Coherent optical communication method and coherent optical communication system

Abstract

The present application provides a coherent optical communication method and a coherent optical communication system. The method includes: performing digital signal processing on a digital signal with error feedback noise shaping to obtain a pre-compensated digital signal; sequentially performing digital-to-analog conversion and signal amplification on the signal to obtain a first amplified analog signal; performing coherent optical modulation on the signal to obtain a modulated optical signal, and transmitting the optical signal to a receiving device based on a standard single-mode optical fiber, so that the receiving device generates a corresponding digital signal according to the optical signal and performs digital signal processing including adaptive equalization based on depolarization in the Stokes domain to obtain a demodulated digital signal. The present application can effectively improve the quality and signal-to-noise ratio of the transmitted signal on the basis of reducing the cost of coherent optical communication and without significantly increasing the computational complexity, and can improve the processing efficiency of the received digital signal, thereby enabling high-quality and efficient transmission of signals applicable to coherent optical communication scenarios.

Description

Technical Field

[0001] The present application relates to the field of optical communication technology, and in particular to a coherent optical communication method and a coherent optical communication system. Background Art

[0002] With the explosive growth of Internet traffic, the demand for data traffic and transmission rate in the field of optical communications has increased dramatically. For short-distance systems, cost-effectiveness is particularly critical.

[0003] In coherent optical communication scenarios, in order to ensure signal quality, the signal transmitter usually needs to use a high-resolution digital-to-analog converter to reduce the impact of quantization noise. However, the use of high-resolution digital-to-analog converters leads to problems in cost, power consumption, and size. On the receiving end, with the evolution of technology, many algorithms have emerged in coherent optical receivers to compensate for various channel impairments. Although these algorithms can improve the performance of the receiving end, they also significantly increase the computational complexity of digital signal processing, thereby greatly increasing the design and manufacturing costs of digital signal processing circuits.

[0004] Therefore, the main challenge facing coherent optical communication systems is how to ensure high-performance signal transmission while reducing the cost of related hardware and not significantly increasing the complexity of digital signal processing. Summary of the invention

[0005] In view of this, embodiments of the present application provide a coherent optical communication method and a coherent optical communication system to eliminate or improve one or more defects existing in the prior art.

[0006] One aspect of the present application provides a coherent optical communication method, comprising:

[0007] Performing digital signal processing including error feedback noise shaping on the currently received digital signal to obtain a pre-compensated digital signal;

[0008] Performing digital-to-analog conversion and signal amplification processing on the pre-compensated digital signal in sequence to obtain an amplified first analog signal;

[0009] The amplified first analog signal is subjected to coherent optical modulation to obtain a modulated optical signal, and the optical signal is transmitted to a receiving device based on a standard single-mode optical fiber, so that the receiving device generates a corresponding digital signal according to the received optical signal and performs digital signal processing including adaptive equalization based on Stokes domain depolarization on the digital signal to obtain a demodulated digital signal.

[0010] In some embodiments of the present application, performing digital signal processing including error feedback noise shaping on the currently received digital signal to obtain a pre-compensated digital signal includes:

[0011] Generate a pseudo-random code sequence corresponding to the currently received digital signal;

[0012] The pseudo-random code sequence is converted into the corresponding PAM4 symbol sequence through Gray coding mapping;

[0013] The PAM4 symbol sequence is converted into a waveform signal sequence using a square root raised cosine filter pulse shaping method;

[0014] Error feedback noise shaping is performed on the waveform signal sequence to obtain a pre-compensated digital signal.

[0015] In some embodiments of the present application, performing error feedback noise shaping on the waveform signal sequence to obtain a pre-compensated digital signal includes:

[0016] Performing amplitude limiting processing on the waveform signal sequence;

[0017] Performing quantization processing on the waveform signal after the amplitude limitation processing;

[0018] The waveform signal after the quantization processing is subjected to time domain filtering in a feedback loop to obtain the pre-compensated digital signal after error feedback noise shaping corresponding to the waveform signal.

[0019] A second aspect of the present application provides a coherent optical communication method, comprising:

[0020] Based on a standard single-mode optical fiber, an optical signal from a transmitting device is received, and the optical signal is mixed and subjected to photoelectric conversion processing to obtain a second analog signal, wherein the optical signal is generated in advance by the transmitting device after performing digital signal processing including error feedback noise shaping, digital-to-analog conversion, signal amplification processing, and coherent optical modulation on the received digital signal;

[0021] Performing analog-to-digital conversion on the second analog signal to convert the second analog signal into a corresponding digital signal;

[0022] The digital signal is subjected to digital signal processing including adaptive equalization based on Stokes domain depolarization to obtain a demodulated digital signal.

[0023] In some embodiments of the present application, performing digital signal processing including adaptive equalization based on Stokes domain depolarization on the digital signal to obtain a demodulated digital signal includes:

[0024] Performing IQ imbalance compensation on the digital signal corresponding to the second analog signal to obtain an IQ imbalance compensated digital signal;

[0025] Performing adaptive equalization processing based on Stokes domain depolarization on the digital signal after the IQ imbalance compensation to obtain a digital signal after adaptive equalization;

[0026] Correcting the frequency offset and phase noise in the adaptively equalized digital signal to obtain a carrier-recovered digital signal;

[0027] The digital signal after carrier recovery is demapped according to a preset modulation method to obtain a demodulated digital signal.

[0028] A third aspect of the present application provides a coherent optical communication system, including a transmitting device and a receiving device for communication connection based on a standard single-mode optical fiber;

[0029] The transmitting device is used to execute the coherent optical communication method provided in the first aspect, and the receiving device is used to execute the coherent optical communication method provided in the second aspect;

[0030] Wherein, the transmitting device comprises:

[0031] The transmitting end digital signal processing module is used to perform digital signal processing including error feedback noise shaping on the currently received digital signal to obtain a pre-compensated digital signal;

[0032] A digital-to-analog conversion and amplification module, used to perform digital-to-analog conversion and signal amplification processing on the pre-compensated digital signal in sequence to obtain an amplified first analog signal;

[0033] A coherent optical modulation module, used for performing coherent optical modulation on the amplified first analog signal to obtain a modulated optical signal, so as to transmit the optical signal to the receiving device based on a standard single-mode optical fiber;

[0034] Wherein, the receiving device comprises:

[0035] An integrated coherent optical receiving module is used to receive an optical signal from a transmitting device based on a standard single-mode optical fiber, and perform frequency mixing and photoelectric conversion processing on the optical signal to obtain a second analog signal;

[0036] an analog-to-digital converter, configured to perform analog-to-digital conversion on the second analog signal to convert the second analog signal into a corresponding digital signal;

[0037] The receiving end digital signal processing module is used to perform digital signal processing including adaptive equalization based on Stokes domain depolarization on the digital signal to obtain a demodulated digital signal.

[0038] In some embodiments of the present application, the transmitting end digital signal processing module includes:

[0039] A pseudo-random code sequence generator, used to generate a pseudo-random code sequence corresponding to the currently received digital signal;

[0040] A symbol mapping module, used for converting a pseudo-random code sequence into a corresponding PAM4 symbol sequence through Gray coding mapping;

[0041] A square root raised cosine filter, configured to convert the PAM4 symbol sequence into a waveform signal sequence using a square root raised cosine filter pulse shaping method;

[0042] The error feedback noise shaping module is used to perform error feedback noise shaping on the waveform signal sequence to obtain a pre-compensated digital signal.

[0043] In some embodiments of the present application, the error feedback noise shaping module includes:

[0044] A limiter, used for performing amplitude limiting processing on the waveform signal sequence;

[0045] A quantizer, used for performing quantization processing on the waveform signal after the amplitude limitation processing;

[0046] The loop filter is used to perform time domain filtering in a feedback loop on the waveform signal after the quantization processing to obtain the pre-compensated digital signal after error feedback noise shaping corresponding to the waveform signal.

[0047] In some embodiments of the present application, the receiving end digital signal processing module includes:

[0048] An IQ imbalance compensation module, configured to perform IQ imbalance compensation on the digital signal corresponding to the second analog signal to obtain an IQ imbalance compensated digital signal;

[0049] An adaptive equalization module based on Stokes domain depolarization is used to perform adaptive equalization processing based on Stokes domain depolarization on the digital signal after IQ imbalance compensation to obtain a digital signal after adaptive equalization;

[0050] A carrier recovery module, used to correct the frequency offset and phase noise in the digital signal after adaptive equalization to obtain a digital signal after carrier recovery;

[0051] The decision demapping module is used to demap the digital signal after the carrier recovery according to a preset modulation mode to obtain a demodulated digital signal.

[0052] In some embodiments of the present application, the coherent optical communication system further includes: a first erbium-doped fiber amplifier and a second erbium-doped fiber amplifier disposed between the transmitting device and the receiving device;

[0053] The first erbium-doped fiber amplifier is used to control the fiber-input optical power of the modulated optical signal output by the coherent optical modulation module, so that the optical signal after the fiber-input optical power control is transmitted to the receiving device based on a standard single-mode optical fiber;

[0054] The second erbium-doped fiber amplifier is used to amplify the optical signal transmitted to the receiving device side via the standard single-mode optical fiber, so that the integrated coherent optical receiving module receives the optical signal after amplification.

[0055] The coherent optical communication method provided by the present application performs digital signal processing including error feedback noise shaping on the currently received digital signal to obtain a pre-compensated digital signal, performs digital-to-analog conversion and signal amplification processing on the pre-compensated digital signal in sequence to obtain an amplified first analog signal; performs coherent optical modulation on the amplified first analog signal to obtain a modulated optical signal, and transmits the optical signal to a receiving device based on a standard single-mode optical fiber, so that the receiving device generates a corresponding digital signal according to the received optical signal and performs digital signal processing including adaptive equalization based on Stokes domain depolarization on the digital signal to obtain a demodulated digital signal. The method can effectively improve the quality and signal-to-noise ratio of the transmission signal based on the error feedback noise shaping method while reducing the cost of coherent optical communication and not significantly increasing the computational complexity, and can improve the processing efficiency of the received digital signal by adaptive equalization based on the Stokes domain depolarization scheme, thereby achieving high-quality and efficient transmission of signals suitable for coherent optical communication scenarios.

[0056] Additional advantages, purposes, and features of the present application will be partially described in the following description, and will become partially apparent to those skilled in the art after studying the following, or may be learned from the practice of the present application. The purposes and other advantages of the present application can be achieved and obtained by the structures specifically pointed out in the specification and the drawings.

[0057] Those skilled in the art will understand that the purposes and advantages that can be achieved by the present application are not limited to the above specific description, and the above and other purposes that can be achieved by the present application will be more clearly understood based on the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The drawings described herein are used to provide a further understanding of the present application, constitute a part of the present application, and do not constitute a limitation of the present application. The components in the drawings are not drawn to scale, but are only for the purpose of illustrating the principles of the present application. In order to facilitate the illustration and description of some parts of the present application, the corresponding parts in the drawings may be enlarged, that is, they may become larger relative to other components in the exemplary device actually manufactured according to the present application. In the drawings:

[0059] Figure 1 Schematic diagram of a first process flow of a first coherent optical communication method in an embodiment of the present application.

[0060] Figure 2 Schematic diagram of a second process of the first coherent optical communication method in one embodiment of the present application.

[0061] Figure 3 This is a logic diagram of digital signal processing at the transmitting end in the first coherent optical communication method in one embodiment of the present application.

[0062] Figure 4 Schematic diagram of a third process of the first coherent optical communication method in one embodiment of the present application.

[0063] Figure 5 FIG. 4 is a schematic diagram of a time domain model of an error feedback noise shaping module in an embodiment of the present application.

[0064] Figure 6 FIG. 4 is a schematic diagram of a z-domain model of an error feedback noise shaping module in an embodiment of the present application.

[0065] Figure 7 4 is a schematic diagram of a first flow chart of a second coherent optical communication method in an embodiment of the present application.

[0066] Figure 8 4 is a second flow chart of a second coherent optical communication method in one embodiment of the present application.

[0067] Fig. 9 This is a logic diagram of digital signal processing at the receiving end in the second coherent optical communication method in one embodiment of the present application.

[0068] Fig.10 The figure is a schematic diagram of the calculation logic of the adaptive equalization module based on Stokes domain depolarization in one embodiment of the present application.

[0069] Fig.11 Schematic diagram of the structure of a coherent optical communication system in one embodiment of the present application.

[0070] Fig.12 Schematic diagram of the structure of a digital signal processing module at the transmitting end in one embodiment of the present application.

[0071] Fig.13 Schematic diagram of the structure of a digital signal processing module at the receiving end in one embodiment of the present application.

[0072] Fig.14 Schematic diagram of the application of a coherent optical communication system in a coherent optical communication system in an embodiment of the present application. DETAILED DESCRIPTION

[0073] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the implementation modes and the accompanying drawings. Here, the illustrative implementation modes and descriptions of the present application are used to explain the present application, but are not intended to limit the present application.

[0074] It should also be noted here that in order to avoid obscuring the present application due to unnecessary details, only the structures and / or processing steps closely related to the scheme according to the present application are shown in the accompanying drawings, while other details that are not very relevant to the present application are omitted.

[0075] It should be emphasized that the term “include / comprises” when used herein refers to the presence of features, elements, steps or components, but does not exclude the presence or addition of one or more other features, elements, steps or components.

[0076] It should also be noted that, unless otherwise specified, the term “connection” herein may refer not only to a direct connection but also to an indirect connection with an intermediate.

[0077] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. In the accompanying drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

[0078] In order to ensure high-performance signal transmission while reducing the cost of related hardware and not significantly increasing the complexity of digital signal processing, the embodiments of the present application respectively provide a coherent optical communication method that can be implemented by a transmitting device, a coherent optical communication method that can be implemented by a receiving device, and a coherent optical communication system including a transmitting device and a receiving device, which can effectively improve the quality and signal-to-noise ratio of the transmitted signal on the basis of reducing the cost of coherent optical communication, and can improve the processing efficiency of the received digital signal, thereby realizing high-quality and efficient transmission of signals suitable for coherent optical communication scenarios.

[0079] The details are described in detail through the following examples.

[0080] Based on this, the embodiment of the present application provides a coherent optical communication method that can be implemented by a transmitting device, see Figure 1 , the first coherent optical communication method specifically includes the following contents:

[0081] Step 100: performing digital signal processing including error feedback noise shaping on the currently received digital signal to obtain a pre-compensated digital signal.

[0082] In step 100, the transmitting end digital signal processing module in the transmitting device can perform digital signal processing including error feedback noise shaping on the currently received digital signal to obtain a pre-compensated digital signal. Specifically, a set of pseudo-random code sequences are generated by a pseudo-random code sequence generator; the pseudo-random code sequence is converted into a corresponding PAM4 symbol sequence through Gray coding mapping; the discrete PAM4 symbol sequence is converted into a waveform signal sequence by a square root raised cosine filter pulse shaping method; and then the waveform signal sequence is subjected to error feedback noise shaping, specifically including: firstly, the amplitude of the signal is limited by a limiter, and then the signal is quantized by a quantizer, and then the quantized signal is filtered by a loop filter, and the noise spectrum is shaped to obtain a pre-compensated digital signal.

[0083] It can be understood that Error-Feedback Noise Shaping (EFNS) refers to: a noise shaping technology based on a quantized linear model, which can simultaneously shape the limiting noise and the quantization noise. Error feedback noise shaping can be implemented by an error feedback noise shaper, which is specifically used to transfer the quantization noise within the used bandwidth of the signal to the unused bandwidth by using a feedback loop for the quantization error generated by the quantized signal, thereby greatly reducing the quantization noise within the used bandwidth of the signal. In one or more embodiments of the present application, error feedback noise shaping can be implemented by using an existing error feedback noise shaping method.

[0084] Step 200: performing digital-to-analog conversion and signal amplification processing on the pre-compensated digital signal in sequence to obtain an amplified first analog signal.

[0085] In step 200, the transmitting device may use a digital-to-analog converter to perform digital-to-analog conversion on the pre-compensated digital signal, converting the pre-compensated digital signal into a first analog signal, and use an electrical amplifier to amplify the input first analog signal to increase the signal power, thereby obtaining an amplified first analog signal.

[0086] Step 300: Perform coherent optical modulation on the amplified first analog signal to obtain a modulated optical signal, and transmit the optical signal to a receiving device based on a standard single-mode optical fiber, so that the receiving device generates a corresponding digital signal according to the received optical signal and performs digital signal processing including adaptive equalization based on Stokes domain depolarization on the digital signal to obtain a demodulated digital signal.

[0087] In step 300, the transmitting device may use a coherent optical modulator to receive the local oscillator light output by the laser, and modulate the amplified first analog signal onto the local oscillator light to obtain a modulated optical signal.

[0088] It can be understood that Stokes domain depolarization (Polarization demultiplexing in Stokesspace) refers to a method for polarization alignment in the Stokes domain based on the least squares method; the adaptive equalization based on Stokes domain depolarization can be implemented by an adaptive equalizer based on Stokes domain depolarization, and the adaptive equalizer based on Stokes domain depolarization (Adaptive equalizer based on Polarization demultiplexing inStokes space, SS-AEQ) refers to a low-complexity adaptive equalizer that is insensitive to polarization-related loss and dispersion; it is used to reduce the difficulty of finding optimal parameters and speed up convergence after receiving a higher quality digital signal.

[0089] From the above description, it can be seen that the first coherent optical communication method provided in the embodiment of the present application can reduce the cost of coherent optical communication and not significantly increase the computational complexity, and can effectively improve the quality and signal-to-noise ratio of the transmission signal based on the error feedback noise shaping method, and can improve the processing efficiency of the received digital signal through adaptive equalization based on the Stokes domain depolarization scheme, thereby realizing high-quality and efficient transmission of signals suitable for coherent optical communication scenarios.

[0090] That is to say, this application proposes for the first time a low-cost and low-complexity coherent optical communication system using error feedback noise shaping technology and an adaptive equalizer based on a Stokes domain depolarization scheme. Using these two technologies simultaneously can achieve more efficient optical signal transmission under the condition of a low-cost system.

[0091] Error feedback noise shaping technology targets the quantization error generated by the quantized signal, and uses a feedback loop to transfer the quantization noise in the signal's used bandwidth to the unused bandwidth, thereby significantly reducing the quantization noise in the signal's used bandwidth. Quantization noise, as an additional noise, directly affects the quality of the received signal. Low quantization noise enables the digital signal received by the digital signal processing module at the receiving end to have higher quality and signal-to-noise ratio. The adaptive equalization technology based on the Stokes domain depolarization scheme can reduce the difficulty of finding the optimal parameters and speed up the convergence speed after receiving a higher quality digital signal. Therefore, the system can achieve high-quality signal transmission at a low cost.

[0092] On the other hand, while the error feedback noise shaping technology is used at the transmitter to suppress the quantization noise, the complexity of the transmitter algorithm is increased, while the adaptive equalization technology based on the Stokes domain depolarization scheme is used at the receiver to significantly reduce the complexity of the receiver algorithm. The reduced complexity at the receiver can balance the increased complexity at the transmitter, thereby maintaining the overall complexity level of the coherent optical communication system design.

[0093] In order to reduce the quantization noise within the signal used bandwidth so that the digital signal received by the receiving device has higher quality and signal-to-noise ratio, in a first coherent optical communication method that can be implemented by a transmitting device provided in an embodiment of the present application, see Figure 2 and Figure 3 , step 100 in the first coherent optical communication method specifically includes the following contents:

[0094] Step 110: Generate a pseudo-random code sequence corresponding to the currently received digital signal;

[0095] Step 120: Convert the pseudo-random code sequence into a corresponding PAM4 symbol sequence through Gray coding mapping;

[0096] Step 130: converting the PAM4 symbol sequence into a waveform signal sequence using a square root raised cosine filter pulse shaping method;

[0097] Step 140: performing error feedback noise shaping on the waveform signal sequence to obtain a pre-compensated digital signal.

[0098] It can be understood that the pseudo-random code sequence (PRBS) refers to a pseudo-random signal composed of a digital sequence generated by a specific algorithm; the Gray code mapping (Gray Code) refers to the mapping of the pseudo-random code sequence to the PAM4 symbol sequence according to the Gray coding result; the PAM4 symbol sequence refers to a four-level pulse amplitude modulation signal, which is -3, -1, 1, and 3 respectively; the square root raised cosine filter (SRRC) pulse shaping method refers to the use of a square root raised cosine filter for pulse shaping, which effectively transmits signals within a limited bandwidth while reducing inter-symbol interference.

[0099] Specifically, the pseudo-random code sequence generator in the transmitting end digital signal processing module in the transmitting device generates a pseudo-random code sequence corresponding to the currently received digital signal; the symbol mapping module converts the pseudo-random code sequence into a corresponding PAM4 symbol sequence through Gray coding mapping; the square root raised cosine filter adopts a square root raised cosine filter pulse shaping method to convert the PAM4 symbol sequence into a waveform signal sequence; the error feedback noise shaping module performs error feedback noise shaping on the waveform signal sequence to obtain a pre-compensated digital signal.

[0100] In order to further significantly reduce the quantization noise within the signal used bandwidth, so that the digital signal received by the receiving device has higher quality and signal-to-noise ratio, in a first coherent optical communication method that can be implemented by a transmitting device provided in an embodiment of the present application, see Figure 4 , step 140 in the first coherent optical communication method specifically includes the following contents:

[0101] Step 141: performing amplitude limiting processing on the waveform signal sequence;

[0102] Step 142: performing quantization processing on the waveform signal after the amplitude limiting processing;

[0103] Step 143: performing time domain filtering in a feedback loop on the waveform signal after the quantization processing to obtain the pre-compensated digital signal after error feedback noise shaping corresponding to the waveform signal.

[0104] Specifically, the error feedback noise shaping module in the transmitting end digital signal processing module in the transmitting device includes a limiter for performing amplitude limitation processing on the waveform signal sequence; a quantizer for performing quantization processing on the waveform signal after the amplitude limitation processing; and a loop filter for performing time domain filtering in a feedback loop on the waveform signal after the quantization processing, so as to obtain the pre-compensated digital signal after error feedback noise shaping corresponding to the waveform signal.

[0105] The output of the limiter is expressed as:

[0106]

[0107] where x c (n) represents the output of the limiter, x in (n) represents the input of the limiter, e c (n) represents clipping noise, k represents the scaling factor of clipping, Cov() represents covariance, and D() represents variance.

[0108] The output of the quantizer is represented as: q (n) = x c (n)+e q (n), where e q (n) represents the quantization noise.

[0109] The time domain model of the error feedback noise shaping module can be found in Figure 5 , specifically:

[0110] y(n)=kx(n)+(1+g(n))(e q (n)+e c (n))

[0111] Where y(n) represents the output signal after error feedback noise shaping in the time domain.

[0112] x(n) represents the input signal sequence in the time domain.

[0113] g(n) represents the impulse response of the time domain filter (ie, loop filter) in the feedback loop.

[0114] e q (n) represents the time domain quantization noise generated by the quantizer.

[0115] e c (n) represents the time domain limiting noise produced by the limiter.

[0116] The z-domain model of the error feedback noise shaping module can be found in Figure 6 , specifically:

[0117] Y(z)=kX(z)+(1+G(z))(E q (z)+E c (z)), where g i is a real constant, is the coefficient of the filter, and P is the filter order.

[0118] Wherein, Y(z) represents the output signal after error feedback noise shaping in the z domain.

[0119] X(z) represents the z-transform of the input signal in the z-domain.

[0120] G(z) represents the transfer function of the z-domain filter in the feedback loop.

[0121] E q (z) represents the z-domain quantization noise generated by the quantizer.

[0122] E c (z) represents the z-domain limiting noise produced by the limiter.

[0123] z -i Represents the delay factor in the z-domain, corresponding to the signal delay in the time domain.

[0124] The spectrum of the limiting and quantization noise can be shaped by (1+G(z)).

[0125] G(z) is located in the feedback loop and is a loop filter, usually a FIR filter. Its coefficients can be obtained by solving the following optimization problem: Among them, W(e jω ) is the weight function, Ω is the sampling frequency band of the digital-to-analog converter, G(e jω ) is the frequency response of the filter.

[0126] In some embodiments of the present application, the filter order is 5, the weight function is 15 in the signal frequency band, and is 1 in the unused frequency band.

[0127] In order to reduce the cost of related hardware and ensure high-performance signal transmission without significantly increasing the complexity of digital signal processing, the embodiment of the present application also provides a second coherent optical communication method that can be implemented by a receiving device, see Figure 7 , the second coherent optical communication method specifically includes the following contents:

[0128] Step 400: Receive an optical signal from a transmitting device based on a standard single-mode optical fiber, and perform frequency mixing and photoelectric conversion on the optical signal to obtain a second analog signal, wherein the optical signal is generated in advance by the transmitting device performing digital signal processing including error feedback noise shaping, digital-to-analog conversion, signal amplification, and coherent optical modulation on the received digital signal.

[0129] In step 400, the integrated coherent optical receiving module in the receiving device receives the optical signal from the transmitting device based on the standard single-mode optical fiber, and performs frequency mixing and photoelectric conversion processing on the optical signal to obtain a second analog signal.

[0130] Step 500: Perform analog-to-digital conversion on the second analog signal to convert the second analog signal into a corresponding digital signal.

[0131] In step 500, an analog-to-digital converter in a receiving device performs analog-to-digital conversion on the second analog signal to convert the second analog signal into a corresponding digital signal.

[0132] Step 600: Perform digital signal processing including adaptive equalization based on Stokes domain depolarization on the digital signal to obtain a demodulated digital signal.

[0133] In step 600, the receiving end digital signal processing module in the receiving device can perform digital signal processing on the received digital signal through IQ imbalance compensation, adaptive equalization, carrier recovery and decision demapping to obtain a demodulated digital signal.

[0134] From the above description, it can be seen that the second coherent optical communication method provided in the embodiment of the present application can reduce the cost of coherent optical communication and not significantly increase the computational complexity, and can effectively improve the quality and signal-to-noise ratio of the transmission signal based on the error feedback noise shaping method, and can improve the processing efficiency of the received digital signal through adaptive equalization based on the Stokes domain depolarization scheme, thereby realizing high-quality and efficient transmission of signals suitable for coherent optical communication scenarios.

[0135] In order to reduce the difficulty of finding the optimal parameters, speed up the convergence speed and significantly reduce the algorithm complexity of the receiving end, in the embodiment of the second coherent optical communication method that can be implemented by the receiving device provided in the present application, see Figure 8 and Fig. 9 , step 600 in the second coherent optical communication method specifically includes the following contents:

[0136] Step 610: Perform IQ imbalance compensation on the digital signal corresponding to the second analog signal to obtain an IQ imbalance compensated digital signal.

[0137] Step 620: Perform adaptive equalization processing based on Stokes domain depolarization on the digital signal after IQ imbalance compensation to obtain a digital signal after adaptive equalization.

[0138] Step 630: Correct the frequency offset and phase noise in the adaptively equalized digital signal to obtain a carrier-recovered digital signal.

[0139] Step 640: Demap the digital signal after carrier recovery according to a preset modulation method to obtain a demodulated digital signal.

[0140] Among them, the digital signal output by the analog-to-digital converter is subjected to IQ imbalance compensation to compensate for the imbalance phenomenon of the two signals caused by channel transmission and other reasons, so as to obtain a digital signal after IQ imbalance compensation; the digital signal after IQ imbalance compensation is subjected to an adaptive equalization algorithm based on Stokes domain depolarization to obtain a digital signal after adaptive equalization; the digital signal after adaptive equalization is subjected to frequency offset estimation based on fast Fourier transform and carrier recovery algorithm based on blind phase search algorithm to correct the frequency offset and phase noise in the signal to obtain a digital signal after carrier recovery; the digital signal after carrier recovery is demapped according to the modulation mode, and the symbol value is mapped back to the bit stream to obtain a demodulated digital signal.

[0141] The adaptive equalization module based on Stokes domain depolarization specifically includes: a butterfly filter and an N-tap complex FIR filter. Fig.10 , the Jones vector received by the receiver is:

[0142]

[0143] where e x and e y They represent the two mutually orthogonal polarization states at the receiving end. The Jones vector is converted to the Stokes domain to obtain the Stokes vector:

[0144]

[0145] Among them, S0 Indicates total power, S 1 Represents 0° linear polarized light, S 2 Represents 45° linear polarized light, S 3 Represents circularly polarized light.

[0146] Receiver x and e y Two polarization states orthogonal to the transmitting end xt and e yt The relationship is:

[0147]

[0148] Where M is the chief matrix, [] -1 is the inverse of the matrix, in Δφ=arctan(s 2 ,s 3 ).

[0149] Fig.10 Medium E X,输入 , E Y,输入 are the signals of X polarization state and Y polarization state input to the adaptive equalizer, E X,输出 , E Y,输入 They are respectively the signals of X polarization state and Y polarization state output by the adaptive equalizer. Represents the elements of the inverse matrix of the chief matrix, where i,j=1,2. x It is an N-tap FIR filter.

[0150] The present application also provides a coherent optical communication system, see Fig.11 , the coherent optical communication system specifically includes the following contents:

[0151] The transmitting device 1 and the receiving device 2 are connected for communication based on a standard single-mode optical fiber 3.

[0152] The transmitting device 1 is used for the aforementioned first coherent optical communication method, and the receiving device 2 is used for executing the aforementioned second coherent optical communication method.

[0153] The transmitting device 1 specifically includes the following contents:

[0154] The transmitting end digital signal processing module 11 is used to perform digital signal processing including error feedback noise shaping on the currently received digital signal to obtain a pre-compensated digital signal;

[0155] A digital-to-analog conversion and amplification module 12, configured to sequentially perform digital-to-analog conversion and signal amplification processing on the pre-compensated digital signal to obtain an amplified first analog signal;

[0156] The coherent optical modulation module 13 is used to perform coherent optical modulation on the amplified first analog signal to obtain a modulated optical signal, so as to transmit the optical signal to the receiving device 2 based on the standard single-mode optical fiber 3 .

[0157] The transmitting end digital signal processing module 11, the digital-to-analog conversion and amplification module 12 and the coherent light modulation module 13 are connected in sequence. The coherent light modulation module 13 can be composed of a laser and a coherent light modulator.

[0158] The receiving device 2 specifically includes the following contents:

[0159] An integrated coherent optical receiving module 21 is used to receive an optical signal from the transmitting device 1 based on a standard single-mode optical fiber, and perform frequency mixing and photoelectric conversion processing on the optical signal to obtain a second analog signal;

[0160] an analog-to-digital converter 22, configured to perform analog-to-digital conversion on the second analog signal to convert the second analog signal into a corresponding digital signal;

[0161] The receiving end digital signal processing module 23 is used to perform digital signal processing including adaptive equalization based on Stokes domain depolarization on the digital signal to obtain a demodulated digital signal.

[0162] The integrated coherent optical receiving module 21, the analog-to-digital converter 22 and the receiving end digital signal processing module 23 are connected in sequence. The integrated coherent optical receiving module 21 can be composed of a laser and an integrated coherent optical receiver.

[0163] From the above description, it can be seen that the coherent optical communication system provided in the embodiment of the present application can effectively improve the quality and signal-to-noise ratio of the transmission signal based on the error feedback noise shaping method while reducing the cost of coherent optical communication and not significantly increasing the computational complexity, and can improve the processing efficiency of the received digital signal through adaptive equalization based on the Stokes domain depolarization scheme, thereby realizing high-quality and efficient transmission of signals suitable for coherent optical communication scenarios.

[0164] That is to say, this application proposes for the first time a low-cost and low-complexity coherent optical communication system using error feedback noise shaping technology and an adaptive equalizer based on a Stokes domain depolarization scheme. Using these two technologies simultaneously can achieve more efficient optical signal transmission under the condition of a low-cost system.

[0165] The error feedback noise shaping module uses a feedback loop to transfer the quantization noise in the used bandwidth of the signal to the unused bandwidth for the quantization error generated by the quantized signal, thereby significantly reducing the quantization noise in the used bandwidth of the signal. As an additional noise, quantization noise directly affects the quality of the received signal. Low quantization noise enables the digital signal received by the digital signal processing module at the receiving end to have higher quality and signal-to-noise ratio. After receiving a higher quality digital signal, the adaptive equalizer based on the Stokes domain depolarization scheme can reduce the difficulty of finding the optimal parameters and accelerate the convergence speed. Therefore, the system can achieve high-quality signal transmission at a low cost.

[0166] On the other hand, while the error feedback noise shaping module is used at the transmitter to suppress quantization noise, the complexity of the transmitter algorithm is increased, while the adaptive equalizer based on the Stokes domain depolarization scheme is used at the receiver to significantly reduce the complexity of the receiver algorithm. The reduced complexity at the receiver can balance the increased complexity at the transmitter, thereby maintaining the overall complexity level of the system design.

[0167] In order to reduce the quantization noise within the signal used bandwidth, so that the digital signal received by the receiving device has higher quality and signal-to-noise ratio, in a coherent optical communication system provided in an embodiment of the present application, see Fig.12 The transmitting end digital signal processing module 11 in the transmitting device 1 in the coherent optical communication system specifically includes the following contents:

[0168] A pseudo-random code sequence generator 111, used to generate a pseudo-random code sequence corresponding to the currently received digital signal;

[0169] A symbol mapping module 112, configured to convert a pseudo-random code sequence into a corresponding PAM4 symbol sequence by Gray coding mapping;

[0170] A square root raised cosine filter 113, configured to convert the PAM4 symbol sequence into a waveform signal sequence by adopting a square root raised cosine filter pulse shaping method;

[0171] The error feedback noise shaping module 114 is used to perform error feedback noise shaping on the waveform signal sequence to obtain a pre-compensated digital signal.

[0172] The pseudo-random code sequence generator 111 , the symbol mapping module 112 , the square root raised cosine filter 113 and the error feedback noise shaping module 114 are connected in sequence.

[0173] In order to further significantly reduce the quantization noise within the signal used bandwidth so that the digital signal received by the receiving device has higher quality and signal-to-noise ratio, in a coherent optical communication system provided in an embodiment of the present application, the error feedback noise shaping module 114 in the transmitting device 1 in the coherent optical communication system specifically includes the following contents:

[0174] A limiter is used to perform amplitude limiting processing on the waveform signal sequence.

[0175] A quantizer is used to quantize the waveform signal after the amplitude limitation processing.

[0176] The loop filter is used to perform time domain filtering in a feedback loop on the waveform signal after the quantization processing to obtain the pre-compensated digital signal after error feedback noise shaping corresponding to the waveform signal.

[0177] In order to reduce the difficulty of finding the optimal parameters, speed up the convergence speed and significantly reduce the algorithm complexity of the receiving end, in a coherent optical communication system provided in an embodiment of the present application, see Fig.13 The receiving end digital signal processing module 23 in the receiving device 2 in the coherent optical communication system specifically includes the following contents:

[0178] An IQ imbalance compensation module 231 is used to perform IQ imbalance compensation on the digital signal corresponding to the second analog signal to obtain an IQ imbalance compensated digital signal;

[0179] The Stokes domain depolarization-based adaptive equalization module 232 is used to perform adaptive equalization processing based on Stokes domain depolarization on the digital signal after the IQ imbalance compensation to obtain a digital signal after adaptive equalization;

[0180] The carrier recovery module 233 is used to correct the frequency offset and phase noise in the digital signal after the adaptive equalization to obtain a digital signal after the carrier is recovered;

[0181] The decision demapping module 234 is used to demap the digital signal after the carrier recovery according to a preset modulation method to obtain a demodulated digital signal.

[0182] The IQ imbalance compensation module 231 , the adaptive equalization module 232 based on Stokes domain depolarization, the carrier recovery module 233 and the decision demapping module 234 are connected in sequence.

[0183] In order to further improve the application effectiveness and reliability of the coherent optical communication system, the embodiment of the present application provides a coherent optical communication system for data transmission between a transmitting end and a receiving end. The transmitting end of the system includes a transmitting end digital signal processing module, a digital-to-analog converter, an electrical amplifier, a laser and a coherent optical modulator. The receiving end of the system includes an integrated coherent optical receiver, an analog-to-digital converter and a receiving end digital signal processing module. The transmitting end of the system and the receiving end of the system are connected through a standard single-mode optical fiber, and specifically include the following steps:

[0184] The transmitting end digital signal processing module and the transmitting end digital-to-analog converter convert the transmitting end digital signal into a first analog signal. After the electric amplifier amplifies the first analog signal, the laser and the coherent optical modulator convert the amplified first analog signal into an optical signal. The optical signal is transmitted through a standard single-mode optical fiber. The integrated coherent optical receiver converts the optical signal into a second analog signal. The analog-to-digital converter and the receiving end digital signal processing module convert the second analog signal into a demodulated digital signal.

[0185] The digital signal processing module at the transmitting end includes a pseudo-random code sequence generator, a symbol mapping module, a square root raised cosine filter and an error feedback noise shaping module;

[0186] The receiving end digital signal processing module includes an orthogonal amplitude modulation signal imbalance compensation (IQ imbalance compensation) module, an adaptive equalization module based on Stokes domain depolarization, a carrier recovery module and a decision demapping module.

[0187] See also Fig.14 , the coherent optical communication system further comprises a first erbium-doped fiber amplifier and a second erbium-doped fiber amplifier arranged between the transmitting device and the receiving device;

[0188] The first erbium-doped fiber amplifier is used to control the fiber-input optical power of the modulated optical signal output by the coherent optical modulation module, so that the optical signal after the fiber-input optical power control is transmitted to the receiving device based on a standard single-mode optical fiber;

[0189] The second erbium-doped fiber amplifier is used to amplify the optical signal transmitted to the receiving device side via the standard single-mode optical fiber, so that the integrated coherent optical receiver receives the amplified optical signal.

[0190] In the coherent optical communication system, all steps in the digital signal processing at the transmitting end are executed by the digital signal processing module at the transmitting end, which specifically includes the following steps: generating a pseudo-random code sequence, Gray mapping, pulse shaping and error feedback noise shaping in sequence. Among them, a pseudo-random code sequence generator is used to generate a set of pseudo-random code sequences; the pseudo-random code sequence is converted into a corresponding PAM4 symbol sequence through Gray coding mapping; the discrete PAM4 symbol sequence is converted into a waveform signal sequence using a square root raised cosine filter pulse shaping method; and then the waveform signal sequence is subjected to error feedback noise shaping, specifically including: firstly limiting the amplitude of the signal through a limiter, then quantizing the signal through a quantizer, and then filtering the quantized signal through a loop filter, shaping the noise spectrum, and obtaining a pre-compensated digital signal.

[0191] In the coherent optical communication system, all steps in the digital signal processing at the receiving end are executed by the digital signal processing module at the transmitting end, which specifically includes the following steps: IQ imbalance compensation, adaptive equalization, carrier recovery and decision demapping are performed in sequence. Among them, the digital signal output by the analog-to-digital converter is subjected to IQ imbalance compensation, and the imbalance phenomenon of the two signals caused by channel transmission and other reasons is compensated to obtain a digital signal after IQ imbalance compensation; the digital signal after IQ imbalance compensation is subjected to an adaptive equalization algorithm based on Stokes domain depolarization to obtain a digital signal after adaptive equalization; the digital signal after adaptive equalization is subjected to frequency offset estimation based on fast Fourier transform and carrier recovery algorithm based on blind phase search algorithm to correct the frequency offset and phase noise in the signal to obtain a digital signal after carrier recovery; the digital signal after carrier recovery is demapped according to the modulation mode, and the symbol value is mapped back to the bit stream to obtain a demodulated digital signal.

[0192] Based on this, the low-cost coherent optical communication method for joint efficient quantization noise compensation and adaptive equalization implemented by the coherent optical communication system provided in the embodiment of the present application specifically includes the following contents:

[0193] S1. The digital signal processing module at the transmitting end performs digital signal processing on the received digital signal through Gray mapping, pulse shaping and error feedback noise shaping to obtain a pre-compensated digital signal.

[0194] S2. The digital-to-analog converter performs digital-to-analog conversion on the pre-compensated digital signal, and converts the pre-compensated digital signal into a first analog signal.

[0195] S3. The electric amplifier amplifies the input first analog signal to increase the signal power and obtain an amplified first analog signal.

[0196] S4. The coherent optical modulator receives the local oscillator light output by the laser, and modulates the amplified first analog signal onto the local oscillator light to obtain a modulated optical signal.

[0197] S5. The first erbium-doped fiber amplifier controls the input optical power. The optical signal is transmitted through a standard single-mode optical fiber. The second erbium-doped fiber amplifier amplifies the optical signal to compensate for the transmission loss of the optical fiber.

[0198] S6. The integrated coherent optical receiver receives the optical signal, mixes the optical signal with the local oscillator light, and obtains a mixed optical signal, and then performs photoelectric conversion on the mixed optical signal to convert it into a second analog signal.

[0199] S7. The analog-to-digital converter performs analog-to-digital conversion on the second analog signal, converting the second analog signal into a digital signal.

[0200] S8. The digital signal processing module at the receiving end performs digital signal processing on the received digital signal through IQ imbalance compensation, adaptive equalization, carrier recovery and decision demapping to obtain a demodulated digital signal.

[0201] In summary, the error feedback noise shaping technology provided by the present application shapes the signal noise by introducing an error feedback mechanism to optimize the quality of signal transmission. By using error feedback and loop filtering, the error in the transmission signal is shaped and corrected in real time, significantly reducing the interference of quantization noise on the signal. Using error feedback noise shaping technology, the low-resolution digital-to-analog converter can have a transmission performance similar to that of a high-resolution digital-to-analog converter, and has relatively low computational complexity and processing delay, thereby reducing the cost of the transmitter. The adaptive equalization technology based on the Stokes domain depolarization scheme can effectively reduce the impact of polarization mode dispersion and polarization-related loss on the signal by performing polarization state analysis and compensation in the Stokes domain. Using the adaptive equalization technology based on the Stokes domain depolarization scheme can improve the robustness of the algorithm to system damage and effectively reduce the computational complexity of the adaptive equalizer. Compared with the traditional coherent optical communication system, the present application improves the effective resolution of the system under low-cost conditions, reduces the computational complexity of digital signal processing at the receiving end, can achieve higher transmission rates and better signal integrity, and achieve more efficient optical signal transmission.

[0202] It should be understood by those skilled in the art that the exemplary components, systems and methods described in conjunction with the embodiments disclosed herein can be implemented in hardware, software or a combination of the two. Whether it is specifically performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application. When implemented in hardware, it can be, for example, an electronic circuit, an application specific integrated circuit (ASIC), appropriate firmware, a plug-in, a function card, etc. When implemented in software, the elements of this application are programs or code segments used to perform the required tasks. The program or code segment can be stored in a machine-readable medium, or transmitted on a transmission medium or a communication link via a data signal carried in a carrier.

[0203] It should be clear that the present application is not limited to the specific configuration and processing described above and shown in the figures. For the sake of simplicity, a detailed description of the known method is omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present application is not limited to the specific steps described and shown, and those skilled in the art can make various changes, modifications and additions, or change the order between the steps after understanding the spirit of the present application.

[0204] In the present application, features described and / or illustrated for one embodiment may be used in the same manner or in a similar manner in one or more other embodiments, and / or combined with features of other embodiments or replace features of other embodiments.

[0205] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the embodiments of the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A coherent optical communication method, characterized in that: include: Performing digital signal processing including error feedback noise shaping on the currently received digital signal to obtain a pre-compensated digital signal; Performing digital-to-analog conversion and signal amplification processing on the pre-compensated digital signal in sequence to obtain an amplified first analog signal; Performing coherent optical modulation on the amplified first analog signal to obtain a modulated optical signal, and transmitting the optical signal to a receiving device based on a standard single-mode optical fiber, so that the receiving device performs frequency mixing and photoelectric conversion processing on the optical signal to obtain a second analog signal; and causing the receiving device to perform analog-to-digital conversion on the second analog signal to convert the second analog signal into a corresponding digital signal, and then the receiving device performs digital signal processing including adaptive equalization based on Stokes domain depolarization on the digital signal to obtain a demodulated digital signal; The step of performing digital signal processing including error feedback noise shaping on the currently received digital signal to obtain a pre-compensated digital signal includes: Generate a pseudo-random code sequence corresponding to the currently received digital signal; The pseudo-random code sequence is converted into the corresponding PAM4 symbol sequence through Gray coding mapping; The PAM4 symbol sequence is converted into a waveform signal sequence using a square root raised cosine filter pulse shaping method; Performing error feedback noise shaping on the waveform signal sequence to obtain a pre-compensated digital signal; The receiving device performs digital signal processing including adaptive equalization based on Stokes domain depolarization on the digital signal to obtain a demodulated digital signal, including: Performing IQ imbalance compensation on the digital signal corresponding to the second analog signal to obtain an IQ imbalance compensated digital signal; Performing adaptive equalization processing based on Stokes domain depolarization on the digital signal after the IQ imbalance compensation to obtain a digital signal after adaptive equalization; Correcting the frequency offset and phase noise in the adaptively equalized digital signal to obtain a carrier-recovered digital signal; The digital signal after carrier recovery is demapped according to a preset modulation method to obtain a demodulated digital signal.

2. The coherent optical communication method according to claim 1, characterized in that: The step of performing error feedback noise shaping on the waveform signal sequence to obtain a pre-compensated digital signal comprises: Performing amplitude limiting processing on the waveform signal sequence; Performing quantization processing on the waveform signal after the amplitude limitation processing; The waveform signal after the quantization processing is subjected to time domain filtering in a feedback loop to obtain the pre-compensated digital signal after error feedback noise shaping corresponding to the waveform signal.

3. A coherent optical communication system, characterized in that: It includes a transmitting device and a receiving device for communication connection based on standard single-mode optical fiber; The transmitting device is used to execute the following: Performing digital signal processing including error feedback noise shaping on the currently received digital signal to obtain a pre-compensated digital signal; Performing digital-to-analog conversion and signal amplification processing on the pre-compensated digital signal in sequence to obtain an amplified first analog signal; Performing coherent optical modulation on the amplified first analog signal to obtain a modulated optical signal, and transmitting the optical signal to a receiving device based on a standard single-mode optical fiber, so that the receiving device performs frequency mixing and photoelectric conversion processing on the optical signal to obtain a second analog signal; and causing the receiving device to perform analog-to-digital conversion on the second analog signal to convert the second analog signal into a corresponding digital signal, and then the receiving device performs digital signal processing including adaptive equalization based on Stokes domain depolarization on the digital signal to obtain a demodulated digital signal; The step of performing digital signal processing including error feedback noise shaping on the currently received digital signal to obtain a pre-compensated digital signal includes: Generate a pseudo-random code sequence corresponding to the currently received digital signal; The pseudo-random code sequence is converted into the corresponding PAM4 symbol sequence through Gray coding mapping; The PAM4 symbol sequence is converted into a waveform signal sequence using a square root raised cosine filter pulse shaping method; Performing error feedback noise shaping on the waveform signal sequence to obtain a pre-compensated digital signal; The receiving device is used to perform the following contents: Based on a standard single-mode optical fiber, an optical signal from a transmitting device is received, and the optical signal is mixed and subjected to photoelectric conversion processing to obtain a second analog signal, wherein the optical signal is generated in advance by the transmitting device after performing digital signal processing including error feedback noise shaping, digital-to-analog conversion, signal amplification processing, and coherent optical modulation on the received digital signal; Performing analog-to-digital conversion on the second analog signal to convert the second analog signal into a corresponding digital signal; performing digital signal processing including adaptive equalization based on Stokes domain depolarization on the digital signal to obtain a demodulated digital signal; performing digital signal processing including adaptive equalization based on Stokes domain depolarization on the digital signal to obtain a demodulated digital signal, including: Performing IQ imbalance compensation on the digital signal corresponding to the second analog signal to obtain an IQ imbalance compensated digital signal; Performing adaptive equalization processing based on Stokes domain depolarization on the digital signal after the IQ imbalance compensation to obtain a digital signal after adaptive equalization; Correcting the frequency offset and phase noise in the adaptively equalized digital signal to obtain a carrier-recovered digital signal; Demapping the digital signal after carrier recovery according to a preset modulation method to obtain a demodulated digital signal; The transmitting device includes: a transmitting end digital signal processing module, which is used to perform digital signal processing including error feedback noise shaping on the currently received digital signal to obtain a pre-compensated digital signal; a digital-to-analog conversion and amplification module, which is used to perform digital-to-analog conversion and signal amplification processing on the pre-compensated digital signal in sequence to obtain an amplified first analog signal; A coherent optical modulation module, used for performing coherent optical modulation on the amplified first analog signal to obtain a modulated optical signal, so as to transmit the optical signal to the receiving device based on a standard single-mode optical fiber; The receiving device includes: an integrated coherent optical receiving module, which is used to receive an optical signal from a transmitting device based on a standard single-mode optical fiber, and perform frequency mixing and photoelectric conversion processing on the optical signal to obtain a second analog signal; an analog-to-digital converter, configured to perform analog-to-digital conversion on the second analog signal to convert the second analog signal into a corresponding digital signal; The receiving end digital signal processing module is used to perform digital signal processing including adaptive equalization based on Stokes domain depolarization on the digital signal to obtain a demodulated digital signal.

4. The coherent optical communication system according to claim 3, characterized in that: The transmitting end digital signal processing module comprises: A pseudo-random code sequence generator, used to generate a pseudo-random code sequence corresponding to the currently received digital signal; A symbol mapping module, used for converting a pseudo-random code sequence into a corresponding PAM4 symbol sequence through Gray coding mapping; A square root raised cosine filter is used to convert the PAM4 symbol sequence into a waveform signal sequence by adopting a square root raised cosine filter pulse shaping method; an error feedback noise shaping module is used to perform error feedback noise shaping on the waveform signal sequence to obtain a pre-compensated digital signal.

5. The coherent optical communication system according to claim 4, characterized in that: The error feedback noise shaping module comprises: A limiter, used for performing amplitude limiting processing on the waveform signal sequence; A quantizer, used for performing quantization processing on the waveform signal after the amplitude limitation processing; The loop filter is used to perform time domain filtering in a feedback loop on the waveform signal after the quantization processing to obtain the pre-compensated digital signal after error feedback noise shaping corresponding to the waveform signal.

6. The coherent optical communication system according to claim 3, characterized in that: The receiving end digital signal processing module comprises: An IQ imbalance compensation module, configured to perform IQ imbalance compensation on the digital signal corresponding to the second analog signal to obtain an IQ imbalance compensated digital signal; An adaptive equalization module based on Stokes domain depolarization is used to perform adaptive equalization processing based on Stokes domain depolarization on the digital signal after IQ imbalance compensation to obtain a digital signal after adaptive equalization; A carrier recovery module, used to correct the frequency offset and phase noise in the digital signal after adaptive equalization to obtain a digital signal after carrier recovery; The decision demapping module is used to demap the digital signal after the carrier recovery according to a preset modulation mode to obtain a demodulated digital signal.

7. The coherent optical communication system according to claim 3, characterized in that: Also includes: A first erbium-doped fiber amplifier and a second erbium-doped fiber amplifier disposed between the transmitting device and the receiving device; The first erbium-doped fiber amplifier is used to control the fiber-input optical power of the modulated optical signal output by the coherent optical modulation module, so that the optical signal after the fiber-input optical power control is transmitted to the receiving device based on a standard single-mode optical fiber; The second erbium-doped fiber amplifier is used to amplify the optical signal transmitted to the receiving device side via the standard single-mode optical fiber, so that the integrated coherent optical receiving module receives the optical signal after amplification.

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