Optical system

Abstract

The invention 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 second quarter-wave plate, a polarizing film and a fourth lens 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, the first side surface of the third lens is a concave surface, and the second side surface is a convex surface; the fourth lens has positive focal power, the first side surface of the fourth lens is a plane, and the second side surface is a convex surface; the effective focal length f1 of the first lens and the effective focal length f2 of the second lens meet the following conditions: 0.05 lt; f1 / f2lt; 0.5 part; the combined focal length fz1 of the reflective polarizing element, the first quarter-wave plate and the second lens and the curvature radius R4 of the second side surface of the second lens meet the following formula:-2.1 lt; fz1 / R4lt; and 1.9.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical devices, in particular to a catadioptric optical system. BACKGROUND

[0002] The catadioptric optical system utilizes the polarization light characteristics to shorten the body length of the optical system, effectively reduces the volume of the optical system, and reserves space for the overall design of the electronic device including the optical system. Therefore, the catadioptric optical system is widely used in the fields of virtual reality technology or augmented reality technology.

[0003] However, the existing catadioptric optical system usually adopts two lenses, which can cause the picture of the catadioptric optical system to be relatively blurred and the imaging quality to be poor. SUMMARY

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

[0005] In one aspect, the present application provides an optical system which comprises, in order from a first side to a second side along an optical axis, a first lens, a second lens, a third lens and a fourth lens. The first lens has a positive focal power, and a first side thereof is a convex surface and a second side thereof is a concave surface. The second lens has a positive focal power, and a first side thereof is a plane and a second side thereof is a convex surface. The third lens has a negative focal power, and a first side thereof is a concave surface and a second side thereof is a convex surface. The fourth lens has a positive focal power, and a first side thereof is a plane and a second side thereof is a convex surface. The optical system further comprises a first quarter-wave plate, a reflective polarizing element, a partially reflective element, a polarizer and a second quarter-wave plate. 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 partially reflective element is disposed on the second side of the third lens. The polarizer is disposed on the first side of the fourth lens. The second quarter-wave plate is disposed on the first side of the polarizer. An effective focal length f1 of the first lens and an effective focal length f2 of the second lens satisfy: 0.05 < f1 / f2 < 0.5. A combined focal length fz1 of the reflective polarizing element, the first quarter-wave plate and the second lens and a curvature radius R4 of the second side of the second lens satisfy: -2.1 < fz1 / R4 < -1.9.

[0006] According to an exemplary embodiment of the present application, a refractive index NQ1 of the first quarter-wave plate and a refractive index N2 of the second lens satisfy: 0.95 < N2 / NQ1 < 1.05.

[0007] According to an exemplary embodiment of the present application, an Abbe number V1 of the first lens and an Abbe number V3 of the third lens satisfy: 2.0 < V1 / V3 < 2.5.

[0008] According to an example embodiment of the present application, the effective focal length f1 of the first lens, the curvature radius R1 of the first side of the first lens, and the curvature radius R2 of the second side of the first lens satisfy: 0.4 < f1 / (R1+R2) < 1.0.

[0009] According to an example embodiment of the present application, the curvature radius R5 of the first side of the third lens and the curvature radius R6 of the second side of the third lens satisfy: 0.2 < R5 / R6 < 0.6.

[0010] According to an example embodiment of the present application, the total effective focal length f of the optical system and the effective focal length f3 of the third lens satisfy: -0.55 < f / f3 < -0.15.

[0011] According to an example embodiment of the present application, the central thickness CT3 of the third lens on the optical axis, the central thickness CTQ2 of the second quarter-wave plate on the optical axis, the central thickness CTL of the polarizer on the optical axis, and the central thickness CT4 of the fourth lens on the optical axis satisfy: 2.5 < CT3 / (CTQ2+CTL+CT4) < 4.4.

[0012] According to an example embodiment of the present application, the on-axis distance T12 from the second side of the first lens to the first side of the second lens, 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: 0.2 < T12 / (CTR+CTQ1+CT2) < 1.4.

[0013] According to an example embodiment of the present application, the effective focal length f4 of the fourth lens and the curvature radius R8 of the second side of the fourth lens satisfy: -0.9 < R8 / f4 < -0.5.

[0014] According to an example embodiment of the present application, the Abbe number VR of the reflective polarizing element, the Abbe number VQ1 of the first quarter-wave plate, and the Abbe number V2 of the second lens satisfy: 1.6 < (VR+VQ1) / V2 < 2.0.

[0015] According to an example embodiment of the present application, the optical system further comprises a stop arranged between the first side and the first lens. Wherein the on-axis distance SR of the stop to the first side of the first lens and the central thickness CT1 of the first lens on the optical axis satisfy: 3.3 < SR / CT1 < 4.2.

[0016] According to an example embodiment of the present application, the on-axis distance SAG11 between the intersection of the first side surface of the first lens and the optical axis and the effective semi-aperture vertex of the first side surface of the first lens and the on-axis distance SAG12 between the intersection of the second side surface of the first lens and the optical axis and the effective semi-aperture vertex of the second side surface of the first lens satisfy: 0.1 < SAG12 / SAG11 < 0.4.

[0017] According to an example embodiment of the present application, the on-axis distance SAG31 between the intersection of the first side surface of the third lens and the optical axis and the effective semi-aperture vertex of the first side surface of the third lens, the on-axis distance SAG32 between the intersection of the second side surface of the third lens and the optical axis and the effective semi-aperture vertex of the second side surface of the third lens and the central thickness CT3 of the third lens on the optical axis satisfy: 6.3 < CT3 / |SAG31+SAG32| < 10.9.

[0018] The optical system provided by the present application adopts four lenses, reasonably configures the focal power of the four lenses and makes the optical system satisfy "0.05 < f1 / f2 < 0.5", which is beneficial to improve the imaging quality of the optical system; meanwhile, cooperating with limiting the ratio of the combined focal length of the reflective polarizing element, the first quarter wave plate and the second lens to the curvature radius of the second side surface of the second lens, it is beneficial to control the polarization performance of the optical system, realize the constraint on the polarization characteristics of the optical system, and also can balance the imaging quality, polarization performance and design complexity of the optical system, so as to ensure that the optical system realizes better overall performance. BRIEF DESCRIPTION OF DRAWINGS

[0019] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting examples made with reference to the accompanying drawings. Among them:

[0020] Figure 1 The structure schematic diagram of the optical system according to the embodiment 1 of the present application is shown;

[0021] Figures 2A to 2D The on-axis chromatic aberration curve, the astigmatism curve, the distortion curve and the modulation transfer function (MTF) curve of the optical system according to the embodiment 1 of the present application are respectively shown;

[0022] Figure 3 The structure schematic diagram of the optical system according to the embodiment 2 of the present application is shown;

[0023] Figures 4A to 4D The on-axis chromatic aberration curve, the astigmatism curve, the distortion curve and the modulation transfer function curve of the optical system according to the embodiment 2 of the present application are respectively shown;

[0024] Figure 5A structural diagram of an optical system according to Embodiment 3 of the present application is shown;

[0025] Figures 6A to 6D Axial chromatic aberration curves, astigmatism curves, distortion curves, and modulation transfer function curves of the optical system according to Embodiment 3 of the present application are shown respectively;

[0026] Figure 7 A structural diagram of an optical system according to Embodiment 4 of the present application is shown;

[0027] Figures 8A to 8D Axial chromatic aberration curves, astigmatism curves, distortion curves, and modulation transfer function curves of the optical system according to Embodiment 4 of the present application are shown respectively;

[0028] Figure 9 A structural diagram of an optical system according to Embodiment 5 of the present application is shown; and

[0029] Figures 10A to 10D Axial chromatic aberration curves, astigmatism curves, distortion curves, and modulation transfer function curves of the optical system according to Embodiment 5 of the present application are shown respectively. DETAILED DESCRIPTION

[0030] For a better understanding of the present application, various aspects of the present application will be described in more detail below with reference to the accompanying drawings. It is to be noted that these detailed description are descriptions of exemplary embodiments of the present application only and are not meant in any way to limit the scope of the present application. Throughout the specification, like reference numerals will be used to refer to like elements throughout the specification.

[0031] It should be noted that the terms first, second, etc. in the present specification are only used to distinguish one feature from another feature, and do not represent any limitation on the features. Thus, the first lens discussed below can also be referred to as the second lens without departing from the teachings of the present application.

[0032] In the drawings, the thickness, size, and shape of the lenses have been slightly exaggerated for ease of explanation. Specifically, the shape of the spherical or aspherical surface shown in the drawings is shown by way of example. That is, the shape of the spherical or aspherical surface is not limited to the shape of the spherical or aspherical surface shown in the drawings. The drawings are merely examples and are not drawn to scale.

[0033] In the present specification, the paraxial region refers to a region near the optical axis. If a lens surface is convex and the position of the convex surface is not specified, it means that the lens surface is convex at least in the paraxial region. If a lens surface is concave and the position of the concave surface is not specified, 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 side of the human eye) is referred to as the first side surface of the lens, and the surface of each lens closest to the second side (e.g., the side of the display screen) is referred to as the second side surface of the lens.

[0034] It should also be understood that the words "comprise," "comprising," "include," "including," and / or "has," "having," when used in this specification, specify the presence of stated features, elements, and / or components, but do not preclude the presence or addition of one or more other features, elements, components, and / or groups thereof. In addition, when describing the embodiments of the present application, the word "may" is used to mean one or more embodiments of the present application. Also, the word "exemplary" is intended to mean an example or an illustration.

[0035] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an overly literal or overly formal sense unless expressly so defined herein.

[0036] It should be noted that the embodiments and features of the embodiments in the present application can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0037] The features, principles, and other aspects of the present application are described in detail below.

[0038] Reference Figure 1 , Figure 3 , Figure 5 , Figure 7 and Figure 9 The first aspect of the present application provides such an optical system, which can include, in order along an optical axis from a first side to a second side, a first lens, a second lens, a third lens, and a fourth lens.

[0039] In an exemplary embodiment, the first lens can have a positive optical power. The second lens can have a positive optical power. The third lens can have a negative optical power. The fourth lens can have a positive optical power. Reasonably configuring the optical power of each lens is conducive to improving the imaging quality of the optical system.

[0040] In an exemplary embodiment, the first side of the first lens can be convex, and the second side can be concave.

[0041] In an exemplary embodiment, the first side of the second lens can be a plane, and the second side can be convex.

[0042] In an exemplary embodiment, the first side of the third lens can be concave, and the second side can be convex.

[0043] In an example embodiment, the first side surface of the fourth lens can be planar, and the second side surface of the fourth lens can be convex.

[0044] In an example embodiment, the optical system can further include a first quarter wave plate. The first quarter wave plate is configured to change a polarization state of the light, such as converting circularly polarized light into linearly polarized light, or converting linearly polarized light into circularly polarized light. The circularly polarized light can include right-handed circularly polarized light or left-handed circularly polarized light. The linearly polarized light can include S linearly polarized light or P linearly polarized light.

[0045] In an example embodiment, the optical system can further include a reflective polarizing element. The reflective polarizing element is configured to reflect linearly polarized light in a predetermined direction and transmit linearly polarized light orthogonal to the predetermined direction. For example, the reflective polarizing element can reflect S linearly polarized light and transmit P linearly polarized light, or the reflective polarizing element can reflect P linearly polarized light and transmit S linearly polarized light.

[0046] In an example embodiment, the first quarter wave plate can be disposed on the first side surface of the second lens and at least partially attached to the first side surface of the second lens. The reflective polarizing element can be disposed on the first side surface of the first quarter wave plate and at least partially attached to the first side surface of the first quarter wave plate.

[0047] In an example embodiment, the first side surface of the second lens can be planar. The reflective polarizing element and the first quarter wave plate are attached and affixed to the first side surface of the second lens, and 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 affixing them to the first side surface of the second lens, the difficulty of the affixing process can be reduced, the affixing quality can be improved, and thus the performance of the optical system can be improved.

[0048] In an example embodiment, the optical system can further include a partial reflection element. The partial reflection element can be disposed on the second side surface of the third lens and at least partially attached to the second side surface of the third lens. The partial reflection element can have a semi-transmissive and semi-reflective effect on the light. By disposing the partial reflection element on the second side surface of the third lens in combination with the reflective polarizing element and the first quarter wave plate, the light can be folded multiple times, and the length of the optical system can be effectively reduced.

[0049] In an example embodiment, the optical system can further include a second quarter wave plate and a polarizer. The polarizer can be disposed on and at least partially conform to the first side of the fourth lens. The second quarter wave plate can be disposed on and at least partially conform to the first side of the polarizer. The polarizer is configured to convert the natural light emitted by the display screen on the second side into linearly polarized light, and the second quarter wave plate is configured to convert the linearly polarized light from the polarizer into circularly polarized light (e.g., right-handed or left-handed circularly polarized light). The use of the second quarter wave plate and the polarizer can convert the natural light emitted by the display screen into circularly polarized light, reduce the material stress effects of the elements between the display screen and the polarizer, and improve the contrast of the optical system.

[0050] In an example embodiment, the first side of the fourth lens can be planar. The second quarter wave plate and the polarizer can be conformed and attached to the first side of the fourth lens, with the polarizer being closer to the fourth lens than the second quarter wave plate. By conforming the second quarter wave plate and the polarizer together and then attaching them to the first side of the fourth lens, the attachment process can be made easier, the attachment quality can be improved, and the performance of the optical system can be improved.

[0051] In an example embodiment, the optical system can further include a stop, which can be disposed between the first side and the first lens. The image light from the second side can be refracted and reflected multiple times by the fourth lens, the polarizer, the second quarter wave plate, the third lens, the second lens, the first quarter wave plate, the reflective polarizing element, the first lens, and the like, and finally projected to the eye of the user on the first side.

[0052] In an example embodiment, the first side can be, for example, the side of the human eye, and the second side can be, for example, the side of the display screen. Accordingly, the first side of each element (the first lens, the second lens, the third lens, the fourth lens, the first quarter wave plate, the polarizer) can be referred to as the near-eye side, and the second side can be referred to as the near-screen side.

[0053] In the example embodiment, the second side of the optical system can be provided with an image plane. The image plane can be provided with a display screen. Image light from the display screen can sequentially pass through the fourth lens, the polarizer, the second quarter wave plate, the third lens, the second lens, the first quarter wave plate, reach the 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 then reaches the partially reflective element on the second side of the third lens, and then is reflected at the partially reflective 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, reaches the diaphragm, and is finally projected into the user's eye. The optical system provided in the present application effectively shortens the body length of the optical system by combining light reflection and refraction without affecting the projection quality.

[0054] In the example embodiment, the effective focal length f1 of the first lens and the effective focal length f2 of the second lens can satisfy: 0.05 < f1 / f2 < 0.5; and the combined focal length fz1 of the reflective polarizing element, the first quarter wave plate and the second lens and the curvature radius R4 of the second side of the second lens can satisfy: -2.1 < fz1 / R4 < -1.9. By controlling the optical system to satisfy "0.05 < f1 / f2 < 0.5", the imaging quality of the optical system is improved; and by limiting the ratio of the combined focal length of the reflective polarizing element, the first quarter wave plate and the second lens and the curvature radius of the second side of the second lens, the polarization performance of the optical system is controlled, the polarization characteristics of the optical system are constrained, and the imaging quality, the polarization performance and the design complexity of the optical system are balanced, so that the optical system achieves better overall performance.

[0055] In the example embodiment, the refractive index NQ1 of the first quarter wave plate and the refractive index N2 of the second lens can satisfy: 0.95 < N2 / NQ1 < 1.05. Reasonably configuring the ratio of the refractive index of the second lens and the refractive index of the first quarter wave plate can avoid total reflection of light caused by too large difference between the refractive indices of the first quarter wave plate and the second lens, reduce light reflection and light refraction loss in the optical system, and improve light transmission efficiency; and at the same time, the chromatic dispersion effect of the optical system is improved.

[0056] In the example embodiment, the Abbe number V1 of the first lens and the Abbe number V3 of the third lens can satisfy: 2.0 < V1 / V3 < 2.5. The dispersion effect of the optical system can cause the focusing positions of light rays of different wavelengths to be different, thereby affecting the imaging quality of the optical system. Reasonably configuring the ratio of the Abbe number of the first lens to the Abbe number of the third lens can effectively reduce the dispersion effect of the optical system, improve the resolution, contrast, imaging quality and other performances of the optical system, so that the optical system is more stable and reliable; at the same time, it can also simplify the design and manufacturing process of the optical system, reduce the cost and time, and improve the production efficiency.

[0057] In the example embodiment, the effective focal length f1 of the first lens, the curvature radius R1 of the first side of the first lens and the curvature radius R2 of the second side of the first lens can satisfy: 0.4 < f1 / (R1+R2) < 1.0. Reasonably configuring the ratio of the effective focal length of the first lens to the sum of the curvature radii of the first side and the second side of the first lens can reduce the aberrations such as spherical aberration and astigmatism of the optical system, improve the imaging quality of the optical system, so that the image formed by the optical system is clearer and more accurate; at the same time, it can also simplify the manufacturing process of the optical system, reduce the process difficulty and cost.

[0058] In the example embodiment, the curvature radius R5 of the first side of the third lens and the curvature radius R6 of the second side of the third lens can satisfy: 0.2 < R5 / R6 < 0.6. Reasonably configuring the ratio of the curvature radius of the first side of the third lens to the curvature radius of the second side of the third lens can constrain the shape of the third lens, better control the focusing and transmission of light, reduce the aberration of the optical system, and improve the optical performance of the optical system.

[0059] In the example embodiment, the total effective focal length f of the optical system and the effective focal length f3 of the third lens can satisfy: -0.55 < f / f3 < -0.15. Reasonably configuring the ratio of the total effective focal length of the optical system to the effective focal length of the third lens can improve the imaging quality of the optical system, enhance the focusing ability of light, and reduce the distortion of the optical system.

[0060] In the example embodiment, the center thickness CT3 of the third lens on the optical axis, the center thickness CTQ2 of the second quarter-wave plate on the optical axis, the center thickness CTL of the polarizer on the optical axis and the center thickness CT4 of the fourth lens on the optical axis can satisfy: 2.5 < CT3 / (CTQ2+CTL+CT4) < 4.4. By controlling the above condition, the compact design of the optical system can be realized, thereby reducing the volume and weight of the electronic device comprising the optical system, improving the convenience of wearing the electronic device; at the same time, it can also avoid the thickness of the fourth lens being too thin, reduce the difficulty of processing, forming and assembling of the fourth lens, and be conducive to the attachment of the polarizer and the second quarter-wave plate.

[0061] In the example embodiment, the axial distance T12 from the second side surface of the first lens to the first side surface of the second lens, 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 can satisfy: 0.2 < T12 / (CTR+CTQ1+CT2) < 1.4. By controlling the above condition, the compact design of the optical system can be achieved, thereby reducing the volume and weight of the electronic device comprising the optical system, improving the convenience of wearing the electronic device; at the same time, it can also avoid the thickness of the second lens being too thin, reducing the difficulty of processing, molding and assembling of the second lens, and being conducive to the attachment of the reflective polarizing element and the first quarter-wave plate.

[0062] In the example embodiment, the effective focal length f4 of the fourth lens and the curvature radius R8 of the second side surface of the fourth lens can satisfy: -0.9 < R8 / f4 < -0.5. Reasonably configuring the ratio of the curvature radius of the second side surface of the fourth lens to the effective focal length of the fourth lens can constrain the shape of the fourth lens, so that the propagation of light in the fourth lens is more appropriate and effective, thereby ensuring the refraction and focusing effect of light in the fourth lens.

[0063] In the example embodiment, the Abbe number VR of the reflective polarizing element, the Abbe number VQ1 of the first quarter-wave plate, and the Abbe number V2 of the second lens can satisfy: 1.6 < (VR+VQ1) / V2 < 2.0. The dispersion effect of the optical system will cause the focusing positions of light rays of different wavelengths to be different, thereby affecting the imaging quality of the optical system. Reasonably configuring the ratio of the sum of the Abbe numbers of the reflective polarizing element and the first quarter-wave plate to the Abbe number of the second lens can effectively reduce the dispersion effect of the optical system, improve the resolution, contrast and imaging quality of the optical system, and make the optical system more stable and reliable.

[0064] In the example embodiment, the axial distance SR from the diaphragm to the first side surface of the first lens and the central thickness CT1 of the first lens on the optical axis can satisfy: 3.3 < SR / CT1 < 4.2. Reasonably configuring the ratio of the axial distance from the diaphragm to the first side surface of the first lens to the central thickness of the first lens on the optical axis is conducive to constraining the angle and position of the incident light, reducing the defocus and astigmatism phenomena of the optical system, improving the clarity and accuracy of the imaging of the optical system, and improving the imaging effect of the optical system.

[0065] In the example embodiment, the on-axis distance SAG11 between the intersection of the first side surface of the first lens and the optical axis and the effective semi-aperture vertex of the first side surface of the first lens and the on-axis distance SAG12 between the intersection of the second side surface of the first lens and the optical axis and the effective semi-aperture vertex of the second side surface of the first lens can satisfy: 0.1 < SAG12 / SAG11 < 0.4. By controlling the above condition, the compact design of the optical system can be achieved, thereby reducing the volume and weight of the electronic device comprising the optical system, improving the convenience of wearing the electronic device; at the same time, it can also avoid the thickness of the first lens being too thin, reducing the difficulty of processing, molding and assembling of the first lens.

[0066] In the example embodiment, the on-axis distance SAG31 between the intersection of the first side surface of the third lens and the optical axis and the effective semi-aperture vertex of the first side surface of the third lens, the on-axis distance SAG32 between the intersection of the second side surface of the third lens and the optical axis and the effective semi-aperture vertex of the second side surface of the third lens and the central thickness CT3 of the third lens on the optical axis can satisfy: 6.3 < CT3 / |SAG31+SAG32| < 10.9. By controlling the above condition, the compact design of the optical system can be achieved, thereby reducing the volume and weight of the electronic device comprising the optical system, improving the convenience of wearing the electronic device; at the same time, it can also avoid the thickness of the third lens being too thin, reducing the difficulty of processing, molding and assembling of the third lens.

[0067] The optical system according to the above embodiments of the present application can adopt multiple lenses, for example, 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, and the imaging quality of the optical system can be improved. The optical system configured as above has the characteristics of miniaturization and good imaging quality, and can well meet the use requirements of various portable electronic products in the projection scene.

[0068] In the embodiments of the present application, at least one of the surfaces of the second lens, the third lens and the fourth lens is a non-spherical surface. The characteristic of the aspherical lens is that the curvature is continuously changed from the center of the lens to the periphery of the lens. Unlike the spherical lens with constant curvature from the center of the lens to the periphery of the lens, the aspherical lens has better curvature radius characteristics, and has the advantages of improving the distortion aberration and improving the astigmatism aberration. After using the aspherical lens, the aberration that occurs during imaging can be eliminated as much as possible, thereby improving the imaging quality.

[0069] Reference Figure 1 , Figure 3 , Figure 5 , Figure 7 and Figure 9The second aspect of the present application provides an optical system including, in order from a first side to a second side along an optical axis, a first lens, a second lens, a third lens, and a fourth lens. The first lens has positive refractive power, a first side surface thereof is convex, and a second side surface thereof is concave. The second lens has positive refractive power, a first side surface thereof is flat, and a second side surface thereof is convex. The third lens has negative refractive power, a first side surface thereof is concave, and a second side surface thereof is convex. The fourth lens has positive refractive power, a first side surface thereof is flat, and a second side surface thereof is convex. The optical system further includes a first quarter-wave plate, a reflective polarizing element, a partially reflective element, a polarizer, and a second quarter-wave plate. The first quarter-wave plate is disposed on the first side surface of the second lens. The reflective polarizing element is disposed on a first side surface of the first quarter-wave plate. The partially reflective element is disposed on the second side surface of the third lens. The polarizer is disposed on the first side surface of the fourth lens. The second quarter-wave plate is disposed on a first side surface of the polarizer. The optical system further includes a stop disposed between the first side and the first lens.

[0070] The effective focal length f1 of the first lens and the effective focal length f2 of the second lens satisfy 0.05 < f1 / f2 < 0.5, and the on-axis distance SR from the stop to the first side surface of the first lens and the central thickness CT1 of the first lens on the optical axis satisfy 3.3 < SR / CT1 < 4.2. The optical system provided by the present application uses four lenses, and the refractive powers of the four lenses are reasonably configured to satisfy 0.05 < f1 / f2 < 0.5, which is beneficial to improving the imaging quality of the optical system. Meanwhile, the ratio of the on-axis distance from the stop to the first side surface of the first lens and the central thickness of the first lens on the optical axis is limited, which is beneficial to restricting the angle and position of the incident light, reducing the defocus and astigmatism of the optical system, improving the definition and accuracy of the imaging of the optical system, and improving the imaging effect of the optical system.

[0071] However, those skilled in the art should understand that the number of lenses constituting the optical system can be changed without departing from the technical solutions claimed by the present application, to obtain the various results and advantages described in the present specification.

[0072] The specific embodiments of the optical system applicable to the above-described embodiments are further described below with reference to the accompanying drawings.

[0073] Example 1

[0074] The optical system of the embodiment 1 of the present application is described below with reference to Figure 1 , Figure 2A , Figure 2B , Figure 2C and Figure 2D .

[0075] As Figure 1As shown, the optical system can include, in order along the optical axis from the first side to the second side, a first lens E1, a reflective polarizing element RP, a first quarter wave plate QWP1, a second lens E2, a third lens E3, a partially reflective element BS, a second quarter wave plate QWP2, a polarizer LP, and a fourth lens E4. A stop STO can be disposed between the first side and the first lens E1. In the present embodiment, the first side refers to the side of the human eye, and the second side refers to the side of the display screen. The first side of each element is referred to as the proximate human eye side, and the second side of each element is referred to as the proximate screen side.

[0076] The first lens E1 has a positive focal power, with the proximate human eye side S1 being convex and the proximate screen side S2 being concave. The second lens E2 has a positive focal power, with the proximate human eye side S3 being planar and the proximate screen side S4 being convex. The third lens E3 has a negative focal power, with the proximate human eye side S5 being concave and the proximate screen side S6 being convex. The fourth lens E4 has a positive focal power, with the proximate human eye side S7 being planar and the proximate screen side S8 being convex. The reflective polarizing element RP and the first quarter wave plate QWP1 are attached to the proximate human eye side S3 of the second lens E2. The partially reflective element BS is attached to the proximate screen side S6 of the third lens E3. The second quarter wave plate QWP2 and the polarizer LP are attached to the proximate human eye side S7 of the fourth lens E4. It should be noted that the surfaces S1-S8 are not shown in the following figures. Figure 1

[0077] In the present example, the second side of the optical system can be provided with an image plane IMG, which can be provided with a display screen, for example. Image light from the image plane IMG passes through the fourth lens E4, the polarizer LP, the second quarter wave plate QWP2, the third lens E3, the second lens E2, the first quarter wave plate QWP1, and reaches the reflective polarizing element RP, where a 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 partially reflective element BS on the proximate screen side of the third lens E3, where a second reflection occurs. The light after the second reflection 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, the stop STO, and finally projects into the user's eye. For example, the light of the optical system after two reflections finally projects into the user's eye. A protective glass (not shown) can also be disposed between the image plane IMG and the fourth lens E4.

[0078] Table 1 shows a table of basic parameters of the optical system of Embodiment 1, where the units of the radius of curvature, thickness / distance are millimeters (mm). Image light from the image plane IMG passes through each element in the order of No. 23 to No. 1 and finally projects into the human eye.​

[0079]

[0080]

[0081] Table 1

[0082] In this embodiment, the near-eye side S5 and near-screen side S6 of the third lens E3, and the near-screen side S8 of the fourth lens E4 are all aspherical. The surface shape x of each aspherical lens can be defined using, but is not limited to, the following aspherical formula:

[0083]

[0084] Where x is the distance vector from the vertex of the aspherical surface at a height of h along the optical axis; 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 i-th order correction coefficient of the aspherical surface. Table 2 gives the higher-order coefficients A4, A6, A8, A14, A25, A36, A46, A58 that can be used for the aspherical surfaces S5, S6, and S8 in Example 1. 10 A 12 A 14 A 16 A 18 and A 20 .

[0085] Face number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -1.1484E-01 -4.3240E-02 -1.8153E-01 -9.0684E-02 -3.6076E-02 -1.0030E-02 -1.4527E-03 0.0000E+00 0.0000E+00 S6 2.8668E-01 -1.4136E-02 -1.1010E-01 -7.0024E-02 -3.0565E-02 -8.7823E-03 -1.3157E-03 0.0000E+00 0.0000E+00 S8 -7.4713E-02 2.2604E-02 -1.0719E-03 -7.8212E-04 5.5282E-04 -2.7132E-04 -5.0273E-05 0.0000E+00 0.0000E+00

[0086] Table 2

[0087] Figure 2A The on-axis chromatic aberration curve of the optical system of Embodiment 1 is shown, which represents the deviation of the focal point of light of different wavelengths after passing through the optical system. Figure 2B The astigmatism curves of the optical system of Example 1 are shown, which represent the meridional image plane curvature and sagittal image plane curvature corresponding to different field of view angles. Figure 2C The distortion curves of the optical system of Example 1 are shown, which represent the distortion magnitude values ​​corresponding to different field of view angles. Figure 2D The modulation transfer function curve of the optical system in Example 1 is shown. According to... Figures 2A to 2D It can be seen that the optical system given in Example 1 can achieve good imaging quality.

[0088] Example 2

[0089] The following is for reference Figure 3 , Figure 4A , Figure 4B , Figure 4C and Figure 4D The optical system of Embodiment 2 of this application is described.

[0090] like Figure 3 As 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 reflective element BS, a second quarter-wave plate QWP2, a polarizer LP, and a fourth lens E4, arranged sequentially along the optical axis from the first side to the second side. An 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 referred to as the near-human eye side, and the second side is referred to as the near-screen side.

[0091] The first lens E1 has positive optical power, with its eye-facing side S1 being convex and its screen-facing side S2 being concave. The second lens E2 has positive optical power, with its eye-facing side S3 being planar and its screen-facing side S4 being convex. The third lens E3 has negative optical power, with its eye-facing side S5 being concave and its screen-facing side S6 being convex. The fourth lens E4 has positive optical power, with its eye-facing side S7 being planar and its screen-facing side S8 being convex. A reflective polarizing element RP and a first quarter-wave plate QWP1 are attached to the eye-facing side S3 of the second lens E2. A partially reflective element BS is attached to the screen-facing side S6 of the third lens E3. A second quarter-wave plate QWP2 and a polarizer LP are attached to the eye-facing side S7 of the fourth lens E4. It should be noted that surfaces S1-S8 are... Figure 3 Not shown in the image.

[0092] In this example, an image plane IMG can be provided on the second side of the optical system, and the image plane IMG can, for example, be a display screen. Image light from the image plane IMG passes sequentially through the fourth lens E4, polarizer LP, second quarter-wave plate QWP2, third lens E3, second lens E2, and first quarter-wave plate QWP1, and reaches the reflective polarizing element RP, where it undergoes a first reflection. The light after the first reflection passes through the first quarter-wave plate QWP1, second lens E2, and third lens E3, and reaches the partial reflective element BS located near the screen side of the third lens E3, where it undergoes a second reflection. The light after the second reflection passes sequentially through the third lens E3, second lens E2, first quarter-wave plate QWP1, reflective polarizing element RP, and first lens E1 to the aperture stop and is finally projected into the user's eye. For example, the light from this optical system after two reflections is finally projected into the user's eye. A protective glass (not shown) can also be provided between the image plane IMG and the fourth lens E4.

[0093] Table 3 shows the basic parameters of the optical system of Embodiment 2, where the units for radius of curvature and thickness / distance are millimeters (mm). Image light from the image plane IMG passes through each element in the order of number 23 to number 1 and is finally projected into the human eye.

[0094]

[0095]

[0096] Table 3

[0097] In this embodiment, the near-eye side S5 and near-screen side S6 of the third lens E3, and the near-screen side S8 of the fourth lens E4 are both aspherical surfaces. Table 4 shows the higher-order coefficients A4, A6, A8, and A6 of the aspherical surfaces S5, S6, and S8 that can be used in Embodiment 2. 10 A 12 A 14 A 16 A 18 and A 20 .

[0098] Face number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -4.3410E-01 1.1114E-01 -4.1613E-02 -2.5404E-04 3.3580E-03 1.8738E-03 4.9089E-04 0.0000E+00 0.0000E+00 S6 3.8184E-01 1.5502E-01 1.8114E-02 4.7055E-03 4.4412E-04 -3.0054E-05 1.8337E-06 0.0000E+00 0.0000E+00 S8 -1.2977E-01 2.3621E-02 -1.3190E-03 -1.4779E-04 1.3903E-04 -1.7295E-04 -7.2783E-05 0.0000E+00 0.0000E+00

[0099] Table 4

[0100] Figure 4A The on-axis chromatic aberration curve of the optical system of Embodiment 2 is shown, which represents the deviation of the focal point of light of different wavelengths after passing through the optical system. Figure 4B The astigmatism curves of the optical system of Example 2 are shown, which represent the meridional image plane curvature and sagittal image plane curvature corresponding to different field of view angles. Figure 4C The distortion curves of the optical system of Example 2 are shown, which represent the distortion magnitude values ​​corresponding to different field of view angles. Figure 4D The modulation transfer function curve of the optical system in Example 2 is shown. According to... Figures 4A to 4D It can be seen that the optical system given in Example 2 can achieve good imaging quality.

[0101] Example 3

[0102] The following is for reference Figure 5 , Figure 6A , Figure 6B , Figure 6C and Figure 6D The optical system of Embodiment 3 of this application is described.

[0103] like Figure 5As shown, the optical system can include, in order along the optical axis from the first side to the second side, a first lens E1, a reflective polarizing element RP, a first quarter wave plate QWP1, a second lens E2, a third lens E3, a partially reflective element BS, a second quarter wave plate QWP2, a polarizer LP, and a fourth lens E4. A stop STO can be disposed between the first side and the first lens E1. In the present embodiment, the first side refers to the side of the human eye, and the second side refers to the side of the display screen. The first side of each element is referred to as the proximate human eye side, and the second side of each element is referred to as the proximate screen side.

[0104] The first lens E1 has a positive focal power, with the proximate human eye side S1 being convex and the proximate screen side S2 being concave. The second lens E2 has a positive focal power, with the proximate human eye side S3 being planar and the proximate screen side S4 being convex. The third lens E3 has a negative focal power, with the proximate human eye side S5 being concave and the proximate screen side S6 being convex. The fourth lens E4 has a positive focal power, with the proximate human eye side S7 being planar and the proximate screen side S8 being convex. The reflective polarizing element RP and the first quarter wave plate QWP1 are attached to the proximate human eye side S3 of the second lens E2. The partially reflective element BS is attached to the proximate screen side S6 of the third lens E3. The second quarter wave plate QWP2 and the polarizer LP are attached to the proximate human eye side S7 of the fourth lens E4. It should be noted that the surfaces S1-S8 are not shown in the following figures. Figure 5

[0105] In the present example, the second side of the optical system can be provided with an image plane IMG, which can be provided with a display screen, for example. Image light from the image plane IMG passes through the fourth lens E4, the polarizer LP, the second quarter wave plate QWP2, the third lens E3, the second lens E2, the first quarter wave plate QWP1, and reaches the reflective polarizing element RP, where a 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 partially reflective element BS on the proximate screen side of the third lens E3, where a second reflection occurs. The light after the second reflection 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, the stop STO, and finally projects into the user's eye. For example, the light of the optical system after two reflections finally projects into the user's eye. A protective glass (not shown) can also be disposed between the image plane IMG and the fourth lens E4.

[0106] Table 5 shows a table of basic parameters of the optical system of Example 3, where the units of the radius of curvature, thickness / distance are millimeters (mm). Image light from the image plane IMG passes through each element in the order of No. 23 to No. 1 and finally projects into the human eye.​

[0107]

[0108] Table 5

[0109] In this embodiment, the near-screen side S4 of the second lens E2, the near-eye side S5 and near-screen side S6 of the third lens E3, and the near-screen side S8 of the fourth lens E4 are all aspherical surfaces. Table 6 shows the higher-order coefficients A4, A6, A8, and A6 of the aspherical surfaces S4, S5, S6, and S8 that can be used in Embodiment 3. 10 A 12 A 14 A 16 A 18 and A 20 .

[0110] Face number A4 A6 A8 A10 A12 A14 A16 A18 A20 S4 3.2530E-02 -2.7702E-03 -1.9171E-04 2.0197E-04 -2.9287E-05 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 S5 -3.5666E-01 3.8444E-02 -4.2280E-02 -2.2584E-02 -8.0897E-03 -4.3337E-04 -1.5128E-04 0.0000E+00 0.0000E+00 S6 1.5672E-01 6.3412E-02 -1.4093E-03 -4.7976E-03 -2.8644E-03 -5.9418E-04 -1.3646E-04 0.0000E+00 0.0000E+00 S8 -7.5675E-02 1.3219E-02 -2.0133E-04 -2.0736E-04 1.0836E-04 -5.7616E-05 -5.4961E-05 0.0000E+00 0.0000E+00

[0111] Table 6

[0112] Figure 6A The on-axis chromatic aberration curve of the optical system of Embodiment 3 is shown, which represents the deviation of the focal point of light of different wavelengths after passing through the optical system. Figure 6B The astigmatism curves of the optical system of Example 3 are shown, which represent the meridional image plane curvature and sagittal image plane curvature corresponding to different field of view angles. Figure 6C The distortion curves of the optical system of Example 3 are shown, which represent the distortion magnitude values ​​corresponding to different field of view angles. Figure 6D The modulation transfer function curve of the optical system in Example 3 is shown. According to... Figures 6A to 6D It can be seen that the optical system given in Example 3 can achieve good imaging quality.

[0113] Example 4

[0114] The following is for reference Figure 7 , Figure 8A , Figure 8B , Figure 8C and Figure 8D The optical system of Embodiment 4 of this application is described.

[0115] like Figure 7As shown, the optical system can include, in order along the optical axis from the first side to the second side, a first lens E1, a reflective polarizing element RP, a first quarter wave plate QWP1, a second lens E2, a third lens E3, a partially reflective element BS, a second quarter wave plate QWP2, a polarizer LP, and a fourth lens E4. A stop STO can be disposed between the first side and the first lens E1. In the present embodiment, the first side refers to the side of the human eye, and the second side refers to the side of the display screen. The first side of each element is referred to as the proximate human eye side, and the second side of each element is referred to as the proximate screen side.

[0116] The first lens E1 has a positive focal power, with the proximate human eye side S1 being convex and the proximate screen side S2 being concave. The second lens E2 has a positive focal power, with the proximate human eye side S3 being planar and the proximate screen side S4 being convex. The third lens E3 has a negative focal power, with the proximate human eye side S5 being concave and the proximate screen side S6 being convex. The fourth lens E4 has a positive focal power, with the proximate human eye side S7 being planar and the proximate screen side S8 being convex. The reflective polarizing element RP and the first quarter wave plate QWP1 are attached to the proximate human eye side S3 of the second lens E2. The partially reflective element BS is attached to the proximate screen side S6 of the third lens E3. The second quarter wave plate QWP2 and the polarizer LP are attached to the proximate human eye side S7 of the fourth lens E4. It should be noted that the surfaces S1-S8 are not shown in the Figure 7

[0117] In the present example, the second side of the optical system can be provided with an image plane IMG, which can be provided with a display screen, for example. Image light from the image plane IMG passes through the fourth lens E4, the polarizer LP, the second quarter wave plate QWP2, the third lens E3, the second lens E2, the first quarter wave plate QWP1, and reaches the reflective polarizing element RP, where a 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 partially reflective element BS on the proximate screen side of the third lens E3, where a second reflection occurs. The light after the second reflection 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, the stop STO, and finally projects into the eye of the user. For example, the light of the optical system after two reflections finally projects into the eye of the user. A protective glass (not shown) can also be disposed between the image plane IMG and the fourth lens E4.

[0118] Table 7 shows a table of basic parameters of the optical system of Example 4, where the units of the radius of curvature, thickness / distance are millimeters (mm). Image light from the image plane IMG passes through each element in the order of No. 23 to No. 1 and finally projects into the human eye.​

[0119]

[0120] Table 7

[0121] In this embodiment, the near-eye side S5 and near-screen side S6 of the third lens E3, and the near-screen side S8 of the fourth lens E4 are both aspherical surfaces. Table 8 shows the higher-order coefficients A4, A6, A8, and A6 of the aspherical surfaces S5, S6, and S8 that can be used in Embodiment 4. 10 A 12 A 14 A 16 A 18 and A 20 .

[0122] Face number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -1.2655E+00 -6.7949E-01 -5.3222E-01 -2.6516E-01 -1.0177E-01 -2.6735E-02 -3.6799E-03 0.0000E+00 0.0000E+00 S6 -3.7357E-01 -5.0463E-01 -3.8787E-01 -1.9594E-01 -7.2611E-02 -1.8009E-02 -2.3212E-03 0.0000E+00 0.0000E+00 S8 -6.1539E-02 1.5299E-02 1.8727E-03 -6.5188E-04 4.1568E-04 -1.2510E-04 1.3397E-04 0.0000E+00 0.0000E+00

[0123] Table 8

[0124] Figure 8A The on-axis chromatic aberration curve of the optical system of Embodiment 4 is shown, which represents the deviation of the focal point of light of different wavelengths after passing through the optical system. Figure 8B The astigmatism curves of the optical system of Example 4 are shown, which represent the meridional image plane curvature and sagittal image plane curvature corresponding to different field of view angles. Figure 8C The distortion curves of the optical system of Example 4 are shown, representing the distortion magnitude values ​​corresponding to different field of view angles. Figure 8D The modulation transfer function curve of the optical system in Example 4 is shown. According to... Figures 8A to 8D It can be seen that the optical system given in Example 4 can achieve good imaging quality.

[0125] Example 5

[0126] The following is for reference Figure 9 , Figure 10A , Figure 10B , Figure 10C and Figure 10D The optical system of Embodiment 5 of this application is described.

[0127] like Figure 9 As 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 reflective element BS, a second quarter-wave plate QWP2, a polarizer LP, and a fourth lens E4, arranged sequentially along the optical axis from the first side to the second side. An 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 referred to as the near-human eye side, and the second side is referred to as the near-screen side.

[0128] The first lens E1 has positive focal power, its proximal eye side surface S1 is convex, and its proximal screen side surface S2 is concave. The second lens E2 has positive focal power, its proximal eye side surface S3 is flat, and its proximal screen side surface S4 is convex. The third lens E3 has negative focal power, its proximal eye side surface S5 is concave, and its proximal screen side surface S6 is convex. The fourth lens E4 has positive focal power, its proximal eye side surface S7 is flat, and its proximal screen side surface S8 is convex. The reflective polarizing element RP and the first quarter wave plate QWP1 are attached to the proximal eye side surface S3 of the second lens E2. The partial reflection element BS is attached to the proximal screen side surface S6 of the third lens E3. The second quarter wave plate QWP2 and the polarizer LP are attached to the proximal eye side surface S7 of the fourth lens E4. It should be noted that the surfaces S1-S8 are not shown in Figure 9 .

[0129] In this example, the second side of the optical system can be provided with an image plane IMG, which can for example be provided with a display screen. The image light from the image plane IMG passes sequentially through the fourth lens E4, the polarizer LP, the second quarter wave plate QWP2, the third lens E3, the second lens E2, the first quarter wave plate QWP1, and the reflective polarizing element RP, where a 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 the partial reflection element BS on the proximal screen side of the third lens E3, where a second reflection occurs. The light after the second reflection passes sequentially through the third lens E3, the second lens E2, the first quarter wave plate QWP1, the reflective polarizing element RP, the first lens E1, the aperture, and finally into the eye of the user. For example, the light of the optical system after two reflections is finally projected into the eye of the user. A protective glass (not shown) can also be provided between the image plane IMG and the fourth lens E4.

[0130] Table 9 shows the basic parameter table of the optical system of Example 5, where the units of the radius of curvature, thickness / distance are all millimeters (mm). The image light from the image plane IMG passes through each element in the order of No. 23 to No. 1 and is finally projected into the eye.

[0131]

[0132]

[0133] Table 9

[0134] In this embodiment, the near-eye side S5 and near-screen side S6 of the third lens E3, and the near-screen side S8 of the fourth lens E4 are both aspherical surfaces. Table 10 lists the higher-order coefficients A4, A6, A8, and A6 of the aspherical surfaces S5, S6, and S8 that can be used in Embodiment 5. 10 A 12 A 14 A 16 A 18 and A 20 .

[0135] Face number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -1.5837E+00 -6.4837E-01 -6.2169E-01 -2.9333E-01 -1.0731E-01 -2.6438E-02 -2.9174E-03 0.0000E+00 0.0000E+00 S6 -1.7603E-01 -2.7204E-01 -2.8992E-01 -1.5499E-01 -6.0855E-02 -1.5901E-02 -2.0740E-03 0.0000E+00 0.0000E+00 S8 -3.4819E-02 2.7662E-03 4.0296E-03 -2.3324E-03 1.2051E-03 -4.8623E-04 7.0302E-05 0.0000E+00 0.0000E+00

[0136] Table 10

[0137] Figure 10A The on-axis chromatic aberration curve of the optical system of Embodiment 5 is shown, which represents the deviation of the focal point of light of different wavelengths after passing through the optical system. Figure 10B The astigmatism curves of the optical system of Example 5 are shown, which represent the meridional image plane curvature and sagittal image plane curvature corresponding to different field of view angles. Figure 10C The distortion curves of the optical system of Example 5 are shown, which represent the distortion magnitude values ​​corresponding to different field of view angles. Figure 10D The modulation transfer function curve of the optical system in Example 5 is shown. According to... Figures 10A to 10D It can be seen that the optical system given in Example 5 can achieve good imaging quality.

[0138] Table 11 gives the basic parameters of each embodiment in Examples 1 to 5, such as the values ​​of f, f1, f2, f3, f4, SR, fz1, SAG11, SAG12, SAG31, and SAG32.

[0139]

[0140]

[0141] Table 11

[0142] In summary, Table 12 shows the values ​​of the conditional expressions for each of the embodiments in Examples 1 to 5.

[0143] Conditional / Example 1 2 3 4 5 f1 / f2 0.10 0.33 0.45 0.45 0.32 fz1 / R4 -1.99 -2.00 -2.04 -1.91 -1.91 N2 / NQ1 1.00 1.00 0.99 1.01 1.01 V1 / V3 2.47 2.26 2.18 2.09 2.09 f1 / (R1+R2) 0.98 0.61 0.75 0.45 0.90 R5 / R6 0.57 0.31 0.31 0.21 0.35 f / f3 -0.19 -0.40 -0.35 -0.50 -0.38 CT3 / (CTQ2+CTL+CT4) 2.94 3.20 4.25 4.36 2.52 T12 / (CTR+CTQ1+CT2) 1.38 0.37 0.49 0.21 0.93 R8 / f4 -0.55 -0.67 -0.86 -0.55 -0.85 (VR+VQ1) / V2 1.73 1.99 1.62 1.83 1.83 SR / CT1 4.11 3.35 3.85 3.39 3.68 SAG12 / SAG11 0.38 0.23 0.29 0.18 0.32 CT3 / |SAG31+SAG32| 10.82 8.21 10.51 9.13 6.34

[0144] Table 12

[0145] This application also provides an optical device, which can be a standalone projection device such as a projector, or a projection module integrated into a mobile electronic device such as a virtual reality device. The optical device is equipped with the optical system described above.

[0146] The above description is only the preferred embodiment of the present application and the explanation of the technical principles. It should be understood by those skilled in the art that the scope of the disclosure of the present application is not limited to the technical solutions with the specific combination of the above technical features, and should also cover other technical solutions formed by combining the above technical features or their equivalent features without departing from the concept of the present application. For example, the technical solutions formed by replacing the above features with the technical features disclosed in the present application (but not limited to) with similar functions.

Claims

1. An optical system, characterized in that, Along the optical axis, from the first side to the second side, the following are included in sequence: A first lens with positive optical power has a first side surface that is convex and a second side surface that is concave. A second lens with positive optical power has a first side surface that is flat and a second side surface that is convex. A third lens with negative optical power, wherein its first side surface is concave and its second side surface is convex; and A fourth lens with positive optical power has a first side surface that is flat and a second side surface that is convex. The optical system further includes: A first quarter-wave plate is disposed on the first side of the second lens; A reflective polarizing element is disposed on the first side of the first quarter-wave plate; A portion of the reflective element is disposed on the second side of the third lens; A polarizer is disposed on the first side of the fourth lens; and A second quarter-wave plate is disposed on the first side of the polarizer; The effective focal length f1 of the first lens and the effective focal length f2 of the second lens satisfy: 0.05 <f1 / f2<0.5; The combined focal length fz1 of the reflective polarizing element, the first quarter-wave plate, and the second lens satisfies the following relationship with the radius of curvature R4 of the second side surface of the second lens: -2.1 <fz1 / R4<-1.9。 2. The optical system according to claim 1, wherein, The refractive index NQ1 of the first quarter-wave plate and the refractive index N2 of the second lens satisfy: 0.95 <N2 / NQ1<1.05。 3. The optical system according to claim 1, wherein, The Abbe number V1 of the first lens and the Abbe number V3 of the third lens satisfy: 2.0 <V1 / V3<2.5。 4. The optical system according to claim 1, wherein, The effective focal length f1 of the first lens, the radius of curvature R1 of the first side surface of the first lens, and the radius of curvature R2 of the second side surface of the first lens satisfy: 0.4 <f1 / (R1+R2)<1.0。 5. The optical system according to claim 1, wherein, The radius of curvature R5 of the first side surface of the third lens and the radius of curvature R6 of the second side surface of the third lens satisfy: 0.2 <R5 / R6<0.6。 6. The optical system according to claim 1, wherein, The total effective focal length f of the optical system and the effective focal length f3 of the third lens satisfy: -0.55 <f / f3<-0.15。 7. The optical system according to any one of claims 1-6, wherein, The center thickness CT3 of the third lens on the optical axis, the center thickness CTQ2 of the second quarter-wave plate on the optical axis, the center thickness CTL of the polarizer on the optical axis, and the center thickness CT4 of the fourth lens on the optical axis satisfy: 2.5 <CT3 / (CTQ2+CTL+CT4)<4.4。 8. The optical system according to any one of claims 1-6, wherein, The axial distance T12 between the second side surface of the first lens and the first side surface of the second lens, 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: 0.2 <T12 / (CTR+CTQ1+CT2)<1.4。 9. The optical system according to any one of claims 1-6, wherein, The effective focal length f4 of the fourth lens and the radius of curvature R8 of the second side surface of the fourth lens satisfy: -0.9 <R8 / f4<-0.5。 10. The optical system according to any one of claims 1-6, wherein, The Abbe number VR of the reflective polarizing element, the Abbe number VQ1 of the first quarter-wave plate, and the Abbe number V2 of the second lens satisfy: 1.6 < (VR + VQ1) / V2 < 2.

0.

11. The optical system according to any one of claims 1-6, wherein, The optical system further includes an aperture stop disposed between the first side and the first lens; Wherein, the axial distance SR from the aperture to the first side surface of the first lens and the center thickness CT1 of the first lens on the optical axis satisfy: 3.3 <SR / CT1<4.2。 12. The optical system according to any one of claims 1-6, wherein, The axial distance SAG11 between the intersection of the first side surface of the first lens and the optical axis to the vertex of the effective half-aperture of the first side surface of the first lens, and the axial distance SAG12 between the intersection of the second side surface of the first lens and the optical axis to the vertex of the effective half-aperture of the second side surface of the first lens, satisfy: 0.1 <SAG12 / SAG11<0.4。 13. The optical system according to any one of claims 1-6, wherein, The axial distance SAG31 between the intersection of the first side surface of the third lens and the optical axis to the vertex of the effective half-aperture of the first side surface of the third lens, the axial distance SAG32 between the intersection of the second side surface of the third lens and the optical axis to the vertex of the effective half-aperture of the second side surface of the third lens, and the center thickness CT3 of the third lens on the optical axis satisfy: 6.3 <CT3 / |SAG31+SAG32|<10.9。

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