A method for optical fiber nonlinear compensation

Abstract

The present invention discloses a method for compensating fiber optic nonlinearity, which relates to the technical field of fiber optic communication. The method includes the following steps: S1. Receive time-domain data, perform downsampling and clock recovery processing on the time-domain data to obtain processed time-domain data; S2. Calculate the nonlinear operator #imgabs0#; S3. Group the processed time-domain data according to the number of points FFT of the fast Fourier transform in the algorithm size ; S4. Perform dispersion and nonlinear compensation on each segment of the data grouped in S3 respectively, assign a value to the amplitude term coefficient λ and calculate the bit error rate under the corresponding amplitude term coefficient λ; Use the particle swarm algorithm to select the value of the amplitude term coefficient λ with the minimum bit error rate; S5. Substitute the value of the amplitude term coefficient λ into the nonlinear operator #imgabs1# to perform nonlinear compensation on the optical signal. The present invention is beneficial to improving the transmission performance of fiber optic communication.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber communication technology, and in particular to an optical fiber nonlinear compensation method. Background Art

[0002] With the rapid growth of the demand for communication capacity in modern society, optical fiber communication is developing towards high-speed and long-distance. In long-distance optical communication, increasing the signal light power can extend the maximum transmission length of a single-segment optical fiber, reduce the use of Erbium Doped Fiber Application Amplifier (EDFA), and reduce the bit error rate at the receiving end. However, the increase in signal light power will enhance the self-phase modulation (SPM), and interact with dispersion and amplifier spontaneous emission noise (ASE), becoming a difficulty in optical fiber nonlinear damage compensation.

[0003] The traditional algorithms for compensating nonlinear optical fiber damage mainly include nonlinear equalization based on Volterra series and digital back-propagation (DBP) algorithm. Both are nonlinear Schrödinger equations. The DBP algorithm attempts to model the fiber channel by solving the NLSE and compensate the optical signal using digital signal processing technology. The DBP algorithm separates the linear damage from the nonlinear damage in the optical fiber, and uses the Split-Step Fast Fourier Transformation (SSFFT) method to convert the linear part to the frequency domain for compensation, while the nonlinear part is inversely transformed to the time domain for compensation, thus constructing a virtual link in the digital domain to compensate the optical signal.

[0004] Although there are relatively comprehensive calculation and compensation methods for nonlinear compensation, in the compensation process, the nonlinearity is mainly compensated by reverse simulation through algorithm approximation and approximation. Especially for the calculation of nonlinear phase, in the previous nonlinear calculation process, the partial phase modulation was mainly considered, while other nonlinear phase noise was ignored. This caused errors in the back-end digital signal processing process, and the calculated nonlinear phase could not be very close to the actual fiber propagation process. Therefore, seeking a more accurate nonlinear phase calculation method is conducive to improving the transmission performance of optical fiber communication and meeting the current urgent demand for capacity.

[0005] Therefore, proposing a fiber nonlinear compensation method is beneficial to improving the transmission performance of optical fiber communication, which is an urgent problem to be solved by technical personnel in this field. Summary of the invention

[0006] In view of this, the present invention provides a method for optical fiber nonlinear compensation to solve the problems existing in the prior art.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A method for optical fiber nonlinear compensation comprises the following steps:

[0009] S1, receiving time domain data, downsampling the time domain data, and performing clock recovery processing on the time domain data to obtain processed time domain data;

[0010] S2. Perform nonlinear operators Calculation of

[0011] S3, the processed time domain data is processed according to the number of points of fast Fourier transform FFT size To group;

[0012] S4, performing dispersion and nonlinear compensation on each segment of data after grouping in S3, assigning a value to the amplitude term coefficient λ and calculating the bit error rate under the corresponding amplitude term coefficient λ; using a particle swarm algorithm to select the value of the amplitude term coefficient λ with the minimum bit error rate;

[0013] S5. Substitute the value of the amplitude term coefficient λ into the nonlinear operator Perform nonlinear compensation on optical signals.

[0014] In the above method, optionally, the nonlinear operator in S2 The calculation formula is as follows:

[0015]

[0016] Where ω0 is the center frequency, T R is the first order moment of the Raman response function, A is the received signal, γ is the nonlinear parameter, i is the imaginary unit, μ is the quantity that characterizes the relationship between the peak-to-peak value of the signal and the change in the signal amplitude, and is the only uncertain value in λ that requires algorithm optimization, υ represents the relationship between the signal period and the sampling rate, which is generally 2, T0 is the period of the transmitted signal, |A peak is the peak-to-peak value.

[0017] In the above method, optionally, the length of the group in S3 depends on the number of points of the fast Fourier transform FFT when the back end performs frequency domain dispersion compensation. size .

[0018] In the above method, optionally, the specific content of S4 is: each segment of data is processed N times step and N LOOP The dispersion and nonlinear compensation of the amplitude term coefficient λ is calculated, and the bit error rate under the value of the amplitude term coefficient λ is calculated; the value of λ with the minimum bit error rate is sought; the bit error rate corresponding to the value of the amplitude term coefficient λ to be calculated is calculated. step Indicates the number of steps of nonlinear compensation in each span; N LOOP is the number of spans of the fiber link.

[0019] The above method can optionally assign an initial value range to the amplitude term coefficient λ according to the amplitude term coefficient λ formula in S2, and then calculate the nonlinear operator and perform nonlinear compensation for each value of the amplitude term coefficient λ within the current assigned range, and then calculate the corresponding bit error rate, and take the value of the amplitude term coefficient λ corresponding to the minimum bit error rate.

[0020] In the above method, optionally, the nonlinear compensation in S4 adopts a DBP compensation algorithm to find the optimal value of the amplitude term coefficient λ.

[0021] It can be seen from the above technical solutions that, compared with the prior art, the present invention provides a method for optical fiber nonlinear compensation, which has the following beneficial effects:

[0022] 1) Seeking a more accurate nonlinear phase calculation method is beneficial to improving the transmission performance of optical fiber communication and meeting the current urgent demand for capacity;

[0023] 2) Compared with traditional nonlinear damage only considering part of various nonlinear damages in optical fiber, it is more comprehensive and more in line with the actual propagation process of optical fiber, so it has better performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0025] Figure 1 A flow chart of a method for optical fiber nonlinear compensation disclosed in the present invention;

[0026] Figure 2 It is a flow chart of the DBP algorithm disclosed in the present invention;

[0027] Figure 3 It is the flow chart of the traditional DBP algorithm;

[0028] Figure 4Flowchart of DBP algorithm for optimizing nonlinear coefficients;

[0029] Figure 5 This is the flow chart of the extended nonlinear operator. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] In this application, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. The terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, the elements defined by the sentence "comprise one..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0032] See also Figure 1 As shown, the present invention discloses a method for optical fiber nonlinear compensation, comprising the following steps:

[0033] S1, receiving time domain data, downsampling the time domain data, and performing clock recovery processing on the time domain data to obtain processed time domain data;

[0034] S2. Perform nonlinear operators Calculation of

[0035] S3, the processed time domain data is processed according to FFT size To group;

[0036] S4, performing dispersion and nonlinear compensation on each segment of data after grouping in S3, assigning a value to the amplitude term coefficient λ and calculating the bit error rate under the corresponding amplitude term coefficient λ; using a particle swarm algorithm to select the value of the amplitude term coefficient λ with the minimum bit error rate;

[0037] S5. Substitute the value of the amplitude term coefficient λ into the nonlinear operator Perform nonlinear compensation on the optical signal; for specific compensation steps, refer to Figure 5 Flowchart of the process.

[0038] Furthermore, the nonlinear operator in S2 The calculation formula is as follows:

[0039]

[0040] Where ω0 is the center frequency, T R is the first order moment of the Raman response function, A is the received signal, γ is the nonlinear parameter, i is the imaginary unit, μ is the quantity that characterizes the relationship between the peak-to-peak value of the signal and the change in the signal amplitude, and is the only uncertain value in λ that requires algorithm optimization, υ represents the relationship between the signal period and the sampling rate, which is generally 2, T0 is the period of the transmitted signal, |A peak is the peak-to-peak value.

[0041] Furthermore, the length of the packet in S3 depends on the number of points of the fast Fourier transform (FFT) when the backend performs frequency domain dispersion compensation. size .

[0042] Furthermore, the specific content of S4 is: each segment of data is processed N step and N LOOP The dispersion and nonlinear compensation of the amplitude term coefficient λ is calculated, and the bit error rate under the corresponding value of the amplitude term coefficient λ is calculated; the value of the amplitude term coefficient λ with the minimum bit error rate is sought; the bit error rate corresponding to the value of the amplitude term coefficient λ to be calculated is calculated. Among them, N step Indicates the number of steps of nonlinear compensation in each span; N LOOP is the number of spans of the fiber link.

[0043] Furthermore, an initial value range is assigned to the amplitude term coefficient λ according to the formula of the amplitude term coefficient λ in S2, and then a nonlinear operator is calculated and nonlinear compensation is performed for each value of the amplitude term coefficient λ within the current assigned range, and then the corresponding bit error rate is calculated, and the value of the amplitude term coefficient λ corresponding to the minimum bit error rate is taken.

[0044] Furthermore, the nonlinear compensation in S4 uses the DBP compensation algorithm to find the optimal value of the amplitude term coefficient λ. The structure of the DBP compensation algorithm used in the calculation process is as follows: Figure 2 shown.

[0045] In order to specifically illustrate the nonlinear operator calculation method proposed in this paper, the following flowchart will be used to show the traditional DBP algorithm, the optimized DBP algorithm and the DBP algorithm based on the extended nonlinear operator proposed in this invention, as follows:

[0046] Reference Figure 3 As shown in the flowchart of the traditional DBP algorithm, the nonlinear operator used is: N = iγA 2 ;

[0047] Reference Figure 4As shown in the flowchart of the optimized DBP algorithm, the algorithm mainly calculates the nonlinear coefficients to find the most matching nonlinear operator. The nonlinear operator used is: N = iγkA 2 , k = [0, 2];

[0048] Reference Figure 5 As shown, the nonlinear operator calculation method proposed by the present invention mainly relies on the peak-to-peak value of the calculated signal and the sampling frequency to calculate the nonlinear operator. The nonlinear operator used is: exist Figure 5 First, the dispersion parameter β and the nonlinear parameter γ need to be given, the range of the amplitude term coefficient λ determined by S2 above, and the number of values ​​b to be searched within the range of the amplitude term coefficient λ during compensation; the larger the value of b, the finer the search; in the process of dispersion compensation, the calculation of dispersion mainly depends on: Where ω=ω-ω0 is the equivalent baseband angular frequency of the signal, λ0 is the central wavelength, and c is the speed of light in vacuum. D is the dispersion parameter, expressed as:

[0049]

[0050] Specifically, in Figure 5 In the flowchart shown in Figure 3 and Figure 4 Yes, Figure 5 The main formulas used to calculate nonlinear operators are different. Figure 5 In addition to considering the nonlinear effects brought by the power term, the nonlinear effects brought by other components of the signal are also considered. Compared with the other two calculation methods, the method proposed in this article is more comprehensive and has stronger theoretical basis and higher accuracy for nonlinear calculation. The specific implementation process still relies on the formula: and The latter is a range that needs to be determined at the beginning of the algorithm operation in this paper. Each bit error rate calculation is performed within this range. Then, in the compensation process, the nonlinear operator proposed in this paper is mainly used for nonlinear compensation, and the bit error rate is calculated. Then, the amplitude term coefficient λ corresponding to the lowest bit error rate is found. At this time, the nonlinear operator is also the most suitable expression form for the actual propagation link in the compensation process.

[0051] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without creative work.

[0052] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for optical fiber nonlinear compensation, characterized in that: The following steps are involved: S1, receiving time domain data, downsampling the time domain data, and performing clock recovery processing to obtain processed time domain data; S2, perform nonlinear operator Calculation of S3, the processed time domain data is processed according to FFT size To group; S4, perform dispersion and nonlinear compensation on each segment of data after grouping in S3, and adjust the amplitude coefficient Assign and calculate the corresponding amplitude term coefficient The bit error rate under the condition of The value of S5, the amplitude term coefficient Substitute the value of into the nonlinear operator Perform nonlinear compensation on optical signals; Nonlinear operators in S2 The calculation formula is as follows: in, is the center frequency, is the first order moment of the Raman response function, A is the received signal, is a nonlinear parameter, i is an imaginary unit, It is a quantity that characterizes the relationship between the peak-to-peak value of the signal and the change in the signal amplitude. Represents the relationship between the signal period and the sampling rate, is the period of the transmission signal, is the peak-to-peak value.

2. The optical fiber nonlinear compensation method according to claim 1, characterized in that: The length of the packet in S3 depends on the number of fast Fourier transform points when the backend performs frequency domain dispersion compensation. .

3. The optical fiber nonlinear compensation method according to claim 2, characterized in that: The specific content of S4 is: each segment of data is and Dispersion and nonlinear compensation, and calculate the corresponding amplitude term coefficients The bit error rate under the value of; Find the amplitude term coefficient with the minimum bit error rate The value of; For the amplitude term coefficient to be calculated The bit error rate corresponding to the value of Indicates how many steps of nonlinear compensation are performed in each span; is the number of spans of the fiber link.

4. The optical fiber nonlinear compensation method according to claim 3, characterized in that: According to the amplitude term coefficient in S2 The formula for the amplitude term coefficient Assign an initial value range, and then for each amplitude term coefficient within the current assignment range The value of is used to calculate the nonlinear operator and perform nonlinear compensation, then calculate the corresponding bit error rate, and take the amplitude term coefficient corresponding to the minimum bit error rate The value of .

5. The optical fiber nonlinear compensation method according to claim 3, characterized in that: The nonlinear compensation in S4 uses the DBP compensation algorithm to find the optimal amplitude term coefficient The value of .

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