Preparation method of optical system, optical system and near-to-eye display device

Abstract

The invention provides a preparation method of an optical system, the optical system and a near-to-eye display device.The optical system comprises a Fresnel lens, the Fresnel lens comprises a Fresnel surface, the Fresnel surface is provided with an ineffective surface, and at least part of the ineffective surface is provided with a super surface layer; the reflectivity of the metasurface layer to visible light with an incident angle of 0-30 degrees is 0-15%, and the incident angle is an included angle between light rays incident to the metasurface layer and the ineffective surface. Compared with the prior art, the optical system disclosed by the invention can simultaneously meet the requirements of high light efficiency, lightness, thinness and low stray light.

Description

Technical Field

[0001] This disclosure relates to the field of optical technology. More specifically, it relates to a method for fabricating an optical system, the optical system itself, and a near-eye display device. Background Technology

[0002] In Virtual Reality (VR) technology, optical systems need to meet the requirements of a large field of view (FOV), a large eyebox, and a thin and light design.

[0003] The mainstream optical systems in current VR devices include direct-through aspherical lens systems, pancake folded optical path systems, and direct-through Fresnel lens systems. However, none of these optical systems can simultaneously meet the requirements of high light efficiency, thinness, and low stray light. Summary of the Invention

[0004] The purpose of this disclosure is to provide a method for fabricating an optical system, an optical system, and a near-eye display device, so as to suppress stray light and improve imaging quality while achieving high luminous efficiency and thinness of the optical system.

[0005] To achieve the above objectives, the present disclosure adopts the following technical solution:

[0006] The first aspect of this disclosure provides an optical system including a Fresnel lens, the Fresnel lens including a Fresnel surface having an ineffective surface, at least a portion of the ineffective surface having a metasurface layer, the metasurface layer having a reflectivity of 0 to 15% for visible light with an incident angle of 0 to 30°, the incident angle being the angle between the light ray incident on the metasurface layer and the ineffective surface.

[0007] Optionally, the metasurface layer has a reflectivity of 0 to 9% for visible light with an incident angle of 0 to 30°.

[0008] Optionally, the metasurface layer includes a substrate and nanostructures arrayed on one side of the surface of the substrate. The materials of the substrate and the nanostructures are selected from silver, gold, aluminum and titanium, respectively. The shape of the nanostructures is one of ring, square and V-shape, and the period of the nanostructures is 300nm to 500nm.

[0009] Optionally, the nanostructure is a nanoring, the height of the nanoring is in the range of 135nm to 145nm, the inner diameter of the nanoring is in the range of 160nm to 300nm, and the outer diameter of the nanoring is in the range of 295nm to 305nm.

[0010] Optionally, the length of the metasurface layer in the direction of the central axis of the Fresnel lens is 0.3 mm to 0.5 mm.

[0011] Optionally, the Fresnel surface includes a plurality of concentrically arranged annular protrusions, each annular protrusion having an ineffective surface and an effective surface. The effective surface is used to deflect and focus incident light rays, and the angle between the ineffective surface and the central axis of the Fresnel lens ranges from -5° to 5°.

[0012] Optionally, the height of each annular protrusion is the same, and the length of the metasurface layer disposed on each ineffective surface is the same along the central axis of the Fresnel lens; or

[0013] The width of each of the annular protrusions is the same, and the length of the metasurface layer disposed on each ineffective surface in the direction of the central axis of the Fresnel lens is positively correlated with the height of the annular protrusion.

[0014] Optionally, the optical system includes a first lens, a second lens, a third lens, and a fourth lens stacked sequentially. The second lens and the fourth lens are Fresnel lenses. The first lens is a biconcave aspherical lens. The third lens is an aspherical lens and includes a concave surface and a convex surface. The surface of the second lens opposite to the Fresnel surface is an aspherical convex surface. The surface of the fourth lens opposite to the Fresnel surface is an aspherical concave surface. The aspherical convex surfaces of the first lens and the second lens are adjacent. The Fresnel surface of the second lens is adjacent to the convex surface of the third lens. The concave surface of the third lens is adjacent to the Fresnel surface of the fourth lens.

[0015] Optionally, the optical power of the first lens, the second lens, the third lens, and the fourth lens satisfies the following:

[0016] 1.6<f1 / F<1.8, -80<f2 / F<-70, 0.5<f3 / F<1, -0.8<f4 / F<-0.5, -50<f2 / f1<-40, -1<f4 / f3<-0.7, and -76<(f1+f2+f3+f4) / F<-74;

[0017] Wherein, f1 represents the optical power of the first lens, f2 represents the optical power of the second lens, f3 represents the optical power of the third lens, f4 represents the optical power of the fourth lens, and F represents the equivalent focal length of the optical system.

[0018] A second aspect of this disclosure provides a method for fabricating an optical system, comprising the following steps:

[0019] A Fresnel lens is fabricated, the Fresnel lens comprising a Fresnel surface, the Fresnel surface having an ineffective surface;

[0020] A metasurface layer is fabricated using nanoimprint technology. The metasurface layer includes a substrate and an array of nanostructures distributed on a surface on one side of the substrate. The metasurface layer has a reflectivity of 0-15% for visible light with an incident angle of 0-30°, where the incident angle is the angle between the light ray incident on the metasurface layer and the ineffective surface.

[0021] The metasurface layer is bonded to at least a portion of the invalid surface.

[0022] A third aspect of this disclosure provides a near-eye display device, including a display module and an optical system as described above, wherein the optical system is disposed on the light-emitting side of the display module and is used to deflect and focus the light emitted by the display module onto the eye movement region.

[0023] The beneficial effects of this disclosure are as follows:

[0024] The optical system of this disclosure provides a metasurface layer on the ineffective surface of a Fresnel lens. The metasurface layer has a reflectivity of less than 15% for visible light with an incident angle of 0 to 30°, which can effectively suppress stray light generated on the ineffective surface of the Fresnel lens and improve image quality. Furthermore, the Fresnel lens has the characteristics of high light efficiency and thinness. Therefore, this optical system can simultaneously meet the requirements of high light efficiency, thinness, and low stray light. Attached Figure Description

[0025] The specific embodiments of this disclosure will be described in further detail below with reference to the accompanying drawings.

[0026] Figure 1 A schematic diagram illustrating stray light generated by the ineffective surface of a through-type Fresnel lens in related technologies;

[0027] Figure 2 This is a schematic diagram of the structure of an embodiment of the optical system provided in this disclosure;

[0028] Figure 3 To utilize Figure 2 A schematic diagram showing how the optical system focuses incident light rays onto the eye movement region;

[0029] Figure 4 This is a schematic diagram of the structure of an embodiment of the Fresnel lens provided in this disclosure;

[0030] Figure 5 This is a schematic diagram of the structure of an embodiment of the metasurface layer provided in this disclosure;

[0031] Figure 6 The curves show the relationship between the reflectivity of the metasurface layer and the inner diameter of the nanoring as well as the wavelength of the incident light.

[0032] Figure 7The curves show the relationship between the reflectivity and absorptivity of the metasurface layer for visible light of different wavelengths when the incident angle is 0°.

[0033] Figure 8 The curves show the relationship between the reflectivity of the metasurface layer for visible light of different wavelengths and incident angles when the incident angle is greater than 0° and less than or equal to 30°.

[0034] Figure 9 Schematic diagram of the imaging effect before and after applying a metasurface layer to the ineffective surface;

[0035] Figure 10 This is a schematic diagram of another embodiment of the optical system provided in this disclosure;

[0036] Figure 11 A flowchart of an embodiment of the method for fabricating the optical system provided in this disclosure. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0038] Unless otherwise defined, the technical or scientific terms used in this disclosure shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms “first,” “second,” and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms “an,” “a,” or “the,” and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms “including,” “comprising,” or “containing,” and similar terms mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. The terms “connected,” “linked,” or similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The terms “upper,” “lower,” “left,” and “right,” etc., are used only to indicate relative positional relationships, and these relative positional relationships may change accordingly when the absolute position of the described objects changes.

[0039] In traditional VR optical solutions, the through-type aspherical lens system has advantages such as low design and manufacturing difficulty, high luminous efficacy (usually greater than 90%), and no stray light. However, the overall system length and thickness are usually greater than 35mm, which is not conducive to the product's thinness. The pancake folded optical path system has the advantages of better imaging quality and a thinner overall system length, usually less than or equal to 30mm, but the luminous efficacy is lower, usually less than 25%. The through-type Fresnel lens system has the advantages of high luminous efficacy (usually greater than 80%) and thinness, but the ineffective surface of the Fresnel lens will generate more stray light, affecting the imaging quality.

[0040] Please refer to Figure 1 , Figure 1 A schematic diagram illustrating stray light generated at the ineffective surface of a through-type Fresnel lens, as shown below. Figure 1 As shown, when light enters the ineffective surface, due to its high reflectivity, some of the light is reflected into the effective surface, resulting in stray light entering the eye. To suppress stray light, related technologies have proposed placing a black light-blocking layer on the ineffective surface. However, the black light-blocking layer still has a high reflectivity. Specifically, the reflectivity of the black light-blocking layer for incident light with an incident angle of 0° is around 5%, and for incident light with an incident angle of 30°, the reflectivity is greater than 15%. Therefore, strong stray light still exists on the ineffective surface, leading to poor imaging. In other words, existing optical solutions cannot simultaneously meet the requirements of high luminous efficiency, thinness, and no stray light.

[0041] To address the aforementioned technical problems, this disclosure provides an optical system, please refer to... Figures 2 to 3 , Figure 2 This is a schematic diagram of the structure of an embodiment of the optical system provided in this disclosure. Figure 3 To utilize Figure 2 The diagram shows how the optical system focuses incident light onto the eye-tracking region (also known as the Eyebox region).

[0042] like Figures 2 to 3 As shown, the optical system includes a Fresnel lens 10, which includes a Fresnel surface 110. The Fresnel surface 110 has an ineffective surface 110a. At least a portion of the ineffective surface 110a is provided with a metasurface layer 120. The metasurface layer 120 has a reflectivity of 0 to 15% for visible light with an incident angle of 0 to 30°. The incident angle is the angle between the light ray incident on the metasurface layer 120 and the ineffective surface 110a.

[0043] For example, such as Figure 2 As shown, the angle of incidence is Figure 2 The midpoint angle θ is shown.

[0044] The wavelength range of visible light is 450nm to 650nm. In this embodiment of the metasurface layer 120, for any wavelength of light within the wavelength range of 450nm to 650nm, when the light is incident at any angle within the range of 0° to 30°, the reflectivity of the metasurface layer 120 is less than 15%.

[0045] Please refer to Figure 4 , Figure 4 This is a schematic diagram of the Fresnel lens structure, as shown below. Figure 4 As shown, the Fresnel lens 10 includes multiple concentric circles of increasing size. Each concentric circle includes an elliptical arc at its center and a protrusion between adjacent concentric circles. This protrusion includes serrated arcs, and the serrated arcs and the central elliptical arc form a convex lens structure. Compared to traditional lens structures, the Fresnel structure 10 decomposes the curved surface structure of a traditional lens into multiple concentric rings, each ring performing an independent lens function. This design allows the edge portion of the lens to retain the necessary optical curvature, while the central portion is eliminated. Therefore, the overall thickness can be significantly reduced, as well as the amount of material used, resulting in a substantial weight reduction of up to 50%. Consequently, the weight and thickness of the Fresnel lens are much smaller than those of traditional lenses.

[0046] In this lens, the surface of the Fresnel lens 10 that is machined into a sawtooth ring structure (concentric stepped teeth) is typically referred to as the Fresnel surface 110. The other surface opposite the Fresnel surface 110 is typically designed as a conventional optical surface, such as a plane, spherical surface, or aspherical surface. For example, in... Figure 2 In the embodiment shown, the other surface opposite the Fresnel surface 110 is an aspherical convex surface.

[0047] Optionally, the Fresnel surface 110 includes a plurality of concentrically arranged annular protrusions. Each annular protrusion has an ineffective surface 110a and an effective surface 110b. The effective surface 110b is used to deflect and focus incident light. Specifically, the effective surface 110b refers to the inclined working surface (i.e., the slope surface of the teeth) of the annular protrusion, which is the optical functional area that actually participates in the deflection of light. The effective surface 110b is used to image the light. The ineffective surface 110a refers to the part that does not participate in optical modulation and only serves as a mechanical support structure. The connecting surface or transition surface between two adjacent effective surfaces 110b is the ineffective surface 110a. When light passes through the ineffective surface 110a, stray light will be generated, affecting the image quality.

[0048] In this embodiment of the disclosure, at least a portion of the invalid surface 110a is provided with a metasurface layer 120. This means that in the Fresnel lens 10, at least one annular protrusion of the invalid surface 110a is provided with a metasurface layer 120, and the metasurface layer 120 can cover all or part of the invalid surface 110a. In specific implementation, the position of the metasurface layer 120 can be adjusted according to the stray light suppression effect. In this embodiment of the disclosure, the metasurface layer 120 and the invalid surface 110a have the same size, that is, the invalid surface 110a is completely covered by the metasurface layer 120.

[0049] In traditional through-type Fresnel lens systems, when a black light-shielding layer is used, the reflectivity of the black light-shielding layer for visible light of different wavelengths at an incident angle of 30° is greater than 15%, resulting in poor stray light suppression. However, in the embodiment of this disclosure, the metasurface layer 120 has a reflectivity of less than 15% for visible light at incident angles of 0–30°. Therefore, most of the light entering the ineffective surface 110a is absorbed, and the stray light entering the effective surface after reflection by the metasurface layer 120 is greatly reduced. It has a better blocking effect than the black light-shielding layer, effectively suppressing stray light and improving glare. Figure 2 The dashed line with arrows indicates that the light rays incident on the invalid surface 110a will not form stray light, thus improving the image quality.

[0050] Compared with related technologies, the optical system of this disclosure provides a metasurface layer on the ineffective surface of the Fresnel lens. The metasurface layer has a reflectivity of less than 15% for visible light with an incident angle of 0 to 30°, which can effectively suppress stray light generated on the ineffective surface of the Fresnel lens and improve image quality. In addition, the Fresnel lens has the characteristics of high light efficiency and thinness. Therefore, this optical system can simultaneously meet the requirements of high light efficiency, thinness, and low stray light.

[0051] In some embodiments, the angle between the ineffective surface 110a and the central axis O-O' of the Fresnel lens 10 ranges from -5° to 5°, that is, the ineffective surface 110a is tilted at a small angle relative to the central axis O-O'. In specific implementations, the angle between the ineffective surface 110a and the central axis O-O' can be determined according to the actual application scenario.

[0052] Optionally, the angle between the invalid surface 110a and the central axis O-O' of the Fresnel lens 10 is 0°.

[0053] At this point, the ineffective surface 110a is parallel to the central axis O-O', which can also be understood as the ineffective surface 110a being parallel to the thickness direction of the Fresnel lens 10. The angle between the incident ray and the central axis O-O' of the Fresnel lens 10 is the same as the aforementioned incident angle θ, that is... Figure 2 The incident angle θ shown is equal to the angle between the incident ray and the central axis O-O' (e.g., Figure 3 Angle θ1 is shown.

[0054] When a Fresnel lens is applied to a near-eye display device, the angle between the incident light and the central axis O-O' of the Fresnel lens 10 is a small angle range, typically 0 to 30° or slightly greater than 30°. By setting the ineffective surface 110a parallel to the central axis O-O' of the Fresnel lens 10, the incident light can enter the ineffective surface 110a at a small angle range. Since the reflectivity of the ineffective surface 110a for visible light in the range of 0 to 30° is less than 9%, the stray light generated by the ineffective surface 110a can be effectively reduced.

[0055] Optionally, the metasurface layer 110 has a reflectivity of 0 to 9% for visible light with an incident angle of 0 to 30°. That is, for any wavelength of light within the wavelength range of 450nm to 650nm, when the light is incident on the metasurface layer 120 at any angle within the range of 0 to 30°, the reflectivity of the metasurface layer 120 is less than 9%.

[0056] In practice, by changing the shape, size, period, and material parameters of the nanostructures on the metasurface layer 120, the reflectivity of the metasurface layer 120 for visible light with an incident angle of 0 to 30° can be reduced to less than 9%.

[0057] In some embodiments, the metasurface layer 120 includes a substrate 1210 and nanostructures 1220 arrayed on a surface on one side of the substrate 1210. The materials of the substrate 1210 and the nanostructures 1220 are selected from silver, gold, aluminum and titanium, respectively. The shape of the nanostructures 1220 is one of ring, square and V-shape, and the period of the nanostructures is 300nm to 500nm.

[0058] It is understood that the substrate 1210 and nanostructure 1220 of this embodiment can also be other metallic materials, and are not limited to the materials mentioned in the examples above. Similarly, the shape of the nanostructure 1220 can also be other symmetrical structures, and is not limited to the shapes mentioned in the examples above.

[0059] Optionally, the nanostructure 1220 is a nanoring, the height of the nanoring is in the range of 135nm to 145nm, the inner diameter of the nanoring is in the range of 160nm to 300nm, the outer diameter of the nanoring is in the range of 295nm to 305nm, the substrate 1210 is made of silver, and the nanoring is made of titanium (Ti).

[0060] For example, please refer to Figure 5 , Figure 5 This is a schematic diagram of the structure of one embodiment of the metasurface layer. Figure 5 The left side of the middle diagram (a) shows the three-dimensional structure of the metasurface layer at a nanostructure. Figure 5 The diagram on the right (b) shows a top view of the metasurface layer, as shown below. Figure 5 As shown, the nanostructure 1220 adopts a Ti nanoring, the thickness H of the substrate 1210 is 100 nm, the period P of the nanostructure 1220 is 400 nm, the height h of the nanoring ranges from 135 nm to 145 nm, the inner diameter d of the nanoring ranges from 160 nm to 300 nm, and the outer diameter D of the nanoring ranges from 295 nm to 305 nm.

[0061] Here, the period P can be understood as the distance between the center points of adjacent nanostructures 1220. Each period P contains one nanostructure 1220. The inner diameter d represents the diameter of the inner circle of the nanoring, and the outer diameter D represents the diameter of the outer circle of the nanoring. By adjusting the geometric parameters of the nanostructure 1220, the absorptivity and reflectivity of the metasurface layer to incident light can be changed.

[0062] The relationship between the reflectivity of the metasurface layer and the half-inner radius of the nanoring as well as the wavelength of the incident light is shown in the curve. Figure 6 As shown, Figure 6 The horizontal axis represents the wavelength of the incident light, the vertical axis represents half the inner diameter d of the nanoring, and the color represents reflectivity. The inventors further discovered through optical simulations that the metasurface layer 120 exhibits the lowest reflectivity for visible light when the height h = 140 nm, the outer diameter D = 300 nm, and the inner diameter d = 220 nm. Specifically, at an incident angle of 0°, the relationship between the reflectivity and absorptivity of the metasurface layer for different wavelengths of visible light is shown in the curves below. Figure 7 As shown, Figure 7 The graph on the left shows the relationship between wavelength and absorptivity, while the graph on the right shows the relationship between wavelength and reflectivity. Figure 7 As shown, when the incident angle of the incident light is 0° and the wavelength is in the range of 450nm to 650nm, the reflectivity is less than 1% and the absorptivity is greater than 99%. When the incident angle is greater than 0° but less than or equal to 30°, the relationship curves of the reflectivity of the metasurface layer for visible light of different wavelengths and incident angles are shown in the figure. Figure 8 As shown, Figure 8 The horizontal axis represents wavelength, the vertical axis represents the angle of incidence, and the color represents reflectivity. Figure 8 It can be seen that when the incident angle is less than or equal to 30°, the reflectivity is less than 9% in the wavelength range of 450nm to 650nm. The metasurface layer 120 significantly improves stray light, which can improve imaging quality and enhance visual effects.

[0063] The imaging effects before and after setting the metasurface layer 120 on the ineffective surface 110a are as follows: Figure 9 As shown, Figure 9 The left side of the image shows the imaging effect without a metasurface layer, while the right side shows the imaging effect with a metasurface layer. It can be seen that after setting a metasurface layer of 120, the trailing at the dots is basically eliminated and invisible, significantly improving the imaging quality.

[0064] In this embodiment of the disclosure, the Fresnel lens can adopt either a structure with equal height or equal width.

[0065] In one possible implementation, the height of each of the annular protrusions is the same, and the length of the metasurface layer disposed on each ineffective surface is the same in the direction of the central axis of the Fresnel lens.

[0066] For example, such as Figure 4 As shown in Figure (b), it is a cross-sectional view of Fresnel lens 10 at A-A'. Fresnel lens 10 adopts an equal height structure, that is, the height of each annular protrusion is the same, and the width of the annular protrusion at different positions in the equal height structure is different. At this time, the dimensions of each ineffective surface 110a on the central axis O-O' are the same.

[0067] Due to manufacturing limitations, the maximum height of each tooth in the Fresnel lens 10 is 0.5 mm, and the tooth height range is typically 0.3 mm to 0.5 mm. Since the dimensions of the metasurface layer 120 on the central axis O-O' vary with the tooth height, for a Fresnel lens 10 with a uniform height structure, the dimensions of the metasurface layer 120 on each ineffective surface 110a can be set to a value between 0.3 mm and 0.5 mm. That is, the length of the metasurface layer 120 on the central axis O-O' of the Fresnel lens thickness ranges from 0.3 mm to 0.5 mm.

[0068] The aperture D0 of the Fresnel lens 10 is generally around 30mm to 40mm. If the Fresnel lens 10 includes N (e.g., N=10) annular protrusions, that is, N tooth-shaped structures, then the average tooth width is D0 / N=3mm to 4mm.

[0069] In one possible implementation, the width of each of the annular protrusions is the same, and the length of the metasurface layer disposed on each ineffective surface in the direction of the central axis of the Fresnel lens is positively correlated with the height of the annular protrusion.

[0070] For example, such as Figure 4As shown in Figure (c), which is a cross-sectional view of the Fresnel lens 10 at A-A', the Fresnel lens 10 adopts a constant width structure. The width of the annular protrusions is the same at different positions, but the tooth height is different, that is, the height of each annular protrusion is different. For the ineffective surface 110a in different annular protrusions, the larger the tooth height, the larger the dimension of the metasurface layer 120 disposed on it in the direction of the central axis O-O'.

[0071] For example, a metasurface layer 120 is provided in the entire area of ​​the invalid surface 110a. In this case, the dimension of the metasurface layer 120 provided on each invalid surface 110a in the direction of the central axis O-O' of the Fresnel lens is the same as the height of the annular protrusion.

[0072] Similarly, due to manufacturing limitations, the thickness of the metasurface layer 120 in the direction of the central axis O-O' of the Fresnel lens ranges from 0.3 mm to 0.5 mm. Correspondingly, the tooth width is related to the aperture D0 of the Fresnel lens 10 and the number of teeth, and the tooth width is typically 3 mm to 4 mm.

[0073] In this embodiment, the optical system may include one or more Fresnel lenses. In addition to Fresnel lenses, the optical system may also include one or more conventional lens structures.

[0074] For example, in Figure 3 In the embodiment shown, the optical system includes a Fresnel lens 10.

[0075] In a specific example, the Fresnel surface 110 has a radius of curvature greater than -19 mm, the surface of the Fresnel lens 10 opposite to the Fresnel surface 110 is an aspherical convex surface with a radius of curvature less than 100 mm, the lens thickness of the Fresnel lens 10 is less than 5 mm, the field of view is 60°, the radial length of the eye movement area is 8 mm, and the angle θ1 between the light emitted by the display module and the central axis O-O' of the Fresnel lens 10 is 21.047°.

[0076] In some embodiments, as Figure 10As shown, the optical system includes a first lens Lens1, a second lens Lens3, a third lens Lens4, and a fourth lens Lens4 stacked sequentially. The second lens Lens2 and the fourth lens Lens4 are Fresnel lenses. The first lens Lens1 is a biconcave aspherical lens. The third lens Lens3 is an aspherical lens including a concave surface and a convex surface. The surface of the second lens Lens2 opposite to the Fresnel surface is an aspherical convex surface. The surface of the fourth lens Lens4 opposite to the Fresnel surface is an aspherical concave surface. The aspherical convex surfaces of the first lens Lens1 and the second lens Lens2 are adjacent. The Fresnel surface of the second lens Lens2 is adjacent to the convex surface of the third lens Lens3. The concave surface of the third lens Lens3 is adjacent to the Fresnel surface of the fourth lens Lens4.

[0077] Figure 10 In the embodiment shown, the optical system includes four lenses, two of which are Fresnel lenses 10 as described above, and two of which have a conventional lens structure.

[0078] Specifically, the first lens, lens1, is a double aspherical lens with two concave surfaces. The first lens, lens1, provides a positive optical power f1 to converge the incident light rays, which are also the light rays emitted by the display module.

[0079] The second lens, lens2, is a Fresnel lens, and the surface facing away from the first lens, lens1, is a Fresnel surface, denoted as Fresnel surface 1. The surface close to the first lens, lens1, is an aspherical convex surface. The second lens, lens2, provides a negative optical power f2 to significantly diverge the incident light rays and expand the field of view (FOV), for example, by expanding the field of view to 90°.

[0080] The third lens, lens 3, is a double aspherical lens, with the surface near the second lens, lens 2, being convex and the surface away from lens 2 being concave. Specifically, the third lens, lens 3, is a positive meniscus lens, providing a positive optical power f3. The third lens, lens 3, is used to converge light rays and correct the aberrations of the second lens, lens 2.

[0081] The fourth lens, lens 4, is a Fresnel lens, with its surface near the third lens, lens 3, being a Fresnel surface, denoted as Fresnel surface 2, and its surface away from the third lens, lens 3, being an aspherical concave surface. The fourth lens, lens 4, provides a negative optical power f4, used to control the angle of the outgoing light rays, causing the light rays to be deflected before entering the eye movement region.

[0082] This embodiment utilizes Zemax software to design an optical system. During the design process, the angle at which light rays are incident on each lens can be changed by adjusting the structural parameters of each lens. Under the premise of ensuring optical parameters (such as field of view, total length of the optical system, etc.) and imaging effect, the angle between the incident light ray and the central axis O-O' of the Fresnel lens is controlled as close as possible to within 30° or slightly greater than 30° to reduce stray light generated by the ineffective surface.

[0083] In a specific example, the field of view of the optical system is 90°, the radial dimension of the eye-tracking region is 8 mm, and the total length of the optical system is less than 30 mm. The optical powers of the first, second, third, and fourth lenses satisfy the following conditions: 1.6 < f1 / F < 1.8, -80 < f2 / F < -70, 0.5 < f3 / F < 1, -0.8 < f4 / F < -0.5, -50 < f2 / f1 < -40, -1 < f4 / f3 < -0.7, and -76 < (f1 + f2 + f3 + f4) / F < -74; where f1 represents the optical power of the first lens. f2 represents the optical power of the second lens, f3 represents the optical power of the third lens, f4 represents the optical power of the fourth lens, F represents the equivalent focal length of the optical system, and the angle θ2 between the light rays emitted from the first lens 1 and the Fresnel surface 1 of the second lens 2 and the central axis O-O' of the second lens 2 is 17.647°. The angle θ3 between the light rays emitted from the third lens 3 and the Fresnel surface 2 of the fourth lens 4 and the central axis O-O' of the fourth lens 4 is 30.449°.

[0084] It is understood that the optical system of this disclosure embodiment may also be other structures including the Fresnel lens shown above, and this disclosure embodiment will not provide examples of each one.

[0085] Based on the same inventive concept, a second aspect of this disclosure provides a method for fabricating an optical system, as shown in the embodiments above, specifically, as follows: Figure 11 As shown, the preparation method includes the following steps:

[0086] Step S101: Prepare a Fresnel lens, the Fresnel lens including a Fresnel surface, the Fresnel surface having an ineffective surface.

[0087] Step S102: A metasurface layer is fabricated using nanoimprint technology. The metasurface layer includes a substrate and nanostructures arrayed on a surface on one side of the substrate. The metasurface layer has a reflectivity of 0-15% for visible light with an incident angle of 0-30°. The incident angle is the angle between the light ray incident on the metasurface layer and the ineffective surface.

[0088] For example, the preparation process of the metasurface layer includes: (1) providing a substrate and pretreating the substrate, the substrate material being Ag; (2) spin-coating a nanoimprinting adhesive on the substrate surface, aligning the pre-made nanoring pattern template with the imprinting adhesive, applying pressure to make the template sink into the adhesive layer to form a ring cavity structure, curing the imprinting adhesive by ultraviolet exposure to fix the nanoring pattern, vertically separating the pre-made nanoring pattern template and the imprinting adhesive, retaining only the nanoring cavity of the imprinting adhesive; (3) depositing a titanium film on the surface of the imprinting adhesive, the titanium film covering the nanoring cavity of the imprinting adhesive; (4) dissolving the imprinting adhesive layer, the titanium film on the adhesive layer falling off with the adhesive, retaining only the titanium ring structure in the cavity.

[0089] Step S103: Adhere the metasurface layer to at least a portion of the invalid surface.

[0090] It should be noted that the metasurface layer in this embodiment is an independent structure, which can be applied to optical systems employing single or multiple Fresnel lenses in related technologies. In specific implementations, the metasurface layer can suppress stray light and improve image quality by being adhered and fixed to the ineffective surface of the Fresnel lens.

[0091] Based on the same inventive concept, a third aspect of this disclosure provides a near-eye display device, including a display module and an optical system as described above, wherein the optical system is disposed on the light-emitting side of the display module and is used to deflect and focus the light emitted by the display module onto the eye movement region.

[0092] The near-eye display device can be a virtual reality device or an augmented reality device, which can use the optical system of the present disclosure to perform imaging and improve the imaging effect.

[0093] The display module can be a top-emitting organic light-emitting diode (OLED) display module. It is understood that other types of top-emitting display modules can also be configured as needed, such as top-emitting quantum dot light-emitting diode (QLED) or micro light-emitting diode (Micro LED) display modules.

[0094] Obviously, the above embodiments of this disclosure are merely examples for clearly illustrating this disclosure, and are not intended to limit the implementation of this disclosure. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all implementation methods here. Any obvious variations or modifications derived from the technical solutions of this disclosure are still within the protection scope of this disclosure.

Claims

1. An optical system, characterized in that, The invention includes a Fresnel lens, the Fresnel lens comprising a Fresnel surface having an ineffective surface, and at least a portion of the ineffective surface having a metasurface layer, the metasurface layer having a reflectivity of 0 to 15% for visible light with an incident angle of 0 to 30°, the incident angle being the angle between the light ray incident on the metasurface layer and the ineffective surface.

2. The optical system according to claim 1, characterized in that, The metasurface layer has a reflectivity of 0-9% for visible light with an incident angle of 0-30°.

3. The optical system according to claim 2, characterized in that, The metasurface layer includes a substrate and nanostructures arrayed on one side of the substrate. The materials of the substrate and the nanostructures are selected from silver, gold, aluminum and titanium, respectively. The shape of the nanostructures is one of ring, square and V-shape, and the period of the nanostructures is 300nm to 500nm.

4. The optical system according to claim 3, characterized in that, The nanostructure is a nanoring, with a height ranging from 135 nm to 145 nm, an inner diameter ranging from 160 nm to 300 nm, and an outer diameter ranging from 295 nm to 305 nm.

5. The optical system according to claim 4, characterized in that, The length of the metasurface layer in the direction of the central axis of the Fresnel lens is 0.3 mm to 0.5 mm.

6. The optical system according to claim 1, characterized in that, The Fresnel surface includes a plurality of concentric annular protrusions, each annular protrusion having an ineffective surface and an effective surface. The effective surface is used to deflect and focus incident light rays, and the angle between the ineffective surface and the central axis of the Fresnel lens ranges from -5° to 5°.

7. The optical system according to claim 6, characterized in that, The height of each of the aforementioned annular protrusions is the same, and the length of the metasurface layer disposed on each ineffective surface is the same along the central axis of the Fresnel lens; or The width of each of the annular protrusions is the same, and the length of the metasurface layer disposed on each ineffective surface in the direction of the central axis of the Fresnel lens is positively correlated with the height of the annular protrusion.

8. The optical system according to claim 1, characterized in that, The optical system includes a first lens, a second lens, a third lens, and a fourth lens stacked sequentially. The second and fourth lenses are Fresnel lenses. The first lens is a biconcave aspherical lens. The third lens is an aspherical lens and includes a concave surface and a convex surface. The surface of the second lens opposite to the Fresnel surface is an aspherical convex surface. The surface of the fourth lens opposite to the Fresnel surface is an aspherical concave surface. The aspherical convex surfaces of the first and second lenses are adjacent. The Fresnel surface of the second lens is adjacent to the convex surface of the third lens. The concave surface of the third lens is adjacent to the Fresnel surface of the fourth lens.

9. The optical system according to claim 8, characterized in that, The optical power of the first lens, the second lens, the third lens, and the fourth lens satisfies the following: 1.6<f1 / F<1.8, -80<f2 / F<-70, 0.5<f3 / F<1, -0.8<f4 / F<-0.5, -50<f2 / f1<-40, -1<f4 / f3<-0.7, and -76<(f1+f2+f3+f4) / F<-74; Wherein, f1 represents the optical power of the first lens, f2 represents the optical power of the second lens, f3 represents the optical power of the third lens, f4 represents the optical power of the fourth lens, and F represents the equivalent focal length of the optical system.

10. A method for fabricating an optical system, characterized in that, Includes the following steps: A Fresnel lens is fabricated, the Fresnel lens comprising a Fresnel surface, the Fresnel surface having an ineffective surface; A metasurface layer is fabricated using nanoimprint technology. The metasurface layer includes a substrate and an array of nanostructures distributed on a surface on one side of the substrate. The metasurface layer has a reflectivity of 0-15% for visible light with an incident angle of 0-30°, where the incident angle is the angle between the light ray incident on the metasurface layer and the ineffective surface. The metasurface layer is bonded to at least a portion of the invalid surface.

11. A near-eye display device, characterized in that, The device includes a display module and an optical system as described in any one of claims 1 to 9, wherein the optical system is disposed on the light-emitting side of the display module and is used to deflect and focus the light emitted by the display module onto the eye-tracking region.

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