Metasurface lens structure and preparation method therefor, and display device

Abstract

A metasurface lens structure and a preparation method therefor, and a display device. The metasurface lens structure (1) comprises a plurality of phase modulation units (10). The phase value distribution of each phase modulation unit (10) satisfies a first phase formula, i.e., formula (1), wherein ψ is the phase value of each phase modulation unit (10), λ is the wavelength of incident light, x and y are coordinates of each phase modulation unit (10) in the metasurface lens structure (1) using the geometric center of the metasurface lens structure (1) as a circle center, f is the focal length of the metasurface lens structure (1), u is a normalized radius coordinate of the phase modulation unit (10) and is a rotation angle coordinate of a corresponding position of the phase modulation unit (10), and L and ε are spiral phase parameters. The metasurface lens structure (1) can solve the problem that existing multi-focal-surface geometric lens structures are thick and complex.

Description

Metasurface lens structure and preparation method thereof, and display device Technical Field

[0001] The present disclosure belongs to the field of display technology, and particularly relates to a metasurface lens structure, a preparation method thereof, and a display device. Background Art

[0002] Near-eye display devices, such as virtual reality (VR) and augmented reality (AR), have been gradually applied to various fields, including display, gaming, and healthcare. Near-eye display technology used to implement VR / AR is also receiving increasing attention and research. Near-eye display devices typically use an eyepiece to form a magnified virtual image on a display panel (usually at a distance of 1 meter from the eye). This magnified virtual image creates an immersive viewing experience, or can be superimposed on a real scene to provide specific, directional information. Summary of the Invention

[0003] The present disclosure aims to solve at least one of the technical problems existing in the prior art, and provides a metasurface lens structure, a preparation method thereof, and a display device.

[0004] In a first aspect, an embodiment of the present disclosure provides a metasurface lens structure, wherein the metasurface lens structure includes: a plurality of phase modulation units; the phase value distribution of each phase modulation unit satisfies a first phase formula; the first phase formula is:

[0005] Wherein, ψ is the phase value of each phase modulation unit, λ is the wavelength of the incident light, x and y are the coordinates of each phase modulation unit in the metasurface lens structure with the geometric center of the metasurface lens structure as the center, f is the focal length of the metasurface lens structure, and u is the normalized radius coordinate of the phase modulation unit. is the rotation angle coordinate of the corresponding position of the phase modulation unit, and L and ε are the spiral phase parameters.

[0006] In some embodiments, the phase modulation unit includes: a substrate, a column located on the substrate;

[0007] The refractive index of the pillars is greater than the refractive index of the substrate.

[0008] In some embodiments, a difference between a refractive index of the pillars and a refractive index of the substrate is greater than or equal to 0.5.

[0009] In some embodiments, the material of the substrate includes silicon oxide; the material of the pillar includes at least one of silicon nitride, titanium oxide, and gallium nitride.

[0010] In some embodiments, the phase value of the cylinder satisfies a second phase formula; the second phase formula is:

[0011] in, is the phase value of the cylinder, n eff is the equivalent refractive index, H is the height of the column, and λ is the wavelength of the incident light.

[0012] In some embodiments, the height of the pillars is 500 nm to 800 nm.

[0013] In some embodiments, the pillar is a cylinder, and the radius of the cylinder is 20 nm to 120 nm.

[0014] In some embodiments, the period of the pillars is 200 nm to 300 nm.

[0015] In some embodiments, the phase modulation unit further includes: a filling material located between adjacent columns on the substrate;

[0016] The refractive index of the filling material is smaller than the refractive index of the substrate and smaller than the refractive index of the pillars.

[0017] In some embodiments, the refractive index of the filling material is 1.0 to 1.3.

[0018] In a second aspect, an embodiment of the present disclosure provides a display device, wherein the display device includes the metasurface lens structure provided above.

[0019] In some embodiments, the display device further comprises: a display panel;

[0020] The display panel is located on the light incident side of the metasurface lens structure and displays images corresponding to different depths in a time-sharing or partitioned manner.

[0021] In some embodiments, the distance between the metasurface lens structure and the display panel is less than the focal length of the metasurface lens structure.

[0022] In some embodiments, the distance between the metasurface lens structure and the display panel is between one and two times the focal length of the metasurface lens structure.

[0023] In some embodiments, the display device further comprises: an eyepiece assembly;

[0024] The eyepiece group is located on a side of the metasurface lens structure away from the display panel.

[0025] In a third aspect, an embodiment of the present disclosure provides a method for preparing a metasurface lens structure, wherein the method for preparing the metasurface lens structure comprises:

[0026] sequentially depositing a phase modulation material layer and a hard mask layer on a substrate;

[0027] coating an etching glue layer on the hard mask layer;

[0028] forming a pattern on the etching glue layer by using an electron beam exposure process;

[0029] Transferring the pattern to the hard mask layer and the phase modulation material layer using a dry etching process;

[0030] The hard mask layer is removed to form a plurality of phase modulation units; the phase value distribution of each phase modulation unit satisfies a first phase formula; the first phase formula is:

[0031] Wherein, ψ is the phase value of each phase modulation unit, λ is the wavelength of the incident light, x and y are the coordinates of each phase modulation unit in the metasurface lens structure with the geometric center of the metasurface lens structure as the center, f is the focal length of the metasurface lens structure, and u is the normalized radius coordinate of the phase modulation unit. is the rotation angle coordinate of the corresponding position of the phase modulation unit, and L and ε are the spiral phase parameters.

[0032] In some embodiments, the hard mask layer is removed to form a plurality of pillars to form a plurality of phase modulation units, and then the method further includes:

[0033] A filling material is formed between adjacent columns on the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1a is a schematic diagram of a front view of a metasurface lens structure provided in an embodiment of the present disclosure.

[0035] FIG1b is a schematic side view of a metasurface lens structure provided in an embodiment of the present disclosure.

[0036] Figure 2 is a schematic diagram of the imaging of point sources at different depths passing through a single spiral phase plane.

[0037] FIG3 a is a schematic diagram of the phase distribution of a focusing lens.

[0038] FIG3 b is a schematic diagram of a single spiral phase distribution.

[0039] FIG3 c is a schematic diagram of the phase distribution at various positions in a metasurface lens structure.

[0040] FIG4 is a schematic structural diagram of a phase modulation unit provided in an embodiment of the present disclosure.

[0041] FIG. 5 is a schematic diagram showing the corresponding relationship between the radius and the phase value of the phase modulation unit shown in FIG. 4 .

[0042] FIG6 is a schematic diagram showing the arrangement of 7×7 phase modulation units in the center of the metasurface lens structure provided in an embodiment of the present disclosure.

[0043] FIG7 is a schematic diagram of the display principle of a display device provided by an embodiment of the present disclosure.

[0044] FIG8 a is a schematic diagram showing the corresponding relationship between the axial distance and the angular coordinate.

[0045] FIG8 b is a schematic diagram of image source information with different angle offsets and image points with different axial distances.

[0046] FIG9 is a schematic diagram of the display principle of another display device provided by an embodiment of the present disclosure.

[0047] FIG10 is a schematic diagram of the display principle of another display device provided in an embodiment of the present disclosure.

[0048] FIG11 is a flow chart of a method for preparing a metasurface lens structure provided in an embodiment of the present disclosure.

[0049] 12a to 12g are schematic diagrams of intermediate structures corresponding to various steps in the method for preparing the metasurface lens structure shown in FIG11 . DETAILED DESCRIPTION

[0050] In order to enable those skilled in the art to better understand the technical solutions of the present disclosure, the present disclosure is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0051] Unless otherwise defined, the technical or scientific terms used in this disclosure should have the usual meanings understood by people with ordinary skills in the field to which this disclosure belongs. The words "first", "second" and similar words used in this disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one", "an" or "the" do not indicate a quantity limitation, but rather indicate the existence of at least one. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0052] The scales of the figures in this disclosure can be used as a reference for actual processes, but are not limited to such. For example, the width-to-length ratio of the channel, the thickness and spacing of the various film layers, and the width and spacing of the various signal lines can be adjusted according to actual needs. The number of pixels in the display substrate and the number of sub-pixels in each pixel are not limited to the numbers shown in the figures. The figures described in this disclosure are merely schematic structural diagrams, and one embodiment of this disclosure is not limited to the shapes or values ​​shown in the figures.

[0053] In this specification, for convenience, words and phrases indicating orientation or positional relationships, such as "middle," "upper," "front," "back," "vertical," "horizontal," "top," "bottom," "inside," and "outside," are used to illustrate the positional relationships of constituent elements with reference to the accompanying drawings. This is merely for the convenience of describing this specification and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, it should not be understood as a limitation of the present disclosure. The positional relationships of constituent elements may be appropriately changed according to the direction in which each constituent element is described. Therefore, the words and phrases are not limited to those described in the specification and may be appropriately replaced according to the circumstances.

[0054] In this specification, "parallel" means a state where the angle formed by two straight lines is greater than -10° and less than 10°, and therefore includes a state where the angle is greater than -5° and less than 5°. In addition, "perpendicular" means a state where the angle formed by two straight lines is greater than 80° and less than 100°, and therefore includes a state where the angle is greater than 85° and less than 95°.

[0055] In this specification, "film" and "layer" can be interchanged. For example, "conductive layer" can sometimes be replaced by "conductive film". Similarly, "insulating film" can sometimes be replaced by "insulating layer". In this specification, the "same-layer arrangement" used refers to a structure formed by patterning two (or more) structures through the same patterning process, and their materials can be the same or different. For example, the materials of the precursors forming the multiple structures arranged in the same layer are the same, and the materials finally formed can be the same or different.

[0056] The eyepieces in current VR / AR devices can only achieve single-focal-length imaging. When rendering 3D images (containing information at varying depths), when the human eye observes objects near and far, a mismatch between the cues received by the brain regarding eye accommodation and convergence occurs, leading to a vergence-accommodation conflict (VAC). This creates eye strain and is one of the main reasons for the low wearing comfort of AR / VR displays.

[0057] Currently, the integrated imaging light field 3D optical path solution of microlens array + eyepiece group is mainly used to reproduce 3D images, or a mechanical structure is superimposed to change the focal length of the lens to achieve multi-focal plane 3D display. However, both will cause resolution loss or increase the system volume, thereby affecting the near-eye display effect.

[0058] In order to solve at least one of the above-mentioned technical problems, the embodiments of the present disclosure provide a metasurface lens structure, a preparation method thereof, and a display device. The metasurface lens structure, a preparation method thereof, and a display device provided by the embodiments of the present disclosure will be further described in detail below in combination with the accompanying drawings and specific implementation methods.

[0059] In the first aspect, an embodiment of the present disclosure provides a metasurface lens structure. FIG1a is a schematic diagram of a front view structure of a metasurface lens structure provided by an embodiment of the present disclosure, and FIG1b is a schematic diagram of a side view structure of a metasurface lens structure provided by an embodiment of the present disclosure. As shown in FIG1a and FIG1b, the metasurface lens structure 1 includes: a plurality of phase modulation units 10; the phase value distribution of each phase modulation unit 10 satisfies a first phase formula; the first phase formula is:

[0060] Wherein, ψ is the phase value of each phase modulation unit 10, λ is the wavelength of the incident light, x and y are the coordinates of each phase modulation unit 10 in the metasurface lens structure 1 with the geometric center of the metasurface lens structure 1 as the center, f is the focal length of the metasurface lens structure 1, and u is the normalized radius coordinate of the phase modulation unit 10. is the rotation angle coordinate of the corresponding position of the phase modulation unit 10, and L and ε are the spiral phase parameters.

[0061] A metasurface is an electromagnetic wave modulation device constructed from a unit structure of high-refractive-index materials or metal materials whose scale is smaller than the wavelength of the incident wave. The arrangement and design of the relevant unit structures can be used to achieve a variety of electromagnetic wave corresponding effects.

[0062] Metalens is the most widely used metasurface device in the field of imaging and display. Its phase value distribution can be expressed as:

[0063] Among them, ψ1 is the phase value of each position in the metasurface lens, λ is the wavelength of the incident light, x and y are the coordinates of each phase modulation unit in the metasurface lens structure 1 with the geometric center of the metasurface lens structure 1 as the center of the circle, and f is the focal length of the metasurface lens structure 1, which can achieve a geometric lens modulation effect equivalent to that with a focal length of f.

[0064] The single-helix point spread function (SSPF) phase is a special vortex beam modulation phase that can convert the depth information of the spot into the relative rotation information of the spot on the imaging surface. Its phase distribution can be expressed as:

[0065] Where u is the normalized radius coordinate of the modulation structure, is the rotation angle coordinate of the corresponding position, L and ε are the spiral phase parameters.

[0066] After point light sources at different distances on the axis pass through the single spiral phase structure, the image point's rotation information is presented on the imaging surface. Its energy distribution can be expressed as:

[0067] Among them, r is the relative radius of the image point, is the image point rotation coordinate information, For the structure with entrance pupil radius R, different object distance z obj Relative focus object distance z f The defocus deviation caused by Affects the image point rotation coordinate value When the defocus deviation satisfies ζ<<2πL, there exists ζ=1 / L, and the rotation coordinate transforms 1 radian (1 rad). Figure 2 is a schematic diagram of the imaging of point sources at different depths through a single spiral phase plane. As can be seen from Figure 2, different object distances z obj The deviation value from the focal length of the element can be converted into the rotation deviation of the image point on the image plane.

[0068] The metasurface lens structure 1 provided by the embodiment of the present disclosure can be constructed by superimposing the lens phase ψ1 and the single spiral phase ψ2, and is arranged by a metasurface unit structure having a certain order phase expression value within the range of 0 to 2π. The phase value distribution of each phase modulation unit satisfies the first phase formula (such as the expression of the above-mentioned first phase formula), that is, ψ=ψ1+ψ2; ψ1 and ψ2 are respectively the lens phase and the single spiral modulation phase that satisfy the above-mentioned formula (1) and formula (2). Taking the lens radius r as 0.4mm and the focal length as 6mm as an example, the focusing lens phase distribution can be calculated by formula (1) as shown in Figure 3a, and the single spiral phase distribution can be calculated by formula (2) with L=8 and ε=0.5 (according to the image point separation optimization design) as shown in Figure 3b. Therefore, by performing phase superposition by ψ=ψ1+ψ2, the phase arrangement of each phase modulation unit 10 in the metasurface lens structure 1 can be obtained as shown in Figure 3c.

[0069] Among them, in order to use the metasurface lens structure 1 for phase expression, the phase is gridded and discretely calculated according to the period size of the phase modulation unit 10 in the metasurface lens structure 1, and the phase is folded by taking the remainder of 2ππ (that is, the phase value is classified into the range of 0 to 2π) and then the adjacent assignment is performed according to the number of phase modulation units 10 (taking 8 phase modulation units 10 with a phase covering 2π as an example, the phase after grid partitioning is classified into 1 / 4π, 1 / 2π, 3 / 4π, π, 5 / 4π, 3 / 2π, and 2π), and finally expressed by the corresponding phase modulation unit 10.

[0070] In the metasurface lens structure 1 provided in the embodiment of the present disclosure, the metasurface lens structure 1 can be composed of phase modulation units 10 whose size is smaller than the wavelength of the incident light, arranged according to a certain arrangement rule. The phase modulation unit 10 can accurately modulate the phase of the incident light with its micro-nanostructure optical modulation characteristics, thereby realizing the combination of the imaging function and the light deflection function of the metasurface lens, thereby realizing the effect of converting the image source rotation information into depth information (depth range is 2% to 5% of the focal length), avoiding the VAC effect (convergence accommodation conflict) caused by the human eye accommodation problem. Due to the high design freedom and inherent scale advantage of the metasurface unit (structure thickness of the order of hundreds of nanometers), it can break through the processing difficulty of traditional optical components, is not restricted by traditional geometric optics theory, and can realize arbitrary light field control requirements. Ultra-thin, flat, and aberration-free optical devices can be manufactured on a smaller scale using simple processes. Compared with geometric lens multi-depth of field 3D display solutions such as microlens arrays, free-form surface lens groups, and mechanical zoom lens groups, it has a volume advantage, which is conducive to the integration and lightweight of near-eye display devices.

[0071] FIG4 is a schematic structural diagram of a phase modulation unit provided in an embodiment of the present disclosure. As shown in FIG4 , the phase modulation unit 10 includes: a substrate 101; a column 102 positioned on the substrate 101; the refractive index of the column 102 is greater than the refractive index of the substrate 101. The difference between the refractive index of the column 102 and the refractive index of the substrate 101 is greater than or equal to 0.5. The material of the substrate 101 includes: silicon oxide; the material of the column 102 includes: at least one of silicon nitride, titanium oxide, and gallium nitride. The height of the column 102 is 500 nm to 800 nm. When the column 102 is cylindrical, the radius of the cylinder 102 is 20 nm to 120 nm. The period of the column 102 is 200 nm to 300 nm.

[0072] In an exemplary embodiment, the column 102 may be a circular cylinder. In some possible exemplary embodiments, the column 102 may be an elliptical cylinder, a triangular cylinder, a rectangular cylinder, or a polygonal cylinder, which is not limited in the present disclosure.

[0073] In some embodiments, the phase modulation unit 10 is implemented by a nano-cylinder of an organic or inorganic material with a refractive index n greater than 1.5 constructed on a glass substrate. The higher the refractive index of the material selected for the column 102, the lower the height of the column 102 can be. For example, it is constructed using a silicon nitride SiNx material with a refractive index n of 2.0 to 2.03 (it can also be constructed using materials such as titanium oxide TiO2, gallium nitride GaNx, etc. with a higher refractive index, and the height of the corresponding nano-columns can be reduced), and filled with a low-refractive index material with a refractive index n of 1.0 to 1.3. The phase modulation unit 10 can be a column 102 such as a cylinder or a square column that can achieve scale adjustment in the direction parallel to the substrate 101 (i.e., the horizontal direction), or it can be a column 102 with a fixed horizontal scale and adjustable height.

[0074] The phase value of the cylinder 102 satisfies the second phase formula; the second phase formula is:

[0075] in, is the phase value of the cylinder 102, n eff is the equivalent refractive index, H is the height of the column 102, and λ is the wavelength of the incident light.

[0076] Taking silicon nitride SiNx cylinders with a unit period of 250nm and a height of 600nm as an example, a set of feasible solutions is illustrated. The structural schematic is shown in Figure 4. By changing the radius r of the cylinder, different phase values ​​can be expressed. The specific corresponding relationship is shown in Figure 5. A group of nanocylinders with a radius of 25nm to 120nm can be used to express phase values ​​from 0 to 2π.

[0077] Specifically, the phase modulation unit 10 is composed of approximately 241,008 silicon nitride SiNx nanocylinders constructed on a glass substrate. The specific structure of the nanocylinders can be referred to Figure 4, wherein the period P of the phase modulation unit 10 is 250nm, the height H is 600nm, and the radius r is 25nm to 200nm, wherein circles of different sizes correspond to different phase modulation units 10 (as shown in Figure 1a), that is, nanocylinders of different radii r and the same height H are arranged at equal intervals on the glass substrate.

[0078] Taking the central 7×7 area as an example, the structural coordinate distribution, the corresponding point phase value, and the corresponding nanocylinder radius are shown in Table 1-3:

[0079] Table 1 - Coordinates of the 7×7 phase modulation unit at the center of the metasurface lens structure (unit: μm)

[0080] Table 2 - Phase values ​​of the 7×7 phase modulation unit at the center of the metasurface lens structure

[0081] Table 3 - Radius of the 7×7 phase modulation unit at the center of the metasurface lens structure (unit: nm)

[0082] Figure 6 is a schematic diagram of the arrangement of the 7×7 phase modulation units in the center of the metasurface lens structure provided by an embodiment of the present disclosure. Specifically, the phase values ​​of each position in the metasurface lens structure 1 can be calculated by the first phase formula based on the coordinate positions in Table 1, as shown in Table 2. The structure of the phase modulation unit 10 shown in Figure 4 is further matched to obtain the radius of the cylinder 102 of the phase modulation unit 10 at the corresponding coordinate position, that is, the structural arrangement corresponding to Table 1 in Table 3 is obtained, and finally the local structural arrangement effect as shown in Figure 6 can be obtained.

[0083] The metasurface lens structure 1 provided in the embodiment of the present disclosure can achieve the effect of converting image source rotation information into depth display (depth range is 2% to 5% of the focal length) under the condition of ensuring that the lens transmittance is greater than 90%. At the same time, the overall aperture of the metasurface lens structure 1 is 0.4mm and the thickness is only 0.2mm to 0.5mm. The main thickness comes from the glass substrate. Compared with geometric lens multi-depth of field 3D display solutions such as microlens arrays, free-form surface lens groups, and mechanical zoom lens groups, it has a volume advantage, which is conducive to the integration and lightweight of near-eye display devices.

[0084] In the second aspect, an embodiment of the present disclosure provides a display device, which includes a metasurface lens structure 1 as provided in any of the above embodiments. Figure 7 is a schematic diagram of the display principle of a display device provided by an embodiment of the present disclosure. As shown in Figure 7, the display device also includes: a display panel 2; the display panel 2 is located on the light incident side of the metasurface lens structure 1, and displays images corresponding to different depths in a time-sharing or partitioned manner. Figure 7 takes the partitioned display of images corresponding to different depths as an example for illustration.

[0085] The metasurface lens structure 1 in the display device provided by the embodiment of the present disclosure has a single spiral adjustment characteristic, which can be used to perform imaging at different rotation coordinate values ​​according to different on-axis distances. By adding different rotation coordinate information of the image source, the imaging effect at different on-axis distances can be achieved, thereby realizing a 3D image display with depth information. Taking the metasurface lens structure 1 with a lens diameter of 10mm and an image distance of 100mm (spiral phase parameters L=8 and ε=0.5) as an example, as shown in Figure 7, the target image plane z is set to the target image plane z. f The discrete image planes z1 to z n The information at the object plane is offset according to the rotation offset corresponding to its distance (as shown in Figures 8a and 8b). According to the lens phase, the image target surface satisfies the lens object image relationship. According to the spiral phase The image source rotates one cycle (-3.14 rad to 3.14 rad) to achieve an axial coordinate offset range of ±1.7 mm. Through spatial multiplexing (partitioned display) or temporal multiplexing (framed display) at the display panel, a 3D display effect is achieved within a 3mm depth range near the target image plane. By varying the spiral phase parameters and lens parameters, the depth of field can be further expanded (for example, decreasing the lens numerical aperture (NA) increases the depth of field).

[0086] Images of different depths are displayed in partitions through the display panel 2, and a 3D display effect is constructed by performing a primary imaging through the metasurface lens structure 1. Then, the corresponding eyepiece group 3 (which will be marked in subsequent drawings) can perform a secondary imaging of the 3D image, thereby realizing near-eye 3D display.

[0087] Figure 9 is a schematic diagram of the display principle of another display device provided in an embodiment of the present disclosure. As shown in Figure 9, the display device can specifically be a VR display device, and the distance between the metasurface lens structure 1 and the display panel 2 is less than the focal length f of the metasurface lens structure 1.

[0088] The metasurface lens structure 1 is used to image the display panel 2's multi-depth image information at corresponding depths, achieving 3D imaging. The distance h between the metasurface lens structure 1 and the display panel 2 is less than the metasurface lens structure's focal length f, resulting in a magnified virtual image. The metasurface lens structure 1 can be a single lens or an array of metasurface lens structures with the same NA.

[0089] The display panel 2 can display images of different depths in different zones / time divisions, and can specifically be any one or more of the following: a liquid crystal display (LCD) panel, an organic light emitting diode (OLED) display panel, a light emitting diode (LED) display panel, an inorganic electroluminescent display (EL) panel, a field emission display (FED) panel, a surface-conduction electron-emitter display (SED) panel, a plasma display panel (PDP), and an electrophoretic display (EPD) panel. For near-eye display, the optimal size requirement is less than or equal to 1 inch.

[0090] The eyepiece assembly 3 can be a single lens or a lens group, such as a Fresnel lens or a Pancake lens group, and is used to magnify the 3D primary image, allowing the 3D image to enter the eye. The lens aperture (and the equivalent aperture of the lens group) is determined by the size of the near-eye display device and the display panel 2, and the imaging field of view (optimally 120°). The focal length is determined by the human eye's comfortable near-eye viewing distance (CDP). The distance between the eyepiece assembly 3 and the metasurface lens structure 1 is determined by the magnification, so that the pixel size of the display panel 2 meets the human eye's resolution requirements (greater than 30PPD, with an optimal value of 60PPD).

[0091] Taking the 1-inch display panel 2 solution as an example, if FOV = 120°, PPD = 60, optimal viewing distance CDP = 1m, system eye distance of 18.8mm, eyepiece group 3 (which can be a pancake optical system) with an equivalent aperture of 25mm and an equivalent NA of 0.66, a microlens array can be designed as a primary 3D image magnification lens group. In this case, the lens phase aperture is 0.22mm and the focal length is 7.919mm, ensuring an overall system magnification of 136, meeting the requirements for optimal eye viewing. The single helix parameters of the microlens array are L = 8 and ε = 0.5, which can achieve a 3D primary image with a depth range of 6.714mm. After secondary imaging, the overall designable depth range can be expanded to 4.7m.

[0092] Figure 10 is a schematic diagram of the display principle of another display device provided in an embodiment of the present disclosure. As shown in Figure 10, the display device can specifically be an AR display device, and the distance between the metasurface lens structure 1 and the display panel 2 is between one times and twice the focal length of the metasurface lens structure 1.

[0093] The metasurface lens structure 1 is used to image the display panel 2's multi-depth image information at corresponding depths, achieving 3D imaging. The distance between the metasurface lens structure 1 and the display panel 2 is between one and two times the focal length of the metasurface lens structure 1, resulting in a reduced 3D image. The metasurface lens structure 1 can be a solid lens or an array of metasurface lens structures with the same NA.

[0094] The display panel 2 can display images of different depths in different zones / time divisions, and can specifically be any one or more of the following: a liquid crystal display (LCD) panel, an organic light emitting diode (OLED) display panel, a light emitting diode (LED) display panel, an inorganic electroluminescent display (EL) panel, a field emission display (FED) panel, a surface-conduction electron-emitter display (SED) panel, a plasma display panel (PDP), and an electrophoretic display (EPD) panel. For near-eye display, the optimal size requirement is less than or equal to 1 inch.

[0095] The eyepiece assembly 3 can be a single lens or a lens group, and can be an imaging lens solution that realizes light path steering, such as a Birdbath lens group or a free-form surface lens group, to transmit the light entering the eye of the 3D primary real image and magnify the image to realize the 3D image entering the eye. The equivalent aperture of the lens group is determined by the size of the near-eye display device and the display panel 2 and the imaging field of view (optimally 120°). The focal length is determined by the human eye's comfortable near-eye viewing distance (CDP). The distance between the eyepiece assembly 3 and the metasurface lens structure 1 is determined by the system magnification, so that the display panel display pixel size meets the human eye's resolution requirements (greater than 30PPD).

[0096] In the third aspect, an embodiment of the present disclosure provides a method for preparing a metasurface lens structure. Figure 11 is a flow chart of a method for preparing a metasurface lens structure provided by an embodiment of the present disclosure. As shown in Figure 11, the method for preparing the metasurface lens structure includes the following steps S101 to S105.

[0097] S101 , sequentially depositing a phase modulation material layer and a hard mask layer on a substrate.

[0098] As shown in FIG12a , a phase modulation material layer 201 made of silicon nitride SiNx material that is highly consistent with the designed metasurface lens structure and a hard mask layer 202 (Hard Mask) can be deposited on the surface of a glass substrate 101 (i.e., the glass cover of the device), and aluminum Al can usually be selected.

[0099] S102, coating an etching glue layer on the hard mask layer.

[0100] As shown in FIG12 b , the material of the etching glue layer 203 can be a special glue for electron beam exposure such as ZEP500.

[0101] S103, forming a pattern on the etched glue layer by using an electron beam exposure process.

[0102] As shown in FIG12 c , a pattern having a shape opposite to that of the phase modulation unit 10 may be formed on the etching resist layer 203 by an electron beam exposure process.

[0103] S104 , transferring the patterned pattern to the hard mask layer and the phase modulation material layer using a dry etching process.

[0104] S105 , removing the hard mask layer to form a plurality of pillars to form a plurality of phase modulation units.

[0105] As shown in Figures 12d to 12f, the pattern on the etchant layer 203 is transferred to the hard mask layer 202 through a dry etching process. After the etchant layer 203 is washed away, the pattern on the hard mask layer 202 is transferred to the phase modulation material layer 201 through another dry etching process. The hard mask layer 202 is then removed to form multiple pillars 102, and the final metasurface lens structure composed of multiple phase modulation units 10 is obtained.

[0106] The phase value distribution of each phase modulation unit 10 satisfies the first phase formula; the first phase formula is:

[0107] Wherein, ψ is the phase value of each phase modulation unit 10, λ is the wavelength of the incident light, x and y are the coordinates of each phase modulation unit 10 in the metasurface lens structure with the geometric center of the metasurface lens structure as the center, f is the focal length of the metasurface lens structure, and u is the normalized radius coordinate of the phase modulation unit. is the rotation angle coordinate of the corresponding position of the phase modulation unit 10, and L and ε are the spiral phase parameters.

[0108] In some embodiments, as shown in FIG. 11 , in step S105 , the hard mask layer is removed to form a plurality of pillars to form a plurality of phase modulation units, and then the process further includes: step S106 , forming a filling material between adjacent pillars on the substrate.

[0109] As shown in Figure 12g, a filling material 103 may be formed between adjacent columns 102. The filling material 103 is a low-refractive index material with a refractive index n of 1.0 to 1.3, which provides structural protection and support without affecting the phase modulation effect.

[0110] It should be noted here that the metasurface lens structure formed by the preparation method of the metasurface lens structure provided by the embodiment of the present disclosure has the same implementation principle as the metasurface lens structure provided by any of the above embodiments, and will not be described in detail here.

[0111] It is understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present disclosure, and the present disclosure is not limited thereto. Those skilled in the art may make various modifications and improvements without departing from the spirit and substance of the present disclosure, and such modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. A metasurface lens structure, wherein: The metasurface lens structure includes: a plurality of phase modulation units; the phase value distribution of each phase modulation unit satisfies a first phase formula; the first phase formula is: Wherein, ψ is the phase value of each phase modulation unit, λ is the wavelength of the incident light, x and y are the coordinates of each phase modulation unit in the metasurface lens structure with the geometric center of the metasurface lens structure as the center, f is the focal length of the metasurface lens structure, and u is the normalized radius coordinate of the phase modulation unit. is the rotation angle coordinate of the corresponding position of the phase modulation unit, and L and ε are the spiral phase parameters.

2. The metasurface lens structure according to claim 1, wherein: The phase modulation unit includes: a substrate, and a column located on the substrate; The refractive index of the pillars is greater than the refractive index of the substrate.

3. The metasurface lens structure according to claim 2, wherein: A difference between a refractive index of the column and a refractive index of the substrate is greater than or equal to 0.

5.

4. The metasurface lens structure according to claim 2, wherein: The material of the substrate includes silicon oxide; the material of the column includes at least one of silicon nitride, titanium oxide, and gallium nitride.

5. The metasurface lens structure according to claim 2, wherein: The phase value of the cylinder satisfies the second phase formula; the second phase formula is: in, is the phase value of the cylinder, n eff is the equivalent refractive index, H is the height of the column, and λ is the wavelength of the incident light.

6. The metasurface lens structure according to claim 2, wherein: The height of the pillars is 500 nm to 800 nm.

7. The metasurface lens structure according to claim 2, wherein: The column is a cylinder, and the radius of the cylinder is 20 nm to 120 nm.

8. The metasurface lens structure according to claim 2, wherein: The period of the columns is 200 nm to 300 nm.

9. The metasurface lens structure according to claim 2, wherein: The phase modulation unit further includes: a filling material located between adjacent columns on the substrate; The refractive index of the filling material is smaller than the refractive index of the substrate and smaller than the refractive index of the pillars.

10. The metasurface lens structure according to claim 9, wherein: The refractive index of the filling material is 1.0 to 1.

3.

11. A display device, wherein: The display device comprises the metasurface lens structure according to any one of claims 1 to 10.

12. The display device according to claim 11, wherein The display device further includes: a display panel; The display panel is located on the light incident side of the metasurface lens structure and displays images corresponding to different depths in a time-sharing or partitioned manner.

13. The display device according to claim 12, wherein: The distance between the metasurface lens structure and the display panel is smaller than the focal length of the metasurface lens structure.

14. The display device according to claim 12, wherein: The distance between the metasurface lens structure and the display panel is between one times the focal length and two times the focal length of the metasurface lens structure.

15. The display device according to claim 13 or 14, wherein: The display device further includes: an eyepiece assembly; The eyepiece group is located on a side of the metasurface lens structure away from the display panel.

16. A method for preparing a metasurface lens structure, wherein: The preparation method of the metasurface lens structure comprises: sequentially depositing a phase modulation material layer and a hard mask layer on a substrate; coating an etching glue layer on the hard mask layer; forming a pattern on the etching glue layer by using an electron beam exposure process; Transferring the pattern to the hard mask layer and the phase modulation material layer using a dry etching process; The hard mask layer is removed to form a plurality of columns to form a plurality of phase modulation units; the phase value distribution of each phase modulation unit satisfies a first phase formula; the first phase formula is: Wherein, ψ is the phase value of each phase modulation unit, λ is the wavelength of the incident light, x and y are the coordinates of each phase modulation unit in the metasurface lens structure with the geometric center of the metasurface lens structure as the center, f is the focal length of the metasurface lens structure, and u is the normalized radius coordinate of the phase modulation unit. is the rotation angle coordinate of the corresponding position of the phase modulation unit, and L and ε are the spiral phase parameters.

17. The method for preparing a metasurface lens structure according to claim 16, wherein: The hard mask layer is removed to form a plurality of pillars to form a plurality of phase modulation units, and then the method further includes: A filling material is formed between adjacent columns on the substrate.

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