CN110350982B - Self-coherent signal receiving and transmitting method and device - Google Patents
Self-coherent signal receiving and transmitting method and device Download PDFInfo
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- CN110350982B CN110350982B CN201910477384.9A CN201910477384A CN110350982B CN 110350982 B CN110350982 B CN 110350982B CN 201910477384 A CN201910477384 A CN 201910477384A CN 110350982 B CN110350982 B CN 110350982B
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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
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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]
- H04B10/5561—Digital phase modulation
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- H—ELECTRICITY
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- 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
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- 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
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- H—ELECTRICITY
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- 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
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Abstract
An autocorrelation signal receiving and transmitting method and device relate to the field of short-distance optical transmission, and the method comprises the following steps: generating an IQ signal to perform IQ modulation and outputting an IQ modulated optical signal; meanwhile, two paths of clock signals are generated to carry out IQ modulation, and light pilot signals are output, so that the intensity of the light pilot signals is greater than that of IQ modulation light signals; and synthesizing the IQ modulation optical signal and the optical frequency guide signal into a self-coherent optical signal and sending the self-coherent optical signal. Receiving and sampling an auto-coherent optical signal, obtaining an optical signal amplitude A (n) by taking a square root, then obtaining an optical signal amplitude A' (m) by up-sampling, taking a natural logarithm of the up-sampled signal, then performing Hilbert transform, and extracting a phase
And output the signal
The invention reduces the complexity of the system and improves the signal receiving sensitivity by IQ modulation and direct detection.
Description
Technical Field
The invention relates to the field of short-distance optical transmission, in particular to an autocorrelation signal receiving and transmitting method and device.
Background
The optical system architecture of intensity modulation and direct detection is widely applied to the field of short-distance optical transmission within 20 kilometers due to the simple structure. However, with the increasing transmission rate, the short-distance optical transmission field faces the following bottlenecks: (1) the system has high dispersion cost, and the wavelength needs to be close to a zero dispersion area; (2) the optoelectronic devices are bandwidth limited and the above system will introduce greater inter-symbol crosstalk.
On the one hand, the optical spectrum resources are limited, in particular the zero dispersion region. New wavelength plans tend to be far from the zero dispersion wavelength and the system must employ a dispersion compensation module in order to overcome the dispersion problem. If a dispersion compensation module is used, the system complexity increases, thereby increasing the system implementation cost. On the other hand, due to the bandwidth limitation of optoelectronic devices, higher order modulation methods with higher spectral efficiency must be adopted to increase the transmission rate, such as: four-level Pulse Amplitude Modulation (PAM4, 4Pulse Amplitude Modulation). However, the implementation apparatus and the test method of the high-order modulation are more complicated, and the receiving sensitivity of the signal is significantly reduced.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide an autocorrelation signal transceiving method and device, which reduce the complexity of a system and improve the signal receiving sensitivity in an IQ modulation and direct detection mode. According to the KK (Kramers-Kronig) relationship, as long as the intensity of the pilot light signal is significantly greater than the intensity of the modulated light signal, the Phase information of the IQ signal can be recovered from the intensity signal by directly detecting the obtained intensity signal to satisfy the Minimum Phase (Minimum Phase) criterion. The restored IQ signal can be further dispersion compensated by digital signal processing.
In order to achieve the above object, in one aspect, an autocorrelation signal transmission method includes:
i, Q two paths of components of the IQ signal are generated, IQ modulation is carried out after filtering and amplification, and an IQ modulation optical signal is output;
meanwhile, a Cos clock signal and a Sin clock signal are generated, IQ modulation is carried out after amplification, and an optical pilot signal is output;
and carrying out optical power adjustment on the IQ modulation optical signal and the optical frequency guide signal to enable the intensity of the optical frequency guide signal to be greater than that of the IQ modulation optical signal, and synthesizing an auto-coherent optical signal to be emitted, wherein the two paths of IQ modulation adopt the same continuous light source.
Preferably, the two paths of IQ modulation are performed by optical IQ modulators of mach-zehnder structures, each optical IQ modulator inputs a continuous light generated by a continuous light source, the IQ modulated optical signal and the optical frequency guide signal are respectively input to a radio frequency port of one IQ modulator, and during modulation, the bias of the optical IQ modulator is set to a NULL point.
Preferably, 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 cut-off frequency of the IQ signal during filtering, and the self-coherent optical signal reserves a guard band between the optical frequency guide signal and the IQ modulation optical signal.
In one aspect, an autocorrelation signal receiving method is further provided, including:
receiving an auto-coherent optical signal, performing analog-to-digital conversion and sampling to obtain a real number signal, taking the square root of the real number signal to obtain the amplitude A (n) of the optical signal, performing up-sampling to obtain the amplitude A' (m) of the sampled optical signal, taking the natural logarithm of the up-sampled signal, performing Hilbert transform to output a complex number signal, and extracting the phase
And output the signal
Wherein n represents a sample sequence index and m represents an upsampled sequence index;
for the signal
Carrying out digital down-conversion to obtain a baseband signal, then carrying out down-sampling, and finally carrying out dispersion compensation and signal recovery on the baseband signal;
the self-coherent optical signal is synthesized by optical frequency guide signals and IQ modulation optical signal intensity, and the optical frequency guide signal intensity is greater than the IQ modulation optical signal intensity;
preferably, the self-coherent optical signal is received by a single-ended photodetector, the optical pilot signal is obtained by amplifying and IQ modulating a Cos clock signal and a Sin clock signal generated by a high-speed clock source, the IQ modulated optical signal is obtained by filtering, amplifying and IQ modulating an IQ signal, and a bandwidth of the single-ended photodetector is greater than or equal to a clock frequency of the high-speed clock source plus a cutoff frequency of the IQ signal during filtering.
Preferably, the multiple of the upsampling is more than or equal to 3; the optical frequency guide signal and the IQ modulation optical signal are both output through an optical IQ modulator, the optical IQ modulator receives a continuous light source, and the frequency of the Cos clock signal and the frequency of the Sin clock signal are the frequency interval between the optical frequency guide signal and the continuous light source.
In another aspect, an apparatus for transmitting an autocorrelation signal is provided, including:
an IQ signal generation module for generating I, Q two-way components of the IQ signal;
the first optical IQ modulator is used for respectively receiving and modulating the I, Q two paths of components through two radio frequency ports and outputting IQ modulation optical signals;
a clock signal generation module for generating a Cos clock signal and a Sin clock signal;
the second optical IQ modulator is used for respectively receiving and modulating the Cos clock signal and the Sin clock signal through two radio frequency ports and outputting an optical pilot signal;
the two variable optical attenuators are respectively used for adjusting the optical power of the IQ modulation optical signal and the optical frequency guide signal, so that the intensity of the optical frequency guide signal is greater than that of the IQ modulation optical signal;
and the second optical power divider is used for synthesizing the IQ modulation optical signal after optical power adjustment and the optical frequency guide signal into an autocorrelation optical signal and transmitting the autocorrelation optical signal.
A continuous light source for outputting continuous light;
and the first optical power divider is used for dividing the continuous light into two paths and respectively connected with the first optical IQ modulator and the second optical IQ modulator.
Preferably, the clock signal generating module includes:
a high-speed clock source for generating a Cos clock signal and a Sin clock signal;
two second electrical drivers for amplifying the Cos clock signal and Sin clock signal, respectively.
Preferably, the IQ signal generation module comprises:
an IQ signal source for generating I, Q two-path components of an IQ signal;
two filters, which are used for respectively filtering the I, Q two paths of components;
two first electrical drivers for amplifying the filtered I, Q two-way components, respectively.
Preferably, 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, and a guard band is reserved between the optical frequency guide signal and the IQ modulation optical signal.
Preferably, the first optical IQ modulator and the second optical IQ modulator are both of a mach-zehnder structure, and the offset during modulation is set to a NULL point.
On the other hand, the self-coherent signal receiving device comprises a single-ended photoelectric detector, a high-speed analog-to-digital converter and a digital signal processor, wherein the single-ended photoelectric detector receives a self-coherent optical signal and converts the self-coherent optical signal into a photocurrent, the high-speed analog-to-digital converter performs sampling and inputs the sample into the digital signal processor, the self-coherent optical signal is synthesized by the intensities of an optical frequency guide signal and an IQ modulation optical signal, and the intensity of the optical frequency guide signal is greater than the intensity of the IQ modulation optical signal;
the digital signal processor includes:
a KK signal processing module, which is used for taking the square root of a real number signal obtained by sampling of the high-speed analog-to-digital converter to obtain an optical signal amplitude A (n), then carrying out up-sampling to obtain a sampled optical signal amplitude A' (m), and also used for taking a natural logarithm of the up-sampling signal, carrying out Hilbert transform to output a complex number signal, and extracting a phase
And output the signal
Wherein n represents a sample sequence index and m represents an upsampled sequence index;
the digital down-conversion module is used for down-converting the signal output by the KK signal processing module to obtain a baseband signal, and then down-sampling is carried out to recover the sampling rate of the signal received by the KK signal processing module;
the CD compensation module is used for carrying out dispersion compensation on the signal output by the digital down-conversion module;
and IQ signal decoding for recovering the constellation diagram of the IQ signal and mapping the constellation diagram symbols into a binary code stream.
Preferably, the optical pilot signal is obtained by amplifying and IQ modulating a Cos clock signal and a Sin clock signal generated by a high-speed clock source, the IQ modulated optical signal is obtained by filtering, amplifying and IQ modulating an IQ signal, and the bandwidth of the single-ended photodetector is greater than or equal to the clock frequency of the high-speed clock source and the cutoff frequency of the filter when filtering the IQ signal.
Preferably, the IQ-modulated optical signal is output through a first optical IQ modulator, the optical frequency guide signal is output through a second optical IQ modulator, and the first optical IQ modulator and the second optical IQ modulator both receive continuous light emitted by a continuous light source, and the frequency of the Cos clock signal and the frequency of the Sin clock signal are frequency intervals between the optical frequency guide signal and the continuous light source.
Preferably, the KK signal processing module performs upsampling by a multiple greater than or equal to 3.
One of the above technical solutions has the following beneficial effects:
1. due to the fact that IQ signal modulation is adopted, the spectral efficiency in a direct detection system is twice of that of corresponding intensity modulation, the bandwidth requirement of a photoelectric device at a sending end is only half of that of the intensity modulation for the same transmission rate, high-order modulation (such as PAM4) and a modulation format are avoided, the complexity of the direct detection system is reduced, and the signal receiving sensitivity is improved. Taking 50Gbps rate as an example, 50Gbps IQ signal (such as QPSK) requires 25GHz bandwidth, while NRZ (Non-Return to Zero) intensity modulation requires 50GHz bandwidth.
2. Because the intensity signal detected by the receiving device meets the minimum phase criterion, the phase information of the IQ signal can be recovered based on the single-ended photoelectric detector and the digital signal processing, so that the dispersion compensation can be carried out in a digital domain, a dispersion compensation module is avoided, and the device cost is reduced.
Drawings
Fig. 1 is a flowchart illustrating processing of a KK signal in an autocorrelation signal receiving method according to an embodiment of the present invention;
FIG. 2 is a diagram of an apparatus for sending self-coherent signals 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 frequency spectrum diagram of an embodiment of an incoherent optical signal;
FIG. 6 is a schematic frequency spectrum diagram of another self-coherent optical signal in accordance with an embodiment of the present invention;
FIG. 7 is a diagram of an apparatus for receiving an autocorrelation signal according to an embodiment of the present invention;
fig. 8 is a schematic diagram of a frequency spectrum of an output signal of the KK signal processing module according to the embodiment of the present invention.
Description of the drawings:
the IQ signal generating module 1, the IQ signal source 11, the filter 12, the first electric driver 13, the clock signal generating module 2, the high-speed clock source 21, the second electric driver 22, the CW light source 3, the first optical power splitter 41, the second optical power splitter 42, the first optical IQ modulator 51, the second optical IQ modulator 52, the first variable optical attenuator 61, and the first variable optical attenuator 62.
The device comprises a single-ended photoelectric detector 7, a high-speed analog-to-digital converter 8, a digital signal processor 9, a KK signal processing module 91, a digital down-conversion module 92, a CD compensation module 93 and an IQ signal decoding module 94.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
The embodiment provides an autocorrelation signal sending method, including the steps of:
and I, Q two paths of components of the IQ signal are generated, are subjected to IQ modulation after being filtered and amplified respectively, and output IQ modulated optical signals. The IQ signal may be a Quadrature Phase Shift Keying (QPSK) signal, a 16QAM (16Quadrature Amplitude Modulation) signal, a 256QAM signal, or the like.
Meanwhile, Cos clock signals and Sin clock signals are generated, and the two paths of clock signals are amplified respectively and then subjected to IQ modulation to output optical pilot signals.
And finally, carrying out optical power adjustment on the IQ modulation optical signal and the optical frequency guide signal, and synthesizing the IQ modulation optical signal and the optical frequency guide signal into a self-coherent optical signal to be sent out. The optical power is adjusted to make the optical frequency signal intensity greater than the IQ modulation optical signal intensity. In general, in order to make the transmitted signal satisfy the minimum phase criterion when being received, the power ratio between the optical frequency guide signal and the IQ-modulated optical signal is preferably 6dB to 8dB, and the specific value depends on the relationship between the intensities of the output optical signals of the IQ-modulator.
In the above process, the two paths of IQ modulation use Continuous light generated by the same Continuous light source (CW). Two paths of IQ modulation are respectively carried out through optical IQ modulators with Mach-Zehnder (MZM) structures, each optical IQ Modulator inputs a path of continuous light, IQ modulation optical signals and optical frequency guide signals are respectively input into a radio frequency port of one IQ Modulator, and in modulation, the bias of each optical IQ Modulator is set to a NULL point to suppress the intensity of optical carriers.
On the basis of the above embodiment, a preferred embodiment is proposed, in which the self-coherent optical signal includes a guard band. Specifically, in the optical frequency signal generation process, 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 cut-off frequency during the IQ signal filtering, and a certain guard band is reserved between the optical frequency signal and the IQ modulated optical signal.
The present invention further provides an embodiment of an autocorrelation signal receiving method, which can be used to receive and detect the autocorrelation signal sent in the above embodiment, that is, the autocorrelation optical signal is synthesized by the optical pilot signal and the strength of the IQ modulated optical signal, and the strength of the optical pilot signal is greater than the strength of the IQ modulated optical signal.
The method for receiving the self-coherent signal in the embodiment comprises the following steps: the method comprises the steps of receiving an auto-coherent optical signal, converting the auto-coherent optical signal into a photocurrent and amplifying the photocurrent, sampling the amplified optical signal through analog-to-digital conversion to obtain a real number signal, processing a KK (Kramers-Kronig) signal, performing digital down-conversion on the signal obtained after the KK processing to obtain a baseband signal, then performing down-sampling, and finally performing dispersion compensation on the baseband signal to recover an IQ signal.
As shown in fig. 1, the KK signal processing process specifically includes the steps of:
s101, taking a square root of a real number signal obtained by sampling to obtain an optical signal amplitude A (n), wherein n is a sampling sequence index.
S102, up-sampling the optical signal amplitude A (n) to obtain a sampled optical signal amplitude A' (m), wherein m is a sequence index after up-sampling.
Preferably, the upsampling multiple needs to be greater than or equal to 3 in order to minimize loss of signal recovery accuracy.
S103, taking the natural logarithm of the up-sampled signal.
And S104, performing Hilbert transform on the natural logarithm, and outputting a complex signal.
S105, extracting the phase of the complex signal output by the Hilbert transform
S106, outputting the processed signal
In this embodiment, the self-coherent optical signal may be received by a single-ended photodetector, in the self-coherent optical signal, the optical frequency guide signal is obtained by amplifying and IQ modulating after the Cos clock signal and the Sin clock signal are generated by the high-speed clock source, the IQ modulated optical signal is obtained by filtering, amplifying and IQ modulating the IQ signal, and the bandwidth of the single-ended photodetector is greater than or equal to the clock frequency of the high-speed clock source plus the cutoff frequency of the IQ signal during filtering, so as to ensure that the IQ modulated optical signal can be detected completely. According to nyquist's sampling law, the sampling rate of analog-to-digital conversion sampling needs to be greater than or equal to 2 times the bandwidth of a single-ended photodetector. And the multiple of up-sampling in KK signal processing needs to be more than or equal to 3, and after down-sampling, the signal is restored to the multiple after analog-to-digital conversion sampling.
The optical frequency signal and the IQ-modulated optical signal are both output through an optical IQ modulator, which receives a CW light source, and the frequencies of the Cos clock signal and the Sin clock signal (radio frequency signal) are the frequency intervals between the optical frequency signal and the CW light source.
As shown in fig. 2, the present invention further provides an autocorrelation signal transmitting apparatus, which includes an IQ signal generating module 1, a clock signal generating module 2, a CW light source 3, a first optical power splitter 41, a second optical power splitter 42, a first optical IQ modulator 51, a second optical IQ modulator 52, a first variable optical attenuator 61, and a second variable optical attenuator 62.
The CW light source 3 is configured to output continuous light, and the continuous light is divided into two paths by the first optical power splitter 41, and the two paths are respectively connected to the first optical IQ modulator 51 and the second optical IQ modulator 52.
The IQ signal generating module 1 is configured to generate I, Q two paths of components of the IQ signal, where the two paths of components are respectively connected to two rf ports of the first optical IQ modulator 51. The first optical IQ modulator 51 IQ-modulates the received quadrature phase-shifted monitor signal, outputs an IQ-modulated optical signal, and performs optical power adjustment by the first variable optical attenuator 61.
The clock signal generating module 2 is configured to generate a Cos clock signal and a Sin clock signal, and respectively connect to two radio frequency ports of the second optical IQ modulator 42, where the second optical IQ modulator 42 modulates the received Cos clock signal and Sin clock signal, outputs an optical pilot signal, and adjusts optical power through the second adjustable optical attenuator 62.
After the optical power adjustment is performed by the first variable optical attenuator 61 and the second variable optical attenuator 62, the optical pilot signal intensity is made greater than the IQ-modulated optical signal intensity.
The second optical power splitter 42 is configured to combine the IQ-modulated optical signal and the optical frequency-guided signal after the optical power adjustment into an auto-coherent optical signal and transmit the auto-coherent optical signal.
Preferably, the IQ signal generation module 1 comprises an IQ signal source 11, two filters 12 and two first electrical drivers 13. The IQ signal source 11 is configured to generate I, Q two-way components of an IQ signal, which are then filtered by two filters 12, amplified by two first electrical drivers 13, and input to two rf ports of the first optical IQ modulator 51.
Preferably, the clock signal generation module 2 comprises a high-speed clock source 21 and two second electrical drivers 22. The high-speed clock source 21 is configured to generate a Cos clock signal and a Sin clock signal, and then the Cos clock signal and the Sin clock signal are amplified by the two second electrical drivers 22, respectively, and then input to the two rf ports of the second optical IQ modulator 52.
On the basis of the above embodiment, a more specific embodiment is provided, in which both the filters 12 are nyquist filters, and assuming that the cut-off frequency of the two filters 12 is B and the frequency of the CW light source is F, the spectrum of the IQ modulated optical signal output after being modulated by the first optical IQ modulator 51 is as shown in fig. 3. The clock frequency of the high-speed clock source 21 is the cutoff frequency B of the filter 12, and the spectrum of the optical pilot signal output after being modulated by the second optical IQ modulator 52 is as shown in fig. 4.
It is feasible that both the first optical IQ modulator 51 and the second optical IQ modulator 52 implement signal modulation using a mach-zehnder (MZM) -based structure, and the bias of the two optical IQ modulators in the modulation is set to a NULL point for suppressing the intensity of the optical carrier.
The IQ-modulated optical signal and the optical frequency-guided signal are respectively adjusted by the light-adjusting attenuator to adjust the power ratio of the two optical signals, so that the intensity of the optical frequency-guided signal is greater than that of the IQ-modulated optical signal, and then the optical frequency-guided signal is synthesized into the self-coherent optical signal by the second optical power splitter 42, and the spectrogram of the self-coherent optical signal is shown in fig. 5.
On the basis of the above embodiment, there is also provided a preferred embodiment, in the optical frequency guiding signal generating process, the clock frequency of the high-speed clock source 21 is greater than the cut-off frequency B of the filter 12, a certain guard band is reserved between the optical frequency guiding signal and the IQ-modulated optical signal, and the frequency spectrum of the synthesized self-coherent optical signal with the guard band is as shown in fig. 6. The guard band can prevent the frequency deviation of the optical frequency guide signal and also can prevent the IQ modulation optical signal from still having larger residual signals beyond the cut-off frequency, so that the optical frequency guide signal and the IQ modulation optical signal have frequency spectrum overlapping.
The invention also provides an autocorrelation signal receiving device, which can be used for receiving the autocorrelation optical signal sent by the autocorrelation signal sending device in the embodiment. As shown in fig. 7, the self-coherent Signal receiving apparatus includes a single-ended photodetector 7, a high-speed analog-to-Digital converter 8, and a Digital Signal Processor (DSP) 9. The single-ended photodetector 7 is configured to receive an auto-coherent optical signal and convert the auto-coherent optical signal into a photocurrent, the photocurrent is amplified by a transimpedance amplifier inside the single-ended photodetector 7, and then sampled by a high-speed Analog-to-Digital Converter (ADC) 8, and a sampled Digital signal is input to a Digital signal processor 9 to recover an IQ signal. The sampling rate of the high-speed analog-to-digital converter 8 needs to be greater than or equal to 2 times the bandwidth of the single-ended photodetector according to the nyquist sampling law.
In this embodiment, the receiving is an auto-coherent optical signal transmitted by the auto-coherent signal transmitting apparatus, and the intensity of the optical pilot signal is synthesized with the intensity of the IQ modulated optical signal, and the intensity of the optical pilot signal is greater than the intensity of the IQ modulated optical signal. And the bandwidth of the single-ended photoelectric detector is more than or equal to the clock frequency of the high-speed clock source and the cut-off frequency of the filter when the IQ signal is filtered.
Specifically, the digital signal processor 9 includes a KK signal processing module 91, a digital down-conversion module 92, a CD (Chromatic Dispersion) compensation module 93, and an IQ signal decoding module 94.
The KK signal processing module 91 is configured to take a square root of a real number signal sampled by the high-speed analog-to-digital converter 8 to obtain an optical signal amplitude a (n), where n represents a sampling sequence index. The optical signal amplitude a (n) is up-sampled to obtain a sampled optical signal amplitude a' (m), where m represents the up-sampled sequence index. Taking natural logarithm of up-sampled signal, Hilbert transforming to output complex signal, and extracting phase of the auxiliary signal
Finally, the KK signal processing module 91 outputs a signal
In general, the upsampling multiple needs to be greater than or equal to 3 in order to reduce the signal recovery accuracy as little as possible.
And the digital down-conversion module 92 is configured 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. In this embodiment, the input of the KK signal processing module is 2 times of sampling of the high-speed analog-to-digital converter 8, and after digital up-sampling, down-conversion and down-sampling, the sampling is restored to 2 times of sampling.
Since the high-speed analog-to-digital converter 8 is a sampling device of an analog signal, belonging to the sampling of a physical layer, the device is required to support; and the up-sampling in the KK signal processing module is the sampling of a mathematical layer, has no support of a physical device and is obtained by mathematical calculation. The latter mathematical calculations are avoided if the high speed analog to digital converter 8 is capable of multiple sampling, but this presupposes a higher cost, which in this embodiment can be further reduced.
In addition, the down-conversion frequency is the frequency of the clock source signal of the transmitting device, and 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 a radio frequency signal, and the frequency spectrum thereof is shown in fig. 8, where dc (direct current) represents direct current. Assuming that the radio frequency of the down-sampled complex signal is C, that is: c is the frequency separation between the optical frequency guide signal and the CW light source.
The CD compensation module 93 is configured to perform dispersion compensation on the signal output by the digital down-conversion module 92 by using a time domain or frequency domain compensation method, so as to overcome inter-symbol crosstalk caused by dispersion.
An IQ signal decoding module 94, configured to recover the constellation of the IQ signal and map the constellation symbols into a binary code stream.
And carrying out digital down-conversion on the radio frequency signal to obtain a baseband signal. Finally, the baseband signal may be dispersion compensated and the original IQ signal may be recovered.
In the above embodiment, the digital dispersion compensation is mainly used for the electrical signal, that is, the electrical signal detected by the single-ended photodetector 7. If the electrical signal does not contain the phase information carried by the optical signal, then a strict dispersion compensation cannot be performed. The device and the method can recover the phase information, so that the final form of the electric dispersion compensation is a DSP chip (certainly, the device also comprises other DSP functions and is integrated together), the size is small, the device can be integrated into a board card or an optical module, the price is low, and if the amount is large, the cost is low.
The present invention is not limited to the above-described embodiments, and it will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the principle of the present invention, and such modifications and improvements are also considered to be within the scope of the present invention. Those not described in detail in this specification are within the skill of the art.
Claims (13)
1. An auto-coherent signal transmission method, comprising:
i, Q two paths of components of the IQ signal are generated, IQ modulation is carried out after filtering and amplification, and an IQ modulation optical signal is output;
meanwhile, a Cos clock signal and a Sin clock signal are generated, IQ modulation is carried out after amplification, and an optical pilot signal is output;
and carrying out optical power adjustment on the IQ modulation optical signal and the optical frequency guide signal to enable the intensity of the optical frequency guide signal to be greater than that of the IQ modulation optical signal, and synthesizing an auto-coherent optical signal to be emitted, wherein the two paths of IQ modulation adopt the same continuous light source.
2. The method of transmitting an autocorrelation signal as defined in claim 1, wherein: two paths of IQ modulation are respectively carried out through optical IQ modulators with Mach-Zehnder structures, each optical IQ modulator inputs continuous light generated by one path of continuous light source, IQ modulation optical signals and optical frequency guide signals are respectively input into a radio frequency port of one IQ modulator, and during modulation, the bias of the optical IQ modulators is set as a NULL point.
3. The method of transmitting an autocorrelation signal as defined in claim 1, wherein: 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 cut-off frequency of the IQ signal during filtering, and a guard band is reserved between the optical frequency guide signal and the IQ modulation optical signal by the self-coherent optical signal.
4. An autocorrelation signal receiving method, comprising:
receiving an auto-coherent optical signal, performing analog-to-digital conversion and sampling to obtain a real number signal, taking the square root of the real number signal to obtain the amplitude A (n) of the optical signal, performing up-sampling to obtain the amplitude A' (m) of the sampled optical signal, taking the natural logarithm of the up-sampled signal, performing Hilbert transform to output a complex number signal, and extracting the phase
And output the signal
Wherein n represents a sample sequence index and m represents an upsampled sequence index;
for the signal
Carrying out digital down-conversion to obtain a baseband signal, then carrying out down-sampling, and finally carrying out dispersion compensation and signal recovery on the baseband signal;
the self-coherent optical signal is synthesized by optical frequency guide signals and IQ modulation optical signal intensity, and the optical frequency guide signal intensity is greater than the IQ modulation optical signal intensity;
the self-coherent optical signal is received by a single-ended photoelectric detector, the optical pilot signal is obtained by amplifying and IQ modulating a Cos clock signal and a Sin clock signal generated by a high-speed clock source, the IQ modulated optical signal is obtained by filtering, amplifying and IQ modulating an IQ signal, and the bandwidth of the single-ended photoelectric detector is more than or equal to the clock frequency of the high-speed clock source and the cut-off frequency of the IQ signal during filtering.
5. The method of self-coherent signal reception according to claim 4, characterized in that: the multiple of the up-sampling is more than or equal to 3;
the optical frequency guide signal and the IQ modulation optical signal are both output through an optical IQ modulator, the optical IQ modulator receives a continuous light source, and the frequency of the Cos clock signal and the frequency of the Sin clock signal are the frequency interval between the optical frequency guide signal and the continuous light source.
6. An apparatus for transmitting an autocorrelation signal, comprising:
an IQ signal generation module for generating I, Q two-way components of the IQ signal;
the first optical IQ modulator is used for respectively receiving and modulating the I, Q two paths of components through two radio frequency ports and outputting IQ modulation optical signals;
a clock signal generation module for generating a Cos clock signal and a Sin clock signal;
the second optical IQ modulator is used for respectively receiving and modulating the Cos clock signal and the Sin clock signal through two radio frequency ports and outputting an optical pilot signal;
the two variable optical attenuators are respectively used for adjusting the optical power of the IQ modulation optical signal and the optical frequency guide signal, so that the intensity of the optical frequency guide signal is greater than that of the IQ modulation optical signal;
the second optical power divider is used for synthesizing the IQ modulation optical signal after the optical power is adjusted and the optical frequency guide signal into an autocorrelation optical signal and sending the autocorrelation optical signal;
a continuous light source for outputting continuous light;
and the first optical power divider is used for dividing the continuous light into two paths and respectively connected with the first optical IQ modulator and the second optical IQ modulator.
7. The self-coherent signal transmission apparatus according to claim 6, wherein said clock signal generation module comprises:
a high-speed clock source for generating a Cos clock signal and a Sin clock signal;
two second electrical drivers for amplifying the Cos clock signal and Sin clock signal, respectively.
8. The apparatus for transmitting an autocorrelation signal as defined in claim 7 wherein said IQ signal generation module comprises:
an IQ signal source for generating I, Q two-path components of an IQ signal;
two filters, which are used for respectively filtering the I, Q two paths of components;
two first electrical drivers for amplifying the filtered I, Q two-way components, respectively.
9. The self-coherent signal transmission apparatus according to claim 8, wherein said filter is a nyquist filter, a clock frequency of said high-speed clock source is greater than or equal to a cutoff frequency of said filter, and a guard band is reserved between said optical frequency signal and the IQ-modulated optical signal.
10. The self-coherent signal transmitting apparatus according to claim 6, wherein said first and second optical IQ modulators are each of a mach-zehnder structure, and an offset in modulation is set to a NULL point.
11. An autocorrelation signal receiving device comprises a single-ended photoelectric detector, a high-speed analog-to-digital converter and a digital signal processor, wherein the single-ended photoelectric detector receives an autocorrelation optical signal and converts the autocorrelation optical signal into photocurrent, and the high-speed analog-to-digital converter performs sampling and inputs the photocurrent into the digital signal processor, and is characterized in that:
the self-coherent optical signal is synthesized by optical frequency guide signals and IQ modulation optical signal intensity, and the optical frequency guide signal intensity is greater than the IQ modulation optical signal intensity;
the digital signal processor includes:
a KK signal processing module for squaring the real signal sampled by the high-speed analog-to-digital converter to obtain the optical signal amplitude A (n)) Then up-sampling to obtain the sampled optical signal amplitude A' (m), taking the natural logarithm of the up-sampled signal, Hilbert transforming to output complex signal, and extracting phase
And output the signal
Wherein n represents a sample sequence index and m represents an upsampled sequence index;
the digital down-conversion module is used for down-converting the signal output by the KK signal processing module to obtain a baseband signal, and then down-sampling is carried out to recover the sampling rate of the signal received by the KK signal processing module;
the CD compensation module is used for carrying out dispersion compensation on the signal output by the digital down-conversion module;
IQ signal decoding for recovering the constellation diagram of the IQ signal and mapping the constellation diagram symbols into a binary code stream;
the optical pilot signal is obtained by amplifying and IQ modulating a Cos clock signal and a Sin clock signal generated by a high-speed clock source, the IQ modulated optical signal is obtained by filtering, amplifying and IQ modulating an IQ signal, and the bandwidth of the single-ended photoelectric detector is more than or equal to the clock frequency of the high-speed clock source and the cut-off frequency of a filter when the IQ signal is filtered.
12. The self-coherent signal receiving apparatus of claim 11, wherein: the IQ modulation optical signal is output through a first optical IQ modulator, the optical frequency guide signal is output through a second optical IQ modulator, the first optical IQ modulator and the second optical IQ modulator both receive continuous light emitted by a continuous light source, and the frequency of the Cos clock signal and the frequency of the Sin clock signal are the frequency interval between the optical frequency guide signal and the continuous light source.
13. The self-coherent signal receiving apparatus of claim 11, wherein: and the KK signal processing module performs upsampling multiple more than or equal to 3.
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| US12007454B2 (en) * | 2021-03-11 | 2024-06-11 | Hi Llc | Devices, systems, and methods for suppressing optical noise in optically pumped magnetometers |
| CN113098620B (en) * | 2021-03-22 | 2022-02-18 | 杭州电子科技大学 | Device and method for generating arbitrary waveform based on IQ modulator |
| CN115913387A (en) * | 2022-11-30 | 2023-04-04 | 天津大学 | High-efficiency self-coherent receiving method based on space division multiplexing system |
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