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] This disclosure relates to the field of display technology, and more specifically to an optical system and a display device. Background Technology

[0002] With the development of VR (Virtual Reality) technology, users' requirements for VR devices are gradually increasing. They not only require VR devices to have excellent image quality, but also to be small in size and lightweight. In order to reduce the size of VR devices, catadioptric optical systems are usually used. However, catadioptric optical systems cause a lot of light energy waste, resulting in low light efficiency, making it difficult for VR devices to simultaneously meet the requirements of being thin and light and having high light efficiency.

[0003] Summary of the Invention

[0004] This disclosure aims to address 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 this disclosure, an optical system is provided, comprising at least four lenses arranged sequentially from a first side to a second side along an optical axis, each lens comprising two opposing sides, at least one of the lenses being a double-sided Fresnel lens, wherein both sides of the double-sided Fresnel lens are Fresnel surfaces, and the double-sided Fresnel lens is located between the lens closest to the first side and the lens closest to the second side among the at least four lenses.

[0006] Among all the lenses, at least three of the side surfaces are Fresnel surfaces, and at least three Fresnel surfaces are arranged adjacent to each other.

[0007] The Fresnel surface includes a central portion and a toothed ring portion arranged coaxially. The toothed ring portion surrounds the central portion and has multiple coaxially arranged annular tooth structures. The ratio of the tooth height 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 central portion and a toothed ring portion arranged coaxially. The toothed ring portion has a plurality of coaxially nested annular tooth structures, and the annular tooth structures satisfy at least one of the following:

[0009] The tooth width of the plurality of the ring-shaped tooth structures increases toward the center portion;

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

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

[0012] The tips of the ring-shaped tooth structure are rounded.

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

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

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

[0016] The Fresnel surface comprises a coaxially arranged central portion and a toothed ring portion. The toothed ring portion has multiple coaxially nested annular tooth structures. The Fresnel surface facing the first side in the double-sided Fresnel lens is the first Fresnel surface, and the Fresnel surface facing the second side in 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:

[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 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.

[0021] 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, the 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, the 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, the 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 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] The effective focal length f of the optical system satisfies: f≤17mm.

[0027] The total optical length (TTL) of the optical system satisfies: TTL≤30mm.

[0028] Among the at least four lenses, the lens closest to the second side has a concave side facing the second side.

[0029] Of all the lenses, the one closest to the second side has an effective focal length greater than 8 mm in absolute value.

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

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

[0032] At least two of the lenses are fitted together.

[0033] All of the lenses are lenses with optical power.

[0034] In this embodiment, at least one of the lenses has a center thickness of less than 8 millimeters.

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

[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] In each of the lenses, the side closest to the first side is the first side, and the side closest to the second side is the second side. 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 radius of curvature of the sides 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] Wherein, the side of each lens closer to the first side is the first side, and the side closer to the second side is the second side, and the optical system satisfies at least one of the following:

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

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

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

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

[0046] According to another aspect of this disclosure, a display device is provided, comprising:

[0047] Display screen;

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

[0049] The diagonal length of the display screen is greater than or equal to 20 mm and less than or equal to 110 mm. Attached Figure Description

[0050] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0051] Figure 1 shows a schematic diagram of the structure of an optical system according to an alternative embodiment of the present disclosure;

[0052] Figure 2 shows the modulation transfer function curve of the optical system in Figure 1;

[0053] Figure 3 shows a schematic diagram of the optical system according to another alternative embodiment of the present disclosure;

[0054] Figure 4 shows the modulation transfer function curve of the optical system in Figure 3;

[0055] Figure 5 shows a schematic diagram of the optical system according to another alternative embodiment of the present disclosure;

[0056] Figure 6 shows the modulation transfer function curve of the optical system in Figure 5;

[0057] Figure 7 shows a schematic diagram of the optical system according to another alternative embodiment of the present disclosure;

[0058] Figure 8 shows the modulation transfer function curve of the optical system in Figure 7;

[0059] Figure 9 shows a longitudinal sectional view of the structure of a Fresnel lens in an alternative embodiment of this disclosure;

[0060] Figure 10 shows a view of the annular tooth structure in Figure 9 from one angle;

[0061] Figure 11 shows a stray light distribution diagram of an optical system in an alternative embodiment of this disclosure;

[0062] Figure 12 shows a stray light distribution diagram of an example optical system. Detailed Implementation

[0063] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0064] Unless otherwise defined, the technical or scientific terms used in the embodiments of this disclosure should have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms "first," "second," and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely 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 "comprising" or "including" mean that the element or object preceding the word encompasses the element or object listed following the word and its equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships, and these relative positional relationships may change accordingly when the absolute position of the described object changes.

[0065] As used herein, “parallel” and “perpendicular” include the described situation and situations that are similar to the described situation, within an acceptable range of deviation, which is determined by those skilled in the art taking into account the measurement under discussion and the error associated with the measurement of a particular quantity (i.e., the limitations of the measurement system). For example, “parallel” includes absolute parallelism and approximate parallelism, where an acceptable range of deviation for approximate parallelism may be, for example, within 5°; “perpendicular” includes absolute perpendicularity and approximate perpendicularity, where an acceptable range of deviation for approximate perpendicularity may also be, for example, within 5°.

[0066] It should be understood that when a layer or element is referred to as being on another layer or substrate, it can mean that the layer or element is directly on the other layer or substrate, or that there is an intermediate layer between the layer or element and the other layer or substrate.

[0067] This document describes exemplary embodiments with reference to sectional views and / or plan views, which are idealized exemplary drawings. In the drawings, the thickness of layers and regions is enlarged for clarity. Therefore, variations in shape relative to the drawings are contemplated due to, for example, manufacturing techniques and / or tolerances. Therefore, exemplary embodiments should not be construed as limited to the shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing processes. Thus, the regions shown in the drawings are schematic in nature, and their shapes are not intended to show the actual shapes of the regions of the device, nor are they intended to limit the scope of the exemplary embodiments.

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

[0069] In this paper, the paraxial region refers to the region near the optical axis. If the lens surface is convex and the location of the convexity is not defined, it means that the lens surface is convex at least in the paraxial region; if the lens surface is concave and the location of the concaveness is not defined, it means that the lens surface is concave at least in the paraxial region. In the attached figures, 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 determined according to the judgment method commonly known in the field, using the R value (R refers to the radius of curvature of the paraxial region, usually the R value in the lens database of optical software) to determine concavity or convexity. For the first side, when the R value is positive, it is determined to be convex, and when the R value is negative, it is determined to be concave; for the second side, when the R value is positive, it is determined to be concave, and when the R value is negative, it is determined to be convex.

[0070] The optical system disclosed herein can be used, for example, as a projection lens or a lidar 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 rays 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 in this 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] Furthermore, the optical system in this disclosure can also be used as a regular lens, such as a vehicle lens or a general lens, where light from the object side can form an image from the image side.

[0073] The optical system described below is used in detail as a VR lens.

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

[0075] By incorporating at least one double-sided Fresnel lens into an optical system, the weight of the lens can be effectively reduced, thus facilitating the development of thinner and lighter optical systems. Double-sided Fresnel lenses can reduce spherical aberration and ghosting, ensuring the imaging quality of the optical system. Simultaneously, light energy loss is minimal when passing through a double-sided Fresnel lens, ensuring a light efficiency of over 50% for the visual system. This allows the optical system to simultaneously achieve both thinness and high light efficiency. In each lens, of the two opposing sides, the side closer to the first side is called the first side, and the side closer to the second side is called 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, the 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 can see the image displayed on the display screen S9.

[0077] In an optical system, all sides except the Fresnel surface are either spherical or aspherical. When the side surface of a lens is aspherical, it satisfies formula (1).

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

[0079] In the specific embodiments shown in Figures 1, 3, 5, and 7, the double-sided Fresnel lens is located between the lens closest to the first side and the lens furthest from the first side. The lens closest to the first side is the first lens L1, and the lens furthest from the first side (and closest to the second side) is the last lens. The double-sided Fresnel lens is located between the first lens L1 and the last lens. This arrangement avoids the annular tooth structure on the Fresnel surface from affecting the light entering the visual imaging system, ensuring more light enters the optical system, and also facilitates the smooth exit of light from the optical system, thus ensuring the display effect of the optical system.

[0080] In some alternative embodiments, at least three of the sides of all lenses are Fresnel surfaces, and at least three Fresnel surfaces are arranged adjacent to each other. When the number of Fresnel surfaces is greater than three, there may be one or more double-sided Fresnel lenses, or one or more single-sided Fresnel lenses; no specific limitation is made here.

[0081] For example, in the four-element optical system shown in Figures 5 and 7, one of the four lenses is a double-sided Fresnel lens and one is a single-sided Fresnel lens. Therefore, all the lenses in the entire optical system have at least three Fresnel surfaces on their sides, and 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 of the third lens is a Fresnel surface. For example, the third lens is a double-sided Fresnel lens, and the first side of the fourth lens is a Fresnel surface.

[0082] It should be noted that adjacent Fresnel surfaces mean that there are no other surfaces between two adjacent Fresnel surfaces.

[0083] In the specific embodiment shown in Figure 9, the Fresnel surface includes a central portion 20 and a toothed ring portion 10 arranged coaxially. The toothed ring portion 10 surrounds the central portion 20 and has a plurality of coaxially nested annular tooth structures 11. The ratio of the tooth height 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 luminous efficiency of the optical system 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 to the tooth width of the annular tooth structure 11 is 1; another example is that the ratio of the tooth height to the tooth width of the annular tooth structure 11 is 0.5; yet another example is that the ratio of the tooth height to the tooth width of the annular tooth structure 11 is 1.5.

[0084] In some alternative embodiments, referring to Figure 9, the tooth width of the plurality of annular tooth structures 11 increases towards the center. By setting the tooth width of the annular tooth structures 11 at different positions to a gradient, the generation of stray light is reduced, ensuring the display effect of the optical system. At the same time, under the same lens aperture, this gradient design has a smaller total number of teeth, which can ensure that the optically effective area of ​​the lens has a better imaging effect due to the smaller 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 large, which easily reflects light and generates stray light. Limiting the tooth width of the annular tooth structure 11 to less than or equal to 10 mm can reduce stray light and ensure display effect. For example, the tooth width is greater than or equal to 0.3 mm and less than or equal to 5 mm. Another example is a tooth width of 0.5 mm; another example is a tooth width of 2 mm; another example is a tooth width of 1 mm; another example is a tooth width of 3 mm; another example is a tooth width of 4 mm.

[0086] In some alternative 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 large space on the lens, resulting in poor structural strength of the lens. Limiting the tooth height of the annular tooth structure 11 to less than or equal to 1 mm reduces the weight of the lens while ensuring its structural strength, thereby achieving a thinner and lighter 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. Another example is a tooth height of 0.2 mm; yet another example is a tooth height of 0.3 mm; and yet another example is a tooth height of 0.4 mm.

[0087] In some alternative embodiments, referring to Figure 10, the tips of the annular tooth structure 11 are rounded. Rounding the tips of the annular tooth structure 11 reduces light reflection and stray light generation. The radius of the rounded corner is greater than 0 and less than or equal to 50 micrometers. Limiting the radius of the rounded corner to the range of 0 to 50 micrometers helps reduce stray light and improve image quality. For example, the radius of the rounded corner is greater than or equal to 10 micrometers and less than or equal to 40 micrometers. Another example is a radius of 20 micrometers, 25 micrometers, 30 micrometers, or 35 micrometers.

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

[0089] In some alternative embodiments, the draft angle of the ring tooth structure 11 is greater than 0 and less than or equal to 10°. Double-sided and single-sided Fresnel lenses are mostly injection molded. To ensure smooth demolding, both double-sided and single-sided Fresnel lenses have a draft angle. The size of the draft angle affects stray light. Limiting the draft angle to the range of 0 to 10° can reduce stray light and improve image quality. For example, the draft angle of the ring tooth structure 11 is greater than or equal to 1° and less than or equal to 5°. Another example is a draft angle of 2°; yet another example is a draft angle of 3°; still another example is a draft angle of 4°.

[0090] In some optional embodiments, 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 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 between the Fresnel surfaces, it is possible to ensure that light enters the Fresnel surface smoothly while reducing multiple reflections of light within the Fresnel surface, thus improving light utilization. In addition, it can also reduce the reflection of light out of the lens by the Fresnel surface, reduce the generation of stray light, optimize the entire optical system, improve image quality, and ensure 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 between the Fresnel surfaces, it is beneficial for light to enter the Fresnel lens smoothly, while reducing the amount of light emitted after reflection from the Fresnel surfaces, reducing stray light generation, optimizing the entire optical system, improving image quality, and ensuring 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 alternative embodiments, the draft angle of the annular tooth structure 11 of the first Fresnel surface is less than or equal to the draft angle of the annular tooth structure 11 of the second Fresnel surface. By matching the draft angles between the Fresnel surfaces, the reflection of light from the draft surfaces can be reduced, thereby reducing stray light generation, optimizing the entire optical system, improving image quality, and ensuring display performance. For example, the ratio of the draft angle of the annular tooth structure 11 of the first Fresnel surface to the draft angle of the annular tooth structure 11 of 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 tips of the annular tooth structures 11 on both the first and second Fresnel surfaces are rounded, and the radius of the rounded corner of the first Fresnel surface annular tooth structure 11 is less than or equal to the radius of the rounded corner of the second Fresnel surface annular tooth structure 11. By matching the tips of the Fresnel surfaces, light reflection can be reduced, which facilitates the smooth entry of light into the rear optical system. At the same time, stray light generation can be reduced, improving image quality and ensuring display effect. For example, the ratio of the radius of the rounded corner of the first Fresnel surface annular tooth structure 11 to the radius of the rounded corner of the second Fresnel surface annular tooth structure 11 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, so 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 effective focal length f of the optical system and the total optical length TTL of the optical system satisfy: 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 the miniaturization of the optical system while ensuring the 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 the 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 the image light from the second side to ensure the display effect.

[0100] 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 rays from the second side, so as to reduce the situation where marginal light rays cannot enter the optical system, effectively reducing the occurrence of picture missing and improving the display effect.

[0101] In some alternative embodiments, referring to Figures 2, 4, 6, and 8, the contrast ratio at a spatial frequency of 30 lp / mm in the modulation transfer function curve of the optical system is greater than or equal to 0.05. In the modulation transfer function curve of the field of view, most field-of-view curves have a contrast ratio of not less than 0.1 at 30 lp / mm, which can guarantee full-field high-definition display.

[0102] In some alternative 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 beneficial to control the deflection angle of light to reduce the generation of stray light, while ensuring a uniform thickness distribution of the lens and reducing the sensitivity of the lens.

[0103] For example, a lens can be made of glass with a refractive index greater than or equal to 1.73 and less than or equal to 1.96. A lens can also be made of plastic with a refractive index greater than or equal to 1.51 and less than or equal to 1.66.

[0104] In some alternative embodiments, the field of view of the optical system is greater than or equal to 90 degrees. A large field of view allows large-angle image light from the second side to enter the optical system, thus avoiding incomplete display and ensuring optimal display quality.

[0105] In some alternative embodiments, at least two lenses are bonded together. This arrangement reduces the spacing between adjacent lenses, thereby reducing the overall optical length of the optical system and making the optical system thinner and lighter. For example, adjacent lenses can be bonded together using optical adhesives such as UV-curable adhesives or epoxy resins.

[0106] In some alternative embodiments, the lenses are all lenses with optical power. This arrangement helps to distribute the optical power of the optical system more evenly among the lenses, and facilitates a smooth transition of light to ensure display quality.

[0107] In some alternative embodiments, the center thickness of at least one lens is less than 8 mm. This arrangement prevents the center thickness of the lens from becoming excessively thick, which is beneficial for making the optical system thinner and lighter. For example, the center thickness of each lens is less than 8 mm.

[0108] In some alternative embodiments, the distance between any two adjacent lenses on the optical axis is less than or equal to 10 mm. This arrangement allows the distance between adjacent lenses to be controlled within a reasonable range, thereby controlling the overall optical length of the optical system and enabling miniaturization.

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

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

[0111] In some alternative 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 can help shorten the overall length of the optical system while ensuring the display effect.

[0112] In some alternative 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 can help shorten the overall length of the optical system while ensuring the display effect, thus achieving miniaturization.

[0113] In some optional embodiments, the side of each lens 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. At least four lenses are included, in sequence 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 absolute value of the radius of curvature of the sides of the first lens L1 to 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 sides of the first lens L1 to the fourth lens L4 within a reasonable range, the shape of the lenses is easily processed, avoiding the problem of low yield due to high processing difficulty.

[0114] In some optional embodiments, the radius of curvature R11 of the first side surface S1 of the first lens and the radius of curvature R12 of the second side surface S2 of the first lens satisfy: 0.2 ≤ |R11 / R12| ≤ 0.5. By controlling |R11 / R12| within a reasonable range, the radii of curvature of the two sides of the first lens L1 are limited, which helps to correct field curvature and ensure display effect.

[0115] In some optional embodiments, the radius of curvature R21 of the first side surface S3 of the second lens and the radius of curvature R22 of the second side surface S4 of the second lens satisfy: 2 ≤ |R21 / R22| ≤ 5. By controlling |R21 / R22| within a reasonable range, the radii of curvature of the two sides of the second lens L2 are limited, which helps to correct field curvature and ensure display effect.

[0116] In some optional embodiments, the radius of curvature R31 of the first side surface S5 of the third lens and the radius of curvature R32 of the second side surface S6 of the third lens satisfy: 0.2 ≤ |R31 / R32| ≤ 0.7. By controlling |R31 / R32| within a reasonable range, the radii of curvature of the two sides of the third lens L3 are limited, which helps to correct field curvature and ensure display effect.

[0117] In some optional embodiments, the radius of curvature R41 of the first side S7 of the fourth lens and the radius of curvature R42 of the second side S8 of the fourth lens satisfy: 0.2 ≤ |R41 / R42| ≤ 0.7. By controlling |R41 / R42| within a reasonable range, the radii of curvature of the two sides of the third lens L3 are limited, which helps to correct field curvature and ensure display effect.

[0118] The optical system disclosed herein employs four lenses, one of which is a double-sided Fresnel lens, simultaneously achieving high luminous efficiency, ultra-short focal length, ultra-thinness, a large field of view, and full-field high-definition display. Furthermore, the luminous efficiency of this optical system exceeds 50%, avoiding the drawbacks of low luminous efficiency and ghosting inherent in folding optical systems, which typically have a luminous efficiency below 25%. Therefore, the brightness requirements for the display screen S9 in a head-mounted display device using this optical system are reduced. For example, when the optical system is applied to VR lenses, the human eye requires a brightness of 100 to 150 nits. Using 150 nits as an example, the brightness of the display screen S9 in this disclosure is less than 300 nits, while the folding optical system requires a brightness of over 600 nits for the display screen S9. Clearly, the brightness of the display screen S9 in a head-mounted display device using a folding optical system is more than twice that of the display screen S9 in a head-mounted display device using a folding optical system. However, the higher brightness of the display screen S9 leads to greater wear and tear on the display screen S9, resulting not only in a shorter lifespan but also increased temperature in the head-mounted display device.

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

[0120] In one embodiment, referring to Figure 1, the optical system is a four-element optical system. The four lenses, from the first side to the second side, are the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4, respectively. Each lens has a first side surface near the first side and a second side surface near 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 value of the radius of curvature of all sides of the first lens L1 to the fourth lens L4 is greater than or equal to 5 mm and less than or equal to 70 mm.

[0122] The ratio of the radius of curvature R11 of the first side surface S1 of the first lens to the radius of curvature 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] The ratio of the radius of curvature R21 of the first side surface S3 of the second lens to the radius of curvature 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] The ratio of the radius of curvature R31 of the first side surface S5 of the third lens to the radius of curvature 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] The ratio of the radius of curvature R41 of the first side surface S7 of the fourth lens to the radius of curvature 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 in the range of 0-7 mm, the distance between the second lens L2 and the third lens L3 is in the range of 0-7 mm, and the distance between the third lens L3 and the fourth lens L4 is in 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, and 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] To ensure the optimal optical performance of the entire optical system and reduce stray light generation within the system, the two Fresnel annular tooth structures 11 need to be matched. From the first side to the second side, they are the first Fresnel surface and the second Fresnel surface, respectively. The ratio of the tooth height H1 of the first Fresnel annular tooth structure 11 to the tooth height H2 of the second Fresnel annular tooth structure 11 is H1 / H2 = 0.9.

[0132] The software simulation results show that, compared with the unmatched optical simulation within the tooth height range, the combination of the three elements within the range indicates that, in the process of designing an optical system, for an optical system containing multiple Fresnel lenses, the tooth height of the Fresnel lenses can be matched to optimize the entire optical system to a certain extent, thus ensuring the overall effect of the optical system.

[0133] The ratio of the maximum tooth width W1 of the annular tooth structure 11 on the first Fresnel surface to the maximum tooth width W2 of the annular tooth structure on 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 on the first Fresnel surface to the draft angle θ2 of the annular tooth structure on the second Fresnel surface is θ1 / θ2 = 1.

[0137] The luminous efficacy in this embodiment is 70%.

[0138] In another embodiment, please refer to Figure 3. The optical system is a four-element optical system. The four lenses are, from the first side to the second side, the first lens L1, the second lens L2, the third lens L3 and the fourth lens L4. Each lens has a first side surface near the first side and a second side surface near 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 value of the radius of curvature of all sides of the first lens L1 to the fourth lens L4 is greater than or equal to 5 mm and less than or equal to 80 mm.

[0140] The ratio of the radius of curvature R11 of the first side surface S1 of the first lens to the radius of curvature 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] The ratio of the radius of curvature R21 of the first side surface S3 of the second lens to the radius of curvature 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] The ratio of the radius of curvature R31 of the first side surface S5 of the third lens to the radius of curvature 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] The ratio of the radius of curvature R41 of the first side surface S7 of the fourth lens to the radius of curvature 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 in the range of 0-5 mm, the distance between the second lens L2 and the third lens L3 is in the range of 0-5 mm, and the distance between the third lens L3 and the fourth lens L4 is in 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, and 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] To ensure the optimal optical performance of the entire optical system and reduce stray light generation within the system, the two Fresnel annular tooth structures 11 need to be matched. From the first side to the second side, they are the first Fresnel surface and the second Fresnel surface, respectively. The ratio of the tooth height H1 of the first Fresnel annular tooth structure 11 to the tooth height H2 of the second Fresnel annular tooth structure 11 is H1 / H2 = 0.9.

[0150] The software simulation results show that, compared with the unmatched optical simulation within the tooth height range, the combination of the three elements within the range indicates that, in the process of designing an optical system, for an optical system containing multiple Fresnel lenses, the tooth height of the Fresnel lenses can be matched to optimize the entire optical system to a certain extent, thus ensuring the overall effect of the optical system.

[0151] The ratio of the maximum tooth width W1 of the annular tooth structure 11 on the first Fresnel surface to the maximum tooth width W2 of the annular tooth structure on 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 on the first Fresnel surface to the draft angle θ2 of the annular tooth structure on the second Fresnel surface is θ1 / θ2 = 1.

[0155] The luminous efficacy in this embodiment is 70%.

[0156] In another embodiment, please refer to Figure 5. The optical system is a four-element optical system. The four lenses are, from the first side to the second side, the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4. Each lens has a first side surface near the first side and a second side surface near 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 value of the radius of curvature of all sides of the first lens L1 to the fourth lens L4 is greater than or equal to 5 mm and less than or equal to 90 mm.

[0158] The ratio of the radius of curvature R11 of the first side surface S1 of the first lens to the radius of curvature 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] The ratio of the radius of curvature R21 of the first side surface S3 of the second lens to the radius of curvature 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] The ratio of the radius of curvature R31 of the first side surface S5 of the third lens to the radius of curvature 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] The ratio of the radius of curvature R41 of the first side surface S7 of the fourth lens to the radius of curvature 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 in the range of 0-8 mm, the distance between the second lens L2 and the third lens L3 is in the range of 0-8 mm, and the distance between the third lens L3 and the fourth lens L4 is in 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, and 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] To ensure optimal optical performance of the entire optical system and reduce stray light generation, the three Fresnel ring tooth structures 11 need to be matched. The first side of the double-sided Fresnel lens is the first Fresnel surface, the second side 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 first Fresnel surface ring tooth structure 11, the tooth height H2 of the second Fresnel surface ring tooth structure, and the tooth height H3 of the third Fresnel surface ring tooth structure is H1:H2:H3 = 2:3:4.

[0168] The software simulation results show that, compared with the unmatched optical simulation within the tooth height range, the combination of the three elements within the range indicates that, in the process of designing an optical system, for an optical system containing multiple Fresnel lenses, the tooth height of the Fresnel lenses can be matched to optimize the entire optical system to a certain extent, thus ensuring the overall effect of the optical system.

[0169] The ratio of the maximum tooth width W1 of the annular tooth structure 11 on the first Fresnel surface, the maximum tooth width W2 of the annular tooth structure on the second Fresnel surface, and the maximum tooth width W3 of the annular tooth structure 11 on 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 to the radius R1:R2:R3 is 2:2:3.

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

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

[0173] The luminous efficacy in this embodiment is 70%.

[0174] In another embodiment, please refer to Figure 7. The optical system is a four-element optical system. The four lenses are, from the first side to the second side, the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4. Each lens has a first side surface near the first side and a second side surface near 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, and the first side surface S5 and the second side surface S6 of the third lens are both Fresnel surfaces.

[0175] The absolute value of the radius of curvature of all sides of the first lens L1 to the fourth lens L4 is greater than or equal to 5 mm and less than or equal to 90 mm.

[0176] The ratio of the radius of curvature R11 of the first side surface S1 of the first lens to the radius of curvature 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] The ratio of the radius of curvature R21 of the first side surface S3 of the second lens to the radius of curvature 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] The ratio of the radius of curvature R31 of the first side surface S5 of the third lens to the radius of curvature 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] The ratio of the radius of curvature R41 of the first side surface S7 of the fourth lens to the radius of curvature 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 in the range of 0-8 mm, the distance between the second lens L2 and the third lens L3 is in the range of 0-9 mm, and the distance between the third lens L3 and the fourth lens L4 is in 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, and 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] To ensure optimal optical performance of the entire optical system and reduce stray light generation, the three Fresnel ring tooth structures 11 need to be matched. The first side of the double-sided Fresnel lens is the first Fresnel surface, the second side 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 first Fresnel surface ring tooth structure 11, the tooth height H2 of the second Fresnel surface ring tooth structure, and the tooth height H3 of the third Fresnel surface ring tooth structure is H1:H2:H3 = 2:3:4.

[0186] The software simulation results show that, compared with the unmatched optical simulation within the tooth height range, the combination of the three elements within the range indicates that, in the process of designing an optical system, for an optical system containing multiple Fresnel lenses, the tooth height of the Fresnel lenses can be matched to optimize the entire optical system to a certain extent, thus ensuring the overall effect of the optical system.

[0187] The ratio of the maximum tooth width W1 of the annular tooth structure 11 on the first Fresnel surface, the maximum tooth width W2 of the annular tooth structure on the second Fresnel surface, and the maximum tooth width W3 of the annular tooth structure 11 on 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 to the radius R1:R2:R3 is 2:2:3.

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

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

[0191] The luminous efficacy in this embodiment is 70%.

[0192] On another front, a display device is provided, comprising a display screen S9 and the aforementioned optical system. The display screen S9 is located on the second side of the optical system, and the image from the display screen S9 is transmitted to the first side via the optical system. The display screen S9 is positioned at the imaging surface of the optical system, and the display device having the aforementioned optical system has the advantages of being thin and light, and having good display effects.

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

[0194] The display 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 one alternative 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. Alternatively, the diagonal length of the display screen S9 is the same as the image height of the optical system mounted therein.

[0196] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

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

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

3. The optical system of claim 1, wherein, The Fresnel surface comprises a coaxially arranged central part and a tooth ring part, the tooth ring part surrounds the central part, the tooth ring part has a plurality of coaxially sleeved annular tooth structures, a ratio of a tooth height of the annular tooth structure to a 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 of any one of claims 1 to 3, wherein, The Fresnel surface comprises a coaxially arranged central part and a tooth ring part, the tooth ring part has a plurality of coaxially sleeved annular tooth structures, the annular tooth structures satisfy at least one of the following conditions: Tooth widths of the annular tooth structures increase in a direction close to the central part; 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; A tooth tip of the annular tooth structure is a rounded corner; A number of the annular tooth structures is less than 50; A draft angle of the annular tooth structure is greater than 0 and less than or equal to 10°.

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

6. The optical system of any one of claims 1 to 3, wherein, The Fresnel surface comprises a coaxially arranged central part and a tooth ring part, the tooth ring part has a plurality of coaxially sleeved annular tooth structures, a Fresnel surface of the double-sided Fresnel lens facing the first side is a first Fresnel surface, a Fresnel surface of the double-sided Fresnel lens facing the second side is a second Fresnel surface, the annular tooth structures of the first Fresnel surface and the annular tooth structures 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 tip of the annular tooth structure of the first Fresnel surface and the second Fresnel surface is a rounded corner, a radius of the rounded corner of the annular tooth structure of the first Fresnel surface is less than or equal to a 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, the 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, the 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, 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. The optical system has four lenses, and the effective focal length f of the optical system and the total track length TTL of the optical system satisfy: 0.1 < f / TTL < 8.

5.

8. The optical system of any one of claims 1 to 7, wherein, The effective focal length f of the optical system satisfies: f ≤ 17 mm.

9. The optical system of any one of claims 1 to 8, wherein, The total track length TTL of the optical system satisfies: TTL ≤ 30 mm.

10. The optical system of any one of claims 1 to 9, wherein, The lens closest to the second side among the at least four lenses is concave toward the side surface of the second side.

11. The optical system of any one of claims 1 to 10, wherein, The absolute value of the effective focal length of the lens closest to the second side among all the lenses is greater than 8 mm.

12. The optical system of any one of claims 1 to 11, wherein, The refractive index of the lens is greater than or equal to 1 and less than or equal to 2.

1.

13. The optical system of any one of claims 1 to 12, wherein, The field of view angle of the optical system is greater than or equal to 90 degrees.

14. The optical system of any one of claims 1 to 13, wherein, At least two of the lenses are arranged in abutment.

15. The optical system of any one of claims 1 to 14, wherein, All the lenses are lenses with optical power.

16. The optical system of any one of claims 1 to 15, wherein, The center thickness of at least one of the lenses is less than 8 mm.

17. The optical system of any one of claims 1 to 16, wherein, The interval between two adjacent lenses among all the lenses on the optical axis is less than or equal to 10 mm.

18. 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 in sequence from the first side to the second side, and the optical system satisfies at least one of the following conditions:

19. The optical system of claim 18, wherein, The interval between the first lens and the second lens on the optical axis is less than or equal to 8 mm; The interval between the second lens and the third lens on the optical axis is less than or equal to 9 mm; The interval between the third lens and the fourth lens on the optical axis is less than or equal to 10 mm. The at least four lenses include a first lens, a second lens, a third lens and a fourth lens arranged in sequence from the first side to the second side, and the absolute value of the curvature radius of the side surface of the first lens to the fourth lens is greater than or equal to 5 mm and less than or equal to 90 mm.

20. The optical system of any one of claims 1-17, wherein, The side surface close to the first side in each lens 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 in sequence from the first side to the second side, and the optical system satisfies at least one of the following conditions:

21. The optical system of any one of claims 1-17, wherein, ​ The radius of curvature R11 of the first side of the first lens and the radius of curvature R12 of the second side of the first lens satisfy: 0.2≤︱R11 / R12︱≤0.5; The radius of curvature R21 of the first side of the second lens and the radius of curvature R22 of the second side of the second lens satisfy: 2≤︱R21 / R22︱≤5; The radius of curvature R31 of the first side of the third lens and the radius of curvature R32 of the second side of the third lens satisfy: 0.2≤︱R31 / R32︱≤0.7; The radius of curvature R41 of the first side of the fourth lens and the radius of curvature R42 of the second side of the fourth lens satisfy: 0.2≤︱R41 / R42︱≤0.

7.

22. A display device, wherein, comprising: a display screen; the optical system of any one of claims 1 to 21, the display screen being located at the second side of the optical system, the picture light of the display screen being transmitted to the first side through the optical system.

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