Low-complexity nonlinear compensation method and system for digital subcarrier multiplexing optical communication

Abstract

The invention provides a low-complexity nonlinear compensation method and system for digital subcarrier multiplexing optical communication, and the method comprises the steps: calculating a nonlinear coefficient of a digital subcarrier multiplexing optical communication system, and carrying out the quantization processing of the nonlinear coefficient through employing a uniform quantization mode; by taking the cross-section length as a processing step length, converting the time domain signal of each subcarrier to a frequency domain for dispersion compensation, and then converting the compensated signal back to the time domain; calculating nonlinear phase noise in the subcarriers based on the time domain signal intensity of each subcarrier by taking the cross-section length as a processing step length, and performing phase rotation compensation; and calculating inter-subcarrier nonlinear phase noise and inter-polarization crosstalk based on the quantized nonlinear coefficient, subcarrier signal strength and inter-polarization crosstalk strength by taking the cross-section length as a processing step length, constructing a nonlinear compensation matrix and performing matrix compensation. According to the invention, the calculation complexity of an optical fiber nonlinear compensation algorithm is reduced, and efficient nonlinear compensation of a digital subcarrier multiplexing optical communication system is realized.

Description

Technical Field

[0001] This invention relates to the field of optical communication system technology, and more specifically, to a low-complexity nonlinear compensation method and system for digital subcarrier multiplexed optical communication. Background Technology

[0002] With the development of coherent optical transmission technology and digital processing chip technology, the speed of optical communication systems is constantly increasing. In high-speed optical communication systems, fiber nonlinearity has become a significant limiting factor for further capacity improvements. On the other hand, digital subcarrier multiplexing technology, with its friendliness to EEPN and DSP chip performance and high tolerance to nonlinear noise, has become a powerful solution for building high-speed optical communication systems. However, as the speed of optical communication systems increases, the number of subcarriers in digital subcarrier systems also increases, leading to a continuous increase in the computational complexity of nonlinear compensation algorithms. Designing low-complexity nonlinear compensation schemes has become an important issue for improving the capacity of high-speed digital subcarrier systems.

[0003] Therefore, in the prior art, the "Single-Step Improved Fiber Nonlinear Compensation Algorithm" was disclosed in the December 2019 issue of the journal "Optical Express" (pages 36680-36690). This paper uses an IIR filter to perform filtering in the time domain, thereby calculating the nonlinear phase noise and nonlinear polarization crosstalk between subcarriers. However, this method does not consider the sharing and quantization of the nonlinear compensation coefficients for each subcarrier, and the computational complexity still increases with the number of subcarriers.

[0004] Patent application CN114422035A discloses a method and system for compensating for nonlinear impairments in optical fibers in a coherent optical communication system, including the following steps: a noise acquisition step: obtaining perturbation noise by reducing perturbation terms and performing multiplication calculations; an impairment compensation step: processing the perturbation noise to compensate for nonlinear impairments in the optical fiber channel. This method can be used at the transmitting end based on transmitted symbols or at the receiving end based on received symbols, effectively compensating for nonlinear impairments in optical fibers while significantly reducing implementation complexity. However, this patent cannot completely solve the existing technical problems, nor can it meet the needs of this invention. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a low-complexity nonlinear compensation method and system for digital subcarrier multiplexed optical communication.

[0006] The low-complexity nonlinear compensation method for digital subcarrier multiplexed optical communication provided by the present invention includes: Step 1: Based on the baud rate, subcarrier spacing, and span length of each subcarrier, calculate the nonlinear coefficients of the digital subcarrier multiplexing optical communication system, and quantize the nonlinear coefficients using a uniform quantization method; Step 2: Using the segment length as the processing step size, convert the time-domain signal of each subcarrier to the frequency domain for dispersion compensation, and then convert the compensated signal back to the time domain. Step 3: Using the segment length as the processing step size, calculate the nonlinear phase noise within each subcarrier based on the time-domain signal strength of each subcarrier, and perform phase rotation compensation. Step 4: Using the segment length as the processing step size, calculate the nonlinear phase noise and interpolarization crosstalk between subcarriers based on the quantized nonlinear coefficients, subcarrier signal strength, and interpolarization crosstalk strength, construct the nonlinear compensation matrix, and perform matrix compensation. Steps 2 to 4 are executed iteratively until all cross-segment compensation processes are completed.

[0007] Preferably, step 1 includes: Obtain the baud rate, subcarrier spacing, and span length for each subcarrier; The nonlinear coefficient is calculated using the following formula. :

[0008] in, It is the fiber attenuation coefficient. It is the fiber dispersion coefficient. It is the segment length. It is the subcarrier spacing. It is a symbol period. It is the angular frequency of the signal. The imaginary unit is m, and the symbol index is m. For the nonlinear coefficients Perform uniform quantization.

[0009] Preferably, step 2 includes: Step 2.1: Transform each subcarrier signal to the frequency domain using Fourier transform, the expression is:

[0010] in, and These are the expressions for the subcarrier signal in the time domain and frequency domain, respectively, and their subscripts are... This indicates that the signal is x- and y-polarized. It is a unit of time; Step 2.2: Based on the subcarrier center frequency Given the segment length, calculate the dispersion value. The expression is:

[0011] Step 2.3: Compensate the frequency domain signal based on the dispersion value, expressed as:

[0012] in, This indicates the compensated signal. It is the dispersion compensation coefficient; Step 2.4: Convert the compensated frequency domain signal back to the time domain using an inverse Fourier transform. The expression is: .

[0013] Preferably, step 3 includes: Step 3.1: Calculate the subcarrier signal strength, expressed as:

[0014] in, The subcarrier signal strength; Step 3.2: Calculate the nonlinear phase noise within the subcarrier, expressed as:

[0015] in, This refers to nonlinear phase noise within the subcarrier. It is the nonlinear coefficient of the optical fiber; Step 3.3: Based on the nonlinear phase noise within the subcarrier, perform intra-subcarrier nonlinear compensation on each subcarrier signal. The expression is as follows:

[0016] in, This indicates the compensated signal. It is the nonlinear compensation coefficient within the subcarrier.

[0017] Preferably, step 4 includes: Step 4.1: Calculate the inter-polarization crosstalk intensity of the subcarriers, expressed as:

[0018] in, The crosstalk intensity between subcarrier polarizations; yes The complex conjugate; Step 4.2: Calculate the inter-carrier nonlinear phase noise and inter-carrier nonlinear polarization crosstalk, expressed as follows:

[0019]

[0020] in, These are the quantized nonlinear coefficients. This indicates that this is the q-th quantized value. and These are inter-carrier nonlinear phase noise and inter-carrier nonlinear polarization crosstalk, respectively. Step 4.3: Calculate the inter-carrier nonlinear compensation matrix based on the phase noise and crosstalk, expressed as:

[0021] in, This is the nonlinear compensation matrix between subcarriers. It is the nonlinear compensation coefficient between subcarriers; Step 4.4: Compensate the subcarrier signal using the compensation matrix, expressed as:

[0022] in, This indicates the compensated signal. and They are Signals polarized in both x and y directions; and They are Signals polarized in both x and y directions.

[0023] The low-complexity nonlinear compensation system for digital subcarrier multiplexed optical communication provided by the present invention includes: Module M1: Based on the baud rate, subcarrier spacing, and span length of each subcarrier, calculate the nonlinear coefficients of the digital subcarrier multiplexed optical communication system, and quantize the nonlinear coefficients using a uniform quantization method; Module M2: Using the segment length as the processing step size, it converts the time-domain signal of each subcarrier to the frequency domain for dispersion compensation, and then converts the compensated signal back to the time domain. Module M3: Using the segment length as the processing step size, it calculates the nonlinear phase noise within each subcarrier based on the time-domain signal strength of each subcarrier and performs phase rotation compensation. Module M4: Using the segment length as the processing step size, based on the quantized nonlinear coefficients, subcarrier signal strength, and interpolarization crosstalk strength, it calculates the nonlinear phase noise and interpolarization crosstalk between subcarriers, constructs the nonlinear compensation matrix, and performs matrix compensation. The process iterates from module M2 to module M4 until all cross-segment compensation is completed.

[0024] Preferably, the module M1 includes: Obtain the baud rate, subcarrier spacing, and span length for each subcarrier; The nonlinear coefficient is calculated using the following formula. :

[0025] in, It is the fiber attenuation coefficient. It is the fiber dispersion coefficient. It is the segment length. It is the subcarrier spacing. It is a symbol period. It is the angular frequency of the signal. The imaginary unit is m, and the symbol index is m. For the nonlinear coefficients Perform uniform quantization.

[0026] Preferably, the module M2 includes: Module M2.1: Transforms each subcarrier signal to the frequency domain using Fourier transform, expressed as:

[0027] in, and These are the expressions for the subcarrier signal in the time domain and frequency domain, respectively, and their subscripts are... This indicates that the signal is x- and y-polarized. It is a unit of time; Module M2.2: Based on the subcarrier center frequency Given the segment length, calculate the dispersion value. The expression is:

[0028] Module M2.3: Compensates the frequency domain signal based on the dispersion value, expressed as:

[0029] in, This indicates the compensated signal. It is the dispersion compensation coefficient; Module M2.4: Converts the compensated frequency domain signal back to the time domain using an inverse Fourier transform, expressed as: .

[0030] Preferably, the module M3 includes: Module M3.1: Calculates subcarrier signal strength, with the following expression:

[0031] in, The subcarrier signal strength; Module M3.2: Calculates the nonlinear phase noise within the subcarrier, expressed as:

[0032] in, This refers to nonlinear phase noise within the subcarrier. It is the nonlinear coefficient of the optical fiber; Module M3.3: Based on the nonlinear phase noise within the subcarrier, perform intra-subcarrier nonlinear compensation on each subcarrier signal. The expression is as follows:

[0033] in, This indicates the compensated signal. It is the nonlinear compensation coefficient within the subcarrier.

[0034] Preferably, the module M4 includes: Module M4.1: Calculates the inter-polarization crosstalk intensity of subcarriers, with the following expression:

[0035] in, The crosstalk intensity between subcarrier polarizations; yes The complex conjugate; Module M4.2: Calculates inter-carrier nonlinear phase noise and inter-carrier nonlinear polarization crosstalk, with the following expressions:

[0036]

[0037] in, These are the quantized nonlinear coefficients. This indicates that this is the q-th quantized value. and These are inter-carrier nonlinear phase noise and inter-carrier nonlinear polarization crosstalk, respectively. Module M4.3: Calculates the inter-carrier nonlinear compensation matrix based on the phase noise and crosstalk, with the following expression:

[0038] in, This is the nonlinear compensation matrix between subcarriers. It is the nonlinear compensation coefficient between subcarriers; Module M4.4: Uses the compensation matrix to compensate the subcarrier signal, expressed as:

[0039] in, This indicates the compensated signal. and They are Signals polarized in both x and y directions; and They are Signals polarized in both x and y directions.

[0040] Compared with the prior art, the present invention has the following beneficial effects: (1) By adopting a time-varying symbol crosstalk model, sharing nonlinear compensation coefficients, and using quantization to reduce the number of nonlinear compensation coefficients, the problem of needing to use a large number of Fourier transforms and a large number of complex multiplications for nonlinear compensation between subcarriers is solved, thus achieving the effect of reducing the computational complexity of nonlinear compensation steps between subcarriers. (2) By combining the calculations of each subcarrier, the computational complexity of nonlinear compensation between subcarriers is further decoupled from the number of subcarriers, which solves the problem that the computational complexity of the nonlinear compensation algorithm increases with the number of subcarriers, and achieves the effect of efficiently compensating for the nonlinear effects of high-speed digital subcarrier optical communication systems. Attached Figure Description

[0041] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a block diagram illustrating the principle of an optical fiber nonlinear compensation algorithm. Figure 2 A block diagram illustrating the principle of fiber nonlinearity compensation between subcarriers; Figure 3 A block diagram of the transceiver and its links; Figure 4 This is a graph showing the algorithm's performance. Detailed Implementation

[0042] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0043] Example 1 like Figure 1 and Figure 2 This invention provides a low-complexity nonlinear compensation method for digital subcarrier multiplexed optical communication, comprising the following steps: Step 1: In the digital subcarrier multiplexing optical communication system, obtain information such as the baud rate, subcarrier spacing, and span length of each subcarrier, and calculate the nonlinear coefficients of the digital subcarrier multiplexing optical communication system. The expression is:

[0044] in, It is the fiber attenuation coefficient. It is the fiber dispersion coefficient. It is the segment length. It is the subcarrier spacing. It is a symbol period. This refers to the angular frequency of the signal. After calculating the nonlinear coefficients of the digital subcarrier multiplexed optical communication system, uniform quantization is also required to quantize the coefficients. Step 2: Perform dispersion compensation using the segment length as the step size; Step 3: Perform intra-subcarrier nonlinear compensation using the segment length as the step size; Step 4: Perform nonlinear compensation between subcarriers using the segment length as the step size; Repeat steps 2 through 4 until all compensation is completed.

[0045] Step 2 includes the following steps: Step 2.1: Transform each subcarrier signal to the frequency domain using Fourier transform, the expression is:

[0046] in, and These are the expressions for the subcarrier signal in the time domain and frequency domain, respectively, and their subscripts are... This indicates that the signal is x- and y-polarized. It is the imaginary unit; Step 2.2: Calculate the dispersion value of each subcarrier according to the dispersion compensation step size and the center frequency of each subcarrier. The expression is:

[0047] in, It is the dispersion value. It is the center frequency of the subcarrier; Step 2.3: Perform dispersion compensation on the frequency domain subcarrier signal obtained in Step 2.1 according to the dispersion value obtained in Step 2.2. The expression is:

[0048] in, This indicates the compensated signal. It is the dispersion compensation coefficient; Step 2.4: The compensated frequency-domain subcarrier signal obtained in Step 2.3 is transferred to the time domain through inverse Fourier transform to obtain the time-domain subcarrier signal. The inverse Fourier transform expression is as follows:

[0049] Step 3 includes the following steps: Step 3.1: Based on the subcarrier signals obtained in Step 2, calculate the subcarrier signal strength, expressed as:

[0050] in, The subcarrier signal strength; Step 3.2: Based on the subcarrier signal strength obtained in Step 3.1, calculate the nonlinear phase noise within each subcarrier signal. The expression is:

[0051] in, This refers to nonlinear phase noise within the subcarrier. Step 3.3: Based on the intra-subcarrier nonlinear phase noise obtained in Step 3.2, perform intra-subcarrier nonlinear compensation on each subcarrier signal, expressed as:

[0052] in, This indicates the compensated signal. It is the nonlinear compensation coefficient within the subcarrier.

[0053] Step 4 includes the following steps: Step 4.1: Based on the subcarrier signals obtained in Step 3, calculate the inter-polarization crosstalk intensity of the subcarriers. The expression is:

[0054] in, The crosstalk intensity between subcarrier polarizations; Step 4.2: Based on the quantized nonlinear coefficients obtained in Step 1, the subcarrier signal strength obtained in Step 3.1, and the subcarrier inter-polarization crosstalk strength obtained in Step 4.1, calculate the inter-subcarrier nonlinear phase noise and the inter-subcarrier nonlinear inter-polarization crosstalk. The expressions are as follows:

[0055]

[0056] in, These are the quantized nonlinear coefficients. This indicates that this is the q-th quantized value. and These are inter-carrier nonlinear phase noise and inter-carrier nonlinear polarization crosstalk, respectively. Step 4.3: Based on the inter-carrier nonlinear phase noise and inter-carrier nonlinear polarization crosstalk obtained in Step 4.2, calculate the inter-carrier nonlinear compensation matrix, expressed as:

[0057] in, This is the nonlinear compensation matrix between subcarriers. It is the nonlinear compensation coefficient between subcarriers; Step 4.4: Based on the inter-carrier nonlinearity compensation matrix obtained in Step 4.3, perform inter-carrier nonlinearity compensation on each subcarrier signal. The expression is as follows:

[0058] in, This indicates the signal after compensation.

[0059] like Figure 3 This is a block diagram of the transceiver and the link; like Figure 4 The graph shows the transmit power-receive SNR curves for both uncompensated and algorithm-compensated versions.

[0060] Example 2 This invention also provides a low-complexity nonlinear compensation system for digital subcarrier multiplexed optical communication, comprising: Module M1: Based on the baud rate, subcarrier spacing, and span length of each subcarrier, calculate the nonlinear coefficients of the digital subcarrier multiplexed optical communication system, and quantize the nonlinear coefficients using a uniform quantization method; Module M2: Using the segment length as the processing step size, it converts the time-domain signal of each subcarrier to the frequency domain for dispersion compensation, and then converts the compensated signal back to the time domain. Module M3: Using the segment length as the processing step size, it calculates the nonlinear phase noise within each subcarrier based on the time-domain signal strength of each subcarrier and performs phase rotation compensation. Module M4: Using the segment length as the processing step size, based on the quantized nonlinear coefficients, subcarrier signal strength, and interpolarization crosstalk strength, it calculates the nonlinear phase noise and interpolarization crosstalk between subcarriers, constructs the nonlinear compensation matrix, and performs matrix compensation. The process iterates from module M2 to module M4 until all cross-segment compensation is completed.

[0061] The module M1 includes: Obtain the baud rate, subcarrier spacing, and span length for each subcarrier; The nonlinear coefficient is calculated using the following formula. :

[0062] in, It is the fiber attenuation coefficient. It is the fiber dispersion coefficient. It is the segment length. It is the subcarrier spacing. It is a symbol period. It is the angular frequency of the signal. The imaginary unit is m, and the symbol index is m. For the nonlinear coefficients Perform uniform quantization.

[0063] The module M2 includes: Module M2.1: Transforms each subcarrier signal to the frequency domain using Fourier transform, expressed as:

[0064] in, and These are the expressions for the subcarrier signal in the time domain and frequency domain, respectively, and their subscripts are... This indicates that the signal is x- and y-polarized. It is a unit of time; Module M2.2: Based on the subcarrier center frequency Given the segment length, calculate the dispersion value. The expression is:

[0065] Module M2.3: Compensates the frequency domain signal based on the dispersion value, expressed as:

[0066] in, This indicates the compensated signal. It is the dispersion compensation coefficient; Module M2.4: Converts the compensated frequency domain signal back to the time domain using an inverse Fourier transform, expressed as: .

[0067] The module M3 includes: Module M3.1: Calculates subcarrier signal strength, with the following expression:

[0068] in, The subcarrier signal strength; Module M3.2: Calculates the nonlinear phase noise within the subcarrier, expressed as:

[0069] in, This refers to nonlinear phase noise within the subcarrier. It is the nonlinear coefficient of the optical fiber; Module M3.3: Based on the nonlinear phase noise within the subcarrier, perform intra-subcarrier nonlinear compensation on each subcarrier signal. The expression is as follows:

[0070] in, This indicates the compensated signal. It is the nonlinear compensation coefficient within the subcarrier.

[0071] The module M4 includes: Module M4.1: Calculates the inter-polarization crosstalk intensity of subcarriers, with the following expression:

[0072] in, The crosstalk intensity between subcarrier polarizations; yes The complex conjugate; Module M4.2: Calculates inter-carrier nonlinear phase noise and inter-carrier nonlinear polarization crosstalk, with the following expressions:

[0073]

[0074] in, These are the quantized nonlinear coefficients. This indicates that this is the q-th quantized value. and These are inter-carrier nonlinear phase noise and inter-carrier nonlinear polarization crosstalk, respectively. Module M4.3: Calculates the inter-carrier nonlinear compensation matrix based on the phase noise and crosstalk, with the following expression:

[0075] in, This is the nonlinear compensation matrix between subcarriers. It is the nonlinear compensation coefficient between subcarriers; Module M4.4: Uses the compensation matrix to compensate the subcarrier signal, expressed as:

[0076] in, This indicates the compensated signal. and They are Signals polarized in both x and y directions; and They are Signals polarized in both x and y directions.

[0077] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0078] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A low-complexity nonlinear compensation method for digital subcarrier multiplexed optical communication, characterized in that, include: Step 1: Based on the baud rate, subcarrier spacing, and span length of each subcarrier, calculate the nonlinear coefficients of the digital subcarrier multiplexing optical communication system, and quantize the nonlinear coefficients using a uniform quantization method; Step 2: Using the segment length as the processing step size, convert the time-domain signal of each subcarrier to the frequency domain for dispersion compensation, and then convert the compensated signal back to the time domain. Step 3: Using the segment length as the processing step size, calculate the nonlinear phase noise within each subcarrier based on the time-domain signal strength of each subcarrier, and perform phase rotation compensation. Step 4: Using the segment length as the processing step size, calculate the nonlinear phase noise and interpolarization crosstalk between subcarriers based on the quantized nonlinear coefficients, subcarrier signal strength, and interpolarization crosstalk strength, construct the nonlinear compensation matrix, and perform matrix compensation. Steps 2 to 4 are executed iteratively until all cross-segment compensation processes are completed.

2. The low-complexity nonlinear compensation method for digital subcarrier multiplexed optical communication according to claim 1, characterized in that, Step 1 includes: Obtain the baud rate, subcarrier spacing, and span length for each subcarrier; The nonlinear coefficient is calculated using the following formula. : in, It is the fiber attenuation coefficient. It is the fiber dispersion coefficient. It is the segment length. It is the subcarrier spacing. It is a symbol period. It is the angular frequency of the signal. The imaginary unit is m, and the symbol index is m. For the nonlinear coefficients Perform uniform quantization.

3. The low-complexity nonlinear compensation method for digital subcarrier multiplexed optical communication according to claim 2, characterized in that, Step 2 includes: Step 2.1: Transform each subcarrier signal to the frequency domain using Fourier transform, the expression is: in, and These are the expressions for the subcarrier signal in the time domain and frequency domain, respectively, and their subscripts are... This indicates that the signal is x- and y-polarized. It is a unit of time; Step 2.2: Based on the subcarrier center frequency Given the segment length, calculate the dispersion value. The expression is: Step 2.3: Compensate the frequency domain signal based on the dispersion value, expressed as: in, This indicates the compensated signal. It is the dispersion compensation coefficient; Step 2.4: Convert the compensated frequency domain signal back to the time domain using an inverse Fourier transform. The expression is: 。 4. The low-complexity nonlinear compensation method for digital subcarrier multiplexed optical communication according to claim 3, characterized in that, Step 3 includes: Step 3.1: Calculate the subcarrier signal strength, expressed as: in, The subcarrier signal strength; Step 3.2: Calculate the nonlinear phase noise within the subcarrier, expressed as: in, This refers to nonlinear phase noise within the subcarrier. It is the nonlinear coefficient of the optical fiber; Step 3.3: Based on the nonlinear phase noise within the subcarrier, perform intra-subcarrier nonlinear compensation on each subcarrier signal. The expression is as follows: in, This indicates the compensated signal. It is the nonlinear compensation coefficient within the subcarrier.

5. The low-complexity nonlinear compensation method for digital subcarrier multiplexed optical communication according to claim 4, characterized in that, Step 4 includes: Step 4.1: Calculate the inter-polarization crosstalk intensity of the subcarriers, expressed as: in, The crosstalk intensity between subcarrier polarizations; yes The complex conjugate; Step 4.2: Calculate the inter-carrier nonlinear phase noise and inter-carrier nonlinear polarization crosstalk, expressed as follows: in, These are the quantized nonlinear coefficients. This indicates that this is the q-th quantized value. and These are inter-carrier nonlinear phase noise and inter-carrier nonlinear polarization crosstalk, respectively. Step 4.3: Calculate the inter-carrier nonlinear compensation matrix based on the phase noise and crosstalk, expressed as: in, This is the nonlinear compensation matrix between subcarriers. It is the nonlinear compensation coefficient between subcarriers; Step 4.4: Compensate the subcarrier signal using the compensation matrix, expressed as: in, This indicates the compensated signal. and They are Signals polarized in both x and y directions; and They are Signals polarized in both x and y directions.

6. A low-complexity nonlinear compensation system for digital subcarrier multiplexed optical communication, characterized in that, include: Module M1: Based on the baud rate, subcarrier spacing, and span length of each subcarrier, calculate the nonlinear coefficients of the digital subcarrier multiplexed optical communication system, and quantize the nonlinear coefficients using a uniform quantization method; Module M2: Using the segment length as the processing step size, it converts the time-domain signal of each subcarrier to the frequency domain for dispersion compensation, and then converts the compensated signal back to the time domain. Module M3: Using the segment length as the processing step size, it calculates the nonlinear phase noise within each subcarrier based on the time-domain signal strength of each subcarrier and performs phase rotation compensation. Module M4: Using the segment length as the processing step size, based on the quantized nonlinear coefficients, subcarrier signal strength, and interpolarization crosstalk strength, it calculates the nonlinear phase noise and interpolarization crosstalk between subcarriers, constructs the nonlinear compensation matrix, and performs matrix compensation. The process iterates from module M2 to module M4 until all cross-segment compensation is completed.

7. The low-complexity nonlinear compensation system for digital subcarrier multiplexed optical communication according to claim 6, characterized in that, The module M1 includes: Obtain the baud rate, subcarrier spacing, and span length for each subcarrier; The nonlinear coefficient is calculated using the following formula. : in, It is the fiber attenuation coefficient. It is the fiber dispersion coefficient. It is the segment length. It is the subcarrier spacing. It is a symbol period. It is the angular frequency of the signal. The imaginary unit is m, and the symbol index is m. For the nonlinear coefficients Perform uniform quantization.

8. The low-complexity nonlinear compensation system for digital subcarrier multiplexed optical communication according to claim 7, characterized in that, The module M2 includes: Module M2.1: Transforms each subcarrier signal to the frequency domain using Fourier transform, expressed as: in, and These are the expressions for the subcarrier signal in the time domain and frequency domain, respectively, and their subscripts are... This indicates that the signal is x- and y-polarized. It is a unit of time; Module M2.2: Based on the subcarrier center frequency Given the segment length, calculate the dispersion value. The expression is: Module M2.3: Compensates the frequency domain signal based on the dispersion value, expressed as: in, This indicates the compensated signal. It is the dispersion compensation coefficient; Module M2.4: Converts the compensated frequency domain signal back to the time domain using an inverse Fourier transform, expressed as: 。 9. The low-complexity nonlinear compensation system for digital subcarrier multiplexed optical communication according to claim 8, characterized in that, The module M3 includes: Module M3.1: Calculates subcarrier signal strength, with the following expression: in, The subcarrier signal strength; Module M3.2: Calculates the nonlinear phase noise within the subcarrier, expressed as: in, This refers to nonlinear phase noise within the subcarrier. It is the nonlinear coefficient of the optical fiber; Module M3.3: Based on the nonlinear phase noise within the subcarrier, perform intra-subcarrier nonlinear compensation on each subcarrier signal. The expression is as follows: in, This indicates the compensated signal. It is the nonlinear compensation coefficient within the subcarrier.

10. The low-complexity nonlinear compensation system for digital subcarrier multiplexed optical communication according to claim 9, characterized in that, The module M4 includes: Module M4.1: Calculates the inter-polarization crosstalk intensity of subcarriers, with the following expression: in, The crosstalk intensity between subcarrier polarizations; yes The complex conjugate; Module M4.2: Calculates inter-carrier nonlinear phase noise and inter-carrier nonlinear polarization crosstalk, with the following expressions: in, These are the quantized nonlinear coefficients. This indicates that this is the q-th quantized value. and These are inter-carrier nonlinear phase noise and inter-carrier nonlinear polarization crosstalk, respectively. Module M4.3: Calculates the inter-carrier nonlinear compensation matrix based on the phase noise and crosstalk, with the following expression: in, This is the nonlinear compensation matrix between subcarriers. It is the nonlinear compensation coefficient between subcarriers; Module M4.4: Uses the compensation matrix to compensate the subcarrier signal, expressed as: in, This indicates the compensated signal. and They are Signals polarized in both x and y directions; and They are Signals polarized in both x and y directions.

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