Novel Fresnel lens, optical system composed of novel Fresnel lens and design method
Through the optimized design of the new Fresnel lens, the Fresnel surface composed of multiple annular curved surfaces and spherical crown-shaped curved surfaces are solved, and the high-quality imaging effect is achieved.
Patent Information
- Application Number
- CN202310844620.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-07-11
- Publication Date
- 2025-01-14
AI Technical Summary
Due to the chromatic aberration and aberration problems, the imaging quality of existing lens imaging systems is poor, especially in the field of imaging, which is difficult to meet high requirements.
A new Fresnel lens with an optimized design is adopted. The Fresnel surface is composed of multiple annular curved surfaces and spherical crown-shaped curved surfaces. By adjusting the radius of curvature, cone coefficient and position, aberration is reduced to form a high-quality imaging optical system.
It significantly improves the imaging quality, reduces aberration by 30-50%, and has a simple structure and convenient processing.
Smart Images
Figure CN119310734A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of optical imaging systems, and in particular to a novel Fresnel lens and an optical system and a design method thereof. Background Art
[0002] Using a lens group composed of multiple lenses is one of the main methods of constructing an optical imaging system. Due to the existence of chromatic aberration and aberration, multiple lenses and complex mirror designs are often required, making the designed lens imaging optical systems very complex and the imaging quality is often poor.
[0003] Since the refraction of a lens only occurs on the optical surface (such as the lens surface), the Fresnel lens removes as much optical material as possible while retaining the optical surface, thereby reducing the lens material and reducing the weight of the lens. Although the Fresnel lens reduces the cost, it reduces the imaging quality. It is mainly used in non-imaging systems such as lighting, solar concentration and other fields. In the imaging field, it can only be used in fields with low requirements. For example, the recent US patent application number: US201815886623A "Head-mounted display device with Fresnel lens" also uses the advantage of the light weight of the Fresnel lens. At the same time, the imaging requirements of the head-mounted display device are relatively low, so it can meet the needs. Summary of the invention
[0004] The purpose of the present invention is to make up for the defect of poor imaging quality of the existing lens technology, and to provide a new type of Fresnel lens and an optical system and design method composed of it. The present invention adopts a structure similar to that of the Fresnel lens, but the shape of each Fresnel sub-surface, including the curvature radius and coefficient, is optimized to minimize the lens aberration composed of each Fresnel sub-surface, thereby forming a high-quality imaging optical system. This is a new type of Fresnel lens structure, which is different from the traditional Fresnel lens in improving the imaging quality by increasing the number of annular Fresnel sub-surfaces.
[0005] The present invention is achieved through the following technical solutions: A novel Fresnel lens, wherein the refractive surface facing an object or a light source is a Fresnel surface, and the Fresnel surface is an axisymmetric surface composed of at least one annular surface; the shape of each annular surface, including the radius of curvature and the cone coefficient, as well as the position, is optimized to minimize the aberration of each image formed by the annular surface; the other surface of the Fresnel lens is a spherical surface, a plane surface, or a curved surface.
[0006] The Fresnel surface is an axisymmetric surface composed of at least one annular surface and a spherical cap-shaped surface. The shape of each spherical cap-shaped surface and annular surface, including the curvature radius and cone coefficient, and the position are optimized to minimize the aberration of each image formed through the annular surface.
[0007] Taking the minimum aberration of imaging of each annular surface on the focal plane as the optimization goal, the curvature radius and cone coefficient of each spherical cap-shaped surface and annular surface, as well as the vertex position are determined.
[0008] Taking minimizing the maximum aberration of the light refracted by the center line of each annular surface on the meridian plane and the sagittal plane as the optimization goal, the curvature radius and cone coefficient of each spherical cap-shaped surface and annular surface, as well as the vertex position are determined.
[0009] The Fresnel surface is a continuous surface.
[0010] The spherical cap-shaped curved surface and the annular curved surface are spherical surfaces or aspherical surfaces.
[0011] The invention discloses an optical system based on a Fresnel lens, wherein one or more lenses or reflectors are connected behind the Fresnel lens to form an optical system with high imaging quality.
[0012] A method for designing an optical system based on a Fresnel lens specifically comprises the following steps: The first step is to determine the light transmission radius R0 of the optical system according to the requirements; The second step is to determine the focal ratio f / R0 according to the purpose of the optical system, thereby determining the focal length f and the total length of the optical system; The third step is to design a common optical imaging system according to conventional methods, including a lens group or a lens reflector group, and obtain the radius of curvature of each mirror surface, the cone coefficient and the distance between the lens vertices. The aberration of the optical imaging system is less than about 1.5-2 times the requirement. The fourth step is that the first surface of the common optical imaging system facing the object or light source is the Fresnel surface; the Fresnel surface is divided into one or more annular areas plus a central spherical crown area, and the parameters of other surfaces of the optical system are maintained, with the goal of minimizing the imaging aberration of the center of each area on the focal plane, or minimizing the maximum aberration on the meridian plane and the sagittal plane, and the curvature radius of each surface facing the light source, the cone coefficient, and the distance from the lens surface to the vertex of the spherical crown surface are determined in turn by adding the continuity of the Fresnel surface; The fifth step is to establish a ray tracing program to calculate the system aberration on the focal plane. If the system aberration does not meet the requirements, reduce the width of each sub-surface that makes up the Fresnel surface and repeat the fourth and fifth steps until a design that meets the requirements is obtained.
[0013] The advantages of the present invention are: based on the common imaging optical design, the present invention changes the surface facing the light source or object into a Fresnel surface composed of multiple annular curved surfaces, and each Fresnel sub-surface is optimized separately to reduce their aberrations, thereby significantly improving the imaging quality of the novel Fresnel lens and the optical system based on the novel Fresnel lens, and reducing the aberration by 30-50% compared with the original design. The present invention only needs to change the curved surface shape of the Fresnel surface, has a simple structure, and is relatively convenient and easy to process. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Figure 1 The figure is a schematic diagram of the cross-sectional structure and the working principle of the novel Fresnel lens of the present invention; Figure 2 This is a schematic diagram of a novel achromatic Fresnel lens according to Example 1; Figure 3 is a spot diagram of the first embodiment of the present invention; Figure 4 is a point diagram of an achromatic lens corresponding to the first embodiment of the present invention; Figure 5 It is a schematic diagram of the optical system structure of the second embodiment; Figure 6 is a point diagram of the second embodiment of the present invention; Figure 7 This is a point diagram of a common lens imaging optical system corresponding to the second embodiment of the present invention. DETAILED DESCRIPTION
[0015] A novel Fresnel lens, wherein the refractive surface facing the object or light source is a Fresnel surface, and the Fresnel surface is an axisymmetric surface composed of one or more annular surfaces, or a spherical cap-shaped surface. The curvature radius and cone coefficient of each spherical cap-shaped surface and annular surface are selected, and high-order aspherical coefficients can also be selected to minimize the aberration of the light refracted by the center line of each surface; the other surface of the Fresnel lens is a spherical surface, a plane or a curved surface. Figure 1 As shown in FIG. 1 , it is a schematic diagram of the cross-sectional structure of a Fresnel lens, including an object 1, a meridian light 2 passing through the center of the Fresnel lens, a meridian light 3 passing through the center point of the Fresnel sub-mirror surface, a coronal sub-surface 4 in the Fresnel surface, a ring sub-surface 5 in the Fresnel surface, another surface 6 of the Fresnel lens, and an image 7. The Fresnel surface facing the light source is composed of two curved surfaces. The actual Fresnel surface is very different from the original curved surface it replaces. Here, the difference is magnified to show its characteristics. The other surface is a spherical surface.
[0016] Taking the minimization of the aberration of imaging of each annular surface on the focal plane as the optimization goal, or taking the minimization of the maximum aberration of the light refracted by the center line of each annular surface on the meridian plane and the sagittal plane as the optimization goal, the curvature radius and cone coefficient of each spherical cap and annular surface, as well as the vertex position are determined.
[0017] The Fresnel surface mentioned above can be designed as a continuous surface.
[0018] The spherical cap-shaped curved surface and the annular curved surface are spherical surfaces or aspherical surfaces.
[0019] An optical system based on the novel Fresnel lens, wherein one or more lenses or reflectors are connected behind the Fresnel lens to form an optical system with high imaging quality.
[0020] An optical system design method based on a novel Fresnel lens specifically comprises the following steps: The first step is to determine the light transmission radius R0 of the optical system according to the requirements; The second step is to determine the focal ratio f / R0 according to the purpose of the optical system, thereby determining the focal length f and the total length of the optical system; The third step is to design a common optical imaging system according to conventional methods, including a lens group or a lens plus a reflector group, and obtain the radius of curvature of each mirror surface, the cone coefficient and the distance between the lens vertices, so that the aberration of the optical imaging system is less than about 1.5-2 times the requirement; In the fourth step, the first surface of the common optical imaging system facing the object or light source is a Fresnel surface; the Fresnel surface is divided into one or more annular areas plus a central spherical crown area, and the parameters of other surfaces of the optical system are maintained, with the goal of minimizing the imaging aberration of the center of each annular area on the focal plane, or minimizing the maximum aberration on the meridian plane and the sagittal plane, and the curvature radius and cone coefficient of each surface facing the object or light source and the distance from the vertex of the surface to the vertex of the spherical crown surface are determined in sequence by adding the continuity of the Fresnel surface; The fifth step is to establish a ray tracing program to calculate the system aberration on the focal plane. If the system aberration does not meet the imaging aberration requirements, reduce the width of the annular surface and repeat the fourth and fifth steps until a design that meets the requirements is obtained.
[0021] Embodiment 1 is to improve an ordinary achromatic lens into a novel Fresnel achromatic lens. The ordinary achromatic lens is made by gluing two pieces of glass with different dispersion capabilities together. Figure 2 As shown, it includes a Fresnel refractive surface 8 facing the object (a continuous surface composed of 5 conical surfaces), two lens cemented surfaces 9 and a surface 10 facing the image. The materials are H-K9L and H-ZF1 glass from Chengdu Guangming Company. The three surfaces are spherical surfaces with curvature radii of 223.102, -146.340 and -474.048 mm, thicknesses of 8.5, 3.0 and 354.288 mm, clear diameter of 6 mm and image spot radius of 8.5 microns. The surface facing the object is modified to a Fresnel surface, in which the spherical crown part with a central clear diameter of 1.2 mm keeps the original design, and the width of the four annular spherical parts behind is 0.6 mm. Their main design parameters are: Surface number Curvature radius mm Cone coefficient Vertex distance from original vertex mm 1 223.102 0 0 2 225.566 821.176 0.0000 3 226.166 415.976 0.0000 4 226.019 197.035 0.0000 5 225.471 85.162 0.0001 The results of ray tracing calculations show that the maximum aberration of the image point on the focal plane is 7.9 microns, including an aberration of 4.2 microns at 80% energy; compared with the original design with a maximum aberration of 15.0 microns, including an aberration of 8.5 microns at 80% energy, this solution is more than 100% larger. Figure 3 , 4 This is a spot diagram comparison of the two designs at a 6-degree viewing angle.
[0022] Embodiment 2, an optical imaging system with a fixed focal length design for a mobile phone, with a light transmission diameter of 1.4 mm, a system length of 6.2 mm, and a maximum viewing angle of 46 degrees. Figure 5 As shown. First, the common lens optical imaging system designed according to the conventional method includes an aperture 11, a lens 12, a lens 2 13, a lens 3 14, an infrared filter 15 and a CMOS image sensor 16. From left to right, there are 8 refractive surfaces. The radius of curvature of the first refractive surface is -3.545mm, and the cone coefficient is 0; the refractive index at 550nm is 1.5371, the distance between the vertex of the second refractive surface and the vertex of the first refractive surface is 0.326mm, the radius of curvature is -1.630mm, the cone coefficient is -3.683; the refractive index is 1.000; the distance between the vertex of the third refractive surface and the vertex of the second refractive surface is 0.601mm, the radius of curvature is 1.468mm, the cone coefficient is -2.541; the refractive index is 1.641; The distance between the fourth refractive surface vertex and the third refractive surface vertex is 0.300mm, the radius of curvature is 0.9065mm, the cone coefficient is -2.184, and the refractive index is 1.000; the distance between the fifth refractive surface vertex and the fourth refractive surface vertex is 0.475mm, the radius of curvature is -10.090mm, the cone coefficient is 0, and the refractive index is 1.537; the distance between the sixth refractive surface vertex and the fifth refractive surface vertex is 0.295mm, the radius of curvature is -1.917mm, the cone coefficient is -3.458, and the refractive index is 1.000; the distance between the seventh refractive surface vertex and the sixth refractive surface vertex is 0.500mm, the radius of curvature is infinite, and the cone coefficient is 0; the refractive index is 1.518; the distance between the eighth refractive surface vertex and the seventh refractive surface vertex is 0.600mm, the radius of curvature is infinite, the cone coefficient is 0, and the refractive index is 1.000; the main design parameters are as follows: Surface number Curvature radius mm Cone coefficient Vertex thickness mm Refractive index at 550nm 1 -3.545 0.000 0.000 1.537 2 -1.630 -3.683 0.326 1.000 3 1.468 -2.541 0.601 1.641 4 0.907 -2.184 0.300 1.000 5 -10.090 0.000 0.475 1.537 6 -1.917 -0.346 0.295 1.000 7 Inf 0.000 0.500 1.518 8 Inf 0.000 0.600 1.000 Secondly, the first refractive surface is changed to a continuous Fresnel surface, which is composed of 150 sub-surfaces. The first Fresnel refractive sub-surface is a curved surface including vertices, and the original design can be maintained. Starting from the second Fresnel refractive sub-surface, each Fresnel sub-surface is optimized for aberration. For example, the parameters of the last refractive sub-surface are that the distance between the vertex and the first Fresnel refractive sub-surface is 0.0021mm, the radius of curvature is -3.306mm, and the cone coefficient is -4.283. Other sub-surfaces cannot be listed one by one. When the viewing angle is 46 degrees, the imaging radius of the system on the focal plane is 2.193mm. The ray tracing calculation results show that the maximum aberration of the image point on the focal plane is 9.7 microns, including the aberration of 80% energy is 2.57 microns; compared with the original design, the maximum aberration is 24.9 microns, including the aberration of 80% energy is 3.93 microns, which is more than 50% larger than this solution. Figure 6 , 7 This is a comparison of the spot diagrams of the two designs at a 46-degree viewing angle.
Claims
1. A novel Fresnel lens, characterized in that: The refractive surface facing the object or light source in the Fresnel lens is a Fresnel surface, and the Fresnel surface is an axisymmetric surface composed of at least one annular surface; the shape of each annular surface is optimized, including the curvature radius, cone coefficient and position, so that the aberration of imaging through the annular surface is minimized; the other surface of the Fresnel lens is a spherical surface, a plane or a curved surface.
2. A novel Fresnel lens according to claim 1, characterized in that: The Fresnel surface is an axisymmetric surface composed of at least one annular surface and a spherical cap-shaped surface. The shape of each spherical cap-shaped surface and annular surface, including the curvature radius, cone coefficient and position, is optimized to minimize the aberration of imaging through the annular surface.
3. A novel Fresnel lens according to claim 2, characterized in that: Taking the minimum aberration of imaging of each annular surface on the focal plane as the optimization goal, the curvature radius and cone coefficient of each spherical cap-shaped surface and annular surface, as well as the vertex position are determined.
4. A novel Fresnel lens according to claim 2, characterized in that: Taking minimizing the maximum aberration of the light refracted by the center line of each annular surface on the meridian plane and the sagittal plane as the optimization goal, the curvature radius and cone coefficient of each spherical cap-shaped surface and annular surface, as well as the vertex position are determined.
5. A novel Fresnel lens according to any one of claims 1 to 4, characterized in that: The Fresnel surface is a continuous surface.
6. The novel Fresnel lens according to claim 5, characterized in that: The spherical cap-shaped curved surface and the annular curved surface are spherical surfaces or aspherical surfaces.
7. An optical system based on a novel Fresnel lens, characterized in that: One or more lenses or reflectors are connected behind the Fresnel lens to form an optical system with high imaging quality.
8. An optical system design method based on a novel Fresnel lens, characterized in that: The specific steps include: The first step is to determine the light transmission radius R0 of the optical system according to the requirements; The second step is to determine the focal ratio f / R0 according to the purpose of the optical system, thereby determining the focal length f and the total length of the optical system; The third step is to design a common optical imaging system, including a lens group or a lens reflector group, and obtain the radius of curvature of each mirror surface, the cone coefficient and the distance between the lens vertices. The aberration of the optical imaging system is less than 1.5-2 times the requirement. The fourth step is that the first surface of the common optical imaging system facing the object or light source is the Fresnel surface; the Fresnel surface is divided into one or more annular areas plus a central spherical crown area, and the parameters of other surfaces of the optical system are maintained, with the goal of minimizing the imaging aberration of the center of each area on the focal plane, or minimizing the maximum aberration on the meridian plane and the sagittal plane, and with the continuity of the Fresnel surface, the curvature radius of each surface facing the light source, the cone coefficient, and the distance from the lens surface to the vertex of the spherical crown surface are determined in turn; The fifth step is to establish a ray tracing program to calculate the system aberration on the focal plane. If the system aberration does not meet the requirements, reduce the width of each sub-surface that makes up the Fresnel surface and repeat the fourth and fifth steps until a design that meets the requirements is obtained.