A method and system for suppressing stimulated Brillouin scattering in optical fibers

Abstract

This invention discloses a method and system for suppressing stimulated Brillouin scattering (SBS) in optical fibers. The method includes: S100: A signal light output from a seed source and a pump light output from a pump source are injected, and the injected pump light is rapidly converted into signal light; S200: The forward signal light is polarized using a 45-degree tilted fiber grating, the light intensity is detected by a photodetector, and the result is transmitted to a control module for analysis. The control module performs analysis according to an algorithm and sends instructions to a polarization controller to precisely adjust the polarization state of the light, control the power of the output light, and output the signal light with the polarization state of maximum power; S300: When the signal light intensity exceeds a threshold, the SBS effect occurs, and the pump light injected into the doped fiber is converted into reverse Stokes light; S400: The reverse Stokes light is polarized using a 45-degree tilted fiber grating, and the light intensity is detected by a photodetector. This invention achieves the function of maintaining the forward signal light while efficiently suppressing the reverse Stokes light through a dual polarization control loop system.

Description

Technical Field

[0001] This invention belongs to the field of fiber laser technology, and more specifically, relates to a method and system for suppressing stimulated Brillouin scattering in optical fibers. Background Technology

[0002] Fiber lasers, characterized by high beam quality, high conversion efficiency, high integration, and easy thermal management, have become one of the most popular laser technologies, with applications spanning optical communication, industrial processing, national defense, and biomedicine. Narrow-linewidth fiber lasers, with spectral widths less than or on the order of 0.1 nm, hold particular promise for applications in beam combining, nonlinear frequency conversion, and gravitational wave detection due to their high coherence and low noise figure. However, when the laser power in the fiber core reaches the stimulated Brillouin scattering threshold, the resulting back-propagating Stokes light can severely damage the fiber laser system, thus being considered the primary factor limiting the output power of narrow-linewidth lasers.

[0003] Currently, the suppression of stimulated Brillouin scattering (SBS) is mainly achieved by optimizing the optical fiber, pump structure, and gain spectrum. Increasing the effective mode area and decreasing the fiber length and effective length can help improve the SBS threshold, but this easily excites higher-order modes, which is detrimental to suppressing mode instability effects. Optimizing the main amplifier pump structure to raise the threshold has limited effect on suppressing the Brillouin scattering threshold. Methods that broaden the Brillouin gain spectrum by applying temperature or stress gradients and optimizing the phase modulation signal to achieve spectral broadening are complex and susceptible to environmental disturbances. Patent document CN109378687B discloses a method for suppressing SBS in a fiber laser amplifier, utilizing the high loss characteristics of tilted fiber gratings in the Brillouin band to suppress backscattered Stokes light generated in the fiber laser amplifier system, thereby increasing the SBS threshold of the fiber laser amplifier. It has been reported that this tilted Bragg grating achieves an average filtering efficiency of over 16 dB for backward Stokes light (Tian Xin, Wang Meng, Wang Zefeng. Stimulated Brillouin Scattering Filter Based on Tilted Bragg Grating. Acta Optica Sinica, 2020, 40(10)). However, this method causes signal light loss, affecting laser amplification performance. Since this method requires the signal light wavelength and the backward Stokes light wavelength to be located in the passband and stopband regions of the grating, respectively, the fabrication process of the grating is highly demanding. Summary of the Invention

[0004] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a method for suppressing stimulated Brillouin scattering in optical fibers. The forward signal light / reverse Stokes light undergoes polarization processing via a 45-degree tilted fiber grating. The light intensity is detected by a photodetector and transmitted to a control module. The control module analyzes the data according to a control algorithm and sends instructions to a polarization controller to precisely adjust the light polarization state. This dual-polarization control loop system achieves the function of maintaining the forward signal light while efficiently suppressing the reverse Stokes light.

[0005] To achieve the above objective, according to a first aspect of the present invention, a method for suppressing stimulated Brillouin scattering in an optical fiber is provided, comprising:

[0006] S100: The signal light output from the seed source and the pump light output from the pump source are injected into the doped fiber through the signal pump combiner, and the injected pump light is quickly converted into signal light.

[0007] S200: The forward signal light is polarized using a 45-degree tilted fiber optic grating. The light intensity is detected by a photodetector and transmitted to the control module for analysis. The control module analyzes the signal light according to the algorithm and sends instructions to the polarization controller to precisely adjust the polarization state of the light, control the power of the output light, and output the signal light with the polarization state of maximum power.

[0008] S300: When the signal light intensity exceeds the threshold, the SBS effect is generated, and the pump light injected into the doped fiber is converted into reverse Stokes light.

[0009] S400: The reverse Stokes light is polarized using a 45-degree tilted fiber optic grating. The light intensity is detected by a photodetector and transmitted to the control module. The control module analyzes the signal according to the algorithm and sends a command to the polarization controller to precisely adjust the polarization state of the light and control the power of the output light, so that the reverse Stokes light is output with the minimum power polarization state.

[0010] Furthermore, the algorithm includes:

[0011] S201: Randomly set an initial control voltage u on the control module. (0) =(u1,u2,u3,u4), which are output to the control terminals of the polarization controller respectively;

[0012] S202: The initial evaluation function J is quickly calculated using the signal acquired by the photodetector. (n) ;

[0013] S203: Regenerate random disturbance voltage δu (n) =(δu1,δu2,δu3,δu4) (n) And save;

[0014] S204: The disturbance voltage δu (n) With control voltage u (n) The output is sent to the control terminal of the polarization controller;

[0015] S205: Evaluation function J obtained after measuring the previous perturbation. + (n) ;

[0016] S206: The random disturbance voltage δu (n) Invert and compare with the control voltage u (n) The accumulated values ​​are then output to the control terminal of the polarization controller.

[0017] S207: Obtain the evaluation function J after the previous perturbation. - (n) ;

[0018] S208: Calculate the change ΔJ of the evaluation function between the two evaluations. (n) =J + (n) -J - (n) ;

[0019] S209: According to formula u (n+1) =u (n) +γδu (n) ΔJ (n) Update the control voltage output to the polarization controller, perform the (n+1)th iteration, repeat steps 201 to 208, and continue voltage control until the system is stable.

[0020] Among them, u (0) = (u1, u2, u3, u4) is the disturbance voltage vector of the initial control parameters; δu (n) =(δu1,δu2,δu3,δu4) (n) It is the disturbance voltage vector of the control parameters after the nth iteration; u (n) It is the disturbance voltage of the control parameters after the nth iteration; u (n+1) It is the disturbance voltage of the control parameters after the (n+1)th iteration; γ is the gain coefficient; γδu (n) It is the change in the nth system performance index measurement value; ΔJ (n) It is the perturbation voltage of the nth iteration.

[0021] Furthermore, in steps S204 and S205, the gain coefficient γ > 0.

[0022] Furthermore, in step S209, the gain coefficient γ < 0.

[0023] Furthermore, in step S200, when the signal light passes through a 45-degree tilted fiber optic grating, the light with the s-polarization state is converted into a radiation mode, and the energy is dissipated in free space, while the light with the p-polarization state will be transmitted in the fiber core in a low-loss form.

[0024] Furthermore, in step S200, after the signal light passes through the fiber optic coupler, most of the light continues to propagate forward, while a small portion of the light passes through a photodetector and is converted into an electrical signal, which is then transmitted to the control module as an evaluation function.

[0025] Furthermore, in step S200, the control module parses the control signals required by the polarization controller according to the algorithm and transmits them to each control port of the vibration controller to quickly correct the polarization state of the signal light, thereby realizing high-precision closed-loop control of the signal light.

[0026] Further, in step S400, the reverse Stokes light reaches the 45-degree tilted fiber grating after passing through the fiber coupler. When the signal light passes through the 45-degree tilted fiber grating, the light with the s-polarization state is converted into radiation mode energy and dissipated in free space, while the light with the p-polarization state will be transmitted in the fiber core in a low-loss form.

[0027] Furthermore, in step S400, the control module parses the control signals required by the polarization controller according to the algorithm and transmits them to each control port of the polarization controller to quickly correct the polarization state of the reverse Stokes light, thereby realizing high-precision closed-loop control of the reverse Stokes light.

[0028] According to a second aspect of the present invention, a system for suppressing stimulated Brillouin scattering in an optical fiber is provided, comprising a seed source, a pump source, a signal pump combiner, a circulator, a first polarization controller, a 45-degree tilted fiber grating, an optical fiber coupler, a second polarization controller, a first photodetector, a first control module, a second photodetector, and a second control module connected in sequence in an optical path.

[0029] A dual polarization control loop is connected between the signal pump combiner and the doped fiber. A 45-degree tilted fiber grating, a fiber coupler, a first photodetector, a first control module, and a first polarization controller are fused together in sequence to form the signal light polarization control loop.

[0030] An optical fiber coupler, a 45-degree tilted fiber grating, a circulator, a second photodetector, a second control module, and a polarization controller are fused together in sequence to form a reverse Stokes optical polarization control loop.

[0031] Furthermore, the first polarization controller and the second polarization controller are used to adjust the polarization state of the light and control the power of the output light.

[0032] Furthermore, the first photodetector and the second photodetector are used to convert the optical signal into an electrical signal and transmit it to the first control module and the second control module. The corresponding control module analyzes the signal according to the control algorithm and sends instructions to the corresponding polarization controller to precisely adjust the polarization state of the light and control the power of the output light.

[0033] Furthermore, the fiber optic coupler is used to distribute optical signal power among different optical fibers, ensuring that the signal light and the reverse Stokes light can enter their respective control loops.

[0034] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0035] 1. The method of this invention involves polarizing the forward signal light / reverse Stokes light through a 45-degree tilted fiber optic grating. The light intensity is detected by a photodetector and transmitted to a control module. The control module analyzes the signal according to a control algorithm and sends instructions to a polarization controller to precisely adjust the polarization state. This dual polarization control loop system achieves the function of maintaining the forward signal light while efficiently suppressing the reverse Stokes light.

[0036] 2. The method of the present invention provides a 45-degree tilted fiber optic grating with good polarization characteristics: it has high transmittance for p-polarized light, high loss for s-polarized light, and the lost energy is dissipated in the cladding in the form of radiation modes, providing excellent isolation for backward Stokes light.

[0037] 3. The method of the present invention enables the dual polarization control loop system to achieve real-time control and tuning of polarization state, and has strong resistance to environmental disturbances. Attached Figure Description

[0038] Figure 1 This is a schematic flowchart of a method for suppressing stimulated Brillouin scattering in an optical fiber according to an embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram of a structure for suppressing stimulated Brillouin scattering in an optical fiber according to an embodiment of the present invention;

[0040] Figure 3 This is a schematic diagram of another structure of a system for suppressing stimulated Brillouin scattering in an optical fiber according to an embodiment of the present invention;

[0041] Figure 4 This is a schematic diagram illustrating the principle of suppressing the axial distribution characteristics of the radiation mode in a 45-degree tilted fiber grating used in a stimulated Brillouin scattering system in an optical fiber, according to an embodiment of the present invention.

[0042] In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1-seed source, 2-pump source, 3-signal pump combiner, 4-circulator, 5-first polarization controller, 6-45-degree tilted fiber grating, 7-fiber coupler, 8-second polarization controller, 9-doped fiber, 10-first photodetector, 11-first control module, 12-second photodetector, 13-second control module, 14-fiber core. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0044] Example 1

[0045] like Figure 1 As shown, this embodiment of the invention provides a method for suppressing stimulated Brillouin scattering in an optical fiber, with the following specific steps:

[0046] S100: The signal light output from the seed source and the pump light output from the pump source are injected into the doped fiber through the signal pump combiner. The injected pump light is quickly converted into signal light.

[0047] S200: The forward signal light is polarized using a 45-degree tilted fiber optic grating. The light intensity is detected by a photodetector and transmitted to the control module. The control module analyzes the signal light according to the algorithm and sends a command to the polarization controller to precisely adjust the polarization state of the light and control the power of the output light, so that the signal light is output with the polarization state of maximum power.

[0048] S300: When the signal light intensity exceeds a certain threshold, the SBS effect is generated, and the pump light injected into the doped fiber is converted into reverse Stokes light.

[0049] S400: The reverse Stokes light is polarized using a 45-degree tilted fiber optic grating. The light intensity is detected by a photodetector and transmitted to the control module. The control module analyzes the signal according to the algorithm and sends a command to the polarization controller to precisely adjust the polarization state of the light and control the power of the output light, so that the reverse Stokes light is output with the minimum optical power polarization state.

[0050] Example 2

[0051] like Figure 2As shown, this embodiment of the invention provides a system for suppressing stimulated Brillouin scattering in an optical fiber, including a seed source 1, a pump source 2, a signal pump combiner 3, a circulator 4, a first polarization controller 5, a 45-degree tilted fiber grating 6, an optical fiber coupler 7, a second polarization controller 8, a doped optical fiber 9, a first photodetector 10, a first control module 11, a second photodetector 12, and a second control module 13.

[0052] More specifically, a dual polarization control loop is connected between the signal pump combiner 3 and the doped fiber 9. Specifically, the 45-degree tilted fiber grating 6, fiber coupler 7, first photodetector 10, first control module 11, and first polarization controller 5 are sequentially connected by fusion splicing to form the signal light polarization control loop; the fiber coupler 7, 45-degree tilted fiber grating 6, circulator 4, second photodetector 12, second control module 13, and polarization controller 8 are sequentially connected by fusion splicing to form the reverse Stokes light polarization control loop. Furthermore, the first polarization controller 5 is not involved in the modulation of the reverse Stokes light.

[0053] More specifically, the parameters of seed source 1, pump source 2, and signal pump combiner 3, as well as the wavelength and output power of doped fiber 9, vary depending on the actual situation and there are no special requirements.

[0054] More specifically, the circulator 4 is an optical isolation device that ensures the signal is transmitted only along a fixed optical path. The first polarization controller 5 and the second polarization controller 8 can adjust the optical polarization state and control the output light power. The fiber coupler distributes the optical signal power between different optical fibers, ensuring that the signal light and the reverse Stokes light can enter their respective control loops. The first photodetector 10 and the second photodetector 12 can convert the optical signal into an electrical signal and transmit it to the first control module 11 and the second control module 13. Then, the corresponding control modules analyze the signal according to the control algorithm and issue instructions to the corresponding polarization controllers to accurately adjust the optical polarization state and control the output light power.

[0055] More specifically, the 45-degree tilted fiber grating 6 is a special type of tilted fiber grating whose tilt angle is equal to the Brewster angle, and the Brewster angle satisfies:

[0056]

[0057] n is the refractive index of the fiber core, and Δn is the refractive index modulation amount introduced during the grating fabrication process.

[0058] Furthermore, this grating can couple the s-polarized light in the fiber core mode into a radiation mode and diffract it directly into free space, while retaining the p-polarized light to propagate within it, thus achieving a polarization function, such as... Figure 4As shown. Therefore, the 45-degree tilted fiber grating is an excellent all-fiber polarization device. The polarization performance of the 45-degree tilted fiber grating is related to its length; the longer the length, the greater the polarization correlation loss, and the better the polarization performance. Compared to traditional bulk polarization devices, the 45-degree tilted fiber grating has lower insertion loss, can withstand higher input power, and the light transmission characteristics of optical fiber allow external signal light to be directly transmitted to the 45-degree tilted fiber grating. This overcomes the shortcomings of traditional dispersive devices that require collimation modules in applications, making it an ideal replacement for traditional bulk diffraction gratings. This enables the miniaturization of spectral analysis systems, improving system integration and portability. It also offers greater stability and compatibility, and lower cost.

[0059] More specifically, the forward signal optical control loop and the reverse Stokes optical control loop include the following steps:

[0060] Forward signal optical control loop:

[0061] Step 1: First, the forward signal light passes through the fiber optic circulator 4 and the first polarization controller 5 before reaching the 45-degree tilted fiber optic grating 6.

[0062] Step 2: Since linearly polarized light in any direction can be decomposed into orthogonally polarized light composed of s-polarization and p-polarization states, when light passes through a 45-degree tilted fiber grating, the light with the s-polarization state is converted into a radiation mode, and its energy is dissipated in free space. The light with the p-polarization state will then propagate in the fiber core in a low-loss manner, such as... Figure 4 As shown;

[0063] Step 3: When the signal light passes through the fiber optic coupler 7, most of the light continues to propagate forward, while a small portion of the light passes through the first photodetector 10 and is converted into an electrical signal, which is then transmitted to the first control module 11 as an evaluation function.

[0064] Step 4: The first control module 11 parses the control signal required by the first polarization controller 5 according to the algorithm, and then transmits it to each control port of the first polarization controller 5 to quickly correct the polarization state of the signal light, thereby realizing high-precision closed-loop control of the signal light.

[0065] Step 5: The control module iterates the control signal according to the algorithm. When the algorithm is optimized to the maximum value, the polarization state of the signal light is stabilized in the p polarization state. The signal light is transmitted in the fiber core in a low-loss form after passing through the 45-degree tilted fiber grating. The evaluation function collected by the first photodetector 10 is stabilized at the maximum value, that is, the low-loss output of the signal light is realized.

[0066] Reverse Stokes light control loop:

[0067] Step 6: First, the reverse Stokes light passes through the fiber coupler 7 and reaches the 45-degree tilted fiber grating 6.

[0068] Step 7: When light passes through the 45-degree tilted fiber grating 6, the light with the s-polarization state is converted into a radiation mode, and its energy is dissipated in free space. The light with the p-polarization state will then propagate in the fiber core in a low-loss manner, such as... Figure 4 As shown;

[0069] Step 8: The first polarization controller 5 does not regulate the reverse Stokes light. When the reverse Stokes light passes through the fiber optic circulator 4, the light passes through the second photodetector 12 and is converted into an electrical signal, which is then transmitted to the second control module 13 as an evaluation function.

[0070] Step 9: The second control module 13 parses the control signals required by the second polarization controller 8 according to the algorithm, and then transmits them to each control port of the second polarization controller 8 to quickly correct the polarization state of the reverse Stokes light, thereby realizing high-precision closed-loop control of the reverse Stokes light.

[0071] Step 10: The control module iterates the control signal according to the algorithm. When the algorithm is optimized to a minimum value, the polarization state of the reverse Stokes light stabilizes at the minimum value of the p-polarization state, and the evaluation function collected by the second photodetector 12 stabilizes at the minimum value, thus achieving low-loss output of the reverse Stokes light. The algorithm used in steps 4, 5, 9, and 10 is the stochastic parallel gradient descent method, and its implementation process includes the following steps:

[0072] Step 1: First, randomly set an initial control voltage u on the control module. (0) = (u1, u2, u3, u4), which are output to the four control terminals of the polarization controller respectively;

[0073] Step two: Then, the initial evaluation function J is quickly calculated using the signal collected by the photodetector. (n) ;

[0074] Step 3: Generate the random disturbance voltage δu (n) =(δu1,δu2,δu3,δu4) (n) And save;

[0075] Step 4, the disturbance voltage δu (n) With control voltage u (n) The output is sent to the four control terminals of the polarization controller;

[0076] Step 5: Measure the evaluation function J obtained after the perturbation in the previous step. + (n) ;

[0077] Step six, the random disturbance voltage δu (n) Invert and compare with the control voltage u (n) The accumulated values ​​are then output to the four control terminals of the polarization controller.

[0078] Step 7: Obtain the evaluation function J after the perturbation in the previous step. - (n) ;

[0079] Step 8: Calculate the change ΔJ between the two evaluation functions. (n) =J + (n) -J - (n) ;

[0080] Step nine, according to formula u (n+1) =u (n) +γδu (n) ΔJ (n) Update the control voltage output to the polarization controller and perform the (n+1)th iteration;

[0081] Step 10: Repeat steps 1-9 to continue voltage control until the system stabilizes;

[0082] Among them, u (0) = (u1, u2, u3, u4) is the disturbance voltage vector of the initial control parameters; δu (n) =(δu1,δu2,δu3,δu4) (n) It is the disturbance voltage vector of the control parameters after the nth iteration; u (n) It is the disturbance voltage of the control parameters after the nth iteration; u (n+1) It is the disturbance voltage of the control parameters after the (n+1)th iteration; γ is the gain coefficient; γδu (n) It is the change in the nth system performance index measurement value; ΔJ (n) It is the perturbation voltage of the nth iteration.

[0083] Furthermore, in steps four and five, γ > 0; in steps nine and ten, γ < 0.

[0084] Example 3

[0085] like Figure 3 As shown, this embodiment of the invention provides another system for suppressing stimulated Brillouin scattering in optical fibers. The difference from Embodiment 2 is that in this embodiment, the circulator 4 is positioned between the first polarization controller 5 and the 45-degree tilted fiber grating 6, preventing the reverse Stokes light from passing through the first polarization controller 5 of the forward signal control loop, thus allowing for more precise modulation of the signal light. The components involved are the same as in Embodiment 2.

[0086] More specifically, it only involves the forward signal optical control loop and the reverse Stokes optical control loop, and includes the following steps:

[0087] Forward signal optical control loop:

[0088] Step 1: First, the forward signal light passes through the first polarization controller 5 and the fiber optic circulator 4 and then reaches the 45-degree tilted fiber optic grating 6.

[0089] Step 2: Since linearly polarized light in any direction can be decomposed into orthogonally polarized light composed of s-polarization and p-polarization states, when the light passes through a 45-degree tilted fiber grating, the light with the s-polarization state is converted into a radiation mode, and its energy is dissipated in free space. The light with the p-polarization state will then be transmitted in the fiber core 14 in a low-loss manner, such as... Figure 4 As shown;

[0090] Step 3: When the signal light passes through the fiber optic coupler 7, most of the light continues to propagate forward, while a small portion of the light passes through the first photodetector 10 and is converted into an electrical signal, which is then transmitted to the first control module 11 as an evaluation function.

[0091] Step 4: The first control module 11 parses the control signal required by the first polarization controller 5 according to the algorithm, and then transmits it to each control port of the first polarization controller 5 to quickly correct the polarization state of the signal light, thereby realizing high-precision closed-loop control of the signal light.

[0092] Step 5: The control module iterates the control signal according to the algorithm. When the algorithm is optimized to the maximum value, the polarization state of the signal light is stabilized in the p polarization state. The signal light is transmitted in the fiber core 14 in a low-loss form after passing through the circulator 4 and the 45-degree tilted fiber grating 6. The evaluation function collected by the first photodetector 10 is stabilized at the maximum value, that is, the low-loss output of the signal light is realized.

[0093] Reverse Stokes light control loop:

[0094] Step 6: First, the reverse Stokes light passes through the fiber coupler 7 and reaches the 45-degree tilted fiber grating 6.

[0095] Step 7: When light passes through the 45-degree tilted fiber grating 6, the light with the s-polarization state is converted into a radiation mode, and its energy is dissipated in free space. The light with the p-polarization state will then propagate in the fiber core in a low-loss manner, such as... Figure 4 As shown;

[0096] Step 8: When the reverse Stokes light passes through the fiber optic circulator 4, the light passes through the second photodetector 12 and is converted into an electrical signal, which is then transmitted to the second control module 13 as an evaluation function.

[0097] Step 9: The second control module 13 parses the control signals required by the second polarization controller 8 according to the algorithm, and then transmits them to each control port of the second polarization controller 8 to quickly correct the polarization state of the reverse Stokes light, thereby realizing high-precision closed-loop control of the reverse Stokes light.

[0098] Step 10: The control module iterates the control signal according to the algorithm. When the algorithm is optimized to a minimum value, the polarization state of the reverse Stokes light stabilizes at the minimum value of the p-polarization state, and the evaluation function collected by the second photodetector 12 stabilizes at the minimum value, thus achieving low-loss output of the reverse Stokes light. The algorithm used in steps 4, 5, 9, and 10 is the stochastic parallel gradient descent method, and its implementation process includes the following steps:

[0099] Step 1: First, randomly set an initial control voltage u on the control module. (0) = (u1, u2, u3, u4), which are output to the four control terminals of the polarization controller respectively;

[0100] Step two: Then, the initial evaluation function J is quickly calculated using the signal collected by the photodetector. (n) ;

[0101] Step 3: Generate the random disturbance voltage δu (n) =(δu1,δu2,δu3,δu4) (n) And save;

[0102] Step 4, the disturbance voltage δu (n) With control voltage u (n) The output is sent to the four control terminals of the polarization controller;

[0103] Step 5: Measure the evaluation function J obtained after the perturbation in the previous step. + (n) ;

[0104] Step six, the random disturbance voltage δu (n) Invert and compare with the control voltage u (n) The accumulated values ​​are then output to the four control terminals of the polarization controller.

[0105] Step 7: Obtain the evaluation function J after the perturbation in the previous step. - (n) ;

[0106] Step 8: Calculate the change ΔJ between the two evaluation functions. (n) =J + (n) -J - (n) ;

[0107] Step nine, according to formula u (n+1) =u (n) +γδu (n) ΔJ (n) Update the control voltage output to the polarization controller and perform the (n+1)th iteration;

[0108] Step 10: Repeat steps 1-9 to continue voltage control until the system stabilizes;

[0109] Among them, u (0) = (u1, u2, u3, u4) is the disturbance voltage vector of the initial control parameters; δu (n) =(δu1,δu2,δu3,δu4) (n) It is the disturbance voltage vector of the control parameters after the nth iteration; u (n) It is the disturbance voltage of the control parameters after the nth iteration; u (n+1) It is the disturbance voltage of the control parameters after the (n+1)th iteration; γ is the gain coefficient; γδu (n) It is the change in the nth system performance index measurement value; ΔJ (n) It is the perturbation voltage of the nth iteration.

[0110] Furthermore, in steps four and five, γ > 0; in steps nine and ten, γ < 0.

[0111] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for suppressing stimulated Brillouin scattering in an optical fiber, characterized in that, include: S100: The signal light output from the seed source and the pump light output from the pump source are injected into the doped fiber through the signal pump combiner, and the injected pump light is quickly converted into signal light. S200: The forward signal light is polarized using a 45-degree tilted fiber optic grating. The light intensity is detected by a photodetector and transmitted to the control module for analysis. The control module analyzes the signal light according to the algorithm and sends instructions to the polarization controller to precisely adjust the polarization state of the light, control the power of the output light, and output the signal light with the polarization state of maximum power. S300: When the signal light intensity exceeds the threshold, the SBS effect is generated, and the pump light injected into the doped fiber is converted into reverse Stokes light. S400: The reverse Stokes light is polarized using a 45-degree tilted fiber optic grating. The light intensity is detected by a photodetector and transmitted to the control module. The control module analyzes the light according to the algorithm and sends a command to the polarization controller to precisely adjust the polarization state of the light and control the power of the output light, so that the reverse Stokes light is output with the minimum power polarization state. The algorithm includes: S201: Randomly set an initial control voltage on the control module. The outputs are respectively sent to the control terminals of the polarization controller; S202: Quickly calculate the initial evaluation function using the signal collected by the photodetector. ; S203: Regenerate random disturbance voltage And save; S204: Disturbance voltage With control voltage The output is sent to the control terminal of the polarization controller; S205: Evaluation function obtained after measuring the previous perturbation. ; S206: Random disturbance voltage Invert and compare with the control voltage The accumulated values ​​are then output to the control terminal of the polarization controller. S207: Obtain the evaluation function after the perturbation in the previous step. ; S208: Calculate the change in the evaluation function between the two tests. ; S209: According to the formula Update the control voltage output to the polarization controller, perform the (n+1)th iteration, repeat steps 201 to 208, and continue voltage control until the system is stable. in, It is the disturbance voltage vector of the initial control parameters; It is the disturbance voltage vector of the control parameters after the nth iteration; It is the disturbance voltage of the control parameters after the nth iteration; It is the disturbance voltage of the control parameters after the (n+1)th iteration; It is the gain coefficient; It is the change in the system performance index measurement value of the nth time; It is the perturbation voltage of the nth iteration.

2. The method for suppressing stimulated Brillouin scattering in an optical fiber according to claim 1, characterized in that, In steps S204 and S205, the gain coefficient >

0.

3. The method for suppressing stimulated Brillouin scattering in an optical fiber according to claim 1, characterized in that, In step S209, the gain coefficient <0.

4. A method for suppressing stimulated Brillouin scattering in an optical fiber according to any one of claims 1-3, characterized in that, In step S200, when the signal light passes through a 45-degree tilted fiber optic grating, the light with the s-polarization state is converted into a radiation mode, and the energy is dissipated in free space, while the light with the p-polarization state will be transmitted in the fiber core in a low-loss form.

5. The method for suppressing stimulated Brillouin scattering in an optical fiber according to claim 4, characterized in that, In step S200, after the signal light passes through the fiber optic coupler, most of the light continues to propagate forward, while a small portion of the light passes through the photodetector and is converted into an electrical signal, which is then transmitted to the control module as an evaluation function.

6. The method for suppressing stimulated Brillouin scattering in an optical fiber according to claim 5, characterized in that, In step S200, the control module parses the control signals required by the polarization controller according to the algorithm and transmits them to each control port of the vibration controller to quickly correct the polarization state of the signal light, thereby realizing high-precision closed-loop control of the signal light.

7. The method for suppressing stimulated Brillouin scattering in an optical fiber according to claim 6, characterized in that, In step S400, the reverse Stokes light reaches the 45-degree tilted fiber grating after passing through the fiber coupler. When the signal light passes through the 45-degree tilted fiber grating, the light with the s-polarization state is converted into a radiation mode and its energy is dissipated in free space, while the light with the p-polarization state will be transmitted in the fiber core in a low-loss form.

8. A method for suppressing stimulated Brillouin scattering in an optical fiber according to any one of claims 1-3, characterized in that, In step S400, the control module parses the control signals required by the polarization controller according to the algorithm and transmits them to each control port of the polarization controller to quickly correct the polarization state of the reverse Stokes light, thereby realizing high-precision closed-loop control of the reverse Stokes light.

Images