WO2020248820A1 - 一种光通信中信号收发的方法、光收发机和系统 - Google Patents

一种光通信中信号收发的方法、光收发机和系统 Download PDF

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Publication number
WO2020248820A1
WO2020248820A1 PCT/CN2020/092635 CN2020092635W WO2020248820A1 WO 2020248820 A1 WO2020248820 A1 WO 2020248820A1 CN 2020092635 W CN2020092635 W CN 2020092635W WO 2020248820 A1 WO2020248820 A1 WO 2020248820A1
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signal
subcarrier
sop
optical
subcarriers
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PCT/CN2020/092635
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English (en)
French (fr)
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刘玲
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华为技术有限公司
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Priority to EP20822403.0A priority Critical patent/EP3968548A4/en
Publication of WO2020248820A1 publication Critical patent/WO2020248820A1/zh
Priority to US17/550,665 priority patent/US11984929B2/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/40—Transceivers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
    • H04B10/2569—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to polarisation mode dispersion [PMD]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/5165—Carrier suppressed; Single sideband; Double sideband or vestigial
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/532—Polarisation modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H04B10/614—Coherent receivers comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H04B10/616—Details of the electronic signal processing in coherent optical receivers
    • H04B10/6162—Compensation of polarization related effects, e.g., PMD, PDL
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/06—Polarisation multiplex systems

Definitions

  • This application relates to the field of communications, and in particular to a method, optical transceiver and system for transmitting and receiving signals in optical communications.
  • the coherent optical communication system supports multi-ary modulation format and polarization multiplexing to achieve high spectral efficiency transmission.
  • Polarization multiplexing uses two orthogonal polarization states of light to simultaneously transmit two independent orthogonal polarization signals within the same bandwidth, thereby increasing the channel transmission efficiency by two times.
  • polarization multiplexing combined with coherent receiving technology, long-distance transmission of more than 100Gb/s can be realized.
  • the optical fiber is affected by the external environment to produce the birefringence effect, and the birefringence axis of the optical fiber changes randomly with time, the two orthogonal polarization signals generated by the polarization multiplexing at the transmitting end are transmitted through the optical fiber, and the optical fiber polarization-dependent loss ( The impact of polarization-dependent loss (PDL) brings system costs and causes system performance fluctuations.
  • PDL polarization-dependent loss
  • OSNR margin optical signal-to-noise ratio
  • the present application provides a method, optical transceiver, and system for signal transmission and reception in optical communication, which can solve the performance fluctuation and system cost caused by PDL.
  • the present application provides a signal transmission method in optical communication.
  • the method may include: an optical transmitter obtains a bit stream, and distributes the obtained bit stream into at least two bit streams, and for each bit stream after distribution.
  • the bit stream is modulated into one sub-carrier, thereby generating at least two first sub-carriers.
  • the optical transmitter performs polarization SOP rotation on one or more of the second sub-carriers, so that there are at least two sub-carriers with a relative SOP rotation angle, where the relative SOP rotation angle is not zero and not an integer multiple of 90 degrees .
  • the optical transmitter modulates at least two first subcarriers onto the optical signal and sends the optical signal.
  • the OSNR cost of the sub-carriers with a relative SOP rotation angle can be averaged and offset, which can reduce system performance fluctuations and system costs caused by PDL.
  • the relative SOP rotation angle is 45 degrees.
  • the OSNR curve of the two sub-carriers can be complementary, which reduces the performance fluctuation and system cost of the system.
  • the relative SOP rotation angle may also be other angles, for example, 30, 135, 225 degrees and so on.
  • the SOP rotation includes: by formula Perform SOP rotation on a second subcarrier in the first carrier, where Xin and Yin are the second subcarrier before the SOP rotation, and Xout and Yout are the second subcarrier after the SOP rotation , ⁇ is the angle of rotation of the SOP.
  • each channel of second subcarrier may be used to perform SOP rotation using the above formula.
  • the optical transmitter after the SOP is rotated, the optical transmitter performs spectrum shift on the first subcarrier that has undergone the SOP rotation. Or, before the SOP is rotated, the optical transmitter performs spectrum shift on the generated first subcarrier.
  • the purpose of the spectrum shift is to enable the receiving end to separate at least two first subcarriers, and the spectrum shift only needs to be implemented before the first subcarrier is combined.
  • the optical transmitter multiplexes the first sub-carrier after SOP rotation and spectrum shift. After the first sub-carrier is multiplexed and output, it can be modulated into an optical signal, which is carried and sent by the optical signal.
  • this application provides an optical transmitter, which includes a digital signal processor DSP and a modulator.
  • the DSP obtains the bit stream, distributes the obtained bit stream into at least two bit streams, and modulates each bit stream after distribution into one sub-carrier, thereby generating at least two first sub-carriers.
  • the DSP performs polarization SOP rotation on one or more of the second subcarriers, so that there are at least two subcarriers with relative SOP rotation angles, where the relative SOP rotation angle is not zero and not an integer multiple of 90 degrees.
  • the modulator modulates at least two first sub-carriers onto the optical signal and sends the optical signal.
  • the relative SOP rotation angle is 45 degrees.
  • the OSNR curve of the two sub-carriers can be complementary, which reduces the performance fluctuation and system cost of the system.
  • the relative SOP rotation angle may also be other angles, for example, 30, 135, 225 degrees and so on.
  • DSP uses the formula Perform SOP rotation on a second subcarrier, where Xin and Yin are the second subcarrier before the SOP rotation, Xout and Yout are the second subcarrier after the SOP rotation, and ⁇ is the SOP rotation Angle.
  • each channel of second subcarrier may be used to perform SOP rotation using the above formula.
  • the DSP is further configured to: after the SOP is rotated, perform spectrum shift on the first subcarrier after the SOP is rotated.
  • the DSP is further configured to: perform spectrum shift on the acquired first subcarrier before the SOP is rotated.
  • the purpose of the spectrum shift is to enable the receiving end to separate at least two first subcarriers, and the spectrum shift only needs to be implemented before the first subcarrier is combined.
  • the DSP is further used to: multiplex the first sub-carrier after the SOP rotation and spectrum shift. After the first sub-carrier is multiplexed and output, it can be modulated into an optical signal, which is carried and sent by the optical signal.
  • the present application provides a method for receiving signals in optical communications.
  • the method may include: an optical receiver receives an optical signal and converts the optical signal into an electrical signal, wherein the electrical signal includes a first signal and The second signal, the first signal and the second signal correspond to different polarization states; the optical receiver generates a first coefficient, a second coefficient, and a third coefficient, and performs processing on the first signal based on the first coefficient Filtering to obtain a third signal; filtering the second signal based on the second coefficient to obtain a fourth signal; filtering the second signal based on the third coefficient to obtain a fifth signal; The receiver sums the third signal and the fourth signal to obtain a seventh signal, and obtains the decision sequence of the first signal and the second signal according to the fifth signal and the seventh signal .
  • the first signal and the second signal may be two orthogonally polarized signals.
  • the first signal has an X polarization state and the second signal has a Y polarization state.
  • the optical receiver performs joint detection through signals of different polarization states, which can reduce the system cost caused by PDL and improve performance.
  • the first signal and the second signal respectively have at least two subcarriers, and the relative polarization state SOP rotation angle between the at least two subcarriers is not zero and not an integer of 90 degrees. Times, so that the third coefficient is not zero.
  • the relative SOP rotation angle between the two subcarriers makes the filter coefficient between signals of different polarization states not zero, so as to realize joint detection between signals of different polarization states.
  • the obtaining the decision sequence of the first signal and the second signal includes: obtaining the decision sequence of the first signal and the second signal by minimizing a cost function.
  • this application provides an optical receiver, including: an optical receiver front end and a DSP.
  • the front end of the optical receiver can include a mixer, a balanced receiver, etc., and can be used for photoelectric conversion.
  • the front end of the optical receiver receives the optical signal and converts the optical signal into an electrical signal, wherein the electrical signal includes a first signal and a second signal, and the first signal and the second signal correspond to different polarization states.
  • the DSP generates a first coefficient, a second coefficient, and a third coefficient, and filters the first signal based on the first coefficient to obtain a third signal; and filters the second signal based on the second coefficient to obtain The fourth signal; filtering the second signal based on the third coefficient to obtain a fifth signal.
  • the DSP sums the third signal and the fourth signal to obtain a seventh signal, and obtains the decision sequence of the first signal and the second signal according to the fifth signal and the seventh signal.
  • the first signal and the second signal may be two orthogonally polarized signals.
  • the first signal has an X polarization state and the second signal has a Y polarization state.
  • the optical receiver performs joint detection through signals of different polarization states, which can reduce the system cost caused by PDL and improve performance.
  • the first signal and the second signal respectively have at least two subcarriers, and the relative polarization state SOP rotation angle between the at least two subcarriers is not zero and not an integer of 90 degrees. Times, so that the third coefficient is not zero.
  • the relative SOP rotation angle between the two subcarriers makes the filter coefficient between signals of different polarization states not zero, so as to realize joint detection between signals of different polarization states.
  • the DSP is used to obtain the decision sequence of the first signal and the second signal by minimizing the cost function.
  • the present application provides an optical communication system, the optical communication system including the optical transmitter in any one of the foregoing second aspect or the second aspect, and/or the foregoing fourth aspect or fourth aspect Optical receiver in any possible implementation.
  • Another aspect of the present application provides a readable storage medium having instructions stored in the readable storage medium, which when run on an optical transceiver, cause the optical transceiver to perform the methods described in the above aspects.
  • Another aspect of the present application provides a program product containing instructions, which when run on an optical transceiver, causes the optical transceiver to execute the methods described in the above aspects.
  • FIG. 1 is a schematic structural diagram of a coherent optical communication system provided by an embodiment of the present invention
  • FIG. 2 is a schematic structural diagram of an optical transmitter provided by an embodiment of the present invention.
  • Figure 3a is a schematic diagram of a logical structure of a TxDSP provided by an embodiment of the present invention.
  • Fig. 3b is a schematic diagram of the logical structure of a TxDSP provided by an embodiment of the present invention.
  • FIG. 4 is a schematic diagram of the variation curve of OSNR cost with SOP angle provided by an embodiment of the present invention.
  • FIG. 5 is a schematic diagram of subcarrier frequency spectrum provided by an embodiment of the present invention.
  • FIG. 6 is a schematic diagram of a logical structure of a TxDSP provided by an embodiment of the present invention.
  • FIG. 7 is a schematic structural diagram of an optical receiver provided by an embodiment of the present invention.
  • Fig. 8a is a schematic diagram of a logical structure of an RxDSP provided by an embodiment of the present invention.
  • FIG. 8b is a schematic diagram of a logical structure of an RxDSP provided by an embodiment of the present invention.
  • FIG. 9a is a schematic diagram of the logical structure of another RxDSP provided by an embodiment of the present invention.
  • FIG. 9b is a schematic diagram of the logical structure of another RxDSP provided by an embodiment of the present invention.
  • Figure 10a is a schematic diagram of a logical structure of a joint detection provided by an embodiment of the present invention.
  • Figure 10b is a schematic diagram of another logical structure of joint detection provided by an embodiment of the present invention.
  • FIG. 11 is a graph of OSNR cost of joint detection provided by an embodiment of the present invention.
  • FIG. 12 is a graph of OSNR cost of joint detection provided by an embodiment of the present invention.
  • FIG. 13a is a schematic diagram of a logical structure of filter coefficient generation in joint detection according to an embodiment of the present invention.
  • FIG. 13b is a schematic diagram of the logical structure of generating filter coefficients in another joint detection according to an embodiment of the present invention.
  • the sending end 110 may also include a digital signal processor (digital signal processor, DSP) or a digital signal processing chip for generating electrical signals.
  • the receiving end 130 may include a local oscillator light source 105, a balanced receiver 106, a PBS (not shown in the figure), a mixer 107, and an electrical demodulation circuit 108.
  • the electrical demodulation circuit 108 may include a DSP or a digital signal processing chip.
  • the sender and receiver can be on the same device, or on different devices.
  • the technical solutions of the embodiments of the present invention can be applied to polarization multiplexing coherent optical communication systems, and can also be applied to other forms of coherent optical communication systems. For example, it can be used in a single-polarization coherent optical communication system. PBS and PBC can be eliminated in the coherent optical communication system.
  • the signal light source 101 may be a laser.
  • the optical signal from the signal light source 101 is divided into two optical signals X and Y by the polarization beam splitter 103, and the modulator 102 loads one electrical signal on the X-ray signal, and the other electrical signal on the Y optical signal.
  • the electrical signal can be obtained by one or more processes of FEC, constellation mapping, and pulse shaping on the information bit stream by the DSP (TxDSP) at the transmitting end.
  • the modulator 102 may be an I/Q modulator, and each electrical signal includes a signal I and a signal Q respectively, and the phase difference between the I and Q signals is 90 degrees.
  • the modulator 102 After passing through the modulator 102, four signals are formed: XI, XQ, YI, and YQ. Then, the X and Y optical signals loaded with electrical signals are multiplexed and combined by the polarization beam combiner 104, and sent out through the optical fiber 120.
  • the polarization beam splitter decomposes the received optical signal into two orthogonal signals, and each orthogonal signal is related to the optical signal generated by a local oscillator light source 105.
  • the local oscillator light source 105 may be a laser.
  • 4 polarization and phase orthogonal optical signals XI, XQ, YI, YQ are obtained, and then the optical signals are converted into analog electrical signals by the balanced receiver 106, and the analog electrical signals are converted into 4 by the analog-to-digital conversion circuit.
  • Road digital electrical signal The digital electric signal passes through the DSP (RxDSP) at the receiving end to realize one or more functions such as dispersion compensation, polarization demultiplexing, equalization and decoding.
  • Fig. 2 is a schematic structural diagram of an optical transmitter provided by an embodiment of the present invention.
  • the optical transmitter may include DSP (TxDSP) 201 at the transmitting end, digital-to-analog converter (DAC) 202, signal light source 203, modulator 204, polarization beam splitter (PBS) 205, polarization beam combiner ⁇ (PBC)206 and so on.
  • the TxDSP201 may include one or more functional modules such as FEC, constellation mapping, pulse shaping, state of polarization (SOP) rotation, and spectrum movement.
  • the functional modules on TxDSP can be implemented based on hardware, software, or a combination of hardware and software.
  • the TxDSP can be implemented by an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), and a digital logic circuit.
  • ASIC application-specific integrated circuit
  • FPGA field-programmable gate array
  • the TxDSP may include a processor and a memory, and the processor realizes the functions of one or more functional modules by running the program code stored on the memory.
  • TxDSP may not have the function of storing program codes, but only have the function of a processor.
  • For the working principle of the optical transmitter refer to the description of the transmitting end in the embodiment of FIG. 1.
  • Fig. 3a is a schematic diagram of a logical structure of a TxDSP provided by an embodiment of the present invention.
  • the TxDSP may include forward error correction (FEC) 301, pulse shaping 302, SOP rotation 303, spectrum shift 304, and combiner 305.
  • FIG. 3b is a schematic diagram of the logical structure of a TxDSP provided by an embodiment of the present invention. The difference between FIG. 3b and FIG. 3a is that the spectrum shift 304 can be performed before the SOP rotation 303.
  • FEC forward error correction
  • FEC 301 obtains a binary bit stream.
  • the binary bit stream can be an electrical signal generated locally by the device or an electrical signal received from an external device.
  • FEC 301 distributes the obtained binary bit stream into two bit streams, and modulates the distributed two bit streams into two sub-carriers through pulse shaping 302, including sub-carrier A and sub-carrier B.
  • the sub-carriers can also be electrical signals.
  • subcarrier A includes XA and YA
  • subcarrier B includes XB and YB.
  • pulse shaping 302 in order to make the two sub-carriers form a relative polarization state (SOP) rotation angle, any one of the sub-carriers can be subjected to SOP rotation 303.
  • SOP relative polarization state
  • the SOP rotation of subcarrier B is performed by 45 degrees through the following expression (1), so that there is a 45 degree SOP rotation angle between subcarrier A and subcarrier B.
  • SOP rotation angle can also be any other angles such as 30, 135, 225, 315, etc., but the SOP rotation angle is not zero and not an integral multiple of 90 degrees.
  • Xin and Yin are the input signals of SOP rotation
  • Xout and Yout are the output signals of SOP rotation.
  • SOP refers to the vibration direction of the photon of the optical signal, and the vibration direction of the photon is usually perpendicular to the propagation direction of the optical signal.
  • the optical signal is divided into two polarization states in X and Y directions perpendicular to each other by a polarization beam splitter.
  • the angle of the optical fiber's main axis will change randomly with the environment, resulting in a random change in the signal SOP relative to the optical fiber's main axis.
  • the signal SOP is different, resulting in a difference in PDL cost. For example, as the angle of SOP changes, the cost of PDL changes.
  • FIG. 4 is a schematic diagram of the variation curve of OSNR cost with SOP angle provided by an embodiment of the present invention.
  • the OSNR cost of a single subcarrier changes with the SOP angle, resulting in system performance fluctuations.
  • the OSNR cost curves of the subcarrier A and the subcarrier B are just complementary, that is, the two subcarriers cannot work at the worst SOP at the same time.
  • the average OSNR cost curve of the two sub-carriers (shown as the solid line in Figure 4) is relatively flat relative to the curve of a single sub-carrier, and it also reduces the maximum OSNR cost value.
  • the SOP rotation of the sub-carriers can reduce the fluctuation of system performance and reduce the OSNR margin reserved by the system for PDL.
  • the SOP rotation angle between the two subcarriers is not 45 degrees, the OSNR cost curves of the two subcarriers may not be completely complementary, but as long as they do not completely overlap, the OSNR cost can be offset.
  • the solution in the embodiment of the present invention is not limited to a dual-subcarrier solution, and can also be applied to a solution with three or more subcarriers, and it is sufficient to ensure that at least two subcarriers have a relative SOP rotation angle.
  • FEC distributes the bit stream into three channels and modulates the three-channel bit stream into three sub-carriers. You can perform SOP rotation on one of the subcarriers, or perform SOP rotation on two or three of the subcarriers.
  • the above formula (1) can be used to perform SOP rotation on each second subcarrier.
  • SOP rotation is performed on subcarrier A, so that subcarriers A and B and subcarriers A and C have a relative SOP rotation angle, and there is no relative SOP rotation angle between subcarriers B and C. It is also possible to perform SOP rotation on subcarriers A and B, so that subcarriers A and B, subcarriers A and C, and subcarriers B and C have relative SOP rotation angles.
  • the technical solutions of the embodiments of the present invention are not limited to scenarios of polarization multiplexing, and are also applicable to scenarios of single polarization.
  • the two sub-carriers output by the FEC may include only one polarization state
  • the sub-carrier A may include XA or YA
  • the sub-carrier B may include XB or YB.
  • Fig. 5 is a schematic diagram of a subcarrier frequency spectrum provided by an embodiment of the present invention.
  • the two sub-carriers perform spectrum shift 304 respectively, and the frequency-shifted sub-carrier spectrum diagram is shown in FIG. 5.
  • the spectrum shift 304 can be implemented by a frequency shifter, thereby changing the spectrum position of the subcarrier.
  • the subcarriers XA, YA are multiplied by the coefficient exp(-j2 ⁇ f 0 t) and moved from zero frequency to frequency -f 0
  • the subcarriers XB, YB are multiplied by the coefficient exp(j2 ⁇ f 0 t), and the frequency is moved from zero frequency to frequency.
  • f 0 on the subcarriers XA, YA are multiplied by the coefficient exp(-j2 ⁇ f 0 t) and moved from zero frequency to frequency -f 0
  • the subcarriers XB, YB are multiplied by the coefficient exp(j2 ⁇ f 0
  • each sub-carrier can be moved to a different frequency.
  • the two sub-carriers pass through the combiner 305 to generate electrical modulation signals XI, XQ, YI, and YQ.
  • the combiner 305 may be implemented by an adder.
  • the electrical modulation signal passes through a modulator 204, such as an I/Q modulator, and is loaded on the optical signal, and then the optical signal is sent out through an optical fiber.
  • Fig. 6 is a schematic diagram of a logical structure of a TxDSP provided by an embodiment of the present invention.
  • the TxDSP may include FEC 601, constellation mapping 602, pulse shaping 603, SOP rotation 604, frequency shifter 606, and combiner 606.
  • the functions of FEC, pulse shaping, SOP rotation, frequency shifter, and combiner in Figure 6 are similar to those of Figures 3a and 3b.
  • FEC 601 distributes 4 bit streams based on the obtained binary bit stream, and modulates the distributed 4 bit streams into two sub-carriers through constellation mapping 602 and pulse shaping 603, including sub-carrier A and sub-carrier B.
  • the sub-carriers can be electronically signal.
  • subcarrier A includes XA and YA
  • subcarrier B includes XB and YB
  • the 4 bit streams are respectively modulated into sub-carriers XA, YA, XB, and YB.
  • the constellation mapping 602 can map the binary bit stream to the constellation points of a certain modulation format, for example, quadrature phase shift keying (quadrature phase shift keying, QPSK), quadrature amplitude modulation (quadrature amplitude modulation, QAM) (such as 8QAM, 16QAM, 256QAM) and other modulation formats.
  • the pulse shaping 603 can convert the constellation data stream with a double sampling rate into other suitable waveforms, such as a raised cosine waveform.
  • sub-carriers XA and YA can include I and Q signals respectively
  • sub-carriers XB and YB can include I and Q signals respectively, that is, there are XIA, XQA, YIA, YQA, XIB, XQB, YIB, YQB eight signal components.
  • a manner similar to formula (1) can be used to perform SOP rotation 604 on one or two sub-carriers.
  • SOP rotation 604 After SOP rotation 604, sub-carrier A and sub-carrier B perform spectrum shift 605 respectively, and the frequency-shifted sub-carrier spectrum diagram is shown in FIG. 5.
  • the spectrum shift 605 can be implemented by a frequency shifter, thereby changing the spectrum position of the subcarrier.
  • the subcarriers XA, YA are multiplied by the coefficient exp(-j2 ⁇ f 0 t) and moved from zero frequency to frequency -f 0
  • the subcarriers XB, YB are multiplied by the coefficient exp(j2 ⁇ f 0 t)
  • the frequency is moved from zero frequency to frequency. f 0 on.
  • it can also move based on other frequencies, which is not limited in the present invention.
  • the purpose of spectrum movement is to move the two sub-carriers to different frequencies to facilitate separation at the receiving end. In the case of three or more sub-carriers, each sub-carrier can be moved to a different frequency.
  • the spectrum shift 605 can also be performed before the SOP is rotated 604.
  • the subcarriers XA and XB are generated by the combiner 606 to generate electrical modulation signals XI and XQ
  • the subcarriers YA and YB are generated by the combiner 606 to generate electrical modulation signals YI and YQ.
  • the combiner 606 may be realized by an adder.
  • the electrical modulation signals XI, XQ, YI, and YQ pass through a modulator 204, such as an I/Q modulator, and are loaded on an optical signal, and then the optical signal is sent out through an optical fiber.
  • the OSNR cost curve obtained is relatively flat (as shown in FIG. 4), which reduces the performance fluctuation of the system.
  • the maximum OSNR generation value is reduced, thereby reducing the OSNR margin reserved for PDL.
  • FIG. 7 is a schematic structural diagram of an optical receiver provided by an embodiment of the present invention.
  • the optical receiver may include a local oscillator light source 701, a polarization beam splitter (PBS) 702, a beam splitter (BS) 703, a mixer 704, a balanced receiver 705, and an analog-to-digital converter (analog-to-digital converter).
  • converter, ADC) 706 and DSP (RxDSP) 707 at the receiving end.
  • RxDSP 707 may include one or more functional modules such as dispersion compensation, equalization, polarization demultiplexing, phase recovery, and FEC.
  • the functional modules on RxDSP can be implemented based on hardware, software, or a combination of hardware and software.
  • RxDSP can be realized by ASIC, FPGA, digital logic circuit.
  • the RxDSP may include a processor and a memory, and the processor realizes the functions of one or more functional modules by running the program code stored on the memory.
  • RxDSP may not have the function of storing program codes, but only have the function of a processor.
  • Fig. 8a is a schematic diagram of a logical structure of an RxDSP provided by an embodiment of the present invention.
  • the RxDSP may include dispersion compensation 811, multi-input multi-output (MIMO) equalization and demultiplexing 812, phase recovery 813, XY joint detection 814, and FEC 815.
  • MIMO multi-input multi-output
  • phase recovery 813 phase recovery 813
  • XY joint detection 814 XY joint detection
  • FEC 815 FEC
  • an analog electrical signal is obtained after coherent detection with the local oscillator light, and the analog electrical signal is converted into a digital electrical signal through an analog-to-digital converter, such as XI, XQ, YI, YQ.
  • dispersion compensation 811 and MIMO equalization and demultiplexing 812 are performed.
  • the dispersion compensation 811 may adopt fixed coefficient frequency domain equalization to compensate most of the dispersion in the link.
  • the MIMO equalization and demultiplexing 812 can be implemented with a 2*2 (dual polarization scene) or 2*1 (single polarization scene) butterfly filter. By adaptively updating the filter coefficients, the polarization state changes in the link are tracked, demultiplexing is completed, and other residual damages in the system are compensated at the same time.
  • the output signal of MIMO equalization and demultiplexing 812 passes through phase recovery 813 to recover the phase of the signal. Due to the influence of PDL, there is a certain crosstalk between the X and Y signals of two different polarization states after MIMO equalization. Therefore, XY joint detection 814 is required to further reduce the system cost caused by signal crosstalk.
  • the XY joint detection 814 may include two sets of MIMO post filtering 8141 and joint XY sequence detection 8142 to process I and Q signals respectively.
  • One group of MIMO post filtering and joint XY sequence detection performs joint detection on XI and YI
  • the other group of MIMO post filtering and joint XY sequence detection performs joint detection on XQ and YQ.
  • the signal after XY joint detection 814 enters FEC 815 for decoding.
  • FIG. 8a is a schematic diagram of a logical structure of an RxDSP provided by an embodiment of the present invention, taking dual subcarriers as an example for description.
  • the difference between FIG. 8b and FIG. 8a is that the signal after dispersion compensation 811 is separated into two sub-carrier signals, sub-carrier A and sub-carrier B by frequency divider 816.
  • subcarrier A may include XA and YA
  • subcarrier B may include subcarriers XB and YB.
  • the two subcarrier signals are respectively processed in a manner similar to FIG. 8a, and processed through two sets of MIMO equalization and demultiplexing 812, phase recovery 813, and XY joint detection 814 similar to those in FIG. 8a.
  • the last two subcarriers enter FEC 815 at the same time for decoding.
  • Fig. 9a is a schematic diagram of the logical structure of another RxDSP provided by an embodiment of the present invention. If there is channel damage (asymmetric transfer function) in the channel that causes IQ to be not independent, causing a certain degree of interference between the I and Q phase signals, the XY and IQ joint detection and promotion system shown in Figure 9a can be used performance.
  • the functions of the dispersion compensation 911, MIMO equalization and demultiplexing 912, phase recovery 913, and FEC 915 in FIG. 9a are similar to those of the corresponding functional modules in FIG. 8a.
  • the difference between FIG. 9a and FIG. 8a is that XY and IQ joint detection 914 is used instead of XY joint detection 814.
  • the XY and IQ joint detection 914 may only include a set of MIMO post filtering 9141 and the joint XY sequence detection 9142 for joint detection of the signals XI+jXQ and YI+jYQ.
  • FIG. 9a is a schematic diagram of the logical structure of another RxDSP provided by an embodiment of the present invention, taking dual subcarriers as an example for description.
  • the difference between FIG. 9b and FIG. 9a is that the signal after dispersion compensation 911 is separated into two subcarrier signals, subcarrier A and subcarrier B by frequency divider 916.
  • subcarrier A may include XA and YA
  • subcarrier B may include subcarriers XB and YB.
  • the two sub-carrier signals are respectively processed in a manner similar to FIG.
  • Figure 10a is a schematic diagram of a logical structure of a joint detection provided by an embodiment of the present invention. As shown in Fig. 10a, the signal X is filtered by the filter of the coefficient Tap11, and the signal Y is filtered by the filter of the coefficient Tap12, and the two are summed to obtain a signal. The signal Y is filtered by a filter with coefficient Tap22 to obtain another signal. Two signal inputs are combined with XY sequence detection 1001 to improve performance.
  • the joint XY sequence detection 100 by minimizing the joint Euclidean distance of the received sequence signal X, signal Y, and the decision signal of the signal X, signal Y, realizes the sequence joint judgment of the signal X and the signal Y, and improves the performance.
  • the signal X after phase recovery is RX0 and the signal Y is RY0
  • two signals are obtained through MIMO post filtering.
  • k is the time sequence number
  • N is the tap length of the filters Tap11, Tap12, and Tap22.
  • the above summation corresponds to the convolution operation, which is filtering. Joint XY sequence detection by minimizing the cost function
  • DX(k) and DY(k) are the decisions of signal X and signal Y respectively. If the XY joint sequence detection 1001 and FEC 1002 adopt soft value iteration, the performance can be further improved.
  • Figure 10b is a schematic diagram of another logical structure of joint detection provided by an embodiment of the present invention.
  • the signal X is filtered by the filter of the coefficient Tap21
  • the signal Y is filtered by the filter of the coefficient Tap22
  • the two are summed to obtain a signal.
  • the signal X is filtered by the filter of the coefficient Tap11 to obtain another signal.
  • Two signal inputs are combined with XY sequence detection 1001 to improve performance.
  • k is the time sequence number
  • N is the tap length of the filters Tap11, Tap21, and Tap22.
  • DX(k) and DY(k) are the decisions of signal X and signal Y. If the XY joint sequence detection 1001 and FEC 1002 adopt soft value iteration, the performance can be further improved.
  • the filters in Figures 10a and 10b may be finite impulse response (FIR) filters.
  • the signal X may include XI and XQ
  • the signal Y may include YI and YQ.
  • XI, YI can use a structure shown in Figure 10a or Figure 10b for XY joint detection
  • XQ, YQ can use another structure shown in Figure 10a or Figure 10b for XY joint detection.
  • the signal X can be XI+jXQ
  • the signal Y can be YI+jYQ.
  • XI+jXQ, YI+jYQ can adopt a structure shown in Figure 10a or Figure 10b for XY and IQ joint detection.
  • FIG. 11 is a graph of the OSNR cost of joint detection provided by an embodiment of the present invention.
  • the solid line is the OSNR cost curve using XY joint detection in the single-subcarrier scenario
  • the dotted line is the OSNR cost curve using XY independent detection in the single-subcarrier scenario.
  • the maximum OSNR value when the SOP is zero is basically the same. There is no obvious benefit from the joint detection, but the OSNR generation value of other SOP angles has decreased.
  • FIG. 12 is a graph of the cost of joint detection OSNR provided by an embodiment of the present invention. As shown in FIG.
  • the solid line is the OSNR cost curve using XY joint detection in the dual subcarrier scenario
  • the dotted line is the OSNR cost curve using XY independent detection in the dual subcarrier scenario.
  • joint detection is compared with independent detection. There are benefits to adopting joint detection under any SOP angle, which improves the performance of the system.
  • Fig. 13a is a schematic diagram of a logical structure of filter coefficient generation in joint detection according to an embodiment of the present invention. As shown in Fig. 13a, taking XY joint detection and input signals XI and YI as examples, the calculation process of the filter coefficients Tap11, Tap12, and Tap22 will be described in detail.
  • phase recovery 813 or 913 output signal is XI(k), where k is the time sequence number.
  • the original transmission signal corresponding to XI(k) is DXI(k).
  • DXI(k) can be derived from the original data of a known transmitter (for example, a training sequence), or can be derived from a decision on XI(k).
  • the noise value of signal X NoiseXI(k) XI(k)-DXI(k).
  • phase recovery 813 or 913 output signal is YI(k), where k is the time sequence number.
  • the original transmission signal corresponding to YI(k) is DYI(k).
  • DYI(k) can be derived from the original data of a known transmitter (such as a training sequence), or it can be derived from a decision on YI(k).
  • the noise value of the signal Y NoiseYI(k) YI(k)-DYI(k).
  • the correlation matrix is calculated as an L ⁇ L matrix, where L is the correlation delay length, which can be greater than or equal to N.
  • B21 is the B12 Hermitian matrix.
  • NoiseYI(k) is a real number
  • C11 is a self-conjugate matrix, which can be written in the following form
  • U 12 is also a Hermitian matrix, which can be written in the following form
  • Y YI+jYQ.
  • the original transmission signal corresponding to X(k) is DXI(k)+jDXQ(k), DXI(k)+jDXQ(k) can be derived from the raw data of a known reflector (such as training sequence), or it can be derived from X (k) Judgment.
  • the noise value of the signal X NoiseX(k) (XI(k)-DXI(k))+j(XQ(k)-DXQ(k)).
  • the original transmission signal corresponding to Y(k) is DYI(k)+jDYQ(k), DYI(k)+jDYQ(k) can be derived from the original data of a known reflector (such as training sequence), or it can be (k) Judgment.
  • the noise value of the signal Y NoiseY(k) (YI(k)-DYI(k))+j(YQ(k)-DYQ(k)). Similar to the above XY joint detection process, part of the correlation function in the correlation matrix can be changed to a complex number.
  • FIG. 13b is a schematic diagram of the logical structure of generating filter coefficients in another joint detection according to an embodiment of the present invention.
  • the implementation of FIG. 13b is similar to that of FIG. 13a, and the noise value of the signal X inputted in FIG. 13a and the noise value of the signal Y can be exchanged to obtain the implementation of FIG. 13b, which will not be repeated here.
  • the above embodiments it may be implemented in whole or in part by software, hardware, firmware or any combination thereof.
  • software it can be implemented in the form of a program product in whole or in part.
  • the program product includes one or more instructions.
  • the program instructions When the program instructions are loaded and executed on the optical transceiver, the processes or functions described in the embodiments of the present invention are generated in whole or in part.
  • the optical transceiver may be an optical module, with optical transmitting function or optical receiving function, or both optical transmitting and receiving functions.
  • the instructions may be stored in a readable storage medium, or transmitted from a readable storage medium of one device to a readable storage medium of another device.
  • the readable storage medium may be any available medium that can be accessed by the optical transceiver or a data storage device such as a server or data center integrated with one or more available media.
  • the usable medium may be a magnetic medium (for example, a floppy disk, a hard disk, a magnetic tape), an optical medium (for example, a DVD), or a semiconductor medium (for example, a solid state disk (SSD)).

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Abstract

本发明实施例提供了一种光通信中信号收发的方法、光收发机和系统。其中，信号发送的方法包括：发射机基于获取到的比特流生成第一子载波，所述第一子载波包括至少两路子载波。光发射机对所述第一载波中的第二子载波进行偏振态SOP旋转，使得所述第一子载波中存在至少两路具有相对SOP旋转角度的子载波，其中，所述第二子载波包括一路或多路子载波，所述相对SOP旋转角度不为零且不为90度的整数倍。光发射机将所述SOP旋转后的第一子载波调制到光信号上，将所述光信号发送出去。通过对子载波设置相对的SOP旋转角度，可以降低偏振相关损耗PDL带来的系统代价，提升系统性能。

Description

一种光通信中信号收发的方法、光收发机和系统
本申请要求于2019年6月14日提交中国专利局、申请号为201910516696.6，发明名称为“一种光通信中信号收发的方法、光收发机和系统”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及通信领域，尤其涉及一种光通信中信号收发的方法、光收发机和系统。
背景技术
随着高速数字信号处理(digital signal processing，DSP)技术和模数转换技术的进步，相干光通信成为研究的热点。相干光通信系统支持多进制调制格式和偏振复用，实现高频谱效率的传输。
偏振复用是利用光的两个正交偏振态，在相同的带宽内同时传输两个独立的正交偏振信号，从而将信道传输效率提高两倍。采用偏振复用结合相干接收技术，可以实现100Gb/s以上长距离传输。但是由于光纤受外界环境影响产生双折射效应，且光纤的双折射轴随时间变化而随机变化，发射端经过偏振复用产生的两个正交偏振信号经过光纤传输后，受到光纤偏振相关损耗(polarization-dependent loss，PDL)的影响带来系统代价，造成系统性能波动。常规的链路设计，需要为这种波动预留一定(optical signal-to-noise ratio，OSNR)余量，保证传输系统FEC纠后无误码。通常PDL为6dB，需要预留3dB左右的OSNR余量。如果预留的OSNR较大，则会降低通信系统的传输距离。因此，需要解决降低PDL带来的系统性能波动，从而降低PDL带来的系统代价(预留OSNR余量)的问题。
发明内容
有鉴于此，本申请提供一种光通信中信号收发的方法、光收发机和系统，可以解决PDL带来的性能波动和系统代价。
第一方面，本申请提供一种光通信中信号发送的方法，该方法可以包括：光发射机获取比特流，将获取到的比特流分发为至少两路比特流，并针对分发后的每一路比特流调制为一路子载波，从而生成至少两路第一子载波。光发射机对其中一路或多路第二子载波进行偏振态SOP旋转，使得存在至少两路具有相对SOP旋转角度的子载波，其中，相对SOP旋转角度不为零且不为90度的整数倍。经过SOP旋转之后，光发射机将至少两路第一子载波调制到光信号上，并将光信号发送出去。通过对第二子载波进行SOP旋转，使得具有相对SOP旋转角度的子载波的OSNR代价得到平均和抵消，可以降低PDL带来的系统性能的波动以及系统代价。
在一种可能的实现方式中，相对SOP旋转角度为45度。两路子载波之间的相对SOP旋转角度为45度时，可以实现两路子载波的OSNR曲线互补，降低了系统的性能波动和系统代价。当然，相对SOP旋转角度也可以为其他角度，例如，30、135、225度等。
在一种可能的实现方式中，所述SOP旋转包括：通过公式
Figure PCTCN2020092635-appb-000001
对所述第一载波中的一路第二子载波进行SOP旋转，其中，Xin、Yin为所述SOP旋转前的一路第二子载波，Xout、Yout为所述SOP旋转后的一路第二子载波，α为所述SOP旋转的角度。当 对多路第二子载波进行SOP旋转时，可以对每一路第二子载波分别采用上述的公式进行SOP旋转。
在一种可能的实现方式中，在SOP旋转之后，光发射机对经过SOP旋转的第一子载波进行频谱搬移。或者，在SOP旋转之前，光发射机对生成的第一子载波进行频谱搬移。频谱搬移的目的是为了使收端能够对至少两路第一子载波进行分离，频谱搬移只要在第一子载波合波之前实现即可。
在一种可能的实现方式中，光发射机对经过SOP旋转和频谱搬移之后的第一子载波进行合波。第一子载波合波输出后可调制到光信号，通过光信号承载并发送。
第二方面，本申请提供一种光发射机，光发射机包括数字信号处理器DSP和调制器。其中，DSP获取比特流，将获取到的比特流分发为至少两路比特流，并针对分发后的每一路比特流调制为一路子载波，从而生成至少两路第一子载波。DSP对其中一路或多路第二子载波进行偏振态SOP旋转，使得存在至少两路具有相对SOP旋转角度的子载波，其中，相对SOP旋转角度不为零且不为90度的整数倍。经过SOP旋转之后，调制器将至少两路第一子载波调制到光信号上，并将光信号发送出去。通过对第二子载波进行SOP旋转，使得具有相对SOP旋转角度的子载波的OSNR代价得到平均和抵消，可以降低PDL带来的系统性能的波动以及系统代价。
在一种可能的实现方式中，相对SOP旋转角度为45度。两路子载波之间的相对SOP旋转角度为45度时，可以实现两路子载波的OSNR曲线互补，降低了系统的性能波动和系统代价。当然，相对SOP旋转角度也可以为其他角度，例如，30、135、225度等。
在一种可能的实现方式中，DSP通过公式
Figure PCTCN2020092635-appb-000002
对一路第二子载波进行SOP旋转，其中，Xin、Yin为所述SOP旋转前的一路第二子载波，Xout、Yout为所述SOP旋转后的一路第二子载波，α为所述SOP旋转的角度。当对多路第二子载波进行SOP旋转时，可以对每一路第二子载波分别采用上述的公式进行SOP旋转。
在一种可能的实现方式中，所述DSP，还用于：在所述SOP旋转之后，对所述SOP旋转之后的第一子载波进行频谱搬移。或者，所述DSP，还用于：在所述SOP旋转之前，对所述获取的第一子载波进行频谱搬移。频谱搬移的目的是为了使收端能够对至少两路第一子载波进行分离，频谱搬移只要在第一子载波合波之前实现即可。
在一种可能的实现方式中，所述DSP，还用于：对经过所述SOP旋转和频谱搬移之后的第一子载波进行合波。第一子载波合波输出后可调制到光信号，通过光信号承载并发送。
第三方面，本申请提供一种光通信中信号接收的方法，该方法可以包括：光接收机接收光信号，将所述光信号转换为电信号，其中，所述电信号包括第一信号和第二信号，所述第一信号和第二信号对应不同的偏振态；所述光接收机生成第一系数、第二系数和第三系数，基于所述第一系数对所述第一信号进行滤波，得到第三信号；基于所述第二系数对所述第二信号进行滤波，得到第四信号；基于所述第三系数对所述第二信号进行滤波，得到第五信号；所述光接收机对所述第三信号和所述第四信号进行求和，得到第七信号，根据所述第五信号和所述第七信号获取所述第一信号和所述第二信号的判决序列。第一信号和第二信号可以是两个正交偏振的信号，例如，第一信号具有X偏振态，第二信号具有Y偏振态。光接收机通过不同偏振态的信号进行联合检测，可以降低PDL带来的系统代价，提升性 能。
在一种可能的实现方式中，所述第一信号和第二信号分别具有至少两个子载波，所述至少两个子载波之间相对的偏振态SOP旋转角度不为零且不为90度的整数倍，使得所述第三系数不为零。在双子载波的场景中，两个子载波之间相对的SOP旋转角度使得不同偏振态的信号之间的滤波系数不为零，以实现不同偏振态信号之间的联合检测。
在一种可能的实现方式中，所述获取所述第一信号和所述第二信号的判决序列，包括：通过最小化代价函数获取所述第一信号和所述第二信号的判决序列。
第四方面，本申请提供一种光接收机，包括：光接收机前端和DSP。光接收机前端可以包括混频器、平衡接收机等，可以用于光电转换。光接收机前端接收光信号，将所述光信号转换为电信号，其中，所述电信号包括第一信号和第二信号，所述第一信号和第二信号对应不同的偏振态。DSP生成第一系数、第二系数和第三系数，基于所述第一系数对所述第一信号进行滤波，得到第三信号；基于所述第二系数对所述第二信号进行滤波，得到第四信号；基于所述第三系数对所述第二信号进行滤波，得到第五信号。DSP对所述第三信号和所述第四信号进行求和，得到第七信号，根据所述第五信号和所述第七信号获取所述第一信号和所述第二信号的判决序列。第一信号和第二信号可以是两个正交偏振的信号，例如，第一信号具有X偏振态，第二信号具有Y偏振态。光接收机通过不同偏振态的信号进行联合检测，可以降低PDL带来的系统代价，提升性能。
在一种可能的实现方式中，所述第一信号和第二信号分别具有至少两个子载波，所述至少两个子载波之间相对的偏振态SOP旋转角度不为零且不为90度的整数倍，使得所述第三系数不为零。在双子载波的场景中，两个子载波之间相对的SOP旋转角度使得不同偏振态的信号之间的滤波系数不为零，以实现不同偏振态信号之间的联合检测。
在一种可能的实现方式中，DSP用于通过最小化代价函数获取所述第一信号和所述第二信号的判决序列。
第五方面，本申请提供一种光通信系统，该光通信系统包括上述第二方面或第二方面任意一种可能的实现方式中的光发射机，和/或上述第四方面或第四方面任意一种可能的实现方式中的光接收机。
本申请的又一方面提供了一种可读存储介质，所述可读存储介质中存储有指令，当其在光收发机上运行时，使得光收发机执行上述各方面所述的方法。
本申请的又一方面提供了一种包含指令的程序产品，当其在光收发机上运行时，使得光收发机执行上述各方面所述的方法。
附图说明
为了说明本发明实施例的技术方案，下面将对描述实施例时所使用的附图作简单的介绍。
图1为本发明实施例提供的一种相干光通信系统的结构示意图；
图2为本发明实施例提供的一种光发射机的结构示意图；
图3a为本发明实施例提供的一种TxDSP的逻辑结构示意图；
图3b为本发明实施例提供的一种TxDSP的逻辑结构示意图；
图4为本发明实施例提供的OSNR代价随SOP角度的变化曲线示意图；
图5为本发明实施例提供的子载波频谱示意图；
图6为本发明实施例提供的一种TxDSP的逻辑结构示意图；
图7为本发明实施例提供的一种光接收机的结构示意图；
图8a为本发明实施例提供的一种RxDSP的逻辑结构示意图；
图8b为本发明实施例提供的一种RxDSP的逻辑结构示意图；
图9a为本发明实施例提供的另一种RxDSP的逻辑结构示意图；
图9b为本发明实施例提供的另一种RxDSP的逻辑结构示意图；
图10a为本发明实施例提供的一种联合检测的逻辑结构示意图；
图10b为本发明实施例提供的另一种联合检测的逻辑结构示意图；
图11为本发明实施例提供的联合检测OSNR代价曲线图；
图12为本发明实施例提供的联合检测OSNR代价曲线图；
图13a为本发明实施例提供的一种联合检测中滤波系数生成的逻辑结构示意图；
图13b为本发明实施例提供的另一种联合检测中滤波系数生成的逻辑结构示意图。
具体实施方式
以下结合附图及实施例，对本发明进行进一步详细说明。
本发明实施例的技术方案可以应用于多种类型光通信系统中，例如，相干光通信系统、直检光通信系统、以及其他可能实现本发明技术方案的通信系统中。本发明实施例以相干光通信系统为例进行说明。图1为本发明实施例提供的一种相干光通信系统的结构示意图。相干光通信系统包括发送端110、光纤120和接收端130。发送端110可以包括信号光光源101、调制器102、偏振分束器(polarization beam splitter，PBS)103和偏振合束器(polarization beam combiner，PBC)104。发送端110还可以包括数字信号处理器(digital signal processor，DSP)或数字信号处理芯片，用于产生电信号。接收端130可以包括本振光光源105、平衡接收机106、PBS(图中未示出)、混频器107和电解调电路108。其中，电解调电路108可以包括DSP或数字信号处理芯片。发送端和接收端可以在同一个设备上，也可以在不同的设备上。本发明实施例的技术方案可以应用于偏振复用的相干光通信系统，还可以应用于其他形式的相干光通信系统中，比如，可以用于单偏振态的相干光通信系统中，单偏振态的相干光通信系统中可以没有PBS和PBC。
发送端110上，信号光光源101可以为激光器。信号光光源101发出的光信号经过偏振分束器103分为X、Y两路光信号，调制器102将一路电信号加载到X光信号上，另一路电信号加载到Y光信号上。电信号可以由发送端的DSP(TxDSP)对信息比特流进行FEC、星座映射、脉冲整形等一项或多项处理后获得。调制器102可以为I/Q调制器，每一路电信号分别包括信号I和信号Q，I、Q两路信号的相位差为90度。经过调制器102后，形成四路信号：XI、XQ、YI、YQ。然后通过偏振合束器104把加载了电信号的X、Y光信号复用合并在一起，通过光纤120发送出去。
接收端130接收到经过光纤120传输的光信号后，偏振分束器将接收到的光信号分解成两个正交的信号，每个正交信号都与一个本振光光源105产生的光信号混频107。本振光光源105可以为激光器。混频后得到4个偏振和相位正交的光信号XI、XQ、YI、YQ，然后通过平衡接收机106将光信号转换为模拟电信号，并由模数转换电路将模拟电信号转化为4路数字电信号。数字电信号通过接收端的DSP(RxDSP)以实现色散补偿、偏振解复用、均衡和解码等一项或多项功能。
图2是本发明实施例提供的一种光发射机的结构示意图。光发射机可以包括发送端的DSP(TxDSP)201、数模转换器(digital-to-analog converter，DAC)202、信号光光源203、调制器204、偏振分束器(PBS)205、偏振合束器(PBC)206等。其中，TxDSP201可以包括FEC、星座映射、脉冲整形、偏振态(state of polarization，SOP)旋转、频谱搬移等一个或多个功能模块。TxDSP上的功能模块可以基于硬件实现，也可以基于软件实现，还可以结合硬件和软件实现。例如，TxDSP可以通过专用集成电路(application-specific integrated circuit，ASIC)、现场可编程门阵列(field-programmable gate array，FPGA)、数字逻辑电路来实现。又例如，TxDSP上可以包括处理器和存储器，处理器通过运行保存在存储器上的程序代码，实现上述一个或多个功能模块的功能。又例如，TxDSP可以没有存储程序代码的功能，只具备处理器的功能。光发射机的工作原理可以参考图1实施例发送端的描述。
图3a为本发明实施例提供的一种TxDSP的逻辑结构示意图。TxDSP可以包括前向纠错(forward error correction，FEC)301、脉冲整形302、SOP旋转303、频谱搬移304、合并器305。图3b为本发明实施例提供的一种TxDSP的逻辑结构示意图，图3b和图3a的区别在于，频谱搬移304可以在SOP旋转303之前执行。
以图3a为例进行说明，FEC 301获取二进制比特流。该二进制比特流可以是设备本地产生的电信号，也可以是从外部设备接收的电信号。FEC 301将获取到的二进制比特流分发为两路比特流，通过脉冲整形302将分发的两路比特流调制为两路子载波，包括子载波A和子载波B，子载波也可以是电信号。其中，子载波A包括XA和YA，子载波B包括XB和YB。经过脉冲整形302之后，为了使两路子载波形成相对的偏振态(SOP)旋转角度，可以对其中任意一路子载波进行SOP旋转303。例如，通过下列的表达式(1)对子载波B进行SOP旋转45度，使得子载波A和子载波B之间具有45度的SOP旋转角度。当然，也可以同时对两路子载波进行SOP旋转，使得两路子载波之间形成相对的SOP旋转角度。SOP旋转的角度还可以是30、135、225、315等其他任意角度，但SOP旋转角度不为零且不为90度的整数倍。
Figure PCTCN2020092635-appb-000003
其中，Xin、Yin为SOP旋转的输入信号，Xout、Yout为SOP旋转的输出信号。
SOP指的是光信号光子的振动方向，光子的振动方向通常垂直于光信号的传播方向，例如，光信号通过偏振分束器分为X、Y两个相互垂直方向的偏振态。光纤的主轴角度会随着环境随机变化，导致信号SOP相对光纤主轴随机变化。信号SOP不同，导致PDL代价差异。例如，随着SOP角度的变化，PDL的代价发生变化。图4为本发明实施例提供的OSNR代价随SOP角度的变化曲线示意图。如图4所示，单个子载波(如图4中任一条虚线所示)的OSNR代价随着SOP角度发生变化，从而产生系统性能波动。经过SOP旋转45度之后，子载波A和子载波B的OSNR代价曲线刚好是互补的，即两个子载波不可能同时工作在最差SOP。两个子载波平均的OSNR代价曲线(如图4中实线所示)相对于单个子载波的曲线比较平缓，同时也降低了最大的OSNR代价值。可见，通过子载波的SOP旋转，可以降低系统性能的波动，减少系统为PDL预留的OSNR余量。当两个子载波之间的SOP旋转角度不为45度时，两个子载波的OSNR代价曲线可能不是完全互补，但只要不完全重合，即可实现OSNR代价的抵消。
本发明实施例的方案不限于双子载波的方案，还可以应用到三个或以上子载波的方案， 保证至少有两个子载波存在相对SOP旋转角度即可。例如，三个子载波的情况，FEC将比特流分发为三路，并将三路比特流调制为三路子载波。可以对其中一路子载波进行SOP旋转，也可以对其中的两路或三路子载波进行SOP旋转。当对多路子载波进行SOP旋转时，可以对每一路第二子载波分别采用上述的公式(1)进行SOP旋转。一个例子中，对子载波A进行SOP旋转，使得子载波A、B以及子载波A、C之间具有相对的SOP旋转角度，子载波B、C之间没有相对的SOP旋转角度。还可以对子载波A和B进行SOP旋转，使得子载波A、B，子载波A、C，子载波B、C之间都具有相对的SOP旋转角度。此外，本发明实施例的技术方案不限于偏振复用的场景，对于单偏振态的场景也适用。在单偏振态的场景中，FEC输出两路子载波可以仅包含一种偏振态，子载波A可以包括XA或YA，子载波B包括XB或YB。
图5为本发明实施例提供的子载波频谱示意图。经过SOP旋转303之后，两路子载波分别进行频谱搬移304，频移后的子载波的频谱图如图5所示。频谱搬移304可以通过移频器来实现，从而改变子载波的频谱位置。例如，子载波XA、YA乘以系数exp(-j2πf 0t)，从零频搬移到频率-f 0上，子载波XB、YB乘以系数exp(j2πf 0t)，从零频搬移到频率f 0上。除了基于零频搬移，还可以基于其他的频率进行搬移，本发明不进行限定。频谱搬移的目的是为了将两路子载波搬移到不同的频率上，便于接收端进行分离。针对三个或以上子载波的情形，可以将每一个子载波都搬移到不同的频率上。
频谱搬移204之后，两路子载波经过合并器305生成电调制信号XI、XQ、YI、YQ。合并器305可以为通过加法器实现。电调制信号经过调制器204，例如I/Q调制器，加载到光信号上，然后光信号通过光纤发送出去。
图6为本发明实施例提供的一种TxDSP的逻辑结构示意图。TxDSP可以包括FEC 601、星座映射602、脉冲整形603、SOP旋转604、频移器606、合并器606。图6中的FEC、脉冲整形、SOP旋转、频移器、合并器的功能和图3a、图3b类似。FEC 601基于获取到的二进制比特流分发为4路比特流，并通过星座映射602和脉冲整形603将分发的4路比特流调制为两路子载波，包括子载波A和子载波B，子载波可以电信号。其中，子载波A包括XA、YA，子载波B包括XB、YB。4路比特流分别调制为子载波XA、YA、XB、YB。星座映射602可以将二进制的比特流映射到某种调制格式的星座点上，例如，正交相移键控(quadrature phase shift keying，QPSK)，正交幅度调制(quadrature amplitude modulation，QAM)(如8QAM、16QAM、256QAM)等调制格式。脉冲整形603可以将一倍采样率的星座数据流转换为其他合适的波形，例如升余弦波形。经过星座映射602和脉冲整形603之后，子载波XA、YA可以分别包括I、Q两路信号，子载波XB、YB可以分别包括I、Q两路信号，即存在XIA、XQA、YIA、YQA、XIB、XQB、YIB、YQB八个信号分量。其中子载波XA可以表示为XA＝XIA+jXQA，子载波YA可以表示为YA＝YIA+jYQA；子载波XB可以表示为XB＝XIB+jXQB，子载波YB可以表示为YB＝YIB+jYQB。
为了使两路子载波形成相对的SOP旋转角度，可以采用类似公式(1)的方式对其中一路或两路子载波进行SOP旋转604。经过SOP旋转604之后，子载波A和子载波B分别进行频谱搬移605，频移后的子载波频谱图如图5所示。频谱搬移605可以通过移频器来实现，从而改变子载波的频谱位置。例如，子载波XA、YA乘以系数exp(-j2πf 0t)，从零频搬移到频率-f 0上，子载波XB、YB乘以系数exp(j2πf 0t)，从零频搬移到频率f 0上。除了基于零频搬移，还可以基于其他的频率进行搬移，本发明不进行限定。频谱搬移的目的是为了将两路子载波搬移到不同的频率上，便于接收端进行分离。针对三个或以上子载波的情形，可以将每 一个子载波都搬移到不同的频率上。此外，频谱搬移605还可以在SOP旋转604之前执行。
经过频谱搬移605之后，子载波XA、XB由合并器606生成电调制信号XI、XQ，子载波YA、YB由合并器606生成电调制信号YI、YQ。合并器606可以为通过加法器实现。电调制信号XI、XQ、YI、YQ经过调制器204，例如I/Q调制器，加载到光信号上，然后光信号通过光纤发送出去。
本发明实施例中，子载波经过SOP旋转之后，得到的OSNR代价曲线比较平缓(如图4所示)，降低了系统的性能波动。同时降低了最大OSNR代价值，从而降低了为PDL预留的OSNR余量。
图7是本发明实施例提供的一种光接收机的结构示意图。光接收机可以包括本振光光源701、偏振分束器(PBS)702、分束器(beamsplitter，BS)703、混频器704、平衡接收机705、模数转换器(analog-to-digital converter,ADC)706和接收端的DSP(RxDSP)707。RxDSP 707可以包括色散补偿、均衡、偏振解复用、相位恢复、FEC等一个或多个功能模块。RxDSP上的功能模块可以基于硬件实现，也可以基于软件实现，还可以结合硬件和软件实现。例如，RxDSP可以通过ASIC、FPGA、数字逻辑电路来实现。又例如，RxDSP上可以包括处理器和存储器，处理器通过运行保存在存储器上的程序代码，实现上述一个或多个功能模块的功能。又例如，RxDSP可以没有存储程序代码的功能，只具备处理器的功能。光发射机的工作原理可以参考图1实施例发送端的描述。光接收机的原理可以参考图1实施例接收端的描述。
图8a为本发明实施例提供的一种RxDSP的逻辑结构示意图。如图8a所示，RxDSP可以包括色散补偿811、多输入多输出(multi-input multi-output，MIMO)均衡及解复用812、相位恢复813、XY联合检测814和FEC 815。信号光被光接收机接收后，与本振光相干检测后得到模拟电信号，通过模数转换器将模拟电信号转换为数字电信号，例如XI、XQ、YI、YQ。数字电信号XI、XQ、YI、YQ输入RxDSP后，进行色散补偿811和MIMO均衡及解复用812。其中，色散补偿811可以采用固定系数的频域均衡，补偿链路中的大部分色散。MIMO均衡及解复用812的可以采用2*2(双偏振态场景)或者2*1(单偏振态场景)蝶形滤波器实现。通过自适应更新滤波器系数，跟踪链路中的偏振态变化，完成解复用，同时补偿系统中残余的其他损伤。MIMO均衡及解复用812输出信号通过相位恢复813，恢复信号的相位。由于PDL的影响，MIMO均衡之后的X、Y两种不同偏振态的信号之间存在一定的串扰，因此需要XY联合检测814来进一步减低信号串扰带来的系统代价。XY联合检测814可以包括两组MIMO后置滤波8141和联合XY序列检测8142，分别处理I、Q信号。其中一组MIMO后置滤波和联合XY序列检测对XI、YI进行联合检测，另一组MIMO后置滤波和联合XY序列检测对XQ、YQ进行联合检测。经过XY联合检测814的信号进入FEC 815进行译码。
图8a实施例的技术方案可以应用于单子载波的光通信系统，还可以应用于双子载波或三个及以上子载波的光通信系统。图8b为本发明实施例提供的一种RxDSP的逻辑结构示意图，以双子载波为例进行说明。图8b和图8a差异在于，色散补偿811后的信号通过分频器816分离为两个子载波信号，子载波A和子载波B。其中，子载波A可以包括XA、YA，子载波B可以包括子载波XB、YB。两个子载波信号分别通过类似图8a的方式进行信号处理，通过两组类似图8a中的MIMO均衡及解复用812、相位恢复813、XY联合检测814进行处理。最后两个子载波同时进入FEC 815进行译码。
图9a为本发明实施例提供的另一种RxDSP的逻辑结构示意图。如果信道中存在信道损伤 (非对称传递函数)导致IQ不独立，使得I、Q两种相位的信号之间产生一定程度上的干扰，可以采用如图9a所示的XY、IQ联合检测提升系统性能。图9a中的色散补偿911、MIMO均衡及解复用912、相位恢复913、FEC 915的作用和图8a中相应的功能模块类似。图9a和图8a的区别在于，采用XY、IQ联合检测914替代XY联合检测814。XY、IQ联合检测914可以仅包含一组MIMO后置滤波9141和联合XY序列检测9142，用于对信号XI+jXQ、YI+jYQ进行联合检测。
图9a实施例的技术方案可以应用于单子载波的光通信系统，还可以应用于双子载波或三个及以上子载波的光通信系统。图9b为本发明实施例提供的另一种RxDSP的逻辑结构示意图，以双子载波为例进行说明。图9b和图9a差异在于，色散补偿911后的信号通过分频器916分离为两个子载波信号，子载波A和子载波B。其中，子载波A可以包括XA、YA，子载波B可以包括子载波XB、YB。两个子载波信号分别通过类似图9a的方式进行信号处理，通过两组类似图9a中的MIMO均衡及解复用912、相位恢复913、XY、IQ联合检测914进行处理。最后两个子载波同时进入FEC 915进行译码。
XY联合检测814以及XY、IQ联合检测914的实现方式有多种，本发明实施例提供两种等效的可能的实现方式。图10a为本发明实施例提供的一种联合检测的逻辑结构示意图。如图10a所示，信号X通过系数Tap11的滤波器滤波，信号Y通过系数Tap12的滤波器滤波，两者求和得到一路信号。信号Y通过系数Tap22的滤波器滤波，得到另一路信号。两路信号输入联合XY序列检测1001，提升性能。联合XY序列检测1001，通过最小化接收序列信号X、信号Y和信号X、信号Y的判决信号的联合欧式距离，实现信号X、信号Y的序列联合判定，提升性能。例如，相位恢复后的信号X为RX0，信号Y为RY0，通过MIMO后置滤波得到两路信号。以图10a为例，MIMO后置滤波输出的两路信号RX(k)、RY(k)：
Figure PCTCN2020092635-appb-000004
Figure PCTCN2020092635-appb-000005
其中，k是时间序号，N是滤波器Tap11，Tap12，Tap22的抽头长度，上面的求和对应卷积运算，即为滤波。联合XY序列检测通过最小化代价函数
Figure PCTCN2020092635-appb-000006
得到信号X、信号Y的判决序列。其中DX(k)、DY(k)分别为信号X、信号Y的判决。如果XY联合序列检测1001和FEC 1002采用软值迭代，可以进一步提升性能。
图10b为本发明实施例提供的另一种联合检测的逻辑结构示意图。如图10b所示，信号X通过系数Tap21的滤波器滤波，信号Y通过系数Tap22的滤波器滤波，两者求和得到一路信号。信号X通过系数Tap11的滤波器滤波，得到另一路信号。两路信号输入联合XY序列检测1001，提升性能。图10b中MIMO后置滤波输出的两路信号RX(k)、RY(k)：
Figure PCTCN2020092635-appb-000007
Figure PCTCN2020092635-appb-000008
其中，k是时间序号，N是滤波器Tap11，Tap21，Tap22的抽头长度，上面的求和对应卷积运算，即为滤波。联合XY序列检测通过最小化代价函数
Figure PCTCN2020092635-appb-000009
得到信号X、信号Y的判决序列。其中DX(k)和DY(k)为信号X、信号Y的判决。如果XY联合序列检测1001和FEC 1002采用软值迭代，可以进一步提升性能。图10a、10b中滤波器可以为有限冲激响应(finite impulse response，FIR)滤波器。
当图10a、图10b所示的逻辑结构用于XY联合检测时，信号X可以包括XI、XQ，信号Y可以包括YI、YQ。XI、YI可以采用一个图10a或图10b所示的结构进行XY联合检测，XQ、YQ可以采用另一个图10a或图10b所示的结构进行XY联合检测。当图10a、图10b所示的逻辑结构用于XY、IQ联合检测时，信号X可以为XI+jXQ，信号Y可以为YI+jYQ。XI+jXQ、YI+jYQ可以采用一个图10a或图10b所示的结构进行XY、IQ联合检测。
下面分别对单子载波和双子载波场景中采用联合检测的效果进行说明。图11为本发明实施例提供的联合检测OSNR代价曲线图。如图11所示，实线为单子载波场景中采用XY联合检测的OSNR代价曲线，虚线为单子载波场景中采用XY独立检测的OSNR代价曲线。单子载波的场景中，联合检测和独立检测比较，SOP为零度时的最大OSNR值基本不变，采用联合检测无明显收益，但其他SOP角度的OSNR代价值都下降了。图12为本发明实施例提供的联合检测OSNR代价曲线图。如图12所示，如图12所示，实线为双子载波场景中采用XY联合检测的OSNR代价曲线，虚线为双子载波场景中采用XY独立检测的OSNR代价曲线。双子载波的场景中，联合检测和独立检测比较，任何的SOP角度下采用联合检测都有收益，提升了系统的性能。
图13a为本发明实施例提供的一种联合检测中滤波系数生成的逻辑结构示意图。如图13a所示，以XY联合检测，输入信号XI，YI为例，对滤波系数Tap11、Tap12、Tap22的计算过程进行详细说明。
如果相位恢复813或913输出信号为XI(k)，其中k是时间序号。XI(k)对应的原始发送信号为DXI(k)，DXI(k)可以来源于已知发射机的原始数据(例如训练序列)，也可以来自对XI(k)的判决。信号X的噪声值NoiseXI(k)＝XI(k)-DXI(k)，同样的，如果相位恢复813或913输出信号为YI(k)，其中k是时间序号。YI(k)对应的原始发送信号为DYI(k)，DYI(k)可以来源于已知发送机的原始数据(例如训练序列)，也可以来自对YI(k)的判决。信号Y的噪声值NoiseYI(k)＝YI(k)-DYI(k)。
下面介绍通过NoiseXI(k)，NoiseYI(k)计算Tap11，Tap12，Tap22。假定Tap11，Tap12，Tap22抽头长度为N，相关矩阵计算L×L的矩阵，其中，L为相关延时长度，可以大于或者等于N。
NoiseXI(k)的自相关矩阵B11
Figure PCTCN2020092635-appb-000010
其中，NoiseXI(k)延时k的自相关Rxx(k)＝Σ iNoiseXI(i)*(NoiseXI(i+k)) *。
由于NoiseXI(k)是实数，上面表达式可以简单记为
Figure PCTCN2020092635-appb-000011
同样的，NoiseYI(k)的自相关矩阵：
Figure PCTCN2020092635-appb-000012
其中，NoiseYI(k)延时k的自相关Ryy(k)＝Σ iNoiseYI(i)*(NoiseYI(i+k)) *。
NoiseXI(k)和NoiseYI(k)的互相关矩阵：
Figure PCTCN2020092635-appb-000013
B 21＝B 12 H
其中，NoiseXI(k)和NoiseYI(k)延时k的互相关Rxy(k)＝Σ iNoiseXI(i)*(NoiseYI(i+k)) *。B21是B12埃尔米特矩阵。
同样，由于NoiseYI(k)是实数，
B 21＝B 12
通过矩阵计算得到C11
Figure PCTCN2020092635-appb-000014
C11是自共轭矩阵，可以写成下面的形式
Figure PCTCN2020092635-appb-000015
根据C11计算Tap11：
Figure PCTCN2020092635-appb-000016
Figure PCTCN2020092635-appb-000017
Figure PCTCN2020092635-appb-000018
U＝(unn u)
将U表示为
U＝(u 0 u 1 u 2 … u N-1)
U即为Tap11。
与根据C11计算Tap11类似，根据B22计算得到Tap22。
由U可以得到：
Figure PCTCN2020092635-appb-000019
计算
Figure PCTCN2020092635-appb-000020
U 12也是埃尔米特矩阵，可以写成下面的形式
Figure PCTCN2020092635-appb-000021
得到Tap12为：
(w 0 w 1 … w L-1)
如果是XY、IQ联合检测，输入信号即为以X＝XI+jXQ，Y＝YI+jYQ。相位恢复813或913输出信号为X(k)＝XI(k)+jXQ(k)，其中k是时间序号。X(k)对应的原始发送信号为DXI(k)+jDXQ(k)，DXI(k)+jDXQ(k)可以来源于已知反射机的原始数据(例如训练序列)，也可以来自对X(k)的判决。信号X的噪声值NoiseX(k)＝(XI(k)-DXI(k))+j(XQ(k)-DXQ(k))。同样的，相位恢复813或913输出信号为Y(k)＝YI(k)+jYQ(k)，其中k是时间序号。Y(k)对应的原始发送信号为DYI(k)+jDYQ(k)，DYI(k)+jDYQ(k)可以来源于已知反射机的原始数据(例如训练序列)，也可以来自对Y(k)的判决。信号Y的噪声值NoiseY(k)＝(YI(k)-DYI(k))+j(YQ(k)-DYQ(k))。与上面的XY联合检测过程类似，相关矩阵中的部分相关函数改为复数即可。
图13b为本发明实施例提供的另一种联合检测中滤波系数生成的逻辑结构示意图。图13b的实现方式与图13a类似，将图13a输入的信号X的噪声值和信号Y的噪声值交换位置即可得到图13b的实施方式，此处不再赘述。
在上述实施例中，可以全部或部分地通过软件、硬件、固件或者其任意组合来实现。当使用软件实现时，可以全部或部分地以程序产品的形式实现。所述程序产品包括一个或多个指令。在光收发机上加载和执行所述程序指令时，全部或部分地产生按照本发明实施例所述的流程或功能。光收发机可以是光模块，具备光发送功能或光接收功能，还可以同时具备光发送和接收功能。所述指令可以存储在可读存储介质中，或者从一个设备的可读存储介质向另一个设备的可读存储介质传输。所述可读存储介质可以是光收发机机能够存取的任何可用介质或者是包含一个或多个可用介质集成的服务器、数据中心等数据存储设备。所述可用介质可以是磁性介质，(例如，软盘、硬盘、磁带)、光介质(例如，DVD)、或者半导体介质(例如固态硬盘Solid State Disk(SSD))等。
以上所述，仅为本发明的具体实施方式，但本发明的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明揭露的技术范围内，可轻易想到变化或替换，都应涵盖在本发明的保护范围之内。因此，本发明的保护范围应以所述权利要求的保护范围为准。

Claims (18)

  1. 一种光通信中信号发送的方法，其特征在于，所述方法包括：
    光发射机基于获取到的比特流生成第一子载波，所述第一子载波包括至少两路子载波；
    光发射机对所述第一载波中的第二子载波进行偏振态SOP旋转，使得所述第一子载波中存在至少两路具有相对SOP旋转角度的子载波，其中，所述第二子载波包括一路或多路子载波，所述相对SOP旋转角度不为零且不为90度的整数倍；
    光发射机将所述SOP旋转后的第一子载波调制到光信号上，将所述光信号发送出去。
  2. 如权利要求1所述的方法，其特征在于，所述相对SOP旋转角度为45度。
  3. 如权利要求1或2所述的方法，其特征在于，所述第二子载波包括一路子载波时，所述对所述第一载波中的第二子载波进行SOP旋转包括：
    通过公式
    Figure PCTCN2020092635-appb-100001
    对所述第一载波中的第二子载波进行SOP旋转，其中，Xin、Yin为所述SOP旋转前的第二子载波，Xout、Yout为所述SOP旋转后的第二子载波，α为所述SOP旋转的角度。
  4. 如权利要求1-3任一所述的方法，其特征在于，在所述SOP旋转之后，所述方法还包括：
    所述光发射机对所述SOP旋转之后的第一子载波进行频谱搬移。
  5. 如权利要求1-3任一所述的方法，其特征在于，在所述SOP旋转之前，所述方法还包括：
    所述光发射机对所述生成的第一子载波进行频谱搬移。
  6. 如权利要求4或5所述的方法，其特征在于，所述方法还包括：
    所述光发射机对经过所述SOP旋转和频谱搬移之后的第一子载波进行合波。
  7. 一种光发射机，其特征在于，所述光发射机包括数字信号处理器DSP和调制器，
    所述DSP，用于基于获取到的比特流生成第一子载波，所述第一子载波包括至少两路子载波；
    所述DSP，用于对所述第一载波中的第二子载波进行偏振态SOP旋转，使得所述第一子载波中存在至少两路具有相对SOP旋转角度的子载波，其中，所述第二子载波包括一路或多路子载波，所述相对SOP旋转角度不为零且不为90度的整数倍；
    所述调制器，用于将所述SOP旋转后的第一子载波调制到光信号上，将所述光信号发送出去。
  8. 如权利要求7所述的光发射机，其特征在于，所述相对SOP旋转角度为45度。
  9. 如权利要求8所述的光发射机，其特征在于，所述DSP，用于所述第二子载波包括一路子载波时，通过公式
    Figure PCTCN2020092635-appb-100002
    对所述第一载波中的第二子载波进行SOP旋转，其中，Xin、Yin为所述SOP旋转前的第二子载波，Xout、Yout为所述SOP旋转后的第二子载波，α为所述SOP旋转的角度。
  10. 如权利要求7-9任一所述的光发射机，其特征在于，所述DSP，还用于：
    在所述SOP旋转之后，对所述SOP旋转之后的第一子载波进行频谱搬移。
  11. 如权利要求7-9任一所述的光发射机，其特征在于，所述DSP，还用于：
    在所述SOP旋转之前，对所述获取的第一子载波进行频谱搬移。
  12. 如权利要求10或11所述的光发射机，其特征在于，所述DSP，还用于：
    对经过所述SOP旋转和频谱搬移之后的第一子载波进行合波。
  13. 一种光通信中信号接收的方法，其特征在于，所述方法包括：
    光接收机接收光信号，将所述光信号转换为电信号，其中，所述电信号包括第一信号和第二信号，所述第一信号和第二信号对应不同的偏振态；
    所述光接收机生成第一系数、第二系数和第三系数，基于所述第一系数对所述第一信号进行滤波，得到第三信号；基于所述第二系数对所述第二信号进行滤波，得到第四信号；基于所述第三系数对所述第二信号进行滤波，得到第五信号；
    所述光接收机对所述第三信号和所述第四信号进行求和，得到第七信号，根据所述第五信号和所述第七信号获取所述第一信号和所述第二信号的判决序列。
  14. 如权利要求13所述的方法，其特征在于，所述第一信号和第二信号分别具有至少两个子载波，所述至少两个子载波之间的相对偏振态SOP旋转角度不为零且不为90度的整数倍，使得所述第三系数不为零。
  15. 如权利要求13或14所述的方法，其特征在于，所述获取所述第一信号和所述第二信号的判决序列，包括：
    通过最小化代价函数获取所述第一信号和所述第二信号的判决序列。
  16. 一种光通信系统，其特征在于，所述光通信系统包括如权利要求7-12任一所述的光发射机。
  17. 一种可读存储介质，包括指令，当其在光收发机上运行时，使得光收发机执行如权利要求1-6、13-15任意一项所述的方法。
  18. 一种包含指令的程序产品，当其在光收发机上运行时，使得光收发机执行如权利要求1-6、13-15任意一项所述的方法。
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