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 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, and the first side surface of the first lens is a convex surface; the second lens has negative focal power, the first side surface of the second lens is a plane, and the second side surface is a concave surface; the second side surface of the third lens is a convex surface; the first side surface of the fourth lens is a plane; the effective focal length f1 of the first lens and the effective focal length f2 of the second lens meet the following formula:-0.7 lt; f1 / f2lt; -0.15, < = 0.15; the combined focal length fz2 of the second quarter-wave plate, the polaroid and the fourth lens and the curvature radius R8 of the second side face of the fourth lens meet the condition that fz2 / R8 is larger than or equal to-2.0 and smaller than or equal to-1.5.

Description

Technical Field

[0001] The present 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 or augmented 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 or augmented 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 optical path, thereby shifting the center of gravity of the virtual reality device or augmented reality device backward and improving 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] The present 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, the present application provides such an optical system that 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, and its first side is a convex surface. The second lens has a negative optical power, its first side is a plane, and its second side is a concave surface. The third lens has an optical power, and its second side is a convex surface. The fourth lens has an optical power, and its first side is a plane. Wherein, the optical system further includes a first quarter-wave plate, a reflective polarizing element, a partial reflection 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 partial reflection 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. The effective focal length f1 of the first lens and the effective focal length f2 of the second lens satisfy: -0.7 < f1 / f2 < -0.15; the combined focal length fz2 of the second quarter-wave plate, the polarizer, and the fourth lens and the curvature radius R8 of the second side of the fourth lens satisfy: -2.0 ≤ fz2 / R8 ≤ -1.5.

[0006] According to an exemplary embodiment of the present application, the refractive index NR of the reflective polarizing element, the refractive index NQ1 of the first quarter-wave plate, and the refractive index N2 of the second lens satisfy: 1.6 < (NR + NQ1) / N2 < 1.75.

[0007] According to an exemplary embodiment of the present application, the refractive index NQ2 of the second quarter-wave plate, the refractive index NL of the polarizer, and the refractive index N4 of the fourth lens satisfy: 1.75 < (NQ2 + NL) / N4 < 2.05.

[0008] According to an exemplary embodiment of the present application, the central thickness CT4 of the fourth lens on the optical axis, 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: 5.7 < CT4 / (CTQ2 + CTL) ≤ 9.1.

[0009] According to an exemplary embodiment of the present application, 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, the central thickness CT2 of the second lens on the optical axis, and the axial distance SAG22 between the intersection of the second side surface of the second lens and the optical axis and the vertex of the effective semi-aperture of the second side surface of the second lens satisfy: 3.6 < (CTR + CTQ1 + CT2) / SAG22 < 4.6.

[0010] According to an exemplary embodiment of the present application, the effective focal length f1 of the first lens, 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, and 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 satisfy: 4.9 < f1 / (SAG11 + SAG12) < 8.2.

[0011] According to an exemplary embodiment of the present application, the edge thickness ET1 of the first lens and the edge thickness ET3 of the third lens satisfy: 4.4 < ET3 / ET1 < 5.2.

[0012] According to an exemplary embodiment of the present application, the refractive index N1 of the first lens and the Abbe number V1 of the first lens satisfy: 40 < V1 / N1 < 44; the refractive index N2 of the second lens and the Abbe number V2 of the second lens satisfy: 12.8 < V2 / N2 < 20.

[0013] According to an exemplary embodiment of the present application, the combined focal length fz1 of the reflective polarizing element, the first quarter-wave plate, and the second lens and the total effective focal length f of the optical system satisfy: -1.0 < f / fz1 < -0.1.

[0014] According to an exemplary embodiment of the present application, the radius of curvature R1 of the first side surface of the first lens and the central thickness CT1 of the first lens on the optical axis satisfy: 2.2 < R1 / CT1 < 4.2.

[0015] According to an exemplary embodiment of the present application, 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 axial distance SAG42 between the intersection of the second side surface of the fourth lens and the optical axis and the vertex of the effective semi-aperture of the second side surface of the fourth lens satisfy: 0.3 < (CTQ2 + CTL) / |SAG42| < 1.4.

[0016] According to an exemplary embodiment of the present application, the radius of curvature R4 of the second side surface of the second lens and the radius of curvature R6 of the second side surface of the third lens satisfy: -2.1 ≤ R4 / R6 < 0.

[0017] According to an exemplary embodiment of the present application, the optical system further includes a diaphragm disposed between the first side and the first lens; wherein, the axial distance TD from the first side surface of the first lens to the second side surface of the fourth lens and the axial distance SR from the diaphragm to the first side surface of the first lens satisfy: 1.2 < TD / SR < 1.3.

[0018] The optical system provided by the present application uses four lenses, rationally configures the optical powers of the four lenses and enables the optical system to satisfy "-0.7 < f1 / f2 < -0.15", which is beneficial to improving the imaging quality of the optical system; at the same time, by cooperating with restricting the ratio of the combined focal length of the second quarter-wave plate, the polarizer and the fourth lens to the radius of curvature of the second side surface of the fourth lens, it is beneficial to provide a wider field of view angle, enabling the user to see more display content, enhancing the user's immersion and experience, 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

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

[0020] Figure 1 Fig. 1 shows a schematic structural diagram of the optical system according to Embodiment 1 of the present application;

[0021] Figures 2A to 2D Figs. 2-5 respectively show the axial chromatic aberration curve, astigmatism curve, distortion curve, and modulation transfer function (MTF) curve of the optical system according to Embodiment 1 of the present application;

[0022] Figure 3 Fig. 6 shows a schematic structural diagram of the optical system according to Embodiment 2 of the present application;

[0023] Figures 4A to 4DRespectively shown are the axial chromatic aberration curve, astigmatism curve, distortion curve, and modulation transfer function curve of the optical system according to Embodiment 2 of the present application;

[0024] Figure 5 Shown is a schematic structural diagram of the optical system according to Embodiment 3 of the present application;

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

[0026] Figure 7 Shown is a schematic structural diagram of the optical system according to Embodiment 4 of the present application; and

[0027] Figures 8A to 8D Respectively shown are the axial chromatic aberration curve, astigmatism curve, distortion curve, and modulation transfer function curve of the optical system according to Embodiment 4 of the present application. Detailed implementation manners

[0028] 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.

[0029] It should be noted that in this specification, the expressions such as first and second are only used to distinguish one feature from another feature and do not represent any limitation on the feature. Therefore, without departing from the teachings of the present application, the first lens discussed below may also be referred to as the second lens.

[0030] In the drawings, for the sake of illustration, the thickness, size, and shape of the lens have been slightly exaggerated. Specifically, the shapes of the spherical or aspherical surfaces shown in the drawings are shown by way of example. That is, the shapes of the spherical or aspherical surfaces are not limited to the spherical or aspherical shapes shown in the drawings. The drawings are only examples and are not drawn strictly to scale.

[0031] In this article, the paraxial region refers to the region near the optical axis. If the lens surface is convex and the position of the convex surface is 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 (such as the human eye side) is called the first side surface of the lens, and the surface of each lens closest to the second side (such as the display screen side) is called the second side surface of the lens.

[0032] It should also be understood that the terms "comprising", "comprises", "having", "include" and / or "including", 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 embodiments of the present application, the use of "may" means "one or more embodiments of the present application". Also, the term "exemplary" is intended to refer to an example or illustration.

[0033] 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.

[0034] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0035] The features, principles and other aspects of the present application will be described in detail below.

[0036] Referring to Figure 1 、 Figure 3 、 Figure 5 and Figure 7 , a first aspect of the present application provides an optical system that may include 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.

[0037] In an exemplary embodiment, the first lens may have a positive optical power. The second lens may have a negative optical power. The third lens may have a positive optical power or 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 conducive to improving the imaging quality of the optical system.

[0038] In an exemplary embodiment, the first side of the first lens is convex, and the second side is convex or concave.

[0039] In an exemplary embodiment, the first side of the second lens is planar, and the second side is concave.

[0040] In an exemplary embodiment, the first side of the third lens is convex or concave, and the second side is convex.

[0041] In an exemplary embodiment, the first side of the fourth lens is planar, and the second side is convex or concave. ​

[0042] 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 a first side surface of the second lens. The reflective polarizing element may be disposed on a first side surface of the first quarter-wave plate.

[0043] 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 difficulty of the attaching process can be reduced, the attaching quality can be improved, and thus the performance of the optical system can be enhanced.

[0044] In an exemplary embodiment, the optical system may further include a partial reflection element. The partial reflection element may be disposed on a 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 overall length of the optical system.

[0045] In an exemplary embodiment, the optical system may further include a second quarter-wave plate and a polarizer. The polarizer may be disposed on a first side surface of the fourth lens. The second quarter-wave plate may be disposed on a first side surface of the polarizer. The polarizer is used 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 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 by the display screen can be converted into circularly polarized light, thereby reducing the influence of the material stress of the components between the display screen and the polarizer and improving the contrast of the optical system.

[0046] In an exemplary embodiment, the first side surface of the fourth lens is a flat surface. The second quarter-wave plate and the polarizer are bonded and attached to the first side surface of the fourth lens, wherein the polarizer is closer to the fourth lens than the second quarter-wave plate. By combining the second quarter-wave plate and the polarizer together and then attaching them to the first side surface of the fourth lens, the difficulty of the attaching process can be reduced, the attaching quality can be improved, and thus the performance of the optical system can be enhanced.

[0047] In an exemplary embodiment, the optical system may further include a diaphragm, and the diaphragm may be disposed between the first side and the first lens. The image light from the second side passes through 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, etc., and is finally projected onto the eyes of the user on the first side after multiple refractions and reflections.

[0048] In an exemplary embodiment, the first side may be, for example, the side facing the human eye, and the second side may be, for example, the side facing the display screen. Accordingly, the first side surfaces of the respective elements (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 side surfaces near the human eye, and the second side surfaces may be referred to as the side surfaces near the screen.

[0049] 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 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 reaches the 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 finally projects into the user's eyes. The optical system provided in the present 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.

[0050] 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: -0.7 < f1 / f2 < -0.15; the combined focal length fz2 of the second quarter-wave plate, the polarizer and the fourth lens and the radius of curvature R8 of the second side surface of the fourth lens may satisfy: -2.0 ≤ fz2 / R8 ≤ -1.5. By controlling the optical system to satisfy "-0.7 < f1 / f2 < -0.15", 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 second quarter-wave plate, the polarizer and the fourth lens to the radius of curvature of the second side surface of the fourth lens, it is beneficial to provide a wider viewing angle, enabling the user to see more display content, enhancing the user's immersion and experience, and also being able to reduce or eliminate optical problems such as distortion and aberration, improving the clarity and accuracy of the image formed by the optical system.

[0051] In an exemplary embodiment, the refractive index NR of the reflective polarizing element, the refractive index NQ1 of the first quarter-wave plate, and the refractive index N2 of the second lens may satisfy: 1.6 < (NR + NQ1) / N2 < 1.75. By controlling the ratio of the sum of the refractive indices of the reflective polarizing element and the first quarter-wave plate to the refractive index of the second lens, total internal reflection of light caused by excessive differences in the refractive indices of the reflective polarizing element, the first quarter-wave plate, and the second lens can be avoided, light reflection and light refraction losses in the optical system can be reduced, the light transmission efficiency can be improved, and at the same time, it is also beneficial to improve the dispersion effect of the optical system.

[0052] In an exemplary embodiment, the refractive index NQ2 of the second quarter-wave plate, the refractive index NL of the polarizer, and the refractive index N4 of the fourth lens may satisfy: 1.75 < (NQ2 + NL) / N4 < 2.05. By controlling the ratio of the sum of the refractive indices of the second quarter-wave plate and the polarizer to the refractive index of the fourth lens, total internal reflection of light caused by excessive differences in the refractive indices of the second quarter-wave plate, the polarizer, and the fourth lens can be avoided, light reflection and light refraction losses in the optical system can be reduced, the light transmission efficiency can be improved, and at the same time, it is also beneficial to improve the dispersion effect of the optical system.

[0053] In an exemplary embodiment, the central thickness CT4 of the fourth lens on the optical axis, 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: 5.7 < CT4 / (CTQ2 + CTL) ≤ 9.1. By controlling the ratio of the central thickness of the fourth lens to the sum of the central thicknesses of the second quarter-wave plate and the polarizer, the body length of the optical system can be shortened, and at the same time, it will be beneficial to the attachment of the second quarter-wave plate and the polarizer.

[0054] In an exemplary embodiment, 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, the central thickness CT2 of the second lens on the optical axis, and the axial distance SAG22 between the intersection of the second side surface of the second lens and the optical axis and the vertex of the effective semi-aperture of the second side surface of the second lens may satisfy: 3.6 < (CTR + CTQ1 + CT2) / SAG22 < 4.6. By controlling the above conditional formula, a compact design of the optical system can be achieved, thereby reducing the volume and weight of the electronic device including the optical system, improving the convenience of wearing the electronic device, and at the same time, it can also avoid the second lens being too thin and reduce the difficulty of processing, forming, and assembling the second lens.

[0055] In an exemplary embodiment, the effective focal length f1 of the first lens, 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, and 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 may satisfy: 4.9 < f1 / (SAG11 + SAG12) < 8.2. By controlling the above conditional expression, it is possible to constrain the effective focal length of the first lens and the sag heights of the first side surface and the second side surface of the first lens, reduce the axial distance ratio between adjacent lenses, thereby reducing the generation of aberrations and improving the clarity and accuracy of the image formed by the optical system.

[0056] In an exemplary embodiment, the edge thickness ET1 of the first lens and the edge thickness ET3 of the third lens may satisfy: 4.4 < ET3 / ET1 < 5.2. By controlling the ratio of the edge thickness of the third lens to that of the first lens, a compact design of the optical system can be achieved, thereby reducing the volume and weight of the electronic device including the optical system, improving the convenience of wearing the electronic device, and at the same time avoiding the edge thicknesses of the first lens and the third lens being too thin, reducing the difficulty of processing, forming, and assembling the first lens and the third lens, and also helping to reduce the risk of optical system failures and increase the service life of the optical system.

[0057] In an exemplary embodiment, the refractive index N1 of the first lens and the Abbe number V1 of the first lens may satisfy: 40 < V1 / N1 < 44; the refractive index N2 of the second lens and the Abbe number V2 of the second lens may satisfy: 12.8 < V2 / N2 < 20. By controlling the ratio of the Abbe number to the refractive index of the first lens and the ratio of the Abbe number to the refractive index of the second lens, the dispersion characteristics of the first lens and the second lens can be optimized, the color reproduction ability and imaging quality of the optical system can be improved, and at the same time, it is beneficial to reduce the aberrations that may occur in the optical system, reduce the distortion and image blur of the optical system.

[0058] In an exemplary embodiment, the combined focal length fz1 of the reflective polarizing element, the first quarter-wave plate, and the second lens and the total effective focal length f of the optical system may satisfy: -1.0 < f / fz1 < -0.1. By controlling the ratio of the total effective focal length of the optical system to the combined focal length of the reflective polarizing element, the first quarter-wave plate, and the second lens, the imaging quality of the optical system can be improved, the light focusing ability can be enhanced, and the distortion can be reduced.

[0059] In an exemplary embodiment, the radius of curvature R1 of the first side surface of the first lens and the central thickness CT1 of the first lens on the optical axis may satisfy: 2.2 < R1 / CT1 < 4.2. By controlling the ratio of the radius of curvature of the first side surface of the first lens to the central thickness of the first lens on the optical axis, spherical aberration can be reduced, the image quality and overall optical characteristics of the optical system can be improved. At the same time, it is also beneficial to enhance the stability and reliability of the design of the first lens, better constrain the optical characteristics of the first lens, and reduce the possibility of unexpected optical behaviors or performance problems.

[0060] In an exemplary embodiment, 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 axial distance SAG42 between the intersection of the second side surface of the fourth lens and the optical axis and the vertex of the effective semi-aperture of the second side surface of the fourth lens may satisfy: 0.3 < (CTQ2 + CTL) / |SAG42| < 1.4. During the use of the optical system, it is vulnerable to vibration, which may cause the formed image to be blurred or distorted. By controlling the ratio of the sum of the central thicknesses of the second quarter-wave plate and the polarizer to the absolute value of the sagitta of the second side surface of the fourth lens, the structure and stability of the fourth lens can be optimized, the anti-vibration ability of the optical system can be improved, and the formed image can be made more stable and clear.

[0061] In an exemplary embodiment, the radius of curvature R4 of the second side surface of the second lens and the radius of curvature R6 of the second side surface of the third lens may satisfy: -2.1 ≤ R4 / R6 < 0. By controlling the ratio of the radius of curvature of the second side surface of the second lens to the radius of curvature of the second side surface of the third lens, it is beneficial to reduce or eliminate spherical aberration that may occur in the optical system, improve the imaging quality and clarity of the optical system. At the same time, it is also beneficial to reduce the manufacturing cost and improve the production efficiency.

[0062] 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 and the axial distance SR from the aperture stop to the first side surface of the first lens may satisfy: 1.2 < TD / SR < 1.3. By controlling the above conditional formula, it is beneficial to reduce the spherical aberration of the optical system, improve the clarity and accuracy of the formed image, and achieve higher-quality image output. At the same time, it is also beneficial to reduce the fluctuations and instabilities of the optical system and ensure the long-term stable operation of the optical system.

[0063] 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 immersion and experience of the user 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.

[0064] In an embodiment of the present application, at least one of the surfaces of the third lens and the fourth lens is an aspherical surface. The characteristic of an aspherical lens is that the curvature continuously changes from the center of the lens to the periphery of the lens. Different from a spherical lens having a constant curvature from the center of the lens to the periphery of the lens, an aspherical lens has better curvature radius characteristics and has the advantages of improving distortion aberration and improving astigmatism aberration. After using an aspherical lens, the aberration that appears during imaging can be eliminated as much as possible, thereby improving the imaging quality.

[0065] Reference Figure 1 、 Figure 3 、 Figure 5 and Figure 7 According to, and, a second aspect of the present application provides an optical system that sequentially includes a first lens, a second lens, a third lens, and a fourth lens along the optical axis from a first side to a second side. The first lens has a positive optical power, and its first side is a convex surface. The second lens has a negative optical power, its first side is a plane, and its second side is a concave surface. The third lens has an optical power, and its second side is a convex surface. The fourth lens has an optical power, and its first side is a plane. The optical system further includes a first quarter-wave plate, a reflective polarizing element, a partial reflection 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 partial reflection 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.

[0066] Among them, the effective focal length f1 of the first lens and the effective focal length f2 of the second lens satisfy: -0.7 < f1 / f2 < -0.15; the refractive index NR of the reflective polarizing element, the refractive index NQ1 of the first quarter-wave plate, and the refractive index N2 of the second lens satisfy: 1.6 < (NR + NQ1) / N2 < 1.75. The optical system provided by the present application uses four lenses, rationally configuring the optical power of the four lenses and making the optical system satisfy "-0.7 < f1 / f2 < -0.15", which is beneficial to improving the imaging quality of the optical system; at the same time, by cooperating to limit the ratio of the sum of the refractive indices of the reflective polarizing element and the first quarter-wave plate to the refractive index of the second lens, it is possible to avoid total internal reflection of light caused by too large a difference in the refractive indices of the reflective polarizing element, the first quarter-wave plate, and the second lens, reduce the light reflection and light refraction losses in the optical system, improve the light transmission efficiency, and is also beneficial to improving the dispersion effect of the optical system.

[0067] However, those skilled in the art should understand that without departing from the technical solutions claimed in the present application, the number of lenses constituting the optical system can be changed to obtain the various results and advantages described in this specification.

[0068] The following further describes specific embodiments of the optical system applicable to the above embodiments with reference to the accompanying drawings.

[0069] Example 1

[0070] The following refers to Figure 1 、 Figure 2A 、 Figure 2B 、 Figure 2C and Figure 2D describe the optical system of Embodiment 1 of the present application.

[0071] 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 second quarter-wave plate QWP2, a polarizer LP, and a fourth lens E4 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.

[0072] The first lens E1 has a positive focal power. Its side S1 near the human eye is convex, and its side S2 near the screen is concave. The second lens E2 has a negative focal power. Its side S3 near the human eye is flat, and its side S4 near the screen is concave. The third lens E3 has a positive focal power. Its side S5 near the human eye is convex, and its side S6 near the screen is convex. The fourth lens E4 has a positive focal power. Its side S7 near the human eye is flat, and its side S8 near the screen is convex. The reflective polarizing element RP and the first quarter-wave plate QWP1 are attached to the side S3 of the second lens E2 near the human eye. The partial reflection element BS is attached to the side S6 of the third lens E3 near the screen. The second quarter-wave plate QWP2 and the polarizer LP are attached to the side S7 of the fourth lens E4 near the human eye. It should be noted that the surfaces S1 - S8 are not shown in Figure 1 is not shown.

[0073] 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 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 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 near 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 eyes. For example, the light after two reflections of this optical system finally projects into the user's eyes. A protective glass (not shown) can also be provided between the image plane IMG and the fourth lens E4.

[0074] Table 1 shows the basic parameter table of the optical system of Embodiment 1. Among them, the units of the radius of curvature and the thickness / distance are both millimeters (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.

[0075]

[0076] Table 1

[0077] In this embodiment, the side S5 of the third lens E3 near the human eye and the side S6 near the screen, and the side S8 of the fourth lens E4 near the screen are all aspherical surfaces. The surface profile x of each aspherical lens can be defined by, but not limited to, the following aspherical formula:

[0078]

[0079] Wherein, x is the sagitta, the distance from the vertex of the aspherical surface to the aspherical surface at the position with height 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 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 .

[0080] Face number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -1.7321E-01 3.7503E-01 6.9162E-02 1.0327E-02 2.2502E-03 2.7641E-04 -2.1806E-04 0.0000E+00 0.0000E+00 S6 3.8033E-01 1.7550E-01 2.6809E-02 -6.0262E-03 -6.3487E-03 -2.4129E-03 -4.5348E-04 0.0000E+00 0.0000E+00 S8 -1.3963E-01 1.8549E-02 5.0906E-04 -5.5609E-04 1.8651E-04 -3.0061E-04 -6.7872E-05 0.0000E+00 0.0000E+00

[0081] Table 2

[0082] Figure 2A shows the axial chromatic aberration curve of the optical system of Example 1, which represents the deviation of the focusing 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 2D shows the modulation transfer function curve of the optical system of Example 1. According to Figures 2A to 2D it can be known that the optical system given in Example 1 can achieve good imaging quality.

[0083] Example 2

[0084] The following will describe the optical system of Embodiment 2 of the present application with reference to Figure 3 、 Figure 4A 、 Figure 4B 、 Figure 4C and Figure 4D .

[0085] As Figure 3 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 second quarter-wave plate QWP2, a polarizer LP, and a fourth lens E4 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 the respective elements 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.

[0086] The first lens E1 has a positive optical power, its eye-side surface S1 is convex, and its screen-side surface S2 is convex. The second lens E2 has a negative optical power, its eye-side surface S3 is flat, and its screen-side surface S4 is concave. The third lens E3 has a positive optical power, its eye-side surface S5 is convex, and its screen-side surface S6 is convex. The fourth lens E4 has a negative optical power, its eye-side surface S7 is flat, and its screen-side surface S8 is concave. The reflective polarizing element RP and the first quarter-wave plate QWP1 are attached to the eye-side surface S3 of the second lens E2. The partial reflection element BS is attached to the screen-side surface S6 of the third lens E3. The second quarter-wave plate QWP2 and the polarizer LP are attached to the eye-side surface S7 of the fourth lens E4. It should be noted that the surfaces S1 - S8 are not shown in Figure 1 which is not shown.

[0087] 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 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 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 screen-side surface of the third lens E3, 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 fourth lens E4.

[0088] Table 3 shows the basic parameter table of the optical system of Embodiment 2, where the units of the radius of curvature and the thickness / distance are both millimeters (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.

[0089]

[0090] Table 3

[0091] In this embodiment, the eye-side surface S5 and the screen-side surface S6 of the third lens E3, and the screen-side surface S8 of the fourth lens E4 are all aspherical. Table 4 gives the higher-order coefficients A4, A6, A8, A 10 , A 12 , A 14, A 16 , A 18 and A 20 .

[0092] Face number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -7.1874E-01 7.2814E-01 2.7264E-01 8.7554E-02 2.8686E-02 5.9606E-03 2.2679E-04 0.0000E+00 0.0000E+00 S6 1.0574E+00 3.4208E-01 -1.1471E-01 -1.6160E-01 -8.2154E-02 -2.3484E-02 -3.1671E-03 0.0000E+00 0.0000E+00 S8 -1.8584E-01 -3.6156E-03 -2.2890E-04 3.2741E-04 -8.0570E-04 -3.3659E-04 -3.6592E-04 0.0000E+00 0.0000E+00

[0093] Table 4

[0094] Figure 4A shows the axial chromatic aberration curve of the optical system of Embodiment 2, which represents the deviation of the focusing points of light rays with different wavelengths after passing through the optical system. Figure 4B shows the astigmatism curve of the optical system of Embodiment 2, which represents the meridional image plane curvature and sagittal image plane curvature corresponding to different field angles. Figure 4C shows the distortion curve of the optical system of Embodiment 2, which represents the distortion magnitude values corresponding to different field angles. Figure 4D shows the modulation transfer function curve of the optical system of Embodiment 2. According to Figures 4A to 4D it can be known that the optical system given in Embodiment 2 can achieve good imaging quality.

[0095] Example 3

[0096] The following refers to Figure 5 , Figure 6A , Figure 6B , Figure 6C and Figure 6D to describe the optical system of Embodiment 3 of the present application.

[0097] As Figure 5 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 second quarter-wave plate QWP2, a polarizer LP, and a fourth lens E4 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 surface of each element is referred to as the near-eye side surface, and the second side surface is referred to as the near-screen side surface.

[0098] 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 negative optical power. Its side S3 close to the human eye is flat, and its side S4 close to the screen is concave. The third lens E3 has a positive optical power. Its side S5 close to the human eye is convex, 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 flat, and its side S8 close to the screen is convex. 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 S7 of the fourth lens E4 close to the human eye. It should be noted that the surfaces S1 - S8 are not shown in Figure 1 the following.

[0099] 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 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 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 fourth lens E4.

[0100] Table 5 shows the basic parameter table of the optical system of Embodiment 3. Among them, the units of the radius of curvature and the thickness / distance are both millimeters (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.

[0101]

[0102]

[0103] Table 5

[0104] In this embodiment, the side S5 of the third lens E3 close to the human eye, the side S6 close to the screen, and the side S8 of the fourth lens E4 close to the screen are all aspherical. Table 6 gives the higher-order term coefficients A4, A6, A8, A of the aspherical surfaces S5, S6, S8 that can be used in Embodiment 310 , A 12 , A 14 , A 16 , A 18 and A 20 .

[0105] Face number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -1.1464E-01 2.2587E-01 -4.8393E-03 -1.4819E-02 -6.3860E-03 -2.1304E-03 -5.0213E-04 0.0000E+00 0.0000E+00 S6 2.7153E-01 1.1637E-01 1.4852E-02 -1.5439E-03 -2.1630E-03 -9.0144E-04 -1.9510E-04 0.0000E+00 0.0000E+00 S8 -4.7634E-02 1.0500E-02 -5.1612E-04 8.0158E-05 -2.4031E-06 -3.7978E-05 2.5588E-05 0.0000E+00 0.0000E+00

[0106] Table 6

[0107] Figure 6A shows the axial chromatic aberration curve of the optical system of Example 3, which represents the deviation of the convergence points of light rays with different wavelengths after passing through the optical system. Figure 6B shows the astigmatism curve of the optical system of Example 3, which represents the meridional image plane curvature and sagittal image plane curvature corresponding to different field angles. Figure 6C shows the distortion curve of the optical system of Example 3, which represents the distortion magnitude values corresponding to different field angles. Figure 6D shows the modulation transfer function curve of the optical system of Example 3. According to Figures 6A to 6D it can be seen that the optical system given in Example 3 can achieve good imaging quality.

[0108] Example 4

[0109] The following refers to Figure 7 , Figure 8A , Figure 8B , Figure 8C and Figure 8D to describe the optical system of Embodiment 4 of the present application.

[0110] 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 second quarter-wave plate QWP2, a polarizer LP, and a fourth lens E4 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 the respective elements 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.

[0111] The first lens E1 has a positive optical power, with its side S1 closer to the human eye being convex and its side S2 closer to the screen being concave. The second lens E2 has a negative optical power, with its side S3 closer to the human eye being flat and its side S4 closer to the screen being concave. The third lens E3 has a negative optical power, with its side S5 closer to the human eye being concave and its side S6 closer to the screen being convex. The fourth lens E4 has a positive optical power, with its side S7 closer to the human eye being flat and its side S8 closer to the screen being convex. The reflective polarizing element RP and the first quarter-wave plate QWP1 are attached to the side S3 of the second lens E2 closer to the human eye. The partial reflection element BS is attached to the side S6 of the third lens E3 closer to the screen. The second quarter-wave plate QWP2 and the polarizer LP are attached to the side S7 of the fourth lens E4 closer to the human eye. It should be noted that the surfaces S1 - S8 are not shown in Figure 1 is not shown.

[0112] 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 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 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 of the third lens E3 closer 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 this 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 fourth lens E4.

[0113] Table 7 shows the basic parameter table of the optical system of Example 4, where the units of the radius of curvature and the thickness / distance are both millimeters (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.

[0114]

[0115]

[0116] Table 7

[0117] In this embodiment, the side S5 of the third lens E3 closer to the human eye, the side S6 closer to the screen, and the side S8 of the fourth lens E4 closer to the screen are all aspherical. Table 8 gives the higher-order coefficients A4, A6, A8, A of the aspherical surfaces S5, S6, S8 that can be used in Example 410 , A 12 , A 14 , A 16 , A 18 and A 20 .

[0118] Face number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -2.6123E-02 1.5122E-01 -1.8531E-01 -9.4805E-02 -4.0745E-02 -1.2081E-02 -1.9036E-03 0.0000E+00 0.0000E+00 S6 8.6423E-01 3.7529E-01 4.6176E-02 -1.6842E-02 -1.9169E-02 -7.7663E-03 -1.4327E-03 0.0000E+00 0.0000E+00 S8 -6.9149E-02 2.4710E-02 -2.7986E-03 -2.4106E-04 9.0018E-04 -7.1260E-04 6.8650E-05 0.0000E+00 0.0000E+00

[0119] Table 8

[0120] Figure 8A shows the axial chromatic aberration curve of the optical system of Example 4, which represents the deviation of the focusing points of light rays with different wavelengths after passing through the optical system. Figure 8B shows the astigmatism curve of the optical system of Example 4, 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 Example 4, which represents the distortion magnitude values corresponding to different field angles. Figure 8D shows the modulation transfer function curve of the optical system of Example 4. According to Figures 8A to 8D , it can be seen that the optical system given in Example 4 can achieve good imaging quality.

[0121] Table 9 gives the basic parameters of each of Examples 1 to 4, such as the values of f, f1, f2, f3, f4, SR, TD, fz1, fz2, SAG11, SAG12, SAG22, SAG42, ET1, and ET3, and the units of the parameters in Table 9 are all millimeters (mm).

[0122] Parameter / Example 1 2 3 4 f 42.00 42.00 42.00 42.00 f1 44.89 30.25 54.54 51.08 f2 -68.55 -43.96 -115.25 -306.52 f3 96.19 69.52 145.02 -797.62 f4 472.95 -120.79 220.00 51.91 SR 20.00 20.00 20.00 20.00 TD 25.39 25.20 24.87 25.39 fz1 -68.55 -43.96 -115.25 -306.52 fz2 472.95 -120.79 220.00 51.91 SAG11 5.55 6.32 5.12 6.72 SAG12 0.93 -0.17 1.59 1.84 SAG22 1.38 1.72 0.93 0.33 SAG42 -0.20 0.19 -0.20 -0.82 ET1 1.30 1.30 1.30 1.30 ET3 6.53 6.47 6.68 5.76

[0123] Table 9

[0124] In summary, Table 10 shows the conditional values of each of Examples 1 to 4.

[0125] Condition / Example 1 2 3 4 f1 / f2 -0.65 -0.69 -0.47 -0.17 fz2 / R8 -1.70 -2.00 -1.50 -1.61 (NR + NQ1) / N2 1.71 1.69 1.74 1.62 (NQ2 + NL) / N4 1.89 2.00 1.80 1.85 f / fz1 -0.61 -0.96 -0.36 -0.14 R1 / CT1 3.21 2.27 4.15 2.87 CT4 / (CTQ2 + CTL) 5.78 9.10 5.77 8.14 (CTR + CTQ1 + CT2) / SAG22 3.96 3.61 3.67 4.59 f1 / (SAG11 + SAG12) 6.92 4.92 8.13 5.97 ET3 / ET1 5.02 4.98 5.14 4.43 V1 / N1 41.79 40.23 40.82 43.97 V2 / N2 19.96 19.41 16.91 12.82 (CTQ2 + CTL) / |SAG42| 1.28 1.38 1.30 0.32 R4 / R6 -0.29 -0.07 -0.49 -2.10 TD / SR 1.27 1.26 1.24 1.27

[0126] Table 10

[0127] 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. The optical device is equipped with the optical system described above.

[0128] The above description is only a preferred embodiment of the present application and an explanation of the technical principles applied. Those skilled in the art should understand that the scope of the utility model involved in the present application is not limited to the technical solutions formed by the specific combination of the above technical features, but 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 technical features (but not limited to) disclosed in the present application that have similar functions.

Claims

1. An optical system, characterized in that In sequence from the first side to the second side along the optical axis, it includes: A first lens with positive optical power, whose first side is convex; A second lens with negative optical power, whose first side is flat and second side is concave; A third lens with positive or negative optical power, whose second side is convex; and A fourth lens with positive or negative optical power, whose first side is flat; Wherein, the optical system further includes: A first quarter-wave plate, disposed on the first side of the second lens; A reflective polarizing element, disposed on the first side of the first quarter-wave plate; A partial reflection element, disposed on the second side of the third lens; A polarizer, disposed on the first side of the fourth lens; and A second quarter-wave plate, disposed on the first side of the polarizer; The number of lenses with 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: -0.7 < f1 / f2 < -0.15; The combined focal length fz2 of the second quarter-wave plate, the polarizer and the fourth lens and the radius of curvature R8 of the second side of the fourth lens satisfy: -2.0 ≤ fz2 / R8 ≤ -1.

5.

2. The optical system according to claim 1, characterized in that The refractive index NR of the reflective polarizing element, the refractive index NQ1 of the first quarter-wave plate and the refractive index N2 of the second lens satisfy: 1.6 < (NR + NQ1) / N2 < 1.

75.

3. The optical system according to claim 1, characterized in that The refractive index NQ2 of the second quarter-wave plate, the refractive index NL of the polarizer and the refractive index N4 of the fourth lens satisfy: 1.75 < (NQ2 + NL) / N4 < 2.

05.

4. The optical system according to claim 1, characterized in that The central thickness CT4 of the fourth lens on the optical axis, 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: 5.77 ≤ CT4 / (CTQ2 + CTL) ≤ 9.

1.

5. The optical system according to claim 1, characterized in that 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, the central thickness CT2 of the second lens on the optical axis and the axial distance SAG22 between the intersection of the second side of the second lens and the optical axis and the vertex of the effective semi-aperture of the second side of the second lens satisfy: 3.6 < (CTR + CTQ1 + CT2) / SAG22 < 4.

6.

6. The optical system according to claim 1, characterized in that The effective focal length f1 of the first lens, the axial distance SAG11 between the intersection of the first side of the first lens and the optical axis and the vertex of the effective semi-aperture of the first side of the first lens and the axial distance SAG12 between the intersection of the second side of the first lens and the optical axis and the vertex of the effective semi-aperture of the second side of the first lens satisfy: 4.9 < f1 / (SAG11 + SAG12) ≤ 8.

13.

7. The optical system according to claim 1, characterized in that The edge thickness ET1 of the first lens and the edge thickness ET3 of the third lens satisfy: 4.4 < ET3 / ET1 ≤ 5.

14.

8. The optical system according to claim 1, characterized in that The refractive index N1 of the first lens and the Abbe number V1 of the first lens satisfy: 40.23≤V1 / N1<44; the refractive index N2 of the second lens and the Abbe number V2 of the second lens satisfy: 12.8 <V2 / N2<20。 9. The optical system according to any one of claims 1 to 8, characterized in that: The combined focal length fz1 of the reflective polarizing element, the first quarter-wave plate and the second lens and the total effective focal length f of the optical system satisfy: -1.0 <f / fz1<-0.1。 10. The optical system according to any one of claims 1 to 8, characterized in that: A curvature radius R1 of the first side surface of the first lens and a center thickness CT1 of the first lens on the optical axis satisfy: 2.27≤R1 / CT1<4.

2.

11. The optical system according to any one of claims 1 to 8, characterized in that: 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 on-axis distance SAG42 between the intersection of the second side surface of the fourth lens and the optical axis and the effective half-aperture vertex of the second side surface of the fourth lens satisfy: 0.3<(CTQ2+CTL) / |SAG42|<1.

4.

12. The optical system according to any one of claims 1 to 8, characterized in that: A curvature radius R4 of the second side surface of the second lens and a curvature radius R6 of the second side surface of the third lens satisfy: -2.1≤R4 / R6≤-0.

07.

13. The optical system according to any one of claims 1 to 8, characterized in that: The optical system further includes a stop disposed between the first side and the first lens; The axial distance TD from the first side surface of the first lens to the second side surface of the fourth lens and the axial distance SR from the aperture to the first side surface of the first lens satisfy: 1.2 <TD / SR<1.3。

Images