A method and apparatus for calculating nonlinear noise in a raman amplification scenario

Abstract

The present application relates to a kind of method and device for calculating the nonlinear noise of Raman amplification scene.The method part mainly includes: obtaining the equivalent in-fiber optical power spectrum of each channel according to Raman coupling equation or obtaining the equivalent in-fiber optical power spectrum of each channel according to Raman analytical equation;According to the equivalent in-fiber optical power spectrum of each channel and related fiber parameters, the equivalent nonlinear noise signal ratio of each channel is obtained by calculation, and the equivalent signal noise ratio caused by nonlinearity in Raman amplification scene is finally obtained.The present application can solve the problem that traditional model is too complex and backward Raman amplification scene is difficult to solve, and is more practical.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber communication technology, in particular to a method and device for calculating nonlinear noise in a Raman amplification scenario. BACKGROUND

[0002] With the continuous development of video services, cloud technology, and the like, communication traffic is growing in a sustained explosive manner, which puts forward the requirements of high rate, large capacity transmission and low network construction cost for optical transport networks. In order to further expand the system capacity, it is necessary to use Dense Wavelength-Division Multiplexing (DWDM) to expand the number of channels, and at the same time, to expand the wavelength range of channel operation as much as possible. Using a Distributed Raman Amplifier (DRA) is an effective solution. However, DRA also has its defects. Compared with the traditional Erbium-Doped Fiber Amplifier (EDFA), the signal in the optical fiber is gradually reduced mainly affected by the fiber attenuation. However, DRA gradually amplifies the signal power in the optical fiber, so the change of signal optical power in the optical fiber cannot only consider the influence of fiber attenuation.

[0003] At the same time, with the development of transmission technology, the frequency band occupied by the signal is becoming wider and wider. When the frequency interval between channels is large enough, the inter-band Raman effect will also change the change process of signal optical power in the optical fiber, and the influence cannot be ignored.

[0004] The change process of signal optical power with the length of the optical fiber directly affects the size of the channel nonlinear noise. In the conventional nonlinear calculation method, it is generally approximated that the change of signal optical power in the optical fiber is determined by the fiber attenuation, and the optical power at the input of the fiber is considered only. However, in the scenario with Raman amplification effect, the change of signal optical power in the optical fiber is also affected by SRS (Stimulated Raman Scattering), and the original calculation scheme of nonlinear noise will introduce a large error.

[0005] Therefore, it is necessary to establish a fast and accurate calculation method to calculate the nonlinear noise of the signal in the optical fiber in the scenario with Raman amplification effect. Let the complex evaluation process be realized in simulation instead of engineering, and ensure the reliability of the transmission system.

[0006] Therefore, how to overcome the defects of the prior art, establish a fast and accurate calculation method, calculate the nonlinear noise effect of the signal in the optical fiber in the presence of Raman amplification scene, and let the complex evaluation process be realized in simulation rather than engineering to ensure the reliability of the transmission system is a difficult problem to be solved in the technical field. SUMMARY

[0007] In view of the defects or improvement needs in the prior art, the present application provides a method and device for calculating the nonlinear noise of the Raman amplification scene, aiming to simulate and calculate the signal-to-noise ratio caused by the fiber nonlinear noise of each channel in the Raman amplification system as fast as possible with high precision, for evaluating the performance of the system.

[0008] The embodiment of the present application adopts the following technical scheme:

[0009] In a first aspect, the present application provides a method for calculating the nonlinear noise of the Raman amplification scene, comprising:

[0010] According to the Raman coupling equation, the equivalent in-fiber optical power spectrum of each channel is obtained, or according to the Raman analytical equation, the equivalent in-fiber optical power spectrum of each channel is obtained.

[0011] According to the equivalent in-fiber optical power spectrum of each channel and the related fiber parameters, the equivalent nonlinear noise signal ratio of each channel is calculated, and finally the equivalent signal-to-noise ratio caused by the nonlinear of the Raman amplification scene is obtained.

[0012] Further, the equivalent in-fiber optical power spectrum of each channel obtained according to the Raman coupling equation specifically comprises:

[0013] For the scene with backward Raman amplification or the scene without backward Raman amplification but with high precision requirement, the signal optical power at each length of the fiber is obtained according to the Raman power coupling equation.

[0014] The integral result of the calculated signal optical power with respect to the fiber length is divided by the nonlinear effective length of the fiber, thereby obtaining the equivalent in-fiber optical power of the Raman amplification scene without nonlinear signal-to-noise ratio.

[0015] Further, the signal optical power at each length of the fiber obtained according to the Raman power coupling equation specifically comprises:

[0016] The Raman power coupling equation is used to calculate the power of each channel, which has the form:

[0017]

[0018] Where, P i(z) represents the power of the ith channel at the transmission distance z, the signal power at position 0 and the pump power are directly obtained from the input parameters, a i represents the loss coefficient of the ith channel in the optical fiber, C R (f j , f i ) represents the Raman coupling coefficient between the pump with frequency f j and the signal with frequency f i , the superscript + of the pump power represents the forward pump, the superscript - represents the backward pump, h is the Planck constant, k is the Boltzmann constant, and T is the open temperature;

[0019] Solving the Raman power coupling equation to obtain the signal light power P i (L) at the fiber length L, that is, obtaining the signal light power P i (l) at each point of the fiber length 0~L, 0≤l≤L.

[0020] Further, the integral result of the calculated signal light power with respect to the fiber length is divided by the nonlinear effective length of the fiber, so as to obtain the equivalent in-fiber optical power in the Raman-free amplification scene which is equal to the nonlinear signal-to-noise ratio in the Raman amplification scene, and the equivalent in-fiber optical power specifically comprises:

[0021]

[0022] Wherein, P i_eff (0) represents the equivalent in-fiber optical power, P i (z|SRS) represents the signal light power at the fiber z when the Raman effect exists, represents the integral result of the signal light power with respect to the fiber length, represents the nonlinear effective length of the fiber at the frequency of the ith channel.

[0023] Further, the equivalent in-fiber optical power spectrum of each channel obtained according to the Raman analytical equation specifically comprises:

[0024] For the scene of forward Raman amplification, the Raman analytical equation is simplified, only the attenuation of the pump light power and the signal light power by the fiber loss is considered, and the influence of Raman scattering is ignored;

[0025] Obtaining the optical power expression of each channel in the fiber considering the Raman effect, and simplifying the obtained optical power expression;

[0026] Calculating the ratio of the integral result of the signal light power with respect to the fiber length and the nonlinear effective length of the fiber, and replacing the attenuation coefficient of the pump channel with the attenuation coefficient of the signal channel to obtain the equivalent in-fiber optical power.

[0027] Further, the simplified Raman analysis equation only considers the attenuation of the fiber loss to the pump light power and the signal light power, and ignores the influence of Raman scattering, and specifically includes:

[0028] P j (0)exp(-α j z); j

[0029] P i (0)exp(-α i z); i

[0030] wherein P j j represents the power of the jth pump channel at a transmission distance z, P j (0) represents the pump power of the jth pump channel at position 0, α j represents the loss coefficient of the jth pump channel in the optical fiber, and z represents the transmission distance, P i i represents the power of the ith signal at a transmission distance z, P i (0) represents the power of the ith signal at position 0, and α i represents the loss coefficient of the ith channel in the optical fiber.

[0031] Further, the optical power expression of each channel considering Raman effect in the optical fiber is obtained, and the obtained optical power expression is simplified, and specifically includes:

[0032] The optical power expression of the ith channel considering Raman effect in the optical fiber is obtained:

[0033]

[0034] wherein P i (z|SRS) represents the power of the ith channel at a transmission distance z, P i (0) represents the signal power of the ith channel at position 0, α i represents the loss coefficient of the ith pump channel in the optical fiber, g ij represents the Raman gain of the jth channel to the ith channel, P j (0) represents the pump power of the jth pump channel at position 0, α j represents the loss coefficient of the jth pump channel in the optical fiber, and z represents the transmission distance.

[0035] The second e exponential function on the right side of the optical power expression is Taylor expanded, and the first order is retained, to obtain a simplified signal light power expression:

[0036]

[0037] ​​Furthermore, the calculation of the ratio of the integral result of the signal optical power and the fiber length to the effective nonlinear length of the fiber, while replacing the attenuation coefficient of the pump channel with the attenuation coefficient of the signal channel, to obtain the equivalent fiber input power specifically includes:

[0038] Calculate P i The integral of (z|SRS) with respect to length and P i (0)L eff (α i The ratio of ) to the attenuation coefficient α of the pump channel, while also considering the ratio of ) to the attenuation coefficient α of the pump channel. j Using the signal channel attenuation coefficient α i By substitution, the equivalent fiber-inserted optical power is obtained:

[0039]

[0040] Among them, P i (z|SRS) represents the power of the i-th channel at a transmission distance z, P i (0) represents the power of the i-th channel at position 0, L eff (α i ) represents the nonlinear effective length of the i-th fiber channel, g ij P represents the Raman gain coefficient of channel j to channel i. j (0) represents the pump power of the j-th pump channel at position 0; P i_eff (0) represents the equivalent fiber power of the i-th channel at position 0, and z represents the transmission distance.

[0041] Furthermore, when calculating the equivalent nonlinear noise signal-to-noise ratio (SNR) of each channel based on the equivalent input optical power spectrum and related fiber parameters, only the nonlinear noise component is considered in the SNR calculation. The SNR caused by the nonlinear noise is in the following form:

[0042]

[0043] Among them, SNR i P represents the equivalent signal-to-noise ratio caused by the nonlinearity of the i-th channel; i_eff (0) represents the equivalent fiber input power of the i-th channel, which is calculated; P n exp(-α i L) represents the equivalent nonlinear noise power of the i-th channel at the fiber optic output, and α i η represents the loss coefficient of the i-th channel in the optical fiber, where L is the length of the optical fiber; n This is the nonlinear crosstalk coefficient.

[0044] In a second aspect, the present application provides a device for calculating nonlinear noise in a Raman amplification scenario, comprising at least one processor and a memory, the at least one processor and the memory are connected through a data bus, the memory stores instructions executable by the at least one processor, and the instructions are used to complete the method for calculating nonlinear noise in a Raman amplification scenario as described in the first aspect when executed by the processor.

[0045] Compared with the prior art, the present application has the following beneficial effects:

[0046] (1) The present application has a significant advantage in accuracy compared to other simplified simulation methods, but the complexity is not particularly improved;

[0047] (2) The present application can solve the problem of too complex traditional model and difficulty in solving backward Raman amplification scenario, and is more practical;

[0048] (3) The model established according to the method of the present application needs parameters which are easy to determine, and many parameters can be directly obtained from product manual. BRIEF DESCRIPTION OF DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0050] Figure 1 A flowchart of a method for calculating nonlinear noise in a Raman amplification scenario is provided for the embodiment 1 of the present application;

[0051] Figure 2 The expanded illustration of step 100 of obtaining the equivalent in-fiber optical power spectrum of each channel according to the Raman coupling equation is provided for the embodiment 1 of the present application;

[0052] Figure 3 The expanded illustration of step 100 of obtaining the equivalent in-fiber optical power spectrum of each channel according to the Raman analytical equation is provided for the embodiment 1 of the present application;

[0053] Figure 4 A specific example flowchart is provided for the embodiment 2 of the present application;

[0054] Figure 5a A scenario example diagram of a backward Raman amplification system of a 150km G.652 long fiber is provided for the embodiment of the present application;

[0055] Figure 5b A scenario example diagram of a forward Raman amplification system is provided for the embodiment of the present application;

[0056] Figure 5c A scene example diagram of the forward Raman + backward Raman amplification system provided by the embodiment of the present application is shown in the figure;

[0057] Figure 6 A simulation result comparison diagram provided by the embodiment 2 of the present application is shown in the figure;

[0058] Figure 7 A device architecture diagram of the device for calculating the nonlinear noise in the Raman amplification scene provided by the embodiment 3 of the present application is shown in the figure. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solutions and advantages of the present application clearer and more apparent, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0060] The present application is a system architecture of a specific function system, and therefore the function logical relationship of each structure module is mainly described in the specific embodiments, and the specific software and hardware implementation is not limited.

[0061] In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other, and each step can also be exchanged in the order of the logic and without conflict. The present application is described in detail below in combination with the drawings and embodiments.

[0062] Embodiment 1:

[0063] The embodiment of the present application provides a method for calculating the nonlinear noise in the Raman amplification scene, as shown in the figure, the method comprises the following steps. Figure 1

[0064] Step 100: obtaining the equivalent in-fiber optical power spectrum of each channel according to the Raman coupling equation or obtaining the equivalent in-fiber optical power spectrum of each channel according to the Raman analytical equation.

[0065] Step 200: calculating according to the equivalent in-fiber optical power spectrum of each channel and the related fiber parameters to obtain the equivalent nonlinear noise signal ratio of each channel. That is, the equivalent signal noise ratio caused by the nonlinearity in the Raman amplification scene is obtained.

[0066] It should be noted that the embodiment of the present application can first obtain the inference that the nonlinear noise signal ratio in different scenes is approximately equal when the product of the signal optical power and the nonlinear effective length is equal in different scenes according to the relationship between the refractive index nonlinear phase noise and the signal optical power and the effective length. The inference is as follows:

[0067] The relationship between the refractive index nonlinear phase noise and the signal optical power and the effective length is:​

[0068]

[0069] where represents the nonlinear phase shift caused by the optical signal power, γ is the nonlinear coefficient, P in is the power of the optical signal at the input of the fiber, L eff is the nonlinear effective length of the fiber.

[0070] The equivalent signal-to-noise ratio caused by the nonlinear is proportional to the mean square of the nonlinear noise phase:

[0071]

[0072] Combining (1) and (2), it can be obtained that the signal-to-noise ratio caused by the nonlinear is proportional to the square of the product of the input signal optical power and the effective length:

[0073]

[0074] where SNR NL represents the equivalent signal-to-noise ratio caused by the nonlinear. represents the nonlinear phase shift caused by the optical signal power, P in is the power of the optical signal at the input of the fiber, L eff is the nonlinear effective length of the fiber.

[0075] In addition, the nonlinear noise caused by each channel is independent of each other, and the total noise caused by all channels is the sum of the noise caused by each channel: when multiple channels are transmitted simultaneously, considering that the signals transmitted by each channel in the existing network are random independent signals, there is no correlation between channels. Therefore, the nonlinear effect caused by each channel on the same channel is also independent of each other. The total nonlinear noise of a certain channel can be considered as the linear superposition of the nonlinear noise caused by each channel on the signal:

[0076]

[0077] where represents the total nonlinear equivalent noise on the i-th channel, j represents the optical channel number, and N represents the total number of channels. Noise j represents the equivalent nonlinear noise caused by the j-th channel power on the i-th channel.

[0078] Therefore, when calculating the total SNR caused by the nonlinear noise of a certain channel in a multi-channel system NL , as long as the P in L eff of each channel itself does not change, the SNR NLIt also remains unchanged. Therefore, we can conclude that for different scenarios where the product of signal optical power and effective length is equal, the ratio of nonlinear noise signal in different scenarios is also approximately equal.

[0079] Based on the above inferences, in this preferred embodiment, for scenarios with backward Raman amplification (such as...) Figure 5a or Figure 5c In the Raman amplification system shown (or in scenarios where high precision is required but backscattered Raman amplification is not required), step 100 may include, for example, Figure 2 The following steps are shown:

[0080] Step 110: Obtain the signal optical power at various points along the fiber length using the Raman power coupling equation. For this step, first calculate the power of each channel using the Raman power coupling equation, which is in the form of:

[0081]

[0082] Among them, P i (z) represents the power of the i-th channel at a transmission distance z. The signal power and pump power at position 0 are directly obtained from the input parameters, α. i C represents the loss coefficient of the i-th channel in the optical fiber. R (f j ,f i ) indicates a frequency of f j The pump and frequency are f i The Raman coupling coefficient between the signals; the pump power is indicated by the superscript + indicating forward pumping and the superscript - indicating backward pumping.

[0083] Then, the Raman power coupling equation is solved to obtain the signal optical power P at fiber length L. i (L), which means obtaining the signal optical power P at each point along the fiber length from 0 to L. i (l), 0≤l≤L.

[0084] Step 111: Calculate the integral of the signal optical power with respect to the fiber length and divide it by the nonlinear effective length of the fiber to obtain the equivalent input optical power in the scenario without Raman amplification. Based on the previous deduction that "when the product of signal optical power and nonlinear effective length is equal in different scenarios, the nonlinear noise signal ratio in different scenarios is also approximately equal," it can be concluded that the nonlinear noise signal ratio without considering Raman amplification is equal to the nonlinear noise signal ratio in the scenario with Raman amplification at this equivalent input optical power. The equivalent input optical power in this step is calculated using the following formula:

[0085]

[0086] Among them, P i_eff (0) represents the equivalent input fiber power, Pi P(z|SRS) represents the signal optical power at the z position of the fiber with Raman effect, P(z|SRS) represents the signal optical power at the z position of the fiber with Raman effect, L eff,i represents the effective length of the fiber at the i channel frequency.

[0087] In the preferred embodiment, for the scenario of only forward Raman amplification (e.g. the Raman amplification system shown in FIG. 1), step 100 can include the following steps as shown in FIG. 2: Figure 5b In the preferred embodiment, for the scenario of only forward Raman amplification (e.g. the Raman amplification system shown in FIG. 1), step 100 can include the following steps as shown in FIG. 2: Figure 3 In the preferred embodiment, for the scenario of only forward Raman amplification (e.g. the Raman amplification system shown in FIG. 1), step 100 can include the following steps as shown in FIG. 2:

[0088] Step 120: Simplify the Raman analytical equation, only consider the attenuation of fiber loss to pump optical power and signal optical power, ignore the influence of Raman scattering. For this step, the simplified formula can be expressed as:

[0089] P j (z|SRS) = P j (0) exp(-α j z);

[0090] P i (z|SRS) = P i (0) exp(-α i z);

[0091] wherein P j j represents the power of the jth pump channel at the transmission distance z, P j (0) represents the pump power of the jth pump channel at position 0, α j represents the loss coefficient of the jth pump channel in the fiber, z represents the transmission distance, P i i represents the power of the ith signal at the transmission distance z, P i (0) represents the power of the ith signal at position 0, α i represents the loss coefficient of the ith channel in the fiber.

[0092] Step 121: Obtain the optical power expression of each channel in the fiber considering Raman effect, and simplify the obtained optical power expression. For this step, first obtain the optical power expression of the ith channel in the fiber considering Raman effect:

[0093]

[0094] wherein P i (z|SRS) represents the power of the ith channel at the transmission distance z, P i (0) represents the signal power of the ith channel at position 0, α i represents the loss coefficient of the ith pump channel in the fiber, g ijP (0) represents the power of the jthpump channel at position 0, and j P (0) represents the power of the jthpump channel at position 0, and j P (0) represents the power of the jthpump channel at position 0, and

[0095] P (0) represents the power of the jthpump channel at position 0, and

[0096] P (0) represents the power of the jthpump channel at position 0, and P (0) represents the power of the jthpump channel at position 0, and P (0) represents the power of the jthpump channel at position 0, and

[0097] Step 122: Calculate the ratio of the integral result of the signal light power and the fiber length to the effective nonlinear length of the fiber, and replace the attenuation coefficient of the pump channel with the attenuation coefficient of the signal channel to obtain the equivalent in-fiber light power. For this step, calculate P i (z|SRS) with the ratio of the integral of P i (0) L eff (α i ) to P j (0), and replace the attenuation coefficient of the pump channel with the attenuation coefficient of the signal channel to obtain the equivalent in-fiber light power: i

[0098]

[0099] P i_eff (0) ≈ P i (0) (1 + 0.5 * L eff (α i ) ∑ j≠i g ij P j (0) ) ;

[0100] P (0) represents the power of the i th channel at position 0, and L i (z|SRS) represents the power of the i th channel at a transmission distance z, P i (0) represents the power of the i th channel at position 0, and L eff (α i ) represents the effective nonlinear length of the i th channel fiber, and g ij P (0) represents the power of the jthpump channel at position 0, and P j (0) represents the power of the jthpump channel at position 0, and P i_eff (0) represents the equivalent in-fiber light power of the i th channel at position 0, and z represents the transmission distance.

[0101] In the preferred embodiment, the SNR is calculated only from the nonlinear noise part when calculating the equivalent nonlinear noise signal ratio of each channel in step 200, and the form of the SNR caused by the nonlinear noise is:

[0102]

[0103] where SNR i represents the equivalent SNR caused by the nonlinear noise of the ith channel; P i_eff (0) is the equivalent input optical power of the ith channel, which is given by calculation; P n exp(-α i L) is the equivalent nonlinear noise power of the ith channel at the output end of the fiber, α i represents the loss coefficient of the ith channel in the fiber, and L is the fiber length; and η n is the nonlinear crosstalk coefficient.

[0104] It should be noted that the nonlinear crosstalk coefficient η n in the above formula is related to the signal frequency, and its form is:

[0105]

[0106] where f i is the center frequency of the ith channel, B ch is the signal bandwidth, G(f) is the power spectral density of the nonlinear crosstalk, and P i_eff (0) is the signal optical power of the ith channel.

[0107] The power spectral density G(f) of the nonlinear crosstalk is calculated by integration, and its form is:

[0108]

[0109] where γ is the nonlinear coefficient, G Tx is the input signal power spectral density, Φ = -4π 2 (f1-f)(f2-f)[β2+πβ3(f1+f2)]z, β2 is the group velocity dispersion parameter, β3 is the slope of the group velocity dispersion parameter, and p(z,f) is the normalized signal power distribution.

[0110] The normalized signal power distribution p(z,f) is calculated according to the Raman gain, and its form is:

[0111] where P tot is the total input signal power, α i is the loss coefficient of the signal in the fiber, z is the transmission distance, and C Ris the Raman coupling coefficient, is the effective transmission distance, f is a center frequency of the channel, G Tx is the input signal power spectral density.

[0112] In summary, for the scene with backward Raman amplification, it is difficult to solve, and currently there is no relevant solving method, and the embodiment of the application obtains the equivalent in-fiber optical power spectrum of each channel through the Raman coupling equation, and then calculates the equivalent nonlinear noise signal ratio of each channel, which can solve the problem of difficulty in solving the scene with backward Raman amplification, and is more practical. In addition, the complex process of nonlinear noise change caused by Raman power transfer is calculated by introducing the calculation of equivalent in-fiber optical power, which has a significant advantage in precision compared with the method of directly using the real in-fiber power to calculate the nonlinear noise by ignoring the influence of Raman power transfer on the nonlinear noise, but the complexity is not particularly improved. The model established according to the method of the embodiment of the application needs parameters that are easy to determine, and many parameters can be directly obtained from the product manual, such as the attenuation, effective area, nonlinear coefficient and Raman coefficient of the optical fiber, which can be obtained from the manual. Of course, because there are individual differences in related parameters, if high accuracy is required, real test needs to be performed to obtain.

[0113] Embodiment 2:

[0114] Based on the method for calculating the nonlinear noise in the Raman amplification scene provided in Embodiment 1, Embodiment 2 provides a specific example to further illustrate the application.

[0115] As shown in Figure 4 , step 1 of Embodiment 2 first performs Raman amplification system optical power calculation: calculates the optical signal power curve with the change of the optical fiber length by using the Raman coupling equation, and outputs the integral result of the signal optical power and the optical fiber length. The input parameters of step 1 are shown in Figure 4 , including the input pump power, the input signal power, the optical fiber type, the optical fiber length, and the input end signal optical signal-to-noise ratio (signal OSNR).

[0116] Then, step 2 performs equivalent in-fiber optical power calculation: according to the signal frequency and the optical fiber coefficient, the nonlinear effective length of the optical fiber at each frequency is obtained, and the integral result of the calculated output signal optical power and the optical fiber length is taken as the input parameter, and the equivalent in-fiber optical power of the same nonlinear noise signal ratio in the Raman-free scene is calculated in combination with the optical fiber type and length.

[0117] Finally, step 3 performs GN model nonlinear noise calculation: the calculated equivalent in-fiber optical power, fiber type and fiber length, etc. are input into the GN (Gaussian Noise Model) model for calculation, and the signal noise ratio caused by nonlinear noise is output.

[0118] Specifically, the steps of the embodiment are extended as follows:

[0119] In step 1, the parameters of the system to be simulated are determined, including the variables in the simulation process: input pump power, input signal power and input end signal optical signal-to-noise ratio, and the constant quantities of the simulation system: fiber type, fiber length; among them, the variables include input pump power, input signal power, input end OSNR; while the fiber type and fiber length need to be determined and cannot be changed.

[0120] Further, the fiber type is determined, and its loss characteristics and Raman gain characteristics for different frequencies of light are also determined, that is, the loss coefficient a i and the Raman coupling coefficient C R (f j ,f i ) should also be determined.

[0121] For step 1, when simulating a Raman amplification system, various parameters that affect system performance are considered, and accurate determination of these parameters ensures accurate calculation in the following steps.

[0122] In step 2, the equivalent signal in-fiber optical power of each channel is solved by using the Raman power coupling equation according to the parameters obtained in step 1, and in step 3, the equivalent signal noise ratio caused by nonlinearity of each channel is solved by using the GN model; specifically, the signal power of each channel is calculated by using the conventional Raman power coupling equation, which has the form:

[0123] where P i (z) represents the power of the i-th channel at a transmission distance z, the signal power at position 0 is determined by the input signal power in step 1, a i represents the loss coefficient of the i-th channel in the fiber, C R (f j ,f i ) represents the Raman coupling coefficient between the pump with frequency f j and the signal with frequency f i , the superscript + of the pump power represents forward pumping, and the superscript - represents backward pumping; this coupling equation is easy to solve, which can be completed by using the Runge-Kutta method combined with the shooting method.

[0124] The conventional Raman power coupling equation can be solved to obtain the signal power P i(L), that is, the signal optical power P at each point of the fiber length 0~L can be obtained i (l), 0≤l≤L. Then the integral result of the signal optical power with the fiber length is calculated, and divided by the nonlinear effective length of the fiber, so as to obtain the equivalent in-fiber optical power in the scenario without Raman amplification, which is the same as the nonlinear signal noise ratio in the scenario with Raman amplification:

[0125] Where P i_eff (0) represents the equivalent in-fiber optical power, P i (z|SRS) represents the signal optical power at the fiber z with Raman effect, represents the nonlinear effective length of the i-th channel fiber.

[0126] The equivalent in-fiber power is brought into the GN model to solve the signal-to-noise ratio caused by nonlinear noise of each channel. Specifically, only the nonlinear noise part is considered to calculate the signal-to-noise ratio, and the form of the signal-to-noise ratio caused by nonlinear noise is:

[0127]

[0128] Where SNR i represents the equivalent signal-to-noise ratio of the i-th channel caused by nonlinear; P i_eff (0) is the equivalent in-fiber optical power of the i-th channel, which is given by calculation; P n exp(-α i L) is the equivalent nonlinear noise power of the i-th channel at the output end of the fiber, α i represents the loss coefficient of the i-th channel in the fiber, and L is the fiber length; η n is the nonlinear crosstalk coefficient.

[0129] The nonlinear noise is calculated by the GN model, wherein the nonlinear crosstalk coefficient η n is related to the signal frequency, and the form is:

[0130] In the formula, f i is the center frequency of the i-th channel, B ch is the signal bandwidth, G(f) is the power spectral density of nonlinear crosstalk, and P i_eff (0) is the equivalent in-fiber signal optical power of the i-th channel.

[0131] The power spectral density G(f) of nonlinear crosstalk is calculated by integration, and the form is:

[0132] Where γ is the nonlinear coefficient, G Tx is the input signal power spectral density, and Φ=-4π 2(f1-f)(f2-f)[β2+πβ3(f1+f2)]z, where β2 is the group velocity dispersion parameter, β3 is the slope of the group velocity dispersion parameter, and ρ(z,f) is the normalized signal power distribution.

[0133] The normalized signal power distribution ρ(z,f) can be calculated based on the Raman gain, and its form is:

[0134] Where P tot α is the total power of the input signal. i Let z be the signal loss coefficient in the optical fiber, z be the transmission distance, and C be the signal loss coefficient in the optical fiber. R It is the Raman coupling coefficient. For the effective transmission distance, f is the center frequency of the channel, and G... Tx It is the power spectral density of the input signal.

[0135] In steps 2 and 3, the Raman power coupling equation and GN model used are low-complexity methods that have good accuracy while having short computation time.

[0136] In step 2, we perform precise and rapid calculations on the equivalent fiber-mounted optical power of a non-Raman amplification scenario with the same signal-to-noise ratio caused by nonlinear noise as in a Raman amplification scenario, ensuring sufficient accuracy in calculating the impact of system nonlinear noise. For example, with 5 pump sources before and after, a total of 120 signals in the C+L band, pump wavelengths of 1423.1, 1436.1, 1450.4, 1466, and 1494.4 nm, signal frequencies of 186.225–196.025 THz, and a 75 GHz interval, for scenarios such as… Figure 5a A simulation of the back-axis Raman amplification system with a 150km long G.652 fiber, as shown, yielded the following results: Figure 6 The comparison between experimental and simulation results shown in this embodiment is as follows: Figure 6 (a) compares the actual input optical power and equivalent input optical power of 120 signals, while (b) compares the nonlinear costs calculated for each signal based on both the actual and equivalent input optical power. Figure 6 As can be seen, both the equivalent fiber-inserted power and the nonlinear cost effectively demonstrate the increase in signal power and nonlinear noise in the long wavelength range caused by Raman amplification, thus effectively addressing the difficulty in calculating nonlinear noise in Raman amplification scenarios. It should be noted that the actual fiber-inserted power is the power that actually enters the optical fiber, while the equivalent fiber-inserted power is an equivalent power value obtained through various simplified calculations in this embodiment of the invention. The purpose of this embodiment is to replace the actual fiber-inserted power with an equivalent power, and then calculate a more accurate nonlinear noise signal-to-noise ratio.

[0137] In summary, for the backward Raman amplification scene, the embodiment of the application obtains the equivalent in-fiber optical power spectrum of each channel through the Raman coupling equation, and then calculates the equivalent nonlinear noise signal ratio of each channel, so as to solve the problem of difficulty in solving the backward Raman amplification scene, and is more practical. In addition, the embodiment of the application realizes the calculation of the complex process of the change of the nonlinear noise caused by the Raman power transfer by introducing the calculation of the equivalent in-fiber optical power, and has a significant advantage in precision compared with the method of directly calculating the nonlinear noise by using the real in-fiber power without considering the influence of the Raman power transfer on the nonlinear noise, but the complexity is not particularly improved. The model established according to the method of the embodiment of the application needs parameters that are easy to determine, and many parameters can be directly obtained by consulting the product manual, for example, the attenuation, effective area, nonlinear coefficient and Raman coefficient of the optical fiber can be obtained by consulting the manual. Of course, because there are individual differences in related parameters, if high accuracy is required, real test needs to be performed to obtain.

[0138] Embodiment 3:

[0139] Based on the method for calculating the nonlinear noise in the Raman amplification scene provided in the above-mentioned embodiment 1 and embodiment 2, the application further provides a device for calculating the nonlinear noise in the Raman amplification scene, as shown in Figure 7 The device architecture schematic diagram of the device for calculating the nonlinear noise in the Raman amplification scene according to the embodiment of the application includes one or more processors 21 and a memory 22. In the embodiment, the processor 21 is taken as an example. Figure 7

[0140] The processor 21 and the memory 22 can be connected through a bus or other means, Figure 7 In the embodiment, the connection through the bus is taken as an example.

[0141] The memory 22 is a non-volatile computer readable storage medium, which can be used to store non-volatile software programs, non-volatile computer executable programs and modules, such as the method for calculating the nonlinear noise in the Raman amplification scene in the embodiment 1. The processor 21 performs various functional applications and data processing of the device for calculating the nonlinear noise in the Raman amplification scene by running the non-volatile software programs, instructions and modules stored in the memory 22, that is, the method for calculating the nonlinear noise in the Raman amplification scene in the embodiment 1 is realized.

[0142] ​The memory 22 can include a high-speed random access memory, and can also include a non-volatile memory, such as at least one magnetic disk storage device, a flash memory device, or other non-volatile solid-state memory device. In some embodiments, the memory 22 can optionally include a memory that is remotely located with respect to the processor 21, and these remotely located memories can be connected to the processor 21 through a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0143] The program instructions / modules are stored in the memory 22, and when executed by the one or more processors 21, perform the method of calculating the nonlinear noise of the Raman amplification scenario as described in Embodiment 1 above, for example, perform the above-described Figures 1-3 each of the steps shown.

[0144] Those of ordinary skill in the art can understand that all or part of the steps in the various methods of the embodiments can be completed by instructing the relevant hardware through a program, and the program can be stored in a computer-readable storage medium, which can include a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, etc.

[0145] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application. The contents not described in detail in the specification are the prior art known to those skilled in the art.

Claims

1. A method for calculating nonlinear noise in a Raman amplified scene, characterized in that, include: The equivalent fiber-to-fiber power spectrum of each channel can be obtained from the Raman coupling equation or from the Raman analytical equation. The process of obtaining the equivalent fiber-to-fiber power spectrum for each channel based on the Raman coupling equation specifically includes: For scenarios with backward Raman amplification, the signal power at various points along the fiber length is obtained according to the Raman power coupling equation. The integral of the calculated signal power with fiber length is divided by the nonlinear effective length of the fiber to obtain the equivalent input fiber power for a scenario without Raman amplification that has the same nonlinear signal-to-noise ratio as the scenario with Raman amplification. The process of obtaining the equivalent fiber-to-fiber power spectrum for each channel based on the Raman analytical equation specifically includes: For the forward Raman amplification scenario, the Raman analytical equation is simplified by considering only the attenuation of pump light power and signal light power due to fiber loss, while ignoring the effect of Raman scattering. The optical power expressions in the fiber after considering the Raman effect for each channel are obtained and simplified. The ratio of the integral result of the signal light power and fiber length to the effective nonlinear length of the fiber is calculated. At the same time, the attenuation coefficient of the pump channel is replaced by the attenuation coefficient of the signal channel to obtain the equivalent input fiber light power. The equivalent input optical power spectrum and related fiber parameters of each channel are used to calculate the equivalent nonlinear noise ratio of each channel, and finally the equivalent signal-to-noise ratio caused by nonlinearity in the Raman amplification scenario is obtained.

2. The method for calculating nonlinear noise in a Raman amplified scene according to claim 1, characterized in that, The specific steps for obtaining the signal optical power at various points along the fiber length based on the Raman power coupling equation include: The power of each channel is calculated using the Raman power coupling equation, which takes the following form: Among them, P i (z) represents the power of the i-th channel at a transmission distance z. The signal power and pump power at position 0 are directly obtained from the input parameters, α. i C represents the loss coefficient of the i-th channel in the optical fiber. R (f j ,f i ) indicates a frequency of f j The pump and frequency are f i The Raman coupling coefficient between the signals; the pump power is indicated by the superscript + indicating forward pumping and the superscript - indicating backward pumping. Solve the Raman power coupling equation to obtain the signal optical power P at fiber length L. i (L), which means obtaining the signal optical power P at each point along the fiber length from 0 to L. i (l), 0≤l≤L.

3. The method for calculating nonlinear noise in a Raman amplified scene according to claim 2, characterized in that, The integral of the calculated signal optical power with respect to the fiber length, divided by the nonlinear effective length of the fiber, yields the equivalent input optical power in the nonlinear signal-to-noise ratio scenario (without Raman amplification) that is equal to that in the scenario with Raman amplification. Specifically, this includes: Among them, P i_eff (0) represents the equivalent input fiber power, P i (z|SRS) represents the signal power at point z in the optical fiber when the Raman effect is present. This represents the integral result of the signal optical power with respect to the fiber length. This represents the nonlinear effective length of the optical fiber at the i-channel frequency.

4. The method for calculating nonlinear noise in a Raman amplified scene according to claim 1, characterized in that, The simplified Raman analytical equation, which only considers the attenuation of pump light power and signal light power due to fiber loss and ignores the effect of Raman scattering, specifically includes: P j =P j (0)exp(-α j from); P i =P i (0)exp(-α i from); Among them, P j P represents the power of the j-th pump channel at a transmission distance z. j (0) represents the pump power of the j-th pump channel at position 0, α j Let P represent the loss coefficient of the j-th pump channel in the optical fiber, z represent the transmission distance, and P represent the distance to be transmitted. i P represents the power of the i-th signal at a transmission distance z. i (0) represents the power of the i-th signal at position 0, α i This represents the loss coefficient of the i-th channel in the optical fiber.

5. The method for calculating nonlinear noise in a Raman amplified scene according to claim 4, characterized in that, The process of obtaining the optical power expression for each channel in the optical fiber after considering the Raman effect, and simplifying the obtained optical power expression specifically includes: The expression for the optical power in the fiber after considering the Raman effect in the i-th channel is obtained as follows: Among them, P i (z|SRS) represents the power of the i-th channel at a transmission distance z, P i (0) represents the signal power of the i-th channel at position 0, α i Let g represent the loss coefficient of the i-th pump channel in the optical fiber. ij P represents the Raman gain of channel j over channel i. j (0) represents the pump power of the j-th pump channel at position 0, α j Let z represent the loss coefficient of the j-th pump channel in the optical fiber, and z represent the transmission distance. Performing a Taylor expansion on the second exponential function e on the right-hand side of the optical power expression, and rounding it down to the first bit, yields the simplified expression for the signal optical power:

6. The method for calculating nonlinear noise in a Raman amplified scene according to claim 5, characterized in that, The calculation of the ratio of the integral result of the signal optical power and fiber length to the effective nonlinear length of the fiber, while replacing the attenuation coefficient of the pump channel with the attenuation coefficient of the signal channel, to obtain the equivalent fiber input power specifically includes: Calculate P i The integral of (z|SRS) with respect to length and P i (0)L eff (α i The ratio of ) to the attenuation coefficient α of the pump channel, while also considering the ratio of ) to the attenuation coefficient α of the pump channel. j Using the signal channel attenuation coefficient α i By substitution, the equivalent fiber-inserted optical power is obtained: P i_eff (0)≈P i (0)(1+0.5*L eff (α i )∑ j≠i g ij P j (0)); Among them, P i (z|SRS) represents the power of the i-th channel at a transmission distance z, P i (0) represents the power of the i-th channel at position 0, L eff (α i ) represents the nonlinear effective length of the i-th fiber channel, g ij P represents the Raman gain coefficient of channel j to channel i. j (0) represents the pump power of the j-th pump channel at position 0; P i_eff (0) represents the equivalent fiber power of the i-th channel at position 0, and z represents the transmission distance.

7. The method for calculating nonlinear noise in a Raman amplified scene according to any one of claims 1-6, characterized in that, When calculating the equivalent nonlinear noise signal-to-noise ratio (SNR) for each channel based on the equivalent input optical power spectrum and related fiber parameters, only the nonlinear noise component is considered in the SNR calculation. The SNR caused by the nonlinear noise is in the following form: Among them, SNR i P represents the equivalent signal-to-noise ratio caused by the nonlinearity of the i-th channel; i_eff (0) represents the equivalent fiber input power of the i-th channel, which is calculated; P n exp(-α i L) represents the equivalent nonlinear noise power of the i-th channel at the fiber optic output, and α i η represents the loss coefficient of the i-th channel in the optical fiber, where L is the length of the optical fiber; n This is the nonlinear crosstalk coefficient.

8. An apparatus for calculating nonlinear noise in a Raman amplified scene, characterized in that: The method includes at least one processor and a memory, which are connected via a data bus. The memory stores instructions that can be executed by the at least one processor. When executed by the processor, the instructions are used to perform a method for calculating nonlinear noise in a Raman amplified scene as described in any one of claims 1-7.

Images