WO2020244187A1 - 一种自相干信号收发方法及装置 - Google Patents

一种自相干信号收发方法及装置 Download PDF

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WO2020244187A1
WO2020244187A1 PCT/CN2019/125024 CN2019125024W WO2020244187A1 WO 2020244187 A1 WO2020244187 A1 WO 2020244187A1 CN 2019125024 W CN2019125024 W CN 2019125024W WO 2020244187 A1 WO2020244187 A1 WO 2020244187A1
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signal
optical
self
coherent
clock
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PCT/CN2019/125024
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English (en)
French (fr)
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胡荣
王志军
王素椅
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烽火通信科技股份有限公司
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Publication of WO2020244187A1 publication Critical patent/WO2020244187A1/zh

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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
    • H04B10/54—Intensity modulation
    • H04B10/541—Digital intensity or amplitude 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
    • H04B10/50—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]
    • H04B10/5561—Digital phase 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
    • H04B10/612—Coherent receivers for optical signals modulated with a format different from binary or higher-order PSK [X-PSK], e.g. QAM, DPSK, FSK, MSK, ASK
    • 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
    • H04B10/6161—Compensation of chromatic dispersion
    • 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
    • H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H04B10/114—Indoor or close-range type systems

Definitions

  • the invention relates to the field of short-distance optical transmission, in particular to a method and device for transmitting and receiving self-coherent signals.
  • the optical system architecture of intensity modulation and direct detection is widely used in the field of short-distance optical transmission within 20 kilometers.
  • the field of short-distance optical transmission is facing the following bottlenecks: (1) The above-mentioned system has a high dispersion cost, and the wavelength needs to be close to the zero-dispersion region; (2) The bandwidth of optoelectronic devices is limited, and the above-mentioned system will introduce more Crosstalk between symbols.
  • optical spectrum resources are limited, especially in the zero-dispersion area.
  • the new wavelength plan is bound to be far away from the zero-dispersion wavelength, so in order to overcome the dispersion problem, the system must adopt a dispersion compensation module. If the dispersion compensation module is used, the complexity of the system will increase, thereby increasing the cost of system implementation.
  • higher-order modulation methods with higher spectral efficiency must be used to increase the transmission rate, such as four-level pulse amplitude modulation (PAM4, 4 Pulse Amplitude Modulation).
  • PAM4 Pulse Amplitude Modulation four-level pulse amplitude modulation
  • the implementation device and test method of high-order modulation are more complicated, and the signal receiving sensitivity will be significantly reduced.
  • the purpose of the present invention is to provide a self-coherent signal transceiving method and device, which reduce the complexity of the system and improve the signal receiving sensitivity through IQ modulation and direct detection.
  • the intensity signal can be recovered Output the phase information of the IQ signal.
  • the recovered IQ signal can be further compensated for dispersion.
  • a self-coherent signal transmission method which is characterized in that it includes:
  • the I and Q components of the IQ signal are generated, filtered and amplified, and then subjected to IQ modulation, and the IQ modulated optical signal is output;
  • the Cos clock signal and Sin clock signal are generated, after amplification, IQ modulation is performed, and the optical pilot signal is output;
  • the optical power of the IQ modulated optical signal and the optical pilot signal are adjusted so that the strength of the optical pilot signal is greater than the strength of the IQ modulated optical signal, and then the self-coherent optical signal is synthesized and sent, wherein the two IQ modulations use the same continuous light source.
  • the two IQ modulations are respectively performed by an optical IQ modulator with a Mach-Zehnder structure, each optical IQ modulator inputs continuous light generated by a continuous light source, and the IQ modulated optical signal and the optical pilot signal are respectively inputted into an IQ modulation During modulation, the bias of the optical IQ modulator is set to NULL point.
  • the Cos clock signal and the Sin clock signal are generated by a high-speed clock source, the clock frequency of the high-speed clock source is greater than or equal to the cutoff frequency of the IQ signal filtering, and the self-coherent optical signal is in the light guide frequency and the IQ modulated light Reserve a guard band between the signals.
  • a self-coherent signal receiving method including:
  • n represents the sampling sequence index
  • m represents the sequence index after upsampling
  • Pair signal Perform digital down-conversion to obtain the baseband signal, then perform down-sampling, and finally perform dispersion compensation and signal recovery on the baseband signal;
  • the self-coherent optical signal is synthesized from the signal of the optical pilot and the strength of the IQ modulated optical signal, and the signal strength of the optical pilot is greater than the strength of the IQ modulated optical signal.
  • the self-coherent optical signal is received by a single-ended photodetector, and the optical pilot frequency is obtained by generating a Cos clock signal and a Sin clock signal from a high-speed clock source, then amplifying and IQ modulating the signal, and the IQ modulating optical signal is obtained by the IQ signal It is obtained after filtering, amplifying and IQ modulation, and the bandwidth of the single-ended photodetector is greater than or equal to the clock frequency of the high-speed clock source + the cutoff frequency when the IQ signal is filtered.
  • the multiplier of the up-sampling is greater than or equal to 3; the optical pilot signal and the IQ modulated optical signal are both output through an optical IQ modulator, and the optical IQ modulator receives a continuous light source, and the Cos clock signal and the Sin clock signal The frequency is the frequency interval between the light guide and the continuous light source.
  • a self-coherent signal sending device including:
  • IQ signal generation module which is used to generate I and Q components of the IQ signal
  • the first optical IQ modulator which is configured to receive and modulate the I and Q components through two radio frequency ports, and output an IQ modulated optical signal
  • Clock signal generation module which is used to generate Cos clock signal and Sin clock signal
  • the second optical IQ modulator which is used to receive and modulate the Cos clock signal and the Sin clock signal respectively through two radio frequency ports, and output an optical pilot signal;
  • Two adjustable optical attenuators respectively used to adjust the optical power of the IQ modulated optical signal and the optical pilot signal, so that the signal strength of the optical pilot is greater than the strength of the IQ modulated optical signal;
  • the second optical power splitter is used for synthesizing and transmitting the IQ modulated optical signal and the optical pilot signal after the optical power is adjusted to the coherent optical signal.
  • Continuous light source which is used to output continuous light
  • the first optical power splitter is used to divide the continuous light into two paths, which are respectively connected to the first optical IQ modulator and the second optical IQ modulator.
  • the clock signal generating module includes:
  • High-speed clock source which is used to generate Cos clock signal and Sin clock signal;
  • Two second electric drivers which are used to amplify the Cos clock signal and the Sin clock signal respectively.
  • the IQ signal generating module includes:
  • IQ signal source which is used to generate the I and Q components of the IQ signal
  • Two first electric drivers which are used to respectively amplify the filtered I and Q components.
  • the filter is a Nyquist filter
  • the clock frequency of the high-speed clock source is greater than or equal to the cutoff frequency of the filter
  • a guard band is reserved between the optical pilot frequency and the IQ modulated optical signal.
  • the first optical IQ modulator and the second optical IQ modulator both have a Mach-Zehnder structure, and the bias in the modulation is set to a NULL point.
  • a self-coherent signal receiving device including a single-ended photodetector, a high-speed analog-to-digital converter, and a digital signal processor.
  • the single-ended photodetector receives the self-coherent optical signal and converts it into a photocurrent.
  • the high-speed analog-to-digital converter samples and inputs the digital signal processor, the self-coherent optical signal is synthesized by the signal of the optical pilot and the intensity of the IQ modulated optical signal, and the signal intensity of the optical pilot is greater than the intensity of the IQ modulated optical signal;
  • the digital signal processor includes:
  • KK signal processing module which is used to take the square root of the real number signal sampled by the high-speed analog-to-digital converter to obtain the optical signal amplitude A(n), and then perform up-sampling to obtain the sampled optical signal amplitude A′(m), which is also used Take the natural logarithm of the up-sampled signal and perform Hilbert transform to output the complex signal, and extract the phase And output signal
  • n represents the sampling sequence index
  • m represents the sequence index after upsampling
  • the digital down-conversion module is used to down-convert the signal output by the KK signal processing module to obtain a baseband signal, and then perform down-sampling to restore the sampling rate of the signal received by the KK signal processing module;
  • CD compensation module which is used to perform dispersion compensation on the signal output by the digital down-conversion module
  • IQ signal decoding is used to recover the constellation diagram of the IQ signal and map the constellation diagram symbols into a binary code stream.
  • the optical pilot frequency is generated by a high-speed clock source, and the optical pilot frequency is obtained by a high-speed clock source generating a Cos clock signal and a Sin clock signal through amplification and IQ modulation, and the IQ modulated optical signal is filtered and amplified by the IQ signal And IQ modulation is obtained, and the bandwidth of the single-ended photodetector is greater than or equal to the clock frequency of the high-speed clock source + the cutoff frequency of the filter when the IQ signal is filtered.
  • the IQ modulated optical signal is output through the first optical IQ modulator
  • the signal of the optical pilot frequency is output through the second optical IQ modulator
  • both the first optical IQ modulator and the second optical IQ modulator receive continuous light sources to emit
  • the frequency of the Cos clock signal and the Sin clock signal is the frequency interval between the light guide and the continuous light source.
  • the upsampling multiple of the KK signal processing module is greater than or equal to 3.
  • the bandwidth of the photoelectric device at the transmitting end is only half that of the intensity modulation, avoiding the use of high-order Modulation (such as PAM4), modulation format, reduce the complexity of the direct detection system, and improve the signal receiving sensitivity.
  • PAM4 high-order Modulation
  • the bandwidth requirement of 50Gbps IQ signal is 25GHz
  • the bandwidth required for NRZ (Non-Return to Zero) intensity modulation is 50GHz.
  • the phase information of the IQ signal can be recovered based on the single-ended photodetector and digital signal processing. Therefore, dispersion compensation can be performed in the digital domain, avoiding the use of dispersion compensation modules. Reduce equipment costs.
  • FIG. 1 is a flowchart of KK signal processing in a self-coherent signal receiving method according to an embodiment of the present invention
  • FIG. 2 is a schematic diagram of a self-coherent signal sending device according to an embodiment of the present invention
  • FIG. 3 is a schematic diagram of a frequency spectrum of an IQ modulated optical signal according to an embodiment of the present invention
  • FIG. 4 is a schematic diagram of a frequency spectrum of an optical pilot signal according to an embodiment of the present invention.
  • FIG. 5 is a schematic diagram of the frequency spectrum of a self-coherent optical signal according to an embodiment of the present invention.
  • FIG. 6 is a schematic diagram of the frequency spectrum of another self-coherent optical signal according to an embodiment of the present invention.
  • FIG. 7 is a schematic diagram of a self-coherent signal receiving device according to an embodiment of the present invention.
  • FIG. 8 is a schematic diagram of the frequency spectrum of the output signal of the KK signal processing module according to the embodiment of the present invention.
  • IQ signal generation module 1 IQ signal source 11, filter 12, first electric driver 13, clock signal generation module 2, high-speed clock source 21, second electric driver 22, CW light source 3, first optical power divider 41, The second optical power splitter 42, the first optical IQ modulator 51, the second optical IQ modulator 52, the first adjustable optical attenuator 61, and the first adjustable optical attenuator 62.
  • This embodiment provides a self-coherent signal sending method, which includes the steps:
  • the I and Q components of the IQ signal are respectively filtered and amplified, and then subjected to IQ modulation to output an IQ modulated optical signal.
  • the IQ signal can be a Quadrature Phase Shift Keying (Quadrature Phase Shift Keying, QPSK) signal, and can also be a 16QAM (16 Quadrature Amplitude Modulation) signal, a 256QAM signal, etc.
  • the Cos clock signal and the Sin clock signal are generated. After the two clock signals are amplified respectively, they are subjected to IQ modulation to output the optical pilot signal.
  • the optical power of the IQ modulated optical signal and the optical pilot signal adjusts the optical power of the IQ modulated optical signal and the optical pilot signal, and synthesize the self-coherent optical signal to send out.
  • the signal intensity of the optical pilot is greater than the IQ modulated optical signal intensity.
  • the power ratio between the optical pilot signal and the IQ modulated optical signal is preferably 6dB to 8dB, and the specific value depends on the output optical signal intensity of the IQ modulator The relationship between.
  • the two IQ modulations use continuous light generated by the same continuous wave (CW) light source.
  • the two channels of IQ modulation are respectively carried out by an optical IQ modulator with MZM (Mach-Zehnder Modulator) structure.
  • MZM Machine-Zehnder Modulator
  • Each optical IQ modulator inputs one continuous light, and the IQ modulated optical signal and the optical pilot signal are respectively input into an IQ modulator.
  • the bias of each optical IQ modulator is set to NULL point to suppress the intensity of the optical carrier.
  • the self-coherent optical signal includes a guard band.
  • both the Cos clock signal and the Sin clock signal are generated by a high-speed clock source.
  • the clock frequency of the high-speed clock source is greater than or equal to the cutoff frequency when the IQ signal is filtered, which is between the optical pilot frequency and the IQ modulated optical signal. Reserve a certain guard band.
  • the present invention also provides an embodiment of a self-coherent signal receiving method, which can be used to receive and detect the self-coherent signal sent in the above-mentioned embodiment, that is, the self-coherent optical signal is synthesized by the signal of the optical pilot and the intensity of the IQ modulated optical signal, and The signal strength of the optical pilot is greater than the IQ modulated optical signal strength.
  • the self-coherent signal receiving method in this embodiment includes: receiving a self-coherent optical signal, converting it into a photocurrent and amplifying, the amplified optical signal undergoes analog-to-digital conversion sampling to obtain a real number signal, and then performing KK (Kramers-Kronig) signal processing, The signal obtained after KK processing is digitally down-converted to obtain a baseband signal, and then down-sampling is performed, and finally the baseband signal is subjected to dispersion compensation to recover the IQ signal.
  • KK Kinramers-Kronig
  • the process of KK signal processing includes the following steps:
  • the upsampling multiple needs to be greater than or equal to 3.
  • the self-coherent optical signal can be received by a single-ended photodetector.
  • the optical pilot signal is generated by a high-speed clock source and the Cos clock signal and Sin clock signal are amplified and IQ modulated.
  • IQ modulated light The signal is obtained by filtering, amplifying, and IQ modulation of the IQ signal.
  • the bandwidth of the single-ended photodetector is ⁇ the clock frequency of the high-speed clock source + the cutoff frequency of IQ signal filtering to ensure that the IQ modulated optical signal can be completely detected.
  • the sampling rate of analog-to-digital conversion sampling must be greater than or equal to twice the bandwidth of the single-ended photodetector.
  • the up-sampling multiple must be greater than or equal to 3. After down-sampling, the signal is restored to the multiple after the analog-to-digital conversion sampling.
  • Both the optical pilot signal and the IQ modulated optical signal are output through the optical IQ modulator, the optical IQ modulator receives the CW light source, and the frequency of the above Cos clock signal and Sin clock signal (radio frequency signal) is the frequency between the optical pilot and the CW light source interval.
  • the present invention also provides a self-coherent signal sending device, including an IQ signal generating module 1, a clock signal generating module 2, a CW light source 3, a first optical power splitter 41, and a second optical power splitter 42 , The first optical IQ modulator 51, the second optical IQ modulator 52, the first adjustable optical attenuator 61 and the second adjustable optical attenuator 62.
  • the CW light source 3 is used to output continuous light, and the continuous light is divided into two paths by the first optical power splitter 41, which are respectively connected to the first optical IQ modulator 51 and the second optical IQ modulator 52.
  • the IQ signal generating module 1 is used to generate two I and Q components of an IQ signal, and the two generated components are respectively connected to two radio frequency ports of the first optical IQ modulator 51.
  • the first optical IQ modulator 51 performs IQ modulation on the received quadrature phase shift monitoring signal, outputs an IQ modulated optical signal, and performs optical power adjustment through the first adjustable optical attenuator 61.
  • the clock signal generation module 2 is used to generate the Cos clock signal and the Sin clock signal, respectively connect to the two radio frequency ports of the second optical IQ modulator 42.
  • the second optical IQ modulator 42 performs processing on the received Cos clock signal and Sin clock signal.
  • the optical pilot signal is modulated, and the optical power is adjusted through the second adjustable optical attenuator 62.
  • the signal strength of the optical pilot is greater than the IQ modulated optical signal strength.
  • the second optical power divider 42 is used for synthesizing the self-coherent optical signal and transmitting the IQ modulated optical signal and the optical pilot signal after the optical power is adjusted.
  • the IQ signal generating module 1 includes an IQ signal source 11, two filters 12 and two first electric drivers 13.
  • the IQ signal source 11 is used to generate the I and Q components of the IQ signal, which are then filtered by two filters 12 respectively, and then amplified by the two first electric drivers 13, and then input to the first optical IQ modulator 51 Of two RF ports.
  • the clock signal generating module 2 includes a high-speed clock source 21 and two second electric drivers 22.
  • the high-speed clock source 21 is used to generate the Cos clock signal and the Sin clock signal, which are then amplified by the two second electric drivers 22 and input to the two radio frequency ports of the second optical IQ modulator 52.
  • the two filters 12 are both Nyquist filters, assuming that the cut-off frequency of the two filters 12 is B and the frequency of the CW light source is F , Then the spectrum of the IQ modulated optical signal output after modulation by the first optical IQ modulator 51 is shown in FIG. 3.
  • the clock frequency of the high-speed clock source 21 is the cut-off frequency B of the filter 12, and the frequency spectrum of the optical pilot output after being modulated by the second optical IQ modulator 52 is shown in FIG. 4.
  • the first optical IQ modulator 51 and the second optical IQ modulator 52 both adopt a Mach-Zehnder (MZM) structure to achieve signal modulation.
  • MZM Mach-Zehnder
  • the offset of the two optical IQ modulators in the modulation is set to NULL point, and To suppress the intensity of the optical carrier.
  • the IQ modulated optical signal and the optical pilot frequency are adjusted separately through the dimming attenuator, which is used to adjust the power ratio of the two optical signals so that the signal intensity of the optical pilot frequency is greater than the IQ modulated optical signal strength, and then it is synthesized by the second optical power divider 42
  • the spectrogram of coherent optical signal and self-coherent optical signal is shown in Figure 5.
  • the clock frequency of the high-speed clock source 21 is greater than the cutoff frequency B of the filter 12, which is between the optical pilot frequency and the IQ modulated optical signal Reserve a certain guard band, and the spectrum of the self-coherent optical signal containing the guard band after synthesis is shown in Figure 6.
  • the above guard band can prevent the frequency deviation of the optical pilot, and also prevent the IQ modulated optical signal from still having a large residual signal outside the cut-off frequency, so that the optical pilot and the IQ modulated optical signal have spectrum overlap.
  • the present invention also provides a self-coherent signal receiving device, which can be used to receive the self-coherent optical signal sent by the self-coherent signal sending device in the foregoing embodiment.
  • the self-coherent signal receiving device includes a single-ended photodetector 7, a high-speed analog-to-digital converter 8, and a digital signal processor (Digital Signal Processor, DSP) 9.
  • the single-ended photodetector 7 is used to receive the self-coherent optical signal and convert it into photocurrent.
  • the photocurrent is amplified by the transimpedance amplifier inside the single-ended photodetector 7, it is amplified by a high-speed analog-to-digital converter (Analog-to-Digital Converter, ADC 8 performs sampling, and the sampled digital signal is input to digital signal processor 9 to restore the IQ signal.
  • ADC 8 Analog-to-Digital Converter
  • the sampling rate of the high-speed analog-to-digital converter 8 needs to be greater than or equal to twice the bandwidth of the single-ended photodetector.
  • the receiving is a self-coherent optical signal sent from the coherent signal sending device, which is synthesized by the signal of the optical pilot and the intensity of the IQ modulated optical signal, and the signal intensity of the optical pilot is greater than the intensity of the IQ modulated optical signal.
  • the bandwidth of the single-ended photodetector ⁇ the clock frequency of the high-speed clock source + the cutoff frequency of the filter when filtering the IQ signal.
  • the digital signal processor 9 includes a KK signal processing module 91, a digital down-conversion module 92, a CD (Chromatic Dispersion, chromatic dispersion) compensation module 93, and an IQ signal decoding module 94.
  • the KK signal processing module 91 is used to take the square root of the real number signal sampled by the high-speed analog-to-digital converter 8 to obtain the optical signal amplitude A(n), where n represents the sampling sequence index.
  • the optical signal amplitude A(n) is up-sampled to obtain the sampled optical signal amplitude A′(m), where m represents the sequence index after up-sampling.
  • KK signal processing module 91 outputs the signal Under normal circumstances, in order to minimize the loss of signal restoration accuracy, the upsampling multiple needs to be greater than or equal to 3.
  • the digital down-conversion module 92 is used to down-convert the signal output by the KK signal processing module to obtain a baseband signal, and then perform down-sampling to restore the sampling rate of the signal received by the KK signal processing module.
  • the input of the KK signal processing module is the double sampling of the high-speed analog-to-digital converter 8. After digital up-sampling, down-conversion and down-sampling, it is restored to the double-sampling.
  • the high-speed analog-to-digital converter 8 Since the high-speed analog-to-digital converter 8 is a sampling device for analog signals, it belongs to the sampling of the "physical layer", which needs device support; and the upsampling in the KK signal processing module is sampling of the "mathematics layer” without physical devices. The support is calculated mathematically. If the high-speed analog-to-digital converter 8 can perform multiple sampling, the subsequent mathematical calculations will be avoided. However, this premise requires a higher cost, and the method in this embodiment can further reduce the cost.
  • the down-conversion frequency is the frequency of the clock source signal of the sending device. Since the output signal of the KK signal processing module 91 is an up-sampled complex signal, the down-sampled complex signal still belongs to the radio frequency signal. Its frequency spectrum is shown in Figure 8, where DC (Direct Current) means direct current.
  • C the radio frequency of the complex signal after downsampling is C, that is, C is the frequency interval between the light guide and the CW light source.
  • the CD compensation module 93 is used to perform dispersion compensation on the signal output by the digital down-conversion module 92 through a time domain or frequency domain compensation method to overcome inter-symbol crosstalk caused by dispersion.
  • the IQ signal decoding module 94 is used for recovering the constellation diagram of the IQ signal and mapping the constellation diagram symbols into a binary code stream.
  • digital dispersion compensation is used, mainly for electrical signals, that is, electrical signals detected by the single-ended photodetector 7. If this electrical signal does not contain the phase information carried by the optical signal, then it is impossible to perform dispersion compensation in a strict sense.
  • the device and method used in the present invention can recover phase information, so the final form of electric dispersion compensation is a DSP chip (of course, it also contains other DSP functions, integrated together), which is small in size and can be integrated into the board Or the optical module, the price is low, if the quantity is large, the cost will be low.

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Abstract

一种自相干信号收发方法及装置，涉及短距离光传输领域，方法包括：产生IQ信号进行IQ调制，输出IQ调制光信号；同时，产生两路时钟信号进行IQ调制，输出光导频信号，使光导频信号强度大于IQ调制光信号强度；将IQ调制光信号和光导频信号合成自相干光信号发出。接收自相干光信号并采样，取平方根得到光信号幅度A(n)后，上采样得到光信号幅度A'(m)，对上采样信号取自然对数再进行希尔伯特变换，提取相位ϕ(m)并输出信号A'(m)·ϕ(m)，进行数字下变频得到基带信号，再进行下采样，最后对基带信号进行色散补偿和信号恢复，本发明通过IQ调制和直接检测的方式，降低系统的复杂程度，提高信号接收灵敏度。

Description

一种自相干信号收发方法及装置 技术领域
本发明涉及短距离光传输领域，具体来讲涉及一种自相干信号收发方法及装置。
背景技术
强度调制与直接检测的光系统架构由于其结构简单，被广泛应用于20公里以内的短距离光传输领域。但是，随着传输速率的不断提升，短距离光传输领域面临以下瓶颈：(1)上述系统色散代价大，波长需要临近零色散区域；(2)光电器件带宽受限，上述系统将引入更大的符号间串扰。
一方面，光频谱资源有限，特别是零色散区域。新的波长规划势必远离零色散波长，那么为了克服色散问题，系统必须采用色散补偿模块。如果采用色散补偿模块，会使得系统复杂度提高，从而增加系统实施成本。另一方面，受光电器件的带宽限制，提高传输速率必须采用更高频谱效率的高阶调制方法，如：四电平脉冲幅度调制(PAM4，4 Pulse Amplitude Modulation)。但是，高阶调制的实现装置与测试方法更加复杂，信号的接收灵敏度会显著降低。
发明内容
针对现有技术中存在的缺陷，本发明的目的在于提供一种自相干信号收发方法及装置，通过IQ调制和直接检测的方式，降低系统的复杂程度，提高信号接收灵敏度。根据KK(Kramers-Kronig)关系， 只要导频的光信号强度显著大于调制后的光信号强度，经过直接检测所得到的强度信号满足最小相位(Minimum Phase)准则，就可以从该强度信号中恢复出IQ信号的相位信息。通过数字信号处理，可以进一步对所恢复的IQ信号进行色散补偿。
为达到以上目的，一方面，采取一种自相干信号发送方法，其特征在于，包括：
产生IQ信号的I、Q两路分量，经过滤波、放大后进行IQ调制，输出IQ调制光信号；
同时，产生Cos时钟信号和Sin时钟信号，经过放大后进行IQ调制，输出光导频信号；
将IQ调制光信号和光导频信号进行光功率调节，使所述光导频信号强度大于IQ调制光信号强度，再合成自相干光信号发出，其中，两路IQ调制采用同一个连续光源。
优选的，两路IQ调制分别通过马赫曾德结构的光IQ调制器进行，每个光IQ调制器输入一路连续光源产生的连续光，所述IQ调制光信号和光导频信号分别输入一个IQ调制器的射频端口，调制中，光IQ调制器的偏置设为NULL点。
优选的，所述Cos时钟信号和Sin时钟信号通过高速时钟源产生，高速时钟源的时钟频率大于或等于所述IQ信号滤波时的截止频率，所述自相干光信号在光导频与IQ调制光信号之间预留保护频带。
一方面，还提供一种自相干信号接收方法，包括：
接收自相干光信号并经过模数转换采样得到实数信号，对实数信号取平方根得到光信号幅度A(n)后，进行上采样得到采样后的光信号幅度A′(m)，对上采样信号取自然对数再进行希尔伯特变换输出复 数信号，提取相位
Figure PCTCN2019125024-appb-000001
并输出信号
Figure PCTCN2019125024-appb-000002
其中n表示采样序列索引，m表示上采样后的序列索引；
对信号
Figure PCTCN2019125024-appb-000003
进行数字下变频得到基带信号，再进行下采样，最后对基带信号进行色散补偿和信号恢复；
其中，所述自相干光信号由光导频的信号和IQ调制光信号强度合成，且所述光导频的信号强度大于IQ调制光信号强度。
优选的，所述自相干光信号通过单端光电探测器接收，所述光导频由高速时钟源产生Cos时钟信号和Sin时钟信号再经过放大和IQ调制得到，所述IQ调制光信号由IQ信号经过滤波、放大后及IQ调制得到，且所述单端光电探测器的带宽≥高速时钟源的时钟频率+IQ信号滤波时的截止频率。
优选的，所述上采样的倍数大于等于3；所述光导频的信号和IQ调制光信号均通过光IQ调制器输出，光IQ调制器接收连续光源，所述Cos时钟信号和Sin时钟信号的频率为光导频与连续光源之间的频率间隔。
另一方面，提供一种自相干信号发送装置，包括：
IQ信号产生模块，其用于产生IQ信号的I、Q两路分量；
第一光IQ调制器，其用于通过两个射频端口分别接收所述I、Q两路分量并进行调制，输出IQ调制光信号；
时钟信号产生模块，其用于产生Cos时钟信号和Sin时钟信号；
第二光IQ调制器，其用于通过两个射频端口分别接收所述Cos时钟信号和Sin时钟信号并进行调制，输出光导频信号；
两个可调光衰减器，分别用于调节所述IQ调制光信号和光导频信号的光功率，使所述光导频的信号强度大于IQ调制光信号强度；
第二光功分器，其用于将光功率调节后的IQ调制光信号和光导频信号合成自相干光信号并发送。
连续光源，其用于输出连续光；
第一光功分器，其用于将连续光为两路，分别连接第一光IQ调制器和第二光IQ调制器。
优选的，所述时钟信号产生模块包括：
高速时钟源，其用于产生Cos时钟信号和Sin时钟信号；
两个第二电驱动器，其用于分别放大所述Cos时钟信号和Sin时钟信号。
优选的，所述IQ信号产生模块包括：
IQ信号源，其用于产生IQ信号的I、Q两路分量；
两个滤波器，其用于分别对所述I、Q两路分量进行滤波；
两个第一电驱动器，其用于分别放大滤波后的I、Q两路分量。
优选的，所述滤波器为奈奎斯特滤波器，所述高速时钟源的时钟频率大于或等于所述滤波器的截止频率，所述光导频与IQ调制光信号之间预留保护频带。
优选的，所述第一光IQ调制器和第二光IQ调制器均为马赫曾德结构，调制中偏置设为NULL点。
另一方面，还提供一种自相干信号接收装置，包括单端光电探测器、高速模数转换器和数字信号处理器，所述单端光电探测器接收自相干光信号并转换为光电流，高速模数转换器进行采样并输入数字信号处理器，所述自相干光信号由光导频的信号和IQ调制光信号强度合成，且所述光导频的信号强度大于IQ调制光信号强度；
所述数字信号处理器包括：
KK信号处理模块，其用于将高速模数转换器采样得到的实数信号取平方根得到光信号幅度A(n)，再进行上采样得到采样后的光信号幅度A′(m)，还用于对上采样信号取自然对数进行希尔伯特变换输出复数信号，提取相位
Figure PCTCN2019125024-appb-000004
并输出信号
Figure PCTCN2019125024-appb-000005
其中n表示采样序列索引，m表示上采样后的序列索引；
数字下变频模块，其用于将KK信号处理模块输出的信号下变频得到基带信号，再进行下采样使之恢复KK信号处理模块所接收信号的采样率；
CD补偿模块，其用于对数字下变频模块输出的信号进行色散补偿；
IQ信号解码，其用于恢复出IQ信号的星座图并将星座图符号映射为二进制码流。
优选的，所述光导频由高速时钟源产生，所述光导频由高速时钟源产生Cos时钟信号和Sin时钟信号经放大和IQ调制得到，所述IQ调制光信号由IQ信号经过滤波、放大后及IQ调制得到，且所述单端光电探测器的带宽≥高速时钟源的时钟频率+IQ信号滤波时滤波器的截止频率。
优选的，所述IQ调制光信号通过第一光IQ调制器输出，光导频的信号通过第二光IQ调制器输出，且第一光IQ调制器和第二光IQ调制器均接收连续光源发出的连续光，所述Cos时钟信号和Sin时钟信号的频率为光导频与连续光源之间的频率间隔。
优选的，所述KK信号处理模块进行上采样倍数大于或等于3。
上述技术方案中的一个具有如下有益效果：
1、由于采用IQ信号调制，在直接检测系统中频谱效率是相应强度调制的两倍，因此对于相同的传输速率，发送端的光电器件带宽要 求仅为强度调制的二分之一，避免使用高阶调制(如PAM4)，调制格式，降低直接检测系统的复杂程度，提高信号接收灵敏度。以50Gbps速率为例，50Gbps的IQ信号(如QPSK)的带宽要求为25GHz，而NRZ(Non-Return to Zero，不归零码)强度调制需要的带宽为50GHz。
2、由于接收装置检测的强度信号满足最小相位准则，基于单端光电探测器与数字信号处理，就可以恢复出IQ信号的相位信息，因此可以在数字域进行色散补偿，避免使用色散补偿模块，降低装置成本。
附图说明
图1为本发明实施例自相干信号接收方法中KK信号处理流程图；
图2为本发明实施例自相干信号发送装置示意图；
图3为本发明实施例IQ调制光信号的频谱示意图；
图4为本发明实施例光导频信号的频谱示意图；
图5为本发明实施例自相干光信号的频谱示意图；
图6为本发明实施例另一种自相干光信号的频谱示意图；
图7为本发明实施例自相干信号接收装置示意图；
图8为本发明实施例KK信号处理模块输出信号的频谱示意图。
附图说明：
IQ信号产生模块1、IQ信号源11、滤波器12、第一电驱动器13、时钟信号产生模块2、高速时钟源21、第二电驱动器22、CW光源3、第一光功分器41、第二光功分器42、第一光IQ调制器51、第二光IQ调制器52、第一可调光衰减器61、第一可调光衰减器62。
单端光电探测器7、高速模数转换器8、数字信号处理器9，KK信号处理模块91、数字下变频模块92、CD补偿模块93、IQ信号解码模块94。
具体实施方式
以下结合附图及实施例对本发明作进一步详细说明。
本实施例中提供一种自相干信号发送方法，包括步骤：
产生IQ信号的I、Q两路分量，分别经过滤波再放大后，进行IQ调制，输出IQ调制光信号。IQ信号可以采用正交相移键控(Quadrature Phase Shift Keying，QPSK)信号，还可以为16QAM(16 Quadrature Amplitude Modulation，正交幅度调制)信号、256QAM信号等。
同时，产生Cos时钟信号和Sin时钟信号，两路时钟信号分别经过放大后，再进行IQ调制，输出光导频信号。
最后，将IQ调制光信号和光导频信号进行光功率调节，合成自相干光信号发出。通过光功率调节，使光导频的信号强度大于IQ调制光信号强度。通常情况下，为了使发送出的信号在被接收时满足最小相位准则，光导频信号与IQ调制光信号之间的功率比值优选为6dB～8dB，具体数值取决于IQ调制器的输出光信号强度之间的关系。
上述过程中，两路IQ调制采用同一个连续光源(Continuous Wave，CW)产生的连续光。两路IQ调制分别通过马赫曾德(MZM，Mach-Zehnder Modulator)结构的光IQ调制器进行，每个光IQ调制器输入一路连续光，IQ调制光信号和光导频信号分别输入一个IQ调制器的射频端口，调制中，每个光IQ调制器的偏置设为NULL点，用以抑制光载波的强度。
在上述实施例的基础上，提出一种优选的实施例，自相干光信号含保护频带。具体的，光导频产生过程中，Cos时钟信号和Sin时钟信号均通过高速时钟源产生，高速时钟源的时钟频率大于或等于IQ信号滤波时的截止频率，在光导频与IQ调制光信号之间预留一定的保护频带。
本发明还提供一种自相干信号接收方法的实施例，可以用来接收并检测上述实施例中发送的自相干信号，即自相干光信号由光导频的信号和IQ调制光信号强度合成，且所述光导频的信号强度大于IQ调制光信号强度。
本实施例中自相干信号接收方法包括：接收自相干光信号，转换为光电流并进行放大，放大后的光信号经过模数转换采样得到实数信号，再进行KK(Kramers-Kronig)信号处理，对KK处理后得到的信号进行数字下变频得到基带信号，再进行下采样，最后对基带信号进行色散补偿，恢复出IQ信号。
如图1所示，为KK信号处理的过程，具体包括步骤：
S101.对采样得到的实数信号取平方根，得到光信号幅度A(n)，其中，n为采样序列索引。
S102.对光信号幅度A(n)进行上采样得到采样后的光信号幅度A′(m)，其中，m为上采样后的序列索引。
优选的，为了尽量少的损失信号还原精度，上采样倍数需要大于或等于3。
S103.对上采样信号取自然对数。
S104.对自然对数进行希尔伯特变换，输出复数信号。
S105.提取希尔伯特变换输出复数信号的相位
Figure PCTCN2019125024-appb-000006
S106.输出处理后的信号
Figure PCTCN2019125024-appb-000007
本实施例中，自相干光信号可以通过单端光电探测器接收，自相干光信号中，光导频由高速时钟源产生Cos时钟信号和Sin时钟信号后，经过放大和IQ调制得到，IQ调制光信号由IQ信号经过滤波、放大后及IQ调制得到，单端光电探测器的带宽≥高速时钟源的时钟频率+IQ信号滤波时的截止频率，以保证IQ调制光信号能够被完整探测。根据奈奎斯特采样定律，模数转换采样的采样率需大于或等于单端光电探测器的带宽的2倍。KK信号处理中上采样的倍数需要大于或等于3，经过下采样之后，使信号恢复到模数转换采样后的倍数。
光导频的信号和IQ调制光信号均通过光IQ调制器输出，光IQ调制器接收CW光源，而上述Cos时钟信号和Sin时钟信号(射频信号)的频率为光导频与CW光源之间的频率间隔。
如图2所示，本发明还提供一种自相干信号发送装置，包括IQ信号产生模块1、时钟信号产生模块2、CW光源3、第一光功分器41、第二光功分器42、第一光IQ调制器51、第二光IQ调制器52、第一可调光衰减器61和第二可调光衰减器62。
CW光源3用于输出连续光，连续光通过第一光功分器41分为两路，分别连接第一光IQ调制器51和第二光IQ调制器52。
IQ信号产生模块1，用于产生IQ信号的I、Q两路分量，产生的两路分量分别连接第一光IQ调制器51的两个射频端口。第一光IQ调制器51对收到的正交相移监控信号进行IQ调制，输出IQ调制光信号，并通过第一可调光衰减器61进行光功率调节。
时钟信号产生模块2用于产生Cos时钟信号和Sin时钟信号，分别连接第二光IQ调制器42的两个射频端口，第二光IQ调制器42对收到的Cos时钟信号和Sin时钟信号进行调制，输出光导频信号，并通过第二可调光衰减器62进行光功率调节。
经过第一可调光衰减器61和第二可调光衰减器62进行光功率调节后，使光导频的信号强度大于IQ调制光信号强度。
第二光功分器42用于将光功率调节后的IQ调制光信号和光导频信号合成自相干光信号并发送。
优选的，IQ信号产生模块1包括IQ信号源11、两个滤波器12和两个第一电驱动器13。IQ信号源11用于产生IQ信号的I、Q两路分量，然后通过两个滤波器12分别进行滤波，再通过两个第一电驱动器13进行放大后，输入到第一光IQ调制器51的两个射频端口。
优选的，时钟信号产生模块2包括高速时钟源21和两个第二电驱动器22。高速时钟源21用于产生Cos时钟信号和Sin时钟信号，然后经过两个第二电驱动器22分别进行放大后，输入到第二光IQ调制器52的两个射频端口。
在上述实施例的基础上，提供一种更为具体的实施例，两个滤波器12均为奈奎斯特滤波器，假设两个滤波器12的截止频率为B，CW光源的频率为F，那么经过第一光IQ调制器51调制后输出的IQ调制光信号频谱如图3所示。另外，高速时钟源21的时钟频率为滤波器12的截止频率B，经过第二光IQ调制器52调制后输出的光导频的频谱如图4所示。
可行的，第一光IQ调制器51和第二光IQ调制器52都采用基于马赫曾德(MZM)结构来实现信号调制，调制中两个光IQ调制器的偏置设为NULL点，用以抑制光载波的强度。
通过调光衰减器分别调节IQ调制光信号和光导频，用于调整两路光信号的功率比，使光导频的信号强度大于IQ调制光信号强度，然后经过第二光功分器42合成自相干光信号，自相干光信号的频谱图如图5所示。
在上一个实施例的基础上，还提供一种优选的实施例，光导频产生过程中，高速时钟源21的时钟频率大于滤波器12的截止频率B，在光导频与IQ调制光信号之间预留一定的保护频带，合成后含保护频带的自相干光信号的频谱如图6所示。上述保护频带可以防止光导频的频率偏移，还可以防止IQ调制光信号在截止频率外仍存较大残留信号，使光导频与IQ调制光信号存在频谱交叠。
本发明还提供一种自相干信号接收装置，可以用来接收上述实施例中自相干信号发送装置发送的自相干光信号。如图7所示，自相干信号接收装置包括单端光电探测器7、高速模数转换器8和数字信号处理器(Digital Signal Processor，DSP)9。单端光电探测器7用于接收自相干光信号并转换为光电流，光电流经过单端光电探测器7内部的跨阻放大器放大后，由高速模数转换器(Analog-to-Digital Converter，ADC)8进行采样，采样后的数字信号输入数字信号处理器9，以恢复IQ信号。根据奈奎斯特采样定律，高速模数转换器8的采样率需大于或等于单端光电探测器的带宽的2倍。
本实施例中，接收是自相干信号发送装置发送的自相干光信号，由光导频的信号和IQ调制光信号强度合成，且光导频的信号强度大于IQ调制光信号强度。并且，单端光电探测器的带宽≥高速时钟源的时钟频率+IQ信号滤波时滤波器的截止频率。
具体的，数字信号处理器9包括KK信号处理模块91、数字下变频模块92、CD(Chromatic Dispersion，色散)补偿模块93和IQ信号解码模块94。
KK信号处理模块91用于将高速模数转换器8采样得到的实数信号取平方根，得到光信号幅度A(n)，其中n表示采样序列索引。对光信号幅度A(n)进行上采样，得到采样后的光信号幅度A′(m)，m 表示上采样后的序列索引。对上采样信号取自然对数，然后进行希尔伯特变换输出复数信号，提取该附属信号的相位
Figure PCTCN2019125024-appb-000008
最后KK信号处理模块91输出信号
Figure PCTCN2019125024-appb-000009
通常情况下，为了尽量少的损失信号还原精度，上采样倍数需要大于或等于3。
数字下变频模块92，用于将KK信号处理模块输出的信号下变频得到基带信号，再进行下采样使之恢复KK信号处理模块所接收信号的采样率。本实施例中，KK信号处理模块输入的是高速模数转换器8的2倍采样，经过数字的上采样、下变频以及下采样之后，再恢复成2倍采样。
由于高速模数转换器8是模拟信号的采样器件，属于“物理层”的采样，这个是需要器件支撑的；而KK信号处理模块中的上采样是“数学层”的采样，没有物理器件的支撑，是数学计算得到的。如果高速模数转换器8能够进行多倍的采样，就会避免了后面的数学计算，但这个前提需要更高的成本，本实施例中的方式能够进一步降低成本。
另外，下变频频率为发送装置时钟源信号频率，由于KK信号处理模块91输出信号为上采样的复数信号，经过下采样后的复数信号仍然属于射频信号，其频谱如图8所示，其中DC(Direct Current)表示直流电。假设下采样后复数信号的射频频率为C，即：C为光导频与CW光源之间的频率间隔。
CD补偿模块93，用于通过时域或者频域补偿方法，对数字下变频模块92输出的信号进行色散补偿，克服由色散导致的符号间串扰。
IQ信号解码模块94，用于恢复出IQ信号的星座图并将星座图符号映射为二进制码流。
对该射频信号进行数字下变频，得到基带信号。最后，可以对基带信号进行色散补偿并恢复出原始IQ信号。
上述实施例中，采用数字色散补偿，主要针对的是电信号，也就是单端光电探测器7探测下来的电信号。如果这个电信号不含光信号所携带的相位信息，那么是无法进行严格意义的色散补偿的。本发明采用的装置和方法可以恢复出相位信息，所以电色散补偿的最终形态是一颗DSP芯片(当然，里面还包含其它的DSP功能，集成到一起)，体积很小，能够集成到板卡或者光模块，价格低，如果量很大，成本会低。
本发明不局限于上述实施方式，对于本技术领域的普通技术人员来说，在不脱离本发明原理的前提下，还可以做出若干改进和润饰，这些改进和润饰也视为本发明的保护范围之内。本说明书中未作详细描述的内容属于本领域专业技术人员公知的现有技术。

Claims (15)

  1. 一种自相干信号发送方法，其特征在于，包括：
    产生IQ信号的I、Q两路分量，经过滤波、放大后进行IQ调制，输出IQ调制光信号；
    同时，产生Cos时钟信号和Sin时钟信号，经过放大后进行IQ调制，输出光导频信号；
    将IQ调制光信号和光导频信号进行光功率调节，使所述光导频信号强度大于IQ调制光信号强度，再合成自相干光信号发出，其中，两路IQ调制采用同一个连续光源。
  2. 如权利要求1所述的自相干信号发送方法，其特征在于：两路IQ调制分别通过马赫曾德结构的光IQ调制器进行，每个光IQ调制器输入一路连续光源产生的连续光，所述IQ调制光信号和光导频信号分别输入一个IQ调制器的射频端口，调制中，光IQ调制器的偏置设为NULL点。
  3. 如权利要求1所述的自相干信号发送方法，其特征在于：所述Cos时钟信号和Sin时钟信号通过高速时钟源产生，高速时钟源的时钟频率大于或等于所述IQ信号滤波时的截止频率，所述自相干光信号在光导频与IQ调制光信号之间预留保护频带。
  4. 一种自相干信号接收方法，其特征在于，包括：
    接收自相干光信号并经过模数转换采样得到实数信号，对实数信号取平方根得到光信号幅度A(n)后，进行上采样得到采样后的光信号幅度A′(m)，对上采样信号取自然对数再进行希尔伯特变换输出复数信号，提取相位
    Figure PCTCN2019125024-appb-100001
    并输出信号
    Figure PCTCN2019125024-appb-100002
    其中n表示采样序列索引，m表示上采样后的序列索引；
    对信号
    Figure PCTCN2019125024-appb-100003
    进行数字下变频得到基带信号，再进行下采样，最后对基带信号进行色散补偿和信号恢复；
    其中，所述自相干光信号由光导频的信号和IQ调制光信号强度合成，且所述光导频的信号强度大于IQ调制光信号强度。
  5. 如权利要求4所述的自相干信号接收方法，其特征在于：所述自相干光信号通过单端光电探测器接收，所述光导频由高速时钟源产生Cos时钟信号和Sin时钟信号再经过放大和IQ调制得到，所述IQ调制光信号由IQ信号经过滤波、放大后及IQ调制得到，且所述单端光电探测器的带宽≥高速时钟源的时钟频率+IQ信号滤波时的截止频率。
  6. 如权利要求4所述的自相干信号接收方法，其特征在于：所述上采样的倍数大于等于3；
    所述光导频的信号和IQ调制光信号均通过光IQ调制器输出，光IQ调制器接收连续光源，所述Cos时钟信号和Sin时钟信号的频率为光导频与连续光源之间的频率间隔。
  7. 一种自相干信号发送装置，其特征在于，包括：
    IQ信号产生模块，其用于产生IQ信号的I、Q两路分量；
    第一光IQ调制器，其用于通过两个射频端口分别接收所述I、Q两路分量并进行调制，输出IQ调制光信号；
    时钟信号产生模块，其用于产生Cos时钟信号和Sin时钟信号；
    第二光IQ调制器，其用于通过两个射频端口分别接收所述Cos时钟信号和Sin时钟信号并进行调制，输出光导频信号；
    两个可调光衰减器，分别用于调节所述IQ调制光信号和光导频信号的光功率，使所述光导频的信号强度大于IQ调制光信号强度；
    第二光功分器，其用于将光功率调节后的IQ调制光信号和光导频信号合成自相干光信号并发送。
    连续光源，其用于输出连续光；
    第一光功分器，其用于将连续光为两路，分别连接第一光IQ调制器和第二光IQ调制器。
  8. 如权利要求7所述的自相干信号发送装置，其特征在于，所述时钟信号产生模块包括：
    高速时钟源，其用于产生Cos时钟信号和Sin时钟信号；
    两个第二电驱动器，其用于分别放大所述Cos时钟信号和Sin时钟信号。
  9. 如权利要求8所述的自相干信号发送装置，其特征在于，所述IQ信号产生模块包括：
    IQ信号源，其用于产生IQ信号的I、Q两路分量；
    两个滤波器，其用于分别对所述I、Q两路分量进行滤波；
    两个第一电驱动器，其用于分别放大滤波后的I、Q两路分量。
  10. 如权利要求9所述的自相干信号发送装置，其特征在于，所述滤波器为奈奎斯特滤波器，所述高速时钟源的时钟频率大于或等于所述滤波器的截止频率，所述光导频与IQ调制光信号之间预留保护频带。
  11. 如权利要求7所述的自相干信号发送装置，其特征在于，所述第一光IQ调制器和第二光IQ调制器均为马赫曾德结构，调制中偏置设为NULL点。
  12. 一种自相干信号接收装置，包括单端光电探测器、高速模数转换器和数字信号处理器，所述单端光电探测器接收自相干光信号并 转换为光电流，高速模数转换器进行采样并输入数字信号处理器，其特征在于：
    所述自相干光信号由光导频的信号和IQ调制光信号强度合成，且所述光导频的信号强度大于IQ调制光信号强度；
    所述数字信号处理器包括：
    KK信号处理模块，其用于将高速模数转换器采样得到的实数信号取平方根得到光信号幅度A(n)，再进行上采样得到采样后的光信号幅度A′(m)，还用于对上采样信号取自然对数进行希尔伯特变换输出复数信号，提取相位
    Figure PCTCN2019125024-appb-100004
    并输出信号
    Figure PCTCN2019125024-appb-100005
    其中n表示采样序列索引，m表示上采样后的序列索引；
    数字下变频模块，其用于将KK信号处理模块输出的信号下变频得到基带信号，再进行下采样使之恢复KK信号处理模块所接收信号的采样率；
    CD补偿模块，其用于对数字下变频模块输出的信号进行色散补偿；
    IQ信号解码，其用于恢复出IQ信号的星座图并将星座图符号映射为二进制码流。
  13. 如权利要求12所述的自相干信号接收装置，其特征在于：所述光导频由高速时钟源产生，所述光导频由高速时钟源产生Cos时钟信号和Sin时钟信号经放大和IQ调制得到，所述IQ调制光信号由IQ信号经过滤波、放大后及IQ调制得到，且所述单端光电探测器的带宽≥高速时钟源的时钟频率+IQ信号滤波时滤波器的截止频率。
  14. 如权利要求12所述的自相干信号接收装置，其特征在于：所述IQ调制光信号通过第一光IQ调制器输出，光导频的信号通过第二光IQ调制器输出，且第一光IQ调制器和第二光IQ调制器均接收 连续光源发出的连续光，所述Cos时钟信号和Sin时钟信号的频率为光导频与连续光源之间的频率间隔。
  15. 如权利要求12所述的自相干信号接收装置，其特征在于：所述KK信号处理模块进行上采样倍数大于或等于3。
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