Optical systems and head-mounted display devices

Abstract

Some embodiments of the present application disclose an optical system and a head-mounted display device. The optical system includes a third lens, a second lens, and a first lens installed sequentially along the propagation direction of incident light, wherein the effective focal length (f1) of the first lens and the effective focal length (f2) of the second lens are both greater than the effective focal length (f) of the optical system. The embodiments of the present application provide a single-focus, high-resolution direct-transmission optical structure design solution, thereby having excellent imaging quality.

Description

Technology Field

[0001] This application claims priority to a Chinese patent application filed with the Chinese Intellectual Property Office on November 30, 2021, with application number 202111446819.7 and title of invention 'Optical system and head-mounted display device', the entire contents of which are incorporated by reference into this application.

[0002] This application relates to the field of optical imaging technology, and more specifically to optical systems and head-mounted display devices. Background Technology

[0003] Recently, Augmented Reality (AR) and Virtual Reality (VR) technologies are being applied to smart wearable devices and are rapidly developing. The core components of both Augmented Reality and Virtual Reality technologies are display optical systems. The quality of the display effects of the display optical system directly determines the quality of the smart wearable device.

[0004] VR devices can be cited as an example of existing related technologies. Most conventional VR devices utilize display optical systems formed by combining a single lens and a display screen. However, due to optical path imaging requirements, the lens must be positioned far from the display screen, which increases the size of the VR device and hinders product miniaturization; furthermore, this can result in a poor user experience when worn. Additionally, there are currently solutions for VR devices that utilize a folded optical path. While this solution enables the miniaturization and lightweighting of VR devices, it suffers from high production costs, low light efficiency (<25%), and ghosting issues. The problem to be solved

[0005] The purpose of this application is to provide a new technical solution for optical systems and head-mounted display devices. means of solving the problem

[0006] According to one aspect of the present application, an optical system is provided. The optical system comprises a lens group consisting of a third lens, a second lens, and a first lens installed sequentially along the propagation direction of incident light, wherein the effective focal length (f1) of the first lens and the effective focal length (f2) of the second lens are both greater than the effective focal length (f) of the optical system, and the effective focal length (f1) of the first lens is set to 20mm ≤ f1 ≤ 40mm, the effective focal length (f2) of the second lens is set to 20mm ≤ f2 ≤ 40mm, and the effective focal length (f3) of the third lens is set to -100mm ≤ f3 ≤ -50mm, a gap (T1) is installed between the first lens and the second lens, and the gap (T1) is set to 0.1mm ≤ T1 ≤ 0.5mm, and a gap (Y) is installed between the second lens and the third lens, and the gap (Y) is set to 2mm ≤ Y ≤ 4.5mm, and the first lens, the second lens, and the third The lenses are located on the same optical axis.

[0007] Optionally, the refractive power of the first lens and the second lens are both positive, and the refractive power of the third lens is negative.

[0008] Optionally, the first lens and the second lens are installed by adhesion.

[0009] Optionally, the two bonded surfaces of the first lens and the second lens are both Fresnel surfaces.

[0010] Optionally, the sum of the effective focal length (f1) of the first lens and the effective focal length (f2) of the second lens is greater than the absolute value of the effective focal length (f3) of the third lens. delete

[0012] Optionally, the effective focal length (f) of the lens group satisfies 15mm ≤ f ≤ 25mm.

[0013] Optionally, a gap (T1) is provided between the first lens and the second lens, and the gap (T1) is set to 0.1 mm ≤ T1 ≤ 0.5 mm, and a gap (Y) is provided between the second lens and the third lens, and the gap (Y) is set to 2 mm ≤ Y ≤ 4.5 mm, and the first lens, the second lens, and the third lens are located on the same optical axis.

[0014] Optionally, the first lens and the second lens are both made of the same material, specifically COP material, and the third lens is made of OKP material or EP material.

[0015] According to another aspect of the present application, a head-mounted display device is provided.

[0016] The head-mounted display device described above includes any of the aforementioned optical systems. Effects of the invention

[0017] In the solution provided by the embodiment of the present application, by using multiple lenses and rationally configuring the effective focal lengths of the lenses, it is advantageous to realize optical requirements for a short focal length, high light efficiency, and high resolution for the overall optical path structure, thereby contributing to the improvement of imaging quality. The embodiment of the present application proposes a design solution for a short focal length, high resolution direct-transmission optical path structure, and the formed optical system can be applied to head-mounted display devices (e.g., VR devices), etc.

[0018] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application with reference to the accompanying drawings. Brief explanation of the drawing

[0019] In order to more clearly explain the technical solutions of the embodiments of the present application or the prior art, the attached drawings necessary for describing the embodiments or prior art are briefly introduced below. The drawings in the following description are merely a part of the drawings of the present application, and it is obvious that a person skilled in the art can obtain other drawings from the provided drawings without creative effort. FIG. 1 is a schematic diagram of the structure of an optical system according to an embodiment of the present application. FIG. 2 is a schematic diagram of the imaging principle of an optical system according to an embodiment of the present application. FIG. 3 to 5 are diagrams showing the relationship between the aperture x of the third lens and the gap Y between the third lens and the second lens in an optical system according to an embodiment of the present application. FIG. 6 is a spot diagram of an optical system according to Embodiment 1 of the present application. FIG. 7 is a diagram of the field curvature and distortion of an optical system according to Embodiment 1 of the present application. FIG. 8 is a diagram of the chromatic dispersion of an optical system according to Embodiment 1 of the present application. Specific details for implementing the invention

[0020] Hereinafter, technical solutions in the embodiments of the present application will be described with reference to the drawings of the embodiments of the present application; however, the above-described embodiments are merely some of the embodiments of the present application and are of all embodiments. All other embodiments obtained by a person skilled in the art without creative effort based on the embodiments of the present application fall within the scope of protection of the present application.

[0021] The following description of at least one exemplary embodiment is by nature merely illustrative and is by no means intended to limit its application or use.

[0022] Techniques, methods, and devices known to a person of ordinary skill in the relevant technical field may not be described in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification.

[0023] In all examples described and discussed herein, all specific values ​​are to be interpreted merely as exemplary and not as restrictive. Accordingly, other cases of exemplary embodiments may have different values.

[0024] It should be noted that similar symbols and characters indicate similar items in subsequent drawings, so once an item is defined in one drawing, no further discussion is necessary in subsequent drawings.

[0025] Hereinafter, an optical system and a head-mounted display device according to an embodiment of the present application will be described in detail with reference to FIGS. 1 to 8.

[0026] According to one aspect of an embodiment of the present application, an optical system is provided.

[0027] The above optical system is a short-focus, high-resolution direct-transmission optical system suitable for application in electronic devices such as head-mounted displays (HMDs), including VR devices (VR glasses or VR helmets, etc.). Therefore, it has good application prospects.

[0028] An optical system according to an embodiment of the present application includes a third lens (3), a second lens (2), and a first lens (1) installed sequentially along the propagation direction of incident light as shown in FIGS. 1 and 2, and the effective focal length (f1) of the first lens and the effective focal length (f2) of the second lens are both greater than the effective focal length (f) of the optical system.

[0029] The optical system according to the embodiment of the present application has a direct-transmission optical path structure, and since the optical path design is relatively simple, the fabrication of the entire optical system becomes relatively easy.

[0030] It is necessary to explain that the above optical system may also include, for example, a display screen (4).

[0031] The above display screen (4) can be used to emit a light beam, that is, the incident light described above, in a light path structure.

[0032] That is, in the optical system solution according to the embodiment of the present application, a lens group having, for example, three lenses is designed, and as shown in FIGS. 1 and 2, each of the lenses is positioned at the exit side of the display screen (4), specifically in the direction of propagation of the incident light emitted by the display screen (4), and can be used to project incident light onto a person's eye (5) to implement imaging.

[0033] As illustrated in FIGS. 1 and 2, the solution according to the embodiment of the present application uses multiple lenses (e.g., three lenses) and reasonably sets the effective focal length of the lenses, which is advantageous for realizing optical requirements of short focal length, high light efficiency, and high resolution of the entire optical path structure and helps to improve image quality.

[0034] The embodiments of the present application propose a design solution for a short-focus, high-resolution direct-transmission optical path structure, and the formed optical system can be applied, for example, to a head-mounted display device (VR device), and also help to achieve miniaturization and weight reduction of the head-mounted display device.

[0035] In summary, the solution according to the embodiment of the present application resolves the problems associated with conventional combination solutions of a monolithic lens and a display screen, where the lens is positioned relatively far from the display screen, resulting in a larger VR device size that is disadvantageous for product miniaturization and low light efficiency. At the same time, the drawbacks associated with using a folded optical path can also be improved, leading to relatively lower processing difficulty and production costs, and the direct-transmission optical structure is simpler than that of a folded optical path.

[0036] For example, as illustrated in FIGS. 1 and 2, the optical system is equipped with a display screen (4) of, for example, a 1.4-inch display to achieve a viewing angle of 100 degrees. Based on this, neither the conventional single-lens (1P) structure nor the double-lens (2P) structure is sufficient to resolve this type of display screen. The reasons are as follows.

[0037] A single-piece lens (1P) can only optimize the planar degrees of freedom of two surfaces, so the focusing function is limited, and it cannot correct aberrations or color differences, and the pixel size (i.e., imaging spot size) that can be seen in the entire field of view is about 80μm to 100μm, and more importantly, it cannot achieve the purpose of a single focal point.

[0038] The dual-piece lens (2P) can achieve a single focal point by increasing the degree of freedom when optimizing the surface shape of the lens, but there is still a limit to the resolution, so the pixel size (i.e., imaging spot size) that can be resolved in the entire field of view is about 60μm to 80μm.

[0039] The optical lens combination employed in the embodiment of the present application further improves resolution and can correct color difference to some extent, and forms a type of direct-transmission short-focus optical path structure.

[0040] In some examples of the present application, the refractive power of the first lens (1) and the second lens (2) is positive, and the refractive power of the third lens (3) is negative.

[0041] In an optical system according to an embodiment of the present application, it can be understood that the first lens (1) and the second lens (2) are both designed as positive lenses, and the third lens (3) is designed as a negative lens. The two positive lenses provide relatively large positive refractive power, and the negative lens can be used to eliminate color difference.

[0042] In some examples of the present application, the first lens and the second lens are installed by adhesion.

[0043] That is, in an embodiment of the present application, two positive lenses are installed by bonding them together, and a negative lens is designed to be separated from the two bonded positive lenses.

[0044] As illustrated in FIGS. 1 and 2, it can be understood that the first lens (1) and the second lens (2) located far from the display screen (4) in the optical path structure are installed so as to be bonded together to help reduce stray light, and the third lens (3) located close to the display screen (4) is arranged independently and has a separate structure from the two lenses bonded together to help improve imaging quality.

[0045] In addition, the design of bonding the first lens (1) and the second lens (2) can reduce the difficulty of assembling structural members and reduce the risk of impurities occurring between the lenses due to assembly, thereby increasing the yield rate.

[0046] In some examples of the present application, as shown in FIGS. 1 and 2, the two surfaces to which the first lens (1) and the second lens (2) are bonded are both Fresnel surfaces.

[0047] That is, the optical system is designed with two adjacent Fresnel planes, and the two Fresnel planes are bonded together. This design enables low chromatic dispersion and short focal length of the optical path structure and reduces stray light, thereby allowing the formed optical system to have high optical efficiency and enable high-quality imaging.

[0048] In some examples of the present application, as shown in FIG. 1, the first lens (1) includes a first surface (11) and a second surface (12), and the second lens (2) includes a third surface (11) and a fourth surface (22). In the overall optical path structure, the second surface (12) and the third surface (11) are arranged adjacent to each other and are both arranged as Fresnel surfaces, and the first surface (11) and the fourth surface (22) are both aspherical (also, both of these surfaces are convex).

[0049] The first surface (11) of the first lens (1) is located outside and directly facing the human eye (5), and the second surface (12) of the first lens (1) and the third surface (21) of the second lens are installed adjacently. In the present application, the first surface (11) of the first lens (1) is installed as an aspherical surface (e.g., a convex surface), and the second surface (12) of the first lens (1) is installed as a Fresnel surface, so that the first lens (1) (positive lens) forms a combination of two surface shapes: an aspherical surface and a Fresnel surface.

[0050] Optionally, in an embodiment of the present application, an anti-reflective coating (AR) is coated on the first surface (11) and the second surface (12) of the first lens (1), respectively.

[0051] After coating each of the two sides of the first lens (1) with an anti-reflection film, the reflected light can be reduced by the anti-reflection film, thereby increasing the light transmittance on both sides of the first lens (1).

[0052] Optionally, in addition to the anti-reflective film, a hardened film may also be coated on the first surface (11) of the first lens (1).

[0053] The reason is that the first surface (11) of the first lens (1) faces outward and needs to be protected from damage caused by scratches, collisions, etc., so the lifespan of the first lens (2) can be improved by coating a hardened film. By coating a hardened film on the first surface (11), that is, by applying a hardening treatment to the first surface (11), the hardness, strength, etc., of the first surface (11) can be improved. This is useful for extending the lifespan of the entire optical system.

[0054] Of course, the embodiments of the present application are not limited to coating a hardened film on the first surface (11) of the first lens (2), and a hardened film may also be coated on the second surface (12) of the first lens (1), and those skilled in the art may flexibly adjust according to specific requirements, which is not specifically limited in the present application.

[0055] In addition, in an embodiment of the present application, the first lens (1) also has the following parameters.

[0056] For example, the absolute value of the radius (R1) of the first surface (11) of the first lens (1) satisfies 35mm ≤ R1 ≤ 65mm, the absolute value of the radius (R2) of the second surface (11) of the first lens (1) satisfies 20mm ≤ R2 ≤ 40mm, and the absolute value of the conic coefficient (K1) of the first surface (11) and the second surface (12) of the first lens (1) satisfies K1 ≤ 20.

[0057] The surface design of the first surface (11) and the second surface (12) is different.

[0058] Specifically, the first surface (11) facing outward is designed as an aspherical surface (e.g., a convex surface), and the second surface (22) is designed as a Fresnel surface; by applying the first lens (1), formed by a combination of the Fresnel surface and the aspherical surface, to the optical path structure, the effects of a short focal length and high resolution can be obtained.

[0059] In an embodiment of the present application, after optimizing the surface shape of the first lens (1), considering the difficulty and cost of processing, the value of the conic constant, i.e., K1, of the first lens (1) is set to, for example, [-10, 10], and it is more preferable that the radius of the Fresnel surface of the first lens (1) is R>23mm.

[0060] In some examples of the present application, the planar combination of the second lens (2) and the first lens (1) may be the same, and as shown in FIGS. 1 and 2, the second lens (2) includes a third surface (21) and a fourth surface (22), the third surface (21) is a Fresnel surface, and the fourth surface (22) is installed as an aspherical surface (e.g., a convex surface).

[0061] Optionally, an anti-reflective coating is also applied to the third surface (21) and the fourth surface (22).

[0062] Among them, reflected light is reduced by the anti-reflection film, and the transmittance of light is increased on both sides of the second lens (2).

[0063] In addition, in an embodiment of the present application, the second lens (2) has the following parameters.

[0064] In some examples of the present application, the absolute value of the radius (R3) of the third surface (31) of the second lens (3) satisfies 20mm ≤ R3 ≤ 40mm, the absolute value of the radius (R4) of the fourth surface (32) of the second lens (3) satisfies 35mm ≤ R4 ≤ 80mm, and the absolute value of the conic coefficient (K2) of the third surface (21) and the fourth surface (22) of the second lens (3) satisfies K2 ≤ 20.

[0065] In the embodiment of the present application, after optimizing the surface shape of the second lens (2), it is more preferable to set the conic coefficient, i.e., K2 value of the second lens (2) to [-10, 10], taking into account the difficulty and cost of processing, and the radius of the Fresnel surface of the second lens (2) is greater than 23 mm. This is basically the same as the first lens (1).

[0066] It is necessary to explain that both the first lens (1) and the second lens (2) have Fresnel surfaces. Considering the processing of the lens surface shape, it is necessary to set the surface shape parameters within a certain range. Otherwise, there is a risk that the processing accuracy will be lowered or the blade will break (this is because processing the sawtooth shape is difficult, and the smaller the acute angle of the sawtooth shape, the more difficult the processing angle and operation become). Therefore, it is more desirable to set the conic coefficient (K) value to the range [-10, 10], and the R value of the Fresnel surface of each lens is 23mm or more.

[0067] In the solution of the embodiment of the present application, for the first lens (2) and the second lens (3), that is, two positive lenses, a combination of "aspherical (e.g., convex) + Fresnel surface" is used for both, and based on the selection and combination of materials with different refractive indices and Abbe numbers, low chromatic dispersion and short focal length of the optical path structure are realized.

[0068] In some examples of the present application, as shown in FIG. 1, the third lens (3) includes a fifth surface (31) and a sixth surface (32), the fifth surface (31) is installed adjacent to the fourth surface (22) of the second lens (2), and at least one of the fifth surface (31) and the sixth surface (32) is installed as an aspherical surface.

[0069] For example, the refractive power of the third lens (3) is negative.

[0070] That is, in the solution of the present application, the third lens (3) is designed as a negative lens, and as a lens that is thin in the center and thick at the periphery, it has the ability to emit light. The third lens (3) can be used for color difference removal in the entire light path structure.

[0071] The third lens (3) may be, for example, a double-sided concave lens (i.e., both sides are concave) or a flat concave lens (i.e., one side is concave and the other side is flat).

[0072] More preferably, the fifth surface (31) is installed as a flat surface, and the sixth surface (32) is installed as a concave surface. That is, in the entire optical path structure, the surface adjacent to the fourth surface (22) is flat, and the surface adjacent to the display screen (4) is concave.

[0073] Optionally, an anti-reflective coating (AR) is applied to both the fifth surface (31) and the sixth surface (32).

[0074] After each of the two surfaces of the third lens (3) is coated with an anti-reflective film, the reflected light can be reduced by the anti-reflective film, thereby increasing the light transmittance on both sides of the third lens (3).

[0075] In a specific example of the present application, as illustrated in FIG. 1, the optical system comprises a display screen (4), a first lens (1), a second lens (2), and a third lens (3). The display screen (4) can be used as a display light source. Both the first lens (1) and the second lens (2) are positive lenses of an "aspherical + Fresnel" surface, and the third lens (4) located on the side closer to the display screen (4) is installed as a negative lens. Each surface of the three lenses is treated with an anti-reflective coating, and the first surface (11) of the first lens (1) is treated with a "cured film + anti-reflective film." Based on this, it becomes as illustrated in FIG. 2.

[0076] Incident light emitted from the display screen (4) passes through the sixth surface (32) of the third lens (3), which is coated with an anti-reflective film, and enters the interior of the third lens (3). The propagating light passing through the third lens (3) undergoes diffusion and then enters the second lens (2). Since both sides of the second lens (2) are also coated with an anti-reflective film, the light is focused after passing through the second lens (2) and enters the first lens (1). Since the first lens (1) is still a focusing positive lens, the light passing through the first lens (1) is transmitted and enters the human eye (5) to perform imaging. There is no optical path folding in the entire optical system, and since the surface of each lens is coated with an anti-reflective film, the light propagation efficiency is high.

[0077] In some examples of the present application, the edge regions of the first lens (1) and the second lens (2) are installed by bonding.

[0078] That is, the first lens (1) and the second lens (2) are bonded only at the edges using a frame adhesive method.

[0079] For example, the edge regions of the first lens (1) and the second lens (2) are bonded and connected by a light-transmitting optical adhesive. Here, the refractive index of the optical adhesive is lower than the refractive index of each lens, for example, the refractive index is 1.1 to 1.3.

[0080] In the above manner, the first lens (1) and the second lens (2) can be combined with an adhesive system. Meanwhile, the adhesive system can reduce the effect of stray light caused by the serration of the Fresnel surface. After bonding, the two positive lenses are assembled into an optical element within the optical path structure, thereby reducing the difficulty of assembly. In addition, the first lens (1) and the second lens (2) are bonded in the edge area by dispensing adhesive, thereby reducing the risk of impurities occurring between the two lenses due to assembly and improving the yield rate.

[0081] In some examples of the present application, as shown in FIGS. 1 and 2, a gap (T1) is provided between the first lens (1) and the second lens (2), and the gap (T1) is set to 0.1 mm ≤ T1 ≤ 0.5 mm, and a gap (Y) is provided between the second lens (2) and the third lens (3), and the gap (Y) is set to 2 mm ≤ Y ≤ 4.5 mm, and the first lens (1), the second lens (2), and the third lens (3) are located on the same optical axis.

[0082] Since the first lens (1) and the second lens (2) are installed by adhesion, the gap between them is very small.

[0083] A gap (Y) is set between the second lens (2) and the third lens (3), and the following relationship is satisfied between the gap (Y) and the aperture (x) of the third lens (3). Y=ax+b; among them, -0.8≤a≤-0.39, 30≤b≤35

[0084] That is, in the solution provided in the embodiment of the present application, there is a constant gap (Y) between the second lens (2) and the third lens (3), and a kind of linear negative correlation is formed between the value of this gap (Y) and the value of the aperture (x) of the third lens (3).

[0085] In the overall optical path structure, when the second lens (2) does not move, the size of the light passage aperture of the third lens (3) can be changed by adjusting the distance of the third lens (3) to the second lens (2). For example, the relationship between the gap value (Y) and the aperture value (x) satisfies Y=ax+b, where -0.8≤a≤-0.39 and 30≤b≤35.

[0086] It can be seen that as the third lens (3) approaches the second lens (2), the aperture (x) of the third lens (3) increases. In other words, it can be understood that the smaller the value of the gap (Y) between the two, the larger the aperture (x) of the third lens (3).

[0087] In addition, when a display screen (4) is installed in the optical system, after reasonably arranging the spacing of each lens, it is also necessary to consider the size of the gap between the third lens (3) and the display screen (4).

[0088] For example, a third gap (T2) is set between the third lens (3) and the display screen (4).

[0089] Optionally, the third interval (T3) is set to 8mm ≤ T2 ≤ 15mm.

[0090] In some examples of the present application, the first lens (1) and the second lens (2) are made of the same material, both being COP material, and the third lens (3) is OKP material or EP material.

[0091] Since COP, OKP, and EP materials are all light-transmitting resin materials, manufacturing lenses using these materials can reduce the weight of the lens group and achieve lightweighting.

[0092] In terms of material selection, each lens is optimally designed by combining materials with high refractive indices and high or low Abbe numbers, taking into account single focal length and chromatic aberration.

[0093] In addition, the materials of the first lens (1), the second lens (2), and the third lens (3) can be reasonably selected by a person skilled in the art according to actual needs and are not limited to the materials described above.

[0094] In some examples of the present application, the center thickness value (h1) of the first lens (1) is 2mm ≤ h1 ≤ 4mm, the center thickness value (h2) of the second lens (2) is 3mm ≤ h2 ≤ 5mm, and the center thickness value (h3) of the third lens (3) is 2mm ≤ h3 ≤ 4mm.

[0095] Since the thickness of each lens cannot be excessive, it is also advantageous for reducing the weight of the entire optical path structure.

[0096] In some examples of the present application, the sum of the effective focal length (f1) of the first lens (1) and the effective focal length (f2) of the second lens (2) is greater than the absolute value of the effective focal length (f3) of the third lens (3).

[0097] Optionally, the effective focal length (f1) of the first lens is set to 20mm ≤ f1 ≤ 40mm, the effective focal length (f2) of the second lens is set to 20mm ≤ f2 ≤ 40mm, and the effective focal length (f3) of the third lens is set to -100mm ≤ f3 ≤ -50mm.

[0098] In some examples of the present application, the effective focal length (f) of the optical system satisfies 15mm ≤ f ≤ 25mm.

[0099] The present application provides a single-focus optical system. It is a direct-transmission optical system capable of high-quality imaging and free from optical path folding in the entire optical system.

[0100] The following is an example of the application of the solution provided in the embodiment of the present application. (1) A 90-degree viewing angle was achieved by matching the 1.4-inch display screen (4). (2) The distortion is less than 34.6%, and the curvature of the upper surface is less than 0.5mm. (3) The color difference is less than 178 µm. The virtual image distance is 1500 mm. (4) The spot size of 0~1.0F is smaller than 2 display pixels and enables clear imaging in the visible light band (450nm~630nm). (5) The effective focal length (f) of the optical system is 19.13 mm, the total track length (TTL) is 23.31 mm, and the aperture (x) of the third lens (3) is 33.2 mm. Example 1

[0101] Example 1 provides an optical system that employs the structural parameters of the optical system according to Table 1. Table 1 lists the optical surface numbers (Surface) sequentially numbered from the human eye (5) (aperture) to the display screen (4), the curvature (C) of each optical surface on the optical axis, the distance (T) between each optical surface on the optical axis from the human eye (5) (aperture) to the display screen (4) and the next optical surface, and the even-order aspherical coefficients α2, α3, and α4, respectively.

[0102] Here, the aspherical coefficient can satisfy the following equation. (1) In Equation (1), z is a coordinate along the optical axis direction, Y is a radial coordinate in units of lens length, C is the curvature (1 / R), K is the conic coefficient, and α iis the coefficient of each higher-order term, and 2i is the order of the aspherical high-order term. In the solution design of the present application, the smoothness of the surface curvature is considered, and the spherical coefficient of the higher-order term reaches up to the 6th order.

[0103] The quality of the optical system performance of Example 1 of the present application is reflected by the following parameters.

[0104] As shown in Fig. 6, the spot size is maximum at a maximum field of view of 1.0F, and the maximum value is smaller than 44μm.

[0105] As shown in Fig. 7, the RGB wavelengths of the T&S direction surface curvature are all smaller than 0.5 mm, and the maximum distortion at the maximum field of view is smaller than 34.5%.

[0106] As shown in Fig. 8, the maximum RGB chromatic dispersion is the maximum position of the field of view, the total RGB is 460nm to 610nm, and the LCA is 178nm.

[0107] In the optical system provided by the embodiment of the present application, the relationship between the aperture value (x) of the third lens (3) and the gap value (Y) between the third lens (3) and the second lens (2) is as follows.

[0108] The closer the third lens (3) is to the second lens (2), the larger the aperture value (x) of the third lens (3) becomes, and a kind of linear negative correlation appears between the two.

[0109] As illustrated in FIGS. 3 to 5, three embodiments will be explained below. Example 2

[0110] In the above optical system, the refractive power of the first lens (1) and the second lens (2) are both set to positive, and the surface parameter is as follows. The first lens (1) has a radius of R1=45mm on the first surface (11) (convex surface) and a radius of R2=25mm on the second surface (12) (Fresnel surface). The second lens (2) has a radius of R3=25mm on the third surface (21) (Fresnel surface) and a radius of R4=45mm on the fourth surface (22) (convex surface). The refractive power of the third lens (3) is negative, and it is positioned close to the display screen (4). When the gap value (Y) between the second lens (2) and the third lens (3) is set to 2mm, the corresponding aperture value (x) of the third lens (3) is 31.14mm. When the gap value (Y) between the second lens (2) and the third lens (3) is set to 3mm, the corresponding aperture value (x) of the third lens (3) is 30.1mm. When the gap value (Y) between the second lens (2) and the third lens (3) is set to 3.5 mm, the corresponding aperture value (x) of the third lens (3) is 29.7 mm. When the gap value (Y) between the second lens (2) and the third lens (3) is set to 4mm, the corresponding aperture value (x) of the third lens (3) is 29.4mm. When the gap value (Y) between the second lens (2) and the third lens (3) is set to 4.5 mm, the corresponding aperture value (x) of the third lens (3) is 29.2 mm.

[0111] According to the relationship between the gap value (Y) between the second lens (2) and the third lens (3) listed above and the aperture value (x) of the third lens (3), as shown in FIG. 3, it can be confirmed that the two have a linear negative correlation Y=-0.7854x+32.578. Example 3

[0112] In the above optical system, the refractive power of the first lens (1) and the second lens (2) are both set to positive, and the surface parameter is as follows. The first lens (1) has a radius of R1=35mm on the first surface (11) (convex surface) and a radius of R2=25~29mm on the second surface (12) (Fresnel surface). The second lens (2) has a radius of R3 = 25 to 29 mm on the third surface (21) (Fresnel surface) and a radius of R4 = 35 mm on the fourth surface (22) (convex surface). The effective focal length (f1) of the first lens (1) The effective focal length (f2) of the second lens (2) is 29 mm, and the refractive power of the third lens (3) is negative, and it is installed close to the display screen (4). When the gap value (Y) between the second lens (2) and the third lens (3) is set to 2mm, the corresponding aperture value (x) of the third lens (3) is 30.06mm. When the gap value (Y) between the second lens (2) and the third lens (3) is set to 3mm, the corresponding aperture value (x) of the third lens (3) is 29.3mm. When the gap value (Y) between the second lens (2) and the third lens (3) is set to 3.5 mm, the corresponding aperture value (x) of the third lens (3) is 29.2 mm. When the gap value (Y) between the second lens (2) and the third lens (3) is set to 4mm, the corresponding aperture value (x) of the third lens (3) is 29.07mm. When the gap value (Y) between the second lens (2) and the third lens (3) is set to 4.5 mm, the corresponding aperture value (x) of the third lens (3) is 28.6 mm.

[0113] According to the relationship between the gap value (Y) between the second lens (2) and the third lens (3) listed above and the aperture value (x) of the third lens (3), as shown in FIG. 4, it can be confirmed that the two have a linear negative correlation Y=-0.5357x+31.078. Example 4

[0114] In the above optical system, the refractive power of the first lens (1) and the second lens (2) are both set to positive, and the surface parameter is as follows. The first lens (1) has a radius of R1=50mm on the first surface (11) (convex surface) and a radius of R2=25mm on the second surface (12) (Fresnel surface). The second lens (2) has a radius of R3=25mm on the third surface (21) (Fresnel surface) and a radius of R4=50mm on the fourth surface (22) (convex surface). The effective focal length (f1) of the first lens (1) The effective focal length (f2) of the second lens (2) is 29 mm, and the refractive power of the third lens (3) is negative, and it is installed close to the display screen (4). When the gap value (Y) between the second lens (2) and the third lens (3) is set to 2mm, the corresponding aperture value (x) of the third lens (3) is 30.1mm. When the gap value (Y) between the second lens (2) and the third lens (3) is set to 3mm, the corresponding aperture value (x) of the third lens (3) is 29.7mm. When the gap value (Y) between the second lens (2) and the third lens (3) is set to 3.5 mm, the corresponding aperture value (x) of the third lens (3) is 29.5 mm. When the gap value (Y) between the second lens (2) and the third lens (3) is set to 4mm, the corresponding aperture value (x) of the third lens (3) is 29.38mm. When the gap value (Y) between the second lens (2) and the third lens (3) is set to 4.5 mm, the corresponding aperture value (x) of the third lens (3) is 29.08 mm.

[0115] According to the relationship between the gap value (Y) between the second lens (2) and the third lens (3) listed above and the aperture value (x) of the third lens (3), as shown in FIG. 5, it can be confirmed that the two have a linear negative correlation Y=-0.393x+30.888.

[0116] From the aforementioned Examples 2 to 4, it can be seen that the gap size (Y) between the third lens (3) and the second lens (2) has a linear negative correlation with the aperture value (x) of the third lens (3). However, the linear coefficients obtained with different lens surface parameters are slightly different. For example, Y=ax+b; among them -0.8≤a≤-0.39, 30≤b≤35, Y is the distance (T) between the second lens (2) and the third lens (3), and x is the aperture value of the third lens (3).

[0117] An embodiment of the present application provides a single-focus direct-transmission optical system that does not include a folded optical path. (1) A combination of several optical lenses (e.g., three lenses) including two bonded positive lenses and a separate negative lens can be effectively implemented. (2) The Fresnel surfaces of the two positive lenses can be treated with adhesive to reduce stray light, and at the same time, the assembly of the two positive lenses in the light path structure is aided, making the assembly process simpler. (3) The parameters of the negative lens close to the display screen (4) are specially designed to help improve the imaging quality.

[0118] According to another aspect of the present application, a head-mounted display device is provided.

[0119] The head-mounted display device described above includes any of the aforementioned optical systems.

[0120] The head-mounted display device mentioned above is, for example, a VR device.

[0121] The embodiments described above have focused on explaining the differences between various embodiments, and better embodiments can be formed by combining the different optimization features among the various embodiments, provided that the different optimization features among them are not contradictory. For the sake of brevity, repetitive descriptions are not provided herein.

[0122] Although some specific embodiments of this application have been described in detail by way of example, those skilled in the art should understand that said embodiments are for illustrative purposes only and are not intended to limit the scope of this application. Those skilled in the art will understand that modifications to said embodiments may be made without departing from the scope and spirit of this application. The scope of the application is limited by the appended claims. Explanation of the symbols 1. First lens; 2. Second lens; 3. Third lens; 4. Display screen; 5. Human eye; 11. First surface; 12. Second surface; 21. Third surface; 22. Fourth surface; 31. Fifth surface; 31. Sixth surface.

Claims

Claim 1 An optical system comprises a third lens (3), a second lens (2), and a first lens (1) installed sequentially along the propagation direction of incident light, wherein the effective focal length (f1) of the first lens (1) and the effective focal length (f2) of the second lens (2) are both greater than the effective focal length (f) of the optical system, the effective focal length (f1) of the first lens (1) is installed such that 20mm ≤ f1 ≤ 40mm, the effective focal length (f2) of the second lens (2) is installed such that 20mm ≤ f2 ≤ 40mm, the effective focal length (f3) of the third lens (3) is installed such that -100mm ≤ f3 ≤ -50mm, a gap (T1) is installed between the first lens (1) and the second lens (2), the gap (T1) is set such that 0.1mm ≤ T1 ≤ 0.5mm, and between the second lens (2) and the third lens (3) An optical system characterized in that a gap (Y) is installed, the gap (Y) is set to 2mm ≤ Y ≤ 4.5mm, and the first lens (1), the second lens (2), and the third lens (3) are located on the same optical axis. Claim 2 An optical system according to claim 1, characterized in that the refractive power of the first lens (1) and the second lens (2) are both positive, and the refractive power of the third lens (3) is negative. Claim 3 An optical system according to claim 1, characterized in that the first lens (1) and the second lens (2) are installed by adhesion. Claim 4 An optical system according to claim 3, characterized in that the two surfaces joined by the first lens (1) and the second lens (2) are both Fresnel surfaces. Claim 5 An optical system according to claim 1, characterized in that the sum of the effective focal length (f1) of the first lens (1) and the effective focal length (f2) of the second lens (2) is greater than the absolute value of the effective focal length (f3) of the third lens (3). Claim 6 An optical system according to claim 1, characterized in that the effective focal length (f) of the optical system satisfies 15mm ≤ f ≤ 25mm. Claim 7 An optical system according to claim 1, wherein the first lens (1) and the second lens (2) are both made of the same material and are both COP material, and the third lens (3) is made of OKP material or EP material. Claim 8 A head-mounted display device characterized by including an optical system described in any one of claims 1 to 7. Claim 9 delete Claim 10 delete

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