Metasurface reflector, projection device, and near-to-eye wearable device

Abstract

A metasurface reflector is provided with: a first metal layer and a second metal layer laminated 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 on the opposite side from the dielectric layer, the dielectric layer having a main surface on which the second metal layer is provided, the metasurface reflector being divided into a plurality of unit regions arranged in a second direction along the main surface and in a third direction along the main surface and intersecting the second direction, the second metal layer includes metal cells provided in all or some of the plurality of unit regions, and the protective layer is configured from a metal having a standard electrode potential greater than that of the metal constituting the second metal layer.

Description

Technical Field

[0001] This application claims the advantage of priority to Japanese Patent Application No. 2023-160141 filed with the Japan Patent Office on September 25, 2023, the contents of which are incorporated herein by reference in their entirety.

[0002] The present disclosure relates to a metasurface reflector, a projection device, and a near-eye wearable device. Background Art

[0003] Reflectors using metasurface technology are known. For example, U.S. Patent Application Publication No. 2018 / 0113310 describes a near-eye display component that includes an image source and a combiner including a nanostructure surface optically coupled to the image source. The unit cell of the nanostructure surface is composed of a base layer, a dielectric layer, and a meta-atomic layer stacked in sequence. Summary of the invention

[0004] In the near-eye display component described in the specification of U.S. Patent Application Publication No. 2018 / 0113310, the superatomic layer is exposed. When a metal layer such as silver or aluminum is used as the superatomic layer, the metal layer is exposed to the air, and sometimes the metal layer is oxidized or sulfided. In this case, the optical properties change and the reflective properties may deteriorate.

[0005] The present disclosure describes a metasurface reflector, a projection device, and a near-eye wearable device capable of suppressing degradation of reflective properties.

[0006] One aspect of the present disclosure provides a metasurface reflector, which comprises: a first metal layer and a second metal layer, which are stacked in a first direction; a dielectric layer, which is arranged between the first metal layer and the second metal layer in the first direction; and a protective layer, which covers the surface of the second metal layer on the opposite side to the dielectric layer. The dielectric layer has a main surface provided with a second metal layer. 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 in all or part of the unit areas arranged in the plurality of unit areas. The protective layer is composed of a metal having a standard electrode potential greater than that of the metal constituting the second metal layer.

[0007] In the metasurface reflector, the protective layer covers the surface of the second metal layer on the opposite side to the dielectric layer. Therefore, when the metasurface reflector is used, the surface of the second metal layer is not exposed to the air, thereby reducing the possibility of oxidation and sulfidation of the second metal layer. Furthermore, the protective layer is composed of a metal having a larger standard electrode potential than the metal constituting the second metal layer, so the protective layer is less likely to be oxidized and sulfided than the second metal layer. Therefore, in the metasurface reflector, the optical properties are not easily changed. As a result, the degradation of the reflection properties can be suppressed.

[0008] The length of the protective layer in the first direction may also be 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. In this case, the protective layer can be provided while suppressing the influence on the reflection characteristics of the metasurface reflector. Therefore, the degradation of the reflection characteristics can be further suppressed.

[0009] The metal unit may also 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 a case where the metal unit is composed of a plurality of metal bodies. Therefore, the metasurface reflector can be easily manufactured.

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

[0011] The protective layer may be made of a metal containing at least one element selected from gold, ruthenium, and iridium. In this case, the degradation of the reflection characteristics can be suppressed compared with molybdenum, titanium, tungsten, and the like.

[0012] The second metal layer may also be composed of a metal containing at least one element selected from silver, aluminum, and copper. In this case, a second metal layer having a high reflectivity to a certain extent and a high conductivity to a certain extent is obtained. Therefore, the electromagnetic resonance between the first metal layer and the second metal layer can be enhanced, and the reflection efficiency can be improved.

[0013] The dielectric layer may be made of a material that is transparent in the visible light region. In this case, the absorption rate of visible light in the dielectric layer is suppressed, so the reflection efficiency of visible light can be improved.

[0014] The dielectric layer may also be composed of a compound selected from silicon oxide, titanium oxide, magnesium oxide, and aluminum oxide. In this case, a dielectric layer having a dielectric constant that does not hinder electromagnetic action is obtained. Therefore, the electromagnetic resonance between the first metal layer and the second metal layer can be enhanced, and the reflection efficiency can be improved.

[0015] The length of the dielectric layer in the first direction may also be greater than 10 nm and less than 100 nm. The length of the first metal layer in the first direction may also be greater than 50 nm and less than 1000 nm. In this case, the possibility of the dielectric layer obstructing electromagnetic action can be reduced, and the possibility of laser transmission through the first metal layer can be reduced. Therefore, the reflection efficiency can be improved.

[0016] Another aspect of the present disclosure provides a projection device mounted on a near-eye wearable device, which includes: a light source that emits laser light; a movable reflector that is used to perform scanning using the laser light; and the metasurface reflector that reflects the laser light passing through the movable reflector so that a user wearing the near-eye wearable device can recognize an image. In the projection device, it is also possible to suppress degradation of the reflection characteristics.

[0017] Another aspect of the present disclosure provides a near-eye wearable device, which includes the projection device and a lens provided with a metasurface reflector. In the near-eye wearable device, degradation of reflection characteristics can also be suppressed.

[0018] According to the aspects and embodiments of the present disclosure, it is possible to suppress degradation of reflection characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 1 is a stereoscopic diagram showing the appearance of a near-eye wearable device that uses a metasurface reflector according to one embodiment.

[0020] Figure 2 It roughly indicates Figure 1 The structural diagram of the projection device shown.

[0021] Figure 3 Yes Figure 2 An enlarged representation of the metasurface reflector is shown.

[0022] Figure 4 It roughly indicates Figure 3 A stereogram of the unit area shown.

[0023] Figure 5 It is along Figure 4 Cross-sectional view of line VV.

[0024] Figure 6 It is used to illustrate Figure 2 Diagram of the reflection principle of the metasurface reflector shown.

[0025] Figure 7 Graph showing the amount of phase change of reflected light at a position in the X-axis direction of a metasurface reflector.

[0026] Figure 8 This 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.

[0027] Fig. 9 It is a graph showing the relationship between the ratio of the protective layer and the reflected electric field intensity. DETAILED DESCRIPTION

[0028] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, in the description of the accompanying drawings, the same reference numerals are used for the same elements, and repeated descriptions are omitted. In each figure, an XYZ coordinate system is sometimes shown. The Y-axis direction (third direction) is a direction that intersects (for example, is orthogonal to) the X-axis direction (second direction) and the Z-axis direction (first direction). The Z-axis direction is a direction that intersects (for example, is orthogonal to) the X-axis direction and the Y-axis direction. In this specification, the numerical range represented by "to" indicates a range that includes the numerical values ​​recorded before and after the "to" as the minimum value and the maximum value, respectively. The upper limit value and the lower limit value recorded separately can be combined arbitrarily.

[0029] Reference Figure 1 A near-eye wearable device utilizing a metasurface reflector according to one embodiment is described. Figure 1 1 is a stereoscopic diagram showing the appearance of a near-eye wearable device that uses a metasurface reflector according to one embodiment. Figure 1 The near-eye wearable device 1 shown is a device that overlaps images in the field of view of the real world. The near-eye wearable device 1 is, for example, a head-mounted device (head-mounted device), which can be in the form of glasses, goggles, hats, and helmets. As examples of the near-eye wearable device 1, smart glasses such as AR (Augmented Reality) glasses and MR (Mixed Reality) glasses can be cited. The near-eye wearable device 1 includes a frame 2, a lens 3, and a projection device 10.

[0030] The frame 2 includes a pair of eye rings 2a, a nose bridge 2b, and a pair of temples 2c. The eye ring 2a is a portion that holds the lens 3. The nose bridge 2b is a portion that connects the pair of eye rings 2a. The temple 2c is a portion that extends from the eye ring 2a and hangs on the user's ear. The frame 2 may also be a frame without eye rings. The lens 3 has a contact with the eyeball E of the user wearing the near-eye wearable device 1 (see Figure 6 ) facing inner surface 3a (refer to Figure 2 ).

[0031] In this embodiment, the projection device 10 projects light onto the retina RE (refer to FIG. Figure 6 ) is a device for directly projecting (drawing) an image. The projection device 10 is mounted on the near-eye wearable device 1. In this embodiment, in order to project an image to the left and right retinas RE, the near-eye wearable device 1 includes two projection devices 10, but it may also include only one projection device 10.

[0032] Next, refer to Figure 2 The projection device 10 will be described in detail. Figure 2 It roughly indicates Figure 1 The structural diagram of the projection device shown in FIG. Figure 2 As shown, the projection device 10 includes an optical engine 20 and a metasurface reflector 30.

[0033] The optical engine 20 is a device that generates laser light Ls of a color and intensity corresponding to the pixel of the image projected to 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 reflector 23, a laser driver 24, a reflector driver 25, and a controller 26.

[0034] The light source unit 21 emits laser light. As the light source unit 21, for example, a full-color laser module can be used. The light source unit 21 includes a red laser diode, a green laser diode, a blue laser diode, and a combining unit that combines the laser light emitted from each laser diode into one laser light. The light source unit 21 emits the combined laser light. The combined 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 pixel of the image projected onto the retina RE.

[0035] The optical component 22 is a component that performs optical processing on the laser light emitted from the light source unit 21. In the present embodiment, the optical component 22 includes a collimating lens 22a, a slit 22b, and a subtractive optical filter 22c. The collimating lens 22a, the slit 22b, and the subtractive optical filter 22c are arranged in sequence along the optical path of the laser light. The optical component 22 may also have other structures.

[0036] The movable reflector 23 is an optical component for scanning with the laser light Ls. The movable reflector 23 is disposed in the emission direction of the laser light processed by the optical component 22. The movable reflector 23 is configured to be able to swing around an axis extending in the lateral direction (X-axis direction) of the lens 3 and an axis extending in the longitudinal direction (Y-axis direction) of the lens 3, and to change the angle in the X-axis direction and the Y-axis direction to reflect the laser light. As the movable reflector 23, for example, a MEMS (Micro Electro Mechanical Systems) reflector can be used.

[0037] The laser driver 24 is a driving circuit for driving 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 driving circuit for driving the movable mirror 23. The mirror driver 25 causes the movable mirror 23 to swing within a predetermined angle range and timing. The controller 26 is a device for controlling the laser driver 24 and the mirror driver 25.

[0038] In the optical engine 20, laser light of color and intensity corresponding to the pixel of the image projected on the retina RE is emitted from the light source unit 21, and is reflected by the movable mirror 23 through the optical component 22. The laser light reflected by the movable mirror 23 is emitted toward the metasurface reflector 30 as laser light Ls.

[0039] The metasurface reflector 30 is an optical component that reflects the laser light Ls passed through the movable reflector 23 and allows the user wearing the near-eye wearable device 1 to 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.

[0040] Next, refer to Figure 3 to Figure 5 The structure of the metasurface reflector 30 will be described. Figure 3 Yes Figure 2 An enlarged representation of the metasurface reflector is shown. Figure 4 It roughly indicates Figure 3 A stereogram of the unit area shown. Figure 5 It is along Figure 4 Cross-sectional view of line VV.

[0041] like Figure 3 As shown, the metasurface reflector 30 is divided into a plurality of unit areas 31. The plurality of unit areas 31 are arranged along the inner surface 3a of the lens 3. The plurality of unit areas 31 are arranged in a two-dimensional array in the transverse direction (X-axis direction) and the longitudinal direction (Y-axis direction) of the lens 3.

[0042] like Figure 4 and Figure 5As shown, the metasurface reflector 30 includes a metal layer 41 (first metal layer), a dielectric layer 42, a metal layer 43 (second metal layer), and a protective layer 44 in sequence in the Z-axis direction.

[0043] The metal layer 41 is a layer that serves as a base. 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 reflective properties in the visible light region. The metal layer 41 is made of, for example, a metal containing at least one element selected from gold (Au), copper (Cu), silver (Ag), and aluminum (Al). The length of the metal layer 41 in the Z-axis direction (thickness d1) is sufficient as long as the metal layer 41 can pass a resonant current and reflect light, and is, for example, 50 nm to 1000 nm. Hereinafter, the length in the Z-axis direction is sometimes referred to as "thickness".

[0044] The dielectric layer 42 is a layer that functions as a spacer. The dielectric layer 42 is disposed between the metal layer 41 and the metal layer 43 in the Z-axis direction. In the present embodiment, the dielectric layer 42 is disposed on the metal layer 41. The dielectric layer 42 has a main surface 42a on which the metal layer 43 is disposed. The dielectric layer 42 has a dielectric constant that does not hinder the electromagnetic action performed by the metal layer 41 and the metal layer 43. The dielectric layer 42 is composed of a material that is transparent in the visible light region. In order to achieve high reflection characteristics, the dielectric layer 42 may also be composed of a material with a high dielectric constant. The dielectric layer 42 is composed of, for example, a compound selected from silicon oxide (for example, SiO2), titanium oxide (for example, TiO2), magnesium oxide (for example, MgO), and aluminum oxide (for example, Al2O3). The thickness d2 of the dielectric layer 42 is, for example, 10 nm to 100 nm.

[0045] 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 the present embodiment, the metal layer 43 is provided on the main surface 42a of the dielectric layer 42. The metal layer 43 is composed of a metal having a high reflective property in the visible light region. For example, the metal layer 43 is composed of a metal containing at least one element selected from silver (Ag), aluminum (Al), and copper (Cu).

[0046] The metal layer 43 includes a plurality of metal units 45. The metal unit 45 is provided in each of the plurality of unit regions 31. Each metal unit 45 is configured so that the phase change amount of the reflected light Lr generated by the metal unit 45 is The phase change amount of the reflected light Lr changes linearly from one end 31a (first end) in the X-axis direction of the unit area 31 provided with the metal unit 45 toward the other end 31b (second end). The phase change of the reflected light Lr is 360° (2π radians) from one end 31a to the other end 31b. The phase change amount of the reflected light Lr when the length of the metal unit 45 in the Y-axis direction is changed is 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".

[0047] In the present embodiment, each metal unit 45 is a 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 area 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.

[0048] The length (width W1) of the short side of each metal unit 45 is set, for example, to be close to the resolution of the exposure device used when forming the metal unit 45. The width W1 is, for example, 10 nm to 200 nm. The length (width W2) of the long side of each metal unit 45 is set to be greater than the width W1 and to obtain a phase difference of 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.

[0049] 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 on the opposite side to the dielectric layer 42. The protective layer 44 is composed of a metal that is difficult to oxidize and sulfidize and has high corrosion resistance than the metal layer 43. In other words, the protective layer 44 is composed of a metal having a larger standard electrode potential than the metal constituting the metal layer 43. For example, the protective layer 44 is composed of a metal containing at least one element selected from gold (Au), ruthenium (Ru), and iridium (Ir). In the combination of these metals and the metal constituting the metal layer 43 (for example, silver), the attenuation of the near-field light is small.

[0050] In this embodiment, the protective layer 44 includes a plurality of metal bodies having the same shape as the metal unit 45 when viewed from the Z axis direction. The thickness d4 of the protective layer 44 (metal body) is less than 20% of the total thickness d3 and thickness d4, that is, the thickness d5. The thickness d4 is, for example, 2.5 nm to 25 nm.

[0051] Next, refer to Figures 5 to 8 The reflection principle performed by the metasurface reflector 30 and the method for determining the length Lx are described. Figure 6 Is used to illustrate the Figure 2 Diagram of the reflection principle performed by the metasurface reflector shown. Figure 7 Graph showing the amount of phase change of reflected light at a position in the X-axis direction of a metasurface reflector. Figure 8 This 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.

[0052] like Figure 5 and Figure 6 As shown in the figure, each unit area 31 is configured so that when the laser light Ls is incident at an angle θ corresponding to the position where the unit area 31 is provided, i When incident, the reflection angle θ corresponding to the position where the unit area 31 is set r The nanostructure that reflects the laser light Ls. The reflection angle θ of each unit area 31 is set to r , so that the laser light Ls (reflected light Lr) reflected by each unit area 31 passes through the center of the pupil PP. Therefore, the incident angle θ i and reflection angle θ r The unit area 31 is determined according to the position where the unit area 31 is provided. The unit area 31 is configured so as to obtain an incident angle θ corresponding to the position where the unit area 31 is provided. i and reflection angle θ r .

[0053] Here, the incident angle θ i It is the angle between the normal line of the surface irradiated with the laser Ls and the incident direction of the laser Ls. r The reflection angle θ is the angle between the normal line of the surface irradiated with the laser Ls and the emission direction of the reflected light Lr. In the plane containing the laser Ls and the reflected light Lr, when the reflected light Lr is emitted to the opposite side of the incident light (laser Ls) with the normal line as the boundary, the reflection angle θ is r The reflection angle θ is represented by a positive value. When the reflected light Lr is emitted to the same side as the incident light (laser light Ls) with the normal as the boundary, the reflection angle θ r Indicated by negative value.

[0054] For example, Figure 6 As shown, when the user's pupil PP faces forward, the unit areas 31 set at positions Pa to Pc in the X-axis direction are used. The laser light Ls reflected by the unit area 31 set at position Pa corresponds to the pixel at the right end of the image. Position Pb is located between position Pa and position Pc, and the laser light Ls reflected by the unit area 31 set at position Pb corresponds to the pixel at the center of the image. The laser light Ls reflected by the unit area 31 set at position Pc corresponds to the pixel at the left end of the image.

[0055] In the unit area 31 provided at the position Pa, the laser light Ls is incident at an angle θ of 30°. i The incident laser Ls is reflected at an angle of θ of 5°. rThe laser beam Ls is reflected and emitted as reflected light Lr. In the unit area 31 provided at the position Pb, the laser beam Ls is incident at an angle θ of 40°. i The incident laser Ls is reflected at an angle of -5° r The laser beam Ls is reflected and emitted as reflected light Lr. In the unit area 31 provided at the position Pc, the laser beam Ls is incident at an angle θ of 50°. i The incident laser Ls is reflected at an angle of -10° r It is reflected and emitted as reflected light Lr.

[0056] like Figure 7 As shown in FIG. 1 , the width of the metal unit 45 increases from the width W1 to the width W2 as it moves from the one end 31a toward the other end 31b. The phase change amount at each position of the metal unit 45 in the X-axis direction is Phase change of a metal body with a square having sides of the same length as the width at that position when viewed from above The larger the area of ​​the square metal body when viewed from above, the greater the phase change at that position. Therefore, the phase change amount varies depending on the position in the X-axis direction. The laser light Ls is reflected, and thus a wavefront is formed due to interference between the reflected lights. That is, a wavefront having a phase shift amount and a position x in the X-axis direction is generated. The function of the relationship The slope of the plane wave is taken as the wave number vector Φ.

[0057] Here, if Figure 5 As shown, Snell's law generally uses the wave number vector k0 of the laser Ls and the incident angle θ i , reflection angle θ r , and the wave number vector Φ are expressed as formula (1).

[0058] [Mathematical formula 1]

[0059] k0×sinθ i +Φ=k0×sinθ r (1)

[0060] The wave number vector k0 is represented by 2π / λ using the wavelength λ of the laser light Ls. The wave number vector Φ is represented by 2π / Lx using the length Lx in the X-axis direction of the unit area 31. By modifying the equation (1) using these relationships, the equation (2) is obtained.

[0061] [Mathematical formula 2]

[0062]

[0063] By substituting the wavelength λ of the laser light Ls and the incident angle θ of the laser light Ls corresponding to the position where the unit area 31 is provided into the equation (2), i and reflection angle θ r , and the length Lx of the unit area 31 is obtained. The laser light Ls contains a red component, a green component, and a blue component, but 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.

[0064] 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 toward 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 toward the other end 31b.

[0065] As described above, the length Lx of each unit area 31 is determined by the wavelength λ of the reflection object 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 the same as 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 object and the incident angle θ corresponding to the position of the unit area 31 where the metal unit 45 is provided. i and reflection angle θ r Sure.

[0066] At the reflection angle θ r Less than the incident angle θ i When the incident angle θ i With the reflection angle θ r The difference between the two becomes larger, and the absolute value of the length Lx becomes smaller. Figure 8 As shown, in the near-eye wearable device 1, as it moves away from the movable reflector 23, the reflection angle θ r becomes smaller, the incident angle θ i With the reflection angle θ r Therefore, the lengths Lx of the unit regions 31 included in the same arrangement in the X-axis direction are different from each other, and the lengths of the metal units 45 included in the same arrangement in the X-axis direction are also different from each other.

[0067] In addition, 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 can also be the length of the width W2 plus the resolution (e.g., 100nm) of the exposure device used when forming the metal unit 45, for example, set to 600nm. The width W1 and width W2 of each metal unit 45 are predetermined fixed values. As described above, the width W1 is set to be near the resolution of the exposure device used when forming the metal unit 45 (e.g., 100nm). The width W2 is set to a length (e.g., 350nm) that obtains a phase difference of actually 360° (2π radians) from the phase of the reflected light Lr at the width W1.

[0068] Next, refer to Fig. 9 The influence of the protective layer 44 on the intensity of the reflected light Lr will be described. Fig. 9 It is a graph showing the relationship between the ratio of the protective layer and the reflected electric field intensity. Fig. 9 The horizontal axis of represents the ratio (unit: %) of the protective layer 44. The ratio of the protective layer 44 is represented by the ratio of the thickness d4 to the thickness d5. Fig. 9 The vertical axis represents the reflected electric field intensity normalized by taking the reflected electric field intensity when the protective layer 44 is not provided as 1.0.

[0069] Fig. 9 The characteristics shown are obtained by calculation. Specifically, silver is used as the constituent material of the metal layer 41 and the metal layer 43 (metal unit 45), and SiO2 is used as the constituent material of the dielectric layer 42. The thickness d1 is set to 200nm, the thickness d2 is set to 40nm, and the thickness d3 is set to 40nm. The width W1 is set to 120nm, and the width W2 is set to 300nm. The length of the metal unit 45 in the X-axis direction is set to 2250nm. In addition, gold, ruthenium, and iridium are used as the constituent materials of the protective layer 44. For each constituent material, the thickness of the protective layer 44 is changed, and the reflected electric field intensity of each thickness is calculated.

[0070] like Fig. 9 As shown, it can be seen that for any constituent material, as the proportion of the protective layer 44 increases, the reflected electric field intensity decreases. When the proportion of the protective layer 44 is less than 20%, the reflected electric field intensity is almost not reduced from the reflected electric field intensity when the protective layer 44 is not provided, and is maintained at more than 90%. On the other hand, if the proportion of the protective layer 44 exceeds 20%, the reflected electric field intensity decreases sharply, and if the proportion of the protective layer 44 becomes more than 30% to 40%, the reflected electric field intensity becomes almost zero. From the above, it can be said that if the proportion of the protective layer 44 is less than 20%, the intensity of the reflected light Lr can be maintained.

[0071] Next, a method for manufacturing the near-eye wearable device 1 is described. First, a lens 3 is prepared and placed in a vacuum film forming device. 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 composed of any metal selected from gold (Au), copper (Cu), silver (Ag), and aluminum (Al), or a metal alloy containing at least one element selected from the above group.

[0072] Next, 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.

[0073] Next, a metal layer serving as a basis for the metal layer 43 is formed on the dielectric layer 42. The method for forming the metal layer serving as a basis for the metal layer 43 is the same as that for the metal layer 41, and therefore, a detailed description thereof is omitted. In addition, in forming the metal layer serving as a basis for the metal layer 43, a metal material consisting of any metal selected from copper (Cu), silver (Ag), and aluminum (Al), or a metal alloy containing at least one element selected from the above group can be used.

[0074] Next, a metal layer (hereinafter sometimes referred to as the "outermost metal layer") that becomes the basis of the protective layer 44 is formed on the metal layer that becomes the basis of the metal layer 43. The method for forming the outermost metal layer is the same as that for the metal layer 41, and therefore, a detailed description thereof is omitted. In addition, a metal material composed of any metal selected from gold (Au), ruthenium (Ru), and iridium (Ir), or a metal alloy containing at least one element selected from the above group can be used in the formation of the outermost metal layer.

[0075] Next, a metal layer 43 (a plurality of metal units 45) and a protective layer 44 are formed by photolithography and etching. 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, a pattern corresponding to the metal unit 45 is transferred to the resist film using an exposure device such as a KrF exposure device and an electron beam drawing device.

[0076] Then, a developer is used to develop the pattern transferred to the resist film. Then, the metal layer that becomes the basis of the metal layer 43 and the portion of the outermost metal layer not covered by the pattern are removed by ion milling, and then the resist film is removed by an organic solvent (NMP). Thus, the metal layer 43 and the protective layer 44 are formed. Through the above, the super surface reflector 30 is formed on the inner surface 3a of the lens 3.

[0077] Next, the frame 2 on which the optical engine 20 is mounted is prepared, and the lens 3 on which the metasurface reflector 30 is formed is mounted on the frame 2a of the frame 2. In the above manner, the near-eye wearable device 1 is manufactured.

[0078] The metasurface reflector 30 may not be directly formed 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 also be formed on the substrate. Then, by cutting the substrate, a portion including a metasurface reflector 30 is obtained. Then, by attaching the substrate of the portion to a specified area of ​​the inner surface 3a of the lens 3, a metasurface reflector 30 is formed on the inner surface 3a of the lens 3.

[0079] 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 along the X-axis direction of the main surface 42a and along the Y-axis direction intersecting (orthogonal) with the X-axis direction, and a metal unit 45 is provided in each unit area 31, 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 the air, thereby reducing the possibility of oxidation and sulfurization of the metal unit 45. Furthermore, the protective layer 44 is composed of a metal having a larger standard electrode potential than the metal constituting the metal layer 43, and therefore, 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 not easily changed. As a result, the degradation of the reflection characteristics can be suppressed.

[0080] As described above, in the manufacturing process of the metasurface reflector 30, the anti-corrosion film is removed by an organic solvent (NMP). At this time, when 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. The protective layer 44 is composed of a metal having a larger standard electrode potential than the metal constituting the metal layer 43, and therefore, 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 corrosion of the metal layer 43 can be reduced, and the corrosion resistance can be improved.

[0081] As the ratio of thickness d4 to thickness d5 increases, the influence of protective layer 44 on the reflective characteristics of metasurface reflector 30 increases. For example, although gold (Au) reflects red light, it easily absorbs green light and blue light. Ruthenium and iridium easily absorb light in the visible light region. Therefore, if the ratio of thickness d4 to thickness d5 increases, the reflective characteristics of metasurface reflector 30 may deteriorate. In contrast, in metasurface reflector 30, thickness d4 is less than 20% of thickness d5. Therefore, protective layer 44 can be provided while suppressing the influence of protective layer 44 on the reflective characteristics of metasurface reflector 30. Therefore, the degradation of reflective characteristics can be further suppressed.

[0082] Metals such as molybdenum, titanium, and tungsten are also difficult to oxidize and sulfide, and have high corrosion resistance, but have a large absorption coefficient in the visible light region. Therefore, when the protective layer 44 is composed of these metals, the reflection characteristics of the super surface reflector 30 may deteriorate. The absorption coefficient in the visible light region of gold, ruthenium, and iridium is less than the absorption coefficient in the visible light region of metals such as molybdenum, titanium, and tungsten. Therefore, when the protective layer 44 is composed of a metal containing at least one element selected from gold, ruthenium, and iridium, the degradation of the reflection characteristics of the super surface reflector 30 can be further suppressed.

[0083] 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 a plurality of metal bodies. Therefore, the metasurface reflector 30 can be easily manufactured.

[0084] When the length of the metal unit 45 in the X-axis direction is greater than 500nm and less than 2500nm, a reflected light Lr corresponding to a viewing angle of 40° to 60° can be obtained. When the thickness d3 is greater than 10nm and less than 100nm, electromagnetic resonance with the metal layer 41 via the dielectric layer 42 can be effectively generated to obtain reflected light Lr with a strong electric field intensity. When the width W1 is greater than 10nm and less than 200nm, and the width W2 is greater than 100nm and less than 500nm, 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 can be set to 360° (2π radians) with respect to the visible light laser Ls. Based on the above, by setting the dimensions of the metal unit 45 within the above range, the reflection efficiency of visible light can be improved.

[0085] The metal layer 43 is made of a metal containing at least one element selected from silver, aluminum, and copper. Therefore, a metal layer 43 having a high reflectivity to a certain extent in the visible light region and a high conductivity to a certain extent is obtained. Therefore, the electromagnetic resonance between the metal layer 41 and the metal layer 43 can be enhanced, and the reflection efficiency can be improved.

[0086] The dielectric layer 42 is made of a material that is transparent in the visible light region. Therefore, the absorption rate of visible light in the dielectric layer 42 is suppressed, and thus the reflection efficiency of visible light can be improved.

[0087] The dielectric layer 42 is composed of, for example, a compound selected from silicon oxide, titanium oxide, magnesium oxide, and aluminum oxide. In this case, a dielectric layer 42 having a dielectric constant that does not hinder electromagnetic action is obtained. Therefore, the electromagnetic resonance between the metal layer 41 and the metal layer 43 can be enhanced, and the reflection efficiency can be improved.

[0088] The thickness d1 is, for example, not less than 50 nm and not more than 1000 nm. The thickness d2 is, for example, not less than 10 nm and not more than 100 nm. In this case, the possibility that the dielectric layer 42 blocks the electromagnetic effect can be reduced, and the possibility that the laser light Ls passes through the metal layer 41 can be reduced. Therefore, the reflection efficiency can be improved.

[0089] In addition, the metasurface reflector, projection device, and near-eye wearable device disclosed in the present invention are not limited to the above-mentioned embodiments.

[0090] The near-eye wearable device 1 may also be VR (Virtual Reality) glasses.

[0091] In the above-mentioned embodiment, the projection device 10 directly projects (draws) an image onto the retina RE of the user of the near-eye wearable device 1 , but the image may also be projected onto the meta-surface reflector 30 .

[0092] The metasurface reflector 30 may also be applied to devices other than the projection device 10. For example, the metasurface reflector 30 may also be applied to a common image projection surface such as an image screen.

[0093] The plurality of unit regions 31 may include a unit region 31 for a red component, a unit region 31 for a green component, and a unit region 31 for a blue component. In the X-axis direction, the unit region 31 for a red component, the unit region 31 for a green component, and the unit region 31 for a blue component may be repeatedly arranged in sequence. In the Y-axis direction, the unit region 31 for a red component, the unit region 31 for a green component, and the unit region 31 for a blue component may be repeatedly arranged in sequence.

[0094] In the above embodiment, the metal unit 45 is provided in each of all the unit regions 31 among the plurality of unit regions 31 , but the metal unit 45 may be provided in each of a part of the unit regions 31 among the plurality of unit regions 31 .

[0095] The method for 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 at both ends of the metasurface reflector 30 in the X-axis direction is determined by the above method, and the length Lx of the unit area 31 in the middle can also be determined to gradually change from the length Lx of the unit area 31 at one end of the metasurface reflector 30 in the X-axis direction to the length Lx of the unit area 31 at the other end.

[0096] The metal unit 45 is not limited to a single metal body of a trapezoidal shape, and may be composed of, for example, a plurality of metal bodies arranged in the X-axis direction.

[0097] (Note)

[0098] [Article 1]

[0099] A metasurface reflector having:

[0100] A first metal layer and a second metal layer, which are stacked in a first direction;

[0101] a dielectric layer disposed between the first metal layer and the second metal layer in the first direction;

[0102] a protective layer covering a surface of the second metal layer opposite to the dielectric layer,

[0103] The dielectric layer has a main surface provided with the second metal layer,

[0104] 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.

[0105] The second metal layer includes metal units disposed in all or part of the plurality of unit regions.

[0106] The protective layer is made of a metal having a larger standard electrode potential than a metal constituting the second metal layer.

[0107] [Article 2]

[0108] A metasurface reflector according to clause 1, wherein:

[0109] The length of the protective layer in the first direction is less than or equal to 20% of the total length of the second metal layer in the first direction and the length of the protective layer in the first direction.

[0110] [Article 3]

[0111] A metasurface reflector according to clause 1 or 2, wherein:

[0112] The metal unit is a metal body having a trapezoidal shape when viewed from the first direction.

[0113] [Article 4]

[0114] A metasurface reflector according to clause 3, wherein:

[0115] The length of the metal body in the second direction is greater than or equal to 500 nm and less than or equal to 2500 nm,

[0116] The length of the metal body in the first direction is greater than or equal to 10 nm and less than or equal to 100 nm,

[0117] The length of the short side of the metal body is greater than or equal to 10 nm and less than or equal to 200 nm,

[0118] 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.

[0119] [Article 5]

[0120] A metasurface reflector according to any one of clauses 1 to 4, wherein:

[0121] The protective layer is composed of a metal containing at least one element selected from the group consisting of gold, ruthenium, and iridium.

[0122] [Article 6]

[0123] A metasurface reflector according to any one of clauses 1 to 5, wherein:

[0124] The second metal layer is made of a metal containing at least one element selected from the group consisting of silver, aluminum, and copper.

[0125] [Article 7]

[0126] A metasurface reflector according to any one of clauses 1 to 6, wherein:

[0127] The dielectric layer is made of a material that is transparent in the visible light region.

[0128] [Article 8]

[0129] A metasurface reflector according to clause 7, wherein:

[0130] The dielectric layer is composed of a compound selected from silicon oxide, titanium oxide, magnesium oxide, and aluminum oxide.

[0131] [Article 9]

[0132] A metasurface reflector according to any one of clauses 1 to 8, wherein:

[0133] The length of the dielectric layer in the first direction is greater than or equal to 10 nm and less than or equal to 100 nm.

[0134] The length of the first metal layer in the first direction is greater than or equal to 50 nm and less than or equal to 1000 nm.

[0135] [Article 10]

[0136] A projection device, mounted on a near-eye wearable device, comprises:

[0137] a light source that emits laser light;

[0138] a movable reflecting mirror for performing scanning using the laser light;

[0139] The metasurface reflector described in any one of Items 1 to 9 reflects the laser light passing through the movable reflector so that a user wearing the near-eye wearable device can recognize an image.

[0140] [Article 11]

[0141] A near-eye wearable device comprising:

[0142] The projection device as described in clause 10;

[0143] A lens is provided with the metasurface reflector.

Claims

1. A metasurface reflector, wherein: have: A first metal layer and a second metal layer, which are stacked in a first direction; a dielectric layer disposed between the first metal layer and the second metal layer in the first direction; and a protective layer covering a surface of the second metal layer opposite to the dielectric layer, The dielectric layer has a main surface provided with the second metal layer, 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 disposed in all or part of the plurality of unit regions. The protective layer is made of a metal having a larger standard electrode potential than a metal constituting the second metal layer.

2. The metasurface reflector according to claim 1, wherein: The length of the protective layer in the first direction is less than or equal to 20% of the total 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 metasurface reflector according to claim 3, wherein: The length of the metal body in the second direction is greater than or equal to 500 nm and less than or equal to 2500 nm, The length of the metal body in the first direction is greater than or equal to 10 nm and less than or equal to 100 nm, The length of the short side of the metal body is greater than or equal to 10 nm and less than or equal to 200 nm, 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.

5. The metasurface reflector according to any one of claims 1 to 4, wherein: The protective layer is composed of a metal containing at least one element selected from the group consisting of gold, ruthenium, and iridium.

6. The metasurface reflector according to any one of claims 1 to 5, wherein: The second metal layer is made of a metal containing at least one element selected from the group consisting of silver, aluminum, and copper.

7. The metasurface reflector according to any one of claims 1 to 6, 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 a compound selected from silicon oxide, titanium oxide, magnesium oxide, and aluminum oxide.

9. The metasurface reflector according to any one of claims 1 to 8, wherein: The length of the dielectric layer in the first direction is greater than or equal to 10 nm and less than or equal to 100 nm. The length of the first metal layer in the first direction is greater than or equal to 50 nm and less than or equal to 1000 nm.

10. A projection device, wherein: Mounted on a near-eye wearable device, have: a light source that emits laser light; a movable reflecting mirror for performing scanning using the laser light; and The metasurface reflector according to any one of claims 1 to 9 reflects the laser light through the movable reflector so that a user wearing the near-eye wearable device can recognize an image.

11. A near-eye wearable device, wherein: have: The projection device according to claim 10; and A lens is provided with the metasurface reflector.

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