Raman amplifier gain control method and raman optical fiber amplifier

Abstract

The present invention relates to the technical field of communications, and provides a Raman amplifier gain control method and a Raman optical fiber amplifier. The method comprises: inputting pump light of a corresponding wavelength into an optical fiber, and measuring out-of-band ASE power of the optical fiber in each preset frequency band; determining an actual gain coefficient of each preset frequency band on the basis of the out-of-band ASE power of each preset frequency band; matching the actual gain coefficient of each preset frequency band with a preset Raman gain coefficient of each preset frequency band, using an optical fiber corresponding to an actual gain coefficient having the highest similarity obtained by means of matching as a first optical fiber, and using an adjustment parameter of the first optical fiber to perform gain control of a Raman amplifier. The present invention, by means of deriving a Raman gain coefficient in reverse by using the out-of-band ASE power, can measure the Raman gain coefficient during the working process of the Raman amplifier, resolving the problem of it being difficult for a distributed amplifier to acquire a gain coefficient of optical fiber.

Description

Raman amplifier gain control method and Raman fiber amplifier

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the following patent application:

[0003] (1) Chinese patent application No. 202410757711.7, filed on June 13, 2024, entitled "Raman amplifier gain control method and Raman fiber amplifier". TECHNICAL FIELD

[0004] The present application relates to the technical field of communication, in particular to a Raman amplifier gain control method and a Raman fiber amplifier. BACKGROUND

[0005] Raman fiber amplifier is an important part of high-speed and long-distance optical fiber communication system. With the establishment of "Internet+" as a national strategy, the development of mobile Internet, cloud computing, big data and Internet of Things has put forward higher requirements on the bandwidth and speed of existing communication networks. The main factor restricting the large-scale application of high-speed and ultra-long distance communication systems is the optical signal noise ratio (OSNR), and Raman fiber amplifier has unique advantages in improving system OSNR. Its low noise coefficient can significantly reduce the optical signal noise ratio degradation speed in optical fiber communication systems, which is of great significance to prolong transmission distance, expand inter-span distance and reduce system cost.

[0006] The distributed Raman fiber amplifier uses transmission fiber as the gain medium, and the interaction between the pump and the signal is completed in the transmission fiber. The distributed amplifier cannot simultaneously detect the unamplified signal power and the amplified signal output power, so the gain control of the distributed Raman fiber amplifier cannot be performed by subtracting the input power (unit: dBm) from the output power (unit: dBm) as in the lumped amplifier (because the lumped amplifier can simultaneously detect the unamplified input signal power and the amplified output signal power), which leads to difficulties in gain control of the distributed Raman fiber amplifier.

[0007] Therefore, it is urgent to overcome the defects of the prior art in the technical field.

[0008] CONTENT OF THE APPLICATION

[0009] The technical problem to be solved by the present application is the difficulty in gain control of the distributed Raman fiber amplifier in the prior art.

[0010] The present application adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a Raman amplifier gain control method, which predetermines the adjustment parameters required for different optical fibers and pre-stores the preset Raman gain coefficients for each preset frequency band corresponding to different optical fibers under the corresponding pump wavelength conditions. The method includes:

[0012] Pump light of the corresponding wavelength is input into the optical fiber, and the out-of-band ASE power of the optical fiber in each preset frequency band is measured.

[0013] The actual gain coefficient of each preset frequency band is determined based on the out-of-band ASE power of each preset frequency band.

[0014] The actual gain coefficient of each preset frequency band is matched with the preset Raman gain coefficient of each preset frequency band. The optical fiber corresponding to the actual gain coefficient with the highest similarity obtained by matching is used as the first optical fiber, and the gain control of the Raman amplifier is performed using the adjustment parameters of the first optical fiber.

[0015] Preferably, determining the actual gain coefficient of each preset frequency band based on the out-of-band ASE power of each preset frequency band specifically includes:

[0016] The Raman gain of the first preset frequency band is calculated based on the out-of-band ASE power and the first relationship.

[0017] The actual gain coefficient of the first preset frequency band is calculated based on the Raman gain of the first preset frequency band.

[0018] Preferably, the first relationship is specifically as follows:

[0019] Gain = k1 × Pase 2 +k2×Pase+b; where k1, k2 and b are the corresponding coefficients obtained by measurement, Pase is the out-of-band ASE power of the first preset frequency band, and Gain is the Raman gain of the first preset frequency band.

[0020] Preferably, the step of calculating the actual gain coefficient of the first preset frequency band based on the Raman gain of the first preset frequency band specifically includes:

[0021] The actual gain coefficient is calculated using the first formula; wherein, the first formula is: C R =Gain×α p / (k3×P0); k3 is the first preset coefficient, P0 is the optical power of the pump light in the input fiber, α p C is the pump light attenuation coefficient, Gain is the Raman gain of the first preset frequency band, and C is the value of C. R This is the actual gain coefficient for the first preset frequency band.

[0022] Preferably, the pre-stored preset Raman gain coefficients of the different optical fibers corresponding to the respective preset frequency bands under the respective pump wavelength conditions are specifically as follows:

[0023] Pre-storing a second relationship of the different optical fibers under the respective pump wavelength conditions; wherein the second relationship is a relationship between the preset Raman gain coefficients of the respective optical fibers corresponding to the respective preset frequency bands under the respective pump wavelength conditions and the respective preset frequency bands;

[0024] The matching of the actual gain coefficients of the respective preset frequency bands with the preset Raman gain coefficients of the respective preset frequency bands specifically includes:

[0025] Fitting the actual gain coefficients of the respective preset frequency bands with the respective preset frequency bands to obtain a third relationship; and matching the third relationship with the respective second relationships.

[0026] Preferably, the fitting of the actual gain coefficients of the respective preset frequency bands with the respective preset frequency bands specifically includes using a linear function to fit the actual gain coefficients of the respective preset frequency bands with the respective preset frequency bands.

[0027] The matching of the third relationship with the respective second relationships specifically includes calculating a difference between the linear coefficients in the third relationship and the linear coefficients in the second relationships, and the smaller the difference is, the higher the similarity is.

[0028] Preferably, the method further includes compensating a gain control process of the Raman amplifier using the actual gain coefficients of the respective preset frequency bands, specifically including:

[0029] Selecting a maximum actual gain coefficient from the actual gain coefficients of the respective preset frequency bands as a first actual gain coefficient, and selecting a preset frequency band corresponding to the first actual gain coefficient as a second preset frequency band.

[0030] Dividing a first preset Raman gain coefficient of the first optical fiber by the first actual gain coefficient to obtain a compensation coefficient; wherein the first preset Raman gain coefficient is a preset Raman gain coefficient of the first optical fiber at the second preset frequency band.

[0031] Multiplying the compensation coefficient by a reference optical power to obtain an actual pump power used for gain control; wherein the reference optical power is a pump power calculated using the adjustment parameters of the first optical fiber.

[0032] In a second aspect, the present application provides a Raman fiber amplifier using the Raman amplifier gain control method of the first aspect for gain control; the amplifier includes a Raman fiber amplification part 1, the Raman fiber amplification part includes a pump laser assembly 11, a wavelength division multiplexer 12 and a Raman fiber 13, the amplifier further includes a first light splitting assembly 2, a first out-of-band detection assembly 3, a wavelength division multiplexing assembly 4 and a second out-of-band detection assembly 5.

[0033] The input end of the first light splitting component 2 and the first output end of the first light splitting component 2 are coupled on the transmission light path of the pump light, and the second output end of the first light splitting component 2 is connected with the first out-band detection component 3;

[0034] The common end of the wavelength division multiplexing component 4 and the reflection end of the wavelength division multiplexing component 4 are coupled on the transmission light path of the signal light, and the transmission end of the wavelength division multiplexing component 4 is connected to the second out-band detection component 5;

[0035] The wavelength division multiplexer 12 is used for splitting the gain light to obtain the first out-band light and the residual light while constituting the Raman fiber amplification part 1, and the first out-band light is transmitted to the first light splitting component 2, and the residual light is transmitted to the wavelength division multiplexing component 4;

[0036] The first light splitting component 2 is used for transmitting the first out-band light to the first out-band detection component 3;

[0037] The first out-band detection component 3 is used for detecting the out-band ASE power of the corresponding preset frequency band in the first out-band light;

[0038] The wavelength division multiplexing component 4 is used for splitting the residual light to obtain the second out-band light and the in-band gain light, and the second out-band light is transmitted to the second out-band detection component 5, and the in-band gain light continues to propagate along the transmission light path of the signal light;

[0039] The second out-band detection component 5 is used for detecting the out-band ASE power of the corresponding preset frequency band in the second out-band light.

[0040] Preferably, the first out-band detection component 3 comprises a second light splitting component 31, n filter components and n detection components;

[0041] The input end of the second light splitting component 31 is connected to the second output end of the first light splitting component 2, the second light splitting component 31 comprises n output ends, the i-th output end of the second light splitting component 31 is connected to the i-th filter component 32-i, and the output end of the i-th filter component 32-i is connected to the i-th detection component 33-i;

[0042] The second light splitting component 31 is used for splitting the first out-band light into n sub-band out-band lights, and the i-th sub-band out-band light is transmitted to the i-th filter component 32-i;

[0043] The i-th filter component 32-i is used for filtering the i-th sub-band out-band light to obtain the out-band light of the i-th preset frequency band;

[0044] The ith probe component 33-i is used for optical detection of the out-of-band light of the ith preset frequency band to obtain the out-of-band ASE power of the ith preset frequency band.

[0045] Preferably, the third light splitting component 6 and the in-band probe component 7 are further included.

[0046] The input end of the third light splitting component 6 and the first output end of the first light splitting component 2 are coupled on the transmission light path of the in-band gain light, and the second output end of the third light splitting component 6 is connected to the in-band probe component 7.

[0047] The third light splitting component 6 is used for splitting the in-band gain light to obtain the sub-gain light, and the in-band probe component 7 is used for optical detection of the sub-gain light to obtain the in-band gain power, which is used for Raman gain control.

[0048] The present application obtains the actual gain coefficient by actually measuring the out-of-band ASE power of each preset frequency band, compares the actual gain coefficient with the preset Raman gain coefficient, determines the currently used optical fiber, and then selects the adjustment parameter corresponding to the optical fiber for gain control. BRIEF DESCRIPTION OF DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced below. 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] Fig. 1 is a flowchart of a Raman amplifier gain control method according to an embodiment of the present application;

[0051] Fig. 2 is a flowchart of a Raman amplifier gain control method according to an embodiment of the present application;

[0052] Fig. 3 is a schematic diagram of a first relationship in a Raman amplifier gain control method according to an embodiment of the present application;

[0053] Fig. 4 is a schematic diagram of a second relationship in a Raman amplifier gain control method according to an embodiment of the present application;

[0054] Fig. 5 is a flowchart of a Raman amplifier gain control method according to an embodiment of the present application;

[0055] Fig. 6 is a structural schematic diagram of a Raman optical fiber amplifier according to an embodiment of the present application;

[0056] Fig. 7 is a structural schematic diagram of a Raman optical fiber amplifier according to an embodiment of the present application;

[0057] Fig. 8 is a structural schematic diagram of a Raman fiber amplifier according to an embodiment of the present application;

[0058] Fig. 9 is a structural schematic diagram of a Raman fiber amplifier according to an embodiment of the present application;

[0059] Fig. 10 is a structural schematic diagram of a Raman fiber amplifier according to an embodiment of the present application;

[0060] Fig. 11 is a structural schematic diagram of a Raman fiber amplifier according to an embodiment of the present application.

[0061] In all the drawings, the same reference signs are used to denote the same elements or structures, in which:

[0062] 1, Raman fiber amplification part; 11, pump laser assembly; 11-i, the i-th pump laser; 12, wavelength division multiplexer; 13, Raman fiber; 2, first light splitting assembly; 3, first out-of-band detection assembly; 31, second light splitting assembly; 32-i, the i-th filter assembly; 33-i, the i-th detection assembly; 4, wavelength division multiplexing assembly; 5, second out-of-band detection assembly; 6, third light splitting assembly; 7, in-band detection assembly; 8, control unit. DETAILED DESCRIPTION

[0063] In order to make the objectives, technical solutions and advantages of the present application clearer, further detailed description will be given 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 are not used to limit the present application.

[0064] In the present application, the terms "first", "second", and the like are used only for descriptive purposes, and should not be construed as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second", and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0065] In the present application, unless otherwise specified and limited, the term "connection" should be understood broadly, for example, "connection" can be fixed connection, or detachable connection, or integral; can be directly connected, or indirectly connected through intermediate medium. In addition, the term "coupling" can be an electrically connected way to achieve signal transmission.

[0066] In addition, the technical features involved in each of the embodiments of the present application described below can be combined with each other as long as there is no conflict.

[0067] Embodiment 1:

[0068] The gain of distributed Raman fiber amplifier in the prior art is difficult to control. Although several methods for controlling Raman gain are provided in the prior art, they all have corresponding shortcomings. For example, a method for real-time gain control using out-of-band ASE is described in patent CN02147746.9, but in this method, the out-of-band ASE is too close to the in-band, and is easily affected by the SSE of the signal itself and the ASE generated by the EDFA.

[0069] Chinese patent CN201110174019.4 describes a method for gain control using out-of-band ASE, discloses the linear relationship between out-of-band ASE and gain, and discloses the relationship between ASE correction and different input powers. However, this control method is still affected by the performance of the transmission line, such as the length of the transmission fiber, the loss coefficient of the fiber, and the joint loss in the transmission line.

[0070] Chinese patent CN201210235491.9 describes a method for calculating joint loss using out-of-band ASE power. This method has been applied to a certain extent, but it cannot distinguish between the fiber attenuation coefficient, the mode field diameter or the effective area of the fiber, and the joint loss value caused by the fixed loss point. In addition, the joint loss determined for the fiber with a water peak is related to the selected pump wavelength.

[0071] US patent US8643941 describes a method for gain control using out-of-band ASE. The method discloses a method for calculating gain by subtracting input power from output power. This method is achieved by detecting the total power of the signal and the out-of-band ASE power, calculating the in-band ASE power using the linear relationship between in-band and out-of-band ASE, and then calculating the pure signal power after amplification. In the control process, the target signal power is set as the target gain plus the signal power before the pump is turned on. This method is similar to the gain control of EDFA. In the control process, the pump ratio and the gain satisfy a linear relationship. This method can only be applied under certain gain slope conditions and when the length of the fiber exceeds a certain length. In addition, this method still cannot overcome the influence of the performance of the transmission line, such as the length of the transmission fiber, the loss coefficient of the fiber, and the joint loss in the transmission line.

[0072] US6519082 describes a control method of distributed Raman amplifier integrated with OTDR, which discloses a method of calculating Raman gain coefficient by using OTDR to detect transmission line loss, joint loss and fiber length, fiber dispersion and Raman gain in real time. The method has a pump power configuration table for different gain inside the amplifier, and realizes Raman gain and gain slope control by detecting the power of each channel or the total power in each sub-band at the output end of the Raman amplifier. The method of using OTDR to detect fiber loss is greatly affected by Raman gain, and the method of calculating Raman gain coefficient needs to solve differential equations, so the data processing requires a high control unit. Due to the complexity of the calculation process, the time is very slow, the built-in table is greatly affected by environmental factors, a large table needs to be established to adapt to all situations, and the hardware cost is high.

[0073] Embodiment 1 of the present application provides a Raman amplifier gain control method, which determines the adjustment parameters required by different optical fibers in advance, and pre-stores the preset Raman gain coefficients of each preset frequency band corresponding to different optical fibers under the condition of corresponding pump wavelength, as shown in FIG. 1, the method comprises:

[0074] In step 201, the pump light of the corresponding wavelength is input into the optical fiber, and the out-of-band ASE power of the optical fiber in each preset frequency band is measured; that is, the other parameters are kept unchanged, including the optical power of the signal light, the wavelength of the pump light, and the fixed optical fiber, so that the out-of-band ASE power of the optical fiber in each preset frequency band is measured. The wavelength of the pump light is also referred to as the pump wavelength in subsequent embodiments. The preset frequency bands are analyzed by those skilled in the art, and it is found through test analysis that the gain coefficient of each frequency band of the same optical fiber has a good linear relationship with the frequency band within a frequency band range with a frequency shift of less than or equal to 13.2 THz from the pump wavelength, so a plurality of frequency bands with a frequency shift of less than or equal to 13.2 THz from the pump wavelength are selected as the preset frequency bands, i.e. the frequency shift of each preset frequency band from the pump wavelength is less than or equal to 13.2 THz. The gain coefficient is the out-of-band Raman gain coefficient.

[0075] In step 202, the actual gain coefficient of each preset frequency band is determined according to the out-of-band ASE power of each preset frequency band; the preset Raman gain coefficient of each preset frequency band corresponding to different optical fibers under the condition of corresponding pump wavelength is obtained by test or other methods by those skilled in the art in advance, and the preset Raman gain coefficient of each preset frequency band is still the out-of-band Raman gain coefficient.

[0076] In step 203, the actual gain coefficients of each preset frequency band are matched with the preset Raman gain coefficients of each preset frequency band. The optical fiber corresponding to the actual gain coefficient with the highest similarity obtained from the matching is used as the first optical fiber, and the gain control of the Raman amplifier is performed using the adjustment parameters of the first optical fiber. The adjustment parameters are obtained in advance by those skilled in the art for each type of optical fiber, that is, the power of each pump wavelength used when the corresponding in-band gain is measured.

[0077] The first optical fiber can be considered as the optical fiber currently in use. The matching of the actual gain coefficient of each preset frequency band with the preset Raman gain coefficient of each preset frequency band can be done by calculating the difference between the actual gain coefficient and the preset Raman gain coefficient in each preset frequency band, and then calculating the average value of the difference in all preset frequency bands. When the average value is the smallest, the similarity is higher.

[0078] This embodiment uses actual measurements of the out-of-band ASE power of each preset frequency band to deduce the actual gain coefficient. The actual gain coefficient is then compared with the preset Raman gain coefficient to determine the optical fiber currently being used, and the corresponding adjustment parameters for gain control are selected.

[0079] In an optional implementation, determining the actual gain coefficient of each preset frequency band based on the out-of-band ASE power of each preset frequency band, as shown in Figure 2, specifically includes:

[0080] In step 301, the Raman gain of the first preset frequency band is calculated based on the out-of-band ASE power and the first relationship. Analysis shows that there is a quadratic relationship between the out-of-band ASE power and the Raman gain of the corresponding frequency band, as shown in Figure 3. Specifically, the first relationship is: Gain = k1 × Pase 2 +k2×Pase+b; where k1, k2, and b are the measured coefficients, Pase is the out-of-band ASE power of the first preset frequency band, and Gain is the Raman gain of the first preset frequency band. The first relationship is obtained in advance by those skilled in the art through testing or other methods.

[0081] In step 302, the actual gain coefficient of the first preset frequency band is calculated based on the Raman gain of the first preset frequency band.

[0082] The step of calculating the actual gain coefficient of the first preset frequency band based on the Raman gain of the first preset frequency band specifically includes: calculating the actual gain coefficient using a first formula; wherein, the first formula is: C R =Gain×α p / (k3×P0); k3 is the first preset coefficient, P0 is the optical power of the pump light in the input fiber, αp is the pump light attenuation coefficient, Gain is the Raman gain of the first preset frequency band, in units of dB, C R is the actual gain coefficient of the first preset frequency band, which is analyzed by a person skilled in the art, and in actual use, the first preset coefficient can be 4.343 2 .

[0083] The preset Raman gain coefficients of each preset frequency band corresponding to the different optical fibers under the condition of the corresponding pump wavelength are specifically: a second relationship of the different optical fibers under the condition of the corresponding pump wavelength is pre-stored; wherein the second relationship is a relationship between the preset Raman gain coefficients of each preset frequency band corresponding to the corresponding optical fiber under the condition of the corresponding pump wavelength and each preset frequency band.

[0084] The actual gain coefficients of each preset frequency band are matched with the preset Raman gain coefficients of each preset frequency band, specifically including: fitting the actual gain coefficients of each preset frequency band with each preset frequency band to obtain a third relationship; and matching the third relationship with each second relationship.

[0085] Wherein, the second relationship and the third relationship are both the relationships between the Raman gain coefficients and the frequency bands, and in order to distinguish, the relationship between the Raman gain coefficients and the frequency bands pre-stored in the processor is called the second relationship, and the relationship between the Raman gain coefficients and the frequency bands of the optical fiber currently used actually measured is called the third relationship.

[0086] In an optional embodiment, the optical fiber to which the embodiment is applicable includes one or more of G.652D-SSMF optical fiber, Leaf optical fiber, Truewave optical fiber and G.654 optical fiber, wherein G.652D-SSMF, Leaf, Truewave and G.654 are all common commercial optical fiber models.

[0087] In actual use, the fitting of the actual gain coefficients of each preset frequency band to each preset frequency band is specifically: using a linear function to fit the actual gain coefficients of each preset frequency band to each preset frequency band; as shown in FIG. 4, the second relationship corresponding to five kinds of optical fibers obtained by fitting includes the second relationship of the five kinds of optical fibers, i.e., optical fiber G.652D-SSMF, optical fiber Leaf, optical fiber TrueWave, optical fiber G.654-110, and optical fiber G.654-130, under the condition of a preset pump wavelength. In a preferred embodiment, considering that the gain coefficients of some frequency bands with relatively large frequency shifts may have errors, resulting in a decrease in fitting accuracy, the preset frequency band range can be limited by a person skilled in the art according to experience, and the actual gain coefficients within the preset frequency band range are used for fitting, and the actual gain coefficients outside the preset frequency band range are not used for fitting. The preset frequency band range can be 6-13.2 THz.

[0088] The matching of the third relationship to each second relationship is specifically: calculating the difference between the linear coefficients in the third relationship and the linear coefficients in the second relationship, and the smaller the difference, the higher the similarity. The linear coefficient can be understood as the slope of the curve after the corresponding relationship is transformed into a curve. The linear function is y=kx+b, where k and b are the coefficients obtained by fitting, x is the frequency band, and y is the Raman gain coefficient. For example, a second relationship is y1=k1x+b1, and a third relationship is y1=k2x+b2. The difference between the two is D=|k2-k1|. In actual use, b1 and b2 can also be involved in the calculation of the difference, i.e., D1=|k2-k1|, D2=|b2-b1|, and finally D=a×D1+b×D2 is calculated, where the smaller D is, the higher the similarity is. Wherein, a and b are weight coefficients obtained by a person skilled in the art according to experience analysis.

[0089] In order to further improve the control accuracy of the gain, the method of the embodiment further includes: using the actual gain coefficients of each preset frequency band to compensate the gain control process of the Raman amplifier. As shown in FIG. 5, the compensation process specifically includes:

[0090] In step 401, the maximum actual gain coefficient is selected from the actual gain coefficients of each preset frequency band as a first actual gain coefficient, and the preset frequency band corresponding to the first actual gain coefficient is selected as a second preset frequency band.

[0091] In step 402, the first preset Raman gain coefficient of the first optical fiber is divided by the first actual gain coefficient to obtain a compensation coefficient, wherein the first preset Raman gain coefficient is the preset Raman gain coefficient of the first optical fiber at the second preset frequency band.

[0092] In step 403, the compensation coefficient is used to multiply the reference optical power to obtain the actual pump power for gain control; wherein the reference optical power is the pump power calculated using the adjustment parameters of the first optical fiber. That is, P=P0xCR_0 / CR_1; wherein P is the actual pump power, P0 is the reference optical power, CR_0 is the first preset Raman gain coefficient, and CR_1 is the first actual gain coefficient, that is, the maximum value in the actual gain coefficients of each preset frequency band.

[0093] The embodiment calculates the compensation coefficient through the actual gain coefficient, and then compensates the pump power using the compensation coefficient, so that the actual application scenario can be approached more closely, the influence of environmental factors such as optical attenuation, joint loss, etc. on the gain control is reduced, and the Raman gain control is more accurate.

[0094] In actual use, the Raman amplifier may need to use pump light of different wavelengths. At this time, the determination of the first optical fiber can be specified by a person skilled in the art to a pump light of a wavelength, and the second relationship of the optical fiber under the condition of the pump wavelength is pre-stored. After the third relationship under the pump wavelength is obtained by inputting the pump light into the optical fiber and executing the above steps 201-203, the third relationship under the pump wavelength is matched with the second relationship of each optical fiber under the condition of the pump wavelength, so that the corresponding first optical fiber is determined.

[0095] The pump light of different wavelengths can also be input into the optical fiber respectively, and the third relationship corresponding to each wavelength is measured to obtain the third relationship corresponding to each wavelength. The third relationship corresponding to each wavelength is matched with the second relationship of each optical fiber corresponding to the wavelength to match the optical fiber with the highest total similarity as the first optical fiber. For example, if the Raman amplifier needs to use n different wavelengths of pump light, namely pump wavelength 1, pump wavelength 2, …, and pump wavelength n, n third relationships are obtained, which are respectively referred to as third relationship 1, third relationship 2, …, and third relationship n. The second relationship of various optical fibers under various pump wavelengths is pre-stored. Assuming that there are two optical fibers, namely optical fiber 1 and optical fiber 2, the second relationship 1-1 of optical fiber 1 under the condition of pump wavelength 1, the second relationship 1-2 of optical fiber 1 under the condition of pump wavelength 2, …, the second relationship 1-n of optical fiber 1 under the condition of pump wavelength n, and the second relationship 2-1 of optical fiber 2 under the condition of pump wavelength 1, the second relationship 2-2 of optical fiber 2 under the condition of pump wavelength 2, …, and the second relationship 2-n of optical fiber 2 under the condition of pump wavelength n are pre-stored.

[0096] diff(i, j) represents the difference between the linear coefficient in the third relationship i and the linear coefficient in the second relationship j-i, a fiber with the minimum difference value is selected for each pump wavelength, that is, the j value corresponding to the minimum value between diff(i, 1) and diff(i, 2) is selected, the number of fibers with the minimum difference value corresponding to all pump wavelengths is calculated, and the fiber with the maximum number is selected as the first fiber. For example, if diff(1, 1) < diff(1, 2), the pump wavelength 1 selects the fiber 1; if diff(2, 1) > diff(2, 2), the pump wavelength 2 selects the fiber 2; when diff(i, 1) is equal to diff(i, 2), the pump wavelength i is not included in the calculation, that is, the fiber is not selected. Assuming that the number num1 of pump wavelengths selecting the fiber 1 is greater than the number num2 of pump wavelengths selecting the fiber 2 in the calculation of n pump wavelengths, the fiber 1 is finally determined as the first fiber.

[0097] Moreover, when different wavelengths of pump light can be required for the Raman amplifier, the compensation process of steps 401-403 is performed for each pump wavelength used. For example, using the first fiber, the first preset Raman gain coefficient under the first pump wavelength is divided by the first actual gain coefficient under the first pump wavelength to obtain the compensation coefficient of the first pump wavelength; wherein the first actual gain coefficient is the maximum value of the actual gain coefficients of each preset frequency band corresponding to the first fiber under the first pump wavelength, and the first preset Raman gain coefficient is the preset Raman gain coefficient corresponding to the preset frequency band where the maximum value is located. For example, there are four preset frequency bands, namely, preset frequency band 1, preset frequency band 2, preset frequency band 3, and preset frequency band 4. Among them, the actual gain coefficient CR_2 of the preset frequency band 2 corresponding to the first fiber under the pump wavelength 1 is the maximum, and the preset Raman gain coefficient of the preset frequency band 2 corresponding to the first fiber under the pump wavelength 1 is CR_base_2. Therefore, the compensation coefficient corresponding to the pump wavelength 1 is CR_base_2 / CR_2.

[0098] The compensation coefficient of the first pump wavelength is multiplied by the reference optical power of the first pump wavelength to obtain the actual pump power for gain control; wherein the reference optical power is the pump power of the first pump wavelength calculated by using the adjustment parameters of the first fiber.

[0099] Embodiment 2:

[0100] Based on the method described in Embodiment 1, this embodiment also provides a Raman fiber amplifier using the Raman amplifier gain control method described in Embodiment 1 for gain control, the amplifier comprising a Raman fiber amplification part 1, the Raman amplification part comprising a pump laser assembly 11, a wavelength division multiplexer 12 and a Raman fiber 13, the amplifier further comprising a first light splitting assembly 2, a first out-of-band detection assembly 3, a wavelength division multiplexing assembly 4 and a second out-of-band detection assembly 5; wherein the Raman fiber amplification part 1 is specifically implemented by those skilled in the art, and has two forms of backward Raman amplification as shown in FIG. 6 and forward Raman amplification as shown in FIG. 7.

[0101] As shown in FIG. 8, the input end of the first light splitting assembly 2 and the first output end of the first light splitting assembly 2 are coupled on the transmission light path of the pump light, and the second output end of the first light splitting assembly 2 is connected with the first out-of-band detection assembly 3.

[0102] The common end of the wavelength division multiplexing assembly 4 and the reflection end of the wavelength division multiplexing assembly 4 are coupled on the transmission light path of the signal light, and the transmission end of the wavelength division multiplexing assembly 4 is connected to the second out-of-band detection assembly 5.

[0103] The wavelength division multiplexer 12 is used for dividing the gain light while constituting the Raman fiber amplification part 1, to obtain first out-of-band light and residual light, the first out-of-band light is transmitted to the first light splitting assembly 2, and the residual light is transmitted to the wavelength division multiplexing assembly 4.

[0104] The first light splitting assembly 2 is used for transmitting the first out-of-band light to the first out-of-band detection assembly 3; and the first out-of-band detection assembly 3 is used for detecting the out-of-band ASE power of the corresponding preset frequency band in the first out-of-band light.

[0105] The wavelength division multiplexing assembly 4 is used for dividing the residual light to obtain second out-of-band light and in-band gain light, the second out-of-band light is transmitted to the second out-of-band detection assembly 5, and the in-band gain light continues to propagate along the transmission light path of the signal light.

[0106] The second out-of-band detection assembly 5 is used for detecting the out-of-band ASE power of the corresponding preset frequency band in the second out-of-band light.

[0107] In actual application scenarios, as shown in FIG. 9, the first out-of-band detection assembly 3 comprises a second light splitting assembly 31, n filter assemblies and n detection assemblies.

[0108] The input end of the second light splitting component 31 is connected to the second output end of the first light splitting component 2, the second light splitting component 31 includes n output ends, the i-th output end of the second light splitting component 31 is connected to the i-th filter component 32-i, and the output end of the i-th filter component 32-i is connected to the i-th detection component 33-i.

[0109] The second light splitting component 31 is used to divide the first out-of-band light into n out-of-band sub-lights, and the i-th out-of-band sub-light is transmitted to the i-th filter component 32-i.

[0110] The i-th filter component 32-i is used to filter the i-th out-of-band sub-light to obtain out-of-band light of the i-th preset frequency band.

[0111] The i-th detection component 33-i is used to perform optical detection on the out-of-band light of the i-th preset frequency band to obtain the out-of-band ASE power of the i-th preset frequency band.

[0112] The pump laser component 11 can include a plurality of pump lasers of different wavelengths, and the corresponding wavelength of pump light is input into the optical fiber through the switch control of each pump laser. For example, the pump laser component 11 includes n pump lasers, and the i-th pump laser 11-i has a pump wavelength i.

[0113] In actual use, the actual control is the in-band gain, so the amplifier in the embodiment further includes a third light splitting component 6 and an in-band detection component 7.

[0114] The input end of the third light splitting component 6 and the first output end of the first light splitting component 2 are coupled on the transmission light path of the in-band gain light, and the second output end of the third light splitting component 6 is connected to the in-band detection component 7.

[0115] The third light splitting component 6 is used to split the in-band gain light to obtain sub-gain light, and the in-band detection component 7 is used to perform optical detection on the sub-gain light to obtain the in-band gain power for Raman gain control.

[0116] The Raman amplifier gain control method in the embodiment 1 can be applied to the Raman fiber amplifier by manual operation, or a control unit 8 (such as including a processor and a memory) can be set to complete the Raman amplifier gain control method in the embodiment 1 using the control unit 8. The required out-of-band ASE power of each preset frequency band in the embodiment 1 is obtained by the first out-of-band detection component 3 and the second out-of-band detection component 5.

[0117] As shown in Fig. 10 or Fig. 11, the embodiment exemplified by the setting control unit 8 can be understood as a complete Raman pump module except the transmission fiber (i.e. the Raman fiber 13), which includes the control unit 8, the pump laser assembly 11, the wavelength division multiplexer 12, the first light splitting assembly 2, the second out-of-band detection assembly 5, the third light splitting assembly 6, the in-band detection assembly 7, the second light splitting assembly 31, the n filter assemblies and the n detection assemblies. The i-th pump laser 11-i in the pump laser assembly 11 has a pump wavelength i as the outgoing wavelength, so that the pump laser assembly 11 emits pump light of different wavelengths, including the pump wavelength 1, the pump wavelength 2, the pump wavelength 3, …, the pump wavelength n. The second out-of-band detection assembly 5 has the longest detection wavelength (i.e. the wavelength closest to the signal light), and the n filter assemblies have different filter wavelengths (i.e. the wavelengths of the light allowed to pass, also called the center wavelength), such as the filter wavelength of the i-th filter assembly 32-i being the out-of-band wavelength i, and the detection wavelength of the corresponding i-th detection assembly 33-i also being the out-of-band wavelength i.

[0118] The second out-of-band detection assembly 5 is placed on the signal branch side of the wavelength division multiplexer 12, and each filter assembly is placed on the pump branch side of the wavelength division multiplexer 12.

[0119] The center wavelengths of the filter assemblies can be the same as or different from the pump wavelengths. In order to simultaneously achieve reflection detection and reduce the number of devices, in the backward Raman amplification mode shown in Fig. 11, the center wavelengths of the filter assemblies are the same as the pump wavelengths, and the center wavelength of each filter assembly is defined as follows: the center wavelength of the first filter assembly 32-1 is the pump wavelength 1, the center wavelength of the second filter assembly 32-2 is the pump wavelength 2, the center wavelength of the third filter assembly 32-3 is the pump wavelength 3, …, and the center wavelength of the n-th filter assembly 32-n is the pump wavelength n.

[0120] The corresponding first detection assembly 33-1 detects the power of the same wavelength as the pump wavelength 1, the second detection assembly 33-2 detects the power of the same wavelength as the pump wavelength 2, the third detection assembly 33-3 detects the power of the same wavelength as the pump wavelength 3, …, and the first detection assembly 33-4 detects the power of the same wavelength as the pump wavelength n.

[0121] The common port of the first light splitting assembly 2 is connected to the pump port of the wavelength division multiplexer 12, the large splitting ratio port of the first light splitting assembly 2 is connected to the pump laser assembly 11, the small splitting ratio port of the first light splitting assembly 2 is connected to the second light splitting assembly 31, and each output port of the second light splitting assembly 31 is connected to each filter assembly. The pump laser assembly 11 is integrated with a pulse function, and the second out-of-band detection assembly 5 and the first out-of-band detection assembly 3 are integrated with a pulse demodulation circuit function.

[0122] In the forward Raman amplification mode shown in Fig. 10, each preset frequency band and each pump wavelength do not overlap with each other, so that the wavelength division multiplexer 12 transmits the first out-of-band light in the gain light to the first light splitting component 2 while transmitting the pump light to the Raman fiber 13.

[0123] It is to be noted that the pump laser component 11 can be an integrated multi-wavelength laser, and the embodiment does not limit the integration mode. The first light splitting component 2, the third light splitting component 6 and the second light splitting component 31 can all be couplers, and the second light splitting component 31 can also be a 1*n splitter, where n is the number of filter components. In actual use, the filter components are filters, and the probe components and the second out-of-band probe component 5 are photodetectors.

[0124] Based on the Raman fiber amplifier described in the embodiment, the methods shown in Embodiment 1 and Embodiment 2 are specifically as follows:

[0125] In the initialization process, the control unit 8 first obtains the attenuation coefficient of each pump wavelength in the fiber, the joint loss and the back loss performance through the pulse driving function of the pump laser component 11 and the pulse demodulation function (which is actually the OTDR function) of the second out-of-band probe component 5 and the first out-of-band probe component 3. The control unit determines whether the line back loss is normal according to the reflection detection. If it is abnormal, the fiber end face or the connection point is cleaned. If it is normal, the pump wavelength 1 (i.e., the first pump laser 11-1) is turned on, and the power of the pump wavelength 1 is appropriately increased to a relatively large level P_pump1_1 (less than or equal to 200 mW). When the pump power is stable, the power of each probe component and the second out-of-band probe component 5 is recorded at each pump power.

[0126] In the formula, the frequency intervals of the pump wavelength 1 and the first probe component 33-1, the second probe component 33-2, the second probe component 33-2, …, the n-th probe component 33-n are △f1_1, △f1_2, △f1_3, …, △f1_n, respectively. Through our research, it is found that the out-of-band ASE power (unit: dBm) at a certain wavelength of several commercially available transmission fibers (SSMF, Leaf, Truewave, G.654) and the gain (unit: dB) substantially satisfy the same quadratic polynomial relationship, i.e., Gain=k1×Pase+k2×Pase+b; where k1, k2 and b are corresponding coefficients measured, Pase is the out-of-band ASE power, and Gain is the Raman gain of the fiber. 2

[0127] In actual operation, we can obtain the ASE power at different frequency shifts by setting the power of a certain pump wavelength, and thus obtain the corresponding gain value.

[0128] ​For distributed Raman fiber amplifier, if the input fiber pump power is P0mW, the Raman gain coefficient is CR, then the gain Gain (linear unit) is: Gain = exp (P0 x CR x Leff).

[0129] Taking the logarithm of both sides of the equation, Gain = 4.343 x P0 x CR x Leff = 4.343 2 x P0 x CR / ap, finally converted to Raman gain coefficient CR = Gain x ap p / (4.343 2 x P0), wherein Gain is the Raman gain, unit dB, ap is the pump light attenuation coefficient, unit dB / km, Leff is the effective length of the fiber. p

[0130] Through this method, the gain coefficients CR_1, CR_2, CR_3, …, CR_n (i.e. the actual gain coefficients of each preset frequency band) at different frequency shifts △f1_1, △f1_2, △f1_3, …, △f1_n corresponding to the pump wavelength 1 can be obtained. The relationship curve between the gain coefficient CR and the corresponding frequency shift in the range of 6-13.2THz is fitted to obtain a third relationship. The slope of the linearly fitted straight line is compared with the slope of the fitted straight line of the gain slope and frequency shift relationship of different fibers built in the control unit (i.e. each second relationship). The gain slope that is closest to the same type of fiber is used as the first fiber, and the adjustment parameter of the gain is controlled according to the adjustment parameter of the fiber (i.e. the fiber is used as the first fiber), wherein the adjustment parameter of each fiber is measured by a person skilled in the art in advance. The adjustment parameter can be represented as the relationship between the power of each pump wavelength and the in-band gain.

[0131] In order to obtain higher precision gain control, after determining the corresponding first fiber, the maximum gain coefficient CR_max (i.e. the maximum value in CR_1, CR_2, CR_3, …, CR_n, i.e. the first actual gain coefficient) obtained by the method at the corresponding pump wavelength can be compared with the Raman gain coefficient CR_0 (i.e. the first preset Raman gain coefficient) of the same frequency shift of the fiber built in the control unit, i.e. CR_max / CR_0. In order to maintain the same as the calibration gain, the actual pump power becomes P0 x CR_0 / CR_max, wherein P0 is the pump power of the corresponding pump wavelength calculated using the adjustment parameter of the first fiber. The above operation is performed for each pump wavelength to obtain the actual gain coefficient of each wavelength and the corresponding pump parameter adjustment.

[0132] ​That is, after the first pump laser 11-1 is turned on and the third relationship of the actually used optical fiber at the pump wavelength 1 is measured, the third relationship is used to determine which kind of optical fiber the actually used optical fiber is, that is, the first optical fiber is determined, and the compensation coefficient of the first optical fiber at the pump wavelength 1 is calculated; the first pump laser 11-1 is turned off, and under the condition that all the other pump lasers are turned off, the second pump laser 11-2 is turned on and the second relationship of the first optical fiber at the pump wavelength 2 is measured, and then the compensation coefficient of the first optical fiber at the pump wavelength 2 is calculated, and the same is done in turn for the other pump lasers, so that the compensation coefficient at the pump wavelength is calculated, and in the subsequent use, the compensation coefficient at the corresponding pump wavelength is used to calculate the adjustment parameter to compensate the pump power at the corresponding pump wavelength, so that the actual pump power at the pump wavelength is obtained, and the Raman gain control is performed using the actual pump power.

[0133] The method in Embodiment 1 is applicable in this embodiment, and will not be repeated here. The above method can be executed in the processor (i.e., the control unit 8), as shown in FIG. 11.

[0134] Those skilled in the art can understand that all or part of the steps in the various methods of the embodiments can be completed by programs instructing the related hardware, and the programs 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.

[0135] The above only describes the preferred embodiments of the present application and is not used 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.

Claims

1. A method of Raman amplifier gain control, characterized by, The method comprises the following steps: inputting pump light of corresponding wavelength into the optical fiber, and measuring out-of-band ASE power of the optical fiber in each preset frequency band; determining actual gain coefficients of each preset frequency band according to the out-of-band ASE power of each preset frequency band; matching the actual gain coefficients of each preset frequency band with preset Raman gain coefficients of each preset frequency band, using the optical fiber corresponding to the actual gain coefficient with the highest similarity obtained by matching as the first optical fiber, and using the adjustment parameters of the first optical fiber to control the gain of the Raman amplifier.

2. The Raman amplifier gain control method according to claim 1, wherein, The method comprises the following steps: calculating the Raman gain of the first preset frequency band according to the out-of-band ASE power of the first preset frequency band and a first relationship; calculating the actual gain coefficient of the first preset frequency band according to the Raman gain of the first preset frequency band.

3. The Raman amplifier gain control method according to claim 2, wherein, The first relationship is as follows: Gain = k1 x Pase 2 + k2 x Pase + b; wherein k1, k2 and b are respective coefficients measured, Pase is the out-of-band ASE power of the first preset frequency band, and Gain is the Raman gain of the first preset frequency band.

4. The Raman amplifier gain control method of claim 2, wherein, The method comprises the following steps: The actual gain coefficient is calculated by using a first formula; wherein the first formula is: C R = Gain x a p / (k3 x P0); k3 is a first preset coefficient, P0 is the optical power of the pump light input into the optical fiber, a p is a pump light attenuation coefficient, Gain is the Raman gain of a first preset frequency band, and C R is the actual gain coefficient of the first preset frequency band.

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The Raman amplifier gain control method of any of claims 1-6, wherein, The applicable optical fiber includes one or more of G.652D-SSMF optical fiber, Leaf optical fiber, Truewave optical fiber and G.654 optical fiber.

10. A Raman fiber amplifier, characterized by, The Raman amplifier gain control method of any one of claims 1-9 is used for gain control; the amplifier comprises a Raman fiber amplification part (1), the Raman fiber amplification part comprises a pump laser assembly (11), a wavelength division multiplexer (12) and a Raman fiber (13), the amplifier further comprises a first light splitting assembly (2), a first out-band detection assembly (3), a wavelength division multiplexing assembly (4) and a second out-band detection assembly (5); The input end of the first light splitting assembly (2) is coupled with the first output end of the first light splitting assembly (2) On the transmission path of the pump light, the second output end of the first light splitting assembly (2) is connected with the first out-band detection assembly (3); The common end of the wavelength division multiplexing assembly (4) is coupled with the reflection end of the wavelength division multiplexing assembly (4) on the transmission path of the signal light, and the transmission end of the wavelength division multiplexing assembly (4) is connected to the second out-band detection assembly (5); The wavelength division multiplexer (12) is used for dividing the gain light to obtain first out-band light and residual light while constituting the Raman fiber amplification part (1), the first out-band light is transmitted to the first light splitting assembly (2), and the residual light is transmitted to the wavelength division multiplexing assembly (4); The first light splitting assembly (2) is used for transmitting the first out-band light to the first out-band detection assembly (3); and the first out-band detection assembly (3) is used for detecting the out-band ASE power of the corresponding preset frequency band in the first out-band light. The wavelength division multiplexing assembly (4) is used for dividing the residual light to obtain second out-band light and in-band gain light, the second out-band light is transmitted to the second out-band detection assembly (5), and the in-band gain light continues to propagate along the transmission path of the signal light. The second out-band detection assembly (5) is used for detecting the out-band ASE power of the corresponding preset frequency band in the second out-band light.

11. The Raman fiber amplifier of claim 10, wherein, The first out-band detection assembly (3) comprises a second light splitting assembly (31), n filter assemblies and n detection assemblies; The input end of the second light splitting assembly (31) is connected to the second output end of the first light splitting assembly (2), the second light splitting assembly (31) comprises n output ends, the i-th output end of the second light splitting assembly (31) is connected to the i-th filter assembly (32-i), and the output end of the i-th filter assembly (32-i) is connected to the i-th detection assembly (33-i); The second light splitting assembly (31) is used for splitting the first out-band light into n parts of sub-band out-band light, and transmitting the i-th part of the sub-band out-band light to the i-th filter assembly (32-i); The i-th filter assembly (32-i) is used for filtering the i-th part of the sub-band out-band light to obtain out-band light of the i-th preset frequency band; The i-th detection assembly (33-i) is used for detecting the out-band light of the i-th preset frequency band to obtain the out-band ASE power of the i-th preset frequency band.

12. The Raman fiber amplifier of claim 11, wherein, Further comprising a third light splitting assembly (6) and an in-band detection assembly (7); The input end of the third light splitting component (6) and the first output end of the first light splitting component (2) are coupled on the transmission light path of the in-band gain light, and the second output end of the third light splitting component (6) is connected to the in-band detection component (7); The third light splitting component (6) is used for splitting the in-band gain light to obtain a sub-gain light, and the in-band detection component (7) is used for performing optical detection on the sub-gain light to obtain an in-band gain power, which is used for Raman gain control.

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