Fresnel lens and its preparation method, optical module and optical imaging device

Abstract

The present disclosure provides a Fresnel lens and a preparation method thereof, an optical module and an optical imaging device. The Fresnel lens comprises: a first surface and a second surface arranged opposite to each other, at least the first surface is arranged as a Fresnel surface, the Fresnel surface has a plurality of sawtooth structures, the sawtooth structure comprises an effective surface and an invalid surface, the effective surface is away from the center of the Fresnel lens relative to the invalid surface. The inclination angle of the invalid surface of the sawtooth structure is arranged corresponding to the angle of the incident light.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to the field of display technologies, and in particular, to a Fresnel lens, a preparation method thereof, an optical module, and an optical imaging device. Background Art

[0002] The Fresnel lens has advantages such as being thin and light, and is applied in many imaging optical fields. For example, it can be applied in the field of head-mounted displays, which is conducive to the development of thin and light head-mounted display devices. However, in the Fresnel lens, due to the existence of ineffective surfaces, when obliquely incident light passes through the ineffective surfaces, the direction of the outgoing light will change, forming stray light, reducing the effective light efficiency, and at the same time, it is easy to generate adverse phenomena such as ghost images and glare. Summary of the Invention

[0003] Embodiments of the present disclosure provide a Fresnel lens, a preparation method thereof, an optical module, and an optical imaging device.

[0004] In a first aspect, embodiments of the present disclosure provide a Fresnel lens, including: a first surface and a second surface arranged opposite to each other, at least the first surface is set as a Fresnel surface, the Fresnel surface has a plurality of serrated structures, the serrated structures include effective surfaces and ineffective surfaces, the effective surfaces are farther from the center of the Fresnel lens than the ineffective surfaces, wherein the inclination angle of the ineffective surface of the serrated structure is correspondingly set with the incident light angle.

[0005] Further, the inclination angle of the ineffective surface is the angle between the ineffective surface and the central axis of the Fresnel lens, and the incident light angle is the angle between the incident light ray and the central axis of the Fresnel lens.

[0006] The difference between the inclination angle of the ineffective surface and the incident light angle is within a preset range, and the preset range is -5° to 5°.

[0007] Further, the Fresnel surface includes a plurality of dimming areas divided along the radial direction, each dimming area includes at least one serrated structure, the inclination angles of the ineffective surfaces in the same dimming area are the same, the inclination angles of the ineffective surfaces of at least two dimming areas are different, and the inclination angle of the ineffective surface in each dimming area is correspondingly set with the incident light angle of that dimming area.

[0008] Further, the inclination angle of the ineffective surface of each dimming area is the same as the incident angle of the principal ray of that dimming area, so that the principal ray is incident parallel to the ineffective surface in the corresponding dimming area.

[0009] Further, the viewing angle of the optical system where the Fresnel lens is located is divided into a plurality of angular ranges, and the area corresponding to each angular range on the Fresnel surface is respectively divided into one of the dimming areas.

[0010] Further, the first surface is closer to the light source relative to the second surface. The first surface and the second surface are different Fresnel surfaces. The Fresnel surface includes a circular dimming area at the center and at least one annular dimming area surrounding the circular dimming area. The ineffective surface inclination angle of at least one annular dimming area in the first surface is smaller than the ineffective surface inclination angle of the corresponding annular dimming area in the second surface.

[0011] In a second aspect, an embodiment of the present disclosure provides a method for manufacturing a Fresnel lens, including:

[0012] Determining the incident light angle data of the Fresnel lens to be manufactured in the optical system to which it belongs;

[0013] Based on the incident light angle data, determining the ineffective surface inclination angle of the serrated structure in the Fresnel lens;

[0014] Manufacturing the Fresnel lens according to the determined ineffective surface inclination angle.

[0015] In a third aspect, an embodiment of the present disclosure provides an optical module, including: multiple Fresnel lenses provided in the first aspect above, and the optical axes of the multiple Fresnel lenses coincide.

[0016] In a fourth aspect, an embodiment of the present disclosure provides an optical imaging device, including: the Fresnel lens provided in the first aspect above; or, the optical module provided in the third aspect above.

[0017] Further, the optical imaging device is a head-mounted display device, and the optical imaging device further includes: a display module, and the first surface of the Fresnel lens faces the display module.

[0018] The technical solution provided by the embodiment of the present disclosure has at least the following technical effects or advantages:

[0019] The Fresnel lens provided by the embodiment of the present disclosure corresponds to the ineffective surface inclination angle and the incident light angle, ensuring that the ineffective surface inclination angle is as close as possible to the incident light angle, or even the same as the incident light angle, so that the incident light rays are close to parallel to the ineffective surface, thereby effectively reducing the light passing through the ineffective surface, reducing stray light, improving the effective light efficiency, and being beneficial to improving adverse phenomena such as ghosting and glare, making the picture clearer. Description of the Drawings

[0020] By reading the detailed description of the preferred embodiments below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present application. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0021] Figure 1 Schematic diagram of the planar structure of an exemplary Fresnel lens;

[0022] Figure 2 is Figure 1 Schematic diagram of the AA cross-section of;

[0023] Figure 3 Schematic diagram of the cross-section of an exemplary Fresnel lens in an embodiment of the present disclosure;

[0024] Figure 4 Schematic diagram of the design of the inclination angle of the ineffective surface corresponding to different incident light angles in an embodiment of the present disclosure;

[0025] Figure 5 Schematic diagram of an exemplary partition in an embodiment of the present disclosure;

[0026] Figure 6 Ray tracing effect diagram of the comparative experiment in an embodiment of the present disclosure;

[0027] Figure 7 Flow chart of a preparation method of a Fresnel lens in an embodiment of the present disclosure;

[0028] Figure 8 Schematic diagram of the structure of an exemplary optical module in an embodiment of the present disclosure;

[0029] Figure 9 Schematic diagram of a light distribution situation in an embodiment of the present disclosure. Detailed implementation manners

[0030] As Figure 1 shown, multiple concentric circles from small to large are engraved on the surface of the Fresnel lens, which is formed by removing the redundant optical material in the ordinary lens on the basis of the ordinary lens. Therefore, the Fresnel lens has the advantages of being lighter in weight and thinner in thickness than the ordinary lens.

[0031] Figure 2 Schematic diagram of the cross-sectional structure of an exemplary Fresnel lens. As Figure 2 shown, the Fresnel lens 10 includes a first surface and a second surface that are oppositely arranged. The first surface is the light incident surface, and the second surface is the light exiting surface. The first surface is the Fresnel surface, and is provided with a plurality of serrated structures 100. The serrated structures 100 include effective surfaces 101 and ineffective surfaces 102. The effective surfaces 101 and the ineffective surfaces 102 are connected, and are both the side surfaces of the serrated structures 100.

[0032] Generally, light rays are refracted through the effective surfaces 101 of the Fresnel surface and finally form an image on the human eye; however, light rays may also pass through the ineffective surfaces 102 of the Fresnel surface. The propagation of this part of the light rays deviates from the normal path, forming stray light (i.e., non-sequential light). The appearance of stray light will cause the image contrast to decrease.

[0033] For example, as shown in the enlarged partial view in Figure 2 After most of the light enters the Fresnel lens 10 from the effective surface 101, such as the light ray L1, it undergoes a first refraction in the serrated structure 100 and then exits along a predetermined path to achieve the desired light path adjustment effect. However, there is a small portion of light, such as the light ray L2, which enters the Fresnel lens 10 from the edge position of the effective surface 101 close to the ineffective surface 102. After undergoing a first refraction in the serrated structure 100, it exits from the ineffective surface 102, enters the adjacent serrated structure 100, and then undergoes a second refraction and exits again in this serrated structure 100. In this way, the optical path direction of this portion of light changes, deviates from the original exit path, and exits in other directions. These lights will continue to propagate disorderly within the system and eventually form stray light that interferes with the image. Therefore, when the Fresnel lens 10 is applied to an optical imaging device such as a head-mounted display device, it is prone to adverse phenomena such as ghosting and glare, affecting the clarity of the display image.

[0034] To prevent stray light from interfering with the image, in some examples, a scheme of blocking the ineffective surface and / or the tooth tips is adopted to reduce the light passing through the ineffective surface. However, although this scheme can effectively reduce the influence of stray light such as glare, it is also prone to bring adverse effects such as reduced light efficiency and image breakage.

[0035] In view of this, the embodiments of the present disclosure propose a scheme without occlusion and without reducing light efficiency. The inclination angle of the ineffective surface in the serrated structure is customized and adjusted skillfully according to the imaging light path angle, so that the incident light passes through the ineffective surface as little as possible, thereby reducing stray light and improving adverse phenomena such as ghosting and glare caused by stray light.

[0036] Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. It should be noted that in the drawings, the dimensions of layers and regions may be exaggerated for clarity of illustration. Although the exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be fully conveyed to those skilled in the art.

[0037] Figure 3 Shows a schematic cross-sectional structure diagram of a Fresnel lens in an embodiment of the present disclosure. As Figure 3As shown in the figure, the Fresnel lens 20 provided by the embodiments of the present disclosure includes a first surface 21 and a second surface 22 that are oppositely arranged. The first surface 21 is the light incident surface, and the second surface 22 is the light exit surface. That is, during use, the first surface 21 is closer to the light source of the optical system where it is located than the second surface 22. At least the first surface 21 is set as a Fresnel surface. The Fresnel surface refers to the surface of the Fresnel lens 20 on which a plurality of concentric circles from small to large are engraved. The Fresnel surface has a plurality of serrated structures 200. The serrated structure 200 includes an effective surface 201 and an ineffective surface 202. The effective surface 201 is farther from the center of the Fresnel lens 20 than the ineffective surface 202.

[0038] The effective surface 201 can be an arc surface, or it can also be a flat surface, which is specifically set according to the optical path adjustment requirements of the actual scenario. This embodiment does not limit this.

[0039] The ineffective surface 202 is a flat surface, and the inclination angle of the ineffective surface is set corresponding to the incident light angle. In some examples, the inclination angles of the ineffective surfaces of the serrated structures 200 on the Fresnel surface can all be set corresponding to the incident light angle, ensuring that the inclination angle of the ineffective surface is as close as possible to the incident light angle, so that the incident light rays are close to parallel to the ineffective surface 202, thereby reducing the light rays passing through the ineffective surface 202 and reducing stray light.

[0040] It should be noted that the above-mentioned inclination angle of the ineffective surface is the angle α between the ineffective surface 202 and the central axis OO′ of the Fresnel lens 20, and the above-mentioned incident light angle is the angle θ between the light rays incident on the corresponding serrated structure 200 and the central axis OO′ of the Fresnel lens 20.

[0041] During specific implementation, it is necessary to pre-determine the optical system to which the Fresnel lens is applied and determine the incident angle of the light beam incident on the Fresnel lens in the optical system. For example, the incident light angle data of the Fresnel lens can be determined by performing optical simulation on the optical system. Then, the inclination angle of the ineffective surface of the Fresnel lens is set corresponding to the determined incident light angle data. This customized design can make the inclination angle of the ineffective surface of the Fresnel lens match the incident light angle, making the incident light rays as close as possible to parallel to the ineffective surface 202, thereby reducing the light rays hitting the ineffective surface 202. Without blocking the ineffective surface 202 and the tooth tips, stray light can be effectively reduced and the light efficiency can be improved.

[0042] For example, when the incident light is a parallel light beam, the inclination angle of the ineffective surface can be set to be the same as the incident light angle. For example, Figure 4 shows a schematic diagram of the inclination angle design of the ineffective surface corresponding to different incident light angles, Figure 4 The straight line with an arrow in the figure represents the incident light ray. As Figure 4As shown in Figures (a) and (b), when the incident light angle is different, the inclination angle of the ineffective surface of the Fresnel lens used is also different, and the inclination angle of the ineffective surface is basically parallel to the incident light.

[0043] When the incident light is a non-parallel light beam, there are differences in the angles of the light rays incident at different positions. At this time, the inclination angle of the ineffective surface of each serrated structure 200 in the Fresnel surface can be set to be basically the same as the incident light angle at the corresponding position. Here, "basically the same" means that the difference between the inclination angle of the ineffective surface and the incident light angle is within a preset range. The preset range is a relatively small range close to 0°, which can be determined according to the needs of the actual application scenario. For example, the preset range can be -5° to 5°.

[0044] For example, for each serrated structure 200, the inclination angle of the ineffective surface can be designed according to the incident light angle, so that the inclination angle of the ineffective surface is as close as possible to the incident light angle of the serrated structure 200.

[0045] Considering that designing the inclination angle of the ineffective surface for each serrated structure 200 separately involves a large amount of data and complex processing, in some examples, the same Fresnel surface can be partitioned, and the inclination angle of the ineffective surface can be set by partitioning. While achieving the effect of reducing stray light, the design and processing complexity can be reduced. At this time, the Fresnel surface includes multiple light-adjusting areas, and each light-adjusting area includes at least one serrated structure 200. The number of serrated structures 200 included in different light-adjusting areas can be the same, or they can be different, which is specifically divided according to the needs of the actual application scenario. The inclination angle of the ineffective surface of the same light-adjusting area is the same. The inclination angle of the ineffective surface in each light-adjusting area is set corresponding to the incident light angle of the light-adjusting area to adapt to the incident light at the corresponding position, and the difference between the inclination angle of the ineffective surface of each serrated structure 200 and the incident light angle is minimized, thereby reducing stray light.

[0046] The inclination angles of at least two light-adjusting areas are different. In some examples, the inclination angles of different light-adjusting areas can be different from each other. For example, in an application scenario, the light distribution satisfies the rule that the closer to the center, the smaller the incident light angle. Then, the closer to the center the light-adjusting area is, the smaller the inclination angle of the ineffective surface. Of course, in other examples, there may also be two spaced light-adjusting areas with the same inclination angle of the ineffective surface, which is specifically set according to the light conditions of the actual application scenario.

[0047] During specific implementation, considering that each serrated structure 200 is arranged in a closed shape around the center of the Fresnel lens, the Fresnel surface can be divided into the above-mentioned multiple light-adjusting areas along the radial direction, such as Figure 5Q1, Q2, Q3, Q4, and Q5 shown. At this time, the above-mentioned multiple dimming areas include: a circular dimming area located at the center and at least one annular dimming area surrounding the circular dimming area. For example, taking the Fresnel surface divided into five dimming areas along the radial direction as an example, these five dimming areas can be respectively: a circular dimming area located at the center, and four annular dimming areas successively surrounding the circular dimming area. It should be noted that the specific number of divided dimming areas can be determined according to the angular distribution of the incident light beam in the actual application scenario, and this embodiment does not limit this.

[0048] In some examples, the Fresnel surface can be divided into dimming areas according to the perspective of the optical system where the Fresnel lens is located. For example, as Figure 5 shown, the perspective (the perspective mentioned in this article refers to the semi-perspective) can be divided into multiple angular ranges, and the area corresponding to each angular range on the Fresnel surface is divided into a dimming area. For example, when the perspective is 45 degrees, the area of the Fresnel surface corresponding to 0 degrees to 10 degrees can be divided into the first dimming area, the area of the Fresnel surface corresponding to 10 degrees to 20 degrees can be divided into the second dimming area, the area of the Fresnel surface corresponding to 20 degrees to 30 degrees can be divided into the third dimming area, the area of the Fresnel surface corresponding to 30 degrees to 40 degrees can be divided into the fourth dimming area, and the area of the Fresnel surface corresponding to 40 degrees to 45 degrees can be divided into the fifth dimming area.

[0049] It should be noted that in addition to dividing according to the perspective, other partitioning methods can also be used. For example, the radius of the Fresnel surface can also be equally divided into multiple segments, and the area corresponding to each segment is a dimming area. During specific implementation, the partitioning method can be determined according to the needs of the actual application scenario, and this embodiment does not limit this.

[0050] Considering that the angles of different light rays incident on the same dimming area may vary slightly, in some examples, the inclination angle of the ineffective surface in each dimming area can be the same as the incident angle of the principal ray of that dimming area, so that the principal ray is parallel to the ineffective surface 202 in the corresponding dimming area. It can be understood that the principal ray of the dimming area refers to the ray passing through the center position of the dimming area. For example, for a circular dimming area, the principal ray is the ray passing through the center of the circle; for an annular dimming area, the principal ray can be the ray passing through any point on its center line. For example, if the principal ray is perpendicularly incident on the center position of the dimming area, the inclination angle of the ineffective surface of the corresponding dimming area can be set to 0 degrees. If the principal ray is obliquely incident on the center position of the dimming area and the incident angle is 45 degrees, the inclination angle of the ineffective surface of the corresponding dimming area can be set to 45 degrees.

[0051] Of course, in addition to setting the inclination angle of the ineffective surface of each dimming area according to the incident angle of the chief ray, in other examples, the inclination angle of the ineffective surface can also be set according to the incident angles of other rays in the dimming area. Or, for each dimming area, optical simulation can be performed in combination with the incident light angle range of the dimming area, the inclination angle of the ineffective surface of the dimming area can be set within the incident light angle range, and adjusted in a certain step, and the inclination angle with the least stray light and the highest light efficiency is determined as the inclination angle of the ineffective surface of the dimming area in the final product.

[0052] Based on the first surface 21 being a Fresnel surface, the second surface 22 can be a spherical surface or an aspherical surface, which is specifically set according to actual application needs. In some examples, the second surface 22 can also be set as a Fresnel surface. Considering that in addition to the light rays incident perpendicularly along the optical axis, the angles of the remaining light rays will change after passing through the first surface 21. Therefore, there is a difference between the inclination angle of the ineffective surface of the second surface 22 and that of the first surface 21, and it needs to be set separately according to the incident light angle of the second surface 22.

[0053] For example, in the same zoning method, the first surface 21 and the second surface 22 are divided into: a circular dimming area at the center and at least one annular dimming area surrounding the circular dimming area. When the Fresnel lens is applied to the imaging optical system of a head-mounted display device, the optical axis of the Fresnel lens coincides with the central axis of the display screen. At this time, the inclination angle of the ineffective surface of the circular dimming area of the first surface and the second surface can both be set to 0 degrees. For the annular dimming area surrounding the circular dimming area, the inclination angle of at least one annular dimming area in the first surface is less than the inclination angle of the corresponding annular dimming area in the second surface. It is specifically determined according to the actual light field distribution and the surface shape of the Fresnel lens.

[0054] For example, taking the five dimming areas in the above example as an example, the inclination angles of the ineffective surfaces of the first dimming areas of the two surfaces can be the same, both being 0 degrees. In some Fresnel lenses, for the second to fifth dimming areas, the inclination angle of the ineffective surface of the first surface is less than that of the second surface respectively; in some Fresnel lenses, for the second to fourth dimming areas, the inclination angle of the ineffective surface of the first surface is less than that of the second surface respectively, but the inclination angle of the ineffective surface of the fifth dimming area of the first surface is greater than that of the fifth dimming area of the second surface.

[0055] In order to further verify the effect of this solution, a simulation test was carried out. Specifically, for the parallel light incident scenario, two groups of optical models were established by taking the Fresnel lens product with the first surface 21 as the Fresnel surface and the second surface 22 as a plane as an example. The invalid surface inclination angle was customized for one group of optical models, that is, the invalid surface inclination angle of the serrated structure 200 of the first surface 21 was set to be the same as the angle of the incident light. The invalid surface inclination angle of the other group of optical models was set conventionally (for example, usually set to 0 degrees, that is, parallel to the central axis of the Fresnel lens) as a comparison example without inclination customization. After the modeling settings were completed, ray tracing was performed separately, and the results are as follows Figure 6 shown. Figure 6 Figure (a) shows the ray tracing result of the comparative example without tilt angle customization. Figure 6 Figure (b) shows the ray tracing result after the inclination angle of the invalid surface is customized. Figure 6 As can be seen from Figures (a) and (b) in the figure, after the inclination angle of the invalid surface is customized, the stray light is significantly reduced. In addition, from the light efficiency data obtained from the experiment, compared with the solution without inclination customization, the light efficiency of the system after inclination customization is improved by 12.9%.

[0056] Therefore, the Fresnel lens provided in the embodiment of the present disclosure can effectively reduce stray light and improve the adverse phenomena such as ghosting and glare caused by stray light by setting the inclination angle of the invalid surface of the Fresnel surface corresponding to the angle of the incident light. Compared with the solution of shielding the invalid surface 202 and / or the tooth tip, it is conducive to improving the light effect.

[0057] Figure 7 A flow chart of a method for preparing a Fresnel lens is shown. Figure 7 As shown, the method may include the following steps:

[0058] Step S101, determining incident light angle data of the Fresnel lens to be prepared in the corresponding optical system;

[0059] Step S102, determining the inclination angle of the invalid surface of the sawtooth structure in the Fresnel lens based on the incident light angle data;

[0060] Step S103, preparing a Fresnel lens according to the determined inclination angle of the null surface.

[0061] It should be noted that the incident light angle data of the Fresnel lens can be determined by constructing an optical model and simulating the optical system including the light source and the optical path components before the Fresnel lens. Then, the inclination angle of the ineffective surface is customized according to the incident light angle data. For example, in the case of parallel light incidence, the incident light angle is single, and the inclination angle of the ineffective surface can be set to be the same as the incident light angle; for the non-parallel light incidence scenario, the inclination angle of the ineffective surface can be set according to the incident light angle in zones, and the specific implementation process can refer to the relevant descriptions in the above text.

[0062] In addition to determining the inclination angle of the ineffective surface, other structural parameters also need to be determined. For example, according to the requirements of optical characteristics, the shapes of the serrated structures of the Fresnel lens and the lens structure parameters need to be designed. The design of these structural parameters can specifically refer to the related technologies and will not be elaborated here.

[0063] For example, first, the Fresnel lens mold can be processed according to the designed structural parameters and the customized inclination angle of the ineffective surface, and then the Fresnel lens mold can be used to prepare the Fresnel lens by means of liquid glue coating and curing or hot pressing. Of course, other processing methods can also be used to prepare the Fresnel lens, and this embodiment does not limit this.

[0064] In addition, an embodiment of the present disclosure also provides an optical module including the above-mentioned Fresnel lens. The optical module includes: multiple Fresnel lenses provided in any embodiment of the present disclosure, and the centers of the multiple Fresnel lenses are on the same straight line, that is, the optical axes coincide.

[0065] Figure 8 FIG. shows a partial cross-sectional schematic diagram of an exemplary optical module. The optical module 30 includes: a first Fresnel lens 801, a second Fresnel lens 802, and a third Fresnel lens 803. The second Fresnel lens 802 is located between the first Fresnel lens 801 and the third Fresnel lens 803. The distance between the second Fresnel lens 802 and the third Fresnel lens 803 is less than the distance between the second Fresnel lens 802 and the first Fresnel lens 801.

[0066] Each Fresnel lens includes two surfaces, and the three Fresnel lenses have six surfaces. Taking the six surfaces being Fresnel surfaces as an example, for obliquely incident light, the incident angles corresponding to the light when it reaches each surface are different, as Figure 8 shown. Thus, for each surface, the inclination angle of its ineffective surface can be set according to the incident light angle. This can effectively reduce the stray light formed by the optical module, and even reduce the light passing through the ineffective surface by more than 90%, so that the light efficiency of the entire optical module is greatly improved.

[0067] For example, when Figure 8When the shown three - piece optical module is applied to a head - mounted display device, the light distribution is as follows Figure 9 As shown, when the display screen 901 displays an image, the light emitted passes through the Fresnel lenses lens3, lens2, and lens1 in sequence and then forms an image on the human eye 902. The optical axes of lens1, lens2, and lens3 coincide with the central axis of the display screen 901. At this time, the front and rear surfaces of lens1, lens2, and lens3 can be divided into multiple dimming zones along the radial direction respectively. For each dimming zone, the inclination angle of the ineffective surface is set according to the respective incident light angle.

[0068] For example, the viewing angle of the optical system where the optical module is located is 45 degrees. The front and rear surfaces of lens1, lens2, and lens3 are respectively divided into five dimming zones according to the viewing angle. For each surface, the first dimming zone is the area corresponding to the viewing angle range from 0 degrees to 10 degrees, the second dimming zone is the area corresponding to the viewing angle range from 10 degrees to 20 degrees, the third dimming zone is the area corresponding to the viewing angle range from 20 degrees to 30 degrees, the fourth dimming zone is the area corresponding to the viewing angle range from 30 degrees to 40 degrees, and the fifth dimming zone is the area corresponding to the viewing angle range from 40 degrees to 45 degrees. At this time, the partition ranges and the inclination angles of the ineffective surfaces of different dimming zones on each surface can be designed as shown in Table 1.

[0069] Table 1

[0070]

[0071] It should be noted that "front" and "back" in Table 1 refer to the front surface and the back surface of the lens respectively. In this article, the surface of each Fresnel lens facing the human eye 902 is called the front surface, that is, the second surface mentioned above, and the surface facing the display screen 901 is called the back surface, that is, the first surface mentioned above. The partition range in Table 1 refers to the y - coordinate range, with the origin of the coordinate being the center point of the lens and the unit being millimeters. Figure 9 As can be seen from Table 1, in the optical module composed of three Fresnel lenses, among the same surface of the same Fresnel lens, the inclination angles of the ineffective surfaces of different dimming zones are different. Except for the first dimming zone, the inclination angles of the ineffective surfaces of the front and back surfaces of the same Fresnel lens are different.

[0072] Comparing the inclination angles of the ineffective surfaces of each dimming zone on the same surface of the same Fresnel lens, it can be seen that: on the front and back surfaces of lens1, the front and back surfaces of lens2, and the back surface of lens3, from the center to the edge, the inclination angles of the ineffective surfaces of each dimming zone increase in sequence; for the first to fourth dimming zones on the front surface of lens3, the inclination angles of the ineffective surfaces increase in sequence, and the inclination angle of the ineffective surface of the fifth dimming zone is less than that of the fourth dimming zone.

[0073] ​

[0074] By comparing the inclination angles of the ineffective surfaces of different surfaces of the same Fresnel lens, it can be seen that: for the first dimming area, the inclination angles of the ineffective surfaces of the front and rear surfaces of lens1, lens2, and lens3 are the same, all being 0 degrees. For the second to fifth dimming areas, the rear surface of lens1 and lens2 is smaller than the front surface, the rear surface of lens3 in the second to fourth dimming areas is smaller than the front surface, and the rear surface of the fifth dimming area is larger than the front surface.

[0075] In addition, an embodiment of the present disclosure further provides an optical imaging device, including: the Fresnel lens provided in any embodiment of the present disclosure. For example, the optical imaging device may be an optical microscope or a head-mounted display device such as a VR helmet, VR glasses, etc., and this embodiment does not limit this.

[0076] When the optical imaging device is a head-mounted display device, the optical imaging device further includes: a display module. The first surface of the Fresnel lens faces the display module.

[0077] An embodiment of the present disclosure further provides an optical imaging device, including: the optical module provided in any embodiment of the present disclosure. This optical module may be used as the eyepiece of the optical imaging device or as part of the components of the eyepiece. When the optical imaging device is a head-mounted display device, the optical imaging device further includes: a display module. The first surface of the Fresnel lens in the optical module close to the display module faces the display module. For example, Figure 9 the first surface of lens3 faces the display module.

[0078] The optical imaging device of the embodiment of the present disclosure, by adopting a Fresnel lens and correspondingly setting the inclination angle of the ineffective surface of the Fresnel lens with the incident light angle, effectively reduces stray light, improves adverse phenomena such as ghosting and glare, and makes the picture clearer. Moreover, compared with the solution of blocking the ineffective surface and / or the tooth tip, it is beneficial to improve the light efficiency and ensure the picture quality.

[0079] In the above description, no detailed description is made of technical details such as the composition of the product. However, those skilled in the art should understand that various technical means can be used to form a structure of the required shape. In addition, in order to form the same structure, those skilled in the art can also design a method that is not exactly the same as the method described above. Although the above embodiments are described separately, this does not mean that the measures in each embodiment cannot be used in combination advantageously.

[0080] In addition, those of ordinary skill in the art should understand that: the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the present disclosure is limited to these examples; under the concept of the present disclosure, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of one or more embodiments of the present specification as described above, and they are not provided in detail for the sake of brevity.

[0081] Although the exemplary embodiments of the present disclosure have been described, those skilled in the art can make additional changes and modifications once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the exemplary embodiments and all changes and modifications that fall within the scope of the present disclosure.

Claims

1. An optical imaging device, characterized in that, the optical imaging device is a head-mounted display device, the head-mounted display device includes a display module and multiple Fresnel lenses, the optical axes of the multiple Fresnel lenses coincide with the central axis of the display module, and the light emitted by the display module when displaying an image sequentially passes through the multiple Fresnel lenses to form an image on the human eye. The Fresnel lens includes: a first surface and a second surface arranged opposite to each other, the first surface faces the display module, the first surface and the second surface are arranged as Fresnel surfaces, the Fresnel surface has multiple serrated structures, the serrated structure includes an effective surface and an ineffective surface, the effective surface is farther from the center of the Fresnel lens than the ineffective surface, wherein the inclination angle of the ineffective surface of the serrated structure is correspondingly set according to the incident light angle; the Fresnel surface includes multiple dimming areas divided along the radial direction, the viewing angle of the head-mounted display device is divided into multiple angular ranges, and the area corresponding to each angular range on the Fresnel surface is one of the dimming areas. Each dimming area includes at least one serrated structure, the inclination angle of the ineffective surface in each dimming area is correspondingly set according to the incident light angle of the dimming area, the inclination angles of the ineffective surfaces in the same dimming area of the same Fresnel surface are the same, and the inclination angles of the ineffective surfaces in different dimming areas of the same Fresnel surface are different; among the multiple Fresnel lenses, at least for the near-eye Fresnel lens, the inclination angles of the ineffective surfaces of the multiple dimming areas gradually increase from the center to the edge, and at least the partition ranges of the multiple dimming areas of the near-eye Fresnel lens gradually increase from the center to the edge. The near-eye Fresnel lens is the Fresnel lens farthest from the display module.

2. The optical imaging device according to claim 1, characterized in that, the inclination angle of the ineffective surface is the angle between the ineffective surface and the central axis of the Fresnel lens, and the incident light angle is the angle between the light incident on the corresponding serrated structure and the central axis of the Fresnel lens, the difference between the inclination angle of the ineffective surface and the incident light angle is within a preset range, and the preset range is -5° to 5°.

3. The optical imaging device according to claim 1, characterized in that, the inclination angle of the ineffective surface of each dimming area is the same as the incident angle of the chief ray of the dimming area, so that the chief ray is incident parallel to the ineffective surface in the corresponding dimming area.

4. The optical imaging device according to claim 1, characterized in that, the first surface is closer to the light source than the second surface, the first surface and the second surface are different Fresnel surfaces, the Fresnel surface includes a circular dimming area at the center and at least one annular dimming area surrounding the circular dimming area, and the inclination angle of the ineffective surface of at least one annular dimming area in the first surface is smaller than the inclination angle of the corresponding annular dimming area in the second surface.

5. A method for manufacturing a Fresnel lens, characterized in that, for manufacturing the Fresnel lens in the optical imaging device according to any one of claims 1-4, the method includes: Determine the incident light angle data of the Fresnel lens to be prepared in the optical system to which it belongs; Based on the incident light angle data, determine the invalid surface inclination angle of the serrated structure in the Fresnel lens; Prepare the Fresnel lens according to the determined invalid surface inclination angle.

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