Preparation method of Fresnel lens array and Fresnel lens array

Abstract

The invention discloses a preparation method of a Fresnel lens array and the Fresnel lens array, and the preparation method comprises the steps: preparing a substrate and a plurality of Fresnel lens units, each Fresnel lens unit comprises an incident plane and an emergent plane which are oppositely arranged, and the emergent plane is provided with Fresnel optical lines; positioning features are arranged on the substrate, and the positioning features are used for positioning the positions of the Fresnel lens units on the substrate; the incident planes of all the Fresnel lens units are correspondingly bonded to the preset installation area of the substrate through optical cement according to positioning guiding of the positioning characteristics, the multiple Fresnel lens units are arranged on the substrate in an array mode, and after the optical cement is cured, the Fresnel lens array is obtained. The Fresnel lens array prepared by the invention is low in manufacturing cost, good in optical performance and good in mass production economy.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic technology, and in particular to a preparation method of a Fresnel lens array and the Fresnel lens array. Background Art

[0002] Fresnel Lens is an optical element invented by French physicist Augustin Fresnel in 1822. Its working principle is based on the fact that the refraction of light only occurs on the surface of the lens. By optimizing the angle and spacing of the grooves, the light can be focused on a single focal point or adjusted to parallel light. It is widely used in projection, infrared detection, solar concentration and other fields. Fresnel lenses are mostly made of polyolefins or glass. They are lightweight (thickness of about 1-3mm), low-cost (compression molding or injection molding process) and can be processed over a large area. Therefore, they are very suitable for use in the field of concentrated solar energy. In concentrated photovoltaic (CPV) systems, Fresnel lenses serve as the core concentrating element, which can focus sunlight and significantly increase the light energy density, thereby reducing the use of high-efficiency solar cells (such as III-V multi-junction cells) and reducing system costs.

[0003] Typically, a CPV module consists of a Fresnel lens and corresponding concentrating photovoltaic cells. Large-scale CPV systems typically include multiple CPV modules arranged in an array. During the production of CPV systems, existing technology often uses side-by-side splicing of multiple CPV modules. However, this method is costly and cumbersome, significantly increasing production time and costs.

[0004] To address the splicing issue, the industry has attempted to adopt integrated injection or compression molding processes. However, large-scale Fresnel lens arrays (e.g., diameters greater than 1 meter) require custom large molds and specialized injection molding equipment, with the cost of a single mold reaching hundreds of thousands of yuan. Furthermore, the injection molding process can easily lead to optical distortion due to uneven material shrinkage, significantly reducing product yield and making mass production uneconomical.

[0005] In summary, there is an urgent need to develop a new preparation method for preparing large-size Fresnel lens arrays to solve the above problems. Summary of the Invention

[0006] In view of this, the present invention provides a method for preparing a Fresnel lens array and a Fresnel lens array, which are used to solve the problem of low product yield when preparing large-size Fresnel lens arrays in the prior art.

[0007] To achieve one, part, or all of the above objectives or other objectives, a first aspect of the present invention provides a method for preparing a Fresnel lens array, the method comprising:

[0008] Prepare a substrate and a plurality of Fresnel lens units, wherein the Fresnel lens units include an incident plane and an exit surface that are oppositely arranged, wherein the exit surface is provided with Fresnel optical patterns;

[0009] Providing positioning features on the substrate, wherein the positioning features are used to locate the position of each Fresnel lens unit on the substrate;

[0010] The incident planes of the respective Fresnel lens units are guided according to the positioning features and bonded to the preset mounting areas of the substrate using optical adhesive. The Fresnel lens units are arranged in an array on the substrate. After the optical adhesive is cured, the Fresnel lens array is obtained.

[0011] Furthermore, the substrate comprises an upper surface and an embossed bottom surface that are arranged opposite to each other;

[0012] The steps of guiding the incident planes of the respective Fresnel lens units according to the positioning features, adhering the same to the preset mounting areas of the substrate using optical adhesive, arranging the plurality of Fresnel lens units in an array on the substrate, and curing the optical adhesive to obtain the Fresnel lens array include:

[0013] Applying optical adhesive on the incident plane of a Fresnel lens unit;

[0014] Laying the incident plane of the Fresnel lens unit coated with optical adhesive in a preset installation area on the embossed bottom surface of the substrate according to the positioning guidance of the positioning features;

[0015] Performing a first-time curing treatment on the bonded Fresnel lens unit;

[0016] The bonding of the next Fresnel lens unit is repeated until all the Fresnel lens units are bonded to obtain a lens array to be cured;

[0017] The lens array to be cured is placed in a vacuum environment for evacuation, and the lens array to be cured is cured for a second time period to obtain the Fresnel lens array, where the second time period is greater than the first time period.

[0018] Furthermore, the step of applying optical adhesive on the incident plane of a Fresnel lens unit includes:

[0019] The incident plane of the Fresnel lens unit is divided into a peripheral area and a central area. An optical glue dot array is applied to the central area. The glue dots are arranged at intervals. The ratio of the glue dot diameter to the spacing between adjacent glue dots is 30% to 50%. The width of the peripheral area is greater than or equal to twice the spacing between adjacent glue dots.

[0020] Furthermore, the step of providing positioning features on the substrate, wherein the positioning features are used to locate the position of each Fresnel lens unit on the substrate, includes:

[0021] A laser locator is used to perform laser marking on the surface of the substrate, and a number of mutually perpendicular grid lines are divided by the laser marking. The size of the formed grid matches the peripheral size of the Fresnel lens unit.

[0022] A second aspect of the present invention provides a Fresnel lens array, comprising a substrate and a plurality of Fresnel lens units, wherein the Fresnel lens units include an incident plane and an exit surface arranged opposite to each other, wherein the exit surface is provided with Fresnel optical patterns, and the substrate includes positioning features, wherein the positioning features are used to locate the position of each Fresnel lens unit on the substrate; the incident planes of the plurality of Fresnel lens units are respectively adhered to a preset mounting area of ​​the substrate through an optical adhesive layer according to the positioning guidance of the positioning features, and the plurality of Fresnel lens units are arranged in an array on the substrate.

[0023] Furthermore, the substrate comprises an upper surface and an embossed bottom surface which are arranged opposite to each other; the incident plane of the Fresnel lens unit is bonded to the embossed bottom surface of the substrate via an optical adhesive layer.

[0024] Furthermore, the pattern shape of the embossed bottom surface is a closely spaced polygon, and the polygon includes at least one of a regular hexagon, a long hexagon, a regular tetragon, and a rhombus.

[0025] Furthermore, the optical adhesive layer is made of an optical adhesive with a refractive index of 1.49-1.50, a room temperature viscosity of 200-500 cp, and a transmittance greater than or equal to 98%; the Fresnel lens unit is made of polymethyl methacrylate, and the substrate is made of glass.

[0026] Furthermore, there is a gap between the optical adhesive layers corresponding to adjacent Fresnel lens units.

[0027] Furthermore, the positioning features are grid lines formed by laser marking, the grid lines are perpendicular to each other, and the size of the formed grid matches the outer peripheral size of the Fresnel lens unit.

[0028] Implementing the embodiments of the present invention will have at least the following beneficial effects:

[0029] The method for preparing a Fresnel lens array of the present invention uses optical adhesive to bond the incident plane of the Fresnel lens units to a substrate. Compared to traditional side-bonding methods, this method provides a larger bonding area and higher bond strength, making it less susceptible to debonding under temperature fluctuations and vibrations, thereby enhancing the structural strength of the entire lens array. By bonding small Fresnel lens units to form a large Fresnel lens array, production costs are reduced while avoiding defects such as high optical distortion that can occur with one-piece molding. The Fresnel lens array prepared by the present invention offers low manufacturing costs, excellent optical performance, and excellent mass production economics. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] in:

[0032] Figure 1 1 is a schematic flow chart of a method for preparing a Fresnel lens array in one embodiment;

[0033] Figure 2 Schematic diagrams of the structure of a Fresnel lens unit in one embodiment, wherein (a) is a schematic top view of the Fresnel lens unit, and (b) is a schematic cross-sectional structure diagram of the Fresnel lens;

[0034] Figure 3 is a schematic diagram of a method for processing positioning features of a substrate in one embodiment;

[0035] Figure 4 is a schematic diagram of a process of laminating a Fresnel lens unit to a substrate in one embodiment;

[0036] Figure 5 FIG1 is a schematic diagram of a top view of a Fresnel lens array in one embodiment;

[0037] Figure 6 is a schematic cross-sectional structural diagram of a substrate in one embodiment;

[0038] Figure 7 Schematic diagrams of the structure of the pattern shapes of the embossed bottom surface in one embodiment, wherein the pattern shape of (a) is a regular hexagon, the pattern shape of (b) is a long hexagon, the pattern shape of (c) is a regular tetragon, and the pattern shape of (d) is a rhombus;

[0039] Figure 8 Schematic diagram of glue point distribution on the incident plane of a Fresnel lens unit in one embodiment;

[0040] Figure 9 FIG. 1 is a schematic diagram of the cross-sectional structure of a Fresnel lens unit and a lens after bonding in one embodiment. FIG.

[0041] Description of the accompanying figures:

[0042] 1: Substrate; 101: Top surface; 102: Embossed bottom surface; 2: Fresnel lens unit; 201: Incident plane; 202: Exit surface; 3: Positioning feature; 4: Optical adhesive layer; 5: Glue point. DETAILED DESCRIPTION

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this invention belongs. The terms used in the description of the invention herein are for the purpose of describing specific embodiments only and are not intended to limit the invention. The terms "including" and "having" and any variations thereof in the description and claims of the invention and the accompanying drawings are intended to cover non-exclusive inclusions. The terms "first" and "second" in the description and claims of the invention and the accompanying drawings are used to distinguish different objects, not to describe a specific order.

[0044] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute a separate or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0045] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0046] Reference Figure 1 , an embodiment of the present invention shows a method for preparing a Fresnel lens array, the preparation method comprising:

[0047] S1: preparing a substrate 1 and a plurality of Fresnel lens units 2, wherein the Fresnel lens units 2 include an incident plane 201 and an exit surface 202 arranged opposite to each other, wherein the exit surface 202 is provided with Fresnel optical patterns;

[0048] S2: providing positioning features 3 on the substrate 1, wherein the positioning features 3 are used to locate the position of each Fresnel lens unit 2 on the substrate 1;

[0049] S3: The incident plane 201 of each of the Fresnel lens units 2 is respectively guided by the positioning features 3 and bonded to the preset installation area of ​​the substrate 1 through optical glue. Several Fresnel lens units 2 are arranged in an array on the substrate 1. After the optical glue is cured, the Fresnel lens array is obtained.

[0050] In this embodiment, in the above step S1, the substrate 1 is made of high-transmittance photovoltaic glass with a thickness of several millimeters. The size of the substrate 1 can be customized according to the size and number of the Fresnel lens units 2 to be carried. Photovoltaic glass has the advantages of high rigidity and strong weather resistance. The Fresnel lens unit 2 is injection molded using, for example, PMMA (polymethyl methacrylate) material. Figure 2 (a) and Figure 2 As shown in (b), the exit surface 202 is machined with Fresnel optical patterns. For example, a Fresnel lens array is constructed by splicing 16 concentric circular square Fresnel lens units 2, each with a side length of 5 cm by 5 cm. The substrate 1 is constructed from square photovoltaic glass with a side length slightly greater than 20 cm. The small size of the Fresnel lens units 2 reduces mold costs, and the lens material cools and shrinks more evenly during the injection molding process, resulting in lower optical distortion.

[0051] In the above step S2, the positioning features 3 can be selected from structures such as positioning lines, positioning holes or positioning marks. For example, positioning lines can be laser engraved on the substrate 1 to form a grid that matches the size of the lens unit; or positioning holes can be set on the edge of the substrate 1 to cooperate with the positioning mark structure of the lens unit. The positioning features 3 are set on the side of the substrate 1 that contacts the Fresnel lens unit 2; in some other embodiments, they can also be set on the side of the substrate 1 that does not contact the Fresnel lens unit 2. In a specific embodiment, refer to Figure 3 The step S2 of setting a positioning feature 3 on the substrate 1, wherein the positioning feature 3 is used to locate the position of each Fresnel lens unit 2 on the substrate 1, includes: S201: using a laser locator to perform laser marking on the surface of the substrate 1, and dividing the surface of the substrate 1 into a plurality of mutually perpendicular grid lines by the laser marking, and the size of the formed grid matches the outer peripheral size of the Fresnel lens unit 2.

[0052] In the above step S3, the optical adhesive can be selected from, for example, UV-curable optical adhesive, such as acrylate UV-curable optical adhesive, silicone UV-curable adhesive, etc.; hot melt adhesive, such as EVA (ethylene vinyl acetate), etc. Figure 4 During bonding, the incident plane 201 of the Fresnel lens unit coated with optical adhesive is aligned with the preset mounting area on the substrate 1 using the positioning feature 3 on the substrate 1 as a reference. Lightly press to tightly bond the lens unit to the substrate 1. After bonding is completed, the optical adhesive is cured using the curing method corresponding to the selected optical adhesive. After all lens units are bonded and cured, the following is obtained. Figure 5 The Fresnel lens array shown.

[0053] This embodiment uses optical adhesive to bond the incident plane 201 of the Fresnel lens unit to the substrate. Compared to traditional side-bonding methods, this method provides a larger bonding area and higher bond strength, making it less susceptible to debonding under conditions of temperature fluctuations and vibration, thereby enhancing the structural strength of the entire lens array. Furthermore, by bonding smaller Fresnel lens units together to form a larger Fresnel lens array, production costs are reduced while avoiding defects such as high optical distortion that can occur with one-piece molding. The Fresnel lens array prepared using the method of this embodiment boasts low manufacturing costs, excellent optical performance, and excellent mass production economics.

[0054] In some embodiments, reference Figure 6 , the substrate 1 includes an upper surface 101 and an embossed bottom surface 102 that are arranged opposite to each other;

[0055] The incident plane 201 of each Fresnel lens unit 2 is respectively adhered to the preset mounting area of ​​the substrate 1 using optical adhesive according to the positioning guidance of the positioning feature 3, and the multiple Fresnel lens units 2 are arranged in an array on the substrate 1. After the optical adhesive is cured, step S3 of obtaining the Fresnel lens array includes:

[0056] S301: Applying optical adhesive on the incident plane 201 of a Fresnel lens unit 2;

[0057] S302: attaching the incident plane 201 of the Fresnel lens unit 2 coated with optical adhesive to a preset installation area on the embossed bottom surface 102 of the substrate 1 according to the positioning guidance of the positioning features 3;

[0058] S303: performing a first curing treatment on the bonded Fresnel lens unit 2;

[0059] S304: cyclically bonding the next Fresnel lens unit 2 until all Fresnel lens units 2 are bonded to obtain a lens array to be cured;

[0060] S305: placing the lens array to be cured in a vacuum environment for evacuation, and performing a curing process on the lens array to be cured for a second time period to obtain the Fresnel lens array, where the second time period is greater than the first time period.

[0061] In this embodiment, the substrate 1 is made of high-transmittance photovoltaic glass with an embossed bottom surface 102, with a light transmittance greater than 98%. The pattern shape of the embossed bottom surface 102 is a densely packed polygon, such as Figure 7 As shown, polygons include regular hexagons (such as Figure 7 (a)), long hexagon (such as Figure 7 (b)), regular quadrilateral (such as Figure 7 (c)), diamond (e.g. Figure 7 (d)). Compared to when the Fresnel lens unit 2 is bonded to a smooth surface, a clear optical interface is formed between the Fresnel lens and the glass, resulting in inevitable reflection loss. At the same time, plane bonding is prone to produce bubbles and stress, reducing optical efficiency. However, when the incident surface of the Fresnel lens is bonded to the patterned bottom surface 102 of the embossed glass, the microprism structure of the patterned bottom surface 102 can be used to disrupt total internal reflection at the interface. When used in conjunction with the Fresnel lens unit 2, sunlight passes through the embossed glass upper surface 101 → embossed bottom surface 102 → optical adhesive layer 4 → Fresnel lens unit 2 in sequence, ultimately forming a focused light spot. Compared to bonding smooth surfaces, this can reduce reflection loss and significantly improve light transmittance. Taking a substrate with a regular hexagonal pattern on the embossed bottom surface 102 as an example, the regular hexagonal microprisms are symmetrically distributed at 120°, with a controllable scattering angle, which can avoid local hot spots and improve light spot uniformity. Furthermore, the close-packed conditions are met, and the units can be seamlessly spliced, reducing invalid light loss.

[0062] In the above step S301, the glue is applied by dispensing, for example, an automatic glue dispensing machine is used to evenly dispense glue in the center and surrounding areas of the incident plane 201. The distribution of glue dots is adjusted according to the size of the lens to ensure that the glue layer can evenly cover the preset bonding area after bonding.

[0063] In the above step S302 , the Fresnel lens unit 2 is placed in the corresponding area with reference to the positioning features 3 on the substrate 1 during lamination, and the lens is lightly pressed to ensure that the optical adhesive is in full contact with the embossed bottom surface 102 .

[0064] In the above step S303, if UV-curing optical adhesive is selected, the first duration can be set to 10-30 seconds, and preliminary curing is achieved by UV lamp irradiation, so that the single Fresnel lens unit 2 is temporarily fixed on the substrate 1 to avoid displacement during subsequent operations; the adhesive layer after preliminary curing does not need to be completely cured, and a certain viscosity is retained to adapt to subsequent adjustments.

[0065] In the above step S304, each time a lens unit is bonded and initially cured, the next one is moved on to ensure the position accuracy of each unit. After all are bonded, visual inspection is performed to confirm whether the arrangement of all lenses is neat. If there is a slight deviation, slight adjustment can be made (because the initial curing does not completely fix it).

[0066] In step S305, vacuuming further removes air bubbles from the adhesive layer and the gap between the lenses. The degree of vacuum can be adjusted based on actual needs. Curing is then performed for a second duration in the vacuum environment. For UV-curable optical adhesive, the second duration can be set to 40-80 seconds to fully cure the optical adhesive and enhance bonding strength. A longer second duration allows the optical adhesive layer 4 to fully crosslink, ensuring overall bonding stability.

[0067] Reference Figure 8 In some specific embodiments, the step S301 of applying optical adhesive on the incident plane 201 of a Fresnel lens unit 2 includes:

[0068] S3011: Divide the incident plane 201 of the Fresnel lens unit 2 into a peripheral area and a central area, and apply an array of optical glue dots 5 in the central area, with each glue dot 5 arranged at intervals. The ratio of the diameter of the glue dot 5 to the spacing between adjacent glue dots 5 is 30% to 50%, and the width of the peripheral area is greater than or equal to twice the spacing between adjacent glue dots 5.

[0069] In this embodiment, the incident plane 201 of the Fresnel lens unit 2 is divided into regions to determine the periphery and center regions. For a Fresnel lens unit 2 with an overall square incident plane 201, the area indented inward from the edges by a certain width is defined as the periphery, and the remaining center portion is defined as the center region. The ratio of the diameter of the glue dots 5 to the spacing between adjacent glue dots 5 can be 30%, 35%, 40%, 45%, 50%, etc. The width of the periphery region is greater than or equal to twice the spacing between adjacent glue dots 5 and less than or equal to four times the spacing between adjacent glue dots 5. For example, taking a Fresnel lens unit 2 with a side length of 5 cm x 5 cm, and the spacing between adjacent glue dots 5 is set to 0.6 mm, the width of the periphery region must be greater than or equal to 1.2 mm, for example, 1.5 mm. In this case, the center region is a square with sides of 4.7 cm x 4.7 cm, and the periphery region forms a ring with a width of 1.5 mm. Glue dispensing is then performed using precision dispensing equipment. The glue dots 5 are circular and spaced apart to form a regular array (such as a matrix or honeycomb pattern) such that the ratio of the diameter of the glue dots 5 to the spacing between adjacent glue dots 5 is 30% to 50%. For example, the diameter of the glue dots 5 is controlled to be 0.4 mm, and the spacing between adjacent glue dots 5 is 0.6 mm.

[0070] By arranging the glue dots 5 at intervals, the shrinkage stress during the curing process can be dispersed to multiple independent glue dots 5, avoiding unidirectional stress concentration formed by continuous glue layers, and preventing the lens unit from warping due to excessive local stress, which in turn leads to poor optical efficiency.

[0071] Furthermore, by controlling the applied pressure during lamination, in some cases, the glue dots 5 in the center area can fuse after lamination, forming a continuous adhesive layer. However, the peripheral areas, with a width greater than or equal to twice the spacing between adjacent glue dots 5, have no contact between the glue dots 5 and remain unfused. In this case, the fused adhesive layer in the center provides ample bonding area, ensuring a secure connection between the Fresnel lens unit 2 and the substrate 1. The unfused edges provide a buffer for differential thermal expansion between the lens and substrate 1, effectively eliminating stress concentration caused by glue layer shrinkage during curing. Furthermore, in temperature-stable environments, this reduces interfacial stress accumulation, facilitates thermal deformation control, and reduces the risk of debonding or cracking.

[0072] The adhesive dot coating method of this embodiment not only disperses stress concentration areas through discrete adhesive dots, but also flexibly controls the fusion state of the adhesive dots. While ensuring bond strength, it effectively addresses the stress concentration and thermal deformation issues associated with traditional continuous coating, significantly improving the performance and reliability of Fresnel lens arrays. Furthermore, the dot coating method reduces the amount of optical adhesive used, lowers material costs, increases curing speed, and enhances overall production efficiency.

[0073] In a specific embodiment, referring to Figure 5 Sixteen concentric square Fresnel lens units (PMMA) with sides measuring 5 cm x 5 cm are assembled into a lens array. The incident surface of each concentric Fresnel lens unit is flat, while the refractive surface is divided by multiple concentric annular grooves, creating a convex, sawtooth-like pattern. The substrate 1 is made of patterned glass with a regular hexagonal bottom surface 102. A high-transmittance adhesive (>98%), such as Norland NOA81, is used, whose refractive index matches that of the PMMA Fresnel lens units (n≈1.49), minimizing optical deflection and enhancing focusing.

[0074] Array dispensing is used, using a precision piezoelectric jet valve (such as the Nordson PICO series) to dispense glue onto incident plane 201. The dot line diameter is Φ = 0.6mm, the spacing d2 = 0.6mm, and the single dispense volume is 1-3μL. During dispensing, a gap of d1 = 1.5mm is left at the edge of the lens (i.e., the peripheral area). This prevents glue from overflowing and contaminating the lens' refractive surface. More importantly, this blank area absorbs the difference in thermal expansion between PMMA and glass (PMMA's thermal expansion coefficient is approximately 70-90ppm / °C, while glass's is approximately 2.5-9ppm / °C), reducing interfacial stress under temperature fluctuations.

[0075] The embossed bottom surface 102 of the substrate 1 is divided into a positioning grid using a laser locator. During lamination, the lens entrance surface is bonded to the corresponding area of ​​the embossed surface from the inside out, ensuring that the lenses are aligned along the grid lines. During the bonding process, the lenses are gently pressed. The substrate's regular hexagonal pattern size matches the minimum ring-band spacing (1mm) of the Fresnel lens unit (pattern size 1200-1300 mesh / m) to avoid moiré fringing.

[0076] After each unit lens is bonded, use a light source with a wavelength of 405 to 365 nm and an intensity of 50 mW / cm 2 The LED light source is pre-cured for 10 seconds (the first duration). Pre-curing can initially shape the adhesive layer and temporarily fix the lens on the substrate 1 to prevent displacement when other lenses are subsequently attached. At the same time, due to the low degree of curing, a certain amount of adjustment space is reserved to facilitate the correction of minor position deviations.

[0077] Attach 16 lenses sequentially from the inside out, aligning each lens with the grid lines to ensure a neat array. After all lenses are attached, perform a visual inspection to confirm there is no noticeable offset. If any individual lenses are slightly tilted, fine-tune them using the adhesive of the pre-cured adhesive layer.

[0078] The lens array to be cured is placed in a vacuum drying oven, where vacuum is applied to further expel air bubbles from the adhesive layer and lens gaps. After vacuuming, full curing is performed using the same LED light source used for pre-curing, lasting 50 seconds (second duration). The pre-curing stage secures the lens array in position, while the full curing stage slowly completes cross-linking, avoiding the unidirectional stress concentration associated with traditional, long-lasting, one-time curing, effectively preventing lens warping.

[0079] Reference Figures 2 to 5 An embodiment of the present invention provides a Fresnel lens array, comprising a substrate 1 and a plurality of Fresnel lens units 2. The Fresnel lens units 2 include an incident plane 201 and an exit surface 202 that are oppositely arranged, wherein the exit surface 202 is provided with Fresnel optical patterns. The substrate 1 includes a positioning feature 3, which is used to locate the position of each Fresnel lens unit 2 on the substrate 1. The incident planes 201 of the plurality of Fresnel lens units 2 are respectively adhered to a preset mounting area of ​​the substrate 1 through an optical adhesive layer 4 according to the positioning guidance of the positioning feature 3. The plurality of Fresnel lens units 2 are arranged in an array on the substrate 1.

[0080] In this embodiment, the substrate 1 is made of high-transmittance photovoltaic glass with a thickness of several millimeters. Its size can be customized according to the specifications of the array (such as 22 cm × 22 cm), which can provide stable support for the entire array. The above-mentioned positioning features 3 can be selected from structures such as positioning lines, positioning holes or positioning marks. For example, positioning lines are laser engraved on the substrate 1 to form a grid that matches the size of the lens unit; or positioning holes are set on the edge of the substrate 1 to be used in conjunction with the positioning mark structure of the lens unit. The above-mentioned positioning features 3 can be set on the side of the substrate 1 that contacts the Fresnel lens unit 2, or on the side of the substrate 1 that does not contact the Fresnel lens unit 2. In a specific embodiment, the positioning features 3 are grid lines formed by laser marking, the grid lines are perpendicular to each other, and the size of the grid formed matches the outer peripheral size of the Fresnel lens unit 2.

[0081] The Fresnel lens unit 2 is made of PMMA. The size of a single unit can be customized (e.g., 5 cm x 5 cm). It comprises an incident plane 201 and an exit surface 202, which are positioned opposite each other. The incident plane 201 is a smooth surface, bonded to the substrate 1 via an optical adhesive layer 4. The exit surface 202 is patterned with Fresnel optical grooves with a depth of 0.1-0.3 mm and a minimum inter-ring spacing of 1 mm, enabling precise focusing of light. Several Fresnel lens units 2 are arranged in an array on the substrate 1, their arrangement corresponding to the positioning features 3.

[0082] The optical adhesive layer 4 is located between the incident plane 201 of the Fresnel lens unit 2 and the substrate 1. The optical adhesive can be, for example, UV-curing optical adhesive, such as acrylate UV-curing optical adhesive, silicone UV-curing adhesive, etc.; hot melt adhesive, such as EVA (ethylene vinyl acetate), etc.

[0083] The incident plane 201 of the Fresnel lens unit 2 in this embodiment is bonded to the substrate 1 via an optical adhesive layer 4. Compared to traditional side-bonding, this provides a larger bonding area and a stronger bond, making it less susceptible to debonding under temperature fluctuations and vibrations, thereby improving the structural stability of the array. Arranging multiple Fresnel lens units 2 in an array to form a large-scale lens array eliminates the need for large-scale, integrated molding, reducing production complexity and costs. Furthermore, the small units offer low optical distortion, ensuring the optical performance of the entire array.

[0084] In some specific embodiments, referring to Figure 6 The substrate 1 includes an upper surface 101 and an embossed bottom surface 102 that are arranged opposite to each other; the incident plane 201 of the Fresnel lens unit 2 is bonded to the embossed bottom surface 102 of the substrate 1 through an optical adhesive layer 4.

[0085] In this embodiment, the upper surface 101 of the substrate 1 is a smooth plane, and the embossed bottom surface 102 is the surface bonded to the Fresnel lens unit 2, with a light transmittance greater than 98%. Figure 7The pattern shape of the embossed bottom surface 102 is a densely packed polygon, and the polygon includes a regular hexagon (such as Figure 7 (a)), long hexagon (such as Figure 7 (b)), regular quadrilateral (such as Figure 7 (c)), diamond (e.g. Figure 7 (d)).

[0086] Reference Figure 9 The incident plane 201 of the Fresnel lens unit 2 is bonded to the embossed bottom surface 102 of the substrate 1 through the optical adhesive layer 4. During the bonding process, the optical adhesive layer 4 fills the gaps in the pattern of the embossed bottom surface 102 to reduce the generation of bubbles. From the perspective of optical performance, when sunlight is incident from the upper surface 101 of the substrate 1 and passes through the embossed bottom surface 102, the embossed micro-prism structure refracts and scatters the light, avoiding the total reflection phenomenon that occurs when smooth surfaces are bonded. Compared with bonding the Fresnel lens unit 2 to a smooth surface, this bonding method can improve light transmittance, reduce light loss, and allow more light to enter the Fresnel lens unit 2 and be focused. Taking a substrate with a regular hexagonal pattern on the embossed bottom surface 102 as an example, the regular hexagonal micro-prisms are symmetrically distributed at 120°, with a controllable scattering angle, which can avoid local hot spots, improve the uniformity of the light spot, and meet the dense packing conditions. The units can be seamlessly spliced ​​to reduce invalid light loss. Furthermore, when the minimum ring-zone spacing of the optical texture of the Fresnel lens unit 2 is 1 mm, the pattern size of the embossed bottom surface 102 is preferably 1200-1300 mesh / m. By matching the pattern size with the Fresnel ring-zone size, moiré fringe interference can be avoided, and at the same time, light spot diffusion caused by diffraction can be avoided.

[0087] In some specific embodiments, the optical adhesive layer 4 is made of an optical adhesive with a refractive index of 1.49-1.50, a room temperature viscosity of 200-500 cp, and a transmittance greater than or equal to 98%; the Fresnel lens unit 2 is made of polymethyl methacrylate, and the substrate 1 is made of glass.

[0088] In this embodiment, the refractive index of the optical adhesive (1.49 to 1.50) is close to the refractive index of the Fresnel lens unit 2 (PMMA, with a refractive index of approximately 1.49) and the substrate 1 (glass, with a refractive index of approximately 1.51), thereby reducing the reflection loss of light at the "glass-adhesive layer" and "adhesive layer-PMMA" interfaces. The room temperature viscosity of the optical adhesive is 200 to 500 cp, so that after lamination and pressure application, it can well fill the embossed pattern of the embossed bottom surface 102 of the substrate 1 to ensure that there are no bubbles remaining in the adhesive layer. Optical adhesive with high transmittance can reduce its own absorption of light, thereby improving the light energy utilization rate of the overall concentrating photovoltaic system. By way of example, the optical adhesive layer 4 adopts Norland NOA81 UV-curing optical adhesive.

[0089] In some specific embodiments, there is a gap between the optical adhesive layers corresponding to adjacent Fresnel lens units 2. The above-mentioned gap is naturally formed during the bonding process of the Fresnel lens units 2. The optical adhesive layer 4 on the incident plane 201 of each Fresnel lens unit 2 only covers its own preset bonding area, and the adhesive layers of adjacent units are not fused, thereby forming a physical separation. The Fresnel lens unit 2 is made of PMMA material, and the substrate 1 is made of glass material. The thermal expansion coefficients of the two are quite different, with PMMA being approximately 70 to 90 ppm / °C and glass being approximately 2.5 to 9 ppm / °C. When the temperature changes, the PMMA lens unit expands and contracts much more than the glass substrate, and the gap 5 between adjacent optical adhesive layers can provide a buffer space for the thermal expansion difference between the lens and the substrate 1, reducing the accumulation of interfacial stress and preventing the lens unit from warping or the adhesive layer from cracking.

[0090] Obviously, the embodiments described above are only some embodiments of the present invention, rather than all embodiments. The preferred embodiments of the present invention are given in the accompanying drawings, but they do not limit the patent scope of the present invention. The present invention can be implemented in many different forms. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. Although the present invention has been described in detail with reference to the aforementioned embodiments, for those skilled in the art, it is still possible to modify the technical solutions described in the aforementioned specific embodiments, or to make equivalent replacements for some of the technical features therein. Any equivalent structure made using the contents of the present invention specification and drawings, directly or indirectly used in other related technical fields, is also within the scope of patent protection of the present invention.

Claims

1. A method for preparing a Fresnel lens array, characterized in that: The preparation method comprises: Prepare a substrate and a plurality of Fresnel lens units, wherein the Fresnel lens units include an incident plane and an exit surface that are oppositely arranged, wherein the exit surface is provided with Fresnel optical patterns; Providing positioning features on the substrate, wherein the positioning features are used to locate the position of each Fresnel lens unit on the substrate; The incident planes of the respective Fresnel lens units are guided according to the positioning features and bonded to the preset mounting areas of the substrate using optical adhesive. The Fresnel lens units are arranged in an array on the substrate. After the optical adhesive is cured, the Fresnel lens array is obtained.

2. The method for preparing a Fresnel lens array according to claim 1, wherein: The substrate comprises an upper surface and an embossed bottom surface which are arranged opposite to each other; The steps of guiding the incident planes of the respective Fresnel lens units according to the positioning features, adhering the same to the preset mounting areas of the substrate using optical adhesive, arranging the plurality of Fresnel lens units in an array on the substrate, and curing the optical adhesive to obtain the Fresnel lens array include: Applying optical adhesive on the incident plane of a Fresnel lens unit; Laying the incident plane of the Fresnel lens unit coated with optical adhesive in a preset installation area on the embossed bottom surface of the substrate according to the positioning guidance of the positioning features; Performing a first-time curing treatment on the bonded Fresnel lens unit; The bonding of the next Fresnel lens unit is repeated until all the Fresnel lens units are bonded to obtain a lens array to be cured; The lens array to be cured is placed in a vacuum environment for evacuation, and the lens array to be cured is cured for a second time period to obtain the Fresnel lens array, where the second time period is greater than the first time period.

3. The method for preparing a Fresnel lens array according to claim 2, wherein: The step of applying optical adhesive on the incident plane of a Fresnel lens unit includes: The incident plane of the Fresnel lens unit is divided into a peripheral area and a central area. An optical glue dot array is applied to the central area. The glue dots are arranged at intervals. The ratio of the glue dot diameter to the spacing between adjacent glue dots is 30% to 50%. The width of the peripheral area is greater than or equal to twice the spacing between adjacent glue dots.

4. The method for preparing a Fresnel lens array according to claim 1, wherein: The step of providing positioning features on the substrate, wherein the positioning features are used to locate the position of each Fresnel lens unit on the substrate, comprises: A laser locator is used to perform laser marking on the surface of the substrate, and a number of mutually perpendicular grid lines are divided by the laser marking. The size of the formed grid matches the peripheral size of the Fresnel lens unit.

5. A Fresnel lens array, characterized in that: The invention comprises a substrate and a plurality of Fresnel lens units, wherein the Fresnel lens units include an incident plane and an exit surface arranged opposite to each other, wherein the exit surface is provided with Fresnel optical patterns, and the substrate includes positioning features for locating the position of each Fresnel lens unit on the substrate; the incident planes of the plurality of Fresnel lens units are respectively adhered to a preset mounting area of ​​the substrate through an optical adhesive layer according to the positioning guidance of the positioning features, and the plurality of Fresnel lens units are arranged in an array on the substrate.

6. The Fresnel lens array according to claim 5, wherein: The substrate comprises an upper surface and an embossed bottom surface which are arranged opposite to each other; the incident plane of the Fresnel lens unit is bonded to the embossed bottom surface of the substrate via an optical adhesive layer.

7. The Fresnel lens array according to claim 6, wherein: The pattern shape of the embossed bottom surface is a closely spaced polygon, and the polygon includes at least one of a regular hexagon, a long hexagon, a regular square, and a rhombus.

8. The Fresnel lens array according to claim 5, wherein: The optical adhesive used for the optical adhesive layer has a refractive index of 1.49-1.50, a room temperature viscosity of 200-500 cp, and a transmittance greater than or equal to 98%; the Fresnel lens unit is made of polymethyl methacrylate, and the substrate is made of glass material.

9. The Fresnel lens array according to claim 5, wherein: There is a gap between the optical adhesive layers corresponding to adjacent Fresnel lens units.

10. The Fresnel lens array according to claim 5, wherein: The positioning features are grid lines formed by laser marking, the grid lines are perpendicular to each other, and the size of the formed grid matches the outer peripheral size of the Fresnel lens unit.

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