A polarization maintaining device and method for a polarization maintaining fiber

Abstract

This application discloses an active feedback polarization-maintaining fiber polarization stabilization device and method, comprising: a polarization compensation module disposed before the input end of the polarization-maintaining fiber to adjust the linear polarization direction of the incident laser; a polarization detection module disposed after the output end of the polarization-maintaining fiber to convert the output laser into multiple light intensity signals related to the polarization state; and a signal processing and control module connected to the polarization detection module and the polarization compensation module respectively, generating a normalized differential error signal based on the multiple light intensity signals, and generating a control signal based on the difference between the error signal and the target error signal value to drive the polarization compensation module to adjust the linear polarization direction of the incident laser in a closed loop, thereby continuously aligning it with the preset intrinsic axis of the polarization-maintaining fiber. This application suppresses optical power fluctuation interference through the normalized differential error signal, and combined with initialization calibration and closed-loop feedback control, can compensate for polarization deviations caused by environmental disturbances, mechanical drift, and long-term system operation in real time, thereby improving the polarization stability of the output laser from the polarization-maintaining fiber.

Description

Technical Field

[0001] This application belongs to the field of quantum optics and fiber laser technology, and specifically relates to an active feedback polarization-maintaining fiber polarization stabilization device and method. Background Technology

[0002] In fields such as cold atom physics, quantum optics, precision measurement, and fiber optic communication, optical fibers are frequently used to achieve long-distance, high-fidelity transmission of lasers. Especially when there are strict requirements for the polarization state of the laser, polarization-maintaining fiber is typically used as the transmission medium. Polarization-maintaining fiber introduces birefringence through its special internal stress structure, forming two mutually orthogonal intrinsic polarization axes: a fast axis and a slow axis. Theoretically, only when the linear polarization direction of the incident laser is precisely aligned with one of these intrinsic axes can the laser transmit in a single polarization mode, thus maintaining a stable linear polarization state at the output.

[0003] However, in practical applications, changes in ambient temperature, platform vibration and mechanical stress release, as well as the slow drift during long-term system operation, can all cause the originally aligned incident polarization direction to gradually deviate from the intrinsic axis of the polarization-maintaining fiber. Once this deviation occurs, the polarization state at the output end will evolve into elliptic polarization, severely affecting the contrast and stability of subsequent optical measurements. Existing manual adjustment or passive stabilization methods cannot compensate for dynamic drift in real time, while schemes based on single-path optical intensity feedback are susceptible to power fluctuations and lack direct control objectives.

[0004] Therefore, there is an urgent need for a novel polarization stabilization device and method that has a clear feedback target, strong anti-interference ability, and can stably lock the incident polarization in the direction of the intrinsic axis of the polarization-maintaining fiber for a long period of time. Summary of the Invention

[0005] The purpose of this application is to provide an active feedback polarization-maintaining fiber polarization stabilization device and method. This addresses the problems in the prior art where the polarization state of the output laser from polarization-maintaining fibers is easily affected by environmental disturbances and lacks high-precision real-time active compensation.

[0006] To achieve the above objectives, this application adopts the following technical solution: In a first aspect, an active feedback polarization-maintaining fiber polarization stabilization device is provided, comprising: A polarization compensation module is located before the input end of the polarization-maintaining fiber and is used to adjust the linear polarization direction of the laser incident on the polarization-maintaining fiber. A polarization detection module is located after the output end of the polarization-maintaining fiber and is used to convert the output laser of the polarization-maintaining fiber into multiple light intensity signals related to the polarization state. The signal processing and control module is connected to the polarization detection module and the polarization compensation module, respectively. It is used to generate a normalized error signal based on the multi-channel light intensity signal, and generate a control signal based on the difference between the error signal and the target error signal value, so as to drive the polarization compensation module to adjust the linear polarization direction of the incident laser in a closed loop, so that it is continuously aligned with the preset intrinsic axis of the polarization-maintaining fiber.

[0007] In one possible implementation, the polarization compensation module includes a rotatable half-wave plate and a drive assembly for driving the half-wave plate to rotate. The drive component is any one of a hollow motor, a servo motor, a stepper motor, or a piezoelectric rotary actuator.

[0008] In one possible implementation, the polarization detection module includes: A beam splitter is used to split the output laser of the polarization-maintaining fiber into a main optical path and a detection optical path. A quarter-wave plate is disposed on the detection optical path; A polarization beam splitter, positioned after the quarter-wave plate, is used to split the light beam in the detection optical path into two orthogonal linearly polarized beams. The first photodetector and the second photodetector are respectively used to receive the two orthogonal linearly polarized beams of light and convert them into a first light intensity signal and a second light intensity signal.

[0009] In one possible implementation, the signal processing and control module includes a signal processing unit and a drive control unit; The signal processing unit is used to calculate the normalized error signal, which is the difference between the first light intensity signal and the second light intensity signal divided by the sum of the two. The drive control unit is used to generate the control signal based on the difference between the error signal and the target error signal value.

[0010] In one possible implementation, the signal processing and control module is further configured to perform initialization calibration: In the initial alignment state, the value of the normalized error signal at this time is recorded as the target error signal value, and the deviation between the real-time error signal and the target error signal value is used as the control basis in the subsequent closed-loop control.

[0011] In one possible implementation, the signal processing and control module further includes a total light intensity judgment unit, used to detect the sum of the multiple light intensity signals, and when the sum is lower than a preset threshold, to pause updating the control signal in order to maintain the current state of the polarization compensation module.

[0012] In one possible implementation, the signal processing and control module uses any one of a proportional-integral-derivative control algorithm, a proportional-integral control algorithm, or an adaptive control algorithm to generate the control signal.

[0013] Secondly, an active feedback polarization-maintaining fiber polarization stabilization method is provided, including the following steps: Initialization calibration steps: Adjust the linear polarization direction of the laser incident on the polarization-maintaining fiber to align it with the preset intrinsic axis of the polarization-maintaining fiber, and detect the polarization state of the laser output from the polarization-maintaining fiber at this time, and record the target error signal value corresponding to the polarization state. Closed-loop control steps: Real-time detection of the polarization state of the laser output from the polarization-maintaining fiber, generation of a normalized real-time error signal, and use the difference between the real-time error signal and the target error signal as the control error; Feedback adjustment step: Generate a control signal based on the control error to drive the polarization compensation element set before the polarization-maintaining fiber input end to close the loop and correct the linear polarization direction of the incident laser so that it is continuously aligned with the preset intrinsic axis.

[0014] In one possible implementation, generating the normalized real-time error signal includes: The output laser from the polarization-maintaining fiber is decomposed into two orthogonal linearly polarized components. The light intensities of the two orthogonally linearly polarized components are detected respectively to obtain a first light intensity signal and a second light intensity signal; The normalized real-time error signal is calculated by dividing the difference between the first light intensity signal and the second light intensity signal by the sum of the two.

[0015] In one possible implementation, the closed-loop control step further includes a total light intensity effectiveness determination: The sum of the light intensity signals of the two orthogonally linearly polarized components is calculated. When the sum is lower than a preset threshold, the current control signal output is frozen, so that the polarization compensation element remains in the state of the previous moment.

[0016] Compared with the prior art, this application has the following beneficial effects: This application provides an active feedback polarization-maintaining fiber polarization stabilization device. Through a polarization compensation module at the input end and a polarization detection module at the output end of the polarization-maintaining fiber, combined with a signal processing and control module, a closed-loop feedback is formed. The direct control target is to continuously align the incident polarization direction with the preset intrinsic axis of the polarization-maintaining fiber. This overcomes the shortcomings of manual adjustment, which cannot compensate for dynamic drift in real time; passive stabilization, which cannot be actively adjusted; and single-path light intensity feedback, which is susceptible to power fluctuation interference. In particular, the error signal is constructed using a normalized differential method with dual-path light intensity signals, effectively eliminating the interference of light source power fluctuations and coupling efficiency changes on the feedback signal. This ensures that the control error, within the effective feedback range determined by initial calibration, mainly reflects the deviation of the incident polarization direction from the target intrinsic axis alignment, significantly improving the system's anti-interference capability and long-term operational stability.

[0017] In one possible implementation, a rotatable half-wave plate and driving components are used as polarization compensation actuators, enabling continuous and high-resolution electronic control adjustment of the incident laser's linear polarization direction. Compared to the traditional method of manually adjusting the wave plate group, this scheme can automatically compensate in response to closed-loop feedback signals, providing a reliable and fast execution means for real-time polarization locking, and its structure is simple and easy to integrate.

[0018] In one possible implementation, a detection link is constructed using a beam splitter, a quarter-wave plate, a polarization beam splitter, and first and second photodetectors, and a normalized differential error signal is calculated. This detection scheme has the advantages of simple optical path, fast response speed, and high detection sensitivity. The normalization process can suppress the fluctuation of total optical power, provide a stable and linear error feedback for closed-loop control, and significantly improve the accuracy and reliability of polarization detection.

[0019] In one possible implementation, the target error signal value is recorded in the initial alignment state, and the deviation between the real-time error signal and the target error signal is used as the control basis in the subsequent closed-loop control. This mechanism effectively eliminates the influence of factors such as the quarter-wave plate installation angle deviation, the non-ideal characteristics of the polarization beam splitter, and the fixed bias of the detection link, enabling the system to adapt to various hardware conditions without the need for strict theoretical zero-point setting, thus improving the practicality and control accuracy of the system.

[0020] In one possible implementation, by detecting the sum of multiple light intensity signals, when the sum is lower than a preset threshold, the update of the control signal is paused and the current state of the polarization compensation module is maintained. This safety protection mechanism avoids the system from going out of control due to actuator malfunction under weak light or no light conditions, thus enhancing the robustness and safety of the system.

[0021] In one possible implementation, a proportional-integral-derivative (PID) control algorithm, a proportional-integral (PI) control algorithm, or an adaptive control algorithm can be used to generate the control signal. Among them, the PID control algorithm has the advantages of fast response and small steady-state error, and can achieve high-precision, low-residual polarization locking. The PI or adaptive algorithm can be flexibly selected according to the specific application scenario, which improves the versatility and adaptability of the solution.

[0022] An active feedback polarization-maintaining fiber polarization stabilization method is proposed, which forms a complete adaptive polarization locking method through three steps: initialization calibration, closed-loop control, and feedback adjustment. This method can detect the polarization state of the output laser in real time and correct the incident polarization direction in a closed loop, realizing active compensation for temperature drift, mechanical vibration, and long-term drift. At the same time, by recording the target error signal value through initialization calibration, the fixed bias of the system is eliminated, and the zero-point of locking is adaptively determined, which significantly improves the anti-interference ability and environmental adaptability of the method.

[0023] In one possible implementation, the output laser from the polarization-maintaining fiber is decomposed into two orthogonally linearly polarized components. The intensity of each component is detected, and the difference is calculated and divided by the sum to obtain a normalized real-time error signal. This method is simple to calculate and has clear physical meaning. It can effectively suppress the influence of light source power fluctuations on the feedback signal, making the error signal correlated with the polarization deviation angle within the effective feedback range, thus providing a reliable error input for high-precision closed-loop control.

[0024] In one possible implementation, the sum of the light intensities of the two orthogonally linearly polarized components is calculated in the closed-loop control. When the sum is lower than a preset threshold, the control signal output is frozen, so that the polarization compensation element remains in the state of the previous moment. This step serves as a safety protection mechanism at the method level, preventing actuator malfunctions in low light or no light conditions, and ensuring the safety and stability of the method under abnormal operating conditions. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall structure of an active feedback polarization-maintaining fiber polarization stabilization device provided in this application.

[0026] The figure includes the following reference numerals: 1. Laser source module; 2. Polarization compensation module; 21. Rotatable half-wave plate; 22. Drive assembly; 3. Optical path transmission module; 31. Input-side fiber coupler; 32. Polarization-maintaining fiber; 33. Output-side fiber coupler; 4. Polarization detection module; 41. Beam splitter; 42. Quarter-wave plate; 43. Polarization beam splitter; 44. First photodetector; 45. Second photodetector; 5. Signal processing module; 6. Drive control module. Detailed Implementation

[0027] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0028] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0029] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly defined. The specific embodiments of this application will be further described in detail below with reference to the accompanying drawings.

[0030] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0031] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0032] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] Example 1: like Figure 1 As shown, this embodiment provides an active feedback polarization-maintaining fiber polarization stabilization device. The device includes: a laser source module 1, a polarization compensation module 2, an optical path transmission module 3, a polarization detection module 4, a signal processing module 5, and a drive control module 6.

[0034] Laser source module 1 is used to output linearly polarized laser light. The laser source can be a single-frequency laser, an external cavity semiconductor laser, or a fiber laser. The output wavelength is determined according to the actual application, such as 780nm, 795nm, 852nm, or 1064nm commonly used in cold atom experiments.

[0035] The polarization compensation module 2 is located before the input end of the optical path transmission module 3 (i.e., before the input-side fiber coupler 31) and is used to adjust the linear polarization direction of the laser incident on the polarization-maintaining fiber 32. The polarization compensation module 2 includes a rotatable half-wave plate 21 and a drive assembly 22 for driving the rotatable half-wave plate 21 to rotate. The drive assembly 22 is preferably a hollow motor. The rotatable half-wave plate 21 is mounted on the rotating support structure of the hollow motor. The laser propagates along the central through hole of the hollow motor, causing the rotatable half-wave plate 21 to rotate coaxially around the principal optical axis.

[0036] Set the angle between the input linear polarization direction and the x-axis of the laboratory coordinate system as: The rotatable half-wave plate 21 has an angle between its optical axis and the x-axis of 0°. The output linear polarization direction after passing through the rotatable half-wave plate 21 is... satisfy: (1) As can be seen from this formula, by adjusting the optical axis angle of the half-wave plate... This allows for continuous adjustment of the linear polarization direction of the laser incident on the polarization-maintaining fiber 32. The drive assembly 22 can also be a rotary driver capable of high-resolution angle control, such as a servo motor, stepper motor, or piezoelectric rotary actuator.

[0037] The optical path transmission module 3 includes an input-side fiber coupler 31, a polarization-maintaining fiber 32, and an output-side fiber coupler 33. The polarization-maintaining fiber 32 has two fixed intrinsic axes: a fast axis and a slow axis. In this embodiment, one of them (e.g., the slow axis) is pre-selected as the target intrinsic axis.

[0038] The angle between the incident ray polarization direction and the intrinsic axis of the polarization-maintaining fiber target is set to... Then the incident light field can be expressed as: (2) in This represents the intensity of the light field.

[0039] After transmission through polarization-maintaining fiber 32, due to the different propagation constants of the fast and slow axes, the two components accumulate a relative phase difference. The output light field is: (3) when At that time, the output is still linearly polarized light; when At this time, the incident light simultaneously excites the two intrinsic axis components of the polarization-maintaining fiber, and the output polarized light depends on the relative phase difference between the two intrinsic axis components. It usually appears as elliptically polarized light, but... In special cases, it manifests as linearly polarized light.

[0040] The polarization detection module 4 is located after the output fiber coupler 33 and includes: a beam splitter 41, a quarter-wave plate 42, a polarization beam splitter 43, a first photodetector 44, and a second photodetector 45.

[0041] The output light from the polarization-maintaining fiber 32 enters the beam splitter 41 after being output through the output-side fiber coupler 33. The beam splitter 41 is a polarization-independent beam splitter with a sampling ratio preferably between 1% and 10%, splitting the output light into a main beam (reflected light) and a detection beam (transmitted light). The main beam output is used for subsequent experiments, while the detection beam is input to the polarization detection link.

[0042] The detection light passes sequentially through a quarter-wave plate 42 and a polarizing beam splitter 43. Let the angle between the optical axis of the quarter-wave plate 42 and the x-axis of the laboratory coordinate system be θ. The light field of the laser output from the optical fiber after passing through a quarter-wave plate can be expressed as: (4) in, The Jones transfer matrix for a quarter-wave plate. and These represent the two orthogonal components of the light field.

[0043] The detection light is split into two orthogonal linearly polarized components by polarization beam splitter 43, which are received by the first photodetector 44 and the second photodetector 45 respectively, and the first light intensity signal is output. Second light intensity signal Their relationship with the orthogonal components of the light field is as follows: , (5) Signal processing module 5 receives and And construct a normalized differential error signal : (6) Since the instantaneous drift caused by various factors is extremely small, it can be approximated as... ,at this time , The error signal can be simplified as follows: (7) in This is a DC bias, and k is the slope. Therefore, for any angle... Error signals typically have a DC bias, therefore, in practical systems, the initial error signal at zero point needs to be determined through initialization calibration. Instead of assuming that the zero point must be at 0.

[0044] In a preferred embodiment of this example, the optical axis angle of the quarter-wave plate 42 is... Set to 45°. At this point, the normalized difference error signal simplifies to: (8) From equation (8), we can notice the error signal. Not only with It is related to, and also to, the relative phase difference. Relevant. Therefore, in In actual closed-loop control, error signals cannot be used as the basis for control. Using the zero point as the sole control basis, it is also necessary to determine the local feedback slope of the error signal near the target error signal as the polarization compensation module adjusts during the initialization calibration process, ensuring it remains within the effective feedback range. If ,when When =0, e=0, meaning the error signal is zero when the incident polarization is aligned with the intrinsic axis; when At that time, the error signal deviates from zero; when In When = 0, if right If the response is approximately linear and the absolute value of the local feedback slope is not lower than the required preset threshold, then the target point can be used as the error signal for closed-loop feedback control.

[0045] Signal processing module 5 also performs the following functions: Correct the background electrical signals of the two photodetectors in the absence of light; Determine the total light intensity Whether it is higher than the set threshold, when the total light intensity is lower than the threshold, pause the update of the control quantity and keep the current half-wave plate angle unchanged; A normalized differential error signal is constructed for the corrected optical intensity signal to reduce the impact of total optical power fluctuation on the feedback.

[0046] Initialization Calibration: The polarization detection module 4 and signal processing module 5 need to be initialized and calibrated before entering the closed-loop control process. This process requires adjusting the polarization direction of the incident line to the target's intrinsic axis and recording the target error signal value in this state. Specifically, the rotatable half-wave plate 21 in the polarization compensation module 2 is manually or automatically adjusted to scan the half-wave plate angle with a preset step size, and the real-time error signal value is recorded. Based on the zero-crossing point of the error signal, the extreme point of the error signal, or a preset criterion, the target angle corresponding to the target's intrinsic axis alignment state is determined, and the target error signal value in that state is recorded. .

[0047] It should be noted that the relative phase difference between the fast and slow axes of the polarization-maintaining fiber is affected by factors such as fiber length, temperature, stress, and bending state. The error signal does not necessarily correspond to the deviation of the incident polarization direction from the intrinsic axis in every operating state. Therefore, during the initial calibration process, when determining the target error signal value, it is also necessary to determine the local feedback slope of the error signal near that target error signal value as the polarization compensation module adjusts. When the local feedback slope is higher than a preset threshold (e.g., the absolute value of the local feedback slope is higher than a preset threshold), the error signal can be used for closed-loop adjustment of the incident polarization direction; when the local feedback slope is lower than a preset threshold, the system pauses closed-loop updates and requires re-execution of the initial calibration.

[0048] Therefore, the control error used in subsequent closed-loop control Defined as: (9) Drive control module 6 is used to adjust according to control error Generate control quantity The drive control module 6 drives the rotatable half-wave plate 21 in the polarization compensation module 2 to perform compensation adjustment. In this embodiment, the drive control module 6 preferentially uses a proportional-integral-derivative (PID) control algorithm to generate the control quantity. The control error is then... As the input to the PID controller, the control quantity Represented as: (10) in, , and These represent the proportional coefficient, integral coefficient, and differential coefficient, respectively.

[0049] Drive control module 6 will control the quantity The rotation angle command is converted into a drive component 22 (such as a hollow motor), causing the rotatable half-wave plate 21 to rotate, thereby correcting the linear polarization direction of the laser incident on the polarization-maintaining fiber 32.

[0050] Through the closed-loop feedback described above, the system can compensate in real time for polarization direction deviations caused by temperature changes, mechanical vibrations, or long-term drift, so that the incident polarization direction is stably locked on the target intrinsic axis of the polarization-maintaining fiber for a long time.

[0051] Compared with the prior art, this embodiment has the following beneficial effects: This application takes the continuous alignment of the linear polarization direction input to the polarization-maintaining fiber with the intrinsic axis direction of the polarization-maintaining fiber as the control target, and is applicable to application scenarios such as cold atom, quantum optics and precision measurement that require stable transmission of linearly polarized light through polarization-maintaining fiber.

[0052] This application sets up a polarization compensation module at the input end of the polarization-maintaining fiber and a polarization detection module at the output end, and forms a closed-loop feedback through a drive control module, which can actively compensate for polarization deviation caused by changes in ambient temperature, mechanical stress, mechanical vibration and long-term drift.

[0053] This application employs a normalized differential method for dual-path optical intensity signals to construct the error signal, which can reduce the impact of total optical power fluctuations on the feedback quantity and improve control stability during long-term operation. Especially... In the preferred embodiment, the error signal is simplified to The physical meaning is clear, and the zero point is well-defined.

[0054] This application uses a single rotatable half-wave plate as the actuator, which has a relatively simple structure and is easy to integrate and implement.

[0055] This application introduces an initialization calibration mechanism (Equation 9) to... As a locking reference, it eliminates the influence of device installation deviations and non-ideal factors, improving the applicability and control accuracy of the actual system.

[0056] Example 2: This embodiment provides an active feedback polarization-maintaining fiber polarization stabilization method, which can be implemented based on the device described in Embodiment 1, to continuously align the linear polarization direction incident on the polarization-maintaining fiber with a pre-selected target intrinsic axis as the control target. The method includes an initialization calibration stage and a closed-loop operation stage, with the specific steps as follows: Step 1: Select the target intrinsic axis Select one of the intrinsic axes (fast axis or slow axis) of the polarization-maintaining fiber as the target intrinsic axis.

[0057] Step 2: Background Correction The background electrical signals of the first and second photodetectors in the absence of light are collected, and background correction is performed on the subsequently collected light intensity signals.

[0058] Step 3: Half-wave plate scanning The rotatable half-wave plate in the polarization compensation module is manually or automatically adjusted to scan the half-wave plate angle with a preset step size, while the normalized differential error signal is calculated in real time. =( / ( ).

[0059] Step 4: Determine the target error signal value Based on the zero-crossing point, extreme point, or preset criterion of the error signal, determine the target angle corresponding to the target's intrinsic axis alignment state, and record the target error signal value in that state. For example, when the optical axis of the quarter-wave plate is 45°, the error signal is within the effective feedback range. The zero-crossing point can be used as one of the criteria for determining whether the target is in alignment.

[0060] Step 5: Enter closed-loop control After completing the above initialization calibration, the system enters the closed-loop operation phase, using the deviation between the real-time error signal and the target error signal value as the basis for measurement. As a control error.

[0061] Step Six: Real-time Acquisition and Correction Real-time acquisition of first light intensity signal Second light intensity signal And perform background correction on the acquired signals.

[0062] Step 7: Determining the effectiveness of total light intensity Calculate total light intensity = .like If the value is below the preset threshold, the current control value remains unchanged and the next acquisition cycle begins (i.e., the control output is frozen); if the value is above the threshold, the subsequent steps continue.

[0063] Step 8: Calculate the real-time error signal Calculate the current normalized differential error signal =( ) / ( Then calculate the control error according to equation (9). .

[0064] Step 9: Generate control variables and execute them. The drive control module determines the control error. Generate control quantity This embodiment uses a PID control algorithm to calculate the control quantity according to equation (10). Control quantity The command is converted into a rotation angle command for the drive component, which drives the rotatable half-wave plate to rotate in order to correct the linear polarization direction incident on the polarization-maintaining fiber.

[0065] Step 10: Repeat the closed loop Repeat steps six through nine to form a continuously operating closed-loop feedback control, ensuring that the linear polarization direction of the incident laser is stably aligned with the target intrinsic axis of the polarization-maintaining fiber over a long period of time.

[0066] Using the above method, the system can automatically compensate for polarization deviation when the external environment changes (temperature, vibration, etc.), so that the incident polarization direction is locked stably on the target intrinsic axis of the polarization-maintaining fiber for a long time.

[0067] Other implementation methods Those skilled in the art will understand that the above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. For example: The drive component can be replaced with a servo motor, stepper motor, piezoelectric rotary actuator, or other rotary drive mechanism with precise angle adjustment capability.

[0068] The half-wave plate can be replaced with a zero-order half-wave plate, an achromatic half-wave plate, or a composite half-wave plate.

[0069] The beam splitter can be replaced with other polarization-independent sampling elements, such as non-polarizing beam splitters, wedge-shaped sampling plates, etc.

[0070] The installation angle of the quarter-wave plate in the polarization detection module can be optimized according to the linear region of the working point, and is not limited to 45°; the polarization beam splitter can also be replaced by a combination of polarizers with equivalent separation function.

[0071] The selected target intrinsic axis can be either the fast axis or the slow axis.

[0072] The PID control algorithm can be replaced by PI control, adaptive control algorithm, or other control methods that can achieve closed-loop correction based on the error signal.

[0073] This application applies to both continuous lasers and pulsed lasers.

[0074] Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this application shall be included within the scope of protection of this application.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions for some or all of the technical features, do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An active feedback polarization-maintaining fiber polarization stabilization device, characterized in that, include: A polarization compensation module (2) is disposed before the input end of the polarization-maintaining fiber (32) and is used to adjust the linear polarization direction of the laser incident on the polarization-maintaining fiber (32). The polarization detection module (4) is located after the output end of the polarization-maintaining fiber (32) and is used to convert the output laser of the polarization-maintaining fiber (32) into a multi-channel light intensity signal related to the polarization state. The signal processing and control module is connected to the polarization detection module (4) and the polarization compensation module (2) respectively. It is used to generate a normalized error signal based on the multi-channel light intensity signal, and generate a control signal based on the difference between the error signal and the target error signal value, so as to drive the polarization compensation module (2) to adjust the linear polarization direction of the incident laser in a closed loop, so that it is continuously aligned with the preset intrinsic axis of the polarization-maintaining fiber (32).

2. The active feedback polarization-maintaining fiber polarization stabilization device according to claim 1, characterized in that, The polarization compensation module (2) includes a rotatable half-wave plate and a drive assembly (22) for driving the half-wave plate to rotate. The drive component (22) is any one of a hollow motor, a servo motor, a stepper motor, or a piezoelectric rotary actuator.

3. The active feedback polarization-maintaining fiber polarization stabilization device according to claim 1, characterized in that, The polarization detection module (4) includes: The beam splitting element is used to split the output laser of the polarization-maintaining fiber (32) into a main optical path and a detection optical path; A quarter-wave plate (42) is disposed on the detection optical path; A polarization beam splitter (43) is disposed after the quarter-wave plate (42) to split the light beam of the detection optical path into two orthogonal linearly polarized beams; The first photodetector (44) and the second photodetector (45) are respectively used to receive the two orthogonal linearly polarized beams and convert them into a first light intensity signal and a second light intensity signal.

4. The active feedback polarization-maintaining fiber polarization stabilization device according to claim 3, characterized in that, The signal processing and control module includes a signal processing unit and a drive control unit; The signal processing unit is used to calculate the normalized error signal, which is the difference between the first light intensity signal and the second light intensity signal divided by the sum of the two. The drive control unit is used to generate the control signal based on the difference between the error signal and the target error signal value.

5. The active feedback polarization-maintaining fiber polarization stabilization device according to claim 1, characterized in that, The signal processing and control module is also used to perform initialization calibration: In the initial alignment state, the value of the normalized error signal at this time is recorded as the target error signal value, and the local feedback slope of the error signal near the target error signal value as the polarization compensation module adjusts is detected. When the local feedback slope meets the preset threshold condition, the deviation between the real-time error signal and the target error signal value is used as the control basis in the subsequent closed-loop control.

6. The active feedback polarization-maintaining fiber polarization stabilization device according to claim 1, characterized in that, The signal processing and control module further includes a total light intensity judgment unit, which is used to detect the sum of the multiple light intensity signals. When the sum is lower than a preset threshold, the control signal is paused to maintain the current state of the polarization compensation module (2).

7. The active feedback polarization-maintaining fiber polarization stabilization device according to claim 1, characterized in that, The signal processing and control module uses any one of the proportional-integral-derivative control algorithm, proportional-integral control algorithm, or adaptive control algorithm to generate the control signal.

8. An active feedback polarization-maintaining fiber polarization stabilization method, characterized in that, Includes the following steps: Initialization calibration steps: Adjust the linear polarization direction of the laser incident on the polarization-maintaining fiber (32) so that it is aligned with the preset intrinsic axis of the polarization-maintaining fiber (32), and detect the polarization state of the laser output by the polarization-maintaining fiber (32) at this time, and record the target error signal value corresponding to the polarization state. Closed-loop control steps: Real-time detection of the polarization state of the laser output from the polarization-maintaining fiber (32), generation of a normalized real-time error signal, and using the difference between the real-time error signal and the target error signal as the control error; Feedback adjustment step: Generate a control signal based on the control error, drive the polarization compensation element set before the input end of the polarization-maintaining fiber (32) to close the loop and correct the linear polarization direction of the incident laser, so that it is continuously aligned with the preset intrinsic axis.

9. The active feedback polarization-maintaining fiber polarization stabilization method according to claim 8, characterized in that, The generation of the normalized real-time error signal includes: The output laser of the polarization-maintaining fiber (32) is decomposed into two orthogonal linearly polarized components; The light intensities of the two orthogonally linearly polarized components are detected respectively to obtain a first light intensity signal and a second light intensity signal; The normalized real-time error signal is calculated by dividing the difference between the first light intensity signal and the second light intensity signal by the sum of the two.

10. The active feedback polarization-maintaining fiber polarization stabilization method according to claim 8, characterized in that, The closed-loop control steps also include a total light intensity effectiveness determination: The sum of the light intensity signals of the two orthogonally linearly polarized components is calculated. When the sum is lower than a preset threshold, the current control signal output is frozen, so that the polarization compensation element remains in the state of the previous moment.

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