Optical system and display device

Abstract

The present disclosure provides an optical system and a display device. The optical system comprises at least four lenses which are sequentially arranged from a first side to a second side along an optical axis. Each lens comprises two side surfaces opposite to each other. At least one lens is a double-sided Fresnel lens; two side surfaces of the double-sided Fresnel lens are Fresnel surfaces; and the double-sided Fresnel lens is located between the lens among the at least four lenses that is closest to the first side and the lens among the at least four lenses that is closest to the second side. The optical system in the present disclosure has the advantages of both structural miniaturization and high light transmission efficiency.

Description

Optical systems and display devices Technical Field

[0001] The present disclosure relates to the field of display technology, and in particular to an optical system and a display device. Background Art

[0002] With the development of VR (Virtual Reality) technology, users' requirements for VR devices are gradually increasing. They not only require excellent image quality, but also require small size and light weight. To reduce the size of VR devices, catadioptric optical systems are often used. However, catadioptric optical systems waste a lot of light energy, resulting in low light efficiency, making it difficult for VR devices to meet the requirements of both thinness and high light efficiency.

[0003] Summary of the Invention

[0004] The present disclosure aims to solve at least one of the technical problems existing in the prior art, and proposes an optical system and a display device.

[0005] To achieve the above objectives, according to one aspect of the present disclosure, an optical system is provided, comprising at least four lenses arranged sequentially from a first side to a second side on an optical axis, each of the lenses comprising two oppositely arranged side surfaces, at least one of the lenses being a double-sided Fresnel lens, both side surfaces of the double-sided Fresnel lens being Fresnel surfaces, and the double-sided Fresnel lens being located between a lens closest to the first side and a lens closest to the second side of the at least four lenses.

[0006] Among all the side surfaces of the lens, at least three side surfaces are Fresnel surfaces, and at least three Fresnel surfaces are adjacently arranged.

[0007] The Fresnel surface includes a coaxially arranged central portion and a toothed ring portion, the toothed ring portion surrounds the central portion, and the toothed ring portion has a plurality of coaxially arranged annular tooth structures, and the ratio of the tooth height of the annular tooth structure to the tooth width of the annular tooth structure is greater than or equal to 0.2 and less than or equal to 2.

[0008] The Fresnel surface includes a coaxially arranged central portion and a toothed ring portion, wherein the toothed ring portion has a plurality of coaxially sleeved annular tooth structures, and the annular tooth structures meet at least one of the following requirements:

[0009] The tooth widths of the plurality of annular tooth structures increase gradually toward the center portion;

[0010] The tooth width of the annular tooth structure is greater than 0 and less than or equal to 10 mm;

[0011] The tooth height of the annular tooth structure is greater than 0 and less than or equal to 1 mm;

[0012] The tooth tips of the annular tooth structure are rounded;

[0013] The number of the annular tooth structures is less than 50;

[0014] The draft angle of the annular tooth structure is greater than 0 and less than or equal to 10°.

[0015] Wherein, when the tooth tip of the annular tooth structure is rounded, the radius of the rounded corner is greater than 0 and less than or equal to 50 microns.

[0016] The Fresnel surface includes a coaxially arranged central portion and a toothed ring portion, the toothed ring portion having a plurality of coaxially sleeved annular tooth structures. The Fresnel surface facing the first side of the double-sided Fresnel lens is the first Fresnel surface, and the Fresnel surface facing the second side of the double-sided Fresnel lens is the second Fresnel surface. The annular tooth structure of the first Fresnel surface and the annular tooth structure of the second Fresnel surface satisfy at least one of the following conditions:

[0017] The tooth height of the annular tooth structure of the first Fresnel surface is less than or equal to the tooth height of the annular tooth structure of the second Fresnel surface;

[0018] The maximum tooth width of the annular tooth structure of the first Fresnel surface is less than or equal to the maximum tooth width of the annular tooth structure of the second Fresnel surface;

[0019] The draft angle of the annular tooth structure of the first Fresnel surface is less than or equal to the draft angle of the annular tooth structure of the second Fresnel surface;

[0020] The tooth tips of the annular tooth structures of the first Fresnel surface and the second Fresnel surface are both rounded, and the radius of the rounded corner of the annular tooth structure of the first Fresnel surface is smaller than or equal to the radius of the rounded corner of the annular tooth structure of the second Fresnel surface.

[0021] When the tooth height of the annular tooth structure of the first Fresnel surface is less than or equal to the tooth height of the annular tooth structure of the second Fresnel surface, a ratio of the tooth height of the annular tooth structure of the first Fresnel surface to the tooth height of the annular tooth structure of the second Fresnel surface is greater than or equal to 0.9 and less than or equal to 1;

[0022] When the maximum tooth width of the annular tooth structure of the first Fresnel surface is less than or equal to the maximum tooth width of the annular tooth structure of the second Fresnel surface, a ratio of the maximum tooth width of the annular tooth structure of the first Fresnel surface to the maximum tooth width of the annular tooth structure of the second Fresnel surface is greater than or equal to 0.889 and less than or equal to 1;

[0023] When the draft angle of the annular tooth structure of the first Fresnel surface is less than or equal to the draft angle of the annular tooth structure of the second Fresnel surface, a ratio of the draft angle of the annular tooth structure of the first Fresnel surface to the draft angle of the annular tooth structure of the second Fresnel surface is greater than or equal to 0.667 and less than or equal to 1;

[0024] When the tooth tips of the annular tooth structures of the first Fresnel surface and the second Fresnel surface are both rounded, and the radius of the rounded corner of the annular tooth structure of the first Fresnel surface is less than or equal to the radius of the rounded corner of the annular tooth structure of the second Fresnel surface, the ratio of the radius of the rounded corner of the annular tooth structure of the first Fresnel surface to the radius of the rounded corner of the annular tooth structure of the second Fresnel surface is greater than or equal to 0.9 and less than or equal to 1.

[0025] The optical system has four lenses, and the effective focal length f of the optical system satisfies the following relationship with the total optical length TTL of the optical system: 0.1 <f / TTL<8.5。

[0026] Wherein, the effective focal length f of the optical system satisfies: f≤17 mm.

[0027] Wherein, the total optical length TTL of the optical system satisfies: TTL≤30 mm.

[0028] The side surface of the lens closest to the second side among the at least four lenses facing the second side is a concave surface.

[0029] The absolute value of the effective focal length of the one of all the lenses closest to the second side is greater than 8 mm.

[0030] Wherein, the refractive index of the lens is greater than or equal to 1 and less than or equal to 2.1.

[0031] Wherein, the field of view angle of the optical system is greater than or equal to 90 degrees.

[0032] Wherein, at least two of the lenses are arranged in close contact.

[0033] Wherein, the lenses are all lenses with optical power.

[0034] Wherein, the center thickness of at least one of the lenses is less than 8 mm.

[0035] Among all the lenses, the interval between two adjacent lenses on the optical axis is less than or equal to 10 mm.

[0036] The at least four lenses include a first lens, a second lens, a third lens, and a fourth lens arranged sequentially from the first side to the second side, and the optical system satisfies at least one of the following:

[0037] The distance between the first lens and the second lens on the optical axis is less than or equal to 8 mm;

[0038] The distance between the second lens and the third lens on the optical axis is less than or equal to 9 mm;

[0039] The distance between the third lens and the fourth lens on the optical axis is less than or equal to 10 mm.

[0040] The side surface of each lens close to the first side is a first side surface, and the side surface close to the second side is a second side surface. The at least four lenses include a first lens, a second lens, a third lens, and a fourth lens arranged sequentially from the first side to the second side. The absolute value of the curvature radius of the side surfaces of the first lens to the fourth lens is greater than or equal to 5 mm and less than or equal to 90 mm.

[0041] The side surface of each lens close to the first side is a first side surface, and the side surface close to the second side is a second side surface. The optical system satisfies at least one of the following conditions:

[0042] A curvature radius R11 of the first side surface of the first lens and a curvature radius R12 of the second side surface of the first lens satisfy: 0.2≤︱︱R11 / R12︱≤0.5;

[0043] A curvature radius R21 of the first side surface of the second lens and a curvature radius R22 of the second side surface of the second lens satisfy: 2≤|R21 / R22|≤5;

[0044] The curvature radius R31 of the first side surface of the third lens and the curvature radius R32 of the second side surface of the third lens satisfy: 0.2≤|R31 / R32|≤0.7;

[0045] A curvature radius R41 of the first side surface of the fourth lens and a curvature radius R42 of the second side surface of the fourth lens satisfy: 0.2≤|R41 / R42|≤0.7.

[0046] According to another aspect of the present disclosure, there is provided a display device, including:

[0047] Display screen;

[0048] In the above optical system, the display screen is located on the second side of the optical system, and the image light of the display screen is transmitted to the first side through the optical system.

[0049] Wherein, the diagonal length of the display screen is greater than or equal to 20 mm and less than or equal to 110 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following detailed description, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0051] FIG1 shows a schematic structural diagram of an optical system according to an optional embodiment of the present disclosure;

[0052] FIG2 shows a modulation transfer function graph of the optical system in FIG1 ;

[0053] FIG3 is a schematic structural diagram of an optical system according to another optional embodiment of the present disclosure;

[0054] FIG4 shows a modulation transfer function graph of the optical system in FIG3 ;

[0055] FIG5 is a schematic structural diagram of an optical system according to another optional embodiment of the present disclosure;

[0056] FIG6 shows a modulation transfer function graph of the optical system in FIG5 ;

[0057] FIG7 is a schematic structural diagram of an optical system according to another optional embodiment of the present disclosure;

[0058] FIG8 shows a modulation transfer function graph of the optical system in FIG7 ;

[0059] FIG9 shows a longitudinal cross-sectional view of the structure of a Fresnel lens in an optional embodiment of the present disclosure;

[0060] FIG10 shows an angled view of the annular tooth structure in FIG9 ;

[0061] FIG11 shows a stray light distribution diagram of an optical system in an optional embodiment of the present disclosure;

[0062] FIG. 12 shows a stray light distribution diagram of an optical system in one example. DETAILED DESCRIPTION

[0063] The following describes the specific embodiments of the present disclosure in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0064] Unless otherwise defined, technical or scientific terms used in the embodiments of the present disclosure should have the ordinary meaning understood by a person of ordinary skill in the field to which the present disclosure belongs. The terms "first," "second," and similar terms used in the present disclosure do not denote any order, quantity, or importance, but are simply used to distinguish different components. Therefore, without departing from the teachings of this application, the first lens discussed below may also be referred to as the second lens or the third lens. Similarly, terms such as "include" or "comprise" mean that the element or object preceding the term includes the elements or objects listed after the term and their equivalents, but do not exclude other elements or objects. Terms such as "connected" or "connected" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0065] As used herein, "parallel" and "perpendicular" include the conditions described and conditions similar to the conditions described, and the range of the similar conditions is within an acceptable deviation range, wherein the acceptable deviation range is determined by a person of ordinary skill in the art taking into account the measurement in question and the errors associated with the measurement of the specific quantity (i.e., the limitations of the measurement system). For example, "parallel" includes absolute parallelism and approximate parallelism, wherein the acceptable deviation range for approximate parallelism can be, for example, a deviation within 5°; "perpendicular" includes absolute perpendicularity and approximate perpendicularity, wherein the acceptable deviation range for approximate perpendicularity can also be, for example, a deviation within 5°.

[0066] It will be understood that when a layer or element is referred to as being on another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may be present therebetween.

[0067] Exemplary embodiments are described herein with reference to cross-sectional and / or plan views that are idealized exemplary drawings. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Therefore, variations in shape relative to the drawings due to, for example, manufacturing techniques and / or tolerances are contemplated. Therefore, the exemplary embodiments should not be construed as limited to the shapes of the regions shown herein, but rather include deviations in shape due to, for example, manufacturing. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to illustrate the actual shape of regions of the device and are not intended to limit the scope of the exemplary embodiments.

[0068] In the drawings, the thickness, size, and shape of the lenses are slightly exaggerated for ease of illustration. Specifically, the shapes of the spherical and aspherical surfaces shown in the drawings are provided by way of example. That is, the shapes of the spherical and aspherical surfaces are not limited to those shown in the drawings. The drawings are for illustration only and are not drawn strictly to scale.

[0069] In this article, the paraxial region refers to the region near the optical axis. If the lens surface is convex and the position of the convex surface is undefined, it means that the lens surface is convex at least in the paraxial region; if the lens surface is concave and the position of the concave surface is undefined, it means that the lens surface is concave at least in the paraxial region. In the accompanying drawings, the left side is the object side and the right side is the image side, that is, the first side is the object side, and the second side is the image side. The surface of each lens closest to the object side is called the first side of the lens, and the surface of each lens closest to the image side is called the second side of the lens. The surface shape in the paraxial region can be judged according to the judgment method commonly used by those skilled in the art, using the positive and negative R value (R refers to the radius of curvature of the paraxial region, usually referring to the R value in the lens database (lens data) in optical software) to determine whether it is concave or convex. For the first side, when the R value is positive, it is judged to be convex, and when the R value is negative, it is judged to be concave. For the second side, when the R value is positive, it is judged to be concave, and when the R value is negative, it is judged to be convex.

[0070] The optical system provided herein can be used, for example, as a projection lens or a laser radar transmitter lens. In this case, the image side of the optical system can be the image source side, and the object side can be the imaging side. Light from the image source side can be imaged on the imaging side. The imaging surface of the optical system is the image source surface.

[0071] In an exemplary embodiment, the visual imaging system provided by the present disclosure can be used as a VR lens. In this case, the image side of the optical system can be the image source side, or the second side, and the object side can be the imaging side, or the first side, or the human eye side. The imaging surface of the optical system is the display screen S9.

[0072] In addition, the optical system disclosed herein can also be used as an ordinary lens, such as a vehicle-mounted lens or an ordinary lens, and light from the object side can be imaged on the image side.

[0073] The following is a detailed introduction to the optical system in the present disclosure used as a VR lens.

[0074] As shown in Figures 1, 3, 5 and 7, the optical system includes at least four lenses (such as the first lens L1 to the fourth lens L4 in Figures 1, 3, 5 and 7) arranged sequentially from a first side to a second side on the optical axis. Each lens includes two opposite side surfaces. At least one lens is a double-sided Fresnel lens, and both side surfaces of the double-sided Fresnel lens are Fresnel surfaces.

[0075] By incorporating at least one double-sided Fresnel lens into an optical system, lens weight can be effectively reduced, further facilitating the development of thinner and lighter optical systems. Double-sided Fresnel lenses can reduce spherical aberration and ghosting, ensuring the optical system's imaging quality. Furthermore, light energy loss is minimized when passing through the double-sided Fresnel lens, ensuring a visual system with a light efficiency greater than 50%, resulting in a lightweight and highly efficient optical system. Of the two opposing side surfaces of each lens, the side closest to the first side is designated as the first side, and the side closest to the second side is designated as the second side.

[0076] It should be noted that light enters the optical system from the second side and exits from the first side. Specifically, image light emitted by the display screen S9 on the second side enters the optical system and enters the human eye from the first side of the optical system, so that the human eye sees the image displayed on the display screen S9.

[0077] In an optical system, all side surfaces except the Fresnel surface are spherical or aspherical. When the side surface of the lens is aspherical, formula (1) is satisfied.

[0078] Where Z is the distance from the plane tangent to the vertex of the surface to the surface, c is the curvature of the aspheric vertex, k is the quadratic surface coefficient, r is the height from the optical axis to the surface, and A 2i is the coefficient of the multiple term.

[0079] In the specific embodiments shown in Figures 1, 3, 5, and 7, a double-sided Fresnel lens is positioned between the lens closest to the first side and the lens farthest from the first side. The lens closest to the first side is first lens L1, and the lens farthest from the first side (the lens closest to the second side) is the last lens. The double-sided Fresnel lens is positioned between first lens L1 and the last lens. This arrangement prevents the annular teeth on the Fresnel surface from interfering with light entering the visual imaging system, ensuring more light enters the optical system. It also facilitates smooth light emission from the optical system, ensuring the best display quality.

[0080] In some optional embodiments, at least three of the side surfaces of all lenses are Fresnel surfaces, and at least three Fresnel surfaces are adjacent to each other. When the number of Fresnel surfaces is greater than three, one or more double-sided Fresnel lenses or one or more single-sided Fresnel lenses may be included, without specific limitation.

[0081] For example, in the four-lens optical system shown in Figures 5 and 7, one of the four lenses has a double-sided Fresnel lens and one has a single-sided Fresnel lens. Therefore, the side surfaces of all lenses in the entire optical system have at least three Fresnel surfaces, and the at least three Fresnel surfaces are arranged adjacent to each other. For example, the second lens is a double-sided Fresnel lens, and the first side surface of the third lens is a Fresnel surface. For example, the third lens is a double-sided Fresnel lens, and the first side surface of the fourth lens is a Fresnel surface.

[0082] It should be noted that the adjacent arrangement of the Fresnel surfaces means that there is no side surface other than the Fresnel surface between two adjacent Fresnel surfaces.

[0083] In the specific embodiment shown in FIG9 , the Fresnel surface includes a coaxially arranged central portion 20 and a toothed ring portion 10. The toothed ring portion 10 surrounds the central portion 20 and has a plurality of coaxially arranged annular tooth structures 11. The ratio of the tooth height of the annular tooth structure 11 to the tooth width of the annular tooth structure 11 is greater than or equal to 0.2 and less than or equal to 2. By limiting the ratio of the tooth height to the tooth width of the annular tooth structure 11 to a reasonable range, while ensuring that the optical system's light efficiency is greater than 50%, it is also beneficial to reduce the generation of stray light and improve the display effect of the optical system. For example, the ratio of the tooth height of the annular tooth structure 11 to the tooth width of the annular tooth structure 11 is 1; for another example, the ratio of the tooth height of the annular tooth structure 11 to the tooth width of the annular tooth structure 11 is 0.5; and for another example, the ratio of the tooth height of the annular tooth structure 11 to the tooth width of the annular tooth structure 11 is 1.5.

[0084] In some optional embodiments, as shown in Figure 9 , the tooth widths of the multiple annular tooth structures 11 increase toward the center. By gradually varying the tooth widths of the annular tooth structures 11 at different locations, stray light is reduced, ensuring the optical system's display quality. Furthermore, within the same lens aperture, this gradual design results in a smaller number of teeth, ensuring optimal imaging within the lens's optically active area due to the reduced number of teeth.

[0085] In some optional embodiments, the tooth width of the annular tooth structure 11 is greater than 0 and less than or equal to 10 mm. If the tooth width of the annular tooth structure 11 is greater than 10 mm, the inclined surface area of ​​the annular tooth structure 11 is larger, which easily reflects light and generates stray light. Limiting the tooth width of the annular tooth structure 11 to a range of less than or equal to 10 mm can reduce stray light and ensure the display effect. For example, the tooth width is greater than or equal to 0.3 mm and less than or equal to 5 mm. For another example, the tooth width is 0.5 mm; for another example, the tooth width is 2 mm; for another example, the tooth width is 1 mm; for another example, the tooth width is 3 mm; for another example, the tooth width is 4 mm.

[0086] In some optional embodiments, the tooth height of the annular tooth structure 11 is greater than 0 and less than or equal to 1 mm. If the tooth height of the annular tooth structure 11 is greater than 1 mm, the annular tooth structure 11 occupies a larger space on the lens, resulting in poor structural strength of the lens. The tooth height of the annular tooth structure 11 is limited to a range of less than or equal to 1 mm, while ensuring the structural strength of the lens, the weight of the lens is reduced to achieve a thinner optical system. For example, the tooth height of the annular tooth structure 11 is greater than 0.1 mm and less than or equal to 0.5 mm. For another example, the tooth height is 0.2 mm; for another example, the tooth height is 0.3 mm; for another example, the tooth height is 0.4 mm.

[0087] In some optional embodiments, referring to FIG10 , the tooth tips of the annular tooth structure 11 are rounded. Setting the tooth tips of the annular tooth structure 11 as rounded can reduce reflection of light and reduce the generation of stray light. The radius of the rounded corner is greater than 0 and less than or equal to 50 microns. Limiting the radius of the rounded corner to the range of 0 to 50 microns is beneficial to reducing stray light and improving imaging quality. For example, the radius of the rounded corner is greater than or equal to 10 microns and less than or equal to 40 microns. For another example, the radius of the rounded corner is 20 microns, for another example, the radius of the rounded corner is 25 microns, for another example, the radius of the rounded corner is 30 microns, for another example, the radius of the rounded corner is 35 microns.

[0088] In some optional embodiments, the number of annular tooth structures 11 is less than 50. By limiting the number of annular tooth structures 11 to less than 50, stray light can be reduced and imaging quality improved. For example, the number of annular tooth structures 11 is greater than or equal to 10 and less than or equal to 30. For another example, the number of annular tooth structures 11 is 15; for another example, the number of annular tooth structures 11 is 20; and for another example, the number of annular tooth structures 11 is 25.

[0089] In some optional embodiments, the draft angle of the annular tooth structure 11 is greater than 0 and less than or equal to 10°. Double-sided Fresnel lenses and single-sided Fresnel lenses are mostly injection molded by molds. To ensure smooth demolding of the mold, both double-sided Fresnel lenses and single-sided Fresnel lenses have a draft angle, and the size of the draft angle has an impact on stray light. Limiting the draft angle to a range of 0 to 10° can reduce stray light and improve imaging quality. For example, the draft angle of the annular tooth structure 11 is greater than or equal to 1° and less than or equal to 5°. For another example, the draft angle of the annular tooth structure 11 is 2°; for another example, the draft angle of the annular tooth structure 11 is 3°; for another example, the draft angle of the annular tooth structure 11 is 4°.

[0090] In some optional embodiments, the Fresnel surface facing the first side of a double-sided Fresnel lens is the first Fresnel surface, and the Fresnel surface facing the second side of the double-sided Fresnel lens is the second Fresnel surface. The tooth height of the annular tooth structure 11 of the first Fresnel surface is less than or equal to the tooth height of the annular tooth structure 11 of the second Fresnel surface. By matching the tooth heights of the two Fresnel surfaces, light can be smoothly transmitted to the Fresnel surfaces while reducing multiple reflections within the Fresnel surfaces, thereby improving light utilization. Furthermore, the Fresnel surfaces can be reduced from reflecting light out of the lens, reducing the generation of stray light, optimizing the entire optical system, improving imaging quality, and ensuring a good display effect. For example, the ratio of the tooth height of the annular tooth structure 11 of the first Fresnel surface to the tooth height of the annular tooth structure 11 of the second Fresnel surface is greater than or equal to 0.9 and less than or equal to 1.

[0091] In some optional embodiments, the maximum tooth width of the annular tooth structure 11 of the first Fresnel surface is less than or equal to the maximum tooth width of the annular tooth structure 11 of the second Fresnel surface. By matching the maximum tooth widths of the Fresnel surfaces, light can be smoothly transmitted into the Fresnel lens, while also reducing the amount of light reflected from the Fresnel surfaces, reducing the generation of stray light, optimizing the entire optical system, improving imaging quality, and ensuring a good display effect. For example, the ratio of the maximum tooth width of the annular tooth structure 11 of the first Fresnel surface to the maximum tooth width of the annular tooth structure 11 of the second Fresnel surface is greater than or equal to 0.889 and less than or equal to 1.

[0092] In some optional embodiments, the draft angle of the annular tooth structure 11 on the first Fresnel surface is less than or equal to the draft angle of the annular tooth structure 11 on the second Fresnel surface. By matching the draft angles of the Fresnel surfaces, light reflection from the draft surfaces can be reduced, thereby reducing stray light and optimizing the entire optical system to reduce stray light, improve imaging quality, and ensure a good display effect. For example, the ratio of the draft angle of the annular tooth structure 11 on the first Fresnel surface to the draft angle of the annular tooth structure 11 on the second Fresnel surface is greater than or equal to 0.667 and less than or equal to 1.

[0093] In some optional embodiments, the tooth tips of the annular tooth structures 11 on both the first and second Fresnel surfaces are rounded, and the radius of the rounded corners of the annular tooth structures 11 on the first Fresnel surface is less than or equal to the radius of the rounded corners of the annular tooth structures 11 on the second Fresnel surface. By matching the tooth tips between the Fresnel surfaces, light reflection can be reduced, facilitating smooth entry of light into the rear optical system. This can also reduce stray light, improve imaging quality, and ensure effective display. For example, the ratio of the radius of the rounded corners of the annular tooth structures 11 on the first Fresnel surface to the radius of the rounded corners of the annular tooth structures 11 on the second Fresnel surface is greater than or equal to 0.9 and less than or equal to 1.

[0094] FIG. 11 is a stray light distribution diagram of an optical system in an embodiment of the present disclosure. The stray light is within the circle in FIG. 11. FIG. 12 is a stray light distribution diagram of an exemplary optical system. The stray light is within the circle in FIG. 12. FIG. 12 is a stray light distribution diagram of a four-lens optical system with less than 3 Fresnel lenses. From the comparison between FIG. 11 and FIG. 12, it can be seen that the brightness of the stray light of the optical system of the present disclosure is significantly reduced. Therefore, the stray light of the optical system of the present disclosure is reduced.

[0095] In some alternative embodiments, the optical system has four lenses, and the following is satisfied between the effective focal length f of the optical system and the total optical length TTL of the optical system: 0.1 < f / TTL < 8.5. Limiting the effective focal length and the total optical length of the optical system within a reasonable range is beneficial to achieving miniaturization of the optical system while ensuring imaging quality. For example, 0.1 < f / TTL < 2; for another example, f / TTL = 0.5.

[0096] In some alternative embodiments, the effective focal length f of the optical system satisfies: f ≤ 17 mm. Limiting the focal length of the visual optical system within a range less than or equal to 17 millimeters is beneficial to reducing the size of the optical system to achieve miniaturization. Preferably, f ≤ 14 mm to further reduce the size of the optical system.

[0097] In some alternative embodiments, the total optical length TTL of the optical system satisfies: TTL ≤ 30 mm. Limiting the total optical length of the optical system within a range less than or equal to 30 millimeters to achieve miniaturization of the optical system. Preferably, TTL ≤ 28 mm to further reduce the size of the optical system.

[0098] Among them, the total optical length TTL refers to the distance from the first side S1 of the first lens to the imaging surface on the optical axis.

[0099] In some alternative embodiments, the one closest to the second side among all sides is a concave surface. That is, the second side of the last lens is a concave surface. Such a setting is beneficial for the optical system to collect image light from the second side to ensure the display effect.

[0100] [[ID=IS]]In some alternative embodiments, the absolute value of the effective focal length of the one closest to the second side among all lenses is greater than 8 mm. Such a setting is beneficial for the optical system to collect large-angle light from the second side, reducing the situation where marginal light cannot enter the optical system, effectively reducing the occurrence of picture missing, and improving the display effect.

[0101] In some optional embodiments, referring to Figures 2, 4, 6, and 8, in the modulation transfer function curve of the optical system, the contrast ratio at a spatial frequency of 30 lp / mm is greater than or equal to 0.05. In the modulation transfer function curves of the field of view angle, the contrast ratio at 30 lp / mm for most of the field of view curves is no less than 0.1, thereby ensuring high-definition display across the entire field of view.

[0102] In some optional embodiments, the refractive index of the lens is greater than or equal to 1 and less than or equal to 2.1. By limiting the refractive index of the lens to the range of 1 to 2.1, it is helpful to control the deflection angle of light, thereby reducing the generation of stray light, while ensuring that the thickness of the lens is evenly distributed, reducing the sensitivity of the lens.

[0103] For example, the lens may be formed of a glass material having a refractive index greater than or equal to 1.73 and less than or equal to 1.96, or a plastic material having a refractive index greater than or equal to 1.51 and less than or equal to 1.66.

[0104] In some optional embodiments, the field of view of the optical system is greater than or equal to 90 degrees. The optical system has a large field of view, which facilitates the large-angle image light from the second side to enter the optical system, thereby avoiding incomplete display and ensuring the display effect.

[0105] In some optional embodiments, at least two lenses are bonded together. This arrangement can reduce the spacing between adjacent lenses, thereby shortening the overall optical length of the optical system, making the optical system thinner and lighter. For example, two adjacent lenses can be bonded together using optical adhesives such as light-curing adhesives and epoxy resin adhesives.

[0106] In some optional embodiments, all lenses are lenses with optical power. This arrangement is conducive to each lens sharing the optical power of the optical system more evenly, and is conducive to smooth transition of light to ensure display effect.

[0107] In some optional embodiments, the center thickness of at least one lens is less than 8 mm. This configuration prevents the center thickness of the lens from being too thick, which facilitates a thinner and lighter optical system. For example, the center thickness of each lens is less than 8 mm.

[0108] In some optional embodiments, the distance between two adjacent lenses on the optical axis is less than or equal to 10 mm. This arrangement can control the distance between two adjacent lenses within a reasonable range, thereby controlling the total optical length of the optical system and making the optical system miniaturized.

[0109] It should be noted that the spacing between two adjacent lenses on the optical axis refers to the spacing between the two facing side surfaces of the two adjacent lenses on the optical axis, and can be understood as the air gap between the intersection of the two facing side surfaces of the two adjacent lenses with the optical axis. For example, the air gap between the first and second lenses on the optical axis refers to the minimum distance between the intersection of the second side surface of the first lens and the optical axis and the intersection of the first side surface of the second lens and the optical axis.

[0110] In some optional embodiments, the optical system includes only four lenses: from the first side to the second side, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4. The spacing between the first lens L1 and the second lens L2 on the optical axis is less than or equal to 8 mm. Controlling the spacing between the first lens L1 and the second lens L2 helps shorten the overall length of the optical system while ensuring a good display quality.

[0111] In some optional embodiments, the distance between the second lens L2 and the third lens L3 on the optical axis is less than or equal to 9 mm. Controlling the distance between the second lens L2 and the third lens L3 helps shorten the total length of the optical system while ensuring the display effect.

[0112] In some optional embodiments, the distance between the third lens L3 and the fourth lens L4 on the optical axis is less than or equal to 10 mm. Controlling the distance between the third lens L3 and the fourth lens L4 is beneficial to shortening the total length of the optical system while ensuring the display effect, thereby achieving miniaturization.

[0113] In some optional embodiments, the side surface of each lens closest to the first side is designated as the first side surface, and the side surface closest to the second side is designated as the second side surface. The at least four lenses include a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4, arranged sequentially from the first side to the second side. The absolute value of the radius of curvature of the side surfaces of the first lens L1 through the fourth lens L4 is greater than or equal to 5 mm and less than or equal to 90 mm. By controlling the absolute value of the radius of curvature of the side surfaces of the first lens L1 through the fourth lens L4 within a reasonable range, the lens shape is ensured to be easily machined, thereby avoiding problems such as high machining difficulty and low yield.

[0114] In some optional embodiments, the radius of curvature R11 of the first side surface S1 of the first lens element and the radius of curvature R12 of the second side surface S2 of the first lens element satisfy the following relationship: 0.2≤|R11 / R12|≤0.5. By controlling |R11 / R12| within a reasonable range, the radius of curvature of the two side surfaces of the first lens element L1 is limited, thereby facilitating correction of field curvature and ensuring display quality.

[0115] In some optional embodiments, the radius of curvature R21 of the first side surface S3 of the second lens element and the radius of curvature R22 of the second side surface S4 of the second lens element satisfy the following relationship: 2≤|R21 / R22|≤5. By controlling |R21 / R22| within a reasonable range, the radius of curvature of the two side surfaces of the second lens element L2 is limited, thereby facilitating correction of field curvature and ensuring a good display quality.

[0116] In some optional embodiments, the radius of curvature R31 of the first side surface S5 of the third lens element and the radius of curvature R32 of the second side surface S6 of the third lens element satisfy the following relationship: 0.2≤|R31 / R32|≤0.7. By controlling |R31 / R32| within a reasonable range, the radius of curvature of the two side surfaces of the third lens element L3 is limited, thereby facilitating correction of field curvature and ensuring a good display quality.

[0117] In some optional embodiments, the radius of curvature R41 of the first side S7 of the fourth lens element and the radius of curvature R42 of the second side S8 of the fourth lens element satisfy the following relationship: 0.2≤|R41 / R42|≤0.7. By controlling |R41 / R42| within a reasonable range, the radius of curvature of the two side surfaces of the third lens element L3 is limited, thereby facilitating correction of field curvature and ensuring a good display quality.

[0118] The optical system disclosed herein utilizes four lenses, one of which is a double-sided Fresnel lens, achieving high light efficiency, ultra-short focal length, ultra-thinness, a wide field of view, and full-field HD display. Furthermore, the optical system disclosed herein exhibits a light efficiency exceeding 50%, avoiding the drawbacks of low light efficiency and ghosting associated with reentrant optical systems, which typically exhibit a light efficiency below 25%. Consequently, head-mounted display devices utilizing the optical system disclosed herein have lower brightness requirements for display screen S9. For example, in applications involving VR lenses, the human eye requires a brightness of 100 to 150 nits. Based on this 150 nits, the brightness of display screen S9 in the disclosed embodiment is less than 300 nits, while the reentrant optical system requires a brightness of greater than 600 nits. Clearly, the brightness of display screen S9 in a head-mounted display device utilizing a reentrant optical system is more than twice that of a head-mounted display device utilizing a reentrant optical system. However, the high brightness of display screen S9 consumes significant energy, shortening its lifespan and increasing the temperature of the head-mounted display device.

[0119] The optical system disclosed in the present invention has a light efficiency greater than 50%, an effective focal length less than 17 mm, a total optical length of the optical system less than 30 mm, a field of view angle greater than 90°, and can achieve full-field high-definition display, with the advantages of small dispersion, high light efficiency, no ghosting, and a strong sense of immersion.

[0120] In one embodiment, referring to FIG. 1 , the optical system is a four-lens optical system. The four lenses are, from the first side to the second side, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4. Each lens has a first side surface proximal to the first side and a second side surface proximal to the second side. The second lens L2 is a double-sided Fresnel lens, wherein the first side surface S3 of the second lens is a Fresnel surface, and the second side surface S4 of the second lens is a Fresnel surface.

[0121] The absolute values ​​of the radii of curvature of all side surfaces of the first to fourth lenses L1 to L4 are greater than or equal to 5 mm and less than or equal to 70 mm.

[0122] A ratio of a curvature radius R11 of the first side surface S1 of the first lens to a curvature radius R12 of the second side surface S2 of the first lens is greater than or equal to 0.2 and less than or equal to 0.5.

[0123] A ratio of a curvature radius R21 of the first side surface S3 of the second lens to a curvature radius R22 of the second side surface S4 of the second lens is greater than or equal to 3 and less than or equal to 5.

[0124] A ratio of a curvature radius R31 of the first side surface S5 of the third lens to a curvature radius R32 of the second side surface S6 of the third lens is greater than or equal to 0.286 and less than or equal to 0.4.

[0125] A ratio of a curvature radius R41 of the first side surface S7 of the fourth lens to a curvature radius R42 of the second side surface S8 of the fourth lens is greater than or equal to 0.222 and less than or equal to 0.4.

[0126] The distance between the first lens L1 and the second lens L2 is within the range of 0-7 mm, the distance between the second lens L2 and the third lens L3 is within the range of 0-7 mm, and the distance between the third lens L3 and the fourth lens L4 is within the range of 0-10 mm.

[0127] The refractive indices of the first lens L1, the second lens L2, and the third lens L3 are all greater than or equal to 1.04 and less than or equal to 2.04. The Abbe numbers of the first lens L1, the second lens L2, and the third lens L3 are all greater than or equal to 51.3 and less than or equal to 61.3.

[0128] The refractive index of the fourth lens L4 is greater than or equal to 1.26 and less than or equal to 2.06, and the Abbe number of the fourth lens L4 is greater than or equal to 10.4 and less than or equal to 30.4.

[0129] Table 1 below shows the detailed parameters of the optical system in this embodiment.

[0130] Table 1

[0131] In order to ensure that the optical effect of the entire optical system reaches the optimal state and reduce the generation of stray light in the optical system, the annular tooth structures 11 of the two Fresnel surfaces need to match. From the first side to the second side, there are the first Fresnel surface and the second Fresnel surface respectively. The ratio of the tooth height H1 of the annular tooth structure 11 of the first Fresnel surface to the tooth height H2 of the annular tooth structure of the second Fresnel surface is H1 / H2=0.9.

[0132] The software simulation gives the optical simulation results of the three within the tooth height range compared to those without matching. It can be seen that in the process of designing the optical system, for an optical system containing multiple Fresnel lenses, the tooth heights between the Fresnel lenses can be matched to optimize the entire optical system to a certain extent and ensure the overall effect of the optical system.

[0133] The ratio of the maximum tooth width W1 of the annular tooth structure 11 of the first Fresnel surface to the maximum tooth width W2 of the annular tooth structure of the second Fresnel surface is W1 / W2 =1.

[0134] The ratio R1 / R2 of the radius R1 of the rounded corner of the tooth tip corresponding to the annular tooth structure 11 of the first Fresnel surface to the radius R2 of the rounded corner of the tooth tip corresponding to the annular tooth structure 11 of the second Fresnel surface is 1.

[0135] The ratio of the number of teeth corresponding to the first Fresnel surface to the number of teeth corresponding to the second Fresnel surface is 1.

[0136] The ratio of the draft angle θ1 of the annular tooth structure of the first Fresnel surface to the draft angle θ2 of the annular tooth structure of the second Fresnel surface is θ1 / θ2=1.

[0137] In this embodiment, the light efficiency is 70%.

[0138] In another embodiment, referring to FIG. 3 , the optical system is a four-lens optical system. The four lenses, from the first side to the second side, are a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4. Each lens has a first side surface proximate to the first side and a second side surface proximate to the second side. The third lens L3 is a double-sided Fresnel lens, wherein the first side surface S5 of the third lens is a Fresnel surface, and the second side surface S6 of the third lens is a Fresnel surface.

[0139] The absolute values ​​of the radii of curvature of all side surfaces of the first to fourth lenses L1 to L4 are greater than or equal to 5 mm and less than or equal to 80 mm.

[0140] A ratio of a curvature radius R11 of the first side surface S1 of the first lens to a curvature radius R12 of the second side surface S2 of the first lens is greater than or equal to 0.333 and less than or equal to 0.5.

[0141] A ratio of a curvature radius R21 of the first side surface S3 of the second lens to a curvature radius R22 of the second side surface S4 of the second lens is greater than or equal to 2 and less than or equal to 4.

[0142] A ratio of a curvature radius R31 of the first side surface S5 of the third lens to a curvature radius R32 of the second side surface S6 of the third lens is greater than or equal to 0.5 and less than or equal to 0.667.

[0143] A ratio of a curvature radius R41 of the first side surface S7 of the fourth lens to a curvature radius R42 of the second side surface S8 of the fourth lens is greater than or equal to 0.4 and less than or equal to 0.667.

[0144] The distance between the first lens L1 and the second lens L2 is within the range of 0-5 mm, the distance between the second lens L2 and the third lens L3 is within the range of 0-5 mm, and the distance between the third lens L3 and the fourth lens L4 is within the range of 0-8 mm.

[0145] The refractive indices of the first lens L1, the second lens L2, and the third lens L3 are all greater than or equal to 1.04 and less than or equal to 2.04. The Abbe numbers of the first lens L1, the second lens L2, and the third lens L3 are all greater than or equal to 51.3 and less than or equal to 61.3.

[0146] The refractive index of the fourth lens L4 is greater than or equal to 1.26 and less than or equal to 2.06, and the Abbe number of the fourth lens L4 is greater than or equal to 10.4 and less than or equal to 30.4.

[0147] Table 2 below shows the detailed parameters of the optical system in this embodiment.

[0148] Table 2

[0149] In order to ensure that the optical effect of the entire optical system reaches the optimal state and reduce the generation of stray light in the optical system, the annular tooth structures 11 of the two Fresnel surfaces need to match. From the first side to the second side, there are the first Fresnel surface and the second Fresnel surface respectively. The ratio of the tooth height H1 of the annular tooth structure 11 of the first Fresnel surface to the tooth height H2 of the annular tooth structure of the second Fresnel surface is H1 / H2=0.9.

[0150] The software simulation gives the optical simulation results of the three within the tooth height range compared to those without matching. It can be seen that in the process of designing the optical system, for an optical system containing multiple Fresnel lenses, the tooth heights between the Fresnel lenses can be matched to optimize the entire optical system to a certain extent and ensure the overall effect of the optical system.

[0151] The ratio of the maximum tooth width W1 of the annular tooth structure 11 of the first Fresnel surface to the maximum tooth width W2 of the annular tooth structure of the second Fresnel surface is W1 / W2 =1.

[0152] The ratio R1 / R2 of the radius R1 of the rounded corner of the tooth tip corresponding to the annular tooth structure 11 of the first Fresnel surface to the radius R2 of the rounded corner of the tooth tip corresponding to the annular tooth structure 11 of the second Fresnel surface is 1.

[0153] The ratio of the number of teeth corresponding to the first Fresnel surface to the number of teeth corresponding to the second Fresnel surface is 1.

[0154] The ratio of the draft angle θ1 of the annular tooth structure of the first Fresnel surface to the draft angle θ2 of the annular tooth structure of the second Fresnel surface is θ1 / θ2=1.

[0155] In this embodiment, the light efficiency is 70%.

[0156] In another embodiment, referring to FIG. 5 , the optical system is a four-lens optical system. The four lenses are, from the first side to the second side, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4. Each lens has a first side surface proximal to the first side and a second side surface proximal to the second side. The second lens L2 is a double-sided Fresnel lens, and the third lens L3 is a single-sided Fresnel lens. The first side surface S3 of the second lens is a Fresnel surface, the second side surface S4 of the second lens is a Fresnel surface, and the first side surface S5 of the third lens is a Fresnel surface.

[0157] The absolute values ​​of the radii of curvature of all side surfaces of the first to fourth lenses L1 to L4 are greater than or equal to 5 mm and less than or equal to 90 mm.

[0158] A ratio of a curvature radius R11 of the first side surface S1 of the first lens to a curvature radius R12 of the second side surface S2 of the first lens is greater than or equal to 0.333 and less than or equal to 0.5.

[0159] A ratio of a curvature radius R21 of the first side surface S3 of the second lens to a curvature radius R22 of the second side surface S4 of the second lens is greater than or equal to 3 and less than or equal to 4.

[0160] A ratio of a curvature radius R31 of the first side surface S5 of the third lens to a curvature radius R32 of the second side surface S6 of the third lens is greater than or equal to 0.5 and less than or equal to 0.667.

[0161] A ratio of a curvature radius R41 of the first side surface S7 of the fourth lens to a curvature radius R42 of the second side surface S8 of the fourth lens is greater than or equal to 0.5 and less than or equal to 0.667.

[0162] The distance between the first lens L1 and the second lens L2 is within the range of 0-8 mm, the distance between the second lens L2 and the third lens L3 is within the range of 0-8 mm, and the distance between the third lens L3 and the fourth lens L4 is within the range of 0-10 mm.

[0163] The refractive indices of the first lens L1, the second lens L2, and the third lens L3 are all greater than or equal to 1.04 and less than or equal to 2.04. The Abbe numbers of the first lens L1, the second lens L2, and the third lens L3 are all greater than or equal to 51.3 and less than or equal to 61.3.

[0164] The refractive index of the fourth lens L4 is greater than or equal to 1.26 and less than or equal to 2.06, and the Abbe number of the fourth lens L4 is greater than or equal to 10.4 and less than or equal to 30.4.

[0165] Table 3 below shows the detailed parameters of the optical system in this embodiment.

[0166] Table 3

[0167] In order to ensure that the optical effect of the entire optical system reaches the optimal state and reduce the generation of stray light in the optical system, the annular tooth structures 11 of the three Fresnel surfaces need to match. The first side surface of the double-sided Fresnel lens is the first Fresnel surface, the second side surface of the double-sided Fresnel lens is the second Fresnel surface, and the Fresnel surface of the single-sided Fresnel lens is the third Fresnel surface. The ratio of the tooth height H1 of the annular tooth structure 11 of the first Fresnel surface, the tooth height H2 of the annular tooth structure of the second Fresnel surface, and the tooth height H3 of the annular tooth structure of the third Fresnel surface is H1:H2:H3=2:3:4.

[0168] The software simulation gives the optical simulation results of the three within the tooth height range compared to those without matching. It can be seen that in the process of designing the optical system, for an optical system containing multiple Fresnel lenses, the tooth heights between the Fresnel lenses can be matched to optimize the entire optical system to a certain extent and ensure the overall effect of the optical system.

[0169] The ratio of the maximum tooth width W1 of the annular tooth structure 11 of the first Fresnel surface, the maximum tooth width W2 of the annular tooth structure of the second Fresnel surface, and the maximum tooth width W3 of the annular tooth structure 11 of the third Fresnel surface is W1:W2:W3=2:2:3.

[0170] The ratio of the radius R1 of the rounded corner of the tooth tip corresponding to the annular tooth structure 11 of the first Fresnel surface, the radius R2 of the rounded corner of the tooth tip corresponding to the annular tooth structure 11 of the second Fresnel surface, and the radius R3 of the rounded corner of the tooth tip corresponding to the annular tooth structure 11 of the third Fresnel surface is R1:R2:R3=2:2:3.

[0171] The ratio of the number of teeth corresponding to the first Fresnel surface, the number of teeth corresponding to the second Fresnel surface, and the number of teeth corresponding to the third Fresnel surface is 2:2:3.

[0172] The ratio of the draft angle θ1 of the annular tooth structure of the first Fresnel surface, the draft angle θ2 of the annular tooth structure of the second Fresnel surface, and the draft angle θ3 of the annular tooth structure of the third Fresnel surface is θ1:θ2:θ3=2:2:3.

[0173] In this embodiment, the light efficiency is 70%.

[0174] In another embodiment, referring to FIG. 7 , the optical system is a four-lens optical system. The four lenses are, from the first side to the second side, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4. Each lens has a first side surface proximal to the first side and a second side surface proximal to the second side. The second lens L2 is a single-sided Fresnel lens, and the third lens L3 is a double-sided Fresnel lens. The second side surface S4 of the second lens is a Fresnel surface, the first side surface S5 of the third lens is a Fresnel surface, and the second side surface S6 of the third lens is a Fresnel surface.

[0175] The absolute values ​​of the radii of curvature of all side surfaces of the first to fourth lenses L1 to L4 are greater than or equal to 5 mm and less than or equal to 90 mm.

[0176] A ratio of a curvature radius R11 of the first side surface S1 of the first lens to a curvature radius R12 of the second side surface S2 of the first lens is greater than or equal to 0.25 and less than or equal to 0.5.

[0177] A ratio of a curvature radius R21 of the first side surface S3 of the second lens to a curvature radius R22 of the second side surface S4 of the second lens is greater than or equal to 3 and less than or equal to 4.

[0178] A ratio of a curvature radius R31 of the first side surface S5 of the third lens to a curvature radius R32 of the second side surface S6 of the third lens is greater than or equal to 0.5 and less than or equal to 0.667.

[0179] A ratio of a curvature radius R41 of the first side surface S7 of the fourth lens to a curvature radius R42 of the second side surface S8 of the fourth lens is greater than or equal to 0.333 and less than or equal to 0.667.

[0180] The distance between the first lens L1 and the second lens L2 is within the range of 0-8 mm, the distance between the second lens L2 and the third lens L3 is within the range of 0-9 mm, and the distance between the third lens L3 and the fourth lens L4 is within the range of 0-10 mm.

[0181] The refractive indices of the first lens L1, the second lens L2, and the third lens L3 are all greater than or equal to 1.04 and less than or equal to 2.04. The Abbe numbers of the first lens L1, the second lens L2, and the third lens L3 are all greater than or equal to 51.3 and less than or equal to 61.3.

[0182] The refractive index of the fourth lens L4 is greater than or equal to 1.26 and less than or equal to 2.06, and the Abbe number of the fourth lens L4 is greater than or equal to 10.4 and less than or equal to 30.4.

[0183] Table 4 below shows the detailed parameters of the optical system in this embodiment.

[0184] Table 4

[0185] In order to ensure that the optical effect of the entire optical system reaches the optimal state and reduce the generation of stray light in the optical system, the annular tooth structures 11 of the three Fresnel surfaces need to match. The first side surface of the double-sided Fresnel lens is the first Fresnel surface, the second side surface of the double-sided Fresnel lens is the second Fresnel surface, and the Fresnel surface of the single-sided Fresnel lens is the third Fresnel surface. The ratio of the tooth height H1 of the annular tooth structure 11 of the first Fresnel surface, the tooth height H2 of the annular tooth structure of the second Fresnel surface, and the tooth height H3 of the annular tooth structure of the third Fresnel surface is H1:H2:H3=2:3:4.

[0186] The software simulation gives the optical simulation results of the three within the tooth height range compared to those without matching. It can be seen that in the process of designing the optical system, for an optical system containing multiple Fresnel lenses, the tooth heights between the Fresnel lenses can be matched to optimize the entire optical system to a certain extent and ensure the overall effect of the optical system.

[0187] The ratio of the maximum tooth width W1 of the annular tooth structure 11 of the first Fresnel surface, the maximum tooth width W2 of the annular tooth structure of the second Fresnel surface, and the maximum tooth width W3 of the annular tooth structure 11 of the third Fresnel surface is W1:W2:W3=2:2:3.

[0188] The ratio of the radius R1 of the rounded corner of the tooth tip corresponding to the annular tooth structure 11 of the first Fresnel surface, the radius R2 of the rounded corner of the tooth tip corresponding to the annular tooth structure 11 of the second Fresnel surface, and the radius R3 of the rounded corner of the tooth tip corresponding to the annular tooth structure 11 of the third Fresnel surface is R1:R2:R3=2:2:3.

[0189] The ratio of the number of teeth corresponding to the first Fresnel surface, the number of teeth corresponding to the second Fresnel surface, and the number of teeth corresponding to the third Fresnel surface is 2:2:3.

[0190] The ratio of the draft angle θ1 of the annular tooth structure of the first Fresnel surface, the draft angle θ2 of the annular tooth structure of the second Fresnel surface, and the draft angle θ3 of the annular tooth structure of the third Fresnel surface is θ1:θ2:θ3=2:2:3.

[0191] In this embodiment, the light efficiency is 70%.

[0192] In another aspect, a display device is provided, comprising a display screen S9 and the aforementioned optical system. Display screen S9 is located on the second side of the optical system, and the image on display screen S9 is transmitted to the first side via the optical system. Display screen S9 is located on the imaging surface of the optical system. The display device having the aforementioned optical system has the advantages of being lightweight and thin, and having excellent display quality.

[0193] In some optional embodiments, the display device is a head-mounted display device.

[0194] The display screen S9 can be LCD (Liquid Crystal Display), Micro LED (Micro Light Emitting Diode Display), OLED (Organic Light-Emitting Diode), or LCOS (Liquid Crystal on Silicon).

[0195] In an optional embodiment, the diagonal length of the display screen S9 is greater than or equal to 20 mm and less than or equal to 110 mm. The diagonal length of the display screen S9 corresponds to the image height of the optical system. In other words, the diagonal length of the display screen S9 is the same as the image height of the optical system installed therein.

[0196] It is understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present disclosure, and the present disclosure is not limited thereto. Those skilled in the art may make various modifications and improvements without departing from the spirit and substance of the present disclosure, and such modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. An optical system, wherein: The optical system comprises at least four lenses sequentially arranged from a first side to a second side on an optical axis, each of the lenses comprising two side surfaces arranged opposite to each other, at least one of the lenses being a double-sided Fresnel lens, both side surfaces of the double-sided Fresnel lens being Fresnel surfaces, and the double-sided Fresnel lens being located between the lens closest to the first side and the lens closest to the second side of the at least four lenses.

2. The optical system according to claim 1, wherein At least three of the side surfaces of all the lenses are Fresnel surfaces, and at least three of the Fresnel surfaces are adjacently arranged.

3. The optical system according to claim 1, wherein: The Fresnel surface includes a coaxially arranged central portion and a toothed ring portion, the toothed ring portion surrounds the central portion, and the toothed ring portion has a plurality of coaxially arranged annular tooth structures, and the ratio of the tooth height of the annular tooth structure to the tooth width of the annular tooth structure is greater than or equal to 0.2 and less than or equal to 2.

4. The optical system according to any one of claims 1 to 3, wherein: The Fresnel surface includes a coaxially arranged central portion and a toothed ring portion, wherein the toothed ring portion has a plurality of coaxially arranged annular tooth structures, and the annular tooth structures meet at least one of the following conditions: The tooth widths of the plurality of annular tooth structures increase gradually toward the center portion; The tooth width of the annular tooth structure is greater than 0 and less than or equal to 10 mm; The tooth height of the annular tooth structure is greater than 0 and less than or equal to 1 mm; The tooth tips of the annular tooth structure are rounded; The number of the annular tooth structures is less than 50; The draft angle of the annular tooth structure is greater than 0 and less than or equal to 10°.

5. The optical system according to claim 4, wherein: When the tooth tip of the annular tooth structure is rounded, the radius of the rounded corner is greater than 0 and less than or equal to 50 micrometers.

6. The optical system according to any one of claims 1 to 3, wherein: The Fresnel surface includes a coaxially arranged central portion and a toothed ring portion, the toothed ring portion having a plurality of coaxially sleeved annular tooth structures. The Fresnel surface facing the first side of the double-sided Fresnel lens is the first Fresnel surface, and the Fresnel surface facing the second side of the double-sided Fresnel lens is the second Fresnel surface. The annular tooth structure of the first Fresnel surface and the annular tooth structure of the second Fresnel surface satisfy at least one of the following conditions: The tooth height of the annular tooth structure of the first Fresnel surface is less than or equal to the tooth height of the annular tooth structure of the second Fresnel surface; The maximum tooth width of the annular tooth structure of the first Fresnel surface is less than or equal to the maximum tooth width of the annular tooth structure of the second Fresnel surface; The draft angle of the annular tooth structure of the first Fresnel surface is less than or equal to the draft angle of the annular tooth structure of the second Fresnel surface; The tooth tips of the annular tooth structures of the first Fresnel surface and the second Fresnel surface are both rounded, and the radius of the rounded corner of the annular tooth structure of the first Fresnel surface is smaller than or equal to the radius of the rounded corner of the annular tooth structure of the second Fresnel surface.

7. The optical system according to claim 6, wherein: When the tooth height of the annular tooth structure of the first Fresnel surface is less than or equal to the tooth height of the annular tooth structure of the second Fresnel surface, a ratio of the tooth height of the annular tooth structure of the first Fresnel surface to the tooth height of the annular tooth structure of the second Fresnel surface is greater than or equal to 0.9 and less than or equal to 1; When the maximum tooth width of the annular tooth structure of the first Fresnel surface is less than or equal to the maximum tooth width of the annular tooth structure of the second Fresnel surface, a ratio of the maximum tooth width of the annular tooth structure of the first Fresnel surface to the maximum tooth width of the annular tooth structure of the second Fresnel surface is greater than or equal to 0.889 and less than or equal to 1; When the draft angle of the annular tooth structure of the first Fresnel surface is less than or equal to the draft angle of the annular tooth structure of the second Fresnel surface, a ratio of the draft angle of the annular tooth structure of the first Fresnel surface to the draft angle of the annular tooth structure of the second Fresnel surface is greater than or equal to 0.667 and less than or equal to 1; When the tooth tips of the annular tooth structures of the first Fresnel surface and the second Fresnel surface are both rounded, and the radius of the rounded corner of the annular tooth structure of the first Fresnel surface is less than or equal to the radius of the rounded corner of the annular tooth structure of the second Fresnel surface, the ratio of the radius of the rounded corner of the annular tooth structure of the first Fresnel surface to the radius of the rounded corner of the annular tooth structure of the second Fresnel surface is greater than or equal to 0.9 and less than or equal to 1.

8. The optical system according to any one of claims 1 to 7, wherein: The optical system has four lenses, and the effective focal length f of the optical system and the total optical length TTL of the optical system satisfy the following relationship: 0.1 <f / TTL<8.5。 9. The optical system according to any one of claims 1 to 8, wherein: The effective focal length f of the optical system satisfies: f≤17 mm.

10. The optical system according to any one of claims 1 to 9, wherein: The total optical length TTL of the optical system satisfies: TTL≤30 mm.

11. The optical system according to any one of claims 1 to 10, wherein: The side surface of the lens closest to the second side among the at least four lenses facing the second side is a concave surface.

12. The optical system according to any one of claims 1 to 11, wherein: An absolute value of the effective focal length of the one of all the lenses closest to the second side is greater than 8 mm.

13. The optical system according to any one of claims 1 to 12, wherein: The refractive index of the lens is greater than or equal to 1 and less than or equal to 2.

1.

14. The optical system according to any one of claims 1 to 13, wherein: The field of view angle of the optical system is greater than or equal to 90 degrees.

15. The optical system according to any one of claims 1 to 14, wherein: At least two of the lenses are arranged in contact with each other.

16. The optical system according to any one of claims 1 to 15, wherein: The lenses are all lenses with optical power.

17. The optical system according to any one of claims 1 to 16, wherein: At least one of the lenses has a center thickness of less than 8 mm.

18. The optical system according to any one of claims 1 to 17, wherein: The distance between two adjacent lenses in all the lenses on the optical axis is less than or equal to 10 mm.

19. The optical system according to claim 18, wherein The at least four lenses include a first lens, a second lens, a third lens, and a fourth lens arranged sequentially from the first side to the second side, and the optical system satisfies at least one of the following: The distance between the first lens and the second lens on the optical axis is less than or equal to 8 mm; The distance between the second lens and the third lens on the optical axis is less than or equal to 9 mm; The distance between the third lens and the fourth lens on the optical axis is less than or equal to 10 mm.

20. The optical system according to any one of claims 1 to 17, wherein The at least four lenses include a first lens, a second lens, a third lens and a fourth lens arranged sequentially from the first side to the second side, and the absolute values ​​of the curvature radii of the sides of the first lens to the fourth lens are greater than or equal to 5 mm and less than or equal to 90 mm.

21. The optical system according to any one of claims 1 to 17, wherein: A side surface of each lens close to the first side is a first side surface, and a side surface close to the second side is a second side surface. The at least four lenses include a first lens, a second lens, a third lens, and a fourth lens arranged sequentially from the first side to the second side. The optical system satisfies at least one of the following conditions: A curvature radius R11 of the first side surface of the first lens and a curvature radius R12 of the second side surface of the first lens satisfy: 0.2≤|R11 / R12|≤0.5; A curvature radius R21 of the first side surface of the second lens and a curvature radius R22 of the second side surface of the second lens satisfy: 2≤|R21 / R22|≤5; The curvature radius R31 of the first side surface of the third lens and the curvature radius R32 of the second side surface of the third lens satisfy: 0.2≤|R31 / R32|≤0.7; A curvature radius R41 of the first side surface of the fourth lens and a curvature radius R42 of the second side surface of the fourth lens satisfy: 0.2≤|R41 / R42|≤0.

7.

22. A display device, wherein: include: Display screen; The optical system according to any one of claims 1 to 21, wherein the display screen is located on the second side of the optical system, and the picture light of the display screen is transmitted to the first side through the optical system.

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