Optical transmitting / receiving device and optical receiver

Abstract

The optical transmitter (100) includes a modulation signal generation unit (110) that generates a modulation signal, which is a digital signal in which a first pilot symbol signal having a first symbol period and a second pilot symbol signal having a second symbol period are inserted into data to be transmitted, and an optical modulation unit (130) that modulates CW light from a CW light generation unit (140) based on the modulation signal converted into an analog signal by a digital / analog conversion unit (120) to generate modulated light in which the first pilot symbol signal and the second pilot symbol signal are inserted. The optical receiver (200) includes a modulation signal generation unit (110) that generates a modulation signal, which is a digital signal in which a first pilot symbol signal having a first symbol period and a second pilot symbol signal having a second symbol period are inserted into data to be transmitted, and an optical modulation unit (130) that modulates CW light from a CW light generation unit (140) based on the modulation signal converted into an analog signal by a digital / analog conversion unit (120) to generate modulated light in which the first pilot symbol signal and the second pilot symbol signal are inserted. and a receiving-side digital signal processing unit (240) having a frequency difference compensation unit (247) which calculates a phase difference using the first pilot symbol signal and a second pilot symbol signal adjacent to the first pilot symbol signal, which are extracted from the digital signal from the analog / digital converter unit (230) and inserted into the received polarization multiplexed modulated light, and compensates for the frequency of the received digital signal.

Description

[Technical field]

[0001] The present disclosure relates to an optical transceiver device that performs digital coherent optical communication. [Background technology]

[0002] In the field of optical fiber communications, digital coherent technology has been widely applied in metro core networks and submarine optical cable systems. In digital coherent optical communications, efforts are being made to improve performance and functionality, including an increase in data rate.

[0003] In particular, digital coherent optical transceivers can generate multiple subcarrier signals in the digital domain that do not interfere with each other on the frequency axis within a single optical transceiver. In recent years, a method has been proposed in which different information is assigned to each subcarrier, enabling simultaneous support of a variety of services. By accommodating them simultaneously in this way, it is possible to realize efficient hardware utilization and space saving. A digital coherent optical communication technology capable of transmitting and receiving subcarrier signals is disclosed in, for example, Non-Patent Document 1.

[0004] In addition, in a digital coherent system, in order to perform phase compensation in response to phase fluctuations occurring in an optical fiber transmission path between a transmitting device and a receiving device, a pilot symbol is inserted into a data string every K symbols in the transmitting device and output, and a pilot symbol is detected in the data string in the receiving device, the phase fluctuations are estimated from a reference symbol stored in a predetermined storage device, and a residual frequency offset is compensated for based on the phase fluctuation.This optical transmission system is shown in Patent Document 1. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] H. Sun et al, “800G DSP ASIC Design Using Probabilistic Shaping and Digital Sub-Carrier Multiplexing”, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 38, NO. 17, SEPTEMBER 1, 2020, pp4744-4756 [Patent Document 1] WO2014 / 126132 Summary of the Invention [Problem to be solved by the invention]

[0006] The optical receiver disclosed in Non-Patent Document 1 detects signals by optical coherent detection, and converts the output voltage signal into a digital signal by an analog-to-digital converter (ADC). Generally, when the sampling rate of an analog / digital converter is high, the analog received signal before analog-to-digital conversion can be accurately acquired as a digital signal, waveform distortion compensation in digital signal processing can be performed accurately, and the signal quality after reception can be improved.

[0007] However, when an FPGA (Field Programmable Gate Array) with a sampling rate or throughput of several gigabits is used for digital signal processing, or when a low- to medium-speed digital coherent signal is handled in an optical receiver, such as when the modulation speed of each subcarrier is low due to a subcarrier multiplexing method, if there is a frequency difference between the transmitted and received optical carrier waves, the ability to compensate for waveform distortion in the receiving digital signal processing is reduced.

[0008] Although the optical transmission system in Patent Document 1 inserts a pilot symbol every K symbols, if the time interval between adjacent pilot symbols is long and there is a difference between the frequency of the optical carrier wave in the transmitting device and the frequency of the optical carrier wave in the receiving device, an estimation error will occur in phase compensation.

[0009] The present disclosure has been made in consideration of the above-mentioned points, and aims to provide an optical transceiver device that has a compensation function for factors that cause waveform distortion degradation due to the frequency difference between the transmitted and received optical carrier waves in an optical receiver that handles low- to medium-speed digital coherent signals. [Means for solving the problem]

[0010] An optical transmission / reception apparatus according to the present disclosure includes an optical transmitter and an optical receiver, the optical transmitter including a modulation signal generation unit that generates a modulation signal, which is a digital signal for optical modulation, in which a first pilot symbol signal having a first symbol period and a second pilot symbol signal having a second symbol period different from the first symbol period are inserted into data to be transmitted, a digital-to-analog conversion unit that converts the modulation signal, which is a digital 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 based on the modulation signal converted into an analog signal by the digital-to-analog conversion unit to generate modulated light in which the first pilot symbol signal having the first symbol period and the second pilot symbol signal having the second symbol period are inserted, and the optical receiver includes a modulation signal generation unit that converts the first pilot symbol signal having the first symbol period and the second pilot symbol signal having the second symbol period into data to be transmitted, and a receiving-side digital signal processing unit having a frequency difference compensation unit that receives a digital signal from the analog-to-digital conversion unit, and calculates a phase difference using a first pilot symbol signal having the first symbol period and a second pilot symbol signal having a second symbol period different from the first symbol period that is adjacent to the first pilot symbol signal and that is inserted into the received polarization multiplexed modulated light, and an analog electrical signal by performing coherent detection of the received modulated light and outputting a analog electrical signal; Effect of the Invention

[0011] According to the present disclosure, in an optical receiver that handles low- to medium-speed digital coherent signals, it is possible to suppress a decrease in the ability to compensate for waveform distortion in digital signal processing by an analog-to-digital converter. [Brief description of the drawings]

[0012] [Figure 1] 1 is a block diagram showing a configuration of an optical transmitting / receiving device according to a first embodiment. [Diagram 2] 2 is a block diagram showing a configuration of a transmission-side digital signal processing unit in the optical transmitting and receiving device according to the first embodiment. FIG. [Diagram 3] 13 is a block diagram showing a configuration of another transmission-side digital signal processing unit in the optical transmission / reception device according to the first embodiment. FIG. [Figure 4] 2 is a block diagram showing a configuration of a reception-side digital signal processing unit in the optical transmission / reception device according to the first embodiment. [Diagram 5] FIG. 2 is a diagram showing an example of a symbol signal sequence in which a first pilot symbol signal PA and a second pilot symbol signal PB are inserted in a digital coherent system in an optical transmission / reception device according to a first embodiment. [Figure 6] FIG. 11 is a diagram showing another example of a symbol signal sequence in which a first pilot symbol signal PA and a second pilot symbol signal PB are inserted in the digital coherent system in the optical transmission / reception device according to the first embodiment. [Figure 7] 1 is a diagram for explaining a single carrier signal in a digital coherent system used in an optical transmission / reception device according to a first embodiment, on a frequency axis. [Figure 8] 4 is a diagram for explaining the effect of compensation for the difference in optical frequencies in an IQ signal space in the optical transmission / reception device according to the first embodiment; FIG. [Figure 9] FIG. 13 is a diagram illustrating compensation for the difference in optical frequencies in an IQ signal space, shown as a comparative example. [Figure 10]FIG. 13 is a diagram showing an example of a symbol signal sequence into which one pilot symbol signal P is inserted in a digital coherent system in a comparative example. [Figure 11] FIG. 13 is a diagram showing another example of a symbol signal sequence into which one pilot symbol signal P is inserted in the digital coherent system in the comparative example. [Figure 12] 1 is a diagram illustrating a hardware configuration of an optical transmitting / receiving device according to a first embodiment. [Figure 13] 11 is a block diagram showing a configuration of a transmission-side digital signal processing unit in an optical transmission / reception device according to a second embodiment. FIG. [Figure 14] 11 is a block diagram showing a configuration of a reception-side digital signal processing unit in an optical transmission / reception device according to a second embodiment. FIG. [Figure 15] 11 is a diagram for explaining subcarrier signals on the frequency axis in a subcarrier multiplexing method in a digital coherent system used in an optical transmission / reception device according to a second embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Embodiment 1 An optical transmission / reception device according to a first embodiment will be described with reference to FIGS. In the figure, dashed arrows indicate the flow of optical signals, and solid arrows indicate the flow of electrical signals. The optical transmitting / receiving device of embodiment 1 is a device that focuses on the transmission and receiving functions of communication equipment and optical transceivers that control the transmission and reception of optical signals in optical communication network systems that use optical fiber as the transmission medium in optical access and optical core-metro networks, as well as optical communication network systems that do not use optical fiber and use wireless space as the transmission medium, such as for space and free-space optical communications.

[0014] The optical transceiver according to the first embodiment is applied to an optical transceiver that transmits and receives digital coherent signals, which are optical signals that utilize phase orthogonality, such as polarization-multiplexed binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), or quadrature amplitude modulation (QAM) of a digital coherent system. The present invention may also be applied to an optical transceiver that transmits and receives a single-polarized digital coherent signal that does not undergo polarization multiplexing.

[0015] In the following description, it is assumed that in the optical transmission / reception device according to the first embodiment, an optical signal is polarization-multiplexed by a digital coherent method using X-polarized wave and Y-polarized wave, and the X-polarized wave and the Y-polarized wave are modulated into an I signal and a Q signal of quadrature phase, respectively. For example, the X-polarized wave is a horizontally polarized wave, and the Y-polarized wave is a vertically polarized wave. Assume a digital coherent signal that is polarization-multiplexed into an I signal (XI signal) in X polarization, a Q signal (XQ signal) in X polarization, an I signal (YI signal) in Y polarization, and a Q signal (YQ signal) in Y polarization.

[0016] Note that the terminals for the XI signal, XQ signal, YI signal, and YQ signal, respectively (XI output terminal, XQ output terminal, YI output terminal, and YQ output terminal), as well as the lanes through which the electrical signals for the XI signal, XQ signal, YI signal, and YQ signal flow (XI lane, XQ lane, YI lane, and YQ lane), are distinct, but are shown together in the figure.

[0017] As shown in FIG. 1, the optical transmitting and receiving apparatus according to the first embodiment includes an optical transmitter 100, an optical receiver 200, and an optical transmitter / receiver control unit 300. The optical transmitter 100, the optical receiver 200, and the optical transmitter / receiver control unit 300 are housed in the same housing. The optical transmitter 100 generates polarization-multiplexed modulated light in which a first pilot symbol signal having a first symbol period and a second pilot symbol signal having a second symbol period different from the first symbol period are inserted into data to be transmitted, and outputs the generated modulated light to an optical receiver of another optical transmitting / receiving device via a transmission path, which is an optical fiber or a wireless space. In the first embodiment, the modulated light output from the optical transmitter 100 is an optical signal obtained by modulating a CW (Continuous wave) light having one carrier frequency with a modulation signal that is an electrical signal.

[0018] The optical receiver 200 receives polarization-multiplexed modulated light into which a first pilot symbol signal having a first symbol period and a second pilot symbol signal having a second symbol period different from the first symbol period have been inserted, the first pilot symbol signal having a first symbol period and propagating through a transmission path from an optical transmitter of another optical transceiver device, and acquires data from the received modulated light. The data acquired 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 interference light having one carrier frequency.

[0019] The optical transmitter 100 includes a modulated signal generating section 110, a digital-to-analog converter (DAC) section 120, an optical modulating section 130, and a CW light generating section 140. The modulated signal generating section 110 includes a modulated signal generating section 120, a digital-to-analog converter (DAC) section 120, an optical modulating section 130, and a CW light generating section 140. The modulated signal generating unit 110 is a transmitting-side digital signal processing unit (transmitting digital signal processor (DSP: digital signal processor), hereinafter referred to as the transmitting-side DSP 110).

[0020] The transmitting side DSP 110 receives data, which is the information to be sent to a destination, as a digital signal, and generates a modulated signal, which is a digital signal for optical modulation, in which a first pilot symbol signal having a first symbol period and a second pilot symbol signal having a second symbol period different from the first symbol period are inserted into the input data, i.e., the data to be transmitted. The data to be transmitted is constructed by the transmitting DSP 110 into a frame, which is a signal format capable of error correction.

[0021] The transmitting DSP 110 generates four modulated signals: an XI signal, an XQ signal, a YI signal, and a YQ signal. Each of the four modulated signals is a symbol signal sequence in which two types of pilot symbol signals shown in FIG. 5 are inserted, or a symbol signal sequence in which two types of pilot symbol signals shown in FIG. 6 are inserted.

[0022] 5 and 6, the horizontal axis represents time, S represents a data symbol signal, and P A (P A1 , P A2 , P A5 ) is the first pilot symbol signal, P B (P B1 , P BA2 , ···) denotes a second pilot symbol signal. The data symbol signal S is a symbol signal (complex signal) obtained by converting a bit signal of data to be transmitted for IQ modulation. In other words, the data symbol signal S is a digital coherent signal. The first pilot symbol signal P A and the second pilot symbol signal P B are digital coherent signals each containing 1 bit, i.e., the symbol length is 1.

[0023] The symbol signal sequence shown in FIG. 5 is not frame-by-frame, but the first pilot symbol signal P is generated at a first symbol interval, i.e., at a first symbol period, with respect to the data symbol signal S. A The second pilot symbol signal P is inserted not in units of frames, but in units of frames, at a second symbol interval different from the first symbol interval, i.e., at a second symbol period different from the first symbol period, for the data symbol signal S. B is inserted into the symbol signal sequence.

[0024] The second pilot symbol signal P BThe second symbol interval of A The interval is an integer multiple of two or more, and in this example, four times the interval of the first symbol. In other words, the second pilot symbol signal P B The second symbol period of the first pilot symbol signal P A The symbol period is an integer multiple of two or more, and in this example, four times the first symbol period.

[0025] That is, the second pilot symbol signal P B is the first pilot symbol signal P A It is inserted at a frequency of 1 / 4 for the data symbol signal S. The second pilot symbol signal P B is the first pilot symbol signal P A That is, the second pilot symbol signal P B is the first pilot symbol signal P A are placed on adjacent symbols. The first pilot symbol signal and the adjacent second pilot symbol signal are arranged at a short time interval, that is, at one symbol interval in the first embodiment.

[0026] The symbol signal sequence shown in FIG. 6 is a first pilot symbol signal P A A second pilot symbol signal P is generated by inserting a second symbol interval different from the first symbol interval, which is determined at a fixed position in a frame unit, that is, a second symbol period different from the first symbol period. B is inserted into the symbol signal sequence.

[0027] The second pilot symbol signal P B The second symbol interval of A The interval is an integer multiple of two or more, and in this example, four times the interval of the first symbol. In other words, the second pilot symbol signal P B The second symbol period of the first pilot symbol signal P A The symbol period is an integer multiple of two or more, and in this example, four times the first symbol period.

[0028] That is, the second pilot symbol signal P B is the first pilot symbol signal P A It is inserted at a frequency of 1 / 4 for the data symbol signal S. The second pilot symbol signal P B is the first pilot symbol signal P A That is, the second pilot symbol signal P B is the first pilot symbol signal P A are placed on adjacent symbols. The first pilot symbol signal and the adjacent second pilot symbol signal are arranged at a short time interval, that is, at one symbol interval in the first embodiment.

[0029] As shown in FIG. 2, the transmitting side DSP 110 includes digital circuits having the signal processing functions of a frame generating section 111, a mapping section 112, a spectrum shaping section 113, a skew adjusting section (deskewing section) 114, a pilot generating section 115, and a pilot inserting section . The frame generation unit 111 is a framer unit that constructs data to be transmitted in a signal frame format that is a signal format capable of correcting errors.

[0030] The mapping unit 112 converts a data string made up of bit signals in the digital signal from the frame generation unit 111 into a symbol signal (complex signal) for IQ modulation. That is, the mapping unit 112 converts a data string based on data to be transmitted into a modulated signal, which is a digital signal for optical modulation. Generally, as the multilevel degree of IQ modulation increases, the number of bits allocated to the data symbol signal S increases, improving the data rate.

[0031] The mapping unit 112 has four output terminals for the XI signal, the XQ signal, the YI signal, and the YQ signal corresponding to the polarization multiplexed BPSK signal or QPSK signal obtained by the mapping unit 112 . Even when the polarization multiplexed signal obtained by mapping unit 112 is a QAM signal, mapping unit 112 has four output terminals. In summary, the mapping unit 112 has four output terminals for the digital coherent signal.

[0032] The pilot inserter 116 generates a first pilot symbol signal P using the digital coherent signal generated by the pilot generator 115. A is inserted into the data string for each first symbol period before mapping section 112 processes the data string made up of bit signals in the digital signal from frame generation section 111.

[0033] Furthermore, the pilot inserter 116 generates a second pilot symbol signal P using the digital coherent signal generated by the pilot generator 115. B is inserted into the data string for each second symbol period before mapping section 112 processes the data string made up of bit signals in the digital signal from frame generation section 111. In this case, the mapping unit 112 maps the first pilot symbol signal P A and the second pilot symbol signal P B The data string into which the symbol signal sequence is inserted is converted into a modulated signal based on the symbol signal sequence shown in FIG. 5 or the symbol signal sequence shown in FIG.

[0034] As shown in FIG. 3, the pilot inserter 116 generates a first pilot symbol signal P A and the second pilot symbol signal P BWhen mapping unit 112 converts a data sequence of bit signals in the digital signal from frame generation unit 111 into a modulated signal, these may be inserted in symbol units in the first symbol period and the second symbol period, respectively, to obtain a modulated signal based on the symbol signal sequence shown in FIG. 5 or the symbol signal sequence shown in FIG. 6.

[0035] The spectrum shaping unit 113 shapes the frequency characteristics of the modulated signal obtained by the mapping unit 112 in accordance with the frequency characteristics of the optical transmitting / receiving device and the frequency characteristics in the transmission path. The skew adjustment unit 114 compensates for the skew (delay difference) that occurs between signals caused by the optical transmitter 100 due to the XI lane, XQ lane, YI lane, and YQ lane through which the electrical signals of the XI signal, XQ signal, YI signal, and YQ signal, which are the modulated signals from the spectrum shaping unit 113, flow.

[0036] As described above, the transmitting side DSP 110 converts the data to be transmitted into a signal frame format using a digital coherent signal using the frame generation unit 111, converts it into a modulated signal using the mapping unit 112, and generates the first pilot symbol signal P using a digital coherent signal using the pilot insertion unit 116. A and the second pilot symbol signal P B a first pilot symbol signal having a first symbol period and a second pilot symbol signal having a second symbol period different from the first symbol period, the first pilot symbol signal having a first symbol period and the second pilot symbol signal having a second symbol period different from the first symbol period being inserted into the modulated signal, the modulated signal having its frequency characteristics shaped by spectrum shaping section 113 and its skew compensated by skew adjustment section 114, and a modulated signal that is a digital signal for optical modulation is generated in which a first pilot symbol signal having a first symbol period and a second pilot symbol signal having a second symbol period different from the first symbol period are inserted.

[0037] The DAC unit 120 outputs a first pilot symbol signal P A and the second pilot symbol signal P B The modulated signal consisting of a digital signal into which the modulated signal has been inserted is converted into a modulated signal consisting of an analog signal. The optical modulation unit 130 modulates the CW light from the CW light generation unit 140 based on the modulation signal converted into an analog signal by the DAC unit 120 to generate modulated light into which a first pilot symbol signal having a first symbol period and a second pilot symbol signal having a second symbol period different from the first symbol period are inserted, and outputs the generated modulated light to a transmission path.

[0038] Modulated light is an optical signal that is a digital coherent signal in which information is carried by the modulating signal on CW light. The modulated light contains a mixture of information from the XI signal, XQ signal, YI signal, and YQ signal output from independent lanes. The CW light from the CW light generating unit 140 is a single carrier signal in a digital coherent system, as shown on the frequency axis in FIG.

[0039] As shown in FIG. 1, the optical receiver 200 includes an optical coherent detection section 210, an interference light generation section 220, an ADC (Analog-to-digital converter) section 230 which is an analog-to-digital converter, and a receiving side digital signal processing section 240. The receiving side digital signal processing unit 240 is a receiving digital signal processor (DSP), and will be referred to as receiving side DSP 240 hereinafter.

[0040] The optical coherent detection unit 210 receives polarization multiplexed modulated light transmitted through a transmission path from an optical transmitter of another optical transmitting / receiving device, causes the received modulated light to interfere with interference light, which is continuous wave (CW) light having a single carrier frequency fc from the interference light generating unit 220, and performs optical coherent detection to output an analog electrical signal based on a voltage obtained by photoelectric conversion of the optical signal obtained by the interference. The voltage signal output from the optical coherent detection unit 210 is a single-ended output or a differential output.

[0041] In the first embodiment, the analog electrical signals output from the optical coherent detection unit 210 are four signals, an XI signal, an XQ signal, a YI signal, and a YQ signal, which are output from four output terminals, respectively. The XI signal, XQ signal, YI signal, and YQ signal are pre-demodulation signals, which are analog voltage signals used to obtain a demodulated signal obtained by optically interfering the polarization-multiplexed modulated light and the interference light having a single carrier frequency fc using the optical coherent detection unit 210.

[0042] The ADC unit 230 is a collection of ADCs corresponding to the XI lane of the XI signal, the XQ lane of the XQ signal, the YI lane of the YI signal, and the YQ lane of the YQ signal. Each ADC in the ADC unit 230 samples the analog electrical signal input in each corresponding lane based on a sampling frequency, converts it into a digital signal, which is a discrete signal in the digital domain, and obtains a pre-demodulation signal consisting of a digital signal. Each of the XI signal, XQ signal, YI signal, and YQ signal converted into a digital signal by the ADC unit 230 is a symbol signal sequence into which two types of pilot symbol signals are inserted, as shown in FIG. 5 or FIG.

[0043] The receiving side DSP 240 performs digital signal processing on the XI signal, XQ signal, YI signal, and YQ signal that have been converted into digital signals by the ADC unit 230, and demodulates them. In addition, the receiving side DSP 240 may combine the XI signal and XQ signal for the X polarization, which have been converted into digital signals by the ADC unit 230, to obtain a complex signal in the digital domain for the X polarization, and may combine the YI signal and YQ signal for the Y polarization to obtain a complex signal in the digital domain for the Y polarization.

[0044] 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. The receiving DSP 240 compensates for the chromatic dispersion and nonlinear optical effect that the modulated light has experienced along the transmission path, as well as polarization mode dispersion, for the input digital signal, and compensates for the frequency offset that occurs due to the difference in light source frequency of the CW light between the optical transmitter and the optical receiver.

[0045] The receiving DSP 240 performs digital signal processing on each of the XI, XQ, YI, and YQ signals, but to simplify the explanation, FIG. 4 shows the flow of the digital signal processing as the flow of one electrical signal. FIG. 4 mainly illustrates a first pilot symbol signal P inserted into the polarization multiplexed modulated light transmitted from the optical transmitter via the transmission line, which is a feature of the first embodiment. A and the second pilot symbol signal P B This shows the optical demodulation function for detecting the error, but does not show error correction, etc.

[0046] As shown in FIG. 4, 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 band 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 first pilot symbol signal P A A first pilot reading unit 251 that reads a second pilot symbol signal P B and a pilot removal unit 253.

[0047] Note that the XI signal, XQ signal, YI signal, and YQ signal before being input to the demapping unit 249 are pre-demodulation signals that undergo signal processing prior to demodulation, and the data signal output from the demapping unit 249 is a demodulated signal that has undergone demodulation signal processing. In addition, in FIG. 4, the signal input from the ADC unit 230 to the receiving side DSP 240 is a signal before demodulation, but is simply shown as a demodulated signal.

[0048] The skew adjustment unit 241 compensates for the skews originating from the optical transmitter and optical receiver devices of the lane for each of the XI signal, XQ signal, YI signal, and YQ signal. The amplitude adjustment unit 242 adjusts the amplitude differences originating from the optical transmitter and optical receiver devices of the lane for each of the XI signal, XQ signal, YI signal, and YQ signal, as necessary. The dispersion compensator 243 compensates for signal degradation caused by chromatic dispersion occurring in the transmission path. The clock synchronization unit 244 compensates for the clock difference between the optical transmitter and the optical receiver. This function of compensating for the clock difference may be performed on the analog signal before it is converted into digital form by the ADC unit 230.

[0049] The band compensation unit 245 compensates for deterioration of the frequency characteristics under fixed conditions. The adaptive equalizer 246 adaptively compensates for degradation of the polarization separation and frequency characteristics of the X polarization signal (XI signal and XQ signal) and the Y polarization signal (YI signal and YQ signal). In order to determine the compensation conditions for the equalization process in the adaptive equalization unit 246, a first pilot symbol signal P extracted by a first pilot reading unit 251 from a symbol signal sequence into which two types of pilot symbol signals have been inserted is read. A is used. When quadrature phase modulation such as 16QAM is used for the data symbol signal S, the first pilot symbol signal P A Since a QPSK signal with constant IQ amplitude is used, the adaptive equalizer 246 can determine the compensation conditions for the equalization process.

[0050] The skew adjustment section 241, the amplitude adjustment section 242, the dispersion compensation section 243, the clock synchronization section 244, the bandwidth compensation section 245, and the adaptive equalization section 246 are configured as those used in a normal digital coherent system. That is, the signal processing at the pre-stage for demodulation by the receiving DSP 240 is a general method in digital signal processing used in a normal digital coherent system.

[0051] The frequency difference compensating section 247 compensates for the frequency difference between the CW light from the CW light generating section 140 and the interference light from the interference light generating section 220 in the optical transmitter 100 . The frequency difference compensator 247 reads the first pilot symbol signal P extracted by the first pilot reader 251 from the symbol signal sequence into which two types of pilot symbol signals have been inserted. A The first pilot symbol signal P in the symbol signal sequence received by A Detect the position of. When quadrature phase modulation such as 16QAM is used for the data symbol signal S, the first pilot symbol signal P A Since a QPSK signal with a constant IQ amplitude is used, the frequency difference compensator 247 compensates for the first pilot symbol signal P A The position of the

[0052] The frequency difference compensation unit 247 receives the XI signal, the XQ signal, the YI signal, and the YQ signal that have been converted into digital signals by the ADC unit 230, and reads the first pilot symbol signal P extracted by the first pilot reading unit 251 from the received digital signals. A and the second pilot symbol signal P extracted by the second pilot reading unit 252. B ' and the adjacent first pilot symbol signal P ' inserted into the signal of 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 second pilot symbol signal P B The second pilot symbol signal P B The phase difference between the two is calculated and the frequency of the received digital signal is compensated.

[0053] The frequency difference compensator 247 reads the first pilot symbol signal P extracted by the first pilot reader 251 from the symbol signal sequence into which two types of pilot symbol signals have been inserted. Aand a second pilot symbol signal P extracted by the second pilot reading unit 252 from the symbol signal sequence into which two types of pilot symbol signals are inserted. B ', the first pilot symbol signal P A The second pilot symbol signal P B The second pilot symbol signal P B 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 is calculated, and the frequency difference is compensated for, thereby performing frequency compensation for the symbol signal sequence signal in the optical receiver 200.

[0054] The frequency difference compensation unit 247 compensates for the adjacent first pilot symbol signal P A and the second pilot symbol signal P B ', that is, the first pilot symbol signal P A The position indicated by and the extracted first pilot symbol signal P A The second pilot symbol signal P extracted by the second pilot reading unit 252 adjacent to B ' and the first pilot symbol signal P A and the second pilot symbol signal P B In other words, the relative position of the adjacent first pilot symbol signal P inserted into the signal of 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 first pilot symbol signal P A The second pilot symbol signal P B The second pilot symbol signal P B Estimate the frequency difference at

[0055] The estimated second pilot symbol signal P B', the frequency difference between adjacent first pilot symbol signals P A and the second pilot symbol signal P B The phase difference between the first and second phases is analyzed, and the frequency of the received symbol signal sequence is compensated for using the calculated compensation amount. The adjacent first pilot symbol signal P A and the second pilot symbol signal P B are inserted at short time intervals (symbol intervals), the phase rotation relative to the time interval can be made small. As a result, the amount of phase rotation can be read accurately, and accurate compensation for the difference in optical frequency can be performed in the frequency difference compensation unit 247.

[0056] This point will be explained with reference to FIG. FIG. 8 shows an IQ signal space, with the horizontal axis representing the Q axis and the vertical axis representing the I axis. P A is the first pilot symbol signal P A Signal point at P B is the second pilot symbol signal P when there is no frequency difference B Signal point at P B ´ is the second pilot symbol signal P B The signal point at

[0057] In Figure 8, signal point P A is the first pilot symbol signal P extracted by the first pilot reading unit 251. A This is the observed signal point indicated by and serves as the reference point for analyzing the phase difference. signal point P B is the signal point P A , that is, the adjacent first pilot symbol signal P A and the second pilot symbol signal P B These are signal points obtained from the relative positions in the IQ signal space of

[0058] signal point PB ' is the second pilot symbol signal P extracted by the second pilot reading unit 252. B are the observed signal points indicated by signal point P A and signal point P B (No difference) is the signal point P A This indicates the relative positional relationship based on the reference position. signal point P A and signal point P B ´(with difference) is the signal point P in the IQ signal space for the observed signal point. A Signal point P based on B ´ shows the relative positional relationship.

[0059] signal point P A and signal point P B ´(with difference) and signal point P A and signal point P B (No difference) indicates the relative position relationship in the IQ signal space. This results in signal point P A Signal point P based on B ´ is the phase angle (known value: signal point P B ) can be observed. signal point P A Signal point P based on B and signal point P B The phase difference between the two points is calculated by extracting the phase term from the complex number output by multiplication using the complex conjugate when the two points are represented as complex numbers on the complex plane.

[0060] That is, the first pilot symbol signal P A and the second pilot symbol signal P B In the case where there is no difference in frequency between the modulated light 100 from the optical transmitter and the modulated light received by the optical receiver 200 with respect to the relative position of the original IQ signal space, the first pilot symbol signal P A Signal point P indicated byA Based on the second pilot symbol signal P B Signal point P indicated by B An example of the relative positions in the IQ signal space is shown in FIG.

[0061] Also, the first pilot symbol signal P extracted by the first pilot reading unit 251 A Signal point P indicated by A The second pilot symbol signal P extracted by the second pilot reading unit 252 based on B Signal point P indicated by B An example of the relative position of the IQ signal space with respect to the IQ signal space is shown in FIG. The second pilot symbol signal P extracted by the second pilot reader 252 B Signal point P indicated by B ´ is the second pilot symbol signal P B is the first pilot symbol signal P A In the first embodiment, the phase rotation with respect to the time interval can be made small because the symbols are arranged adjacent to each other, that is, at a short time interval, and as a result, the amount of phase rotation can be read accurately.

[0062] In this way, the frequency difference compensator 247 calculates the signal point P B Signal point P at B The first pilot symbol signal P A and the second pilot symbol signal P B The frequency difference (amount of phase rotation per unit time) is calculated from the phase shift during the sampling time between the two. The frequency difference compensating unit 247 generates a sine wave (digital data) of unit amplitude that imparts a phase in the opposite direction at the sampling time so as to cancel the determined frequency difference, and multiplies the generated sine wave by the signal of the symbol signal sequence. As a result, the frequency difference compensating unit 247 compensates for the optical frequency difference between the optical transmitter 100 and the optical receiver 200, i.e., 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.

[0063] That is, the first pilot symbol signal P extracted by the first pilot reading unit 251 A The position in the IQ signal space indicated by and the extracted first pilot symbol signal P A The second pilot symbol signal P extracted by the second pilot reading unit 252 adjacent to B and the adjacent first pilot symbol signal P A and the second pilot symbol signal P B The first pilot symbol signal P extracted by the first pilot reading unit 251 from the relative position of the IQ signal space A The extracted first pilot symbol signal P A The second pilot symbol signal P extracted by the second pilot reading unit 252 adjacent to B The extracted first pilot symbol signal P A The second pilot symbol signal P inserted into the symbol signal sequence by the transmitting side DSP 110 adjacent to B The frequency difference between the two can be analyzed.

[0064] As a result, by using the frequency difference that is the result of the above analysis, the frequency compensation for the symbol signal sequence in the optical receiver 200 can be performed by the frequency difference compensation unit 247 . The first pilot symbol signal P A and the second pilot symbol signal P B The frequency compensation by the above is as explained above, and a technique for performing frequency compensation by using two pilot symbol signals that are generally known between the transmitting side and the receiving side can be used.

[0065] The frequency compensation for the symbol signal sequence in the optical receiver 200 is performed using the first pilot symbol signal P A and the extracted first pilot symbol signal P AThe second pilot symbol signal P B In other words, since two pilot symbol signals with a short time interval of the symbol interval are used, the first pilot symbol signal P A The second pilot symbol signal P B Since the phase rotation of the first pilot symbol signal P A The second pilot symbol signal P B The accurate phase rotation amount in the

[0066] For example, the second pilot symbol signal P B 9, if an optical receiver performs frequency compensation on modulated light based on a symbol signal sequence in which pilot symbol signals P are inserted into a data symbol signal S at symbol intervals rather than on a frame-by-frame basis as shown in FIG. 10, or a symbol signal sequence in which pilot symbol signals P are inserted at fixed symbol intervals at fixed positions on a frame-by-frame basis as shown in FIG. 11, problems may occur as shown in FIG. 9.

[0067] FIG. 9 shows an IQ signal space, with the horizontal axis representing the Q axis and the vertical axis representing the I axis. P1 is a signal point in the first pilot symbol signal P1 for frequency compensation, P2 is a signal point in the second pilot symbol signal P2 when there is no frequency difference, and P2' is a signal point in the second pilot symbol signal P2 when there is a frequency difference.

[0068] In FIG. 9, signal point P1 is an observed signal point indicated by the first pilot symbol signal P1 extracted by a pilot reading unit in the optical receiver, and serves as a reference point for analyzing the phase difference. Signal point P2 has no difference in frequency with respect to signal point P1, that is, it is a signal point obtained from the relative positions in the IQ signal space of adjacent first pilot symbol signal P1 and second pilot symbol signal P2 inserted into the symbol signal sequence signal at the optical transmitter. A signal point P2' is an observed signal point indicated by the second pilot symbol signal P2 extracted by the pilot reading unit.

[0069] As can be seen from Figure 9, if the time interval between the time when the first pilot symbol signal P1 is extracted and the time when the second pilot symbol signal P2 is extracted is long and there is a difference between the frequency of the optical carrier wave from the optical transmitter and the frequency of the optical carrier wave of the interference light in the optical receiver 200, a large phase rotation occurs from the first pilot symbol signal P1 to the signal point P2' from the second pilot symbol signal P2 over a long period of time. In other words, the phase rotation of the second pilot symbol signal P2 due to the frequency shift with respect to the first pilot symbol signal P1 is large, and phase rotation occurs in the IQ signal space, resulting in an erroneous estimation of the amount of phase rotation since the phase rotates cyclically.

[0070] In the optical transmission / reception device according to the first embodiment, the first pilot symbol signal P A and the extracted first pilot symbol signal P A The second pilot symbol signal P B Since the first pilot symbol signal P A The second pilot symbol signal P B The phase rotation is small, there is no estimation error in the amount of phase rotation, and an accurate amount of phase rotation can be obtained.

[0071] In short, the optical transmission / reception device according to the first embodiment generates the first pilot symbol signal P A and the second pilot symbol signal P B into the signal of the symbol signal sequence, and a second pilot symbol signal P B The first pilot symbol signal P A and the second pilot symbol signal P B Therefore, the frequency difference between the frequency of the optical carrier wave in the optical transmitter 100 and the frequency of the interference light in the optical receiver 200 is compensated for.

[0072] Therefore, the optical transmission / reception device according to the first embodiment transmits the first pilot symbol signal P A and the second pilot symbol signal P B The first pilot symbol signal P A and the second pilot symbol signal P B Signal point P by A , P B , P B It is possible to accurately calculate the amount of phase rotation calculated from the information, and in turn the amount of compensation for the waveform distortion caused by the calculated amount of phase rotation (frequency difference).

[0073] This improves the signal quality of the received signal in the optical receiver 200, and in turn expands 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. Therefore, the optical transceiver of embodiment 1 can compensate for degradation factors caused by waveform distortion resulting from, for example, the frequency difference between the optical carrier in the optical transmitter 100 and the frequency of the interference light in the optical receiver 200, for low- and medium-speed digital coherent signals.

[0074] In addition, in estimating the difference in frequency of the modulated light, 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 the first pilot symbol signal P A and the second pilot symbol signal P B The compensation amount may be calculated after averaging the relative positions of the two. By performing averaging processing, the speed response can be adjusted as desired.

[0075] The phase estimation section 248 compensates for phase fluctuations of the light sources constituting the CW light generating section 140 and the interference light generating section 220 . The phase estimation unit 248 is configured using components that are typically used in a digital coherent system. That is, the signal processing for demodulation in the receiving side DSP 240 other than the compensation of the frequency difference by the frequency difference compensating unit 247 is a general method in digital signal processing used in a normal digital coherent system.

[0076] The demapping unit 249 receives the first pilot symbol signal P A and the second pilot symbol signal P B After the distortion is removed, the symbol signal which has been compensated for waveform distortion is converted into a bit signal. A frame synchronization unit 250 obtains frame synchronization from the bit signal sequence. The digital signal of the bit signal sequence synchronized with the frame is then error corrected.

[0077] Next, the hardware configuration of the optical transmitting / receiving device according to the first embodiment will be described with reference to FIG. In FIG. 12, the same reference numerals as those in FIGS. 1 to 4 denote the same or corresponding parts. The optical transmitter / receiver 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 a RAM (Random Access Memory) and a ROM (Read Only Memory), a communication interface 33, and an input / output interface 34. The processor 31, memory 32, communication interface 33, and input / output interface 34 are connected to a bus 35, and data, control signals, and the like are exchanged between them via the bus 35.

[0078] The processor 31 temporarily loads a program recorded in the ROM of the memory 32 into the RAM of the memory 32, and executes processing according to the loaded program. The ROM in the memory 32 stores various data, programs for executing processes in the optical transmitter 100 and the optical receiver 200, processing programs required for starting the optical transmitter / receiver control unit 300, and the like. The communication interface 33 is used for transmitting and receiving data and control signals between each component of the optical transmitter 100, each component of the optical receiver 200, and each component of other optical transmitting and receiving devices.

[0079] The input / output interface 34 transmits and receives control signals and modulation signals between each component in the optical transmitter 100 and each component in the optical receiver 200 via electrical wiring. The input / output interface 34 is, for example, an interface for supplying the interference light generating unit 220 with an injection current to a light source constituting the interference light generating unit 220 for generating light. The input / output interface 34 is an interface for outputting various control signals to, for example, the transmitting DSP unit 110 and the receiving DSP unit.

[0080] As described above, in the optical transmission / reception device according to the first embodiment, the optical transmitter 100 adds the first pilot symbol signal P A and a second pilot symbol signal P having a second symbol period different from the first symbol period. B A modulation signal generator 110 generates a modulation signal into which a first pilot symbol P having a first symbol period is inserted based on the modulation signal converted to an analog signal by a digital / analog converter 120. A and a second pilot symbol P consisting of a second symbol period. B and an optical modulator 130 for generating modulated light into which a first pilot symbol signal P having a first symbol period is inserted. A and a second pilot symbol signal P having a second symbol period different from the first symbol period. Band an optical coherent detection unit 210 that coherently detects the polarization-multiplexed modulated light into which the first pilot symbol signal P is inserted and outputs an analog electrical signal. The analog / digital conversion unit 230 converts the analog electrical signal into a digital signal, and the first pilot symbol signal P A and the first pilot symbol signal P A and the adjacent second pilot symbol signal P B Since the receiving side digital signal processing unit 240 has a frequency difference compensation unit 247 that calculates the phase difference using and compensates for the frequency of the received digital signal, it is possible to compensate for the difference in frequency of the modulated light received by the optical receiver 200 relative to the frequency of the modulated light from the optical transmitter 100.

[0081] As a result, it is possible to compensate for the cause of waveform distortion degradation due to the difference in signal frequency between transmission and reception, improve the signal quality of the received signal at the optical receiver 200, and ultimately expand the compensation range for the difference in optical frequency between the optical transmitter 100 and the optical receiver 200. This is particularly effective in the optical receiver 200 that handles low- and medium-speed digital coherent signals.

[0082] Embodiment 2 The optical transmitting / receiving device according to the second embodiment will be described with reference to FIGS. The optical transmission / reception device according to the first embodiment uses a single carrier signal in a digital coherent system shown on the frequency axis in FIG. 7 as an optical carrier wave. In contrast, the optical transceiver according to the second embodiment is an optical transceiver using subcarrier multiplexing, using, as optical subcarriers, each of N subcarrier signals with different frequency allocations in the digital coherent system shown on the frequency axis in FIG.

[0083] The optical transmission / reception apparatus according to the second embodiment is basically based on the concept of applying the optical transmission / reception apparatus according to the first embodiment to subcarrier signals as N optical subcarriers. Therefore, the following description will focus on the differences from the optical transmitting / receiving device according to the first embodiment. In the second embodiment, as an example, an optical transceiver is assumed that transmits and receives an optical signal multiplexed with N channels formed by N subcarrier signals SC#1 to SC#N of different frequencies in an X polarization and N channels formed by N subcarrier signals SC#1 to SC#N of different frequencies in a Y polarization, as shown in FIG. 15.

[0084] In the optical receiver 200, the modulated light that is polarization-multiplexed onto each of N subcarrier signals with different frequency allocations within a band in which signals can be detected is received collectively by the optical coherent detection unit 210, which performs optical coherent detection on the modulated light received collectively by the optical coherent detection unit 210 and outputs it as an analog electrical signal. The collectively processed analog electrical signals are converted into digital signals by the ADC unit 230 and input to the receiving DSP 240 . The receiving side DSP 240 separates the subcarrier signals SC#1 to SC#N, and demodulates each channel of the subcarrier signals SC#1 to SC#N. The optical transmitting and receiving apparatus according to the second embodiment includes an optical transmitter 100, an optical receiver 200, and an optical transmitter / receiver control unit 300, as shown in FIG.

[0085] The optical transmitter 100 includes a transmitting side DSP 110 A, a DAC section 120 , an optical modulation section 130 , and a CW light generation section 140 . As shown in FIG. 13, the transmitting DSP 110A includes N subcarrier generating units 111 to 11 N The skew adjustment unit (deskew unit) 114 is also provided.

[0086] N subcarrier generation units 111 to 11 NEach of the digital signals receives different data signals #1 to #N, which are information to be sent to a destination, and generates a modulated signal, which is a digital signal for optical modulation, in which a first pilot symbol signal having a first symbol period and a second pilot symbol signal having a second symbol period different from the first symbol period are inserted into the data #1 to #N to be transmitted.

[0087] N subcarrier generation units 111 to 11 N Although the data #1 to #N to be transmitted and the subcarrier signals SC#1 to SC#N as carrier waves are different, they basically have the same configuration. That is, N subcarrier generation units 111 to 11 N The frame generating units 1111 to 111 N and mapping section 1121-112 N and Spectral Shaping Section 1131-113 N and pilot generation units 1151 to 115 N and pilot insertion section 1161-116 N The optical transmitter 110 has a digital circuit having the above-mentioned signal processing functions, and has basically the same configuration as the frame generation unit 111, the mapping unit 112, the spectrum shaping unit 113, the pilot generation unit 115, and the pilot insertion unit 116 in the transmission-side DSP 110 of the optical transmitter 110 in the optical transmission and reception device according to the first embodiment.

[0088] In short, N subcarrier generation units 111 to 11 N The frame generating units 1111 to 111 N The data to be transmitted is converted into a signal frame format using a digital coherent signal by the mapping unit 112, and converted into XI signals, XQ signals, YI signals, and YQ signals corresponding to QPSK signals that are polarization-multiplexed on the frequency axis using different subcarrier signals SC#1 to SC#N by the pilot insertion units 1161 to 1166. N The first pilot symbol signal P A and the second pilot symbol signal P BThe modulated signal is then subjected to shaping of the frequency characteristics by spectrum shaping section 113. N subcarrier generation units 111 to 11 N Each has four output terminals.

[0089] The subcarrier multiplexing unit 117 multiplexes N subcarrier generation units 111 to 11 N The modulated signal from is multiplexed on the frequency axis. The skew adjustment unit 114 compensates for the skew (delay difference) that occurs between signals caused by the optical transmitter 100 due to the XI lane, XQ lane, YI lane, and YQ lane through which the electrical signals of the XI signal, XQ signal, YI signal, and YQ signal, which are modulated signals multiplexed on the frequency axis from the spectrum shaping unit 113, flow.

[0090] The modulated signals thus generated and multiplexed on different frequency axes are converted into analog signals by the DAC section 120 . The optical modulation unit 130 modulates the CW light from the CW light generation unit 140 based on the modulation signal converted into an analog signal by the DAC unit 120 to generate frequency-multiplexed and polarization-multiplexed modulated light from a plurality of different subcarrier signals into which a first pilot symbol having a first symbol period and a second pilot symbol having a second symbol period different from the first symbol period are inserted, and outputs the generated modulated light to a transmission path.

[0091] The optical receiver 200 includes an optical coherent detection section 210, an interference light generation section 220, an ADC section 230, and a receiving side DSP 240A. The optical coherent detector 210 detects a first pilot symbol signal P A and a second pilot symbol signal P having a second symbol period different from the first symbol period. BThe optical coherent detection unit 210 receives modulated light that has been frequency-multiplexed and polarization-multiplexed using a plurality of different subcarrier signals into which have been inserted, causes the received modulated light to interfere with interference light, which is CW light having a single carrier frequency fc, from the interference light generating unit 220, and outputs an analog electrical signal based on the voltage obtained by photoelectric conversion of the optical signal obtained by the interference.

[0092] The ADC unit 230 samples the analog electrical signal from the optical coherent detection unit 210 based on a sampling frequency, converts it into a digital signal, which is a discrete signal in the digital domain, and obtains a pre-demodulation signal consisting of a digital signal for obtaining a demodulated signal. The receiving side DSP 240A includes a skew adjustment unit (deskewing unit) 241, a subcarrier separation unit 254, and N subcarrier detection units 241 to 244. N Equipped with. The skew adjustment unit 241 compensates for the skews originating from the optical transmitter and optical receiver devices of the lane for each of the XI signal, XQ signal, YI signal, and YQ signal.

[0093] The subcarrier separator 254 extracts the first pilot symbol signal P A and the second pilot symbol signal P B The signal before demodulation, which is a digital signal that is frequency-multiplexed and polarization-multiplexed using a plurality of different subcarrier signals into which are inserted, is then subjected to signal separation by corresponding it to N subcarrier signals SC#1 to SC#N on the frequency axis. N subcarrier detection units 241 to 24 N Each of these performs compensation for the N digital signals separated by the subcarrier separation unit 254, such as compensation for chromatic dispersion and nonlinear optical effects and polarization mode dispersion suffered by the modulated light in the transmission path, as well as compensation for the frequency offset caused by the difference in light source frequency of the CW light between the optical transmitter and the optical receiver.

[0094] N subcarrier detection units 241 to 24 N The amplitude adjustment units 2421 to 242 N and the dispersion compensation units 2431 to 243 Nand clock synchronization units 2441 to 244 N and the band compensation units 2451 to 245 N and adaptive equalization units 2461 to 246 N and frequency difference compensation units 2471 to 247 N and phase estimation units 2481 to 248 N and demapping section 2491-249 N and frame synchronization units 2501 to 250 N and the first pilot symbol signal P A The first pilot reading unit 2511 to 251 N and the second pilot symbol signal P B The second pilot reading units 2521 to 252 N and pilot removal units 2531 to 253 N and has basically the same configuration as the amplitude adjustment unit 242, the dispersion compensation unit 243, the clock synchronization unit 244, the bandwidth compensation unit 245, the adaptive equalization unit 246, the frequency difference compensation unit 247, the phase estimation unit 248, the demapping unit 249, the frame synchronization unit 250, the first pilot reading unit 251, the second pilot reading unit 252, and the pilot removal unit 253 in the receiving side DSP 240 of the optical receiver 200 in the optical transmission / reception device according to the first embodiment.

[0095] In short, N subcarrier detection units 241 to 24 N In each of the signals, digital processing similar to that in the receiving DSP 240 in the optical transmitting / receiving device according to the first embodiment is performed. N subcarrier detection units 241 to 24 N The frequency difference compensation units 2471 to 247 N compensates for the frequency difference between the CW light from the CW light generating section 140 in the optical transmitter 100 and the interference light from the interference light generating section 220 for each of the multiple different subcarrier signals SC#1 to SC#N. N subcarrier detection units 241 to 24 constituting the receiving side DSP 240A N Thus, N data signals are output from the receiving DSP 240A.

[0096] The hardware configuration of the optical transceiver of embodiment 2 is similar to that of the optical transceiver of embodiment 1, in that the receiver control unit 30 is composed of a processor 31 such as a CPU or a system LSI, a memory 32 composed of RAM, ROM, etc., a communication interface 33, and an input / output interface 34.

[0097] As described above, in the optical transmission / reception device of embodiment 2, the optical transmitter 100 outputs modulated light that is frequency-multiplexed using subcarrier signals SC#1 to SC#N as N optical subcarriers, and the optical receiver 200 collectively receives the polarization-multiplexed modulated light in which the N subcarrier signals SC#1 to SC#N are frequency-multiplexed on the frequency axis, and the optical transmission / reception device can compensate for the difference in frequency of the optical carrier of the interference light in the optical receiver 200 relative to the frequency of the optical carrier from the optical transmitter 100 for each subcarrier signal SC#1 to SC#N, as in the optical transmission / reception device of embodiment 1.

[0098] It should be noted that the embodiments may be freely combined, or any of the components in each embodiment may be modified, or any of the components in each embodiment may be omitted. [Industrial Applicability]

[0099] The optical transceiver according to the present disclosure is not limited to communication systems that use optical fiber as a transmission medium in optical access and optical core-metro networks, but can also be applied to optical communication systems that do not use optical fiber, such as space or free-space optical communications. [Explanation of symbols]

[0100] 100 Optical transmitter, 110, 110A Modulation signal generator (transmitting side DSP), 111 to 11 N Subcarrier generation unit, 111, 1111 to 111 N Frame generation unit (framer unit), 112, 1121 to 112 N Mapping section, 113, 1131-113 N Spectral shaping section, 114 Skew adjustment section (deskew section), 115, 1151-115 NPilot generation unit, 116, 1161 to 116 N Pilot insertion unit, 117 subcarrier multiplexing unit, 120 digital / analog conversion (DAC) unit, 130 optical modulation unit, 140 CW light generation unit, 200 optical receiver, 210 optical coherent detection unit, 220 interference light generation unit, 230 ADC unit, 240, 240A receiving side digital signal processing unit (receiving side DSP), 241 to 24 N Subcarrier detection unit, 241 Skew adjustment unit, 242, 2421 to 242 N Amplitude adjustment section, 243, 2431~243 N Dispersion compensation section, 244, 2441~244 N Clock synchronization section, 245, 2451-245 N Bandwidth compensation section, 246, 2461-246 N Adaptive equalization section, 247, 2471-247 N Frequency difference compensation section, 248, 2481-248 N Phase estimation section, 249, 2491~249 N Demapping section, 250, 2501-250 N Frame synchronization section, 251, 2511-251 N First pilot reading unit, 252, 2521 to 252 N Second pilot reading unit, 253, 2531 to 253 N Pilot removal section.

Claims

1. An optical transmitter and an optical receiver are provided, The optical transmitter includes: a modulation signal generating unit that generates a modulation signal, which is a digital signal for optical modulation, in which a first pilot symbol signal having a first symbol period and a second pilot symbol signal having a second symbol period different from the first symbol period are inserted into data to be transmitted; a digital / analog conversion unit that converts the modulated signal, which is a digital signal generated by the modulated signal generation unit, into a modulated signal consisting of an analog signal; an optical modulation unit that modulates a CW light from a CW light generation unit based on the modulation signal converted into an analog signal by the digital / analog conversion unit to generate modulated light into which a first pilot symbol signal having the first symbol period and a second pilot symbol signal having the second symbol period are inserted, The optical receiver includes: an optical coherent detection unit that receives polarization multiplexed modulated light into which a first pilot symbol signal having the first symbol period and a second pilot symbol signal having the second symbol period different from the first symbol period are inserted, and that coherently detects the received modulated light and outputs an analog electrical signal; an analog / digital conversion unit that performs analog / digital conversion on the analog electrical signal from the optical coherent detection unit and outputs the digital signal; a receiving-side digital signal processing unit having a frequency difference compensation unit that receives a digital signal from the analog / digital conversion unit, and calculates a phase difference using a first pilot symbol signal having the first symbol period and a second pilot symbol signal having the second symbol period different from the first symbol period and adjacent to the first pilot symbol signal, the first pilot symbol signal being extracted from the received digital signal and inserted into the received polarization multiplexed modulated light, to compensate for a frequency of the received digital signal. Optical transmitter and receiver.

2. The optical modulation unit generates modulated light using a single carrier signal as an optical carrier wave, The optical coherent detection unit converts modulated light having a single carrier signal as an optical carrier into an analog electrical signal, a frequency difference compensation unit in the receiving side digital signal processing unit compensates the frequency of the digital signal for the single carrier signal; 2. The optical transmitter / receiver according to claim 1.

3. The optical modulation unit generates modulated light that is frequency-multiplexed using a plurality of subcarrier signals having different frequency allocations as optical subcarriers, The optical coherent detection unit converts the modulated light, which is frequency-multiplexed using a plurality of subcarrier signals of different frequency allocations as optical subcarriers, into an analog electrical signal, a frequency difference compensation unit in the receiving side digital signal processing unit compensates for the frequency of the digital signal for each of the subcarrier signals having the different frequency allocations; 2. The optical transmitter / receiver according to claim 1.

4. 4. The optical transmitting / receiving device according to claim 1, wherein the modulated light generated by the optical modulation section is an optical signal in which an X-polarized wave and a Y-polarized wave are modulated into an I signal and a Q signal in quadrature phase, respectively.

5. 4. The optical transmission / reception device according to claim 1, wherein the first pilot symbol signal and the second pilot symbol signal are QPSK signals.

6. 4. The optical transmission / reception device according to claim 1, wherein the second symbol period of the second pilot symbol signal is an integer multiple of two or more of the first symbol period of the first pilot symbol signal.

7. an optical coherent detection unit that receives polarization multiplexed modulated light into which a first pilot symbol signal having a first symbol period and a second pilot symbol signal having a second symbol period different from the first symbol period are inserted, and that coherently detects the received modulated light and outputs an analog electrical signal; an analog / digital conversion unit that performs analog / digital conversion on the analog electrical signal from the optical coherent detection unit and outputs the digital signal; a receiving-side digital signal processing unit having a frequency difference compensation unit that receives a digital signal from the analog / digital conversion unit, and calculates a phase difference using a first pilot symbol signal having the first symbol period and a second pilot symbol signal having the second symbol period different from the first symbol period and adjacent to the first pilot symbol signal, the first pilot symbol signal being extracted from the received digital signal and inserted into the received polarization multiplexed modulated light, to thereby compensate for a frequency of the received digital signal. Optical receiver.

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