A mode modulator modulation system and modulation method

Abstract

The application discloses a mode modulator modulation system and a mode modulator modulation method, and belongs to the technical field of optical modulation.The mode modulator modulation system comprises an optical source connected with an optical fiber, the optical fiber passes through a modulation mechanism and is connected with a CCD imaging module, the modulation mechanism is used for realizing the output of different mode light spots by rotating the angle of the optical fiber and bending the arc of the optical fiber under the condition that the same light spot is injected, the output light spot is connected to a computer through the CCD imaging module, the mode modulator modulation system adopts a double-dimension cooperative adjustment mode of the rotating angle and the bending arc, can change the working state of the optical fiber in real time on line, and can flexibly switch a plurality of light spot output modes;uniform input of the optical source ensures the consistency of the reference light spot, the CCD imaging module is matched with the computer to realize real-time collection and operation determination of the light spot form, the whole process is visualized, the mode adjustment precision and the adjustment freedom are greatly improved, and the differentiated mode requirements of a plurality of application scenes are adapted.

Description

Technical Field

[0001] This invention relates to the field of optical modulation technology, and in particular to a mode modulator modulation system and modulation method. Background Technology

[0002] Fiber lasers have many advantages, such as high conversion efficiency, high beam quality, high coherence, compact structure, and convenient thermal management, and are widely used in laser cutting, laser welding, medical and other fields.

[0003] As application scenarios become increasingly diverse, the output modes of fiber lasers will have different requirements in different application scenarios. Therefore, it is necessary to enable fiber lasers to output different modes in different scenarios. Existing fiber mode modulators adopt a structure in which the input fiber is tapered and the output fiber is rotated tapered and then fused with the input fiber. By preset the fiber rotation angle, the beam pattern modulation is achieved, which can change the numerical aperture and energy distribution of the output beam to a certain extent. This is suitable for high-power fiber laser systems.

[0004] However, existing mode modulators rely on fixed rotation angles and welding molding for mode modulation. Once manufactured, they cannot be adjusted online in real time. The modes are singular and unchangeable, and they rely solely on single-dimensional control based on rotation angle. The mode adjustment accuracy and freedom are limited, making it difficult to meet the usage requirements of flexibly switching spot modes in multiple scenarios. Summary of the Invention

[0005] To address the technical problems of existing mode modulators in the background art, which rely on fixed rotation angles and welding molding for mode modulation, making it impossible to adjust the mode online in real time after fabrication, and resulting in a single and unchangeable mode, this invention provides a mode modulator modulation system and modulation method.

[0006] The technical solution of this invention is as follows: This invention provides a mode modulator modulation system, including a light source connected to an optical fiber. The optical fiber passes through a modulation mechanism and is connected to a CCD imaging module. The modulation mechanism is used to output different mode light spots by rotating the optical fiber angle and bending the optical fiber arc when the same light spot is injected. The output light spot is connected to a computer through the CCD imaging module. It adopts a dual-dimensional coordinated adjustment method of rotation angle and bending arc, which can change the working state of the optical fiber online in real time and flexibly switch between multiple light spot output modes. The unified input of the light source ensures the consistency of the reference light spot. The CCD imaging module, together with the computer, realizes real-time acquisition, calculation and judgment of the light spot shape, and provides full-process visual adjustment, which greatly improves the precision and freedom of mode adjustment and adapts to the differentiated mode requirements of various application scenarios.

[0007] Preferably, the modulation mechanism includes a first support, a second support, and a third support. The first and second supports are spaced apart along the extension direction of the optical fiber, and a flame placement area is provided between the first and second supports. The third support is located on the side of the second support away from the first support and is movably connected to the second support. The third support is used to install an optical fiber clamp. The three sets of supports position the optical fiber in segments, and the flame placement area reserves space for heat treatment operations, resulting in a well-organized and reasonable structural layout. The third support can move flexibly relative to the second support, providing an adjustment basis for bending, shaping, and rotating the optical fiber. The clamping and positioning are stable, and the optical fiber is not easily displaced or loosened during adjustment.

[0008] Preferably, the third support includes a rotating part, a connecting part, and a mounting part. The connecting part is slidably connected to the second support to laterally change the overall axial position of the third support. The rotating part is mounted on the connecting part and can rotate around an axis. The mounting part has an L-shaped structure and is fixedly mounted on the rotating part. The mounting part is used for fixing and mounting the fiber optic clamp. A through hole is provided at the center of the rotating part for the fiber optic cable to pass through. The sliding structure of the connecting part can flexibly change the force position of the fiber optic cable and adjust the bending curvature of the fiber optic cable; the independent rotation structure of the rotating part drives the fiber optic cable to rotate smoothly, the angle adjustment is smooth and without jamming, and the central through hole ensures that the fiber optic cable is neatly routed and that the adjustment process does not cause structural interference.

[0009] Preferably, the top opening of the through hole facilitates quick installation, removal, and alignment of the optical fiber, eliminating the need for threading operations, simplifying the optical fiber installation and removal process, and improving the convenience of debugging operations.

[0010] Preferably, the upper surfaces of the first support and the second support are both provided with V-grooves, the two V-grooves are coaxially arranged, and a rubber protective layer is fixedly provided in the V-grooves. The coaxial V-grooves realize the precise positioning of the optical fiber in the center, ensuring the coaxiality of the wiring. The rubber protective layer flexibly fits the outer wall of the optical fiber, avoiding hard contact that could scratch the optical fiber coating and bare fiber, while increasing friction and improving the stability of the optical fiber placement.

[0011] A modulation method for a modulation mode modulator, comprising: When the input fiber and the output fiber are the same type of fiber, remove the coating layer, place the bare fiber with the coating removed directly above the flame placement area, fix the fiber straight, place the fiber clamp corresponding to the fiber size on the third support, and connect the fiber clamp to the fiber. Moving the third support forward or backward creates a curved arc in the mode modulator section. This third support then rotates the optical fiber, and the rotation angle is adjusted according to the shape of the light spot. No additional tapering or fusion splicing is required for the same type of fiber. The two-dimensional, step-by-step adjustment logic—first adjusting the curvature and then fine-tuning the rotation angle—is clear and facilitates rapid matching to the target light spot shape. The operation is simple and easy to master.

[0012] Preferably, when the input fiber and the output fiber are different types of fiber, the thick fiber is tapered so that the diameter of the tapered area is the same as that of the thin fiber, and then the tapered area is cut and fused with the thin fiber. The tapered area is placed directly above the flame placement area, with the flame's active part bypassing the fusion splice point. The third support is moved forward or backward, giving the mode modulator section a curved arc. The third support drives the thin optical fiber to rotate, and the rotation angle is adjusted according to the shape of the light spot. Different-diameter optical fibers are fused together after being tapered to match their outer diameters, ensuring continuous optical path transmission. The flame avoids the fusion splice point to prevent high temperatures from damaging the splice strength, mitigating the risk of fiber breakage. This design adapts to the modulation and processing needs of different fiber specifications, broadening its applicability.

[0013] Preferably, the bending radius is 0.0174-0.122 rad, which can meet the deformation conditions required for mode modulation, and avoid excessive bending that could cause stress concentration, increased loss or even breakage in the optical fiber, thus balancing modulation effect and optical fiber lifespan.

[0014] Preferably, there are two criteria: Criterion A: When the principal axis direction of the light spot changes linearly and synchronously with the increase of the physical rotation angle of the third support, it indicates that the mode is in a controlled torsion state; Criterion B: When the fluctuation of the centroid coordinate of the light spot tends to be minimal, and its normalized distance from the ideal reference center is less than a set threshold, it is determined that the light spot has reached the highest degree of spatial symmetry at this torsion angle. The dual criteria establish a quantitative evaluation standard, realize the objectification and data-driven determination of the modulation state, reduce human error, and improve the consistency and accuracy of mode modulation.

[0015] Preferably, during modulation, the computer calculates the centroid coordinates and principal axis direction angle of the light spot. When the calculation results simultaneously satisfy the linear following of judgment criterion A and the centroid stability of judgment criterion B, the computer provides a prompt that the rotation is in place, and the operator stops adjustment and prepares for cooling and solidification. Relying on real-time data calculation and judgment by the computer, the modulation endpoint is precisely controlled, ensuring that the light spot performance is uniform and stable after each modulation; cooling and solidification promptly fixes the structure, locks in the optimal mode state, and ensures that the modulator maintains a stable output mode during long-term use.

[0016] As can be seen from the above technical solutions, the advantages of the present invention are: With the same light spot injected, different light spot modes can be output by rotating the fiber angle and bending the fiber curvature. The resulting light spot modes are diverse, which can meet different application scenarios. The implementation method is simple, and the fiber type of the mode modulator is not limited. The fiber core loss is low and it can withstand the output of high-power lasers. Attached Figure Description

[0017] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the mode modulator modulation system according to one or more embodiments of the present invention; Figure 2 This is a schematic diagram of the modulation mechanism according to one or more embodiments of the present invention; Figure 3 This is a side view of the modulation mechanism according to one or more embodiments of the present invention. Figure 4 These are schematic diagrams of different types of optical fiber connection structures according to one or more embodiments of the present invention; Figure 5 This is a schematic diagram of the three-dimensional outline of the output light spot before modulation according to one or more embodiments of the present invention. Figure 6 This is a schematic diagram of the three-dimensional contour of the modulated output light spot according to one or more embodiments of the present invention. The components represented by the various reference numerals in the diagram are: 1. Light source; 2. Optical fiber; 3. Modulation mechanism; 4. CCD imaging module; 5. Computer; 6. First support base; 7. Second support base; 8. Flame placement area; 9. Third support base; 91. Rotating part; 92. Connecting part; 93. Mounting part; 94. Mounting hole; 95. Through hole; 10. Thick optical fiber; 11. Thin optical fiber; 12. Tapered area; 13. Fusion splice; 14. Optical fiber core; 15. Optical fiber cladding. Detailed Implementation

[0019] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the specific embodiments. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this patent, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this patent.

[0020] Example 1 In a typical embodiment of the present invention, such as Figures 1-3As shown, a mode modulator modulation system is proposed, including: a light source 1, a modulation mechanism 3, a CCD imaging module 4, and a computer 5. The light source 1 is connected to an optical fiber 2, which is connected to the CCD imaging module 4 via the modulation mechanism 3. The modulation mechanism 3 is used to output different mode light spots by rotating the angle of the optical fiber 2 and bending the arc of the optical fiber 2 under the same injected light spot, so as to meet different application scenarios. The light spot modes are diverse, the implementation method is simple, and the type of optical fiber used to make this mode modulator is not limited. The output light spot is connected to the computer 5 via the CCD imaging module 4 for display. The computer 5 contains a computing system that can calculate the centroid distribution and principal axis direction of the light spot to assist the operator in accurately judging whether the rotation angle has been adjusted correctly.

[0021] like Figure 2 and Figure 3 As shown, the modulation mechanism 3 includes a first support base 6, a second support base 7, a third support base 9, and an optical fiber clamp. The first support base 6 and the second support base 7 are arranged alternately along the extension direction of the optical fiber 2. A flame placement area 8 is provided between the first support base 6 and the second support base 7 for placing a flame system to soften the optical fiber 2 using an oxyhydrogen flame. The first support base 6 and the second support base 7 are both fixedly mounted on the worktable, and V-shaped grooves are formed on the upper surfaces of both the first support base 6 and the second support base 7. The V-shaped grooves extend along the length direction of the corresponding support base, and the two V-shaped grooves are coaxially arranged to limit the optical fiber 2. A rubber protective layer is fixedly provided in the V-shaped grooves to ensure that the surface of the bare fiber is not damaged by mechanical extrusion when rotating the optical fiber 2, and to ensure that the central axis of the optical fiber 2 coincides with the rotation axis. The third support base 9 is located on the side of the second support base 7 away from the first support base 6, and the third support base 9 is movably connected to the second support base 7. The optical fiber clamp is fixedly mounted on the third support base 9 for clamping the optical fiber 2.

[0022] The third support 9 includes a rotating part 91, a connecting part 92, and a mounting part 93. The rotating part 91 is fixedly mounted on the connecting part 92 and can rotate around an axis. The mounting part 93 has an L-shaped structure and is fixedly mounted on the rotating part 91. The mounting part 93 has a mounting hole 94 for fixing the fiber optic clamp. The rotating part 91 has a through hole 95 at its center for the fiber optic cable 2 to pass through. The connecting part 92 is slidably connected to the second support 7 to laterally change the overall axial position of the third support 9.

[0023] The rotating part 91 includes two relatively rotating annular structures, which are coaxially arranged. One annular structure has a protrusion fixedly provided on its end face along its circumferential direction, and the other annular structure has a groove provided on its end face along its circumferential direction. Both the protrusion and the groove are T-shaped structures. The rotational connection between the two annular structures is achieved through the connection between the protrusion and the groove. The rotation angle is ±180°. A through hole 95 is provided at the middle position of both annular structures for the optical fiber 2 to pass through. The top of the through hole 95 is open to facilitate the placement and removal of the optical fiber 2.

[0024] In this embodiment, the annular structure near the second support base 7 is fixedly connected to the connecting part 92, and the end face of the annular structure near the second support base 7 is provided with a scale along its circumferential direction. In the initial state, the zero scale is aligned with the upper opening of the through hole 95, so that when the rotating part 91 is rotated, the specific rotation angle can be determined by the scale.

[0025] The connecting part 92 is slidably connected to the second support base 7. Specifically, the second support base 7 is provided with a guide groove, and the connecting part 92 is fixedly provided with a guide rod. The guide rod is inserted into the guide groove and slidably connected to it, so that the connecting part 92 can be moved straight by pulling, with a movement range of ±2mm.

[0026] Example 2 In another typical embodiment of the present invention, a modulation method for a mode modulator is proposed, comprising: When the input and output optical fibers are required to be the same type of fiber 2, the mode modulator is directly fabricated on fiber 2. Specifically: The coating of optical fiber 2 is stripped off, about 7cm of which is removed. A mode modulator is fabricated on the bare fiber. The bare fiber with the coating removed is placed directly above the flame placement area 8. The placement process can be observed under a microscope. After fixing the position, the left end of optical fiber 2 is fixed to the first support 6 with high-temperature tape. The optical fiber 2 is placed flat. An optical fiber clamp of the corresponding size of optical fiber 2 is placed on the third support 9 to fix the optical fiber 2. It should be noted that fiber optic cable 2 must be kept straight during placement.

[0027] After removing the 7cm coating layer, ultrasonic cleaning with anhydrous ethanol is required to prevent impurities from carbonizing during flame heating, which could cause fiber 2 to become brittle. When placing the bare fiber under the flame, the hydrogen-oxygen content is adjusted to a hydrogen-oxygen ratio of 2:1, and the flame size is adjusted. First, a weak flame is used to uniformly scan the bare fiber area to eliminate residual internal stress. Then, the flame is used to bring fiber 2 to its softening point. Bending and twisting under this state will freeze the stress in the glass network, thereby achieving long-term stability of mode modulation.

[0028] After the fiber 2 is fixed and heated, the fiber 2 is rotated by the third support 9. The rotation angle range is 0°-360°. The light spot output by the fiber 2 is monitored in real time. The rotation angle is adjusted according to the shape of the light spot. The third support 9 can be moved forward or backward so that the mode modulator part has a certain curvature. The curvature should generally be maintained at 0.0174-0.122 rad.

[0029] Specifically, the third support 9 is pushed forward to make the optical fiber 2 bend by 0.0174-0.122 rad. The CCD imaging module 4 is then observed. At this time, the light spot usually splits from a circle into multiple lobes. Then, the third support 9 is rotated while the optical fiber 2 is bent. The evolution of the light spot is recorded once every 15° rotation. Rotation can effectively eliminate the asymmetric distortion of the light spot and make the edge energy distribution more uniform.

[0030] After achieving the ideal light spot, keep the third support 9 in place and slowly reduce the flame power until it is extinguished, allowing the optical fiber 2 to cool naturally in the deformed state. Remove the constraint of the third support 9 and observe the rebound of the light spot. If the rebound is severe, the heat treatment time needs to be increased.

[0031] Specifically, such as Figure 5 and Figure 6 As shown, in actual operation, fiber 2 with a core of 100µm and a cladding of 360µm was selected. The divergence angle of the injected light spot was measured to be NA=0.025 (tested using Dateray software). After modulation, the core transmittance reached 98.5%, and the output light spot achieved NA=0.030, with the output light spot being close to Gaussian and the central energy distribution area being increased. After fabricating a mode modulator on fiber 2, with the same injected light spot and the same core transmittance, the output light spot NA=0.035 could be achieved, with the output light spot being close to a flat-topped light spot and the central energy distribution area being larger.

[0032] When the input fiber and the output fiber require different fiber types 2, specifically: The thick optical fiber 10 is placed on a tapering machine for tapering. After tapering, the diameter of the tapered region 12 of the thick optical fiber 10 is consistent with that of the thin optical fiber 11. Then, the tapered thick optical fiber 10 is cut in the tapered region 12 and fused with the thin optical fiber 11. The structure is as follows. Figure 4 As shown, after the thick optical fiber 10 and the thin optical fiber 11 are fused together, the length of the uncoated part remains at about 7 cm. A mode modulator is fabricated on the tapered region 12 of the thick optical fiber 10. The tapered region 12 of the thick optical fiber 10 is placed directly above the flame placement area 8. The flame action part needs to bypass the fusion splice 13. The placement process can be observed under a microscope. Then, the thick optical fiber 10 is horizontally fixed on the first support 6, and the thin optical fiber 11 is connected to the optical fiber clamp on the third support 9. The thin optical fiber 11 is rotated by the third support 9, with a rotation angle range of 0°-360°. The output light spot is monitored in real time. The rotation angle is adjusted according to the shape of the light spot. The third support 9 can also be moved forward or backward so that the mode modulator part has a certain curvature. The curvature should generally be maintained at 0.0174-0.122 rad.

[0033] In this embodiment, after the thick fiber 10 is tapered, as the diameter decreases, the light divergence angle of the fiber core 14 gradually increases. When the diameter reaches a certain point, a small amount of light does not meet the total internal reflection condition and exceeds the fiber core constraint, reaching the position of the fiber cladding 15. Meanwhile, the core diameter of the thin fiber 11 is slightly larger than the tapered diameter of the input fiber core, which can still collect the leaked light and ensure low insertion loss of the signal. At the same time, the mode modulation region has a certain deflection in the direction perpendicular to the fiber. Different deflection angles will affect the light transmission and will modulate some low-order mode core light to some high-order modes. Different deflection angles will result in different numbers and modes of high-order modes, and the final output light spot will obtain a light spot of the target size.

[0034] During the above modulation process, computer 5 also assists in determining whether the rotation angle is in place, specifically: The far-field light spot image is acquired in real time using a CCD imaging module 4 placed at the fiber optic output end. The computing system performs denoising processing on the image, sets a light intensity threshold, and removes pixels below the background noise level (e.g., 10% of the maximum gray value) to avoid interference from discrete noise in the centroid calculation. Then, a two-dimensional pixel coordinate system is established. ,in and These represent the number of columns and rows of a pixel in the image matrix, respectively.

[0035] For the light intensity distribution function of the denoised image (in (where the pixel grayscale value is used), calculate the zero-order moment, first-order moment, and second-order center distance respectively. The specific calculation formulas are as follows: The zeroth moment, denoted as , representing the total light intensity in the image:

[0036] First-order moment, denoted as and , respectively representing the pixel points in direction and Weighted cumulative energy value in direction:

[0037]

[0038] The second-order central moment, denoted as , and , respectively representing the pixel points in direction and Weighted cumulative energy value in direction:

[0039]

[0040]

[0041] Based on the above moment calculation results, the centroid coordinates of the light spot and the principal axis direction angle of the light spot, used to determine the rotation angle, are further calculated: The centroid coordinates of the light spot are denoted as The centroid represents the geometric center of the energy distribution of the light spot:

[0042]

[0043] The principal axis direction angle of the light spot is denoted as... The main direction used to describe the stretching or splitting of the light spot shape:

[0044] During the bending process of fiber 2, when the third support 9 moves forward and generates the initial bend, the initial circular fundamental mode spot will usually split or be distorted. At this time, the computer 5 displays the centroid coordinates. Significantly deviated from the physical center (reference center) of fiber 2 ), and the direction of the main axis A mutation has occurred.

[0045] During the rotation of fiber 2, the determination benchmark A is: under ideal conditions, with the physical rotation angle of the third support 9... With the increase, the main axis direction of the light spot It exhibits linear synchronous change, i.e., judgment For example, if the light spot rotates by 30 degrees, it will also rotate by about 30 degrees, indicating that the mode is in a controlled torsion state. Judgment Criterion B: When the centroid coordinates The fluctuations tend to be minimal, and it is close to the ideal reference center. normalized distance When the angle of rotation is less than a set threshold (e.g., 0.05), it can be determined that the light spot has achieved the highest degree of spatial symmetry at this twist angle, where D is the fiber core diameter. This refers to the physical distance.

[0046] When the calculation results of computer 5 simultaneously satisfy the linear following of reference A and the centroid stability of reference B, computer 5 will give a prompt that the rotation is in place, and the operator will stop the adjustment and prepare for cooling and solidification. When the calculation results do not meet the judgment criteria, it indicates that the current mode coupling efficiency is low, the mode purity is insufficient, or the phase distribution is asymmetrical. At this time, the cooling and solidification stage cannot be entered, and targeted compensation adjustment is required based on the data offset calculated in real time.

[0047] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A mode modulator modulation system, comprising: The light source (1) connected to the optical fiber (2) is characterized in that the optical fiber (2) is connected in sequence to a modulation mechanism (3) and a CCD imaging module (4). The modulation mechanism (3) is used to output different modes of light spots by rotating the angle of the optical fiber (2) and bending the arc of the optical fiber (2) when the same light spot is injected. The output light spot is connected to a computer (5) through the CCD imaging module (4).

2. The mode modulator modulation system according to claim 1, characterized in that, The modulation mechanism (3) includes a first support base (6), a second support base (7) and a third support base (9). The first support base (6) and the second support base (7) are spaced apart along the extension direction of the optical fiber (2). A flame placement area (8) is provided between the first support base (6) and the second support base (7). The third support base (9) is located on the side of the second support base (7) away from the first support base (6). The third support base (9) is movably connected to the second support base (7). An optical fiber clamp is installed on the third support base (9).

3. The mode modulator modulation system according to claim 2, characterized in that, The third support (9) includes a rotating part (91), a connecting part (92) and a mounting part (93). The connecting part (92) is slidably connected to the second support (7) to change the axial position of the third support (9) in the lateral direction. The rotating part (91) is mounted on the connecting part (92) and can rotate around the axis. The mounting part (93) has an L-shaped structure and is fixedly mounted on the rotating part (91). The mounting part (93) is used for the fixed installation of the fiber optic clamp. A through hole (95) is provided at the center of the rotating part (91) for the fiber optic cable (2) to pass through.

4. The mode modulator modulation system according to claim 3, characterized in that, The top opening of the through hole (95).

5. The mode modulator modulation system according to claim 2, characterized in that, The upper surfaces of the first support base (6) and the second support base (7) are both provided with V-shaped grooves. The two V-shaped grooves are coaxially arranged, and a rubber protective layer is fixedly provided inside the V-shaped grooves.

6. A modulation method for a modulation mode modulator, characterized in that, The modulation system employing the mode modulator as described in any one of claims 2-5 includes: When the input fiber and the output fiber are the same type of fiber, the coating layer is stripped off, and the bare fiber with the coating layer stripped off is placed directly above the flame placement area (8). The fiber (2) is placed flat and fixed. A fiber clamp corresponding to the size of the fiber (2) is placed on the third support (9), and the fiber clamp is connected to the fiber (2). Move the third support (9) forward or backward to make the mode modulator part have a curved arc. Drive the optical fiber (2) to rotate through the third support (9). Adjust the rotation angle according to the shape of the light spot.

7. The modulation method according to claim 6, characterized in that, When the input fiber and the output fiber are different types of fiber, the thick fiber (10) is tapered so that the diameter of the tapered area (12) is the same as that of the thin fiber (11). Then the tapered area (12) is cut and fused with the thin fiber (11). Place the tapered area (12) directly above the flame placement area (8), with the flame action part bypassing the fusion splice (13). Move the third support (9) forward or backward to give the mode modulator part a curved arc. Drive the thin optical fiber (11) to rotate through the third support (9). Adjust the rotation angle according to the shape of the light spot.

8. The modulation method according to claim 6, characterized in that, The curvature is 0.0174-0.122 rad.

9. The modulation method according to claim 6, characterized in that, Judgment Criterion A: When the main axis direction of the light spot changes linearly and synchronously as the physical rotation angle of the third support (9) increases, it indicates that the mode is in a controlled torsion state; Judgment Criterion B: When the fluctuation of the centroid coordinate of the light spot tends to be minimal, and its normalized distance from the ideal reference center is less than the set threshold, it is determined that the light spot has reached the highest degree of spatial symmetry under this torsion angle.

10. The modulation method according to claim 6, characterized in that, During the modulation process, the computer (5) calculates the centroid coordinates and principal axis direction angle of the light spot. When the calculation results simultaneously satisfy the linear following of the judgment criterion A and the centroid stability of the judgment criterion B, the computer (5) gives a prompt that the rotation is in place, and the operator stops the adjustment and prepares for cooling and curing.

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