Optical system and head-mounted display device

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 arranged in sequence along the propagation direction of the incident light, 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. According to the embodiments of the present application, a direct transmission optical structure design scheme with short focus, high light efficiency and high resolution is provided, and has relatively good imaging quality.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims priority to a Chinese patent application filed with the China Patent Office on November 30, 2021, bearing application number 202111446784.7 and titled "Optical system and head-mounted display device," the entire contents of which are incorporated herein by reference.

[0002] This application relates to the technical field of optical imaging, and more particularly, this application relates to optical systems and head mounted display devices. [Background technology]

[0003] In recent years, Augmented Reality (AR) technology and Virtual Reality (VR) technology have been applied to smart wearable devices and are rapidly developing. The core components of both Augmented Reality and Virtual Reality technologies are the display optical system. The quality of smart wearable devices is directly determined by the display effect of the display optical system.

[0004] Take VR devices as an example of related art. Most of the conventional VR devices use a display optical system formed by combining a single lens and a display screen. However, based on the requirements of optical path imaging, the lens is far away from the display screen, which results in a large size of the VR device, which is disadvantageous to the miniaturization of the product, and may cause a poor user experience when worn. In addition, there is a technical solution for the current VR device that adopts a folded optical path, which can realize the miniaturization and weight reduction of the VR device, but has problems such as high manufacturing costs, low light efficiency (<25%), and ghosting. Summary of the Invention [Problem to be solved by the invention]

[0005] The purpose of this application is to provide a new technical proposal for an optical system and a head-mounted display device. [Means for solving the problem]

[0006] According to one aspect of the present application, there is provided an optical system, the optical system including a third lens, a second lens, and a first lens arranged in sequence along a propagation direction of an incident light, 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.

[0007] Optionally, the refractive powers 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 cemented together.

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

[0011] Optionally, the effective focal length f1 of the first lens is set to 20 mm≦f1≦40 mm; The effective focal length f2 of the second lens is set to 20 mm≦f2≦40 mm; The effective focal length f3 of the third lens is set to -100 mm≦f3≦-50 mm.

[0012] Optionally, the effective focal length f of the optical system satisfies 15 mm≦f≦25 mm.

[0013] Optionally, 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; 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; 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 made of the same material, both being COP material; The third lens is an OKP 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 includes the optical system according to any one of the preceding claims. Effect of the Invention

[0017] The beneficial effects of the present application are as follows:

[0018] In the technical solution according to the embodiment of the present application, multiple lenses are adopted, and the effective focal length of the lenses is reasonably set, which is favorable for realizing the optical requirements of the short focus, high light efficiency and high resolution of the entire optical path structure, and contributes to improving the imaging quality. In the embodiment of the present application, a direct transmission type optical path structure design plan with short focus and high resolution is proposed, and the formed optical system can be applied to, for example, head-mounted display devices (such as VR devices).

[0019] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application, taken in conjunction with the drawings. [Brief description of the drawings]

[0020] In order to more clearly describe the technical solutions in the embodiments of the present application or the prior art, the following briefly introduces drawings necessary for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some drawings of the present application, and those skilled in the art can obtain other drawings based on the drawings provided without creative labor.

[0021] [Figure 1] 1 is a structural schematic diagram of an optical system according to an embodiment of the present application; [Diagram 2] FIG. 2 is a schematic diagram of the imaging principle of an optical system according to an embodiment of the present application; [Diagram 3] FIG. 2 is a diagram showing the relationship between the aperture x of a third lens and the distance Y between the third lens and the second lens in an optical system according to an embodiment of the present application. [Figure 4] FIG. 2 is a diagram showing the relationship between the aperture x of a third lens and the distance Y between the third lens and the second lens in an optical system according to an embodiment of the present application. [Diagram 5] FIG. 2 is a diagram showing the relationship between the aperture x of a third lens and the distance Y between the third lens and the second lens in an optical system according to an embodiment of the present application. [Figure 6] 1 is a spot diagram of an optical system according to a first embodiment of the present application. [Figure 7] 3A to 3C are diagrams showing curvature of field and distortion of the optical system according to the first embodiment of the present invention. [Figure 8] 3 is a dispersion map of an optical system according to a first embodiment of the present application. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, the technical solutions of the embodiments of the present application will be described with reference to the drawings in the embodiments of the present application, but it is obvious that the described embodiments are only some of the embodiments of the present application, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative efforts belong to the scope of protection of the present application.

[0023] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to be limiting of the present application and its application or uses.

[0024] Techniques, methods and equipment known to those skilled in the art may not be described in detail, but where appropriate, such techniques, methods and equipment should be considered part of the description.

[0025] In all examples shown and discussed herein, any specific values ​​should not be construed as limiting, but merely as examples, and therefore other examples of example embodiments may have different values.

[0026] It should be noted that like symbols and letters represent like items in the following drawings, and thus, once an item is defined in one drawing, there is no need to discuss it further in subsequent drawings.

[0027] Hereinafter, an optical system and a head mounted display device according to an embodiment of the present invention will be described in detail with reference to FIGS.

[0028] According to one aspect of the present embodiment, an optical system is provided.

[0029] The optical system is a short-focus, high-resolution direct transmission optical system, and is expected to be well suited for use in electronic devices such as head mounted displays (HMDs) including VR devices (e.g., VR glasses and VR helmets), for which good applications are expected.

[0030] As shown in Figures 1 and 2, 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 arranged in sequence along the propagation direction of incident light, and 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.

[0031] The optical system according to the embodiment of the present application has a direct transmission type optical path structure, and the optical path design is relatively simple, so that the entire optical system can be manufactured relatively easily.

[0032] It should be mentioned that the optical system further comprises, for example, a display 4 .

[0033] The display screen 4 can be used to emit light rays, ie the incident light, in a light path configuration.

[0034] In other words, in the technical proposal of the optical system according to the embodiment of the present application, a combination of lenses is designed, and the combination of lenses may include, for example, three lenses, and as shown in Figures 1 and 2, each of the lenses is arranged, for example, at a position on the light output side of the display screen 4, specifically, located in the propagation direction of the incident light emitted from the display screen 4, and can be used to project the incident light to the human eye 5 to form an image,

[0035] As shown in Figures 1 and 2, the technical solution according to the embodiment of the present application adopts multiple lenses (e.g., three lenses), and the effective focal lengths of the lenses are reasonably set, which is beneficial to achieving the optical requirements of short focus, high optical efficiency, and high resolution of the entire optical path structure, and contributes to improving the imaging quality.

[0036] In the embodiments of the present application, a direct transmission type optical path structure design plan with short focal length and high resolution is proposed, and the formed optical system can be applied to, for example, head-mounted display devices (e.g., VR devices), and also contributes to realizing the development trend toward smaller and lighter head-mounted display devices.

[0037] In comparison, the technical solution according to the embodiment of the present application solves the problems of the conventional technical solution of a combination of a single lens and a display screen, such as the lens being far away from the display screen, the size of the VR device being large, which is unfavorable to the miniaturization of the product, and the low light efficiency. At the same time, it can improve the defects caused by using a folded optical path, and its processing difficulty and production cost are relatively low, and the direct transmission optical structure is also simpler than that of the folded optical path.

[0038] For example, as shown in Figures 1 and 2, the optical system is provided with a display screen 4, for example a 1.4-inch display screen, which realizes a viewing angle of 100 degrees. Therefore, neither a normal single-lens (1P) structure nor a normal double-lens (2P) structure is sufficient to resolve this type of display screen. The reasons are as follows:

[0039] The single lens (1P) can only optimize the degree of freedom of the surface shapes of two surfaces, has limited light-gathering ability, cannot correct aberration or chromatic aberration, and has a resolvable pixel size (imaging spot size) of approximately 80 μm to 100 μm over the entire field of view. More importantly, it cannot achieve the goal of a short focal length.

[0040] The two-element lens (2P) increases the degree of freedom in optimizing the surface shape of the lens and can achieve a short focal length, but there are still limitations in analytical power, and the size of the pixel that can be resolved over the entire field of view (imaging spot size) is approximately 60 μm to 80 μm.

[0041] The combination of optical lenses used in the embodiments of the present application can further improve the resolution and correct the chromatic aberration to a certain extent, forming a direct transmission type short focal length optical path structure.

[0042] In some examples herein, the refractive powers of the first lens 1 and the second lens 2 are both positive, and the refractive power of the third lens 3 is negative.

[0043] It can be seen that in the optical system according to the embodiment of the present application, 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 can provide large positive refractive power, while the negative lens can be used to eliminate chromatic aberration.

[0044] In some examples of the present application, the first lens 1 and the second lens 2 are provided in a cemented state.

[0045] That is, in the present embodiment, two positive lenses are designed to be cemented together, while the negative lens is designed to be separate from the positive lens that cements the two together.

[0046] As shown in Figures 1 and 2, in the optical path structure, a design in which the first lens 1 and the second lens 2 on the side away from the display screen 4 are cemented together contributes to reducing stray light, while a structure in which the third lens 3 on the side closer to the display screen 4 is provided independently and separated from the two cemented lenses contributes to improving imaging quality.

[0047] Furthermore, the design in which the first lens 1 and the second lens 2 are cemented together reduces the difficulty of assembling components and reduces the risk of impurities being generated due to assembly between the lenses, thereby improving yields.

[0048] In some examples of the present application, as shown in FIG. 1 and FIG. 2, the two bonding surfaces of the first lens 1 and the second lens 2 are both Fresnel surfaces.

[0049] That is, the optical system is designed with two adjacent Fresnel surfaces that are bonded together, which can realize low dispersion and short focal length of the optical path structure and reduce stray light, so that the optical system has high light efficiency and can achieve high definition imaging.

[0050] 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 21 and a fourth surface 22; thus, in the entire optical path structure, the second surface 12 and the third surface 21 are adjacent to each other and are both set as Fresnel surfaces, and the first surface 11 and the fourth surface 22 are both aspheric (further, these two surfaces are both convex).

[0051] Among them, a first surface 11 of the first lens 1 is located outside and faces directly toward a human eye 5, and a second surface 12 of the first lens 1 and a third surface 21 of the second lens 2 are adjacent to each other. In the present application, the first surface 11 of the first lens 1 is set to an aspheric surface (e.g., a convex surface), and the second surface 12 of the first lens 1 is set to a Fresnel surface. In this manner, the first lens 1 (which is a positive lens) is formed in a combination form of two surface shapes, an aspheric surface and a Fresnel surface.

[0052] Optionally, in the design of the embodiment of the present application, the first surface 11 and the second surface 12 of the first lens 1 are plated with an anti-reflective coating (AR) respectively.

[0053] When an anti-reflective coating is plated on each of the two surfaces of the first lens 1, the anti-reflective coating reduces reflected light, thereby increasing the transmittance of light at the two surfaces of the first lens 1.

[0054] Optionally, the first surface 11 of the first lens 1 is further plated with a hardening film in addition to the anti-reflection film.

[0055] This is because the first surface 11 of the first lens 1 faces the outside and therefore needs to be protected from scratches, dents, and other damage, and plating the hardened film can extend the service life of the first lens 2. Plating the first surface 11 with a hardened film, i.e., performing a hardening treatment on the first surface 11, can improve the hardness, strength, and the like of the first surface 11. This is advantageous for extending the service life of the entire optical system.

[0056] Of course, in the embodiment of the present application, it is not limited to the first surface 11 of the first lens 1 being plated with a hardened film, and the second surface 12 of the first lens 1 may also be plated with a hardened film. Those skilled in the art can flexibly adjust according to specific needs, and the present application does not make any specific limitations thereon.

[0057] In the embodiment of the present application, the first lens 1 further has the following parameters:

[0058] For example, the absolute value of a radius R1 of a first surface 11 of the first lens 1 satisfies 35 mm≦R1≦65 mm, the absolute value of a radius R2 of a second surface 12 of the first lens 1 satisfies 20 mm≦R2≦40 mm, and the absolute value of a conic coefficient K1 of the first surface 11 and the second surface 12 of the first lens 1 satisfies K1≦20.

[0059] Among them, the first surface 11 and the second surface 12 have different surface shape designs.

[0060] Specifically, the first surface 11 facing outward is designed to be aspheric (for example, convex), while the second surface 12 is designed to be a Fresnel surface. By applying the first lens 1 formed by combining the Fresnel surface and the aspheric surface to the optical path structure, it contributes to realizing the effects of a short focal length and high resolution.

[0061] In the embodiment of the present application, after optimizing the surface shape of the first lens 1, taking into consideration the difficulty and cost of processing, it is more preferable to design the conic constant of the first lens 1, i.e., the K1 value, to be, for example, [-10, 10], and to design the radius R of the Fresnel surface of the first lens 1 to be greater than 23 mm.

[0062] In some examples of the present application, the second lens 2 and the first lens 1 may have the same combination of surface shapes, and as shown in Figures 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 set to an aspheric surface (e.g., a convex surface).

[0063] Optionally, the third surface 21 and the fourth surface 22 are also plated with an anti-reflective coating.

[0064] The anti-reflection coating reduces reflected light, thereby increasing the transmittance of light rays through the two surfaces of the second lens 2 .

[0065] In the embodiment of the present application, the second lens 2 further has the following parameters:

[0066] In some examples of the present application, the absolute value of the radius R3 of the third surface 21 of the second lens 2 satisfies 20 mm≦R3≦40 mm, the absolute value of the radius R4 of the fourth surface 22 of the second lens 2 satisfies 35 mm≦R4≦80 mm, and the absolute value of the conic coefficient K2 of the third surface 21 and the fourth surface 22 of the second lens 2 satisfies K2≦20.

[0067] In the embodiment of the present application, after optimizing the surface shape of the second lens 2, in consideration of the difficulty and cost of processing, it is more preferable to design the conic constant, i.e., the K2 value, of the second lens 2 to be [-10, 10] and to design the radius of the Fresnel surface of the second lens 2 to be greater than 23 mm, which is basically the same as that of the first lens 1.

[0068] It should be noted 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 parameters of the surface shape within a certain range, otherwise there is a risk of low processing accuracy or damage to the cutter (this is because processing the tooth shape is difficult, and the smaller the acute angle of the tooth shape, the more difficult the processing inclination angle and operation). That is why it is preferable to set the cone coefficient K value in the range of [-10, 10] and set the R value of the Fresnel surface of each lens to 23 mm or more.

[0069] In the technical solution according to the embodiment of the present application, the first lens 1 and the second lens 2, i.e., two positive lenses, both use a combination of an aspheric surface (e.g., a convex surface) and a Fresnel surface, and the low dispersion and short focal length of the optical path structure are achieved by selecting and combining materials with different refractive indices and Abbe numbers.

[0070] 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 and the fourth surface 22 of the second lens 2 are adjacent to each other, and at least one of the fifth surface 31 and the sixth surface 32 is set to be aspheric.

[0071] For example, the refractive power of the third lens 3 is negative.

[0072] That is, in the design of the technical solution of the present application, the third lens 3 is a negative lens, which is a lens that is thin in the center and thick on the periphery, and has the ability to diverge light. The third lens 3 can be used to eliminate chromatic aberration in the entire optical path structure.

[0073] The third lens 3 may be, for example, a biconcave lens (ie, two surfaces are both concave) or a plano-concave lens (ie, one surface is concave and the other surface is planar).

[0074] Preferably, the fifth surface 31 is set to a plane and the sixth surface 32 is set to a concave surface, that is, in the entire optical path structure, the surface adjacent to the fourth surface 22 is a plane and the surface adjacent to the display screen 4 is a concave surface.

[0075] Optionally, both the fifth surface 31 and the sixth surface 32 are plated with an anti-reflective coating (AR).

[0076] When an anti-reflective coating is plated on each of the two surfaces of the third lens 3, the anti-reflective coating reduces reflected light, thereby increasing the transmittance of light at the two surfaces of the third lens 3.

[0077] 1, the optical system includes a display screen 4, the first lens 1, the second lens 2, and the third lens 3, among which, for example, the display screen 4 can be set as a display light source, the first lens 1 and the second lens 2 can be set as positive lenses having aspheric and Fresnel surfaces, and the third lens 3 closer to the display screen 4 can be set as a negative lens. All of the surfaces of the three lenses are plated with an anti-reflection film, and the first surface 11 of the first lens 1 is hardened by a curing film and is also treated with an anti-reflection film. 2, the incident light emitted from the display screen 4 enters the third lens 3 through the sixth surface 32 of the third lens 3 plated with an anti-reflection film, the transmitted light diverges and enters the second lens 2, both surfaces of which are also plated with an anti-reflection film, so the light passes through the second lens 2 and is condensed, then enters the first lens 1, which is also a condensing positive lens, and after the light transmission of the first lens 1, it enters the human eye 5 and forms an image. The entire optical system has no optical path folding, and each lens surface is plated with an anti-reflection film, so the light transmission efficiency is high.

[0078] In some examples of the present application, the first lens 1 and the second lens 2 are provided so that their edge regions are bonded to each other.

[0079] That is, the first lens 1 and the second lens 2 are bonded together only at the frame by a frame bonding method.

[0080] For example, a light-transmitting optical adhesive is used to bond and connect the edge regions of the first lens 1 and the second lens 2. The refractive index of the optical adhesive is lower than that of each lens, and is, for example, 1.1 to 1.3.

[0081] According to the above embodiment, the first lens 1 and the second lens 2 can form one bonding system. The bonding system can reduce the influence of stray light due to the tooth shape of the Fresnel surface, while the two bonded positive lenses are assembled into an optical path structure as one optical element, reducing the difficulty of assembly. In addition, the bonding is performed by dispensing at the edge region of the first lens 1 and the second lens 2, reducing the risk of impurities occurring during assembly between the two lenses, and improving the yield.

[0082] In some examples of the present application, as shown in FIG. 1 and FIG. 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; 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; The first lens 1, the second lens 2 and the third lens 3 are located on the same optical axis.

[0083] Among them, the first lens 1 and the second lens 2 are provided by being cemented together, so that the distance between them is small.

[0084] Among them, a distance Y is provided between the second lens 2 and the third lens 3, and the distance Y and the aperture x of the third lens 3 are expressed as follows: The relationship Y=ax+b is satisfied, where -0.8≦a≦-0.39 and 30≦b≦35.

[0085] That is, in the technical solution according to the embodiment of the present application, a certain distance Y is provided between the second lens 2 and the third lens 3, and a linear negative correlation is formed between the value of the distance Y and the value of the aperture x of the third lens 3.

[0086] If the second lens 2 is held stationary in the entire optical path structure, it is possible to change the size of the clear aperture of the third lens 3 by adjusting the distance of the third lens 3 relative to the second lens 2. For example, the spacing value Y and the aperture value x should satisfy the relationship Y=ax+b, where -0.8≦a≦-0.39 and 30≦b≦35.

[0087] It can be seen that the closer the third lens 3 is to the second lens 2, the larger the aperture x of the third lens 3; in other words, the smaller the value of the distance Y between the two, the larger the aperture x of the third lens 3.

[0088] In addition, if the optical system further includes a display screen 4, after the spacing between each lens is reasonably arranged, the spacing dimension between the third lens 3 and the display screen 4 also needs to be taken into consideration.

[0089] For example, a third gap T2 is provided between the third lens 3 and the display screen 4.

[0090] Optionally, the third distance T3 is set to 8 mm≦T2≦15 mm.

[0091] 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 being OKP material or EP material.

[0092] COP material, OKP material, and EP material are all light-transmitting resin materials with a light weight, and by using these materials to manufacture lenses, the mass of the lens group can be reduced, resulting in a lighter weight.

[0093] For each lens, an optimization design is performed by selecting a combination of materials with a high refractive index and a high / low Abbe number, taking into consideration short focal length and chromatic aberration.

[0094] Those skilled in the art can reasonably select the materials of the first lens 1, the second lens 2 and the third lens 3 according to actual needs, and the materials are not limited to the above-mentioned types of materials.

[0095] In some examples of the present application, the central thickness value h1 of the first lens 1 is 2 mm≦h1≦4 mm, the central thickness h2 of the second lens 2 is 3 mm≦h2≦5 mm, and the central thickness h3 of the third lens 3 is 2 mm≦h3≦4 mm.

[0096] Since the thickness of each lens is not too thick, it is advantageous to reduce the weight of the entire optical path structure.

[0097] 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.

[0098] Optionally, the effective focal length f1 of the first lens 1 is set to 20 mm≦f1≦40 mm; The effective focal length f2 of the second lens 2 is set to 20 mm≦f2≦40 mm, The effective focal length f3 of the third lens 3 is set to -100 mm≦f3≦-50 mm.

[0099] In some examples of the present application, the effective focal length f of the optical system satisfies 15 mm≦f≦25 mm.

[0100] In the present application, a short-focus optical system is provided. The entire optical system does not have a folded optical path, and is a direct transmission type optical system, which can realize a high-definition image.

[0101] The following is one application example of the technical solution according to the embodiment of the present application.

[0102] (1) Combined with the 1.4-inch display screen4, it achieves a viewing angle of 90 degrees. (2) Distortion is less than 34.6%, and field curvature is less than 0.5 mm. (3) The chromatic aberration is less than 178um. The virtual image distance is 1500mm. (4) The spot sizes from 0 to 1.0F were all smaller than two display pixels, achieving clear imaging in the visible light range (450nm to 630nm). (5) The effective focal length f of the optical system is 19.13 mm, the total optical track length (TTL) is 23.31 mm, and the aperture x of the third lens 3 is 33.2 mm.

[0103] [Example 1] In Example 1, an optical system is provided, and Table 1 shows the structural parameters of the optical system.

[0104] Table 1 shows the optical surface numbers (Surface), which are numbered in order 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 and the next optical surface on the optical axis from the human eye 5 (aperture) to the display screen 4, and the even-order aspheric coefficients α2, α3, and α4.

[0105] Among them, the aspheric coefficients can satisfy the following equation:

number

[0106] In equation (1), z is the coordinate along the optical axis direction, Y is the radial coordinate in lens length units, C is the curvature (1 / R), K is the conic constant, αi is the coefficient of each higher order term, and 2i is the order of the aspherical coefficient. In the technical design of this application, taking into consideration the gradual change in field curvature, the spherical coefficients without higher order terms are limited to the fourth order.

[0107] [Table 1]

[0108] The quality of the performance of the optical system of the first embodiment is reflected by the following parameters.

[0109] As shown in FIG. 6, the spot size is largest at the maximum field of view of 1.0F, and the maximum value is smaller than 44 μm.

[0110] As shown in FIG. 7, the field curvature in the T and S directions is less than 0.5 mm for all RGB wavelengths, and the distortion aberration is maximum at the maximum field of view and is less than 34.5%.

[0111] As shown in FIG. 8, the maximum dispersion of RGB is at the maximum viewing position, and the LCA is 178 nm for the entire RGB range from 460 nm to 610 nm.

[0112] In the optical system according to the embodiment of the present application, the relationship between the aperture value x of the third lens 3 and the value of the distance Y between the third lens 3 and the second lens 2 is as follows.

[0113] 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 there is a linear negative correlation between the two.

[0114] The following will be described with three examples as shown in FIG. 3 to FIG.

[0115] [Example 2] In the optical system, the refractive powers of the first lens 1 and the second lens 2 are both set to be positive, and the parameters of the surface shapes are as follows:

[0116] The first lens 1: the radius R1 of the first surface 11 (convex surface) is 45 mm, and the radius R2 of the second surface 12 (Fresnel surface) is 25 mm; The second lens 2: the radius R3 of the third surface 21 (Fresnel surface) is 25 mm, and the radius R4 of the fourth surface 22 (convex surface) is 45 mm; the third lens 3 has a negative refractive power and is located near the display screen 4; When the distance value Y between the second lens 2 and the third lens 3 is set to 2 mm, the corresponding aperture value x of the third lens 3 is 31.14 mm; When the distance Y between the second lens 2 and the third lens 3 is set to 3 mm, the corresponding aperture value x of the third lens 3 is 30.1 mm; When the distance value Y between the second lens 2 and the third lens 3 is set to 3.5 m, the corresponding aperture value x of the third lens 3 is 29.7 mm; When the distance Y between the second lens 2 and the third lens 3 is set to 4 mm, the corresponding aperture value x of the third lens 3 is 29.4 mm; When the distance 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.

[0117] From the relationship between the spacing value Y between the second lens 2 and the third lens 3 listed above and the aperture value x of the third lens 3, it can be confirmed that there is a linear negative correlation between the two, and as shown in FIG. 3, Y=-0.7854x+32.578.

[0118] [Example 3] In the optical system, the refractive powers of the first lens 1 and the second lens 2 are both set to be positive, and the parameters of the surface shapes are as follows:

[0119] The first lens 1: the radius R1 of the first surface 11 (convex surface) is 35 mm, and the radius R2 of the second surface 12 (Fresnel surface) is 25 to 29 mm; The second lens 2: the radius value R3 of the third surface 21 (Fresnel surface) is 25 to 29 mm, and the radius value R4 of the fourth surface 22 (convex surface) is 35 mm; the effective focal length f1 of the first lens 1≈the effective focal length f2 of the second lens 2=29 mm, the third lens 3 has a negative refractive power and is located near the display screen 4; When the distance Y between the second lens 2 and the third lens 3 is set to 2 mm, the corresponding aperture value x of the third lens 3 is 30.06 mm; When the distance Y between the second lens 2 and the third lens 3 is set to 3 mm, the corresponding aperture value x of the third lens 3 is 29.3 mm; When the distance value Y between the second lens 2 and the third lens 3 is set to 3.5 m, the corresponding aperture value x of the third lens 3 is 29.2 mm; When the distance Y between the second lens 2 and the third lens 3 is set to 4 mm, the corresponding aperture value x of the third lens 3 is 29.07 mm; When the distance 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.

[0120] From the relationship between the spacing value Y between the second lens 2 and the third lens 3 listed above and the aperture value x of the third lens 3, it can be confirmed that there is a linear negative correlation between the two, and as shown in FIG. 4, Y=-0.5357x+31.078.

[0121] [Example 4] In the optical system, the refractive powers of the first lens 1 and the second lens 2 are both set to be positive, and the parameters of the surface shapes are as follows:

[0122] The first lens 1: the radius R1 of the first surface 11 (convex surface) is 50 mm, and the radius R2 of the second surface 12 (Fresnel surface) is 25 mm; The second lens 2: the radius R3 of the third surface 21 (Fresnel surface) is 25 mm, and the radius R4 of the fourth surface 22 (convex surface) is 50 mm; the effective focal length f1 of the first lens 1≈the effective focal length f2 of the second lens 2=29 mm, the third lens 3 has a negative refractive power and is located near the display screen 4; When the distance Y between the second lens 2 and the third lens 3 is set to 2 mm, the corresponding aperture value x of the third lens 3 is 30.1 mm; When the distance Y between the second lens 2 and the third lens 3 is set to 3 mm, the corresponding aperture value x of the third lens 3 is 29.7 mm; When the distance value Y between the second lens 2 and the third lens 3 is set to 3.5 m, the corresponding aperture value x of the third lens 3 is 29.5 mm; When the distance Y between the second lens 2 and the third lens 3 is set to 4 mm, the corresponding aperture x of the third lens 3 is 29.38 mm; When the distance 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.

[0123] From the relationship between the spacing value Y between the second lens 2 and the third lens 3 listed above and the aperture value x of the third lens 3, it can be confirmed that there is a linear negative correlation between the two, and as shown in FIG. 5, Y=-0.393x+30.888.

[0124] As can be seen from the above Examples 2 to 4, there is a linear negative correlation between the distance Y between the third lens 3 and the second lens 2 and the aperture value x of the third lens 3. However, when the parameters of the lens surface shape are different, the obtained linear coefficients will be slightly different, for example, Y=ax+b, where −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 .

[0125] In the present embodiment, a short focal length optical system is provided that does not involve a folded optical path.

[0126] (1) The effect of ultra-short focal length can be well realized by combining multiple (e.g., three) optical lenses, such as two cemented positive lenses and one separately designed negative lens. (2) By bonding the Fresnel surfaces of the two positive lenses, stray light can be reduced and the assembly of the two positive lenses into the optical path structure can be simplified. (3) The parameters of the negative lens close to the display screen 4 are specially designed, which contributes to improving the imaging quality.

[0127] According to another aspect of the present application, a head mounted display device is provided.

[0128] The head mounted display device includes any one of the optical systems described above.

[0129] The head-mounted display device is, for example, a VR device.

[0130] Although the above embodiments have been described with emphasis on the differences between each embodiment, the different optimization features between each embodiment can be combined to form a better embodiment, as long as they are not contradictory, and will not be repeated here for the sake of brevity.

[0131] Although some specific embodiments of the present application have been described in detail through examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the present application. Those skilled in the art should understand that the above embodiments can be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims. [Explanation of symbols]

[0132] 1, the first lens; 2, the second lens; 3, the third lens; 4, the display screen; 5, the human eye; 11, first surface; 12, second surface; 21, third surface; 22, fourth surface; 31, fifth surface; 31, sixth surface.

Claims

1. An optical system comprising: The optical system comprises a third lens (3), a second lens (2) and a first lens (1) arranged in this order along the propagation direction of the incident light, an effective focal length f1 of the first lens (1) and an effective focal length f2 of the second lens (2) are both greater than an effective focal length f of the optical system; The effective focal length f1 of the first lens (1) is set to 20 mm≦f1≦40 mm; The effective focal length f2 of the second lens (2) is set to 20 mm≦f2≦40 mm, The effective focal length f3 of the third lens (3) is set to −100 mm≦f3≦−50 mm, 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); 1. An optical system comprising:

2. 2. The optical system according to claim 1, wherein the first lens (1) and the second lens (2) have positive refractive powers and the third lens (3) has negative refractive power.

3. 2. The optical system according to claim 1, characterized in that the first lens (1) and the second lens (2) are provided in cemented relation.

4. 4. The optical system according to claim 3, wherein the two bonding surfaces of the first lens (1) and the second lens (2) are both Fresnel surfaces.

5. 2. The optical system according to claim 1, wherein an effective focal length f of the optical system satisfies 15 mm≦f≦25 mm.

6. 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; 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; 2. The optical system according to claim 1, wherein the first lens (1), the second lens (2) and the third lens (3) are located on the same optical axis.

7. The first lens (1) and the second lens (2) are made of the same material, and both are COP materials.

2. The optical system according to claim 1, characterized in that the third lens (3) is of OKP or EP material.

8. A head mounted display device comprising an optical system according to any one of claims 1 to 7.

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