Optical transceiver device and optical receiver

Abstract

An optical transmitter (100) is provided with: a modulated signal generation unit (110) that generates a modulated signal, which is a digital signal obtained by inserting a first pilot symbol signal comprising a first symbol period and a second pilot symbol signal comprising a second symbol period into data to be transmitted; and an optical modulation unit (130) that modulates the CW light from the CW light generation unit (140) on the basis of the modulation signal converted into the analog signal by the digital / analog conversion unit (120), and generates modulated light into which the first pilot symbol signal and the second pilot symbol signal are inserted, the optical receiver (200) comprising: an optical coherence detection unit (210) that detects the optical coherence between the CW light and the second pilot symbol signal; a polarization multiplexing receiver that receives polarization multiplexed modulated light into which a first pilot symbol signal comprising a first symbol period and a second pilot symbol signal comprising a second symbol period are inserted, performs coherent detection on the received modulated light, and outputs an analog electric signal; and a reception-side digital signal processing unit (240) having a frequency difference compensation unit (247). And a frequency difference compensation unit (247) that compensates the frequency of the received digital signal by calculating a phase difference using a first pilot symbol signal extracted from the digital signal from the analog / digital converter unit (230) and inserted into the received polarization-multiplexed modulated light and a second pilot symbol signal adjacent to the first pilot symbol signal.

Description

Technical Field

[0001] This disclosure relates to an optical transceiver apparatus for performing digital coherent optical communication. Background Technology

[0002] In the field of optical fiber communication, digital coherent technology is widely used in metropolitan area networks and submarine optical cable systems.

[0003] In digital coherent optical communication, high performance and high functionality have been achieved, including improvements in data rate.

[0004] In particular, digital coherent optical transceivers can generate multiple subcarrier signals in the digital region without interference on the frequency axis within a single optical transceiver. Moreover, in recent years, methods have been shown to allocate different information to each subcarrier to accommodate multiple services simultaneously.

[0005] By accommodating both simultaneously, hardware utilization efficiency and space saving can be achieved.

[0006] As a digital coherent optical communication technology capable of transmitting and receiving subcarrier signals, it is shown, for example, in Non-Patent Document 1.

[0007] In addition, Patent Document 1 discloses an optical transmission system in which, in order to perform phase compensation corresponding to the phase variation generated in the optical fiber transmission path between the transmitting device and the receiving device, pilot symbols are inserted and output for each K symbols in the data train in the transmitting device, and the pilot symbols in the data train are detected in the receiving device, the phase variation is estimated based on a predetermined reference symbol stored in the storage device, and the residual frequency offset is compensated based on the phase variation.

[0008] Existing technical documents

[0009] Non-patent literature

[0010] Non-patent document 1: H. Sun et al, "800G DSP ASIC Design Using ProbabilisticShaping and Digital Sub-Carrier Multiplexing", JOURNAL OF LIGHTWAVETECHNOLOGY, VOL. 38, NO. 17, SEPTEMBER 1, 2020, pp4744-4756

[0011] Patent Document 1: WO2014 / 126132 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] The optical receiver shown in Non-Patent Document 1 converts the voltage signal detected by optical coherent detection and output into a digital signal through an analog-to-digital converter (ADC).

[0014] Typically, when the sampling rate of the analog-to-digital converter is high, the analog received signal before analog-to-digital conversion can be accurately acquired as a digital signal, and waveform distortion compensation in digital signal processing can be accurately performed to improve the signal quality after reception.

[0015] However, in cases where low-to-medium speed digital coherent signals are processed in an optical receiver, such as when using FPGAs (Field Programmable Gate Arrays) with sampling rates or throughputs of several gigabits per second for digital signal processing, or when using factor carrier multiplexing with low modulation speeds for each subcarrier, the ability to compensate for waveform distortion in the digital signal processing on the receiving side will be reduced if there is a frequency difference between the transmitted and received optical carriers.

[0016] In Patent Document 1, the optical transmission system inserts pilot symbols every K symbols. However, if the time interval between adjacent pilot symbols is long, the frequency of the optical carrier of the receiving device will differ from the frequency of the optical carrier of the transmitting device, which will cause a prediction error for phase compensation.

[0017] This disclosure was made in view of the above circumstances, with the aim of providing an optical transceiver apparatus that, in an optical receiver processing low-to-medium speed digital coherent signals, has a compensation function for waveform distortion degradation caused by the frequency difference between the transmitted and received optical carriers.

[0018] Methods for solving problems

[0019] The optical transceiver apparatus disclosed herein includes an optical transmitter and an optical receiver. The optical transmitter includes: a modulation signal generation unit that generates a modulation signal, which is a digital signal for optical modulation obtained by inserting a first pilot symbol signal consisting of a first symbol period and a second pilot symbol signal consisting of a second symbol period different from the first symbol period into data to be transmitted; a digital-to-analog converter that converts the modulation signal generated by the modulation signal generation unit into a modulation signal consisting of an analog signal; and an optical modulation unit that modulates CW light from a CW light generation unit according to the modulation signal converted into an analog signal by the digital-to-analog converter, generating modulated light with a first pilot symbol signal consisting of a first symbol period and a second pilot symbol signal consisting of a second symbol period inserted. The optical receiver includes: an optical coherence detector that receives the data with a first pilot symbol signal consisting of a first symbol period and a second pilot symbol signal consisting of a second symbol period inserted into the data to be transmitted. The system comprises: a first pilot symbol signal consisting of a symbol period and a second pilot symbol signal consisting of a second symbol period different from the first symbol period; a polarization-multiplexed modulated light; a coherent detection unit for receiving the modulated light; an analog-to-digital converter for converting the analog signal from the optical coherent detector into a digital signal; and a receiving-side digital signal processing unit having a frequency difference compensation unit that receives the digital signal from the analog-to-digital converter, calculates the phase difference using the first pilot symbol signal consisting of a first symbol period and inserted into the received polarization-multiplexed modulated light (extracted from the received digital signal) and the second pilot symbol signal consisting of a second symbol period different from the first symbol period adjacent to the first pilot symbol signal, and compensates for the frequency of the received digital signal.

[0020] Invention Effects

[0021] According to this disclosure, in an optical receiver that processes low-to-medium speed digital coherent signals, it is possible to suppress the reduction in the ability to compensate for waveform distortion in digital signal processing based on analog-to-digital converters. Attached Figure Description

[0022] Figure 1 This is a block diagram showing the structure of the optical transceiver device according to Embodiment 1.

[0023] Figure 2 This is a block diagram showing the structure of the transmitting-side digital signal processing unit in the optical transceiver apparatus of Embodiment 1.

[0024] Figure 3 This is a block diagram showing the structure of another transmitting-side digital signal processing unit in the optical transceiver apparatus of Embodiment 1.

[0025] Figure 4 This is a block diagram showing the structure of the receiving-side digital signal processing unit in the optical transceiver apparatus of Embodiment 1.

[0026] Figure 5 In the optical transceiver apparatus of Embodiment 1, a digital coherent mode is shown with the first pilot symbol signal P inserted. A and the second pilot symbol signal P B A diagram of an example of a symbolic signal sequence.

[0027] Figure 6 In the optical transceiver apparatus of Embodiment 1, a digital coherent mode is shown with the first pilot symbol signal P inserted. A and the second pilot symbol signal P B Another example of a symbolic signal sequence is shown in the figure.

[0028] Figure 7 This is a diagram illustrating the single-carrier signal in the digital coherent mode used in the optical transceiver device of Embodiment 1, on the frequency axis.

[0029] Figure 8 This is a diagram illustrating the effect of compensation for differences in optical frequency in the IQ signal space within the optical transceiver apparatus of Embodiment 1.

[0030] Figure 9 This is a diagram illustrating the compensation for differences in optical frequency in the IQ signal space as a comparative example.

[0031] Figure 10 The figure shows an example of a symbol signal sequence with one pilot symbol signal P inserted in a digital coherent mode, as illustrated in the comparative example.

[0032] Figure 11 This is a diagram illustrating another example of a symbol signal sequence with one pilot symbol signal P inserted in a digital coherent mode, as shown in the comparative example.

[0033] Figure 12 This is a diagram showing the hardware structure of the optical transceiver device according to Embodiment 1.

[0034] Figure 13 This is a block diagram showing the structure of the transmitting-side digital signal processing unit in the optical transceiver apparatus of Embodiment 2.

[0035] Figure 14 This is a block diagram showing the structure of the receiving-side digital signal processing unit in the optical transceiver apparatus of Embodiment 2.

[0036] Figure 15 This diagram illustrates the subcarrier signals in the subcarrier multiplexing mode of the digital coherent mode used in the optical transceiver device of Embodiment 2, along the frequency axis. Detailed Implementation

[0037] Implementation method 1.

[0038] according to Figures 1 to 12 The optical transceiver device of Embodiment 1 will be described.

[0039] In the diagram, dashed arrows represent the flow of optical signals, while solid arrows represent the flow of electrical signals.

[0040] The optical transceiver device of Implementation 1 is a communication device and optical transceiver responsible for transmitting and receiving optical signals in optical communication network systems that use optical fiber as the transmission medium in optical access and optical core / metropolitan area networks, as well as in optical communication network systems that do not use optical fiber, such as space and wireless space where space optical communication is envisioned, as the transmission medium. It focuses on its transmission and reception functions.

[0041] The optical transceiver device of Implementation 1 is used to transmit and receive digital coherent signals. The digital coherent signals are optical signals that have undergone polarization multiplexing in a digital coherent manner and utilize the orthogonality of phases such as binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), or quadrature amplitude modulation (QAM).

[0042] In addition, it can also be applied to optical transceivers that transmit and receive digital coherent signals of single-polarization waves without polarization multiplexing.

[0043] In the following description, in the optical transceiver apparatus of Embodiment 1, regarding the optical signal, it is envisioned that an X-polarized wave and a Y-polarized wave are polarized multiplexed using a digital coherent method, and the X-polarized wave and the Y-polarized wave are modulated into I signals and Q signals of orthogonal phase, respectively, to obtain the optical signal. For example, the X-polarized wave is a horizontally polarized wave, and the Y-polarized wave is a vertically polarized wave.

[0044] Imagine polarization multiplexing into digital coherent signals consisting of the I signal (XI signal) in the X-polarized wave, the Q signal (XQ signal) in the X-polarized wave, the I signal (YI signal) in the Y-polarized wave, and the Q signal (YQ signal) in the Y-polarized wave.

[0045] In addition, the terminals (XI output terminal, XQ output terminal, YI output terminal and YQ output terminal) for XI signal, XQ signal, YI signal and YQ signal respectively, and the channels (XI channel, XQ channel, YI channel and YQ channel) for the flow of electrical signals for XI signal, XQ signal, YI signal and YQ signal respectively, are different, but they are shown uniformly in the figure.

[0046] like Figure 1As shown, the optical transceiver device of Embodiment 1 includes an optical transmitter 100, an optical receiver 200, and an optical transceiver control unit 300.

[0047] The optical transmitter 100, the optical receiver 200, and the optical transceiver control unit 300 are housed in the same housing.

[0048] The optical transmitter 100 generates polarization-multiplexed modulated light by inserting a first pilot symbol signal consisting of a first symbol period and a second pilot symbol signal consisting of a second symbol period different from the first symbol period into the data to be transmitted, and outputs the generated modulated light to an optical receiver of other optical transceivers via a transmission path that serves as an optical fiber or wireless space.

[0049] In Embodiment 1, the modulated light output from the optical transmitter 100 is an optical signal obtained by modulating CW (Continuous wave) light with a carrier frequency using a modulation signal that is an electrical signal.

[0050] The optical receiver 200 receives polarization-multiplexed modulated light propagating in the transmission path from the optical transmitter of another optical transceiver, which contains a first pilot symbol signal consisting of a first symbol period and a second pilot symbol signal consisting of a second symbol period different from the first symbol period, and acquires data from the received modulated light.

[0051] The data obtained from the modulated light received by the optical receiver 200 is data demodulated using an analog electrical signal obtained by interfering the modulated light, which is an optical signal, with an interference light having a carrier frequency.

[0052] The optical transmitter 100 includes a modulation signal generation unit 110, a digital-to-analog converter (DAC) unit 120, an optical modulation unit 130, and a CW light generation unit 140.

[0053] The modulation signal generation unit 110 is a transmitting-side digital signal processing unit (transmitting digital signal processor (DSP)), hereinafter referred to as transmitting-side DSP 110.

[0054] The information, i.e., data, to be sent to the destination is input as a digital signal to the transmitting DSP 110. The transmitting DSP 110 generates a modulation signal, which is a digital signal used for optical modulation obtained by inserting a first pilot symbol signal consisting of a first symbol period and a second pilot symbol signal consisting of a second symbol period different from the first symbol period into the input data, i.e., the data to be sent.

[0055] The data to be transmitted is constructed into a frame, a signal form capable of error correction, via the transmitting DSP 110.

[0056] The transmitting DSP 110 generates four modulation signals: XI, XQ, YI, and YQ.

[0057] The four modulation signals are respectively Figure 5 The inserted symbol signal sequence contains two types of pilot symbol signals or Figure 6 The inserted symbol signal sequence contains two types of pilot symbol signals.

[0058] exist Figure 5 and Figure 6 In the diagram, the horizontal axis represents time, S represents the data symbol signal, and P represents the time. A (P) A1 P A2 ...P A5 …) represents the first pilot symbol signal, P B (P) B1 P BA2 , ...) represent the second pilot symbol signal.

[0059] The data symbol signal S is a symbol signal (complex signal) obtained by converting the bit signal of the data to be transmitted for IQ modulation. The so-called data symbol signal S is a digital coherent signal.

[0060] Pilot symbol signal P A and the second pilot symbol signal P B These are 1-bit digital coherent signals, that is, digital coherent signals with a symbol length of 1.

[0061] Figure 5 The symbol signal sequence shown is obtained as follows: instead of being based on frames, it is based on the data symbol signal S, with the first pilot symbol signal P inserted according to the first symbol interval, i.e., the first symbol period. A Furthermore, instead of using frames as a unit, a second pilot symbol signal P is inserted for the data symbol signal S according to a second symbol interval different from the first symbol interval, i.e., a second symbol period different from the first symbol period. B .

[0062] Second pilot symbol signal P B The second symbol interval is the first pilot symbol signal P. A The interval of the first symbol is an integer multiple of 2, which is 4 times the interval in this example.

[0063] In other words, the second pilot symbol signal P B The second symbol period is the first pilot symbol signal P. AThe symbol period is an integer multiple of 2 of the first symbol period, which is 4 times the symbol period in this example.

[0064] That is, the second pilot symbol signal P B Relative to the first pilot symbol signal P A It is inserted into the data symbol signal S at a frequency of 1 / 4.

[0065] Second pilot symbol signal P B Every second symbol period, relative to the first pilot symbol signal P A The signal is inserted in a continuous manner. That is, the second pilot symbol signal P B It is configured in the first pilot symbol signal P every second symbol period. A The adjacent symbols.

[0066] The second pilot symbol signal adjacent to the first pilot symbol signal is configured with a shorter time interval, and in Implementation 1, it is configured with a 1-symbol interval.

[0067] Figure 6 The symbol signal sequence shown is obtained as follows: the first pilot symbol signal P is inserted at a determined position in the frame unit according to a determined first symbol interval, i.e., the first symbol period. A Furthermore, at a defined position within the frame unit, a second pilot symbol signal P is inserted at a defined second symbol interval, which is different from the first symbol interval and thus different from the first symbol period. B .

[0068] Second pilot symbol signal P B The second symbol interval is the first pilot symbol signal P. A The interval of the first symbol is an integer multiple of 2, which is 4 times the interval in this example.

[0069] In other words, the second pilot symbol signal P B The second symbol period is the first pilot symbol signal P. A The symbol period is an integer multiple of 2 of the first symbol period, which is 4 times the symbol period in this example.

[0070] That is, the second pilot symbol signal P B Relative to the first pilot symbol signal P A It is inserted into the data symbol signal S at a frequency of 1 / 4.

[0071] Second pilot symbol signal P B Every second symbol period, relative to the first pilot symbol signal P A The signal is inserted in a continuous manner. That is, the second pilot symbol signal P BIt is configured in the first pilot symbol signal P every second symbol period. A The adjacent symbols.

[0072] The second pilot symbol signal adjacent to the first pilot symbol signal is configured with a shorter time interval, and in Implementation 1, it is configured with a 1-symbol interval.

[0073] like Figure 2 As shown, the transmitting-side DSP 110 has digital circuitry, which includes signal processing functions such as a frame generation unit 111, a mapping unit 112, a spectrum shaping unit 113, a skew adjustment unit (anti-skew unit) 114, a pilot generation unit 115, and a pilot insertion unit 116.

[0074] The frame generation unit 111 is a framing unit that constructs the data to be transmitted into a signal form that can correct errors, i.e., a signal frame form.

[0075] The mapping unit 112 converts the bit-based data columns in the digital signal from the frame generation unit 111 into symbol signals (complex signals) for IQ modulation.

[0076] That is, the mapping unit 112 converts the data column based on the data to be transmitted into a digital signal, i.e., a modulation signal, for optical modulation.

[0077] Typically, as the multi-valuedness of IQ modulation increases, the number of bits allocated to the data symbol signal S increases, and the data rate increases.

[0078] The mapping unit 112 has four output terminals for the XI signal, XQ signal, YI signal, and YQ signal corresponding to the polarization-multiplexed BPSK signal or QPSK signal obtained by the mapping unit 112.

[0079] In addition, when the polarization multiplexed signal obtained by the mapping unit 112 is a QAM signal, the mapping unit 112 also has 4 output terminals.

[0080] In summary, the mapping unit 112 has four output terminals for digital coherent signals.

[0081] Before the mapping unit 112 processes the bit-based data column from the digital signal generated by the frame generation unit 111, the pilot insertion unit 116 inserts a first pilot symbol signal P obtained by using the digital coherent signal generated by the pilot generation unit 115 into the data column every first symbol period. A .

[0082] Furthermore, before the mapping unit 112 processes the bit-based data column from the digital signal generated by the frame generation unit 111, the pilot insertion unit 116 inserts a second pilot symbol signal P obtained by using the digital coherent signal generated by the pilot generation unit 115 into the data column every second symbol period. B .

[0083] In this case, the mapping unit 112 will insert the first pilot symbol signal P. A and the second pilot symbol signal P B Transform data columns into data based on Figure 5 The symbol signal sequence shown or Figure 6 The modulated signal of the symbol signal sequence shown.

[0084] In addition, such as Figure 3 As shown, the pilot insertion unit 116 may also insert, in the mapping unit 112, the first pilot symbol signal P obtained by using the digital coherent signal generated by the pilot generation unit 115 according to the first symbol period and the second symbol period, respectively, when converting the data column based on the bit signal from the digital signal from the frame generation unit 111 into the modulation signal. A and the second pilot symbol signal P B , obtained based on Figure 5 The symbol signal sequence shown or Figure 6 The modulated signal of the symbol signal sequence shown.

[0085] The spectrum shaping unit 113 shapes the frequency characteristics of the modulation signal obtained by the mapping unit 112 based on the frequency characteristics of the optical transceiver and the frequency characteristics in the transmission path.

[0086] The skew adjustment unit 114 compensates for the skew (delay difference) that occurs between signals caused by the optical transmitter 100 due to the electrical signal flow of the modulation signals XI, XQ, YI and YQ signals supplied from the spectrum shaping unit 113 via the XI channel, XQ channel, YI channel and YQ channel respectively.

[0087] As described above, the transmitting-side DSP 110 uses the frame generation unit 111 to convert the data to be transmitted into a signal frame based on a digital coherent signal, uses the mapping unit 112 to convert it into a modulated signal, and uses the pilot insertion unit 116 to make it into a signal P with a first pilot symbol signal P based on the digital coherent signal inserted. A and the second pilot symbol signal P BThe modulation signal is shaped in frequency characteristics by the spectrum shaping unit 113, and the skew is compensated by the skew adjustment unit 114, thereby generating a digital signal for optical modulation, namely the modulation signal, which is inserted with a first pilot symbol signal composed of a first symbol period and a second pilot symbol signal composed of a second symbol period different from the first symbol period.

[0088] DAC section 120 will use the signal P with the first pilot symbol inserted. A and the second pilot symbol signal P B The digital signal is converted into a modulated signal composed of analog signals.

[0089] The optical modulation unit 130 modulates the CW light from the CW light generation unit 140 according to the modulation signal converted into an analog signal by the DAC unit 120, generates modulated light with a first pilot symbol signal consisting of a first symbol period and a second pilot symbol signal consisting of a second symbol period different from the first symbol period, and outputs the generated modulated light to the transmission path.

[0090] Modulated light is an optical signal that is a digital coherent signal obtained by carrying information based on the modulated signal onto CW light.

[0091] Modulated light mixing incorporates information based on the XI, XQ, YI, and YQ signals output from independent channels.

[0092] like Figure 7 As shown on the frequency axis, the CW light from the CW light generation unit 140 is a single-carrier signal in the digital coherent mode.

[0093] 200 optical receivers Figure 1 As shown, it includes an optical coherence detector 210, an interference light generator 220, an ADC (Analog-to-digital converter) 230 as an analog-to-digital converter, and a receiving-side digital signal processing unit 240.

[0094] The receiving-side digital signal processing unit 240 is a receiving digital signal processor (DSP), hereinafter referred to as the receiving-side DSP 240.

[0095] The optical coherent detector 210 performs optical coherent detection. In this detection, it receives polarization-multiplexed modulated light transmitted through the transmission path from the optical transmitter of another optical transceiver. The received modulated light interferes with continuous wave (CW) light (interference light) with a single carrier frequency fc from the interference light generator 220. The resulting optical signal is then photoelectrically converted to a voltage, and an analog electrical signal based on this voltage is output. The voltage signal output from the optical coherent detector 210 can be either single-ended or differential.

[0096] In Embodiment 1, the analog electrical signals output from the optical coherent detector 210 are four signals: XI signal, XQ signal, YI signal, and YQ signal, which are output from four output terminals respectively.

[0097] The XI signal, XQ signal, YI signal, and YQ signal are signals before demodulation of the analog voltage signal. They are used to obtain the demodulated signal obtained by optical interference between the modulated light after polarization multiplexing by the optical coherence detector 210 and the interference light with a single carrier frequency fc.

[0098] The ADC unit 230 is an assembly of ADCs corresponding to the XI channel of the XI signal, the XQ channel of the XQ signal, the YI channel of the YI signal, and the YQ channel of the YQ signal, respectively.

[0099] Each ADC in the ADC unit 230 samples the electrical signal of the input analog region in its corresponding channel according to the sampling frequency, and converts it into a discrete signal in the digital region, i.e. a digital signal, to obtain the signal before demodulation composed of digital signals.

[0100] The XI, XQ, YI, and YQ signals, after being converted into digital signals by the ADC unit 230, are respectively as follows: Figure 5 or Figure 6 As shown, this is a signal with a sequence of symbols containing two types of pilot symbols.

[0101] The receiving-side DSP 240 performs digital signal processing and demodulation on the XI, XQ, YI, and YQ signals after they have been converted into digital signals by the ADC unit 230.

[0102] In addition, the receiving-side DSP 240 can also synthesize the XI signal and XQ signal for X-polarized waves and use them as complex signals in the digital region for X-polarized waves, and synthesize the YI signal and YQ signal for Y-polarized waves and use them as complex signals in the digital region for Y-polarized waves, after the XI signal, XQ signal, YI signal and YQ signal are converted into digital signals by the ADC unit 230.

[0103] The transmitting-side DSP 110 in the optical transmitter 100 generates a modulated signal, while the receiving-side DSP 240 in the optical receiver 200 demodulates the modulated signal to obtain a demodulated signal.

[0104] The receiving-side DSP 240 performs compensation for wavelength dispersion and nonlinear optical effects on the modulated light in the transmission path, polarization mode dispersion, and frequency offset caused by the difference in the source frequency of CW light in the optical transmitter and optical receiver for the input digital signal.

[0105] The receiver-side DSP 240 performs digital signal processing on the XI, XQ, YI, and YQ signals respectively, but to avoid unnecessary explanation, in... Figure 4 The flow of a single electrical signal is used to illustrate the process of digital signal processing.

[0106] In addition, Figure 4 The main feature shown is that of Embodiment 1, namely, the first pilot symbol signal P inserted into the polarization-multiplexed modulated light transmitted from the optical transmitter via the transmission path. A and the second pilot symbol signal P B The optical demodulation function used for testing did not show error correction or other features.

[0107] like Figure 4 As shown, the receiving-side DSP 240 includes a skew adjustment unit 241, an amplitude adjustment unit 242, a dispersion compensation unit 243, a clock synchronization unit 244, a bandwidth compensation unit 245, an adaptive equalization unit 246, a frequency difference compensation unit 247, a phase estimation unit 248, a demapping unit 249, a frame synchronization unit 250, and a unit for reading the first pilot symbol signal P. A The first pilot reading unit 251 reads the second pilot symbol signal P. B The second pilot reading unit 252 and the pilot removal unit 253.

[0108] In addition, the XI signal, XQ signal, YI signal and YQ signal input to the demapping unit 249 are signals before demodulation, which are signals processed in the pre-demodulation stage. The data signal output from the demapping unit 249 is the signal after demodulation, which is processed in the demodulation stage.

[0109] In addition, Figure 4 In this diagram, the signal input from the ADC unit 230 to the receiving-side DSP 240 is the signal before demodulation used for demodulation; however, it is simplified and shown as the demodulated signal.

[0110] The skew adjustment unit 241 compensates for the skew caused by the optical transmitter and optical receiver devices for the channels of the XI signal, XQ signal, YI signal, and YQ signal, respectively.

[0111] The amplitude adjustment unit 242 adjusts the amplitude difference caused by the optical transmitter and optical receiver devices for the channels of the XI signal, XQ signal, YI signal and YQ signal, respectively, as needed.

[0112] The dispersion compensation unit 243 compensates for signal degradation caused by wavelength dispersion generated in the transmission path.

[0113] The clock synchronization unit 244 compensates for the clock difference between the optical transmitter and the optical receiver. This clock difference compensation function can also be performed on the analog signal before digital conversion by the ADC unit 230.

[0114] The frequency band compensation unit 245 compensates for the degradation of frequency characteristics under fixed conditions.

[0115] The adaptive equalization unit 246 adaptively compensates for the polarization separation and frequency characteristic degradation of X-polarized wave signals (XI and XQ signals) and Y-polarized wave signals (YI and YQ signals).

[0116] In the adaptive equalization unit 246, in order to determine the compensation conditions for the equalization process, the first pilot symbol signal P, extracted by the first pilot reading unit 251 from the signal of the symbol signal sequence with two types of pilot symbol signals inserted, is used. A .

[0117] When 16QAM or other quadrature phase modulation is used in the data symbol signal S, the first pilot symbol signal P A Using a QPSK signal with a constant IQ amplitude, the adaptive equalization unit 246 can determine the compensation conditions for the equalization process.

[0118] The skew adjustment unit 241, amplitude adjustment unit 242, dispersion compensation unit 243, clock synchronization unit 244, frequency band compensation unit 245, and adaptive equalization unit 246 are composed of structures used in the usual digital coherent mode.

[0119] That is, the signal processing of the receiver-side DSP 240 for the pre-stage demodulation is a common method in digital signal processing used in typical digital coherence methods.

[0120] The frequency difference compensation unit 247 compensates for the frequency difference between the frequency of the CW light from the CW light generation unit 140 in the light transmitter 100 and the frequency of the interference light from the interference light generation unit 220.

[0121] Frequency difference compensation unit 247 obtains the first pilot symbol signal P from the symbol signal sequence containing two types of pilot symbol signals by the first pilot reading unit 251. AFor the first pilot symbol signal P in the received symbol signal sequence A The location is detected.

[0122] When 16QAM or other quadrature phase modulation is used in the data symbol signal S, the first pilot symbol signal P A Using a QPSK signal with constant IQ amplitude, the frequency difference compensation unit 247 is able to detect the first pilot symbol signal P. A The location.

[0123] Frequency difference compensation unit 247 receives the XI signal, XQ signal, YI signal, and YQ signal after they have been converted into digital signals by ADC unit 230, and uses the first pilot symbol signal P extracted from the received digital signals by first pilot reading unit 251. A The second pilot symbol signal P extracted from the received digital signal by the second pilot reading unit 252 B ´, and the adjacent first pilot symbol signal P inserted into the symbol signal sequence by the transmitting-side DSP 110 in the optical transmitter 100. A With the second pilot symbol signal P B Calculate the relative positional relationship of the second pilot symbol signal P. B ´ Relative to the second pilot symbol signal P B The phase difference is used to compensate for the frequency of the received digital signal.

[0124] Frequency difference compensation unit 247 uses the first pilot symbol signal P extracted by the first pilot reading unit 251 from the signal containing the symbol signal sequence with two types of pilot symbol signals inserted. A The second pilot symbol signal P extracted by the second pilot reading unit 252 from the signal containing the symbol signal sequence with two types of pilot symbol signals inserted. B ´, with the first pilot symbol signal P A Based on the reference, calculate the second pilot symbol signal P. B ´ Relative to the second pilot symbol signal P B The frequency difference is compensated for by compensating for the frequency difference between the CW light from the CW light generating unit 140 in the optical transmitter 100 and the frequency of the interference light from the interference light generating unit 220, and the frequency compensation is performed for the symbol signal sequence in the optical receiver 200.

[0125] Frequency difference compensation unit 247 calculates the frequency difference based on the adjacent first pilot symbol signal P. A and the second pilot symbol signal P B The observation position of the IQ signal space of ´ (i.e., the first pilot symbol signal P extracted by the first pilot readout unit 251). A The position shown is related to the extracted first pilot symbol signal P.A The adjacent second pilot symbol signal P extracted by the second pilot readout unit 252 B (as shown in the image), and the previously known first pilot symbol signal P. A and the second pilot symbol signal P B The relative position of the original IQ signal space (i.e., the adjacent first pilot symbol signal P inserted into the symbol signal sequence by the transmitting-side DSP 110 in the optical transmitter 100). A and the second pilot symbol signal P B The relative position of the IQ signal in space), estimated with the first pilot symbol signal P. A The second pilot symbol signal P is the reference. B ´ Relative to the second pilot symbol signal P B The difference in frequency.

[0126] Based on the estimated second pilot symbol signal P B The frequency difference of ´ is analyzed to identify the adjacent first pilot symbol P in the received symbol signal sequence. A With the second pilot symbol signal P B The phase difference is used to compensate for the frequency of the received symbol signal sequence using the calculated compensation amount.

[0127] Due to the adjacent first pilot symbol signal P A and the second pilot symbol signal P B By inserting symbols at shorter time intervals, the phase rotation relative to the time interval can be reduced. As a result, the amount of phase rotation can be accurately read, and accurate compensation for differences in optical frequency can be performed in the frequency difference compensation unit 247.

[0128] use Figure 8 This point needs clarification.

[0129] Figure 8 The IQ signal space is shown, with the horizontal axis representing the Q axis and the vertical axis representing the I axis.

[0130] P A It is the first pilot symbol signal P A signal point, P B The second pilot symbol signal P is the one with no frequency difference. B signal point, P B ´ is the second pilot symbol signal P when there is a frequency difference. B The signal point.

[0131] exist Figure 8 In the middle, signal point P AThe first pilot symbol signal P is extracted by the first pilot reading unit 251. A The observed signal points shown serve as reference points for analyzing phase differences.

[0132] Signal point P B It is relative to the signal point P A The signal point that has no frequency difference, i.e., the adjacent first pilot symbol signal P inserted into the symbol signal sequence by the transmitting side DSP 110 in the optical transmitter 100. A and the second pilot symbol signal P B The signal point is obtained by determining the relative position of the IQ signal in space.

[0133] Signal point P B ´ is the second pilot symbol signal P extracted by the second pilot readout unit 252 B The observed signal points are shown.

[0134] Signal point P A and signal point P B (No difference) shows the signal point P in the IQ signal space obtained by the transmitting-side DSP 110 during a 1-symbol period in the symbol signal sequence. A The relative positional relationship based on the baseline.

[0135] Signal point P A and signal point P B (Differences exist) indicates the signal point P in the IQ signal space relative to the observed signal point. A The reference signal point P B The relative positional relationship of ´.

[0136] Signal point P A and signal point P B (There are differences) and signal point P A and signal point P B (No difference) shows the relative positional relationship of the IQ signals in space.

[0137] Therefore, it is possible to observe the signal point P. A Based on the signal point P B The phase difference due to the frequency difference (the amount of phase rotation per unit time) changes from the original phase angle (a known value: signal point P) B How much has it deviated?

[0138] By using the multiplication process of complex conjugates of two points represented by complex numbers in the complex plane, the value of the complex number is output, and the phase term is extracted from this value. From this, the signal point P is calculated. A The reference signal point P B With signal point P BThe phase difference of ´.

[0139] That is, as relative to the known first pilot symbol signal P A and the second pilot symbol signal P B The original relative positions of the IQ signal space, and the cases where the frequencies of the modulated light 100 from the optical transmitter and the modulated light received by the optical receiver 200 are not different. Figure 8 The first pilot symbol signal P extracted by the first pilot reading unit 251 A The signal point P shown A Based on this, the second pilot symbol signal P is shown. B The signal point P shown B An example of the relative position of the IQ signal in space.

[0140] in addition, Figure 8 The first pilot symbol signal P extracted by the first pilot reading unit 251 A The signal point P shown A Based on this, the second pilot symbol signal P extracted by the second pilot readout unit 252 is shown. B The signal point P shown B An example of the relative position of the IQ signal in space.

[0141] Regarding the second pilot symbol signal P extracted by the second pilot reading unit 252 B The signal point P shown B ´, due to the second pilot symbol signal P B With the first pilot symbol signal P A By arranging symbols adjacently, i.e., with shorter time intervals, in Implementation 1, the phase rotation relative to the time interval can be reduced. As a result, the amount of phase rotation can be accurately read.

[0142] Frequency difference compensation unit 247 is thus based on signal point P B Relative to signal point P B The first pilot symbol signal P A With the second pilot symbol signal P B The frequency difference (the amount of phase rotation per unit time) is calculated by measuring the phase shift between sampling times.

[0143] The frequency difference compensation unit 247 generates a sine wave (digital data) with a unit amplitude and a phase in the opposite direction during the sampling time in order to eliminate the calculated frequency difference, and multiplies the generated sine wave by the signal of the symbol signal sequence.

[0144] As a result, the frequency difference compensation unit 247 compensates for the optical frequency difference between the optical transmitter 100 and the optical receiver 200, that is, the frequency difference between the frequency of the CW light from the CW light generation unit 140 in the optical transmitter 100 and the frequency of the interference light from the interference light generation unit 220.

[0145] That is, it is possible to extract the first pilot symbol signal P from the first pilot reading unit 251. A The position of the IQ signal in space shown, and the extracted first pilot symbol signal P A The adjacent second pilot symbol signal P extracted by the second pilot readout unit 252 B The spatial position of the IQ signal shown, and the adjacent first pilot symbol signal P inserted into the symbol signal sequence by the transmitting-side DSP 110 in the optical transmitter. A and the second pilot symbol signal P B The relative position of the IQ signal space, as extracted by the first pilot reading unit 251 using the first pilot symbol signal P A Based on this, the extracted first pilot symbol signal P is compared with... A The adjacent second pilot symbol signal P extracted by the second pilot readout unit 252 B Compared to the extracted first pilot symbol signal P A The second pilot symbol P, which is inserted into the symbol signal sequence by the transmitting-side DSP 110, is adjacent to the first pilot symbol signal. B The frequency difference between them was analyzed.

[0146] As a result, the frequency difference compensation unit 247 can compensate for the frequency of the symbol signal sequence in the optical receiver 200 by using the frequency difference as a result of the above analysis.

[0147] As described above, regarding the use of the first pilot symbol signal P A and the second pilot symbol signal P B Frequency compensation can typically be achieved by using two known pilot symbol signals between the transmitting and receiving sides.

[0148] In the frequency compensation of the symbol signal sequence in the optical receiver 200, the first pilot symbol signal P is used. A and the extracted first pilot symbol signal P A The adjacent second pilot symbol signal P B That is, two pilot symbol signals with a relatively short time interval, such as the symbol interval, are therefore relative to the first pilot symbol signal P. A The frequency shift caused by the second pilot symbol signal P BThe phase rotation is small, therefore it is possible to obtain the first pilot symbol signal P. A The second pilot symbol signal P is used as a reference. B The accurate amount of phase rotation.

[0149] If frequency compensation is performed in an optical receiver for modulated light based on the following symbol signal sequence, sometimes as follows: Figure 9 As shown, an undesirable situation occurs, wherein the symbol signal sequence is, for example, not using the second pilot symbol signal P in Embodiment 1. B In an optical transmitter, such as Figure 10 The symbol signal sequence is obtained by inserting pilot symbol signals P into the data symbol signal S at symbol intervals, instead of using frames as units, or as shown in the example. Figure 11 The diagram shows how a symbol signal sequence is obtained by inserting pilot symbol signals P at a defined position and at a defined symbol interval within a frame unit.

[0150] Figure 9 The IQ signal space is shown, with the horizontal axis representing the Q axis and the vertical axis representing the I axis.

[0151] P1 is the signal point of the first pilot symbol signal P1 used for frequency compensation, P2 is the signal point of the second pilot symbol signal P2 when there is no frequency difference, and P2' is the signal point of the second pilot symbol signal P2 when there is a frequency difference.

[0152] exist Figure 9 In this context, signal point P1 is the observation signal point represented by the first pilot symbol signal P1 extracted by the pilot readout unit in the optical receiver, which becomes the reference point for analyzing the phase difference.

[0153] Signal point P2 is a signal point that has no difference in frequency relative to signal point P1. That is, it is a signal point obtained by the relative position of the IQ signal space of the first pilot symbol signal P1 and the second pilot symbol signal P2 inserted into the signal of the symbol signal sequence in the optical transmitter.

[0154] Signal point P2´ is the observation signal point represented by the second pilot symbol signal P2 extracted by the pilot readout unit.

[0155] from Figure 9 It is understandable that when the time interval from the extraction of the first pilot symbol signal P1 to the extraction of the second pilot symbol signal P2 is long, and the frequency of the optical carrier of the interference light in the optical receiver 200 is different from the frequency of the optical carrier from the optical transmitter, the signal point P2' of the second pilot symbol signal P2 will have a large phase rotation relative to the first pilot symbol signal P1 over the long time interval.

[0156] That is, the phase rotation of the second pilot symbol signal P2 is relatively large due to the frequency offset relative to the first pilot symbol signal P1, resulting in phase rotation in the IQ signal space. The phase rotates cyclically, thus causing an error in the estimation of the amount of phase rotation.

[0157] In the optical transceiver device of Embodiment 1, the first pilot symbol signal P is used. A and the extracted first pilot symbol signal P A The adjacent second pilot symbol signal P B Therefore, the frequency shift causes the second pilot symbol signal P to... B Relative to the first pilot symbol signal P A The phase rotation is small, there is no error in predicting the phase rotation amount, and the accurate phase rotation amount can be obtained.

[0158] In summary, the optical transceiver device of Implementation 1 transmits the first pilot symbol signal P, which is composed of different symbol periods. A and the second pilot symbol signal P B The signal of the inserted symbol signal sequence is based on the second pilot symbol signal P. B The second symbol period and the continuous first pilot symbol signal P A and the second pilot symbol signal P B The frequency difference between the optical carrier in the optical transmitter 100 and the interference light in the optical receiver 200 is compensated.

[0159] Therefore, the optical transceiver device of Embodiment 1 can use the first pilot symbol signal P with a shorter time interval. A and the second pilot symbol signal P B Accurately calculate the value of the first pilot symbol signal P in the IQ signal space. A and the second pilot symbol signal P B signal point P A P B P B The phase rotation amount is calculated based on the information, and then the compensation amount for the waveform distortion caused by the calculated phase rotation amount (frequency difference) is accurately calculated.

[0160] This improves the signal quality of the received signal in the optical receiver 200, thereby expanding the compensation range for the frequency difference between the optical carrier in the optical transmitter 100 and the frequency of the interference light in the optical receiver 200.

[0161] Therefore, the optical transceiver device of Embodiment 1 can compensate for degradation factors caused by waveform distortion due to frequency difference between the frequency of the optical carrier in the optical transmitter 100 and the frequency of the interference light in the optical receiver 200 for low-to-medium speed digital coherent signals.

[0162] Furthermore, in estimating the frequency difference of the modulated light, it is also possible to consider the adjacent first pilot symbol signal P. A and the second pilot symbol signal P B The observation location of the IQ signal space and the adjacent first pilot symbol signal P in the optical transmitter 100 A and the second pilot symbol signal P B After averaging the relative positions, the compensation amount is calculated.

[0163] By performing averaging, the speed responsiveness can be adjusted arbitrarily.

[0164] The phase estimation unit 248 compensates for the phase variation of the light source constituting the CW light generation unit 140 and the interference light generation unit 220.

[0165] The phase estimation unit 248 is constructed using a structure typically used in digital coherence methods.

[0166] That is, the signal processing for demodulation in the receiver-side DSP 240, other than the frequency difference compensation performed by the frequency difference compensation unit 247, is a common method in digital signal processing used in a typical digital coherent mode.

[0167] In the first pilot symbol signal P A and the second pilot symbol signal P B After being removed by the pilot removal unit 253, the demapping unit 249 converts the symbol signal, which has undergone waveform distortion compensation, into a bit signal.

[0168] The frame synchronization unit 250 obtains frame synchronization based on the bit signal sequence.

[0169] A digital signal of a sequence of bit signals synchronized for a frame is obtained and then error correction is performed.

[0170] Next, use Figure 12 The hardware structure of the optical transceiver device in Embodiment 1 will be described.

[0171] exist Figure 12 In, and in Figures 1 to 4 The same labels in the text indicate the same or equivalent parts.

[0172] The optical transceiver control unit 300 includes a processor 31 such as a CPU (Central Processing Unit) or a system LSI (Large Scale Integration), a memory 32 consisting of RAM (Random Access Memory) and ROM (Read Only Memory), a communication interface 33, and an input / output interface 34.

[0173] The processor 31, memory 32, communication interface 33 and input / output interface 34 are connected to the bus 35, and exchange data and control signals with each other via the bus 35.

[0174] The processor 31 temporarily reads the program recorded in the ROM in the memory 32 into the RAM in the memory 32, and performs processing according to the read program.

[0175] The ROM in memory 32 stores various data, programs for executing the processing in the optical transmitter 100 and optical receiver 200, and processing programs required to start the optical transceiver control unit 300, etc.

[0176] The communication interface 33 is used for transmitting and receiving data and control signals with the various structural elements in the optical transmitter 100, the various structural elements in the optical receiver 200, and the various structural elements of other optical transceivers.

[0177] The input / output interface 34 transmits and receives control signals and modulation signals between the various structural elements in the optical transmitter 100 and the various structural elements in the optical receiver 200 via electrical wiring.

[0178] The input / output interface 34 is, for example, an interface for supplying injection current to the interference light generating unit 220 for a light source, which is a light source constituting the interference light generating unit 220 for generating light.

[0179] In addition, the input / output interface 34 is, for example, an interface for outputting various control signals to the transmitting-side DSP unit 110 and the receiving-side DSP unit.

[0180] As described above, in the optical transceiver apparatus of Embodiment 1, the optical transmitter 100 includes a modulation signal generation unit 110, which generates a first pilot symbol signal P, consisting of a first symbol period, inserted into the data to be transmitted. A and the second pilot symbol signal P, which is composed of a second symbol period different from the first symbol period. BThe obtained modulation signal; and the optical modulation unit 130, which generates a first pilot symbol P inserted with a first symbol period based on the modulation signal converted into an analog signal by the digital-to-analog converter 120. A and the second pilot symbol P, which is composed of the second symbol period. B The modulated light, the optical receiver 200 has: an optical coherent detector 210, which detects the first pilot symbol signal P inserted with the first symbol period. A and the second pilot symbol signal P, which is composed of a second symbol period different from the first symbol period. B The polarization-multiplexed modulated light is coherently detected and an analog electrical signal is output; and a receiving-side digital signal processing unit 240 has a frequency difference compensation unit 247, which uses a first pilot symbol signal P extracted from the digital signal and inserted into the received polarization-multiplexed modulated light. A and the first pilot symbol signal P A The adjacent second pilot symbol signal P B The phase difference is calculated and the frequency of the received digital signal is compensated. The digital signal is obtained by coherently detecting the modulated light to obtain an analog electrical signal and then converting the analog electrical signal into a digital signal by the analog-to-digital converter 230. Therefore, it is possible to compensate for the difference between the frequency of the modulated light received by the optical receiver 200 and the frequency of the modulated light from the optical transmitter 100.

[0181] As a result, it is possible to compensate for waveform distortion caused by the frequency difference between the transmitted and received signals, improve the signal quality of the received signal in the optical receiver 200, and thus expand the compensation range for the optical frequency difference between the optical transmitter 100 and the optical receiver 200.

[0182] In particular, it is effective in optical receivers 200 that process low-to-medium speed digital coherent signals.

[0183] Implementation method 2.

[0184] according to Figures 13 to 15 The optical transceiver device of Embodiment 2 will be described.

[0185] The optical transceiver used in Implementation Method 1 Figure 7 In the digital coherence mode shown on the frequency axis, the single-carrier signal is used as the optical carrier.

[0186] In contrast, the optical transceiver in Embodiment 2 uses... Figure 15 The N subcarrier signals with different frequency configurations shown on the frequency axis in the digital coherent mode serve as optical subcarriers, and are optical transceivers based on subcarrier multiplexing.

[0187] In the optical transceiver device of Embodiment 2, the basic idea is to apply the subcarrier signals, which are N optical subcarriers, to the optical transceiver device of Embodiment 1.

[0188] Therefore, the following description will focus on the differences from the optical transceiver device of Embodiment 1.

[0189] In Implementation 2, as an example, the following optical transceiver device is envisioned: such as Figure 15 As shown, the multiplexed optical signal is transmitted and received by N channels based on N subcarrier signals SC#1 to SC#N of different frequencies in X-polarized waves and N channels based on N subcarrier signals SC#1 to SC#N of different frequencies in Y-polarized waves.

[0190] In the optical receiver 200, the optical coherent detector 210 receives modulated light that has been polarized and multiplexed to N different frequency configurations of subcarrier signals within the frequency band capable of detecting the signal. The optical coherent detector 210 performs optical coherent detection on the modulated light received by the optical coherent detector 210 and outputs it as an analog electrical signal.

[0191] The analog electrical signal, after being processed together, is converted into a digital signal by the ADC unit 230 and input to the receiving side DSP 240.

[0192] In the receiver-side DSP 240, each subcarrier signal SC#1 to SC#N is separated, and each channel based on the subcarrier signals SC#1 to SC#N is demodulated.

[0193] The optical transceiver device of Embodiment 2 is similar to the optical transceiver device of Embodiment 1, such as... Figure 1 As shown, it includes an optical transmitter 100, an optical receiver 200, and an optical transceiver control unit 300.

[0194] The optical transmitter 100 includes a transmitting-side DSP 110A, a DAC unit 120, an optical modulation unit 130, and a CW optical generation unit 140.

[0195] like Figure 13 As shown, the transmitting-side DSP 110A has N subcarrier generation units 111 to 112. N Subcarrier multiplexing unit 117 and skew adjustment unit (anti-skew unit) 114.

[0196] The information to be sent to the destination, i.e., different data signals #1 to #N, is input as digital signals to N subcarrier generation units 111 to 11. N N subcarrier generation units 111~11 NA modulation signal is generated, which is a digital signal for optical modulation obtained by inserting a first pilot symbol signal consisting of the first symbol period and a second pilot symbol signal consisting of a second symbol period different from the first symbol period into the data to be transmitted #1 to #N.

[0197] Regarding the N subcarrier generation units 111~11 N Each of these, the data to be transmitted #1 to #N and the subcarrier signals SC#1 to SC#N that serve as the carrier are different, but they are basically the same structure.

[0198] That is, N subcarrier generation units 111 to 11 N Each has its own digital circuitry, which includes frame generation units 1111 to 111. N Mapping section 1121~112 N Spectrum Shaping Section 1131~113 N Pilot generation section 1151~115 N and pilot insertion sections 1161 to 116 N The signal processing function is basically the same as the frame generation unit 111, mapping unit 112, spectrum shaping unit 113, pilot generation unit 115 and pilot insertion unit 116 in the transmitting side DSP110 of the optical transmitter 110 in the optical transceiver device of Embodiment 1.

[0199] In summary, there are N subcarrier generation units 111 to 11 N Using frame generation units 1111 to 111 respectively N The data to be transmitted is converted into signal frames based on digital coherent signals. The mapping unit 112 converts these into XI, XQ, YI, and YQ signals, which are polarization-multiplexed QPSK signals on the frequency axis via different subcarrier signals SC#1 to SC#N. Pilot insertion units 1161 to 116... N This makes it into the first pilot symbol signal P inserted with a digital coherent signal. A and the second pilot symbol signal P B The frequency characteristics of the modulated signal are shaped by the spectrum shaping unit 113.

[0200] N subcarrier generation units 111~11 N Each has 4 output terminals.

[0201] Subcarrier multiplexing unit 117 pairs subcarriers from N subcarrier generation units 111 to 112. N The modulated signal is multiplexed on the frequency axis.

[0202] The skew adjustment unit 114 compensates for the skew (delay difference) that occurs between signals caused by the optical transmitter 100 due to the electrical signal flow of the multiplexed modulation signals, namely the XI signal, XQ signal, YI signal, and YQ signal, on the frequency axis supplied by the spectrum shaping unit 113.

[0203] The multiplexed modulation signals generated in this way on different frequency axes are converted into analog signals by the DAC unit 120.

[0204] The optical modulation unit 130 modulates the CW light from the CW light generation unit 140 according to the modulation signal converted into an analog signal by the DAC unit 120, and generates modulated light after frequency multiplexing and polarization multiplexing of multiple different subcarrier signals, which are inserted into a first pilot symbol composed of a first symbol period and a second pilot symbol composed of a second symbol period different from the first symbol period, and outputs the generated modulated light to the transmission path.

[0205] The optical receiver 200 includes an optical coherence detector 210, an interference light generator 220, an ADC 230, and a receiver-side DSP 240A.

[0206] The optical coherent detector 210 performs optical coherent detection, during which it also receives the first pilot symbol signal P, which is inserted with the first symbol period. A and the second pilot symbol signal P, which is composed of a second symbol period different from the first symbol period. B The modulated light obtained by frequency multiplexing and polarization multiplexing of multiple different subcarrier signals is used to interfere with the CW light with a single carrier frequency fc from the interference light generation unit 220, i.e., interference light. The light signal obtained through interference is photoelectrically converted to obtain a voltage, and an analog electrical signal based on the voltage is output.

[0207] The ADC unit 230 samples the electrical signal from the analog region of the optical coherent detector unit 210 according to the sampling frequency, and converts it into a discrete signal, i.e. a digital signal, in the digital region, to obtain the signal before demodulation, which is composed of digital signals for obtaining the demodulated signal.

[0208] The receiver-side DSP 240A includes a skew adjustment section (anti-skew section) 241, a subcarrier separation section 254, and N subcarrier detection sections 241 to 242. N .

[0209] The skew adjustment unit 241 compensates for the skew caused by the optical transmitter and optical receiver devices for the channels of the XI signal, XQ signal, YI signal, and YQ signal, respectively.

[0210] Subcarrier separation unit 254 performs signal separation by corresponding the undemodulated signal with N subcarrier signals SC#1 to SC#N on the frequency axis. The undemodulated signal is then separated by passing through the first pilot symbol signal P. A and the second pilot symbol signal P B Multiple different subcarrier signals are composed of digital signals after frequency multiplexing and polarization multiplexing.

[0211] N subcarrier detection units 241~24 N For each of the N digital signals separated by the subcarrier separation unit 254, compensation is performed for wavelength dispersion and nonlinear optical effects on the modulated light in the transmission path, polarization mode dispersion, and frequency offset caused by the difference in the source frequency of the CW light in the optical transmitter and optical receiver.

[0212] N subcarrier detection units 241~24 N Each has an amplitude adjustment section 2421 to 242 N Dispersion compensation section 2431-243 N Clock synchronization unit 2441-244 N Frequency band compensation section 2451-245 N Adaptive Equalization Section 2461-246 N Frequency difference compensation section 2471-247 N Phase estimation section 2481-248 N Demapping section 2491-249 N Frame synchronization unit 2501-250 N Read the first pilot symbol signal P A First pilot reading section 2511-251 N Read the second pilot symbol signal P B Second pilot reading section 2521-252 N and pilot removal section 2531-253 N The amplitude adjustment unit 242, dispersion compensation unit 243, clock synchronization unit 244, bandwidth compensation unit 245, adaptive equalization unit 246, frequency difference compensation unit 247, phase estimation unit 248, demapping unit 249, frame synchronization unit 250, first pilot reading unit 251, second pilot reading unit 252 and pilot removal unit 253 in the receiving side DSP 240 of the optical receiver 200 in the optical transceiver device of Embodiment 1 are basically the same as those in the optical receiver 200 of Embodiment 1.

[0213] In summary, in the N subcarrier detection units 241 to 24 N In each of them, the same digital processing is performed as in the receiver-side DSP 240 in the optical transceiver device of Embodiment 1.

[0214] N subcarrier detection units 241~24 N Each frequency difference compensation unit 2471-247 N For each of the multiple different subcarrier signals SC#1 to SC#N, the frequency difference between the frequency of the CW light from the CW light generating unit 140 in the optical transmitter 100 and the frequency of the interference light from the interference light generating unit 220 is compensated.

[0215] The receiver-side DSP 240A consists of N subcarrier detection units 241 to 242. N N data signals are output from the receiving side DSP 240A.

[0216] The hardware structure of the optical transceiver in Embodiment 2 is the same as that of the optical transceiver in Embodiment 1. The receiver control unit 30 consists of a processor 31 such as a CPU or system LSI, a memory 32, a communication interface 33, and an input / output interface 34. The memory 32 consists of RAM and ROM.

[0217] As described above, in the optical transceiver apparatus of Embodiment 2, using subcarrier signals SC#1 to SC#N as N optical subcarriers, the optical transmitter 100 outputs frequency-multiplexed modulated light, and the optical receiver 200 simultaneously receives the polarization-multiplexed modulated light obtained by frequency multiplexing the N subcarrier signals SC#1 to SC#N on the frequency axis. In this optical transceiver apparatus, the difference between the frequency of the optical carrier of the interference light in the optical receiver 200 and the frequency of the optical carrier from the optical transmitter 100 can be compensated according to each of the subcarrier signals SC#1 to SC#N, similar to the optical transceiver apparatus of Embodiment 1.

[0218] Furthermore, it is possible to freely combine the various embodiments or modify any structural elements of the various embodiments, or to omit any structural elements in the various embodiments.

[0219] Industrial availability

[0220] The optical transceiver disclosed herein is not limited to communication systems that use optical fiber as the transmission medium in optical access, optical core / metropolitan area networks, but can also be applied to optical communication systems that do not use optical fiber, such as space or space optical communication.

[0221] Label Explanation

[0222] 100: Optical transmitter; 110, 110A: Modulation signal generation unit (transmitter-side DSP); 111~11 N Subcarrier generation unit; 111, 1111~111 N Frame generation unit (framing unit); 112, 1121~112 NMapping section; 113, 1131~113 N : Spectrum shaping section; 114: Skew adjustment section (anti-skew section); 115, 1151~115 N Pilot generation section; 116, 1161~116 N 117: Pilot insertion section; 120: Subcarrier multiplexing section; 130: Digital-to-analog converter (DAC) section; 140: Optical modulation section; 200: CW light generation section; 210: Optical coherent detector section; 220: Interference light generation section; 230: ADC section; 240, 240A: Receiver-side digital signal processing section (receiver-side DSP); 241~24 N 241: Subcarrier detection unit; 242: Skew adjustment unit; 242, 2421~242 N Amplitude adjustment section; 243, 2431~243 N Dispersion compensation section; 244, 2441-244 N Clock synchronization unit; 245, 2451~245 N Frequency band compensation section; 246, 2461~246 N Adaptive equalization unit; 247, 2471~247 N Frequency difference compensation unit; 248, 2481~248 N Phase estimation section; 249, 2491-249 N Demapping section; 250, 2501~250 N Frame synchronization unit; 251, 2511~251 N : First pilot reading unit; 252, 2521~252 N : Second pilot reading unit; 253, 2531~253 N Pilot removal section.

Claims

1. An optical transceiver device comprising an optical transmitter and an optical receiver, The optical transmitter has: The modulation signal generation unit generates a modulation signal, which is a digital signal for optical modulation obtained by inserting a first pilot symbol signal consisting of a first symbol period and a second pilot symbol signal consisting of a second symbol period different from the first symbol period into the data to be transmitted. A digital-to-analog converter that converts the modulated signal generated by the modulated signal generation unit into a modulated signal composed of an analog signal; as well as The optical modulation unit modulates the CW light from the CW light generation unit based on the modulation signal converted into an analog signal by the digital-to-analog converter, generating modulated light with a first pilot symbol signal composed of the first symbol period and a second pilot symbol signal composed of the second symbol period inserted. The optical receiver has: The optical coherent detector receives modulated light after polarization multiplexing, which is inserted with a first pilot symbol signal composed of the first symbol period and a second pilot symbol signal composed of a second symbol period different from the first symbol period. It performs coherent detection on the received modulated light and outputs an analog electrical signal. An analog-to-digital converter performs analog-to-digital conversion on the analog electrical signal from the optical coherence detector and outputs it as a digital signal. as well as The receiving-side digital signal processing unit has a frequency difference compensation unit that receives a digital signal from the analog-to-digital converter and calculates the phase difference using a first pilot symbol signal extracted from the received digital signal and inserted into the received polarization-multiplexed modulated light, which is composed of the first symbol period and a second pilot symbol signal adjacent to the first pilot symbol signal, which is composed of the second symbol period different from the first symbol period, to compensate for the frequency of the received digital signal.

2. The optical transceiver according to claim 1, wherein, The optical modulation unit uses a single-carrier signal as an optical carrier to generate modulated light. The optical coherent detector converts the modulated light obtained by using a single-carrier signal as an optical carrier into an analog electrical signal. The frequency difference compensation unit of the receiving side digital signal processing unit compensates for the frequency of the digital signal for the single carrier signal.

3. The optical transceiver according to claim 1, wherein, The optical modulation unit generates modulated light by frequency multiplexing multiple subcarrier signals configured with different frequencies as optical subcarriers. The optical coherent detector enables the modulated light, which uses multiple subcarrier signals with different frequency configurations as optical subcarriers and then frequency-multiplexes them, to become an analog electrical signal. The frequency difference compensation unit of the receiving side digital signal processing unit compensates for the frequency of the digital signal according to each of the multiple subcarrier signals configured with different frequencies.

4. The optical transceiver according to any one of claims 1 to 3, wherein, The modulated light generated by the optical modulation unit is an optical signal obtained by modulating X-polarized waves and Y-polarized waves into I signals and Q signals with orthogonal phases, respectively.

5. The optical transceiver according to any one of claims 1 to 3, wherein, The first pilot symbol signal and the second pilot symbol signal use QPSK signals.

6. The optical transceiver according to any one of claims 1 to 3, wherein, The second symbol period of the second pilot symbol signal is an integer multiple of 2 or more of the first symbol period of the first pilot symbol signal.

7. A light receiver, comprising: The optical coherent detector receives modulated light after polarization multiplexing, which is inserted with a first pilot symbol signal composed of a first symbol period and a second pilot symbol signal composed of a second symbol period different from the first symbol period. It performs coherent detection on the received modulated light and outputs an analog electrical signal. An analog-to-digital converter performs analog-to-digital conversion on the analog electrical signal from the optical coherence detector and outputs it as a digital signal. as well as The receiving-side digital signal processing unit has a frequency difference compensation unit that receives a digital signal from the analog-to-digital converter and calculates the phase difference using a first pilot symbol signal extracted from the received digital signal and inserted into the received polarization-multiplexed modulated light, which is composed of the first symbol period and a second pilot symbol signal adjacent to the first pilot symbol signal, which is composed of the second symbol period different from the first symbol period, to compensate for the frequency of the received digital signal.

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