WO2021143171A1 - 一种相干发射机、控制相干发射机的方法及相干收发系统 - Google Patents

一种相干发射机、控制相干发射机的方法及相干收发系统 Download PDF

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WO2021143171A1
WO2021143171A1 PCT/CN2020/115479 CN2020115479W WO2021143171A1 WO 2021143171 A1 WO2021143171 A1 WO 2021143171A1 CN 2020115479 W CN2020115479 W CN 2020115479W WO 2021143171 A1 WO2021143171 A1 WO 2021143171A1
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signal
phase
sub
optical
modulation
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PCT/CN2020/115479
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English (en)
French (fr)
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李芮
孙旭
宋小鹿
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华为技术有限公司
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Priority to EP20914212.4A priority Critical patent/EP4075689A4/en
Publication of WO2021143171A1 publication Critical patent/WO2021143171A1/zh
Priority to US17/865,835 priority patent/US11888529B2/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
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/548—Phase or frequency modulation
    • H04B10/556—Digital modulation, e.g. differential phase shift keying [DPSK] or frequency shift keying [FSK]
    • 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
    • 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
    • H04B10/50—Transmitters
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • H04B10/505—Laser transmitters using external modulation
    • H04B10/5053—Laser transmitters using external modulation using a parallel, i.e. shunt, combination of modulators
    • 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
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • H04B10/505—Laser transmitters using external modulation
    • H04B10/5057—Laser transmitters using external modulation using a feedback signal generated by analysing the optical output
    • 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
    • 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
    • H04B10/6165—Estimation of the phase of the received optical signal, phase error estimation or phase error correction

Definitions

  • This application relates to the field of optical communications, and in particular to a coherent transmitter, a method for controlling a coherent transmitter, and a coherent transceiver system.
  • the direct modulation mode is limited by the device bandwidth, and it has been difficult to meet the needs of single-wave 200G or even single-wave 400G.
  • the coherent modulation mode is favored because of its high spectral efficiency and high single-wave modulation rate, and will gradually be applied to short-distance optical transmission systems.
  • Coherent modulation requires a 90° phase shift between In-phase and Quadrature (I/Q) signals.
  • the usual design is to realize by loading a certain voltage on the heater of the integrated chip.
  • the embodiments of the present application provide a coherent transmitter, a method for controlling a coherent transmitter, and a coherent transceiver system.
  • an embodiment of the present application provides a coherent transmitter.
  • the coherent transmitter includes a first signal modulation module, a first photo-diode (Photo-Diode, PD), and a controller.
  • the first signal modulation module, the first PD, and the controller are connected to each other.
  • the first signal modulation module includes a first signal modulation module.
  • the first beam splitter splits the input first optical signal to obtain the second optical signal and the third optical signal.
  • the first modulator modulates the second optical signal to obtain the first modulated signal.
  • the second modulator modulates the third optical signal to obtain a second modulated signal.
  • the phase shift adjustment unit performs phase adjustment on the first sub-signal in the first modulation signal, and performs phase adjustment on the fourth sub-signal in the phase-adjusted first sub-signal.
  • the first beam combiner combines the second sub-signal in the first modulated signal and the phase-adjusted fourth sub-signal to obtain the first combined signal.
  • the second beam combiner combines the third sub-signal and the second modulated signal in the phase-adjusted first sub-signal to obtain a second combined signal.
  • the first PD performs photoelectric conversion on the first combined signal to obtain the first electrical signal.
  • the controller controls the voltage loaded on the phase shift adjustment unit according to the first electrical signal, so that the first phase difference is within a preset range.
  • the coherent transmitter includes I/Q two-way signal modulation, the first modulator is located on the Q path, and the second modulator is located on the I path.
  • the first modulation signal and the second modulation signal have the same phase.
  • part of the light on the Q path of the coherent transmitter is used for phase adjustment and coherently modulated with the light on the I path, and the other part of the light on the Q path is used to monitor whether the phase difference after phase adjustment is within the preset range. If not, the controller can adjust the voltage loaded on the phase shift adjustment unit to adjust the phase difference within the preset range.
  • the structure and control method of the coherent transmitter do not require complex electrical devices such as Digital-to-Analog Converter (DAC) and Analog-to-Digital Converter (ADC) to facilitate integration , And the device cost is lower, the power consumption is smaller.
  • DAC Digital-to-Analog Converter
  • ADC Analog-to-Digital Converter
  • the phase shift adjustment unit includes a phase shifter, a second beam splitter, and a third beam splitter, and the voltage controlled by the controller is applied to the phase shifter.
  • the second beam splitter splits the first modulated signal to obtain the first sub-signal and the second sub-signal.
  • the phase shifter adjusts the phase of the first sub-signal.
  • the third beam splitter splits the phase-adjusted first sub-signal to obtain a third sub-signal and a fourth sub-signal.
  • the phase shifter then adjusts the phase of the fourth sub-signal.
  • phase shift adjustment unit a specific implementation of the phase shift adjustment unit is provided, that is, the optical signal is divided into two paths by arranging beam splitters at the front end and the back end of the phase shifter, one is used for coherent modulation, and the other is used for coherent modulation.
  • One way is used for real-time monitoring of phase changes, which improves the feasibility of this solution.
  • the coherent transmitter further includes a light source, a fourth beam splitter, a second signal modulation module, a second PD and a polarization conversion device, a first signal modulation module and a second signal modulation module Having the same structure and function, the second signal modulation module, the second PD and the controller are connected to each other.
  • the light source outputs an optical signal.
  • the fourth beam splitter splits the optical signal to obtain the first optical signal and the fourth optical signal, and transmits the first optical signal to the first signal modulation module, and transmits the fourth optical signal to the second signal modulation module.
  • the second signal modulation module outputs the third combined signal and the fourth combined signal according to the fourth optical signal, and the polarization mode of the second combined signal and the third combined signal is Transverse Electric (TE).
  • the polarization conversion device combines the second combined signal and the third combined signal to obtain the fifth combined signal, and converts the polarization mode of the second combined signal or the third combined signal into a transverse magnetic field polarization (Transverse Magnetic, TM).
  • Transverse Magnetic, TM Transverse Magnetic
  • the second PD is used to perform photoelectric conversion on the fourth combined signal to obtain the second electrical signal.
  • the controller is used for controlling the voltage loaded on the phase shift adjustment unit of the second signal modulation module according to the second electrical signal.
  • the coherent transmitter may also support dual polarization modes, that is, the polarization modes of the output signals of the first signal modulation module and the second signal modulation module are different, which improves the scalability of the solution.
  • the controller is specifically configured to:
  • the first current value of the first electrical signal If the first current value is greater than the current threshold, the voltage loaded on the phase shifter is increased. After that, the second current value of the first electrical signal is acquired. If the second current value is less than the first current value and greater than the current threshold value, the voltage is continuously increased so that the second current value is less than or equal to the current threshold value. If the second current value is greater than the first current value, the voltage is reduced so that the second current value is less than or equal to the current threshold. It should be noted that when the phase shift achieved by the phase shifter is 90°, the current generated on the first PD is the smallest, and the more the phase shift deviates from 90°, the greater the current generated on the first PD.
  • the correspondence between the voltage loaded on the phase shifter and the current on the first PD may be recorded through experiments to obtain a correspondence table, and the controller is specifically used for:
  • the controller determines the target voltage corresponding to the target current according to the correspondence table. Wherein, the target current is less than or equal to the current threshold. Furthermore, the controller adjusts the voltage applied to the phase shifter to the target voltage.
  • the proportion of the second sub-signal in the first modulated signal is the first proportion
  • the proportion of the fourth sub-signal in the phase-adjusted first sub-signal is the second proportion.
  • Ratio there is a corresponding relationship between the first ratio and the second ratio.
  • the first ratio and the second ratio satisfy the above-mentioned corresponding relationship, that is, the power of the two paths of light input to the first beam combiner Similarly, the current generated on the first PD is minimized when the phase shift is 90°, and the energy consumption of the first PD is reduced.
  • the modulation modes of the first modulator and the second modulator include Amplitude Shift Keying (ASK).
  • ASK Amplitude Shift Keying
  • the types of the first modulator and the second modulator include, but are not limited to, Micro-ring Modulator (MRM), Mach-Zinde modulator, waveguide type electro-optical absorption modulator, and Bragg grating modulator.
  • MRM Micro-ring Modulator
  • Mach-Zinde modulator Mach-Zinde modulator
  • waveguide type electro-optical absorption modulator and Bragg grating modulator.
  • Bragg grating modulator Bragg grating modulator
  • the types of light sources include but are not limited to distributed feedback (Distributed Feedback Laser, DFB) lasers, quantum dot comb lasers, and indium phosphide lasers, and the types of polarization conversion devices include reverse Polarization Splitter and Rotator (PSR) and grating coupler.
  • DFB distributed Feedback Laser
  • PSR reverse Polarization Splitter and Rotator
  • multiple types of light sources and multiple types of polarization conversion devices are provided, which improves the scalability of the solution.
  • the coupling mode for coupling the optical signal to the fourth beam splitter and the coupling mode for coupling the fifth combined signal to the optical fiber include but not limited to side coupling, vertical grating coupling, and lens refraction coupling .
  • a variety of light input and light output coupling modes are provided, which improves the scalability of the solution.
  • the first PD and the first signal modulation module are integrated on an optical chip, and the technology of integration on the optical chip includes but not limited to silicon-on-insulator (SOI) Integration, lithium niobate thin film integration and indium phosphide integration.
  • the first PD may also be integrated with the controller on a printed circuit board (Printed Circuit Board, PCB).
  • PCB printed Circuit Board
  • the first PD can be integrated with the first signal modulation module on the optical chip, or can be integrated with the controller on the PCB, which further improves the scalability of the solution.
  • an embodiment of the present application provides a method for controlling a coherent transmitter.
  • the coherent transmitter includes a first signal modulation module, a first PD, and a controller, and the first signal modulation module, the first PD, and the controller are connected to each other ,
  • the first signal modulation module includes a first modulator, a second modulator, a first beam splitter, a phase shift adjustment unit, a first beam combiner and a second beam combiner.
  • the input first optical signal is split by the first beam splitter to obtain the second optical signal and the third optical signal.
  • the second optical signal is modulated by the first modulator to obtain a first modulated signal
  • the third optical signal is modulated by the second modulator to obtain a second modulated signal.
  • the first modulated signal and the second modulated signal have the same phase.
  • the phase shift adjustment unit performs phase adjustment on the first sub-signal in the first modulation signal, and performs phase adjustment on the fourth sub-signal in the phase-adjusted first sub-signal.
  • the second sub-signal and the phase-adjusted fourth sub-signal in the first modulated signal are combined by the first beam combiner to obtain the first combined signal.
  • the third sub-signal and the second modulated signal in the phase-adjusted first sub-signal are combined by the second beam combiner to obtain a second combined signal.
  • the first electrical signal is obtained by photoelectric conversion of the first combined signal by the first PD.
  • the voltage applied to the phase shift adjustment unit is controlled by the controller and according to the first electrical signal, so that the first phase difference between the phase-adjusted first sub-signal and the first modulation signal is within a preset range.
  • the phase shift adjustment unit includes a phase shifter, a second beam splitter, and a third beam splitter, the voltage is applied to the phase shifter, and the method further includes:
  • the first modulated signal is split by the second beam splitter to obtain the first sub-signal and the second sub-signal.
  • the phase of the first sub-signal is adjusted by the phase shifter.
  • the first sub-signal after the phase adjustment is split by the third beam splitter to obtain the third sub-signal and the fourth sub-signal.
  • the phase of the fourth sub-signal is adjusted by the phase shifter.
  • the coherent transmitter further includes a light source, a fourth beam splitter, a second signal modulation module, a second PD and a polarization conversion device, a first signal modulation module and a second signal modulation module Having the same structure and function, the second signal modulation module, the second PD, and the controller are connected to each other, and the method further includes:
  • the light signal is output through the light source.
  • the optical signal is split by the fourth beam splitter to obtain the first optical signal and the fourth optical signal, and the first optical signal is transmitted to the first signal modulation module, and the fourth optical signal is transmitted to the second signal modulation module.
  • the second signal modulation module outputs the third combined signal and the fourth combined signal according to the fourth optical signal, and the polarization mode of the second combined signal and the third combined signal is TE.
  • the second combined signal and the third combined signal are combined by the polarization conversion device to obtain the fifth combined signal, and the polarization mode of the second combined signal or the third combined signal is converted into TM.
  • the second PD is used to perform photoelectric conversion on the fourth combined signal to obtain the second electrical signal.
  • the voltage applied to the phase shift adjustment unit of the second signal modulation module is controlled by the controller and according to the second electrical signal.
  • controlling the voltage applied to the phase shift adjustment unit by the controller and according to the first electrical signal includes:
  • the voltage loaded on the phase shifter is increased.
  • the second current value of the first electrical signal If the second current value is less than the first current value and greater than the current threshold value, the voltage is continuously increased so that the second current value is less than or equal to the current threshold value. If the second current value is greater than the first current value, the voltage is reduced so that the second current value is less than or equal to the current threshold.
  • controlling the voltage applied to the phase shift adjustment unit by the controller and according to the first electrical signal includes:
  • a corresponding relationship table is obtained, and the corresponding relationship table includes the corresponding relationship between the voltage loaded on the phase shifter and the current value of the first electrical signal.
  • the target voltage corresponding to the target current value is determined according to the correspondence table, and the target current value is less than or equal to the current threshold. Adjust the voltage loaded on the phase shifter to the target voltage.
  • the proportion of the second sub-signal in the first modulated signal is the first proportion
  • the proportion of the fourth sub-signal in the phase-adjusted first sub-signal is the second proportion.
  • Ratio there is a corresponding relationship between the first ratio and the second ratio
  • the modulation modes of the first modulator and the second modulator include ASK, and the types of the first modulator and the second modulator include MRM, Mach-Zinde modulator, and waveguide electro-optic Absorption modulator and Bragg grating modulator.
  • the types of light sources include DFB lasers, quantum dot comb lasers, and indium phosphide lasers, and the types of polarization conversion devices include reverse PSR and grating couplers.
  • the coupling manner of coupling the optical signal to the fourth beam splitter and the coupling manner of coupling the fifth combining signal to the optical fiber include edge coupling, vertical grating coupling, and lens refraction coupling.
  • the first PD and the first signal modulation module are integrated on an optical chip, and the technologies integrated on the optical chip include SOI integration, lithium niobate thin film integration, and indium phosphide integration.
  • the first PD can also be integrated with the controller on the PCB.
  • an embodiment of the present application provides a coherent transceiver system, including a light source, a coherent receiver, and a coherent transmitter as shown in any implementation manner in the first aspect.
  • the light source is used to output light signals.
  • the coherent transmitter is used to output the modulated signal.
  • the coherent receiver is used to mix the optical signal and the modulated signal, and demodulate the mixed signal.
  • the coherent transceiver system further includes a beam splitter.
  • the beam splitter is used to split the optical signal to obtain the first optical signal and the second optical signal.
  • the coherent transmitter is used to modulate the first optical signal to obtain a modulated signal, and output the modulated signal.
  • the coherent receiver is used to mix the second optical signal and the modulated signal, and demodulate the mixed signal.
  • an embodiment of the present application provides a coherent transmitter.
  • the coherent transmitter includes a first signal modulation module, a first PD, and a controller.
  • the first signal modulation module, the first PD and the controller are connected to each other.
  • the first signal modulation module includes a first modulator, a second modulator, The first beam splitter, the phase shifter, the second beam splitter, the third beam splitter, the first beam combiner and the second beam combiner.
  • the first beam splitter splits the input first optical signal to obtain the second optical signal and the third optical signal.
  • the first modulator modulates the second optical signal to obtain the first modulated signal.
  • the second modulator modulates the third optical signal to obtain a second modulated signal, and the first modulated signal and the second modulated signal have the same phase.
  • the second beam splitter splits the first modulated signal to obtain the first sub-signal and the second sub-signal.
  • the phase shifter adjusts the phase of the first sub-signal, and there is a first phase difference between the phase-adjusted first sub-signal and the first modulation signal.
  • the third beam splitter splits the phase-adjusted first sub-signal to obtain a third sub-signal and a fourth sub-signal.
  • the phase shifter then adjusts the phase of the fourth sub-signal.
  • the phase-adjusted fourth sub-signal has a second phase difference with the first modulation signal, and the second phase difference is twice the first phase difference.
  • the first beam combiner combines the second sub-signal in the first modulated signal and the phase-adjusted fourth sub-signal to obtain the first combined signal.
  • the second beam combiner combines the third sub-signal and the second modulated signal in the phase-adjusted first sub-signal to obtain a second combined signal.
  • the first PD performs photoelectric conversion on the first combined signal to obtain the first electrical signal.
  • the controller controls the voltage loaded on the phase shift adjustment unit according to the first electrical signal, so that the first phase difference is within a preset range.
  • the coherent transmitter includes I/Q two-way signal modulation, where a part of the light on the Q path is used for phase adjustment and coherent modulation with the light on the I path, and the other part of the light on the Q path is used for phase monitoring. Whether the adjusted phase difference is within the preset range, if not, the controller can adjust the voltage loaded on the phase shift adjustment unit to adjust the phase difference within the preset range. Through this monitoring and adjustment method, without affecting the service transmission, the phase difference after phase adjustment can be monitored in real time, and the phase difference can be controlled within the preset range, which improves the phase adjustment accuracy and makes the coherent design modulation Coherent signal quality is better.
  • the structure and control method of the coherent transmitter do not require complex electrical devices such as ADCs and DACs, which facilitates integration, and has lower device costs and lower power consumption.
  • FIG. 1 is a schematic structural diagram of a coherent transmitter provided by an embodiment of this application.
  • FIG. 2 is a schematic diagram of the simulation relationship between the current generated on the first PD and the phase shift
  • Figure 3 is an operation flow chart of the controller controlling the voltage
  • FIG. 5 is a schematic structural diagram of another coherent transmitter provided by an embodiment of this application.
  • FIG. 6 is a schematic diagram of a method for controlling a coherent transmitter in an embodiment of this application.
  • FIG. 7 is a schematic structural diagram of a coherent transceiver system in this application.
  • the embodiments of the present application provide a coherent transmitter, a method for controlling a coherent transmitter, and a coherent transceiver system. Without affecting service transmission, the phase difference after phase adjustment can be monitored in real time, and the phase difference can be controlled within a preset range, which improves the accuracy of phase adjustment and makes the quality of the coherent signal modulated by the coherent design better.
  • the structure of the coherent transmitter does not require complex electrical devices such as ADCs and DACs, which is convenient for integration, and has lower device costs and lower power consumption.
  • the terms "first”, “second”, “third”, “fourth”, etc. (if any) in the description and claims of this application and the above-mentioned drawings are used to distinguish similar objects, without having to use To describe a specific order or sequence.
  • FIG. 1 is a schematic structural diagram of a coherent transmitter provided by an embodiment of this application.
  • the coherent transmitter includes a first signal modulation module 10, a first photo-diode (PD) 20 and a controller 30.
  • the first signal modulation module 10 includes a first beam splitter 101, a first modulator 102, a second modulator 103, a second beam splitter 104, a phase shifter 105, a third beam splitter 106, and a first combiner.
  • the beamer 107 and the second beam combiner 108 includes a first beam splitter 101, a first modulator 102, a second modulator 103, a second beam splitter 104, a phase shifter 105, a third beam splitter 106, and a first combiner.
  • the beamer 107 and the second beam combiner 108 includes a first beam splitter 101, a first modulator 102, a second modulator 103, a second beam splitter 104, a phase shifter 105, a
  • the first beam splitter 101 splits the input first optical signal to obtain a second optical signal and a third optical signal. It can be understood that the coherent transmitter needs to divide the signal into two paths (I path and Q path) and modulate them separately, that is, the second optical signal is used for Q path modulation, and the third optical signal is used for I path modulation.
  • the first modulator 102 modulates the second optical signal to obtain the first modulated signal.
  • the second modulator 103 modulates the third optical signal to obtain a second modulated signal.
  • the structure and modulation principle of the first modulator 102 and the second modulator 103 are the same.
  • the first modulator 102 and the second modulator 103 respectively modulate the input optical signals by loading respective independent (same frequency and clock synchronization) radio frequency driving electrical signals (RF driving signals).
  • the coherent modulation implemented by the coherent transmitter is N2-Quadrature Amplitude Modulation (N2-QAM)
  • the modulation performed by the first modulator 102 and the second modulator 103 is N-level Amplitude Shift Keying (N-Amplitude Shift Keying, N-ASK).
  • N-QAM N2-Quadrature Amplitude Modulation
  • the first modulation signal and the second modulation signal are independent 4-ASK signals.
  • the first modulation signal and the second modulation signal have the same phase.
  • the second beam splitter 104 splits the first modulated signal to obtain the first sub-signal and the second sub-signal.
  • the phase shifter 105 adjusts the phase of the first sub-signal.
  • the third beam splitter 106 splits the phase-adjusted first sub-signal to obtain a third sub-signal and a fourth sub-signal.
  • the phase shifter 105 adjusts the phase of the fourth sub-signal. It should be noted that there is a phase difference between the phase-adjusted signal and the signal before the phase-adjustment. In an ideal state, the phase difference is 90°, that is, the phase-adjusted first sub-signal is between the first sub-signal and the first modulated signal. There is a first phase difference.
  • the third sub-signal and the fourth sub-signal also have a first phase difference with the first signal.
  • the fourth sub-signal has a second phase difference with the first modulation signal, and the second phase difference is twice the first phase difference. For example, if the first phase difference is 90°, then the second phase difference is 180°.
  • the second beam splitter 104, the phase shifter 105, and the third beam splitter 106 may be integrated as a phase shift adjustment unit.
  • the second beam combiner 108 combines the third sub-signal and the second modulated signal to obtain a second combined signal and output it. It can be understood that there is a first phase difference between the third sub-signal and the second modulated signal. If the coherent transmitter implements 16-QAM, then the second combined signal obtained by combining two orthogonal 4-ASK signals is a 16-QAM signal.
  • the first beam combiner 107 combines the second sub-signal and the phase-adjusted fourth sub-signal to obtain the first combined signal.
  • the first PD (20) performs photoelectric conversion on the first combined signal to obtain the first electrical signal.
  • the controller 30 controls the voltage applied to the phase shifter 105 according to the first electrical signal to control the first phase difference within a preset range (close to 90°).
  • FIG. 2 is a schematic diagram of the simulation relationship between the current generated on the first PD and the phase shift.
  • the phase shift achieved by the phase shifter 105 is 90°
  • the current generated on the first PD (20) is the smallest, and the more the phase shift deviates from 90°, the greater the current generated on the first PD (20) is. Big.
  • the phase shift achieved by the phase shifter 105 is 90° (the first phase difference is 90°)
  • the second phase difference is 180°
  • the first combiner after the first combiner 107 is combined
  • the intensity of the signal due to light interference is 0, so the current generated by the first PD should also be 0.
  • the current on the first PD (20) is not necessarily 0, but it must be the smallest. That is to say, if the current generated on the first PD (20) is less than the preset value, then the phase shift can be guaranteed to be within the preset range (approximately 90°).
  • the preset current can be set to 50 ⁇ A. If the current value generated on the first PD is less than 50 ⁇ A, the phase shift is 88.5°-91.5 Within the preset range of °, the quality of the modulated signal is within the acceptable range at this time. It can be seen that the controller 30 can determine whether the current phase shift is within the preset range by reading the current value generated on the first PD (20), and if not, adjust the voltage applied to the phase shifter to Control the phase shift within the preset range.
  • the controller 30 can specifically have a variety of different control methods, which will be introduced separately as follows:
  • the first one is to record the correspondence between the voltage loaded on the phase shifter 105 and the current on the first PD (20) through experiments to obtain the correspondence table.
  • the controller 30 may obtain the correspondence table. If the current value generated on the first PD (20) is greater than the current threshold, the controller 30 determines the target voltage corresponding to the target current according to the correspondence table. Wherein, the target current is less than or equal to the current threshold. Furthermore, the controller 30 adjusts the voltage applied to the phase shifter 105 to the target voltage.
  • FIG. 3 is the operation flow chart of the controller controlling the voltage. The operation flow will be described in detail below:
  • the controller 30 reads the real-time current of the first electrical signal generated by the first PD (20).
  • step 305 Determine whether the real-time current I2 is less than the real-time current I1 and greater than the current threshold I0; if yes, repeat step 303 so that the real-time current I2 is less than or equal to the current threshold I0; if not, perform step 306.
  • step 303 is used to test whether the phase shift is large or small. If the real-time current starts to decrease after increasing the voltage, it is proved that the real-time current is greater than the current threshold because the phase shift is less than the preset range, so continue to increase the voltage until the real-time current is less than or equal to the current threshold. If the real-time current is still increasing after the voltage is increased, it proves that the real-time current is greater than the current threshold because the phase shift is greater than the preset range. Then the voltage needs to be reduced until the real-time current is less than or equal to the current threshold.
  • phase shifter 105 there may be multiple types of the phase shifter 105, for example, it may be a heater, and there are two common ways to change the phase through the heat regulator as follows. First, the optical waveguide is covered with metal, and the metal is heated by applying a voltage to the metal to change the refractive index of the optical waveguide, thereby changing the phase. Second, carry out carrier doping in and around the optical waveguide of the modulator (such as silicon-optical integrated optical waveguide and phosphorous atoms around it), and the carrier concentration in the waveguide can be changed by applying voltage, and the refraction of the optical waveguide can also be changed. Rate, thereby changing the phase.
  • the phase shifter 105 may be a heater, and there are two common ways to change the phase through the heat regulator as follows. First, the optical waveguide is covered with metal, and the metal is heated by applying a voltage to the metal to change the refractive index of the optical waveguide, thereby changing the phase. Second, carry out carrier doping in and around the optical waveguide of
  • the power of the two lights input to the first beam combiner 107 should be as close as possible.
  • it can be achieved by setting the splitting ratio of the second beam splitter 104 and the third beam splitter 106.
  • the proportion of the second sub-signal in the first modulation signal is the first proportion (x%)
  • the proportion of the fourth sub-signal in the first sub-signal after the phase adjustment is the second proportion (y%)
  • the design of different light splitting ratios can be realized by changing the length of the waveguide coupling region.
  • the coherent transmitter processing in the embodiment of the present application may support the single polarization mode as shown in FIG. 1 as well as the dual polarization mode, which will be further described below:
  • FIG. 5 is a schematic structural diagram of another coherent transmitter provided by an embodiment of this application.
  • the coherent transmitter further includes a second signal modulation module 60 and a polarization conversion device 80, so that the first signal modulation module 10 and the second signal modulation module 60 have Different polarization modes.
  • the coherent transmitter may also include a light source 40, a fourth beam splitter 50, and a second PD (70).
  • the first signal modulation module 10 and the second signal modulation module 60 have the same structure and function, and the details are not repeated here.
  • the light source 40 outputs a light signal. Furthermore, the fourth beam splitter 50 splits the optical signal to obtain the first optical signal and the fourth optical signal, and transmits the first optical signal to the first signal modulation module 10, and transmits the fourth optical signal to the second signal. Modulation module 60.
  • the second signal modulation module 60 outputs the third combined signal and the fourth combined signal according to the fourth optical signal.
  • the third combined signal corresponds to the second combined signal in the embodiment shown in FIG. 2
  • the fourth combined signal corresponds to the first combined signal in the embodiment shown in FIG. 2.
  • the second PD (70) performs photoelectric conversion on the fourth combined signal to obtain a second electrical signal.
  • the controller 30 can control the voltage applied to the phase shifter of the second signal modulation module 60 according to the second electrical signal.
  • the control method of the controller is similar to the introduction in the foregoing embodiment, and will not be repeated here.
  • the polarization conversion device 80 converts the polarization mode of the second combined signal or the third combined signal, and combines the second combined signal and the third combined signal to obtain a fifth combined signal.
  • the original polarization modes of the second combined signal and the third combined signal are both Transverse Electric (TE).
  • TE Transverse Electric
  • the second combined signal or the third combined signal is The polarization mode is converted to Transverse Magnetic (TM).
  • the types of the first modulator 102 and the second modulator 103 include, but are not limited to, Micro-ring Modulator (MRM), Mach-Zinde modulator, waveguide type electro-optic absorption modulator, and Bragg grating modulation ⁇
  • MRM Micro-ring Modulator
  • Mach-Zinde modulator Mach-Zinde modulator
  • waveguide type electro-optic absorption modulator waveguide type electro-optic absorption modulator
  • the type of the light source 40 in this embodiment includes, but is not limited to, a distributed feedback (Distributed Feedback Laser, DFB) laser, a quantum dot comb laser, an indium phosphide laser, and the like.
  • DFB distributed Feedback Laser
  • the light source 40 may be integrated with the first signal modulation module 10 and the second signal modulation module 60 on the same chip.
  • the light source 40 may also be used as an off-chip light source.
  • the first PD (20), the second PD (70), the first signal modulation module 10, and the second signal modulation module 60 can be integrated on the same chip.
  • the first PD (20) and the second PD (70) are also It can be integrated with the control circuit on a printed circuit board (Printed Circuit Board, PCB).
  • the technologies integrated on the chip include, but are not limited to, silicon-on-insulator (SOI) integration, lithium niobate film integration, and indium phosphide integration.
  • the coupling manner in which the optical signal emitted by the light source 40 is coupled to the fourth beam splitter 50 and the coupling manner in which the fifth combined signal output by the polarization conversion device 80 is coupled to the optical fiber includes, but is not limited to, side coupling, vertical grating coupling, and Lens refraction coupling, etc.
  • the type of the polarization conversion device 80 includes, but is not limited to, a reverse polarization splitter and rotator (PSR) and a grating coupler.
  • PSR reverse polarization splitter and rotator
  • grating coupler a grating coupler
  • the types of the second beam splitter 104 and the third beam splitter 106 include, but are not limited to, a multi-mode interferometer (MMI) and a Y-branch (Y-branch).
  • MMI multi-mode interferometer
  • Y-branch Y-branch
  • the coherent transmitter includes I/Q two-way signal modulation, where a part of the light on the Q path is used for phase adjustment and coherent modulation with the light on the I path, and the other part of the light on the Q path is used for phase monitoring.
  • the controller can adjust the voltage loaded on the phase shift adjustment unit to adjust the phase difference within the preset range.
  • the structure and control method of the coherent transmitter of this solution do not require complex electrical devices such as Digital-to-Analog Converter (DAC) and Analog-to-Digital Converter (ADC). , It is easy to integrate, and the device cost is lower, and the power consumption is smaller.
  • DAC Digital-to-Analog Converter
  • ADC Analog-to-Digital Converter
  • FIG. 6 is a schematic diagram of a method for controlling a coherent transmitter in an embodiment of this application.
  • the coherent transmitter includes a first signal modulation module, a first photodiode PD, and a controller.
  • the first signal modulation module, the first PD, and the controller are connected to each other.
  • the first signal modulation module includes a first modulator, a second The modulator, the first beam splitter, the phase shift adjustment unit, the first beam combiner and the second beam combiner.
  • the method of controlling a coherent transmitter includes the following steps.
  • the second optical signal is modulated by the first modulator to obtain a first modulated signal
  • the third optical signal is modulated by the second modulator to obtain the second modulated signal
  • the structure and modulation principle of the first modulator and the second modulator are the same. And, the first modulation signal and the second modulation signal have the same phase.
  • phase difference there is a first phase difference between the phase-adjusted first sub-signal and the first modulation signal, and there is a second phase difference between the phase-adjusted fourth sub-signal and the first modulation signal, and the second phase is The difference is twice the first phase difference.
  • the phase shift adjustment unit may include a phase shifter, a second beam splitter and a third beam splitter, and the voltage is applied to the phase shifter.
  • the first modulated signal is split by the second beam splitter to obtain the first sub-signal and the second sub-signal.
  • the phase of the first sub-signal is adjusted by the phase shifter.
  • the first sub-signal after the phase adjustment is split by the third beam splitter to obtain the third sub-signal and the fourth sub-signal.
  • the phase of the fourth sub-signal is adjusted by the phase shifter.
  • the coherent transmitter in this embodiment may specifically be the coherent transmitter in any of the embodiments shown in FIG. 1 and FIG. 5.
  • FIG. 7 is a schematic structural diagram of a coherent transceiver system in this application.
  • the coherent transceiver system includes a light source 701, a coherent transmitter 702, and a coherent receiver 703.
  • the light source 701 outputs an optical signal.
  • the coherent transmitter 702 outputs a modulated signal.
  • the coherent receiver 703 mixes the optical signal output by the light source 701 and the modulated signal output by the coherent transmitter 702, and demodulates the mixed signal.
  • the coherent transmitter 702 may be the coherent transmitter shown in any of the embodiments shown in FIG. 1 and FIG. 5.
  • the coherent transceiver system further includes a beam splitter 704.
  • the beam splitter splits the optical signal output by the light source 701 to obtain the first optical signal and the second optical signal.
  • the coherent transmitter 702 modulates the first optical signal to obtain a first modulated signal and outputs the first modulated signal.
  • the coherent receiver 703 mixes the second optical signal and the modulated signal, and demodulates the mixed signal.
  • the light sources used by the coherent transmitter 702 and the coherent receiver 703 may be the same light source or different light sources, which is not specifically limited here.

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Abstract

本申请实施例公开了一种相干发射机、控制相干发射机的方法及相干收发系统。相干发射机包括：第一调制器、第二调制器、第一分束器、相移调整单元、第一合束器、第二合束器、第一PD和控制器。第一分束器对输入的第一光信号进行分路得到第二光信号和第三光信号；第一调制器调制第二光信号得到第一调制信号；相移调整单元对第一调制信号中的第一子信号进行相位调整，并对相位调整后的第一子信号中的第四子信号进行相位调整；第一合束器对第一调制信号中的第二子信号和相位调整后的第四子信号进行合路得到第一合路信号；第一PD对第一合路信号进行光电转换得到第一电信号；控制器根据第一电信号控制加载在相移调整单元上的电压。

Description

一种相干发射机、控制相干发射机的方法及相干收发系统
本申请要求于2020年1月17日提交中国国家知识产权局、申请号为202010057408.8、发明名称为“一种相干发射机、控制相干发射机的方法及相干收发系统”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
本申请涉及光通信领域，尤其涉及一种相干发射机、控制相干发射机的方法及相干收发系统。
背景技术
近年来，随着数据中心内部及数据中心之间的信息交换量极速增长，直接调制模式受限于器件带宽，已难以满足单波200G乃至单波400G的需求。相干调制模式因其频谱效率高、单波调制速率高而受到青睐，将逐步应用于短距光传输系统。
相干调制需要在同相正交(In-phase and Quadrature，I/Q)信号之间实现90°相移。通常的设计是，通过在集成芯片的热调器(heater)上加载一定的电压来实现。然而，在信号的调制过程中，可能会由于热调器的不稳定而导致90°相移存在偏差，使得调制的相干信号质量变差。
发明内容
本申请实施例提供了一种相干发射机、控制相干发射机的方法及相干收发系统。
第一方面，本申请实施例提供了一种相干发射机。相干发射机包括第一信号调制模块、第一光电二极管(Photo-Diode，PD)和控制器，第一信号调制模块、第一PD和控制器相互连接，其中，第一信号调制模块包括第一调制器、第二调制器、第一分束器、相移调整单元、第一合束器和第二合束器。具体地，第一分束器对输入的第一光信号进行分路得到第二光信号和第三光信号。第一调制器调制第二光信号得到第一调制信号。第二调制器调制第三光信号得到第二调制信号。相移调整单元对第一调制信号中的第一子信号进行相位调整，并对相位调整后的第一子信号中的第四子信号进行相位调整。第一合束器对第一调制信号中的第二子信号和相位调整后的第四子信号进行合路得到第一合路信号。第二合束器对相位调整后的第一子信号中的第三子信号和第二调制信号进行合路得到第二合路信号。第一PD对第一合路信号进行光电转换得到第一电信号。控制器根据第一电信号控制加载在相移调整单元上的电压，以使得第一相位差在预设范围内。
需要说明的是，相干发射机包括I/Q两路的信号调制，第一调制器位于Q路上，第二调制器位于I路上。第一调制信号与第二调制信号具有相同相位。相位调整后的第一子信号与第一调制信号之间具有第一相位差，相位调整后的第四子信号与第一调制信号之间具有第二相位差，第二相位差是第一相位差的二倍。
在该实施方式中，相干发射机的Q路上的一部分光用于相位调整并和I路上的光进行相 干调制，Q路上的另一部分光用于监控相位调整后的相位差是否在预设范围内，若否，则控制器可以调整加载在相移调整单元上的电压，以将相位差调整到预设范围内。通过这种监控和调节的方式，在不影响业务传输的前提下，可以实时监控相位调整后的相位差，并将相位差控制在预设范围内，提高了相位调整精度，使得相干设计调制的相干信号质量更好。另外，相干发射机的结构和控制方法中无需设置数模转换器(Digital-to-Analog Converter，DAC)和模数转换器(Analog-to-Digital Converter，ADC)等复杂的电器件，便于集成，且器件成本更低，功耗更小。
可选地，在一些可能的实施方式中，相移调整单元包括相移器、第二分束器和第三分束器，控制器所控制的电压加载在相移器上。具体地，第二分束器对第一调制信号进行分路得到第一子信号和第二子信号。相移器对第一子信号进行相位调整。第三分束器对相位调整后的第一子信号进行分路得到第三子信号和第四子信号。相移器再对第四子信号进行相位调整。
在该实施方式中，提供了一种相移调整单元的具体实现方式，即通过在相移器的前端和后端分别设置分束器将光信号分为两路，一路用于相干调制，另一路用于实时监控相位变化，提高了本方案的可实现性。
可选地，在一些可能的实施方式中，相干发射机还包括光源、第四分束器、第二信号调制模块、第二PD和偏振转换装置，第一信号调制模块和第二信号调制模块具有相同的结构和功能，第二信号调制模块、第二PD和控制器相互连接。具体地，光源输出光信号。第四分束器对光信号进行分路得到第一光信号和第四光信号，并将第一光信号传输至第一信号调制模块，将第四光信号传输至第二信号调制模块。第二信号调制模块根据第四光信号输出第三合路信号和第四合路信号，第二合路信号和第三合路信号的偏振模式为横向电场偏振(Transverse Electric，TE)。偏振转换装置对第二合路信号和第三合路信号进行合路得到第五合路信号，并将第二合路信号或第三合路信号的偏振模式转换为横向磁场偏振(Transverse Magnetic，TM)。第二PD用于对第四合路信号进行光电转换得到第二电信号。控制器用于根据第二电信号控制加载在第二信号调制模块的相移调整单元上的电压。
在该实施方式中，相干发射机还可以支持双偏振模式，即第一信号调制模块和第二信号调制模块输出信号的偏振模式不同，提高了本方案的扩展性。
可选地，在一些可能的实施方式中，控制器具体用于：
获取第一电信号的第一电流值。若第一电流值大于电流阈值，则提高加载在相移器上的电压。之后，获取第一电信号的第二电流值。若第二电流值小于第一电流值且大于电流阈值，则持续提高电压，以使得第二电流值小于或等于电流阈值。若第二电流值大于第一电流值，则降低电压，以使得第二电流值小于或等于电流阈值。需要说明的是，在相移器实现的相移为90°时，第一PD上产生的电流最小，而相移越偏离90°，第一PD上产生的电流越大。
在该实施方式中，提供了一种控制器根据PD上产生的电流大小来实时控制加载在相移器上电压的具体实现方式，提高了本方案的实用性。
可选地，在一些可能的实施方式中，可以通过实验将加载在相移器上的电压和第一PD上的电流之间的对应关系记录下来，得到对应关系表，控制器具体用于：
获取该对应关系表，若第一PD上产生的电流值大于电流阈值，那么控制器根据对应关系表确定目标电流对应的目标电压。其中，该目标电流小于或等于电流阈值。进而，控制器将 加载在相移器上的电压调整为目标电压。
在该实施方式中，提供了另一种控制器根据PD上产生的电流大小来实时控制加载在相移器上电压的具体实现方式，提高了本方案的灵活性。
可选地，在一些可能的实施方式中，第二子信号在第一调制信号中的占比为第一比例，第四子信号在相位调整后的第一子信号中的占比为第二比例，第一比例与第二比例之间具有对应关系式。
对应关系式包括：(1-x％)*y％＝x％；其中，x％表示第一比例，y％表示第二比例。
在该实施方式中，通过控制第二分束器和第三分束器的分光比使得第一比例和第二比例满足上述对应关系式，即输入到第一合束器的两路光的功率相同，使得相移90°时第一PD上产生的电流最小，降低了第一PD的能耗。
可选地，在一些可能的实施方式中，第一调制器和第二调制器的调制方式包括幅移键控(Amplitude Shift Keying，ASK)。第一调制器和第二调制器的类型包括但不限于微环调制器(Micro-ring Modulator，MRM)、马赫增德调制器、波导型电光吸收调制器和布拉格光栅调制器。在该实施方式中，提供了多种第一调制器和第二调制器所适用的类型，提高了本方案的扩展性。
可选地，在一些可能的实施方式中，光源的类型包括但不限于分布式反馈(Distributed Feedback Laser，DFB)激光器、量子点光梳激光器和磷化铟激光器，偏振转换装置的类型包括反向偏振分束旋转器(Polarization Splitter and Rotator，PSR)和光栅耦合器。在该实施方式中，提供了多种光源的类型和多种偏振转换装置的类型，提高了本方案的扩展性。
可选地，在一些可能的实施方式中，光信号耦合至第四分束器的耦合方式和第五合路信号耦合至光纤的耦合方式包括但不限于边耦合、垂直光栅耦合和透镜折射耦合。在该实施方式中，提供了多种光输入和光输出的耦合方式，提高了本方案的扩展性。
可选地，在一些可能的实施方式中，第一PD与第一信号调制模块集成在光芯片上，集成在光芯片上的技术包括但不限于绝缘体上硅(Silicon-on-Insulator，SOI)集成、铌酸锂薄膜集成和磷化铟集成。此外，第一PD也可以与控制器集成在印制电路板(Printed Circuit Board，PCB)上。在该实施方式中，第一PD可以与第一信号调制模块集成在光芯片上，也可以是与控制器集成在PCB上，进一步提高了本方案的扩展性。
第二方面，本申请实施例提供了一种控制相干发射机的方法，相干发射机包括第一信号调制模块、第一PD和控制器，第一信号调制模块、第一PD和控制器相互连接，其中，第一信号调制模块包括第一调制器、第二调制器、第一分束器、相移调整单元、第一合束器和第二合束器。方法包括：
通过第一分束器对输入的第一光信号进行分路得到第二光信号和第三光信号。通过第一调制器调制第二光信号得到第一调制信号，并通过第二调制器调制第三光信号得到第二调制信号，第一调制信号与第二调制信号具有相同相位。通过相移调整单元对第一调制信号中的第一子信号进行相位调整，并对相位调整后的第一子信号中的第四子信号进行相位调整，相位调整后的第一子信号与第一调制信号之间具有第一相位差，相位调整后的第四子信号与第一调制信号之间具有第二相位差，第二相位差是第一相位差的二倍。通过第一合束器对第一调制信号中的第二子信号和相位调整后的第四子信号进行合路得到第一合路信号。通过第二 合束器对相位调整后的第一子信号中的第三子信号和第二调制信号进行合路得到第二合路信号。通过第一PD对第一合路信号进行光电转换得到第一电信号。通过控制器并根据第一电信号控制加载在相移调整单元上的电压，以使得相位调整后的第一子信号与第一调制信号之间的第一相位差在预设范围内。
可选地，在一些可能的实施方式中，相移调整单元包括相移器、第二分束器和第三分束器，电压加载在相移器上，方法还包括：
通过第二分束器对第一调制信号进行分路得到第一子信号和第二子信号。通过相移器对第一子信号进行相位调整。通过第三分束器对相位调整后的第一子信号进行分路得到第三子信号和第四子信号。通过相移器对第四子信号进行相位调整。
可选地，在一些可能的实施方式中，相干发射机还包括光源、第四分束器、第二信号调制模块、第二PD和偏振转换装置，第一信号调制模块和第二信号调制模块具有相同的结构和功能，第二信号调制模块、第二PD和控制器相互连接，方法还包括：
通过光源输出光信号。通过第四分束器对光信号进行分路得到第一光信号和第四光信号，并将第一光信号传输至第一信号调制模块，将第四光信号传输至第二信号调制模块。通过第二信号调制模块并根据第四光信号输出第三合路信号和第四合路信号，第二合路信号和第三合路信号的偏振模式为TE。通过偏振转换装置对第二合路信号和第三合路信号进行合路得到第五合路信号，并将第二合路信号或第三合路信号的偏振模式转换为TM。通过第二PD对第四合路信号进行光电转换得到第二电信号。通过控制器并根据第二电信号控制加载在第二信号调制模块的相移调整单元上的电压。
可选地，在一些可能的实施方式中，通过控制器并根据第一电信号控制加载在相移调整单元上的电压包括：
获取第一电信号的第一电流值。若第一电流值大于电流阈值，则提高加载在相移器上的电压。获取第一电信号的第二电流值。若第二电流值小于第一电流值且大于电流阈值，则持续提高电压，以使得第二电流值小于或等于电流阈值。若第二电流值大于第一电流值，则降低电压，以使得第二电流值小于或等于电流阈值。
可选地，在一些可能的实施方式中，通过控制器并根据第一电信号控制加载在相移调整单元上的电压包括：
获取对应关系表，对应关系表包括加载在相移器上的电压和第一电信号的电流值之间的对应关系。根据对应关系表确定目标电流值对应的目标电压，目标电流值小于或等于电流阈值。将加载在相移器上的电压调整为目标电压。
可选地，在一些可能的实施方式中，第二子信号在第一调制信号中的占比为第一比例，第四子信号在相位调整后的第一子信号中的占比为第二比例，第一比例与第二比例之间具有对应关系式；
对应关系式包括：(1-x％)*y％＝x％；其中，x％表示第一比例，y％表示第二比例。
可选地，在一些可能的实施方式中，第一调制器和第二调制器的调制方式包括ASK，第一调制器和第二调制器的类型包括MRM、马赫增德调制器、波导型电光吸收调制器和布拉格光栅调制器。
可选地，在一些可能的实施方式中，光源的类型包括DFB激光器、量子点光梳激光器和 磷化铟激光器，偏振转换装置的类型包括反向PSR和光栅耦合器。
可选地，在一些可能的实施方式中，光信号耦合至第四分束器的耦合方式和第五合路信号耦合至光纤的耦合方式包括边耦合、垂直光栅耦合和透镜折射耦合。
可选地，在一些可能的实施方式中，第一PD与第一信号调制模块集成在光芯片上，集成在光芯片上的技术包括SOI集成、铌酸锂薄膜集成和磷化铟集成。此外，第一PD也可以与控制器集成在PCB上。
第三方面，本申请实施例提供了一种相干收发系统，包括光源、相干接收机和如第一方面中任一实施方式所示的相干发射机。具体地，光源用于输出光信号。相干发射机用于输出调制信号。相干接收机用于对光信号和调制信号进行混频，并对混频后的信号进行解调。
可选地，在一些可能的实施方式中，相干收发系统还包括分束器。分束器用于对光信号进行分路得到第一光信号和第二光信号。相干发射机用于调制第一光信号得到调制信号，并输出调制信号。相干接收机用于对第二光信号和调制信号进行混频，并对混频后的信号进行解调。
第四方面，本申请实施例提供了一种相干发射机。相干发射机包括第一信号调制模块、第一PD和控制器，第一信号调制模块、第一PD和控制器相互连接，其中，第一信号调制模块包括第一调制器、第二调制器、第一分束器、相移器、第二分束器、第三分束器、第一合束器和第二合束器。具体地，第一分束器对输入的第一光信号进行分路得到第二光信号和第三光信号。第一调制器调制第二光信号得到第一调制信号。第二调制器调制第三光信号得到第二调制信号，第一调制信号与第二调制信号具有相同相位。第二分束器对第一调制信号进行分路得到第一子信号和第二子信号。相移器对第一子信号进行相位调整，相位调整后的第一子信号与第一调制信号之间具有第一相位差。第三分束器对相位调整后的第一子信号进行分路得到第三子信号和第四子信号。相移器再对第四子信号进行相位调整，相位调整后的第四子信号与第一调制信号之间具有第二相位差，第二相位差是第一相位差的二倍。第一合束器对第一调制信号中的第二子信号和相位调整后的第四子信号进行合路得到第一合路信号。第二合束器对相位调整后的第一子信号中的第三子信号和第二调制信号进行合路得到第二合路信号。第一PD对第一合路信号进行光电转换得到第一电信号。控制器根据第一电信号控制加载在相移调整单元上的电压，以使得第一相位差在预设范围内。
从以上技术方案可以看出，本申请实施例具有以下优点：
本申请实施例中，相干发射机包括I/Q两路的信号调制，其中，Q路上的一部分光用于相位调整并和I路上的光进行相干调制，Q路上的另一部分光用于监控相位调整后的相位差是否在预设范围内，若否，则控制器可以调整加载在相移调整单元上的电压，以将相位差调整到预设范围内。通过这种监控和调节的方式，在不影响业务传输的前提下，可以实时监控相位调整后的相位差，并将相位差控制在预设范围内，提高了相位调整精度，使得相干设计调制的相干信号质量更好。另外，相干发射机的结构和控制方法中无需设置ADC和DAC等复杂的电器件，便于集成，且器件成本更低，功耗更小。
附图说明
图1为本申请实施例提供的一种相干发射机的结构示意图；
图2为第一PD上产生的电流与相移之间的仿真关系示意图；
图3为控制器控制电压的操作流程图；
图4为不同分光比对应的第一PD上产生的电流大小的示意图；
图5为本申请实施例提供的另一种相干发射机的结构示意图；
图6为本申请实施例中一种控制相干发射机的方法的示意图；
图7为本申请中一种相干收发系统的结构示意图。
具体实施方式
本申请实施例提供了一种相干发射机、控制相干发射机的方法及相干收发系统。在不影响业务传输的前提下，可以实时监控相位调整后的相位差，并将相位差控制在预设范围内，提高了相位调整精度，使得相干设计调制的相干信号质量更好。另外，相干发射机的结构中无需设置ADC和DAC等复杂的电器件，便于集成，且器件成本更低，功耗更小。本申请的说明书和权利要求书及上述附图中的术语“第一”、“第二”、“第三”、“第四”等(如果存在)是用于区别类似的对象，而不必用于描述特定的顺序或先后次序。应该理解这样使用的数据在适当情况下可以互换，以便这里描述的实施例能够以除了在这里图示或描述的内容以外的顺序实施。此外，术语“包括”和“具有”以及他们的任何变形，意图在于覆盖不排他的包含，例如，包含了一系列步骤或单元的过程、方法、系统、产品或设备不必限于清楚地列出的那些步骤或单元，而是可包括没有清楚地列出的或对于这些过程、方法、产品或设备固有的其它步骤或单元。
图1为本申请实施例提供的一种相干发射机的结构示意图。该相干发射机包括第一信号调制模块10、第一光电二极管(Photo-Diode，PD)20和控制器30。其中，第一信号调制模块10包括第一分束器101、第一调制器102、第二调制器103、第二分束器104、相移器105、第三分束器106、第一合束器107和第二合束器108。
下面分别对上述相干发射机中各组成部分的功能进行介绍：
第一分束器101对输入的第一光信号进行分路得到第二光信号和第三光信号。可以理解的是，相干发射机需要将信号分为两路(I路和Q路)并分别进行调制，即第二光信号用于Q路调制，第三光信号用于I路调制。
第一调制器102调制第二光信号得到第一调制信号。第二调制器103调制第三光信号得到第二调制信号。其中，第一调制器102和第二调制器103的结构和调制原理相同。具体地，第一调制器102和第二调制器103通过加载各自独立(同频率且时钟同步)的射频驱动电信号(RF driving signals)分别对输入的光信号进行调制。需要说明的是，如果相干发射机实现的相干调制是N2级正交振幅调制(N2-Quadrature Amplitude Modulation，N2-QAM)，那么第一调制器102和第二调制器103进行的调制是N级幅移键控(N-Amplitude Shift Keying,N-ASK)。例如，相干发射机实现的是16-QAM，则第一调制信号和第二调制信号为相互独立的4-ASK信号。并且，该第一调制信号和第二调制信号具有相同相位。
第二分束器104对第一调制信号进行分路得到第一子信号和第二子信号。相移器105对第一子信号进行相位调整。第三分束器106对相位调整后的第一子信号进行分路得到第三子信号和第四子信号。相移器105对第四子信号进行相位调整。需要说明的是，相位调整后的 信号与相位调整前的信号具有相位差，理想状态下该相位差为90°，也即是说，相位调整后的第一子信号与第一调制信号之间具有第一相位差。那么，第三子信号和第四子信号同样与第一信号之间具有第一相位差。而第四子信号经过相位调整后与第一调制信号之间具有第二相位差，并且该第二相位差是第一相位差的二倍。例如，若第一相位差为90°，那么第二相位差就是180°。另外，第二分束器104、相移器105和第三分束器106可以集成为相移调整单元。
第二合束器108对第三子信号和第二调制信号进行合路得到第二合路信号并输出。可以理解的是，第三子信号和第二调制信号之间具有第一相位差。如果该相干发射机实现的是16-QAM，那么由两路正交的4-ASK信号合路得到的第二合路信号即为16-QAM信号。
第一合束器107对第二子信号和相位调整后的第四子信号进行合路得到第一合路信号。第一PD(20)对第一合路信号进行光电转换得到第一电信号。控制器30根据第一电信号控制加载在相移器105上的电压，以控制第一相位差在预设范围内(接近90°)。
图2为第一PD上产生的电流与相移之间的仿真关系示意图。根据仿真结果可知，在相移器105实现的相移为90°时，第一PD(20)上产生的电流最小，而相移越偏离90°，第一PD(20)上产生的电流越大。理论上来说，若相移器105实现的相移为90°(第一相位差为90°)，那么第二相位差为180°，在第一合束器107合束后的第一合路信号由于光的干涉光强为0，那么第一PD产生的电流也应为0。不过实际上，由于分光不均或器件损耗等原因，在相移为90°时，第一PD(20)上电流并不一定为0，但是必定是最小的。那么也即是说，若第一PD(20)上产生的电流小于预设值，那么即可保证相移在预设范围内(近似90°)。例如，如图2所示，90°相移时电流的最小值约为47μA，可以将预置电流设置为50μA，若第一PD上产生的电流值小于50μA，那么相移在88.5°-91.5°的预设范围内，此时调制信号的质量在可接受范围内。由此可知，控制器30可以通过读取第一PD(20)上产生的电流值来判断当前的相移是否在预设范围内，若否，则调整加载在相移器上的电压，以将相移控制在预设范围内。
控制器30具体可以有多种不同的控制方式，下面分别进行介绍：
第一种、可以通过实验将加载在相移器105上的电压和第一PD(20)上的电流之间的对应关系记录下来，得到对应关系表。控制器30可以获取该对应关系表，若第一PD(20)上产生的电流值大于电流阈值，那么控制器30根据对应关系表确定目标电流对应的目标电压。其中，该目标电流小于或等于电流阈值。进而，控制器30将加载在相移器105上的电压调整为目标电压。
第二种、控制器按照预置的操作机制调整加载电压。图3为控制器控制电压的操作流程图，下面对该操作流程进行详细介绍：
301、获取第一PD上的实时电流I1。
控制器30读取第一PD(20)产生的第一电信号的实时电流。
302、判断实时电流I1是否小于或等于电流阈值I0；若是，则保持当前电压；若否，则执行步骤303。
303、提高加载在相移器上的电压。
304、获取第一PD上的实时电流I2。
305、判断实时电流I2是否小于实时电流I1且大于电流阈值I0；若是，则重复执行步骤303，以使得实时电流I2小于或等于电流阈值I0；若否，则执行步骤306。
306、降低加载在相移器上的电压，以使得实时电流I2小于或等于电流阈值I0。
需要说明的是，相移大于预设范围或小于预设范围都会导致实时电流大于电流阈值。因此，通过步骤303测试相移是大了还是小了。如果提高电压后实时电流开始变小，则证明实时电流大于电流阈值是由于相移小于预设范围引起的，那么继续提高电压直至实时电流小于或等于电流阈值即可。如果提高电压后实时电流还在变大，则证明实时电流大于电流阈值是由于相移大于预设范围引起的，那么则需要开始降低电压直至实时电流小于或等于电流阈值。
可选地，相移器105的类型可以有多种，例如具体可以是热调器(heater)，通过热调器改变相位的常见方式有如下两种。第一、在光波导上覆盖金属，通过在金属上加电压使金属发热，改变光波导的折射率，从而改变相位。第二、在调制器光波导及周围进行载流子掺杂(如硅光集成的光波导及周围掺杂磷原子)，通过加载电压改变波导内载流子浓度，也能改变光波导的折射率，从而改变相位。需要说明的是，除了上述列举的热调器，其他类型用于实现相位调整的相移器均属于本申请的保护范围，具体此处不做限定。
可选地，为了使得相移90°时第一PD(20)上产生的电流尽可能的小，输入到第一合束器107的两路光的功率应当越接近越好。具体地，可以通过设置第二分束器104和第三分束器106的分光比来实现。第二子信号在第一调制信号中的占比为第一比例(x％)，第四子信号在相位调整后的第一子信号中的占比为第二比例(y％)，那么第一比例和第二比例之间应当具有如下关系式：(1-x％)*y％＝x％。其中，可以通过改变波导耦合区域的长度来实现不同的分光比设计。
图4为不同分光比对应的第一PD上产生的电流大小的示意图。按照上述关系式，若x％＝5％，那么y％＝5.2％。从图4中可以看出，x％＝5％且y％＝5.2％的条件下第一PD上产生的电流最小，小于x％＝5％且y％＝6和x％＝5％且y％＝4的两种条件下第一PD上产生的电流。需要说明的是，在实际应用中，第一比例和第二比例也可以不满足上述关系式，具体此处不做限定。
可选地，本申请实施例中的相干发射机处理可以支持如图1所示的单偏振模式外，还可以支持双偏振模式，下面进一步进行介绍：
图5为本申请实施例提供的另一种相干发射机的结构示意图。与上述图1所示的相干发射机的主要不同之处在于，相干发射机还包括第二信号调制模块60和偏振转换装置80，从而实现第一信号调制模块10和第二信号调制模块60具有不同的偏振模式。另外，该相干发射机还可以包括光源40、第四分束器50和第二PD(70)。其中，第一信号调制模块10和第二信号调制模块60具有相同的结构和功能，具体此处不再赘述。
光源40输出光信号。进而，第四分束器50对光信号进行分路得到第一光信号和第四光信号，并将第一光信号传输至第一信号调制模块10，将第四光信号传输至第二信号调制模块60。
第二信号调制模块60根据第四光信号输出第三合路信号和第四合路信号。其中，第三合路信号对应图2所示实施例中的第二合路信号，第四合路信号对应图2所示实施例中的第一合路信号。
第二PD(70)对第四合路信号进行光电装换得到第二电信号。同理，控制器30可以根 据第二电信号控制加载在第二信号调制模块60的相移器上的电压。具体地，控制器的控制方式与上述实施例中的介绍类似，此处不再赘述。
偏振转换装置80转换第二合路信号或第三合路信号的偏振模式，并对第二合路信号和第三合路信号进行合路得到第五合路信号。例如，第二合路信号和第三合路信号原本的偏振模式均为横向电场偏振(Transverse Electric，TE)，经过偏振转换装置80的处理后，第二合路信号或第三合路信号的偏振模式转换为横向磁场偏振(Transverse Magnetic，TM)。
可选地，第一调制器102和第二调制器103的类型包括但不限于微环调制器(Micro-ring Modulator，MRM)、马赫增德调制器、波导型电光吸收调制器和布拉格光栅调制器等。
可选地，本实施例中的光源40类型包括但不限于分布式反馈(Distributed Feedback Laser，DFB)激光器、量子点光梳激光器和磷化铟激光器等。
可选地，光源40可以同第一信号调制模块10和第二信号调制模块60集成在同一芯片上，此外，光源40也可以作为芯片外的光源。第一PD(20)、第二PD(70)、第一信号调制模块10和第二信号调制模块60可以集成咋同一芯片上，此外，第一PD(20)和第二PD(70)也可以同控制电路集成在印制电路板(Printed Circuit Board，PCB)上。其中，集成在芯片上的技术包括但不限于绝缘体上硅(Silicon-on-Insulator，SOI)集成、铌酸锂薄膜集成和磷化铟集成等。
可选地，光源40发射的光信号耦合至第四分束器50的耦合方式以及偏振转换装置80输出的第五合路信号耦合至光纤的耦合方式包括但不限于边耦合、垂直光栅耦合和透镜折射耦合等。
可选地，偏振转换装置80的类型包括但不限于反向偏振分束旋转器(Polarization Splitter and Rotator，PSR)和光栅耦合器。
可选地，第二分束器104和第三分束器106的类型包括但不限于多模干涉仪(Multi-mode Interferometer，MMI)和Y型分束器(Y-branch)等。
本申请实施例中，相干发射机包括I/Q两路的信号调制，其中，Q路上的一部分光用于相位调整并和I路上的光进行相干调制，Q路上的另一部分光用于监控相位调整后的相位差是否在预设范围内，若否，则控制器可以调整加载在相移调整单元上的电压，以将相位差调整到预设范围内。通过这种监控和调节的方式，在不影响业务传输的前提下，可以实时监控相位调整后的相位差，并将相位差控制在预设范围内，提高了相位调整精度，使得相干设计调制的相干信号质量更好。另外，本方案的相干发射机的结构和控制方法中无需设置数模转换器(Digital-to-Analog Converter，DAC)和模数转换器(Analog-to-Digital Converter，ADC)等复杂的电器件，便于集成，且器件成本更低，功耗更小。
下面请参阅图6，图6为本申请实施例中一种控制相干发射机的方法的示意图。该相干发射机包括第一信号调制模块、第一光电二极管PD和控制器，第一信号调制模块、第一PD和控制器相互连接，其中，第一信号调制模块包括第一调制器、第二调制器、第一分束器、相移调整单元、第一合束器和第二合束器。
在该示例中，控制相干发射机的方法包括如下步骤。
601、通过第一分束器对输入的第一光信号进行分路得到第二光信号和第三光信号。
602、通过第一调制器调制第二光信号得到第一调制信号，并通过第二调制器调制第三光 信号得到第二调制信号。
本实施例中，第一调制器和第二调制器的结构和调制原理相同。并且，该第一调制信号和第二调制信号具有相同相位。
603、通过相移调整单元对第一调制信号中的第一子信号进行相位调整，并对相位调整后的第一子信号中的第四子信号进行相位调整。
本实施例中，相位调整后的第一子信号与第一调制信号之间具有第一相位差，相位调整后的第四子信号与第一调制信号之间具有第二相位差，第二相位差是第一相位差的二倍。
其中，相移调整单元可以包括相移器、第二分束器和第三分束器，电压加载在相移器上。具体地，通过第二分束器对第一调制信号进行分路得到第一子信号和第二子信号。通过相移器对第一子信号进行相位调整。通过第三分束器对相位调整后的第一子信号进行分路得到第三子信号和第四子信号。通过相移器对第四子信号进行相位调整。
604、通过第一合束器对第一调制信号中的第二子信号和相位调整后的第四子信号进行合路得到第一合路信号。
605、通过第二合束器对相位调整后的第一子信号中的第三子信号和第二调制信号进行合路得到第二合路信号。
606、通过第一PD对第一合路信号进行光电转换得到第一电信号。
607、通过控制器并根据第一电信号控制加载在相移调整单元上的电压，以使得相位调整后的第一子信号与第一调制信号之间的第一相位差在预设范围内。
需要说明的是，本实施例中的相干发射机具体可以是如上述图1和图5所示任一实施例中的相干发射机。
下面请参阅图7，图7为本申请中一种相干收发系统的结构示意图。相干收发系统包括光源701、相干发射机702和相干接收机703。光源701输出光信号。相干发射机702输出调制信号。相干接收机703对光源701输出的光信号和相干发射机702输出的调制信号进行混频，并对混频后的信号进行解调。具体地，相干发射机702可以是图1和图5中任一实施例所示的相干发射机，相干发射机702的功能介绍请参阅上述图1和图5所示实施例中的相关描述，此处不再赘述。
可选地，该相干收发系统还包括分束器704。分束器对光源701输出的光信号进行分路得到第一光信号和第二光信号。相干发射机702调制第一光信号得到第一调制信号并输出该第一调制信号。相干接收机703对第二光信号和调制信号进行混频，并对混频后的信号进行解调。
可选地，相干发射机702和相干接收机703所采用的光源可以是同一光源，也可以是不同光源，具体此处不做限定。
需要说明的是，以上实施例仅用以说明本申请的技术方案，而非对其限制。尽管参照前述实施例对本申请进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本申请各实施例技术方案的精神和范围。

Claims (14)

  1. 一种相干发射机，其特征在于，包括第一信号调制模块、第一光电二极管PD和控制器，所述第一信号调制模块、所述第一PD和所述控制器相互连接，其中，所述第一信号调制模块包括第一调制器、第二调制器、第一分束器、相移调整单元、第一合束器和第二合束器；
    所述第一分束器用于对输入的第一光信号进行分路得到第二光信号和第三光信号；
    所述第一调制器用于调制所述第二光信号得到第一调制信号；
    所述第二调制器用于调制所述第三光信号得到第二调制信号，所述第一调制信号与所述第二调制信号具有相同相位；
    所述相移调整单元用于对所述第一调制信号中的第一子信号进行相位调整，并对所述相位调整后的第一子信号中的第四子信号进行相位调整，相位调整后的第一子信号与所述第一调制信号之间具有第一相位差，相位调整后的第四子信号与所述第一调制信号之间具有第二相位差，所述第二相位差是所述第一相位差的二倍；
    所述第一合束器用于对所述第一调制信号中的第二子信号和相位调整后的第四子信号进行合路得到第一合路信号；
    所述第二合束器用于对相位调整后的第一子信号中的第三子信号和所述第二调制信号进行合路得到第二合路信号；
    所述第一PD用于对所述第一合路信号进行光电转换得到第一电信号；
    所述控制器用于根据所述第一电信号控制加载在所述相移调整单元上的电压，以使得所述第一相位差在预设范围内。
  2. 根据权利要求1所述的相干发射机，其特征在于，所述相移调整单元包括相移器、第二分束器和第三分束器，所述电压加载在所述相移器上；
    所述第二分束器用于对所述第一调制信号进行分路得到所述第一子信号和所述第二子信号；
    所述相移器用于对所述第一子信号进行相位调整；
    所述第三分束器用于对相位调整后的第一子信号进行分路得到所述第三子信号和所述第四子信号；
    所述相移器用于对所述第四子信号进行相位调整。
  3. 根据权利要求1或2所述的相干发射机，其特征在于，所述相干发射机还包括光源、第四分束器、第二信号调制模块、第二PD和偏振转换装置，所述第一信号调制模块和所述第二信号调制模块结构相同，所述第二信号调制模块、所述第二PD和所述控制器相互连接；
    所述光源用于输出光信号；
    所述第四分束器用于对所述光信号进行分路得到所述第一光信号和第四光信号，并将所述第一光信号传输至所述第一信号调制模块，将所述第四光信号传输至所述第二信号调制模块；
    所述第二信号调制模块用于根据所述第四光信号输出第三合路信号和第四合路信号，所述第二合路信号和所述第三合路信号的偏振模式为横向电场偏振TE；
    所述偏振转换装置用于对所述第二合路信号和所述第三合路信号进行合路得到第五合路信号，并将所述第二合路信号或所述第三合路信号的偏振模式转换为横向磁场偏振TM；
    所述第二PD用于对所述第四合路信号进行光电转换得到第二电信号；
    所述控制器用于根据所述第二电信号控制加载在所述第二信号调制模块的相移调整单元上的电压。
  4. 根据权利要求1至3中任一项所述的相干发射机，其特征在于，所述控制器具体用于：
    获取所述第一电信号的第一电流值；
    若所述第一电流值大于电流阈值，则提高加载在所述相移调整单元上的电压；
    获取所述第一电信号的第二电流值；
    若所述第二电流值小于所述第一电流值且大于所述电流阈值，则持续提高所述电压，以使得所述第二电流值小于或等于所述电流阈值；
    若所述第二电流值大于所述第一电流值，则降低所述电压，以使得所述第二电流值小于或等于所述电流阈值。
  5. 根据权利要求1至3中任一项所述的相干发射机，其特征在于，所述控制器具体用于：
    获取对应关系表，所述对应关系表包括加载在所述相移调整单元上的电压和所述第一电信号的电流值之间的对应关系；
    根据所述对应关系表确定目标电流值对应的目标电压，所述目标电流值小于或等于所述电流阈值；
    将加载在所述相移调整单元上的电压调整为所述目标电压。
  6. 根据权利要求1至5中任一项所述的相干发射机，其特征在于，所述第二子信号在所述第一调制信号中的占比为第一比例，所述第四子信号在相位调整后的第一子信号中的占比为第二比例，所述第一比例与所述第二比例之间具有对应关系式；
    所述对应关系式包括：(1-x％)*y％＝x％；
    其中，所述x％表示所述第一比例，所述y％表示所述第二比例。
  7. 根据权利要求1至6中任一项所述的相干发射机，其特征在于，所述第一调制器和所述第二调制器的调制方式包括幅移键控ASK，所述第一调制器和所述第二调制器的类型包括微环调制器MRM、马赫增德调制器、波导型电光吸收调制器和布拉格光栅调制器。
  8. 根据权利要求3至7中任一项所述的相干发射机，其特征在于，所述光源的类型包括分布式反馈DFB激光器、量子点光梳激光器和磷化铟激光器，所述偏振转换装置的类型包括反向偏振分束旋转器PSR和光栅耦合器。
  9. 根据权利要求3至8中任一项所述的相干发射机，其特征在于，所述光信号耦合至所述第四分束器的耦合方式和所述第五合路信号耦合至光纤的耦合方式包括边耦合、垂直光栅耦合和透镜折射耦合。
  10. 根据权利要求1至9中任一项所述的相干发射机，其特征在于，所述第一PD与所述第一信号调制模块集成在光芯片上，所述集成在光芯片上的技术包括绝缘体上硅SOI集成、铌酸锂薄膜集成和磷化铟集成；或者，所述第一PD与所述控制器集成在印制电路板PCB上。
  11. 一种控制相干发射机的方法，其特征在于，所述相干发射机包括第一信号调制模块、第一光电二极管PD和控制器，所述第一信号调制模块、所述第一PD和所述控制器相互连接，其中，所述第一信号调制模块包括第一调制器、第二调制器、第一分束器、相移调整单元、第一合束器和第二合束器；所述方法包括：
    通过所述第一分束器对输入的第一光信号进行分路得到第二光信号和第三光信号；
    通过所述第一调制器调制所述第二光信号得到第一调制信号，并通过所述第二调制器调制所述第三光信号得到第二调制信号，所述第一调制信号与所述第二调制信号具有相同相位；
    通过所述相移调整单元对所述第一调制信号中的第一子信号进行相位调整，并对相位调整后的第一子信号中的第四子信号进行相位调整，相位调整后的第一子信号与所述第一调制信号之间具有第一相位差，相位调整后的第四子信号与所述第一调制信号之间具有第二相位差，所述第二相位差是所述第一相位差的二倍；
    通过所述第一合束器对所述第一调制信号中的第二子信号和相位调整后的第四子信号进行合路得到第一合路信号；
    通过所述第二合束器对相位调整后的第一子信号中的第三子信号和所述第二调制信号进行合路得到第二合路信号；
    通过所述第一PD对所述第一合路信号进行光电转换得到第一电信号；
    通过所述控制器并根据所述第一电信号控制加载在所述相移调整单元上的电压，以使得相位调整后的第一子信号与所述第一调制信号之间的第一相位差在预设范围内。
  12. 根据权利要求11所述的方法，其特征在于，所述相移调整单元包括相移器、第二分束器和第三分束器，所述电压加载在所述相移器上，所述方法还包括：
    通过所述第二分束器对所述第一调制信号进行分路得到所述第一子信号和所述第二子信号；
    通过所述相移器对所述第一子信号进行相位调整；
    通过所述第三分束器对相位调整后的第一子信号进行分路得到所述第三子信号和所述第四子信号；
    通过所述相移器对所述第四子信号进行相位调整。
  13. 一种相干收发系统，其特征在于，包括：光源、相干发射机和相干接收机，所述相干发射机包括权利要求1-10中任一项所述的相干发射机；
    所述光源用于输出光信号；
    所述相干发射机用于输出调制信号；
    所述相干接收机用于对所述光信号和所述调制信号进行混频，并对混频后的信号进行解调。
  14. 根据权利要求13所述的相干收发系统，其特征在于，所述相干收发系统还包括分束器；
    所述分束器用于对所述光信号进行分路得到第一光信号和第二光信号；
    所述相干发射机用于调制所述第一光信号得到所述调制信号，并输出所述调制信号；
    所述相干接收机用于对所述第二光信号和所述调制信号进行混频，并对混频后的信号进行解调。
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