Three-dimensional optical waveguide laser direct writing system and method

Abstract

The application discloses a kind of three-dimensional optical waveguide laser direct writing system and method, the system includes laser, beam expander, rotating motor, slit, focusing lens, motion platform and control system successively arranged along optical path;The light beam incident end of slit is installed with dove prism, rotating motor drives dove prism and slit without relative motion Synchronous rotation;Laser beam is refracted after dove prism with 2ω angular velocity rotation, then penetrates the slit of synchronous rotation and forms high-speed rotating elliptical light spot, forms time average, space isotropic equivalent spherical focus in sample after focusing lens focusing.This application converts dynamic elliptical light spot into equivalent spherical focus by the synchronous linkage of dove prism and rotating slit, eliminates the dependence of traditional direct writing technology on scanning direction, realizes the direct writing processing of high roundness three-dimensional optical waveguide in any scanning direction, and can further improve light field quality and processing precision by adding 4f imaging system.

Description

Technical Field

[0001] This invention relates to the field of laser processing equipment technology, specifically to a three-dimensional optical waveguide laser direct writing system and method. Background Technology

[0002] Femtosecond laser direct writing (FLDW) equipment can be used for three-dimensional micromachining of transparent optical materials and has been widely used in many research fields such as microfluidics, micro-optics, microelectronics, photonics, and optofluidics.

[0003] Existing processing systems shape the laser spot by introducing fixed or adjustable slits in the optical path to improve the circular symmetry of the waveguide cross-section. Existing equipment usually controls the laser power, scanning speed or slit width independently, lacking effective integration and coordinated control of the key parameter of laser polarization state. It is difficult to maintain the consistency and functionality of the waveguide cross-section morphology on complex three-dimensional paths. Parameter debugging relies on manual trial and error, which is inefficient and inconsistent.

[0004] In summary, existing laser direct writing equipment and its control methods suffer from three major drawbacks in waveguide morphology control: single target, lack of dimension, and insufficient intelligence. These shortcomings fail to meet the growing demand of integrated photonic devices for complex functional waveguides (such as anisotropic waveguides and mode converters). Summary of the Invention

[0005] In view of the above, the present invention provides a three-dimensional optical waveguide laser direct writing system and method, which aims to solve the technical problem that it is difficult to efficiently and flexibly write three-dimensional optical waveguides with high circularity cross-sections in transparent media.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A three-dimensional optical waveguide laser direct writing system includes a laser, a beam expander, a rotary motor, a slit, a focusing lens, a motion platform, and a control system arranged sequentially along the optical path.

[0007] The laser emits a laser beam toward the beam expander, which expands and collimates the original laser beam, allowing it to enter the slit in a straight line. A Dowell prism is mounted at the beam entrance of the slit, and the central axes of the Dowell prism and the slit coincide with the optical axis of the beam expander. The rotation axis of the rotary motor coincides with the central axis of the Dowell prism and the slit, driving the Dowell prism and the slit to rotate around their central axes at an angular velocity ω; the slit and the Dowell prism rotate synchronously without relative motion under the drive of the rotary motor.

[0008] The focusing lens is positioned on the outgoing light path of the slit to focus the laser beam into the sample; the motion platform carries the sample and drives its movement; the control system is electrically connected to the laser, slit, rotary motor, and motion platform to coordinate the control of processing parameters.

[0009] Its working principle is as follows: the original beam output by the laser is incident on the Dowell prism after passing through the beam expander, and is refracted by the Dowell prism to form a first beam. The first beam rotates around the optical axis at an angular velocity of 2ω. After the first beam passes through the synchronously rotating slit, it is shaped into a second beam with an elliptical cross section. The elliptical spot of the second beam rotates at high speed around its own optical axis at an angular velocity of 2ω. After being focused by the focusing lens, the second beam forms an equivalent spherical focus that is time-averaged and spatially isotropic inside the sample.

[0010] Preferably, the control system dynamically adjusts the slit width d in real time according to preset optical waveguide cross-sectional size parameters.

[0011] Preferably, the angular velocity ω of the rotary motor is in the range of 0-50000 rpm.

[0012] Preferably, the numerical aperture (NA) of the focusing lens is between 0.05 and 1.4.

[0013] Preferably, the motion platform is configured as a nano-displacement platform, an air-bearing platform, or a linear motor module, which can drive the sample to achieve nanometer or submicron level precision motion in the X, Y, and Z dimensions.

[0014] Furthermore, the system also includes a 4f imaging system disposed between the slit and the focusing lens. The 4f imaging system includes a first lens and a second lens arranged sequentially along the optical path, the first lens and the second lens sharing the system's principal optical axis; the plane containing the slit is located at the front focal plane of the first lens, the rear focal plane of the first lens coincides with the front focal plane of the second lens, and the rear focal plane of the second lens coincides with the entrance pupil plane or the front focal plane of the focusing lens.

[0015] Furthermore, the 4f imaging system also includes an aperture stop disposed on the spectral plane where the first lens and the second lens coincide, for filtering out high-frequency diffraction noise.

[0016] Furthermore, by adjusting the focal length ratio of the first lens to the second lens, the size of the light spot after the slit is shaped can be scaled to match the entrance pupil diameter of the focusing lens.

[0017] The present invention also provides a three-dimensional optical waveguide laser direct writing method based on any of the above system schemes, comprising the following steps: S1. The system presets the laser's output power, wavelength, pulse frequency, the rotary motor's rotational angular velocity ω, the slit's initial width d, the focusing lens's focal position, and the motion platform's three-dimensional scanning path. S2. Fix the sample on the motion platform and calibrate it to the initial processing position; S3. Start the laser to output a pulsed laser beam, and at the same time drive the rotary motor to drive the Dowell prism and the slit to rotate synchronously at high speed; after the laser beam passes through the beam expander, the Dowell prism and the slit in sequence, it forms a dynamically high-speed rotating elliptical spot. S4. After the dynamically rotating elliptical light spot is focused by the focusing lens, it forms a time-averaged equivalent spherical focus inside the sample; the control system drives the motion platform to move the sample relative to the equivalent spherical focus along a preset three-dimensional trajectory, thereby performing laser modification on the sample material and etching a three-dimensional optical waveguide structure.

[0018] In the above method, the formation condition of the equivalent spherical focal spot is that the optical axis rotation speed of the elliptical spot is higher than the laser modification time constant of the sample material.

[0019] The beneficial effects of this invention are as follows: 1. High-roundness three-dimensional waveguide direct writing: By designing a combination of "Dowell prism + synchronous rotating slit", an equivalent spherical focus is dynamically generated, which fundamentally solves the problem of poor waveguide cross-section roundness caused by the ellipsoid of the focus. The directly written waveguide has extremely low birefringence and transmission loss.

[0020] 2. Simple system structure and controllable cost: Compared with SLM or complex beam shaping optical paths, the present invention adopts a pure optical-mechanical structure, which does not require complex computational holograms or high-speed electronically controlled polarization modulation, resulting in high system stability and significantly reduced cost.

[0021] 3. High processing efficiency and flexibility: By controlling the rotation speed of the rotary motor and adjusting the slit width, the isotropy of the dynamic focus can be adjusted in real time, the waveguide cross-sectional size can be changed, and with the help of the motion platform, high-quality waveguide direct writing of any three-dimensional path can be quickly achieved.

[0022] 4. Wide material versatility: Suitable for a variety of transparent materials, including but not limited to... , , , Inorganic optical materials, as well as polymer and semiconductor materials. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a three-dimensional optical waveguide laser direct writing system provided in Embodiment 1 of the present invention.

[0024] Figure 2This is a schematic diagram showing the local structure and rotational relationship of the Dowell prism and slit.

[0025] Figure 3 This is a schematic diagram illustrating the dynamic beam pattern change after the beam passes through the Dowell prism and rotating slit in this invention.

[0026] Figure 4 This is a schematic diagram of the structure of the three-dimensional optical waveguide laser direct writing system provided in Embodiment 2 of the present invention.

[0027] Figure 5 This is a schematic diagram of the beam transmission principle of the 4f imaging system in Embodiment 2 of the present invention.

[0028] Figure 6 This is a schematic diagram of a three-dimensional helical waveguide written directly in a transparent material and its local cross-section magnified.

[0029] Explanation of reference numerals in the attached figures: 1. Laser; 2. Beam expander; 3. First reflector; 4. Second reflector; 5. Dowell prism; 6. Rotary motor; 7. Slit; 8. Third reflector; 9. Focusing lens; 10. Sample; 11. Motion platform; 12. Control system; 13. First lens; 14. Second lens; 21. First beam; 22. Second beam. Detailed Implementation

[0030] The specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this application.

[0031] Example 1 Please see Figure 1 This embodiment provides a three-dimensional optical waveguide laser direct writing system, which includes, arranged sequentially along the optical path: a laser 1, a beam expander 2, a first reflector 3, a second reflector 4, a Dowell prism 5, a slit 7, a third reflector 8, a focusing lens 9, a motion platform 11 for carrying a sample 10, and a control system 12 for coordinated control.

[0032] Laser 1 is used to output pulsed laser (femtosecond laser, picosecond laser, or nanosecond laser), and the wavelength of the pulsed laser used is between 180nm and 1600nm. In this embodiment, a femtosecond laser with a center wavelength of 1030nm and a pulse width of 300fs is preferably used to obtain a stable nonlinear absorption effect.

[0033] Beam expander 2 is positioned in the output optical path of laser 1 to expand and collimate the laser beam, thereby controlling the beam diameter and divergence angle. When the laser beam output from laser 1 enters beam expander 2, it expands the beam, reduces the beam divergence angle, and adjusts the laser beam diameter to match the aperture of subsequent optical elements. The beam expansion factor can be adjusted within the range of 0.5-10 times according to actual needs.

[0034] Both the first reflecting mirror 3 and the second reflecting mirror 4 are high-reflectivity medium mirrors, used to deflect the direction of the expanded laser beam so that it can be accurately incident along the optical axis center of the Dowell prism 5, thus ensuring imaging quality.

[0035] The Dove prism 5 is positioned in the output light path of the second reflecting mirror 4, such as... Figure 2 As shown in (b), the image formed by the laser beam after passing through the Dowell prism 5 rotates 180° around its optical axis. The central axis of the Dowell prism 5 coincides with the optical axis.

[0036] The rotary motor 6 is a high-precision, high-speed hollow shaft motor. The rotating shaft of the rotary motor 6 is fixedly aligned with the center of the Daowei prism 5. The rotary motor 6 can drive the Daowei prism 5 to rotate at high speed around the optical axis at an angular velocity ω, with the preferred operating range of angular velocity ω being 0-50000 rpm.

[0037] like Figure 2 As shown in (a), slit 7 is positioned in the output light path of the Dowell prism 5 and mounted on the rotating shaft of the rotary motor 6, with the centerline of slit 7 coinciding with the optical axis. The slit width d of slit 7 can be adjusted and controlled by the control system 12 to spatially shape the output beam and generate an elliptical light spot. The orientation of slit 7 is parallel or perpendicular to the bottom surface of the Dowell prism 5. Driven by the rotary motor 6, the Dowell prism 5 and slit 7 achieve synchronous high-speed rotation without relative motion.

[0038] The third reflecting mirror 8 is used to reflect the rotated and shaped laser beam so that it is incident on the focusing mirror 9 perpendicularly or at a designed angle.

[0039] Focusing lens 9 is used to focus the incident laser beam into the interior of the sample, and it has a high numerical aperture (NA). The focal length of focusing lens 9 is f, which is used to converge the incident parallel laser beam into a very small focal spot that acts on the interior of sample 10. NA is between 0.05 and 1.4, preferably NA=0.28, and f=17mm.

[0040] The motion platform 11 is configured as a high-precision nanometer displacement platform, air-bearing platform, or linear motor module to support the sample 10 and drive it to move precisely in the X, Y, and Z dimensions, with motion accuracy reaching the nanometer or sub-micrometer level. The sample 10 covers the following area: Glass, Crystals film, Ceramic, polymer (such as PMMA), or semiconductor materials such as silicon, silicon carbide (SiC), gallium arsenide (CaAs).

[0041] The control system 12 is configured as a computer or embedded controller, electrically connected to the laser 1, slit 7, rotary motor 6, focusing lens 9 (e.g., electrically adjustable), and motion platform 11. It is used to coordinate the control of laser output power, slit width, rotary motor speed, focal point Z-axis position, and the scanning path of the motion platform.

[0042] When the laser direct writing system is in operation: After the equipment is started, the control system 12 outputs a preset processing command, controlling the laser 1 to emit a Gaussian beam with an original circular cross-section; the original beam is expanded and collimated by the beam expander 2, and converted into a uniform parallel beam; the parallel beam is then deflected and guided by the first reflector 3 and the second reflector 4, and then precisely incident on the Daowei prism 5 along the main optical axis of the system. At the same time, the control system 12 drives the rotary motor 6 to rotate at a preset angular velocity ω at high speed, synchronously driving the Daowei prism 5 and the slit 7 to rotate synchronously without relative motion. Based on the optical imaging characteristics of the Daowei prism 5, the incident beam is refracted by the Daowei prism 5 to form a first beam 21, which rotates around the optical axis at an angular velocity of 2ω, and its cross-sectional intensity distribution is as follows. Figure 3 As shown in section (a) of Figure I1, the rotating first beam 21, after penetrating the synchronously rotating slit 7, completes spatial shaping to form a second beam 22 with an elliptical cross-section. The intensity distribution of the cross-section of the second beam 22 is as follows. Figure 3 I2 is shown at (a) in the diagram.

[0043] Under static conditions, after the laser beam is shaped by the fixed-width slit 7 arranged along the y-direction, the circular spot can be converted into a standard elliptical spot, with the major axis of the ellipse perpendicular to the length direction of the slit 7. When the slit 7 rotates with the rotary motor 6 at an angular velocity ω, the elliptical optical axis of the second beam 22 rotates synchronously with ω; combined with the 2ω beam rotation effect brought by the Dowell prism 5, the two movements are superimposed, and the second beam 22, which is finally incident on the focusing lens 9, rotates at high speed around its own optical axis at an angular velocity of 2ω. During the processing, the control system 12 can dynamically adjust the slit width d of the slit 7 according to the preset optical waveguide cross-sectional size parameters to accurately match different processing specifications.

[0044] After being focused by focusing lens 9, the high-speed dynamically rotating elliptical light spot forms a time-averaged, spatially isotropic equivalent spherical focal spot in the focal region inside sample 10. The specific principle is as follows: when the rotational speed of the elliptical light spot is much higher than the laser modification time constant of the sample material, the instantaneously changing material modification region at the focal point will tend to become uniform under the time integration effect, ultimately forming an isotropic spherical equivalent focal spot. The equivalent spot effects are as follows: Figure 3 (b) Figure 3 As shown in (c) in the figure.

[0045] During processing, the control system 12 drives the motion platform 11 to perform a three-dimensional relative scan of the sample 10 relative to the equivalent spherical focal spot. The scanning path can be adapted to any three-dimensional trajectory, such as a straight line, curve, or spiral. Since the equivalent focal spot is a standard spherical spot, the cross-section of the laser modification mark in any scanning direction inside the sample material is a highly rounded circle, which can directly and efficiently complete the direct writing processing of high-precision three-dimensional optical waveguides.

[0046] In this embodiment, the slit 7 is arranged along the y-direction, and after shaping and focusing, it can form a standard three-dimensional ellipsoidal focal spot. The xoy plane is a standard elliptical spot, the xoz plane is a standard circular spot, and the yoz plane is a standard elliptical spot. The intensity distribution of the spot on each plane corresponds to... Figure 3 I3, I4, and I5 are shown at (a) in the diagram. The spot size, depth of focus parameters, and optical element parameters of this system satisfy the following correspondence:

[0047]

[0048]

[0049]

[0050] In the formula, M² is the beam quality factor of the output beam of laser 1, λ is the laser wavelength, D is the diameter of the expanded beam, and f is the focal length of the focusing lens. , These are the focal spot diameters in the x and y directions, respectively. , These are the focal depths in the x and y directions, respectively.

[0051] In this embodiment, the preferred slit width d enables the focal spot diameter to be the same as the depth of focus within the xoz plane, i.e. (When the slit is rotated to the z-direction, the focal spot diameter and depth of focus can be the same in the yoz plane, i.e.) At this point, the three-dimensional intensity distribution of the focal point of the focusing lens is a standard ellipsoid whose central axis coincides with the optical axis of the focusing lens, and its intensity distribution is a standard circle in the xoz plane and a standard ellipse in the yoz plane.

[0052] Example 2 This embodiment is a further optimization based on Embodiment 1. The same structures, connections, and working principles as Embodiment 1 will not be repeated here. Figure 4As shown, the core improvement feature of this embodiment is: a 4f imaging system is added between the third reflecting mirror 8 and the focusing mirror 9. The 4f imaging system can also be placed at any optical path position between the slit 7 and the focusing mirror 9 according to the optical path layout requirements, and the same optical optimization effect can be achieved.

[0053] Specifically, the 4f imaging system includes a first lens 13 and a second lens 14 arranged sequentially along the optical path. The focal length of the first lens 13 is f1, and the focal length of the second lens 14 is f2. The first lens 13 and the second lens 14 are coaxially arranged and share the system's principal optical axis. Their optical arrangement is as follows: Figure 5 As shown: the plane where the slit 7 is located is located at the front focal plane of the first lens 13; the rear focal plane of the first lens 13 coincides with the front focal plane of the second lens 14; the rear focal plane of the second lens 14 coincides with the entrance pupil (or front focal plane) of the focusing lens 9, thereby achieving accurate transmission of the light field.

[0054] The addition of a 4f imaging system can optimize the system's processing performance in two dimensions: diffraction suppression and spot matching. Specific functions are as follows: First, it eliminates diffraction interference and optimizes the optical field quality. After the laser beam undergoes spatial shaping through slit 7, Fresnel diffraction occurs, generating high-frequency diffraction stray light, which leads to disordered downstream optical field distribution and reduces the purity of the focused spot and processing accuracy. This 4f imaging system can image the original optical field distribution of the slit 7 plane onto the entrance pupil of the focusing lens 9 without distortion. At the same time, an aperture can be placed at the spectral plane where the first lens 13 and the second lens 14 coincide to filter out high-frequency diffraction noise and stray light, so that the beam incident on the focusing lens 9 has a clean, uniform, and stable intensity distribution, completely avoiding the influence of diffraction on the focusing quality.

[0055] Second, adapting the light spot size improves energy utilization. This is achieved by adjusting the focal length ratio of the first lens 13 and the second lens 14 ( / This allows for precise scaling and adjustment of the beam size after slit 7 shaping, ensuring optimal matching between the incident beam size and the entrance pupil diameter of focusing lens 9. This maximizes the utilization of laser energy while fully leveraging the numerical aperture performance of focusing lens 9, thereby improving focusing accuracy. Based on optical derivation, when... > At the same time, the 4f imaging system can realize the proportional amplification of scanning angle and spot size, can be adapted to large numerical aperture focusing mirrors, and can prepare smaller focusing points, further improving the processing accuracy of optical waveguides.

[0056] Based on the above system principle, it can be deduced that after passing through the 4f system, the scanning angle and spot size are magnified proportionally (when...). > (At times), it is advantageous to use a focusing lens with a large numerical aperture to obtain a smaller focal point. Except for the addition of a 4f imaging system, the structural parameters, assembly relationships, and working principles of the remaining structures (such as the Dove prism, rotating slit, motion platform, etc.) in this embodiment are completely consistent with those in Embodiment 1. By introducing the 4f system, this system can obtain a higher quality equivalent spherical focal point, thereby directly constructing a three-dimensional optical waveguide with lower loss and higher roundness.

[0057] Based on the three-dimensional optical waveguide laser direct writing system disclosed in Embodiments 1 and 2 above, its direct writing method includes the following steps: S1. Based on the material of the sample 10 to be processed, the cross-sectional dimensions, trajectory shape, and accuracy requirements of the target three-dimensional optical waveguide, the processing parameters are preset through the control system 12. These parameters include the output power, laser wavelength, and pulse frequency of the laser 1, the beam expansion factor of the beam expander 2, the rotational angular velocity ω of the rotary motor 6, the initial slit width d of the slit 7, the Z-axis focal position of the focusing lens 9, and the three-dimensional scanning path and moving speed of the motion platform 11. Simultaneously, the optical path calibration of each optical component is completed to ensure that the laser beam is accurately transmitted along the main optical axis, without eccentricity or obstruction.

[0058] S2. The sample 10 to be processed is stably fixed on the bearing end face of the motion platform 11. The motion platform 11 is adjusted by the control system 12 to complete the initial position calibration of the sample 10, so that the processing area of ​​the sample 10 corresponds to the initial processing position of the laser focus, thus completing the pre-processing positioning.

[0059] S3. Start the equipment. The control system 12 controls the laser 1 to output a pulsed laser with preset parameters. After the laser beam is expanded and collimated by the beam expander 2, it is deflected and guided by the first reflector 3 and the second reflector 4 and then incident on the Dowell prism 5. The synchronous drive rotary motor 6 drives the Dowell prism 5 and the slit 7 to rotate synchronously at high speed. The beam spatial shaping is completed through the slit 7 to form a dynamically rotating elliptical light spot. If the equipment of Embodiment 2 is used, after the shaped beam is diffracted and filtered by the 4f imaging system and the light spot size is adapted, it is transmitted to the subsequent focusing unit.

[0060] S4. After being shaped, the dynamic rotating elliptical light spot is guided by the third reflecting mirror 8 and focused by the focusing mirror 9, forming a time-averaged equivalent spherical focus inside the sample 10. The control system 12 drives the motion platform 11 to move the sample 10 precisely along a preset three-dimensional trajectory relative to the spherical focus. The isotropic spherical focus is used to perform laser modification on the sample material, continuously etching a three-dimensional optical waveguide structure with a high roundness cross-section.

[0061] S5. During the processing, the control system 12 dynamically fine-tunes the slit width 7, motor speed, focal position and scanning speed according to real-time processing feedback data to ensure the dimensional accuracy and uniformity of the optical waveguide. After completing the preset trajectory scanning processing, the laser 1 is turned off, all moving parts and optical adjustment parts are reset, the processed sample is removed, and the single three-dimensional optical waveguide direct writing processing is completed.

[0062] In summary, this invention, by setting up a synchronous linkage structure between the Dowell prism and the rotating slit, utilizes the optical axis rotation imaging characteristics of the Dowell prism and the spatial shaping characteristics of the slit. Through the superposition of beam rotation angular velocities, a dynamic elliptical spot is converted into a time-averaged equivalent spherical focus, overcoming the shortcomings of anisotropy of the spot and strong dependence on the scanning direction in traditional laser direct writing technology. This invention achieves high roundness shaping of the optical waveguide cross-section under arbitrary scanning directions without the need for complex optical path compensation structures, resulting in high processing efficiency and wide material compatibility. Furthermore, by adding a 4f imaging system, the light field quality is further optimized, focusing accuracy is improved, and optical waveguide transmission loss is effectively reduced, significantly improving the processing accuracy and product consistency of three-dimensional optical waveguides, thus meeting the large-scale processing needs of high-precision and complex three-dimensional optical waveguides.

[0063] The embodiments described above merely illustrate implementation methods of the present invention and should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A three-dimensional optical waveguide laser direct writing system, comprising a laser (1), a beam expander (2), a rotary motor (6), a slit (7), a focusing lens (9), a motion platform (11), and a control system (12) arranged sequentially along the optical path, characterized in that: The laser (1) emits a laser beam toward the beam expander (2), which expands and collimates the original laser beam so that the laser beam can be straight into the slit (7). The beam incident end of the slit (7) is equipped with a Dowell prism (5), and the central axis of the Dowell prism (5) and the slit (7) coincides with the optical axis of the beam expander (2); The rotating motor (6) has its rotating shaft coincides with the central axis of the Dowell prism (5) and the slit (7). The rotating motor (6) drives the Dowell prism (5) and the slit (7) to rotate around their central axis at an angular velocity ω. The slit (7) and the Dowell prism (5) rotate synchronously without relative motion under the drive of the rotating motor (6). The focusing lens (9) is set on the outgoing light path of the slit (7) to focus the laser beam into the sample (10); the motion platform (11) carries the sample (10) and drives the sample to move; the control system (12) is electrically connected to the laser (1), the slit (7), the rotary motor (6) and the motion platform (11) to coordinate the control of the processing parameters. The original beam output by the laser (1) is incident on the Dowell prism (5) after passing through the beam expander (2). After being refracted by the Dowell prism (5), a first beam (21) is formed. The first beam (21) rotates around the optical axis at an angular velocity of 2ω. After the first beam (21) passes through the synchronously rotating slit (7), it is shaped into a second beam (22) with an elliptical cross section. The elliptical spot of the second beam (22) rotates at high speed around its own optical axis at an angular velocity of 2ω. After being focused by the focusing lens (9), the second beam (22) forms an equivalent spherical focus that is time-averaged and spatially isotropic inside the sample (10).

2. The three-dimensional optical waveguide laser direct writing system according to claim 1, characterized in that, The control system (12) adjusts the slit width d of the slit (7) according to the preset optical waveguide cross-sectional size parameters.

3. The three-dimensional optical waveguide laser direct writing system according to claim 1, characterized in that, The angular velocity ω of the rotary motor (6) ranges from 0 to 50000 rpm.

4. The three-dimensional optical waveguide laser direct writing system according to claim 1, characterized in that, The numerical aperture NA of the focusing lens (9) is between 0.05 and 1.

4.

5. The three-dimensional optical waveguide laser direct writing system according to claim 1, characterized in that, The motion platform (11) is configured as a nano-displacement platform, an air-floating platform, or a linear motor module, which can drive the sample to achieve nano- or sub-micron level motion in the three dimensions of X, Y, and Z.

6. The three-dimensional optical waveguide laser direct writing system according to claim 1, characterized in that, It also includes a 4f imaging system disposed between the slit (7) and the focusing lens (9). The 4f imaging system includes a first lens (13) and a second lens (14) arranged sequentially along the optical path. The first lens (13) and the second lens (14) share the main optical axis of the system. The plane where the slit (7) is located is located at the front focal plane of the first lens (13). The rear focal plane of the first lens (13) coincides with the front focal plane of the second lens (14). The rear focal plane of the second lens (14) coincides with the entrance pupil plane or the front focal plane of the focusing lens (9).

7. The three-dimensional optical waveguide laser direct writing system according to claim 6, characterized in that, The 4f imaging system also includes an aperture on the spectral plane where the first lens (13) and the second lens (14) overlap, for filtering out high-frequency diffraction noise.

8. The three-dimensional optical waveguide laser direct writing system according to claim 6, characterized in that, By adjusting the focal length ratio of the first lens (13) and the second lens (14), the size of the light spot after the slit (7) is shaped is scaled to match the entrance pupil diameter of the focusing lens (9).

9. A direct writing method based on the three-dimensional optical waveguide laser direct writing system according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Preset processing parameters: The output power, wavelength, and pulse frequency of the laser (1), the rotational angular velocity ω of the rotary motor (6), the initial slit width d of the slit (7), the focal position of the focusing lens (9), and the three-dimensional scanning path of the motion platform (11) are preset by the control system (12). S2. Positioning the sample: Fix the sample (10) on the motion platform (11) and calibrate it to the initial processing position; S3. Synchronous rotation and beam shaping: The laser (1) is started to output a pulsed laser beam, and at the same time, the rotary motor (6) drives the Dowell prism (5) and the slit (7) to rotate synchronously at high speed; the laser beam passes through the beam expander (2), the Dowell prism (5) and the slit (7) in sequence to form a dynamically rotating elliptical spot; S4. Focusing scanning processing: After the dynamic high-speed rotating elliptical spot is focused by the focusing lens (9), a time-averaged equivalent spherical focus is formed inside the sample (10); the control system (12) drives the motion platform (11) to move the sample (10) relative to the equivalent spherical focus along a preset three-dimensional trajectory, and performs laser modification on the sample material to form a three-dimensional optical waveguide structure.

10. The direct writing method according to claim 9, characterized in that, In step S4, the formation condition of the equivalent spherical focal spot is that the optical axis rotation speed of the elliptical spot is higher than the laser modification time constant of the sample (10) material.

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