Metasurface reflector, projection device, and near-eyewear device

Abstract

To provide a metasurface reflector, etc., capable of reducing chromatic aberration. [Solution] The metasurface reflector 1 comprises a first metal layer 30 and a second metal layer 10 stacked in the z-axis direction, a dielectric layer 20 provided between the first metal layer 30 and the second metal layer 10 in the z-axis direction, and a color filter layer 8 covering the surface of the second metal layer 10 opposite to the dielectric layer 20. The dielectric layer 20 has a main surface 21 on which the second metal layer 10 is provided. The metasurface reflector 1 is divided into a plurality of unit regions arranged in the x-axis direction along the main surface 21 and in the y-axis direction along the main surface 21 and intersecting the x-axis direction. The second metal layer 10 includes metal units 18 provided in all or some of the unit regions of the plurality of unit regions.

Description

Technical Field

[0001] The present invention relates to a metasurface reflector, a projection device, and a near-eye wearable device.

Background Art

[0002] Currently, eyeglass-type terminals are being considered in AR (Augmented Reality) and VR (Virtual Reality). In particular, in recent years, a retinal scanning display (hereinafter also referred to as a "near-eye wearable device") that allows a user to view an image by imaging light scanned on the user's retina has attracted attention.

[0003] In a retinal scanning display, generally, three colors of visible light emitted from a red laser diode, a green laser diode, and a blue laser diode are combined on one optical axis through a planar lightwave circuit (PLC) or the like. The combined three-color visible light is scanned by a MEMS (Micro Electro Mechanical Systems) mirror and reflected by a half mirror in front of the user's eye, and then enters the user's pupil. When this incident light forms an image on the user's retina, the user can view the image (see, for example, Patent Document 1).

[0004] A metasurface reflector is used as the half mirror or mirror. A metasurface reflector is a thin film having a nano-level fine structure (nanostructure) and functions as a reflector of light.

[0005] Patent Document 1 discloses a metasurface reflector in which a plurality of patterns are formed, each pattern being a pattern in which a plurality of rectangular metal bodies of different sizes are arranged in order of size. The reflection angle of the incident laser light is controlled by the size and pattern length of the plurality of rectangular metal bodies constituting each pattern. The laser light irradiated on the metasurface reflector as a mirror is scanned, and the reflected laser light is condensed on the retina to project an image. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2024-94883 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, conventional metasurface reflectors have a problem with chromatic aberration, where the reflection angle of laser light differs depending on the color (wavelength) of the laser light. Chromatic aberration causes the outline of the image formed on the retina to blur, color bleeding occurs, and the clarity of the visible image decreases.

[0008] The present invention has been made in view of the above problems, and aims to provide a metasurface reflector, a projection device, and a near-eyewear device capable of reducing chromatic aberration. [Means for solving the problem]

[0009] To achieve the above objective, the metasurface reflector according to the present invention is a metasurface reflector comprising: a first metal layer and a second metal layer stacked in a first direction; a dielectric layer provided between the first metal layer and the second metal layer in the first direction; and a color filter layer covering the surface of the second metal layer opposite to the dielectric layer, wherein the dielectric layer has a main surface on which the second metal layer is provided, the metasurface reflector is divided into a plurality of unit regions arranged in a second direction along the main surface and a third direction along the main surface and intersecting the second direction, and the second metal layer includes metal units provided in each of all or some of the plurality of unit regions.

[0010] With this configuration, even when RGB combined light, which is a combination of R (red light), G (green light), and B (blue light), is incident on the metasurface reflector of the present invention, only monochromatic light transmitted through the color filter layer is incident on each metal unit. Therefore, chromatic aberration, in which the reflection angle of incident light differs depending on the color of the incident light, can be reduced.

[0011] In the metasurface reflector according to the present invention, the color filter layer may be made of a material that transmits light of a specific wavelength.

[0012] With this configuration, the metasurface reflector of the present invention can reduce chromatic aberration by using a color filter layer that transmits light of a specific wavelength.

[0013] In the metasurface reflector according to the present invention, the metal unit may be a metal body having a trapezoidal shape in a plan view from the first direction.

[0014] With this configuration, the metasurface reflector of the present invention can easily set or control the reflection angle of incident light by using a trapezoidal basic pattern for the metal unit.

[0015] In the metasurface reflector according to the present invention, the length of the metal body in the second direction is 500 nm or more and 2500 nm or less, the length of the metal body in the first direction is 10 nm or more and 100 nm or less, the length of the short side of the trapezoidal shape of the metal body is 10 nm or more and 200 nm or less, and the length of the long side parallel to the short side of the trapezoidal shape of the metal body is greater than the length of the short side and is 100 nm or more and 500 nm or less.

[0016] This configuration allows the metasurface reflector of the present invention to more reliably achieve the reflection of visible light.

[0017] In the metasurface reflector according to the present invention, the color filter layer may be composed of a metal containing at least one element selected from the group consisting of iron, chromium, cobalt, and titanium.

[0018] With this configuration, the metasurface reflector of the present invention can efficiently form the color filter layer with an inorganic pigment.

[0019] In the metasurface reflector according to the present invention, the second metal layer may be composed of a metal containing at least one element selected from the group consisting of silver, aluminum, and copper.

[0020] With this configuration, the metasurface reflector of the present invention can achieve efficient reflection of visible light.

[0021] In the metasurface reflector according to the present invention, the dielectric layer may be composed of a material that is transparent in the visible light region.

[0022] With this configuration, the metasurface reflector of the present invention can achieve efficient reflection of visible light by using a transparent dielectric material.

[0023] In the metasurface reflector according to the present invention, the dielectric layer may be composed of one compound selected from the group consisting of silicon oxide, titanium oxide, magnesium oxide, and aluminum oxide.

[0024] With this configuration, the metasurface reflector of the present invention can achieve efficient reflection of visible light.

[0025] In the metasurface reflector according to the present invention, the length of the dielectric layer in the first direction may be 10 nm or more and 100 nm or less, and the length of the first metal layer in the first direction may be 50 nm or more and 1000 nm or less.

[0026] With this configuration, the metasurface reflector of the present invention can more reliably achieve visible light reflection.

[0027] The projection device according to the present invention is a projection device mounted on a near-eye wearable device, and includes a light source that emits laser light, a movable mirror for scanning with the laser light, and the metasurface reflector according to any one of the above, which reflects the laser light passing through the movable mirror and allows a user wearing the near-eye wearable device to visually recognize an image.

[0028] With this configuration, the projection device of the present invention can realize an AR glass equipped with a metasurface reflector (metamirror) capable of reducing chromatic aberration.

[0029] The near-eye wearable device according to the present invention includes the projection device described above and a lens provided with the metasurface reflector.

[0030] With this configuration, the near-eye wearable device of the present invention can realize an AR glass equipped with a metasurface reflector (metamirror) capable of reducing chromatic aberration.

Effects of the Invention

[0031] According to the present invention, it is possible to provide a metasurface reflector, a projection device, and a near-eye wearable device capable of reducing chromatic aberration.

Brief Description of the Drawings

[0032] [Figure 1] It is a diagram showing an enlarged view of the metasurface reflector according to an embodiment of the present invention attached to a lens of a glasses-type near-eye wearable device. [Figure 2] It is a perspective view schematically showing a unit region of the metasurface reflector shown in FIG. 1. [Figure 3] It is a cross-sectional view taken along line III-III of FIG. 2, showing a cross-sectional configuration of the metasurface reflector according to an embodiment of the present invention. [Figure 4] Figure 2 is a plan view. [Figure 5] This is a plan view showing a two-dimensional arrangement of metal units in a metasurface reflector according to an embodiment of the present invention. [Figure 6] (a) is a cross-sectional view along the line VI-VI in Figure 5, and (b) is a diagram showing the reflection behavior at the metasurface reflector. [Figure 7] (a) is a graph showing the relationship between the metal unit length and the reflection angle for each of the RGB incident light, and (b) is a diagram showing the reflection behavior at the metasurface reflector. [Figure 8] This is a plan view showing a first modified example of a two-dimensional arrangement of metal units in a metasurface reflector according to an embodiment of the present invention. [Figure 9] This is a plan view showing a second modified example of a two-dimensional arrangement of metal units in a metasurface reflector according to an embodiment of the present invention. [Figure 10] This is a plan view showing a third modified example of a two-dimensional arrangement of metal units in a metasurface reflector according to an embodiment of the present invention. [Figure 11] This is a perspective view of a near-eyewear device. [Figure 12] (a) is an enlarged perspective view of the projection device, and (b) is a diagram showing the configuration of the projection device itself. [Figure 13] This diagram illustrates the reflection principle using a metasurface reflector in a glasses-type near-eyewear device. [Figure 14] This figure shows the phase change of reflected light at a position along the x-axis of a metasurface reflector. [Figure 15] This figure shows how reflected light converges in relation to incident light due to metal units arranged so that their length in the x-axis direction changes depending on their position in the x-axis direction. [Figure 16] (a) is a plan view of a conventional metasurface reflector, (b) is a cross-sectional view of (a) along line BB, and (c) is a diagram showing the reflection behavior at the metasurface reflector. [Figure 17](a) is a graph showing the relationship between the pattern length and reflection angle of a conventional metasurface reflector, and (b) is a diagram showing the reflection behavior of the metasurface reflector. [Modes for carrying out the invention]

[0033] Embodiments of the present invention will be described in detail below with reference to the drawings. Note that, for ease of understanding, the scale of the parts in the drawings may differ from the actual scale. In the xyz Cartesian coordinate system set in the drawings, the x-axis and y-axis directions are horizontal, and the z-axis direction is vertical. The positive z-axis direction is also called the upward direction, and the negative z-axis direction is also called the downward direction, but this is unrelated to the direction of gravity. A degree of deviation is permissible in directions such as parallel, perpendicular, orthogonal, horizontal, vertical, up and down, and left and right, as long as it does not impair the effects of the embodiment. Furthermore, the "~" indicating a numerical range means that the values ​​written before and after it are included as the lower and upper limits, respectively.

[0034] First, a metasurface reflector 1 according to an embodiment of the present invention will be described. In the following description, an example will be given in which the metasurface reflector 1 of this embodiment is attached as a half-mirror to the lens 51 of a spectacle-type near-eyewear device 100, but its use is not limited to this.

[0035] (composition) Figure 1 is a magnified view of a metasurface reflector 1 according to an embodiment of the present invention, attached to the lens 51 of a spectacle-type near-eyewear device 100. As shown in Figure 1, the metasurface reflector 1 is provided on the inner surface 51a of the lens 51 and is divided into a plurality of unit regions 5. The plurality of unit regions 5 are arranged in a two-dimensional array in the lateral direction (x-axis direction) and vertical direction (y-axis direction) of the lens 51.

[0036] Figure 2 is a schematic perspective view showing a unit region 5. Figure 3 is a cross-sectional view along line III-III in Figure 2, showing the cross-sectional configuration of the metasurface reflector 1 according to an embodiment of the present invention. As shown in Figures 2 and 3, the metasurface reflector 1 comprises, in each unit region 5, a first metal layer 30 and a second metal layer 10 stacked in the z-axis direction (first direction), a dielectric layer 20 provided between the first metal layer 30 and the second metal layer 10 in the z-axis direction, and a color filter layer 8 covering the surface of the second metal layer 10 opposite to the dielectric layer 20. In other words, the metasurface reflector 1 is a laminate containing, in the positive z-axis direction, the first metal layer 30, the dielectric layer 20, the second metal layer 10, and the color filter layer 8 in that order.

[0037] The dielectric layer 20 has a main surface 21 on which the second metal layer 10 is provided. The metasurface reflector 1 is divided into a plurality of unit regions 5 arranged two-dimensionally in the x-axis direction (second direction) along the main surface 21 and in the y-axis direction (third direction) which is along the main surface 21 and intersects with the x-axis direction. The second metal layer 10 contains metal units 18, which are nanostructures, provided in all or some of the unit regions 5. The metasurface reflector 1 may be, for example, a thin plate or film, and may be rectangular, square, polygonal, circular, etc. in a plan view from the z-axis direction.

[0038] Light incident on the metasurface reflector 1 from the color filter layer 8 side is reflected at a predetermined angle depending on the wavelength, angle of incidence, and shape of the metal unit 18. Figure 3 shows how incident light (laser light) Ls is incident on the metasurface reflector 1 at an angle of incidence θi, and reflected light Lr is reflected at a reflection angle θr. As shown in Figure 3, the angle of incidence θi is the angle between the normal to the surface irradiated by the incident light Ls and the direction of incidence of the incident light Ls. The reflection angle θr is the angle between the normal to the surface irradiated by the incident light Ls and the direction of emission of the reflected light Lr. In a plane containing the incident light Ls and reflected light Lr, the reflection angle θr is expressed as a positive value when the reflected light Lr is emitted on the opposite side of the plane from the incident light Ls, with the normal as the boundary, and the reflection angle θr is expressed as a negative value when the reflected light Lr is emitted on the same side as the incident light Ls, with the normal as the boundary.

[0039] The term "light" as used herein refers to visible light, but is not limited to visible light. It may also refer to infrared light, which has a longer wavelength than visible light, or ultraviolet light, which has a shorter wavelength than visible light. The wavelength of visible light is, for example, 380 nm or more and less than 800 nm. The wavelength of infrared light is, for example, 800 nm or more and less than 1 mm. The wavelength of ultraviolet light is, for example, 200 nm or more and less than 380 nm.

[0040] The following describes each component.

[0041] <First metal layer> The first metal layer 30 is the base layer. The first metal layer 30 is composed of a metal or alloy containing at least one element selected from the group consisting of, for example, gold (Au), copper (Cu), silver (Ag), aluminum (Al), iridium (Ir), ruthenium (Ru), rhodium (Rh), titanium (Ti), tantalum (Ta), tungsten (W), cobalt (Co), iron (Fe), and nickel (Ni). The length (thickness) of the first metal layer 30 in the z-axis direction is such that the first metal layer 30 can conduct a resonant current when light is incident on it and can reflect light, for example, 50 nm to 1000 nm.

[0042] <Dielectric layer> The dielectric layer 20 is a layer that functions as a spacer. The dielectric layer 20 is provided on the first metal layer 30. The dielectric layer 20 is made of a material that is transparent in the visible light region, for example. The dielectric layer 20 has a dielectric constant that does not hinder the electromagnetic interaction between the second metal layer 10 and the first metal layer 30. The dielectric layer 20 may be made of a material with a high dielectric constant in order to achieve high reflectivity. The dielectric layer 20 is made of at least one compound selected from a set consisting of silicon oxide (e.g., SiO2), titanium oxide (e.g., TiO2), magnesium oxide (e.g., MgO), and aluminum oxide (e.g., Al2O3), for example. The length (thickness) of the dielectric layer 20 in the z-axis direction is, for example, 10 nm or more and 100 nm or less.

[0043] <Second metal layer> The second metal layer 10 is made of metal and constitutes a nanostructure, which is a nanoscale structure. The second metal layer 10, together with the first metal layer 30, is a layer that excites electromagnetic resonance. Specifically, the incident electric field of light, an electromagnetic wave incident on the second metal layer 10, resonates through the dielectric layer 20, generating an electric field in the opposite direction in the first metal layer 30. A magnetic field opposite to the incident magnetic field is generated in the dielectric layer 20. As a result, the direction of propagation of light, an electromagnetic wave, is reversed.

[0044] The second metal layer 10 is provided on the main surface 21 of the dielectric layer 20 opposite to the first metal layer 30. The second metal layer 10 is composed of a metal or alloy containing at least one element selected from, for example, a set consisting of silver (Ag), aluminum (Al), and copper (Cu). The second metal layer 10 may be composed of, for example, the same material as the first metal layer 30.

[0045] As shown in Figures 2 and 4, the metal unit 18 is a metal body having a trapezoidal shape in a plan view from the z-axis direction.

[0046] The trapezoidal metal unit 18 has a length L in the x-axis direction (hereinafter also referred to as the "longitudinal direction") perpendicular to both the parallel short and long sides of the trapezoid, for example, between 500 nm and 2500 nm. The thickness d of the metal unit 18 in the z-axis direction is for example between 10 nm and 100 nm. Of the parallel short and long sides in the trapezoidal shape of the metal unit 18, the length W1 of the short side is for example between 10 nm and 200 nm, and the length W2 of the long side is greater than the length W1 of the short side, for example between 100 nm and 500 nm. By making the metal unit 18 this size, the reflectivity for visible light can be increased.

[0047] The second metal layer 10 may include a plurality of metal units 18 arranged two-dimensionally in the x-axis and y-axis directions (see Figures 1, 2, and 5). The spacing between two adjacent metal units 18 in the x-axis direction is set so that the wavefront of the reflected light is continuous. This spacing should be such that the two metal units 18 do not touch, for example, it should be set to less than half the wavelength of the incident light (laser light) Ls. The spacing is, for example, about 20 nm. The plurality of metal units 18 are formed, for example, by photolithography.

[0048] The length Lx of each unit region 5 shown in Figure 4 is determined by the wavelength λ of the object being reflected and the incident angle θi and reflection angle θr corresponding to the position where the unit region 5 is located. The length L of the metal unit 18 in the x-axis direction is the same as or slightly shorter than the length Lx of the unit region 5 in the x-axis direction. Therefore, the length L of the metal unit 18 in the x-axis direction is determined by the wavelength λ of the object being reflected and the incident angle θi and reflection angle θr corresponding to the position where the metal unit 18 is located in the unit region 5.

[0049] In this embodiment, the lengths Lx of the unit regions 5 included in the same row in the x-axis direction in the two-dimensional array are different from each other, and the lengths L in the x-axis direction of the metal units 18 included in the same row in the x-axis direction are also different from each other.

[0050] The length Ly of each unit region 5 is a predetermined fixed value. The length Ly is slightly larger than the width W2. The length Ly may also be the length obtained by adding the resolution of the exposure apparatus used to form the metal unit 18 (e.g., 100 nm) to the width W2, for example, set to 600 nm. The widths W1 and W2 of each metal unit 18 are predetermined fixed values. As described above, the width W1 is set to near the resolution of the exposure apparatus used to form the metal unit 18 (e.g., 100 nm). The width W2 is set to a length (e.g., 350 nm) that yields a phase difference of substantially 360° (2π radians) from the phase of the reflected light Lr in width W1 (see Figure 14).

[0051] <Color filter layer> The color filter layer 8 is composed of a material that transmits light of a specific wavelength or wavelength range. For example, the color filter layer 8 is composed of a metal or alloy containing at least one element selected from the set of iron (Fe), chromium (Cr), cobalt (Co), and titanium (Ti). For example, the color filter layer 8 is a red filter layer 8R that transmits only red light, a green filter layer 8G that transmits only green light, or a blue filter layer 8B that transmits only blue light. For example, the red filter layer 8R may transmit red light (e.g., wavelength range of 590 nm to less than 800 nm or a part thereof), the green filter layer 8G may transmit green light (e.g., wavelength range of 490 nm to less than 590 nm or a part thereof), and the blue filter layer 8B may transmit blue light (e.g., wavelength range of 380 nm to less than 490 nm or a part thereof).

[0052] The red filter layer 8R is composed of, for example, cadmium selenide (CdSe) or iron oxide (Fe2O3). The thickness of the red filter layer 8R is, for example, 50 nm to 250 nm. The green filter layer 8G is composed of, for example, chromium oxide (Cr2O3) or nickel oxide (NiO). The thickness of the green filter layer 8G is, for example, 100 nm to 300 nm. The blue filter layer 8B is composed of, for example, cobalt oxide (CoO) or copper oxide (CuO). The thickness of the blue filter layer 8B is, for example, 150 nm to 350 nm.

[0053] (Arrangement of metal units) First, for comparison, let's describe the conventional metasurface reflector 1000.

[0054] Figure 16(a) is a plan view of a conventional metasurface reflector 1000, Figure 16(b) is a cross-sectional view along line BB in Figure 16(a), and Figure 16(c) shows the reflection behavior of the conventional metasurface reflector 1000. As shown in Figures 16(a) and 16(b), the conventional metasurface reflector 1000 has a first metal layer 30, a dielectric layer 20, and a second metal layer 10 stacked in this order along the z-axis. The second metal layer 10 is composed of a plurality of rectangular metal bodies 19 as a nanostructure. In one unit region, a plurality of rectangular metal bodies 19, whose size gradually increases, are arranged with spacing between them along the x-axis, forming a single pattern (corresponding to a metal unit). The pattern length gradually decreases along the x-axis.

[0055] As shown in Figure 16(c), in a conventional metasurface reflector 1000, when RGB combined light Ls(RGB), which is obtained by combining red, green, and blue laser light, is incident on the pattern of the metal body 19 at a predetermined incident angle, the red reflected light Lr(R), the green reflected light Lr(G), and the blue reflected light Lr(B) are separated and reflected at different reflection angles. In other words, in a conventional metasurface reflector 1000, chromatic aberration occurs when RGB combined light Ls(RGB) is incident on it.

[0056] Figure 17(a) is a graph showing the relationship between the pattern length and reflection angle of a conventional metasurface reflector 1000, and Figure 17(b) is a diagram showing the reflection behavior of a conventional metasurface reflector 1000 with a pattern length of 1000 nm. As shown in Figures 17(a) and 17(b), for example, when RGB combined light Ls(RGB) is incident perpendicularly on a conventional metasurface reflector 1000 with a pattern length of 1000 nm in the x-axis direction (longitudinal direction), the green reflected light Lr(G) is reflected at a reflection angle of 30°, the blue reflected light Lr(B) is reflected at a reflection angle of 40°, and the red reflected light Lr(R) is reflected at a reflection angle of 20°. In other words, chromatic aberration occurs.

[0057] Next, the arrangement of the metal units 18 in the metasurface reflector 1 according to an embodiment of the present invention will be described.

[0058] Figure 5 is a plan view showing a two-dimensional arrangement of metal units 18 in a metasurface reflector 1 according to an embodiment of the present invention. Figure 6(a) is a cross-sectional view along the line VI-VI in Figure 5, and Figure 6(b) shows the reflection behavior in the metasurface reflector 1. As shown in Figures 5 and 6(a), the metasurface reflector 1 is constructed by stacking a first metal layer 30, a dielectric layer 20, a second metal layer 10, and a color filter layer 8 in the positive z-axis direction in this order. Specifically, the color filter layer 8 is, for example, a red filter layer 8R, a green filter layer 8G, or a blue filter layer 8B.

[0059] In Figure 5, the transmitted color of the color filter layer 8 is indicated by the letters "R", "G", or "B" on the trapezoidal metal unit 18. Specifically, "R" indicates that a red filter layer 8R is provided on the metal unit 18, "G" indicates that a green filter layer 8G is provided on the metal unit 18, and "B" indicates that a blue filter layer 8B is provided on the metal unit 18.

[0060] As shown in Figure 5, the metal units 18 arranged in the Y1 row in the x-axis direction are provided with a red filter layer 8R, the metal units 18 arranged in the Y2 row are provided with a green filter layer 8G, and the metal units 18 arranged in the Y3 row are provided with a blue filter layer 8B. Similarly, for the rows following the Y3 row, the transparency color of the color filter layer 8 is set for each row, so that the transparency color of the color filter layer 8 changes when the row changes.

[0061] Figure 6(b) shows the reflection behavior in the three metal units 18 shown in Figure 6(a). As shown in Figure 6(b), when RGB combined light Ls(RGB) is incident on a metal unit 18 equipped with a red filter layer 8R at a predetermined incident angle θi, the red reflected light Lr(R) is reflected at a reflection angle θr. When RGB combined light Ls(RGB) is incident on a metal unit 18 equipped with a green filter layer 8G at a predetermined incident angle θi, the green reflected light Lr(G) is reflected at a reflection angle θr. When RGB combined light Ls(RGB) is incident on a metal unit 18 equipped with a blue filter layer 8B at a predetermined incident angle θi, the blue reflected light Lr(B) is reflected at a reflection angle θr.

[0062] Thus, when RGB combined light Ls(RGB) is incident at a predetermined incidence angle θi on these three types of metal units 18, which are all located at the same position in the x-axis direction, the red reflected light Lr(R), the green reflected light Lr(G), and the blue reflected light Lr(B) are all reflected at the same reflection angle θr. For this reason, in the two-dimensional array, the length of the metal units 18 is changed for each transmitted color of the color filter layer 8, depending on the position in the x-axis direction.

[0063] Figure 7(a) is a graph showing the relationship between the metal unit length and the reflection angle for each color of incident light (R, G, B), and Figure 7(b) shows the reflection behavior at the metasurface reflector 1. As shown in Figure 7(a), the relationship between the metal unit length and the reflection angle differs for each color of incident light (R, G, B).

[0064] In the metasurface reflector 1 used in the near-eyewearable device 100, metal units 18 that are at the same or close proximity on the x-axis must have the same or nearly the same reflection angles for red reflected light Lr(R), green reflected light Lr(G), and blue reflected light Lr(B). To achieve this, the longitudinal lengths (metal unit lengths) of the metal units 18 are varied to ensure that the reflection angles are aligned.

[0065] For example, as shown in Figure 7(b), if the length of the metal unit 18 provided with the red filter layer 8R is set to 1200 nm, the reflection angle of the red reflected light Lr(R) becomes 30°. If the length of the metal unit 18 provided with the green filter layer 8G is set to 1000 nm, the reflection angle of the green reflected light Lr(G) becomes 30°. If the length of the metal unit 18 provided with the blue filter layer 8B is set to 800 nm, the reflection angle of the blue reflected light Lr(B) becomes 30°. By arranging these metal units 18 at the same or close proximity positions on the x-axis, the red reflected light Lr(R), green reflected light Lr(G), and blue reflected light Lr(B) can be reflected at the same reflection angle. This makes it possible to realize a metasurface reflector 1 that can be used in the near-eyewearable device 100 without generating chromatic aberration.

[0066] As described above, the metasurface reflector 1 according to this embodiment reduces chromatic aberration by using a color filter layer 8. The RGB color filter layer 8 is arranged on a trapezoidal metal unit 18, which is the basic element pattern. As a result, even when RGB combined light Ls(RGB) is irradiated onto the metal unit 18, each metal unit 18 reflects only one wavelength, i.e., one color of laser light that has passed through the color filter layer 8, so no chromatic aberration occurs. Furthermore, by adjusting the size of the metal unit 18 on which the color filter layer 8 is provided (for example, the length of the metal unit), it is possible to make all RGB reflection angles the same at the same position in the x-axis direction and in its vicinity.

[0067] (First variation of the arrangement of metal units) Figure 8 is a plan view showing a first modified example of a two-dimensional arrangement of metal units 18 in a metasurface reflector 1 according to an embodiment of the present invention.

[0068] As shown in Figure 8, the metal units 18 arranged in column X1 in the y-axis direction are provided with a red filter layer 8R, the metal units 18 arranged in column X2 in the y-axis direction are provided with a green filter layer 8G, and the metal units 18 arranged in column X3 in the y-axis direction are provided with a blue filter layer 8B. Similarly, for the columns following column X3, the transparency color of the color filter layer 8 is set for each column, so that the transparency color of the color filter layer 8 changes when the column changes.

[0069] The metal units 18, arranged in a row Y1 along the x-axis, are provided with a red filter layer 8R, a green filter layer 8G, and a blue filter layer 8B, which are repeated in sequence. The same applies to the rows Y2, Y3, etc., that follow Y1.

[0070] In the first modified example, when RGB combined light is incident at a predetermined incident angle on metal units 18 that are the same or nearly the same in the x-axis direction, the red reflected light, green reflected light, and blue reflected light are reflected at the same reflection angle. For this reason, the length of the metal units 18 in the two-dimensional array is changed for each transmitted color of the color filter layer 8, depending on the position in the x-axis direction.

[0071] With this configuration, for example, in the near-eyewear device 100, chromatic aberration can be reduced and full-color images can be projected clearly onto the retina.

[0072] (Second variation of the arrangement of metal units) Figure 9 is a plan view showing a second modified example of the two-dimensional arrangement of metal units 18 in the metasurface reflector 1 according to an embodiment of the present invention.

[0073] As shown in Figure 9, the metal units 18 arranged in the Y1 row along the x-axis are provided with a red filter layer 8R, a green filter layer 8G, and a blue filter layer 8B in a repeating sequence. The metal units 18 arranged in the Y2 row along the x-axis are provided with a green filter layer 8G, a blue filter layer 8B, and a red filter layer 8R in a repeating sequence. The metal units 18 arranged in the Y3 row along the x-axis are provided with a blue filter layer 8B, a red filter layer 8R, and a green filter layer 8G in a repeating sequence. The same applies to the rows following the Y3 row.

[0074] The metal units 18 arranged in column X1 along the y-axis are provided with a red filter layer 8R, a green filter layer 8G, and a blue filter layer 8B in a repeating sequence. The metal units 18 arranged in column X2 along the y-axis are provided with a green filter layer 8G, a blue filter layer 8B, and a red filter layer 8R in a repeating sequence. The metal units 18 arranged in column X3 along the y-axis are provided with a blue filter layer 8B, a red filter layer 8R, and a green filter layer 8G in a repeating sequence. The same applies to the columns following column X3 and beyond.

[0075] In the second modified example, when RGB combined light is incident at a predetermined incident angle on metal units 18 that are in the same or nearly the same position in the x-axis direction, the red reflected light, green reflected light, and blue reflected light are reflected at the same reflection angle. For this reason, in the two-dimensional array, the length of the metal units 18 is changed for each transmitted color of the color filter layer 8, depending on the position in the x-axis direction.

[0076] With this configuration, for example, in the near-eyewear device 100, chromatic aberration can be reduced and full-color images can be projected clearly onto the retina.

[0077] (Third variation of the arrangement of metal units) Figure 10 is a plan view showing a third modified example of a two-dimensional arrangement of metal units 18 in a metasurface reflector 1 according to an embodiment of the present invention.

[0078] As shown in Figure 10, the metal units 18 arranged in the Y1 row in the x-axis direction are provided with a red filter layer 8R, the metal units 18 arranged in the Y2 row are provided with a green filter layer 8G, and the metal units 18 arranged in the Y3 row are provided with a blue filter layer 8B. In the third modified example, the metal units 18 in the Y2 row are offset in the x-axis direction from the metal units 18 in the Y1 and Y3 rows. Similarly, for the rows following the Y3 row, the transparency color of the color filter layer 8 is set for each row, so that the transparency color of the color filter layer 8 changes when the row changes.

[0079] In the third modified example, when RGB combined light is incident at a predetermined incident angle on metal units 18 that are the same or nearly the same in the x-axis direction, the red reflected light, green reflected light, and blue reflected light are reflected at the same reflection angle. For this reason, in the two-dimensional array, the length of the metal units 18 is changed for each transmitted color of the color filter layer 8, depending on the position in the x-axis direction.

[0080] With this configuration, for example, in the near-eyewear device 100, chromatic aberration can be reduced and full-color images can be projected clearly onto the retina.

[0081] (Manufacturing process) The metasurface reflector 1 is obtained by sequentially fabricating a first metal layer 30, a dielectric layer 20, a second metal layer 10, and a color filter layer 8 on some substrate using techniques such as sputtering and photolithography. The substrate may be a sapphire substrate, a flexible sheet, or a quartz substrate.

[0082] Specifically, a first metal layer 30 is formed on the substrate by vacuum deposition using a method such as DC (Direct Current) sputtering. For the formation of the first metal layer 30, a metal material is used that is composed of any metal selected from the set consisting of gold (Au), copper (Cu), silver (Ag), iridium (Ir), ruthenium (Ru), rhodium (Rh), titanium (Ti), tantalum (Ta), tungsten (W), cobalt (Co), iron (Fe), and nickel (Ni), or a metal alloy containing at least one element selected from the above set. The first metal layer 30 is formed with a film thickness of, for example, 50 nm to 1000 nm.

[0083] Next, a dielectric layer 20 is formed on the first metal layer 30. Specifically, the dielectric layer 20 is formed by vacuum deposition using a method such as RF (Radio Frequency) sputtering. For the formation of the dielectric layer 20, dielectric materials such as silicon oxide (e.g., SiO2), titanium oxide (e.g., TiO2), magnesium oxide (e.g., MgO), and aluminum oxide (e.g., Al2O3), which can be formed in semiconductor processes, are used. The dielectric layer 20 is formed with a film thickness of, for example, 10 nm to 100 nm.

[0084] Next, a metal layer (hereinafter referred to as the "outermost metal layer") which will form the second metal layer 10 is formed on the dielectric layer 20. The outermost metal layer is composed of a metal or alloy containing at least one element selected from a set consisting of silver (Ag), aluminum (Al), and copper (Cu), and is formed by a method such as sputtering, similar to the first metal layer 30. The outermost metal layer is formed with a thickness of, for example, 10 nm to 100 nm.

[0085] Next, a second metal layer 10 (multiple nanostructures) is formed by a photolithography process and an etching process. Specifically, a liquid resist is applied to the outermost metal layer using a spin coater or the like, and the applied liquid resist is dried to form a resist film (photoresist). Then, using an exposure device such as a KrF exposure machine or an electron beam lithography system, a pattern corresponding to the metal units 18 of the nanostructures is transferred to the resist film. Then, using a developer, the pattern transferred to the resist film is developed. Finally, by ion milling, the parts of the outermost metal layer that are not covered by the pattern are removed, and then the resist film is removed. This forms the second metal layer 10. The width W1 of each metal unit 18 is, for example, 10 nm to 200 nm, the width W2 is, for example, 100 nm to 500 nm, and the length L is, for example, 500 nm to 2500 nm (see Figure 4).

[0086] Next, a color filter layer 8 is formed on top of the second metal layer 10 using a method such as sputtering. At this time, areas where the color filter layer 8 is not to be formed are masked. Through these steps, the metasurface reflector 1 is formed.

[0087] Depending on the application, the metasurface reflector 1 may be formed directly on the lens of eyeglasses or a half-mirror instead of on a substrate. The formation method is the same as the method for forming the metasurface reflector 1 on a substrate.

[0088] (Projection device and near-eyewear device) The metasurface reflector 1 according to this embodiment can be applied, for example, to a projection device 60 or a near eyewear trouble device 100 equipped with a projection device 60.

[0089] Figure 11 is a perspective view of the Near Eyewearable Device 100. The Near Eyewearable Device 100 is a device that superimposes images onto the field of view of the real world. The Near Eyewearable Device 100 is, for example, a head-mounted device. In this example, it is a glasses-type device, but it can take the form of goggles, a hat, or a helmet. Examples of Near Eyewearable Device 100 include smart glasses such as AR glasses and MR (Mixed Reality) glasses. The Near Eyewearable Device 100 in Figure 11 includes a frame 50, a lens 51 attached to the rim 50a, and a projection device 60 attached to the temple 50c. The lens 51 is provided with a metasurface reflector 1.

[0090] The frame 50 includes a pair of rims 50a, a bridge 50b, and a pair of temples 50c. The rims 50a are the parts that hold the lens 51. The bridge 50b is the part that connects the pair of rims 50a. The temples 50c extend from the rims 50a and are the parts that rest on the user's ears. The frame 50 may be a rimless frame. The lens 51 has an inner surface 51a (see Figure 1) that faces the eyeball E (see Figure 13) of the user wearing the near eyewear device 100.

[0091] Figure 12(a) is an enlarged perspective view of the projection device 60, and Figure 12(b) is a configuration diagram of the optical engine 70. The projection device 60 is a device that directly projects (draws) an image onto the retina RE of a user wearing the near-eyewear device 100. The projection device 60 is mounted on the near-eyewear device 100. The projection device 60 comprises an optical engine 70 attached to the frame 50 and a metasurface reflector 1 attached to the lens 51.

[0092] The optical engine 70 is a device that generates laser light Ls of color and intensity corresponding to the pixels of the image projected onto the retina RE, and emits the laser light Ls to the metasurface reflector 1. The optical engine 70 is mounted on each temple 50c. The optical engine 70 includes a light source unit (light source) 71, optical components 72, a movable mirror 73, a laser driver 74, a mirror driver 75, and a controller 76.

[0093] The light source unit 71 emits laser light. For example, a full-color laser module is used as the light source unit 71. The light source unit 71 includes a red laser diode, a green laser diode, a blue laser diode, and a combiner that combines the laser light emitted from each laser diode into a single laser beam. The light source unit 71 emits the combined laser beam. The combined laser beam includes a component having a red wavelength (red component), a component having a green wavelength (green component), and a component having a blue wavelength (blue component). The light source unit 71 emits laser light of a color and intensity corresponding to the pixels of the image projected onto the retina RE.

[0094] The optical component 72 is a component that optically processes the laser light emitted from the light source unit 71. In this embodiment, the optical component 72 includes a collimator lens 72a, a slit 72b, and a neutral density filter 72c. The collimator lens 72a, the slit 72b, and the neutral density filter 72c are arranged in that order along the optical path of the laser light. The optical component 72 may have other configurations.

[0095] The movable mirror 73 is a component for scanning with laser light Ls. The movable mirror 73 is positioned in the direction of emission of the laser light processed by the optical component 72. The movable mirror 73 is configured to swing, for example, around an axis extending in the lateral direction (x-axis direction) of the lens 51 and around an axis extending in the vertical direction (y-axis direction) of the lens 51, and reflects the laser light by changing the angle in the x-axis and y-axis directions. For example, a MEMS mirror can be used as the movable mirror 73.

[0096] The laser driver 74 is a drive circuit that drives the light source unit 71. The laser driver 74 drives the light source unit 71 based, for example, on the optical power of the laser light and the temperature of the light source unit 71. The mirror driver 75 is a drive circuit that drives the movable mirror 73. The mirror driver 75 oscillates the movable mirror 73 within a predetermined angular range and timing. The controller 76 is a device that controls the laser driver 74 and the mirror driver 75.

[0097] In the optical engine 70, laser light of color and intensity corresponding to the pixels of the image projected onto the retina RE is emitted from the light source unit 71, passes through the optical component 72, and is reflected by the movable mirror 73. The movable mirror 73 is a component for scanning with laser light (incident light). The laser light reflected by the movable mirror 73 is emitted as laser light Ls to the metasurface reflector 1.

[0098] The metasurface reflector 1 is a component that reflects laser light Ls via the movable mirror 73 and projects an image onto the retina RE of a user wearing the near-eyewear device 100 by irradiating the reflected light Lr onto the retina RE. The user views the image projected onto the retina RE. No image is displayed on the metasurface reflector 1.

[0099] In this embodiment, the near-eyewearable device 100 includes two projection devices 60 to project images onto both the left and right retinas, but it may also include only one of the projection devices 60.

[0100] (Reflection by metasurface reflectors in near-eyewearable devices) Next, the principle of light reflection by the metasurface reflector 1 in the near-eyewear device 100 according to an embodiment of the present invention will be explained.

[0101] As shown in Figure 1, the metasurface reflector 1 has a plurality of unit regions 5. Each unit region 5 has a metal unit 18 configured to reflect incident light (laser light) Ls at a reflection angle θr corresponding to the position where the unit region 5 is located, when incident light Ls is incident at an incident angle θi corresponding to the position where the unit region 5 is located (Figure 2). For example, the reflection angle θr of each unit region 5 is set so that the incident light Ls reflected by each unit region 5 (i.e., reflected light Lr) passes through the center of the pupil PP in the user's eyeball E. Therefore, the incident angle θi and the reflection angle θr are determined by the position where the unit region 5 is located. The unit region 5 is configured so that an incident angle θi and a reflection angle θr corresponding to the position where the unit region 5 is located are obtained.

[0102] Figure 13 is a diagram illustrating the reflection principle by the metasurface reflector 1 in the eyeglass-type near-eyewear device 100. As shown in Figure 13, for example, when the user's pupil PP is facing forward, the unit region 5 located from position Pa to position Pc in the x-axis direction is used. The incident light Ls reflected by the unit region 5 located at position Pa corresponds to the pixel at the right edge of the image projected onto the retina RE. Position Pb is located midway between position Pa and position Pc, and the incident light Ls reflected by the unit region 5 located at position Pb corresponds to the pixel in the center of the image. The incident light Ls reflected by the unit region 5 located at position Pc corresponds to the pixel at the left edge of the image.

[0103] Specifically, in the unit region 5 located at position Pa, for example, incident light Ls is incident at an incident angle θi of 30°, and the incident light Ls is reflected at a reflection angle θr of 5° and emitted as reflected light Lr. In the unit region 5 located at position Pb, for example, incident light Ls is incident at an incident angle θi of 40°, and the incident light Ls is reflected at a reflection angle θr of -5° and emitted as reflected light Lr. In the unit region 5 located at position Pc, for example, incident light Ls is incident at an incident angle θi of 50°, and the incident light Ls is reflected at a reflection angle θr of -10° and emitted as reflected light Lr.

[0104] Figure 14 shows the phase change of reflected light Lr at different positions along the x-axis of the metasurface reflector 1. As shown in Figure 14, the width of the metal unit 18 increases along the x-axis from width W1 to width W2. The phase change at each position along the x-axis of the metal unit 18 is substantially the same as the phase change caused by a square metal body (shown by a dashed line) with sides of the same length as the width at that position in a plan view. The larger the area of ​​the square metal body in a plan view, the larger the phase change (phase delay) at that position. Thus, the incident light Ls is reflected with different phase changes depending on the position along the x-axis, and a wavefront is formed by interference between the reflected light. That is, a plane wave is generated that propagates in a direction determined by the relationship between the position along the x-axis and the phase change. The reflection angle changes depending on the length (pattern length) of the metal unit 18 in the x-axis direction, etc.

[0105] Figure 15 illustrates a metasurface reflector 1 that functions as a mirror using metal units 18, which are nanostructures. Multiple metal units 18 arranged in the x-axis direction have varying lengths in the x-axis direction depending on their position in the x-axis direction. For example, even if the position in the x-axis direction from which the incident light Ls enters changes due to the movable mirror 73 in Figure 13, the reflected light Lr will still converge. In this way, by accumulating patterns in which the longitudinal length (metal unit length) of the metal units 18 is varied, multiple reflection angles spanning both positive and negative directions can be created.

[0106] In this way, in the metasurface reflector 1 of Figure 15, in which multiple metal units 18 are arranged such that the length of the metal unit changes depending on the position in the x-axis direction, reflected light generated at positive and negative angles is focused. In the near-eyewear device 100 shown in Figure 13, incident light Ls is incident on the metasurface reflector 1 from an oblique angle, and the reflected light Lr can be focused to the position of the pupil PP in front.

[0107] The metasurface reflector according to this disclosure is not limited to the embodiments described above. In the embodiments described above, it was assumed that metal units 18 are provided in all unit regions 5, but metal units 18 may be provided in only some of the unit regions 5.

[0108] By combining a trapezoidal patterned metal unit 18 with RGB color filter layers 8, it is possible to illuminate the metal unit 18 with only a single wavelength (single color) of laser light from the RGB combined laser beam. By setting the size (metal unit length) of the metal unit 18 according to the transmitted color of each color filter layer 8, it is possible to make the reflection angles of each RGB laser beam incident at the same or nearby position the same.

[0109] As described above, the present invention has the effect of reducing chromatic aberration and is useful in metasurface reflectors, projection devices, and near-eyewear devices in general. [Explanation of Symbols]

[0110] 1. Metasurface reflector 5 Unit Area 8 color filter layers 8R Red Filter Layer 8G Green Filter Layer 8B Blue filter layer 10 Second metal layer 18 Metal Units 19 Metal body 20 Dielectric layer 21 Main surface 30 1st metal layer 50 frames 50a rim 50b Bridge 50c Temple 51 lenses 51a Inner surface 60 Projection device 70 Optical Engines 71 Light source unit (light source) 72 Optical Components 72a Collimator lens 72b Slit 72c Neutral Density Filter 73. Movable Mirror 74 Laser Drivers 75 Mirror Driver 76 Controllers 100 Near Eyewear Trouble Device 1000 Conventional metasurface reflectors E Eyeball PP Pupil RE (Retina)

Claims

1. A metasurface reflector, A first metal layer and a second metal layer stacked in the first direction, In the first direction, a dielectric layer is provided between the first metal layer and the second metal layer, The second metal layer comprises a color filter layer covering the surface opposite to the dielectric layer, The dielectric layer has a main surface on which the second metal layer is provided, The metasurface reflector is divided into a plurality of unit regions arranged in a second direction along the main surface and a third direction along the main surface and intersecting the second direction. The second metal layer is a metasurface reflector that includes metal units provided in each of the unit regions of all or some of the plurality of unit regions.

2. The metasurface reflector according to claim 1, wherein the color filter layer is made of a material that transmits light of a specific wavelength.

3. The metasurface reflector according to claim 1, wherein the metal unit is a metal body having a trapezoidal shape in a plan view from the first direction.

4. The length of the metal body in the second direction is 500 nm or more and 2500 nm or less. The length of the metal body in the first direction is 10 nm or more and 100 nm or less. The length of the shorter side of the trapezoidal shape of the metal body is 10 nm or more and 200 nm or less. The metasurface reflector according to claim 3, wherein the length of the long side parallel to the short side in the trapezoidal shape of the metal body is greater than the length of the short side and is 100 nm or more and 500 nm or less.

5. The metasurface reflector according to claim 1, wherein the color filter layer is made of a metal containing at least one element selected from the set of iron, chromium, cobalt, and titanium.

6. The metasurface reflector according to claim 1, wherein the second metal layer is composed of a metal containing at least one element selected from the set of silver, aluminum, and copper.

7. The metasurface reflector according to claim 1, wherein the dielectric layer is made of a material that is transparent in the visible light region.

8. The metasurface reflector according to claim 7, wherein the dielectric layer is composed of one compound selected from a set consisting of silicon oxide, titanium oxide, magnesium oxide, and aluminum oxide.

9. The length of the dielectric layer in the first direction is 10 nm or more and 100 nm or less. The metasurface reflector according to claim 1, wherein the length of the first metal layer in the first direction is 50 nm or more and 1000 nm or less.

10. A projection device mounted on a near-eyewear device, A light source that emits laser light, A movable mirror for performing scanning with the aforementioned laser light, A projection device comprising: a metasurface reflector according to any one of claims 1 to 9, the metasurface reflector which reflects the laser light that has passed through the movable mirror to cause an image to be visible to a user wearing the near eyewear device.

11. The projection apparatus according to claim 10, A lens provided with the aforementioned metasurface reflector, A near-eyewear trouble device equipped with the following features.

Images