CN117176259B - Four-way multiplexing optical communication method and device based on self-coherence - Google Patents
Four-way multiplexing optical communication method and device based on self-coherence Download PDFInfo
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Abstract
The application particularly relates to a four-way multiplexing optical communication method and device based on self-coherence, wherein the method comprises the following steps: s10, dividing a light beam emitted by a laser into signal light and local oscillation light through a power divider; s20, at a transmitting end, signal light is sequentially polarized, modulated and combined through a dual-polarization IQ modulator, and the modulation comprises: respectively loading four pilot signals with different frequencies to the virtual parts and the real parts of two baseband signals obtained by polarization on the baseband signals in X and Y polarization states generated by polarization; s30, at a receiving end, carrying out polarization alignment on the signal light and the local oscillation light through polarization control, carrying out phase recovery on the signal light by utilizing the pilot signal loaded in the step S20, and then respectively carrying out self-coherent detection on polarization states corresponding to the signal light and the local oscillation light to obtain four paths of independent electric signals, so that the method has the advantages of low power consumption, large transmission capacity and the like.
Description
Technical Field
The present disclosure relates to the field of optical communications technologies, and in particular, to a four-way multiplexing optical communication method and apparatus based on self-coherence.
Background
With the rapid growth of internet traffic, people's demand for communication capacity has grown exponentially. And the capacity expansion technology of the communication capacity comprises optical time division multiplexing and wavelength division multiplexing. The coherent optical communication technology based on polarization multiplexing, advanced modulation code pattern, coherent detection and Digital Signal Processing (DSP) technology in the prior art has the advantages of high sensitivity, high spectral efficiency and damage resistance, and is a main technology of a metropolitan area network and a long-distance trunk line transmission network. On the medium-short distance scene such as a data center, the system with the direct detection of the Intensity Modulation (IMDD) of the Coarse Wavelength Division Multiplexing (CWDM) is the first choice for the application of the data center due to the simple structure and lower cost. However, limited by the number of wavelengths and bandwidth density used, they have difficulty in coping with challenges presented by the ever-increasing data center rates.
It is expected that after 2022 years the speed of the switch interface will reach 800Gb/s, even 1.6Tb/s. Traditional coherent detection systems used in metropolitan area networks and long distance scenarios are a potential solution for high capacity data exchange required for data centers due to their higher sensitivity and spectral efficiency. However, due to the requirement of conventional coherent detection techniques for narrow linewidth lasers and complex DSP algorithms, such systems are too expensive, bulky and power hungry for short range applications.
For this reason, many schemes have been proposed to reduce power consumption, transceiver cost and DSP complexity. Among these methods, the homologous homodyne self-coherent detection technique is considered as one of the most promising candidate methods for data center optical interfaces. The main principle of the homologous system is to send the modulated signal and a part of the energy from the same light source as a Local Oscillator (LO) to the receiving end for coherent reception, so it is also called self-coherent detection. This approach can greatly reduce the effects of laser phase noise and does not require frequency offset estimation, allowing the use of uncooled large linewidth Distributed Feedback (DFB) lasers and simplifying DSP algorithms. The simplified DSP algorithm of the optical transmission system aiming at the homologous homodyne self-coherent detection technology is mainly concentrated on polarization demultiplexing of a local oscillator light source, and the technical scheme of demultiplexing through dual-polarization signal light is basically absent. On the one hand, the power consumption and the cost required by the method are too high, and on the other hand, the phase noise of the electric signal obtained by demultiplexing is large.
Disclosure of Invention
Aiming at the technical problems of complex structure, high cost and large phase noise in the double-polarization demultiplexing in the prior art, the application provides the four-way multiplexing optical communication method and device based on self-coherence, which at least have the advantages of simple structure, low power consumption, large transmission capacity, small phase noise and the like.
In a first aspect, the present application provides a four-way multiplexing optical communication method based on self-coherence, at least including the following steps:
s10, dividing a light beam emitted by a laser into signal light and local oscillation light through a power divider;
s20, at a transmitting end, signal light is sequentially polarized, modulated and combined through a dual-polarization IQ modulator, and the modulation comprises: respectively loading four pilot signals with different frequencies to the virtual parts and the real parts of two baseband signals obtained by polarization on the baseband signals in X and Y polarization states generated by polarization;
s30, at a receiving end, carrying out polarization alignment on the signal light and the local oscillation light through polarization control, carrying out phase recovery on the signal light by utilizing the pilot signal loaded in the step S20, and then respectively carrying out self-coherent detection on polarization states corresponding to the signal light and the local oscillation light to obtain four paths of independent electric signals.
Specifically, one of the concepts of the present application is that, by loading pilot signals with different frequencies on the real part of the baseband signal in the X polarization state, the imaginary part of the baseband signal in the X polarization state, the real part of the baseband signal in the Y polarization state, and the imaginary part of the baseband signal in the Y polarization state at the transmitting end, and adding a polarization control board at the receiving end, the polarization and phase compensation functions of the signal light in the self-coherent optical fiber transmission system are realized, and four paths of electric signals acquired by the receiving end are completely independent, thereby achieving the purposes of improving the optical fiber communication capacity and reducing the power consumption.
Further, the pilot signal is a single frequency baseband signal comprising real and imaginary parts, typically expressed mathematically as exp (2jpi ft), where f is the pilot frequency, which is a single frequency signal of cos (2pi ft) and sin (2pi ft) at the real and imaginary parts, respectively.
Further, in step S30, the phase recovery includes: and extracting power information of virtual parts and real parts of the two baseband signals at different pilot frequency signal frequency points, and adjusting the voltage in the phase recovery process according to the power information.
Specifically, another concept of the present application is that signal collection is performed by using a polarization phase control board, and power of four paths of signals at frequency points of loaded pilot signals is extracted, and because the polarization phase control board can adjust phase and voltage, the four paths of signals only have power at the frequency points of the pilot signals corresponding to the loading, and power at the frequency points of the other three pilot signals is very low, so that it is ensured that the four paths of electric signals can be successfully separated after the optical signals are subjected to polarization and phase control, and independence is achieved without interference.
Further, signal acquisition is performed by a low bandwidth low sampling rate ADC module.
Further, when polarizing the signal light, the method further comprises phase adjustment:
and detecting and tracking each path of electric signal obtained by final detection to obtain phase noise information, so that the phase of the signal light in polarization is adjusted according to the phase noise information.
Specifically, the method and the device realize phase recovery through pilot signals, and further comprise phase compensation operation when received signal light is polarized, phase noise information is acquired by detecting and tracking each path of electric signal finally detected and acquired, and the phase of the signal light when polarized is adjusted by utilizing the phase noise information, so that phase noise generated after the signal light is transmitted is compensated, and the phase precision of the signal light is improved.
In step S30, the polarization alignment includes: and detecting and tracking the polarization state of the signal light to acquire polarization rotation information of the signal light, so that the polarization rotation angle of the local oscillation light in polarization is adjusted according to the polarization rotation information of the signal light.
Specifically, the signal polarization is compensated in a polarization alignment mode, so that the signal polarization is aligned with the local oscillation light.
Further, in step S20, the value range of each pilot frequency signal frequency is 30 kHz-90 kHz.
Further, the frequency difference of each pilot signal is more than or equal to 10kHz.
Further, the frequencies of the pilot signals loaded by the real part of the base band signal in the X polarization state, the imaginary part of the base band signal in the X polarization state, the real part of the base band signal in the Y polarization state and the imaginary part of the base band signal in the Y polarization state are 40kHz, 50kHz, 60kHz and 70kHz respectively.
Specifically, the difference of different frequency intervals between pilot signals affects tracking accuracy, and the larger the difference of the frequency is, the better the tracking accuracy is, otherwise, the worse the tracking accuracy is.
Furthermore, the frequency range and the frequency interval of the pilot signal provided by the application can be applied to modulation methods mainly used for the self-coherent optical fiber transmission such as DP-QPSK, DP-8QAM, DP-16QAM, DP-32QAM, DP-64QAM and the like.
In some embodiments, after step S30, step S40 is further included;
s40, inputting the acquired four paths of independent electric signals into a PAM4 mathematical signal processing chip for demodulation.
Specifically, because the four paths of electric signals extracted by the method have good independence, subsequent clock recovery and signal judgment can be completed by adopting a traditional PAM4 digital signal processing chip, the reutilization of the traditional client-side PAM4 digital signal processing chip is realized, a novel chip is not required to be replaced or adopted, and the power consumption and the cost of the self-coherent detection system are effectively reduced.
In some embodiments, the optical communication method is applied to the O-band.
Specifically, in a short-distance transmission scene, the O wave band can effectively avoid the influence of chromatic dispersion on the system.
Further, the transmission band is specifically 1300nm to 1320nm.
Further, the optical communication method is used for double-polarization 16QAM signal communication under the 53G baud rate.
In a second aspect, the present application provides a four-way multiplexing optical communication device based on self-coherence, configured to implement any one of the four-way multiplexing optical communication methods based on self-coherence provided in the first aspect, where the optical communication device at least includes:
a transmitter for transmitting local oscillation light and modulated signal light;
the transmitter has: a laser, a power divider and a dual-polarization IQ modulator;
the power divider is used for dividing the light beam emitted by the laser into signal light and local oscillation light;
the dual-polarization IQ modulator is configured to sequentially polarize, modulate and combine signal light, where the modulation includes: respectively loading four pilot frequencies with different frequencies on real and imaginary optical signals of X and Y polarized signal light generated by polarization;
a receiver for receiving and demodulating the local oscillation light and the signal light from the transmitter;
the receiver includes:
the polarization phase control plate is used for polarizing the signal light into X and Y polarized signal light again and performing photoelectric conversion on the signal light respectively;
the polarization control board is used for enabling the local oscillation light to be polarized into X and Y polarization states and performing photoelectric conversion on the local oscillation light respectively;
the 90-degree mixer is used for beating the self-coherent electric signal;
and the balance detector is used for demodulating the electric signal obtained by the 90-degree mixer processing.
Specifically, the device is used for realizing the four-way multiplexing optical communication method based on self-coherence provided by any embodiment of the first aspect. The device provided by the application can be functionally divided into two parts, wherein one part is a transmitter, the other part is a receiver, and the transmitter and the receiver are connected through a transmission optical fiber.
The transmitter generates two identical beams of light through the laser and the power divider, wherein one beam of light is used as self-coherent local oscillation light and is directly transmitted through the transmission optical fiber, and the other beam of light becomes signal light carrying signals after passing through the dual-polarization IQ modulator. The receiver aligns the two polarization states of the signal light with the two polarization states of the local oscillation light through a polarization phase control board, separates the signal light received by the receiving end according to the frequency point power of the pilot signal applied by the dual-polarization IQ modulator, and obtains independent four paths of electric signals, thereby achieving the purposes of improving the transmission capacity of optical communication, reducing the power consumption and reducing the phase noise.
Further, the dual-polarization IQ modulator includes: the device comprises a polarization beam splitter, a power divider, a modulation resistor, a data signal modulator, a bias controller, a light combiner and a polarization beam combiner;
the polarization beam splitter is used for polarizing signal light of X and Y polarization states;
the power divider is used for dividing signal light in X polarization state and Y polarization state respectively;
the modulation resistor is used for modulating the data signal modulator and the bias controller;
the data signal modulator is used for loading four paths of signals to real parts and imaginary parts of baseband signals in X and Y polarization states respectively;
the bias controller is used for loading four pilot signals with different frequencies to the virtual part and the real part of the baseband signals in the X polarization state and the Y polarization state obtained by polarization respectively;
the light combiner is used for respectively combining the X and Y polarized signal lights after light splitting;
the polarization beam combiner is used for combining the X and Y polarization state signal light.
Specifically, four paths of information can be loaded for one beam of optical signals through the combination of the devices, and different pilot signals are loaded for the four paths of information respectively.
Further, the polarization phase control plate includes: the device comprises a polarization rotator, a first light splitter, a second light splitter, a first phase controller, a second phase controller, a digital signal processing and digital-to-analog converter, an Ix digital-to-analog converter, a Qx digital-to-analog converter, an Iy digital-to-analog converter and a Qy digital-to-analog converter;
the polarization rotator is used for correcting the incident signal light;
the first beam splitter and the second beam splitter are used for performing power division on light;
one end of the digital signal processing and digital-analog converter is respectively connected with the Ix digital-analog converter, the Qx digital-analog converter, the Iy digital-analog converter and the Qy digital-analog converter, the other end of the digital signal processing and digital-analog converter is respectively connected with the first phase controller and the second phase controller, and the adjustment of the phase of light is realized by applying different pressures to the first phase controller and the second phase controller.
Specifically, through the combination of the devices, the signal acquisition can be performed through the polarization phase control board, the power of the four paths of signals at the frequency point of the loaded pilot signals is extracted, and the polarization phase control board can adjust the phase and the voltage, so that the four paths of signals only have power at the frequency point of the pilot signals corresponding to the loading, and the power at the frequency point of the other three pilot signals is very low, thereby ensuring that the four paths of electric signals can be successfully separated after the optical signals are subjected to polarization and phase control, realizing independence and mutual noninterference.
Further, the application provides a four-way multiplexing optical communication device based on self-coherence, which includes: and the PAM4 digital signal processing chip is used for processing four paths of independent electric signals obtained by the receiver in a separated mode.
In summary, the present application provides a four-way multiplexing optical communication method and apparatus based on self-coherence, because the present application modulates a dual-polarization signal at a transmitting end, four dimensions of the dual-polarization modulation signal: the real part of the baseband signal in the x polarization state, the imaginary part of the baseband signal in the x polarization state, the real part of the baseband signal in the y polarization state and the imaginary part of the baseband signal in the y polarization state are loaded with pilot signals with different frequencies, so that the optical signals and the local oscillation light are respectively transmitted in two paths of optical fibers under the short-distance transmission scene of the data center. After the signal light and the local oscillation light are transmitted through the optical fiber, the phase and the polarization state of the signal light and the polarization state of the local oscillation light are adjusted through the polarization phase control plate and the polarization control plate respectively. And the signal light after polarization state and phase adjustment and the local oscillation light after polarization state adjustment are subjected to beat frequency in the receiving end, so that four recovered independent electric signals can be obtained. Because the four recovered electric signals are completely independent, the subsequent clock recovery and signal judgment can be completed by adopting a traditional PAM4 digital signal processing chip. Therefore, the four-way multiplexing optical communication method based on self-coherence has the advantages of being simple in structure, low in power consumption, large in transmission capacity, small in phase noise and the like.
Drawings
The present application will be described in further detail below in conjunction with the drawings and preferred embodiments, but it will be appreciated by those skilled in the art that these drawings are drawn for the purpose of illustrating the preferred embodiments only and thus should not be taken as limiting the scope of the present application. Moreover, unless specifically indicated otherwise, the drawings are merely schematic representations, not necessarily to scale, of the compositions or constructions of the described objects and may include exaggerated representations.
Fig. 1 is a schematic flow chart of a four-way multiplexing optical communication method based on self-coherence according to an embodiment of the present application;
fig. 2 is a schematic working diagram of a four-way multiplexing optical communication method based on self-coherence according to an embodiment of the present application;
fig. 3 is a schematic structural diagram of a four-way multiplexing optical communication device based on self-coherence according to an embodiment of the present application;
FIG. 4 is a schematic diagram of a dual-polarization IQ modulator according to an embodiment of the present disclosure;
FIG. 5 is a schematic diagram of a structure of a polarization phase control plate according to an embodiment of the present disclosure;
FIG. 6 is a schematic structural diagram of a polarization controller according to an embodiment of the present disclosure;
fig. 7 is a diagram of demodulation results of a dual-polarization 16QAM signal in a 53G baud rate scenario according to an embodiment of the present application.
Detailed Description
The present application will be described in detail with reference to fig. 1 to 7.
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.
The application provides a four-way multiplexing optical communication method and device based on self-coherence, which at least have the advantages of simple structure, low power consumption, large transmission capacity, small phase noise and the like.
Referring to fig. 1, a flow chart of a four-way multiplexing optical communication method based on self-coherence is provided in the embodiment of fig. 1.
Specifically, in the four-way multiplexing optical communication method based on self-coherence, the light beam emitted by the laser is divided into the signal light and the local oscillation light by the power divider through the step S10, namely, the step S10 provides the signal light and the local oscillation light for self-coherence transmission; then, at the transmitting end, the signal light is sequentially polarized, modulated and combined by a dual-polarization IQ modulator in the step S20, the step aims to modulate four paths of signals to the signal light by a dual-polarization and IQ modulation mode, pilot signals with different frequencies are loaded for the four paths of signals respectively, and the loaded pilot signals provide indexing for the receiving end to extract four paths of independent electric signals; and finally, performing self-coherent beat frequency and demodulation on the signal light in the X polarization state, the local oscillation light and the signal light in the Y polarization state respectively through a polarization phase control plate, a polarization control plate and loaded pilot frequencies at a receiving end, namely, the receiving end carries out phase calculation on the electric signals obtained through photoelectric regulation and the frequency mixer of the electric signals by using phase recovery information provided by the corresponding pilot signals loaded by a transmitting end, and carrying out phase recovery on the corresponding virtual electric signals and real electric signals in the X polarization state and the Y polarization state, thereby obtaining four paths of independent electric signals.
It should be noted that, the polarization in step S20 includes polarizing the signal light into a baseband signal in the X polarization state and a baseband signal in the Y polarization state; the modulation includes: respectively loading four pilot signals with different frequencies to the virtual parts and the real parts of two baseband signals obtained by polarization on the baseband signals in X and Y polarization states generated by polarization; the beam combination comprises the following steps: and combining the four paths of signal light subjected to the modulation and pilot signal loading. At this time, the signal light after beam combination can be transmitted in one path of optical fiber, so that the transmission capacity of the optical fiber is greatly improved.
Further, the four-way multiplexing optical communication method based on self-coherence further includes step S40 of inputting the obtained four-way independent electrical signals into a PAM4 mathematical signal processing chip for demodulation. Based on the optical communication method provided by the application, four paths of electric signals obtained through final extraction have good independence, so that subsequent clock recovery and signal judgment can be completed by adopting a traditional PAM4 digital signal processing chip, and the reutilization of the traditional client-side PAM4 digital signal processing chip is realized. Therefore, the optical communication method provided by the application does not need to replace or adopt a novel chip, and the traditional PAM4 chip can be directly used, so that the power consumption and the cost of the self-coherent detection system can be effectively reduced.
In order to make the workflow of the four-way multiplexing optical communication method based on self-coherence provided by the present application more intuitive, please refer to fig. 2, which is a schematic diagram of the four-way multiplexing optical communication method based on self-coherence provided in the embodiment of the present application.
Specifically, the four-way multiplexing optical communication method based on self-coherence comprises a transmitting end and a receiving end, wherein the transmitting end and the receiving end communicate through optical fibers with equal lengths. The laser emitted by the laser is divided into two paths of same signal light and local oscillation light through the power divider, namely, the transmission of the signal light and the local oscillation light can be understood to be synchronous. The signal light needs to be modulated and loaded with pilot signals, and then is transmitted through optical fibers until the signal light is transmitted to a receiving end, and local oscillation light is directly transmitted to the receiving end without processing. After the signal light reaches the receiving end, not only the X-polarized signal light and the Y-polarized signal light are obtained through polarization, but also the phases of the two polarized signals are compensated, so that the influence of phase noise on the signal light is eliminated. Then, the signal light with the phase compensation is taken as a group according to the polarization states of the signal light with the X polarization state and the local oscillation light with the X polarization state, the signal light with the Y polarization state and the local oscillation light with the Y polarization state are taken as a group, the signal acquisition and beat frequency recovery operation are respectively carried out, and finally, the Ix electric signal and the Qx electric signal with the X polarization state and the Iy electric signal and the Qy electric signal with the Y polarization state are obtained through the phase recovery of the electric signals, so that the separation of four electric signals is completed.
It should be noted that the 90 ° frequency mixer is input with two paths of local oscillation light LOx and LOy, and signal light Rx and Ry, respectivelyLOx×Rx，LOx×Ry and LOy×Rx，LOyAnd calculating the X Ry, and carrying out addition or subtraction operation by a balance detector arranged behind the 90-degree mixer to respectively obtain an Ix electric signal and a Qx electric signal corresponding to the X polarization state, and an Iy electric signal and a Qy electric signal corresponding to the Y polarization state.
Further, the pilot signal is a single frequency baseband signal comprising real and imaginary parts, typically expressed mathematically as exp (2jpi ft), where f is the pilot frequency, which is a single frequency signal of cos (2pi ft) and sin (2pi ft) at the real and imaginary parts, respectively.
Further, in step S20, the value range of each pilot frequency signal frequency is 30 kHz-90 kHz.
Further, the frequency difference of each pilot signal is more than or equal to 10kHz.
Further, the frequency of the pilot signal loaded by the real part of the base band signal in the X polarization state, the imaginary part of the base band signal in the X polarization state, the real part of the base band signal in the Y polarization state and the imaginary part of the base band signal in the Y polarization state is f 1 =40kHz、f 2 =50kHz、f 3 =60 kHz and f 4 =70kHz。
Specifically, the difference of different frequency intervals between pilot signals affects tracking accuracy, and the larger the frequency output value is, the better the tracking accuracy is, otherwise, the worse the tracking accuracy is.
Illustratively, f 1 、f 2 、f 3 And f 4 The values are not necessarily increased in sequence, and can be combined arbitrarily, so long as any frequency value is within the value range, or the requirement of the frequency difference is met.
Furthermore, the frequency range and the frequency interval of the pilot signal provided by the application can be applied to modulation methods mainly used for the self-coherent optical fiber transmission such as DP-QPSK, DP-8QAM, DP-16QAM, DP-32QAM, DP-64QAM and the like.
Further, in step S30, the corresponding pilot signal provides phase recovery information, and the phase calculation is performed on the electric signal obtained through the photo-adjustment and the mixer of the electric signal, so as to perform phase recovery on the electric signal of each virtual part and real part of the corresponding X and Y polarization states.
Specifically, another concept of the present application is that signal collection is performed by using a polarization phase control board, and power of four paths of signals at frequency points of loaded pilot signals is extracted, and because the polarization phase control board can adjust phase and voltage, the four paths of signals only have power at the frequency points of the pilot signals corresponding to the loading, and power at the frequency points of the other three pilot signals is very low, so that it is ensured that the four paths of electric signals can be successfully separated after the optical signals are subjected to polarization and phase control, and independence is achieved without interference.
Further, signal acquisition is performed by a low bandwidth low sampling rate ADC module.
For an explanation of the four-way optical communication device based on self-coherence provided in the application, please refer to fig. 3, which is a schematic structural diagram of the four-way optical communication device based on self-coherence provided in the embodiment of fig. 3.
Specifically, the optical communication device includes at least: and a transmitter for transmitting the local oscillation light and the modulated signal light, and a receiver for receiving and demodulating the local oscillation light and the signal light from the transmitter. The transmitter and the receiver are connected through two transmission optical fibers, one optical fiber is used for transmitting signal light, and the other optical fiber is used for transmitting local oscillation light.
Wherein the transmitter has: a laser, a power divider and a dual-polarization IQ modulator; the power divider is used for dividing the light beam emitted by the laser into signal light and local oscillation light; the dual polarization IQ modulator is used for sequentially carrying out polarization, modulation and beam combination on signal light, and the modulation comprises the following steps: four pilots with different frequencies are respectively loaded on real and imaginary optical signals of X and Y polarized signal light generated by polarization.
It should be noted that the transmitter has a function of dividing a light beam emitted by the laser into signal light and local oscillation light for subsequent self-coherent detection, modulating the signal light and loading pilot signals, so that the finally combined signal light can carry four different signals, and pilot signals with different pilot frequencies are loaded between the different signals, thereby enabling the transmitter to transmit four signals at a time.
And the receiver includes: the polarization phase control plate is used for polarizing the signal light into X and Y polarized signal light again and performing photoelectric conversion on the signal light respectively; the polarization control board is used for enabling the local oscillation light to be polarized into X and Y polarization states and performing photoelectric conversion on the local oscillation light respectively; the 90-degree mixer is used for beating the self-coherent electric signal; and the balance detector is used for demodulating the electric signal obtained by the 90-degree mixer processing.
The four-path balance detector also outputs the polarization and phase information to be tracked respectively, and is used for regulating the polarization and the phase of the signal light by the polarization phase control plate.
In order to further explain the working principle of the dual-polarization IQ modulator provided in the present application, please refer to fig. 4, which is a schematic structural diagram of the dual-polarization IQ modulator provided in the embodiment of the present application in fig. 4.
Specifically, after the signal light separated by the power divider enters the dual-polarization IQ modulator, the signal light is first separated into a baseband signal in an X polarization state and a baseband signal in a Y polarization state by the polarization beam splitter. The baseband signal of X polarization state is divided into two beams of signal light with the same power through a power divider and is respectively transmitted to a modulation resistor, when one beam of signal light passes through the modulation resistor, a data signal modulator loads an Ix signal to the beam of signal light, and meanwhile, a bias controller also loads the signal light with the frequency of f 1 Loading the beam of signal light with a pilot signal of (a); while the other beam of signal light passes through the modulation resistor, the data signal modulator loads the Qx signal to the beam of signal light, and the bias controller also applies a frequency f 2 The pilot signal of the beam is loaded, so that the X polarization state signal light after beam combination carries two paths of information of Ix and Qx, and the two paths of signals are respectively loaded with the frequency f 1 And f 2 Is used for the pilot signal of the (a). Similarly, after the baseband signal in Y polarization state passes through the operation similar to the baseband signal in X polarization state, the combined Y polarization state signal light carries two paths of information of Iy and Qy, and the two paths of signals are respectively loaded with frequency f 3 And f 4 Is used for the pilot signal of the (a). Finally, the signal light in the X polarization state and the signal light in the Y polarization state are combined by a polarization beam combiner to obtain the signal light finally used for optical fiber transmission, four paths of signals of the signal light are respectively loaded with four pilot signals with different frequencies at the moment, namely, in the step S20, the baseband signals in the X polarization state and the baseband signals in the Y polarization state generated by polarization are respectively loaded with four pilot signals with different frequencies to the virtual parts and the real parts of the two baseband signals obtained by polarization.
In step S20, the process of loading the signal by the data signal modulator is hidden.
The polarization beam splitter is used for polarizing signal light of X and Y polarization states; the power divider is used for dividing the signal light in the X polarization state and the Y polarization state respectively; the modulation resistor is used for modulating the data signal modulator and the bias controller; the data signal modulator is used for loading four paths of signals to real parts and imaginary parts of baseband signals in X and Y polarization states respectively; the bias controller is used for loading four pilot signals with different frequencies to virtual parts and real parts of baseband signals in X and Y polarization states obtained by polarization respectively; the light combiner is used for respectively combining the X and Y polarized signal lights after light splitting; the polarization beam combiner is used for combining the X and Y polarization state signal light.
Further, a phase shifter is arranged behind any modulation resistor before the light combiner, and the phase shifter is connected with a bias controller. And the offset voltage tracking device is used for tracking the offset voltage of the signal light through the arrangement of the phase shifter.
Further, the frequency f of the pilot signal loaded by the real part of the X-polarized signal light 1 Frequency f of pilot signal loaded by imaginary part of x polarization state signal light=40 khz 2 Frequency f of pilot signal loading real part of Y polarized signal light =50 kHz 3 Frequency f of pilot signal of imaginary loading of y polarization state signal light 4 =70 kHz. While the magnitude of the pilot signal loading has a negligible effect on the optical signal performance.
In order to further explain the working principle of the polarization phase control board provided in the present application, please refer to fig. 5, which is a schematic structural diagram of the polarization phase control board provided in the embodiment of the present application in fig. 5.
Specifically, after the signal light enters the polarization phase controller in the receiver, the signal light is divided into the X-polarization signal light and the Y-polarization signal light by the polarization rotator, and the digital-to-analog converter for digital signal processing performs phase compensation on the X-polarization signal light and the Y-polarization signal light obtained by polarization through the first phase controller and the second phase controller respectively.
Wherein 3dB refers to the optical splitter, i.e. the illustration comprises a first optical splitter and a second optical splitter;
v1 is the voltage applied to the first phase controller and V2 is the voltage applied to the second phase controller;
φ 1 refers to the corresponding phase of the first phase controller, phi 2 The phase corresponding to the second phase controller is referred to, so that polarization control of X, Y local oscillation light is realized through a double interference structure of an upper arm and a lower arm.
Further, the control algorithm of the polarization phase control board controls the phase of the polarization control so that each signal only has corresponding pilot information and no pilot information of the other three paths.
For example, the real part of the X polarization signal light only has the pilot signal corresponding to the loading after being adjusted, and the power of the pilot signals of the rest three frequency offsets is very low. Therefore, any two paths of the four paths of signals are not coupled due to polarization rotation or phase rotation, and correct demodulation of the signals is further guaranteed.
Further, the RF signal generated after the beat frequency of the pilot signal and the local oscillation light at the receiving end is filtered out by a low-pass filter or a digital signal processing mode, multiplied by the signal light, and then sampled by four ADC (analog-to-digital converter) to obtain independent four-channel electric signal information.
It should be noted that, since the polarization phase control board only needs to detect the power of the pilot frequency, the sampling rate of the required analog-to-digital converter is very low, which is far lower than the baud rate of the optical signal.
Further, the sampling rate of the analog-to-digital converter is 100MSa/s.
In order to further explain the working principle of the polarization control board provided in the present application, please refer to fig. 6, which is a schematic structural diagram of the polarization controller provided in the embodiment of fig. 6.
Specifically, after entering the polarization rotator, the local oscillation light is also divided into an X polarization state local oscillation light and a Y polarization state local oscillation light, and signal detection is performed by a digital signal processing, a digital-to-analog conversion and driver and a connected photoelectric detector. The difference is that the photoelectric detector also carries out tracking control on the X polarization state local oscillation light and the Y polarization state local oscillation light. And the power of the X polarization state local oscillation light is consistent with that of the Y polarization state local oscillation light.
In order to illustrate the effects of the four-way multiplexing communication method and device based on self-coherence, which are provided in the present application, please refer to fig. 7, which is a diagram of a demodulation result of a dual-polarization 16QAM signal in a 53G baud rate scene provided in the embodiment of the present application in fig. 7.
Specifically, it can be seen through the illustration that through loading the pilot signals that the frequency is different to four routes signal respectively at the transmitting terminal to through the cooperation of polarization phase control board and the polarization control board that the receiving terminal set up, make the receiving terminal can obtain independent four routes signal, and basically do not receive the influence of phase noise and polarization rotation between each way signal, thereby make the independent four routes signal that obtains have good practicality.
The foregoing has outlined rather broadly the more detailed description of the present application in order that the detailed description of the invention may be better understood, and in order that the present principles and embodiments may be better understood. It should be noted that it would be obvious to those skilled in the art that various improvements and modifications can be made to the present application without departing from the principles of the present application, and such improvements and modifications fall within the scope of the claims of the present application.
Claims (10)
1. The four-way multiplexing optical communication method based on self-coherence is characterized by at least comprising the following steps:
s10, dividing a light beam emitted by a laser into signal light and local oscillation light through a power divider;
s20, at a transmitting end, signal light is sequentially polarized, modulated and combined through a dual-polarization IQ modulator, and the modulation comprises: respectively loading four pilot signals with different frequencies to the virtual parts and the real parts of two baseband signals obtained by polarization on the baseband signals in X and Y polarization states generated by polarization;
s30, at a receiving end, carrying out polarization alignment on the signal light and the local oscillation light through polarization control, carrying out phase recovery on the signal light by utilizing the pilot signal loaded in the step S20, and then respectively carrying out self-coherent detection on polarization states corresponding to the signal light and the local oscillation light to obtain four paths of independent electric signals.
2. The method of four-way multiplexing optical communication according to claim 1, wherein in step S30, the phase recovery includes:
and extracting power information of virtual parts and real parts of the two baseband signals at different pilot frequency signal frequency points, and adjusting the voltage in the phase recovery process according to the power information.
3. The method for four-way multiplexed optical communication based on self-coherence as recited in claim 2, further comprising phase adjustment when polarizing signal light:
and detecting and tracking each path of electric signal obtained by final detection to obtain phase noise information, so that the phase of the signal light in polarization is adjusted according to the phase noise information.
4. The method of four-way multiplexed optical communication based on self-coherence as recited in claim 1, wherein in step S30, the polarization alignment includes:
and detecting and tracking the polarization state of the signal light to acquire polarization rotation information of the signal light, so that the polarization rotation angle of the local oscillation light in polarization is adjusted according to the polarization rotation information of the signal light.
5. The four-way multiplexing optical communication method according to any one of claims 1 to 4, wherein the range of the pilot signal frequency in step S20 is 30khz to 90khz.
6. The four-way multiplexing optical communication method based on self-coherence according to claim 5, wherein the frequency difference of each pilot signal is not less than 10kHz.
7. The method for four-way multiplexing optical communication according to claim 1, further comprising step S40 after step S30;
s40, inputting the acquired four paths of independent electric signals into a PAM4 mathematical signal processing chip for demodulation.
8. A four-way multiplexing optical communication apparatus based on self-coherence, for implementing a four-way multiplexing optical communication method based on self-coherence as recited in any one of claims 1 to 7, wherein the optical communication apparatus at least comprises:
a transmitter for transmitting local oscillation light and modulated signal light;
the transmitter has: a laser, a power divider and a dual-polarization IQ modulator;
the power divider is used for dividing the light beam emitted by the laser into signal light and local oscillation light;
the dual-polarization IQ modulator is configured to sequentially polarize, modulate and combine signal light, where the modulation includes: respectively loading four pilot frequencies with different frequencies on real and imaginary optical signals of X and Y polarized signal light generated by polarization;
a receiver for receiving and demodulating the local oscillation light and the signal light from the transmitter;
the receiver includes:
the polarization phase control plate is used for carrying out polarization and phase adjustment on the signal light;
the polarization control board is used for polarizing the local oscillation light;
the 90-degree mixer is used for beating the self-coherent signal light;
and the balance detector is used for photoelectric conversion.
9. The self-coherent based four-way multiplexing optical communication device according to claim 8, wherein said dual-polarization IQ modulator comprises: the device comprises a polarization beam splitter, a power divider, a modulation resistor, a data signal modulator, a bias controller, a light combiner and a polarization beam combiner;
the polarization beam splitter is used for polarizing signal light of X and Y polarization states;
the power divider is used for dividing signal light in X polarization state and Y polarization state respectively;
the modulation resistor is used for modulating the data signal modulator and the bias controller;
the data signal modulator is used for loading four paths of signals to real parts and imaginary parts of baseband signals in X and Y polarization states respectively;
the bias controller is used for loading four pilot signals with different frequencies to the virtual part and the real part of the baseband signals in the X polarization state and the Y polarization state obtained by polarization respectively;
the light combiner is used for respectively combining the X and Y polarized signal lights after light splitting;
the polarization beam combiner is used for combining the X and Y polarization state signal light.
10. The self-coherent based four-way multiplexing optical communication device of claim 8, wherein said polarization phase control plate comprises: the device comprises a polarization rotator, a first light splitter, a second light splitter, a first phase controller, a second phase controller, a digital signal processing and digital-to-analog converter, an Ix digital-to-analog converter, a Qx digital-to-analog converter, an Iy digital-to-analog converter and a Qy digital-to-analog converter;
the polarization rotator is used for polarizing the incident signal light;
the first beam splitter and the second beam splitter are used for performing power division on light;
one end of the digital signal processing and digital-analog converter is respectively connected with the Ix digital-analog converter, the Qx digital-analog converter, the Iy digital-analog converter and the Qy digital-analog converter, the other end of the digital signal processing and digital-analog converter is respectively connected with the first phase controller and the second phase controller, and the adjustment of the phase of light is realized by applying different pressures to the first phase controller and the second phase controller.
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