WO2017029753A1 - Communication device, optical transmission system, and frequency control method - Google Patents

Abstract

A communication device 1 according to the present invention is provided with: an optical transmitter/receiver 12-1 which adds a first frequency fluctuation to an optical signal having a first optical frequency, and transmits said optical signal; and an optical transmitter/receiver 12-2 which adds, to an optical signal having a second optical frequency, a second frequency fluctuation synchronized with the first optical frequency, and transmits said optical signal. Optical transmitter/receiver 12-1 calculates, on the basis of an error signal calculated on the basis of the reception quality of the optical signal having the first optical frequency and the reception quality of the optical signal having the second frequency, a first shift amount by which the optical frequency of the optical signal having the first optical frequency is to be shifted, and shifts the optical frequency of the optical signal having the first optical frequency by the first shift amount. Optical transmitter/receiver 12-2 calculates, on the basis of the error signal, a second shift amount by which the optical frequency of the optical signal having the second optical frequency is to be shifted, and shifts the optical frequency of the optical signal having the second optical frequency by the second shift amount.

Description

Communication apparatus, optical transmission system, and frequency control method

The present invention relates to a communication apparatus, an optical transmission system, and a frequency control method for controlling the frequency of an optical signal.

In trunk-system optical communication networks, large-capacity transmission exceeding 100 Gbps within one optical fiber, that is, ultra 100 Gbps class transmission is required. As a technique for realizing ultra 100 Gbps class transmission, super channel technology for allocating a large amount of information by superimposing a plurality of subcarriers called subcarriers has been studied. Super-channel transmission increases the use efficiency of optical frequencies and realizes large capacity. On the other hand, in super channel transmission, since subcarriers are arranged with high density on the optical frequency, there is a problem that signal quality deteriorates due to interference between adjacent subcarriers.

Also, in super channel transmission of a trunk optical communication network, optical filters for wavelength selection are arranged in multiple stages in a transmission path, and demultiplexing, multiplexing, and path switching of signals of arbitrary plural subcarriers are performed. For this reason, there is a problem that signal quality is deteriorated due to the reduction of the subcarrier signal band other than the transmission band of the optical filter, that is, the signal band narrowing.

In super-channel transmission in trunk optical communication networks, optimizing the optical frequency arrangement of subcarriers is important to suppress signal quality degradation due to inter-subcarrier interference and signal band narrowing. Even if the optical frequency arrangement is optimized at the start of system operation, the optical frequency of the light source shifts due to changes in the surrounding environment or changes over time, and the optimal conditions for optical frequency arrangement cannot be maintained. Therefore, in order to maintain the signal quality from the start to the end of system operation, it is necessary to optimally control the optical frequency arrangement following the change in optical frequency of each subcarrier signal.

For example, in the conventional method disclosed in Patent Document 1, the optical transmitter transmits a signal with frequency fluctuation added, and the optical receiver measures the signal quality. And in this conventional system, control which corrects the optical frequency shift of each subcarrier of an optical transmission part for every subcarrier based on the change information of the signal quality measured by the optical receiving part is performed.

JP 2007-104008 A

However, according to the conventional method described in Patent Document 1, since crosstalk is evaluated for each subcarrier to obtain a wavelength shift, the crosstalk can be reduced. However, the arrangement of optical frequencies of subcarriers can be reduced. Cannot be controlled in consideration of the signal quality of the entire optical transmission system.

The present invention has been made in view of the above, and an object of the present invention is to obtain a communication device capable of appropriately controlling the arrangement of optical frequencies of subcarriers in consideration of the signal quality of the entire optical transmission system. To do.

In order to solve the above-described problems and achieve the object, a communication apparatus according to the present invention includes a first optical transceiver that transmits an optical signal having a first optical frequency by adding a first frequency fluctuation; And a second optical transceiver that transmits the optical signal having the second optical frequency by adding a second frequency fluctuation synchronized with the first optical frequency. Further, the first optical transceiver is configured to output the first optical transceiver based on the error signal calculated based on the reception quality of the optical signal having the first optical frequency and the reception quality of the optical signal having the second frequency. Calculating a first shift amount, which is a shift amount for shifting the optical frequency of the optical signal of the first optical frequency, shifting the optical frequency of the optical signal of the first optical frequency by the first shift amount, and The second optical transceiver calculates a second shift amount, which is a shift amount for shifting the optical frequency of the optical signal of the second optical frequency, based on the error signal, and outputs the light of the second optical frequency. The optical frequency of the signal is shifted by the second shift amount.

According to the present invention, it is possible to appropriately control the arrangement of optical frequencies of subcarriers in consideration of the signal quality of the entire optical transmission system.

1 is a diagram illustrating a configuration example of an optical transmission system according to a first embodiment. The figure which shows the structural example of the optical transmitter-receiver of the communication apparatus of Embodiment 1. The figure which shows the structural example of the optical transmitter / receiver of the communication apparatus which is an opposing apparatus of Embodiment 1. The figure which shows the structural example of an opposing apparatus in case the communication apparatus which is an opposing apparatus of Embodiment 1 transmits a data signal. A flowchart showing an example of an optical frequency control procedure according to the first embodiment. The schematic diagram which shows an example of the change of the average optical frequency by the polarity of a dither at the time of performing the average optical frequency control of Embodiment 1 Schematic diagram showing an example of a temporal change in the optical frequency of the optical signal of each subcarrier transmitted from the communication apparatus when the average optical frequency control of the first embodiment is performed. Schematic diagram illustrating an example of a change in signal quality of each subcarrier transmitted from a communication apparatus when average optical frequency control according to Embodiment 1 is performed The schematic diagram which shows an example of the change of the optical frequency interval by the polarity of a dither at the time of performing the optical frequency interval control of Embodiment 1 Schematic diagram showing an example of temporal change of the optical frequency of the optical signal of each subcarrier transmitted from the communication device when the optical frequency interval control of the first embodiment is performed. Schematic diagram illustrating an example of a change in signal quality of each subcarrier transmitted from a communication apparatus when optical frequency interval control according to Embodiment 1 is performed 7 is a flowchart illustrating an example of a processing procedure in the optical frequency shift synchronization apparatus according to the first embodiment. 6 is a flowchart illustrating an example of a processing procedure in the optical frequency shifter according to the first embodiment. FIG. 3 illustrates a configuration example of a processing circuit according to the first embodiment. FIG. 3 is a diagram illustrating a configuration example of a control circuit according to the first embodiment. The figure which shows an example of the control procedure in the case of processing in order of the optical frequency interval control of Embodiment 1, and an average optical frequency control The flowchart which shows an example of the process sequence in the case of performing the average optical frequency control of Embodiment 1. The figure which shows the structural example of the optical transmission system concerning Embodiment 2. FIG. The figure which shows the structural example of the optical transmitter-receiver of the communication apparatus of Embodiment 2. The figure which shows the structural example of the optical transmitter-receiver of the communication apparatus which is an opposing apparatus of Embodiment 2.

Hereinafter, a communication apparatus, an optical transmission system, and a frequency control method according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of an optical transmission system according to a first embodiment of the present invention. As shown in FIG. 1, the optical transmission system of the present embodiment includes a communication device 1, a communication device 2, and a transmission path 3. In the present embodiment, an example will be described in which the optical frequency of an optical signal transmitted from the communication device 1 and received by the communication device 2 via the transmission path 3 is adjusted.

The optical transmission system according to the present embodiment is a communication system that transmits an optical signal by a super channel transmission method, and is a communication network called a trunk optical communication network, for example. Although FIG. 1 shows an example in which two subcarriers are multiplexed, the number of subcarriers to be multiplexed is not limited to this example. In FIG. 1, a portion indicating an optical signal path among lines connecting each component is indicated by a solid line, and a portion indicating an electric signal path is indicated by a dotted line.

The communication device 1 as the first communication device includes an optical frequency shift synchronization device 11, optical transceivers 12-1 and 12-2, and an optical coupler 13. The optical frequency shift synchronization device 11 corrects an optical frequency shift that is a frequency shift of the optical signal based on the error signal indicating the frequency error of the optical signal calculated in the communication device 2. The optical transceiver 12-1 generates and outputs an optical signal of subcarrier # 1, which is the first subcarrier. The optical transceiver 12-2 generates and outputs an optical signal of subcarrier # 2, which is the second subcarrier. The first subcarrier and the second subcarrier are carriers having different optical frequencies, that is, different optical wavelengths. The optical coupler 13 combines the optical signal output from the optical transceiver 12-1 and the optical signal output from the optical transceiver 12-2, and outputs the combined signal to the transmission path 3. The optical coupler 13 demultiplexes the optical signal received from the communication device 2 via the transmission path 3 into two, and outputs one to the optical transceiver 12-1 and the other to the optical transceiver 12-2.

The communication device 2 as the second communication device includes an optical demultiplexer 21, optical transceivers 22-1 and 22-2, and an error signal calculation unit 23. The optical demultiplexer 21 demultiplexes the optical signal received from the communication device 2 via the transmission path 3 into two, and outputs one to the optical transceiver 22-1 and the other to the optical transceiver 22-2. The optical demultiplexer 21 combines the optical signal output from the optical transmitter / receiver 22-1 and the optical signal output from the optical transmitter / receiver 22-2, and outputs the combined signal to the transmission line 3. The error signal calculation unit 23 calculates an error signal indicating an optical frequency shift using the signal quality calculated by the optical transceiver 22-1 and the optical transceiver 22-2.

FIG. 2 is a diagram illustrating a configuration example of the optical transceiver 12-1 of the communication device 1 according to the present embodiment. As shown in FIG. 2, the optical transceiver 12-1 includes an optical signal generation unit 121, a transmission digital signal processing unit 122, and an optical demodulation unit 123. The configuration of the optical transceiver 12-2 is the same as that of the optical transceiver 12-1. The optical signal generation unit 121 includes a light source 124 and an optical modulator 125. The light source 124 emits continuous light. The optical modulator 125 modulates the continuous light transmitted from the light source 124 according to a data signal that is an electrical signal, generates an optical signal, and outputs the generated optical signal to the optical coupler 13.

The transmission digital signal processing unit 122 includes an optical frequency shifter 126, an optical frequency shift amount calculator 127, and a data signal generation unit 128. The data signal generation unit 128 generates a data signal. Specifically, the data signal generation unit 128 performs, for example, a process of error correction encoding information to be transmitted, binary phase modulation (BPSK: Binary Phase Shift Keying), quaternary phase modulation (QPSK: Quadrature Phase Shift Keying). Alternatively, a data signal is generated by performing a symbol mapping process according to a modulation method such as 16-value amplitude phase modulation (16QAM (Quadrature Amplitude Modulation)), a process for shaping a signal spectrum, and the like. There are no particular restrictions on the specific processing content of the data signal generation unit 128 and the configuration of the data signal generation unit 128. The optical frequency shift amount calculator 127 calculates the optical frequency shift amount using the error signal notified from the communication device 2, and outputs the calculated frequency shift amount to the optical frequency shifter 126. The optical frequency shifter 126 electrically adds a frequency shift of the optical frequency shift amount notified from the optical frequency shift amount calculator 127 to the data signal. Further, the optical frequency shifter 126 can apply a dither having a predetermined frequency amplitude of Δf to the data signal. That is, the optical frequency shifter 126 changes the dither frequency between + Δf and −Δf. Dither refers to frequency fluctuation. Thus, dithering may increase the frequency or decrease the frequency. That is, the dither frequency polarity may be positive or negative. Hereinafter, the polarity of the dither frequency is simply referred to as the dither polarity. In the following, an example in which the amplitude of the dither frequency is fixed will be described. However, the amplitude of the dither frequency may not be fixed. Hereinafter, the amplitude of the dither frequency is appropriately referred to as dither amplitude. For example, the dither is generated by changing the optical frequency shift amount at regular time intervals using a rectangular electric clock signal. For example, when the optical frequency shifter 126 is mounted by a DSP (Digital Signal Processor), the register in the DSP is rewritten so as to shift the optical frequency by + Δf when the voltage a changes to b. On the other hand, when the voltage b changes to a, the DSP register is rewritten so as to shift the frequency by −Δf.

The optical demodulator 123 includes a coherent receiver 130 and a reception digital signal processor 129. The coherent receiver 130 converts the optical signal received from the communication device 2 via the transmission path 3 and the optical coupler 13 into an electrical signal and outputs the electrical signal. Specifically, light having a desired wavelength is converted into an electric signal by causing the optical signal input from the optical coupler 13 and the light transmitted from the light source 124 to interfere with each other. The reception digital signal processor 129 demodulates the electrical signal output from the coherent receiver 130. Also, the reception digital signal processor 129 outputs an error signal notified from the communication device 2 among the data obtained by demodulation to the optical frequency shift amount calculator 127.

FIG. 3 is a diagram illustrating a configuration example of the optical transceiver 22-1 of the communication device 2 which is the opposite device of the present embodiment. In the present embodiment, the opposing device refers to a device that is opposed to the communication device 1 that is a device to be controlled of the optical frequency, that is, a device that receives a signal transmitted from the communication device 1. As shown in FIG. 3, the optical transceiver 22-1 includes an optical demodulator 221 and an optical signal generator 222. The configuration of the optical transceiver 22-2 is the same as that of the optical transceiver 22-1.

The optical demodulator 221 includes a coherent receiver 223, a received digital signal processor 224, a signal quality monitor 225, and a frequency offset unit 226. The coherent receiver 223 performs coherent detection on the optical signal input from the optical demultiplexer 21 and converts it into an electrical signal. That is, the coherent receiver 223 converts light having a desired wavelength into an electrical signal by causing the optical signal input from the optical demultiplexer 21 to interfere with the light transmitted from the light source 227.

The reception digital signal processor 224 restores the information transmitted from the communication device 1 on the transmission side. That is, for example, when the data signal generation unit 128 of the communication apparatus 1 on the transmission side performs modulation, demodulation corresponding to the modulation is performed, and the data signal generation unit 128 performs error correction coding. If so, error correction decoding is performed. The signal quality monitor 225 calculates the quality of the signal received from the communication apparatus 1 using the information output from the reception digital signal processor 224 and outputs the calculated result to the error signal calculation unit 23. As a signal quality calculation method in the signal quality monitor 225, for example, there is a method of calculating a Q value indicating the quality of an optical signal using a noise distribution of received signal point arrangement on a complex plane. In this case, the information output from the reception digital signal processor 224 is the noise distribution of the reception signal point arrangement on the complex plane. As another method for calculating the signal quality in the signal quality monitor 225, there is a method for calculating a BER (Bit Error Rate) using the number of bits corrected in error correction decoding. In this case, the information output from the reception digital signal processor 224 is the number of bits subjected to error correction in error correction decoding. The signal quality calculation method in the signal quality monitor 225 is not limited to the method described above, and any method may be used. The frequency offset unit 226 calculates the polarity of the optical frequency shift of the dither added in the communication device 1 and outputs the calculated polarity to the error signal calculation unit 23.

The optical signal generator 222 includes a light source 227 and an optical modulator 228. The light source 227 emits continuous light. The optical modulator 228 modulates the continuous light transmitted from the light source 227 according to an error signal that is an electrical signal, generates an optical signal, and outputs the generated optical signal to the optical demultiplexer 21.

Next, the operation of this embodiment will be described. Here, an operation for controlling the optical frequency of an optical signal transmitted from the communication device 1 toward the opposite communication device 2 will be described. The optical frequency shift synchronizer 11 instructs the optical transceivers 12-1 and 12-2 to add synchronized dither or reverse phase dither according to a predetermined control sequence. As will be described later, the optical frequency control of the present embodiment is configured by average optical frequency control and optical frequency interval control. The control sequence indicates which one of the average optical frequency control, that is, the control with the added in-phase dither, and the optical frequency interval control, ie, the control with the anti-phase dither added, performed first. In the optical transceiver 12-1 of the communication apparatus 1, the data signal generation unit 128 generates a data signal and inputs the data signal to the optical frequency shifter 126. The optical frequency shifter 126 of the optical transceiver 12-1 adds a dither having a predetermined amplitude Δf to the input data signal. The data signal with the dither added is input to the optical modulator 125 of the optical transceiver 12-1. The optical modulator 125 of the optical transceiver 12-1 optically modulates the light transmitted from the light source 124 based on the data signal input from the optical frequency shifter 126, and generates an optical signal of subcarrier # 1. .

The optical transceiver 12-2 of the communication device 1 generates an optical signal of subcarrier # 2 by the same operation as that of the optical transceiver 12-1. At this time, when the optical frequency shifter 126 of the optical transceiver 12-2 is instructed to add the synchronized in-phase dither from the frequency shift synchronizer 11, the optical frequency shifter of the optical transceiver 12-1 In-phase dither, that is, the same dither is added in synchronization with 126. The optical frequency shifter 126 of the optical transceiver 12-2, when instructed by the frequency shift synchronizer 11 to add a reverse phase dither, is an optical frequency shifter of the optical transceiver 12-1. A dither having a phase different from that of the dither added by the optical frequency shifter 126 of the optical transceiver 12-1 by 180 degrees is added. The light source 124 of the optical transceiver 12-2 transmits light having a different optical frequency, that is, a light wavelength different from that of the light source 124 of the optical transceiver 12-1. That is, the light source 124 of the optical transceiver 12-1 transmits light having an optical wavelength corresponding to subcarrier # 1, and the light source 124 of the optical transceiver 12-2 transmits light having an optical wavelength corresponding to subcarrier # 2. To do.

As described above, the optical transmitter / receiver 12-1 is the first optical transmitter / receiver that transmits the optical signal having the first optical frequency by adding the first frequency fluctuation, and the optical transmitter / receiver 12-2 A second optical transceiver that transmits an optical signal having a second optical frequency by adding a second frequency fluctuation synchronized with the first optical frequency to transmit the optical signal. The optical signal of the first optical frequency is an optical signal of subcarrier # 1, and the optical signal of the second optical frequency is an optical signal of subcarrier # 2. The first frequency fluctuation is an optical frequency fluctuation added to the optical signal of the subcarrier # 1 by the dither added by the optical frequency shifter 126 of the optical transceiver 12-1, and the second frequency fluctuation is the second frequency fluctuation. The fluctuation of the optical frequency added to the optical signal of subcarrier # 2 by the dither added by the optical frequency shifter 126 of the optical transceiver 12-2.

The optical coupler 13 combines the optical signal of the subcarrier # 1 and the optical signal of the subcarrier # 2 and outputs the multiplexed signal to the transmission path 3. The optical demultiplexer 21 of the communication device 2 receives the optical signal combined by the optical coupler 13 of the communication device 1 via the transmission path 3, demultiplexes the received optical signal into two, To the optical transceiver 22-1 and the other to the optical transceiver 22-2.

In the optical transceiver 22-1, the coherent receiver 223 converts the optical signal received using the light transmitted from the light source 227 into an electrical signal and outputs the electrical signal to the reception digital signal processor 224. The light source 227 of the optical transceiver 22-1 transmits light having an optical wavelength corresponding to the subcarrier # 1. Therefore, in the coherent receiver 223 of the optical transceiver 22-1, the optical signal of subcarrier # 1 is detected and converted into an electrical signal. The reception digital signal processor 224 of the optical transceiver 22-1 restores the electrical signal output from the coherent receiver 223 to the transmitted information, and outputs information used for signal quality calculation to the signal quality monitor 225. As described above, the information used to calculate the signal quality is, for example, the noise distribution of the received signal point arrangement on the complex plane or the number of error-corrected bits. The reception digital signal processor 224 outputs the electrical signal output from the coherent receiver 223 to the frequency offset unit 226.

The signal quality monitor 225 of the optical transceiver 22-1 calculates the signal quality based on the information output from the received digital signal processor 224, and outputs the calculated signal quality to the error signal calculator 23. The signal quality calculated by the signal quality monitor 225 is, for example, a Q value based on the noise distribution of the received signal point arrangement on the complex plane, or a BER calculated based on the number of error-corrected bits. The frequency offset unit 226 of the optical transceiver 22-1 calculates the dither optical frequency shift polarity based on the electrical signal output from the received digital signal processor 224, and outputs it to the error signal calculator 23. For example, when the dither is a square wave, the frequency offset unit 226 adds -Δf to the optical frequency of the optical signal transmitted from the communication apparatus 1 for half the dither period and the other half of the dither period. Is added with + Δf. Therefore, for example, the frequency offset unit 226 calculates the frequency of the electrical signal output from the reception digital signal processor 224, and determines the dither polarity based on whether the calculated frequency is higher or lower than the frequency of the corresponding subcarrier. To do. Alternatively, the frequency offset unit 226 observes the time change of the calculated frequency, for example, the amount of change of the frequency per fixed time, and the polarity is − from the time when the frequency is decreased by a certain amount to the time when the frequency is increased by a certain amount It can be determined that the polarity is determined to be + from the time when the frequency is increased by a certain amount or more until the frequency is decreased by a certain amount or more.

The optical transmitter / receiver 22-2 calculates the optical frequency shift polarity and signal quality corresponding to the subcarrier # 2 by the same processing as the optical transmitter / receiver 22-1 and calculates the calculated optical frequency shift polarity and signal quality. Are input to the error signal calculator 23. The light source 227 of the optical transceiver 22-2 transmits light having an optical wavelength corresponding to the subcarrier # 2. Thereby, in the coherent receiver 223 of the optical transceiver 22-2, the optical signal of the subcarrier # 2 is detected and converted into an electrical signal.

The error signal calculation unit 23 determines the order of calculation using the dither optical frequency shift polarity, and the signal quality of the subcarrier # 1 output from the optical transceiver 21-1, that is, the reception quality and the optical transceiver 21- 2, an error signal is calculated based on the signal quality of subcarrier # 2, that is, the reception quality. A method for calculating the error signal will be described later. The optical modulator 228 of the optical transceiver 22-1 modulates the light transmitted from the light source 227 according to the error signal to generate an optical signal, and outputs the generated optical signal to the optical demultiplexer 21. The optical demultiplexer 21 outputs the optical signal output from the optical modulator 228 to the transmission path 3. The optical signal receives the optical signal transmitted from the communication device 2 via the transmission path 3. As a result, the error signal calculated by the communication device 2 is transmitted to the communication device 1 as an optical signal. That is, an error signal indicating an optical frequency error of the optical signal transmitted from the communication device 1 is fed back to the communication device 1. The error signal is used for controlling the optical frequency in the communication device 1.

Here, the operation in which the optical transceiver 22-1 transmits the error signal to the communication device 1 has been described. Similarly, the optical transceiver 22-2 also transmits the error signal to the communication device 1. Note that either the optical transceiver 22-1 or the optical transceiver 22-2 may transmit the error signal. When one of the optical transceiver 22-1 and the optical transceiver 22-2 transmits an error signal, in the communication device 1, either the optical transceiver 12-1 or the optical transceiver 12-2 transmits the error signal. Will receive. Therefore, the optical transceiver 12-1 or the optical transceiver 12-2 that has received the error signal sends the error signal to the optical frequency shift amount calculator 127 of the other optical transceiver 12-1 or the optical transceiver 12-2. Notice.

The error signal may be transmitted separately from the data signal. When the data signal is also transmitted from the communication device 2 to the communication device 1, the error signal is input to the optical modulator 288 together with the data signal and used for modulation. May be. Moreover, you may transmit using the area | region which can be utilized in the data frame which is a frame for transmitting a data signal. For example, when a data signal is transmitted as a data frame of an OTN (Optical-channel Transport Unit) frame defined in ITU-T (International Telecommunication Union Telecommunication standardization sector) G.709, the communication channel in the data frame is Can be used. When the error signal is transmitted using the area in the data frame, the communication device 2 also has a function on the data signal transmission side as shown in FIG.

FIG. 4 is a diagram illustrating a configuration example of the communication device 2 when the communication device 2 transmits a data signal. In this case, the optical transceiver 22-1 of the communication apparatus 2 has a configuration in which a transmission digital signal processing unit 230 is added to the optical transceiver 22-1 shown in FIG. The transmission digital signal processing unit 230 includes a data signal generation unit 232 and a framer 231 that generate a data signal. The data signal generation unit 232 generates a data signal similarly to the data signal generation unit 128 of the communication device 1. The framer 231 arranges a data signal and an error signal in a data frame such as an OTN frame and outputs the data signal to the optical modulator 228.

In addition, when there is an empty optical fiber called a dark fiber, that is, an empty transmission line, the error signal may be transmitted using the dark fiber. In this case, it is assumed that the signal output from the optical demultiplexer 21 of the communication device 2 can be output to the dark fiber, and the signal via the dark fiber can be input to the optical coupler 13 of the communication device 1. Further, the error signal may be transmitted using a free optical frequency that is not used for data transmission, that is, a free wavelength. When transmitting at an empty wavelength, the communication device 2 includes an optical transceiver corresponding to an optical frequency different from that of the optical transceivers 22-1 and 22-2, in addition to the illustrated optical transceivers 22-1 and 22-2. Assume that the communication apparatus 1 includes an optical transceiver corresponding to an optical frequency different from that of the optical transceivers 12-1 and 12-2, in addition to the illustrated optical transceivers 12-1 and 12-2. In any case, it is assumed that how the error signal is transmitted is determined in advance and is set in the communication device 1 and the communication device 2.

The optical coupler 13 of the communication apparatus 1 receives the error signal as an optical signal via the optical transmission path 3, demultiplexes the received optical signal into two, and inputs one to the optical transceiver 12-1. The other is input to the optical transceiver 12-2. Here, assuming that an error signal is transmitted from the optical transceiver 22-1 of the communication apparatus 2, the optical transceiver 12-1 receives the error signal. Specifically, the coherent receiver 130 of the optical demodulator 123 of the optical transceiver 12-1 converts the optical signal into an electrical signal, and the received digital signal processor 129 extracts the error signal from the electrical signal and the optical frequency shift amount. Input to the calculator 127. The optical frequency shift amount calculator 127 converts the error signal into the optical frequency shift amount, that is, calculates the optical frequency shift amount based on the error signal, and notifies the optical frequency shifter 126 of the optical frequency shift amount. The optical frequency shifter 126 generates a data signal for shifting the optical frequency by the optical frequency shift amount notified from the optical frequency shift amount calculator 127. As a result, the optical signal generated by the optical signal generator 121 of the optical transceiver 12-1 is shifted by the optical frequency shift amount. Similarly, the optical transceiver 12-2 calculates the optical frequency shift amount based on the received error signal, and shifts the optical frequency shift amount of the optical signal generated by the optical signal generation unit 121 of the optical transceiver 12-2. .

That is, the optical transceiver 12-1 uses the first optical frequency based on the error signal calculated based on the reception quality of the optical signal of the first optical frequency and the reception quality of the optical signal of the second frequency. The first shift amount, which is a shift amount for shifting the optical frequency of the optical signal of subcarrier # 1, which is an optical signal of the first optical frequency, is calculated, and the optical frequency of the optical signal of the first optical frequency is shifted by the first shift amount. . Further, the optical transceiver 12-2 calculates a second shift amount that is a shift amount for shifting the optical frequency of the optical signal of the subcarrier # 2 that is the optical signal of the second optical frequency, based on the error signal. Then, the optical frequency of the optical signal having the second optical frequency is shifted by the second shift amount.

Next, the optical frequency control of the optical signal transmitted by the communication apparatus 1 according to the present embodiment will be described in detail. FIG. 5 is a flowchart showing an example of the optical frequency control procedure of the present embodiment. The optical frequency control of the present embodiment includes (A) average optical frequency control and (B) optical frequency interval control. The example of FIG. 5 shows an example in which (B) optical frequency interval control is performed after (A) average optical frequency control is performed.

First, in order to perform the average optical frequency control, the communication device 1 adds in-phase frequency fluctuations or dithers synchronized in amplitude Δf to the subcarrier # 1 and the subcarrier # 2 (step S1). Specifically, the optical frequency shift synchronizer 11 instructs the optical transceivers 12-1 and 12-2 to add synchronized in-phase dither. The optical frequency shifter 126 of the optical transceiver 12-1 and the optical frequency shifter 126 of the optical transceiver 12-2 add the same synchronized dither according to the instruction from the optical frequency shift synchronizer 11. As a synchronization method, for example, the optical frequency shift synchronizer 11 instructs the optical frequency shifters 126 of the optical transceivers 12-1 and 12-2 to start adding dither simultaneously. The optical frequency shifters 126 of the optical transceivers 12-1 and 12-2 are configured to be able to generate the same dither. For example, the optical frequency shifters 126 of the optical transceivers 12-1 and 12-2 are configured to be able to generate the same square wave, sine wave, or the like. The optical frequency shifters 126 of the optical transceivers 12-1 and 12-2 simultaneously generate the same dither based on an instruction from the optical frequency shift synchronizer 11 and add it to the data signal. The optical modulators 125 of the optical transceivers 12-1 and 12-2 generate optical signals corresponding to the electrical signals output from the optical frequency shifter 126, respectively, and output the optical signals to the optical coupler 13. The optical coupler 13 combines the optical signal output from the optical transceiver 12-1 and the optical signal output from the optical transceiver 12-2, and outputs the combined signal to the transmission path 3.

Next, the communication device 2 via the transmission path 3 receives the optical signal, calculates an error signal E _a (step S2). Specifically, the optical transmitter / receiver 22-1 and the optical demodulator 221 of the optical transmitter / receiver 22-2 via the optical demultiplexer 21 convert the optical signal into an electrical signal as described above, and transmit the transmitted information. Restore and calculate dither polarity and signal quality. Based on the dither polarity and signal quality calculated by the optical demodulator 221 of the optical transceiver 22-1 and optical transceiver 22-2, the error signal calculator 23 calculates the error signal E _a according to the following equation (1). calculate. Here, it is assumed that the signal quality is the Q value, and the Q value of the subcarrier number # iε {1,2} corresponding to the dither polarity jε {+, −} is defined as Q _ij . That is, the Q value optical transceiver 22-1 is calculated when the polarity of the dither + a Q _1+, the polarity of the dither - the Q value optical transceiver 22-1 to calculate the time for Q _{1 The} Q value calculated by the optical transceiver 22-2 when the dither polarity is + is Q ₂₊ and the Q value calculated by the optical transceiver 22-2 when the dither polarity is- Q _2- . Min {x, y} represents the minimum value of x and y. Here, it is assumed that the smaller the signal quality, the lower the signal quality.
E _a = Min {Q ₁₊ , Q ₂₊ } −Min {Q ₁₋ , Q ₂₋ } (1)

As described above, the error signal is transmitted from the communication device 2 to the communication device 1 as an optical signal. In the communication device 1, proportional-integral control is performed, and the optical frequency shift amount f _{i, FC} is updated by the following equations (2), (3) (step S3). Note that k _α is a proportional coefficient, and is assumed to be predetermined, for example. The optical frequency shift amount corresponding to the subcarrier #i is described as _{fi, FC} . The initial optical frequency shift amount, that is, the initial value of f _{i, FC} is 0 Hz.
f _{1, FC} = f _{1, FC} + k _α E _a (2)
_{f 2, FC = f 2,} FC + k α E a ... (3)

Specifically, the optical frequency shift amount calculator 127 of the optical transceiver 12-1 calculates f _{1, FC} by the above equation (2) _, and the optical frequency shift amount calculator 127 of the optical transceiver 12-2 Then, f2 _{, FC} is calculated by the above equation (3). The optical frequency shift amount calculator 127 of the optical transceiver 12-1 notifies f _{1 and FC} as the optical frequency shift amount to the optical frequency shifter 126 of the optical transceiver 12-1. The optical frequency shift amount calculator 127 of the transceiver 12-2 notifies f _{2 and FC} as the optical frequency shift amount to the optical frequency shifter 126 of the optical transceiver 12-2. The optical frequency shifters 126 of the optical transceiver 12-1 and the optical transceiver 12-2 shift the data signal based on the notified optical frequency shift amount.

As described above, the first and second frequency fluctuations are the same in the first control period, which is a period during which the average optical frequency control is performed, and the first and second frequency fluctuations increase the optical frequency. 1 period and a second period for decreasing the optical frequency. Further, in the first control period, the error signal has a value of the lower quality of the reception quality of the optical signal of the first optical frequency and the reception quality of the optical signal of the second frequency in the first period. The signal indicating the difference between the reception quality of the optical signal of the first optical frequency and the reception quality of the optical signal of the second frequency in the second period, the value having the lower quality. In the first control period, the optical transceiver 12-1 performs control to update the first shift amount with a value obtained by adding a value obtained by multiplying the error signal to the proportional coefficient to the first shift amount, The optical transceiver 12-2 performs control to update the second shift amount with a value obtained by adding a value obtained by multiplying the error signal by the proportional coefficient to the second shift amount. In the present embodiment, the error signal is calculated in the communication device 2 which is the opposite device that receives the optical signals of the first and second frequencies, and the optical transceiver 12-1 receives the error received from the opposite device. The first shift amount is calculated based on the signal, and the optical transceiver 12-2 calculates the second shift amount based on the error signal received from the opposite device.

By the processing described above, it is possible to control the average optical frequency of two subcarriers so as to improve the signal quality of both subcarriers without deviation. The average optical frequency of the two subcarriers indicates a value obtained by averaging the center frequencies of the two subcarriers, that is, an average value. Specifically, the difference between the case where the average optical frequency of the two subcarriers is changed in the direction of increasing the optical frequency and the case where the average optical frequency of the two subcarriers is changed in the direction of decreasing the optical frequency. As an error signal, the average optical frequency can be set so as to reduce the error signal. As a result, when the band is narrowed by the optical filter or the like of the transmission line 3, the signal cut by the optical filter or the like can be reduced. As a result, even when the transmission band itself is unknown due to the optical filter or the like of the transmission path 3, the average optical frequency is set near the center of the entire transmission band due to the optical filter or the like of the transmission path 3.

FIG. 6 is a schematic diagram illustrating an example of a change in average optical frequency due to dither polarity when average optical frequency control is performed. SC # 1 in FIG. 6 indicates subcarrier # 1, and SC # 2 indicates subcarrier # 2. The horizontal axis in FIG. 6 is the frequency, and the vertical axis is the intensity of the optical signal. FIG. 6 shows the frequency distribution of the intensity of the optical signal of each subcarrier transmitted from the communication apparatus 1. F _{1, +} indicates the frequency range when the dither polarity of the optical signal of subcarrier # 1 is +, and F _{1, −} indicates the frequency range when the dither polarity of the optical signal of subcarrier # 1 is −. Indicates the range. F _{2, +} indicates the frequency range when the dither polarity of the optical signal of subcarrier # 2 is +, and F _{2, −} indicates the frequency range when the dither polarity of the optical signal of subcarrier # 2 is −. Indicates the range. As shown in FIG. 6, since the dither synchronized with two subcarriers is added in the average optical frequency control, when the polarities of both subcarriers are +, the average optical frequency indicated by white circles in FIG. The direction changes to the direction indicated by the black arrow in FIG. Further, when the polarities of both subcarriers are −, the average optical frequency indicated by white circles in FIG. 6 changes in the direction indicated by white arrows in FIG.

FIG. 7 is a schematic diagram illustrating an example of a temporal change in the optical frequency of the optical signal of each subcarrier transmitted from the communication apparatus 1 when average optical frequency control is performed. FIG. 7 shows an example in which a square wave is added as dither. The horizontal axis in FIG. 7 is time, and the vertical axis is frequency. f _{1, FC} and f _{2, FC} are optical frequencies after the above-described frequency offset of subcarrier # 1 and subcarrier # 2.

FIG. 8 is a schematic diagram illustrating an example of a change in signal quality of each subcarrier transmitted from the communication apparatus 1 when average optical frequency control is performed. In FIG. 8, the horizontal axis indicates the average optical frequency, and the vertical axis indicates the signal quality. Also, signal quality 61 shows the signal quality to Q ₁ subcarrier # 1 of the optical signal, the signal quality. 62 shows the signal quality Q ₂ of the sub-carrier # 2 of the optical signal. Min {Q ₁ , Q ₂ } is indicated by a solid line in the figure. 8 shows the frequency distribution of subcarrier # 1 and subcarrier # 2 in a state where the average optical frequency of subcarrier # 1 and subcarrier # 2 is shifted to the lower side of the optical frequency. ing. The frequency distribution 64 indicates the frequency distribution of subcarrier # 1 and subcarrier # 2 in a state where the average optical frequency of subcarrier # 1 and subcarrier # 2 is shifted in the direction in which the optical frequency increases. The frequency distribution 65 shows the frequency distribution of subcarrier # 1 and subcarrier # 2 in an appropriate state. A dotted line superimposed on the frequency distributions 63, 64, and 65 in the upper part of FIG. The frequency distribution 65 in an appropriate state indicates that the average optical frequency is in the center of the transmission band of the optical filter. F _M in FIG. 8, the average light frequency when a frequency distribution 65 of the appropriate state. By controlling the error signal calculated in step S2 shown in FIG. 5 to approach 0, the average optical frequency can be controlled to approach f _M.

Returning to the description of FIG. 5, the communication apparatus 1 changes the setting to the optical frequency interval control (step S4), and the subcarrier # 1 and the subcarrier # 2 have opposite phase frequency fluctuations or dithers synchronized with each other in amplitude Δf. Is added. Specifically, the optical frequency shift synchronizer 11 changes the setting to optical frequency interval control, instructs the optical transceivers 12-1 and 12-2 to start dither generation, and the optical transceiver 12-2 is instructed to add a dither having an opposite phase. The optical frequency shifters 126 of the optical transceivers 12-1 and 12-2 add anti-phase frequency fluctuations or dithers synchronized with each other in amplitude Δf (step S5). For example, as described above, the optical frequency shifters 126 of the optical transceivers 12-1 and 12-2 can generate the same dither. When the optical frequency shift synchronizer 11 gives an instruction to add a reverse phase dither, the optical frequency shifter 126 of the optical transceiver 12-1 is instructed by the optical frequency shift synchronizer 11 in the same manner as in step S1. The dither generation is started and the dither is added, and the optical frequency shifter 126 of the optical transmitter / receiver 12-1 starts generating the dither having the reverse phase at the timing instructed by the optical frequency shift synchronizer 11. And add dither. Alternatively, instead of instructing the optical transceiver 12-2 to add a dither having an opposite phase to the optical transceiver 12-2, the optical frequency shift synchronizer 11 performs a dither having an opposite phase to the optical transceiver 12-1. You may instruct to add.

Next, the communication device 2 receives the optical signal via the transmission path 3, and calculates the error signal _Eb (step S6). Specifically, the optical transmitter / receiver 22-1 and the optical demodulator 221 of the optical transmitter / receiver 22-2 via the optical demultiplexer 21 convert the optical signal into an electrical signal as described above, and transmit the transmitted information. Restore and calculate dither polarity and signal quality. Based on the dither polarity and signal quality calculated by the optical demodulator 221 of the optical transceiver 22-1 and the optical transceiver 22-2, the error signal calculator 23 calculates the error signal E _b according to the following equation (4). calculate. The communication device 2 is notified from the communication device 1 whether the average optical frequency control is being performed or the optical frequency interval control is being performed, and the signal quality monitor 25 receives the signal received from the communication device 2. Based on the above, it can be determined whether average optical frequency control is being performed or whether optical frequency interval control is being performed.
E _b = Min {Q ₁₋ , Q ₂₊ } −Min {Q ₁₊ , Q ₂₋ } (4)

As described above, the error signal is transmitted from the communication device 2 to the communication device 1 as an optical signal. In the communication device 1, proportional-integral control is performed, and the optical frequency shift amount f _{i, FC} is updated by the following equations (5), (6) (step S7). Note that _kβ is a proportionality coefficient and is set in advance, for example. The optical frequency shift amount corresponding to the subcarrier #i is described as _{fi, FC} .
f _{1, FC} = f _{1, FC} + k _β E _b (5)
f _{2, FC} = f _{2, FC} −k _β E _b (6)

Specifically, the optical frequency shift amount calculator 127 of the optical transceiver 12-1 calculates f _{1, FC} by the above equation (5) _, and the optical frequency shift amount calculator 127 of the optical transceiver 12-2 F _{2 FC} is calculated from the above equation (6). The optical frequency shift amount calculator 127 of the optical transceiver 12-1 notifies f _{1 and FC} as the optical frequency shift amount to the optical frequency shifter 126 of the optical transceiver 12-1. The optical frequency shift amount calculator 127 of the transceiver 12-2 notifies f _{2 and FC} as the optical frequency shift amount to the optical frequency shifter 126 of the optical transceiver 12-2. The optical frequency shifter 126 of the optical transceiver 12-1 and the optical transceiver 12-2 shifts the data signal of the notified optical frequency shift amount.

As described above, in the period in which the optical frequency interval control, which is the second control period, is performed, the first and second frequency fluctuations have the same amplitude and opposite phases, and the optical frequency is set by the first frequency fluctuation. A first anti-phase period for decreasing and increasing the optical frequency by the second frequency fluctuation, and a second anti-phase period for increasing the optical frequency by the first frequency fluctuation and decreasing the optical frequency by the second frequency fluctuation The first and second frequency fluctuations are generated to include the period. Further, in the second control period, the error signal has a lower quality of the reception quality of the optical signal of the first optical frequency and the reception quality of the optical signal of the second frequency in the first reverse phase period. It is a signal indicating the difference between the value and the value with the lower quality of the reception quality of the optical signal of the first optical frequency and the reception quality of the optical signal of the second frequency in the second reverse phase period. Further, in the second control period, the optical transceiver 12-1 performs control to update the first shift amount with a value obtained by adding a value obtained by multiplying the error signal by the proportional coefficient to the first shift amount, The optical transceiver 12-2 performs control to update the second shift amount by a value obtained by subtracting a value obtained by multiplying the error signal by the proportional coefficient from the second shift amount.

Returning to the description of FIG. 5, the communication device 1 changes the setting to the average optical frequency control (step S8), and returns to step S1. Specifically, the optical frequency shift synchronizer 11 changes the setting to average optical frequency control.

In the average optical frequency control of the optical transceivers 12-1 and 12-2, deterioration due to band narrowing can be suppressed. In the present embodiment, as described above, optical frequency interval control for adjusting the optical frequency interval of two subcarriers is performed so that deterioration due to band narrowing and deterioration due to interference between subcarrier signals are balanced. FIG. 9 is a schematic diagram illustrating an example of a change in the optical frequency interval depending on the dither polarity when the optical frequency interval control is performed. SC # 1 in FIG. 9 indicates subcarrier # 1, and SC # 2 indicates subcarrier # 2. In FIG. 9, the horizontal axis represents frequency, and the vertical axis represents optical signal intensity. FIG. 9 shows the frequency distribution of the intensity of the optical signal of each subcarrier transmitted from the communication apparatus 1. d _{+, −} is the optical frequency interval, that is, the optical signal of subcarrier # 1 when the dither polarity of the optical signal of subcarrier # 1 is + and the dither polarity of the optical signal of subcarrier # 2 is − , And the center frequency of the optical signal of subcarrier # 2. d _{−, +} indicates an optical frequency interval when the dither polarity of the optical signal of subcarrier # 1 is − and the dither polarity of the optical signal of subcarrier # 2 is +. As shown in FIG. 9, the optical frequency interval is narrowed or widened by changing the optical frequencies of the two subcarriers in opposite directions and in the same amount.

FIG. 10 is a schematic diagram illustrating an example of a temporal change in the optical frequency of the optical signal of each subcarrier transmitted from the communication device 1 when the optical frequency interval control is performed. FIG. 10 shows an example in which the dither frequency changes in a square wave shape. The horizontal axis in FIG. 10 is time, and the vertical axis is frequency. Further, f1 _{, FC} and f2 _{, FC} are optical frequencies after the frequency offset of the subcarrier # 1 and the subcarrier # 2 described above. As shown in FIG. 10, in the optical frequency interval control, unlike the example of FIG. 7, the dither polarities of subcarrier # 1 and subcarrier # 2 are reversed. Thus, in the example of FIG. 10, the dither of the two subcarriers is changed by the same amount in the opposite direction with respect to time.

FIG. 11 is a schematic diagram illustrating an example of a change in signal quality of each subcarrier transmitted from the communication apparatus 1 when optical frequency interval control is performed. The horizontal axis in FIG. 11 indicates the optical frequency interval, and the vertical axis indicates the signal quality. Also, the frequency distribution 67 in the upper part of FIG. 11 shows the frequency distribution of subcarrier # 1 and subcarrier # 2 in a state where the optical frequency interval between subcarrier # 1 and subcarrier # 2 is shifted to the lower side of the optical frequency interval. Show. The frequency distribution 68 indicates the frequency distribution of subcarrier # 1 and subcarrier # 2 in a state where the optical frequency interval between subcarrier # 1 and subcarrier # 2 is shifted in the direction in which the optical frequency interval is increased. The frequency distribution 69 shows the frequency distribution of subcarrier # 1 and subcarrier # 2 in which the optical frequency interval is in an appropriate state. An appropriate optical frequency interval means that the optical frequency interval between subcarrier # 1 and subcarrier # 2 is such that the optical signals of subcarrier # 1 and subcarrier # 2 do not interfere with each other and the optical frequency is too far away. For example, it shows a state that is within a predetermined range. FIG. 11 shows that signal quality deteriorates due to crosstalk as the optical frequency interval becomes narrower, and signal quality deteriorates due to band narrowing as the optical frequency interval becomes wider. It shows that there is a point with the highest quality.

As described above, by performing proportional integral control for average optical frequency control and proportional integral control for optical frequency interval control, the optical frequency interval between two subcarriers is affected by the narrowing by the optical filter. Therefore, it is possible to perform control so that crosstalk between subcarriers does not occur, and it is possible to improve the quality of two subcarrier signals without deviation. Further, it is possible to control so that the influence of crosstalk and the influence of band narrowing are balanced. In this embodiment, an example using proportional-integral control based on an error signal has been described. However, the present invention is not limited to proportional-integral control, and any method that controls to reduce an error based on an error signal can be used. A control method may be used.

FIG. 12 is a flowchart showing an example of a processing procedure in the optical frequency shift synchronizer 11 of the present embodiment. First, the optical frequency shift synchronizer 11 instructs the subcarrier # 1 and the subcarrier # 2 to generate in-phase dithers synchronized in amplitude Δf for average optical frequency control (step S21). After a predetermined time has elapsed, the optical frequency shift synchronizer 11 instructs the subcarrier # 1 and the subcarrier # 2 to generate dithers having opposite phases with the amplitude Δf in order to control the optical frequency interval (step S22). . After a certain time has elapsed, the process returns to step S21.

FIG. 13 is a flowchart showing an example of a processing procedure in the optical frequency shifter 126 of the present embodiment. The optical frequency shifter 126 determines whether or not the start of dither generation is instructed from the frequency shift synchronizer 11 (step S31). When the start of dither generation is instructed (Yes in step S31), the reverse phase dither is determined. It is determined whether or not generation of the instruction is instructed (step S32). When instructed to generate diphase dither (Yes in step S32), addition of diphase dither to the data signal is started at the timing instructed by the frequency shift synchronizer 11 (step S33), and the process returns to step S31. . When the generation of the reverse phase dither is not instructed (No in step S32), the addition of the dither to the data signal is started at the timing instructed by the frequency shift synchronizer 11 (step S34), and the process returns to step S31. Independent of this processing, when the optical frequency shift amount is notified from the optical frequency shift amount calculator 127, the optical frequency shifter 126 converts the notified shift of the optical frequency shift amount into a data signal. give. If the start of dither generation is not instructed (No in step S31), step S31 is repeated.

Next, the hardware configuration of the communication device 1 and the communication device 2 according to the present embodiment will be described. Each component of the communication device 1 and the communication device 2 can be realized by hardware. The light source 124 and the light source 227 are, for example, semiconductor lasers, and the optical modulator 125 is, for example, an LN (lithium niobate) modulator or an InP (indium phosphide) modulator. These other components are each configured as a processing circuit, for example. In addition, a plurality of components may be configured as one processing circuit, and one component may be configured by a plurality of processing circuits.

Further, even if the above processing circuit is dedicated hardware, a CPU (Central Processing Unit, a central processing unit, a processing unit, a processing unit, a microprocessor, a microcomputer, which executes a program stored in the memory, A control circuit including a processor and a DSP (Digital Signal Processor) may also be used. Here, the memory is, for example, RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory, etc.) Volatile semiconductor memories, magnetic disks, flexible disks, optical disks, compact disks, mini disks, DVDs (Digital Versatile Disks), and the like are applicable.

When the above processing circuit is realized by dedicated hardware, the processing circuit is, for example, the processing circuit 300 shown in FIG. The processing circuit 300 is, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof.

When the above processing circuit is realized by a control circuit including a CPU, this control circuit is, for example, a control circuit 400 having a configuration shown in FIG. As shown in FIG. 15, the control circuit 400 includes a processor 401 that is a CPU and a memory 402. When the above processing circuit is realized by the control circuit 400, the processor 401 reads out and executes a program stored in the memory 402 corresponding to each process of each component. The memory 402 is also used as a temporary memory in each process executed by the processor 401.

The components constituting the communication device 1 and the communication device 2 may be partially realized by dedicated hardware and partially realized by a control circuit including a CPU.

As described above, in this embodiment, optical frequency control in superchannel transmission is performed by adding in-phase or anti-phase dither synchronized between subcarriers and performing control in consideration of the signal quality of both subcarriers. Can be realized with a low-cost and small-scale configuration. In addition, the signal quality is constantly monitored directly and controlled to improve the signal quality, thereby improving the signal quality of the entire network according to the transmission path, and tracking optical frequency drift due to aging and changes in the surrounding environment. Can be realized.

Next, a modification of this embodiment will be described. In the above example, the optical frequency control is performed in the order of (A) average optical frequency control and (B) optical frequency interval control. However, the order of control is not limited to this example, and as shown in FIG. 16, (B) optical frequency interval control and (A) average optical frequency control may be performed in this order. FIG. 16 is a diagram illustrating an example of a control procedure when processing is performed in the order of (B) optical frequency interval control and (A) average optical frequency control. Steps S11 to S14 are the same as steps S5 to S8 in FIG. 5, and steps S15 to S18 are the same as steps S1 to S4 in FIG. Even if the control is performed in the order shown in FIG. 16, the optical frequency arrangement at the time of convergence is the same as that in the case of performing the process shown in FIG.

Also, instead of performing both (A) average optical frequency control and (B) optical frequency interval control, either one may be implemented. For example, only average optical frequency control may be performed. FIG. 17 is a flowchart illustrating an example of a processing procedure when average optical frequency control is performed. Steps S21 to S23 are the same as steps S1 to S3 in FIG. In the example shown in FIG. 17, the subcarrier interval is not optimized as compared with the case where (A) average optical frequency control and (B) optical frequency interval control are combined. There is an advantage that can be made.

Embodiment 2. FIG.
FIG. 18 is a diagram of a configuration example of the optical transmission system according to the second embodiment of the present invention. As shown in FIG. 18, the optical transmission system of the present embodiment includes a communication device 1a, a communication device 2a, and a transmission path 3. In the present embodiment, an example will be described in which the optical frequency of an optical signal transmitted from the communication device 1a and received by the communication device 2a via the transmission path 3 is adjusted. Hereinafter, a different part from Embodiment 1 is demonstrated, and the description which overlaps with Embodiment 1 is abbreviate | omitted.

The communication device 1a is different from the communication device 1 of the first embodiment except that an error signal calculation unit 14 is added and optical transceivers 12a-1 and 12a-2 are provided instead of the optical transceivers 12-1 and 12-2. These are the same as those of the communication apparatus 1 of the first embodiment. The error signal calculation unit 14 receives subcarriers # 1 and subcarriers received from the communication device 2a that is an opposite device that receives optical signals of the first and second frequencies, that is, optical signals of subcarrier # 1 and subcarrier # 2. An error signal is calculated based on the reception quality of the optical signal # 2. The communication device 2a is the same as the communication device 2 of the first embodiment except that the error signal calculation unit 23 is deleted and the optical transceivers 22a-1 and 22a-2 are provided instead of the optical transceivers 22-1 and 22-2. This is the same as the communication device 2 of the first embodiment. Components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and redundant description is omitted.

FIG. 19 is a diagram illustrating a configuration example of the optical transceiver 12a-1 of the communication device 1 according to the present embodiment. As shown in FIG. 19, the optical transceiver 12a-1 of the present embodiment includes an optical signal generation unit 121, a transmission digital signal processing unit 122a, and an optical demodulation unit 123a similar to those of the first embodiment.

The transmission digital signal processing unit 123a is the same as the transmission digital signal processing unit 123 of the first embodiment except that the transmission digital signal processing unit 123a includes an optical frequency shift amount calculation unit 127a instead of the optical frequency shift amount calculation unit 127 of the first embodiment. . The optical frequency shift amount calculation unit 127a is the same as the embodiment except for calculating the optical frequency shift amount based on the error signal input from the error signal calculation unit 14 instead of the error signal input from the reception digital signal processor 128. This is the same as the first embodiment and the optical frequency shift amount calculation unit 127.

The optical demodulator 123a is the same as the optical demodulator 123 of the first embodiment except that it includes a received digital signal processor 129a instead of the received digital signal processor 129. The reception digital signal processor 129 a extracts the signal quality and the dither polarity from the electrical signal output from the coherent receiver 130 and inputs the extracted signal quality and the dither polarity to the error signal calculation unit 14.

FIG. 20 is a diagram illustrating a configuration example of the optical transceiver 22a-1 of the communication device 2 according to the present embodiment. The optical transceiver 22 a-1 inputs the signal quality output from the optical demodulator 221 and the dither polarity to the optical modulator 229. As a result, the optical modulator 229 converts the signal quality, which is an electrical signal, and the dither polarity into an optical signal, and outputs the optical signal to the optical demultiplexing unit 21. Thereby, the signal quality and the dither polarity are transmitted as optical signals to the communication device 1a.

In Embodiment 1, the communication device 2 that receives the optical signal calculates the error signal. However, in the present embodiment, the communication device 1a calculates the error signal. Accordingly, the communication device on the receiving side does not need to add a function corresponding to the processing described in the first embodiment, and can use a conventional communication device.

In the present embodiment, in step S2 and step S6 shown in FIG. 5, the error signal calculation unit 14 calculates an error signal based on the signal quality and the dither polarity transmitted from the communication device 1a. . The optical frequency control of the present embodiment is the same as that of the first embodiment except that the error signal is calculated by the error calculator 14.

The error signal calculation unit 14 of the communication device 1a of the present embodiment can also be realized by a processing circuit in the same manner as the error signal calculation unit 23 of the first embodiment. This processing circuit may be the processing circuit 300 shown in FIG. 14 or the control circuit 400 having the configuration shown in FIG. When the error signal calculation unit 14 is realized by the control circuit 400, it is realized by the processor 401 reading and executing a program stored in the memory 402 and corresponding to the processing of the error signal calculation unit 14.

As described above, in the present embodiment, the communication device 1a that transmits the optical signal whose optical frequency is to be adjusted calculates the error signal based on the signal quality and the dither polarity calculated by the communication device 2a on the receiving side. I tried to do it. For this reason, the same effects as those of the first embodiment can be obtained, and the hardware configuration of the communication device 2a can be simplified as compared with the first embodiment.

The configuration described in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and can be combined with other configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

1, 1a, 2, 2a communication device, 3 transmission path, 11 optical frequency shift synchronization device, 12-1, 12-2, 12a-1, 12a-2, 22-1, 22-2 optical transceiver, 13 light Coupler, 14, 23 error signal calculation unit, 21 optical demultiplexer, 121, 222 optical signal generation unit, 122 transmission digital signal processing unit, 123, 221 optical demodulation unit, 124, 227 light source, 125, 228 optical modulator , 126 optical frequency shifter, 127, 127a optical frequency shift amount calculator, 128, 128a data signal generator, 129, 224 received digital signal processor, 130, 223 coherent receiver, 225 signal quality monitor, 226 frequency offset device.

Claims (11)

1. A first optical transceiver for adding a first frequency fluctuation to an optical signal having a first optical frequency and transmitting the optical signal;
   A second optical transceiver for transmitting an optical signal having a second optical frequency by adding a second frequency fluctuation synchronized with the first optical frequency;
   With
   The first optical transceiver receives the first signal based on the error signal calculated based on the reception quality of the optical signal of the first optical frequency and the reception quality of the optical signal of the second frequency. Calculating a first shift amount, which is a shift amount for shifting the optical frequency of the optical signal of the optical frequency, shifting the optical frequency of the optical signal of the first optical frequency by the first shift amount;
   The second optical transceiver calculates a second shift amount that is a shift amount for shifting the optical frequency of the optical signal of the second optical frequency based on the error signal, and the second optical frequency. An optical frequency of the optical signal is shifted by the second shift amount.
2. The first and second frequency fluctuations are the same;
   The first and second frequency fluctuations are generated to include a first period for increasing an optical frequency and a second period for decreasing an optical frequency;
   The error signal has a value of the poor quality of the reception quality of the optical signal of the first optical frequency and the reception quality of the optical signal of the second frequency in the first period, and the second signal. The signal indicating a difference between a reception quality of the optical signal of the first optical frequency and a reception quality of the optical signal of the second frequency in a period, which is a lower quality value. The communication apparatus according to 1.
3. The first optical transceiver performs control to update the first shift amount with a value obtained by adding a value obtained by multiplying the error signal by a proportional coefficient to the first shift amount,
   The second optical transceiver performs control to update the second shift amount with a value obtained by adding a value obtained by multiplying the error signal by the proportional coefficient to the second shift amount. The communication apparatus according to claim 2.
4. The first and second frequency fluctuations have the same amplitude and opposite phases;
   A first reverse phase period in which an optical frequency is decreased by the first frequency fluctuation and an optical frequency is increased by the second frequency fluctuation; an optical frequency is increased by the first frequency fluctuation; and the second frequency fluctuation The first and second frequency fluctuations are generated to include a second anti-phase period in which the optical frequency is reduced by frequency fluctuations;
   The error signal has a lower quality value among the reception quality of the optical signal of the first optical frequency and the reception quality of the optical signal of the second frequency in the first reverse phase period, And a signal indicating a difference between a reception quality of the optical signal of the first optical frequency and a reception quality of the optical signal of the second frequency in the opposite phase period of 2, which has a lower quality. The communication device according to claim 1.
5. The first optical transceiver performs control to update the first shift amount with a value obtained by adding a value obtained by multiplying the error signal by a proportional coefficient to the first shift amount,
   The second optical transceiver performs control to update the second shift amount by a value obtained by subtracting a value obtained by multiplying the error signal by the proportional coefficient from the second shift amount. The communication apparatus according to claim 4.
6. In the first control period, the first and second frequency fluctuations are the same,
   In the first control period, the first and second frequency fluctuations are generated to include a first period for increasing an optical frequency and a second period for decreasing an optical frequency,
   In the first control period, the error signal has a lower quality of the reception quality of the optical signal of the first optical frequency and the reception quality of the optical signal of the second frequency in the first period. And a signal indicating a difference between the reception quality of the optical signal having the first optical frequency and the reception quality of the optical signal having the second frequency in the second period. Yes,
   In the second control period, the first and second frequency fluctuations have the same amplitude and opposite phases,
   In the second control period, a first reverse phase period in which an optical frequency is decreased by the first frequency fluctuation and an optical frequency is increased by the second frequency fluctuation, and an optical frequency by the first frequency fluctuation. The first and second frequency fluctuations are generated to include a second anti-phase period in which the second frequency fluctuations and an optical frequency is reduced by the second frequency fluctuations,
   In the second control period, the error signal has a quality of the reception quality of the optical signal of the first optical frequency and the reception quality of the optical signal of the second frequency in the first reverse phase period. The difference between the worse value and the worse quality value of the reception quality of the optical signal of the first optical frequency and the reception quality of the optical signal of the second frequency in the second reverse phase period. The communication apparatus according to claim 1, wherein the communication apparatus is a signal indicating
7. In the first control period, the first optical transmitter / receiver updates the first shift amount by a value obtained by adding a value obtained by multiplying the error signal by a proportional coefficient to the first shift amount. And
   In the first control period, the second optical transceiver updates the second shift amount with a value obtained by adding a value obtained by multiplying the error signal to the proportional coefficient to the second shift amount. Control
   In the second control period, the first optical transceiver updates the first shift amount with a value obtained by adding a value obtained by multiplying the error signal by a proportional coefficient to the first shift amount. And
   In the second control period, the second optical transceiver updates the second shift amount with a value obtained by subtracting a value obtained by multiplying the error signal by the proportional coefficient from the second shift amount. The communication apparatus according to claim 6, wherein control is performed.
8. The error signal is calculated in a counter device that receives the optical signals of the first and second frequencies,
   The first optical transceiver calculates the first shift amount based on the error signal received from the opposite device;
   8. The communication apparatus according to claim 1, wherein the second optical transceiver calculates the second shift amount based on the error signal received from the opposite apparatus. 9. .
9. The error based on the reception quality of the optical signal of the first optical frequency and the reception quality of the optical signal of the second frequency received from the opposite device that receives the optical signals of the first and second frequencies. An error signal calculation unit for calculating a signal,
   The communication apparatus according to any one of claims 1 to 7, further comprising:
10. A first communication device;
    A second communication device;
    With
    The first communication device is:
    A first optical transceiver for adding a first frequency fluctuation to an optical signal having a first optical frequency and transmitting the optical signal;
    A second optical transceiver for transmitting an optical signal having a second optical frequency by adding a second frequency fluctuation synchronized with the first optical frequency;
    With
    The first optical transceiver receives the first signal based on the error signal calculated based on the reception quality of the optical signal of the first optical frequency and the reception quality of the optical signal of the second frequency. Calculating a first shift amount, which is a shift amount for shifting the optical frequency of the optical signal of the optical frequency, shifting the optical frequency of the optical signal of the first optical frequency by the first shift amount;
    The second optical transceiver calculates a second shift amount that is a shift amount for shifting the optical frequency of the optical signal of the second optical frequency based on the error signal, and the second optical frequency. The optical frequency of the optical signal is shifted by the second shift amount,
    The second communication device is based on the optical signal of the first optical frequency received from the first communication device and the optical signal of the first optical frequency received from the first communication device. An error signal calculation unit for calculating an error signal;
    An optical transmission system comprising:
11. A first step of transmitting by adding a first frequency fluctuation to an optical signal of a first optical frequency;
    A second step of transmitting an optical signal having a second optical frequency by adding a second frequency fluctuation synchronized with the first optical frequency;
    A third step of calculating an error signal based on the reception quality of the optical signal of the first optical frequency and the reception quality of the optical signal of the second frequency;
    A first shift amount, which is a shift amount for shifting the optical frequency of the optical signal of the first optical frequency, is calculated, and an optical frequency of the optical signal of the first optical frequency is shifted by the first shift amount. 4 steps,
    Based on the error signal, a second shift amount, which is a shift amount for shifting the optical frequency of the optical signal of the second optical frequency, is calculated, and the optical frequency of the optical signal of the second optical frequency is calculated. A fifth step of shifting the shift amount by 2;
    An optical frequency control method comprising:

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