Flexible Fresnel lens and preparation method thereof

Abstract

The invention provides a flexible Fresnel lens and a preparation method thereof, and belongs to the field of optical lenses. The method comprises the following steps: designing a Fresnel lens structure, wherein the Fresnel lens is composed of a plurality of concentric rings; drawing a Fresnel lens reverse mold by using 3D modeling software according to the designed Fresnel lens structure; printing a model of the Fresnel lens reverse mold by using a 3D printer; a silicon release agent is sprayed on the surface of the Fresnel lens reverse mold, and the Fresnel lens reverse mold is placed on a heating table to be heated and dried; preparing polymer colloid in proportion, fully and uniformly stirring, and vacuumizing until no bubble is generated; pouring the prepared polymer colloid into a mold, putting into a drying oven, and heating until the colloid is completely cured; and demolding the cured colloid from the mold to complete the preparation of the flexible Fresnel lens. The invention also provides a Fresnel lens prepared by the method. The preparation method disclosed by the invention has the characteristics of low manufacturing cost, simple manufacturing process and convenience in preparation. And the prepared Fresnel lens has high condensation degree and high flexibility.

Description

Technical Field

[0001] This invention belongs to the field of optical lens design technology, and particularly relates to a flexible Fresnel lens and its fabrication method. Background Technology

[0002] Traditional lenses are thick and heavy. Fresnel lenses divide traditional lenses into a series of concentric toroidal surfaces, which reduces the thickness and weight of the lens, thereby saving costs, while still having excellent light-gathering ability.

[0003] With the development of polymer materials technology, various flexible materials (such as polymers) have been widely used. These materials are lightweight, durable, and easy to process, allowing Fresnel lenses to be manufactured into flexible sheets, thus expanding their application range.

[0004] Modern technology is driving an increasing demand for flexible optical devices, such as wearable devices, flexible displays, and smart clothing. Flexible Fresnel lenses can be integrated with these devices to provide lightweight, flexible optical solutions that meet the needs of various applications.

[0005] Flexible Fresnel lenses are widely used in solar energy concentrators, optical sensors, augmented reality (AR) and virtual reality (VR) devices, lighting fixtures, and other fields. These applications place higher demands on the weight, thickness, and flexibility of lenses, driving the rapid development of flexible Fresnel lens technology. Flexible Fresnel lenses combine the advantages of Fresnel lenses with the properties of flexible materials, making them highly promising for applications in modern optical and electronic devices. Summary of the Invention

[0006] The purpose of this invention is to provide a flexible Fresnel lens and its manufacturing method, so as to solve the technical problems of large lens thickness and weight, high manufacturing cost, complex manufacturing process and the demand for flexible lenses in various fields.

[0007] To solve the above-mentioned technical problems, the specific technical solution of the present invention is as follows:

[0008] A method for fabricating a flexible Fresnel lens, characterized by comprising the following steps:

[0009] Step S1: Design the Fresnel lens structure according to the lens requirements. The Fresnel lens consists of several concentric rings.

[0010] Step S2: Draw the Fresnel lens mold using 3D modeling software based on the designed Fresnel lens structure;

[0011] Step S3: Print the Fresnel lens casting mold model using a 3D printer;

[0012] Step S4: Spray a silicone release agent onto the surface of the Fresnel lens molding die and place it on a heating table to dry it.

[0013] Step S5: Prepare the polymer colloid according to the ratio, stir it thoroughly and evenly, and vacuum until no bubbles are generated;

[0014] Step S6: Pour the prepared polymer colloid into the mold and place it in a drying oven to heat until the colloid is completely cured;

[0015] Step S7: Demold the cured colloid from the mold to complete the fabrication of the flexible Fresnel lens.

[0016] Furthermore, in step S1, the Fresnel lens structure is calculated from a plano-convex lens and consists of several concentric rings. When light is incident on a plano-convex lens, due to the lens's thickness, the light will experience some loss during propagation. The Fresnel lens, however, omits the redundant portion in the middle of the plano-convex lens.

[0017] When a lens is positioned in air, the focal length of a plano-convex lens can be calculated using the following formula:

[0018]

[0019] f is the focal length of the plano-convex lens; R is the radius of curvature (convex surface) of the plano-convex lens; n is the refractive index of the plano-convex lens material.

[0020] A Fresnel lens consists of a series of concentric rings, each of which is part of a plano-convex lens. The radius of curvature of each ring in a Fresnel lens is equal to the radius of curvature of the plano-convex lens.

[0021] The focal length of a Fresnel lens can be calculated using the following formula, based on the focal length of a plano-convex lens:

[0022]

[0023] Where x is the distance from the center of the bottom circle.

[0024] Further, in step S3, the 3D printing parameters are: exposure time 4.2 seconds, bottom layer exposure time 40 seconds, lift distance 3 mm, layer thickness 0.025-0.050 mm, lift speed 25 mm / min, and return speed 320 mm / min. The printed model is placed in anhydrous alcohol and ultrasonically vibrated for 5 minutes to clean the uncured resin. Then it is placed in a UV curing device for 1 hour for curing.

[0025] Furthermore, in step S4, the temperature of the heating platform is set to 100°C and the heating time is set to 10 minutes.

[0026] Further, in step S5, the polymer colloid includes polydimethylsiloxane polymer, crosslinking agent, and platinum accelerated curing agent. The ratio of dimethylsiloxane polymer, crosslinking agent, and platinum accelerated curing agent is 100:5 to 20:1 to 3. The polymer colloid is prepared according to the ratio, stirred thoroughly and evenly, and vacuumed until no bubbles are generated.

[0027] Furthermore, in step S6, the drying oven temperature is 60°C and the heating time is 24 hours.

[0028] The present invention also provides a Fresnel lens, which is prepared by the above-described Fresnel lens preparation method. The Fresnel lens is composed of several concentric rings and is flexible and bendable.

[0029] Furthermore, the tensile properties of the Fresnel lens are determined by the ratio of dimethylsiloxane polymer, crosslinking agent, and platinum accelerated curing agent, as well as the thickness of the Fresnel lens.

[0030] Furthermore, the transmittance of the Fresnel lens is determined by the thickness of the Fresnel lens.

[0031] Furthermore, the refractive index and Abbe number of the Fresnel lens are determined by the ratio of dimethylsiloxane polymer, crosslinking agent, and platinum accelerated curing agent.

[0032] Compared with the prior art, the present invention has the following beneficial technical effects:

[0033] This invention proposes a method for fabricating Fresnel lenses using 3D printing technology. This method features low manufacturing cost, simple manufacturing process, and ease of fabrication. The Fresnel lenses fabricated by this method possess high light focusing power and high flexibility. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This represents the transmittance of the polymer colloidal film of the present invention.

[0036] Figure 2 is the refractive index of the polymer colloidal film of the present invention.

[0037] Figure 3 This is a schematic diagram of the two-dimensional structure of a Fresnel lens according to Embodiment 1 of the present invention.

[0038] Figure 4This is a physical image of the lens mold prepared by 3D printing technology according to Embodiment 1 of the present invention.

[0039] Figure 5 This is a physical image of a flexible Fresnel lens according to Embodiment 1 of the present invention.

[0040] Figure 6 This is a detailed view of the flexible Fresnel lens according to Embodiment 1 of the present invention.

[0041] Figure 7 This is a diagram illustrating the light-gathering effect of a flexible Fresnel lens according to Embodiment 1 of the present invention.

[0042] Figure 8 This is a graph showing the test data of the focusing magnification of the flexible Fresnel lens in Embodiment 1 of the present invention.

[0043] Figure 9 Example 1, a flexible Fresnel lens optical path diagram, is simulated using simulation software according to Embodiment 1 of the present invention.

[0044] Figure 10 This is an example of the light-gathering effect of a flexible Fresnel lens simulated using simulation software.

[0045] Figure 11 This is a schematic diagram of the two-dimensional structure of a Fresnel lens according to Embodiment 2 of the present invention.

[0046] Figure 12 This is a physical image of the lens mold prepared by 3D printing technology according to Embodiment 2 of the present invention.

[0047] Figure 13 This is a physical image of the flexible Fresnel lens according to Embodiment 2 of the present invention.

[0048] Figure 14 This is a detailed view of the flexible Fresnel lens in Embodiment 2 of the present invention.

[0049] Figure 15 This is a diagram illustrating the focusing effect of a flexible Fresnel lens in Embodiment 2 of the present invention.

[0050] Figure 16 This is a graph showing the test data of the focusing magnification of the flexible Fresnel lens in Embodiment 2 of the present invention.

[0051] Figure 17 Example 1, a flexible Fresnel lens optical path diagram, is simulated using simulation software in Embodiment 2 of the present invention.

[0052] Figure 18 Example 2: Light-gathering effect of a flexible Fresnel lens simulated using simulation software. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] Since existing lenses are made of glass, plastic, etc., and lack stretchability, this invention uses 3D printing and molding to prepare flexible Fresnel lenses. By designing molds, the size and focal length of the lens are controlled, and the prepared lens has high light transmission and high light focusing performance, while also possessing stretchability.

[0055] The method for fabricating a flexible Fresnel lens proposed in this invention includes the following steps:

[0056] Step S1: Design the Fresnel lens structure according to the lens requirements. The Fresnel lens consists of several concentric rings.

[0057] The Fresnel lens structure is calculated from that of a plano-convex lens and consists of several concentric rings. When light is incident on a plano-convex lens, due to the lens's thickness, some light is lost during propagation. The Fresnel lens, however, omits the unnecessary middle portion of the plano-convex lens.

[0058] When a lens is positioned in air, the focal length of a plano-convex lens can be calculated using the following formula:

[0059]

[0060] f is the focal length of the plano-convex lens; R is the radius of curvature (convex surface) of the plano-convex lens; n is the refractive index of the plano-convex lens material.

[0061] A Fresnel lens consists of a series of concentric rings, each of which is part of a plano-convex lens. The radius of curvature of each ring in a Fresnel lens is equal to the radius of curvature of the corresponding plano-convex lens.

[0062] The focal length of a Fresnel lens can be calculated using the following formula, based on the focal length of a plano-convex lens:

[0063]

[0064] Where x is the distance from the center of the bottom circle.

[0065] Step S2: Draw the Fresnel lens mold using 3D modeling software based on the designed Fresnel lens structure.

[0066] Step S3: Print the Fresnel lens casting mold model using a 3D printer.

[0067] Specifically, the 3D printing parameters are: exposure time 4.2 seconds, bottom layer exposure time 40 seconds, lift distance 3 mm, layer thickness 0.025-0.050 mm, lift speed 25 mm / min, and return speed 320 mm / min. The printed model is placed in anhydrous alcohol and ultrasonically vibrated for 5 minutes to clean the uncured resin. Then it is placed in a UV curing device for 1 hour for curing.

[0068] Step S4: Spray a silicone release agent onto the surface of the Fresnel lens mold and place it on a heating table to heat and dry.

[0069] Specifically, the temperature of the heating platform is set to 100℃, and the heating time is set to 10 minutes.

[0070] Step S5: Prepare the polymer colloid according to the ratio, stir it thoroughly and evenly, and evacuate the vacuum until no bubbles are generated.

[0071] To achieve the specific flexibility of the Fresnel lens, this invention uses polydimethylsiloxane (PDMS) to prepare a polymer colloid.

[0072] The polymer colloid of the present invention comprises a polydimethylsiloxane polymer, a crosslinking agent, and a platinum accelerated curing agent. The ratio of the dimethylsiloxane polymer, the crosslinking agent, and the platinum accelerated curing agent is 100:5 to 20:1 to 3. The polymer colloid is prepared in proportion, thoroughly stirred until homogeneous, and then evacuated until no bubbles are generated.

[0073] Figure 1 The figure shows the transmittance of a polymer colloidal film with a thickness of 1 mm for sunlight (wavelength range 0.3-2.5 μm). The polymer colloidal film exhibits high transmittance in the sunlight wavelength range (0.3-2.5 μm), according to the formula...

[0074]

[0075] It is defined as the ratio of the transmitted solar spectral intensity within a certain wavelength range (λ1-λ2) to the total incident solar spectral intensity within the same wavelength range; T(λ) is the transmittance of the polymer at wavelength λ; Isolar(λ) is the standardized ASTM G173 global solar spectral irradiance.

[0076] The transmittance of the polymer film in the solar light band (0.3-2.5 μm) was measured using a UV-Vis spectrophotometer. Based on this formula, the average transmittance in the solar light band (0.3-2.5 μm) was calculated to be 94.65% when the polymer thickness was 1 mm.

[0077] Figure 2The figure shows the refractive index of the polymer colloidal film in the wavelength range of 0.4-0.8 μm. It can be seen that the refractive index varies slightly with different wavelengths. In this invention, the wavelength λ = 0.55 μm is taken, and the refractive index n = 1.41 is used as the refractive index of the material when calculating lens parameters. The calculation will have corresponding spherical aberration.

[0078] Step S6: Pour the prepared polymer colloid into the mold and place it in a drying oven to heat until the colloid is completely cured.

[0079] Specifically, the drying oven temperature is 60℃, and the heating time is 24 hours.

[0080] Step S7: Demold the cured colloid from the mold to complete the fabrication of the flexible Fresnel lens.

[0081] The present invention also proposes a Fresnel lens prepared by the above-mentioned flexible Fresnel lens preparation method. The Fresnel lens is composed of several concentric rings and has the flexibility to be bent.

[0082] Furthermore, the tensile properties of the Fresnel lens are determined by the ratio of dimethylsiloxane polymer, crosslinking agent, and platinum accelerated curing agent, as well as the thickness of the Fresnel lens.

[0083] The lower the proportion of crosslinking agent in the polymer, the better the tensile properties of the prepared Fresnel lens; the smaller the thickness of the Fresnel lens, the better its tensile properties. Furthermore, the transmittance of the Fresnel lens is determined by the ratio of dimethylsiloxane polymer, crosslinking agent, and platinum accelerated curing agent, which influences its tensile properties.

[0084] Furthermore, the refractive index of the Fresnel lens is determined by the tensile properties of the Fresnel lens, which are determined by the ratio of dimethylsiloxane polymer, crosslinking agent, and platinum accelerated curing agent.

[0085] Furthermore, the Abbe number of the Fresnel lens is determined by the tensile properties of the Fresnel lens, which are determined by the ratio of dimethylsiloxane polymer, crosslinking agent, and platinum accelerated curing agent.

[0086] The following two embodiments will be used to describe in detail the method for fabricating the flexible Fresnel lens of the present invention.

[0087] Example 1

[0088] A method for fabricating a flexible Fresnel lens, the purpose of which in this embodiment is to fabricate a flexible Fresnel lens with a radius r = 4 cm, includes the following steps:

[0089] Step S1: Design the Fresnel lens structure according to the lens requirements. The Fresnel lens consists of several concentric rings.

[0090] Specifically, such as Figure 3 As shown, first draw a hemispherical plano-convex lens with a radius of curvature of R cm, where R is greater than r; in this example, R = 8 cm. Then, cut a spherical notch with a base radius of 4 cm from this hemispherical plano-convex lens. The height H of the notch is calculated using the following formula:

[0091]

[0092] Substituting the values ​​of R and r into the calculation, we get H = 1.07 cm.

[0093] A Fresnel lens contains a = 10 rings of equal height. If a truncated spherical segment is divided into 10 equal parts along a direction parallel to the base, then the height of each ring is... The height of the ring is obtained as h = 0.107 cm. Remove the redundant cylinders of equal height but different radii from each part, and translate the remaining part to the bottom surface to obtain the Fresnel lens model.

[0094] The width of the obtained Fresnel lens ring is calculated using the following formula:

[0095]

[0096] d N R is the width of the Nth ring; N is the ring number; R is the radius of curvature of the plano-convex lens; H is the height of the spherical cap; a is the number of rings.

[0097] Table 1. Fresnel Lens Ring Width and Radius of Curvature Parameters

[0098] Circular serial number 1 2 3 4 5 6 7 8 9 10 Ring width (cm) 1.30 0.53 0.41 0.34 0.29 0.26 0.24 0.22 0.20 0.19 Radius of curvature (cm) 8 8 8 8 8 8 8 8 8 8

[0099] The radius of curvature of each Fresnel lens ring is R; the focal length f0 of the Fresnel lens is:

[0100]

[0101] Where f is the focal length of the plano-convex lens; R is the radius of curvature of the Fresnel lens ring, which is equal to the radius of curvature (convex surface) of the plano-convex lens; n is the refractive index of the plano-convex lens material; and x is the distance from the center of the bottom circle.

[0102] Step S2: Draw the Fresnel lens mold using 3D modeling software based on the designed Fresnel lens structure.

[0103] Step S3: Print a model of the Fresnel lens casting mold using a 3D printer, such as... Figure 4 As shown.

[0104] Step S4: Spray silicone release agent onto the mold surface and heat it on a heating table at 100°C for 10 minutes.

[0105] Step S5: Prepare the polymer colloid by mixing dimethylsiloxane polymer, crosslinking agent, and platinum accelerated curing agent in a ratio of 100:10:3, stir thoroughly until homogeneous, and then vacuum until no bubbles are generated.

[0106] Step S6: Pour the prepared polymer colloid into the mold and place it in a drying oven to heat until the colloid is completely cured; the drying oven temperature is 60℃ and the heating time is 24 hours.

[0107] Step S7: Demold the cured colloid from the mold to complete the fabrication of the flexible Fresnel lens.

[0108] A physical image of the Fresnel lens prepared by this method is shown below. Figure 5 As shown, the Fresnel lens is flexible and bendable. Figure 6 A detailed image of a Fresnel lens prepared using this method, showing three Fresnel lens rings. Figure 7 The effect of a flexible Fresnel lens in focusing parallel sunlight emitted by a xenon lamp (simulating sunlight) is demonstrated, showing that the fabricated flexible Fresnel lens has a very obvious light-focusing effect. Figure 8 This is a graph showing the magnification test data for a flexible Fresnel lens. The optical power density meter has a test range of 0-2000 W / m². 2 The xenon lamp power was reduced, and the luminous intensity of the xenon lamp source was measured to be 151.24 W / m² using a light power density meter. 2 A flexible Fresnel lens was placed at the xenon lamp light source (at the same height as the xenon lamp intensity test). The light intensity measured at the lens's focal length was 1898.64 W / m. 2 It can be seen that the focused light intensity of the fabricated flexible Fresnel lens is 12.55 times that of the light without the lens. Figure 9 The image shows the optical path diagram of a flexible Fresnel lens simulated by simulation software. The diagram shows the ray trajectory of parallel light incident on the Fresnel lens model, and the light rays converge in one place. Figure 10 The image shows a simulation of the light-gathering effect of a flexible Fresnel lens using simulation software. As can be seen from the image, 96% of the light rays converge into a square area with a side length of 1 cm, indicating that the Fresnel lens model has a very good focusing effect.

[0109] Example 2

[0110] A method for fabricating a flexible Fresnel lens, the purpose of which in this embodiment is to fabricate a flexible Fresnel lens with a focal length f0 = 10 cm, includes the following steps:

[0111] Step S1: Design the Fresnel lens structure according to the lens requirements. The Fresnel lens consists of several concentric rings.

[0112] Specifically, a Fresnel lens consists of multiple rings, with the width of each ring decreasing outward from the center. The structural parameters of the Fresnel lens are calculated from the parameters of a plano-convex lens. In this example, the Fresnel lens consists of multiple rings, each with a different radius of curvature. The rings at different positions in this example are obtained by subtracting a portion of the cylinder perpendicular to the bottom surface from the portion of the hemispherical plano-convex lens corresponding to the ring's position, and then translating the remaining portion to the bottom surface. The focal length of the ring at that position is the difference between the focal length of the corresponding hemispherical plano-convex lens and the height of the subtracted cylinder. Figure 11 This is a two-dimensional diagram illustrating the principle of the Fresnel lens in this example. If the focal length of the Fresnel lens is determined, the radius of curvature R of the annulus at a distance x from the center of the base can be derived using the following formula.

[0113]

[0114] n is the refractive index of the lens; f0 is the required focal length of the Fresnel lens in this example; x is the distance between the ring in the Fresnel lens and the center of the bottom surface; f is the focal length of the plano-convex lens.

[0115] Table 2 shows the Fresnel lens ring width and radius of curvature parameters when n = 1.41 and f0 = 10 cm. The Fresnel ring width is set by the user according to their needs.

[0116] Table 2. Fresnel Lens Ring Width and Radius of Curvature Parameters

[0117] Circular serial number 1 2 3 4 5 6 7 8 Ring width (cm) 0.75 0.5 0.5 0.35 0.2 0.2 0.2 0.2 Radius of curvature (cm) 6.638 6.587 6.507 6.432 6.381 6.323 6.258 6.185

[0118] 9 10 11 12 13 14 15 16 17 18 0.2 0.2 0.2 0.15 0.1 0.1 0.1 0.1 0.1 0.1 6.103 6.008 5.900 5.806 5.736 5.659 5.572 5.472 5.352 5.195

[0119] Step S2: Draw the Fresnel lens mold using 3D modeling software based on the designed Fresnel lens structure.

[0120] Step S3: Print a model of the Fresnel lens casting mold using a 3D printer, such as... Figure 12 As shown.

[0121] Step S4: Spray silicone release agent onto the mold surface and heat it on a heating table at 100°C for 10 minutes.

[0122] Step S5: Prepare the polymer colloid by mixing dimethylsiloxane polymer, crosslinking agent, and platinum accelerated curing agent in a ratio of 100:10:3, stir thoroughly until homogeneous, and then vacuum until no bubbles are generated.

[0123] Step S6: Pour the prepared polymer colloid into the mold and place it in a drying oven to heat until the colloid is completely cured; the drying oven temperature is 60℃ and the heating time is 24 hours.

[0124] Step S7: Demold the cured colloid from the mold to complete the fabrication of the flexible Fresnel lens.

[0125] A physical image of the Fresnel lens prepared by this method is shown below. Figure 13 As shown, the Fresnel lens is flexible and bendable. Figure 14 A detailed image of a Fresnel lens prepared using this method, showing seven Fresnel lens rings. Figure 15 The effect of a flexible Fresnel lens in focusing parallel sunlight emitted by a xenon lamp (simulating sunlight) is demonstrated, showing that the fabricated flexible Fresnel lens has a very obvious light-focusing effect. Figure 16 This is a graph showing the magnification test data for a flexible Fresnel lens, with the optical power density meter measuring range (0-2000W / m). 2 The xenon lamp power was reduced, and the luminous intensity of the xenon lamp source was measured to be 123.6 W / m² using a light power density meter. 2 A flexible Fresnel lens was placed at the xenon lamp light source (at the same height as the xenon lamp intensity test). The light intensity measured at the lens's focal length was 1810.4 W / m. 2 It can be seen that the focused light intensity of the fabricated flexible Fresnel lens is 14.65 times that of the light intensity without the lens. Figure 17 The image shows the optical path diagram of a flexible Fresnel lens simulated by simulation software. The diagram shows the ray trajectory of parallel light incident on the Fresnel lens model, and the light rays converge in one place. Figure 18 The image shows a simulation of the light-gathering effect of a flexible Fresnel lens. As can be seen from the image, 92% of the light rays converge into a square area with a side length of 1 cm, indicating that the Fresnel lens model has a very good focusing effect.

[0126] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method of manufacturing a flexible Fresnel lens, characterized by, The method comprises the following steps: Step S1: design the Fresnel lens structure according to the lens requirements, the Fresnel lens is composed of a plurality of concentric rings; Step S2: draw the Fresnel lens inverse mold mold according to the designed Fresnel lens structure with 3D modeling software; Step S3: print the model of the Fresnel lens inverse mold mold with a 3D printer; Step S4: spray silicon release agent on the surface of the Fresnel lens inverse mold mold, and place it on a heating table to heat and dry; Step S5: proportionally configure the polymer colloid, fully stir it to be uniform, and vacuumize it until no bubbles are generated; Step S6: pour the configured polymer colloid into the mold, and place it in a drying oven to heat until the colloid is completely solidified; Step S7: demold the solidified colloid from the mold, and complete the preparation of the flexible Fresnel lens.

2. The method of claim 1, wherein the flexible Fresnel lens is prepared by a process comprising: In step S1, The Fresnel lens structure is calculated from a plano-convex lens and is composed of a plurality of concentric rings. When light is incident on the plano-convex lens, there is a certain loss in the propagation process due to the thick thickness of the lens, and the Fresnel lens omits the redundant part in the middle of the plano-convex lens. The lens is located in the air, and the focal length of the plano-convex lens can be calculated by the following formula: f is the focal length of the plano-convex lens; R is the radius of curvature (convex surface) of the plano-convex lens; n is the refractive index of the material of the plano-convex lens. The Fresnel lens is composed of a series of concentric rings, each ring is a part of the plano-convex lens, and the radius of curvature of each ring of the Fresnel lens is equal to the radius of curvature of the corresponding plano-convex lens. The focal length of the Fresnel lens can be calculated according to the focal length of the plano-convex lens by the following formula: Wherein, x is the distance from the bottom center.

3. The method of claim 1, wherein the flexible Fresnel lens is prepared by a process comprising: In step S3, The 3D printing parameters are exposure time 4.2 seconds, bottom layer exposure time 40 seconds, lifting distance 3 millimeters, layer thickness 0.025-0.050 millimeters, lifting speed 25 millimeters per minute, and return speed 320 millimeters per minute; Put the printed model into anhydrous alcohol and ultrasonically oscillate for 5 minutes to clean the un-solidified resin. Then put it into a UV curing UV lamp device and cure for 1 hour.

4. The method of claim 1, wherein the flexible Fresnel lens is prepared by a process comprising: The temperature of the heating table in step S4 is set to 100℃, and the heating time is set to 10 minutes.

5. The method of claim 1, wherein the flexible Fresnel lens is prepared by a process comprising: In step S5, the polymer colloid includes polydimethylsiloxane polymer, crosslinking agent, and platinum gold curing accelerator. The ratio of polydimethylsiloxane polymer, crosslinking agent, and platinum gold curing accelerator is 100:5-20:1-3. The polymer colloid is proportionally configured, fully stirred to be uniform, and vacuumized until no bubbles are generated.

6. The method of claim 1, wherein the flexible Fresnel lens is prepared by a process comprising: The drying oven temperature in step S6 is 60℃, and the heating time is 24 hours.

7. A Fresnel lens prepared by the method of any one of claims 1-6, the Fresnel lens is composed of a plurality of concentric rings and has flexibility and can be bent.

8. The flexible Fresnel lens of claim 7, wherein, The tensile properties of the Fresnel lens are determined by the ratio of dimethylsiloxane polymer, crosslinking agent, and platinum gold curing accelerator, and the thickness of the Fresnel lens.

9. The flexible Fresnel lens of claim 7, wherein, The transmittance, refractive index, and Abbe number of the Fresnel lens are determined by the ratio of dimethylsiloxane polymer, crosslinking agent, and platinum gold curing accelerator.

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