Fresnel lens and method for manufacturing the same

Abstract

The application provides a Fresnel lens and a preparation method thereof, and relates to the technical field of optics, and comprises a transparent substrate, a Fresnel structure layer is arranged on the transparent substrate, the Fresnel structure layer comprises a plurality of step structures, each step structure comprises a plurality of concentric steps arranged along a thickness direction, a plurality of grooves penetrating through the Fresnel structure layer along the thickness direction are arranged on the Fresnel structure layer, one end of the groove extends to the edge of the Fresnel structure layer, and the other end extends to the center of the Fresnel structure layer. The plurality of grooves divide the Fresnel structure layer into a plurality of regions, so that the plurality of regions are separated by the grooves, and in this way, when the Fresnel lens is prepared, residual imprint glue can be discharged outward along the grooves, glue residue is reduced, air bubbles generated in the imprint process are avoided, and the preparation yield of the Fresnel lens can be greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical technology, in particular to a Fresnel lens and a preparation method thereof. BACKGROUND

[0002] Fresnel lens is a new type of optical element invented by a famous French physicist, which replaces the curved surface of the traditional lens with a series of concentric grooves, and is cast into a thin and light plastic plate. The stepped Fresnel lens is a special form, which can be used to realize focusing or collimation function, and has a wide range of applications in the field of 3D depth sensing such as structured light and TOF. It is essentially a diffractive optical element, which is composed of multiple stepped distribution and can be prepared by photolithography and etching in semiconductor process and nanoimprint.

[0003] Patent CN107976732B discloses a variable-step diffractive element and a preparation method thereof, which uses laser direct writing to prepare a multi-step diffractive optical element. However, this patent only solves the balance between the focusing efficiency of the Fresnel lens and the process, and cannot fundamentally solve the problem of low yield in the preparation of the stepped Fresnel lens in the nanoimprint process. SUMMARY

[0004] The purpose of the embodiments of the present application is to provide a Fresnel lens and a preparation method thereof, which can improve the processing yield of the stepped Fresnel lens.

[0005] In one aspect of the embodiments of the present application, a Fresnel lens is provided, which comprises a transparent substrate, a Fresnel structure layer is arranged on the transparent substrate, the Fresnel structure layer comprises a plurality of stepped structures, each stepped structure comprises a plurality of concentric steps arranged in a thickness direction, a plurality of grooves penetrating the Fresnel structure layer in the thickness direction are arranged on the Fresnel structure layer, one end of the groove extends to the edge of the Fresnel structure layer, and the other end extends to the center of the Fresnel structure layer.

[0006] Optionally, the number of steps of the stepped structure is 2 N , and N is a positive integer.

[0007] Optionally, the height of each layer of steps is wherein l is the number of steps whose height needs to be calculated, L is the total number of steps, λ is the working wavelength of the Fresnel lens, and n is the refractive index of the material of the Fresnel lens.

[0008] Optionally, the radius of each layer of steps is wherein m is the number of rings of concentric circles on the Fresnel lens, l is the number of steps whose height and radius need to be calculated, L is the total number of steps, λ is the working wavelength of the Fresnel lens, and f is the focal length of the Fresnel lens.

[0009] Optionally, the width of the groove is between 1um and 10um.

[0010] Optionally, one end of the groove extending to the center of the Fresnel structure layer extends to at least a third concentric circle on the Fresnel lens, and the concentric circle located at the center of the Fresnel lens is a first ring concentric circle.

[0011] Optionally, the projection of the plurality of grooves in the thickness direction forms at least a cross shape or a hufu shape.

[0012] Another aspect of the embodiments of the present application provides a preparation method of a Fresnel lens, for preparing the Fresnel lens described above, comprising: obtaining a master, forming a Fresnel structure layer on the master; etching a groove on the Fresnel structure layer, so that the groove penetrates the Fresnel structure layer; and transferring the master on a transparent substrate to form the Fresnel structure layer on the transparent substrate.

[0013] Optionally, the obtaining of the master and the forming of the Fresnel structure layer on the master comprises: sequentially obtaining the Fresnel structure layer on the master by photolithography and dry etching; and the number of steps on the Fresnel structure layer is 2. N When the number of steps is N, the number of times of photolithography and dry etching is N.

[0014] Optionally, the transferring of the master on the transparent substrate to form the Fresnel structure layer on the transparent substrate comprises: transferring in a vacuum environment below 100pa.

[0015] The Fresnel lens and the preparation method thereof provided by the embodiments of the present application are characterized in that a Fresnel structure layer is arranged on a transparent substrate, the Fresnel structure layer comprises a plurality of step structures, each step structure comprises a plurality of concentric steps, a plurality of grooves are arranged on the Fresnel structure layer, the plurality of grooves penetrate the thickness direction of the Fresnel structure layer, one end of the groove extends to the edge of the Fresnel structure layer, and the other end of the groove approaches the center of the Fresnel structure layer, so as to divide the Fresnel structure layer into a plurality of regions, and the plurality of regions are separated by the grooves. In this way, when the Fresnel lens is prepared, the residual imprinting glue can be discharged outward along the groove, the glue residue is reduced, the air bubbles generated in the imprinting process are avoided, and the preparation yield of the Fresnel lens can be greatly improved.

[0016] The preparation of the Fresnel lens comprises the preparation of the master and nano-imprinting, and the preparation of the master of the Fresnel lens comprises DUV photolithography and dry etching. After the preparation of the master of the Fresnel lens is completed, the master needs to be transferred to a transparent substrate of glass or resin in batches through nano-imprinting. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those of ordinary skill in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0018] Figure 1 is a schematic diagram of the existing Fresnel lens structure;

[0019] Figure 2 is one of the schematic diagrams of the Fresnel lens structure provided by the present embodiment;

[0020] Figure 3 is another schematic diagram of the Fresnel lens structure provided by the present embodiment;

[0021] Figure 4 is a schematic diagram of the cross-shaped slot structure of the Fresnel lens provided by the present embodiment;

[0022] Figure 5 is a schematic diagram of the rice-shaped slot structure of the Fresnel lens provided by the present embodiment;

[0023] Figure 6 is a schematic diagram of the Fresnel lens structure with a groove width of 2um provided by the present embodiment;

[0024] Figure 7 is a schematic diagram of the Fresnel lens structure with a groove width of 6um provided by the present embodiment;

[0025] Figure 8 is a schematic diagram of the Fresnel lens structure with a groove width of 10um provided by the present embodiment;

[0026] Figure 9 is one of the schematic diagrams of the focusing efficiency of the four-order Fresnel lens provided by the present embodiment;

[0027] Figure 10 is a schematic diagram of the focusing efficiency of the eight-order Fresnel lens provided by the present embodiment;

[0028] Figure 11 is a schematic diagram of the Fresnel lens structure with the groove extending to the center provided by the present embodiment;

[0029] Figure 12 is a schematic diagram of the Fresnel lens structure with the groove extending to the first ring periphery provided by the present embodiment;

[0030] Figure 13 is a schematic diagram of the Fresnel lens structure with the groove extending to the second ring periphery provided by the present embodiment;

[0031] Figure 14Fig. 2 is a second schematic diagram of focusing efficiency of a fourth-order Fresnel lens provided in the embodiment;

[0032] Figure 15 Fig. 3 is a collimation diagram of a Fresnel lens provided in the embodiment;

[0033] Figure 16 Fig. 4 is a focusing diagram of a Fresnel lens provided in the embodiment;

[0034] Figures 17-18 Fig. 5 is an effect diagram of a Fresnel lens after preparation in the prior art;

[0035] Figures 19-20 Fig. 6 is an effect diagram of a Fresnel lens after preparation provided in the embodiment.

[0036] Fig. 1 is a schematic diagram of a Fresnel lens provided in the embodiment. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the drawings in the embodiments of the present application.

[0038] In the description of the present application, it should be noted that the directions or position relationships indicated by the terms "inner", "outer" and the like are based on the directions or position relationships shown in the drawings, or the directions or position relationships in which the products of the present application are usually placed, and are only for the convenience of describing the present application and simplifying the description, and thus cannot be understood as indicating or implying that the devices or elements must have a particular direction, be constructed and operated in a particular direction, and thus cannot be understood as limiting the present application. In addition, the terms "first", "second" and the like are only used for differentiation in description, and cannot be understood as indicating or implying relative importance.

[0039] It should also be noted that, unless otherwise explicitly specified and limited, the terms "provided", "connected" should be understood broadly, for example, can be fixedly connected, or can be detachably connected, or integrally connected; can be directly connected, or indirectly connected through an intermediate medium, or can be connected inside two elements. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0040] The preparation of the step-type Fresnel lens is generally through photoetching or laser direct writing to make a master plate, and then through nanoimprinting to mass transfer to the transparent substrate 10. Due to the nature of the commonly used imprinting glue, the imprinting glue is blocked by the sidewall of the high step of the Fresnel layer during the process of being discharged from the middle to the outside, resulting in glue residue and forming hollow bubbles. Once bubbles are generated, the Fresnel lens cannot be used normally, and thus Figure 1 The yield of the conventional step-type Fresnel lens nanoimprinting process is very low.

[0041] On this basis, in view of the above-mentioned deficiencies, the application provides a groove 12 arranged on the Fresnel structure layer, which can help the pressure-out of the glue, avoid the generation of bubbles, greatly improve the processing yield of the step-type Fresnel lens without affecting the optical performance.

[0042] Specifically, referring to Figure 2 The embodiment of the application provides a Fresnel lens which can reduce the generation of bubbles in the preparation process of the Fresnel lens and improve the preparation yield of the lens while ensuring the focusing or collimating function of the Fresnel lens. The Fresnel lens provided by the embodiment of the application comprises a transparent substrate 10, the transparent substrate 10 is provided with a Fresnel structure layer, the Fresnel structure layer comprises a plurality of step structures 11, each step structure 11 comprises a plurality of concentric steps arranged along the thickness direction, a plurality of grooves 12 penetrating the Fresnel structure layer along the thickness direction are arranged on the Fresnel structure layer, one end of the groove 12 extends to the edge of the Fresnel structure layer, and the other end extends to the center of the Fresnel structure layer.

[0043] The composition material of the transparent substrate 10 can be glass or resin, a plurality of step structures 11 are arranged on the transparent substrate 10, the plurality of step structures 11 form the Fresnel structure layer, and the Fresnel structure layer is divided into a plurality of regions by the plurality of grooves 12, the grooves 12 penetrate the Fresnel structure layer along the thickness direction, and the arrangement of the grooves 12 helps the pressure-out of the glue.

[0044] Each step structure 11 is provided with a plurality of concentric steps, each step structure 11 takes the center of the transparent substrate 10, that is, the center of the Fresnel lens as the center, and all the concentric steps share one center.

[0045] The Fresnel structure layer is a step structure 11, the number of steps of the step structure 11 is two N , and N is a positive integer. For example, the number of steps can be four, eight or sixteen, and the composition material can be silicon, glass or pressure-out glue. In one embodiment of the application, Figure 2 and Figure 3 respectively show a four-step Fresnel structure layer and an eight-step Fresnel structure layer, and of course, the number of steps can be arranged according to specific needs, and is not limited to the above-mentioned four steps and eight steps.

[0046] Therefore, the Fresnel lens provided in this application embodiment has a Fresnel structure layer disposed on a transparent substrate 10. The Fresnel structure layer includes multiple step structures 11, each of which includes multiple concentric steps. Multiple grooves 12 are disposed on the Fresnel structure layer, and the multiple grooves 12 penetrate through the thickness direction of the Fresnel structure layer. One end of the groove 12 extends to the edge of the Fresnel structure layer, and the other end approaches the center of the Fresnel structure layer, so as to divide the Fresnel structure layer into multiple regions. The multiple regions are separated by the grooves 12. In this way, when the Fresnel lens is manufactured, the residual imprinting adhesive can be discharged outward along the grooves 12, reducing adhesive residue and avoiding the generation of air bubbles during the imprinting process, which can significantly improve the manufacturing yield of the Fresnel lens.

[0047] Furthermore, the height of each step Where l is the number of steps with a height h to be calculated; L is the total number of steps; λ is the working wavelength of the Fresnel lens; and n is the refractive index of the Fresnel lens material.

[0048] For example, with Figure 1 Taking the fourth-order Fresnel structure as an example, each step structure 11 has four total steps, i.e., L = 4. The bottom step is the first layer, and its step height h is l = 1 when substituted into the above formula (1); when calculating the step height h of the second layer, l = 2, and so on.

[0049] In addition, the radius of each step (2), where m is the number of concentric rings on the Fresnel lens; l is the number of steps whose height h and radius r need to be calculated; L is the total number of steps; λ is the working wavelength of the Fresnel lens; and f is the focal length of the Fresnel lens.

[0050] The radius r refers to the distance from the center of the Fresnel lens to the edge of the step to be calculated. The height h and radius r of each step can be obtained using formulas (1) and (2), thereby determining the step's location and dimensions.

[0051] Furthermore, the groove 12 in this application allows for effective drainage of the imprinting adhesive during Fresnel lens fabrication, preventing air bubble formation and significantly improving the processing yield of stepped Fresnel lenses. Therefore, the groove 12 is highly correlated with the processing yield of stepped Fresnel lenses. Taking the width of the groove 12 as an example, for different types of slotted Fresnel lenses, the groove width affects the focusing efficiency of the Fresnel lens. Generally, Figure 9 The theoretical focusing efficiency of a fourth-order Fresnel lens is 81.5%. Figure 10The theoretical focusing efficiency of an eighth-order Fresnel lens is 95%. Considering the processing yield of Fresnel lenses, as well as the effects of focusing efficiency and appearance, specifically in this application, the width of the groove 12 is between 1µm and 10µm. A groove width of 3µm is preferred, at which point the efficiency reduction is less than 1 percentage point. Figures 6-8 The groove 12 forms with groove widths of 2um, 6um, and 10um are shown respectively.

[0052] Furthermore, the length of each groove 12 is also different. The end of the groove 12 extending toward the center of the Fresnel structure layer extends at least to the third concentric circle on the Fresnel lens. The concentric circle at the center of the Fresnel lens is the first ring concentric circle.

[0053] Each groove 12 can be made of Figure 11 The center of the Fresnel lens shown can be set starting from the center, or it can be set by... Figure 12 The Fresnel lens shown can be set starting from the outer periphery of the first ring, or it can be... Figure 13 The groove 12 is formed starting from the outer periphery of the second or third ring of the Fresnel lens. Considering the manufacturing yield and focusing efficiency of the Fresnel lens, it is preferable to form the groove 12 starting from the outer periphery of the second ring of the Fresnel lens. The concentric circle at the center of the Fresnel lens is the first ring concentric circle, and the second ring concentric circle, third ring concentric circle, etc., are formed sequentially from the center to the edge. Figure 14 The focusing efficiency is shown when the groove 12 extends to concentric circles with different numbers of rings.

[0054] The structural shape formed by multiple grooves 12 can also take many forms, and the projection of multiple grooves 12 in the thickness direction can form at least Figure 4 The cross shape or Figure 5 The pattern shown is a star-shaped pattern. In addition, multiple grooves 12 can also form other structural forms besides the cross-shaped and star-shaped patterns, which will not be elaborated here, and can be set by those skilled in the art as needed.

[0055] On the other hand, this application also provides a method for fabricating a Fresnel lens, used to fabricate the above-mentioned Fresnel lens, the method comprising:

[0056] S100: Obtain the master plate and form a Fresnel structure layer on the master plate.

[0057] The Fresnel structure layer was sequentially obtained on the master substrate through photolithography and dry etching; the number of steps on the Fresnel structure layer was 2. N At that time, the number of photolithography and dry etching operations is N.

[0058] Fresnel lenses are fabricated using a master substrate through multiple photolithography and etching processes. The number of overlay steps depends on the number of steps in the Fresnel layer, which is 2. N The number of overlay operations is N. The master plate is then transferred in batches onto the selected substrate using nanoimprinting to complete the fabrication.

[0059] For example, when the number of steps is eight as shown in the figure, N = 3, and three times of photolithography and dry etching are required to obtain the Fresnel structure layer on the master. Figure 2 It can be understood that after one time of photolithography and dry etching, two steps are formed, and then the first time of photolithography and dry etching forms two steps into four steps, the second time of photolithography and dry etching forms four steps into eight steps, and other different step numbers are sequentially deduced.

[0060] S110: etching a groove 12 on the Fresnel structure layer so that the groove 12 penetrates the Fresnel structure layer.

[0061] The preparation of the Fresnel lens includes the preparation of the master and nanoimprinting, the preparation of the master of the Fresnel lens includes DUV photolithography and dry etching, and the four-step Fresnel lens needs to be etched twice through two times of photolithography and dry etching, and the eight-step Fresnel lens needs to be etched three times through three times of photolithography and dry etching. After the preparation of the master of the Fresnel lens, it needs to be transferred to the transparent substrate 10 of glass or resin in batches through nanoimprinting.

[0062] S120: transferring the master on the transparent substrate 10 to form a Fresnel structure layer on the transparent substrate 10.

[0063] Specifically, the imprinting process can be performed in a vacuum environment with a pressure of 100 Pa or less, which can promote the glue filling of the microstructure, reduce the bubble defects caused by insufficient filling, and improve the yield.

[0064] In the nanoimprinting forming process of the conventional step-type Fresnel lens, due to the glue filling mode of the imprinting process, the flow filling performance affected by the viscosity of the glue, and the influence of the high-step side wall ring structure, part of the imprinting glue is difficult to completely fill the microstructure, forming a hollow bubble, which greatly affects the preparation yield of the step-type Fresnel lens. Moreover, a glue with a higher refractive index can be used for imprinting to reduce the depth of the Fresnel lens. The Fresnel lens provided in the embodiments of the present application can discharge the residual imprinting glue outward along the groove 12, reduce the glue residue, avoid the generation of bubbles in the imprinting process, and greatly improve the preparation yield of the Fresnel lens. The shape of the slotted area of the Fresnel lens, the slot width, and the starting position of each slot can be freely determined according to the development of the imprinting process and the chemical properties of the selected imprinting glue.

[0065] Moreover, the preparation of the Fresnel lens of the present application is completely based on the semiconductor process technology, which is completely the same as the process of the conventional step Fresnel lens, and does not introduce additional processes. In addition, the Fresnel lens processed by the present application has basically the same light efficiency as the conventional Fresnel lens, and can realize the functions of collimation or focusing. The appearance of the prepared product is basically the same, and theFigure 15 and Figure 16 The collimation and focusing performance shown are unaffected.

[0066] like Figure 17 and Figure 18 As shown, samples processed using traditional methods have air bubbles in the white center, affecting the normal use of the Fresnel lens; while samples processed using this application have air bubbles in the center. Figure 19 The cross shape shown and as Figure 20 The cross-shaped pattern shown has largely eliminated the air bubbles in the middle.

[0067] The method for fabricating this Fresnel lens includes the same structure and beneficial effects as the Fresnel lens in the foregoing embodiments. The structure and beneficial effects of the Fresnel lens have been described in detail in the foregoing embodiments and will not be repeated here.

[0068] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A Fresnel lens, characterized in that, include: A transparent substrate, wherein a Fresnel structure layer is disposed on the transparent substrate, the Fresnel structure layer includes multiple step structures, each of the step structures includes multiple concentric steps disposed along the thickness direction, and multiple grooves are disposed on the Fresnel structure layer that penetrate the Fresnel structure layer along the thickness direction, one end of the grooves extending to the edge of the Fresnel structure layer and the other end extending towards the center of the Fresnel structure layer; The height of each step Where l is the number of steps whose height needs to be calculated; L is the total number of steps; λ is the operating wavelength of the Fresnel lens; and n is the refractive index of the Fresnel lens material. Radius of each step Where m is the number of concentric rings on the Fresnel lens; l is the number of steps whose height and radius need to be calculated; L is the total number of steps; λ is the working wavelength of the Fresnel lens; and f is the focal length of the Fresnel lens.

2. The Fresnel lens according to claim 1, characterized in that, The number of steps in the stepped structure is 2. N N is a positive integer.

3. The Fresnel lens according to claim 1, characterized in that, The width of the trench is between 1µm and 10µm.

4. The Fresnel lens according to claim 1 or 3, characterized in that, One end of the groove extending toward the center of the Fresnel structure layer extends at least to the third concentric circle on the Fresnel lens, where the concentric circle at the center of the Fresnel lens is the first ring of concentric circles.

5. The Fresnel lens according to claim 1, characterized in that, The projections of the plurality of grooves in the thickness direction form at least a cross shape or a star shape.

6. A method for manufacturing a Fresnel lens, used to manufacture the Fresnel lens according to any one of claims 1-5, characterized in that, include: Obtain a master template and form a Fresnel structure layer on the master template; Trenches are etched in the Fresnel structure layer so that the trenches penetrate the Fresnel structure layer; The master print is transferred onto a transparent substrate to form the Fresnel structure layer on the transparent substrate.

7. The method for preparing a Fresnel lens according to claim 6, characterized in that, The step of obtaining the master template and forming a Fresnel structure layer on the master template includes: The Fresnel structure layer is obtained on the master substrate by photolithography and dry etching sequentially; the number of steps on the Fresnel structure layer is 2. N At that time, the number of photolithography and dry etching operations is N.

8. The method for preparing a Fresnel lens according to claim 6, characterized in that, The step of transferring the master print onto a transparent substrate to form the Fresnel structure layer on the transparent substrate includes: The transfer is performed in a vacuum environment below 100 Pa.

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