Optical system and VR device including the same

Abstract

This application discloses an optical system comprising, in order from a first side to a second side along an optical axis, a first element group and a second element group. The first element group has positive optical power and includes a reflective polarizing element, a first lens, and a quarter-wave plate. The second element group has positive or negative optical power and includes a partially reflective element and a second lens, the second side surface of the second lens being aspherical. The effective focal length FG1 of the first element group and the effective focal length FG2 of the second element group satisfy the following: 0.5 < (FG2 + FG1) / (FG2-FG1) < 2.0.

Description

Technical Field

[0001] The present application relates to the field of optical elements, and more specifically, to an optical system and a VR device including the optical system. Background Art

[0002] With the increasing demand for online work, the requirements for online interaction are becoming increasingly diverse. To achieve this interaction, the development of mixed reality (MR) has attracted widespread attention. In particular, virtual reality (VR), which was developed earlier, has seen widespread application due to its increasingly mature solutions.

[0003] Currently, VR lenses primarily include aspherical, Fresnel, and pancake lenses. In the pancake structure, coating and lamination can be used to fold the optical path, thereby shortening the overall length of the device. However, varying the coating and lamination positions can alter the overall length of the device and its optical performance. Therefore, optimizing the design and improving system performance is a critical issue. Summary of the Invention

[0004] The present application provides an optical system, comprising a first element group and a second element group in sequence from a first side to a second side along an optical axis, wherein the first element group has positive optical power and comprises a reflective polarizing element, a first lens, and a quarter-wave plate; the second element group has positive optical power or negative optical power and comprises a partially reflective element and a second lens, and the second side surface of the second lens is aspherical; and the effective focal length FG1 of the first element group and the effective focal length FG2 of the second element group can satisfy the following: 0.5<(FG2+FG1) / (FG2-FG1)<2.0.

[0005] In one embodiment, a curvature radius R2 of the second side surface of the first lens and a curvature radius R4 of the second side surface of the second lens may satisfy: 0.2<|R2 / R4|<2.5.

[0006] In one embodiment, the distance TD from the first side surface of the first lens to the second side surface of the second lens on the optical axis and the center thickness CT1 of the first lens on the optical axis may satisfy: 1.4 <TD / CT1<3.7。

[0007] In one embodiment, the effective focal length f of the optical system and the entrance pupil diameter EPD of the optical system may satisfy: 5.5 <f / EPD<6.0。

[0008] In one embodiment, the effective focal length f of the optical system and the refractive index N1 of the first lens and the refractive index N2 of the second lens may satisfy: 28 mm <f×(N2 / N1)<29.1mm。

[0009] In one embodiment, a center thickness CT2 of the second lens on the optical axis and an air interval T12 between the first lens and the second lens on the optical axis may satisfy: 1.0<(CT2+T12) / (CT2-T12)<4.9.

[0010] In one embodiment, the optical system further comprises an aperture, and a distance SD from the aperture to the second side surface of the second lens on the optical axis and a distance ER from the aperture to the first side surface of the first lens on the optical axis may satisfy: 2 <SD / ER<3。

[0011] In one embodiment, the optical system further includes an image surface provided on the second side, and the effective focal length f of the optical system and the distance BFL from the second side surface of the second lens to the image surface on the optical axis may satisfy: 4.3 <f / BFL<9.8。

[0012] In one embodiment, the optical system further includes an image surface provided on the second side, and the distance BFL from the second side surface of the second lens to the image surface on the optical axis, the center thickness CTR of the reflective polarizing element on the optical axis, and the center thickness CTQ of the quarter-wave plate on the optical axis may satisfy: 5.8 <BFL / (CTR+CTQ)<16.2。

[0013] In one embodiment, the curvature radius R2 of the second side surface of the first lens, the Abbe number V1 of the first lens, and the Abbe number V2 of the second lens may satisfy the following: 0.4 mm<|R2| / (V1+V2)<2.7 mm.

[0014] In one embodiment, the effective focal length FG1 of the first element group and the center thickness CT1 of the first lens on the optical axis may satisfy: 2.0 <FG1 / CT1<5.2。

[0015] In one embodiment, the center thickness CT2 of the second lens on the optical axis and the entrance pupil diameter EPD of the optical system may satisfy: 0.7 <CT2 / EPD<2.9。

[0016] On the other hand, the present application also provides a VR device, which includes the optical system provided by at least one of the above-mentioned embodiments, wherein the first side is the human eye side and the second side is the display side.

[0017] The optical system disclosed in this application includes, in order from the first side to the second side along the optical axis, a first element group and a second element group. The first element group includes a reflective polarizing element, a first lens, and a quarter-wave plate; the second element group includes a second lens and a partially reflecting element. The reflective polarizing element can be configured to reflect light of a certain polarization direction and transmit polarized light perpendicular to the reflected polarized light. The quarter-wave plate can change the state of polarized light, converting linear polarized light into circular polarized light and vice versa. The partially reflecting element can reflect a portion of polarized light and transmit another portion of polarized light. By setting the optical focal length of the first element group, including the reflective polarizing element, the first lens, and the quarter-wave plate, to be positive, light can be converged. In addition, a partial reflective element is provided on the aspheric surface of the second side surface of the second lens to realize light path reflection; combined with controlling the effective focal length ratio of the two element groups to meet 0.5<(FG2+FG1) / (FG2-FG1)<2.0, the optical focal length can be reasonably distributed and the light path can be refracted, which can shorten the length of the VR headset and make it lighter and more comfortable to wear; at the same time, it is beneficial to correct the system's aberrations and improve the system's performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Other features, purposes and advantages of the present application will become more apparent through the following detailed description of non-limiting embodiments in conjunction with the accompanying drawings. In the accompanying drawings:

[0019] Figure 1 1 shows a schematic structural diagram of an optical system according to Example 1 of the present application;

[0020] Figures 2A to 2C The axial chromatic aberration curve, astigmatism curve, and distortion curve of the optical system of Example 1 are shown respectively;

[0021] Figure 3 1 shows a schematic structural diagram of an optical system according to Example 2 of the present application;

[0022] Figures 4A to 4C The axial chromatic aberration curve, astigmatism curve, and distortion curve of the optical system of Example 2 are respectively shown;

[0023] Figure 5 1 shows a schematic structural diagram of an optical system according to Example 3 of the present application;

[0024] Figures 6A to 6C axial chromatic aberration curve, astigmatism curve, and distortion curve of the optical system of Example 3 are respectively shown;

[0025] Figure 7 1 shows a schematic structural diagram of an optical system according to Example 4 of the present application;

[0026] Figures 8A to 8CThe axial chromatic aberration curve, astigmatism curve, and distortion curve of the optical system of Example 4 are respectively shown;

[0027] Figure 9 1 shows a schematic structural diagram of an optical system according to Example 5 of the present application;

[0028] 10A to 10C The axial chromatic aberration curve, astigmatism curve, and distortion curve of the optical system of Example 5 are shown respectively;

[0029] Figure 11 shows a schematic structural diagram of an optical system according to Example 6 of the present application; and

[0030] 12A to 12C The axial chromatic aberration curve, astigmatism curve, and distortion curve of the optical system of Example 6 are respectively shown. DETAILED DESCRIPTION

[0031] For a better understanding of the present application, various aspects of the present application will be described in more detail with reference to the accompanying drawings. It should be understood that these detailed descriptions are merely descriptions of exemplary embodiments of the present application and are not intended to limit the scope of the present application in any way. Throughout the specification, the same reference numerals refer to the same elements. The expression "and / or" includes any and all combinations of one or more of the associated listed items.

[0032] It should be noted that in this specification, the terms "first," "second," etc., are used solely to distinguish one feature from another and do not limit the features. Thus, without departing from the teachings of this application, the first lens discussed below could also be referred to as the second lens, and the second lens could also be referred to as the first lens.

[0033] In the drawings, the thickness, size, and shape of the lenses are slightly exaggerated for ease of illustration. Specifically, the shapes of the spherical and aspherical surfaces shown in the drawings are provided by way of example. That is, the shapes of the spherical and aspherical surfaces are not limited to those shown in the drawings. The drawings are for illustration only and are not drawn strictly to scale.

[0034] In this article, the paraxial region refers to the region near the optical axis. If a lens surface is convex and the location of the convex surface is undefined, it means that the lens surface is convex at least in the paraxial region; if a lens surface is concave and the location of the concave surface is undefined, it means that the lens surface is concave at least in the paraxial region.

[0035] It should also be understood that the terms "comprises," "including," "having," "includes," and / or "comprising," when used in this specification, indicate 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 expressions such as "at least one of..." appear after a list of listed features, they modify the entire list of features rather than modifying the individual elements in the list. In addition, when describing embodiments of the present application, "may" is used to mean "one or more embodiments of the present application." And, the term "exemplary" is intended to refer to an example or illustration.

[0036] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by those skilled in the art to which this application belongs. It should also be understood that terms (such as those defined in commonly used dictionaries) should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology and will not be interpreted in an idealized or overly formal sense unless expressly defined as such herein.

[0037] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0038] The features, principles and other aspects of the present application are described in detail below.

[0039] According to an exemplary embodiment of the present application, an optical system may include a first element group and a second element group arranged in sequence from a first side to a second side along an optical axis, wherein the first element group may include a reflective polarizing element, a first lens and a quarter-wave plate, and the second element group may include a partially reflective element and a second lens.

[0040] The following will refer to Figure 1 An example description of the optical system is given below. Figure 1As shown, an optical system according to an exemplary embodiment of the present application may include a reflective polarizer RP, a first lens E1, a quarter-wave plate QWP, a partially reflecting element BS, and a second lens E2, arranged in sequence from a first side to a second side. The reflective polarizer RP, the first lens E1, and the quarter-wave plate QWP constitute a first element group, while the partially reflecting element BS and the second lens E2 constitute a second element group. In actual use, the optical system according to an exemplary embodiment of the present application can be used as a VR lens, in which case the first side corresponds to the human eye side and the second side corresponds to the display side. The optical system may also include an image surface IMG located on the display side. A light beam emitted from the image surface IMG sequentially passes through the second lens E2 and the partially reflecting element BS of the second element group, and the quarter-wave plate QWP and first lens E1 of the first element group. The light beam is then reflected and passes through the first lens E1 and the quarter-wave plate QWP again to reach the partially reflecting element BS. The light beam is then reflected again by the reflecting element BS and sequentially passes through the quarter-wave plate QWP, the first lens E1, and the reflective polarizer RP to be emitted toward the human eye side. In an exemplary embodiment, the partially reflective element BS may be a semi-transmissive and semi-reflective film layer coated on the first side surface of the second lens E2.

[0041] In an exemplary embodiment, the first element group including the reflective polarizer RP, the first lens E1, and the quarter-wave plate QWP may have positive refractive power, while the second element group including the partially reflective element BS and the second lens E2 may have positive or negative refractive power.

[0042] In an exemplary embodiment, the second side surface of the second lens E2, i.e., the surface closest to the display, may be aspherical. Aspherical lenses have a better curvature radius and can improve distortion and astigmatism. Using an aspherical lens can minimize aberrations that occur during imaging, thereby improving image quality.

[0043] In an exemplary embodiment, the optical system of the present application may satisfy the conditional expression 0.5<(FG2+FG1) / (FG2-FG1)<2.0, where FG1 is the effective focal length of the first element group and FG2 is the effective focal length of the second element group.

[0044] According to the optical system of the exemplary embodiment of the present application, the provided reflective polarizing element RP can reflect light of a certain polarization direction and can transmit polarized light perpendicular to the reflected polarized light; the quarter-wave plate QWP can change the state of polarized light and can convert linearly polarized light and circularly polarized light into each other; the partial reflection element BS can reflect a part of polarized light and transmit another part of polarized light. By setting the optical power of the first element group including the reflective polarizing element RP, the first lens E1, and the quarter-wave plate QWP to be positive, the light can be converged. Moreover, the aspherical surface of the second lens E2 close to the display side surface can be laminated to achieve light path reflection; by combining and controlling the ratio of the effective focal lengths of the two element groups to satisfy 0.5 < (FG2 + FG1) / (FG2 - FG1) < 2.0, the optical power can be reasonably distributed, the light path can be refolded, the length of the VR head-mounted device can be shortened, and it can be worn more lightly and comfortably; at the same time, it is beneficial to correct the aberration of the system and improve the performance of the system.

[0045] In an exemplary embodiment, the optical system of the present application can satisfy the conditional formula 0.2 < |R2 / R4| < 2.5, where R2 is the radius of curvature of the second side surface of the first lens and R4 is the radius of curvature of the second side surface of the second lens. By controlling the absolute value of the ratio of the radius of curvature of the second side surface of the first lens to the radius of curvature of the second side surface of the second lens within this range, on the one hand, it is beneficial to reduce the light height, thereby reducing the Display size, and on the other hand, it is beneficial to eliminate the reflected ghost image of the Display and the lens on the display side surface, improving the consumer experience.

[0046] In an exemplary embodiment, the optical system of the present application can satisfy the conditional formula 1.4 < TD / CT1 < 3.7, where TD is the distance on the optical axis from the first side surface of the first lens to the second side surface of the second lens, and CT1 is the central thickness of the first lens on the optical axis. By controlling the ratio of the distance on the optical axis from the first side surface of the first lens to the second side surface of the second lens to the central thickness of the first lens on the optical axis within this range, on the one hand, it is beneficial to the processing of the first lens, and on the other hand, it is beneficial to shorten the height of the system and miniaturize the VR system.

[0047] In an exemplary embodiment, the optical system of the present application can satisfy the conditional formula 5.5 < f / EPD < 6.0, where f is the effective focal length of the optical system and EPD is the entrance pupil diameter of the optical system. By controlling the ratio of the effective focal length of the optical system to the entrance pupil diameter of the optical system within this range, on the premise of a certain focal length, the entrance pupil diameter can be increased, which is beneficial to improving the performance degradation caused by pupil offset when the human eye rotates, thereby improving the comfort during visual inspection.

[0048] In an exemplary embodiment, the optical system of the present application can satisfy the conditional formula 28 mm < f×(N2 / N1) < 29.1 mm, where f is the effective focal length of the optical system, N1 is the refractive index of the first lens, and N2 is the refractive index of the second lens. By controlling the effective focal length of the optical system and the refractive indices of the first lens and the second lens to satisfy 28 mm < f×(N2 / N1) < 29.1 mm, materials with low refractive index and low stress can be selected to reduce the influence of stress on the polarization state of the system.

[0049] In an exemplary embodiment, the optical system of the present application can satisfy the conditional formula 1.0 < (CT2 + T12) / (CT2 - T12) < 4.9, where CT2 is the central thickness of the second lens on the optical axis, and T12 is the air gap between the first lens and the second lens on the optical axis. By controlling the central thickness of the second lens on the optical axis and the air gap between the first lens and the second lens on the optical axis to satisfy 1.0 < (CT2 + T12) / (CT2 - T12) < 4.9, the height of the system can be effectively reduced, which is beneficial to the miniaturization of the VR lens and also beneficial to the molding of the second lens.

[0050] In an exemplary embodiment, the optical system of the present application further includes an aperture, and the optical system of the present application can satisfy the conditional formula 2 < SD / ER < 3, where SD is the distance from the aperture to the second side surface of the second lens on the optical axis, and ER is the distance from the aperture to the first side surface of the first lens on the optical axis. By controlling the ratio of the distance from the aperture to the second side surface of the second lens on the optical axis to the distance from the aperture to the first side surface of the first lens on the optical axis within this range, the requirements for the viewing distance of the head-mounted device can be met.

[0051] In an exemplary embodiment, the optical system of the present application further includes an image plane provided on the second side, and the optical system of the present application can satisfy the conditional formula 4.3 < f / BFL < 9.8, where f is the effective focal length of the optical system, and BFL is the distance from the second side surface of the second lens to the image plane on the optical axis. By controlling the ratio of the effective focal length of the optical system to the distance from the second side surface of the second lens to the image plane on the optical axis within this range, on the one hand, the aberration of the VR lens, especially the lateral aberration, can be balanced; on the other hand, the angle of light can be controlled to avoid the generation of tail-end stray light in the system.

[0052] In an exemplary embodiment, the optical system of the present application further includes an image plane disposed on the second side, and the optical system of the present application can satisfy the conditional formula 5.8 < BFL / (CTR + CTQ) < 16.2, where BFL is the distance from the second side surface of the second lens to the image plane on the optical axis, CTR is the central thickness of the reflective polarizing element on the optical axis, and CTQ is the central thickness of the quarter-wave plate on the optical axis. By controlling the ratio of the distance from the second side surface of the second lens to the image plane on the optical axis to the sum of the central thickness of the reflective polarizing element on the optical axis and the central thickness of the quarter-wave plate on the optical axis within this range, on the one hand, the back focal length of the lens can be effectively controlled, thereby restricting the height of the VR lens, and on the other hand, the processability of the film can be ensured.

[0053] In an exemplary embodiment, the optical system of the present application can satisfy the conditional formula 0.4 mm < |R2| / (V1 + V2) < 2.7 mm, where R2 is the radius of curvature of the second side surface of the first lens, V1 is the Abbe number of the first lens, and V2 is the Abbe number of the second lens. By controlling the radius of curvature of the second side surface of the first lens to satisfy 0.4 mm < |R2| / (V1 + V2) < 2.7 mm with the Abbe numbers of the first lens and the second lens, not only can the shape of the lens be restricted, but it is also beneficial to correct the chromatic aberration of the system and improve the imaging quality of the VR system.

[0054] In an exemplary embodiment, the optical system of the present application can satisfy the conditional formula 2.0 < FG1 / CT1 < 5.2, where FG1 is the effective focal length of the first element group and CT1 is the central thickness of the first lens on the optical axis. By controlling the ratio of the effective focal length of the first element group to the central thickness of the first lens on the optical axis within this range, on the one hand, the central thickness of the lens can be ensured, and on the other hand, it is ensured that the lens is not too curved, which is beneficial to the formability of the lens.

[0055] In an exemplary embodiment, the optical system of the present application can satisfy the conditional formula 0.7 < CT2 / EPD < 2.9, where CT2 is the central thickness of the second lens on the optical axis and EPD is the entrance pupil diameter of the optical system. By controlling the ratio of the central thickness of the second lens on the optical axis to the entrance pupil diameter of the optical system within this range, it is beneficial to the processing and forming of the lens and can ensure that the aperture is not too small to ensure that the performance of the system is not affected.

[0056] In an exemplary embodiment, the optical system of the present application may include at least one aperture stop. The aperture stop can restrict the optical path and control the light intensity. The aperture stop can be disposed at an appropriate position in the optical system. For example, the aperture stop can be located between the human eye side and the reflective polarizing element.

[0057] In an exemplary embodiment, optionally, the above optical system may further include a protective glass for protecting the photosensitive element located on the imaging surface.

[0058] In an exemplary embodiment, the effective focal length f of the optical system can be, for example, in the range of 28.01 mm to 29.00 mm, the effective focal length FG1 of the first element group can be, for example, in the range of 26.97 mm to 28.75 mm, and the effective focal length FG2 of the second element group can be, for example, in the range of -14136.56 mm to 728.24 mm.

[0059] According to the optical system of the above-described embodiment of the present application, a reflective polarizer RP is provided to reflect light of a certain polarization direction and transmit light polarized perpendicular to the reflected polarization. A quarter-wave plate QWP can change the polarization state of light, converting linear polarization to circular polarization and vice versa. The partially reflective element BS can reflect a portion of the polarized light and transmit another portion of the polarized light. By setting the first element group, including the reflective polarizer RP, the first lens E1, and the quarter-wave plate QWP, to have a positive optical power, light can be converged. Furthermore, the aspheric surface of the second lens E2, near the display side, can be coated to achieve optical path reflection. Combined with controlling the effective focal length ratio of the two element groups to satisfy 0.5 < (FG2 + FG1) / (FG2 - FG1) < 2.0, optical power can be rationally distributed and the optical path can be refracted, shortening the length of the VR headset, making it lighter and more comfortable to wear. This also helps correct system aberrations and improve system performance.

[0060] According to some embodiments of the present application, by properly setting parameters such as the center thickness, refractive index, Abbe number, radius of curvature of the lens, as well as the effective focal length and entrance pupil diameter of the optical system, and by properly setting parameters such as the aperture, lens, and the distance between the image planes, the screen size can be reasonably constrained; this can be beneficial to the processing and molding performance of the lens; this can also facilitate system miniaturization; and it can also improve the performance degradation caused by pupil shift when the human eye rotates, thereby improving visual comfort. In addition, the impact of lens stress on the system's polarization state can be reduced; the viewing distance requirements of the head-mounted device can be met; the aberrations of the VR lens, especially the vertical axis aberration, can be balanced, and the angle of the light can be controlled to avoid the system generating end stray light; at the same time, it is also beneficial to correct the system's chromatic aberration and improve the imaging quality of the VR system.

[0061] Specific embodiments of the optical system applicable to the above-mentioned embodiments will be further described below with reference to the accompanying drawings.

[0062] Example 1

[0063] The following reference Figures 1 to 2C An optical system according to Example 1 of the present application is described. Figure 1 A structural schematic diagram of an optical system according to Example 1 of the present application is shown.

[0064] like Figure 1 As shown, the optical system includes, along the optical axis from the human eye side to the display side, an aperture STO, a reflective polarizer RP, a first lens E1, a quarter-wave plate QWP, a partially reflecting element BS, a second lens E2 and an image surface IMG.

[0065] In this embodiment, the first lens group, including the reflective polarizer RP, the first lens E1, and the quarter-wave plate QWP, has positive optical power. The second lens group, including the partially reflecting element BS and the second lens E2, also has positive optical power. The surface of the first lens E1 closest to the eye is convex, and the surface closest to the display is also convex. The second lens E2 has positive optical power, with a planar surface closest to the eye and a convex surface closest to the display.

[0066] In this embodiment, the light beam emitted from the image surface IMG sequentially passes through the second lens E2 and the partially reflecting element BS of the second element group, and the quarter-wave plate QWP and the first lens E1 of the first element group. After that, the light beam is reflected and passes through the first lens E1 and the quarter-wave plate QWP again to reach the partially reflecting element BS. Thereafter, the light beam is reflected again at the reflecting element BS and sequentially passes through the quarter-wave plate QWP, the first lens E1, and the reflective polarizing element RP to be emitted toward the human eye.

[0067] Table 1 shows basic parameters of the optical system of Example 1, wherein the units of the curvature radius and thickness are both millimeters (mm).

[0068] surface element Surface type Radius of curvature thickness Refractive index Abbe number Refraction / Reflection S0 spherical surface endless endless refraction S1 Aperture (STO) spherical surface endless 15.0000 refraction S2 Reflective polarizer (RP) Aspheric 102.8726 0.2000 1.50 57.00 refraction S3 First lens (E1) Aspheric 102.8726 10.6739 1.54 56.05 refraction S4 Quarter Wave Plate (QWP) Aspheric -291.5529 0.2000 1.50 57.00 refraction S5 Aspheric -291.5529 5.0402 refraction S6 Partially reflective element (BS) spherical surface endless -5.0402 reflection S7 Quarter Wave Plate (QWP) Aspheric -291.5529 -0.2000 1.50 57.00 refraction S8 First lens (E1) Aspheric -291.5529 -10.6739 1.54 56.05 refraction S9 Reflective polarizer (RP) Aspheric 102.8726 10.6739 1.54 56.05 reflection S10 Quarter Wave Plate (QWP) Aspheric -291.5529 0.2000 1.50 57.00 refraction S11 Aspheric -291.5529 5.0402 refraction S12 Second lens (E2) spherical surface endless 13.5891 1.54 56.05 refraction S13 Aspheric -121.3236 0.1000 refraction S14 spherical surface endless 0.0000 refraction S15 spherical surface endless 2.9929 refraction S16 Image surface (IMG) spherical surface endless 0.0000 refraction

[0069] Table 1

[0070] In Example 1, the surface S3 of the first lens element E1 near the eye side and the surface S4 of the first lens element E1 near the display side, as well as the surface S13 of the second lens element E2 near the display side, are both aspherical surfaces. The surface shape x of each aspherical lens can be defined by, but is not limited to, the following aspherical surface formula:

[0071]

[0072] Wherein, x is the distance vector height of the aspheric surface from the vertex of the aspheric surface at a height of h along the optical axis; c is the paraxial curvature of the aspheric surface, c = 1 / R (i.e., the paraxial curvature c is the reciprocal of the curvature radius R in Table 1 above); k is the conic coefficient; Ai is the correction coefficient of the i-th order of the aspheric surface. Table 2 below lists the high-order coefficients A4, A6, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21, A22, A23, A24, A25, A26, A27, A28, A30, A31, A32, A33, A34, A35, A36, A37, A38, A39, A40 10 、A 12 、A 14 、A 16 、A18 and A 20 .

[0073] Coefficient\Surface S3 S4 S13 A4 -4.5615E-07 -3.7629E-07 8.4964E-01 A6 1.6609E-10 6.9490E-10 -2.2732E+00 A8 -3.8120E-14 -3.7752E-14 1.5776E+00 A10 3.5762E-17 -3.1941E-17 -1.8215E+00 A12 2.1853E-20 9.4280E-20 1.4237E+00 A14 0.0000E+00 0.0000E+00 -1.0013E+00 A16 0.0000E+00 0.0000E+00 6.1038E-01 A18 0.0000E+00 0.0000E+00 -2.4360E-01 A20 0.0000E+00 0.0000E+00 8.5505E-02

[0074] Table 2

[0075] Figure 2A The axial chromatic aberration curve of the optical system of Example 1 is shown, which indicates the deviation of the convergent focus of light of different wavelengths passing through the lens. Figure 2B The astigmatism curve of the optical system of Example 1 is shown, which indicates meridional field curvature and sagittal field curvature. Figure 2C The distortion curve of the optical system of Example 1 is shown, which represents the distortion value corresponding to different field angles. Figures 2A to 2C It can be seen that the optical system provided in Example 1 can achieve good imaging quality.

[0076] Example 2

[0077] The following reference Figures 3 to 4C The optical system according to Example 2 of the present application is described. In this embodiment and the following embodiments, some descriptions similar to those in Example 1 will be omitted for the sake of brevity. Figure 3 A structural schematic diagram of an optical system according to Example 2 of the present application is shown.

[0078] like Figure 3 As shown, the optical system includes, along the optical axis from the human eye side to the display side, an aperture STO, a reflective polarizer RP, a first lens E1, a quarter-wave plate QWP, a partially reflecting element BS, a second lens E2 and an image surface IMG.

[0079] In this embodiment, the first lens group, including the reflective polarizer RP, the first lens E1, and the quarter-wave plate QWP, has positive optical power. The second lens group, including the partially reflecting element BS and the second lens E2, also has positive optical power. The surface of the first lens E1 closest to the eye is flat, while the surface closest to the display is convex. The second lens E2 has positive optical power, with a concave surface closest to the eye and a convex surface closest to the display.

[0080] In this embodiment, the light beam emitted from the image surface IMG sequentially passes through the second lens E2 and the partially reflecting element BS of the second element group, and the quarter-wave plate QWP and the first lens E1 of the first element group. After that, the light beam is reflected and passes through the first lens E1 and the quarter-wave plate QWP again to reach the partially reflecting element BS. Thereafter, the light beam is reflected again at the reflecting element BS and sequentially passes through the quarter-wave plate QWP, the first lens E1, and the reflective polarizing element RP to be emitted toward the human eye.

[0081] Table 3 shows the basic parameters of the optical system of Example 2, where the units of the curvature radius and thickness are both in millimeters (mm). In this embodiment, the surface S4 of the first lens E1 close to the display side and the surface S13 of the second lens E2 close to the display side are both aspherical surfaces. Table 4 shows the high-order coefficients A4, A6, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21, A22, A23, A24, A25, A26, A27, A28, A29, A30, A31, A32, A33, A34, A35, A36, A37, A38, A39, A40, A41, A42, A43, A44, A45, A46, A47, A4 10 、A 12 、A 14 、A 16 、A 18 and A 20 , wherein each aspheric surface shape can be defined by formula (1) given in the above embodiment 1.

[0082]

[0083] Table 3

[0084] Coefficient\Surface S4 S13 A4 4.3618E-07 1.9248E+00 A6 3.9507E-11 1.5522E+00 A8 2.8660E-13 3.9858E+00 A10 1.7307E-16 -2.8316E+00 A12 2.3184E-21 -2.5660E+00 A14 0.0000E+00 2.0596E-01 A16 0.0000E+00 2.4026E+00 A18 0.0000E+00 -1.5529E+00 A20 0.0000E+00 2.3077E-01

[0085] Table 4

[0086] Figure 4A The axial chromatic aberration curve of the optical system of Example 2 is shown, which indicates the deviation of the convergent focus of light of different wavelengths passing through the lens. Figure 4B The astigmatism curve of the optical system of Example 2 is shown, which indicates meridional field curvature and sagittal field curvature. Figure 4C The distortion curve of the optical system of Example 2 is shown, which represents the distortion value corresponding to different field angles. Figures 4A to 4C It can be seen that the optical system provided in Example 2 can achieve good imaging quality.

[0087] Example 3

[0088] The following reference Figures 5 to 6C An optical system according to Example 3 of the present application is described. Figure 5 A structural schematic diagram of an optical system according to Example 3 of the present application is shown.

[0089] like Figure 5 As shown, the optical system includes, along the optical axis from the human eye side to the display side, an aperture STO, a reflective polarizer RP, a first lens E1, a quarter-wave plate QWP, a partially reflecting element BS, a second lens E2 and an image surface IMG.

[0090] In this embodiment, the first lens group, including the reflective polarizer RP, the first lens E1, and the quarter-wave plate QWP, has positive optical power. The second lens group, including the partially reflecting element BS and the second lens E2, also has positive optical power. The surface of the first lens E1 closest to the eye is convex, and the surface closest to the display is also convex. The second lens E2 has positive optical power, and its surface closest to the eye is also convex, and the surface closest to the display is also convex.

[0091] In this embodiment, the light beam emitted from the image surface IMG sequentially passes through the second lens E2 and the partially reflecting element BS of the second element group, and the quarter-wave plate QWP and the first lens E1 of the first element group. After that, the light beam is reflected and passes through the first lens E1 and the quarter-wave plate QWP again to reach the partially reflecting element BS. Thereafter, the light beam is reflected again at the reflecting element BS and sequentially passes through the quarter-wave plate QWP, the first lens E1, and the reflective polarizing element RP to be emitted toward the human eye.

[0092] Table 5 shows the basic parameters of the optical system of Example 3, where the units of the curvature radius and thickness are both in millimeters (mm). In this embodiment, the surface S3 on the side closest to the human eye and the surface S4 on the side closest to the display of the first lens E1, as well as the surface S12 on the side closest to the human eye and the surface S13 on the side closest to the display of the second lens E2, are all aspherical surfaces. Table 6 shows the high-order coefficients A4, A6, A8, A9, A10, A11, A12, A13 of the aspherical mirror surfaces S3, S4, S12, and S13 that can be used in Example 3. 10 、A 12 、A 14 、A 16 、A 18 and A 20 , wherein each aspheric surface shape can be defined by formula (1) given in the above embodiment 1.

[0093] surface element Surface type Radius of curvature thickness Refractive index Abbe number Refraction / Reflection S0 spherical surface endless endless refraction S1 Aperture (STO) spherical surface endless 15.0000 refraction S2 Reflective polarizer (RP) Aspheric 92.7583 0.2000 1.54 56.05 refraction S3 First lens (E1) Aspheric 92.7583 11.3021 1.54 56.05 refraction S4 Quarter Wave Plate (QWP) Aspheric -279.3877 0.2000 1.54 56.05 refraction S5 Aspheric -279.3877 5.4783 refraction S6 Partially reflective element (BS) Aspheric 500.0000 -5.4783 reflection S7 Quarter Wave Plate (QWP) Aspheric -279.3877 -0.2000 1.54 56.05 refraction S8 First lens (E1) Aspheric -279.3877 -11.3021 1.54 56.05 refraction S9 Reflective polarizer (RP) Aspheric 92.7583 11.3021 1.54 56.05 reflection S10 Quarter Wave Plate (QWP) Aspheric -279.3877 0.2000 1.54 56.05 refraction S11 Aspheric -279.3877 5.4783 refraction S12 Second lens (E2) Aspheric 500.0000 12.5795 1.54 56.05 refraction S13 Aspheric -256.8689 0.1000 refraction S14 spherical surface endless 2.9847 refraction S15 Image surface (IMG) spherical surface endless 0.0000 refraction

[0094] Table 5

[0095] Coefficient\Surface S3 S4 S12 S13 A4 -1.0907E-07 6.1004E-07 6.3791E-09 4.1212E+00 A6 2.5124E-10 6.1119E-10 3.1678E-10 -2.1041E+00 A8 -1.1596E-14 -6.8482E-14 -1.0313E-13 1.1955E+00 A10 1.5192E-17 -1.3701E-17 -6.7100E-17 -1.1551E+00 A12 1.4988E-20 7.3051E-20 -3.8115E-20 9.2832E-01 A14 0.0000E+00 0.0000E+00 4.4840E-23 -3.7778E-01 A16 0.0000E+00 0.0000E+00 0.0000E+00 1.8188E-01 A18 0.0000E+00 0.0000E+00 0.0000E+00 -4.3669E-03 A20 0.0000E+00 0.0000E+00 0.0000E+00 2.4682E-02

[0096] Table 6

[0097] Figure 6A The axial chromatic aberration curve of the optical system of Example 3 is shown, which indicates the deviation of the convergent focus of light of different wavelengths passing through the lens. Figure 6B The astigmatism curve of the optical system of Example 3 is shown, which indicates the meridional field curvature and the sagittal field curvature. Figure 6C The distortion curve of the optical system of Example 3 is shown, which represents the distortion value corresponding to different field angles. Figures 6A to 6CIt can be seen that the optical system provided in Example 3 can achieve good imaging quality.

[0098] Example 4

[0099] The following reference Figures 7 to 8C An optical system according to Example 4 of the present application is described. Figure 7 A structural schematic diagram of an optical system according to Example 4 of the present application is shown.

[0100] like Figure 7 As shown, the optical system includes, along the optical axis from the human eye side to the display side, an aperture STO, a reflective polarizer RP, a first lens E1, a quarter-wave plate QWP, a partially reflecting element BS, a second lens E2 and an image surface IMG.

[0101] In this embodiment, the first lens group, including the reflective polarizer RP, the first lens E1, and the quarter-wave plate QWP, has positive optical power. The second lens group, including the partially reflecting element BS and the second lens E2, has negative optical power. The surface of the first lens E1 closest to the eye is convex, and the surface closest to the display is also convex. The second lens E2 has negative optical power, with a convex surface closest to the eye and a concave surface closest to the display.

[0102] In this embodiment, the light beam emitted from the image surface IMG sequentially passes through the second lens E2 and the partially reflecting element BS of the second element group, and the quarter-wave plate QWP and the first lens E1 of the first element group. After that, the light beam is reflected and passes through the first lens E1 and the quarter-wave plate QWP again to reach the partially reflecting element BS. Thereafter, the light beam is reflected again at the reflecting element BS and sequentially passes through the quarter-wave plate QWP, the first lens E1, and the reflective polarizing element RP to be emitted toward the human eye.

[0103] Table 7 shows the basic parameters of the optical system of Example 4, where the units of the curvature radius and thickness are both in millimeters (mm). In this embodiment, the surface S3 on the side closest to the human eye and the surface S4 on the side closest to the display of the first lens E1, as well as the surface S12 on the side closest to the human eye and the surface S13 on the side closest to the display of the second lens E2, are all aspherical surfaces. Table 8 shows the high-order coefficients A4, A6, A8, A9, A10, A11, A12, A13 of the aspherical mirror surfaces S3, S4, S12, and S13 that can be used in Example 4. 10 、A 12 、A 14 、A 16 、A 18 and A 20 , wherein each aspheric surface shape can be defined by formula (1) given in the above embodiment 1.

[0104] surface element Surface type Radius of curvature thickness Refractive index Abbe number Refraction / Reflection S0 spherical surface endless endless refraction S1 Aperture (STO) spherical surface endless 15.0000 refraction S2 Reflective polarizer (RP) Aspheric 101.3611 0.2000 1.54 56.05 refraction S3 First lens (E1) Aspheric 101.3611 13.5579 1.54 56.05 refraction S4 Quarter Wave Plate (QWP) Aspheric -181.5605 0.2000 1.54 56.05 refraction S5 Aspheric -181.5605 3.2974 refraction S6 Partially reflective element (BS) Aspheric 835.5231 -3.2974 reflection S7 Quarter Wave Plate (QWP) Aspheric -181.5605 -0.2000 1.54 56.05 refraction S8 First lens (E1) Aspheric -181.5605 -13.5579 1.54 56.05 refraction S9 Reflective polarizer (RP) Aspheric 101.3611 13.5579 1.54 56.05 reflection S10 Quarter Wave Plate (QWP) Aspheric -181.5605 0.2000 1.54 56.05 refraction S11 Aspheric -181.5605 3.2974 refraction S12 Second lens (E2) Aspheric 835.5231 11.9512 1.54 56.05 refraction S13 Aspheric 750.0000 0.6535 refraction S14 spherical surface endless 2.9871 refraction S15 Image surface (IMG) spherical surface endless 0.0000 refraction

[0105] Table 7

[0106] Coefficient\Surface S3 S4 S12 S13 A4 -2.6532E-07 2.8085E-07 -1.8800E-07 -2.7535E-05 A6 2.5534E-10 6.0174E-10 2.8389E-10 2.8866E-07 A8 -5.1982E-14 -5.4782E-14 -4.5956E-14 -1.4373E-09 A10 5.2005E-17 9.9831E-17 -2.3456E-17 4.4385E-12 A12 1.2515E-20 2.4717E-20 5.4929E-20 -9.0127E-15 A14 0.0000E+00 0.0000E+00 -3.4896E-23 1.2102E-17 A16 0.0000E+00 0.0000E+00 0.0000E+00 -1.0422E-20 A18 0.0000E+00 0.0000E+00 0.0000E+00 5.2404E-24 A20 0.0000E+00 0.0000E+00 0.0000E+00 -1.1708E-27

[0107] Table 8

[0108] Figure 8A The axial chromatic aberration curve of the optical system of Example 4 is shown, which indicates the deviation of the convergent focus of light of different wavelengths passing through the lens. Figure 8B The astigmatism curve of the optical system of Example 4 is shown, which indicates the meridional field curvature and the sagittal field curvature. Figure 8C The distortion curve of the optical system of Example 4 is shown, which represents the distortion value corresponding to different field angles. Figures 8A to 8C It can be seen that the optical system provided in Example 4 can achieve good imaging quality.

[0109] Example 5

[0110] The following reference Figures 9 to 10C An optical system according to Example 5 of the present application is described. Figure 9 A structural schematic diagram of an optical system according to Example 5 of the present application is shown.

[0111] like Figure 9 As shown, the optical system includes, along the optical axis from the human eye side to the display side, an aperture STO, a reflective polarizer RP, a first lens E1, a quarter-wave plate QWP, a partially reflecting element BS, a second lens E2 and an image surface IMG.

[0112] In this embodiment, the first lens group, including the reflective polarizer RP, the first lens E1, and the quarter-wave plate QWP, has positive optical power. The second lens group, including the partially reflecting element BS and the second lens E2, has negative optical power. The surface of the first lens E1 closest to the eye is flat, and the surface closest to the display is convex. The second lens E2 has negative optical power, and its surface closest to the eye is concave, and its surface closest to the display is also concave.

[0113] In this embodiment, the light beam emitted from the image surface IMG sequentially passes through the second lens E2 and the partially reflecting element BS of the second element group, and the quarter-wave plate QWP and the first lens E1 of the first element group. After that, the light beam is reflected and passes through the first lens E1 and the quarter-wave plate QWP again to reach the partially reflecting element BS. Thereafter, the light beam is reflected again at the reflecting element BS and sequentially passes through the quarter-wave plate QWP, the first lens E1, and the reflective polarizing element RP to be emitted toward the human eye.

[0114] Table 9 shows the basic parameters of the optical system of Example 5, where the units of the curvature radius and thickness are both in millimeters (mm). In this embodiment, the surface S4 of the first lens E1 close to the display side and the surface S13 of the second lens E2 close to the display side are both aspherical surfaces. Table 10 shows the high-order coefficients A4, A6, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21, A22, A23, A24, A25, A26, A27, A28, A29, A30, A31, A32, A33, A34, A35, A36, A37, A38, A39, A40, A41, A42, A43, A44, A45, A46, A47, A 10 、A 12 、A 14 、A 16 、A 18 and A 20 , wherein each aspheric surface shape can be defined by formula (1) given in the above embodiment 1.

[0115] surface element Surface type Radius of curvature thickness Refractive index Abbe number Refraction / Reflection S0 spherical surface endless endless refraction S1 Aperture (STO) spherical surface endless 15.0000 refraction S2 Reflective polarizer (RP) spherical surface endless 0.2000 1.54 56.05 refraction S3 First lens (E1) spherical surface endless 13.2899 1.54 56.05 refraction S4 Quarter Wave Plate (QWP) Aspheric -56.2078 0.3000 1.54 56.05 refraction S5 Aspheric -56.2078 1.2525 refraction S6 Partially reflective element (BS) spherical surface -136.1371 -1.2525 reflection S7 Quarter Wave Plate (QWP) Aspheric -56.2078 -0.3000 1.54 56.05 refraction S8 First lens (E1) Aspheric -56.2078 -13.2899 1.54 56.05 refraction S9 Reflective polarizer (RP) spherical surface endless 13.2899 1.54 56.05 reflection S10 Quarter Wave Plate (QWP) Aspheric -56.2078 0.3000 1.54 56.05 refraction S11 Aspheric -56.2078 1.2525 refraction S12 Second lens (E2) spherical surface -136.1371 4.0000 1.54 56.05 refraction S13 Aspheric 250.0000 3.4741 refraction S14 spherical surface endless 0.0000 refraction S15 spherical surface endless 2.9918 refraction S16 Image surface (IMG) spherical surface endless 0.0000 refraction

[0116] Table 9

[0117]

[0118]

[0119] Table 10

[0120] Figure 10A The axial chromatic aberration curve of the optical system of Example 5 is shown, which indicates the deviation of the convergent focus of light of different wavelengths passing through the lens. Figure 10B The astigmatism curve of the optical system of Example 5 is shown, which indicates the meridional field curvature and the sagittal field curvature. Figure 10C The distortion curve of the optical system of Example 5 is shown, which represents the distortion value corresponding to different field angles. 10A to 10C It can be seen that the optical system provided in Example 5 can achieve good imaging quality.

[0121] Example 6

[0122] The following reference Figures 11 to 12C An optical system according to Example 6 of the present application is described. Figure 11 A structural schematic diagram of an optical system according to Example 6 of the present application is shown.

[0123] like Figure 11 As shown, the optical system includes, along the optical axis from the human eye side to the display side, a reflective polarizer RP, a first lens E1, a quarter-wave plate QWP, a second lens E2, a partially reflective element BS, and an image surface IMG.

[0124] In this embodiment, the light beam emitted from the image surface IMG sequentially passes through the partially reflecting element BS and the second lens E2 of the second element group, and the quarter-wave plate QWP and the first lens E1 of the first element group. Thereafter, the light beam is reflected and passes through the first lens E1, the quarter-wave plate QWP, and the second lens E2 again to reach the partially reflecting element BS. Thereafter, the light beam is reflected again at the reflecting element BS and sequentially passes through the second lens E2, the quarter-wave plate QWP, the first lens E1, and the reflective polarizing element RP to be emitted toward the human eye.

[0125] In this embodiment, the first lens group, including the reflective polarizer RP, the first lens E1, and the quarter-wave plate QWP, has positive optical power. The second lens group, including the second lens E2 and the partially reflecting element BS, also has positive optical power. The surface of the first lens E1 closest to the eye is flat, while the surface closest to the display is convex. The second lens E2 has positive optical power, with a concave surface closest to the eye and a convex surface closest to the display.

[0126] Table 11 shows the basic parameters of the optical system of Example 6, where the units of the curvature radius and thickness are both in millimeters (mm). In this embodiment, the surface S4 of the first lens E1 close to the display side and the surface S14 and surface S15 of the second lens E2 close to the human eye side are all aspherical surfaces. Table 12 shows the high-order coefficients A4, A6, A8, A9, A10, A11, A12, A13, A14, A15 of the aspherical mirror surfaces S4, S14, and S15 that can be used in Example 6. 10 、A 12 、A 14 、A 16 、A 18 and A 20 , wherein each aspheric surface shape can be defined by formula (1) given in the above embodiment 1.

[0127]

[0128]

[0129] Table 11

[0130] Coefficient\Surface S4 S14 S15 A4 2.8267E-06 2.5893E-06 2.9944E-07 A6 5.8216E-10 -7.0459E-10 -1.6032E-10 A8 -6.6755E-13 -4.4694E-14 1.5901E-13 A10 -4.1136E-16 1.2003E-16 8.1619E-17 A12 -1.6492E-19 -5.7252E-19 -8.7340E-20 A14 0.0000E+00 0.0000E+00 0.0000E+00 A16 0.0000E+00 0.0000E+00 0.0000E+00 A18 0.0000E+00 0.0000E+00 0.0000E+00 A20 0.0000E+00 0.0000E+00 0.0000E+00

[0131] Table 12

[0132] Figure 12A The axial chromatic aberration curve of the optical system of Example 6 is shown, which indicates the deviation of the convergent focus of light of different wavelengths passing through the lens. Figure 12B The astigmatism curve of the optical system of Example 6 is shown, which indicates the meridional field curvature and the sagittal field curvature. Figure 12CThe distortion curve of the optical system of Example 6 is shown, which represents the distortion value corresponding to different field angles. 12A to 12C It can be seen that the optical system provided in Example 6 can achieve good imaging quality.

[0133] In addition, in Examples 1 to 6, the effective focal length value FG1 of the first element group, the effective focal length value FG2 of the second element group, the effective focal length f of the optical system, the entrance pupil diameter EPD of the optical system, the distance SD on the optical axis from the aperture stop to the second side surface of the second lens, the distance TD on the optical axis from the first side surface of the first lens to the second side surface of the second lens, the distance BFL on the optical axis from the second side surface of the second lens to the image plane, the distance ER on the optical axis from the aperture stop to the first side surface of the first lens, the center thickness CTR on the optical axis of the reflective polarizer, and the center thickness CTQ on the optical axis of the quarter-wave plate are as shown in Table 13.

[0134] Parameters / Example 1 2 3 4 5 6 FG1(mm) 28.75 28.13 28.40 28.16 26.97 28.69 FG2(mm) 120.25 352.44 728.24 -14136.56 -161.08 398.47 f(mm) 28.01 28.12 28.02 28.02 28.34 29.00 EPD(mm) 5.00 5.00 5.00 5.00 5.00 5.00 SD(mm) 44.70 34.41 44.76 44.21 34.04 35.51 TD(mm) 29.50 19.21 29.56 29.01 18.84 20.31 BFL(mm) 3.09 6.46 3.08 3.64 6.47 2.99 ER(mm) 15.20 15.20 15.20 15.20 15.20 15.20 CTR(mm) 0.20 0.20 0.20 0.20 0.20 0.20 CTQ(mm) 0.20 0.20 0.20 0.20 0.30 0.30

[0135] Table 13

[0136] Examples 1 to 6 respectively satisfy the conditions shown in Table 14.

[0137]

[0138]

[0139] Table 14

[0140] The above description is merely a preferred embodiment of the present application and an illustration of the technical principles employed. Those skilled in the art should understand that the scope of protection provided in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but also encompasses other technical solutions formed by any combination of the above-mentioned technical features or their equivalents without departing from the concept of this application. For example, a technical solution formed by replacing the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. An optical system, characterized in that The optical axis includes a first element group, a second element group, and an image plane in sequence from the first side to the second side, wherein: The first element group has positive optical power and is composed of a reflective polarizing element, a first lens with positive optical power, and a quarter-wave plate in order from the first side to the second side along the optical axis, wherein the second side surface of the first lens is a convex surface; The second element group has positive or negative optical power and is composed of a partially reflecting element and a second lens having positive or negative optical power, the second side surface of the second lens is aspherical, and the partially reflecting element is located on the first side surface or the second side surface of the second lens; The number of lenses having optical power in the optical system is two; The light beam emitted from the imaging surface sequentially passes through the second lens, the partially reflecting element, the quarter-wave plate, and the first lens, and is then reflected by the reflective polarizing element. The light beam then passes through the first lens and the quarter-wave plate again, and is then reflected by the partially reflecting element. The light beam reflected by the partially reflecting element sequentially passes through the quarter-wave plate, the first lens, and the reflective polarizing element to be emitted toward the first side. Alternatively, the light beam emitted from the imaging surface sequentially passes through the partially reflecting element, the second lens, the quarter-wave plate, and the first lens, and is then reflected by the reflective polarizing element. The light beam then passes through the first lens, the quarter-wave plate, and the second lens again, and is then reflected by the partially reflecting element. The light beam reflected by the partially reflecting element sequentially passes through the second lens, the quarter-wave plate, the first lens, and the reflective polarizing element to be emitted toward the first side. The effective focal length FG1 of the first element group and the effective focal length FG2 of the second element group satisfy the following: 0.71≤(FG2+FG1) / (FG2-FG1)≤1.

63.

2. The optical system according to claim 1, wherein: The curvature radius R2 of the second side surface of the first lens and the curvature radius R4 of the second side surface of the second lens satisfy: 0.2<|R2 / R4|≤2.

40.

3. The optical system according to claim 1, wherein: The distance TD from the first side surface of the first lens to the second side surface of the second lens on the optical axis and the center thickness CT1 of the first lens on the optical axis satisfy: 1.4 <TD / CT1≤3.64。 4. The optical system according to claim 1, wherein: The effective focal length f of the optical system and the entrance pupil diameter EPD of the optical system satisfy: 5.60≤f / EPD≤5.

80.

5. The optical system according to claim 1, wherein: The effective focal length f of the optical system, the refractive index N1 of the first lens, and the refractive index N2 of the second lens satisfy: 28mm <f×(N2 / N1)≤29.00mm。 6. The optical system according to claim 1, wherein: The center thickness CT2 of the second lens on the optical axis and the air interval T12 between the first lens and the second lens on the optical axis satisfy: 1.06≤(CT2+T12) / (CT2-T12)<4.

9.

7. The optical system according to claim 1, wherein: The optical system further includes an aperture, wherein a distance SD from the aperture to the second side surface of the second lens on the optical axis and a distance ER from the aperture to the first side surface of the first lens on the optical axis satisfy: 2.24≤SD / ER≤2.

94.

8. The optical system according to claim 1, wherein: The optical system further includes an image surface provided on the second side, and the effective focal length f of the optical system and the distance BFL from the second side surface of the second lens to the image surface on the optical axis satisfy: 4.35≤f / BFL≤9.

71.

9. The optical system according to claim 1, wherein: The optical system further includes an image plane disposed on the second side, and a distance BFL from the second side surface of the second lens to the image plane on the optical axis, a center thickness CTR of the reflective polarizing element on the optical axis, and a center thickness CTQ of the quarter-wave plate on the optical axis satisfy the following conditions: 5.97≤BFL / (CTR+CTQ)≤16.

14.

10. The optical system according to claim 1, wherein: The curvature radius R2 of the second side surface of the first lens, the Abbe number V1 of the first lens, and the Abbe number V2 of the second lens satisfy: 0.50mm≤|R2| / (V1+V2)≤2.60mm.

11. The optical system according to claim 1, wherein: The effective focal length FG1 of the first element group and the center thickness CT1 of the first lens on the optical axis satisfy: 2.0 <FG1 / CT1≤5.14。 12. The optical system according to claim 1, wherein: The center thickness CT2 of the second lens on the optical axis and the entrance pupil diameter EPD of the optical system satisfy: 0.80≤CT2 / EPD<2.

9.

13. A VR device comprising the optical system according to any one of claims 1 to 12, wherein: The first side is a human eye side, and the second side is a display side.

Images