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, preparation method thereof and display device TECHNICAL FIELD

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

[0002] Near-eye display devices, such as virtual reality (VR) and augmented reality (AR) devices, have gradually been applied to many fields such as display, game, medical treatment, and the like, and the near-eye display technology for realizing VR / AR has also attracted more and more attention and research. The near-eye display device usually uses an objective lens group to image an image on a display panel (usually an image at a distance of 1 meter from the eye, an enlarged virtual image), and the human eye watches the enlarged virtual image to produce an immersive viewing effect or superimposes a reality scene to realize specific directional information prompts and the like. SUMMARY

[0003] The present disclosure aims to at least solve 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, the present disclosure provides a metasurface lens structure, wherein the metasurface lens structure comprises: a plurality of phase modulation units; a 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 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, u is the normalized radius coordinate of the phase modulation unit, and is the rotation angle coordinate of the corresponding position of the phase modulation unit, and L and ε are helical phase parameters.

[0006] In some embodiments, the phase modulation unit comprises: a substrate, a column on the substrate.

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

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

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

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

[0011] wherein, is the phase value of the column, 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 column is 500 nm to 800 nm.

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

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

[0015] In some embodiments, the phase modulation unit further comprises a filling material located between the columns adjacent to each other on the substrate.

[0016] The refractive index of the filling material is less than the refractive index of the substrate and less than the refractive index of the column.

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

[0018] In a second aspect, the embodiments of the present disclosure provide a display device, wherein the display device comprises the metasurface lens structure provided in the 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 time division or in zones.

[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 focal length and two focal lengths of the metasurface lens structure.

[0023] In some embodiments, the display device further comprises an eyepiece group.

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

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

[0026] depositing a phase modulation material layer and a hard mask layer on the substrate in sequence;

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

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

[0029] transferring the patterned structure to the hard mask layer and the phase modulation material layer by using a dry etching process;

[0030] removing the hard mask layer to form a plurality of phase modulation units, wherein the phase value distribution of each phase modulation unit satisfies a first phase formula, and the first phase formula is:

[0031] wherein ψ is the phase value of each phase modulation unit, λ is the wavelength of 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, 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 helical phase parameters.

[0032] In some embodiments, the removing the hard mask layer to form a plurality of phase modulation units further comprises:

[0033] forming a filling material between the adjacent columns on the substrate. BRIEF DESCRIPTION OF DRAWINGS

[0034] FIG. 1a is a front view structural schematic diagram of a metasurface lens structure according to an embodiment of the present disclosure.

[0035] FIG. 1b is a side view structural schematic diagram of a metasurface lens structure according to an embodiment of the present disclosure.

[0036] FIG. 2 is a schematic diagram of imaging of a point source with different depths by a single helical phase surface.

[0037] FIG. 3a is a schematic diagram of phase distribution of a focusing lens.

[0038] FIG. 3b is a schematic diagram of single helical phase distribution.

[0039] FIG. 3c is a schematic diagram of phase distribution of each position in a metasurface lens structure.

[0040] FIG. 4 is a structural schematic diagram of a phase modulation unit according to an embodiment of the present disclosure.

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

[0042] FIG. 6 is a schematic diagram of the arrangement of 7x7 phase modulation units in the center of a metasurface lens structure according to an embodiment of the present disclosure.

[0043] FIG. 7 is a schematic diagram of the display principle of a display device according to an embodiment of the present disclosure.

[0044] FIG. 8a is a schematic diagram of the correspondence between the axial distance and the angle coordinate.

[0045] FIG. 8b is a schematic diagram of the imaging of image source information with different angle offsets and different axial distances.

[0046] FIG. 9 is a schematic diagram of the display principle of another display device according to an embodiment of the present disclosure.

[0047] FIG. 10 is a schematic diagram of the display principle of yet another display device according to an embodiment of the present disclosure.

[0048] FIG. 11 is a flowchart of a method for manufacturing a metasurface lens structure according to an embodiment of the present disclosure.

[0049] FIGS. 12a-12g are schematic diagrams of intermediate structures in the method for manufacturing a metasurface lens structure shown in FIG. 11. DETAILED DESCRIPTION

[0050] In order for those skilled in the art to better understand the technical solutions of the present disclosure, the present disclosure will be described in further detail below with reference to the drawings and specific embodiments.

[0051] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be understood as the usual meanings understood by those skilled in the art to which the present disclosure belongs. The terms "first", "second", and similar terms used in the present disclosure do not represent any order, number, or importance, but are only used to distinguish different components. Similarly, the terms "one", "an", or "the" and similar terms do not represent a quantity limitation, but represent the existence of at least one. The terms "include" or "contain" and similar terms mean that the elements or objects before the terms encompass the elements or objects listed after the terms and their equivalents, without excluding other elements or objects. The terms "connect" or "connected" and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The terms "up", "down", "left", "right", and the like only represent relative positional relationships, which can change accordingly when the absolute positions of the described objects change.

[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 scheme 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 realize multi-focal 3D display, but it will cause resolution loss or increase in system volume, thereby affecting the near-eye display effect.

[0058] To solve at least one of the above technical problems, the present disclosure provides a metasurface lens structure and a preparation method thereof, and a display device.

[0059] In a first aspect, the present disclosure provides a metasurface lens structure. FIG. 1a is a front view structural schematic diagram of a metasurface lens structure according to an embodiment of the present disclosure, and FIG. 1b is a side view structural schematic diagram of a metasurface lens structure according to an embodiment of the present disclosure. As shown in FIG. 1a and FIG. 1b, 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; and the first phase formula is:

[0060] wherein ψ is the phase value of each phase modulation unit 10, λ is the wavelength of 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, 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 spiral phase parameters.

[0061] A metasurface is an electromagnetic wave modulator constructed by high refractive index material or metal material unit structure with a scale less than the wavelength of incident wave. A variety of electromagnetic wave effects can be achieved by designing the arrangement of the relevant unit structure.

[0062] A metalens is the most widely used device in the imaging and display fields as a metasurface structure. The phase value distribution of the metalens can be expressed as:

[0063] wherein ψ1 is the phase value of each position in the metalens, λ is the wavelength of 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, f is the focal length of the metasurface lens structure 1, and the metalens can achieve the modulation effect of a geometric lens with an equivalent focal length of f.

[0064] Single-helix Point Spread Function (SPSF) phase is a special vortex beam modulation phase, which can convert the depth information of a light spot into the relative rotation information of the light spot on the imaging plane. The phase distribution can be expressed as:

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

[0066] The point light sources located at different distances on the axis present the rotation information of the image points on the imaging plane after passing through the single-helix phase structure, and the energy distribution can be expressed as:

[0067] wherein r is the relative radius of the image point, is the rotation coordinate information of the image point, is the off-focus deviation caused by the different object distances z obj relative to the focal point object distance z f , and finally affects the rotation coordinate value of the image point . When the off-focus deviation satisfies ζ<<2πL, there is ζ=1 / L, and the rotation coordinate is transformed by 1 radian (1 rad). FIG. 2 is a schematic diagram of the imaging of point sources at different depths passing through the single-helix phase plane. As can be seen from FIG. 2, the deviation value caused by the different object distances z obj and the element focal length can be converted into the rotation deviation of the image point on the image plane.

[0068] The super surface lens structure 1 provided by the embodiments of the present disclosure can be constructed by superimposing a lens phase ψ1 and a single-helix phase ψ2, and arranged by a super surface unit structure which can have a phase expression value in a certain order in 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 first phase formula described above), that is, ψ=ψ1+ψ2; ψ1 and ψ2 are lens phases and single-helix modulation phases which satisfy the above formula (1) and formula (2). Taking the lens radius r as 0.4 mm and the focal length as 6 mm as an example, the focusing lens phase distribution can be calculated by formula (1) as shown in FIG. 3a, and the single-helix phase distribution can be calculated by formula (2) with L=8 and ε=0.5 (obtained according to the image point separation optimization design) as shown in FIG. 3b, so that by phase superposition of ψ=ψ1+ψ2, the phase arrangement of each phase modulation unit 10 in the super surface lens structure 1 can be obtained as shown in FIG. 3c.

[0069] In order to use the metasurface lens structure 1 to express the phase, the phase is discretely calculated according to the period size of the phase modulation unit 10 in the metasurface lens structure 1, and after the phase is folded by taking the remainder of 2ππ (that is, the phase value is brought into the range of 0 to 2π), the adjacent assignment conforming to the number of phase modulation units 10 is performed (for example, 8 phase modulation units 10 cover 2π phase, that is, the phase after the grid partition is brought into 1 / 4π, 1 / 2π, 3 / 4π, π, 5 / 4π, 3 / 2π, and 2π), and finally the corresponding phase modulation unit 10 is expressed.

[0070] In the metasurface lens structure 1 provided by the embodiment of the present disclosure, the metasurface lens structure 1 can be arranged and constituted by phase modulation units 10 with a size smaller than the wavelength of incident light according to a certain arrangement rule. The phase modulation unit 10 can accurately modulate the phase of incident light by its micro-nano structure optical modulation characteristics. Therefore, the combination of the imaging function and the light deflection function of the metasurface lens can be realized, so as to realize the effect of converting the rotation information of the image source into depth information (the depth range is 2% to 5% of the focal length), and avoid the VAC effect (vergence-accommodation conflict) caused by the accommodation problem of the human eye. Due to the high design freedom of the metasurface unit and the advantage of the size itself (the structure thickness is hundreds of nanometers), the processing difficulty of traditional optical components can be broken through, and the traditional geometric optics theory is not limited. The arbitrary light field modulation requirement can be realized. The optical device with ultra-thin, flat and no aberration can be manufactured in a smaller scale by using a simple process. Compared with the multi-depth-of-field 3D display scheme of the geometric lens such as the microlens array, the free-form lens group and the mechanical zoom lens group, the metasurface lens has the advantage of small volume, which is conducive to the integration and thinning of the near-eye display device.

[0071] FIG. 4 is a structural schematic diagram of a phase modulation unit provided by an embodiment of the present disclosure. As shown in FIG. 4, the phase modulation unit 10 includes a substrate 101 and a column 102 located 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 a circular column, the radius of the circular column 102 is 20 nm to 120 nm. The period of the column 102 is 200 nm to 300 nm.

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

[0073] In some embodiments, the phase modulation unit 10 is implemented by nanocylinders of organic or inorganic material with a refractive index n greater than 1.5 built on a glass substrate. The higher the refractive index of the selected material of the column 102, the lower the height of the column 102 can be. For example, a silicon nitride SiNx material with a refractive index n of 2.0 to 2.03 is used to build (it can also be built by materials with higher refractive index such as titanium oxide TiO2, gallium nitride GaNx, etc., and the corresponding nanocolumn height can be reduced), and a low refractive material with a refractive index n of 1.0 to 1.3 is used as filling. The phase modulation unit 10 can be a column 102 that can adjust the size in the direction parallel to the substrate 101 (i.e., the horizontal direction), or a column 102 with a fixed size in the horizontal direction and an adjustable height.

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

[0075] wherein, is the phase value of the column 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 a silicon nitride SiNx column with a unit period of 250 nm and a height of 600 nm as an example, a set of feasible schemes is illustrated, and the structural schematic diagram is shown in FIG. 4. By changing the radius r of the column, different phase value expressions can be realized, and the specific corresponding relationship is shown in FIG. 5. A set of nanocolumns with a radius of 25 nm to 120 nm can be used to express a phase value of 0 to 2π.

[0077] Specifically, the phase modulation unit 10 is composed of about 241008 silicon nitride SiNx nanocolumns built on a glass substrate. The specific structure of the nanocolumns can refer to FIG. 4. The period P of the phase modulation unit 10 is 250 nm, the height H is 600 nm, and the radius r is 25 nm to 200 nm. Different sizes of the columns correspond to different phase modulation units 10 (as shown in FIG. 1a), that is, nanocolumns with different radii r and the same height H are arranged at equal intervals on the glass substrate.

[0078] Taking the center 7x7 region as an example, the structure coordinate distribution, the corresponding point phase value, and the corresponding nanocolumn radius are shown in Tables 1-3:

[0079] Table 1-Coordinate values of phase modulation units in the center 7x7 region of the metasurface lens structure (unit: μm)

[0080] Table 2-Phase values of phase modulation units in the center 7x7 region of the metasurface lens structure

[0081] Table 3 - Radius values (unit: nm) of the 7x7 phase modulation units in the center of the metasurface lens structure

[0082] Figure 6 is a schematic diagram of the arrangement of the 7x7 phase modulation units in the center of the metasurface lens structure according to an embodiment of the present disclosure. Specifically, the phase values of each position in the metasurface lens structure 1 can be calculated according to the coordinate positions in Table 1 using the first phase formula, as shown in Table 2. Further, the structure of the phase modulation unit 10 is matched with the structure shown in Figure 4, to obtain the radius of the cylinder 102 of the phase modulation unit 10 at the corresponding coordinate positions, i.e., the structure arrangement corresponding to Table 1 in Table 3, and finally the local structure arrangement effect shown in Figure 6 can be obtained.

[0083] The metasurface lens structure 1 provided by the embodiments of the present disclosure can realize the effect of converting the rotation information of the image source to depth display (the depth range is 2% to 5% of the focal length) while ensuring that the transmittance of the lens is greater than 90%. Meanwhile, the overall aperture of the metasurface lens structure 1 is 0.4 mm, and the thickness is only 0.2 mm to 0.5 mm, and the main thickness is derived from the glass substrate. Compared with the multi-depth-of-field 3D display solutions of geometric lenses such as microlens arrays, free-form lens groups, and mechanical zoom lens groups, the metasurface lens structure 1 has an advantage in volume, which is conducive to the integration and thinning of near-eye display devices.

[0084] In a second aspect, the present disclosure provides a display device, which includes the metasurface lens structure 1 provided by any of the above embodiments. Figure 7 is a schematic diagram of the display principle of a display device according to an embodiment of the present disclosure. As shown in Figure 7, the display device further includes a display panel 2. The display panel 2 is located on the light entrance side of the metasurface lens structure 1, and displays images corresponding to different depths in time division or in zones. In Figure 7, the display of images corresponding to different depths in zones is taken as an example for illustration.

[0085] The metasurface lens structure 1 in the display device provided by the embodiments of the present disclosure has a single-spiral adjustment characteristic, and can image different rotation coordinate values according to different distances on the axis. By adding different rotation coordinate information of the image source, the imaging effect of the metasurface lens structure 1 at different distances on the axis can be realized, thereby realizing the display of a 3D picture with depth information. Taking a metasurface lens structure 1 with a lens aperture of 10 mm and an image distance of 100 mm (spiral phase parameters L = 8 and ε = 0.5) as an example, as shown in Figure 7, the information of the discrete image planes z1 to z f at a certain depth range is based on the target image plane z n According to the lens phase, the image target image plane satisfies the lens object-image relationship According to the spiral phase The image source rotates one cycle (-3.14 rad to 3.14 rad), and the axial coordinate offset range is ±1.7 mm. Through spatial multiplexing (partition display) or time multiplexing (frame display) at the display panel, the 3D display effect of information in the 3 mm depth range near the target image plane is finally realized. By changing the spiral phase parameters and lens parameters, the depth of field range can be further expanded (for example, the numerical aperture (NA) of the lens is reduced, and the depth of field range is increased).

[0086] The display panel 2 displays images of different depths by partition display, and the 3D display effect is constructed by one imaging through the super surface lens structure 1. Then, the corresponding eyepiece group 3 (which will be marked in the subsequent drawings) can perform secondary imaging of the 3D image, thereby realizing near-eye 3D display.

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

[0088] The super surface lens structure 1 is used to image the partition / time multiplexing multi-depth of field image information of the display panel 2 corresponding to different depth points, to realize one 3D imaging. The distance h between the super surface lens structure 1 and the display panel 2 is less than the focal length f of the super surface lens structure 1, so that the 3D image is a magnified virtual image. The super surface lens structure 1 can be a full-surface lens, or an array of super surface lens structures with the same NA.

[0089] The display panel 2 can display images of different depths by partition / time multiplexing. Specifically, it can 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 best size requirement is less than or equal to 1 inch.

[0090] The eyepiece group 3 can be a single lens or a lens group, can be a Fresnel lens or a Pancake lens group, to magnify the 3D primary image to realize 3D image into the eye. The lens aperture (and the equivalent aperture of the lens group) is determined according to the size of the near-eye display device and the display panel 2 and the imaging field of view angle (optimally 120°), the focal length is determined according to the near-eye comfortable viewing distance CDP of the human eye, the distance between the eyepiece group 3 and the super surface lens structure 1 is determined according to the magnification, so that the display panel 2 satisfies the human eye resolution requirement (more than 30 PPD, optimally 60 PPD) of the display pixel size.

[0091] Taking a 1-inch display panel 2 scheme as an example, when FOV=120°, PPD=60, the optimal viewing distance CDP=1m, the system eye distance is 18.8mm, the equivalent aperture of the eyepiece group 3 (which can be a Pancake optical system) is 25mm, and the equivalent NA is 0.66, the microlens array can be designed as a primary 3D image magnification lens group, at this time the lens phase aperture is 0.22mm, the focal length is 7.919mm, and the overall system magnification is 136, which meets the optimal eye viewing requirement. The single helix parameter of the microlens array is L=8 and ε=0.5, which can realize a 3D primary image with a depth range of 6.714mm, and after secondary imaging, the overall designable depth range can be expanded to 4.7m.

[0092] FIG. 10 is a display principle schematic diagram of another display device provided by the embodiment of the present disclosure, as shown in FIG. 10, the display device can be specifically an AR display device, and the distance between the super surface lens structure 1 and the display panel 2 is between one focal length and two focal lengths of the super surface lens structure 1.

[0093] The super surface lens structure 1 is used to image the partitioned / time-sharing multi-depth-of-field image information of the display panel 2 corresponding to different depth points, to realize primary 3D imaging. The distance between the super surface lens structure 1 and the display panel 2 is between one focal length and two focal lengths of the super surface lens structure 1, so that the 3D image is a reduced real image, and the super surface lens structure 1 can be a full-surface lens or an array of super surface lens structures with the same NA.

[0094] The display panel 2 can display images of different depths in a partitioned or time-division manner, and can 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. The best size requirement for near-eye display is less than or equal to 1 inch.

[0095] The eyepiece group 3 can be a single lens or a lens group, and can be a Birdbass lens group or a free-form lens group to realize light path turning and imaging lens scheme, to transmit and magnify the 3D primary image into the eye, and realize 3D image into the eye. The equivalent aperture of the lens group is determined according to the size of the near-eye display device and the display panel 2 and the imaging field of view angle (best 120°), the focal length is determined according to the comfortable viewing distance CDP of the human eye, and the distance between the eyepiece group 3 and the metasurface lens structure 1 is determined according to the system magnification, so as to meet the requirement that the display pixel size of the display panel meets the resolution requirement of the human eye (more than 30 PPD).

[0096] In a third aspect, the present disclosure provides a preparation method of a metasurface lens structure. FIG. 11 is a flowchart of the preparation method of the metasurface lens structure, which includes the following steps S101-S105.

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

[0098] As shown in FIG. 12a, a phase modulation material layer 201 composed of silicon nitride SiNx material and a hard mask layer 202 (Hard Mask) can be deposited on the surface of a glass substrate 101 (i.e., the glass cover plate of the device), which is consistent with the designed metasurface lens structure. The hard mask layer 202 can be made of aluminum Al.

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

[0100] As shown in FIG. 12b, the material of the etching glue layer 203 can be ZEP500 or the like special glue for electron beam exposure.

[0101] S103, forming a patterned structure on the etching glue layer by using an electron beam exposure process.

[0102] As shown in FIG. 12c, a patterned structure opposite to the shape of the phase modulation unit 10 can be formed on the etching glue layer 203 by using an electron beam exposure process.

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

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

[0105] As shown in FIGS. 12d-12f, the patterned structure on the etching glue layer 203 is transferred to the hard mask layer 202 by using a dry etching process. After the etching glue layer 203 is washed away, the patterned structure on the hard mask layer 202 is transferred to the phase modulation material layer 201 by using a dry etching process. Then, the hard mask layer 202 is removed to form a plurality of columns 102, and a final super surface lens structure composed of a plurality of phase modulation units 10 is obtained.

[0106] The phase value distribution of each phase modulation unit 10 satisfies a 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 incident light, x and y are the coordinates of each phase modulation unit 10 in the super surface lens structure with the geometric center of the super surface lens structure as the center, f is the focal length of the super surface lens structure, 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, S105, the hard mask layer is removed to form a plurality of columns to form a plurality of phase modulation units, and then further comprising: S106, forming a filling material between adjacent columns on the substrate.

[0109] As shown in FIG. 12g, a filling material 103 can be formed between adjacent columns 102. The filling material 103 is a low-refractive material with a refractive index n of 1.0-1.3, which does not affect the phase modulation effect while playing a structural protection and support role.

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

[0111] It can be understood that the above embodiments are only exemplary embodiments adopted for illustrating the principles of the present disclosure, and the present disclosure is not limited thereto. Various modifications and improvements can be made by those of ordinary skill in the art without departing from the spirit and essence of the present disclosure, and these modifications and improvements are also considered to be within the protection scope 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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