Optical system

Abstract

The present application discloses an optical system, which comprises, in order from the first side to the second side along the optical axis direction: a first lens with positive optical power, whose second side surface is a convex surface; a reflective polarizing element; a quarter wave plate; a second lens with negative optical power, whose first side surface is a plane surface and whose second side surface is a concave surface; a third lens with positive optical power, whose first side surface is a convex surface and whose second side surface is a convex surface; and a partial reflecting element; the number of lenses with optical power in the optical system is three; the quarter wave plate is disposed on the first side surface of the second lens and is at least partially bonded to the first side surface of the second lens; the reflective polarizing element is disposed on the first side surface of the quarter wave plate and is at least partially bonded to the first side surface of the quarter wave plate; the second lens is glued to the third lens; the refractive index N2 of the second lens and the refractive index N3 of the third lens satisfy: N2>N3; the combined focal length f23 of the second lens and the third lens and the effective focal length f of the optical system satisfy: 8.1 <f23 / f<9.3。

Description

Technical Field

[0001] The present application relates to the field of optical elements, and in particular, to an optical system including a triplet lens. Background Art

[0002] In recent years, MR (Mixed Reality) technology has continued to develop, and MR devices have become more and more mature. MR technology integrates digital content into the real environment background through an optical imaging system, projects it into the human eye, and brings an immersive experience to users. As the receiving end of the MR device, the human eye is more sensitive to color than resolution. In order to restore the real world more realistically, MR devices have higher requirements for color and color uniformity.

[0003] MR devices usually use a reentrant system as an optical system solution. In the reentrant system, the lenses are generally made of low-refractive index materials due to stress requirements. However, the combination of low-refractive index lenses easily leads to poor chromatic aberration in the reentrant system, which limits the color level of the MR device. Utility Model Content

[0004] According to an embodiment of the present application, an optical system is provided, which includes, in order from the first side to the second side along the optical axis direction: a first lens with positive optical power, whose second side surface is convex; a reflective polarizing element; a quarter wave plate; a second lens with negative optical power, whose first side surface is flat and whose second side surface is concave; a third lens with positive optical power, whose first side surface is convex and whose second side surface is convex; and a partial reflective element; wherein the number of lenses with optical power in the optical system is three; the quarter wave plate is disposed on the first side surface of the second lens and at least partially adheres to the first side surface of the second lens; the reflective polarizing element is disposed on the first side surface of the quarter wave plate and at least partially adheres to the first side surface of the quarter wave plate; the second lens is glued to the third lens; the refractive index N2 of the second lens and the refractive index N3 of the third lens satisfy: N2>N3; and the combined focal length f23 of the second lens and the third lens and the effective focal length f of the optical system satisfy: 8.1 <f23 / f<9.3。

[0005] In some embodiments, the effective focal length f1 of the first lens and the effective focal length f of the optical system satisfy: 3.1 <f1 / f<3.5。

[0006] In some embodiments, the curvature radius R6 of the second side surface of the third lens and the curvature radius R2 of the second side surface of the first lens satisfy: 1.2 <R6 / R2<2.5。

[0007] In some embodiments, the center thickness CT3 of the third lens on the optical axis, the center thickness CTR of the reflective polarizing element on the optical axis, the center thickness CTQ of the quarter wave plate on the optical axis, and the center thickness CT2 of the second lens on the optical axis satisfy: 6.3 <CT3 / (CTR+CTQ+CT2)<7.8。

[0008] In some embodiments, the effective focal length f2 of the second lens and the effective focal length f3 of the third lens satisfy: -1.8 <f2 / f3<-1.5。

[0009] In some embodiments, the optical system further includes an aperture, which is disposed between the first side of the optical system and the first lens, and a distance TD from the first side surface of the first lens to the second side surface of the third lens on the optical axis and a distance SR from the aperture to the first side surface of the first lens on the optical axis satisfy: 1.2 <TD / SR<1.5。

[0010] In some embodiments, the combined focal length f23 of the second lens and the third lens, the dispersion coefficient V2 of the second lens, and the dispersion coefficient V3 of the third lens satisfy: 1.4 mm <f23 / (V2+V3)<1.9mm。

[0011] In some embodiments, the center thickness CT1 of the first lens on the optical axis and the entrance pupil diameter EPD of the optical system satisfy: 1.2 <CT1 / EPD<1.4。

[0012] In some embodiments, the on-axis distance SAG12 between the intersection of the second side surface of the first lens and the optical axis to the vertex of the effective radius of the second side surface of the first lens and the on-axis distance SAG32 between the intersection of the second side surface of the third lens and the optical axis to the vertex of the effective radius of the second side surface of the third lens satisfy: 1.3 <SAG12 / SAG32<1.6。

[0013] In some embodiments, the radius of curvature R6 of the second side surface of the third lens and the effective focal length f3 of the third lens satisfy: -1.2 <R6 / f3<-1.0。

[0014] In some embodiments, the effective focal length f2 of the second lens and the effective focal length f of the optical system satisfy: -6.1 <f2 / f<-5.8。

[0015] In some embodiments, the effective focal length f3 of the third lens and the center thickness CT3 of the third lens on the optical axis satisfy: 6.3 <f3 / CT3<9.5。

[0016] In some embodiments, the effective focal length f1 of the first lens and the center thickness CT1 of the first lens on the optical axis satisfy: 8.7 <f1 / CT1<10.3。

[0017] In some embodiments, the effective focal length f of the optical system and the sum of the center thicknesses ΣCT of the first lens, the second lens, and the third lens on the optical axis satisfy: 1.0 <f / ∑CT<1.4。

[0018] The optical system provided in the embodiment of the present application can be applied to MR equipment, which adopts a three-lens polarization return light path. By reasonably configuring the focal length, surface shape, center thickness on the optical axis, etc. of each lens of the optical system, the height of the main body can be better compressed and the compact design of the optical system can be achieved. By gluing the second lens and the third lens of the optical system, and the refractive index of the second lens is greater than that of the third lens, it is helpful to reduce the angle of the light emitted by the first lens, thereby reducing the aperture of the second lens and the third lens; at the same time, by using a combination of high and low refractive indices and a glued lens with positive and negative optical focal lengths, it is helpful to optimize the chromatic aberration of the return system itself and eliminate the influence on chromaticity, so that the display of the MR device is closer to the real world. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0020] Figure 1 A schematic structural diagram of an optical system according to Embodiment 1 of the present application is shown;

[0021] Figure 2A , Figure 2B and Figure 2C The axial chromatic aberration curve, the astigmatism curve and the distortion curve of the optical system according to Example 1 of the present application are respectively shown;

[0022] Figure 3 shows the MTF curve of the optical system according to Example 1 of the present application;

[0023] Figure 4 A schematic structural diagram of an optical system according to Embodiment 2 of the present application is shown;

[0024] Figure 5A , Figure 5B and Figure 5C The axial chromatic aberration curve, the astigmatism curve and the distortion curve of the optical system according to Example 2 of the present application are respectively shown;

[0025] Figure 6 shows the MTF curve of the optical system according to Example 2 of the present application;

[0026] Figure 7 A schematic structural diagram of an optical system according to Embodiment 2 of the present application is shown;

[0027] Fig. 8A , Figure 8B and Figure 8C The axial chromatic aberration curve, the astigmatism curve and the distortion curve of the optical system according to Example 3 of the present application are respectively shown;

[0028] Fig. 9 shows the MTF curve of the optical system according to Example 3 of the present application;

[0029] Fig.10 A schematic structural diagram of an optical system according to Embodiment 4 of the present application is shown;

[0030] Fig.11A , Fig. 11B and Fig. 11C axial chromatic aberration curve, astigmatism curve and distortion curve of the optical system according to Embodiment 4 of the present application are respectively shown; and

[0031] Fig.12 The MTF curve of the optical system according to Example 4 of the present application is shown. DETAILED DESCRIPTION

[0032] In order to better understand the present application, a more detailed description will be made of various aspects of the present application with reference to the accompanying drawings. It should be understood that these detailed descriptions are only 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.

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

[0034] In the drawings, the thickness, size and shape of the lenses have been slightly exaggerated for ease of explanation. Specifically, the shapes of the spherical or aspherical surfaces shown in the drawings are shown by way of example. That is, the shapes of the spherical or aspherical surfaces are not limited to the shapes of the spherical or aspherical surfaces shown in the drawings. The drawings are only examples and are not drawn strictly to scale.

[0035] In this article, the paraxial region refers to the region near the optical axis. If the lens surface is convex and the convex position 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 concave position is not defined, it means that the lens surface is concave at least in the paraxial region.

[0036] 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 exclude 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 listed 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.

[0037] Unless otherwise defined, all terms (including technical terms and scientific terms) used in this article have the same meaning as those commonly understood by ordinary technicians in the field to which this application belongs. It should also be understood that terms (such as terms defined in commonly used dictionaries) should be interpreted as having the same meaning as their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined in this article.

[0038] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The following embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for those of ordinary skill in the art, without departing from the concept of the present application, several deformations and improvements can also be made, which all belong to the protection scope of the present application. For example, the lens groups (i.e., the first lens to the fourth lens), the lens barrel structure and the spacing elements in the embodiments of the present application can be arbitrarily combined, and are not limited to the lens groups in one embodiment can only be combined with the lens barrel structure, the spacing elements, etc. of the embodiment.

[0039] The features, principles and other aspects of the present application are described in detail below.

[0040] refer to Figure 1 As shown, according to the first aspect of the present application, an optical system is provided, which may include: a first lens E1, a reflective polarizing element RP, a quarter wave plate QWP, a second lens E2, a third lens E3 and a partial reflective element BS arranged in sequence from the first side to the second side along the optical axis. Any adjacent lenses may have an air gap.

[0041] In an exemplary embodiment, the first side of the optical system may be, for example, the human eye side, and the second side may be, for example, the image plane side. Accordingly, each optical element (the first lens, the reflective polarizing element, the quarter wave plate, the second lens, the third lens, and the partial reflective element, etc.) has at least one first side surface relatively close to the human eye side, and at least one second side surface relatively close to the image plane side.

[0042] In example embodiments, the first lens E1 may have positive power, the second lens E2 may have negative power, and the third lens E3 may have positive power.

[0043] In exemplary embodiments, the first side surface of the first lens E1 may be a convex surface or a concave surface, and the second side surface may be a convex surface.

[0044] In an exemplary embodiment, the first side surface of the second lens E2 may be a plane surface, and the second side surface may be a concave surface. The quarter wave plate QWP may be disposed on the first side surface of the second lens E2 and at least partially adhered to the first side surface of the second lens E2; the reflective polarizing element RP may be disposed on the first side surface of the quarter wave plate QWP and at least partially adhered to the first side surface of the quarter wave plate QWP.

[0045] In an exemplary embodiment, the quarter wave plate QWP and the reflective polarizing element RP can be attached to the first side surface of the second lens E2 in sequence. The first side surface is a plane. On the one hand, due to the mature process of plane attachment, the orange peel after attachment is reduced, which is conducive to improving system performance; on the other hand, combined with a partial reflective element, the light is refracted between the two lenses, which is conducive to reducing the total length of the system, thereby facilitating the miniaturization of the whole machine. Exemplarily, the quarter wave plate QWP and the reflective polarizing element RP can also be combined together to achieve one-time attachment, thereby improving production efficiency; at the same time, the combination of the two can also avoid the angular deviation between the optical axis of the reflective polarizing element and the optical axis of the quarter wave plate caused by the attachment process, thereby improving the imaging quality.

[0046] In an exemplary embodiment, the first side surface of the third lens E3 may be a convex surface, and the second side surface may be a convex surface. The partial reflective element BS may be disposed on the second side surface of the third lens E3 and at least partially adhered to the second side surface of the third lens E3. The partial reflective element has a semi-transmissive and semi-reflective effect on light. By arranging the partial reflective element on the second side surface of the third lens E3, for example, and combining the arrangement of a reflective polarizing element and a quarter-wave plate, etc., the light can be refracted multiple times in the optical system, effectively reducing the main body length of the optical system.

[0047] In an exemplary embodiment, the second lens E2 and the third lens E3 form a cemented lens, which is beneficial to optimizing system chromatic aberration and improving color accuracy and clarity of imaging.

[0048] In an exemplary embodiment, the optical system may further include a stop STO, which may be disposed, for example, between the first side (the human eye side) of the optical system and the first lens.

[0049] In an exemplary embodiment, a display screen is provided on the second side of the optical system. The image light from the display screen can sequentially pass through the partially reflective element BS, the third lens E3, the second lens E2, and the quarter-wave plate QWP, reach the reflective polarizing element RP, and then be reflected at the reflective polarizing element RP to form the first reflected image light. The first reflected image light then sequentially passes through the quarter-wave plate QWP, the second lens E2, the third lens E3, and reaches the partially reflective element BS, and then is reflected at the partially reflective element BS to form the second reflected image light. The second reflected image light then sequentially passes through the third lens E3, the second lens E2, the quarter-wave plate QWP, the reflective polarizing element RP, and the first lens E1 to the stop STO and is finally projected onto the user's eye. In other examples, the order in which the image light, the first reflected image light, and the second reflected image light pass through each element can be adjusted as needed. The optical system provided by the embodiments of the present application folds the required optical path in a manner combining light reflection and refraction without affecting the projection quality, effectively shortening the body length of the optical system.

[0050] The optical system provided according to the embodiments of the present application can be applied to the head-mounted device of an MR device. Specifically, it can be used as the visual optical system of the head-mounted device. By folding the optical path, the body length of the lens can be compressed, thereby shifting the center of gravity of the head-mounted device backward and increasing the user experience.

[0051] In an exemplary embodiment, the optical system according to the present application may satisfy the following conditional expressions: N2 > N3; 8.1 < f23 / f < 9.3, where N2 is the refractive index of the second lens, N3 is the refractive index of the third lens, f23 is the combined focal length of the second lens and the third lens, and f is the effective focal length of the optical system. The optical system according to the present application is composed of three lenses, where the second lens is negative and the third lens is positive. By satisfying N2 > N3 and 8.1 < f23 / f < 9.3, the refractive index of the second lens is greater than that of the third lens, which is beneficial to reducing the angle of the light rays emitted from the first lens, thereby reducing the apertures of the second lens and the third lens; at the same time, by gluing the second lens made of a high-refractive-index and low-stress material and the third lens made of a low-refractive-index and low-stress material, and controlling the ratio of the combined focal length of the glued lenses to the effective focal length of the optical system within a reasonable range, it is beneficial to reducing the chromatic aberration of the system and thus improving the imaging quality.

[0052] In an exemplary embodiment, the optical system according to the present application may satisfy the following conditional formula: 3.1 < f1 / f < 3.5, where f1 is the effective focal length of the first lens and f is the effective focal length of the optical system. By satisfying this conditional formula, by controlling the ratio of the effective focal length of the first lens to the effective focal length of the optical system and making the effective focal length of the first lens positive, it is beneficial to reduce the angle of the light rays emitted by the first lens, thereby reducing the apertures of the latter two lenses.

[0053] In an exemplary embodiment, the optical system according to the present application may satisfy the following conditional formula: 1.2 < R6 / R2 < 2.5, where R6 is the radius of curvature of the second side surface of the third lens and R2 is the radius of curvature of the second side surface of the first lens. By satisfying this conditional formula, by controlling the ratio of the radius of curvature of the second side surface of the third lens to the radius of curvature of the second side surface of the first lens, and making both surfaces convex, where the second side surface of the first lens being convex makes the first lens have a positive optical power, and the second side surface of the third lens being convex is beneficial to suppressing the light height, thereby being beneficial to reducing the screen size.

[0054] In an exemplary embodiment, the optical system according to the present application may satisfy the following conditional formula: 6.3 < CT3 / (CTR + CTQ + CT2) < 7.8, where CT3 is the central thickness of the third lens on the optical axis, CTR is the central thickness of the reflective polarizing element on the optical axis, CTQ is the central thickness of the quarter-wave plate on the optical axis, and CT2 is the central thickness of the second lens on the optical axis. By satisfying this conditional formula, by controlling the ratio of the central thickness of the third lens to the sum of the central thicknesses of the film layer and the second lens, and making the thickness of the third lens much larger than the thickness of the second lens, combined with the third lens being a convex lens and the second lens being a concave lens, it is beneficial to the optical power distribution of the second lens and the third lens, and at the same time helps to optimize and balance the optical path, reduce the loss of light rays, and improve the efficiency of the optical system.

[0055] In an exemplary embodiment, the optical system according to the present application may satisfy the following conditional formula: -1.8 < f2 / f3 < -1.5, where f2 is the effective focal length of the second lens and f3 is the effective focal length of the third lens. By satisfying this conditional formula, by controlling the ratio of the effective focal lengths of the second lens and the third lens within a reasonable range and making the optical powers of the two lenses opposite, and then gluing the two lenses with opposite optical powers, it is beneficial to correcting the chromatic aberration of the system, making the image clearer and more real, and better reproducing the colors of the real world.

[0056] In an exemplary embodiment, the optical system according to the present application may satisfy the following conditional formula: 1.2 < TD / SR < 1.5, 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 third lens, and SR is the distance on the optical axis from the aperture stop to the first side surface of the first lens. By satisfying this conditional formula and reasonably 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 third lens to the distance on the optical axis from the aperture stop to the first side surface of the first lens, on the one hand, the mechanical overall length of the system is controlled, and on the other hand, the exit pupil distance of the system is restricted, making the system more in line with the human eye wearing scenario and requirements.

[0057] In an exemplary embodiment, the optical system according to the present application may satisfy the following conditional formula: 1.4 mm < f23 / (V2 + V3) < 1.9 mm, where f23 is the combined focal length of the second lens and the third lens, V2 is the dispersion coefficient of the second lens, and V3 is the dispersion coefficient of the third lens. By satisfying this conditional formula and controlling the ratio of the combined focal length of the second lens and the third lens to the sum of the dispersion coefficients of the second lens and the third lens, on the one hand, the combined focal length of the cemented lens is positive. Combining with the first lens having a positive optical power, it ensures that the focal length of the system is positive; on the other hand, the dispersion coefficient of one of the second lens and the third lens is small, ensuring the matching of the high and low refractive indices of the second lens and the third lens, which is beneficial to correcting the chromatic aberration of the system and improving the color accuracy and clarity of imaging.

[0058] In an exemplary embodiment, the optical system according to the present application may satisfy the following conditional formula: 1.2 < CT1 / EPD < 1.4, where CT1 is the central thickness of the first lens on the optical axis, and EPD is the entrance pupil diameter of the optical system. By satisfying this condition and reasonably controlling the ratio of the central thickness of the first lens to the entrance pupil diameter of the optical system, on the premise that the entrance pupil diameter conforms to the size of the human eye pupil, the central thickness of the first lens is relatively large, which is beneficial to increasing the optical power of the first lens, thereby optimizing the performance of the optical system, including improving the imaging quality and enhancing the light focusing ability, etc.

[0059] In an exemplary embodiment, the optical system according to the present application may satisfy the following conditional formula: 1.3 < SAG12 / SAG32 < 1.6, where SAG12 is the axial distance between the intersection point of the second side surface of the first lens and the optical axis and the vertex of the effective radius of the second side surface of the first lens, and SAG32 is the axial distance between the intersection point of the second side surface of the third lens and the optical axis and the vertex of the effective radius of the second side surface of the third lens. By satisfying this conditional formula and controlling the ratio of the sagittal height of the second side surface of the first lens to the sagittal height of the second side surface of the third lens, and making the sagittal height directions of these two surfaces consistent, both being convex surfaces, the optical powers of the first lens and the third lens of the optical system are made consistent, which is beneficial to controlling the optical power matching of the optical system and improving the optical performance of the system.

[0060] In an exemplary embodiment, the optical system according to the present application may satisfy the following conditional formula: -1.2 < R6 / f3 < -1.0, where R6 is the radius of curvature of the second side surface of the third lens, and f3 is the effective focal length of the third lens. By satisfying this conditional formula, by controlling the ratio of the radius of curvature of the second side surface of the third lens to the effective focal length of the third lens, and making the effective focal length of the third lens positive and the radius of curvature of its second side surface negative, it is beneficial to compress the height of the light rays emitted by the third lens, thereby facilitating the reduction of the screen size.

[0061] In an exemplary embodiment, the optical system according to the present application may satisfy the following conditional formula: -6.1 < f2 / f < -5.8, where f2 is the effective focal length of the second lens, and f is the effective focal length of the optical system. By satisfying this conditional formula, by controlling the ratio of the effective focal length of the second lens to the effective focal length of the optical system, making the second lens negative, combined with the second lens being made of a material with a low dispersion coefficient, and the positive optical power and high dispersion coefficient of the cemented lens, it is beneficial to improve the chromatic aberration of the system, improve the accuracy and authenticity of imaging; at the same time, the resolution of the optical system can be improved, making the image clearer and finer.

[0062] In an exemplary embodiment, the optical system according to the present application may satisfy the following conditional formula: 6.3 < f3 / CT3 < 9.5, where f3 is the effective focal length of the third lens, and CT3 is the central thickness of the third lens on the optical axis. By satisfying this conditional formula, by controlling the ratio of the effective focal length and the central thickness of the third lens, it is beneficial to control the lens shape of the third lens, thereby ensuring the processability of the third lens, and being beneficial to ensuring the stable performance of the optical system.

[0063] In an exemplary embodiment, the optical system according to the present application may satisfy the following conditional formula: 8.7 < f1 / CT1 < 10.3, where f1 is the effective focal length of the first lens, and CT1 is the central thickness of the first lens on the optical axis. By satisfying this conditional formula, by controlling the ratio of the effective focal length and the central thickness of the first lens, it is beneficial to control the lens shape of the first lens, thereby ensuring the processability of the first lens, and further being beneficial to ensuring the stable performance of the optical system.

[0064] In an exemplary embodiment, the optical system according to the present application may satisfy the following conditional formula: 1.0 < f / ∑CT < 1.4, where f is the effective focal length of the optical system, and ∑CT is the sum of the central thicknesses of the first lens, the second lens, and the third lens on the optical axis. By satisfying this conditional formula, by controlling the ratio of the effective focal length of the optical system to the sum of the central thicknesses of the three lenses, on the one hand, the overall shape of each lens is controlled, which is beneficial to the assembly and support between the lenses, and on the other hand, the total length of the system is controlled, which is beneficial to the miniaturization of the system.

[0065] According to a second aspect of the present application, an optical system is provided, which may include, in order from a first side to a second side along the optical axis: a first lens E1, a reflective polarizing element RP, a quarter-wave plate QWP, a second lens E2, a third lens E3, and a partial reflection element BS.

[0066] Wherein, the first lens E1 may have a positive optical power, its first side surface may be convex or concave, and its second side surface may be convex.

[0067] The second lens E2 may have a negative optical power, its first side surface may be planar, and its second side surface may be concave. The quarter-wave plate QWP may be disposed on the first side surface of the second lens and at least partially adhered to the first side surface of the second lens; the reflective polarizing element RP may be disposed on the first side surface of the quarter-wave plate QWP and at least partially adhered to the first side surface of the quarter-wave plate QWP.

[0068] The third lens E3 may have a positive optical power, its first side surface may be convex, and its second side surface may be convex. The partial reflection element BS may be disposed on the second side surface of the third lens and at least partially adhered to the second side surface of the third lens.

[0069] In an exemplary embodiment, the optical system may satisfy the following conditional formula: 1.2 < R6 / R2 < 2.5, where R6 is the radius of curvature of the second side surface of the third lens, and R2 is the radius of curvature of the second side surface of the first lens. By satisfying this conditional formula, by controlling the ratio of the radius of curvature of the second side surface of the third lens to the radius of curvature of the second side surface of the first lens, and making both surfaces convex, where the second side surface of the first lens is convex to make the first lens have a positive optical power, and the convex second side surface of the third lens is beneficial to reducing the ray height, thereby being beneficial to reducing the screen size.

[0070] According to a third aspect of the present application, an optical system is provided, which may include, in order from a first side to a second side along the optical axis: a first lens E1, a reflective polarizing element RP, a quarter-wave plate QWP, a second lens E2, a third lens E3, and a partial reflection element BS.

[0071] Wherein, the first lens E1 may have a positive optical power, its first side surface may be convex or concave, and its second side surface may be convex.

[0072] The second lens E2 may have a negative optical power, its first side surface may be planar, and its second side surface may be concave. The quarter-wave plate QWP may be disposed on the first side surface of the second lens and at least partially adhered to the first side surface of the second lens; the reflective polarizing element RP may be disposed on the first side surface of the quarter-wave plate QWP and at least partially adhered to the first side surface of the quarter-wave plate QWP.

[0073] The third lens E3 may have a positive optical power, its first side may be convex, and its second side may be convex. The partial reflection element BS may be disposed on the second side of the third lens E3 and at least partially attached to the second side of the third lens E3.

[0074] In an exemplary embodiment, the optical system further includes a diaphragm located between the first side and the first lens, and the optical system may satisfy the following conditional formula: 1.2 < TD / SR < 1.5, where TD is the distance on the optical axis from the first side of the first lens to the second side of the third lens, and SR is the distance on the optical axis from the diaphragm to the first side of the first lens. By satisfying this conditional formula, by reasonably controlling the ratio of the distance on the optical axis from the first side of the first lens to the second side of the third lens to the distance on the optical axis from the diaphragm to the first side of the first lens, on the one hand, the mechanical overall length of the system is controlled, and on the other hand, the exit pupil distance of the system is restricted, making the system more in line with the human eye wearing scenario and requirements.

[0075] According to the optical system of the above embodiment of the present application, a three-lens folding scheme can be adopted, and by adopting a polarization folding optical path method, the body height can be better compressed and the imaging quality can be improved; in addition, by reasonably distributing the focal lengths, surface types, central thicknesses of each lens, and the axial distances between each lens, etc., the incident light can be effectively converged, the optical overall length can be reduced, and the processability can be improved, making the optical system more conducive to production and processing.

[0076] In the embodiment of the present application, any one of the optical surfaces of the first side and the second side of the first lens E1, the second side of the second lens E2, and the first side and the second side of the third lens E3 of the optical system may be an aspherical surface. The aspherical lens has better curvature radius characteristics and has the advantages of improving distortion aberration and astigmatism aberration. By using an aspherical lens, the aberration that appears during imaging can be eliminated as much as possible, thereby improving the imaging quality.

[0077] Embodiments 1 to 4 of the optical system applicable to the above exemplary embodiments will be further described below with reference to the drawings and in conjunction with the embodiments.

[0078] Example 1

[0079] Figure 1 The structural schematic diagram of the optical system according to Embodiment 1 of the present application is shown.

[0080] As Figure 1As shown, the optical system includes: a first lens E1, a reflective polarizing element RP, a quarter wave plate QWP, a second lens E2, a third lens E3 and a partial reflective element BS arranged in sequence along the optical axis from the human eye side to the image plane (IMA) side. The optical system may also include a stop STO disposed between the human eye side and the first lens.

[0081] In this embodiment, the first lens E1 has positive focal power, and its first side surface is convex, and its second side surface is convex. The second lens E2 has negative focal power, and its first side surface is flat, and its second side surface is concave. A quarter wave plate QWP and a reflective polarizing element RP are attached to the first side surface of the second lens E2 in sequence. The third lens E3 has positive focal power, and its first side surface is convex, and its second side surface is convex. A partial reflective element BS is attached to the second side surface of the third lens E3.

[0082] In this embodiment, the second lens E2 and the third lens E3 form a cemented lens.

[0083] Table 1 shows the basic parameters of the optical system of Example 1, wherein the units of the radius of curvature and thickness / distance are all millimeters (mm). The image light from the display screen passes through the optical surfaces of each component in turn and is finally projected into the human eye.

[0084]

[0085] Table 1

[0086] In this embodiment, the first side surface S2 and the second side surface S3 of the first lens E1, the first side surface S13 (the second side surface of the second lens E2) and the second side surface S14 of the third lens E3 are all aspherical surfaces, and the surface shape x of each aspherical lens can be defined by but not limited to the following aspherical surface formula:

[0087]

[0088] Among them, x is the distance vector height from the vertex of the aspherical surface when the aspherical surface is at a height of h along the optical axis; c is the paraxial curvature of the aspherical surface, c = 1 / R (that is, the paraxial curvature c is the reciprocal of the curvature radius R in Table 1 above); k is the cone coefficient; Ai is the correction coefficient of the i-th order aspherical surface.

[0089] Table 2 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, A48, A49, A50, A51, A52, A53, A54, A55, A56, A57, A58, A59, A60, A61, A71, A72, A73, A74, A75 10 , A 12 and A 14 , A 16 , A 18 and A 20 .

[0090] Face number / coefficient S2 S3 S13 S14 A4 2.6196E-02 4.1093E-02 -9.6078E-01 -1.6671E-01 A6 3.0598E-01 4.8952E-01 2.7124E-02 -3.6931E-02 A8 -1.1282E-01 -1.9866E-02 6.1027E-02 1.4729E-02 A10 -6.7244E-03 -9.9151E-03 -2.1002E-02 -5.5077E-04 A12 -6.7491E-03 -2.6760E-03 9.3972E-03 -2.5022E-06 A14 7.1525E-04 -2.7755E-05 -4.1310E-04 9.2325E-05 A16 6.9767E-04 5.2418E-05 6.0997E-03 -1.0345E-05 A18 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 A20 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00

[0091] Table 2

[0092] Figure 2A The axial chromatic aberration curve of the optical system of Example 1 is shown, which indicates the deviation of the focusing point of light of different wavelengths after passing through the optical system. Figure 2B The astigmatism curve of the optical system of Example 1 is shown, which represents the meridional image plane curvature and sagittal image plane curvature corresponding to different field angles. Figure 2C The distortion curve of the optical system of Example 1 is shown, which indicates the distortion magnitude values ​​corresponding to different field angles. FIG. 2A to FIG. 2C It can be seen that the optical system provided in Example 1 can achieve good imaging quality.

[0093] Figure 3 The MTF curve of the optical imaging system of Example 1 is shown. Figure 3 It can be seen that the optical system of this embodiment has good contrast within a spatial frequency of 30lp / mm and clear imaging.

[0094] Example 2

[0095] Figure 4 The schematic diagram of the structure of the optical system according to Embodiment 2 of the present application is shown. In this embodiment and the following embodiments, for the sake of brevity, some descriptions similar to Embodiment 1 will be omitted.

[0096] like Figure 4 As shown, the optical system includes: a first lens E1, a reflective polarizing element RP, a quarter wave plate QWP, a second lens E2, a third lens E3 and a partial reflective element BS arranged in sequence along the optical axis from the human eye side to the image plane (IMA) side. The optical system may also include a stop STO disposed between the human eye side and the first lens.

[0097] In this embodiment, the first lens E1 has positive focal power, and its first side surface is convex, and its second side surface is convex. The second lens E2 has negative focal power, and its first side surface is flat, and its second side surface is concave. A quarter wave plate QWP and a reflective polarizing element RP are attached to the first side surface of the second lens E2 in sequence. The third lens E3 has positive focal power, and its first side surface is convex, and its second side surface is convex. A partial reflective element BS is attached to the second side surface of the third lens E3.

[0098] In this embodiment, the second lens E2 and the third lens E3 form a cemented lens.

[0099] Table 3 shows the basic parameters of the optical system of Example 2, wherein the units of the radius of curvature and thickness / distance are all millimeters (mm). The image light from the display screen passes through the optical surfaces of each component in turn and is finally projected into the human eye.

[0100]

[0101] Table 3

[0102] In this embodiment, the first side surface S2 and the second side surface S3 of the first lens E1, the first side surface S13 (the second side surface of the second lens E2) and the second side surface S14 of the third lens E3 are all aspherical surfaces, and the surface shape x of each aspherical lens can be defined by the aspherical surface formula (1) in the aforementioned embodiment 1.

[0103] 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, A 10 , A 12 and A 14 , A 16 , A 18 and A 20 .

[0104] Face number / coefficient S2 S3 S13 S14 A4 -3.1952E-01 -7.4290E-01 -1.0064E+00 -8.3707E-02 A6 4.7989E-01 5.4791E-01 3.0457E-02 -6.8130E-02 A8 -1.7092E-01 2.5985E-03 7.2081E-02 2.0976E-02 A10 -2.4158E-02 -1.2441E-02 -3.0005E-02 -2.2589E-04 A12 -1.2843E-02 -2.5467E-03 1.1567E-02 -3.8036E-04 A14 -3.3370E-03 8.2557E-04 4.9710E-03 2.7732E-04 A16 -7.5791E-04 -1.7958E-04 6.1259E-04 -1.8738E-04 A18 0.0000E+00 0.0000E+00 9.0461E-04 8.2222E-05 A20 0.0000E+00 0.0000E+00 3.7184E-03 -1.2679E-05

[0105] Table 4

[0106] Figure 5A The axial chromatic aberration curve of the optical system of Example 2 is shown, which indicates the deviation of the focusing point of light of different wavelengths after passing through the optical system. Figure 5B The astigmatism curve of the optical system of Example 2 is shown, which represents the meridional image plane curvature and sagittal image plane curvature corresponding to different field angles. Figure 5C The distortion curve of the optical system of Example 2 is shown, which indicates the distortion magnitude values ​​corresponding to different field angles. FIG. 5A to FIG. 5C It can be seen that the optical system provided in Example 1 can achieve good imaging quality.

[0107] Figure 6 The MTF curve of the optical imaging system of Example 2 is shown. Figure 6 It can be seen that the optical system of this embodiment has good contrast within a spatial frequency of 30lp / mm and clear imaging.

[0108] Example 3

[0109] Figure 7 A schematic structural diagram of an optical system according to Example 3 of the present application is shown.

[0110] like Figure 7As shown, the optical system includes: a first lens E1, a reflective polarizing element RP, a quarter wave plate QWP, a second lens E2, a third lens E3 and a partial reflective element BS arranged in sequence along the optical axis from the human eye side to the image plane (IMA) side. The optical system may also include a stop STO disposed between the human eye side and the first lens.

[0111] In this embodiment, the first lens E1 has positive focal power, and its first side surface is convex, and its second side surface is convex. The second lens E2 has negative focal power, and its first side surface is flat, and its second side surface is concave. A quarter wave plate QWP and a reflective polarizing element RP are attached to the first side surface of the second lens E2 in sequence. The third lens E3 has positive focal power, and its first side surface is convex, and its second side surface is convex. A partial reflective element BS is attached to the second side surface of the third lens E3.

[0112] In this embodiment, the second lens E2 and the third lens E3 form a cemented lens.

[0113] Table 5 shows the basic parameters of the optical system of Example 3, wherein the units of the radius of curvature and thickness / distance are all millimeters (mm). The image light from the display screen passes through the optical surfaces of each component in turn and is finally projected into the human eye.

[0114]

[0115]

[0116] Table 5

[0117] In this embodiment, the first side surface S2 and the second side surface S3 of the first lens E1, the first side surface S13 (the second side surface of the second lens E2) and the second side surface S14 of the third lens E3 are all aspherical surfaces, and the surface shape x of each aspherical lens can be defined by the aspherical surface formula (1) in the aforementioned embodiment 1.

[0118] Table 6 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, A 10 , A 12 and A 14 , A 16 , A 18 and A 20 .

[0119] Face number / coefficient S2 S3 S13 S14 A4 -8.1915E-01 -1.0756E+00 -8.0024E-01 1.6036E-01 A6 1.5823E-01 3.9436E-01 -3.0477E-02 -7.1601E-02 A8 -8.6182E-02 -4.3039E-02 1.1012E-01 1.7842E-02 A10 3.1000E-03 -5.5481E-03 2.3037E-03 -7.1358E-04 A12 -5.7006E-03 3.5684E-03 6.4839E-03 -1.0692E-03 A14 -1.2392E-04 -7.9105E-04 -1.3989E-02 4.6059E-04 A16 1.8249E-03 -3.2650E-04 -1.4402E-02 -2.7467E-04 A18 0.0000E+00 0.0000E+00 -8.9852E-03 2.6829E-05 A20 0.0000E+00 0.0000E+00 -1.6935E-03 5.3865E-05

[0120] Table 6

[0121] Fig. 8A The axial chromatic aberration curve of the optical system of Example 3 is shown, which indicates the deviation of the focusing point of light of different wavelengths after passing through the optical system. Figure 8B The astigmatism curve of the optical system of Example 3 is shown, which represents the meridional image plane curvature and sagittal image plane curvature corresponding to different field angles. Figure 8C The distortion curve of the optical system of Example 3 is shown, which indicates the distortion magnitude values ​​corresponding to different field angles. FIG. 8A to FIG. 8C It can be seen that the optical system provided in Example 3 can achieve good imaging quality.

[0122] Fig. 9 The MTF curve of the optical imaging system of Example 3 is shown. Fig. 9 It can be seen that the optical system of this embodiment has good contrast within a spatial frequency of 30lp / mm and clear imaging.

[0123] Example 4

[0124] Fig.10 A schematic structural diagram of an optical system according to Example 4 of the present application is shown.

[0125] like Fig.10 As shown, the optical system includes: a first lens E1, a reflective polarizing element RP, a quarter wave plate QWP, a second lens E2, a third lens E3 and a partial reflective element BS arranged in sequence along the optical axis from the human eye side to the image plane (IMA) side. The optical system may also include a stop STO disposed between the human eye side and the first lens.

[0126] In this embodiment, the first lens E1 has positive focal power, its first side surface is concave, and its second side surface is convex. The second lens E2 has negative focal power, its first side surface is flat, and its second side surface is concave. A quarter wave plate QWP and a reflective polarizing element RP are attached to the first side surface of the second lens E2 in sequence. The third lens E3 has positive focal power, its first side surface is convex, and its second side surface is convex. A partial reflective element BS is attached to the second side surface of the third lens E3.

[0127] In this embodiment, the second lens E2 and the third lens E3 form a cemented lens.

[0128] Table 7 shows the basic parameters of the optical system of Example 4, wherein the units of the radius of curvature and thickness / distance are all millimeters (mm). The image light from the display screen passes through the optical surfaces of each component in turn and is finally projected into the human eye.

[0129]

[0130] Table 7

[0131] In this embodiment, the first side surface S2 and the second side surface S3 of the first lens E1, the first side surface S13 (the second side surface of the second lens E2) and the second side surface S14 of the third lens E3 are all aspherical surfaces, and the surface shape x of each aspherical lens can be defined by the aspherical surface formula (1) in the aforementioned embodiment 1.

[0132] Table 8 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, A 10 , A 12 and A 14 , A 16 , A 18 and A 20 .

[0133] Face number / coefficient S2 S3 S13 S14 A4 2.1793E-01 -1.0746E-01 -6.5555E-01 -1.4919E-02 A6 6.8287E-02 4.1843E-01 5.5902E-02 -5.5518E-02 A8 -1.9616E-01 -5.4370E-02 1.3237E-01 2.1599E-02 A10 -9.8289E-03 -1.1669E-02 5.9879E-02 -3.4507E-03 A12 -1.0996E-02 2.8076E-03 5.9450E-02 6.8282E-05 A14 -2.4714E-03 4.7953E-04 2.8089E-02 1.5261E-04 A16 1.7062E-03 -2.9872E-04 9.6541E-03 -2.0108E-04 A18 0.0000E+00 0.0000E+00 4.0601E-03 1.0900E-05 A20 0.0000E+00 0.0000E+00 1.6881E-03 3.0677E-05

[0134] Table 8

[0135] Fig.11A The axial chromatic aberration curve of the optical system of Example 4 is shown, which indicates the deviation of the focusing point of light of different wavelengths after passing through the optical system. Fig. 11B The astigmatism curve of the optical system of Example 4 is shown, which represents the meridional image plane curvature and sagittal image plane curvature corresponding to different field angles. Fig. 11C The distortion curve of the optical system of Example 4 is shown, which indicates the distortion magnitude values ​​corresponding to different field angles. FIG. 11A to FIG. 11C It can be seen that the optical system provided in Example 4 can achieve good imaging quality.

[0136] Fig.12 The MTF curve of the optical imaging system of Example 4 is shown. Fig.12 It can be seen that the optical system of this embodiment has good contrast within a spatial frequency of 30lp / mm and clear imaging.

[0137] Table 9 shows the optical parameters of the optical systems of the above-mentioned embodiments 1 to 4, such as the effective focal length f of the optical system and the effective focal length of each lens, the entrance pupil diameter EPD of the optical system and other related parameters.

[0138] The unit of each optical parameter is millimeter (mm).

[0139] Parameters / Examples 1 2 3 4 f1(mm) 44.36 45.31 51.53 50.48 f2(mm) -82.67 -82.66 -91.09 -96.22 f3(mm) 49.83 49.59 53.69 59.83 f23(mm) 116.14 114.80 122.68 149.76 f(mm) 13.99 13.99 15.00 16.18 EPD(mm) 4.00 4.00 4.00 4.00 TD(mm) 14.00 14.00 13.86 12.48 SR(mm) 10.00 10.00 10.00 10.00 SAG12(mm) -3.51 -3.55 -3.55 -3.55 SAG32(mm) -2.53 -2.49 -2.36 -2.28 CTR(mm) 0.10 0.10 0.10 0.10 CTQ(mm) 0.10 0.10 0.10 0.10 ∑CT(mm) 13.60 13.60 13.46 12.08

[0140] Table 9 In summary, in Examples 1 to 4, the optical systems respectively satisfy the conditional expressions shown in the following Table 10.

[0141] Conditional / Example 1 2 3 4 f23 / f 8.30 8.20 8.18 9.25 f1 / f 3.17 3.24 3.44 3.12 R6 / R2 2.14 1.93 1.29 2.42 CT3 / (CTR+CTQ+CT2) 7.76 7.75 7.15 6.35 f2 / f3 -1.66 -1.67 -1.70 -1.61 TD / SR 1.40 1.40 1.39 1.25 f23 / (V2+V3)(mm) 1.46 1.45 1.55 1.89 CT1 / EPD 1.26 1.26 1.38 1.23 SAG12 / SAG32 1.38 1.43 1.50 1.56 R6 / f3 -1.05 -1.05 -1.04 -1.10 f2 / f -5.91 -5.91 -6.07 -5.95 f3 / CT3 6.42 6.40 7.51 9.43 f1 / CT1 8.80 8.97 9.36 10.23 f / ∑CT 1.03 1.03 1.11 1.34

[0142] Table 10

[0143] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the utility model involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the concept of the utility model. For example, the above features are replaced with the technical features with similar functions disclosed in the present application (but not limited to) by each other to form a technical solution.

Claims

1. An optical system, characterized in that: The optical axis includes, in order from the first side to the second side: A first lens having positive optical power, wherein the second side surface of the first lens is convex; Reflective polarizing element; quarter wave plate; a second lens having negative optical power, wherein the first side surface is a plane surface and the second side surface is a concave surface; a third lens element having positive optical power, wherein the first side surface is convex and the second side surface is convex; and Partially reflective element; wherein the number of lenses having optical power in the optical system is three; The quarter wave plate is disposed on the first side surface of the second lens and is at least partially attached to the first side surface of the second lens; the reflective polarizing element is disposed on the first side surface of the quarter wave plate and is at least partially attached to the first side surface of the quarter wave plate; The second lens is glued to the third lens; A refractive index N2 of the second lens and a refractive index N3 of the third lens satisfy: N2>N3; and The combined focal length f23 of the second lens and the third lens and the effective focal length f of the optical system satisfy: 8.1 <f23 / f<9.3。 2. The optical system according to claim 1, characterized in that The effective focal length f1 of the first lens and the effective focal length f of the optical system satisfy: 3.1 <f1 / f<3.5。 3. The optical system according to claim 1, characterized in that The curvature radius R6 of the second side surface of the third lens and the curvature radius R2 of the second side surface of the first lens satisfy: 1.2 <R6 / R2<2.5。 4. The optical system according to claim 1, characterized in that The center thickness CT3 of the third lens on the optical axis, the center thickness CTR of the reflective polarizing element on the optical axis, the center thickness CTQ of the quarter wave plate on the optical axis, and the center thickness CT2 of the second lens on the optical axis satisfy: 6.3 <CT3 / (CTR+CTQ+CT2)<7.8。 5. The optical system according to claim 1, characterized in that The effective focal length f2 of the second lens and the effective focal length f3 of the third lens satisfy: -1.8 <f2 / f3<-1.5。 6. The optical system according to claim 1, characterized in that The optical system further comprises an aperture, wherein the aperture is disposed between the first side of the optical system and the first lens. The distance TD from the first side surface of the first lens to the second side surface of the third lens on the optical axis and the distance SR from the aperture to the first side surface of the first lens on the optical axis satisfy: 1.2 <TD / SR<1.5。 7. The optical system according to claim 1, characterized in that The combined focal length f23 of the second lens and the third lens, the dispersion coefficient V2 of the second lens, and the dispersion coefficient V3 of the third lens satisfy: 1.4 mm <f23 / (V2+V3)<1.9mm。 8. The optical system according to claim 1, wherein: The center thickness CT1 of the first lens on the optical axis and the entrance pupil diameter EPD of the optical system satisfy: 1.2 <CT1 / EPD<1.4。 9. The optical system according to claim 1, characterized in that The on-axis distance SAG12 between the intersection of the second side surface of the first lens and the optical axis to the effective radius vertex of the second side surface of the first lens and the on-axis distance SAG32 between the intersection of the second side surface of the third lens and the optical axis to the effective radius vertex of the second side surface of the third lens satisfy: 1.3 <SAG12 / SAG32<1.6。 10. The optical system according to claim 1, characterized in that The curvature radius R6 of the second side surface of the third lens and the effective focal length f3 of the third lens satisfy: -1.2 <R6 / f3<-1.0。 11. The optical system according to any one of claims 1 to 10, characterized in that: The effective focal length f2 of the second lens and the effective focal length f of the optical system satisfy: -6.1 <f2 / f<-5.8。 12. The optical system according to any one of claims 1 to 10, characterized in that: The effective focal length f3 of the third lens and the center thickness CT3 of the third lens on the optical axis satisfy: 6.3 <f3 / CT3<9.5。 13. The optical system according to any one of claims 1 to 10, characterized in that: The effective focal length f1 of the first lens and the center thickness CT1 of the first lens on the optical axis satisfy: 8.7 <f1 / CT1<10.3。 14. The optical system according to any one of claims 1 to 10, characterized in that: The effective focal length f of the optical system and the sum of the center thicknesses ΣCT of the first lens, the second lens and the third lens on the optical axis satisfy: 1.0 <f / ∑CT<1.4。

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