Communication device, communication system, and zero dispersion wavelength estimation method

Abstract

This communication device comprises: a reception unit that receives a plurality of optical signals of different wavelengths transmitted from a communication device serving as a communication partner and connected via an optical transmission path; a data holding unit that holds data to be used in the detection of a frequency attenuated due to wavelength dispersion; and a signal processing unit that estimates a zero dispersion wavelength on the basis of the data and a frequency spectrum of each of the plurality of optical signals received by the reception unit.　

Description

Communication device, communication system, and zero-dispersion wavelength estimation method

[0001] The present invention relates to a communication device, a communication system, and a zero-dispersion wavelength estimation method.

[0002] In optical communication systems that transmit optical signals using optical fibers, if the wavelength deviates from the zero-dispersion wavelength of the optical fiber, the effect of dispersion increases, leading to a larger penalty and making long-distance transmission difficult. Therefore, in order to transmit over long distances, it is necessary to set the wavelength to approach the zero-dispersion wavelength.

[0003] However, because optical fibers exhibit fluctuations in the zero-dispersion wavelength between 1300 and 1324 nm, there is a problem in that the wavelength cannot be set unless the zero-dispersion wavelength value for each optical fiber used is known.

[0004] Therefore, a conventional method for setting the wavelength is to use an OTDR (Optical Time Domain Reflectometer). In this method, for example, light emitted from the OTDR of device A is transmitted to device B, and then reflected back to the OTDR of device A by a mirror in device B to measure the zero dispersion value, thereby switching the path between the transmitter and receiver. However, this method has the problem of complicating the system because it requires additional equipment.

[0005] As described above, a method has also been proposed for estimating the zero-dispersion wavelength of an optical fiber with a simple configuration that does not require additional equipment (see, for example, Patent Document 1). In the method described in Patent Document 1, when detecting the notch frequency, which is the frequency attenuated due to wavelength dispersion, the notch frequency can be detected with greater accuracy by dividing the pre-transmission spectrum data (frequency spectrum data when sent back-to-back) that is held in advance by the spectrum data after transmission (for example, the frequency spectrum of the optical signal received at the receiving end) (taking the difference when viewing the intensity in decibels).

[0006] International Publication No. 2024 / 134710

[0007] However, the method described in Patent Document 1 requires experiments with a pair of transceivers acting as communication partners before the transceivers are shipped or put into operation, in order to obtain the pre-transmission spectral data used to detect the notch frequency. This has resulted in the problem of increased operational costs for estimating the zero-dispersion wavelength of optical fibers in optical communication using optical fibers.

[0008] In view of the above circumstances, the present invention aims to provide a technology that can suppress the increase in operating costs for estimating the zero-dispersion wavelength of optical fibers in optical communications using optical fibers.

[0009] One aspect of the present invention is a communication device comprising: a receiving unit that receives a plurality of optical signals of different wavelengths transmitted from a communication device of a communication partner connected via an optical transmission path; a data holding unit that holds data used to detect frequencies that are attenuated due to chromatic dispersion; and a signal processing unit that estimates a zero-dispersion wavelength based on the data and the frequency spectrum of each of the plurality of optical signals received by the receiving unit.

[0010] One aspect of the present invention is a communication system comprising a first communication device and a second communication device connected via an optical transmission path, wherein the first communication device includes a transmitting unit that transmits a plurality of optical signals of different wavelengths to the second communication device via the optical transmission path, and the second communication device includes a receiving unit that receives a plurality of optical signals of different wavelengths transmitted from the first communication device, a data holding unit that holds data used when detecting frequencies that are attenuated due to chromatic dispersion, and a signal processing unit that estimates a zero-dispersion wavelength based on the data and the frequency spectrum of each of the plurality of optical signals received by the receiving unit.

[0011] One aspect of the present invention is a zero-dispersion wavelength estimation method that receives a plurality of optical signals of different wavelengths transmitted from a communication device of a communication partner connected via an optical transmission path, and estimates the zero-dispersion wavelength based on data used to detect frequencies attenuated due to pre-held chromatic dispersion and the frequency spectrum of each of the received plurality of optical signals.

[0012] This invention makes it possible to suppress the increase in operating costs for estimating the zero-dispersion wavelength of optical fibers in optical communications using optical fibers.

[0013] This figure shows an example configuration of the optical communication system in the first embodiment. This is a sequence diagram showing the processing flow in the optical communication system of the first embodiment. This figure shows the comparison results of the frequency spectrum data of BtB. This figure shows an example configuration of the optical communication system in the second embodiment. This figure shows another example of the optical communication system in the second embodiment.

[0014] One embodiment of the present invention will be described below with reference to the drawings.

[0015] (First Embodiment) Figure 1 shows an example of the configuration of the optical communication system 10 in the first embodiment. The optical communication system 10 comprises a communication device 100A and a communication device 100B. Communication device 100A and communication device 100B perform optical communication via an optical transmission path. The optical transmission path is made of optical fiber. One or more optical amplifiers that amplify the amplitude of optical signals may be installed in the optical transmission path. Communication device 100A and communication device 100B communicate by two-core transmission using two optical transmission paths.

[0016] In the following description, the direction from communication device 100A to communication device 100B is referred to as the downstream direction, and the direction from communication device 100B to communication device 100A is referred to as the upstream direction. Furthermore, the optical transmission path used by communication device 100A for downstream communication is referred to as the downstream optical transmission path, and the optical transmission path used by communication device 100B for upstream communication is referred to as the upstream optical transmission path.

[0017] The communication device 100A includes a signal processing unit 110A, a temperature controller 120A, a transmission unit 130A, a reception unit 140A, and a data holding unit 150A.

[0018] The receiving unit 140A receives the optical signal transmitted from the communication device 100B.

[0019] 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 maintains correspondence information that shows the correspondence between wavelength and temperature. For example, the correspondence information includes information indicating the temperature of the laser corresponding to each wavelength, associated with each wavelength. That is, the correspondence information includes the wavelength λ １ Corresponding to temperature T1 and wavelength λ ２ This includes information such as temperature T2, which is associated with the element. Note that this is just an example, and the temperature value is determined within a predetermined range.

[0020] Therefore, the signal processing unit 110A obtains temperature information corresponding to the wavelength used for communication by referring to the correspondence information, and sets the temperature controller 120A to the temperature indicated by the obtained temperature information. For example, when the signal processing unit 110A obtains information regarding the transmission wavelength from the communication device 100B, it obtains temperature information corresponding to the wavelength specified by the obtained information regarding the transmission wavelength by referring to the correspondence information, and sets the temperature controller 120A to the temperature indicated by the obtained temperature information. The information regarding the transmission wavelength is information that can identify the wavelength used by the communication device 100A to communicate with the communication device 100B, and may be, for example, information indicating the zero-dispersion wavelength, or information indicating the deviation from the zero-dispersion wavelength. As a result, the signal processing unit 110A sets the wavelength of the optical signal to be transmitted to the communication device 100B in the transmission unit 130A.

[0021] The signal processing unit 110A may also have a function for estimating the zero-dispersion wavelength. When the signal processing unit 110A estimates the zero-dispersion wavelength, it estimates it based on the information held by the data holding unit 150A and the optical signals of different wavelengths received by the receiving unit 140A. The information held by the data holding unit 150A is the frequency spectrum data of BtB. The method for estimating the zero-dispersion wavelength will be described later. In this embodiment, the case in which the zero-dispersion wavelength is estimated in the communication device 100B will be explained as an example.

[0022] The temperature controller 120A adjusts the temperature of the transmitting unit 130A so that it reaches the temperature set by the signal processing unit 110A.

[0023] The transmitting unit 130A is, for example, a tunable laser, and transmits an optical signal with a wavelength corresponding to the temperature adjusted by the temperature controller 120A. In this embodiment, the transmitting unit 130A transmits signals with different wavelengths (for example, wavelength λ ａ and wavelength λ ｂ It transmits an optical signal.

[0024] The data storage unit 150A stores the BtB frequency spectrum data described above. The BtB frequency spectrum data stored in the data storage unit 150A is obtained by simulating an experiment of BtB (0km transmission) with respect to the bandwidth of the transmitted signal, the received signal, the modulator, and the receiver in the system being used. It should be noted that not all of the above information is necessarily used in the simulation of the BtB (0km transmission) experiment. For example, the simulation of the BtB (0km transmission) experiment may use at least one or more combinations of the bandwidth of the transmitted signal, the received signal, the modulator, and the receiver in the system being used. The BtB frequency spectrum data is then stored in the data storage unit 150A before operation.

[0025] The communication device 100B includes a signal processing unit 110B, a temperature controller 120B, a transmission unit 130B, a reception unit 140B, and a data holding unit 150B.

[0026] The receiving unit 140B receives optical signals transmitted from the communication device 100A. For example, the receiving unit 140B receives optical signals of different wavelengths transmitted from the communication device 100A.

[0027] The data storage unit 150B stores the frequency spectrum data of BtB. The frequency spectrum data of BtB stored in the data storage unit 150B is determined by simulating experiments of BtB (0km transmission) with respect to the bandwidth of the transmitted signal, the received signal, the modulator, and the receiver in the system being used. The frequency spectrum data of BtB is then stored in the data storage unit 150B before operation.

[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 and the frequency spectrum data of BtB held in the data holding unit 150B. The method for estimating the zero-dispersion wavelength will be described later.

[0029] The signal processing unit 110B, like the signal processing unit 110A, stores correspondence information indicating the relationship between wavelength and temperature. By referring to the correspondence information, the signal processing unit 110B obtains temperature information corresponding to the wavelength used for communication and sets the temperature controller 120B to the temperature indicated by the obtained temperature information.

[0030] The temperature controller 120B adjusts the temperature of the transmission unit 130B so that it reaches the set temperature.

[0031] The transmitting unit 130B is, for example, a tunable laser, and transmits an optical signal with a wavelength corresponding to the temperature adjusted by the temperature controller 120B.

[0032] In the following explanation, communication device 100A will be described as the transmitting communication device, and communication device 100B will be described as the receiving communication device. As mentioned above, the receiving communication device has not only a wavelength setting function but also a function to estimate the zero-dispersion wavelength in the signal processing unit. Since communication devices 100A and 100B have similar configurations, communication device 100A also has a function to estimate the zero-dispersion wavelength in addition to the wavelength setting function. Therefore, communication device 100A can also estimate the zero-dispersion wavelength.

[0033] [Operation of Optical Communication System 10] Next, the flow of processing in the optical communication system 10 will be described. Fig. 2 is a sequence diagram showing the flow of processing in the optical communication system 10 according to the first embodiment. The communication device 100A has a wavelength λ ａ and transmits an optical signal (step S101). Specifically, the signal processing unit 110A acquires temperature information corresponding to the wavelength λ ａ by referring to the correspondence information. The signal processing unit 110A sets the temperature controller 120A so that the temperature becomes the temperature indicated by the acquired temperature information. The temperature controller 120A adjusts the temperature of the transmitting unit 130A to reach the set temperature. Thereby, the transmitting unit 130A transmits the optical signal with the wavelength λ ａ .

[0034] Note that there are no particular restrictions on the data pattern on the transmission side, and for example, a 01 signal or a PRBS (Pseudo-Random Binary Sequence) signal is acceptable. There are also no particular restrictions on the modulation scheme, and an NRZ (Non Return to Zero) signal or a PAM4 (Pulse Amplitude Modulation 4) signal is acceptable. The optical signal with wavelength λ transmitted from the communication device 100A ａ propagates through the downstream optical transmission path and reaches the communication device 100B. The receiving unit 140B of the communication device 100B receives the optical signal with wavelength λ that has propagated through the downstream optical transmission path ａ (step S102).

[0035] The receiving unit 140B outputs the received optical signal with wavelength λ ａ to the signal processing unit 110B. Based on the optical signal with wavelength λ output from the receiving unit 140B ａ and the information held in the data holding unit 150B, the signal processing unit 110B calculates a notch frequency at which a notch appears at a position other than an integer multiple of the frequency of the optical signal with wavelength λ ａ . The notch frequency is a position where the slope of the average line of the frequency spectrum changes from negative to positive, and is a position other than an integer multiple of the frequency of the transmission signal of the opposite device (for example, the communication device 100A).

[0036] Specifically, the signal processing unit 110B is configured such that the received wavelength λ ａA first frequency spectrum is created from the optical signal. Next, the signal processing unit 110B divides the created first frequency spectrum by the frequency spectrum data held in the data holding unit 150B (since the spectral intensity is expressed in dB, the difference is taken in dB) to obtain a frequency spectrum for estimating the zero-dispersion wavelength (hereinafter referred to as the "estimated frequency spectrum"). Then, based on the obtained estimated frequency spectrum, the signal processing unit 110B calculates the wavelength λ ａ The notch frequency f is the frequency at which a notch appears outside of the frequency multiples of the optical signal. ｎ,ａ The notch frequency f is calculated (step S103). ｎ,ａ is the wavelength λ ａ In the frequency spectrum of an optical signal, this refers to the (n+1)th notch frequency from the low-frequency side. Here, n is a non-negative integer.

[0037] Subsequently, the communication device 100A uses a wavelength λ ｂ The optical signal is transmitted (step S104). Specifically, the signal processing unit 110A of the communication device 100A first refers to the correspondence information and determines the wavelength λ ｂ The system acquires temperature information corresponding to the wavelength λ. The signal processing unit 110A sets the temperature controller 120A to the temperature indicated by the acquired temperature information. The temperature controller 120A adjusts the temperature of the transmitting unit 130A to the set temperature. As a result, the transmitting unit 130A transmits at a wavelength λ ｂ The optical signal is transmitted. The process in step S104 may be performed at a predetermined time interval (for example, 10 seconds) after the start time of the process in step S101, or it may be performed using a different low-speed control channel, wavelength, or line control than the main signal. This can be realized if the communication devices 100A and 100B have functions to read high speed, low speed, or waveform. The start timing and execution method of the process in step S104 described above are just examples, and other start timings and execution methods may be used.

[0038] Note that the wavelengths used by the communication device 100A in steps S101 and S104 only need to be pre-set; for example, two wavelengths can be selected from among a plurality of wavelengths that the transmitting unit 130A can output. In Figure 4, for the sake of simplicity, a configuration is shown in which the communication device 100A transmits optical signals of different wavelengths at different timings, but the communication device 100A may also transmit two optical signals of two wavelengths simultaneously.

[0039] Wavelength λ transmitted from communication device 100A ｂ The optical signal propagates down the optical transmission path and reaches the communication device 100B. The receiving unit 140B of the communication device 100B receives the optical signal that has propagated down the optical transmission path (step S105). The receiving unit 140B outputs the received optical signal to the signal processing unit 110B. The signal processing unit 110B processes the wavelength λ output from the receiving unit 140B. ｂ Based on the optical signal and the information held in the data holding unit 150B, the wavelength λ ｂ The notch frequency at which the notch appears is calculated, except at frequency multiples of the optical signal.

[0040] Specifically, the signal processing unit 110B receives the wavelength λ ｂ A second frequency spectrum is created from the optical signal. Next, the signal processing unit 110B obtains an estimated frequency spectrum by dividing the frequency spectrum data held in the data holding unit 150B by the created second frequency spectrum (since the spectral intensity is expressed in dB, the difference is taken in dB). Then, based on the obtained estimated frequency spectrum, the signal processing unit 110B calculates the wavelength λ ｂ The notch frequency f is the frequency at which a notch appears outside of the frequency multiples of the optical signal. ｍ,ｂ The notch frequency f is calculated (step S106). Note that m is a non-negative integer. ｍ,ａ This refers to the wavelength λ ｂ In the frequency spectrum of an optical signal, this refers to the (m+1)th notch frequency from the low-frequency side.

[0041] Furthermore, the signal processing unit 110B will find a local maximum if the method of calculating the difference between the frequency spectrum data of BtB and the spectrum after fiber transmission is reversed (for example, frequency spectrum data of BtB - spectrum after fiber transmission). In the following explanation, it is assumed that the notch frequency is obtained using the local minimum (spectrum after transmission - frequency spectrum data of BtB).

[0042] Next, the signal processing unit 110B calculates multiple notch frequencies f ｎ,ａ , f ｍ,ｂ And, the multiple chirp values ​​α that were determined in advance a , α b Using and based on equation (1), multiple wavelengths λ ０ Calculate (step S107). Multiple wavelengths λ ０ This is a wavelength that is a candidate for the zero-dispersion wavelength. Therefore, the multiple wavelengths λ calculated ０ any of the wavelengths λ ０ This is the zero-dispersion wavelength.

[0043] Chirp's Vα a The wavelength of the light signal is wavelength λ ａ The chirp value in this case is assumed to be pre-calculated. The chirp value α ｂ The wavelength of the light signal is wavelength λ ｂ The chirp value in this case is assumed to be calculated in advance. Between communication device 100A and communication device 100B, the wavelength λ ０ The different wavelengths used when calculating are assumed to be predetermined. Here, in equation (1), λ ａ and λ ｂ This represents the wavelength of the transmission signal sent by the communication device 100A.

[0044]

[0045] In equation (1), "A" and "B" can be any of the patterns shown in equations (2) to (5) below. Therefore, the signal processing unit 110B considers the wavelength λ when "A" and "B" in equation (1) are any of the patterns shown in equations (2) to (5). ０ This will result in the calculation of the four wavelengths λ. ０Calculate.

[0046] Here, the wavelength λ is calculated using "A" and "B" shown in equation (2). ０ Wavelength λ of Pattern 1 ０ The wavelength λ was calculated using "A" and "B" shown in equation (3). ０ Wavelength λ of pattern 2 ０ The wavelength λ was calculated using "A" and "B" shown in equation (4). ０ Wavelength λ of pattern 3 ０ The wavelength λ was calculated using "A" and "B" shown in equation (5). ０ Wavelength λ of pattern 4 ０ Let's assume that.

[0047]

[0048]

[0049]

[0050]

[0051] Subsequently, the signal processing unit 110B calculates the wavelength λ of each pattern. ０ However, it is determined whether the conditions in each of equations (2) to (5) are met (step S108). Specifically, the signal processing unit 110B determines the wavelength λ of pattern 1. ０ However, the condition in equation (2) is the wavelength λ ａ and wavelength λ ｂ Smaller than, and S ０ L is greater than 0 (for example, (λ) ０ <λ ａ and λ ０ <λ ｂ and 0 < S ０ Determine whether the condition L) is met.

[0052] Similarly, the signal processing unit 110B processes the wavelength λ of pattern 2. ０ However, the condition in equation (3) is the wavelength λ ａ and wavelength λ ｂ Larger than, and S ０ L is greater than 0 (for example, (λ) ａ <λ ０ and λｂ <λ ０ and 0<S ０ L) is determined whether the condition is satisfied or not.

[0053] Similarly, the signal processing unit 110B determines whether the wavelength λ of pattern 3 ０ is smaller than the wavelength λ which is the condition in formula (4) ａ , and larger than the wavelength λ ｂ , and S ０ L is greater than 0 (for example, (λ ａ >λ ０ and λ ｂ <λ ０ and 0<S ０ L) is determined whether the condition is satisfied or not.

[0054] Similarly, the signal processing unit 110B determines whether the wavelength λ of pattern 4 ０ is larger than the wavelength λ which is the condition in formula (5) ａ , and smaller than the wavelength λ ｂ , and S ０ L is greater than 0 (for example, (λ ａ <λ ０ and λ ｂ >λ ０ and 0<S ０ L) is determined whether the condition is satisfied or not.

[0055] Here, the above S ０ is a dispersion slope, and may be, for example, a value specified by standardization (0.092 [ps / km / nm for a single mode fiber ２ ), or calculation may be performed using the value of S ０ ×L that can be obtained by an existing estimation method. Note that L is the distance between the communication device 100A and the communication device 100B. S ０ L is calculated based on the following formula (6). Note that in the case of a system where an upper limit of the distance L is determined, using the determined upper limit value L ｍａｘ [km], the condition that S ０ L<0.092L ｍａｘ (that is, 0<S ０ L<0.092L ｍａｘ) is added to equations (2) through (5). For example, if the distance is less than 100 km, S ０ The condition L < 9.2 is added to equations (2) through (5). For example, the upper limit of distance L can be determined based on the requirements of the transceiver used and the maximum transmission distance expected in the network configuration. Note that this is just one example, and the upper limit of distance L may be determined by other methods.

[0056]

[0057] The signal processing unit 110B calculates the wavelength λ of each pattern. ０ If the value does not satisfy the conditions of equations (2) to (5) corresponding to each pattern (i.e., it is outside the range of equations (2) to (5)), or if it is outside the range of the zero-dispersion wavelength of the optical fiber being used, the calculated wavelength λ ０ The value of is excluded. Here, we will explain in detail the cases where the conditions of equations (2) to (5) corresponding to each pattern are not met. As described above, the signal processing unit 110B receives the wavelength λ obtained for each pattern. ０ However, it determines whether the conditions in each of equations (2) through (5) are met.

[0058] The signal processing unit 110B processes the wavelength λ of pattern 1. ０ However, if the conditions in equation (2) are met, the wavelength λ of pattern 1 ０ This is retained as a candidate for the zero-dispersion wavelength. Meanwhile, the signal processing unit 110B considers the wavelength λ of pattern 1. ０ However, if the conditions in equation (2) are not met, the wavelength λ of pattern 1 ０ This is excluded from the list of zero-dispersion wavelength candidates. In this way, the signal processing unit 110B uses "A" and "B" shown in equation (2) to calculate the wavelength λ based on equation (1). ０ For this, we determine whether the conditions in equation (2) are met (conditions in other equations are irrelevant) to determine whether or not to exclude candidates for zero-dispersion wavelengths.

[0059] Similarly, the signal processing unit 110B processes the wavelength λ of pattern 2. ０ However, if the conditions in equation (3) are met, the wavelength λ of pattern 2 ０This is retained as a candidate for the zero-dispersion wavelength. Meanwhile, the signal processing unit 110B considers the wavelength λ of pattern 2. ０ However, if the conditions in equation (3) are not met, the wavelength λ of pattern 2 ０ This is excluded from the list of zero-dispersion wavelength candidates. In this way, the signal processing unit 110B uses "A" and "B" shown in equation (3) to calculate the wavelength λ based on equation (1). ０ For this, we determine whether the conditions in equation (3) are met (the conditions in other equations are irrelevant) to determine whether or not it is necessary to exclude candidates for zero-dispersion wavelengths.

[0060] Similarly, the signal processing unit 110B processes the wavelength λ of pattern 3. ０ However, if the conditions in equation (4) are met, the wavelength λ of pattern 3 ０ This is retained as a candidate for the zero-dispersion wavelength. Meanwhile, the signal processing unit 110B considers the wavelength λ of pattern 3. ０ However, if the conditions in equation (4) are not met, the wavelength λ of pattern 3 ０ This is excluded from the list of zero-dispersion wavelength candidates. In this way, the signal processing unit 110B uses "A" and "B" shown in equation (4) to calculate the wavelength λ based on equation (1). ０ For this, we determine whether the conditions in equation (4) are met (the conditions in other equations are irrelevant) to determine whether or not to exclude the candidate for zero-dispersion wavelength.

[0061] Similarly, the signal processing unit 110B processes the wavelength λ of pattern 4. ０ However, if the conditions in equation (5) are met, the wavelength λ of pattern 4 ０ This is retained as a candidate for the zero-dispersion wavelength. Meanwhile, the signal processing unit 110B considers the wavelength λ of pattern 4. ０ However, if the conditions in equation (5) are not met, the wavelength λ of pattern 4 ０ This is excluded from the list of zero-dispersion wavelength candidates. In this way, the signal processing unit 110B uses "A" and "B" shown in equation (5) to calculate the wavelength λ based on equation (1). ０ For this, we determine whether the conditions in equation (5) are met (the conditions in other equations are irrelevant) to determine whether or not to exclude the candidate for zero-dispersion wavelength.

[0062] As described above, the signal processing unit 110B processes multiple wavelengths λ calculated for each pattern.０ Among them, wavelength λ that does not satisfy the conditions for the corresponding pattern ０ The wavelength λ is excluded from the list of zero-dispersion wavelength candidates. Also, if the optical fiber being used is a standard single-mode fiber, the signal processing unit 110B will use the wavelength λ ０ If the value falls outside the wavelength range of 1300 to 1324 nm, it will be excluded.

[0063] Then, the signal processing unit 110B checks the wavelength λ that satisfies the conditions. ０ And, 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 wavelength dispersion (= wavelength dispersion D × distance L) is calculated by solving for λ using the following equations (7) and (8) (step S109). In equations (7) and (8), "A" and "B" are the wavelength λ that satisfies the conditions. ０ It is one of the values ​​from equations (2) to (5) that correspond to it. For example, the wavelength λ that satisfies the conditions. ０ However, if the values ​​are calculated using the values ​​of "A" and "B" shown in equation (2), then "A" and "B" in equations (7) and (8) are the values ​​of "A" and "B" shown in equation (2).

[0064]

[0065]

[0066] The signal processing unit 110B determines the wavelength λ used for downlink communication within the wavelength range determined based on equations (7) and (8) described above. ＤＳ Determine the wavelength (step S110). ＤＳ This is the wavelength used for transmission from communication device 100A to communication device 100B when communication device 100B is viewed as a downstream from communication device 100A. In this case, communication device 100B transmits information indicating the wavelength range obtained based on the above-described equations (7) and (8) to communication device 100A as information regarding the transmission wavelength (step S111).

[0067] In the signal processing unit 110B, wavelength λ ＤＳWhen determining this, the value closest to the center of the wavelength corresponding to the wavelength within the wavelength range (the range between the upper and lower limits of the allowable amount of wavelength dispersion) is the wavelength λ. ＤＳ This could be the decision. Doing so would minimize penalties and enable even longer-distance transmission.

[0068] As a method for transmitting information regarding the transmission wavelength to a counterpart communication device 100 (for example, communication device 100A), a low-speed control signal can be used. Furthermore, by applying processing such as an equalizer at the signal processing stage, information can be acquired with a relatively high-speed signal. Additionally, for paths where the zero-dispersion wavelength value is known in advance, communication device 100B can set the transmission wavelength to a value near that value, thereby enabling notification with a high-speed signal.

[0069] The receiving unit 140A of the communication device 100A receives information regarding the transmission wavelength transmitted from the communication device 100B. The receiving unit 140A outputs the received information regarding the transmission wavelength to the signal processing unit 110A. The signal processing unit 110A refers to the correspondence information and identifies the wavelength λ specified by the information regarding the transmission wavelength output from the receiving unit 140A. ＤＳ The signal processing unit 110A acquires the corresponding temperature information. The signal processing unit 110A sets the temperature controller 120A to the temperature indicated by the acquired temperature information (step S112). As a result, the signal processing unit 110A sets the transmission wavelength to wavelength λ ＤＳ Change it.

[0070] Subsequently, the same processing as in steps S101 to S112 is performed in the uplink direction (step S113). In this case, communication device 100B performs the processing in steps S101, S104 and S112. Communication device 100A performs the processing in steps S102, S103 and S105 to S111. As a result, the signal processing unit 110A determines the wavelength λ used for uplink communication within the wavelength range determined based on the above-described equations (7) and (8). ｕＳ Determine the wavelength λ. ＵＳThis is the wavelength used for transmission from communication device 100B to communication device 100A, when communication device 100B is viewed as upstream. In this case, communication device 100A transmits information indicating the wavelength range determined based on the above-described equations (7) and (8) to communication device 100B as information regarding the transmission wavelength.

[0071] In the signal processing unit 110A, wavelength λ ｕＳ When determining this, the value closest to the center of the wavelength corresponding to the wavelength within the wavelength range (the range between the upper and lower limits of the allowable amount of wavelength dispersion) is the wavelength λ. ｕＳ This could be the decision. Doing so would minimize penalties and enable even longer-distance transmission.

[0072] As a method for transmitting information regarding the transmission wavelength to the opposing communication device 100 (for example, communication device 100B), a low-speed control signal can be used. Furthermore, by applying processing such as an equalizer at the signal processing stage, information can be acquired with a relatively high-speed signal. Additionally, for paths where the zero-dispersion wavelength value is known in advance, communication device 100A can set the transmission wavelength to a value near that value, thereby enabling notification with a high-speed signal.

[0073] The receiving unit 140B of the communication device 100B receives information regarding the transmission wavelength transmitted from the communication device 100A. The receiving unit 140B outputs the received information regarding the transmission wavelength to the signal processing unit 110B. The signal processing unit 110B refers to the correspondence information and identifies the wavelength λ specified by the information regarding the transmission wavelength output from the receiving unit 140B. ｕＳ The signal processing unit 110B acquires the corresponding temperature information. The signal processing unit 110B sets the temperature controller 120B to the temperature indicated by the acquired temperature information. As a result, the signal processing unit 110B sets the transmission wavelength to wavelength λ. ｕＳ This is changed to allow the transmission wavelength to be set in both communication device 100A and communication device 100B. As a result, communication is initiated between communication device 100A and communication device 100B (step S114).

[0074] Furthermore, if 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 will select the wavelength λ from the range between the upper and lower limits of the permissible value of the chromatic dispersion amount specified by the information indicating the wavelength range. ＤＳ The signal processing unit 110A determines a value close to the center value of the wavelength corresponding to the wavelength λ. ＤＳ It may also be determined as follows. Furthermore, the signal processing unit 110A maintains a list of penalty values ​​due to chromatic dispersion for each chromatic dispersion amount, finds the wavelength value corresponding to the chromatic dispersion amount for which the penalty value is minimized, and sets the value near the found wavelength λ ＤＳ It may be decided as such.

[0075] Furthermore, if the communication device 100A notifies information indicating a wavelength range as information regarding the transmission wavelength, the signal processing unit 110B of the communication device 100B will select the wavelength λ from the range between the upper and lower limits of the permissible value of the chromatic dispersion amount specified by the information indicating the wavelength range. ｕＳ The signal processing unit 110B determines a value close to the center value of the wavelength corresponding to the wavelength λ. ｕＳ It may also be determined as follows. Furthermore, the signal processing unit 110B maintains a list of penalty values ​​due to wavelength dispersion for each wavelength dispersion amount, finds the wavelength value corresponding to the wavelength dispersion amount for which the penalty value is minimized, and sets the value near the found wavelength λ ｕＳ It may be decided as such.

[0076] Figure 3 shows a comparison of frequency spectrum data for BtB. Figure 3(A) shows frequency spectrum data for BtB obtained experimentally using the same method as before, and Figure 3(B) shows frequency spectrum data for BtB obtained through simulation. Comparing Figure 3(A) and Figure 3(B), the minimum notch frequency is the same. Therefore, it can be confirmed that using frequency spectrum data for BtB obtained through simulation, as in the present invention, is actually effective.

[0077] There are no restrictions on the simulation method used to acquire the frequency spectrum data of BtB stored in the data storage units 150A and 150B. For example, a transmission simulator such as VPIphotonics may be used, or numerical simulation may be used. Also, the frequency spectrum data of BtB stored in the data storage units 150A and 150B may be either frequency spectrum data or waveform data of BtB. In the case of waveform data, the frequency spectrum of BtB can be acquired by performing a Fast Fourier Transform in the signal processing units 110A and 110B.

[0078] According to the optical communication system 10 in the first embodiment configured as described above, the communication devices 100A and 100B include: receiving units 140A and 140B that receive a plurality of optical signals of different wavelengths transmitted from a communication device of a communication partner connected via an optical transmission path; data holding units 150A and 150B that hold frequency spectrum data used when detecting frequencies that are attenuated due to chromatic dispersion; and signal processing units 110A and 110B that estimate the zero-dispersion wavelength based on the frequency spectrum data and the frequency spectra of each of the plurality of different optical signals received by the receiving units 140A and 140B.

[0079] Thus, the communication device 100A or communication device 100B that estimates the zero-dispersion wavelength pre-stores BtB frequency spectrum data used when detecting frequencies attenuated due to chromatic dispersion (when detecting notch frequencies). This eliminates the need to conduct experiments using combinations of transceivers to acquire BtB frequency spectrum data. Therefore, it becomes possible to suppress the increase in operational costs for estimating the zero-dispersion wavelength of optical fibers in optical communication using optical fibers.

[0080] (Second Embodiment) In the first embodiment, the case where two optical fibers connect the communication devices was described. In the second embodiment, the case where one optical fiber connects the communication devices will be described.

[0081] Figure 4 shows an example configuration of the optical communication system 20 in the second embodiment. The optical communication system 20 comprises a communication device 200A and a communication device 200B. Communication devices 200A and 200B communicate via an optical transmission path. Communication devices 200A and 200B communicate by single-core bidirectional transmission using one optical transmission path. In the following description, the direction from communication device 200A to communication device 200B is referred to as the downstream direction, and the direction from communication device 200B to communication device 200A is referred to as the upstream direction.

[0082] As shown in Figure 4, the communication devices 200A and 200B are equipped with a wavelength combining or demultiplexing device. Examples of wavelength combining and demultiplexing devices include circulators and wavelength combining and demultiplexing couplers. Wavelength-independent wavelength combining and demultiplexing devices are desirable. Note that optical switches may be used instead of wavelength combining and demultiplexing devices. In the following description, the case in which the communication devices 200A and 200B are equipped with wavelength combining and demultiplexing devices will be described as an example.

[0083] Communication device 200A includes a signal processing unit 110A, a temperature controller 120A, a transmission unit 130A, a reception unit 140A, a data holding unit 150A, and a signal multiplexing / demultiplexing device 160A. Communication device 200B includes a signal processing unit 110B, a temperature controller 120B, a transmission unit 130B, a reception unit 140B, a data holding unit 150B, and a signal multiplexing / demultiplexing device 160B. By including the signal multiplexing / demultiplexing device 160A in communication device 200A and the signal multiplexing / demultiplexing device 160B in communication device 200B, a single-core bidirectional configuration can be achieved. The other functional units of communication devices 200A and 200B are the same as in the first embodiment.

[0084] The signal splitting / demultiplication device 160A outputs the optical signal output from the transmitting unit 130A to the optical transmission path. The signal splitting / demultiplication device 160A also outputs the optical signal transmitted from the optical transmission path to the receiving unit 140A.

[0085] The signal splitting / demultiplication device 160B outputs the optical signal output from the transmitting unit 130B to the optical transmission path. The signal splitting / demultiplication device 160B also outputs the optical signal transmitted from the optical transmission path to the receiving unit 140B.

[0086] In the following explanation, communication device 200A will be described as the transmitting communication device, and communication device 200B will be described as the receiving communication device. As mentioned above, the receiving communication device has not only a wavelength setting function but also a function to estimate the zero-dispersion wavelength in the signal processing unit. Since communication devices 200A and 200B have similar configurations, communication device 200A also has a function to estimate the zero-dispersion wavelength in addition to the wavelength setting function. Therefore, communication device 200A can also estimate the zero-dispersion wavelength.

[0087] Next, the difference between the optical communication system 20 and the optical communication system 10 is that the processing performed by the optical communication system 200A and the optical communication system 200B includes additional processing by the multiplexing / demultiplexing devices 160A and 160B. For example, the 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 160A, and then output to the receiving unit 140B by the multiplexing / demultiplexing device 160B of the communication device 200B. Similarly, the 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 160B, and then output to the receiving unit 140A by the multiplexing / demultiplexing device 160A of the communication device 200A.

[0088] The arrangement of the signal splitting / demultiplier devices 160A and 160B and the optical switch is not particularly limited and may be provided outside the communication devices 200A and 200B.

[0089] [Operation of Optical Communication System 20] Next, the processing flow in the optical communication system 20 will be explained. Note that the processing up to a certain point is the same as the processing shown in Figure 2, so the processing shown in Figure 2 will be used as a reference for explanation. When the processing from step S101 to step S109 is executed, the signal processing unit 110B determines the wavelength λ used for uplink communication within the wavelength range determined based on the above-mentioned equations (7) and (8). ｕＳ To decide.

[0090] In this case, the communication device 200B transmits to the communication device 200A information indicating the wavelength range determined based on the above-described equations (7) and (8) as information regarding the transmission wavelength. Alternatively, the signal processing unit 110B specifies the wavelength λ used for uplink communication within the wavelength range determined based on the above-described equations (7) and (8). ＵＳ And the wavelength λ used for downlink communication ＤＳ Both may be determined. Note that the concepts of upstream and downstream directions may be reversed. In this case, the communication device 200B will determine the wavelength λ ＤＳ Information indicating this may be transmitted to the communication device 200A as information regarding the transmission wavelength. Subsequently, the communication device 200A and the communication device 200B each transmit at different wavelengths λ ＵＳ and wavelength λ ＤＳ Configure the settings and start communication.

[0091] With the optical communication system 20 configured as described above, the same effects as in the first embodiment can be obtained even in a single-core bidirectional configuration.

[0092] (Modification 1 in the second embodiment) In the embodiment described above, since the communication device 200A and the communication device 200B have the same configuration, both the signal processing unit 110A in the communication device 200A and the signal processing unit 110B in the communication device 200B have both a function to set the wavelength and a function to estimate the zero-dispersion wavelength. Here, the function to set the wavelength is a function to control the transmission wavelength of the transmission units 130A and 130B by controlling the temperature controllers 120A and 120B. The function to estimate the zero-dispersion wavelength is a function to estimate the deviation amount Δλ from the zero-dispersion wavelength or the zero-dispersion wavelength.

[0093] When connected by a single optical fiber, the same path is used for transmission and reception, so it is assumed that the zero-dispersion wavelength is the same. Therefore, the function of estimating the zero-dispersion wavelength only needs to be possessed by either the signal processing unit 110A or the signal processing unit 110B. 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, while 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, while the signal processing unit 110B may have only the function of setting the wavelength (without the function of estimating the zero-dispersion wavelength). In such configurations, the signal processing unit 110A or 110B may use the estimated value of the zero-dispersion wavelength to control the wavelengths of both the transmitting unit 130B of its own device (communication device 200B) and the transmitting unit 130A of the communication device 200A.

[0094] Here, we will explain how the signal processing unit 110B controls the wavelengths of both the transmitter 130B of its own device (communication device 200B) and the transmitter 130A of the communication device 200A. For example, the signal processing unit 110B controls the transmitter 130A to send information indicating the estimated zero-dispersion wavelength to the communication device 200A. As a result, information indicating the zero-dispersion wavelength is transmitted to the communication device 200A. This allows the signal processing unit 110B to control the wavelength of the transmitter 130A of the communication device 200A. Furthermore, the signal processing unit 110B refers to the correspondence information and obtains temperature information corresponding to the estimated zero-dispersion wavelength. The signal processing unit 110B sets the temperature controller 120B so that the temperature is as indicated by the obtained temperature information. The temperature controller 120B adjusts the temperature of the transmitter 130B to the set temperature. As a result, the signal processing unit 110A can control the transmission wavelength of the transmitter 130B of its own device.

[0095] 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 this configuration, the signal processing unit 110A controls the wavelength of the transmitter unit 130B of the communication device 200B using the estimated zero-dispersion wavelength value, and the signal processing unit 110B controls the wavelength of the transmitter unit 130A of the communication device 200A using the estimated zero-dispersion wavelength value. For example, in such a case, it is conceivable that communication device 200A transmits a signal that is susceptible to wavelength dispersion, such as a high-speed signal, while communication device 200B transmits a low-speed signal that is less susceptible to wavelength dispersion, or a high-speed signal that has been made less susceptible to wavelength dispersion through pre-compensation or multi-leveling.

[0096] As another example, the signal processing unit 110B may have both a function to set the wavelength and a function to estimate the zero-dispersion wavelength, while the signal processing unit 110A may not have either a function to estimate the zero-dispersion wavelength or a function to set the wavelength (neither a function to set the wavelength nor a function to estimate the zero-dispersion wavelength). Conversely, the signal processing unit 110B may not have either a function to estimate the zero-dispersion wavelength or a function to set the wavelength (neither a function to set the wavelength nor a function to estimate the zero-dispersion wavelength), while the signal processing unit 110A may have both a function to set the wavelength and a function to estimate the zero-dispersion wavelength. In such a configuration, the signal processing unit 110A or 110B controls the wavelength of the transmitter unit 130B provided in its device using the estimated value of the zero-dispersion wavelength. For example, in such a case, it is conceivable that communication device 200A transmits a relatively slow signal that is less susceptible to wavelength dispersion (a slow signal that produces a notch) or a high-speed signal that has been made less susceptible to wavelength dispersion through pre-compensation or multi-leveling, while communication device 200B transmits a high-speed signal that can reduce the effects of wavelength dispersion by setting the wavelength.

[0097] Here, we will describe an example configuration in which the signal processing unit 110B of the communication device 200B has both a function to set the wavelength and a function to estimate the zero-dispersion wavelength, while the signal processing unit 110A of the communication device 200A does not have either a function to estimate the zero-dispersion wavelength or a function to set the wavelength (it has neither a function to set the wavelength nor a function to estimate the zero-dispersion wavelength). The signal processing unit 110B controls the wavelength of the transmitter unit 130B equipped with its own device using one of the zero-dispersion wavelength candidates (up to two candidates) estimated by the method described in the embodiment. The signal processing unit 110B first sets one of the wavelengths that are candidates for the zero-dispersion wavelength (for example, the first wavelength λ ０,１ Select ).

[0098] The signal processing unit 110B selects the first wavelength λ ０,１ The system acquires temperature information corresponding to the acquired temperature information and transmits from the transmission unit 130B at the first wavelength λ ０,１ The optical signal is transmitted to the communication device 200A. When the receiving unit 140A of the communication device 200A receives the optical signal transmitted from the communication device 200B, the communication device 200A starts communication with the communication device 200B. Here, "when it is received" means, for example, within a specific time frame in which a series of operations can be performed, such as the communication device 200A sending an optical signal to the communication device 200B, the communication device 200B estimating the zero-dispersion wavelength, the communication device 200B setting the estimated zero-dispersion wavelength to the transmitting unit 130B and oscillating, and the communication device 200A receiving it, the communication device 200A notifies the communication device 200B to notify an optical signal of a specific piece of information, and within that specific time frame, the communication device 200B notifies the communication device 200A of an optical signal of a specific piece of information. In this case, the communication device 200A transmits a low-speed signal or a high-speed signal that is less susceptible to the effects of wavelength dispersion through pre-compensation or multi-leveling.

[0099] 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 not received. Here, failure to receive means, for example, within a specific time frame in which a series of operations can be performed, such as the communication device 200A sending an optical signal to the communication device 200B, the communication device 200B estimating the zero-dispersion wavelength, the communication device 200B setting the estimated zero-dispersion wavelength to the transmitting unit 130B and oscillating, and the communication device 200A receiving the signal, the communication device 200A notifies the communication device 200B to transmit an optical signal of a specific piece of information, but the communication device 200B does not transmit an optical signal of a specific piece of information to the communication device 200A within that specific time frame. In response to the notification from the communication device 200A that it was not able to receive the signal, the communication device 200B will send another candidate, the first wavelength λ ０,２ The device oscillates using an optical signal. Subsequently, communication begins between communication device 200A and communication device 200B. The method for determining whether reception is possible shown here is just one example; other methods may be used to determine whether reception is possible, and the method is not restricted.

[0100] 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, the cost of the communication device 200 that does not have the function of estimating the zero-dispersion wavelength can be reduced. Furthermore, one communication device 200 (for example, communication device 200B) can estimate the zero-dispersion wavelength and control the wavelength used for communication between the transmitting unit 130 (for example, transmitting unit 130B) of the opposing communication device 200 (for example, communication device 200A) and the transmitting unit 130 (for example, transmitting unit 130A) of the device itself. This enables efficient communication.

[0101] Furthermore, as described above, the present invention can be applied even if one of the communication devices 200 does not have either a function to estimate the zero-dispersion wavelength or a function to set the wavelength (i.e., it has neither a function to set the wavelength nor a function to estimate the zero-dispersion wavelength).

[0102] (Modification 1 common to the first and second embodiments) In the embodiments described above, each communication device 100A, 100B, 200A, and 200B is shown to change the transmission wavelength of the transmission units 130A and 130B using temperature controllers 120A and 120B. However, the configuration for changing the transmission wavelength in each communication device 100A, 100B, 200A, and 200B is not limited to this. For example, a configuration using a current controller or a configuration using an array laser may be applied as a configuration for changing the transmission wavelength in each communication device 100A, 100B, 200A, and 200B.

[0103] First, we will explain the case where a configuration using a current controller is applied. Similar configurations are assumed for communication devices 100A, 100B, 200A, and 200B, but here we will explain using communication device 100A as an example. Communication device 100A includes a signal processing unit 110A, a transmitting unit 130A, a receiving unit 140A, a data holding unit 150A, and a current controller. Communication device 100A is equipped with a current controller instead of a temperature controller 120A.

[0104] 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 maintains correspondence information that shows the correspondence between wavelength and current. This correspondence information includes, for example, information indicating the current to be applied to the laser corresponding to each wavelength, associated with each wavelength. That is, the correspondence information includes the wavelength λ １ Corresponding to current C １ , wavelength λ ２ Corresponding to current C ２ This includes information such as the above. Note that this is just one example, and the current value is determined within a predetermined range.

[0105] Therefore, the signal processing unit 110A obtains current information corresponding to the wavelength used for communication by referring to the correspondence information, and sets the current controller to the current indicated by the obtained current information. For example, if the signal processing unit 110A obtains information indicating a zero-dispersion wavelength from the communication device 100B, it obtains current information corresponding to the wavelength specified by the obtained zero-dispersion wavelength information by referring to the correspondence information, and sets the current controller to the current indicated by the obtained current information. As a result, the signal processing unit 110A sets the wavelength of the optical signal to be transmitted to the communication device 100B in the transmission unit 130A.

[0106] The current controller applies current to the transmitting unit 130A at a current value set by the signal processing unit 110A. The transmitting unit 130A is, for example, a tunable laser, and transmits an optical signal with a wavelength corresponding to the current value.

[0107] Next, we will describe the case where a configuration using an array laser is applied. Similar configurations are assumed for communication devices 100A, 100B, 200A, and 200B, but here we will explain using communication device 100A as an example. Communication device 100A includes a signal processing unit 110A, a receiving unit 140A, a data holding unit 150A, an array laser, and a multiplexer. Communication device 100A includes an array laser and a multiplexer in place of the temperature controller 120A and the transmitting unit 130A.

[0108] 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 oscillating laser corresponding to a desired wavelength and sets the array laser to output a signal from the selected oscillating laser. While the desired wavelength is preferably a zero-dispersion wavelength, it is conceivable that there may be no laser corresponding to the zero-dispersion wavelength value. Therefore, if there is no laser corresponding to the zero-dispersion wavelength value, the signal processing unit 110A may select a laser with the value closest to the zero-dispersion wavelength value. The array laser has a wavelength λ １ from λ ｋThe array laser system comprises multiple lasers capable of oscillating at various wavelengths up to (k being an integer greater than or equal to 1). The array laser drives the set oscillating lasers to output optical signals. The multiplexer combines the optical signals of one or more wavelengths output from the array laser. The multiplexer outputs the combined optical signal to an optical transmission path.

[0109] As described above, any method can be used to change the wavelength. This embodiment is applicable as long as the zero-dispersion wavelength of the optical fiber and the range of the transmission wavelength overlap (it is not limited to wavelengths of 1300 to 1324 nm).

[0110] (Modification 2 common to the first and second embodiments) In each of the embodiments described above, the transmitting communication device (e.g., communication device 100A, 200A) that transmits an optical signal for estimating the zero-dispersion wavelength may simultaneously transmit optical signals of two wavelengths to the receiving communication device (e.g., communication device 100B, 200B). In this configuration, the transmitting communication device (e.g., communication device 100A, 200A) comprises two or more transmitting units (e.g., transmitting unit 130A), and the receiving communication device (e.g., communication device 100B, 200B) comprises two or more receiving units (e.g., 140B). Furthermore, the receiving communication device (e.g., communication device 100B, 200B) is equipped with an optical filter (a tunable filter set to cut one wavelength and allow the other wavelength to pass through) in front of each receiving unit (e.g., 140B). This allows the receiving communication devices (e.g., communication devices 100B and 200B) to receive optical signals of two different wavelengths transmitted through the same optical fiber using different receiving units (e.g., 140B).

[0111] (Modification 3 common to the first and second embodiments) Zero-dispersion wavelength λ ０ The method for narrowing down to one is not limited to the method described above. If it is not possible to narrow down the candidates for the zero-dispersion wavelength to one, the communication devices 100B and 200B may narrow down the candidates for the zero-dispersion wavelength to one using the method shown below. Here, we will explain using the communication device 100B as an example. The communication device 100B uses the first wavelength λ ０,１ Information indicating the value of the first wavelength λ is transmitted to the communication device 100A, ０,１The optical signal is received from the communication device 100A. The signal processing unit 110B receives the first wavelength λ ０,１ From the frequency spectrum data of the optical signal, f ｎ,ａ Check if a notch appears at the following frequencies. More specifically, the signal processing unit 110B checks the first wavelength λ ０,１ In the frequency spectrum data of the optical signal, the (n+1)th notch frequency f ｎ,（０,１） However, wavelength λ ａ The (n+1)th notch frequency f in the spectral data obtained at that time (i.e., the first data obtained) ｎ,ａ It may not be present at a lower frequency, or it may be related to the first wavelength λ. ０,１ In the frequency spectrum data of an optical signal, the notch is wavelength λ ａ The f obtained at that time (i.e., the first one obtained) ０,ａ Check if it's appearing at a lower frequency. f ｎ,ａ If no notch is present at the following frequencies, the signal processing unit 110B controls the transmission unit 130B to send information that the wavelength setting is correct (for example, notch appearance information (none)) to the communication device 100A using a low-speed signal. Upon receiving the information 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.

[0112] On the other hand, f ｎ,ａ If a notch appears at the following frequencies, the signal processing unit 110B controls the transmission unit 130B to provide information that the wavelength setting is incorrect (for example, notch appearance information (present)) and the second wavelength λ ０,２ Information indicating this is sent to the communication device 100A. As a result, the communication device 100A will know that the zero-dispersion wavelength is the second wavelength λ. ０,２ It can be determined that this is the case.

[0113] (Other Application Examples) Each communication device in the first and second embodiments can also be applied to the configuration shown in Figure 5. Figure 5 is a diagram showing another example of the optical communication system 20 in each embodiment. In Figure 5, the case where it is applied to the communication device 200A and communication device 200B in the second embodiment is shown as an example. The optical communication system 20 shown in Figure 5 comprises a plurality of communication devices 200A-1 to 200A-P (P is an integer of 2 or more), a plurality of communication devices 200B-1 to 200B-Q (Q is an integer of 2 or more), a control device 300, and an optical distribution unit 350. Thus, in the optical communication system 20 shown in Figure 5, an optical distribution unit 350 is provided between each communication device 200A and each communication device 200B.

[0114] The optical distribution unit 350 outputs an optical signal input from one optical transmission path to another transmission path. The optical distribution unit 350 may be an optical switch, a ROADM (Reconfigurable Optical Add-Drop Multiplexer), or any configuration that can switch the destination of the optical signal. The optical distribution unit 350 switches the connection path according to the instructions of the control device 300.

[0115] The control device 300 controls the optical distribution unit 350. For example, the control device 300 controls the destination of the optical distribution unit 350 so that communication devices connected to the optical distribution unit 350 can communicate with each other.

[0116] In the embodiments described above, the signal processing units 110A and 110B may be configured using a processor such as a CPU (Central Processing Unit) and memory. In this case, the signal processing units 110A and 110B function when the processor executes a program. Furthermore, all or part of the functions of the signal processing units 110A and 110B may be implemented using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0117] The above program may be recorded on a computer-readable recording medium. Computer-readable recording media include, for example, portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, and semiconductor memory devices (e.g., SSDs: Solid State Drives), as well as storage devices such as hard disks and semiconductor memory devices built into computer systems. The above program may also be transmitted via telecommunications lines.

[0118] While embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention.

[0119] The present invention is applicable to optical communication systems that communicate via optical transmission paths.

[0120] 10, 20... Optical communication system; 100A, 100B, 200A, 200B, 200A-1 to 200A-P, 200B-1 to 200B-Q... Communication device; 110A, 110B... Signal processing unit; 120A, 120B... Temperature controller; 130A, 130B... Transmitter; 140A, 140B... Receiver; 150A, 150B... Data storage unit; 160A, 160B... Multiplexing / demultiplexing device

Claims

1. A communication device comprising: a receiving unit that receives multiple optical signals of different wavelengths transmitted from a communication device of a communication partner connected via an optical transmission path; a data holding unit that holds data used to detect frequencies that are attenuated due to chromatic dispersion; and a signal processing unit that estimates a zero-dispersion wavelength based on the data and the frequency spectrum of each of the multiple optical signals received by the receiving unit.

2. The data held by the data holding unit is determined in advance by simulation, as described in claim 1.

3. The data held by the data holding unit is obtained by simulating 0km transmission for at least one combination of the bandwidth of the transmitted signal, the bandwidth of the received signal, the bandwidth of the modulator, and the bandwidth of the receiver in the system used, as described in claim 2.

4. The communication device according to any one of claims 1 to 3, wherein the signal processing unit obtains frequency spectra for estimating the zero-dispersion wavelength by performing predetermined calculations on the data and the frequency spectra of each of the plurality of optical signals received by the receiving unit, and calculates a notch frequency based on each of the obtained frequency spectra.

5. The communication device according to any one of claims 1 to 3, wherein the data holding unit holds frequency spectrum data used when detecting frequencies that are attenuated due to chromatic dispersion, or waveform data before transmission, as the data.

6. An optical communication system comprising a first communication device and a second communication device connected via an optical transmission path, wherein the first communication device comprises a transmitting unit that transmits a plurality of optical signals of different wavelengths to the second communication device via the optical transmission path, and the second communication device comprises a receiving unit that receives a plurality of optical signals of different wavelengths transmitted from the first communication device, a data holding unit that holds data used when detecting frequencies that are attenuated due to chromatic dispersion, and a signal processing unit that estimates a zero-dispersion wavelength based on the data and the frequency spectrum of each of the plurality of optical signals received by the receiving unit.

7. A zero-dispersion wavelength estimation method that receives multiple optical signals of different wavelengths transmitted from a communication device of a communication partner connected via an optical transmission path, and estimates the zero-dispersion wavelength based on data used to detect frequencies attenuated due to pre-held chromatic dispersion and the frequency spectra of each of the received multiple optical signals.

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