CN216748282U

CN216748282U - Optical system and head-mounted display equipment

Info

Publication number: CN216748282U
Application number: CN202122981542.XU
Authority: CN
Inventors: 孙琦; 赵博刚
Original assignee: Goertek Optical Technology Co Ltd
Current assignee: Goertek Optical Technology Co Ltd
Priority date: 2021-11-30
Filing date: 2021-11-30
Publication date: 2022-06-14
Anticipated expiration: 2031-11-30

Abstract

The application discloses an optical system and a head-mounted display device; wherein the optical system comprises: the Fresnel lens comprises a third lens, a second lens and a first lens which are sequentially arranged along the propagation direction of incident light, wherein two Fresnel surfaces which are adjacently arranged and at least one binary diffraction surface are arranged in the optical system. The embodiment of the application provides an optical structure design scheme with a large FOV, a short TTL and low chromatic aberration, and the optical structure design scheme can have a better imaging effect when being applied to head-mounted display equipment.

Description

Optical system and head-mounted display equipment

Technical Field

The present application relates to the field of optical imaging technology, and more particularly, to an optical system and a head-mounted display device.

Background

In recent years, Augmented Reality (AR) technology, Virtual Reality (VR) technology, and the like have been applied to smart wearable devices, and have been rapidly developed. The core component of both augmented reality technology and virtual reality technology is a display optical system. Therefore, the quality of the display effect of the display optical system directly determines the quality of the intelligent wearable device.

In the related art, a VR device is taken as an example. In the current VR device, if a display screen based on 1.4inch is used, in order to achieve a large field angle (FOV is greater than or equal to 100 degrees) and a short total optical length (TTL is less than or equal to 24mm), an optical lens combination with strong convergence power needs to be adopted, but chromatic aberration is also corrected, and conventional lens combination cannot well correct chromatic aberration, so that imaging quality is poor.

SUMMERY OF THE UTILITY MODEL

The application aims at providing a new technical scheme of an optical system and a head-mounted display device.

According to one aspect of the present application, an optical system is provided. The optical system comprises a third lens, a second lens and a first lens which are sequentially arranged along the propagation direction of incident light;

wherein in the optical system there are two adjacently arranged fresnel surfaces and at least one binary diffractive surface.

Optionally, two adjacent surfaces of the first lens and the second lens are fresnel surfaces.

Optionally, the first lens comprises a first surface and a second surface, and the second lens comprises a third surface and a fourth surface;

the second surface and the third surface are arranged adjacently and are both Fresnel surfaces; the first surface and the fourth surface are both aspheric.

Optionally, the focal power of the first lens and the focal power of the second lens are both positive;

the first lens, the second lens and the third lens are located on the same optical axis.

Optionally, the third lens is a DOE lens comprising fifth and sixth surfaces;

one of the fifth surface and the sixth surface is a binary diffractive surface, and the other of the fifth surface and the sixth surface is an aspheric surface;

the aspheric surface of the third lens and the aspheric surface of the second lens are arranged adjacently.

Optionally, a first interval T is arranged between the first lens and the second lens₁Said first interval T₁Is set to be less than or equal to T of 0.2mm₁≤1mm。

Optionally, a second interval T is provided between the second lens and the third lens₂Said second interval T₂Is set to be less than or equal to T of 0.5mm₂≤1.5mm。

Optionally, the effective focal length f of the first lens₁Comprises the following steps: f is not less than 25mm₁≤35mm；

Focal length f of the second lens₂Comprises the following steps: f is not less than 35mm₂≤45mm；

Focal length f of the third lens₃Comprises the following steps: f is not less than 50mm₃≤65mm。

Optionally, the first lens and the second lens are made of the same material and are all made of PMMA;

the third lens is a COP material.

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

The head-mounted display device comprises an optical system as described in any of the above.

The beneficial effect of this application lies in:

the embodiment of the application provides a design scheme of a direct-transmission optical system, the formed optical system can be applied to head-mounted display equipment (such as VR equipment), two adjacent Fresnel surfaces are designed in the whole optical path structure, and a binary diffraction surface is matched, so that appropriate focal power can be provided, and chromatic aberration can be greatly corrected. The optical system of the embodiment of the application realizes the optical performance of short TTL, large FOV and low chromatic aberration.

Further features of the present application and advantages thereof will become apparent from the following detailed description of exemplary embodiments thereof, which is to be read in connection with the accompanying drawings.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the application and together with the description, serve to explain the principles of the application.

Fig. 1 is a schematic structural diagram of an optical system provided in an embodiment of the present application;

FIG. 2 is a schematic diagram illustrating an imaging principle of an optical system provided by an embodiment of the present application;

FIG. 3 is a dot-column diagram of an optical system provided in embodiment 1 of the present application;

FIG. 4 is a graph of field curvature and distortion for the optical system provided in example 1 of the present application;

fig. 5 is a dispersion map of the optical system provided in embodiment 1 of the present application.

Description of reference numerals:

1. a first lens; 2. a second lens; 3. a third lens; 4. a display screen; 5. the human eye;

11. a first surface; 12. a second surface;

21. a third surface; 22. a fourth surface;

31. a fifth surface; 32. a sixth surface.

Detailed Description

Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that: the relative arrangement of the components and steps, the numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present application unless specifically stated otherwise.

The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the application, its application, or uses.

Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate.

In all examples shown and discussed herein, any particular value should be construed as merely illustrative, and not limiting. Thus, other examples of the exemplary embodiments may have different values.

It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, further discussion thereof is not required in subsequent figures.

The optical system and the head-mounted display device provided by the embodiment of the present application are described in detail below with reference to fig. 1 to 5.

According to an aspect of an embodiment of the present application, there is provided an optical system. The optical system is a direct-transmission optical structure design scheme with short total optical length (TTL is less than or equal to 24mm), large field of view (FOV is more than or equal to 100 degrees) and low chromatic aberration, and is suitable for being applied to electronic equipment, such as Head Mounted Display (HMD) equipment, for example VR equipment (such as VR glasses or VR helmets). It has good application prospect.

An optical system provided in an embodiment of the present application, as shown in fig. 1 and fig. 2, includes a third lens 3, a second lens 2, and a first lens 1, which are sequentially arranged along a propagation direction of incident light; wherein there are two fresnel surfaces arranged adjacently and at least one binary diffractive surface in the optical system.

The optical system that this application embodiment provided, it is direct-through type light path structural design, and the design of whole light path structure is comparatively simple for its preparation is comparatively easy.

It should be noted that the optical system may further include a display screen (display) 4.

The display screen 4 is in the light path configuration available for emitting light, i.e. providing incident light for the optical system.

That is to say, in the optical system solution provided in the embodiment of the present application, a lens combination is designed and applied, the lens combination has two fresnel surfaces that are adjacently disposed and further matches with at least one binary diffraction surface, as shown in fig. 1 and fig. 2, the lens combination is disposed at a position on a light emergent side of the display screen 4, specifically located in a propagation direction of incident light emitted from the display screen 4, and can be used for projecting the incident light into the human eye 5 for imaging, thereby implementing an imaging function of the optical system.

The optical system provided by the embodiment of the application is based on the collocation and combination of three optical lenses, two Fresnel surfaces which are adjacently arranged are designed in the whole optical path structure, the requirement of the ultra-short focus of the optical system can be met, and the single binary diffraction surface (DOE micro-structure) in the optical system can be used for greatly correcting imaging chromatic aberration.

It should be noted that, in the solution provided in the embodiment of the present application, the two fresnel surfaces that are adjacently disposed include, but are not limited to, a planar substrate.

That is, the two adjacently disposed fresnel surfaces may also be curved substrates, for example.

For another example, one of the two adjacent fresnel surfaces may be a curved surface substrate, and the other may be a flat surface substrate. The base form of the fresnel surface can be adjusted by those skilled in the art according to specific situations, and the present application is not limited thereto.

The Fresnel surface design of the curved substrate can enable the corresponding lens to be light and thin, and light weight of the whole optical system is facilitated.

It should be noted that, in the solution provided in the embodiment of the present application, the substrate of the binary diffraction plane may be a planar substrate or a convex substrate, and those skilled in the art may flexibly select the substrate according to needs, and the present application is not limited in particular herein.

Compared comprehensively, the light path design scheme provided by the embodiment of the application overcomes the problems that the size of VR equipment is larger and the miniaturization of products is not facilitated due to the fact that the lens is far away from a display screen in the existing scheme of a single-chip lens and the display screen (display). Meanwhile, the defect problem caused by the adoption of the folded optical path can be solved. The scheme of the folding light path has the defects of high cost, low light efficiency, ghost and the like.

The scheme provided by the embodiment of the application adopts a direct-transmission type optical scheme, and a Fresnel surface is designed and adopted in a light path structure in consideration of the requirement of short total optical length (TTL). In the aspect of correcting chromatic aberration, the correction degree of the conventional lens group is limited, so that a binary diffraction surface is arranged in an optical path structure, and the chromatic aberration can be greatly corrected while a strong focusing power is provided.

For example, as shown in fig. 1 and fig. 2, a Display screen 4 is disposed in the optical system, and the Display screen 4 is, for example, a 1.4inch Display, which realizes a 100-degree field angle. On this basis, the conventional one-piece lens (1P) structure or the two-piece lens (2P) structure is not enough to distinguish the display screen of the type. The reason is that:

the single-chip lens (1P) only has the optimization of the surface type freedom degree of two surfaces, the convergence capability is limited, the aberration or chromatic aberration cannot be corrected, the pixel size (spot size) which can be resolved in a full view field is about 80-100 mu m, and more importantly, the purpose of short focus cannot be achieved.

Although the two-piece lens (2P) increases the degree of freedom of optimization of the surface shape of the lens surface and can realize short focus, the resolution is still limited, and the pixel size (spot size) which can be resolved in the full view field is about 60 to 80 μm.

The optical lens combination structure adopted in the embodiment of the application can further improve the resolving power and correct chromatic aberration to a certain extent, and a direct-transmission short-focus light path structure is formed.

In addition, it should be noted that the optical system provided in the embodiments of the present application is not limited to only two fresnel surfaces and one binary diffractive surface. It is understood that the optical system may further include more lenses, and more fresnel surfaces and binary diffraction surfaces are provided in the optical system, which can be flexibly adjusted by those skilled in the art according to specific situations.

In some examples of the present application, as shown in fig. 1 and 2, two adjacent surfaces of the first lens 1 and the second lens 2 are fresnel surfaces. The use of this design in the optical system helps to reduce stray light and also provides a strong focusing power.

In some examples of the present application, as shown in fig. 1 and 2, 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;

the second surface 12 and the third surface 21 are arranged adjacently and are both fresnel surfaces; both the first surface 11 and the fourth surface 22 are aspherical.

In the optical system provided in the embodiment of the present application, as shown in fig. 1 and fig. 2, a first surface 11 of the first lens 1 directly faces the human eye 5, which is located outside, and the first surface 11 is, for example, provided as an aspheric surface (further, the first surface 11 is a convex surface); the second surface 12 of the first lens 1 is configured as a fresnel surface, so that the first lens 1 (positive lens) forms a two-surface combination of aspheric surface + fresnel surface.

Optionally, the first surface 11 and the second surface 12 of the first lens 1 are respectively coated with an Anti-Reflective coating (AR).

After the two surfaces of the first lens 1 are respectively plated with the antireflection film, the antireflection film can be used for reducing the reflected light, so as to increase the transmittance of the light on the two surfaces of the first lens 1.

Optionally, besides the antireflection film on the first surface 11 of the first lens 1, a hardened film may be plated on the first surface 11.

This is because: the first surface 11 of the first lens 1 is facing outward, which is required to avoid scratches, bruises, etc., and the service life of the first lens 1 can be improved by plating the hardened film. By plating a cured film on the first surface 11, that is, by performing a curing process on the first surface 11, the hardness, strength, and the like of the first surface 11 can be improved. This is advantageous for increasing the lifetime of the entire optical system.

Of course, in the embodiment of the present application, the first surface 11 of the first lens 1 is not limited to be plated with a hardened film, and the second surface 12 of the first lens 1 may also be plated with a hardened film, which can be flexibly adjusted by a person skilled in the art according to specific needs, and the present application is not limited specifically herein.

In addition, in the embodiment of the present application, the first lens 1 further has the following parameters.

In some examples of the present application, the radius R of the first surface 11 of the first lens 1₁Satisfies the following absolute value: 40mm ≤ Abs (R)₁) Less than or equal to 50 mm; radius R of the second surface 12 of the first lens 1₂Satisfies the following absolute value: 20mm ≤ Abs (R)₂) Less than or equal to 40 mm; the conic coefficient K of the first surface 11 and the second surface 12₁Satisfies the following absolute value: abs (K)₁)≤10。

Wherein the first surface 11 and the second surface 12 have different surface designs.

Specifically, the first surface 11 facing outward is designed to be an aspheric surface (e.g., a convex surface), and the second surface 12 is designed to be a fresnel surface, and the first lens 1 formed by combining the fresnel surface and the aspheric surface is applied to the optical path structure to achieve the short-focus and high-resolution effect.

In the embodiment of the present application, after the surface shape of the first lens 1 is optimized, in consideration of the processing difficulty and cost, it is more preferable to set the conic coefficient (Coin Constant), i.e., K, of the first lens 1₁The value is, for example, designed to be [ -10, 10 [)]And a radius R of the Fresnel surface of the first lens 2>23mm。

In some examples of the present application, the surface-type combination of the second lens 2 and the first lens 1 may be the same, and a narrow air space is maintained between the two.

For example, the third surface 21 of the second lens 2 is a fresnel surface, and the fourth surface 22 of the second lens 2 is provided as an aspherical surface (further, the fourth surface 11 is also a convex surface).

The second lens 2 is also a positive lens, and is located between the first lens 1 and the third lens 3, and the second lens 2 is disposed closer to the first lens 1.

Optionally, the third surface 21 and the fourth surface 22 of the second lens 2 are plated with Anti-Reflective coating (AR). The reflection light is reduced by the antireflection film, so that the transmittance of light on the two surfaces of the second lens 2 is increased.

In addition, in the embodiment of the present application, the second lens 2 also has the following parameters.

In some examples of the application, the radius R of the third surface 21 of the second lens 2₃Satisfies the following absolute value: 20mm ≤ Abs (R)₃) Less than or equal to 40 mm; radius R of the fourth surface 22 of the second lens 2₄Satisfies the following absolute value: 80mm ≤ Abs (R)₄) Less than or equal to 100 mm; the conic coefficient K of the third surface 21 and the fourth surface 22₂Satisfies the following absolute value: abs (K)₂)≤10。

In the embodiment of the present application, after the surface shape of the second lens 2 is optimized, in consideration of the processing difficulty and cost, it is more preferable to set the conic coefficient (Coin Constant), i.e., K, of the second lens 2₂The value is designed to be [ -10, 10 [)]And the radius of the Fresnel surface of the second lens 2>23mm。

In some examples of the present application, the optical powers of the first lens 1 and the second lens 2 are both positive; the first lens 1, the second lens 2, and the third lens 3 are located on the same optical axis.

That is, the first lens 1 and the second lens 2 are both positive lenses, and can provide a larger optical power for the whole optical system in cooperation with the design of the fresnel surface.

As shown in fig. 2, light emitted from the display screen 4 enters the second lens 2 (positive lens) as incident light after passing through the third lens 3 (positive lens), the incident light converges after passing through the second lens 2 and then enters the first lens 1, and the first lens 1 is still a converging positive lens and enters the human eye 5 for imaging after passing through the incident light transmission of the first lens 1. The whole optical path structure does not relate to an optical path folding scheme and is a direct transmission type optical path structure.

In some examples of the present application, as shown in fig. 1 and 2, the third lens 3 is a DOE lens including a fifth surface 31 and a sixth surface 32;

one of the fifth surface 31 and the sixth surface 32 is a binary diffractive surface, and the other of the fifth surface 31 and the sixth surface 32 is an aspheric surface; wherein, the aspheric surface of the third lens 3 and the aspheric surface of the second lens 2 are adjacently arranged.

For example, in the optical system, the third lens 3 may be designed such that a binary diffraction surface is adjacent to the aspheric surface, which is the fourth surface 22 of the second lens 2, and the effects of a large FOV, a short TTL, and low chromatic aberration can be similarly achieved. However, it is more preferable that the aspherical surface of the third lens 3 and the aspherical surface of the second lens 2 are disposed adjacent to each other, and the binary diffraction surface of the third lens 3 and the light-emitting surface of the display screen 4 are disposed adjacent to each other.

Optionally, an Anti-Reflective coating (AR) is coated on both the fifth surface 31 and the sixth surface 32.

After the two surfaces of the third lens element 3 are respectively plated with the antireflection film, the antireflection film can be used to reduce the reflected light, so as to increase the transmittance of the light on the two surfaces of the third lens element 3.

In the scheme of the embodiment of the present application, an optical system is optimally designed, wherein the characteristics of short TTL, large FOV and low chromatic aberration are well achieved by using the fresnel surface + aspheric surface (convex surface) of the first lens 1 and the second lens 2 in combination with the binary diffraction surface + aspheric surface combination of the third lens 3.

In addition, in the embodiment of the present application, the third lens 3 further has the following parameters.

In some examples of the application, the radius R of the fifth surface 31 of the third lens 3₅Satisfies the following absolute value: 100mm ≤ Abs (R)₅) Less than or equal to 140 mm; radius R of sixth surface 32 of said third lens 3₆ToThe pair of values satisfies: 80mm ≤ Abs (R)₆) Less than or equal to 120 mm; the conic coefficient K of the fifth surface 31 and the sixth surface 32₃Satisfies the following absolute value: abs (K)₃)≤10。

In the embodiment of the present application, after the surface shape of the third lens 3 is optimized, in consideration of the processing difficulty and cost, it is preferable that the conic coefficient (Coin Constant), i.e., K, of the third lens 3 is set₂The value is designed to be [ -10, 10 [)]And the radius of the Fresnel surface of the third lens 3>23mm。

In the embodiments of the present application, it is necessary to set the surface shape parameters within a certain range in consideration of the processing of the lens surface shape, otherwise, the processing accuracy is low or the risk of cutting is raised (this is because the processing of the tooth shape is difficult, and the inclination angle and the operation of the processing are more difficult as the acute angle of the tooth shape is smaller). Also because of this, the value of the conic coefficient K is preferably set in the range of [ -10, 10], and the R value of the fresnel surface is 23mm or more.

In the scheme provided by the embodiment of the application, the first lens 1 and the second lens 2 are both in a mode of combining an aspheric surface and a fresnel surface, and the third lens 3 is in a mode of combining an aspheric surface and a diffraction surface, and then low dispersion and high resolution of an optical path structure can be realized based on selection and matching of materials with different refractive indexes and abbe numbers.

In the optical system scheme provided by the embodiment of the present application, the optical system includes a display screen 4, and the first lens 1, the second lens 2, and the third lens 3; wherein, the display screen 4 is used as a display light source; the first lens 1 and the second lens 2 are designed to be aspheric (convex surface) + fresnel surface positive lenses, and two surface shapes of the third lens 3 close to the display screen 4 side are designed to be aspheric + diffraction surfaces (binary diffraction surfaces), and antireflection film (AR) plating is performed on each surface of the three lenses, and hardening film hardening + antireflection film processing is performed on the first surface 21 (the surface facing human eyes 5) of the first lens 1. On the basis, as shown in fig. 2:

incident light emitted by the display screen 4 enters the third lens 3 through a sixth surface 32 (binary diffraction surface) of the third lens 3 plated with an antireflection film, the transmitted light passes through the third lens 3 and then enters the second lens 2, antireflection films are also plated on two surfaces of the second lens 2, so that the incident light is converged by the second lens 2 and then enters the first lens 1, the first lens 1 is still a converged positive lens, and the incident light passes through the first lens 1 and then enters human eyes 5 for imaging. The whole optical system has no light path folding, and the surfaces of all the lenses are coated with antireflection films, so that the light transmission efficiency is high.

In some examples of the present application, a first interval T is provided between the first lens 1 and the second lens 2₁Said first interval T₁T is set to be more than or equal to 0.2mm₁≤1mm。

In some examples of the present application, a second interval T is provided between the second lens 2 and the third lens 3₂Said second interval T₂Is set to be less than or equal to T of 0.5mm₁≤1.5mm。

In the solution provided by the embodiment of the present application, an air space with a narrow size is provided between the first lens 1 and the second lens 2; meanwhile, a narrow air space is also provided between the second lens 2 and the third lens 3. In the scheme of the application, through the optimized design of the air space between the lenses, the miniaturization of the whole optical system is facilitated.

In addition, if a display screen 4 is further provided in the optical system, the distance between the lenses needs to be considered after the lenses are arranged properly, and the distance between the third lens 3 and the display screen 4 is also considered.

Wherein the third lens 3 is arranged close to one side of the display screen 4.

For example, a third interval T is provided between the third lens 3 and the display screen 4₃。

Optionally, the third interval T₃T is set to be more than or equal to 5mm₂≤15mm。

In some examples of the present application, the first lens 1 and the second lens 2 are made of the same material and are both made of PMMA (acrylic material or organic glass material); the third lens 3 is a COP material.

In the present embodiment, for each lens (i.e., the first lens 1, the second lens 2, and the third lens 3), a combination of materials having a high refractive index and a high and low abbe number is selected and optimally designed in terms of material selection based on consideration of a short focal length and chromatic aberration.

The first lens 1, the second lens 2, and the third lens 3 are not limited to the above materials, and may be made of other materials, for example, COC material, COP material, OKP material, glass material, and the like.

In some examples of the present application, the first lens 1 has a central thickness value h₁Comprises the following steps: h is not less than 3mm₁Less than or equal to 5 mm; the center thickness h of the second lens 2₂Comprises the following steps: h is not less than 3mm₂Less than or equal to 5 mm; a center thickness h of the third lens 3₃Comprises the following steps: h is not less than 5mm₃≤8mm。

The thickness of each lens is not too thick, which is also beneficial to reducing the weight of the whole light path structure.

In some examples of the application, the effective focal length f of the first lens 1₁Comprises the following steps: f is not less than 25mm₁≤35mm；

Focal length f of the second lens 2₂Comprises the following steps: f is not less than 35mm₂≤45mm；

Focal length f of the third lens 3₃Comprises the following steps: f is not less than 50mm₃≤65mm。

In the scheme of the application, the first lens 1, the second lens 2 and the third lens 3 are matched and combined, so that the optical system has the characteristic of short focus.

Provided is a short-focus optical system. The whole optical system is not provided with a folded light path, is a direct-transmission type optical system and can realize high-definition imaging.

The following is an application example of the scheme provided by the embodiments of the present application:

(1) a 100 degree field of view is achieved in cooperation with the 1.4inch display screen 4.

(2) The distortion is less than 30%, and the field curvature is less than 0.55 mm.

(3) The color difference is less than 16 um. The virtual image distance is 2000 mm.

(4) The spot size of the optical system is less than 70um, and clear imaging of a visible light wave band (450 nm-630 nm) is realized. The effective focal length of the whole optical system is 14.97 mm.

Example 1

Embodiment 1 provides an optical system in which the structural parameters are shown in tables 1 and 2.

The optical Surface numbers (Surface) sequentially numbered from the human eye 5 (stop) to the display screen 4, the curvatures (C) of the respective optical surfaces on the optical axis, the distances (T) of the respective optical surfaces from the human eye 5 (stop) to the display screen 4 on the optical axis to the subsequent optical Surface, and the even aspheric coefficient α are shown in table 1 and table 2, respectively₂、α₃、α₄。

Wherein, the aspheric surface coefficient can satisfy the following equation:

in formula (1): z is a coordinate along the optical axis, Y is a radial coordinate in units of lens length, C is curvature (1/R), K is a conic Coefficient (cone Constant), α i is a Coefficient of each high-order term, 2i is a high-order power of aspheric surface (the order of the optical Coefficient), and the design of the present application considers the smoothness of field curvature and the spherical Coefficient without high-order terms to 4 th order.

TABLE 1

TABLE 2

The performance of the optical system provided in example 1 above is reflected by the following parameters:

as shown in FIG. 3, the spot size is at maximum 1.0F for a maximum field of view, with a maximum value < 68.2 μm;

as shown in fig. 4, the RGB wavelengths of the field curvature in the T & S direction are all less than 0.55mm, and the maximum distortion is less than 30% at the maximum viewing field;

as shown in FIG. 5, the maximum dispersion of RGB is the maximum position of the field of view, the total RGB is 450 nm-610 nm, and the LCA is 15.6 μm.

In the optical system provided in embodiment 1, the weight of the first lens 1 is: 4.88g, the weight of the second lens 2 is 5.52 g; the weight of the third lens 3 was 6.53g, and the total weight of the three lenses was 16.93 g.

The embodiments of the present application provide a short-focus optical system, but do not involve folding the optical path therein

(1) The ultra-short focus of the optical system is realized by adjacently arranging the two Fresnel surfaces;

(2) the low dispersion of the optical system is achieved with a binary diffraction surface.

The head mounted display device is, for example, a VR device.

In the above embodiments, the differences between the embodiments are described in emphasis, and different optimization features between the embodiments can be combined to form a better embodiment as long as the differences are not contradictory, and further description is omitted here in consideration of brevity of the text.

Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present application. It will be appreciated by those skilled in the art that modifications can be made to the above embodiments without departing from the scope and spirit of the present application. The scope of the application is defined by the appended claims.

Claims

1. An optical system comprising a third lens (3), a second lens (2) and a first lens (1) arranged in that order along the direction of propagation of incident light;

2. The optical system according to claim 1, wherein two adjacent surfaces of the first lens (1) and the second lens (2) are fresnel surfaces.

3. The optical system according to claim 2, characterized in that the first lens (1) comprises a first surface (11) and a second surface (12), the second lens (2) comprises a third surface (21) and a fourth surface (22);

the second surface (12) and the third surface (21) are arranged adjacently and are Fresnel surfaces; the first surface (11) and the fourth surface (22) are both aspheric.

4. The optical system according to any one of claims 1 to 3, characterized in that the optical power of the first lens (1) and the second lens (2) are both positive;

the first lens (1), the second lens (2) and the third lens (3) are located on the same optical axis.

5. The optical system according to claim 3, characterized in that the third lens (3) is a DOE lens comprising a fifth surface (31) and a sixth surface (32);

one of the fifth surface (31) and the sixth surface (32) is a binary diffractive surface, and the other of the fifth surface (31) and the sixth surface (32) is an aspheric surface;

wherein the aspheric surface of the third lens (3) and the aspheric surface of the second lens (2) are adjacently arranged.

6. The optics of claim 1System, characterized in that a first space T is provided between the first lens (1) and the second lens (2)₁Said first interval T₁Is set to be less than or equal to T of 0.2mm₁≤1mm。

7. Optical system according to claim 1, characterized in that a second space T is provided between the second lens (2) and the third lens (3)₂Said second interval T₂Is set to be less than or equal to T of 0.5mm₂≤1.5mm。

8. Optical system according to claim 1, characterized in that the effective focal length f of the first lens (1)₁Comprises the following steps: f is not less than 25mm₁≤35mm；

A focal length f of the second lens (2)₂Comprises the following steps: f is not less than 35mm₂≤45mm；

A focal length f of the third lens (3)₃Comprises the following steps: f is not less than 50mm₃≤65mm。

9. The optical system according to claim 1, wherein the first lens (1) and the second lens (2) are made of the same material and are made of PMMA (polymethyl methacrylate);

the third lens (3) is a COP material.

10. A head-mounted display device, characterized in that: the method comprises the following steps:

an optical system as claimed in any one of claims 1 to 9.