Dodging device of combined micro-lens array and preparation method of dodging device

Abstract

The invention discloses a dodging device of a combined micro-lens array and a preparation method of the dodging device, and belongs to the technical field of laser beam shaping. The dodging device of the combined micro-lens array comprises the combined micro-lens array. The combined micro-lens array comprises a plurality of micro-lenses which are closely arranged, and the shape of the micro-lenses is the same as that of a target light spot; the curvature radius and the size of the minimum micro lens are determined according to the size of the target light spot in a preset rise range, and the curvature radiuses and the sizes of the other micro lenses are determined according to the curvature radius and the size of the minimum micro lens in the preset rise range; and the ratio of the aperture to the curvature radius of each micro lens is a constant value. According to the invention, the periodicity of a single micro-lens array can be broken, and the shape of a light spot and the sharpness, uniformity and definition of the edge are ensured at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of laser beam shaping, and in particular to a light homogenizing device combined with a microlens array and a preparation method thereof. Background Art

[0002] Laser beam shaping is the process of redistributing the irradiance and phase distribution of an incident beam. The irradiance distribution determines the beam profile, such as Gaussian, annular, circular, or rectangular, while the phase determines the propagation characteristics of the output beam. Typically, the spatial distribution of a laser beam is Gaussian. However, in many laser systems, to improve laser energy efficiency, it is often necessary to shape a Gaussian or other non-uniform beam distribution into a uniform distribution to meet specific structural or application requirements. Examples include laser material processing, semiconductor lithography, and fluorescence detection in biosensing.

[0003] Various components and optical systems have been developed for laser beam shaping. For example, one approach uses two specially designed aspheric lenses to shape the light into a flat-top distribution. The disadvantage of this system is its strict reliance on the entrance profile and proper alignment. Misalignment and fluctuations in the laser beam significantly impact the uniformity of the shaped beam. Beam shaping using diffractive optical elements is a very powerful method for generating arbitrary spot shapes. However, these elements are typically designed for specific wavelengths and phase functions, requiring expensive, multi-stage components to achieve high performance, particularly in terms of beam uniformity and efficiency. Another approach to beam shaping is to use multi-aperture elements, namely microlens arrays, to split the incident beam into several beams. These beams are then overlapped with the aid of an additional lens. This approach has the advantage of being independent of the incident light intensity distribution and having a wide wavelength spectrum. However, the periodic structure of the microlens array can cause beam overlap, resulting in interference effects and uneven spot shapes, especially when using highly coherent light. Using random microlens arrays, due to their inaccurately calculated design, such as random apertures and heights, can result in varying sub-spot shapes and sizes in the focal plane, affecting the spot shape, edge sharpness, and uniformity. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a light homogenizing device for a combined microlens array and a method for preparing the same, which can break the periodicity of a single microlens array while ensuring the sharpness, uniformity and clarity of the shape and edge of the light spot.

[0005] To achieve the above object, the present invention is implemented by adopting the following technical solutions: In one aspect, the present invention provides a light homogenizing device of a combined microlens array, comprising a combined microlens array; The combined microlens array includes a plurality of closely arranged microlenses, and the shape of the microlenses is the same as the shape of the target light spot; The curvature radius and size of the smallest microlens are determined within a preset sag range based on the target spot size. The curvature radius and size of the other microlenses are also determined within a preset sag range based on the curvature radius and size of the smallest microlens. The ratio of each microlens' aperture to its curvature radius is constant. This ensures that the sub-spots formed by each microlens on the target plane are uniform in size and well-defined, achieving highly uniform light intensity distribution across the entire spot area. Furthermore, the design of the curvature radius and size of the smallest microlens and the other microlenses is not a simple random selection, but rather a rigorous calculation based on optical principles.

[0006] Optionally, the preset sag range is a process window range of the photoresist; The minimum sag height of the microlens is greater than the minimum value of the photoresist process window, and the maximum sag height of the microlens is less than the maximum value of the photoresist process window.

[0007] Optionally, the target spot size calculation formula is: ; in, Indicates the size of the target spot; represents the aperture of the microlens; represents the focal length of the converging lens; Represents the focal length of the microlens.

[0008] Optionally, the combined microlens array includes a plurality of closely arranged microlenses of different sizes but the same shape, and the shape of the microlenses is square, rectangular or regular hexagonal.

[0009] Optionally, the sizes of the other microlenses are obtained by proportionally enlarging the smallest microlens, and the filling rate of the combined microlens array is 100%.

[0010] Optionally, the area of ​​the combined microlens array is larger than the light field area of ​​the laser.

[0011] On the other hand, the present invention further provides a method for preparing a light homogenizing device for a combined microlens array, including the light homogenizing device for a combined microlens array according to the first aspect, the method comprising: densely arranging the combined microlens array to produce a grayscale image of the combined microlens array; Photolithography is performed to form a negative structure of the grayscale image to obtain a combined microlens array opposite to the grayscale image; The combined micro-lens array opposite to the grayscale image is transferred onto a flexible material to obtain a light homogenizing device of the combined micro-lens array.

[0012] Optionally, a laser direct writing technique is used to photoetch a negative structure of the grayscale image on a photoresist plate, and after development, a combined microlens array having a structure opposite to the grayscale image is obtained on the photoresist plate; Nanoimprint technology is used to lay a flexible material flat on a photoresist plate, and after drying, a light-homogenizing device with a combined microlens array is obtained on the flexible material.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. The combined microlens array structure of the present invention is formed by combining microlenses of different sizes and the same shape. This structure breaks the periodicity of traditional single microlens arrays to a certain extent and can reduce the unevenness caused by beamlet interference. The shape of each microlens is consistent with the target light spot, ensuring that the shape of the light spot formed by the sub-beam on the focal plane is consistent with the target light spot. The ratio of the aperture of each microlens to its radius of curvature is constant. Based on the principle of microlens array light homogenization, the light spots formed by the sub-beams on the target plane are of uniform size, which can ensure the sharpness, uniformity and clarity of the light spot shape and edges. The microlenses are continuous, which can fully utilize the incident light and ensure the efficiency of light homogenization.

[0014] 2. The method for preparing a light homogenizing device for a combined microlens array of the present invention can meet the submicron-level preparation precision requirements of the combined microlens array. Microlenses of all sizes can be prepared through a single photolithography process, which has high processing efficiency and can ensure that the size and shape of the microlenses strictly meet the design requirements, thereby ensuring the sharpness and clarity of the light spot. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 FIG2 is a schematic structural diagram of a combined microlens array in one embodiment of the present invention; Figure 2 Shown is a simulated optical path diagram of ZEMAX in one embodiment of the present invention; Figure 3 FIG2 is a diagram showing a uniform light path of a combined microlens array in one embodiment of the present invention; Figure 4 FIG2 is a schematic structural diagram of another embodiment of the combined microlens array of the present invention; Figure 5 FIG2 is a schematic diagram of a target light spot in a ZAMX simulation of a combined microlens array according to an embodiment of the present invention; Figure 6 FIG2 is a schematic diagram of a target light spot in a ZAMX simulation of a single-structure microlens array in the prior art in one embodiment; Figure 7 Shown Figure 5 In one embodiment, a complex amplitude distribution diagram; Figure 8Shown Figure 6 In one embodiment, a complex amplitude distribution diagram; Figure 9 Shown is a SEM characterization image of a combined microlens array in one embodiment of the present invention; Figure 10 Shown is a characteristic diagram of a white light interferometer of a combined microlens array in one embodiment of the present invention. DETAILED DESCRIPTION

[0016] The technical solution of the present invention is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations on the technical solution of the present invention. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0017] The term "and / or" simply describes a relationship between related objects, indicating that three possible relationships exist. For example, "A and / or B" can mean: A exists alone, A and B exist simultaneously, or B exists alone. Additionally, the character " / " generally indicates an "or" relationship between the related objects.

[0018] Example 1

[0019] like Figure 1 As shown, this embodiment introduces a light homogenizing device combined with a microlens array, such as Figure 2 In the light homogenization system shown, the light beam is first split by the microlens array and then converged on the receiving plane by the converging lens. In this embodiment, the converging lens has a diameter of 6 mm, a thickness of 3 mm, a curvature radius of 20 mm, and is made of C79-80 glass. A 1.4 mm × 0.7 mm rectangular light spot needs to be obtained on the target plane.

[0020] The light homogenizing device of the combined microlens array includes a combined microlens array; the combined microlens array includes a plurality of closely arranged microlenses of different sizes and the same shape, and the sizes and curvature radii of these microlenses are strictly calculated based on the principle of beam shaping, rather than simply randomly selected, to ensure the sharpness and uniformity of the light spot while reducing the interference effect caused by periodicity; The shape of the microlens is the same as that of the target light spot, which is generally a square, rectangle or regular hexagon. The ratio of the size of each microlens to its sagittal height is constant, so that the sub-spots generated by each microlens converge on the same focal plane, ensuring that the shape of the final light spot is sharp and the edge uniformity is high.

[0021] The preset sag range of the combined microlens array is determined based on the process window of the photoresist. The sag of the smallest microlens is greater than the minimum value of the photoresist process window, and the sag of the largest microlens is less than the maximum value of the photoresist process window. In this embodiment, the structure height range that can be produced by AZ4562 photoresist is between 0.4 μm and 11.5 μm. Therefore, the sag of the smallest microlens in the combined microlens array should be greater than 0.4 μm, and the sag of the largest microlens should be less than 11.5 μm.

[0022] ZEMAX was used to perform optical simulation of the light homogenization system. Based on the design method of the combined microlens array and the requirements of the target light spot, the shape of the minimum microlens was determined. In this embodiment, the shape of the minimum microlens is rectangular with an aspect ratio of 1:2, a size of 20 μm × 10 μm, a curvature radius of 50 μm, and a sag of 0.51 μm.

[0023] Based on the smallest microlens, other microlenses are designed. Since other microlenses are proportionally enlarged based on the smallest microlens, and the basic units of these microlenses need to be densely packed, this design problem can be transformed into a problem of arranging geometric rectangles to form a rectangle. According to the preset sag range, the combined microlens array can be composed of a 9-order rectangle, that is, 9 rectangular microlenses of different sizes. The specific combination method is as follows: Figure 1 As shown, the numbers in the figure represent the proportions of the rectangle, the proportion of the smallest microlens is 1, and the proportion of the largest microlens is 18.

[0024] After determining the parameters of the smallest microlens, the sizes and curvature radii of other microlenses are determined in sequence according to a certain proportional relationship based on the size and curvature radius of the smallest microlens. The design of this proportional relationship needs to meet the following two requirements to ensure the quality of the light spot: The microlenses are designed through proportional magnification, and the basic units of these microlenses can be densely packed to form a combined microlens array with a filling rate of 100%. The design of the combined microlens array can significantly reduce the interference effect caused by periodicity, improve the uniformity and sharpness of the light spot, and ensure that the overall structure of the combined microlens array is compact and has no gaps, thereby maximizing the use of incident light and improving the utilization rate of light energy.

[0025] like Figure 3 As shown in the figure, from the microlens uniform light path diagram, we can know that the target spot size calculation formula is: ; in, Indicates the size of the target spot; represents the aperture of the microlens; represents the focal length of the converging lens; Represents the focal length of the microlens.

[0026] After the focal length of the converging lens is determined, the size of the target spot is related to the ratio of the microlens aperture to the curvature radius. Therefore, the ratio of the aperture to the curvature radius of the nine microlenses should be constant to ensure that the spot size formed by the sub-beams on the target plane is consistent. The specific design parameters of the nine microlenses are shown in Table 1. The basic unit of their combination is as follows: Figure 4 As shown, the basic unit is rectangular, which can meet the close-packing requirements.

[0027] Table 1 Specific design parameters of microlenses

[0028] The basic units consisting of the combined microlenses are densely packed to obtain a 7.2 mm × 7.2 mm combined microlens array. The area of ​​the combined microlens array needs to be able to completely cover the light field area of ​​the laser. The side length of the combined microlens array is greater than 1.5 times the diameter of the laser beam. In this embodiment, the side length of the combined microlens array is twice the diameter of the laser beam.

[0029] Figure 5 The uniform light effect of the combined micro-lens array in this embodiment is as follows: Figure 6 This is the uniform light effect of a single microlens array in the prior art. It can be seen that the light spot shaped by this embodiment has a significant improvement in energy distribution, and the center and edges of the light spot are also clearer and more uniform. Figure 7 This is the complex amplitude distribution diagram of the light spot after the combined microlens array shaping in this embodiment. Figure 8 This is the complex amplitude distribution diagram of the light spot after shaping by a single microlens array in the prior art. It can be seen from the diagram that this embodiment significantly reduces the interference between the sub-beams by breaking the single periodicity, thereby significantly improving the uniformity of the light spot.

[0030] Example 2

[0031] Based on Example 1, this example introduces a method for preparing a light homogenizing device for a combined microlens array, which can meet the submicron-level preparation precision requirements of the combined microlens array. At the same time, microlenses of all sizes can be prepared by only one photolithography, which is very efficient.

[0032] The method includes three steps: generating a grayscale image, photolithography, and nanoimprinting: Step 1: Create a grayscale image of the basic unit. Import the basic unit model of the combined microlens array designed in ZEMAX into the drawing software Rhino and convert it into the corresponding 8-bit grayscale image.

[0033] Step 2: Use laser direct writing technology to prepare the negative structure of the combined microlens array, specifically: Spin-coat photoresist on the glass substrate. The thickness of the photoresist needs to be greater than the height of the largest microlens. The photoresist model is AZ4562. Use step-by-step spin coating. First, spin at 200 rpm for 10 seconds with an acceleration of 500 rpm, then spin at 800 rpm for 30 seconds with an acceleration of 1000 rpm. Place the glass substrate with the photoresist spin-coated on a flat heater for pre-baking. The starting temperature is 100 degrees and the drying time is 70 seconds at 100 degrees. Import the grayscale image of the basic unit into the 3D digital lithography system and array it into a size of 7.2mm×7.2mm; After the 3D digital lithography system reads the grayscale information, it uses a 355nm light source to perform the first exposure on the photoresist plate. The exposure energy is selected as 300mJ, the spot size is selected as 550nm, the scanning speed is selected as 70mm / s, and the step resolution is selected as 275nm. The exposed photoresist plate was developed with a developer and deionized water ratio of 1:3 for 90 seconds. After development, it was fixed with deionized water and then dried with compressed nitrogen to obtain a combined microlens array that was opposite to the grayscale image.

[0034] Laser direct writing technology has high precision requirements and can produce microlenses of all sizes in one step. It has high processing efficiency and can ensure that the size and shape of the microlens strictly meet the design requirements, thereby ensuring the sharpness and clarity of the light spot.

[0035] Step 3: Using nanoimprint technology, transfer the combined microlens array structure opposite to the grayscale image on the photoresist plate to the flexible material to obtain a combined microlens array light homogenizing device, specifically: Mix the curing agent and PDMS in a mass ratio of 1:10, place the mixed PDMS in a vacuum dish, use a compressor to pump the air pressure in the vacuum dish to about 0.8 kPa, stop pumping, let it stand for 10 minutes, and then slowly release the air. Repeat twice until there are no bubbles in the PDMS; PDMS was coated on the structured side of the photoresist plate by spin coating at a speed of 500 rpm and then allowed to stand for 10 minutes; Place the photoresist coated with PDMS in an oven at 75 degrees for 2 hours. After drying, the area with the printed structure is cut out with a scalpel and attached to a glass sheet to obtain a light-homogenizing device with a combined microlens array.

[0036] Nanoimprint technology can transfer the microlens structure on the photoresist to the flexible material with high fidelity, ensuring the performance of the final light-homogenizing device, such as Figure 9 The SEM characterization of the prepared light homogenizing device is shown as follows: Figure 10 Shown is the white light interferometer characterization diagram of the prepared light homogenizing device.

[0037] This embodiment can meet the submicron-level production precision requirements of the combined microlens array and can produce microlenses of all sizes through only one photolithography process. This has high processing efficiency and can ensure that the size and shape of the microlenses strictly meet the design requirements, thereby ensuring the sharpness and clarity of the light spot.

[0038] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which are all protected by the present invention.

Claims

1. A light homogenizing device combined with a microlens array, characterized in that: including a combined microlens array; The combined microlens array includes a plurality of closely arranged microlenses, and the shape of the microlenses is the same as the shape of the target light spot; The curvature radius and size of the smallest microlens are determined according to the size of the target light spot within a preset sag range, and the curvature radius and size of other microlenses are determined according to the curvature radius and size of the smallest microlens within the preset sag range. The ratio of the aperture of each microlens to its curvature radius is a constant value.

2. The light homogenizing device of the combined microlens array according to claim 1, characterized in that: The preset sag range is the process window range of the photoresist; The minimum sag height of the microlens is greater than the minimum value of the photoresist process window, and the maximum sag height of the microlens is less than the maximum value of the photoresist process window.

3. The light homogenizing device of the combined microlens array according to claim 1, characterized in that: The calculation formula for the size of the target light spot is: ； in, Indicates the size of the target spot; represents the aperture of the microlens; represents the focal length of the converging lens; Represents the focal length of the microlens.

4. The light homogenizing device of the combined microlens array according to claim 1, characterized in that: The combined microlens array includes a plurality of closely arranged microlenses of different sizes but the same shape, and the shape of the microlenses is square, rectangular or regular hexagonal.

5. The light homogenizing device of the combined microlens array according to claim 1 or 5, characterized in that: The sizes of the other microlenses are obtained by proportionally enlarging the smallest microlens, and the filling rate of the combined microlens array is 100%.

6. The light homogenizing device of the combined microlens array according to claim 1, characterized in that: The area of ​​the combined microlens array is larger than the light field area of ​​the laser.

7. A method for preparing a light homogenizing device combined with a microlens array, characterized in that: A light homogenizing device comprising the combined microlens array according to any one of claims 1 to 6, wherein the method comprises: densely arranging the combined microlens array to produce a grayscale image of the combined microlens array; Photolithography is performed to form a negative structure of the grayscale image to obtain a combined microlens array opposite to the grayscale image; The combined micro-lens array opposite to the grayscale image is transferred onto a flexible material to obtain a light homogenizing device of the combined micro-lens array.

8. The method for preparing a light homogenizing device of a combined microlens array according to claim 7, characterized in that: Using laser direct writing technology, a negative structure of the grayscale image is photoetched on a photoresist plate, and after development, a combined microlens array opposite to the grayscale image is obtained on the photoresist plate; Nanoimprint technology is used to lay a flexible material flat on a photoresist plate, and after drying, a light-homogenizing device with a combined microlens array is obtained on the flexible material.

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