An optical system

Abstract

This invention discloses an optical system comprising, from the eye side to the screen side, a reflective polarizing element, a quarter-wave plate, a first lens, a second lens, and a third lens. The surface of the first lens closest to the eye is planar; the surface of the second lens closest to the eye is coated with a partial reflective layer. The center thickness CT2 of the second lens along the optical axis, the center thickness CT3 of the third lens along the optical axis, the effective focal length f2 of the second lens, and the effective focal length f3 of the third lens satisfy: -5.5 ≤ (CT2 + CT3) / (f2 + f3) < -2.5. The optical system, composed of three lenses, is beneficial for increasing the field of view and improving ghosting. By constraining the relationship between the focal lengths and center thicknesses of the second and third lenses, the lens thickness is controlled while satisfying the system's optical power distribution, which is beneficial for the lightweight design of the system.

Description

Technical Field

[0001] This invention belongs to the field of optical imaging, and particularly relates to an optical system comprising three lenses. Background Technology

[0002] With the increasing popularity of virtual reality (VR) devices, consumers are demanding higher standards for their thinness, image quality, and wearing experience. Traditional VR devices based on aspherical and Fresnel technologies are quite bulky and can no longer meet consumer needs. The introduction of optical path folding solutions has significantly improved the thinness of VR devices and has become the mainstream solution. While optical path folding effectively compresses the length of VR devices by folding the optical path, it also... Figure 1 The folding of the optical path shown in the diagram makes the ghosting problem more severe in the two-piece optical path folding scheme, and also limits the field of view.

[0003] Therefore, there is an urgent need for a new optical system that can effectively improve the ghosting problem while reducing system length. Summary of the Invention

[0004] This application aims to provide an optical system composed of three lenses, which effectively improves the ghosting problem while compressing the system length and further increases the field of view by adjusting the folded optical path structure.

[0005] This application proposes an optical system comprising, from the human eye side to the screen side, a reflective polarizing element, a quarter-wave plate, a first lens, a second lens, and a third lens; wherein, the surface of the first lens near the human eye side is planar; the surface of the second lens near the human eye side is coated with a partial reflective layer; the center thickness CT2 of the second lens on the optical axis, the center thickness CT3 of the third lens on the optical axis, the effective focal length f2 of the second lens, and the effective focal length f3 of the third lens satisfy: -5.5≤(CT2+CT3) / (f2+f3)<-2.5.

[0006] According to one embodiment provided in this application, the effective focal length f2 of the second lens, the radius of curvature R3 of the surface of the second lens near the human eye, and the radius of curvature R4 of the surface of the second lens near the screen satisfy: 2.0 < f2 / (R3+R4) < 3.0.

[0007] According to one embodiment provided in this application, the radius of curvature R2 of the surface of the first lens near the screen, the radius of curvature R3 of the surface of the second lens near the human eye, the center thickness CT1 of the first lens on the optical axis, and the air gap T12 between the first lens and the second lens on the optical axis satisfy: 3.5 < R3 / R2 + CT1 / T12 < 4.5.

[0008] According to one embodiment provided in this application, the effective focal length f3 of the third lens, the air gap T23 between the second and third lenses on the optical axis, the center thickness CT3 of the third lens on the optical axis, and the center thickness dqwp of the quarter-wave plate on the optical axis satisfy: 5.0 < f3 / (T23+CT3+dqwp) < 6.0.

[0009] According to one embodiment provided in this application, the center thickness CT2 of the second lens on the optical axis, the center thickness CT3 of the third lens on the optical axis, the center thickness drp of the reflective polarizing element on the optical axis, and the center thickness dqwp of the quarter-wave plate on the optical axis satisfy: 4.5 < CT3 / (CT2 + drp + dqwp) < 5.5.

[0010] According to one embodiment provided in this application, the effective focal length f1 of the first lens, the on-axis distance TD from the surface of the first lens near the human eye to the surface of the last lens near the screen side, and half of the maximum field of view (Semi-FOV) of the optical system satisfy: 3.5 < f1 / (TD*TAN(Semi-FOV)) < 4.5.

[0011] According to one embodiment provided in this application, the center thickness CT1 of the first lens on the optical axis, the center thickness CT3 of the third lens on the optical axis, the air gap T12 between the first and second lenses on the optical axis, and the air gap T23 between the second and third lenses on the optical axis satisfy: 3.0 <CT3 / CT1+T12 / T23<4.0。

[0012] According to one embodiment provided in this application, the effective focal length f1 of the first lens, the refractive index N1 of the first lens, the effective focal length f2 of the second lens, and the refractive index N2 of the second lens satisfy: f1*N1>|f2*N2|.

[0013] According to one embodiment provided in this application, the reflective polarizing element, the quarter-wave plate, and the first lens are attached together.

[0014] According to one embodiment provided in this application, the reflective polarizing element has the same refractive index as the quarter-wave plate.

[0015] According to one embodiment provided in this application, the effective focal length f1 of the first lens, the Abbe number Vrp of the reflective polarizing element, and the Abbe number Vqwp of the quarter-wave plate satisfy: 1.0mm < f1 / (Vrp+Vqwp) ≤ 1.5mm.

[0016] The beneficial effects of this invention are:

[0017] The optical system provided by this invention includes three lenses. The optical power signs of adjacent lenses are opposite, which is beneficial for chromatic aberration correction. Furthermore, the system lenses are distributed in a symmetrical structure. A reflective polarizing element and a quarter-wave plate are attached to the eye-side plane of the first lens, and a partial reflective layer is coated on the eye-side surface of the second lens, which is beneficial for increasing the field of view and improving ghosting. By constraining the relationship between the focal length and center thickness of the second and third lenses, the lens thickness is controlled while satisfying the optical power distribution of the system, which is beneficial for the lightweight design of the system. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram illustrating the formation of ghosting effects in existing technologies.

[0020] Figure 2 This is a schematic diagram of the lens group structure of the optical system of the present invention;

[0021] Figure 3 This is a schematic diagram of the lens group structure of the optical system of the present invention;

[0022] Figure 4 This is a schematic diagram of the lens group structure of Embodiment 1 of the optical system of the present invention;

[0023] Figure 5a , Figure 5b and Figure 5c These are the on-axis chromatic aberration curve, astigmatism curve, and distortion curve of the optical system embodiment 1 of the present invention, respectively.

[0024] Figure 6 This is a schematic diagram of the lens group structure of Embodiment 2 of the optical system of the present invention;

[0025] Figure 7a , Figure 7b and Figure 7c These are the on-axis chromatic aberration curve, astigmatism curve, and distortion curve of the optical system embodiment 2 of the present invention, respectively.

[0026] Figure 8 This is a schematic diagram of the lens group structure in Embodiment 3 of the optical system of the present invention;

[0027] Figure 9a , Figure 9b and Figure 9c These are the on-axis chromatic aberration curve, astigmatism curve, and distortion curve of embodiment 3 of the optical system of the present invention, respectively.

[0028] Figure 10 This is a schematic diagram of the lens group structure of embodiment 4 of the optical system of the present invention;

[0029] Figure 11a , Figure 11b and Figure 11c These are the on-axis chromatic aberration curve, astigmatism curve, and distortion curve of embodiment 4 of the optical system of the present invention, respectively.

[0030] Figure 12 This is a schematic diagram of the lens group structure in embodiment 5 of the optical system of the present invention;

[0031] Figure 13a , Figure 13b and Figure 13c These are the on-axis chromatic aberration curve, astigmatism curve, and distortion curve of embodiment 5 of the optical system of the present invention, respectively. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that in this specification, the terms "first," "second," "third," etc., are used only to distinguish one feature from another and do not imply any limitation on the features. Therefore, without departing from the teachings of the invention, the first lens discussed below may also be referred to as the second lens or the third lens.

[0034] It should also be understood that the terms "comprising," "including," "having," "containing," and / or "comprising," when used in this specification, indicate the presence of the stated features, elements, and / or components, but do not exclude the presence or addition of one or more other features, elements, components, and / or combinations thereof. Furthermore, when expressions such as "at least one of..." appear after a list of listed features, they modify the entire list of features, not individual elements in the list. Additionally, when describing embodiments of this application, the word "may" is used to mean "one or more embodiments of this application." And the term "exemplary" is intended to refer to an example or illustration.

[0035] In the accompanying drawings, the thickness, size, and shape of the lenses have been slightly exaggerated for ease of illustration. Specifically, the shapes of the spherical or aspherical surfaces shown in the drawings are illustrated by way of example. That is, the shapes of the spherical or aspherical surfaces are not limited to those shown in the drawings. The drawings are for illustrative purposes only and are not strictly to scale.

[0036] In the description of this invention, the paraxial region refers to the region near the optical axis. If the lens surface is convex and the location of the convexity is not defined, it means that the lens surface is convex at least in the paraxial region. If the lens surface is concave and the location of the concaveness is not defined, it means that the lens surface is concave at least in the paraxial region. The surface of each lens closest to the subject is called the eye-side surface of the lens, and the surface of each lens closest to the imaging plane is called the screen-side surface of the lens.

[0037] Unless otherwise specified, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms (e.g., those defined in common dictionaries) shall be interpreted as having the meaning consistent with their meaning in the context of the relevant art and shall not be interpreted in an idealized or overly formalized manner unless expressly so specified herein.

[0038] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The features, principles, and other aspects of the present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0039] Exemplary Implementation

[0040] like Figure 2 and Figure 3 As shown in the exemplary embodiment, this optical system comprises, in sequence from the human eye side to the screen side: a reflective polarizing element, a quarter-wave plate, a first lens, a second lens, and a third lens; wherein, the surface of the first lens near the human eye side is planar; and the surface of the second lens near the human eye side is coated with a partial reflective layer. The optical system consists of three lenses with adjacent lenses having opposite signs of optical power, which is beneficial for chromatic aberration correction; furthermore, the system lenses are arranged in a symmetrical structure, with the reflective polarizing element and the quarter-wave plate attached to the human eye side plane of the first lens, and the partial reflective layer coated on the human eye side surface of the second lens, which is beneficial for increasing the field of view and improving ghosting.

[0041] With the above arrangement, the light emitted from the screen undergoes at least two reflections from the screen side to the viewer's eye side. Specifically, the light emitted from the screen passes sequentially through the lens group, the quarter-wave plate, and the reflective polarizing element. The first reflection occurs between the quarter-wave plate and the reflective polarizing element. The light then refracts and passes sequentially through the quarter-wave plate and part of the lens group before finally reaching the viewer's eye. This double reflection of light ensures high image quality while shortening the physical distance along the optical axis from the viewer's eye to the screen side. This reduces system length, effectively improves ghosting issues, and further enhances the field of view.

[0042] Optionally, the lens group with positive optical power may include a first lens and a second lens. The side of the first lens near the screen may be aspherical, and both the side of the second lens near the human eye and the side near the screen may be aspherical. A partial reflective layer may be coated on the side of the second lens near the human eye. Light from the screen passes sequentially through the second lens, the first lens, the quarter-wave plate, and the reflective polarizing element. It undergoes a first reflection at the reflective polarizing element, then the light is refracted and passes sequentially through the partial lens group, the quarter-wave plate, and the first lens. A second reflection occurs on the side of the second lens with the partial reflective layer near the human eye, causing the light to be refracted again and pass sequentially through the first lens, the quarter-wave plate, and the reflective polarizing element before finally reaching the human eye.

[0043] Optionally, the lens group with positive optical power may include a first lens, a second lens, and a third lens. The side of the first lens near the screen may be aspherical, and the sides of either the second or third lens near the eye and near the screen may be aspherical. A partial reflective layer may be coated on the side of the second lens near the eye. Light from the screen passes sequentially through the third lens, the second lens, the first lens, the quarter-wave plate, and the reflective polarizing element. It undergoes a first reflection at the reflective polarizing element, then the light is refracted and passes sequentially through the quarter-wave plate and the first lens. A second reflection occurs on the side of the second lens with the partial reflective layer near the eye, causing the light to be refracted again and pass sequentially through the first lens, the quarter-wave plate, and the reflective polarizing element before finally reaching the eye.

[0044] In this exemplary embodiment, the center thickness CT2 of the second lens on the optical axis, the center thickness CT3 of the third lens on the optical axis, the effective focal length f2 of the second lens, and the effective focal length f3 of the third lens satisfy the following condition: -5.5 ≤ (CT2 + CT3) / (f2 + f3) < -2.5. By constraining the relationship between the focal lengths and center thicknesses of the second and third lenses, the lens thickness is controlled while satisfying the system's optical power distribution, which is beneficial for the lightweight design of the system. More specifically, the center thickness CT2 of the second lens on the optical axis, the center thickness CT3 of the third lens on the optical axis, the effective focal length f2 of the second lens, and the effective focal length f3 of the third lens satisfy the following condition: -5.5 ≤ (CT2 + CT3) / (f2 + f3) < -2.60.

[0045] In this exemplary embodiment, the effective focal length f2 of the second lens, the radius of curvature R3 of the surface of the second lens near the human eye, and the radius of curvature R4 of the surface of the second lens near the screen satisfy the following: 2.0 < f2 / (R3+R4) < 3.0. By controlling the ratio of the effective focal length to the surface radius of curvature of the second lens, its light path is optimized, ensuring the rationality of the second lens structure and contributing to the improvement of ghosting. More specifically, the effective focal length f2 of the second lens, the radius of curvature R3 of the surface of the second lens near the human eye, and the radius of curvature R4 of the surface of the second lens near the screen satisfy the following: 2.20 < f2 / (R3+R4) < 2.70.

[0046] In this exemplary embodiment, the radius of curvature R2 of the surface of the first lens near the screen, the radius of curvature R3 of the surface of the second lens near the human eye, the center thickness CT1 of the first lens on the optical axis, and the air gap T12 between the first and second lenses on the optical axis satisfy: 3.5 < R3 / R2 + CT1 / T12 < 4.5. By controlling the ratio of the radii of curvature of the first and second lenses and the ratio of the center thickness of the first lens to the air gap, the surface structure of the first and second lenses is controlled, ensuring the rationality of the lens structure and lens layout. More specifically, the radius of curvature R2 of the surface of the first lens near the screen, the radius of curvature R3 of the surface of the second lens near the human eye, the center thickness CT1 of the first lens on the optical axis, and the air gap T12 between the first and second lenses on the optical axis satisfy: 3.75 < R3 / R2 + CT1 / T12 < 4.10.

[0047] In this exemplary embodiment, the effective focal length f3 of the third lens, the air gap T23 between the second and third lenses on the optical axis, the center thickness CT3 of the third lens on the optical axis, and the center thickness dqwp of the quarter-wave plate on the optical axis satisfy: 5.0 < f3 / (T23+CT3+dqwp) < 6.0. By controlling the relationship between the effective focal length, center thickness, and air gap of the third lens, it is beneficial to control the spherical aberration and axial chromatic aberration introduced by the third lens, and reduce the risk of ghosting caused by lens inward reflection. More specifically, the effective focal length f3 of the third lens, the air gap T23 between the second and third lenses on the optical axis, the center thickness CT3 of the third lens on the optical axis, and the center thickness dqwp of the quarter-wave plate on the optical axis satisfy: 5.05 < f3 / (T23+CT3+dqwp) < 5.50.

[0048] In the present exemplary embodiment, the central thickness CT2 of the second lens on the optical axis, the central thickness CT3 of the third lens on the optical axis, the central thickness drp of the reflective polarizing element on the optical axis, and the central thickness dqwp of the quarter-wave plate on the optical axis satisfy: 4.5 < CT3 / (CT2 + drp + dqwp) < 5.5. By controlling the relationship between the central thicknesses of the third lens, the second lens, the reflective polarizing element, and the quarter-wave plate, a reasonable distribution of the optical power is achieved, and the thicknesses of the two lenses are ensured to be small, which is beneficial to the miniaturization of the system. More specifically, the central thickness CT2 of the second lens on the optical axis, the central thickness CT3 of the third lens on the optical axis, the central thickness drp of the reflective polarizing element on the optical axis, and the central thickness dqwp of the quarter-wave plate on the optical axis satisfy: 4.60 < CT3 / (CT2 + drp + dqwp) < 5.10.

[0049] In the present exemplary embodiment, the effective focal length f1 of the first lens, the axial distance TD from the surface of the first lens close to the human eye to the surface of the last lens close to the screen side, and the half of the maximum field angle Semi-FOV of the optical system satisfy: 3.5 < f1 / (TD * TAN(Semi-FOV)) < 4.5. By controlling the parameter relationship between the effective focal length of the first lens, the total length of the system, and the FOV, the total length of the system and the distribution of the optical power of the first lens can be constrained while ensuring the field angle. More specifically, the effective focal length f1 of the first lens, the axial distance TD from the surface of the first lens close to the human eye to the surface of the last lens close to the screen side, and the half of the maximum field angle Semi-FOV of the optical system satisfy: 3.80 < f1 / (TD * TAN(Semi-FOV)) < 4.05.

[0050] In the present exemplary embodiment, the central thickness CT1 of the first lens on the optical axis, the central thickness CT3 of the third lens on the optical axis, the air gap T12 between the first lens and the second lens on the optical axis, and the air gap T23 between the second lens and the third lens on the optical axis satisfy: 3.0 < CT3 / CT1 + T12 / T23 < 4.0. By controlling the parameter relationship between the central thicknesses of the first and third lenses and the air gaps, it is beneficial to improve the rationality of the overall layout of the system and reasonably distribute the assembly tolerances, thereby improving the manufacturability of the system. More specifically, the central thickness CT1 of the first lens on the optical axis, the central thickness CT3 of the third lens on the optical axis, the air gap T12 between the first lens and the second lens on the optical axis, and the air gap T23 between the second lens and the third lens on the optical axis satisfy: 3.10 < CT3 / CT1 + T12 / T23 < 3.85.

[0051] In this exemplary embodiment, the effective focal length f1 of the first lens, the refractive index N1 of the first lens, the effective focal length f2 of the second lens, and the refractive index N2 of the second lens satisfy: f1*N1>|f2*N2|. By controlling the parameter relationship between the effective focal length and refractive index of the first and second lenses, the distribution of optical power can be controlled on the one hand, and the direction of light can be controlled to be more reasonable on the other hand.

[0052] In this exemplary embodiment, the reflective polarizing element, the quarter-wave plate, and the first lens are bonded together. The reflective polarizing element and the quarter-wave plate are attached to the surface of the first lens closest to the human eye. Since this surface is flat, attaching them to this surface effectively reduces the difficulty of film application and improves the quality of the film application.

[0053] In this exemplary embodiment, the refractive index of the reflective polarizing element is the same as that of the quarter-wave plate. By controlling the refractive index of the reflective polarizing element and the quarter-wave plate to be the same, additional aberrations introduced by the reflective polarizing element and the quarter-wave plate are avoided.

[0054] In this exemplary embodiment, the effective focal length f1 of the first lens, the Abbe number Vrp of the reflective polarizing element, and the Abbe number Vqwp of the quarter-wave plate satisfy the following condition: 1.0 mm < f1 / (Vrp+Vqwp) ≤ 1.5 mm. By controlling the ratio of the effective focal length of the first lens to the sum of the Abbe numbers of the reflective polarizing element and the quarter-wave plate, the amount of dispersion introduced into the system by the reflective polarizing element and the quarter-wave plate is controlled, which is beneficial for the correction of chromatic aberration in the system. More specifically, the effective focal length f1 of the first lens, the Abbe number Vrp of the reflective polarizing element, and the Abbe number Vqwp of the quarter-wave plate satisfy the following condition: 1.10 mm < f1 / (Vrp+Vqwp) ≤ 1.5 mm.

[0055] In this exemplary embodiment, the side of any one of the first lens E1 to the third lens E3 that is near the human eye and / or near the screen is aspherical. The surface shape x of each aspherical lens can be defined using, but is not limited to, the following aspherical formula:

[0056]

[0057] Where x is the distance vector from the vertex of the aspherical surface along the optical axis at a height of h; c is the paraxial curvature of the aspherical surface, c = 1 / R (that is, the paraxial curvature c is the reciprocal of the radius of curvature R in Table 1); k is the conic coefficient; Ai is the correction coefficient of the i-th order of the aspherical surface.

[0058] In an exemplary embodiment, at least one of the mirror surfaces of each lens is an aspherical mirror surface; that is, at least one mirror surface from the eye-side of the first lens to the screen-side of the third lens is an aspherical mirror surface. The characteristic of an aspherical lens is that its curvature changes continuously from the lens center to the lens periphery. Unlike a spherical lens, which has a constant curvature from the lens center to the lens periphery, an aspherical lens has better curvature radius characteristics, offering advantages in improving distortion aberrations and astigmatism. By using an aspherical lens, aberrations occurring during imaging can be eliminated as much as possible, thereby improving image quality. Optionally, at least one of the eye-side and screen-side surfaces of each of the first, second, and third lenses is an aspherical mirror surface.

[0059] However, those skilled in the art will understand that the number of lenses constituting the optical system can be changed without departing from the technical solutions claimed in this application to obtain the various results and advantages described in this specification. For example, although three lenses are described as an example in the embodiments, the optical system is not limited to including three lenses, and may include other numbers of lenses if necessary.

[0060] The device incorporating the optical system of this application may further include at least one storage mechanism, wherein the storage mechanism is used to compress the volume of the device. For example, the storage mechanism allows the user to compress the volume of the device when it is not in use (e.g., to fold the device).

[0061] The device may further include at least one autofocus device, which corresponds to the optical system settings and is used to move the optical lenses of the optical system. Thus, the autofocus device provides focusing functionality for the optical system and can adjust the focal length for different users' vision. In some embodiments, there is one autofocus device, which can simultaneously adjust the focal length of two optical systems. In other embodiments, there are two autofocus devices to adjust the focal length of each optical system separately.

[0062] It is worth noting that the communication connection mentioned in this article refers to a connection method in which two components exchange signals with each other, for example, through wired or wireless transmission.

[0063] The various technical features in the optical system and device described above can be combined and configured to achieve the corresponding effects.

[0064] In the optical system disclosed in this application, the lens can be made of glass or plastic. If the lens is made of glass, the freedom of refractive power configuration of the optical system can be increased, and the influence of external environmental temperature changes on imaging can be reduced. Glass lenses can be manufactured using techniques such as grinding or molding. If the lens is made of plastic, production costs can be effectively reduced. Furthermore, spherical or aspherical (ASP) surfaces can be provided on the lens surface. Spherical lenses reduce manufacturing difficulty, while aspherical surfaces provide more controllable variables to reduce aberrations, decrease the number of lenses, and effectively reduce the overall length of the optical system of this application. Further, aspherical surfaces can be manufactured using methods such as plastic injection molding or molding glass lenses.

[0065] In the optical system disclosed in this application, if the lens surface is aspherical, it means that all or part of the optically effective area of ​​the lens surface is aspherical.

[0066] In the optical system disclosed in this application, if the lens surface is convex and the location of the convex surface is not defined, it means that the convex surface can be located near the optical axis of the lens surface; if the lens surface is concave and the location of the concave surface is not defined, it means that the concave surface can be located near the optical axis of the lens surface. If the refractive power or focal length of the lens is not defined in its region, it means that the refractive power or focal length of the lens can be the refractive power or focal length of the lens near the optical axis.

[0067] In the optical system disclosed in this application, the inflection point of the lens surface refers to the boundary point where the curvature of the lens surface changes from positive to negative. The critical point of the lens surface refers to the point of tangency on the tangent line between a plane perpendicular to the optical axis and the lens surface, and the critical point is not located on the optical axis.

[0068] In the optical system disclosed in this application, the image surface of the optical system can be a plane or a curved surface with any curvature, depending on the corresponding display, especially a curved surface with a concave surface facing the direction of the human eye.

[0069] The optical system disclosed in this application may include at least one aperture stop, which may be located in front of the first optical lens, between the optical lenses, or after the last optical lens. The aperture stop may be of the type such as a glare stop or a field stop, and may be used to reduce stray light and help improve image quality.

[0070] This application may appropriately incorporate a variable aperture element, which can be a mechanical component or a light-regulating element, and whose aperture size and shape can be controlled electrically or by electrical signals. The mechanical component may include movable parts such as a blade assembly or a shielding plate; the light-regulating element may include a filter element, an electrochromic material, a liquid crystal layer, or other masking materials. The variable aperture element can enhance image adjustment capabilities by controlling the amount of light entering the image or the exposure time. Furthermore, the variable aperture element can also be the aperture of this application, and image quality, such as depth of field or exposure speed, can be adjusted by changing the aperture value.

[0071] Specific embodiments of the optical system applicable to the above embodiments are further described below with reference to the accompanying drawings. Specific Implementation Example 1

[0073] Figure 4 This is a schematic diagram of the lens group structure of Embodiment 1 of the optical system of the present invention. From the eye side to the screen side, it includes, in sequence: a reflective polarizing element, a quarter-wave plate, a first lens, a second lens, and a third lens. The surface of the first lens near the eye side is planar; the surface of the second lens near the eye side is coated with a partial reflective layer. Light emitted from the screen undergoes at least two reflections from the screen side to the eye side, entering the eye in the order of numbers 16 to 0. Light from screen S10 (number 16) passes sequentially through the third lens, the second lens, the first lens, the quarter-wave plate, and the reflective polarizing element. A first reflection occurs at the reflective polarizing element S3 (number 9), followed by a reflection and subsequent passing through the quarter-wave plate and the first lens. A second reflection occurs on the eye-side mirror S6 (number 6) of the second lens, which is coated with a partial reflective layer. This causes the light to be reflected again and sequentially pass through the first lens, the quarter-wave plate, and the reflective polarizing element, finally reaching the eye side S0 (number 0).

[0074] The first optical lens E1 has positive refractive power. Its surface near the human eye is flat, and its surface near the screen is convex. Its surface near the human eye is spherical, and its surface near the screen is aspherical.

[0075] The second optical lens E2 has negative refractive power, and its surface near the human eye is concave, as is its surface near the screen; both of its surfaces are aspherical.

[0076] The third optical lens E3 has positive refractive power, and its surface near the human eye is convex, as is its surface near the screen; both of its surfaces are aspherical.

[0077] A partial reflective layer is coated on the side of the second lens E2 near the human eye, and the partial reflective layer has an average light reflectivity of 50%.

[0078] Table 1 shows the basic parameters of the optical system in Example 1, where the units for radius of curvature, thickness, and focal length are all millimeters (mm).

[0079]

[0080] Table 1

[0081] As shown in Table 2, in Example 1, the effective focal length of the first lens is f1 = 128.65 mm, the effective focal length of the second lens is f2 = -73.90 mm, and the effective focal length of the third lens is f3 = 70.57 mm. The semi-FOV (half of the maximum field of view) of the optical system is 53.0°.

[0082]

[0083]

[0084] Table 2

[0085] The optical system in Example 1 satisfies:

[0086] f2 / (R3+R4)=2.21; where f2 is the effective focal length of the second lens, R3 is the radius of curvature of the surface of the second lens closest to the human eye, and R4 is the radius of curvature of the surface of the second lens closest to the screen.

[0087] R3 / R2+CT1 / T12=4.00; where R2 is the radius of curvature of the surface of the first lens near the screen, R3 is the radius of curvature of the surface of the second lens near the human eye, CT1 is the center thickness of the first lens on the optical axis, and T12 is the air gap between the first and second lenses on the optical axis.

[0088] f3 / (T23+CT3+dqwp)=5.09; where f3 is the effective focal length of the third lens, T23 is the air gap between the second and third lenses on the optical axis, CT3 is the center thickness of the third lens on the optical axis, and dqwp is the center thickness of the quarter-wave plate (QWP) on the optical axis.

[0089] CT3 / (CT2+drp+dqwp)=5.03; where CT2 is the center thickness of the second lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, drp is the center thickness of the reflective polarizing element (RP) on the optical axis, and dqwp is the center thickness of the quarter-wave plate (QWP) on the optical axis.

[0090] (CT2+CT3) / (f2+f3)=-4.23; where CT2 is the center thickness of the second lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, f2 is the effective focal length of the second lens, and f3 is the effective focal length of the third lens.

[0091] f1 / (TD*TAN(Semi-FOV))=3.85; where f1 is the effective focal length of the first lens, TD is the on-axis distance from the surface of the first lens near the human eye to the surface of the last lens near the screen, and Semi-FOV is half of the maximum field of view of the optical system.

[0092] CT3 / CT1+T12 / T23=3.64; where CT1 is the center thickness of the first lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, T12 is the air gap between the first and second lenses on the optical axis, and T23 is the air gap between the second and third lenses on the optical axis.

[0093] f1*N1=198.73; where f1 is the effective focal length of the first lens and N1 is the refractive index of the first lens.

[0094] |f2*N2|=123.41; where f2 is the effective focal length of the second lens, and N2 is the refractive index of the second lens.

[0095] f1 / (Vrp+Vqwp)=1.13; where f1 is the effective focal length of the first lens, Vrp is the Abbe number of the reflective polarizing element (RP), and Vqwp is the Abbe number of the quarter-wave plate (QWP).

[0096] In Example 1, Table 3 shows the higher-order coefficients A4, A6, A8, and A6 that can be used for the aspherical mirrors numbered 5-7 and 11-15 in Example 1. 10 .

[0097] Serial Number Face number A4 A6 A8 A10 5 S5 2.72E-02 9.45E-02 -1.74E-02 8.27E-04 6 S6 -9.54E-02 -2.69E-02 9.92E-03 -1.99E-04 7 S5 2.72E-02 9.45E-02 -1.74E-02 8.27E-04 11 S5 2.72E-02 9.45E-02 -1.74E-02 8.27E-04 12 S6 -9.54E-02 -2.69E-02 9.92E-03 -1.99E-04 13 S7 9.45E-01 -1.26E-01 4.15E-02 -6.69E-03 14 S8 -1.12E+00 -7.59E-03 2.98E-02 -1.11E-02 15 S9 4.13E-02 1.48E-02 -2.64E-02 3.11E-02

[0098] Table 3

[0099] Figure 5a The on-axis chromatic aberration curve of the optical system of Embodiment 1 is shown, which represents the deviation of the focal point of light of different wavelengths after passing through the lens. Figure 5b The astigmatism curve of the optical system of Example 1 is shown, which indicates meridional field curvature and sagittal field curvature. Figure 5c The distortion curves of the optical system of Embodiment 1 are shown, representing the magnitude of distortion under different viewing angles. According to... Figures 5a to 5c As shown, the optical system given in Example 1 can achieve good imaging quality. Specific Implementation Example 2

[0101] Figure 6 This is a schematic diagram of the lens group structure of embodiment 2 of the optical system of the present invention. From the eye side to the screen side, it includes, in sequence: a reflective polarizing element, a quarter-wave plate, a first lens, a second lens, and a third lens. The surface of the first lens near the eye side is planar; the surface of the second lens near the eye side is coated with a partial reflective layer. Light emitted from the screen undergoes at least two reflections from the screen side to the eye side, entering the eye in the order of numbers 16 to 0. Light from screen S10 (number 16) passes sequentially through the third lens, the second lens, the first lens, the quarter-wave plate, and the reflective polarizing element. A first reflection occurs at the reflective polarizing element S3 (number 9), followed by a reflection and sequential passing through the quarter-wave plate and the first lens. A second reflection occurs on the eye-side mirror S6 (number 6) of the second lens, which is coated with a partial reflective layer. This causes the light to be reflected again and sequentially pass through the first lens, the quarter-wave plate, and the reflective polarizing element, finally reaching the eye side S0 (number 0).

[0102] The first optical lens E1 has positive refractive power. Its surface near the human eye is flat, and its surface near the screen is convex. Its surface near the human eye is spherical, and its surface near the screen is aspherical.

[0103] The second optical lens E2 has negative refractive power, and its surface near the human eye is concave, as is its surface near the screen; both of its surfaces are aspherical.

[0104] The third optical lens E3 has positive refractive power, and its surface near the human eye is convex, as is its surface near the screen; both of its surfaces are aspherical.

[0105] A partial reflective layer is coated on the side of the second lens E2 near the human eye, and the partial reflective layer has an average light reflectivity of 50%.

[0106] Table 4 shows the basic parameters of the optical system in Example 2, where the units for radius of curvature, thickness, and focal length are all millimeters (mm).

[0107]

[0108] Table 4

[0109] As shown in Table 5, in Example 2, the effective focal length of the first lens is f1 = 131.25 mm, the effective focal length of the second lens is f2 = -75.45 mm, and the effective focal length of the third lens is f3 = 70.25 mm. The semi-FOV (half of the maximum field of view) of the optical system is 53.0°.

[0110]

[0111] Table 5

[0112] The optical system in Example 2 satisfies:

[0113] f2 / (R3+R4)=2.65; where f2 is the effective focal length of the second lens, R3 is the radius of curvature of the surface of the second lens closest to the human eye, and R4 is the radius of curvature of the surface of the second lens closest to the screen.

[0114] R3 / R2+CT1 / T12=3.86; where R2 is the radius of curvature of the surface of the first lens near the screen, R3 is the radius of curvature of the surface of the second lens near the human eye, CT1 is the center thickness of the first lens on the optical axis, and T12 is the air gap between the first and second lenses on the optical axis.

[0115] f3 / (T23+CT3+dqwp)=5.18; where f3 is the effective focal length of the third lens, T23 is the air gap between the second and third lenses on the optical axis, CT3 is the center thickness of the third lens on the optical axis, and dqwp is the center thickness of the quarter-wave plate (QWP) on the optical axis.

[0116] CT3 / (CT2+drp+dqwp)=4.90; where CT2 is the center thickness of the second lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, drp is the center thickness of the reflective polarizing element (RP) on the optical axis, and dqwp is the center thickness of the quarter-wave plate (QWP) on the optical axis.

[0117] (CT2+CT3) / (f2+f3)=-2.65; where CT2 is the center thickness of the second lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, f2 is the effective focal length of the second lens, and f3 is the effective focal length of the third lens.

[0118] f1 / (TD*TAN(Semi-FOV))=3.99; where f1 is the effective focal length of the first lens, TD is the on-axis distance from the surface of the first lens near the human eye to the surface of the last lens near the screen, and Semi-FOV is half of the maximum field of view of the optical system.

[0119] CT3 / CT1+T12 / T23=3.67; where CT1 is the center thickness of the first lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, T12 is the air gap between the first and second lenses on the optical axis, and T23 is the air gap between the second and third lenses on the optical axis.

[0120] f1*N1=202.75; where f1 is the effective focal length of the first lens and N1 is the refractive index of the first lens.

[0121] |f2*N2|=126.00; where f2 is the effective focal length of the second lens and N2 is the refractive index of the second lens.

[0122] f1 / (Vrp+Vqwp)=1.15; where f1 is the effective focal length of the first lens, Vrp is the Abbe number of the reflective polarizing element (RP), and Vqwp is the Abbe number of the quarter-wave plate (QWP).

[0123] In Example 2, Table 6 shows the higher-order coefficients A4, A6, A8, and A6 that can be used for the aspherical mirrors numbered 5-7 and 11-15 in Example 2. 10 .

[0124]

[0125]

[0126] Table 6

[0127] Figure 7a The on-axis chromatic aberration curve of the optical system of Embodiment 2 is shown, which represents the deviation of the focal point of light of different wavelengths after passing through the lens. Figure 7b The astigmatism curves of the optical system of Embodiment 2 are shown, which represent the meridional image plane curvature and the sagittal image plane curvature. Figure 7c The distortion curves of the optical system in Example 2 are shown, representing the magnitude of distortion under different viewing angles. According to... Figures 7a to 7c As shown, the optical system given in Example 2 can achieve good imaging quality. Specific Implementation Example 3

[0129] Figure 8 This is a schematic diagram of the lens group structure of embodiment 3 of the optical system of the present invention. From the human eye side to the screen side, it includes, in sequence: a reflective polarizing element, a quarter-wave plate, a first lens, a second lens, and a third lens. The surface of the first lens near the human eye side is planar; the surface of the second lens near the human eye side is coated with a partial reflective layer. Light emitted from the screen undergoes at least two reflections from the screen side to the human eye side, entering the human eye in the order of numbers 16 to 0. Light from screen S10 (number 16) passes sequentially through the third lens, the second lens, the first lens, the quarter-wave plate, and the reflective polarizing element. A first reflection occurs at the reflective polarizing element S3 (number 9), followed by a reflection and sequential passing through the quarter-wave plate and the first lens. A second reflection occurs on the human eye side mirror S6 (number 6) of the second lens, which is coated with a partial reflective layer. This causes the light to be reflected again and sequentially pass through the first lens, the quarter-wave plate, and the reflective polarizing element, finally reaching the human eye side S0 (number 0).

[0130] The first optical lens E1 has positive refractive power. Its surface near the human eye is flat, and its surface near the screen is convex. Its surface near the human eye is spherical, and its surface near the screen is aspherical.

[0131] The second optical lens E2 has negative refractive power, and its surface near the human eye is concave, as is its surface near the screen; both of its surfaces are aspherical.

[0132] The third optical lens E3 has positive refractive power, its surface near the human eye is convex, and its surface near the screen is concave; and both of its surfaces are aspherical.

[0133] A partial reflective layer is coated on the side of the second lens E2 near the human eye, and the partial reflective layer has an average light reflectivity of 50%.

[0134] Table 7 shows the basic parameters of the optical system in Example 3, where the units for radius of curvature, thickness, and focal length are millimeters (mm).

[0135]

[0136]

[0137] Table 7

[0138] As shown in Table 8, in Example 3, the effective focal length of the first lens is f1 = 129.80 mm, the effective focal length of the second lens is f2 = -74.48 mm, and the effective focal length of the third lens is f3 = 72.07 mm. The semi-FOV (half of the maximum field of view) of the optical system is 53.0°.

[0139]

[0140] Table 8

[0141] The optical system in Example 3 satisfies:

[0142] f2 / (R3+R4)=2.30; where f2 is the effective focal length of the second lens, R3 is the radius of curvature of the surface of the second lens closest to the human eye, and R4 is the radius of curvature of the surface of the second lens closest to the screen.

[0143] R3 / R2+CT1 / T12=4.07; where R2 is the radius of curvature of the surface of the first lens near the screen, R3 is the radius of curvature of the surface of the second lens near the human eye, CT1 is the center thickness of the first lens on the optical axis, and T12 is the air gap between the first and second lenses on the optical axis.

[0144] f3 / (T23+CT3+dqwp)=5.41; where f3 is the effective focal length of the third lens, T23 is the air gap between the second and third lenses on the optical axis, CT3 is the center thickness of the third lens on the optical axis, and dqwp is the center thickness of the quarter-wave plate (QWP) on the optical axis.

[0145] CT3 / (CT2+drp+dqwp)=4.69; where CT2 is the center thickness of the second lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, drp is the center thickness of the reflective polarizing element (RP) on the optical axis, and dqwp is the center thickness of the quarter-wave plate (QWP) on the optical axis.

[0146] (CT2+CT3) / (f2+f3)=-5.50; where CT2 is the center thickness of the second lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, f2 is the effective focal length of the second lens, and f3 is the effective focal length of the third lens.

[0147] f1 / (TD*TAN(Semi-FOV))=4.01; where f1 is the effective focal length of the first lens, TD is the on-axis distance from the surface of the first lens near the human eye to the surface of the last lens near the screen, and Semi-FOV is half of the maximum field of view of the optical system.

[0148] CT3 / CT1+T12 / T23=3.20; where CT1 is the center thickness of the first lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, T12 is the air gap between the first and second lenses on the optical axis, and T23 is the air gap between the second and third lenses on the optical axis.

[0149] f1*N1=200.51; where f1 is the effective focal length of the first lens and N1 is the refractive index of the first lens.

[0150] |f2*N2|=124.38; where f2 is the effective focal length of the second lens, and N2 is the refractive index of the second lens.

[0151] f1 / (Vrp+Vqwp)=1.14; where f1 is the effective focal length of the first lens, Vrp is the Abbe number of the reflective polarizing element (RP), and Vqwp is the Abbe number of the quarter-wave plate (QWP).

[0152] In Example 3, Table 9 shows the higher-order coefficients A4, A6, A8, and A6 that can be used for the aspherical mirrors numbered 5-7 and 11-15 in Example 3. 10 .

[0153] Serial Number Face number A4 A6 A8 A10 5 S5 -1.73E-01 1.46E-01 -3.54E-02 3.68E-03 6 S6 8.98E-03 -5.45E-02 2.20E-02 -2.52E-03 7 S5 -1.73E-01 1.46E-01 -3.54E-02 3.68E-03 11 S5 -1.73E-01 1.46E-01 -3.54E-02 3.68E-03 12 S6 8.98E-03 -5.45E-02 2.20E-02 -2.52E-03 13 S7 1.16E+00 -1.50E-01 4.31E-02 -1.33E-02 14 S8 -1.56E+00 8.43E-02 1.86E-02 -2.03E-02 15 S9 2.89E-01 -6.59E-02 -1.84E-02 3.89E-02

[0154] Table 9

[0155] Figure 9a The on-axis chromatic aberration curve of the optical system of Embodiment 3 is shown, which represents the deviation of the focal point of light of different wavelengths after passing through the lens. Figure 9b The astigmatism curve of the optical system of Example 3 is shown, which indicates the meridional field curvature and the sagittal field curvature. Figure 9c The distortion curves of the optical system in Example 3 are shown, representing the magnitude of distortion under different viewing angles. According to... Figures 9a to 9c As shown, the optical system given in Example 3 can achieve good imaging quality. Specific Implementation Example 4

[0157] Figure 10 This is a schematic diagram of the lens group structure of embodiment 4 of the optical system of the present invention. From the eye side to the screen side, it includes, in sequence: a reflective polarizing element, a quarter-wave plate, a first lens, a second lens, and a third lens. The surface of the first lens near the eye side is planar; the surface of the second lens near the eye side is coated with a partial reflective layer. Light emitted from the screen undergoes at least two reflections from the screen side to the eye side, entering the eye in the order of numbers 16 to 0. Light from screen S10 (number 16) passes sequentially through the third lens, the second lens, the first lens, the quarter-wave plate, and the reflective polarizing element. A first reflection occurs at the reflective polarizing element S3 (number 9), followed by a reflection and subsequent passing through the quarter-wave plate and the first lens. A second reflection occurs on the eye-side mirror S6 (number 6) of the second lens, which is coated with a partial reflective layer. This causes the light to be reflected again and sequentially pass through the first lens, the quarter-wave plate, and the reflective polarizing element, finally reaching the eye side S0 (number 0).

[0158] The first optical lens E1 has positive refractive power. Its surface near the human eye is flat, and its surface near the screen is convex. Its surface near the human eye is spherical, and its surface near the screen is aspherical.

[0159] The second optical lens E2 has negative refractive power, and its surface near the human eye is concave, as is its surface near the screen; both of its surfaces are aspherical.

[0160] The third optical lens E3 has positive refractive power, and its surface near the human eye is convex, as is its surface near the screen; both of its surfaces are aspherical.

[0161] A partial reflective layer is coated on the side of the second lens E2 near the human eye, and the partial reflective layer has an average light reflectivity of 50%.

[0162] Table 10 shows the basic parameters of the optical system in Example 4, where the units for radius of curvature, thickness, and focal length are all millimeters (mm).

[0163]

[0164]

[0165] Table 10

[0166] As shown in Table 11, in Example 4, the effective focal length of the first lens is f1 = 131.36 mm, the effective focal length of the second lens is f2 = -75.44 mm, and the effective focal length of the third lens is f3 = 70.38 mm. The semi-FOV (half of the maximum field of view) of the optical system is 53.0°.

[0167]

[0168] Table 11

[0169] The optical system in Example 4 satisfies:

[0170] f2 / (R3+R4)=2.63; where f2 is the effective focal length of the second lens, R3 is the radius of curvature of the surface of the second lens closest to the human eye, and R4 is the radius of curvature of the surface of the second lens closest to the screen.

[0171] R3 / R2+CT1 / T12=3.83; where R2 is the radius of curvature of the surface of the first lens near the screen, R3 is the radius of curvature of the surface of the second lens near the human eye, CT1 is the center thickness of the first lens on the optical axis, and T12 is the air gap between the first and second lenses on the optical axis.

[0172] f3 / (T23+CT3+dqwp)=5.21; where f3 is the effective focal length of the third lens, T23 is the air gap between the second and third lenses on the optical axis, CT3 is the center thickness of the third lens on the optical axis, and dqwp is the center thickness of the quarter-wave plate (QWP) on the optical axis.

[0173] CT3 / (CT2+drp+dqwp)=4.89; where CT2 is the center thickness of the second lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, drp is the center thickness of the reflective polarizing element (RP) on the optical axis, and dqwp is the center thickness of the quarter-wave plate (QWP) on the optical axis.

[0174] (CT2+CT3) / (f2+f3)=-2.71; where CT2 is the center thickness of the second lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, f2 is the effective focal length of the second lens, and f3 is the effective focal length of the third lens.

[0175] f1 / (TD*TAN(Semi-FOV))=4.00; where f1 is the effective focal length of the first lens, TD is the on-axis distance from the surface of the first lens near the human eye to the surface of the last lens near the screen, and Semi-FOV is half of the maximum field of view of the optical system.

[0176] CT3 / CT1+T12 / T23=3.70; where CT1 is the center thickness of the first lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, T12 is the air gap between the first and second lenses on the optical axis, and T23 is the air gap between the second and third lenses on the optical axis.

[0177] f1*N1=202.91; where f1 is the effective focal length of the first lens and N1 is the refractive index of the first lens.

[0178] |f2*N2|=125.99; where f2 is the effective focal length of the second lens, and N2 is the refractive index of the second lens.

[0179] f1 / (Vrp+Vqwp)=1.15; where f1 is the effective focal length of the first lens, Vrp is the Abbe number of the reflective polarizing element (RP), and Vqwp is the Abbe number of the quarter-wave plate (QWP).

[0180] In Example 4, Table 12 shows the higher-order coefficients A4, A6, A8, and A6 that can be used for the aspherical mirrors numbered 5-7 and 11-15 in Example 4. 10 .

[0181] Serial Number Face number A4 A6 A8 A10 5 S5 -1.39E-01 1.39E-01 -3.48E-02 3.66E-03 6 S6 -2.35E-03 -5.11E-02 2.10E-02 -2.37E-03 7 S5 -1.39E-01 1.39E-01 -3.48E-02 3.66E-03 11 S5 -1.39E-01 1.39E-01 -3.48E-02 3.66E-03 12 S6 -2.35E-03 -5.11E-02 2.10E-02 -2.37E-03 13 S7 1.23E+00 -1.73E-01 5.46E-02 -1.71E-02 14 S8 -1.26E+00 5.39E-02 2.99E-02 -2.45E-02 15 S9 2.71E-01 -5.59E-02 -1.75E-02 3.65E-02

[0182] Table 12

[0183] Figure 11a The on-axis chromatic aberration curve of the optical system of Embodiment 4 is shown, which represents the deviation of the focal point of light of different wavelengths after passing through the lens. Figure 11b The astigmatism curves of the optical system of Example 4 are shown, which represent the meridional image plane curvature and the sagittal image plane curvature. Figure 11c The distortion curves of the optical system in Example 4 are shown, representing the magnitude of distortion under different viewing angles. According to... Figures 11a to 11c As shown, the optical system given in Example 4 can achieve good imaging quality. Specific Implementation Example 5

[0185] Figure 12 This is a schematic diagram of the lens group structure of embodiment 5 of the optical system of the present invention. From the human eye side to the screen side, it includes, in sequence: a reflective polarizing element, a quarter-wave plate, a first lens, a second lens, and a third lens. The surface of the first lens near the human eye side is planar; the surface of the second lens near the human eye side is coated with a partial reflective layer. Light emitted from the screen undergoes at least two reflections from the screen side to the human eye side, entering the human eye in the order of numbers 16 to 0. Light from screen S10 (number 16) passes sequentially through the third lens, the second lens, the first lens, the quarter-wave plate, and the reflective polarizing element. A first reflection occurs at the reflective polarizing element S3 (number 9), followed by a reflection and sequential passing through the quarter-wave plate and the first lens. A second reflection occurs on the human eye side mirror S6 (number 6) of the second lens, which is coated with a partial reflective layer. This causes the light to be reflected again and sequentially pass through the first lens, the quarter-wave plate, and the reflective polarizing element, finally reaching the human eye side S0 (number 0).

[0186] The first optical lens E1 has positive refractive power. Its surface near the human eye is flat, and its surface near the screen is convex. Its surface near the human eye is spherical, and its surface near the screen is aspherical.

[0187] The second optical lens E2 has negative refractive power, and its surface near the human eye is concave, as is its surface near the screen; both of its surfaces are aspherical.

[0188] The third optical lens E3 has positive refractive power, and its surface near the human eye is convex, as is its surface near the screen; both of its surfaces are aspherical.

[0189] A partial reflective layer is coated on the side of the second lens E2 near the human eye, and the partial reflective layer has an average light reflectivity of 50%.

[0190] Table 13 shows the basic parameters of the optical system in Example 5, where the units for radius of curvature, thickness, and focal length are all millimeters (mm).

[0191]

[0192] Table 13

[0193] As shown in Table 14, in Example 5, the effective focal length of the first lens is f1 = 130.95 mm, the effective focal length of the second lens is f2 = 75.59 mm, and the effective focal length of the third lens is f3 = 70.57 mm. The semi-FOV (half of the maximum field of view) of the optical system is 53.0°.

[0194]

[0195] Table 14

[0196] The optical system in Example 5 satisfies:

[0197] f2 / (R3+R4)=2.64; where f2 is the effective focal length of the second lens, R3 is the radius of curvature of the surface of the second lens closest to the human eye, and R4 is the radius of curvature of the surface of the second lens closest to the screen.

[0198] R3 / R2+CT1 / T12=3.76; where R2 is the radius of curvature of the surface of the first lens near the screen, R3 is the radius of curvature of the surface of the second lens near the human eye, CT1 is the center thickness of the first lens on the optical axis, and T12 is the air gap between the first and second lenses on the optical axis.

[0199] f3 / (T23+CT3+dqwp)=5.17; where f3 is the effective focal length of the third lens, T23 is the air gap between the second and third lenses on the optical axis, CT3 is the center thickness of the third lens on the optical axis, and dqwp is the center thickness of the quarter-wave plate (QWP) on the optical axis.

[0200] CT3 / (CT2+drp+dqwp)=4.96; where CT2 is the center thickness of the second lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, drp is the center thickness of the reflective polarizing element (RP) on the optical axis, and dqwp is the center thickness of the quarter-wave plate (QWP) on the optical axis.

[0201] (CT2+CT3) / (f2+f3)=-2.77; where CT2 is the center thickness of the second lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, f2 is the effective focal length of the second lens, and f3 is the effective focal length of the third lens.

[0202] f1 / (TD*TAN(Semi-FOV))=3.97; where f1 is the effective focal length of the first lens, TD is the on-axis distance from the surface of the first lens near the human eye to the surface of the last lens near the screen, and Semi-FOV is half of the maximum field of view of the optical system.

[0203] CT3 / CT1+T12 / T23=3.83; where CT1 is the center thickness of the first lens on the optical axis, CT3 is the center thickness of the third lens on the optical axis, T12 is the air gap between the first and second lenses on the optical axis, and T23 is the air gap between the second and third lenses on the optical axis.

[0204] f1*N1=202.28; where f1 is the effective focal length of the first lens and N1 is the refractive index of the first lens.

[0205] |f2*N2|=126.24; where f2 is the effective focal length of the second lens and N2 is the refractive index of the second lens.

[0206] f1 / (Vrp+Vqwp)=1.15; where f1 is the effective focal length of the first lens, Vrp is the Abbe number of the reflective polarizing element (RP), and Vqwp is the Abbe number of the quarter-wave plate (QWP).

[0207] In Example 5, Table 15 shows the higher-order coefficients A4, A6, A8, and A6 that can be used for the aspherical mirrors numbered 5-7 and 11-15 in Example 5. 10 .

[0208] Serial Number Face number A4 A6 A8 A10 5 S5 -9.06E-02 1.27E-01 -3.01E-02 2.91E-03 6 S6 -3.11E-02 -4.44E-02 1.81E-02 -1.79E-03 7 S5 -9.06E-02 1.27E-01 -3.01E-02 2.91E-03 11 S5 -9.06E-02 1.27E-01 -3.01E-02 2.91E-03 12 S6 -3.11E-02 -4.44E-02 1.81E-02 -1.79E-03 13 S7 1.23E+00 -1.78E-01 5.72E-02 -1.59E-02 14 S8 -1.07E+00 1.87E-02 3.69E-02 -2.24E-02 15 S9 2.08E-01 -3.86E-02 -1.87E-02 3.50E-02

[0209] Table 15

[0210] Figure 13a The on-axis chromatic aberration curve of the optical system of Embodiment 5 is shown, which represents the deviation of the focal point of light of different wavelengths after passing through the lens. Figure 13b The astigmatism curves of the optical system of Example 5 are shown, which represent the meridional image plane curvature and the sagittal image plane curvature. Figure 13c The distortion curves of the optical system in Example 5 are shown, representing the magnitude of distortion under different viewing angles. According to... Figures 13a to 13c As shown, the optical system given in Example 5 can achieve good imaging quality.

[0211] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, improvements, or equivalent substitutions made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An optical system, characterized in that, The optical system has three lenses with optical power, and the optical system includes, from the human eye side to the screen side, the following: Reflective polarizing element, quarter-wave plate, first lens, second lens and third lens; The first lens has positive optical power, with a flat surface near the human eye and a convex surface near the screen. The second lens has negative optical power, with a concave surface near the human eye and a concave surface near the screen. The third lens has positive optical power, and the surface near the human eye is convex. The second lens has a partially reflective layer on the side closest to the human eye; the center thickness CT2 of the second lens on the optical axis, the center thickness CT3 of the third lens on the optical axis, the effective focal length f2 of the second lens and the effective focal length f3 of the third lens satisfy: -5.5≤(CT2+CT3) / (f2+f3)≤-2.65; The effective focal length f3 of the third lens, the air gap T23 between the second and third lenses on the optical axis, the center thickness CT3 of the third lens on the optical axis, and the center thickness dqwp of the quarter-wave plate on the optical axis satisfy: 5.09≤f3 / (T23+CT3+dqwp)≤5.

41.

2. The optical system according to claim 1, characterized in that, The effective focal length f2 of the second lens, the radius of curvature R3 of the surface of the second lens near the human eye, and the radius of curvature R4 of the surface of the second lens near the screen satisfy: 2.21≤f2 / (R3+R4)≤2.

65.

3. The optical system according to claim 1, characterized in that, The radius of curvature R2 of the surface of the first lens near the screen, the radius of curvature R3 of the surface of the second lens near the human eye, the center thickness CT1 of the first lens on the optical axis, and the air gap T12 between the first and second lenses on the optical axis satisfy: 3.76≤R3 / R2+CT1 / T12≤4.

07.

4. The optical system according to claim 1, characterized in that, The center thickness CT2 of the second lens on the optical axis, the center thickness CT3 of the third lens on the optical axis, the center thickness drp of the reflective polarizing element on the optical axis, and the center thickness dqwp of the quarter-wave plate on the optical axis satisfy: 4.69≤CT3 / (CT2+drp+dqwp)≤5.

03.

5. The optical system according to claim 1, characterized in that, The effective focal length f1 of the first lens, the on-axis distance TD from the surface of the first lens near the human eye to the surface of the last lens near the screen side, and half of the maximum field of view of the optical system, Semi-FOV, satisfy: 3.85≤f1 / (TD*TAN(Semi-FOV))≤4.

01.

6. The optical system according to claim 1, characterized in that, The center thickness CT1 of the first lens on the optical axis, the center thickness CT3 of the third lens on the optical axis, the air gap T12 between the first and second lenses on the optical axis, and the air gap T23 between the second and third lenses on the optical axis satisfy: 3.2≤CT3 / CT1+T12 / T23≤3.

83.

7. The optical system according to claim 1, characterized in that, The effective focal length f1 of the first lens, the refractive index N1 of the first lens, the effective focal length f2 of the second lens, and the refractive index N2 of the second lens satisfy: f1*N1>|f2*N2|.

8. The optical system according to claim 1, characterized in that, The reflective polarizing element, the quarter-wave plate, and the first lens are attached together.

9. The optical system according to claim 1, characterized in that, The reflective polarizing element has the same refractive index as the quarter-wave plate.

10. The optical system according to claim 1, characterized in that, The effective focal length f1 of the first lens, the Abbe number Vrp of the reflective polarizing element, and the Abbe number Vqwp of the quarter-wave plate satisfy the following condition: 1.13mm≤f1 / (Vrp+Vqwp)≤1.15mm.

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