Meta surface reflector, projection device, and near eye wearable device

Abstract

To suppress the deterioration in reflection characteristics.SOLUTION: A meta surface reflector includes a first metal layer and a second metal layer that are 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 protection layer covering a surface of the second metal layer on the opposite side of the dielectric layer. The dielectric layer has a main surface where the second metal layer is provided. The meta surface reflector is sectioned into a plurality of unit regions that is arranged in a second direction extending along the main surface and a third direction extending along the main surface and intersecting with the second direction. The second metal layer includes a metal unit provided in all or some unit regions among the plurality of unit regions. The protection layer is formed of the metal having a larger normal electrode potential than the metal included in the second metal layer.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to metasurface reflectors, projection devices, and near-eye wearable devices. [Background technology]

[0002] Reflectors using metasurface technology are known. For example, Patent Document 1 describes a near-eye display assembly including an image source and a combiner including a nanostructured surface optically coupled to the image source. A unit cell of the nanostructured surface is formed by stacking a base layer, a dielectric layer, and a meta-atom layer in that order. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2018 / 0113310 Summary of the Invention [Problem to be solved by the invention]

[0004] In the near-eye display assembly described in Patent Document 1, the meta-atomic layer is exposed. When a metal layer such as silver or aluminum is used as the meta-atomic layer, the metal layer may be oxidized or sulfurized when exposed to air. In this case, the optical properties may change and the reflective properties may deteriorate.

[0005] The present disclosure describes a metasurface reflector, a projection device, and a near-eye wearable device that can suppress degradation of reflective properties. [Means for solving the problem]

[0006] A metasurface reflector according to one aspect of the present disclosure includes 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 protective layer covering the surface of the second metal layer 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 areas 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 includes metal units provided in all or some of the plurality of unit areas. The protective layer is made of a metal having a standard electrode potential greater than that of the metal constituting the second metal layer.

[0007] In this metasurface reflector, the protective layer covers the surface of the second metal layer opposite to the dielectric layer. Therefore, the surface of the second metal layer is not exposed to air when the metasurface reflector is used, so the possibility of the second metal layer being oxidized and sulfurized is reduced. Furthermore, since the protective layer is made of a metal having a higher standard electrode potential than the metal constituting the second metal layer, the protective layer is less likely to be oxidized and sulfurized than the second metal layer. Therefore, in the above metasurface reflector, the optical characteristics are less likely to change. As a result, it is possible to suppress deterioration of the reflection characteristics.

[0008] The length of the protective layer in the first direction may be 20% or less of the sum of the length of the second metal layer in the first direction and the length of the protective layer in the first direction. In this case, the protective layer can be provided while suppressing the influence on the reflection characteristics of the metasurface reflector. Therefore, it is possible to further suppress the deterioration of the reflection characteristics.

[0009] The metal unit may be a metal body having a trapezoidal shape when viewed from the first direction. In this case, the structure of the metal unit can be simplified compared to when the metal unit is composed of multiple metal bodies. Therefore, it is possible to facilitate the manufacture of the metasurface reflector.

[0010] The length of the metal body in the second direction may be 500 nm or more and 2500 nm or less. The length of the metal body in the first direction may be 10 nm or more and 100 nm or less. The length of the short side of the metal body may be 10 nm or more and 200 nm or less. The length of the long side of the metal body may be greater than the length of the short side, and may be 100 nm or more and 500 nm or less. In this case, the reflection efficiency for visible light can be increased.

[0011] The protective layer may be made of a metal containing at least one element selected from the group consisting of gold, ruthenium, and iridium, which can suppress deterioration of the reflection characteristics compared to molybdenum, titanium, tungsten, etc.

[0012] The second metal layer may be made of a metal containing at least one element selected from the group consisting of silver, aluminum, and copper. In this case, the second metal layer has a relatively high reflectance and a relatively high electrical conductivity. Therefore, the electromagnetic resonance between the first metal layer and the second metal layer can be strengthened, and the reflection efficiency can be increased.

[0013] The dielectric layer may be made of a material that is transparent in the visible light region, in which case the visible light absorption rate in the dielectric layer is reduced, thereby increasing the visible light reflection efficiency.

[0014] The dielectric layer may be made of one compound selected from the group consisting of silicon oxide, titanium oxide, magnesium oxide, and aluminum oxide. In this case, a dielectric layer having a dielectric constant that does not inhibit electromagnetic action is obtained. Therefore, the electromagnetic resonance between the first metal layer and the second metal layer can be strengthened, and the reflection efficiency can be increased.

[0015] The length of the dielectric layer in the first direction may be 10 nm or more and 100 nm or less. The length of the first metal layer in the first direction may be 50 nm or more and 1000 nm or less. In this case, the possibility that the dielectric layer inhibits electromagnetic action can be reduced, and the possibility that the laser light transmits through the first metal layer can be reduced. Therefore, the reflection efficiency can be increased.

[0016] According to another aspect of the present disclosure, there is provided a projection device mounted on a near-eye wearable device, the projection device including a light source for emitting laser light, a movable mirror for scanning with the laser light, and a metasurface reflector that reflects the laser light that has passed through the movable mirror to allow a user wearing the near-eye wearable device to view an image. This projection device can also suppress deterioration of the reflection characteristics.

[0017] According to yet another aspect of the present disclosure, there is provided a near-eye wearable device including the projection device and a lens having a metasurface reflector. In this near-eye wearable device, the deterioration of the reflection characteristics can also be suppressed. Effect of the Invention

[0018] According to each aspect and embodiment of the present disclosure, deterioration of reflection characteristics can be suppressed. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a perspective view showing the appearance of a near-eye wearable device to which a metasurface reflector according to one embodiment is applied. [Diagram 2] FIG. 2 is a schematic diagram of the projection device shown in FIG. [Diagram 3] FIG. 3 is an enlarged view of the metasurface reflector shown in FIG. [Figure 4] FIG. 4 is a perspective view that illustrates a schematic view of the unit area illustrated in FIG. [Diagram 5]FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a diagram for explaining the principle of reflection by the metasurface reflector shown in FIG. [Figure 7] FIG. 7 is a diagram showing the amount of phase change of reflected light at a position in the X-axis direction of the metasurface reflector. [Figure 8] FIG. 8 is a diagram for explaining the relationship between the position in the X-axis direction and the length of the metal unit in the X-axis direction. [Figure 9] FIG. 9 is a diagram showing the relationship between the ratio of the protective layer and the reflected electric field intensity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. In the description of the drawings, the same elements are given the same symbols, and duplicated descriptions are omitted. An XYZ coordinate system may be shown in each drawing. The Y-axis direction (third direction) is a direction that intersects (e.g., perpendicular to) the X-axis direction (second direction) and the Z-axis direction (first direction). The Z-axis direction is a direction that intersects (e.g., perpendicular to) the X-axis direction and the Y-axis direction. In this specification, a numerical range indicated using "~" indicates a range that includes the numerical values ​​written before and after "~" as the minimum and maximum values, respectively. Individually described upper and lower limit values ​​can be arbitrarily combined.

[0021] A near-eye wearable device to which a metasurface reflector according to an embodiment is applied will be described with reference to FIG. 1. FIG. 1 is a perspective view showing the appearance of a near-eye wearable device to which a metasurface reflector according to an embodiment is applied. The near-eye wearable device 1 shown in FIG. 1 is a device that overlays an image on a field of view in the real world. The near-eye wearable device 1 is, for example, a head-mounted device, and may take the form of glasses, goggles, hats, helmets, and the like. Examples of the near-eye wearable device 1 include smart glasses such as AR (Augmented Reality) glasses and MR (Mixed Reality) glasses. The near-eye wearable device 1 includes a frame 2, a lens 3, and a projection device 10.

[0022] The frame 2 includes a pair of rims 2a, a bridge 2b, and a pair of temples 2c. The rims 2a are portions that hold the lenses 3. The bridge 2b is a portion that connects the pair of rims 2a. The temples 2c are portions that extend from the rims 2a and are hung on the ears of a user. The frame 2 may be a rimless frame. The lenses 3 have an inner surface 3a (see FIG. 2) that faces the eyeball E (see FIG. 6) of a user wearing the near eyewear wearable device 1.

[0023] In this embodiment, the projection device 10 is a device that directly projects (draws) an image onto the retina RE (see FIG. 6) of a user wearing the near-eye wearable device 1. The projection device 10 is mounted on the near-eye wearable device 1. In this embodiment, the near-eye wearable device 1 includes two projection devices 10 in order to project images onto both the left and right retinas RE, but may include only one of the projection devices 10.

[0024] Next, the projection device 10 will be described in detail with reference to Fig. 2. Fig. 2 is a schematic diagram of the projection device shown in Fig. 1. As shown in Fig. 2, the projection device 10 includes an optical engine 20 and a metasurface reflector 30.

[0025] The optical engine 20 is a device that generates laser light Ls with a color and intensity corresponding to the pixels of an image to be projected onto the retina RE, and emits the laser light Ls to the metasurface reflector 30. The optical engine 20 is mounted on each temple 2c. The optical engine 20 includes a light source unit 21 (light source), an optical component 22, a movable mirror 23, a laser driver 24, a mirror driver 25, and a controller 26.

[0026] The light source unit 21 emits laser light. For example, a full-color laser module is used as the light source unit 21. The light source unit 21 includes a red laser diode, a green laser diode, a blue laser diode, and a multiplexing section that multiplexes the laser light emitted from each laser diode into one laser light. The light source unit 21 emits the multiplexed laser light. The multiplexed laser light 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 21 emits laser light of a color and intensity corresponding to the pixels of the image to be projected onto the retina RE.

[0027] The optical component 22 is a component that optically processes the laser light emitted from the light source unit 21. In this embodiment, the optical component 22 includes a collimator lens 22a, a slit 22b, and a neutral density filter 22c. The collimator lens 22a, the slit 22b, and the neutral density filter 22c are arranged in this order along the optical path of the laser light. The optical component 22 may have other configurations.

[0028] The movable mirror 23 is an optical component for performing scanning with the laser light Ls. The movable mirror 23 is provided in the emission direction of the laser light processed by the optical component 22. The movable mirror 23 is configured to be swingable, for example, around an axis extending in the horizontal direction (X-axis direction) of the lens 3 and around an axis extending in the vertical direction (Y-axis direction) of the lens 3, and reflects the laser light by changing the angle in the X-axis direction and the Y-axis direction. For example, a MEMS (Micro Electro Mechanical Systems) mirror is used as the movable mirror 23.

[0029] The laser driver 24 is a drive circuit that drives the light source unit 21. The laser driver 24 drives the light source unit 21 based on, for example, the intensity of the laser light and the temperature of the light source unit 21. The mirror driver 25 is a drive circuit that drives the movable mirror 23. The mirror driver 25 oscillates the movable mirror 23 within a predetermined angle range and at a predetermined timing. The controller 26 is a device that controls the laser driver 24 and the mirror driver 25.

[0030] In the optical engine 20, laser light having a color and intensity corresponding to the pixels of an image to be projected onto the retina RE is emitted from the light source unit 21, passes through the optical component 22, and is reflected by the movable mirror 23. The laser light reflected by the movable mirror 23 is emitted to the metasurface reflector 30 as laser light Ls.

[0031] The metasurface reflector 30 is an optical component that reflects the laser light Ls that has passed through the movable mirror 23, allowing a user wearing the near-eye wearable device 1 to visually recognize an image. No image is displayed on the metasurface reflector 30. The metasurface reflector 30 is provided on the inner surface 3a of the lens 3.

[0032] Next, the configuration of the metasurface reflector 30 will be described with reference to Figs. 3 to 5. Fig. 3 is an enlarged view of the metasurface reflector shown in Fig. 2. Fig. 4 is a perspective view that shows a schematic view of a unit area shown in Fig. 3. Fig. 5 is a cross-sectional view taken along line VV in Fig. 4.

[0033] 3, the metasurface reflector 30 is divided into a plurality of unit regions 31. The plurality of unit regions 31 are provided along the inner surface 3a of the lens 3. The plurality of unit regions 31 are arranged in a two-dimensional array in the horizontal direction (X-axis direction) and vertical direction (Y-axis direction) of the lens 3.

[0034] As shown in Figures 4 and 5, the metasurface reflector 30 includes, in the Z-axis direction, a metal layer 41 (first metal layer), a dielectric layer 42, a metal layer 43 (second metal layer), and a protective layer 44, in that order.

[0035] The metal layer 41 is a base layer. The metal layer 41 is provided on the inner surface 3a of the lens 3. The metal layer 41 is made of a metal having high reflectivity in the visible light region. The metal layer 41 is made of a metal containing at least one element selected from the group consisting of gold (Au), copper (Cu), silver (Ag), and aluminum (Al), for example. The length (thickness d1) of the metal layer 41 in the Z-axis direction may be a length that allows the metal layer 41 to pass a resonant current and reflect light, and is, for example, 50 nm to 1000 nm. Hereinafter, the length in the Z-axis direction may be referred to as "thickness".

[0036] The dielectric layer 42 is a layer that functions as a spacer. The dielectric layer 42 is provided between the metal layer 41 and the metal layer 43 in the Z-axis direction. In this embodiment, the dielectric layer 42 is provided on the metal layer 41. The dielectric layer 42 has a main surface 42a on which the metal layer 43 is provided. The dielectric layer 42 has a dielectric constant that does not inhibit the electromagnetic action of the metal layer 41 and the metal layer 43. The dielectric layer 42 is made of a material that is transparent in the visible light range. The dielectric layer 42 may be made of a material with a high dielectric constant to achieve high reflection characteristics. The dielectric layer 42 is made of one compound selected from a group consisting of silicon oxide (e.g., SiO2), titanium oxide (e.g., TiO2), magnesium oxide (e.g., MgO), and aluminum oxide (e.g., Al2O3). The thickness d2 of the dielectric layer 42 is, for example, 10 nm to 100 nm.

[0037] The metal layer 43 is a layer that excites electromagnetic resonance together with the metal layer 41. The metal layer 41 and the metal layer 43 are stacked in the Z-axis direction via the dielectric layer 42. In this embodiment, the metal layer 43 is provided on the main surface 42a of the dielectric layer 42. The metal layer 43 is made of a metal having high reflectivity in the visible light range. The metal layer 43 is made of a metal including at least one element selected from the group consisting of silver (Ag), aluminum (Al), and copper (Cu), for example.

[0038] The metal layer 43 includes a plurality of metal units 45. The metal units 45 are provided in each of the plurality of unit regions 31. Each metal unit 45 is configured such that the phase change amount φ of the reflected light Lr by the metal unit 45 changes linearly from one end 31a (first end) to the other end 31b (second end) in the X-axis direction of the unit region 31 in which the metal unit 45 is provided. Furthermore, each metal unit 45 is configured such that the phase change amount φ of the reflected light Lr changes substantially by 360° (2π radians) from one end 31a to the other end 31b. The phase change amount φ of the reflected light Lr is the phase change amount of the reflected light Lr when the length of the metal unit 45 in the Y-axis direction is changed, based on the phase of the reflected light Lr at a certain length in the Y-axis direction of the metal unit 45. Hereinafter, the length in the Y-axis direction may be referred to as "width".

[0039] In this embodiment, each metal unit 45 is a single metal body having a trapezoidal shape when viewed from the Z-axis direction. The thickness d3 of each metal unit 45 is, for example, 10 nm to 100 nm. The length of each metal unit 45 in the X-axis direction is the same as or slightly shorter than the length Lx of the unit region 31 in the X-axis direction. The length of each metal unit 45 in the X-axis direction is, for example, 500 nm to 2500 nm.

[0040] The length of the short side of each metal unit 45 (width W1) is set, for example, near the resolution of an exposure device used when forming the metal unit 45. The width W1 is, for example, 10 nm to 200 nm. The length of the long side of each metal unit 45 (width W2) is set to be greater than the width W1 and to a length that provides a phase difference of substantially 360° (2π radians) from the phase of the reflected light Lr at the width W1. The width W2 is, for example, 100 nm to 500 nm. Each metal unit 45 is formed, for example, by photolithography.

[0041] The protective layer 44 is a layer that protects the metal layer 43 (metal unit 45). The protective layer 44 is provided on the surface 45a of each metal unit 45 and covers the surface 45a. The surface 45a is the surface of the metal layer 43 opposite to the dielectric layer 42. The protective layer 44 is made of a metal that is less susceptible to oxidation and sulfurization than the metal layer 43 and has high corrosion resistance. In other words, the protective layer 44 is made of a metal that has a higher standard electrode potential than the metal constituting the metal layer 43. The protective layer 44 is made of a metal that includes at least one element selected from the group consisting of gold (Au), ruthenium (Ru), and iridium (Ir), for example. In a combination of these metals with the metal (for example, silver) constituting the metal layer 43, the attenuation of near-field light is small.

[0042] In this embodiment, the protective layer 44 includes a plurality of metal bodies having the same shape as the metal units 45 when viewed from the Z-axis direction. The thickness d4 of the protective layer 44 (metal bodies) is 20% or less of the thickness d5 which is the sum of the thickness d3 and the thickness d4. The thickness d4 is, for example, 2.5 nm to 25 nm.

[0043] Next, the principle of reflection by the metasurface reflector 30 and a method of determining the length Lx will be described with reference to Figs. 5 to 8. Fig. 6 is a diagram for explaining the principle of reflection by the metasurface reflector shown in Fig. 2. Fig. 7 is a diagram showing the amount of phase change of reflected light at a position in the X-axis direction of the metasurface reflector. Fig. 8 is a diagram for explaining the relationship between the position in the X-axis direction and the length of the metal unit in the X-axis direction.

[0044] As shown in FIGS. 5 and 6, each unit area 31 has an incident angle θ corresponding to the position where the unit area 31 is provided. i When the laser light Ls is incident at the unit area 31, the reflection angle θ r The nanostructure is configured to reflect the laser light Ls at a reflection angle θ of each unit area 31 so that the laser light Ls (reflected light Lr) reflected by each unit area 31 passes through the center of the pupil PP. r Therefore, the incidence angle θ i and reflection angle θ r is determined depending on the position where the unit area 31 is provided. The incident angle θ according to the position where the unit area 31 is provided i and reflection angle θ r The unit area 31 is configured so that:

[0045] Here, the incidence angle θ i is the angle between the normal to the surface onto which the laser light Ls is irradiated and the direction of incidence of the laser light Ls. r is the angle between the normal to the surface onto which the laser light Ls is irradiated and the direction of the reflected light Lr. In a plane including the laser light Ls and the reflected light Lr, when the reflected light Lr is emitted on the opposite side of the normal to the incident light (laser light Ls), the reflection angle θ r is expressed as a positive value, and when the reflected light Lr is emitted on the same side as the incident light (laser light Ls) with the normal as the boundary, the reflection angle θ r is expressed as a negative value.

[0046] For example, as shown in Fig. 6, when the user's pupil PP faces forward, the unit area 31 provided from position Pa to position Pc in the X-axis direction is used. The laser light Ls reflected by the unit area 31 provided at position Pa corresponds to the pixel at the right edge of the image. Position Pb is located midway between positions Pa and Pc, and the laser light Ls reflected by the unit area 31 provided at position Pb corresponds to the pixel at the center of the image. The laser light Ls reflected by the unit area 31 provided at position Pc corresponds to the pixel at the left edge of the image.

[0047] In the unit area 31 provided at the position Pa, the incident angle θ of 30° i Laser light Ls is incident at a reflection angle of 5° r The laser light Ls is reflected by the unit area 31 at the position Pb and emitted as reflected light Lr. i Laser light Ls is incident at a reflection angle of -5° θ r The laser light Ls is reflected by the unit area 31 at the position Pc and emitted as reflected light Lr. i Laser light Ls is incident at a reflection angle of -10°. r The laser light Ls is reflected by the reflector 11 and emitted as reflected light Lr.

[0048] As shown in FIG. 7, the width of the metal unit 45 increases from width W1 to width W2 from one end 31a to the other end 31b. The phase change amount φ at each position in the X-axis direction of the metal unit 45 is substantially the same as the phase change amount φ of a square metal body having 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 amount φ (phase delay amount) at that position. Therefore, the laser light Ls is reflected with a phase change amount φ that differs depending on the position in the X-axis direction, and a wavefront is formed by interference between the reflected lights. That is, a plane wave is generated having a wave vector Φ that is the slope of a function φ(x) that indicates the relationship between the position x and the phase change amount φ in the X-axis direction.

[0049] Here, as shown in FIG. 5, Snell's law can be generalized as follows: i , reflection angle θ r and wave vector Φ, as expressed by equation (1).

number

[0050] The wave vector k0 is expressed as 2π / λ using the wavelength λ of the laser light Ls. The wave vector Φ is expressed as 2π / Lx using the length Lx in the X-axis direction of the unit area 31. By transforming formula (1) using these relationships, formula (2) is obtained.

number

[0051] In formula (2), the wavelength λ of the laser light Ls and the incidence angle θ of the laser light Ls according to the position where the unit region 31 is provided are i and reflection angle θ r By substituting the above, the length Lx of the unit area 31 can be obtained. The laser light Ls contains red, green, and blue components, and the length Lx is determined by using, for example, the wavelength of the green component to which the human eye is most sensitive as the wavelength λ.

[0052] When the length Lx is a positive value, the shape of the metal unit 45 is set to a trapezoidal shape in which the width of the metal unit 45 increases from one end 31a to the other end 31b. When the length Lx is a negative value, the shape of the metal unit 45 is set to a trapezoidal shape in which the width of the metal unit 45 decreases from one end 31a to the other end 31b.

[0053] As described above, the length Lx of each unit area 31 is determined by the wavelength λ of the reflection target and the incident angle θ corresponding to the position where the unit area 31 is provided. i and reflection angle θ r The length of the metal unit 45 in the X-axis direction is equal to or slightly shorter than the length Lx of the unit area 31 in the X-axis direction. Therefore, the length of the metal unit 45 in the X-axis direction is determined by the wavelength λ of the reflection target and the incident angle θ i and reflection angle θ r It is determined from.

[0054] reflection angle θ r is the incidence angle θ i If the angle of incidence θ is less than θ, the length Lx will be a negative value.i and the reflection angle θ r As the difference between the reflection angle θ and the reflection angle θ increases, the absolute value of the length Lx decreases. r becomes smaller, and the incident angle θ i and the reflection angle θ r As the difference between the lengths Lx and Lx becomes larger, the unit regions 31 included in the same array in the X-axis direction have different lengths Lx, and the metal units 45 included in the same array in the X-axis direction also have different lengths in the X-axis direction.

[0055] The length Ly of each unit area 31 is a predetermined fixed value. The length Ly is slightly larger than the width W2. The length Ly may be a length obtained by adding the resolution (e.g., 100 nm) of the exposure device used when forming the metal unit 45 to the width W2, and is set to, for example, 600 nm. The widths W1 and W2 of each metal unit 45 are predetermined fixed values. As described above, the width W1 is set to a value close to the resolution (e.g., 100 nm) of the exposure device used when forming the metal unit 45. The width W2 is set to a length (e.g., 350 nm) that provides a phase difference of substantially 360° (2π radians) from the phase of the reflected light Lr at the width W1.

[0056] Next, the effect of the protective layer 44 on the intensity of the reflected light Lr will be described with reference to Fig. 9. Fig. 9 is a diagram showing the relationship between the proportion of the protective layer and the reflected electric field strength. The horizontal axis of Fig. 9 indicates the proportion of the protective layer 44 (unit: %). The proportion of the protective layer 44 is expressed as the ratio of thickness d4 to thickness d5. The vertical axis of Fig. 9 indicates the reflected electric field strength normalized with the reflected electric field strength when the protective layer 44 is not provided being 1.0.

[0057] The characteristics shown in Fig. 9 were obtained by calculation. Specifically, silver was used as the constituent material of the metal layer 41 and the metal layer 43 (metal unit 45), and SiO2 was used as the constituent material of the dielectric layer 42. The thickness d1 was set to 200 nm, the thickness d2 was set to 40 nm, and the thickness d3 was set to 40 nm. The width W1 was set to 120 nm, and the width W2 was set to 300 nm. The length of the metal unit 45 in the X-axis direction was set to 2250 nm. Gold, ruthenium, and iridium were used as the constituent materials of the protective layer 44, and the thickness of the protective layer 44 was changed for each constituent material, and the reflected electric field intensity at each thickness was calculated.

[0058] As shown in Fig. 9, for any of the constituent materials, the reflected electric field strength decreases as the proportion of the protective layer 44 increases. When the proportion of the protective layer 44 is 20% or less, the reflected electric field strength hardly decreases from the reflected electric field strength when the protective layer 44 is not provided, and is maintained at 90% or more. On the other hand, when the proportion of the protective layer 44 exceeds 20%, the reflected electric field strength decreases rapidly, and when the proportion of the protective layer 44 is about 30% to 40% or more, the reflected electric field strength becomes almost zero. From the above, it can be said that the intensity of the reflected light Lr can be maintained if the proportion of the protective layer 44 is 20% or less.

[0059] Next, a manufacturing method of the near-eye wearable device 1 will be described. First, the lens 3 is prepared and set in a vacuum film-forming apparatus. Then, a metal layer 41 is formed in a desired area on the inner surface 3a of the lens 3. Specifically, the metal layer 41 is formed by vacuum film-forming using a method such as DC (Direct Current) sputtering. The metal layer 41 is formed using a metal material selected from a group consisting of gold (Au), copper (Cu), silver (Ag), and aluminum (Al), or a metal alloy containing at least one element selected from the above group.

[0060] Subsequently, a dielectric layer 42 is formed on the metal layer 41. Specifically, the dielectric layer 42 is formed by vacuum film formation using a method such as RF (Radio Frequency) sputtering. The dielectric layer 42 is formed using a dielectric material such as silicon dioxide (SiO2), titanium oxide (TiO2), magnesium oxide (MgO), or aluminum oxide (Al2O3) that can be formed by a semiconductor process.

[0061] Next, a metal layer that will become the metal layer 43 is formed on the dielectric layer 42. The method of forming the metal layer that will become the metal layer 43 is similar to that of the metal layer 41, and therefore a detailed description will be omitted. Note that, to form the metal layer that will become the metal layer 43, a metal material composed of any metal selected from the group consisting of copper (Cu), silver (Ag), and aluminum (Al), or a metal alloy containing at least one element selected from the above group is used.

[0062] Next, a metal layer (hereinafter, sometimes referred to as "outermost metal layer") that will become protective layer 44 is formed on the metal layer that will become metal layer 43. The method for forming the outermost metal layer is similar to that for metal layer 41, and therefore detailed description will be omitted. Note that, to form the outermost metal layer, a metal material composed of any metal selected from the group consisting of gold (Au), ruthenium (Ru), and iridium (Ir), or a metal alloy containing at least one element selected from the above group is used.

[0063] Next, a metal layer 43 (a plurality of metal units 45) and a protective layer 44 are formed by a photolithography process and an etching process. Specifically, a liquid resist is applied onto 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, a pattern corresponding to the metal units 45 is transferred onto the resist film using an exposure device such as a KrF exposure device and an electron beam lithography device.

[0064] Then, the pattern transferred to the resist film is developed using a developing machine. Then, the metal layer that is the base of the metal layer 43 and the part of the outermost metal layer that is not covered with the pattern are removed by ion milling, and then the resist film is removed with an organic solvent (NMP). As a result, the metal layer 43 and the protective layer 44 are formed. As a result, the metasurface reflector 30 is formed on the inner surface 3a of the lens 3.

[0065] Next, a frame 2 on which an optical engine 20 is mounted is prepared, and a lens 3 on which a metasurface reflector 30 is formed is attached to a rim 2a of the frame 2. In this manner, the near-eye wearable device 1 is manufactured.

[0066] The metasurface reflector 30 does not have to be formed directly on the inner surface 3a of the lens 3. For example, the metasurface reflector 30 may be formed on a substrate such as a sapphire substrate or a flexible sheet. The method for forming the metasurface reflector 30 on the substrate is the same as the method for forming the metasurface reflector 30 on the lens 3. In this case, a plurality of metasurface reflectors 30 may be formed on the substrate. Then, the substrate is cut to obtain a portion including one metasurface reflector 30. Then, the substrate of that portion is attached to a predetermined region of the inner surface 3a of the lens 3, thereby forming the metasurface reflector 30 on the inner surface 3a of the lens 3.

[0067] In the near-eye wearable device 1, the projection device 10, and the metasurface reflector 30 described above, the metasurface reflector 30 is divided into a plurality of unit areas 31 arranged in the X-axis direction along the main surface 42a and in the Y-axis direction along the main surface 42a and intersecting (perpendicular to) the X-axis direction, and each unit area 31 is provided with a metal unit 45, and the protective layer 44 covers the surface 45a of the metal unit 45. Therefore, when the near-eye wearable device 1, the projection device 10, and the metasurface reflector 30 are used, the surface 45a of the metal unit 45 is not exposed to air, so that the possibility of the metal unit 45 being oxidized and sulfurized is reduced. Furthermore, since the protective layer 44 is made of a metal having a higher standard electrode potential than the metal constituting the metal layer 43, the protective layer 44 is less likely to be oxidized and sulfurized than the metal layer 43. Therefore, in the near-eye wearable device 1, the projection device 10, and the metasurface reflector 30, the optical characteristics are less likely to change. As a result, it is possible to suppress deterioration of the reflection characteristics.

[0068] As described above, in the manufacturing process of the metasurface reflector 30, the resist film is removed with an organic solvent (NMP). At this time, if the metal layer 43 (metal unit 45) is exposed, the metal layer 43 may be corroded by the organic solvent. In contrast, in the near-eye wearable device 1, the projection device 10, and the metasurface reflector 30, the protective layer 44 covers the surface 45a of the metal unit 45. Since the protective layer 44 is made of a metal having a higher standard electrode potential than the metal constituting the metal layer 43, the protective layer 44 is less likely to corrode than the metal layer 43. Therefore, in the manufacturing process of the metasurface reflector 30, the possibility of the metal layer 43 corroding can be reduced, and the corrosion resistance can be improved.

[0069] As the ratio of the thickness d4 to the thickness d5 increases, the influence of the protective layer 44 on the reflection characteristics of the metasurface reflector 30 increases. For example, gold (Au) reflects red light but is prone to absorbing green and blue light. Ruthenium and iridium are prone to absorbing light in the visible light region. Therefore, when the ratio of the thickness d4 to the thickness d5 increases, the reflection characteristics of the metasurface reflector 30 may deteriorate. In contrast, in the metasurface reflector 30, the thickness d4 is 20% or less of the thickness d5. Therefore, the protective layer 44 can be provided while suppressing the influence of the protective layer 44 on the reflection characteristics of the metasurface reflector 30. Therefore, it is possible to further suppress the deterioration of the reflection characteristics.

[0070] Metals such as molybdenum, titanium, and tungsten are also difficult to oxidize and sulfurize and have high corrosion resistance, but have a large absorption coefficient in the visible light region. Therefore, when the protective layer 44 is made of these metals, the reflection characteristics of the metasurface reflector 30 may deteriorate. The absorption coefficients of gold, ruthenium, and iridium in the visible light region are smaller than the absorption coefficients of metals such as molybdenum, titanium, and tungsten in the visible light region. Therefore, when the protective layer 44 is made of a metal containing at least one element selected from the group consisting of gold, ruthenium, and iridium, the deterioration of the reflection characteristics of the metasurface reflector 30 can be further suppressed.

[0071] The metal unit 45 is a metal body having a trapezoidal shape when viewed from the Z-axis direction. Therefore, the structure of the metal unit 45 can be simplified compared to a case where the metal unit is composed of multiple metal bodies. Therefore, it is possible to facilitate the manufacture of the metasurface reflector 30.

[0072] When the length of the metal unit 45 in the X-axis direction is 500 nm or more and 2500 nm or less, the reflected light Lr corresponding to a viewing angle of 40° to 60° can be obtained. When the thickness d3 is 10 nm or more and 100 nm or less, electromagnetic resonance with the metal layer 41 via the dielectric layer 42 is effectively generated, and the reflected light Lr with a strong electric field intensity can be obtained. When the width W1 is 10 nm or more and 200 nm or less, and the width W2 is 100 nm or more and 500 nm or less, it is possible to make the phase difference between the phase of the reflected light Lr at the width W1 and the phase of the reflected light Lr at the width W2 360° (2π radians) for the visible laser light Ls. From the above, by setting each dimension of the metal unit 45 within the above-mentioned range, the reflection efficiency for visible light can be increased.

[0073] The metal layer 43 is made of a metal containing at least one element selected from the group consisting of silver, aluminum, and copper. Therefore, the metal layer 43 has a relatively high reflectance in the visible light region and a relatively high electrical conductivity. Therefore, the electromagnetic resonance between the metal layer 41 and the metal layer 43 can be strengthened, and the reflection efficiency can be increased.

[0074] The dielectric layer 42 is made of a material that is transparent in the visible light region, which reduces the visible light absorption rate in the dielectric layer 42, thereby increasing the visible light reflection efficiency.

[0075] The dielectric layer 42 is made of, for example, one compound selected from the group consisting of silicon oxide, titanium oxide, magnesium oxide, and aluminum oxide. In this case, the dielectric layer 42 has a dielectric constant that does not inhibit electromagnetic action. Therefore, the electromagnetic resonance between the metal layer 41 and the metal layer 43 can be strengthened, and the reflection efficiency can be increased.

[0076] The thickness d1 is, for example, 50 nm or more and 1000 nm or less. The thickness d2 is, for example, 10 nm or more and 100 nm or less. In this case, the possibility that the dielectric layer 42 inhibits the electromagnetic action can be reduced, and the possibility that the laser light Ls transmits through the metal layer 41 can be reduced. Therefore, the reflection efficiency can be increased.

[0077] It should be noted that the metasurface reflector, projection device, and near-eye wearable device according to the present disclosure are not limited to the above embodiments.

[0078] The near-eye wearable device 1 may be a pair of virtual reality (VR) glasses.

[0079] In the above embodiment, the projection device 10 projects (draws) an image directly onto the retina RE of the user of the near eyewear wearable device 1, but the image may also be projected onto the metasurface reflector 30.

[0080] The metasurface reflector 30 may be applied to devices other than the projection device 10. For example, the metasurface reflector 30 may be applied to a general image projection surface such as a video screen.

[0081] The multiple unit areas 31 may include a unit area 31 for a red component, a unit area 31 for a green component, and a unit area 31 for a blue component. In the X-axis direction, the unit area 31 for the red component, the unit area 31 for the green component, and the unit area 31 for the blue component may be repeatedly arranged in that order. In the Y-axis direction, the unit area 31 for the red component, the unit area 31 for the green component, and the unit area 31 for the blue component may be repeatedly arranged in that order.

[0082] In the above embodiment, the metal unit 45 is provided in each of all of the unit areas 31 among the multiple unit areas 31, but the metal unit 45 may also be provided in each of some of the unit areas 31 among the multiple unit areas 31.

[0083] The method of determining the length Lx is not limited to the method described in the above embodiment. For example, the length Lx of the unit area 31 located at both ends in the X-axis direction of the metasurface reflector 30 may be determined by the above-mentioned method, and the length Lx of the unit area 31 located therebetween may be determined so as to gradually change from the length Lx of the unit area 31 located at one end in the X-axis direction of the metasurface reflector 30 to the length Lx of the unit area 31 located at the other end.

[0084] The metal unit 45 is not limited to a single trapezoidal metal body, and may be configured, for example, by a plurality of metal bodies arranged in the X-axis direction.

[0085] (Additional Note) [Clause 1] A metasurface reflector, 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; a protective layer covering a surface of the second metal layer opposite to the dielectric layer; Equipped with 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 areas 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 includes metal units provided in all or some of the unit areas, A metasurface reflector, wherein the protective layer is composed of a metal having a standard electrode potential greater than that of the metal constituting the second metal layer.

[0086] [Clause 2] The metasurface reflector described in clause 1, wherein the length of the protective layer in the first direction is less than 20% of the sum of the length of the second metal layer in the first direction and the length of the protective layer in the first direction.

[0087] [Clause 3] The metasurface reflector described in clause 1 or clause 2, wherein the metal unit is a metal body having a trapezoidal shape when viewed from the first direction.

[0088] [Article 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 not less than 10 nm and not more than 100 nm, The length of the short side of the metal body is 10 nm or more and 200 nm or less, The metasurface reflector described in clause 3, wherein the length of the long side of the metal body is greater than the length of the short side and is greater than or equal to 100 nm and less than or equal to 500 nm.

[0089] [Article 5] The metasurface reflector of any one of clauses 1 to 4, wherein the protective layer is made of a metal including at least one element selected from the group consisting of gold, ruthenium, and iridium.

[0090] [Article 6] The metasurface reflector of any one of clauses 1 to 5, wherein the second metal layer is composed of a metal including at least one element selected from the group consisting of silver, aluminum, and copper.

[0091] [Article 7] The metasurface reflector of any one of claims 1 to 6, wherein the dielectric layer is made of a material that is transparent in the visible light region.

[0092] [Article 8] The metasurface reflector of claim 7, wherein the dielectric layer is composed of a compound selected from the group consisting of silicon oxide, titanium oxide, magnesium oxide, and aluminum oxide.

[0093] [Article 9] the length of the dielectric layer in the first direction is not less than 10 nm and not more than 100 nm; The metasurface reflector of any one of clauses 1 to 8, wherein the length of the first metal layer in the first direction is 50 nm or more and 1000 nm or less.

[0094] [Article 10] A projection device mounted on a near-eye wearable device, A light source that emits laser light; a movable mirror for performing scanning with the laser light; A metasurface reflector according to any one of clauses 1 to 9, which reflects the laser light passing through the movable mirror to allow a user wearing the near-eye wearable device to view an image; A projection device comprising:

[0095] [Article 11] A projection device as defined in clause 10, A lens provided with the metasurface reflector; A near-eye trouble device comprising: [Explanation of symbols]

[0096] 1...Near eyewear error device, 3...Lens, 10...Projection device, 21...Light source unit (light source), 23...Movable mirror, 30...Metasurface reflector, 31...Unit area, 41...Metal layer (first metal layer), 42...Dielectric layer, 42a...Main surface, 43...Metal layer (second metal layer), 44...Protective layer, 45...Metal unit, 45a...Surface.

Claims

1. A metasurface reflector, 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; a protective layer covering a surface of the second metal layer opposite to the dielectric layer; Equipped with 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 areas 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 includes metal units provided in all or some of the unit areas, A metasurface reflector, wherein the protective layer is composed of a metal having a standard electrode potential greater than that of the metal constituting the second metal layer.

2. The metasurface reflector of claim 1 , wherein the length of the protective layer in the first direction is 20% or less of the sum of the length of the second metal layer in the first direction and the length of the protective layer in the first direction.

3. The metasurface reflector according to claim 1 or 2, wherein the metal unit is a metal body having a trapezoidal shape when viewed 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 equal to or greater than 10 nm and equal to or less than 100 nm, The length of the short side of the metal body is 10 nm or more and 200 nm or less, The metasurface reflector of claim 3 , wherein the length of the long side 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 of claim 1 or 2, wherein the protective layer is composed of a metal including at least one element selected from the group consisting of gold, ruthenium, and iridium.

6. The metasurface reflector of claim 1 or 2, wherein the second metal layer is composed of a metal including at least one element selected from the group consisting of silver, aluminum, and copper.

7. The metasurface reflector of claim 1 or 2, wherein the dielectric layer is made of a material that is transparent in the visible light region.

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

9. the length of the dielectric layer in the first direction is not less than 10 nm and not more than 100 nm; The metasurface reflector of claim 1 or 2, 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-eye wearable device, A light source that emits laser light; a movable mirror for performing scanning with the laser light; 3. The metasurface reflector according to claim 1 or 2, which reflects the laser light passing through the movable mirror to allow a user wearing the near-eye wearable device to view an image; A projection device comprising:

11. A projection device according to claim 10; A lens provided with the metasurface reflector; A near-eye trouble device comprising:

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