Adjustable automatic interface tracking system and method

Abstract

The present invention belongs to the technical field of laser direct writing system, and specifically relates to an adjustable automatic interface tracking system and method, the system comprising: a first beam splitting prism, an objective lens, a glass sheet, a lens, a second beam splitting prism, a first reflector, a second reflector and a CCD camera; a light beam passes through the first beam splitting prism and enters the objective lens to be focused on the glass sheet, and after being reflected by the glass sheet, passes through the lens and is split into two beams by the second beam splitting prism, and is reflected by the first reflector and the second reflector respectively and enters the CCD camera; the system also comprises a controller, the controller obtains the focus position of two light spots entering the CCD camera on the CCD camera and the light intensity difference of several pixels within the focus position setting range, and performs automatic focus adjustment using the maximum and minimum value intervals of the light intensity difference curve, thereby improving the tracking accuracy and stability of the system.

Description

Technical Field

[0001] The invention belongs to the technical field of laser direct writing systems, and in particular relates to an adjustable automatic interface tracking system and method. Background Art

[0002] The autofocus system can realize the control of the direct writing interface of the laser direct writing system. Since the focal depth of the objective lens used in the laser direct writing system is generally in the micrometer level, the slight unevenness on the surface of the object will cause the direct writing pattern to be blurred. The current displacement platform cannot ensure that its Z-axis height change remains within the focal depth after moving horizontally for a long distance. It is necessary to focus through the autofocus system to improve the exposure quality. In addition, in view of the characteristic of two-photon laser direct writing that can be written directly in the material, the direct writing depth needs to be precisely controlled. Therefore, interface detection autofocus is required to find the appropriate interface position.

[0003] At present, most automatic focusing methods ensure that the laser writes directly on the surface of the currently detected medium. If you want to write directly inside the medium, you can only do it by moving the piezoelectric station. However, this method cannot ensure that the actual direct writing focus position is at the expected depth position, and there is no feedback on the actual focus position. Secondly, the range of the light intensity difference curve obtained by the ordinary differential focusing method is fixed, that is, the inclination range of the glass surface and the flatness of the glass that can be processed are fixed, and it cannot cope with situations where the flatness of the glass surface varies greatly. In addition, the differential focusing method often requires the use of two camera hardware and pinholes, which increases costs. Summary of the invention

[0004] The range of the light intensity difference curve obtained by the ordinary differential focusing method is fixed, that is, the inclination range of the glass surface and the flatness of the glass that can be processed are fixed, and it cannot cope with the situation where the flatness of the glass surface varies greatly. The present invention provides an adjustable automatic interface tracking system and method.

[0005] In a first aspect, the technical solution of the present invention provides an adjustable automatic interface tracking system, comprising a first beam splitting prism, an objective lens, a glass sheet, a lens, a second beam splitting prism, a first reflector, a second reflector and a CCD camera; The light beam passes through the first beam splitter prism and enters the objective lens to be focused on the glass sheet. After being reflected by the glass sheet, it passes through the lens and is split into two beams by the second beam splitter prism. The beams are reflected by the first reflector and the second reflector respectively and enter the CCD camera. The system also includes a controller, which obtains the focus position of two light spots entering the CCD camera on the CCD camera and the light intensity difference of several pixels within the focus position setting range, and performs automatic focus adjustment using the maximum and minimum value intervals of the light intensity difference curve.

[0006] As a preferred embodiment of the technical solution of the present invention, a piezoelectric station is provided below the glass sheet, and the piezoelectric station is connected to a controller for controlling the micron-level movement of the glass sheet up and down.

[0007] As a preferred embodiment of the technical solution of the present invention, a translation stage is installed under the first reflector and the second reflector respectively, and each translation stage is connected to a controller respectively to control the distance from the first reflector and the second reflector to the second beam splitting prism, thereby controlling the distance from the CCD camera to the lens.

[0008] As a preferred embodiment of the technical solution of the present invention, the system further includes a third reflecting mirror; The light beam is transmitted through the first beam splitter prism into the objective lens and focused on the glass sheet. The light beam reflected by the glass sheet is controlled by the first beam splitter prism to be transmitted to the third reflector. The light beam reflected by the third reflector is transmitted to the second beam splitter prism through the lens.

[0009] As a preferred embodiment of the technical solution of the present invention, the distance between the CCD camera and the lens is first moved, and then the piezoelectric stage is controlled to lift and lower the glass sheet, the position where the light spot is focused on the CCD camera is found, the camera displacement and the glass sheet displacement are recorded, and the functional relationship between the camera displacement and the glass sheet displacement is obtained by a fitting formula.

[0010] As a preferred embodiment of the technical solution of the present invention, the fitting formula is as follows:

[0011] Where y is the camera displacement, x is the glass displacement, L is the distance between the lens and the objective lens, f1 is the objective lens focal length, f2 is the focal length of the lens, b is the offset of L, a is the offset of the glass displacement, and c is the offset of the camera displacement.

[0012] As a preferred embodiment of the technical solution of the present invention, when the controller uses the maximum and minimum value intervals of the light intensity difference curve to perform automatic focusing adjustment, if the current direct writing position light intensity difference is not 0, the difference between the direct writing position and the z-axis position corresponding to the value of 0 is found in the light intensity difference curve, the displacement of the CCD camera is adjusted, and the position that deviates from the focus is corrected to the focus, thereby achieving automatic focusing.

[0013] As a preferred embodiment of the technical solution of the present invention, the controller controls the range of the maximum value and minimum value interval of the light intensity difference curve by controlling the displacement stage under the reflector.

[0014] In a second aspect, the technical solution of the present invention provides an adjustable automatic interface tracking method, comprising the following steps: Build an autofocus system, obtain two light spots on the CCD camera, and record the light intensity of several pixels from the center of the light spot; the optical path of the autofocus system includes: the light beam is split into two beams by a beam splitter prism, and is reflected by two mirrors into the CCD camera respectively; The optical path structure is simulated, and the relationship between glass displacement and camera displacement is obtained through fitting formula; Based on the simulation results, an interface tracking system is constructed. The optical path of the tracking system includes: the light beam is transmitted through the first beam splitter prism into the objective lens and focused on the glass sheet. The light beam reflected by the glass sheet is controlled by the first beam splitter prism to be transmitted to the third reflector. The light beam reflected by the third reflector is transmitted to the second beam splitter prism through the lens and is split into two beams by the second beam splitter prism. The beams are reflected by the first reflector and the second reflector respectively and enter the CCD camera. First move the distance between the CCD camera and the lens, then raise and lower the glass sheet to find the position where the light spot is focused on the CCD camera, record the light intensity of the two light spots at the focus position on the camera and the set range of several pixels, and use the maximum-minimum value range of the light intensity difference curve to perform automatic focus adjustment.

[0015] As a preferred embodiment of the technical solution of the present invention, the step of automatically adjusting the focus using the maximum-minimum range of the light intensity difference curve includes: If the current direct writing position light intensity difference is not 0, find the difference between the direct writing position and the z-axis position corresponding to 0 in the light intensity difference curve, adjust the displacement of the CCD camera, correct the out-of-focus position to the focus, and achieve automatic focusing.

[0016] It can be seen from the above technical solutions that the present invention has the following advantages: by introducing differential confocal technology, the present invention can accurately measure and track the focal position of the light beam on the reflective interface of the glass sheet. The controller uses the focal position of the two light spots captured by the CCD camera and the light intensity difference of the pixels within the set range to perform automatic focus adjustment through the maximum and minimum value intervals of the light intensity difference curve, achieving high-sensitivity response and precise control of changes in the interface position, thereby improving the tracking accuracy and stability of the system.

[0017] By setting a piezoelectric stage under the glass sheet and connecting it to a controller, the present invention realizes precise control of the micron-level movement of the glass sheet up and down. This fine-tuning mechanism helps to further refine the focus position, ensure that the light beam always remains in the optimal focus state, and improve the resolution and measurement accuracy of the system. The displacement stages installed under the first reflector and the second reflector, respectively, can dynamically adjust their distance to the second beam splitter prism by connecting to the controller, thereby controlling the distance from the CCD camera to the lens. This design enables the system to adjust the magnification of the imaging system according to actual needs, enhancing the adaptability and flexibility of the system.

[0018] By introducing the third reflector, the present invention optimizes the optical path, so that the light beam can be transmitted and focused more efficiently. This design not only improves the utilization rate of light energy, but also simplifies the optical path structure and reduces the complexity and cost of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 It is the optical path diagram of the interface tracking system of the present invention.

[0021] Figure 2 This is a diagram of the autofocus system.

[0022] Figure 3 This is a trend chart of piezoelectric changes of large-scale gratings under long-term direct writing.

[0023] Figure 4 The grating structure diagram of the system using the present invention, wherein (a) is the grating microscopic structure, (b) is the grating electron microscope structure, and (c) is the grating macroscopic structure. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0025] like Figure 1 As shown, an embodiment of the present invention provides an adjustable automatic interface tracking system, comprising a first beam splitting prism 1, an objective lens 2, a glass sheet 3, a lens 5, a second beam splitting prism 6, a first reflector 7, a second reflector 9 and a CCD camera 11; The light beam passes through the first beam splitter prism 1 and enters the objective lens 2 to be focused on the glass sheet 3. After being reflected by the glass sheet 3, the light beam passes through the lens 5 and is split into two beams by the second beam splitter prism 6. The two beams are reflected by the first reflector 7 and the second reflector 9 respectively and enter the CCD camera 11. The system also includes a controller, which obtains the focus position of two light spots entering the CCD camera on the CCD camera and the light intensity difference of several pixels within the focus position setting range, and performs automatic focus adjustment using the maximum and minimum value intervals of the light intensity difference curve.

[0026] In the embodiment of the present invention, a piezoelectric stage (not shown in the drawings) is provided below the glass sheet, and the piezoelectric stage is connected to a controller for controlling the micrometer-level movement of the glass sheet up and down.

[0027] As a preferred embodiment of the technical solution of the present invention, a first translation stage 8 is installed under the first reflecting mirror 7, and a second translation stage 10 is installed under the second reflecting mirror 9. The first translation stage 8 and the second translation stage 10 are respectively connected to the controller to respectively control the distance from the first reflecting mirror 7 and the second reflecting mirror 9 to the second beam splitting prism 6, thereby controlling the distance from the CCD camera to the lens.

[0028] In some embodiments, the system further comprises a third reflector 4; The light beam is transmitted through the first beam splitter prism 1 into the objective lens 2 and focused on the glass sheet 3. The light beam reflected by the glass sheet 3 is controlled by the first beam splitter prism 1 to be transmitted to the third reflector 4. The light beam reflected by the third reflector 4 is transmitted to the second beam splitter prism 6 through the lens 5.

[0029] In some embodiments, the distance between the CCD camera and the lens is first moved, and then the piezoelectric stage is controlled to raise and lower the glass sheet, the position where the light spot is focused on the CCD camera is found, the camera displacement and the glass sheet displacement are recorded, and the functional relationship between the camera displacement and the glass sheet displacement is obtained by a fitting formula.

[0030] The fitting formula is as follows:

[0031] Where y is the camera displacement, x is the glass displacement, L is the distance between the lens and the objective lens, f1 is the objective lens focal length, f2 is the focal length of the lens, b is the offset of L, a is the offset of the glass displacement, and c is the offset of the camera displacement.

[0032] In some embodiments, when the controller uses the maximum and minimum value intervals of the light intensity difference curve to perform automatic focusing adjustment, if the current direct writing position light intensity difference is not 0, the difference between the direct writing position and the z-axis position corresponding to the value of 0 is found in the light intensity difference curve, and the displacement of the CCD camera is adjusted to correct the deviating position to the focus to achieve automatic focusing.

[0033] The controller controls the range of the maximum value and minimum value interval of the light intensity difference curve by controlling the displacement stage under the reflector.

[0034] This system is used for two-photon laser direct writing to directly write large-scale gratings. Since it is difficult for the glass sheet to be completely perpendicular to the laser beam, there must be a certain degree of inclination in the x and y directions. When the glass sheet is moved for direct writing, a height difference will occur, resulting in defocusing, so real-time interface tracking and automatic focusing are required. Figure 3It shows the general trend of piezoelectric changes during the 18-hour long direct writing process. Initially, the system was not stable yet, and the glass needed to be initially leveled to a certain degree before direct writing could begin, which caused the curve to jitter violently at the beginning. The overall curve is in an upward tilt, mainly because the glass is tilted upward along the entire direct writing when writing the grating, and the height difference between the two ends is about 10 microns. The small picture shows that the curve is in a Z-shaped reciprocating motion, because when the grating is written directly from left to right, the glass sheet has an inclination, and the height difference between the left and right is about 5 microns, and the reciprocating direct writing will show a Z-shaped change trend. It can be seen that during the direct writing process, the focusing system has been following the movement of the interface.

[0035] Figure 4 The grating structure diagram after using this system is shown in Figure 1. Figure 4 As shown in (a) in the figure, the electron microscope structure is as follows Figure 4 As shown in (b) in the figure, the macroscopic structure is Figure 4 As shown in (c) in the figure. It can be seen that with the help of the interface adjustable autofocus system in this article, large-scale and uniform gratings can be directly written, and large-scale gratings of 50mm*50mm can be directly written. The displacement of the glass sheet is controlled by moving the camera to control the direct writing depth, and the interface is adjustable. By combining camera displacement and autofocus, direct writing of glass with different roughness and different depths can be achieved, and interface tracking can be achieved. Using an 80x objective lens, a 100mm focal length lens, and a 20mm working range displacement stage, the distance between the objective lens and the lens is controlled to be 700mm, and the interface tracking autofocus can be achieved for glass sheets with a roughness of 5 microns to 20 microns, and a thickness of 40 microns can be directly written inside the glass. Replacing the 40x objective lens can directly write a thickness of 80 microns. By expanding the working range of the displacement stage, replacing the objective lens, lens, and objective lens distance, direct writing of glass with different flatness, different tilt degrees, and different direct writing depths can be achieved.

[0036] The piezoelectric stage mentioned in the embodiment of the present invention is a device that uses the piezoelectric effect to achieve precise displacement control. Piezoelectric materials will generate electric charges when subjected to external forces. Conversely, when voltage is applied to them, the materials will undergo slight deformations. The piezoelectric stage uses this characteristic to achieve micrometer-level or even nanometer-level displacement control by precisely controlling the voltage applied to the piezoelectric material. In this system, the piezoelectric stage is used to control the up and down movement of the glass sheet to adjust its relative position with the objective lens, thereby achieving fine-tuning of the measurement focal length, focal position, etc.

[0037] The displacement stage is a device used to achieve precision displacement control over a large range. It usually contains a precise mechanical structure and drive system that can accurately control the linear or rotational movement of an object. In this system, the displacement stage is installed under the reflector to control the distance from the reflector to the beam splitter prism. By adjusting this distance, the path length of the reflected light entering the camera can be changed, thereby controlling the distance from the CCD (charge-coupled device, a semiconductor device used for image sensing) to the lens. This control is critical to ensuring that the camera can capture clear and accurate images.

[0038] An embodiment of the present invention provides an adjustable automatic interface tracking method, comprising the following steps: Build an autofocus system, such as Figure 2 As shown, two light spots are obtained on the CCD camera, and the light intensity of several pixels outside the center of the light spot is recorded; the optical path of the autofocus system includes: the light beam is split into two beams by a beam splitter prism, and is reflected by two reflectors and enters the CCD camera respectively; The optical path structure is simulated, and the relationship between glass displacement and camera displacement is obtained through fitting formula; Based on the simulation results, an interface tracking system is constructed. The optical path of the tracking system includes: the light beam is transmitted through the first beam splitter prism into the objective lens and focused on the glass sheet. The light beam reflected by the glass sheet is controlled by the first beam splitter prism to be transmitted to the third reflector. The light beam reflected by the third reflector is transmitted to the second beam splitter prism through the lens and is split into two beams by the second beam splitter prism. The beams are reflected by the first reflector and the second reflector respectively and enter the CCD camera. First move the distance between the CCD camera and the lens, then raise and lower the glass sheet to find the position where the light spot is focused on the CCD camera, record the light intensity of the two light spots at the focus position on the camera and the set range of several pixels, and use the maximum-minimum value range of the light intensity difference curve to perform automatic focus adjustment.

[0039] It should be noted that the steps of automatically adjusting the focus using the maximum-minimum range of the light intensity difference curve include: If the current direct writing position light intensity difference is not 0, find the difference between the direct writing position and the z-axis position corresponding to 0 in the light intensity difference curve, adjust the displacement of the CCD camera, correct the out-of-focus position to the focus, and achieve automatic focusing.

[0040] The controller first obtains the focus positions of the two light spots entering the CCD camera on the camera, as well as the light intensity differences of several pixels within the setting range of these focus positions. Then, the controller uses the maximum and minimum value intervals of the light intensity difference curve to determine whether the current focus state deviates from the optimal focus. If it deviates from the optimal focus, the controller will control the movement of the CCD camera to change the focus position of the reflected light beam, thereby trying to refocus the light spot to the optimal focus.

[0041] Through the translation stage under the first and second reflectors, the controller can control the distance from them to the second beam splitter prism, and then control the distance from the CCD camera to the lens. This adjustment can change the magnification of the imaging system and help to further accurately focus. Especially in some advanced applications, it may be necessary to move the displacement of the camera first, and then combine it with the displacement adjustment of the glass sheet to achieve the best focus together.

[0042] When the controller uses the light intensity difference curve for automatic focus adjustment, it will find the difference between the maximum and minimum value intervals in the light intensity difference curve and the z-axis position corresponding to the value 0. This difference represents the offset between the current focus position and the best focus. By adjusting the displacement of the camera, the controller can correct this offset and refocus the light spot to the best focus.

[0043] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0044] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. An adjustable automatic interface tracking system, characterized in that: It includes a first beam splitter prism, an objective lens, a glass sheet, a lens, a second beam splitter prism, a first reflecting mirror, a second reflecting mirror and a CCD camera; The light beam passes through the first beam splitter prism and enters the objective lens to be focused on the glass sheet. After being reflected by the glass sheet, it passes through the lens and is split into two beams by the second beam splitter prism. The beams are reflected by the first reflector and the second reflector respectively and enter the CCD camera. The system also includes a controller, which obtains the focus position of two light spots entering the CCD camera on the CCD camera and the light intensity difference of several pixels within the focus position setting range, and performs automatic focus adjustment using the maximum and minimum value intervals of the light intensity difference curve.

2. The adjustable automatic interface tracking system according to claim 1, characterized in that: A piezoelectric stage is provided below the glass sheet and is connected to a controller for controlling the micrometer-level movement of the glass sheet up and down.

3. The adjustable automatic interface tracking system according to claim 2, characterized in that: A translation stage is installed under the first reflecting mirror and the second reflecting mirror respectively, and each translation stage is connected to a controller respectively to control the distance from the first reflecting mirror and the second reflecting mirror to the second beam splitting prism respectively, and further control the distance from the CCD camera to the lens.

4. The adjustable automatic interface tracking system according to claim 3, characterized in that: The system also includes a third reflector; The light beam is transmitted through the first beam splitter prism into the objective lens and focused on the glass sheet. The light beam reflected by the glass sheet is controlled by the first beam splitter prism to be transmitted to the third reflector. The light beam reflected by the third reflector is transmitted to the second beam splitter prism through the lens.

5. The adjustable automatic interface tracking system according to claim 4, characterized in that: First, move the distance between the CCD camera and the lens, then control the piezoelectric stage to raise and lower the glass sheet, find the position where the light spot is focused on the CCD camera, record the camera displacement and the glass sheet displacement, and obtain the functional relationship between the camera displacement and the glass sheet displacement through the fitting formula.

6. The adjustable automatic interface tracking system according to claim 5, characterized in that: The fitting formula is as follows: Where y is the camera displacement, x is the glass displacement, L is the distance between the lens and the objective lens, f1 is the objective lens focal length, f2 is the focal length of the lens, b is the offset of L, a is the offset of the glass displacement, and c is the offset of the camera displacement.

7. The adjustable automatic interface tracking system according to claim 6, characterized in that: When the controller uses the maximum and minimum value intervals of the light intensity difference curve to perform automatic focusing adjustment, if the current direct writing position light intensity difference is not 0, the difference between the direct writing position and the z-axis position corresponding to the value of 0 is found in the light intensity difference curve, and the displacement of the CCD camera is adjusted to correct the position that deviates from the focus to the focus to achieve automatic focusing.

8. The adjustable automatic interface tracking system according to claim 7, characterized in that: The controller controls the range of the maximum value and minimum value interval of the light intensity difference curve by controlling the displacement stage under the reflector.

9. An adjustable automatic interface tracking method, characterized in that: The steps include: Build an autofocus system, obtain two light spots on the CCD camera, and record the light intensity of several pixels from the center of the light spot; the optical path of the autofocus system includes: the light beam is split into two beams by a beam splitter prism, and is reflected by two mirrors into the CCD camera respectively; The optical path structure is simulated, and the relationship between glass displacement and camera displacement is obtained through fitting formula; Based on the simulation results, an interface tracking system is constructed. The optical path of the tracking system includes: the light beam is transmitted through the first beam splitter prism into the objective lens and focused on the glass sheet. The light beam reflected by the glass sheet is controlled by the first beam splitter prism to be transmitted to the third reflector. The light beam reflected by the third reflector is transmitted to the second beam splitter prism through the lens and is split into two beams by the second beam splitter prism. The beams are reflected by the first reflector and the second reflector respectively and enter the CCD camera. First move the distance between the CCD camera and the lens, then raise and lower the glass sheet to find the position where the light spot is focused on the CCD camera, record the light intensity of the two light spots at the focus position on the camera and the set range of several pixels, and use the maximum-minimum value range of the light intensity difference curve to perform automatic focus adjustment.

10. The adjustable automatic interface tracking method according to claim 9, characterized in that: The steps of automatically adjusting the focus using the maximum-minimum range of the light intensity difference curve include: If the current direct writing position light intensity difference is not 0, find the difference between the direct writing position and the z-axis position corresponding to 0 in the light intensity difference curve, adjust the displacement of the CCD camera, correct the out-of-focus position to the focus, and achieve automatic focusing.

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