexer 300. In this embodiment, the communication devices 200A and 200C are examples of a transmitting device or a first communication device. The communication device 200B is an example of a receiving device or a second communication device.

[0101] In the following description, communication devices 200A and 200C are assumed to be transmitting-side communication devices, and communication device 200B is assumed to be a receiving-side communication device. As described above, the receiving-side communication device has not only a wavelength setting function but also a zero-dispersion wavelength estimation function in the signal processing unit. Note that communication devices 200A, 200B, and 200C have the same configuration, so communication devices 200A and 200C also have not only a wavelength setting function but also a zero-dispersion wavelength estimation function. Therefore, communication devices 200A and 200C can also estimate the zero-dispersion wavelength.

[0102] 8 illustrates a configuration in which communication device 200B is connected to two communication devices 200A and 200B, but communication device 200B may be connected to three or more communication devices 200. Communication device 200A and communication device 200B communicate with communication device 200B using a TDM (Time Division Multiplexing) method.

[0103] The communication device 200A and the communication device 200C perform the same processing as the communication device 200A in the second embodiment, except that they transmit optical signals at the timings assigned to them. ０ For example, the communication device 200B calculates the wavelength λ for the optical fiber from the communication device 200A to the communication device 200B. ０Ａ and wavelength λ for the optical fiber from the communication device 200A to the communication device 200C. ０Ｃ and can be calculated respectively.

[0104] The optical multiplexer / splitter 300 multiplexes the signals transmitted from the communication devices 200A and 200C and outputs the multiplexed signal to the communication device 200B. The optical multiplexer / splitter 300 splits the signal transmitted from the communication device 200B and outputs the split signal to the communication devices 200A and 200C.

[0105] The process performed by the signal processing unit 110B of the communication device 200B in the third embodiment will be specifically described. The signal processing unit 110B processes the wavelength λ 1 transmitted from the communication device 200A at time t1. ａＡ Notch frequency f where a notch appears at a frequency other than double the frequency of the optical signal based on the frequency spectrum of the optical signal ｎ,ａＡ Furthermore, the signal processing unit 110B calculates the wavelength λ transmitted from the communication device 200A at time t3. ｂＡ Notch frequency f where a notch appears at a frequency other than double the frequency of the optical signal based on the frequency spectrum of the optical signal ｍ,ｂＡ The signal processing unit 110B calculates the calculated multiple notch frequencies f ｎ,ａＡ , f ｍ,ｂＡand the multiple chirp values ​​α aＡ , α bＡ and the wavelength λ is calculated based on the above equations (1) and (2). ０ Calculate.

[0106] Chirp value α aＡ is the wavelength of the optical signal λ ａＡ The chirp value α is calculated in advance. bＡ is the wavelength of the optical signal λ bＡ The chirp value in the case of the wavelength λ calculated based on the above formula (1) is assumed to be calculated in advance. ０ The first wavelength λ ０,１Ａ and the wavelength λ calculated based on the above formula (2) ０ The second wavelength λ ０,２Ａ The signal processing unit 110B receives the first wavelength λ ０,１Ａ and the second wavelength λ ０,２Ａ It is determined whether each of these wavelengths is within the range of the zero dispersion wavelength of the optical fiber used for transmission from the communication device 100A to the communication device 100B.

[0107] Similarly, the signal processing unit 110B receives the wavelength λ 1 transmitted from the communication device 200C at time t2. ａＣ Notch frequency f where a notch appears at a frequency other than double the frequency of the optical signal based on the frequency spectrum of the optical signal ｎ,ａＣ Furthermore, the signal processing unit 110B calculates the wavelength λ transmitted from the communication device 200C at time t4. ｂＣ Notch frequency f where a notch appears at a frequency other than double the frequency of the optical signal based on the frequency spectrum of the optical signal ｍ,ｂＣ The signal processing unit 110B calculates the calculated multiple notch frequencies f ｎ,ａＣ , f ｍ,ｂＣ and the multiple chirp values ​​α aＣ , α bＣ and the wavelength λ is calculated based on the above equations (1) and (2). ０ Calculate.

[0108] Chirp value α aＣ is the wavelength of the optical signal λ ａＣThe chirp value α is calculated in advance. bＣ is the wavelength of the optical signal λ bＣ The chirp value in the case of the wavelength λ calculated based on the above formula (1) is assumed to be calculated in advance. ０ The first wavelength λ ０,１Ｃ and the wavelength λ calculated based on the above formula (2) ０ The second wavelength λ ０,２Ｃ The signal processing unit 110B receives the first wavelength λ ０,１Ｃ and the second wavelength λ ０,２Ｃ It is determined whether each of these wavelengths is within the range of the zero dispersion wavelength of the optical fiber used for transmission from the communication device 200C to the communication device 200B.

[0109] As described above, the communication device 200B uses the wavelength λ ０ Thereafter, the communication device 200B may execute the process shown in FIG.

[0110] According to the optical communication system 30 configured as above, it is possible to obtain the same effects as in the first embodiment even in a point-to-multipoint configuration using a time division multiplexing method.

[0111] (Modification) The optical communication system 30 may be modified in the same manner as Modification 1 and Modification 2 of the second embodiment. For example, in the optical communication system 30, the function of estimating the zero-dispersion wavelength may be provided by any one of the signal processing units 110A, 110B, and 110C.

[0112] (First to Third Embodiments) In the first to third embodiments described above, the signal processing units 110A and 110B calculate the wavelength λ based only on equation (1). ０ Here, the signal processing unit 110B will be described as an example, but the same applies to the signal processing unit 110A. When configured in this way, the signal processing unit 110B calculates the wavelength λ when "A" and "B" in equation (1) are in the patterns of the following equations (4) to (7). ０ That is, the signal processing unit 110B calculates the four wavelengths λ ０Here, the wavelength λ calculated using "A" and "B" shown in equation (4) is calculated. ０ The wavelength λ of pattern 1 ０ The wavelength λ is calculated using "A" and "B" shown in equation (5). ０ The wavelength λ of pattern 2 ０ The wavelength λ is calculated using "A" and "B" shown in equation (6). ０ The wavelength λ of pattern 3 ０ The wavelength λ is calculated using "A" and "B" shown in equation (7). ０ The wavelength λ of pattern 4 ０ Let's say.

[0113]

[0114]

[0115]

[0116]

[0117] Thereafter, the signal processing unit 110B calculates the wavelength λ of each pattern. ０ The signal processing unit 110B determines whether the wavelength λ of the pattern 1 satisfies the conditions in each of the formulas (4) to (7). ０ is the wavelength λ, which is the condition in equation (4). ａ and wavelength λ ｂ is smaller than S ０ L is greater than 0 (e.g., (λ ０ <λ ａ and λ ０ <λ ｂ and 0<S ０ Similarly, the signal processing unit 110B determines whether the wavelength λ of pattern 2 is satisfied. ０ is the wavelength λ, which is the condition in equation (5). ａ and wavelength λ ｂ is greater than S ０ L is greater than 0 (e.g., (λ ａ <λ ０ and λ ｂ <λ ０ and 0<S ０Similarly, the signal processing unit 110B determines whether the wavelength λ of pattern 3 is satisfied. ０ is the wavelength λ, which is the condition in equation (6). ａ and the wavelength λ ｂ is greater than S ０ L is greater than 0 (e.g., (λ ａ >λ ０ and λ ｂ <λ ０ and 0<S ０ Similarly, the signal processing unit 110B determines whether the wavelength λ of pattern 4 is satisfied. ０ is the wavelength λ, which is the condition in equation (7). ａ and the wavelength λ ｂ is smaller than S ０ L is greater than 0 (e.g., (λ ａ <λ ０ and λ ｂ >λ ０ and 0<S ０ L) is satisfied.

[0118] Here, the above S ０ is the dispersion slope, and for example, the value specified by standardization (for single-mode fiber, 0.092 [ps / km / nm ２ ]) or S that can be obtained by an existing estimation method ０ ×L, where L is the distance between the communication device 100A and the communication device 100B. ０ L is calculated based on the following formula (8): In the case of a system in which the upper limit of the distance L is determined, the determined upper limit L ｍａｘ [km] to S ０ L<0.092L ｍａｘ (i.e., 0<S ０ L<0.092L ｍａｘ ) is added to equations (4) to (7). For example, for distances less than 100 km, S ０The condition L<9.2 is added to each of equations (4) to (7). For example, the upper limit of the distance L can be determined based on the requirements of the transceiver used, the maximum transmission distance expected in the network configuration, etc. Note that this is just one example, and the upper limit of the distance L may be determined by other methods.

[0119]

[0120] The signal processing unit 110B calculates the wavelength λ of each pattern. ０ If the value of does not satisfy the conditions of the formulas (4) to (7) corresponding to each pattern (if it is outside the range of the formulas (4) to (7)), or if it is outside the range of the zero dispersion wavelength of the optical fiber being used, the calculated wavelength λ ０ Here, a detailed description will be given of the case where the conditions of the formulas (4) to (7) corresponding to each pattern are not satisfied. As described above, the signal processing unit 110B calculates the wavelength λ obtained in each pattern. ０ It is determined whether or not the conditions in each of the formulas (4) to (7) are satisfied.

[0121] The signal processing unit 110B detects the wavelength λ of the pattern 1. ０ If the condition in equation (4) is satisfied, the wavelength λ of pattern 1 ０ As a candidate for the zero-dispersion wavelength, the signal processing unit 110B determines the wavelength λ of pattern 1. ０ However, if the condition in equation (4) is not satisfied, the wavelength λ of pattern 1 ０ In this way, the signal processing unit 110B excludes the wavelength λ calculated based on the formula (1) using "A" and "B" shown in the formula (4). ０ Regarding (1), it is determined whether the condition in equation (4) is satisfied (regardless of the conditions in other equations) to determine whether or not the candidate for the zero-dispersion wavelength needs to be excluded.

[0122] Similarly, the signal processing unit 110B detects the wavelength λ of pattern 2. ０ If the condition in equation (5) is satisfied, the wavelength λ of pattern 2 ０ On the other hand, the signal processing unit 110B determines the wavelength λ of pattern 2 as a candidate for the zero-dispersion wavelength. ０ However, if the condition in equation (5) is not satisfied, the wavelength λ of pattern 2０ In this way, the signal processing unit 110B excludes the wavelength λ calculated based on the formula (1) using "A" and "B" shown in the formula (5). ０ Regarding (1), it is determined whether the condition in equation (5) is satisfied (regardless of the conditions in other equations) to determine whether or not the candidate for the zero-dispersion wavelength needs to be excluded.

[0123] Similarly, the signal processing unit 110B detects the wavelength λ of pattern 3. ０ If the condition in equation (6) is satisfied, the wavelength λ of pattern 3 ０ On the other hand, the signal processing unit 110B determines the wavelength λ of pattern 3 as a candidate for the zero-dispersion wavelength. ０ However, if the condition in equation (6) is not satisfied, the wavelength λ of pattern 3 ０ In this way, the signal processing unit 110B excludes the wavelength λ calculated based on the formula (1) using "A" and "B" shown in the formula (6). ０ Regarding (1), it is determined whether the condition in equation (6) is satisfied (regardless of the conditions in other equations) to determine whether or not the candidate for the zero-dispersion wavelength needs to be excluded.

[0124] Similarly, the signal processing unit 110B detects the wavelength λ of pattern 4. ０ If the condition in equation (7) is satisfied, the wavelength λ of pattern 4 ０ On the other hand, the signal processing unit 110B determines the wavelength λ of pattern 4 as a candidate for the zero-dispersion wavelength. ０ However, if the condition in equation (7) is not satisfied, the wavelength λ of pattern 4 ０ In this way, the signal processing unit 110B excludes the wavelength λ calculated based on the formula (1) using "A" and "B" shown in the formula (7). ０ Regarding (7), it is determined whether the condition in equation (7) is satisfied (regardless of the conditions in other equations) to determine whether or not the candidate for the zero-dispersion wavelength needs to be excluded.

[0125] As described above, the signal processing unit 110B calculates the wavelengths λ calculated for each pattern. ０ Among them, the wavelength λ that does not satisfy the conditions of the corresponding pattern ０In addition, when the optical fiber being used is a standard single mode fiber, the signal processing unit 110B excludes the wavelength λ from the candidates for the zero dispersion wavelength. ０ If the value of is outside the wavelength range of 1300 to 1324 nm, it will be excluded. The subsequent processing is the same as that performed in each embodiment. By performing such processing, the signal processing unit 110B determines the wavelength λ that is a candidate for the final zero-dispersion wavelength. ０ Determine.

[0126] A detailed explanation for deriving the above-mentioned formula (1) is shown in Fig. 9. As shown in Fig. 9, in the present invention, the distance L between the communication device 100A and the communication device 100B and the dispersion slope value S ０ is deleted and not used as shown in formula (C'). By transforming formula (C') into formula (D'), and then transforming formula (D') into formula (E'), formula (1) can finally be derived. In this way, in the present invention, when estimating the value of the zero-dispersion wavelength, it is not necessary to use the value of the dispersion slope and the value of the optical fiber length.

[0127] Fourth Embodiment In the first embodiment, a second communication device (for example, the communication device 100B) that communicates with a first communication device (for example, the communication device 100A) has a zero-dispersion wavelength value λ ０ The estimated zero-dispersion wavelength λ ０ (There is also a configuration in which the first communication device controls the oscillation wavelength of the transmitter of the second communication device.) However, the estimated zero-dispersion wavelength value λ ０ There is a possibility that the estimated zero-dispersion wavelength λ may deviate from the true value, and in such a case, it is assumed that the influence of chromatic dispersion may make long-distance transmission difficult. ０ The neighboring values ​​of λ ０ We will describe a configuration that reduces the effects of chromatic dispersion by notifying the first communication device of information indicating ±Δλ and controlling the oscillation wavelength of the transmitter of the first communication device (there is also a configuration in which the first communication device controls the oscillation wavelength of the transmitter of the second communication device).

[0128] The system configuration and the configuration of the functional units of each device in the fourth embodiment are the same as those in the first embodiment. The communication devices 100A and 100B in the fourth embodiment differ from the first embodiment in the configuration related to the estimation of the zero-dispersion wavelength. Therefore, the following description will focus on the differences from the first embodiment. Furthermore, since the communication devices 100A and 100B have the same functions, they basically perform the same processing. Therefore, the following description will focus on the configuration in which the communication device 100B controls the transmission wavelength of the transmitter 130A of the communication device 100A.

[0129] The value of Δλ described above may be within a range determined by the required conditions for the penalty due to chromatic dispersion in the system being used. For example, the values ​​of Δλ may be the same or different. When the communication devices 100A and 100B are connected by a two-core optical fiber, different optical fibers are used in the upstream direction (e.g., from the communication device 100A to the communication device 100B) and the downstream direction (e.g., from the communication device 100B to the communication device 100A).

[0130] Next, the value of Δλ will be described. The value of Δλ may be set to the tolerance of the penalty due to chromatic dispersion in the optical communication system 10, or to a value within the range of values ​​of the amount of chromatic dispersion permitted by the optical communication system 10. For example, if the tolerance of the penalty due to chromatic dispersion is 1 dB or less, the value of Δλ may be set to a value within the range of −5 to +3 nm as shown in FIG. 10. Note that the range shown in FIG. 10 is an example. The communication device 100B stores in advance data on graphs corresponding to the transmission distance in the optical communication system 10, the chirp value of the transmitter 130A used by the opposing communication device A, the signal speed, and the optical filter. Note that the same applies to the communication device 100A.

[0131] For example, if the allowable value of the penalty due to chromatic dispersion in a 40 km optical fiber system is −60 to 30 ps / nm, the value of Δλ is −60<DL=S as shown in FIG. ０ × L / (4(λ−λ ０ ４ / λ ３) × 40) < 30. Even if one or more wavelengths are used, pulse compression can be achieved and distance extension is also possible by using the minimum value or a value close to the minimum value in the graph of the penalty value due to chromatic dispersion. For example, in the example shown in Figure 11, distance extension is possible with a wavelength shifted by -1 nm from the zero-dispersion wavelength.

[0132] Next, a method for determining a transmission wavelength in the fourth embodiment will be described. ａ The receiving unit 140B of the communication device 100B receives the optical signal propagating through the optical transmission line. The receiving unit 140B outputs the received optical signal to the signal processing unit 110B. The signal processing unit 110B calculates the notch frequency f based on the optical signal output from the receiving unit 140B. ｎ－１,ａ For example, the signal processing unit 110B calculates the wavelength λ output from the receiving unit 140B. ａ The signal processing unit 110B generates a frequency spectrum from an optical signal of wavelength λ ａ The signal processing unit 110B generates a frequency spectrum for estimating the zero-dispersion wavelength by dividing the frequency spectrum of the optical signal f by the frequency spectrum of the BtB signal stored in advance (the spectrum intensity is expressed in dB, so the difference is expressed in dB). From the generated frequency spectrum, the signal processing unit 110B calculates the frequency f that appears as the n-th notch (minimum value) at a frequency other than the frequency multiple of the transmission signal. ｎ－１,ａ is the notch frequency f ｎ－１,ａ (For example, the first is the frequency f ０,ａ (This becomes.)

[0133] Next, the communication device 100A receives a signal of wavelength λ ｂ The receiving unit 140B of the communication device 100B receives the optical signal propagating through the optical transmission line. Here, the communication device 100B transmits an optical signal having a notch frequency f ｎ－１,ｂ It should be noted that a different wavelength (for example, wavelength λ ａ and wavelength λ ｂ ) may be obtained by any method other than that shown in the first embodiment.

[0134] Next, the signal processing unit 110B of the communication device 100B calculates the calculated notch frequency f ｎ－１,ａ and notch frequency f ｍ－１,ｂ and multiple chirp values ​​α a , α b and the wavelength λ is calculated based on the above equation (1). ０ At this time, the signal processing unit 110B calculates the wavelength λ for each pattern of the above-mentioned formulas (4) to (7). ０ That is, the signal processing unit 110B calculates the four wavelengths λ ０ Thereafter, the signal processing unit 110B calculates the calculated wavelength λ of each pattern. ０ It is determined whether or not the conditions in each of formulas (4) to (7) are satisfied. The process of determining whether or not the conditions in each of formulas (4) to (7) are satisfied has also been explained above, so a description thereof will be omitted.

[0135] Then, the signal processing unit 110B selects a wavelength λ that satisfies the condition. ０ , the speed of light c, and the wavelength λ ａ and wavelength λ ｂ Based on this, the wavelength range including the upper and lower limits of the amount of chromatic dispersion (=value of chromatic dispersion D × distance L) is calculated by using the following equations (9) and (10) to solve for λ. Note that "A" and "B" in equations (9) and (10) are wavelengths λ that satisfy the conditions. ０ For example, the wavelength λ ０ is a value calculated using the values ​​of "A" and "B" shown in formula (4), then "A" and "B" in formulas (9) and (10) are the values ​​of "A" and "B" shown in formula (4).

[0136]

[0137]

[0138] An example of the wavelength range when the system's tolerance for the penalty due to chromatic dispersion is -60 to 30 ps / nm is shown in Figure 13. The lower part of Figure 13 shows that when the system's tolerance for the penalty due to chromatic dispersion is -60 to 30 ps / nm, the wavelength range obtained based on the above-mentioned equations (9) and (10) is 1311 nm to 1315 nm. Note that the example shown in Figure 13 is just one example, and the wavelength range will vary depending on the wavelength used and the transmission distance.

[0139] The communication device 100B may transmit information indicating the wavelength range calculated based on the above-described formulas (9) and (10) to the communication device 100A as information regarding the transmission wavelength. Alternatively, the communication device 100B may transmit information indicating the wavelength range calculated based on the above-described formulas (9) and (10) to the communication device 100A as information regarding the transmission wavelength. ＵＳ Determine the wavelength λ ＵＳ In the first embodiment, information indicating the wavelength λ may be transmitted to the communication device 100A as information regarding the transmission wavelength. ＵＳ is the wavelength used for transmission from the communication device 100A to the communication device 100B when the communication device 100B is viewed as an upstream from the communication device 100A. ＵＳ When determining the wavelength λ, a value close to the center value of the wavelength corresponding to the wavelength range (the range between the upper and lower limits of the allowable value of the chromatic dispersion amount) is used. ＵＳ In the example shown in FIG. 13, the upper limit of the allowable value of the amount of chromatic dispersion is 1315 nm, and the lower limit is 1311 nm. Therefore, the signal processing unit 110B determines 1313 nm as the wavelength λ ＵＳ In this way, the penalty can be reduced to the utmost limit, and even longer distance transmission becomes possible.

[0140] As a method for transmitting information regarding the transmission wavelength to the opposing communication device 100 (e.g., the communication device 100A), for example, a low-speed control signal can be used. Also, by applying processing such as an equalizer at the signal processing point, it is possible to obtain information using a relatively high-speed signal. Furthermore, for a route for which the value of the zero-dispersion wavelength is known in advance, the communication device 100B can notify the information using a high-speed signal by setting the transmission wavelength to a value close to that value.

[0141] The receiver 140A of the communication device 100A receives the information about the transmission wavelength transmitted from the communication device 100B. The receiver 140A outputs the received information about the transmission wavelength to the signal processor 110A. The signal processor 110A references the correspondence information and outputs the wavelength λ 2 specified by the information about the transmission wavelength output from the receiver 140A. ＵＳ The signal processing unit 110A sets the temperature controller 120A so that the temperature is the temperature indicated by the temperature information. ＵＳ After that, the transmitter 130A of the communication device 100A changes the wavelength λ ＵＳ This initiates communication between the communication device 100A and the communication device 100B.

[0142] When the communication device 100B notifies information indicating a wavelength range as information regarding the transmission wavelength, the signal processing unit 110A of the communication device 100A selects the wavelength λ from the range between the upper limit and the lower limit of the allowable value of the chromatic dispersion amount specified by the information indicating the wavelength range. ＵＳ In this case, the signal processing unit 110A determines the wavelength λ as a value close to the center value of the wavelength corresponding to the wavelength range. ＵＳ Alternatively, the signal processing unit 110A may hold a list of values ​​of penalty due to chromatic dispersion for each amount of chromatic dispersion, find the value of the wavelength corresponding to the amount of chromatic dispersion that minimizes the penalty value, and determine a value near the found wavelength as the wavelength λ ＵＳ It may be determined as:

[0143] According to the optical communication system 10 of the fourth embodiment configured as described above, it is possible to control the transmission wavelength of the opposite device by taking into account the allowable value of the penalty due to chromatic dispersion, thereby making it possible to extend the transmission distance of the main signal.

[0144] Fifth Embodiment In the fifth embodiment, a configuration will be described in which the transmission wavelength control method shown in the fourth embodiment is applied to the second embodiment.

[0145] The system configuration and the configuration of the functional units of each device in the fifth embodiment are the same as those in the second embodiment. The communication devices 200A and 200B in the fifth embodiment differ from the second embodiment in the configuration related to estimating the zero-dispersion wavelength. Therefore, the following description will focus on the differences from the second embodiment. Furthermore, since the communication devices 200A and 200B have the same configuration, the communication device 200A also has not only a wavelength setting function but also a zero-dispersion wavelength estimation function. Therefore, the communication device 200A can also estimate the zero-dispersion wavelength. In the following description, as an example, a configuration in which the communication device 200B controls the transmission wavelength of the transmitter 130A of the communication device 200A will be described.

[0146] The communication device 200B has a zero-dispersion wavelength value λ ０ is estimated, and the value λ near the zero dispersion wavelength is ０ Information indicating ±Δλ is notified to the communication device 200A, and the oscillation wavelength of the transmitter 130A of the communication device 200A is controlled. The value of Δλ may be within a range determined by the required conditions for penalty due to chromatic dispersion in the system being used. As in the fifth embodiment, when the communication devices 200A and 200B are connected by a single optical fiber, the same optical fiber is used in the upstream direction (e.g., the direction from the communication device 200A to the communication device 200B) and the downstream direction (e.g., the direction from the communication device 200B to the communication device 200A). Therefore, the communication devices 200A and 200B must use different wavelengths, and therefore the values ​​of Δλ may be different. Note that the zero-dispersion wavelength value λ ０ and the neighborhood value λ ０ The wavelength interval of ±Δλ may be any interval as long as the signals do not interfere with each other. For example, when communicating using 50 Gbaud NRZ signals, it is desirable that the interval be 100 GHz or more.

[0147] Here, if only one of the communication devices 200A and 200B has the function of estimating the zero-dispersion wavelength, either the communication device 200A or the communication device 200B that has the function of estimating the zero-dispersion wavelength sets the wavelength of its own transmitter and notifies the opposing communication device 200B or 200A of information about the transmission wavelength using a low-speed control signal or a signal with the set wavelength. The opposing communication device 200B or 200A can set the wavelength of the transmitter 130 based on the notified information, thereby setting the wavelength near the zero-dispersion wavelength.

[0148] Next, a method for determining a transmission wavelength in the fifth embodiment will be described. The process up to the process of determining the wavelength range is the same as the process shown in the fourth embodiment. For example, when the communication device 200B controls the transmission wavelength of the transmitter 130A of the communication device 200A, the signal processor 110B of the communication device 200B determines the wavelength range based on the above-mentioned equations (9) and (10). Thereafter, the signal processor 110B determines the wavelength λ within the determined wavelength range. ＵＳ and wavelength λ ＤＳ In the second embodiment, the wavelength λ ＵＳ is a wavelength used for transmission from the communication device 200A to the communication device 200B when the communication device 200A views the communication device 200B as an upstream. ＤＳ is the wavelength used for transmission from the communication device 200B to the communication device 200A when the communication device 200A is viewed as downstream from the communication device 200B.

[0149] The communication device 200B transmits the determined wavelength λ ＤＳ is set as the transmission wavelength of the transmitter 130A, and the wavelength λ ＵＳThe communication device 200B transmits information indicating the wavelength range calculated based on the above-described formulas (9) and (10) to the communication device 200A as information regarding the transmission wavelength. Note that the communication device 200B may transmit information indicating the wavelength range calculated based on the above-described formulas (9) and (10) to the communication device 200A as information regarding the transmission wavelength. In this case, since the transmission wavelengths of the communication devices 200A and 200B must be different, the information regarding the transmission wavelength may include information indicating the wavelength range and information indicating the wavelength set in the communication device 200A. This allows the communication device 200A to know the wavelength set by the communication device 200B and to set a wavelength different from the wavelength set by the communication device 200B to the transmitter 130A.

[0150] As a method for transmitting information regarding the transmission wavelength to the opposing communication device 200 (e.g., communication device 200A), for example, a low-speed control signal can be used. Also, by applying processing such as an equalizer at the signal processing point, it is possible to obtain information using a relatively high-speed signal. Furthermore, for a route for which the value of the zero-dispersion wavelength is known in advance, the communication device 200B can notify the information using a high-speed signal by setting the transmission wavelength to a value close to that value.

[0151] The receiver 140A of the communication device 200A receives the information about the transmission wavelength transmitted from the communication device 200B. The receiver 140A outputs the received information about the transmission wavelength to the signal processor 110A. The signal processor 110A references the correspondence information and outputs the wavelength λ 2 specified by the information about the transmission wavelength output from the receiver 140A. ＵＳ The signal processing unit 110A sets the temperature controller 120A so that the temperature is the temperature indicated by the temperature information. ＵＳ After that, the transmitter 130A of the communication device 200A changes the wavelength λ ＵＳ This initiates communication between the communication device 200A and the communication device 100B.

[0152] When the communication device 200B notifies information indicating a wavelength range as information regarding the transmission wavelength, the signal processing unit 110A of the communication device 200A selects the wavelength λ set by the communication device 200B from the range between the upper limit and lower limit of the allowable value of the amount of chromatic dispersion specified by the information indicating the wavelength range. ＤＳ Excluding the wavelength λ ＵＳ In this case, the signal processing unit 110A determines the wavelength λ as a value close to the center value of the wavelength corresponding to the wavelength range. ＵＳ Alternatively, the signal processing unit 110A may hold a list of values ​​of penalty due to chromatic dispersion for each amount of chromatic dispersion, find the value of the wavelength corresponding to the amount of chromatic dispersion that minimizes the penalty value, and determine a value near the found wavelength as the wavelength λ ＵＳ It may be determined as:

[0153] In the above description, a configuration has been shown in which communication device 200B controls the transmission wavelengths of transmitter 130B of its own device and transmitter 130A of communication device 200A, but since communication device 200A and communication device 200B have the same configuration, communication device 200A may control the transmission wavelengths of transmitter 130A of its own device and transmitter 130B of communication device 200B. The specific processing is as described above.

[0154] According to the optical communication system 20 of the fifth embodiment configured as described above, even in a configuration in which simultaneous communications are performed over a single optical transmission line, the transmission wavelength of the opposite device can be controlled taking into account the allowable value of the penalty due to chromatic dispersion, thereby making it possible to extend the transmission distance of the main signal.

[0155] The optical communication system 20 in the fifth embodiment may be modified in the same manner as the second embodiment.

[0156] Sixth Embodiment In the sixth embodiment, a configuration will be described in which the transmission wavelength control method shown in the fourth embodiment is applied to the third embodiment.

[0157] The system configuration and the configuration of the functional units of each device in the sixth embodiment are the same as those in the third embodiment. The communication devices 200A to 200C in the sixth embodiment differ from the third embodiment in the configuration related to the estimation of the zero-dispersion wavelength. Therefore, the following explanation will focus on the differences from the third embodiment. Furthermore, since the communication devices 200A to 200C have the same configuration, the communication devices 200A to 200C also have not only the wavelength setting function but also the function of estimating the zero-dispersion wavelength. Therefore, the communication devices 200A to 200C can also estimate the zero-dispersion wavelength. In the following explanation, as an example, a configuration will be described in which the communication device 200B controls the transmission wavelengths of the transmitter 130A of the communication device 200A and the transmitter 130C of the communication device 200C.

[0158] The communication device 200B performs the same processing as the communication device 200B in the fifth embodiment, except that it calculates wavelength ranges for each of the communication devices 200A and 200C. For example, the communication device 200B determines a wavelength range as shown in the second embodiment based on optical signals of different wavelengths transmitted from the communication device 200A, and determines a wavelength range as shown in the second embodiment based on optical signals of different wavelengths transmitted from the communication device 200C. Note that if the distances from the communication devices 200A and 200C to the optical multiplexer / demultiplexer 300 are sufficiently shorter than the distance from the optical multiplexer / demultiplexer 300 to the communication device 200B, the same zero-dispersion wavelength value may be set.

[0159] The processing performed by the signal processing unit 110B of the communication device 200B in the sixth embodiment will be specifically described. The signal processing unit 110B calculates the wavelength λ corresponding to the communication device 200A based on the optical signals of different wavelengths transmitted from the communication device 200A at different times. ０ The wavelength λ corresponding to the communication device 200A is calculated. ０ The method of calculating the wavelength λ corresponding to the communication device 200C is the same as in the fifth embodiment. ０ The wavelength λ corresponding to the communication device 200C is calculated. ０The calculation method is the same as in the fifth embodiment.

[0160] As described above, the communication device 200B uses the wavelength λ ０ After that, the communication device 200B calculates the wavelength λ of each communication device 200. ０ The wavelength range is determined for each communication device 200 by the method shown in the fifth embodiment using the above formula, and the transmission wavelength is determined.

[0161] According to the optical communication system 30 of the sixth embodiment configured as described above, it is possible to control the transmission wavelength of the opposite device by taking into account the allowable value of the penalty due to chromatic dispersion even in a point-to-multipoint configuration using the time division multiplexing method, thereby making it possible to extend the transmission distance of the main signal.

[0162] The optical communication system 30 in the sixth embodiment may be modified in the same manner as the modified example 1 and the modified example 2 of the second embodiment. For example, in the optical communication system 30, the function of estimating the zero-dispersion wavelength may be provided by any one of the signal processing units 110A, 110B, and 110C.

[0163] (Modification 1 common to the first to sixth embodiments) In the above-described embodiments, the communication devices 100A, 100B, 200A, 200B, and 200C each change the transmission wavelength of the transmitter 130A, 130B, or 130C using the temperature controller 120A, 120B, or 120C. However, the configuration for changing the transmission wavelength in each of the communication devices 100A, 100B, 200A, 200B, or 200C is not limited to this. For example, the configuration for changing the transmission wavelength in each of the communication devices 100A, 100B, 200A, 200B, or 200C may be the configuration shown in FIG. 14 or 15. FIG. 14 is a diagram illustrating a first example configuration for changing the transmission wavelength of the communication devices 100A, 100B, 200A, 200B, or 200C. In FIG. 14, the communication device 100A will be described as an example, but the same applies to the communication devices 100A, 100B, 200A, 200B, and 200C.

[0164] The communication device 100A includes a signal processing unit 110A, a transmitting unit 130A, a receiving unit 140A, and a current controller 160A. The communication device 100A shown in Fig. 14 differs in configuration from the communication device 100A shown in Fig. 1 in that it includes a current controller 160A instead of the temperature controller 120A. The following description will focus on the differences from the communication device 100A shown in Fig. 1.

[0165] The signal processing unit 110A performs various signal processing on the optical signal received by the receiving unit 140A. Furthermore, the signal processing unit 110A sets the wavelength of the optical signal to be transmitted to the communication device 100B by the transmitting unit 130A. The signal processing unit 110A holds correspondence information indicating the correspondence relationship between wavelength and current. This correspondence information, for example, associates each wavelength with information indicating the current to be applied to the corresponding laser. That is, the correspondence information includes the wavelength λ １ Corresponding to the current C １ , wavelength λ ２ Corresponding to the current C ２ The information includes the following. Note that this is just an example, and the current value is determined within a predetermined range.

[0166] Therefore, the signal processing unit 110A refers to the correspondence information to obtain current information corresponding to the wavelength used for communication, and sets the current controller 160A to the current indicated by the obtained current information. For example, when the signal processing unit 110A obtains information indicating a zero-dispersion wavelength from the communication device 100B, the signal processing unit 110A refers to the correspondence information to obtain current information corresponding to the wavelength specified by the obtained information indicating the zero-dispersion wavelength, and sets the current controller 160A to the current indicated by the obtained current information. In this way, the signal processing unit 110A sets the wavelength of the optical signal to be transmitted to the communication device 100B in the transmitting unit 130A.

[0167] The current controller 160A applies a current value set by the signal processing unit 110A to the transmitting unit 130A. The transmitting unit 130A is, for example, a wavelength-tunable laser, and transmits an optical signal with a wavelength corresponding to the current value.

[0168] FIG. 15 is a diagram showing a second configuration example for changing the transmission wavelength of the communication devices 100A, 100B, 200A, 200B, and 200C. While FIG. 15 uses the communication device 100A as an example, the same applies to the communication devices 100A, 100B, 200A, 200B, and 200C. The communication device 100A includes a signal processing unit 110A, a receiving unit 140A, an array laser 180A, and a multiplexer 190A. The communication device 100A shown in FIG. 15 differs from the communication device 100A shown in FIG. 1 in that the communication device 100A includes the array laser 180A and the multiplexer 190A instead of the temperature controller 120A and the transmitting unit 130A. The following description will focus on the differences from the communication device 100A shown in FIG. 1.

[0169] The signal processing unit 110A performs various signal processing on the optical signal received by the receiving unit 140A. Furthermore, the signal processing unit 110A selects an oscillation laser corresponding to a desired wavelength and sets the array laser 180A so that a signal is output from the selected oscillation laser. Note that the desired wavelength is preferably a zero-dispersion wavelength, but it is possible that no laser corresponding to the value of the zero-dispersion wavelength exists. Therefore, if there is no laser corresponding to the value of the zero-dispersion wavelength, the signal processing unit 110A may select a laser with a value closest to the value of the zero-dispersion wavelength. The array laser 180A has a wavelength λ １ From λ ｐ (p is an integer of 1 or more). The array laser 180A drives the set oscillation lasers to output optical signals. The multiplexer 190A multiplexes optical signals of one or more wavelengths output from the array lasers 180A. The multiplexer 190A outputs the multiplexed optical signal to an optical transmission path.

[0170] 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).

[0171] (Modification 2 common to the first to sixth embodiments) In the above-described embodiments, the zero dispersion wavelength λ ０The communication device that estimated the zero-dispersion wavelength λ (for example, the communication device 100B in FIG. 1, the communication device 200B in FIGS. 7 and 8) sends the zero-dispersion wavelength λ to the opposite communication device (for example, the communication device 100A in FIG. 1, the communication device 200A in FIG. 7, the communication devices 200A and 200C in FIG. 8). ０ In contrast, the zero-dispersion wavelength λ ０ The communication device that estimates the zero dispersion wavelength λ ０ Based on this, the deviation amount Δλ (for example, Δλ = λ ０ -λ ａ The zero-dispersion wavelength λ may be estimated, and information indicating the estimated deviation Δλ may be transmitted to the opposite communication device. ０ The case where the communication device that estimated the zero dispersion wavelength λ is the communication device 100B will be described. ０ The same applies to any communication device that has the function of estimating the above.

[0172] The signal processing unit 110B included in the communication device 100B calculates the estimated zero-dispersion wavelength λ ０ Then, the signal processing unit 110B transmits information indicating the estimated shift amount Δλ to the opposing communication device via the temperature controller 120B and the transmission unit 130B. The opposing communication device receives the information indicating the shift amount Δλ transmitted from the communication device 100B. The signal processing unit 110 of the opposing communication device estimates the zero-dispersion wavelength (for example, the zero-dispersion wavelength λ ) based on the received shift amount Δλ. ａ +Δλ or λ ａ The signal processing unit 110 of the opposite communication device references the correspondence information and estimates the estimated zero-dispersion wavelength λ ａ +Δλ or λ ａ -Δλ. The opposing communication device sets the temperature controller 120A so that the temperature is the temperature indicated by the temperature information. As a result, the opposing communication device adjusts the transmission wavelength to the zero-dispersion wavelength λ ａ +Δλ or λ ａ Change it to -Δλ.

[0173] When transmitting information indicating the estimated shift amount Δλ to the opposing communication device, the signal processing unit 110B may transmit information indicating one of the estimated shift amounts Δλ (for example, the shift amount +Δλ). In this case, the opposing communication device receives the information indicating the shift amount (+Δλ) transmitted from the communication device 100B. Based on the received shift amount (+Δλ), the opposing communication device determines the zero-dispersion wavelength (for example, the zero-dispersion wavelength λ ａ The opposite communication device references the corresponding information and estimates the estimated zero-dispersion wavelength λ ａ +Δλ. The opposing communication device sets the temperature controller 120A so that the temperature is the temperature indicated by the temperature information. As a result, the opposing communication device adjusts the transmission wavelength to the zero-dispersion wavelength λ ａ After that, the opposite communication device changes the zero dispersion wavelength λ ａ An optical signal of +Δλ is transmitted.

[0174] The communication device 100B detects the zero-dispersion wavelength λ propagated through the optical transmission line. ａ +Δλ optical signal is received, and the received zero dispersion wavelength λ ａ Based on the optical signal +Δλ, it is determined whether a notch has appeared. If it is determined that a notch has not appeared, the communication device 100B transmits notch appearance information (none) to the opposing communication device. In order to receive the notch appearance information (none) transmitted from the communication device 100B, the opposing communication device changes the transmission wavelength to the zero-dispersion wavelength λ ａ Do not change it as +Δλ.

[0175] On the other hand, if it is determined that a notch has appeared, the communication device 100B transmits information indicating notch appearance (present) and the amount of deviation (-Δλ) to the opposing communication device. The opposing communication device receives the information indicating the amount of deviation (-Δλ) and the notch appearance information (present), and determines whether the zero-dispersion wavelength (for example, the zero-dispersion wavelength λ ａ Then, the opposite communication device estimates the transmission wavelength to be the zero-dispersion wavelength λ ａ The signal processing unit 110B may change the estimated zero-dispersion wavelength (for example, the zero-dispersion wavelength λ ａ +Δλ or λ ａ-Δλ), the transmission wavelength of the transmitter 130B of the communication device 100B may be controlled based on the information indicating the wavelength difference Δλ.

[0176] (Modification 3 common to the first to sixth embodiments) In each of the above-described embodiments, the transmitting communication device 100 may simultaneously transmit optical signals of two wavelengths to the receiving communication device 100. In such a configuration, the transmitting communication device 100 includes two or more transmitters 130, and the receiving communication device includes two or more receivers 140. Furthermore, the receiving communication device 100 includes an optical filter (a tunable filter that is set to cut one wavelength and allow the other wavelength to pass) in front of each receiver 140. This allows the receiving communication device 100 to receive optical signals of two wavelengths transmitted through the same optical fiber using different receivers 140.

[0177] In the above-described embodiment, the signal processing units 110A, 110B, and 110C may be configured using a processor such as a CPU (Central Processing Unit) and a memory. In this case, the signal processing units 110A, 110B, and 110C function as the signal processing units 110A, 110B, and 110C by the processor executing a program. Note that all or part of the functions of the signal processing units 110A, 110B, and 110C may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0178] The above program may be recorded on a computer-readable recording medium. Examples of the computer-readable recording medium include portable media such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, and a semiconductor storage device (e.g., an SSD (Solid State Drive)), and storage devices such as a hard disk or semiconductor storage device built into a computer system. The above program may be transmitted via a telecommunications line.

[0179] Although an embodiment of the present invention has been described above in detail 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.

[0180] The present invention is applicable to an optical communication system that performs communication via an optical transmission line.

[0181] 10, 20, 30... Optical communication system, 100A, 100B, 200A, 200B, 200C... Communication device, 110A, 110B, 110C... Signal processing unit, 120A, 120B, 120C... Temperature controller, 130A, 130B, 130C... Transmitting unit, 140A, 140B, 140C... Receiving unit, 150A, 150B, 150C... Multiplexing / demultiplexing device, 160A... Current controller, 170A... Wavelength tunable laser, 180A... Array laser, 190A... Multiplexer, 300... Optical multiplexer / demultiplexer

Claims

1. A receiving device comprising: a receiving unit that receives a plurality of optical signals having different wavelengths transmitted from one or more opposing devices connected via an optical transmission line; and a signal processing unit that calculates, for each received optical signal, a notch frequency at which a notch appears at a frequency excluding a multiple of the frequency of the received optical signal based on the frequency spectrum of each of the plurality of received optical signals, and estimates one or more zero-dispersion wavelengths in the optical transmission line using the calculated plurality of notch frequencies and the chirp values corresponding to the wavelengths of the plurality of optical signals.

2. The receiving device according to claim 1, wherein the signal processing unit excludes, from candidates for wavelengths to be used for communication, the one or more zero-dispersion wavelengths among the estimated one or more zero-dispersion wavelengths that are outside the range of the standard zero-dispersion wavelength of the optical transmission line used for communication with the one or more opposing devices.

3. The receiving device according to claim 1 or 2, further comprising a transmitting unit that transmits setting information including values related to the one or more zero-dispersion wavelengths to the one or more opposing devices.

4. The receiving device according to claim 1 or 2, wherein the signal processing unit controls a transmission wavelength used by a transmitting unit that communicates with the one or more opposing devices based on the estimated one or more zero-dispersion wavelengths.

5. The receiving device according to claim 1 or 2, wherein the signal processing unit estimates a plurality of zero-dispersion wavelengths based on different mathematical formulas, and excludes, from candidates for wavelengths to be used for communication, the zero-dispersion wavelengths among the estimated plurality of zero-dispersion wavelengths that do not satisfy the conditions defined in the mathematical formula used for the estimation.

6. The signal processing unit excludes, from candidates for wavelengths to be used for communication, a first zero-dispersion wavelength estimated based on a first mathematical formula among the plurality of zero-dispersion wavelengths when the first zero-dispersion wavelength is smaller than the first wavelength and the second wavelength of each of the plurality of optical signals and the product of the dispersion slope and the distance between devices is not greater than 0; excludes, from candidates for wavelengths to be used for communication, a second zero-dispersion wavelength estimated based on a second mathematical formula among the plurality of zero-dispersion wavelengths when the second zero-dispersion wavelength is greater than the first wavelength and the second wavelength and the product of the dispersion slope and the distance between devices is not greater than 0; excludes, from candidates for wavelengths to be used for communication, a third zero-dispersion wavelength estimated based on a third mathematical formula among the plurality of zero-dispersion wavelengths when the third zero-dispersion wavelength is smaller than the first wavelength, greater than the second wavelength, and the product of the dispersion slope and the distance between devices is not greater than 0; and excludes, from candidates for wavelengths to be used for communication, a fourth zero-dispersion wavelength estimated based on a fourth mathematical formula among the plurality of zero-dispersion wavelengths when the fourth zero-dispersion wavelength is greater than the first wavelength, smaller than the second wavelength, and the product of the dispersion slope and the distance between devices is not greater than 0. The receiving apparatus according to claim 5.

7. The signal processing unit determines the final one or more zero-dispersion wavelengths based on the first to fourth conditions to which a condition that the product of the dispersion slope and the distance between devices is smaller than the product of the upper limit value and the dispersion slope is added when the upper limit value of the distance between devices is predetermined. The receiving apparatus according to claim 6.

8. The signal processing unit determines information regarding a transmission wavelength used by a transmission unit included in at least the one or more opposing devices based on the estimated one or more zero-dispersion wavelengths and the wavelength dispersion amount allowed in the system. The receiving apparatus according to claim 1 or 2.

9. The signal processing unit determines, as the information regarding the transmission wavelength, information indicating a transmission wavelength used by a transmission unit included in at least the one or more opposing devices or a wavelength range for determining the transmission wavelength. The receiving apparatus according to claim 8.

10. A transmitting apparatus in an optical communication system including a transmitting apparatus and a receiving apparatus, the transmitting apparatus comprising: a transmitting unit that transmits a plurality of optical signals having different wavelengths to the receiving apparatus via an optical transmission line; and a signal processing unit that controls a transmission wavelength used by the transmitting unit according to a value related to one or more zero-dispersion wavelengths in the optical transmission line, the value being calculated based on a plurality of notch frequencies at which notches appear at frequencies excluding multiples of the frequencies of the plurality of optical signals respectively, based on the frequency spectra of the plurality of optical signals, and chirp values corresponding to the wavelengths of the plurality of optical signals respectively.

11. A transmitting apparatus in an optical communication system including a transmitting apparatus and a receiving apparatus, the transmitting apparatus comprising: a transmitting unit that transmits a plurality of optical signals having different wavelengths to the receiving apparatus via an optical transmission line; and a signal processing unit that controls a transmission wavelength used by the transmitting unit using information regarding the transmission wavelength used by the transmitting unit, the information being determined based on a plurality of notch frequencies at which notches appear at frequencies excluding multiples of the frequencies of the plurality of optical signals respectively, based on the frequency spectra of the plurality of optical signals, chirp values corresponding to the wavelengths of the plurality of optical signals respectively, one or more zero-dispersion wavelengths in the optical transmission line, and a wavelength dispersion amount allowed in the system.

12. An optical communication system comprising one or more first communication devices and a second communication device connected via an optical transmission line, wherein the one or more first communication devices include: a transmission unit that transmits a plurality of optical signals having different wavelengths to the second communication device via the optical transmission line; a reception unit that receives setting information including values related to one or more zero-dispersion wavelengths in the optical transmission line from the second communication device; and a signal processing unit that controls a transmission wavelength used by the transmission unit according to the values related to the one or more zero-dispersion wavelengths indicated by the setting information received by the reception unit. The second communication device includes: a reception unit that receives a plurality of optical signals having different wavelengths transmitted from the one or more first communication devices; a signal processing unit that calculates, for each received optical signal, a notch frequency at which a notch appears at a frequency excluding a multiple of the frequency of the received optical signal based on the frequency spectrum of each of the plurality of received optical signals, and estimates the one or more zero-dispersion wavelengths using the calculated plurality of notch frequencies and the chirp values corresponding to the wavelengths of the plurality of optical signals; and a transmission unit that transmits setting information including the calculated values related to the one or more zero-dispersion wavelengths to the one or more first communication devices.

13. An optical communication system including a first communication device and a second communication device, wherein the first communication device includes: a first receiving unit that receives an optical signal having a wavelength that is a candidate for one or more zero-dispersion wavelengths transmitted from the second communication device; and a first transmitting unit that transmits a plurality of optical signals having different wavelengths to the second communication device, or transmits an optical signal to the second communication device when the optical signal having a wavelength that is a candidate for one or more zero-dispersion wavelengths is received by the first receiving unit. The second communication device includes: a second receiving unit that receives a plurality of optical signals having different wavelengths from the first communication device; a second signal processing unit that calculates, for each received optical signal, a notch frequency at which a notch appears at a frequency excluding a multiple of the frequency of the received optical signal based on the frequency spectrum of each of the plurality of received optical signals, estimates one or more candidates for zero-dispersion wavelengths in the optical transmission path using the calculated plurality of notch frequencies and the chirp values corresponding to the wavelengths of the plurality of optical signals, and sets the wavelengths that are candidates for the one or more zero-dispersion wavelengths; and a second transmitting unit that transmits an optical signal having a wavelength that is a candidate for the one or more zero-dispersion wavelengths set by the second signal processing unit to the first communication device.

14. An optical communication system comprising one or more first communication devices and a second communication device connected via an optical transmission line, wherein the one or more first communication devices include: a transmission unit that transmits a plurality of optical signals having different wavelengths to the second communication device via the optical transmission line; and a signal processing unit that controls the transmission wavelength used by the transmission unit by using information regarding the transmission wavelength used by the transmission unit, which is determined based on one or more zero-dispersion wavelengths in the optical transmission line and the wavelength dispersion amount allowed in the system. The second communication device includes: a reception unit that receives a plurality of optical signals having different wavelengths transmitted from the one or more first communication devices; a signal processing unit that estimates the one or more zero-dispersion wavelengths based on a plurality of notch frequencies at which notches appear at frequencies excluding multiples of the frequencies of the received optical signals, based on the frequency spectra of the plurality of received optical signals, and based on the chirp values corresponding to the wavelengths of the plurality of optical signals, and determines information regarding the transmission wavelength used by at least the transmission unit included in the one or more opposing devices, based on the estimated one or more zero-dispersion wavelengths and the wavelength dispersion amount allowed in the system; and a transmission unit that transmits the information regarding the transmission wavelength to the one or more first communication devices.

15. A zero-dispersion wavelength estimation method, which receives a plurality of optical signals having different wavelengths transmitted from one or more opposing devices via an optical transmission line, calculates, for each received optical signal, a notch frequency at which a notch appears at a frequency excluding multiples of the frequency of the received optical signal, based on the frequency spectrum of the plurality of received optical signals, and estimates the one or more zero-dispersion wavelengths in the optical transmission line by using the calculated plurality of notch frequencies and the chirp values corresponding to the wavelengths of the plurality of optical signals.

16. A wavelength determination method that receives a plurality of optical signals with different wavelengths transmitted from one or more opposing devices connected via an optical transmission path, calculates, for each received optical signal, a notch frequency at which a notch appears at a frequency excluding a multiple of the frequency of the received optical signal based on the frequency spectrum of each of the received plurality of optical signals, estimates one or more zero-dispersion wavelengths in the optical transmission path using the calculated plurality of notch frequencies and the chirp values corresponding to the wavelengths of the plurality of optical signals, and determines information regarding a transmission wavelength to be used in a transmission unit included in at least the one or more opposing devices based on the estimated one or more zero-dispersion wavelengths and the amount of wavelength dispersion allowed on the system.

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