Optical system

Abstract

The utility model discloses an optical system. The optical system sequentially comprises a first lens, a reflective polarizing element, a first quarter-wave plate, a second lens, a third lens, a partial reflection element, a fourth lens, a second quarter-wave plate and a polarizing film from a first side to a second side along an optical axis, the first lens has positive focal power, the first side surface of the first lens is a convex surface, and the second side surface is a concave surface; the second lens has positive focal power, the first side surface of the second lens is a plane, and the second side surface is a convex surface; the third lens has negative focal power, and the first side surface of the third lens is a concave surface; the second side surface of the fourth lens is a plane; wherein the effective focal length f1 of the first lens and the effective focal length f2 of the second lens meet the formula: 0.2 lt; f1 / f2 < = 0.5; the combined focal length fz1 of the first lens, the reflective polarizing element, the first quarter-wave plate and the second lens, the curvature radius R1 of the first side surface of the first lens and the curvature radius R4 of the second side surface of the second lens satisfy 0.4 lt; fz1 / R1 + R4lt; and 1.2.

Description

Technical Field

[0001] This application relates to the field of optical devices, and particularly to a catadioptric optical system. Background Art

[0002] The optical systems of virtual reality devices are mainly divided into three types: optical systems using aspherical lenses, optical systems using Fresnel lenses, and catadioptric optical systems. Among them, the catadioptric optical system is a major innovation in the optical system itself and reserves space for the overall design of virtual reality devices, and has become the mainstream trend of research and development.

[0003] The catadioptric optical system shortens the body length of the optical system by refracting the light path, thereby shifting the center of gravity of the virtual reality device backward and enhancing the user experience. However, the existing catadioptric optical systems usually use two lenses, which results in a relatively blurred image and poor imaging quality of the catadioptric optical system. Summary of the Utility Model

[0004] This application provides an optical system that can at least solve or partially solve at least one problem or other problems existing in the prior art.

[0005] On the one hand, this application provides such an optical system, which sequentially includes a first lens, a second lens, a third lens, and a fourth lens along the optical axis from the first side to the second side; the first lens has a positive optical power, its first side is a convex surface, and its second side is a concave surface; the second lens has a positive optical power, its first side is a flat surface, and its second side is a convex surface; the third lens has a negative optical power, its first side is a concave surface; the fourth lens has an optical power, and its second side is a flat surface. Wherein, the optical system further includes a first quarter-wave plate, a reflective polarizing element, a partial reflection element, a second quarter-wave plate, and a polarizer; the first quarter-wave plate is disposed on the first side of the second lens; the reflective polarizing element is disposed on the first side of the first quarter-wave plate; the partial reflection element is disposed on the second side of the third lens; the second quarter-wave plate is disposed on the second side of the fourth lens; the polarizer is disposed on the second side of the second quarter-wave plate. The effective focal length f1 of the first lens and the effective focal length f2 of the second lens satisfy: 0.2 < f1 / f2 ≤ 0.5; the combined focal length fz1 of the first lens, the reflective polarizing element, the first quarter-wave plate, and the second lens, the curvature radius R1 of the first side of the first lens, and the curvature radius R4 of the second side of the second lens satisfy: 0.4 < fz1 / |R1 + R4| < 1.2.

[0006] According to an exemplary embodiment of the present application, the curvature radius R5 of the first side of the third lens and the effective focal length f3 of the third lens satisfy: 0.2 < R5 / f3 ≤ 0.8.

[0007] According to an exemplary embodiment of the present application, the central thickness CT1 of the first lens on the optical axis, the central thickness CTR of the reflective polarizing element on the optical axis, the central thickness CTQ1 of the first quarter-wave plate on the optical axis, and the central thickness CT2 of the second lens on the optical axis satisfy: 0.5 < (CT2 + CTR + CTQ1) / CT1 < 0.9.

[0008] According to an exemplary embodiment of the present application, the effective focal length f4 of the fourth lens and the combined focal length fz2 of the third lens, the fourth lens, the second quarter-wave plate, and the polarizer satisfy: 0.4 < f4 / fz2 < 1.6.

[0009] According to an exemplary embodiment of the present application, the Abbe number V1 of the first lens and the refractive index N1 of the first lens satisfy: 37.5 < V1 / N1 < 47.3.

[0010] According to an exemplary embodiment of the present application, the radius of curvature R7 of the first side surface of the fourth lens and the effective focal length f4 of the fourth lens satisfy: 0.5 < R7 / f4 < 0.9.

[0011] According to an exemplary embodiment of the present application, the axial distance SAG11 between the intersection of the first side surface of the first lens and the optical axis and the vertex of the effective semi-aperture of the first side surface of the first lens, the axial distance SAG12 between the intersection of the second side surface of the first lens and the optical axis and the vertex of the effective semi-aperture of the second side surface of the first lens, and the radius of curvature R1 of the first side surface of the first lens satisfy: 2.7 < R1 / (SAG11 + SAG12) < 3.7.

[0012] According to an exemplary embodiment of the present application, the axial distance SAG41 between the intersection of the first side surface of the fourth lens and the optical axis and the vertex of the effective semi-aperture of the first side surface of the fourth lens and the central thickness CT4 of the fourth lens on the optical axis satisfy: 0.3 < |SAG41| / CT4 < 0.7.

[0013] According to an exemplary embodiment of the present application, the central thickness CT3 of the third lens on the optical axis and the edge thickness ET3 of the third lens satisfy: 0.7 < CT3 / ET3 < 1.0.

[0014] According to an exemplary embodiment of the present application, the axial distance TD from the first side surface of the first lens to the second side surface of the fourth lens, the total effective focal length f of the optical system, and the maximum field of view FOV of the optical system satisfy: 1.8 < TD / (f × tan(FOV)) < 2.0.

[0015] According to an exemplary embodiment of the present application, an image plane is provided on the second side of the optical system, and the on-axis distance TTL from the first side surface of the first lens to the image plane and the total effective focal length f of the optical system satisfy: 0.6 < TTL / f < 0.7.

[0016] According to an exemplary embodiment of the present application, an image plane is provided on the second side of the optical system, and the on-axis distance BFL from the second side surface of the fourth lens to the image plane, the central thickness CTQ2 of the second quarter-wave plate on the optical axis, and the central thickness CTL of the polarizer on the optical axis satisfy: 8.2 < BFL / (CTQ2 + CTL) < 9.1.

[0017] According to an exemplary embodiment of the present application, the sum ∑CT of the central thicknesses of the first lens, the second lens, the third lens, and the fourth lens on the optical axis and the entrance pupil diameter EPD of the optical system satisfy: 0.3 < ∑CT / EPD < 1.0.

[0018] According to an exemplary embodiment of the present application, the total effective focal length f of the optical system and the radius of curvature R2 of the second side surface of the first lens satisfy: 0.2 < f / R2 < 1.2.

[0019] The optical system provided by the present application uses four lenses, reasonably configures the optical power of the four lenses and makes the optical system satisfy "0.2 < f1 / f2 ≤ 0.5", which is beneficial to improving the imaging quality of the optical system; at the same time, by restricting the ratio of the combined focal length of the combination of the first lens, the reflective polarizing element, the first quarter-wave plate, and the second lens to the sum of the radii of curvature of the first side surface of the first lens and the second side surface of the second lens, it is beneficial to provide a wider field of view angle, enabling users to see more display content, enhancing the immersion and experience of users, and also being able to reduce or eliminate optical problems such as distortion and aberration, and improving the clarity and accuracy of the image formed by the optical system. Description of the Drawings

[0020] Other features, objects, and advantages of the present application will become more apparent by reading the detailed description of the non-limiting embodiments with reference to the following drawings. Among them:

[0021] Figure 1 Shows a schematic structural diagram of the optical system according to Embodiment 1 of the present application;

[0022] Figures 2A to 2C Respectively show the axial chromatic aberration curve, astigmatism curve, and distortion curve of the optical system according to Embodiment 1 of the present application;

[0023] Figure 3 Shows the modulation transfer function (MTF) curve of the optical system according to Embodiment 1 of the present application;

[0024] Figure 4 Shows a schematic structural diagram of the optical system according to Embodiment 2 of the present application;

[0025] Figures 5A to 5C Respectively show the axial chromatic aberration curve, astigmatism curve and distortion curve of the optical system according to Embodiment 2 of the present application;

[0026] Figure 6 Shows the modulation transfer function curve of the optical system according to Embodiment 2 of the present application;

[0027] Figure 7 Shows a schematic structural diagram of the optical system according to Embodiment 3 of the present application;

[0028] Figures 8A to 8C Respectively show the axial chromatic aberration curve, astigmatism curve and distortion curve of the optical system according to Embodiment 3 of the present application;

[0029] Figure 9 Shows the modulation transfer function curve of the optical system according to Embodiment 3 of the present application;

[0030] Figure 10 Shows a schematic structural diagram of the optical system according to Embodiment 4 of the present application;

[0031] Figures 11A to 11C Respectively show the axial chromatic aberration curve, astigmatism curve and distortion curve of the optical system according to Embodiment 4 of the present application;

[0032] Figure 12 Shows the modulation transfer function curve of the optical system according to Embodiment 4 of the present application;

[0033] Figure 13 Shows a schematic structural diagram of the optical system according to Embodiment 5 of the present application;

[0034] Figures 14A to 14C Respectively show the axial chromatic aberration curve, astigmatism curve and distortion curve of the optical system according to Embodiment 5 of the present application; and

[0035] Figure 15 Shows the modulation transfer function curve of the optical system according to Embodiment 5 of the present application. Detailed implementation manners

[0036] To better understand the present application, more detailed descriptions of various aspects of the present application will be made with reference to the accompanying drawings. It should be understood that these detailed descriptions are only descriptions of the exemplary embodiments of the present application and do not limit the scope of the present application in any way. Throughout the specification, the same reference numerals refer to the same elements.

[0037] It should be noted that in this specification, the expressions such as first, second, etc. are only used to distinguish one feature from another, and do not represent any limitation on the features. Therefore, without departing from the teachings of this application, the first lens discussed below may also be referred to as the second lens.

[0038] In the drawings, for the sake of clarity, the thickness, dimensions, and shape of the lenses have been slightly exaggerated. Specifically, the spherical or aspherical shapes shown in the drawings are shown by way of example. That is, the spherical or aspherical shapes are not limited to the spherical or aspherical shapes shown in the drawings. The drawings are only examples and are not drawn to an exact scale.

[0039] In this context, 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 not defined, 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 not defined, it means that the lens surface is concave at least in the paraxial region. The surface of each lens closest to the first side (e.g., the human eye side) is called the first side surface of the lens, and the surface of each lens closest to the second side (e.g., the display screen side) is called the second side surface of the lens.

[0040] It should also be understood that the terms "comprises", "comprising", "has", "including", and / or "including having", when used in this specification, denote the presence of the stated features, elements, and / or components, but do not preclude the presence or addition of one or more other features, elements, components, and / or combinations thereof. In addition, when describing the embodiments of this application, the use of "may" means "one or more embodiments of this application". And the term "exemplary" is intended to refer to an example or illustration.

[0041] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It should also be understood that terms (such as those defined in a common dictionary) should be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0042] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments may be combined with each other. The following will refer to the drawings and combine with the embodiments to detail this application.

[0043] The following details the features, principles, and other aspects of this application.

[0044] Refer to Figure 1 、 Figure 4 、 Figure 7 、 Figure 10 and Figure 13, a first aspect of the present application provides an optical system, which may include a first lens, a second lens, a third lens, and a fourth lens arranged in sequence along the optical axis from the first side to the second side.

[0045] In an exemplary embodiment, the first lens may have a positive optical power. The second lens may have a positive optical power. The third lens may have a negative optical power. The fourth lens may have a positive optical power or a negative optical power. Reasonably configuring the optical powers of the respective lenses is beneficial to improving the imaging quality of the optical system.

[0046] In an exemplary embodiment, the first side surface of the first lens is a convex surface, and the second side surface is a concave surface.

[0047] In an exemplary embodiment, the first side surface of the second lens is a flat surface, and the second side surface is a convex surface.

[0048] In an exemplary embodiment, the first side surface of the third lens is a concave surface, and the second side surface is a convex surface or a concave surface.

[0049] In an exemplary embodiment, the first side surface of the fourth lens is a convex surface or a concave surface, and the second side surface is a flat surface.

[0050] In an exemplary embodiment, the optical system may further include a reflective polarizing element and a first quarter-wave plate. The first quarter-wave plate may be disposed on the first side surface of the second lens. The reflective polarizing element may be disposed on the first side surface of the first quarter-wave plate.

[0051] In an exemplary embodiment, the first side surface of the second lens is a flat surface. The reflective polarizing element and the first quarter-wave plate are bonded and attached to the first side surface of the second lens, wherein the first quarter-wave plate is closer to the second lens than the reflective polarizing element. By combining the reflective polarizing element and the first quarter-wave plate together and then attaching them to the first flat side surface of the second lens, the attachment process difficulty can be reduced, the attachment quality can be improved, and thus the performance of the optical system can be improved.

[0052] In an exemplary embodiment, the optical system may further include a partial reflection element. The partial reflection element may be disposed on the second side surface of the third lens. The partial reflection element has a semi-transmissive and semi-reflective effect on light. By disposing the partial reflection element on the second side surface of the third lens and combining it with the reflective polarizing element and the first quarter-wave plate, the light can be refracted and reflected multiple times, effectively reducing the body length of the optical system.

[0053] In an exemplary embodiment, the optical system may further include a second quarter-wave plate and a polarizer. The second quarter-wave plate may be disposed on the second side surface of the fourth lens. The polarizer may be disposed on the second side surface of the second quarter-wave plate. The polarizer is used to convert natural light emitted from the display screen on the second side into linearly polarized light, and the second quarter-wave plate is used to convert the linearly polarized light from the polarizer into circularly polarized light. By using the second quarter-wave plate and the polarizer, the natural light emitted from the display screen can be converted into circularly polarized light, thereby reducing the influence of material stress of the components between the display screen and the polarizer and improving the contrast of the optical system.

[0054] In an exemplary embodiment, the second side surface of the fourth lens is a plane. The second quarter-wave plate and the polarizer are bonded and attached to the second side surface of the fourth lens, wherein the second quarter-wave plate is closer to the fourth lens than the polarizer. By combining the second quarter-wave plate and the polarizer together and then attaching them to the second side plane of the fourth lens, the difficulty of the attachment process can be reduced, the attachment quality can be improved, and thus the performance of the optical system can be improved.

[0055] In an exemplary embodiment, the optical system may further include a diaphragm, which is disposed between the first side and the first lens. The image light from the second side passes through the polarizer, the second quarter-wave plate, the fourth lens, the third lens, the second lens, the first quarter-wave plate, the reflective polarizing element, the first lens and other multiple refractions and reflections and is finally projected onto the eyes of the user on the first side.

[0056] In an exemplary embodiment, the first side may be, for example, the human eye side, and the second side may be, for example, the display screen side. Correspondingly, the first side surfaces of the respective components (the first lens, the second lens, the third lens, the fourth lens, the first quarter-wave plate, the second quarter-wave plate) may be referred to as the near-eye side surfaces, and the second side surfaces may be referred to as the near-screen side surfaces.

[0057] In an exemplary embodiment, an image plane may be provided on the second side of the optical system. A display screen may be provided on the image plane. Image light from the display screen may sequentially pass through a polarizer, a second quarter-wave plate, a fourth lens, a third lens, a second lens, and a first quarter-wave plate, and reach a reflective polarizing element, and then be reflected at the reflective polarizing element to form first reflected image light. The first reflected image light passes through the first quarter-wave plate, the second lens, the third lens and reaches a partial reflection element on the second side surface of the third lens, and then is reflected at the partial reflection element to form second reflected image light. The second reflected image light sequentially passes through the third lens, the second lens, the first quarter-wave plate, the reflective polarizing element, the first lens to the aperture stop and is finally projected into the user's eyes. The optical system provided in this application folds the required optical path in a manner of combining light reflection and refraction without affecting the projection quality, effectively shortening the body length of the optical system.

[0058] In an exemplary embodiment, the effective focal length f1 of the first lens and the effective focal length f2 of the second lens may satisfy: 0.2 < f1 / f2 ≤ 0.5; the combined focal length fz1 of the first lens, the reflective polarizing element, the first quarter-wave plate, and the second lens, the curvature radius R1 of the first side surface of the first lens, and the curvature radius R4 of the second side surface of the second lens may satisfy: 0.4 < fz1 / |R1 + R4| < 1.2. By controlling the optical system to satisfy "0.2 < f1 / f2 ≤ 0.5", it is beneficial to improve the imaging quality of the optical system; at the same time, by restricting the ratio of the combined focal length of the first lens, the reflective polarizing element, the first quarter-wave plate, and the second lens to the sum of the curvature radii of the first side surface of the first lens and the second side surface of the second lens, it is beneficial to provide a wider viewing angle, enabling the user to see more display content (such as virtual reality information or augmented reality information), enhancing the user's immersion and experience, and also being able to reduce or eliminate problems such as distortion and aberration, improving the clarity and accuracy of the image formed by the optical system.

[0059] In an exemplary embodiment, the curvature radius R5 of the first side surface of the third lens and the effective focal length f3 of the third lens may satisfy: 0.2 < R5 / f3 ≤ 0.8. By controlling the ratio of the curvature radius of the first side surface of the third lens to the effective focal length of the third lens, the shape of the third lens can be restricted, ensuring that the refraction and focusing effects of light inside the third lens meet the requirements, and making the propagation of light inside the third lens more reasonable and effective.

[0060] In an exemplary embodiment, the central thickness CT1 of the first lens on the optical axis, the central thickness CTR of the reflective polarizing element on the optical axis, the central thickness CTQ1 of the first quarter-wave plate on the optical axis, and the central thickness CT2 of the second lens on the optical axis may satisfy: 0.5 < (CT2 + CTR + CTQ1) / CT1 < 0.9. By controlling the ratio of the sum of the central thicknesses of the reflective polarizing element, the first quarter-wave plate, and the second lens to the central thickness of the first lens, the body length of the optical system can be constrained within a reasonable range, and at the same time, it is beneficial to the adhesion of the reflective polarizing element and the first quarter-wave plate.

[0061] In an exemplary embodiment, the effective focal length f4 of the fourth lens and the combined focal length fz2 of the third lens, the fourth lens, the second quarter-wave plate, and the polarizer may satisfy: 0.4 < f4 / fz2 < 1.6. By controlling the ratio of the effective focal length of the fourth lens to the combined focal length of the third lens, the fourth lens, the second quarter-wave plate, and the polarizer, it is beneficial to reasonably allocate the focal lengths of the third lens and the fourth lens, thereby ensuring that the focusing effect and transmission effect of light within the optical system meet the requirements.

[0062] In an exemplary embodiment, the Abbe number V1 of the first lens and the refractive index N1 of the first lens may satisfy: 37.5 < V1 / N1 < 47.3. By controlling the ratio of the Abbe number of the first lens to the refractive index, the influence of the dispersion effect on the image formed by the optical system can be reduced, the color accuracy and consistency of the optical system can be improved, and at the same time, the optical system can cover a wider spectral range to meet the application requirements of different wavelengths.

[0063] In an exemplary embodiment, the radius of curvature R7 of the first surface of the fourth lens and the effective focal length f4 of the fourth lens may satisfy: 0.5 < R7 / f4 < 0.9. By controlling the ratio of the radius of curvature of the first surface of the fourth lens to the effective focal length of the fourth lens, the shape of the fourth lens can be constrained, ensuring that the refraction and focusing effects of light within the fourth lens meet the requirements, and at the same time, reducing the sensitivity of the optical system to changes in the lens shape and improving the performance and stability of the optical system.

[0064] In an exemplary embodiment, the axial distance SAG11 between the intersection of the first side surface of the first lens and the optical axis and the vertex of the effective semi-aperture of the first side surface of the first lens, the axial distance SAG12 between the intersection of the second side surface of the first lens and the optical axis and the vertex of the effective semi-aperture of the second side surface of the first lens, and the radius of curvature R1 of the first side surface of the first lens may satisfy: 2.7 < R1 / (SAG11 + SAG12) < 3.7. By controlling the above conditional expression, the radius of curvature of the first side surface of the first lens and the sag heights of the first side surface and the second side surface of the first lens can be constrained, thereby restricting the surface shape of the first lens, making the refraction and focusing effects of light on the surface of the first lens more compliant with requirements.

[0065] In an exemplary embodiment, the axial distance SAG41 between the intersection of the first side surface of the fourth lens and the optical axis and the vertex of the effective semi-aperture of the first side surface of the fourth lens and the central thickness CT4 of the fourth lens on the optical axis may satisfy: 0.3 < |SAG41| / CT4 < 0.7. By controlling the above conditional expression, the shape of the fourth lens can be constrained, making the refraction and focusing effects of light on the surface of the fourth lens more compliant with requirements. At the same time, it helps to improve the imaging quality of the optical system and reduce the forming difficulty of the fourth lens.

[0066] In an exemplary embodiment, the central thickness CT3 of the third lens on the optical axis and the edge thickness ET3 of the third lens may satisfy: 0.7 < CT3 / ET3 < 1.0. By controlling the ratio of the central thickness to the edge thickness of the third lens, the thickness of the third lens can be ensured to be evenly distributed at different positions, reducing the influence of the thickness non-uniformity of the third lens on the imaging quality of the optical system. At the same time, it helps to improve the forming yield of the third lens.

[0067] In an exemplary embodiment, the axial distance TD from the first side surface of the first lens to the second side surface of the fourth lens, the total effective focal length f of the optical system, and the maximum field of view FOV of the optical system satisfy: 1.8 < TD / (f × tan(FOV)) < 2.0. By controlling the above conditional expression, the maximum field of view, the total effective focal length of the optical system, and the axial distance from the first side surface of the first lens to the second side surface of the fourth lens can be constrained, ensuring that the propagation and focusing effects of light in the optical system meet the requirements. At the same time, it can also reduce the sensitivity of the optical system to changes in the total effective focal length and the field of view, improving the performance and stability of the optical system.

[0068] In an exemplary embodiment, the on-axis distance TTL from the first side surface of the first lens to the image plane and the total effective focal length f of the optical system may satisfy: 0.6 < TTL / f < 0.7. By constraining the ratio of the on-axis distance from the first side surface of the first lens to the image plane to the total effective focal length of the optical system within a reasonable range, a compact design of the optical system can be achieved, reducing the volume and weight of the optical system; meanwhile, it is also helpful for the focusing and transmission of light, thereby ensuring that the optical system achieves a good imaging effect.

[0069] In an exemplary embodiment, the on-axis distance BFL from the second side surface of the fourth lens to the image plane, the central thickness CTQ2 of the second quarter-wave plate on the optical axis, and the central thickness CTL of the polarizer on the optical axis may satisfy: 8.2 < BFL / (CTQ2 + CTL) < 9.1. By controlling the ratio of the on-axis distance from the second side surface of the fourth lens to the image plane to the sum of the central thicknesses of the second quarter-wave plate and the polarizer, an indirect constraint on the total effective focal length of the optical system can be achieved, enabling the optical system to provide clear imaging within the expected working distance range; meanwhile, it can also indirectly constrain the air gap between the lenses, which is beneficial to realizing the thin and light design of the optical system.

[0070] In an exemplary embodiment, the sum ∑CT of the central thicknesses of the first lens, the second lens, the third lens, and the fourth lens on the optical axis and the entrance pupil diameter EPD of the optical system may satisfy: 0.3 < ∑CT / EPD < 1.0. By controlling the ratio of the sum of the central thicknesses of the first lens, the second lens, the third lens, and the fourth lens to the entrance pupil diameter of the optical system, a compact design of the optical system can be achieved, reducing the volume and size of the optical system; meanwhile, it is also helpful for reducing the sensitivity of the optical system to thickness changes and incident light changes, improving the performance and stability of the optical system.

[0071] In an exemplary embodiment, the total effective focal length f of the optical system and the curvature radius R2 of the second side surface of the first lens may satisfy: 0.2 < f / R2 < 1.2. By controlling the ratio of the total effective focal length of the optical system to the curvature radius of the second side surface of the first lens, the aberration and distortion can be reduced, improving the clarity, contrast, and accuracy of the image formed by the optical system; meanwhile, it is also helpful for the focusing and transmission of light, thereby ensuring that the optical system achieves a good imaging effect.

[0072] The optical system according to the above-described embodiments of the present application may employ multiple lenses, such as the four lenses described above. By reasonably allocating the parameters of the reflective polarizing element, the first quarter-wave plate, the second quarter-wave plate, the polarizer, and each lens, the body length of the optical system can be reduced, the imaging quality of the optical system can be improved, and the user's immersion and experience can be enhanced. The optical system configured as described above has characteristics such as miniaturization and good imaging quality, and can well meet the usage requirements of various portable electronic products in the projection scenario.

[0073] In an embodiment of the present application, at least one of the surfaces of the second lens, the third lens, and the fourth lens is an aspherical surface. The characteristics of an aspherical lens are that the curvature changes continuously from the center of the lens to the periphery of the lens. Different from a spherical lens with a constant curvature from the center of the lens to the periphery, an aspherical lens has better curvature radius characteristics and has the advantages of improving distortion aberration and astigmatism aberration. After using an aspherical lens, it is possible to eliminate as much as possible the aberration that appears during imaging, thereby improving the imaging quality.

[0074] A second aspect of the present application provides an optical system that includes a first lens, a second lens, a third lens, and a fourth lens arranged in sequence along the optical axis from a first side to a second side. The first lens has a positive optical power, its first side is a convex surface, and its second side is a concave surface. The second lens has a positive optical power, its first side is a flat surface, and its second side is a convex surface. The third lens has a negative optical power, its first side is a concave surface. The fourth lens has an optical power, and its second side is a flat surface. The optical system further includes a first quarter-wave plate, a reflective polarizing element, a partial reflection element, a second quarter-wave plate, and a polarizer. The first quarter-wave plate is disposed on the first side of the second lens. The reflective polarizing element is disposed on the first side of the first quarter-wave plate. The partial reflection element is disposed on the second side of the third lens. The second quarter-wave plate is disposed on the second side of the fourth lens. The polarizer is disposed on the second side of the second quarter-wave plate.

[0075] Among them, the effective focal length f1 of the first lens and the effective focal length f2 of the second lens can satisfy: 0.2 < f1 / f2 ≤ 0.5; the axial distance BFL from the second side of the fourth lens to the image plane, the central thickness CTQ2 of the second quarter-wave plate on the optical axis, and the central thickness CTL of the polarizer on the optical axis can satisfy: 8.2 < BFL / (CTQ2 + CTL) < 9.1. The optical system provided by this application uses four lenses, reasonably configuring the optical power of the four lenses and making the optical system satisfy "0.2 < f1 / f2 ≤ 0.5", which is beneficial to improving the imaging quality of the optical system; at the same time, by cooperating to limit the ratio of the axial distance from the second side of the fourth lens to the image plane to the sum of the central thicknesses of the second quarter-wave plate and the polarizer, the total effective focal length of the optical system can be indirectly constrained, so that the optical system can provide clear imaging within the expected working distance range; it can also indirectly constrain the air gap between the lenses, which is beneficial to realizing the thin and light of the optical system.

[0076] However, those skilled in the art should understand that without departing from the technical solutions claimed in this application, the number of lenses constituting the optical system can be changed to obtain the various results and advantages described in this specification.

[0077] The following further describes specific embodiments of the optical system applicable to the above embodiments with reference to the accompanying drawings.

[0078] Example 1

[0079] The following refers to Figure 1 、 Figures 2A to 2C and Figure 3 Describe the optical system according to Embodiment 1 of this application.

[0080] As Figure 1 shown, the optical system may include a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, and a polarizer LP arranged in sequence along the optical axis from the first side to the second side. The aperture stop STO may be disposed between the first side and the first lens E1. In this embodiment, the first side refers to the human eye side, and the second side refers to the display screen side. The first side of each element is called the near-eye side, and the second side is called the near-screen side.

[0081] The first lens E1 has a positive optical power. Its side S1 close to the human eye is convex, and its side S2 close to the screen is concave. The second lens E2 has a positive optical power. Its side S3 close to the human eye is flat, and its side S4 close to the screen is convex. The third lens E3 has a negative optical power. Its side S5 close to the human eye is concave, and its side S6 close to the screen is convex. The fourth lens E4 has a positive optical power. Its side S7 close to the human eye is convex, and its side S8 close to the screen is flat. The reflective polarizing element RP and the first quarter-wave plate QWP1 are attached to the side S3 of the second lens E2 close to the human eye. The partial reflection element BS is attached to the side S6 of the third lens E3 close to the screen. The second quarter-wave plate QWP2 and the polarizer LP are attached to the side S8 of the fourth lens E4 close to the screen.

[0082] In this example, an image plane IMG can be provided on the second side of the optical system. The image plane IMG can be provided with a display screen, for example. The image light from the image plane IMG sequentially passes through the polarizer LP, the second quarter-wave plate QWP2, the fourth lens E4, the third lens E3, the second lens E2, the first quarter-wave plate QWP1 and reaches the reflective polarizing element RP, where the first reflection occurs. The light after the first reflection passes through the first quarter-wave plate QWP1, the second lens E2, the third lens E3 and reaches the partial reflection element BS located on the side S6 of the third lens E3 close to the screen, where the second reflection occurs. The light after the second reflection sequentially passes through the third lens E3, the second lens E2, the first quarter-wave plate QWP1, the reflective polarizing element RP, the first lens E1 to the aperture stop and finally projects into the user's eye. For example, the light after two reflections of the optical system finally projects into the user's eye. A protective glass (not shown) can also be provided between the image plane IMG and the polarizer LP.

[0083] Table 1 shows the basic parameter table of the optical system of Example 1. Among them, the unit of the radius of curvature and the thickness / distance is millimeter (mm). The image light from the image plane IMG passes through each element in the order from No. 23 to No. 1 and finally projects into the human eye.

[0084]

[0085]

[0086] Table 1

[0087] In this embodiment, the side S5 and the side S6 of the third lens E3 close to the human eye and the side S7 of the fourth lens E4 close to the human eye are all aspherical surfaces. The surface profile x of each aspherical lens can be defined by, but not limited to, the following aspherical formula:

[0088]

[0089] Wherein, x is the sagitta, which is the distance from the vertex of the aspherical surface to the position along the optical axis at a height of h; c is the paraxial curvature of the aspherical surface, c = 1 / R (i.e., the paraxial curvature c is the reciprocal of the radius of curvature R in Table 1 above); k is the conic coefficient; Ai is the correction coefficient of the i-th order of the aspherical surface. Table 2 gives the higher-order coefficients A4, A6, A8, A 10 、A 12 、A 14 、A 16 、A 18 and A 20 .

[0090] Surface number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -4.6221E-01 8.8946E-02 -5.5206E-02 -1.3412E-02 -5.1629E-03 -1.5918E-03 -3.8536E-04 0.0000E+00 0.0000E+00 S6 2.6838E-01 1.6185E-01 5.1195E-02 2.7031E-02 9.7489E-03 2.4221E-03 2.6929E-04 0.0000E+00 0.0000E+00 S7 1.1280E-01 -9.6967E-03 3.3226E-04 -1.9499E-04 -1.4313E-04 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00

[0091] Table 2

[0092] Figure 2A shows the axial chromatic aberration curve of the optical system of Example 1, which represents the deviation of the focus points of light rays of different wavelengths after passing through the optical system. Figure 2B shows the astigmatism curve of the optical system of Example 1, which represents the meridional image plane curvature and sagittal image plane curvature corresponding to different field angles. Figure 2C shows the distortion curve of the optical system of Example 1, which represents the distortion magnitude values corresponding to different field angles. Figure 3 shows the modulation transfer function curve of the optical system of Example 1. According to Figures 2A to 2C and Figure 3 , it can be known that the optical system given in Example 1 can achieve good imaging quality.

[0093] Example 2

[0094] The following describes the optical system according to Embodiment 2 of the present application with reference to Figure 4 、 Figures 5A to 5C and Figure 6 .

[0095] As Figure 4 shown, the optical system may include a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, and a polarizer LP arranged in sequence along the optical axis from the first side to the second side. The stop STO may be disposed between the first side and the first lens E1. In this embodiment, the first side refers to the human eye side, and the second side refers to the display screen side. The first side of each element is referred to as the near-human eye side, and the second side is referred to as the near-screen side.

[0096] The first lens E1 has a positive optical power. Its side S1 close to the human eye is convex, and its side S2 close to the screen is concave. The second lens E2 has a positive optical power. Its side S3 close to the human eye is flat, and its side S4 close to the screen is convex. The third lens E3 has a negative optical power. Its side S5 close to the human eye is concave, and its side S6 close to the screen is concave. The fourth lens E4 has a negative optical power. Its side S7 close to the human eye is concave, and its side S8 close to the screen is flat. The reflective polarizing element RP and the first quarter-wave plate QWP1 are attached to the side S3 of the second lens E2 close to the human eye. The partial reflection element BS is attached to the side S6 of the third lens E3 close to the screen. The second quarter-wave plate QWP2 and the polarizer LP are attached to the side S8 of the fourth lens E4 close to the screen.

[0097] In this example, an image plane IMG can be provided on the second side of the optical system. The image plane IMG can be provided with a display screen, for example. The image light from the image plane IMG sequentially passes through the polarizer LP, the second quarter-wave plate QWP2, the fourth lens E4, the third lens E3, the second lens E2, the first quarter-wave plate QWP1 and reaches the reflective polarizing element RP, where the first reflection occurs at the reflective polarizing element RP. The light after the first reflection passes through the first quarter-wave plate QWP1, the second lens E2, the third lens E3 and reaches the partial reflection element BS located on the side S6 of the third lens E3 close to the screen, where the second reflection occurs at the partial reflection element BS. The light after the second reflection sequentially passes through the third lens E3, the second lens E2, the first quarter-wave plate QWP1, the reflective polarizing element RP, the first lens E1 to the aperture stop and finally projects into the user's eye. For example, the light after two reflections of the optical system finally projects into the user's eye. A protective glass (not shown) can also be provided between the image plane IMG and the polarizer LP.

[0098] Table 3 shows the basic parameter table of the optical system of Example 2, where the unit of the radius of curvature and the thickness / distance is millimeter (mm). The image light from the image plane IMG passes through each element in the order from No. 23 to No. 1 and finally projects into the human eye.

[0099]

[0100]

[0101] Table 3

[0102] In this embodiment, the side S5 of the third lens E3 close to the human eye and the side S6 close to the screen, and the side S7 of the fourth lens E4 close to the human eye are all aspherical surfaces. Table 4 gives the higher-order coefficients A4, A6, A8, A 10 , A 12 , A14 , A 16 , A 18 and A 20 .

[0103] Surface number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -1.7566E+00 -9.1856E-01 -6.6580E-01 -3.1489E-01 -1.1832E-01 -3.0614E-02 -4.3324E-03 0.0000E+00 0.0000E+00 S6 7.7626E-01 1.5793E-01 1.1307E-02 2.3290E-02 1.3885E-02 3.6322E-03 2.4337E-04 0.0000E+00 0.0000E+00 S7 1.0218E-01 -2.8597E-02 -3.6943E-03 -2.9453E-03 -9.3725E-04 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00

[0104] Table 4

[0105] Figure 5A shows the axial chromatic aberration curve of the optical system of Example 2, which represents the deviation of the focusing points of light rays with different wavelengths after passing through the optical system. Figure 5B shows the astigmatism curve of the optical system of Example 2, which represents the meridional image plane curvature and sagittal image plane curvature corresponding to different field angles. Figure 5C shows the distortion curve of the optical system of Example 2, which represents the distortion magnitude values corresponding to different field angles. Figure 6 shows the modulation transfer function curve of the optical system of Example 2. According to Figures 5A to 5C and Figure 6 , it can be seen that the optical system given in Example 2 can achieve good imaging quality.

[0106] Example 3

[0107] The following refers to Figure 7 , Figures 8A to 8C and Figure 9 to describe the optical system according to Embodiment 3 of the present application.

[0108] As Figure 7 shown, the optical system may include a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, and a polarizer LP arranged in sequence along the optical axis from the first side to the second side. The aperture stop STO may be disposed between the first side and the first lens E1. In this embodiment, the first side refers to the human eye side, and the second side refers to the display screen side. The first side surfaces of each element are all referred to as the near-eye side surfaces, and the second side surfaces are all referred to as the near-screen side surfaces.

[0109] The first lens E1 has a positive optical power. Its side S1 close to the human eye is convex, and its side S2 close to the screen is concave. The second lens E2 has a positive optical power. Its side S3 close to the human eye is flat, and its side S4 close to the screen is convex. The third lens E3 has a negative optical power. Its side S5 close to the human eye is concave, and its side S6 close to the screen is convex. The fourth lens E4 has a positive optical power. Its side S7 close to the human eye is convex, and its side S8 close to the screen is flat. The reflective polarizing element RP and the first quarter-wave plate QWP1 are attached to the side S3 of the second lens E2 close to the human eye. The partial reflection element BS is attached to the side S6 of the third lens E3 close to the screen. The second quarter-wave plate QWP2 and the polarizer LP are attached to the side S8 of the fourth lens E4 close to the screen.

[0110] In this example, an image plane IMG can be provided on the second side of the optical system. The image plane IMG can be provided with a display screen, for example. The image light from the image plane IMG sequentially passes through the polarizer LP, the second quarter-wave plate QWP2, the fourth lens E4, the third lens E3, the second lens E2, the first quarter-wave plate QWP1 and reaches the reflective polarizing element RP, where the first reflection occurs. The light after the first reflection passes through the first quarter-wave plate QWP1, the second lens E2, the third lens E3 and reaches the partial reflection element BS located on the side S6 of the third lens E3 close to the screen, where the second reflection occurs. The light after the second reflection sequentially passes through the third lens E3, the second lens E2, the first quarter-wave plate QWP1, the reflective polarizing element RP, the first lens E1 to the aperture stop and finally projects into the user's eye. For example, the light after two reflections of the optical system finally projects into the user's eye. A protective glass (not shown) can also be provided between the image plane IMG and the polarizer LP.

[0111] Table 5 shows the basic parameter table of the optical system of Example 3, where the unit of the radius of curvature and the thickness / distance is millimeter (mm). The image light from the image plane IMG passes through each element in the order from No. 23 to No. 1 and finally projects into the human eye.

[0112]

[0113] Table 5

[0114] In this embodiment, the side S5 of the third lens E3 close to the human eye and the side S6 close to the screen, and the side S7 of the fourth lens E4 close to the human eye are all aspherical surfaces. Table 6 gives the higher-order term coefficients A4, A6, A8, A 10 、A 12 、A 14 、A 16 、A 18 and A20 .

[0115] Surface number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -3.2408E-01 -2.2957E-01 -3.3271E-01 -2.0137E-01 -1.1801E-01 -5.3238E-02 -9.1168E-03 0.0000E+00 0.0000E+00 S6 5.2280E-02 4.6291E-03 -4.7358E-02 -2.6200E-02 -1.7878E-02 -1.0288E-02 -1.8757E-03 0.0000E+00 0.0000E+00 S7 1.7461E-01 -2.2494E-03 -1.6176E-03 1.6677E-04 -3.0210E-04 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00

[0116] Table 6

[0117] Figure 8A shows the axial chromatic aberration curve of the optical system of Embodiment 3, which represents the deviation of the focusing points of light rays of different wavelengths after passing through the optical system. Figure 8B shows the astigmatism curve of the optical system of Embodiment 3, which represents the meridional image plane curvature and sagittal image plane curvature corresponding to different field angles. Figure 8C shows the distortion curve of the optical system of Embodiment 3, which represents the distortion magnitude values corresponding to different field angles. Figure 9 shows the modulation transfer function curve of the optical system of Embodiment 3. According to Figures 8A to 8C and Figure 9 it can be known that the optical system given in Embodiment 3 can achieve good imaging quality.

[0118] Example 4

[0119] The following refers to Figure 10 , Figures 11A to 11C and Figure 12 to describe the optical system according to Embodiment 4 of the present application.

[0120] As Figure 10 shown, the optical system may include a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, and a polarizer LP arranged in sequence along the optical axis from the first side to the second side. The aperture stop STO may be disposed between the first side and the first lens E1. In this embodiment, the first side refers to the human eye side, and the second side refers to the display screen side. The first side surfaces of each element are all referred to as the near-human-eye side surfaces, and the second side surfaces are all referred to as the near-screen side surfaces.

[0121] The first lens E1 has a positive optical power, its near-human-eye side surface S1 is convex, and its near-screen side surface S2 is concave. The second lens E2 has a positive optical power, its near-human-eye side surface S3 is flat, and its near-screen side surface S4 is convex. The third lens E3 has a negative optical power, its near-human-eye side surface S5 is concave, and its near-screen side surface S6 is convex. The fourth lens E4 has a positive optical power, its near-human-eye side surface S7 is convex, and its near-screen side surface S8 is flat. The reflective polarizing element RP and the first quarter-wave plate QWP1 are attached to the near-human-eye side surface S3 of the second lens E2. The partial reflection element BS is attached to the near-screen side surface S6 of the third lens E3. The second quarter-wave plate QWP2 and the polarizer LP are attached to the near-screen side surface S8 of the fourth lens E4.

[0122] In this example, an image plane IMG may be provided on the second side of the optical system. The image plane IMG may be provided with a display screen, for example. The image light from the image plane IMG sequentially passes through a polarizer LP, a second quarter-wave plate QWP2, a fourth lens E4, a third lens E3, a second lens E2, a first quarter-wave plate QWP1 and reaches a reflective polarizing element RP, where a first reflection occurs at the reflective polarizing element RP. The light reflected for the first time passes through the first quarter-wave plate QWP1, the second lens E2, the third lens E3 and reaches a partial reflection element BS on the near-screen side of the third lens E3, where a second reflection occurs at the partial reflection element BS. The light reflected for the second time sequentially passes through the third lens E3, the second lens E2, the first quarter-wave plate QWP1, the reflective polarizing element RP, a first lens E1 to the aperture stop and finally projects into the user's eyes. For example, the light of the optical system after two reflections finally projects into the user's eyes. A protective glass (not shown) may also be provided between the image plane IMG and the polarizer LP.

[0123] Table 7 shows the basic parameter table of the optical system of Example 4, where the unit of the radius of curvature and the thickness / distance is millimeter (mm). The image light from the image plane IMG passes through each element in the order from No. 23 to No. 1 and finally projects into the human eyes.

[0124]

[0125] Table 7

[0126] In this embodiment, the near-screen side S4 of the second lens E2, the near-eye side S5 and the near-screen side S6 of the third lens E3, and the near-eye side S7 of the fourth lens E4 are all aspherical surfaces. Table 8 gives the higher-order term coefficients A4, A6, A8, A 10 , A 12 , A 14 , A 16 , A 18 and A 20 for the aspherical surfaces S4 - S7 that can be used in Example 4.

[0127] Surface number A4 A6 A8 A10 A12 A14 A16 A18 A20 S4 4.3326E-02 -3.0161E-03 -4.3411E-05 -1.6166E-05 3.7953E-06 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 S5 -3.8479E-01 1.1258E-01 6.1473E-02 -5.1302E-03 -2.5956E-02 -1.5649E-02 -3.6736E-03 0.0000E+00 0.0000E+00 S6 -1.7396E-02 2.4428E-04 -1.4953E-02 -1.7120E-02 -1.2611E-02 -5.6990E-03 -1.2368E-03 0.0000E+00 0.0000E+00 S7 1.3806E-01 6.7857E-04 7.1623E-04 -1.4453E-04 2.9049E-05 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00

[0128] Table 8

[0129] Figure 11A shows the axial chromatic aberration curve of the optical system of Example 4, which represents the deviation of the focus points of light rays with different wavelengths after passing through the optical system. Figure 11B shows the astigmatism curve of the optical system of Example 4, which represents the meridional image plane curvature and the sagittal image plane curvature corresponding to different field angles of view. Figure 11CThe distortion curve of the optical system of Embodiment 4 is shown, which represents the distortion magnitude values corresponding to different field angles of view. Figure 12 The modulation transfer function curve of the optical system of Embodiment 4 is shown. According to Figures 11A to 11C and Figure 12 it can be seen that the optical system given in Embodiment 4 can achieve good imaging quality.

[0130] Example 5

[0131] The following refers to Figure 13 , Figures 14A to 14C and Figure 15 to describe the optical system according to Embodiment 5 of the present application.

[0132] As Figure 13 shown, the optical system may include a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, and a polarizer LP arranged in sequence along the optical axis from the first side to the second side. The aperture stop STO may be disposed between the first side and the first lens E1. In this embodiment, the first side refers to the human eye side, and the second side refers to the display screen side. The first side surfaces of each element are all referred to as the near-human-eye side surfaces, and the second side surfaces are all referred to as the near-screen side surfaces.

[0133] The first lens E1 has a positive optical power. Its near-human-eye side surface S1 is convex, and its near-screen side surface S2 is concave. The second lens E2 has a positive optical power. Its near-human-eye side surface S3 is flat, and its near-screen side surface S4 is convex. The third lens E3 has a negative optical power. Its near-human-eye side surface S5 is concave, and its near-screen side surface S6 is convex. The fourth lens E4 has a positive optical power. Its near-human-eye side surface S7 is convex, and its near-screen side surface S8 is flat. The reflective polarizing element RP and the first quarter-wave plate QWP1 are attached to the near-human-eye side surface S3 of the second lens E2. The partial reflection element BS is attached to the near-screen side surface S6 of the third lens E3. The second quarter-wave plate QWP2 and the polarizer LP are attached to the near-screen side surface S8 of the fourth lens E4.

[0134] In this example, an image plane IMG may be provided on the second side of the optical system. The image plane IMG may be provided with a display screen, for example. The image light from the image plane IMG sequentially passes through a polarizer LP, a second quarter-wave plate QWP2, a fourth lens E4, a third lens E3, a second lens E2, a first quarter-wave plate QWP1 and reaches a reflective polarizing element RP, where a first reflection occurs at the reflective polarizing element RP. The light reflected for the first time passes through the first quarter-wave plate QWP1, the second lens E2, the third lens E3 and reaches a partial reflection element BS on the near-screen side of the third lens E3, where a second reflection occurs at the partial reflection element BS. The light reflected for the second time sequentially passes through the third lens E3, the second lens E2, the first quarter-wave plate QWP1, the reflective polarizing element RP, a first lens E1 to the aperture stop and finally projects into the user's eyes. For example, the light of the optical system after two reflections finally projects into the user's eyes. A protective glass (not shown) may also be provided between the image plane IMG and the polarizer LP.

[0135] Table 9 shows the basic parameter table of the optical system of Example 5, where the unit of the radius of curvature and the thickness / distance is millimeter (mm). The image light from the image plane IMG passes through each element in the order from No. 23 to No. 1 and finally projects into the human eyes.

[0136]

[0137]

[0138] Table 9

[0139] In this embodiment, the near-screen side S4 of the second lens E2, the near-eye side S5 and the near-screen side S6 of the third lens E3, and the near-eye side S7 of the fourth lens E4 are all aspherical surfaces. Table 10 gives the higher-order term coefficients A4, A6, A8, A 10 , A 12 , A 14 , A 16 , A 18 and A 20 for the aspherical surfaces S4 - S7 that can be used in Example 5.

[0140] Surface number A4 A6 A8 A10 A12 A14 A16 A18 A20 S4 4.3986E-02 -2.0543E-03 -2.0872E-05 -9.4960E-06 7.6199E-07 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 S5 -1.9456E-01 1.6301E-02 2.0676E-02 -1.3665E-02 -1.6130E-02 -1.2575E-02 -1.2809E-03 0.0000E+00 0.0000E+00 S6 1.9752E-02 -4.9490E-03 -7.2719E-03 -1.1055E-02 -6.8125E-03 -4.4695E-03 -5.0325E-04 0.0000E+00 0.0000E+00 S7 8.6077E-02 8.7608E-04 -1.6652E-04 -1.7153E-04 1.1682E-04 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00

[0141] Table 10

[0142] Figure 14A shows the axial chromatic aberration curve of the optical system of Example 5, which represents the deviation of the focus points of light rays with different wavelengths after passing through the optical system. Figure 14BThe astigmatism curve of the optical system of Embodiment 5 is shown, which represents the meridional image plane curvature and sagittal image plane curvature corresponding to different field angles. Figure 14C The distortion curve of the optical system of Embodiment 5 is shown, which represents the distortion magnitude values corresponding to different field angles. Figure 15 The modulation transfer function curve of the optical system of Embodiment 5 is shown. According to Figures 14A to 14C and Figure 15 it can be known that the optical system given in Embodiment 5 can achieve good imaging quality.

[0143] Table 11 gives the basic parameters of each of Embodiments 1 to 5, such as the values of f, f1, f2, f3, f4, EPD, TD, TTL, fz1, fz2, SAG11, SAG12, SAG41, BFL, ET3, and FOV.

[0144]

[0145]

[0146] Table 11

[0147] In summary, Table 12 shows the conditional values of each of Embodiments 1 to 5.

[0148] Conditional expression / Example 1 2 3 4 5 f1 / f2 0.42 0.40 0.24 0.44 0.50 fz1 / |R1 + R4| 0.86 1.16 0.45 0.84 0.91 R5 / f3 0.45 0.80 0.24 0.35 0.33 (CT2 + CTR + CTQ1) / CT1 0.59 0.82 0.61 0.60 0.65 f4 / fz2 0.44 1.53 0.82 0.73 0.75 TD / (f × tan(FOV)) 1.87 1.87 1.95 1.88 1.89 V1 / N1 40.76 37.52 47.29 47.16 47.16 R7 / f4 0.86 0.75 0.52 0.86 0.86 TTL / f 0.64 0.64 0.67 0.65 0.65 R1 / (SAG11 + SAG12) 2.84 2.76 3.68 3.03 3.16 |SAG41| / CT4 0.31 0.66 0.55 0.47 0.41 BFL / (CTQ2 + CTL) 9.04 9.04 9.04 8.67 8.24 CT3 / ET3 0.93 0.94 0.80 0.74 0.80 ∑CT / EPD 0.66 0.94 0.39 0.43 0.39 f / R2 0.91 0.21 1.11 1.02 1.10

[0149] Table 12

[0150] This application also provides an optical device, which can be an independent projection device such as a projector, or a projection module integrated on a mobile electronic device such as a virtual reality device. This optical device is equipped with the optical system described above.

[0151] The above description is only the preferred embodiments of this application and the explanation of the applied technical principles. Those skilled in the art should understand that the scope of the utility model involved in this application is not limited to the technical solutions formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the technical solutions formed by mutually replacing the above features with the (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. An optical system, characterized in that The method comprises, in order from the first side to the second side along the optical axis: A first lens having positive optical power, wherein the first side surface is convex and the second side surface is concave; a second lens having positive optical power, wherein the first side surface is a flat surface and the second side surface is a convex surface; a third lens element having negative optical power, wherein the first side surface of the third lens element is concave; and a fourth lens having optical power, wherein the second side surface of the fourth lens is a plane; Wherein, the optical system further comprises: A first quarter wave plate, disposed on a first side surface of the second lens; a reflective polarizing element, disposed on a first side surface of the first quarter-wave plate; A partial reflective element, disposed on the second side surface of the third lens; A second quarter wave plate, disposed on a second side surface of the fourth lens; and a polarizing plate, disposed on the second side of the second quarter-wave plate; The number of lenses having optical power in the optical system is four; The effective focal length f1 of the first lens and the effective focal length f2 of the second lens satisfy: 0.2 <f1 / f2≤0.5; The combined focal length fz1 of the first lens, the reflective polarizing element, the first quarter wave plate and the second lens, the curvature radius R1 of the first side surface of the first lens and the curvature radius R4 of the second side surface of the second lens satisfy: 0.4 <fz1 / |R1+R4|<1.2。 2. The optical system according to claim 1, characterized in that The curvature radius R5 of the first side surface of the third lens and the effective focal length f3 of the third lens satisfy: 0.2 <R5 / f3≤0.8。 3. The optical system according to claim 1, characterized in that The center thickness CT1 of the first lens on the optical axis, the center thickness CTR of the reflective polarizing element on the optical axis, the center thickness CTQ1 of the first quarter wave plate on the optical axis and the center thickness CT2 of the second lens on the optical axis satisfy: 0.59≤(CT2+CTR+CTQ1) / CT1≤0.

82.

4. The optical system according to claim 1, characterized in that The effective focal length f4 of the fourth lens and the combined focal length fz2 of the third lens, the fourth lens, the second quarter wave plate and the polarizer satisfy: 0.4 <f4 / fz2≤1.53。 5. The optical system according to claim 1, characterized in that The Abbe number V1 of the first lens and the refractive index N1 of the first lens satisfy: 37.5 <V1 / N1<47.3。 6. The optical system according to claim 1, characterized in that The curvature radius R7 of the first side surface of the fourth lens and the effective focal length f4 of the fourth lens satisfy: 0.5 <R7 / f4<0.9。 7. The optical system according to claim 1, characterized in that The on-axis distance SAG11 between the intersection of the first side surface of the first lens and the optical axis to the effective half-aperture vertex of the first side surface of the first lens, the on-axis distance SAG12 between the intersection of the second side surface of the first lens and the optical axis to the effective half-aperture vertex of the second side surface of the first lens, and the curvature radius R1 of the first side surface of the first lens satisfy: 2.76≤R1 / (SAG11+SAG12)<3.

7.

8. The optical system according to claim 1, characterized in that An axial distance SAG41 from an intersection of the first side surface of the fourth lens and the optical axis to an effective semi-aperture vertex of the first side surface of the fourth lens and a center thickness CT4 of the fourth lens on the optical axis satisfy: 0.3<|SAG41| / CT4<0.

7.

9. The optical system according to claim 1, characterized in that The center thickness CT3 of the third lens on the optical axis and the edge thickness ET3 of the third lens satisfy: 0.7 <CT3 / ET3≤0.94。 10. The optical system according to any one of claims 1 to 9, characterized in that: An axial distance TD from the first side surface of the first lens to the second side surface of the fourth lens, a total effective focal length f of the optical system and a maximum field of view FOV of the optical system satisfy: 1.87≤TD / (f×tan(FOV))<2.

0.

11. The optical system according to any one of claims 1 to 9, characterized in that: The second side of the optical system is provided with an image plane, and the on-axis distance TTL from the first side surface of the first lens to the image plane satisfies the total effective focal length f of the optical system: 0.6 <TTL / f<0.7。 12. The optical system according to any one of claims 1 to 9, characterized in that: The second side of the optical system is provided with an image plane, and the on-axis distance BFL from the second side surface of the fourth lens to the image plane, the center thickness CTQ2 of the second quarter wave plate on the optical axis and the center thickness CTL of the polarizer on the optical axis satisfy: 8.2 <BFL / (CTQ2+CTL)≤9.04。 13. The optical system according to any one of claims 1 to 9, characterized in that: A sum ΣCT of the center thicknesses of the first lens, the second lens, the third lens and the fourth lens on the optical axis and an entrance pupil diameter EPD of the optical system satisfy: 0.39≤ΣCT / EPD≤0.

94.

14. The optical system according to any one of claims 1 to 9, characterized in that: The total effective focal length f of the optical system and the curvature radius R2 of the second side surface of the first lens satisfy: 0.2 <f / R2≤1.11。

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