A Carrier Modulation Method for an Optical Fiber Communication Link

Abstract

The present invention provides a carrier modulation method for an optical fiber communication link, which relates to the technical field of optical fiber communication. At the transmitting end, the high-speed data stream to be transmitted is divided into multiple low-speed data streams, and the multiple low-speed data streams are respectively modulated onto multiple independent subcarriers. A preamble signal is added to the signal to be transmitted on each subcarrier before transmission; at the receiving end, the signals transmitted on the multiple subcarriers received are modulated and synthesized by means of coupled quadrature modulation, and dispersion compensation and nonlinear compensation are performed on the synthesized total carrier signal. The present invention is of great significance for improving the performance of an optical fiber communication system, extending the transmission distance, increasing the system capacity, and reducing the cost.

Description

Technical Field

[0001] The present invention provides a carrier modulation method for an optical fiber communication link, which relates to the technical field of optical fiber communication. Background Art

[0002] With the rapid development of international Internet services and the communication industry, informatization has given a great impetus to the development of world productivity and human society. An optical fiber communication system uses light as a carrier, and uses extremely pure glass drawn into extremely thin optical fibers as a transmission medium, and transmits information by light through photoelectric conversion.

[0003] As Figure 1 shown, an optical fiber communication system includes basic functional modules such as transmission, transmission, and reception. The information source converts user information (voice, image, data, etc.) into an original electrical signal, and this signal is called a baseband signal. The electrical transmitter converts the baseband signal into an electrical signal suitable for channel transmission.

[0004] The electrical signal with information input to the optical transmitter is converted into an optical signal by the optical transmitter through modulation. The optical carrier is transmitted through the optical fiber to a remote optical receiver, and then the information source required by the user is taken out of the carrier through the demodulation of the electrical transmitter.

[0005] With the continuous growth of Internet traffic, optical fiber communication technology will continue to pursue higher transmission rates, larger system capacities, and longer transmission distances, involving more advanced modulation technologies, higher spectral utilization rates, and the development of new optical fibers; at the same time, in high-power and long-distance transmissions, the nonlinear effects of optical fibers will become more significant, and new technologies and methods are needed to manage and suppress them; as the network becomes more complex and dynamic, management and security issues have become more prominent.

[0006] For example, in the prior art, coherent optical communication technology can effectively compensate for dispersion and nonlinear effects in optical fibers by using coherent detection and digital signal processing (DSP) technology, thereby improving the transmission rate and distance.

[0007] For another example, in the prior art, as the transmission rate increases, the nonlinear effects in optical fibers become more significant, and new nonlinear compensation technologies, such as digital post-processing algorithms, are being developed, which can improve the transmission performance and extend the transmission distance.

[0008] However, the carrier modulation method of the prior art optical fiber communication link still has the following technical problems. With the growth of communication capacity requirements, how to further improve the spectral utilization rate is the focus of continuous research in the field of optical fiber communication; in terms of cost and energy efficiency: with the increase in system complexity, how to control costs and improve energy efficiency while ensuring performance is also an issue that needs to be considered in the development of optical fiber communication technology.

[0009] In addition, in long-distance transmission, the non-linear effects of optical fibers can damage signals; however, how to achieve effective dispersion compensation under different transmission distances and conditions remains a challenge. Summary of the Invention

[0010] To solve the above technical problems, the present invention proposes a carrier modulation method for an optical fiber communication link, including the following steps:

[0011] At the sending end, the high-speed data stream to be transmitted is divided into multiple low-speed data streams, and the multiple low-speed data streams are respectively modulated onto multiple independent subcarriers. After adding a preamble signal to the signal to be transmitted on each subcarrier, the signal is transmitted.

[0012] At the receiving end, the signals transmitted on the multiple subcarriers received are modulated and synthesized by means of coupled quadrature modulation, and dispersion compensation and non-linear compensation are performed on the synthesized total carrier signal.

[0013] Further, the preamble signal is a copy of a section of the signal added at the beginning of the signal to be transmitted on each respective subcarrier. The copy is the signal from the t-th period to the end period of the signal to be transmitted on each respective subcarrier, and the t-th period of the signal to be transmitted on the subcarrier is the starting period of the preamble signal.

[0014] Further, the method for determining the starting period of the preamble signal includes:

[0015] (1) F(k) represents the signal sequence of the k-th period of the signal to be transmitted on the subcarrier, k is a natural number, k = 1, 2, 3... T; T represents that there are a total of T periods of the signal to be transmitted on the subcarrier;

[0016] Calculate the phase difference P(k) between the signal sequence of the k-th period and the signal sequence of the (k + Δk)-th period.

[0017] (2) Calculate the amplitude ratio M(k) between the signal sequence of the k-th period and the signal sequence of the (k + Δk)-th period;

[0018] (3) Determine whether the k-th sampling point belongs to the starting period of the preamble signal through M(k) and P(k). If M(k) is less than the amplitude ratio threshold T1 and P(k) is less than the phase difference threshold T2, then the current period k is the starting period of the preamble signal.

[0019] Further, the coupled quadrature modulation method is to modulate the signal through a coupled modulation terminal, specifically including:

[0020] The subcarrier signal S(I) received in the I-th period includes the in-phase branch optical signal phase and the quadrature branch optical signal phase

[0021] The optical signal of the co-directional branch Z and the optical signal of the orthogonal branch J are respectively expressed as:

[0022]

[0023] wherein, are respectively the input modulation signal voltages of the two branches Z and J; are respectively the DC bias signal voltages of the two branches Z and J; V Z , V Q are respectively the half-wave voltages of the modulators of the two branches Z and J.

[0024] Furthermore, the output of each sub-carrier modulation signal at the coupled modulation end is expressed as:

[0025]

[0026] In the I-th time period, the signal H(I) finally synthesized by N sub-carrier modulation signals is expressed as:

[0027]

[0028] wherein, F n (I) is the n-th sub-carrier modulation signal in the I-th time period, N is the number of sub-carriers, ω n is the frequency of the n-th sub-carrier modulation signal.

[0029] Furthermore, the signal finally synthesized by N sub-carrier modulation signals alternately passes through multiple non-linear compensation modules and multiple dispersion compensation modules for compensation, correcting the changes caused by non-linear effects and the signal distortion caused by optical fiber dispersion during the signal transmission.

[0030] Furthermore, perform a fractional Fourier transform FRFT P of order P on the transfer function of the non-linear effect of the synthesized total carrier signal H(I) in the time domain, and obtain the transfer function of the non-linear effect of the synthesized total carrier signal H(I) in the fractional Fourier domain

[0031]

[0032] wherein: h NL (I) is the time-domain transfer function of the non-linear effect, i is the imaginary unit, α is the loss coefficient of the optical fiber, γ is the non-linear coefficient of the optical fiber, |H(I)| is the signal power amplitude, and h is the step size of the compensation algorithm.

[0033] Further, the dispersion of the total carrier signal after non - linear compensation is subjected to a fractional Fourier transform of order 1 - p on the transfer function in the frequency domain, and the transfer function of the dispersion of the total carrier signal after non - linear compensation in the fractional Fourier domain is obtained:

[0034]

[0035] Where: H CD (ω) is the transfer function of the dispersion in the frequency domain, i is the imaginary unit, β is the group - velocity dispersion of the optical fiber, ω is the angular frequency of the total carrier signal, and h is the step size of the compensation algorithm; is the transfer function of the dispersion in the P - th order fractional Fourier domain, and FRFT 1-P represents the fractional Fourier transform of order 1 - P.

[0036] Further, the transfer function of the dispersion in the P - th order fractional Fourier domain is convolved with the transfer function of the non - linear effect in the P - th order fractional Fourier domain to obtain the compensated total signal X(I, ω), and the convolution process can be realized by the following formula:

[0037]

[0038] Let the signal after m times of dispersion compensation and m times of non - linear compensation be denoted as X (m) (I, ω).

[0039] Compared with the prior art, the present invention has the following beneficial technical effects:

[0040] (1), The carrier modulation method of the optical fiber communication link of the present invention divides the high - speed data stream to be transmitted into multiple low - speed data streams at the transmitting end, and modulates the multiple low - speed data streams onto multiple independent sub - carriers respectively. Through the sub - carrier multiplexing technology, more data can be transmitted in the limited spectrum resources, because each sub - carrier can be modulated independently, thus improving the spectrum utilization efficiency.

[0041] (2), The carrier modulation method of the optical fiber communication link of the present invention adds a pre - signal to the signal to be transmitted on each sub - carrier and then transmits it; each sub - carrier can be modulated and demodulated independently, so that even if a certain sub - carrier is interfered, it will not affect other sub - carriers, thus improving the reliability of the whole system.

[0042] (3), The carrier modulation method of the optical fiber communication link of the present invention modulates and synthesizes the signals transmitted on multiple sub - carriers received at the receiving end by means of coupled quadrature modulation. It can effectively reduce or eliminate the inter - symbol interference and is applicable to high - speed data transmission, such as scenarios of 100Gbit / s high - speed optical access, etc.

[0043] (4) The carrier modulation method of the optical fiber communication link of the present invention performs dispersion compensation and nonlinear compensation on the synthesized total carrier signal. It can effectively suppress signal impairments caused by optical fiber nonlinear effects (such as self-phase modulation, cross-phase modulation, and four-wave mixing, etc.), thereby increasing the maximum capacity of the optical fiber transmission network. It improves the Q value and bit error rate (BER) performance of the system, enabling the system to maintain high performance even at higher input fiber powers. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0045] Figure 1 Schematic diagram of the structure of an optical fiber communication system in the prior art;

[0046] Figure 2 Schematic flowchart of the carrier modulation method of the optical fiber communication link of the present invention;

[0047] Figure 3 Schematic diagram of a sine wave and a cosine wave with a 90-degree phase difference;

[0048] Figure 4 Schematic diagram of different dispersion compensation performances corresponding to different incident optical powers. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will couple the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0050] In the drawings of the specific embodiments of the present invention, to better and more clearly describe the working principles of the components in the system and show the connection relationships of the various parts of the device, only the relative positional relationships between the components are clearly distinguished, and it does not constitute a limitation on the signal transmission direction, connection sequence, and the sizes, sizes, and shapes of the various parts of the structure within the components.

[0051] As Figure 2 shown, it is a schematic flowchart of the carrier modulation method of the optical fiber communication link of the present invention, and this carrier modulation method includes the following steps:

[0052] First, at the sending end, the high-speed data stream to be transmitted is split into multiple low-speed data streams, and the multiple low-speed data streams are respectively modulated onto multiple independent subcarriers.

[0053] Subcarriers are the basic transmission units. Each subcarrier carries a part of the information and is transmitted through modulation techniques. For each subcarrier, the signals on each subcarrier are independently modulated. Therefore, they can make full use of their respective bandwidth resources and can also separately select the modulation method (such as QPSK, 16-QAM, etc.) most suitable for their own transmission characteristics to achieve the highest baud rate.

[0054] During the specific modulation process, the following parameters need to be confirmed:

[0055] Baud rate: The baud rate is also called the modulation rate or symbol rate, which represents the number of symbols transmitted through the subcarrier channel per unit time. Each subcarrier can be regarded as an independent transmission channel, and the signals on each channel are transmitted at a certain baud rate.

[0056] Subcarrier spacing: The subcarrier spacing determines the density and number of subcarriers. A smaller subcarrier spacing means that more subcarrier channels can be accommodated within the same bandwidth, but it may also lead to an increase in inter-carrier interference.

[0057] Interference increase.

[0058] Subcarrier length: The subcarrier length determines how many symbols can be transmitted within a symbol period. A longer symbol length can provide better resistance to multipath interference, but it will also reduce the data transmission rate. Therefore, in the design, a trade-off needs to be made between the symbol length and the data transmission rate.

[0059] Modulation method: Different modulation methods will affect the number of bits carried by each symbol.

[0060] For example, QPSK (Quadrature Phase Shift Keying) carries 2 bits of information per symbol, while 16-QAM (16-QAM) carries 4 bits of information per symbol. Therefore, at the same baud rate, using a higher-order modulation method can increase the data transmission rate.

[0061] Secondly, a preamble signal is added to the signal to be transmitted on each subcarrier before transmission.

[0062] The preamble signal is a copy of a section of the signal added at the beginning of the signal to be transmitted on the subcarrier. This copy of the signal is selected from the signal from the t-th period to the end period of the signal to be transmitted on the respective subcarrier. Therefore, it is necessary to determine the t-th period of the signal to be transmitted on the subcarrier, that is, the period at which the preamble signal starts.

[0063] In this embodiment, the starting period of the preamble signal is identified by combining the changes in the amplitude ratio and the phase difference value, which specifically includes the following steps:

[0064] (1) F(k) represents the signal sequence of the k-th period of the signal to be transmitted by the subcarrier. k is a natural number, and k = 1, 2, 3... T; T represents that there are T periods in total for the signal to be transmitted by the subcarrier;

[0065] Calculate the phase difference value P(k) between the signal sequence of the k-th period and the signal sequence of the (k + Δk)-th period.

[0066] (2) Calculate the amplitude ratio M(k) between the signal sequence of the k-th period and the signal sequence of the (k + Δk)-th period;

[0067] (3) Determine whether the k-th sampling point belongs to the starting period of the preamble signal through M(k) and P(k). If M(k) is less than the amplitude ratio threshold T1 and P(k) is less than the phase difference threshold T2, then the current period k is the starting period of the preamble signal.

[0068] Preferably, adjust the phase difference threshold T2 and the amplitude ratio threshold T1 according to the actual signal characteristics and the requirements of the optical fiber communication link.

[0069] Each subcarrier channel transmits the signals to be transmitted after adding the preamble signal respectively. At the receiving end, the signals transmitted by multiple subcarriers received are modulated and synthesized by the method of coupled quadrature modulation. Here, it is assumed that the number of subcarrier signals received is N.

[0070] It should be explained that the method of coupled quadrature modulation transmits data by changing the amplitudes of two orthogonal waves. As Figure 3 shown, these two orthogonal waves are a sine wave and a cosine wave with a phase difference of 90 degrees. In the coupled quadrature modulation mapping, the data signal is mapped onto a complex plane to form a complex modulation symbol, and then the real part and the imaginary part of this complex modulation symbol are modulated onto these two orthogonal waves respectively.

[0071] The method of coupled quadrature modulation can utilize both the amplitude and the phase of the signal wave to transmit information bits, and represents the transmitted information by changing the amplitude of the pulse. Therefore, under the same bandwidth, the method of coupled quadrature modulation can achieve a higher data transmission rate than AM and PM. The more the number of channels of the method of coupled quadrature modulation, the greater the amount of information that each symbol can transmit, but at the same time, the higher the requirement for the signal-to-noise ratio, so it is more vulnerable to noise. Coupled quadrature modulation can transmit more data within the same bandwidth, thereby increasing the data transmission rate.

[0072] In a preferred embodiment, the coupled orthogonal modulation is achieved through a coupled modulation terminal. The coupled modulation terminal better serves the optical fiber data transmission system with its high spectral efficiency performance, thus greatly improving the spectral utilization rate, effectively combating frequency selective fading and narrowband interference, as well as improving the data transmission rate and the signal's ability to resist inter-symbol interference, and is widely used in current optical fiber communication systems.

[0073] Specifically, the subcarrier signal S(I) received in the I-th time period includes the in-phase branch optical signal phase and the quadrature branch optical signal phase As Figure 3 shown, it is.

[0074] The optical signal of the in-phase branch Z and the optical signal of the quadrature branch J are respectively expressed as:

[0075]

[0076] Wherein, are respectively the input modulation signal voltages of the Z and J branches; are respectively the DC bias signal voltages of the Z and J branches; V Z 、V Q are respectively the half-wave voltages of the modulators of the Z and J branches.

[0077] The output of the coupled modulation terminal for each subcarrier modulation signal F(I) is expressed as:

[0078]

[0079] In the I-th time period, the signal H(I) finally synthesized by N subcarrier modulation signals is expressed as follows:

[0080]

[0081] Since a preamble signal is added to the signal to be transmitted on each subcarrier, and the time period interval of the preamble signal is [t, T], the value of I is [0, 2T - t].

[0082] Wherein, F n (I) is the n-th subcarrier modulation signal in the I-th time period, N is the number of subcarriers, and ω n is the frequency of the n-th subcarrier modulation signal.

[0083] Finally, dispersion compensation and non-linear compensation are performed on the synthesized total carrier signal.

[0084] In order to improve the security during signal transmission, further compensation of the synthesized total carrier signal is required at the receiving end.

[0085] Intrachannel cross-phase modulation and intrachannel four-wave mixing are two main nonlinear perturbation terms, which will have a significant impact on the signal transmission quality.

[0086] In a preferred embodiment, the receiving end has a plurality of nonlinear compensation modules and a plurality of dispersion compensation modules, and the synthesized total carrier signal alternately passes through the nonlinear compensation module and the dispersion compensation module.

[0087] The role of the nonlinear compensation module is to correct the changes in the signal caused by nonlinear effects during transmission. The dispersion compensation module is used to correct the problem of signal distortion caused by optical fiber dispersion. These compensation modules can be physical devices or digital signal processing algorithms.

[0088] Specifically, the nonlinear compensation module has a nonlinear compensation algorithm, and the process of performing one nonlinear compensation includes the following steps:

[0089] Perform a fractional Fourier transform FRFT of order P on the transfer function of the nonlinear effect of the synthesized total carrier signal H(I) in the time domain P , to obtain the transfer function of the nonlinear effect of the synthesized total carrier signal H(I) in the fractional Fourier domain

[0090]

[0091] where: h NL (I) is the time-domain transfer function of the nonlinear effect, i is the imaginary unit, α is the loss coefficient of the optical fiber, γ is the nonlinear coefficient of the optical fiber, |H(I)| is the signal power amplitude, and h is the step size of the compensation algorithm.

[0092] The total carrier signal after nonlinear compensation enters the dispersion compensation module to perform the dispersion compensation algorithm.

[0093] Specifically, one dispersion compensation process includes the following steps:

[0094] Perform a fractional Fourier transform of order 1-p on the transfer function of the dispersion of the total carrier signal after nonlinear compensation in the frequency domain, to obtain the transfer function of the dispersion of the total carrier signal after nonlinear compensation in the fractional Fourier domain:

[0095]

[0096] where: H CD (ω) is the transfer function of the dispersion in the frequency domain, i is the imaginary unit, β is the group velocity dispersion of the optical fiber, ω is the angular frequency of the total carrier signal, and h is the step size of the compensation algorithm;

[0097] is the transfer function of dispersion in the P-order fractional Fourier domain, and FRFT 1-P represents the fractional Fourier transform of order 1 - P.

[0098] The convolution operation of the transfer function of dispersion in the P-order fractional Fourier domain and the transfer function of the nonlinear effect in the P-order fractional Fourier domain is performed to obtain the compensated total signal X(I, ω). The convolution process can be implemented through the following formula:

[0099]

[0100] Let the signal after m times of dispersion compensation and m times of nonlinear compensation be denoted as X (m) (I, ω).

[0101] In a preferred embodiment, the dispersion compensation module can also perform pre-compensation at the transmitting end as needed. The dispersion compensation module can compensate signals of multiple wavelengths and has the characteristics of low insertion loss, low polarization mode dispersion, and low polarization-dependent loss. As Figure 4 shown, different dispersion compensation performances corresponding to different incident optical powers are presented. The optical power is set to scan within the range of -10 to 10 dBm. Under the condition of a transmission rate of 10 Gbit / s and three different numbers of dispersion compensation times, the Q value changes with the change of the optical power entering the fiber.

[0102] The combined use of nonlinear compensation and dispersion compensation can significantly improve the transmission quality of signals, especially in high-speed fiber optic communication systems. Through these compensations, inter-symbol interference can be reduced, and the integrity and reliability of signals can be improved.

[0103] It should be understood that the above is only for illustration and does not constitute any limitation to the technical solution of the present invention. In specific applications, those skilled in the art can set according to needs, and the present invention does not make any restrictions on this.

[0104] It should be understood that although the steps in the flowchart in the embodiments of the present application are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless there is a clear indication in this article, the execution of these steps does not have a strict order limit, and they can be executed in other orders. Moreover, at least a part of the steps in the figure may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be executed alternately or alternately with at least a part of other steps or sub-steps or stages of other steps.

[0105] It should be noted that the above-described work process is only illustrative and does not limit the scope of protection of the present invention. In actual applications, those skilled in the art can select some or all of them according to actual needs to achieve the purpose of the solution of this embodiment, and no limitation is made here.

[0106] In addition, it should be noted that in this article, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or system including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, article or system. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, article or system including that element.

[0107] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0108] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A carrier modulation method for an optical fiber communication link, characterized in that The method includes the following steps: At the sending end, the high-speed data stream to be transmitted is split into multiple low-speed data streams, and the multiple low-speed data streams are respectively modulated onto multiple independent subcarriers. A preamble signal is added to the signal to be transmitted on each subcarrier before transmission; At the receiving end, the signals transmitted on the multiple subcarriers received are modulated and synthesized by means of coupled quadrature modulation, and dispersion compensation and non-linear compensation are performed on the synthesized total carrier signal; The way of the coupled quadrature modulation is to modulate the signal through a coupled modulation end, which specifically includes: The subcarrier signal S(I) received during the I-th period includes the in-phase optical signal phase and the quadrature optical signal phase The optical signal of the co-directional branch Z and the optical signal of the orthogonal branch J are respectively expressed as: Among them, are the input modulation signal voltages of branches Z and J respectively; are the DC bias signal voltages of branches Z and J respectively; V Z , V J are the half-wave voltages of the modulators of branches Z and J respectively.

2. The carrier modulation method of the optical fiber communication link according to claim 1, wherein The preamble signal is a copy of a section of the signal added at the beginning of the signal to be transmitted on each subcarrier. The copy is the signal from the t-th period to the end period of the signal to be transmitted on each subcarrier, and the t-th period of the signal to be transmitted on the subcarrier is the starting period of the preamble signal.

3. The carrier modulation method of the optical fiber communication link according to claim 2, wherein, The method for determining the starting period of the preamble signal includes: (1) F(k) represents the signal sequence of the k-th period of the signal to be transmitted on the subcarrier, k is a natural number, k = 1, 2, 3... T; T represents that there are T periods in total for the signal to be transmitted on the subcarrier; Calculate the phase difference P(k) between the signal sequence of the k-th period and the signal sequence of the (k + Δk)-th period; (2) Calculate the amplitude ratio M(k) between the signal sequence of the k-th period and the signal sequence of the (k + Δk)-th period; (3) Determine whether the k-th sampling point belongs to the starting period of the preamble signal through M(k) and P(k). If M(k) is less than the amplitude ratio threshold T1 and P(k) is less than the phase difference threshold T2, then the current period k is the starting period of the preamble signal.

4. The carrier modulation method of the optical fiber communication link according to claim 3, wherein The output of the coupled modulation end for each subcarrier modulation signal is expressed as: In the I-th period, the signal H(I) finally synthesized by N subcarrier modulation signals is expressed as: Among them, F n (I) is the modulation signal of the nth subcarrier in the Ith time period, N is the number of subcarriers, ω n is the frequency of the modulation signal of the nth subcarrier, and t represents the tth time period.

5. The carrier modulation method of the optical fiber communication link according to claim 4, characterized in that, The signal finally synthesized by N subcarrier modulation signals alternately passes through multiple non-linear compensation modules and multiple dispersion compensation modules for compensation to correct the changes caused by non-linear effects and the signal distortion caused by optical fiber dispersion during the transmission process.

6. The carrier modulation method of the optical fiber communication link according to claim 5, wherein Perform a fractional Fourier transform FRFT of order P on the transfer function of the nonlinear effect of the synthesized total carrier signal H(I) in the time domain P , to obtain the transfer function of the nonlinear effect of the synthesized total carrier signal H(I) in the fractional Fourier domain where: h NL (I) is the time-domain transfer function of the nonlinear effect, i is the imaginary unit, α is the loss coefficient of the optical fiber, γ is the nonlinear coefficient of the optical fiber, |H(I)| is the signal power amplitude, and h is the step size of the compensation algorithm.

7. The carrier modulation method of the optical fiber communication link according to claim 6, characterized in that, Perform a fractional Fourier transform of order 1 - p on the transfer function of the dispersion of the total carrier signal after non-linear compensation in the frequency domain to obtain the transfer function of the dispersion of the total carrier signal after non-linear compensation in the fractional Fourier domain: Where: H CD (ω) is the transfer function of dispersion in the frequency domain, i is the imaginary unit, β is the group velocity dispersion of the optical fiber, ω is the angular frequency of the total carrier signal, and h is the step size of the compensation algorithm; is the transfer function of dispersion in the P-th order fractional Fourier domain, and FRFT 1-P represents the fractional Fourier transform of order 1 - P.

8. The carrier modulation method of the optical fiber communication link according to claim 7, wherein Perform a convolution operation on the transfer function of the dispersion in the p-th order fractional Fourier domain and the transfer function of the non-linear effect in the p-th order fractional Fourier domain to obtain the compensated total signal X(I, ω). The convolution process can be realized by the following formula: Let the signal after m times of dispersion compensation and m times of nonlinear compensation be denoted as X (m) (I, ω).

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