Low-polarization high-precision laser power attenuator and method

Abstract

The application discloses a low-polarization high-precision laser power attenuator, which comprises a fixing frame and is integrated with a polarization element, first and second polarization beam splitting elements arranged in quadrature, a driving unit, an angle measuring unit and a controller. The detection end of the angle measuring unit is rigidly connected with the rotating shaft of the output end of the driving unit in a coaxial manner, and the controller carries out closed-loop control on the driving unit according to the actual rotation angle fed back by the angle measuring unit. Through the organic combination of the double-quadrature polarization beam splitting structure and the direct angle feedback of the load end, the s light and the p light are attenuated at the same ratio, the defects of the single-Brewster window piece scheme, such as serious polarization dependence and high polarization-dependent loss, are solved from the root, meanwhile, the precision-polarization mutual restraint problem caused by the coupling of the transmission chain error and the polarization characteristics is eliminated, and the high-precision, high-stable and continuous adjustable attenuation of the laser power is realized under the condition of low polarization-dependent loss.

Description

Technical Field

[0001] This invention belongs to the field of laser technology and relates to a low-polarization, high-precision laser power attenuator and method. Background Technology

[0002] In high-end applications such as high-precision laser processing and precision optoelectronic detection, the polarization stability and low polarization-dependent loss of the output beam of the laser attenuator directly determine the processing uniformity and measurement accuracy. Therefore, low polarization dependence has become a core indicator of high-end attenuators.

[0003] Currently, polarization laser attenuators generally adopt a "half-wave plate + Brewster window" structure. By rotating the half-wave plate, the polarization direction of the incident light entering the Brewster window is changed, thereby achieving continuous adjustment of the transmitted power. Existing polarization laser attenuators include a half-wave plate, a single Brewster window, a stepper motor, a reduction gear transmission mechanism, a motor shaft encoder, and a control unit. During operation, the control unit calculates the target rotation angle of the half-wave plate based on the target power, drives the motor to rotate the half-wave plate via the reduction gear transmission mechanism, and then achieves power attenuation via the single Brewster window. The motor shaft encoder detects the motor shaft rotation angle and feeds it back to the control unit, forming an indirect closed-loop control.

[0004] However, this solution has the following prominent problems in practical applications: 1. Severe polarization dependence and high polarization-dependent loss: The fundamental reason is that only a single Brewster window is used in the optical path. The Brewster window works based on Brewster's law and only achieves high transmission for the p-polarized component, while the s-polarized component is partially reflected. This causes the s-light and p-light in the outgoing beam to not attenuate proportionally. The output polarization state will change with the amount of attenuation. In the entire dynamic range, the polarization-dependent loss introduced by this structure is always maintained at a high level, which is difficult to meet the stringent requirements of low polarization sensitive scenarios.

[0005] 2. Polarization dependence is coupled with transmission error, making it difficult to simultaneously achieve both power regulation accuracy and polarization stability: The inherent polarization dependence of the single Brewster window is not isolated; its influence is amplified with increasing attenuation. In practical systems, the reduction gear mechanism inevitably suffers from transmission chain errors such as backlash, hysteresis, and elastic deformation. The indirect feedback method of the encoder at the motor shaft end cannot accurately reflect the actual rotation angle of the half-wave plate, resulting in a non-negligible control error in the half-wave plate angle. This mechanical error, transmitted through the polarization sensitivity of the single Brewster window, not only directly causes power control deviations but also creates additional disturbances in the polarization state, forming a deep coupling between polarization and accuracy. Ultimately, during power regulation, polarization stability and power control accuracy are mutually constrained, making it impossible to simultaneously meet the comprehensive performance requirements of high precision, high stability, and low polarization.

[0006] In summary, the fundamental flaw of existing polarization attenuators lies in the inherent polarization dependence introduced by a single Brewster window. This flaw directly leads to high polarization-dependent losses and further couples with transmission chain errors, causing a technical dilemma where accuracy and polarization stability are difficult to balance, which severely restricts their application in high-end precision systems. Summary of the Invention

[0007] The purpose of this invention is to address the aforementioned problems in existing technologies by proposing a low-polarization, high-precision laser power attenuator and method. This solves the technical problem mentioned in the background art, where the inherent polarization dependence of existing polarization laser attenuators using a single Brewster window leads to high polarization-dependent losses and deep coupling with transmission chain errors, ultimately resulting in the inability to simultaneously meet the requirements of high-precision systems in terms of power control accuracy and polarization stability over a wide attenuation range.

[0008] The objective of this invention can be achieved through the following technical solutions: A high-precision laser power attenuator with low polarization includes a mounting frame, on which the following are integrated: The laser power attenuation unit includes polarization elements that receive incident laser light arranged coaxially along the optical path, a first polarization beam splitter and a second polarization beam splitter for selectively transmitting or reflecting polarized light modulated by the polarization elements, wherein the second polarization beam splitter and the first polarization beam splitter are orthogonally arranged. The drive unit has its power output end connected to the polarization element and coaxially arranged; An angle measuring unit, whose detection end is rigidly connected coaxially to the rotating shaft of the power output end, is used to directly acquire the actual rotation angle of the polarization element; The controller is electrically connected to the angle measuring unit and the drive unit respectively, and is configured to perform closed-loop control of the drive unit based on the actual rotation angle fed back by the angle measuring unit, so that the polarization element reaches the target rotation angle.

[0009] By integrating polarization elements, orthogonally arranged first and second polarization beam splitting elements, driving unit, and angle measurement unit that is rigidly connected to the detection end and the rotating shaft on a fixed frame, and using the controller to perform closed-loop control of the driving unit based on the actual rotation angle directly fed back, two orthogonally arranged Brewster windows are coaxially arranged in the laser attenuation optical path and used in conjunction with the front half-wave plate to achieve proportional attenuation of s-rays and p-rays in the incident beam, effectively suppressing the change of output polarization state with the attenuation adjustment amount, and significantly reducing polarization-related losses across the entire adjustment range; Compared to the existing technology that uses a single Brewster window with indirect feedback from the motor shaft, this invention fundamentally solves the problem of high polarization-dependent loss caused by severe polarization dependence. At the same time, it eliminates the polarization coupling effect caused by the amplification of transmission chain errors through polarization-sensitive links, laying a structural foundation for achieving low polarization, high precision, and high stability laser power attenuation simultaneously.

[0010] Preferably, a Brewster window mounting bracket is installed on the mounting frame, and the first polarization beam splitter includes a first Brewster window and a first Brewster window clamping plate, wherein the first Brewster window is mounted on the Brewster window mounting bracket via the first Brewster window clamping plate; The second polarization beam splitter includes a second Brewster window and a second Brewster window clip. The second Brewster window is mounted on a Brewster window holder via the second Brewster window clip and is orthogonal to the first Brewster window.

[0011] Preferably, the Brewster window plate holder is connected to the mounting bracket via at least one set screw, and the working angles of the first and second Brewster window plates can be adjusted and locked by turning the set screw.

[0012] In a double-orthogonal Brewster window optical path, the relative orthogonality accuracy of the two windows and the accuracy of their respective incident angles relative to the optical axis directly determine the polarization compensation effect. Precise adjustment and locking via a set-wire structure ensures that the first and second Brewster windows precisely meet the orthogonality relationship and Brewster angle incident conditions during assembly and debugging, thereby ensuring that the design performance of the low polarization attenuation optical path is fully realized.

[0013] Preferably, the drive unit includes a stepper motor and a transmission mechanism; The transmission mechanism includes a driving pulley, a driven pulley, and a transmission belt. The driving pulley is mounted on the output shaft of the stepper motor. The stepper motor is fixed to one end of the fixed frame. The rotating shaft is fixed to one end of the driven pulley. A bearing is sleeved on the rotating shaft and fixed to the fixed frame. The transmission belt is sleeved and engaged between the driving pulley and the driven pulley.

[0014] Preferably, the polarizing element is a half-wave plate, which is rigidly fixed to the driven pulley at the end away from the fixed frame by a half-wave plate retainer.

[0015] Preferably, an annular block is fixed to one end of the driven pulley near the fixed frame, and a stop ring is fitted onto the annular block.

[0016] By setting a stop ring to provide reliable axial limit for the driven pulley and its shaft assembly, the axial movement of the rotating mechanism is prevented from occurring during long-term operation or under vibration. This ensures the long-term stability of the coaxial rigid connection between the angle sensor and the polarization element shaft in the angle measurement unit, thereby ensuring that the closed-loop control accuracy does not decrease due to axial displacement.

[0017] Preferably, the angle measuring unit includes a circular grating and a circular grating reading head, the circular grating being sleeved and fixed to the end of the rotating shaft, and the circular grating reading head being fixed to the mounting bracket.

[0018] A laser power attenuation method based on the above-mentioned low-polarization high-precision laser power attenuator includes the following steps: S1: Obtain the target rotation angle of the polarization element corresponding to the target laser power; S2: The driving unit drives the polarization element to rotate according to the control signal; S3: The actual rotation angle of the polarization element is obtained in real time by an angle measuring unit directly set on the rotation axis of the polarization element; S4: Compare the actual rotation angle with the target rotation angle to generate an error signal; S5: Adjust the control of the drive unit according to the error signal so that the actual rotation angle approaches the target rotation angle, thereby realizing closed-loop control of the output laser power.

[0019] Furthermore, the polarization element is a half-wave plate, and the attenuation is achieved through a Brewster window. In step S2, by controlling the rotation angle of the half-wave plate, the polarization direction of the laser incident on the Brewster window is continuously changed, and the laser power is continuously adjusted according to Malus's law.

[0020] The laser beam sequentially passes through a transmission optical path consisting of a motor-driven half-wave plate, a first Brewster window, and a second Brewster window. The half-wave plate is used to adjust the polarization direction of the incident laser in real time. The two orthogonally arranged Brewster windows form a low-polarization-attenuation optical path, utilizing the polarization-selective transmission characteristics of the Brewster angle to proportionally control the transmission of lasers with different polarization components. This invention achieves continuously adjustable attenuation of laser output power by precisely controlling the rotation angle θ of the half-wave plate, combined with the polarization compensation characteristics of the double orthogonal Brewster optical path, based on Malus's law, while suppressing changes in polarization state with attenuation, thus achieving high-precision, low-polarization-loss laser power control.

[0021] The main technical effects of this invention are reflected in the following aspects: 1. This invention employs a double orthogonal polarization beam splitting structure composed of a first polarization beam splitting element and a second polarization beam splitting element orthogonally arranged, replacing the single Brewster window scheme in the prior art. This structure allows the s-polarization component and p-polarization component in the incident laser to undergo symmetrical transmission and reflection processes in the two orthogonal beam splitting elements, achieving equal attenuation of the two orthogonal polarization components. This effectively suppresses the inherent defect of the output polarization state changing with the attenuation adjustment, significantly reducing polarization-related losses across the entire dynamic range, and meeting the stringent requirements of high-precision polarization-sensitive applications.

[0022] 2. This invention rigidly connects the detection end of the angle measurement unit to the rotation axis of the polarization element, forming a direct angle feedback closed loop at the load end. This configuration can directly acquire the actual rotation angle of the polarization element, truly reflecting the spatial orientation of the optical modulation element. It fundamentally avoids the influence of transmission chain errors such as transmission mechanism gaps, hysteresis, and elastic deformation on the angle control accuracy. Since the dual orthogonal polarization beam splitting structure of this invention has eliminated the inherent polarization-sensitive amplification link of the system, the residual small angle error is no longer amplified by the polarization-dependent characteristics and transformed into a significant polarization state disturbance. This cuts off the mutual constraint relationship between polarization characteristics and power control accuracy, and achieves a synergistic improvement in polarization stability and control accuracy.

[0023] 3. This invention, through the synergistic effect of direct angle closed-loop at the load end and double orthogonal low polarization optical path, suppresses the angle drift of polarization element caused by factors such as wear of transmission mechanism and temperature change, and eliminates the inherent mechanism of polarization state drift with attenuation. It suppresses polarization drift and power accuracy drift from the source, ensures the performance stability of attenuator under long-term continuous operation conditions, and effectively reduces system calibration frequency and maintenance cost. Attached Figure Description

[0024] Figure 1 This is a structural schematic diagram of an embodiment of the present invention. Figure 1 ; Figure 2 This is a schematic diagram of the exploded structure according to an embodiment of the present invention; Figure 3 This is a structural schematic diagram of an embodiment of the present invention. Figure 2 ; Figure 4 This is a partial structural schematic diagram of an embodiment of the present invention; Figure 5 This is a schematic diagram illustrating the working principle of laser attenuation in an embodiment of the present invention.

[0025] Explanation of reference numerals in the attached drawings: 1. Fixing bracket; 11. Controller; 12. Brewster window plate holder; 121. Set screw; 2. Polarizing element; 21. Half-wave plate; 22. Half-wave plate retainer ring; 3. First polarizing beam splitter; 31. First Brewster window; 32. First Brewster window clip; 4. Second polarizing beam splitter; 41. Second Brewster window; 42. Pressed sheet of second Brewster window; 5. Stepper motor; 51. Driving pulley; 52. Driven pulley; 53. Drive belt; 54. Shaft; 541. Bearing; 55. Annular block; 551. Retaining ring; 6. Circular grating; 61. Circular grating readout head. Detailed Implementation

[0026] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings to further illustrate the technical solutions of the present invention. However, the present invention is not limited to these embodiments.

[0027] like Figure 1-3 As shown, a high-precision laser power attenuator with low polarization includes a mounting bracket 1, on which the following are integrated: The laser power attenuation unit includes a polarization element 2 for receiving incident laser light arranged coaxially along the optical path, a first polarization beam splitter 3 and a second polarization beam splitter 4 for selectively transmitting or reflecting polarized light modulated by the polarization element 2, wherein the second polarization beam splitter 4 and the first polarization beam splitter 3 are orthogonally arranged. The drive unit has its power output end connected to the polarization element 2 and coaxially arranged; An angle measuring unit, whose detection end is rigidly connected to the rotating shaft 54 ​​of the power output end, is used to directly acquire the actual rotation angle of the polarization element 2; The controller 11 is electrically connected to the angle measuring unit and the drive unit respectively, and is configured to perform closed-loop control of the drive unit based on the actual rotation angle fed back by the angle measuring unit, so that the polarization element 2 reaches the target rotation angle.

[0028] Reference Figure 4 The fixing frame 1 is equipped with a Brewster window plate fixing seat 12. The first polarization beam splitter 3 includes a first Brewster window plate 31 and a first Brewster window plate pressing sheet 32. The first Brewster window plate 31 is mounted on the Brewster window plate fixing seat 12 through the first Brewster window plate pressing sheet 32. The second polarization beam splitter 4 includes a second Brewster window 41 and a second Brewster window clip 42. The second Brewster window 41 is mounted on the Brewster window holder 12 via the second Brewster window clip 42 and is orthogonally arranged to the first Brewster window 31.

[0029] Reference Figure 1 , 4The Brewster window plate fixing seat 12 is connected to the fixing frame 1 by at least one set screw 121. The working angle of the first Brewster window plate 31 and the second Brewster window plate 41 can be adjusted and locked by turning the set screw 121.

[0030] like Figure 1-2 As shown, the drive unit includes a stepper motor 5 and a transmission mechanism; The transmission mechanism includes a driving pulley 51, a driven pulley 52, and a transmission belt 53. The driving pulley 51 is mounted on the output shaft of the stepper motor 5. The stepper motor 5 is fixed to one end of the fixed frame 1. The rotating shaft 54 ​​is fixed to one end of the driven pulley 52. ​​A bearing 541 is sleeved on the rotating shaft 54 ​​and fixed to the fixed frame 1. The transmission belt 53 is sleeved and engaged between the driving pulley 51 and the driven pulley 52. ​​The polarizing element 2 is a half-wave plate 21. The half-wave plate 21 is rigidly fixed to the end of the driven pulley 52 away from the fixed frame 1 by a half-wave plate pressure ring 22. The half-wave plate 21 and the driven pulley 52 are coaxially and rigidly fixed together to form an integrated polarization adjustment rotation assembly, which reduces the overall rotational inertia of the moving assembly and adapts to the requirements of rapid polarization adjustment of the optical path. The half-wave plate 21 can be replaced by components with polarization direction control functions such as Faraday rotators and liquid crystal tunable waveplates.

[0031] Reference Figure 1 , 2 An annular block 55 is fixed to one end of the driven pulley 52 near the fixed frame 1, and a stop ring 551 is sleeved on the annular block 55. The stop ring 551 provides reliable axial limiting for the driven pulley 52 and its shaft 54 ​​assembly, preventing axial movement of the rotating mechanism under long-term operation or vibration environment, ensuring the long-term stability of the coaxial rigid connection between the angle sensor and the shaft 54 ​​of the polarization element 2 in the angle measurement unit, and thus ensuring that the closed-loop control accuracy does not decrease due to axial displacement.

[0032] The angle measuring unit includes a circular grating 6 and a circular grating reading head 61. The circular grating 6 is sleeved and fixed to the end of the rotating shaft 54, and the circular grating reading head 61 is fixed to the mounting bracket 1. The circular grating 6 can be replaced by angle detection elements that maintain direct feedback function at the load end, such as a high-precision magnetic grating encoder or a laser interferometric angle sensor.

[0033] The working principle of this invention is as follows: The incident laser first passes through a rotatable half-wave plate 21, the function of which is to rotate the polarization direction of the linearly polarized light passing through it.

[0034] Subsequently, the polarization-modulated laser light is incident at a specific angle onto a fixed first Brewster window 31. According to optical principles, when light is incident at a Brewster angle, light with vibration directions parallel to the incident surface is almost completely transmitted, while light with vibration directions perpendicular to the incident surface is mostly reflected. The first Brewster window 31 acts as an efficient polarization selector, performing initial selective transmission and reflection of the two orthogonal polarization components in the incident light.

[0035] The laser light, after being transmitted through the first Brewster window 31, continues to be incident on the second Brewster window 41, which is orthogonal to the first Brewster window 31. Since the transmission axes of the two Brewster windows are orthogonal, the polarization component preferentially transmitted in the first stage will be preferentially reflected in the second stage; conversely, the polarization component preferentially reflected in the first stage will be preferentially transmitted in the second stage. Thus, the s-polarization and p-polarization components of the incident laser undergo symmetrical and complementary transmission and reflection processes in the two orthogonal Brewster windows, ultimately achieving proportional attenuation of the two orthogonal polarization components.

[0036] Ultimately, the laser power transmitted from the second Brewster window 41 depends on the angle between the incident light polarization direction and the transmission axis of the Brewster window, and the output laser power is continuously adjusted according to Malus's law. Throughout the attenuation adjustment range, the polarization state of the output laser remains stable, and polarization-dependent losses are significantly reduced.

[0037] The controller 11 receives the target power command and, based on the mathematical model of Malus's law, converts the target power into the target rotation angle that the half-wave plate 21 needs to achieve.

[0038] The controller 11 sends a pulse signal to the stepper motor 5, which rotates. The torque is transmitted through the synchronous belt drive mechanism, driving the half-wave plate 21, which is rigidly connected to the driven pulley 52, to rotate, thereby modulating the polarization direction of the incident laser.

[0039] The angle measuring unit is rigidly connected coaxially to the rotating shaft 54 ​​of the half-wave plate 21, directly measuring the actual angle of rotation of the half-wave plate 21 around its optical axis. This angle signal comes directly from the load itself, completely avoiding errors such as elastic deformation, slight slippage, or backlash that may exist in the entire synchronous belt drive chain from the motor shaft to the half-wave plate 21.

[0040] The angle measurement unit feeds back the detected actual angle value to the controller 11 in real time. The closed-loop control algorithm inside the controller 11 calculates the error signal between the target angle and the actual feedback angle, and dynamically adjusts the drive signal sent to the stepper motor 5 according to the error signal to control the motor to perform compensatory rotation until the error between the actual feedback angle and the target angle approaches zero, thus completing a complete closed-loop control cycle.

[0041] The system operates continuously, ensuring that the half-wave plate 21 is always driven and stabilized at the precise angle required by theoretical calculations. Through the proportional attenuation characteristics of the optical path of the double orthogonal Brewster window, high precision, high repeatability, and long-term stable control of laser power are achieved under low polarization correlation loss conditions.

[0042] like Figure 5 As shown, a high-precision laser power attenuation method based on low polarization includes the following steps: S1: Obtain the target rotation angle of the polarization element 2 corresponding to the target laser power; S2: The driving unit drives the polarization element 2 to rotate, so that the incident laser is modulated by the polarization element 2 and then sequentially incident on the orthogonally arranged first polarization beam splitter 3 and second polarization beam splitter 4. The transmission of different polarization components is proportionally controlled by the double orthogonal polarization beam splitter structure. S3: The actual rotation angle of the polarization element 2 is directly acquired in real time through an angle measuring unit that is rigidly connected to the rotation axis 54 of the polarization element 2 on the same axis. S4: Compare the actual rotation angle with the target rotation angle to generate an error signal; S5: The driving unit is closed-loop adjusted according to the error signal to make the actual rotation angle approach the target rotation angle, thereby achieving continuous adjustable attenuation of laser power under low polarization correlation loss.

[0043] like Figure 5 As shown in the figure, the optical attenuation principle of the laser power attenuator of the present invention is illustrated symbolically. The laser beam passes sequentially through a path consisting of a half-wave plate 21 driven by a motor, a first Brewster window 31, and a second Brewster window 41. The half-wave plate 21 is used to rotate the polarization direction of the incident laser; the first Brewster window 31 and the second Brewster window 41 are orthogonally arranged, together forming a double orthogonal polarization beam splitter structure. This structure is based on the selective transmission characteristics of the Brewster angle for light rays with different polarization directions, causing the s-polarization component and p-polarization component of the incident laser to undergo symmetrical and complementary transmission and reflection processes in the two orthogonal beam splitter elements, achieving proportional attenuation of the two orthogonal polarization components. The figure visually demonstrates the principle of continuously adjusting the output laser power according to Malus's law by precisely controlling the rotation angle of the half-wave plate 21, while simultaneously suppressing changes in polarization state with attenuation and achieving low polarization-related loss.

[0044] Of course, the above are just typical examples of this application. In addition, this application may have many other specific implementation methods. All technical solutions formed by equivalent substitution or equivalent transformation fall within the scope of protection claimed in this application.

Claims

1. A high-precision laser power attenuator with low polarization, comprising a mounting bracket (1), characterized in that, The fixing frame (1) integrates: The laser power attenuation unit includes a polarization element (2) for receiving incident laser light arranged coaxially along the optical path, a first polarization beam splitter (3) and a second polarization beam splitter (4) for selectively transmitting or reflecting polarized light modulated by the polarization element (2), wherein the second polarization beam splitter (4) and the first polarization beam splitter (3) are orthogonally arranged. The drive unit, whose power output end is connected to the polarization element (2) and coaxially arranged; An angle measuring unit, whose detection end is rigidly connected to the rotating shaft (54) of the power output end, is used to directly collect the actual rotation angle of the polarization element (2); The controller (11) is electrically connected to the angle measuring unit and the drive unit respectively, and is configured to perform closed-loop control on the drive unit according to the actual rotation angle fed back by the angle measuring unit, so that the polarization element (2) reaches the target rotation angle.

2. The low-polarization, high-precision laser power attenuator according to claim 1, characterized in that, The mounting bracket (1) is equipped with a Brewster window plate holder (12). The first polarization beam splitter (3) includes a first Brewster window plate (31) and a first Brewster window plate clamping plate (32). The first Brewster window plate (31) is mounted on the Brewster window plate holder (12) through the first Brewster window plate clamping plate (32). The second polarization beam splitter (4) includes a second Brewster window (41) and a second Brewster window clip (42). The second Brewster window (41) is mounted on the Brewster window holder (12) via the second Brewster window clip (42) and is orthogonal to the first Brewster window (31).

3. The low-polarization, high-precision laser power attenuator according to claim 2, characterized in that, The Brewster window plate holder (12) is connected to the mounting bracket (1) via at least one set screw (121). By turning the set screw (121), the working angles of the first Brewster window plate (31) and the second Brewster window plate (41) can be adjusted and locked.

4. The low-polarization, high-precision laser power attenuator according to claim 1, characterized in that, The drive unit includes a stepper motor (5) and a transmission mechanism; The transmission mechanism includes a driving pulley (51), a driven pulley (52), and a transmission belt (53). The driving pulley (51) is mounted on the output shaft of the stepper motor (5). The stepper motor (5) is fixed to one end of the fixed frame (1). The rotating shaft (54) is fixed to one end of the driven pulley (52). A bearing (541) is sleeved on the rotating shaft (54). The bearing (541) is fixed on the fixed frame (1). The transmission belt (53) is sleeved and meshed between the driving pulley (51) and the driven pulley (52).

5. A high-precision laser power attenuator with low polarization according to claim 4, characterized in that, The polarization element (2) is a half-wave plate (21), which is rigidly fixed to the driven pulley (52) at one end away from the fixed frame (1) by a half-wave plate pressure ring (22).

6. A high-precision laser power attenuator with low polarization according to claim 4, characterized in that, The driven pulley (52) has an annular block (55) fixed at one end near the fixed frame (1), and a stop ring (551) is fitted on the annular block (55).

7. A high-precision laser power attenuator with low polarization according to claim 4, characterized in that, The angle measuring unit includes a circular grating (6) and a circular grating reading head (61). The circular grating (6) is sleeved and fixed to the end of the rotating shaft (54), and the circular grating reading head (61) is fixed to the fixing frame (1).

8. A high-precision laser power attenuation method based on low polarization, applied to a high-precision laser power attenuator with low polarization as described in any one of claims 1-7, characterized in that, Includes the following steps: S1: Obtain the target rotation angle of the polarization element (2) corresponding to the target laser power; S2: The driving unit drives the polarization element (2) to rotate, so that the incident laser is modulated by the polarization element (2) and then sequentially incident on the first polarization beam splitter (3) and the second polarization beam splitter (4) set orthogonally. The transmission of different polarization components is proportionally controlled by the double orthogonal polarization beam splitter structure. S3: The actual rotation angle of the polarization element (2) is directly acquired in real time through an angle measuring unit that is rigidly connected to the rotation axis (54) of the polarization element (2) on the same axis. S4: Compare the actual rotation angle with the target rotation angle to generate an error signal; S5: The driving unit is closed-loop adjusted according to the error signal to make the actual rotation angle approach the target rotation angle, thereby achieving continuous adjustable attenuation of laser power under low polarization correlation loss.

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