Preparation method of infrared equivalent convex lens array with symmetrical flat surfaces

Abstract

The invention discloses a preparation method of an infrared equivalent convex lens array with symmetrical flat surfaces. The preparation method comprises the following steps: processing a regularly arranged ablation pit array on a material I by using laser; carrying out chemical corrosion on the ablation pit array, and processing a concave lens array; under the vacuum condition, the second material and the first material are subjected to hot-pressing compounding, the concave lens array is filled with the second material and covered with the second material, and an infrared equivalent convex lens array with symmetrical flat surfaces is obtained; wherein the transformation temperature Tg1 of the material I and the transformation temperature Tg2 of the material II meet the condition that Tg1-Tg2 is greater than 30 DEG C; the refractive index n1 of the first material and the refractive index n2 of the second material meet the condition that n2 is larger than n1. The infrared transmission range of the first material and the infrared transmission range of the second material have overlapped wave bands. The method is simple, high in operability, low in cost and high in flux, the prepared infrared equivalent convex lens array can remarkably reduce the complexity of an optical system, the discrete assembly problem is avoided, and great application potential is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-opto-electromechanical systems, and in particular to a method for preparing an infrared equivalent convex lens array with a symmetrical flat surface. Background Art

[0002] With the surge in demand for high-resolution, high-sensitivity infrared imaging in scenarios such as military reconnaissance, autonomous driving, environmental monitoring, and consumer electronics, and the maturation of semiconductor micro-nanofabrication technologies (such as CMOS-MEMS compatible technology), infrared detectors are rapidly developing towards large-scale arrays and small pixel sizes. However, this development trend also brings about problems such as reduced light utilization due to the reduction in the area of ​​the photosensitive area, as well as optical crosstalk and heat diffusion between pixels caused by high-density integration.

[0003] Infrared microlens arrays, due to their unique ability to manipulate light fields, have become a crucial technology for optimizing detector performance. Through subwavelength optical structure design and multi-scale beam shaping, infrared microlens arrays can improve photon utilization and compensate for the optical losses associated with small pixels. The light field confinement effect of the microlenses helps reduce diffraction crosstalk and stray light coupling, optimizing the incident light distribution and thus enhancing the imaging performance of infrared imaging systems.

[0004] However, traditional microlens arrays often have non-flat surfaces, making them susceptible to step effects, shadow effects, and curvature radius during the deposition process, making it difficult to control the uniformity of the coating thickness. Furthermore, the assembly of traditional microlens arrays is a key step in achieving their high-performance optical functions, but this process faces a series of technical challenges, particularly in high-precision positioning, multi-physics field coupling, and packaging reliability. These issues have limited the widespread application of microlens arrays. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of existing microlens arrays and provide a method for preparing an infrared equivalent convex lens array with a symmetrical flat surface. The preparation method is simple and highly operable, and can prepare an infrared equivalent convex lens array with a symmetrical flat surface in a low-cost, high-throughput manner. The prepared infrared equivalent convex lens array can significantly reduce the complexity of the optical system, avoid discrete assembly problems, and has great application potential.

[0006] The technical solution adopted by the present invention to solve the above technical problems is: a method for preparing an infrared equivalent convex lens array with a symmetrical flat surface, comprising the following steps:

[0007] S1, using laser to process a regularly arranged ablation pit array on material 1;

[0008] S2, chemically etching the ablation pit array to form a concave lens array;

[0009] S3. Under vacuum conditions, hot-pressing and compounding the second material with the first material so that the second material fills and covers the concave lens array to obtain an infrared equivalent convex lens array with a symmetrical and flat surface;

[0010] in:

[0011] The transition temperature Tg1 of the material 1 and the transition temperature Tg2 of the material 2 satisfy: Tg1-Tg2>30°C;

[0012] The refractive index n1 of the material 1 and the refractive index n2 of the material 2 satisfy: n2>n1;

[0013] The infrared transmittance range of the material one and the infrared transmittance range of the material two have overlapping bands, so as to ensure that the prepared infrared equivalent convex lens array can operate in the transmittance overlapping band and meet the application requirements of different infrared bands and different scenarios.

[0014] The fabrication method of the present invention uses a laser to create an array of ablation pits on a first material. Lasers offer low thermal effects, high machining precision, and wide applicability. By controlling the average laser power, the number of pulses per point, the spacing between laser ablation points, and the chemical etching time, convex lens arrays with the desired arrangement and individual profile characteristics, such as triangular, square, hexagonal, or herringbone arrangements, can be fabricated based on the application scenario.

[0015] The present invention's preparation method utilizes laser processing assisted by chemical etching to produce concave lens arrays. Benefiting from the high precision and efficiency of laser processing and the high throughput of chemical etching, the present method significantly reduces the number of processing steps and process parameter controls required for the concave lens array, ensuring high method repeatability. Compared to traditional photolithography methods, this method not only saves process time and costs, but also increases processing throughput, improves production efficiency, and ensures the quality of the concave lens arrays. Traditional photolithography processes include coating, baking, exposure, development, and etching. Preparing a batch of wafers takes at least 8 to 13 hours. Furthermore, the process uses large amounts of solvents and gases, requiring extensive control of numerous process parameters. Problems in any one of these steps can impact the yield of the concave lens array.

[0016] The preparation method of the present invention combines specific materials one and two by hot-pressing to form an infrared equivalent convex lens array with a symmetrical, flat surface. The method is applicable to a wide variety of materials. During the hot-pressing process, the processing parameters of the hot-pressing process need only be adjusted according to the material properties to efficiently prepare the infrared equivalent convex lens array with a symmetrical, flat surface. Conventional methods for preparing convex lens arrays often employ ion etching, thermal reflow, and other methods. Ion etching or thermal reflowing photoresist typically requires a relatively long initial process preparation time of at least 10 hours. The hot-pressing process employed in the preparation method of the present invention, however, only takes approximately 30 minutes, and the combined laser processing and chemical etching prior to hot-pressing only takes 3 to 4 hours, significantly improving the production efficiency of the entire preparation method.

[0017] Preferably, the temperature of the hot pressing composite is between Tg1 and Tg2. At this temperature, the first material is in an unsoftened state and the second material is in a softened state, which can ensure the hot pressing composite effect and the preparation efficiency of the convex lens array.

[0018] Preferably, the difference in thermal expansion coefficient between the material 1 and the material 2 is less than 3.0×10 -6 / ℃, thus ensuring that material 1 and material 2 have similar shrinkage characteristics during the cooling stage after hot pressing and lamination, which helps to improve the product qualification rate. If the difference in thermal expansion coefficient between material 1 and material 2 is greater than 3.0×10 -6 / ℃, the first and second materials will shrink to varying degrees during the cooling stage after hot pressing and laminating, which may easily lead to cracks in the prepared convex lens and excessive residual stress in some areas. Therefore, the present invention limits the difference in thermal expansion coefficient between the first and second materials to less than 3.0×10 -6 / ℃.

[0019] Preferably, the vacuum degree of the vacuum condition is not greater than 10 -3 Pa.

[0020] Preferably, the hot pressing composite is formed by precision hot pressing.

[0021] Preferably, in the obtained convex lens array, the size of a single sub-lens is on the order of microns.

[0022] Preferably, the second material used in the hot-pressing lamination is a preform having a curved surface. Prior to the hot-pressing lamination, the curved surface faces the concave lens array. Using a preform with a curved surface as the second material facilitates the gradual filling of the concave lens array with the softened second material during the hot-pressing lamination process, allowing for the smooth expulsion of gas trapped between the second material and the concave lens array, thereby further stabilizing the composite structure formed by the first and second materials.

[0023] Preferably, the radius of curvature of the curved surface is greater than 40 mm. A curved surface with a large radius of curvature greater than 40 mm is beneficial for improving the stability of the hot-press bonding of the second and first materials. However, if the radius of curvature of the curved surface does not exceed 40 mm, the preform may easily shift during hot-press bonding, affecting the stability of the hot-press bonding and causing problems such as preform deflection that affect the quality of the convex lens.

[0024] Compared with the prior art, the present invention has the following advantages: the preparation method of the present invention is simple and highly operable, and can prepare an infrared equivalent convex lens array with a symmetrical flat surface in a low-cost, high-throughput manner. Each convex lens constituting the convex lens array has a uniform height and a flat surface, which effectively solves the problem of uneven film thickness in the deposition and coating process of the traditional microlens array. In addition, the preparation method of the present invention can not only modulate the focal plane of the convex lens to the rear surface of the convex lens by controlling the molding thickness of the second material, but also allow the detector material to be directly grown or deposited on the rear surface of the convex lens and patterned to form a pixel structure, while solving the demolding problem in the hot pressing molding process of the traditional ultra-thin convex lens array with the same function. The infrared equivalent convex lens array prepared by the preparation method of the present invention can significantly reduce the complexity of the optical system, avoid discrete assembly problems, and has great application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Flowchart of a method for preparing an infrared equivalent convex lens array having a symmetrical flat surface according to the present invention;

[0026] Figure 2 Schematic diagram of each stage in the preparation process of the infrared equivalent convex lens array having a symmetrical flat surface in Example 1 and Example 2;

[0027] Figure 3 Schematic diagram of the preform of material 2 in Example 1 and Example 2. DETAILED DESCRIPTION

[0028] In order to more clearly express the purpose, technical solutions and advantages of the present invention, the technical solutions in the embodiments of the present invention will be described in detail and completely in conjunction with the drawings in the embodiments of the invention. It should be understood that the following embodiments are only used to illustrate the present invention and are not used to limit the present invention. The embodiments described here are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Raw materials, processes, equipment, etc. not limited in the present invention all adopt conventional technical means in this field.

[0029] The preparation method of the infrared equivalent convex lens array with symmetrical flat surface of embodiment 1 is as follows: Figure 1 As shown, the following steps are included:

[0030] S1, such as Figure 2 As shown in (a), the laser uses a femtosecond laser with low thermal effect and high resolution. On the laser processing platform, the femtosecond laser is used to process the required regularly arranged ablation pit array on Material 1. The process conditions of the femtosecond laser processing are as follows: after polishing Material 1, it is cleaned and dried with alcohol and deionized water, and then the Material 1 is processed by femtosecond laser. The pulse width of the femtosecond laser is 247fs, the repetition frequency is 10kHz, the average power is 2.36mW, and the number of pulses per single point is 1000.

[0031] S2. Under the assistance of an ultrasonic water bath at a water bath temperature of 20°C, the ablation pit array is chemically etched using a 99% concentration of propylamine solution for 85 minutes to produce a concave lens array, such as Figure 2 As shown in (b), the maximum depth standard deviation of the concave lens units of the concave lens array is as low as 0.037 microns. In the focusing ability test of the concave lens array in the near-infrared band, the standard deviation of the normalized maximum intensity of the focused spot is as low as 0.0098, indicating that the concave lens array has excellent depth uniformity and focusing ability. In addition, the surface roughness of the concave lens units is as low as 2.1 nm, indicating that chemical etching methods have great advantages in preparing high-quality micro-optical devices.

[0032] S3. Prepare the preform of material 2, such as Figure 3 As shown, the preform has a curved surface with a curvature radius R greater than 40 mm, and then the concave lens array is placed in a precision hot pressing molding chamber, and the preform of material 2 is placed on the concave lens array, with the curved surface of the preform of material 2 facing the concave lens array, and the vacuum degree is 10 -3 Under the vacuum condition of Pa, the material 2 and the material 1 are precisely hot-pressed, and the pressing temperature, pressure and speed of the precision hot-pressing are controlled, and the molding thickness of the material 2 is controlled to modulate the focal plane of the convex lens to the rear surface of the convex lens ( Figure 2 In (c), the solid line with an arrow represents the light path in the convex lens monomer, and the five black dots on the surface of the second material represent the focused light spots. After the light path passes through the first and second materials, the focused light spots are formed on the surface of the second material. The second material fills and covers the concave lens array. Then, the cooling node and the cooling speed are controlled to obtain an infrared equivalent convex lens array with a symmetrical flat surface, as shown in FIG. Figure 2 As shown in (c) in the figure. Specifically, the process conditions for the precision hot pressing molding are as follows: the hot pressing temperature of the precision hot pressing molding chamber is set to 230°C, the pressing speed during hot pressing is set to 1 mm / s, the pressure is set to 0.5 kN, and the pressure is set to 0.3 kN after the pressing is completed. After the pressing is completed, the temperature of the precision hot pressing molding chamber is cooled at a rate of 1°C / minute to the first node temperature of 180°C, and then cooled at a rate of 5°C / minute to 20°C.

[0033] In Example 1, material 1 is Ge-As-S infrared glass, whose transition temperature Tg1 is about 300°C and whose mid-infrared refractive index n1 is about 2.2; material 2 is As2Se3 infrared glass, whose transition temperature Tg2 is about 185°C and whose mid-infrared refractive index n2 is about 2.8.

[0034] The infrared-equivalent convex lens array with symmetrical, flat surfaces prepared in Example 1 demonstrated excellent optical performance in both infrared imaging and focusing tests. In the infrared imaging test, the convex lens array produced characters with clear boundaries and uniform brightness, and an inverted real image formed near its rear surface, conforming to the imaging principles of a convex lens. In the infrared focusing test, the convex lens array's light spots were neatly arranged and uniformly bright, with a standard deviation of normalized intensity as low as 0.0066.

[0035] The preparation method of the infrared equivalent convex lens array with symmetrical flat surface of embodiment 2 is as follows: Figure 1 As shown, the following steps are included:

[0036] S1, such as Figure 2 As shown in (a), the laser uses a femtosecond laser with low thermal effect and high resolution. On the laser processing platform, the femtosecond laser is used to process the required regularly arranged ablation pit array on Material 1. The process conditions of the femtosecond laser processing are as follows: after polishing Material 1, it is cleaned and dried with alcohol and deionized water, and then the material is processed by femtosecond laser. The pulse width of the femtosecond laser is 247fs, the repetition frequency is 10kHz, the average power is 2.1mW, and the number of pulses per single point is 1000.

[0037] S2. Under the assistance of an ultrasonic water bath at a water bath temperature of 20°C, the ablation pit array is chemically etched using a 98% concentration of ethylenediamine solution for 50 minutes to produce a concave lens array, such as Figure 2 As shown in (b), the maximum depth standard deviation of the concave lens units of the concave lens array is as low as 0.041 microns. In the focusing ability test of the concave lens array in the near-infrared band, the standard deviation of the normalized maximum intensity of the focused spot is as low as 0.010205, indicating that the concave lens array has excellent depth uniformity and focusing ability. In addition, the surface roughness of the concave lens units is as low as 6.2nm, indicating that chemical etching has great advantages in the preparation of high-quality micro-optical devices. After testing, the concave lens array exhibited excellent optical performance in the focusing ability test.

[0038] S3. Prepare the preform of material 2, such as Figure 3As shown, the preform has a curved surface with a curvature radius R greater than 40 mm, and then the concave lens array is placed in a precision hot pressing molding chamber, and the preform of material 2 is placed on the concave lens array, with the curved surface of the preform of material 2 facing the concave lens array, and the vacuum degree is 10 -3 Under the vacuum condition of Pa, the material 2 and the material 1 are precisely hot-pressed, and the pressing temperature, pressure and speed of the precision hot-pressing are controlled. The molding thickness of the material 2 is controlled to modulate the focal plane of the convex lens to the rear surface of the convex lens, so that the material 2 fills and covers the concave lens array. Then, the cooling node and the cooling speed are controlled to obtain an infrared equivalent convex lens array with a symmetrical flat surface, as shown in FIG. Figure 2 As shown in (c) in the figure. Specifically, the process conditions for the precision hot pressing molding are as follows: the hot pressing temperature of the precision hot pressing molding chamber is set to 200°C, the pressing speed during hot pressing is set to 1 mm / s, the pressure is set to 0.5 kN, and the pressure is set to 0.3 kN after the pressing is completed. After the pressing is completed, the temperature of the precision hot pressing molding chamber is cooled at a rate of 1°C / min to the first node temperature of 160°C, and then cooled at a rate of 3°C / min to 20°C.

[0039] In Example 2, material 1 is As2S3 infrared glass, whose transition temperature Tg1 is about 210°C and whose mid-infrared refractive index n1 is about 2.4; material 2 is Se-As-Sb-Sn infrared glass, whose transition temperature Tg2 is about 170°C and whose mid-infrared refractive index n2 is about 2.78.

[0040] The infrared-equivalent convex lens array with symmetrical, flat surfaces prepared in Example 2 demonstrated excellent optical performance in both infrared imaging and focusing tests. In the infrared imaging test, the convex lens array produced characters with clear boundaries and uniform brightness, and an inverted real image formed near its rear surface, conforming to the imaging principles of a convex lens. In the infrared focusing test, the convex lens array's light spots were neatly arranged and uniformly bright, with a standard deviation of normalized intensity as low as 0.00673.

[0041] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with this technical field within the technical scope disclosed in the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing an infrared equivalent convex lens array with a symmetrical flat surface, characterized in that: The following steps are involved: S1, using laser to process a regularly arranged ablation pit array on material 1; S2, chemically etching the ablation pit array to form a concave lens array; S3. Under vacuum conditions, hot-pressing and compounding the second material with the first material so that the second material fills and covers the concave lens array to obtain an infrared equivalent convex lens array with a symmetrical and flat surface; in: The transition temperature Tg1 of the material 1 and the transition temperature Tg2 of the material 2 satisfy: Tg1-Tg2>30°C; The refractive index n1 of the material 1 and the refractive index n2 of the material 2 satisfy: n2>n1; The infrared transmission range of the first material and the infrared transmission range of the second material have an overlapping wavelength band.

2. The method for preparing an infrared equivalent convex lens array having a symmetrical flat surface according to claim 1, characterized in that: The temperature of the hot pressing composite is between Tg1 and Tg2.

3. The method for preparing an infrared equivalent convex lens array having a symmetrical flat surface according to claim 1, wherein: The difference in thermal expansion coefficient between the first material and the second material is less than 3.0×10 -6 / ℃.

4. The method for preparing an infrared equivalent convex lens array having a symmetrical flat surface according to claim 1, characterized in that: The vacuum degree of the vacuum condition is not greater than 10 -3 Pa.

5. The method for preparing an infrared equivalent convex lens array having a symmetrical flat surface according to claim 1, characterized in that: The hot pressing composite is formed by precise hot pressing.

6. The method for preparing an infrared equivalent convex lens array having a symmetrical flat surface according to claim 1, characterized in that: In the obtained convex lens array, the size of a single sub-lens is on the order of microns.

7. The method for preparing an infrared equivalent convex lens array having a symmetrical flat surface according to claim 1, characterized in that: The second material used for the hot pressing composite is a preform, and the preform has a curved surface. Before the hot pressing composite, the curved surface faces the concave lens array.

8. The method for preparing an infrared equivalent convex lens array having a symmetrical flat surface according to claim 7, characterized in that: The curvature radius of the arc surface is greater than 40 mm.

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