An adjustment tool for an electric polarization controller

Abstract

The utility model discloses an electric polarization controller's assembly and adjustment tool, including bottom plate (1) and from left to right setting left side optical fiber fixed pressure block (2), lower cover fixed recess (4) and right side optical fiber fixed pressure block (5) on the bottom plate (1) upper surface in proper order, along the bottom plate (1) center line and be engraved with optical fiber positioning auxiliary line (3). The utility model has the advantages of: aiming at the position problem when optical fiber is placed, and the EPC both ends optical fiber is fixed through the optical fiber fixed pressure block of assembly and adjustment tool both sides respectively, realizes the calibration of optical fiber placement position levelness.

Description

Technical Field

[0001] This utility model belongs to the field of quantum communication and quantum measurement, and specifically relates to an assembly and adjustment fixture for an electric polarization controller. Background Technology

[0002] The electric polarization controller (EPC) is an important type of polarization controller. It uses piezoelectric ceramics to compress single-mode optical fibers, causing them to produce a stress birefringence effect. By changing the magnitude of the applied voltage to the piezoelectric ceramics, the compressive force of the piezoelectric ceramics on the single-mode optical fibers is changed, thereby controlling the birefringence effect of the single-mode optical fibers and ultimately controlling the polarization state of light in the optical fiber.

[0003] Existing electric polarization controllers such as Figure 1 As shown, it mainly consists of piezoelectric ceramic 16, optical fiber underblock 18, single-mode optical fiber 19, EPC upper cover 15, EPC lower cover 17, and data processing board 23. Its assembly process is as follows: 1. Assembly of EPC cover 15: Attach the piezoelectric ceramic 16 to the inside of EPC cover 15 and solder its wires to the data processing board 23 accordingly; 2. Preparation of EPC lower cover 17: Install the fiber optic pressure block 18 onto the EPC lower cover 17; 3. Placement of single-mode fiber 19: Clean the bare single-mode fiber, straighten it manually, and then attach the single-mode fiber 19 to the surface of the fiber pressure block 18. 4. Installation of piezoelectric ceramic 16: Install the assembled EPC cover 15 containing piezoelectric ceramic 16 to the corresponding position of the fiber optic lower pressure block 18 using screws; 5. Testing: Finally, specific tests such as extinction ratio and insertion loss are conducted.

[0004] The existing EPC assembly and subsequent testing processes have the following shortcomings: 1. The placement of single-mode fiber in the fiber clamping block is subjectively determined by the assembly personnel, which can lead to issues such as lateral offset and longitudinal misalignment. Lateral offset causes stress asymmetry, while longitudinal misalignment alters the direction of piezoelectric ceramic action, resulting in uneven distribution of compressive force. The consequences are primarily manifested as decreased EPC polarization modulation accuracy and increased fluctuations in extinction ratio tests.

[0005] 2. The unfixed single-mode fiber at both ends of the EPC during testing will affect the reliability of the device test results. Unfixed single-mode fiber at both ends of the EPC will experience mechanical micro-motion during testing. On the one hand, this causes the direction and magnitude of the compressive force applied by the piezoelectric ceramic to change in real time, resulting in random polarization drift and drastic fluctuations in the extinction ratio measurement. On the other hand, micro-bending loss in the fiber core causes instantaneous inaccuracy in the optical path, additionally increasing insertion loss and affecting the accuracy of the EPC performance parameter test.

[0006] 3. The bare fiber portion of single-mode fiber is unprotected. During assembly, when the surface of the bare fiber comes into direct contact with hard objects, it may cause micron-level scratches, which will expand into cracks under the external stress of the piezoelectric ceramic, resulting in a decrease in the tensile strength of the fiber. Utility Model Content

[0007] The technical problem to be solved by this utility model is how to avoid the error in the placement of optical fibers during EPC assembly.

[0008] The present invention solves the above-mentioned technical problems through the following technical means: an assembly and adjustment fixture for an electric polarization controller, including a base plate (1) and a left fiber fixing block (2), a lower cover fixing groove (4) and a right fiber fixing block (5) arranged sequentially from left to right on the upper surface of the base plate (1), with fiber positioning auxiliary lines (3) engraved along the center line of the base plate (1).

[0009] As a further optimized technical solution, the left optical fiber fixing block (2) and the right optical fiber fixing block (5) have the same structure, both including a lower flip cover (7) and an upper flip cover (10) that are rotatably connected. The upper surface of the lower flip cover (7) is provided with an optical fiber placement groove (8), and the optical fiber placement groove (8) is collinear with the optical fiber positioning auxiliary line (3) on the base plate (1).

[0010] As a further optimized technical solution, the optical fiber placement groove (8) is V-shaped, and when the optical fiber is placed in the V-shaped optical fiber placement groove (8), the top of the optical fiber is not higher than the upper surface of the lower flip cover (7).

[0011] As a further optimized technical solution, the upper flip cover (10) and the lower flip cover (7) are opened and closed by a magnet (11).

[0012] As a further optimized technical solution, a circular groove (12) is provided on the opposite side of the upper flip cover (10) and the lower flip cover (7), and a magnet (11) is placed in each circular groove (12).

[0013] As a further optimized technical solution, the magnet (11) is a button-type strong magnet.

[0014] As a further optimized technical solution, the top of one side of the upper flip cover (10) is provided with a number of spaced first mounting seats, each of which has an axially opened first through hole. All the first through holes are the same size and their axes are on a straight line. Correspondingly, the upper part of one side of the top surface of the lower flip cover (7) is provided with a number of spaced second mounting seats, each of which has an axially opened second through hole. All the second through holes are the same size and their axes are on a straight line. When the upper flip cover (10) and the lower flip cover (7) are connected, the first mounting seats and the second mounting seats are arranged in a cross pattern, and a positioning pin (9) passes through the first through hole and the second through hole.

[0015] As a further optimized technical solution, the opening and closing end of the upper flip cover (10) and the lower flip cover (7) protrudes from the end of the lower flip cover (7).

[0016] As an optional technical solution, the upper flip cover (10) and the lower flip cover (7) are opened and closed by a snap fastener.

[0017] As a further optimized technical solution, a rectangular groove (22) is provided on the back of the base plate (1), and through holes (221) are provided at the four corners of the rectangular groove (22). An acrylic cover plate (20) is provided on the rectangular groove (22), and through holes (201) are provided at the four corners of the acrylic cover plate (20) corresponding to the positions of the through holes (221).

[0018] The advantages of this utility model are: 1. To address the issue of fiber placement, an assembly and adjustment fixture is designed to fix the fibers at both ends of the EPC using fiber fixing blocks on both sides of the fixture, thereby calibrating the fiber placement position and mechanically constraining the fibers. 2. By using the V-groove positioning of the assembly tooling and the fiber positioning auxiliary line for verification, the horizontality of the fiber placement position is calibrated in two stages, reducing the lateral offset of the fiber; by using the flip-up protrusion design of the fiber fixing blocks on both sides of the base plate to raise the fibers at both ends of the EPC to the same height, the longitudinal misalignment of the fibers is reduced, further improving the accuracy of fiber placement at both ends of the EPC. 3. A V-shaped groove is designed on the lower cover of the fiber fixing block, with the size matching the diameter of the fiber. This can completely cover the fiber, ensuring that the fiber is protected from damage when the fiber fixing block is closed, while improving the stability during subsequent testing. 4. The opening and closing method of the fiber optic fixing block adopts magnetic attraction or concealed snap fastener, which simplifies the appearance of the tooling and improves the operation efficiency. 5. For fixing the EPC lower cover, a lower cover fixing groove is designed to place the EPC lower cover, providing a rigid positioning reference for the assembly of the EPC lower cover; 6. The bottom of the base plate is fixed by a combination of nuts and acrylic cover plates. As the tooling is used more frequently, the nuts can be replaced directly when the threads wear out, reducing the replacement frequency of the base plate, extending the service life of the tooling, reducing maintenance costs, and allowing for on-site replacement without delaying production. 7. By setting a size difference between the upper and lower flip covers, the fiber optic fixing block can be quickly opened and closed by simply flipping the upper flip cover without the need for other auxiliary structures. This eliminates the need for cumbersome plugging and unplugging operations and improves production efficiency. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of an existing electric polarization controller. Figure 2 This is the overall design drawing of the assembly and adjustment fixture for the electric polarization controller according to Embodiment 1 of this utility model; Figure 3 This is an exploded view of the optical fiber fixing block of the assembly and adjustment fixture for the electric polarization controller according to Embodiment 1 of this utility model. Figure 4 This is an assembly diagram of the optical fiber fixing block of the assembly and adjustment fixture for the electric polarization controller according to Embodiment 1 of this utility model; Figure 5 This is a schematic diagram of the opening and closing of the optical fiber fixing block of the assembly and adjustment fixture for the electric polarization controller according to Embodiment 2 of this utility model. Figure 6 This is an assembly and adjustment diagram of the electric polarization controller according to Embodiment 3 of this utility model; Figure 7 This is a schematic diagram of the closed left optical fiber fixing block of the assembly and adjustment fixture for the electric polarization controller according to Embodiment 3 of this utility model; Figure 8 This is a rear structural diagram of the assembly and adjustment fixture for the electric polarization controller according to Embodiment 3 of this utility model; Figure 9 This is a back view of the assembly and adjustment fixture for the electric polarization controller according to Embodiment 3 of this utility model. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below in conjunction with the embodiments of this utility model. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0021] It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. Furthermore, the illustrations provided in the following embodiments are merely schematic representations of the basic concept of this utility model. The illustrations only show components relevant to this utility model and are not drawn according to the actual number, shape, and size of the components in implementation. In actual implementation, the form, quantity, and proportion of each component can be arbitrarily changed, and the component layout may also be more complex.

[0022] It should be noted that the directional terms mentioned in the embodiments, such as "up," "down," "front," "back," "left," and "right," are only for reference to the directions in the accompanying drawings and are not intended to limit the scope of protection of this disclosure. Throughout the drawings, the same elements are represented by the same or similar reference numerals. Conventional structures or constructions will be omitted where they may cause confusion in understanding this disclosure.

[0023] The use of ordinal numbers such as "first," "second," and "third" in the specification and claims to modify the corresponding elements does not imply that the element has any ordinal number, nor does it represent the order of one element with another element or the order of manufacturing methods. The use of these ordinal numbers is only to enable a named element to be clearly distinguished from another element with the same name.

[0024] Example 1 This utility model proposes an assembly and adjustment fixture for an electric polarization controller, used for assembly and adjustment. Figure 1 The electric polarization controller is shown. The overall structure of the assembly and adjustment fixture for this electric polarization controller is as follows. Figure 2 As shown, the structure includes a base plate 1 as the main structure, and, from left to right, three optical fiber fixing blocks: a left optical fiber fixing block 2, a lower cover fixing groove 4, and a right optical fiber fixing block 5, all arranged on the upper surface of the base plate 1. An optical fiber positioning auxiliary line 3 is engraved along the centerline of the base plate 1. The left optical fiber fixing block 2 and the right optical fiber fixing block 5 have the same structural design and are used to fix the optical fiber, constrain its displacement, and eliminate insertion loss fluctuations and polarization drift caused by micro-movements of the optical fiber during testing. The lower cover fixing groove 4 is used to place the lower cover of the EPC, providing a rigid positioning reference for the assembly of the EPC lower cover, ensuring that the piezoelectric ceramic force is vertically transmitted to the optical fiber, and avoiding uneven stress distribution caused by vertical gaps. The optical fiber positioning auxiliary line 3 serves as a visual calibration reference for optical fiber placement, controlling the lateral offset of the optical fiber within ±0.05mm, thus avoiding polarization modulation asymmetry problems from the source.

[0025] The mechanical constraints of the optical fiber fixing blocks on both sides, the lower cover positioning reference of the lower cover fixing groove 4, and the guide markings of the optical fiber positioning auxiliary line 3 provide triple protection, significantly improving the mass production consistency of the electric polarization controller.

[0026] Further reading Figure 3 and Figure 4 The left fiber optic fixing block 2 and the right fiber optic fixing block 5 have the same structural design. Taking the left fiber optic fixing block 2 as an example, the composition of the fiber optic fixing block is explained. The fiber optic fixing block includes a lower flip cover 7, an upper flip cover 10, and a magnet 11. The upper flip cover 10 and the lower flip cover 7 are rotatably connected, and the upper flip cover 10 and the lower flip cover 7 are opened and closed by the magnet 11.

[0027] In this embodiment, a plurality of spaced-apart first mounting seats are provided on the top side of one side of the upper flip cover 10. Each first mounting seat has a first through hole axially. The first through holes of all the first mounting seats are of the same size and their axes are aligned. Correspondingly, a plurality of spaced-apart second mounting seats are provided on the upper part of one side of the top surface of the lower flip cover 7. Each second mounting seat has a second through hole axially. The second through holes of all the second mounting seats are of the same size and their axes are aligned. When the upper flip cover 10 and the lower flip cover 7 are connected, the first and second mounting seats are arranged in a crisscross pattern, and a positioning pin 9 passes through the first and second through holes, thereby rotatably connecting the upper flip cover 10 and the lower flip cover 7. To prevent the positioning pin 9 from shifting during use, end caps with dimensions larger than the first and second through holes can be provided at both ends of the positioning pin 9. The rotatable connection between the upper flip cover 10 and the lower flip cover 7 can also adopt other existing conventional connection methods.

[0028] The lower flip cover 7 is provided with a fixing hole 6 that passes through the lower flip cover 7, and the base plate 1 is provided with a screw fixing hole corresponding to the fixing hole 6. After the screw passes through the fixing hole 6, it is screwed into the corresponding screw fixing hole of the base plate 1, thereby fixing the optical fiber fixing block in the corresponding position of the base plate 1.

[0029] The upper cover 10 and lower cover 7 of the fiber optic fixing block open and close magnetically. In this embodiment, a circular groove 12 is provided on the opposite surfaces of the upper cover 10 and the lower cover 7, and a magnet 11 is placed in each circular groove 12 for closing and fixing the upper cover 10 and the lower cover 7. Of course, those skilled in the art should understand that a magnet can also be placed in one of the upper cover 10 or the lower cover 7, and an iron can be placed in the other, which can also achieve the effect of making the upper cover 10 and the lower cover 7 open and close magnetically.

[0030] As a preferred embodiment, the magnet 11 used in the opening and closing mechanism of the upper flip cover 10 and lower flip cover 7 of the fiber optic fixing block in this embodiment is a button-type high-strength magnet. Considering that the temperature in the production workshop is stable at 22-25℃ year-round, there is no high-temperature environment that would disrupt the orderly arrangement of magnetic moments, thus ensuring the magnetic stability of the magnet 11. The magnet 11 is installed in the corresponding circular grooves 12 of the upper flip cover 10 and lower flip cover 7, and will not be frequently subjected to stresses such as impact, vibration, or bending. Therefore, using a button-type high-strength magnet is safe and reliable.

[0031] Furthermore, the opening and closing end of the upper flip cover 10 and the lower flip cover 7 protrudes 3mm-6mm, preferably 5mm, from the end of the lower flip cover 7, thereby realizing a lever-type structure that allows for quick one-handed opening and closing of the fiber optic fixing block without the need for other auxiliary structures.

[0032] The upper surface of the lower flip cover 7 is provided with a V-shaped groove 8. The opening size of the V-shaped groove 8 can be designed according to the diameter of the optical fiber to accurately wrap the optical fiber. When the optical fiber is placed in the V-shaped groove 8, the top of the optical fiber is not higher than the upper surface of the lower flip cover 7. This ensures that the horizontality of the optical fibers at both ends of the EPC is consistent, and also ensures that the optical fiber fixing block will not damage the optical fiber during the opening and closing process. The V-shaped groove 8 is collinear with the optical fiber positioning auxiliary line 3 on the base plate 1, which is used to reconfirm the horizontality of the optical fiber during the EPC assembly process, reduce the lateral displacement of the optical fiber, and ensure the horizontality of the optical fiber. Of course, the groove can also adopt other shapes, such as arc, but the V-shaped groove provides the best support for the optical fiber.

[0033] In the direction of the plane where the vertical base plate 1 is located, this utility model uses a boss design to raise the optical fibers at both ends of the EPC to a uniform height. That is, after the optical fiber fixing block is fixed on the base plate 1, the lower flip cover 7 has a certain thickness, so the lower flip cover 7 protrudes from the plane where the base plate 1 is located to form a boss. The lower flip covers 7 on both sides are at the same height, thereby raising the optical fibers at both ends of the EPC upward, so that the optical fibers at both ends of the EPC are at the same height, reducing the longitudinal misalignment of the optical fibers, and making the optical fibers at both ends of the EPC consistent.

[0034] This utility model employs a dual-level calibration scheme using V-shaped groove 8 for positioning and fiber optic positioning auxiliary line 3 for verification. Combined with coplanar lifting of the lower flip cover 7 at the same height, this multi-protection mechanism improves assembly accuracy while avoiding damage to the optical fiber, thus enhancing the precision of the EPC production process.

[0035] Example 2 The difference between this embodiment and Embodiment 1 is that the opening and closing mechanism of the upper flip cover 10 and lower flip cover 7 of the fiber optic fixing block adopts a concealed snap-fit ​​method, such as... Figure 5 As shown, the upper flip cover 10 has a cylindrical spherical protrusion 13 on the surface opposite to the lower flip cover 7, and the lower flip cover 7 has a circular groove 12 at the corresponding position opposite to the surface opposite to the upper flip cover 10. The circular groove 12 contains a rubber annular retainer 14. The rubber elasticity of the rubber annular retainer 14 can be used to lock the cylindrical spherical protrusion 13 of the upper flip cover 10 when the fiber optic fixing block is closed, thus achieving the stable closure requirement of the fiber optic fixing block.

[0036] Of course, those skilled in the art should understand that a cylindrical spherical protrusion can also be designed on the surface of the lower flip cover 7 relative to the upper flip cover 10, and a circular groove can be provided at the corresponding position of the upper flip cover 10 relative to the lower flip cover 7. The circular groove has a built-in rubber ring sleeve, which can also open and close the upper flip cover 10 and the lower flip cover 7 by means of a snap fastener.

[0037] Example 3 This embodiment provides a process for EPC assembly using the assembly and adjustment fixture of the electric polarization controller described in Embodiment 1 or 2, such as... Figure 6 and Figure 7 As shown, the assembly process is as follows: The piezoelectric ceramic 16 is attached to the inside of the EPC top cover 15 and its wires are soldered to the data processing board (not shown in the figure). Then, the EPC bottom cover 17 is placed in the bottom cover fixing groove 4 in the center of the base plate 1 and fixed to the base plate 1 with screws. Then, the three fiber optic pressure blocks 18 inside the EPC are installed on the EPC bottom cover 17. Then, the single-mode fiber 19 is attached to the surface of the fiber optic pressure block 18, and the fibers at both ends of the EPC are respectively embedded into the V-shaped grooves 8 of the fiber fixing pressure blocks on both sides of the base plate 1. The V-shaped grooves 8 precisely wrap the single-mode fiber 19, and the single-mode fiber 19 is straightened along the fiber positioning auxiliary line 3 to complete the fiber calibration. Then, the upper flip cover 10 of the left fiber fixing pressure block 2 and the right fiber fixing pressure block 5 is closed. The assembled EPC top cover 15 is installed, the fiber status is maintained, and the subsequent assembly and testing are completed.

[0038] Furthermore, in combination Figure 8 and Figure 9 As shown, the back of the mounting base plate 1 of this application has a rectangular groove 22 that matches the size of the EPC lower cover 17. This rectangular groove 22 is the same size as the lower cover fixing groove 4 and coincides with it in the vertical direction, but they are not connected. Through holes 221 are formed at the four corners of the rectangular groove 22, preferably hexagonal-round stepped openings. The screws fixing the EPC lower cover 17 pass through the through holes 221 and are tightened to the screws fixing the EPC lower cover 17 from the back of the base plate 1 using nuts 21, thus fixing the EPC lower cover 17. An acrylic cover plate 20 covers the rectangular groove 22, and its size precisely matches the rectangular groove 22. It is bonded to the base plate 1 with 3M adhesive to support the nuts 21. Through holes 201 are formed at the four corners of the acrylic cover plate 20 corresponding to the positions of the screws fixing the EPC lower cover 17, providing longitudinal extension space for the screws installing the EPC lower cover 17, to accommodate screws of different lengths.

[0039] In existing technologies, threads are typically tapped directly onto the base plate, and then screws are screwed into the threads when fixing the EPC lower cover 17. With frequent use, the threads become damaged, rendering the base plate unusable and requiring replacement with a new base plate with new threads. In this invention, tapping is unnecessary on the base plate. When frequent use of the assembly tooling causes the nut 21 to strip, the detachable acrylic cover plate 20 can be used to directly replace the nut 21, eliminating the need to replace the entire base plate 1. This reduces maintenance costs and allows for on-site replacement without delaying production. This invention combines the high-value base plate 1 with the easily damaged nut 21, reducing production costs and extending the service life of the assembly tooling through modular maintenance.

[0040] The above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A tooling for assembling and adjusting an electric polarization controller, characterized in that: It includes a base plate (1) and, from left to right, a left fiber fixing block (2), a lower cover fixing groove (4) and a right fiber fixing block (5) arranged on the upper surface of the base plate (1). Fiber positioning auxiliary lines (3) are engraved along the center line of the base plate (1).

2. The assembly and adjustment fixture for an electric polarization controller as described in claim 1, characterized in that: The left fiber fixing block (2) and the right fiber fixing block (5) have the same structure, both including a lower flip cover (7) and an upper flip cover (10) that are rotatably connected. The upper surface of the lower flip cover (7) is provided with a fiber placement groove (8), and the fiber placement groove (8) is collinear with the fiber positioning auxiliary line (3) on the base plate (1).

3. The assembly and adjustment fixture for an electric polarization controller as described in claim 2, characterized in that: The fiber placement groove (8) is V-shaped, and when the fiber is placed in the V-shaped fiber placement groove (8), the top of the fiber is not higher than the upper surface of the lower cover (7).

4. The assembly and adjustment fixture for an electric polarization controller as described in claim 2, characterized in that: The upper flip cover (10) and the lower flip cover (7) are opened and closed by a magnet (11).

5. The assembly and adjustment fixture for an electric polarization controller as described in claim 4, characterized in that: The upper flip cover (10) and the lower flip cover (7) are respectively provided with a circular groove (12) on their opposite sides, and a magnet (11) is placed in each circular groove (12).

6. The assembly and adjustment fixture for an electric polarization controller as described in claim 4, characterized in that: The magnet (11) is a button-type strong magnet.

7. The assembly and adjustment fixture for an electric polarization controller as described in claim 2, characterized in that: The top of one side of the upper flip cover (10) is provided with several spaced first mounting seats. Each first mounting seat has an axially opened first through hole. All first through holes have the same size and their axes are on a straight line. Correspondingly, the upper part of one side of the top surface of the lower flip cover (7) is provided with several spaced second mounting seats. Each second mounting seat has an axially opened second through hole. All second through holes have the same size and their axes are on a straight line. When the upper flip cover (10) and the lower flip cover (7) are connected, the first mounting seats and the second mounting seats are arranged in a cross pattern, and a positioning pin (9) passes through the first through hole and the second through hole.

8. The assembly and adjustment fixture for an electric polarization controller as described in claim 2, characterized in that: The opening and closing ends of the upper flip cover (10) and the lower flip cover (7) protrude from the end of the lower flip cover (7).

9. The assembly and adjustment fixture for an electric polarization controller as described in claim 2, characterized in that: The upper flip cover (10) and the lower flip cover (7) are opened and closed by a snap fastener.

10. The assembly and adjustment fixture for an electric polarization controller as described in claim 1, characterized in that: The bottom plate (1) has a rectangular groove (22) on the back side, and through holes (221) are opened at the four corners of the rectangular groove (22). An acrylic cover plate (20) covers the rectangular groove (22), and through holes (201) are opened at the four corners of the acrylic cover plate (20) corresponding to the through holes (221).

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