Patent Application
20250102713
This application claims the benefit of priority from Japanese Patent Application No. 2023-160135 filed with the Japan Patent Office on Sep. 25, 2023, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a metasurface reflector, a projection device, and a near-eye wearable device.
Reflectors using metasurface technology are known. For example, Non-Patent Document 1 (Zhiwei Li, Lirong Huang, Kun Lu, Yali Sun, Li Min, “Continuous metasurface for high-performance anomalous reflection”, Applied Physics Express, The Japan Society of Applied Physics, Oct. 7, 2014, Volume 7) describes a metasurface reflector in which a plurality of trapezoidal antennas is two dimensionally arranged.
In the metasurface reflector described in Non-Patent Document 1, the trapezoidal antennas having the same shape are regularly arranged two dimensionally. Therefore, the plurality of trapezoidal antennas arranged in the vertical direction and the horizontal direction have a periodicity. Due to this periodicity, unnecessary scattered light may occur.
The present disclosure describes a metasurface reflector, a projection device, and a near-eye wearable device capable of reducing unnecessary scattered light.
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; and a dielectric layer provided between the first metal layer and the second metal layer in the first direction. The dielectric layer includes a main surface on which the second metal layer is provided. The metasurface reflector is divided into a plurality of unit regions arranged in a second direction along the main surface and in a third direction along the main surface and intersecting the second direction. The second metal layer includes metal units respectively provided in all or some of the plurality of unit regions. Lengths of metal units, which are arranged in the second direction and set for a same wavelength among the metal units, in the second direction are different from each other.
In the metasurface reflector, the lengths in the second direction of metal units, which are arranged in the second direction and set for the same wavelength among the metal units, are different from each other. For example, when the metal units provided in the unit regions within a certain range have the same length in the second direction, the metal units having the same length are arranged in the second direction, and the periodicity of the metal units occurs in the second direction. On the other hand, in the above-described metasurface reflector, since the periodicity of the metal units is less likely to occur in the second direction, it is possible to reduce the possibility that unnecessary scattered light occurs in the second direction. As a result, unnecessary scattered light can be reduced.
Each metal unit of the metal units may be configured such that a phase change amount of reflected light linearly changes from a first end to a second end in the second direction of a unit region in which the metal unit is provided. A length of the metal unit in the second direction may be determined by a wavelength to be reflected, and an incident angle and a reflection angle corresponding to a position of the unit region in which the metal unit is provided. In this case, a plane wave having the gradient of the function indicating the relationship between the position in the second direction and the phase change amount of the reflected light as the wave vector can be generated. Therefore, by adjusting the length of the metal unit in the second direction, a desired reflection angle can be obtained with respect to the incident angle corresponding to the position of the unit region. Accordingly, since the reflection angles smoothly change in the second direction, it is possible to suppress the light bleeding.
Each of the metal units 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 as compared with the case where the metal unit is composed of a plurality of metal bodies. Accordingly, the manufacturing of the metasurface reflector can be facilitated.
A length of the metal body in the second direction may be 500 nm or more and 2500 nm or less. A length of the metal body in the first direction may be 10 nm or more and 100 nm or less. A length of a short side of the metal body may be 10 nm or more and 200 nm or less. A length of a long side of the metal body may be larger 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 enhanced.
The plurality of unit regions may include reflection regions each provided with one of the metal units and missing regions each without any metal unit. The reflection regions and the missing regions may be arranged irregularly in an arrangement in the third direction. In this case, the metal units are arranged irregularly in the third direction. Accordingly, since the periodicity of the metal units is less likely to occur in the third direction, it is possible to reduce the possibility that unnecessary scattered light occurs in the third direction. As a result, unnecessary scattered light can be further reduced.
The reflection regions and the missing regions may be arranged irregularly in an arrangement in the second direction. In this case, the metal units are arranged irregularly in the second direction. Accordingly, since the periodicity of the metal units is even less likely to occur in the second direction, it is possible to further reduce the possibility that unnecessary scattered light occurs in the second direction. As a result, unnecessary scattered light can be further reduced.
A number of the missing regions may be 10% or more and 20% or less of a total number of unit regions included in the metasurface reflector. In this case, it is possible to reduce unnecessary scattered light while suppressing a decrease in the intensity of the reflected light.
The plurality of unit regions may include first unit regions for a red component, second unit regions for a green component, and third unit regions for a blue component. The first unit regions, the second unit regions, and the third unit regions may be arranged repeatedly one by one in that order in the second direction and the third direction. Lengths of the metal units, which are provided in the first unit regions arranged in the second direction, in the second direction may be different from each other. Lengths of the metal units, which are provided in the second unit regions arranged in the second direction, in the second direction may be different from each other. Lengths of the metal units, which are provided in the third unit regions arranged in the second direction, in the second direction may be different from each other. The reflection angle by the metal unit varies with the wavelength. Therefore, the laser light having a plurality of wavelength components may not be reflected at a desired reflection angle. In the above configuration, since the first unit regions for the red component, the second unit regions for the green component, and the third unit regions for the blue component are provided, each component can be reflected at the desired reflection angle. Further, since the lengths of the metal units for the same wavelength component are different from each other, the periodicity of the metal units is less likely to occur in the second direction. Accordingly, it is possible to reduce the possibility that unnecessary scattered light occurs in the second direction. As a result, it is possible to reflect each component of the laser light at the desired reflection angle while reducing unnecessary scattered light.
The second metal layer may be made of a metal containing at least one element selected from a group consisting of silver, aluminum, copper, and gold. In this case, the second metal layer having a relatively high reflectance and a relatively high electric conductivity can be obtained. Accordingly, the electromagnetic resonance between the first metal layer and the second metal layer can be strengthened, and the reflection efficiency can be enhanced.
The dielectric layer may be made of a material transparent in a visible light region. In this case, since the absorption rate of visible light in the dielectric layer is suppressed, the reflection efficiency for visible light can be enhanced.
The dielectric layer may be made of a compound selected from a group consisting of silicon oxide, titanium oxide, magnesium oxide, and aluminum oxide. In this case, the dielectric layer having a dielectric constant that does not interfere with the electromagnetic action can be obtained. Accordingly, the electromagnetic resonance between the first metal layer and the second metal layer can be strengthened, and the reflection efficiency can be enhanced.
A length of the dielectric layer in the first direction may be 10 nm or more and 100 nm or less. A 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 interferes with the electromagnetic action can be reduced, and the possibility that the laser light passes through the first metal layer can be reduced. Accordingly, the reflection efficiency can be enhanced.
A projection device according to another aspect of the present disclosure is a device mounted on a near-eye wearable device. The projection device includes: a light source that emits laser light; a movable mirror that performs scanning with the laser light; and the above-described metasurface reflector that reflects the laser light having passed through the movable mirror to cause a user wearing the near-eye wearable device to visually recognize an image. In the projection device as well, unnecessary scattered light can be reduced.
A near-eye wearable device according to still another aspect of the present disclosure includes: the above-described projection device; and a lens provided with the metasurface reflector. In the near-eye wearable device as well, unnecessary scattered light can be reduced.
According to each aspect and each embodiment of the present disclosure, unnecessary scattered light can be reduced.
Hereinafter, 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 denoted by the same reference numerals, and redundant description will be omitted. In each figure, an XYZ coordinate system may be shown. The Y-axis direction (third direction) is a direction intersecting (for example, orthogonal to) the X-axis direction (second direction) and the Z-axis direction (first direction). The Z-axis direction is a direction intersecting (for example, orthogonal to) the X-axis direction and the Y-axis direction. In the present specification, the numerical ranges indicated by “to” represent ranges that include the values described before and after “to” as the minimum and maximum values, respectively. The individually described upper and lower limit values can be combined arbitrarily.
A near-eye wearable device to which a metasurface reflector according to an embodiment is applied will be described with reference to
The frame 2 includes a pair of rims 2a, a bridge 2b, and a pair of temples 2c. The rim 2a is a portion for holding the lens 3. The bridge 2b is a portion connecting the pair of rims 2a. The temple 2c extends from the rim 2a and is a portion to be put on an ear of a user. The frame 2 may be a rimless frame. The lens 3 has an inner surface 3a (refer to
In the present embodiment, the projection device 10 is a device for directly projecting (drawing) an image onto a retina RE (refer to
Next, the projection device 10 will be described in detail with reference to
The optical engine 20 is a device that generates laser light Ls having a color and intensity corresponding to a pixel 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), optical components 22, a movable mirror 23, a laser driver 24, a mirror driver 25, and a controller 26.
The light source unit 21 emits laser light. As the light source unit 21, for example, a full-color laser module is used. The light source unit 21 includes a red laser diode, a green laser diode, a blue laser diode, and a multiplexer that multiplexes laser lights emitted from laser diodes into one laser light. The light source unit 21 emits the multiplexed laser light. The multiplexed laser light contains a component having a wavelength of red (red component), a component having a wavelength of green (green component), and a component having a wavelength of blue (blue component). The light source unit 21 emits laser light having a color and intensity corresponding to a pixel of an image to be projected onto the retina RE.
The optical components 22 are components that optically process the laser light emitted from the light source unit 21. In the present embodiment, the optical components 22 include 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 components 22 may have other configurations.
The movable mirror 23 is an optical component for performing scanning with the laser light Ls. The movable mirror 23 is provided in a direction in which the laser light processed by the optical components 22 is emitted. The movable mirror 23 is configured to be swingable about an axis extending in the horizontal direction (X-axis direction) of the lens 3 and about an axis extending in the vertical direction (Y-axis direction) of the lens 3, for example, and reflects the laser light while changing the angle in the X-axis direction and the Y-axis direction. As the movable mirror 23, for example, a micro electro mechanical systems (MEMS) mirror is used.
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 swings the movable mirror 23 within a predetermined angle range and at a predetermined timing. The controller 26 is a device for controlling the laser driver 24 and the mirror driver 25.
In the optical engine 20, laser light having a color and intensity corresponding to a pixel of an image to be projected onto the retina RE is emitted from the light source unit 21, passes through the optical components 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 the laser light Ls.
The metasurface reflector 30 is an optical component that reflects the laser light Ls that has passed through the movable mirror 23 to cause 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.
Next, the configuration of the metasurface reflector 30 will be described with reference to
As shown in
In the arrangement in the Y-axis direction, the reflection regions 32 and the missing regions 33 are arranged irregularly. In other words, in the arrangement in the Y-axis direction, the reflection regions 32 and the missing regions 33 are distributed in a non-uniform sequence.
Hereinafter, the arrangement in the X-axis direction may be referred to as a “row”, and the arrangement in the Y-axis direction may be referred to as a “column”. The number of missing regions 33 is, for example, 10% to 20% of the total number of unit regions 31 included in the metasurface reflector 30. In the present embodiment, all the unit regions 31 in the arrangement (one row) in the X-axis direction are set either as the reflection regions 32 or the missing regions 33. For example, the row of the row number corresponding to the random value obtained by the random function is determined as a row of the missing regions 33.
As shown in
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 reflection characteristics in the visible light region. The metal layer 41 is made of, for example, a metal containing at least one element selected from the group consisting of gold (Au), copper (Cu), silver (Ag), and aluminum (Al). The length (thickness d1) of the metal layer 41 in the Z-axis direction may be any length as long as the metal layer 41 is capable of passing a resonance current and reflecting light. The thickness d1 is, for example, 50 nm to 1000 nm. Hereinafter, the length in the Z-axis direction may be referred to as “thickness”.
The dielectric layer 42 is a layer functioning 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 the present 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 interfere with 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 region. The dielectric layer 42 may be made of a material having a high dielectric constant in order to achieve high reflection characteristics. The dielectric layer 42 is made of, for example, one compound selected from the group consisting of silicon oxides (e.g., SiO2), titanium oxides (e.g., TiO2), magnesium oxides (e.g., MgO), and aluminum oxides (e.g., Al2O3). The thickness d2 of the dielectric layer 42 is, for example, 10 nm to 100 nm.
The metal layer 43 is a layer for exciting electromagnetic resonance together with the metal layer 41. The metal layer 41 and the metal layer 43 are stacked in the Z-axis direction with the dielectric layer 42 interposed therebetween. 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 made of a metal having high reflection characteristics in the visible light region. Similarly to the metal layer 41, the metal layer 43 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 metal layer 43 includes a metal unit 45. The metal unit 45 is provided in each of some of the unit regions 31 (the reflection regions 32) among the plurality of unit regions 31. The 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 32a (first end) to the other end 32b (second end) in the X-axis direction of the reflection region 32 in which the metal unit 45 is provided. Further, the 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 32a to the other end 32b. The phase change amount φ of the reflected light Lr is an amount by which the phase of the reflected light Lr from the phase of the reflected light Lr at a certain length of the metal unit 45 in the Y-axis direction changes when the length of the metal unit 45 in the Y-axis direction is changed. Hereinafter, the length in the Y-axis direction may be referred to as “width”.
In the present embodiment, the metal unit 45 is a single metal body having a trapezoidal shape when viewed from the Z-axis direction. The thickness d3 of the metal unit 45 is, for example, 10 nm to 100 nm. The length of the metal unit 45 in the X-axis direction is equal to or slightly shorter than the length Lx of the reflection region 32 in the X-axis direction. The length of the metal unit 45 in the X-axis direction is, for example, 500 nm to 2500 nm.
The length (width W1) of the short side of the metal unit 45 is set, for example, to a value close to the resolution of the exposure device used for 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 the metal unit 45 is larger than the width W1, and is set to a length that a phase difference of substantially 360° (2π radians) can be obtained from the phase of the reflected light Lr at the width W1. The width W2 is, for example, 100 nm to 500 nm. The metal unit 45 is formed by photolithography, for example.
Next, a method for determining the length Lx as well as the principle of reflection by the metasurface reflector 30 will be described with reference to
As shown in
Here, the incident angle θi is an angle formed by a normal line of a surface irradiated with the laser light Ls and an incident direction of the laser light Ls. The reflection angle θr is an angle formed by a normal line of a surface irradiated with the laser light Ls and an emission direction of the reflected light Lr. In the plane including the laser light Ls and the reflected light Lr, when the reflected light Lr is emitted on the side opposite to the incident light (laser light Ls) with the normal line as a boundary, the reflection angle θr is expressed by 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 line as a boundary, the reflection angle θr is expressed by a negative value.
For example, as shown in
In the reflection region 32 provided at the position Pa, the laser light Ls is incident at an incident angle θi of 30°, and the laser light Ls is reflected at a reflection angle θr of 5° to be emitted as the reflected light Lr. In the reflection region 32 provided at the position Pb, the laser light Ls is incident at an incident angle θi of 40°, and the laser light Ls is reflected at a reflection angle θr of −5° to be emitted as the reflected light Lr. In the reflection region 32 provided at the position Pc, the laser light Ls is incident at an incident angle θi of 50°, and the laser light Ls is reflected at a reflection angle θr of −10° to be emitted as the reflected light Lr.
As shown in
Here, as shown in
The wave vector k0 is expressed by 2π/λ using the wavelength λ of the laser light Ls. The wave vector Φ is expressed by 2π/Lx using the length Lx of the reflection region 32 in the X-axis direction. By transforming Equation (1) using these relations, Equation (2) is obtained.
The length Lx of the reflection region 32 is obtained by substituting the wavelength λ of the laser light Ls and the incident angle θi and the reflection angle θr of the laser light Ls corresponding to the position where the reflection region 32 is provided into Equation (2). The laser light Ls contains a red component, a green component, and a blue component, but the length Lx is determined using, for example, the wavelength of the green component, to which the human eyes have the highest sensitivity, as the wavelength λ.
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 32a to the other end 32b. 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 32a to the other end 32b.
The length Lx of the missing region 33 in the X-axis direction is obtained by substituting the wavelength λ of the laser light Ls, and the incident angle θi and the reflection angle θr of the laser light Ls corresponding to the position where the missing region 33 is provided when the missing region 33 is assumed to be the reflection region 32 into Equation (2).
As described above, the length Lx of each unit region 31 is determined by the wavelength λ to be reflected, and the incident angle θi and the reflection angle θr corresponding to the position where the unit region 31 is provided. The length of the metal unit 45 in the X-axis direction is equal to or slightly shorter than the length Lx of the reflection region 32 in the X-axis direction. Accordingly, the length of the metal unit 45 in the X-axis direction is determined by the wavelength A to be reflected, and the incident angle θi and the reflection angle θr corresponding to the position of the reflection region 32 where the metal unit 45 is provided.
When the reflection angle θr is smaller than the incident angle θi, the length Lx becomes a negative value. As the difference between the incident angle θi and the reflection angle θr increases, the absolute value of the length Lx decreases. As shown in
Note that the length Ly of each unit region 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 (for example, 100 nm) of the exposure device used for forming the metal unit 45 to the width W2, and is set to, for example, 600 nm. The width W1 and the width 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 (for example, 100 nm) of the exposure device used for forming the metal unit 45. The width W2 is set to a length (for example, 350 nm) at which a phase difference of substantially 360° (2π radians) can be obtained from the phase of the reflected light Lr at the width W1.
Next, the influence of the missing region 33 on the intensity of the unnecessary scattered light and the intensity of the reflected light will be described with reference to
As shown in
Next, a method of manufacturing the near-eye wearable device 1 will be described. First, the lens 3 is prepared and set in a vacuum film deposition device. Then, the 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 deposition using a technique such as a direct current (DC) sputtering. For forming the metal layer 41, a metal material composed of any metal 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-described group is used.
Subsequently, the dielectric layer 42 is formed on the metal layer 41. Specifically, the dielectric layer 42 is formed by vacuum film deposition using a technique such as a radio frequency (RF) sputtering. For forming the dielectric layer 42, a dielectric material such as silicon dioxide (SiO2), titanium oxide (TiO2), magnesium oxide (MgO) or aluminum oxide (Al2O3) which can be formed by a semiconductor process is used.
Subsequently, a metal layer (hereinafter referred to as an “outermost metal layer”) which is a base of the metal layer 43 is formed on the dielectric layer 42. Since the method of forming the outermost metal layer is the same as that of the metal layer 41, a detailed description thereof will be omitted.
Subsequently, the metal layer 43 (the plurality of metal units 45) is 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. Then, the pattern transferred to the resist film is developed using a developing machine. Then, a portion of the outermost metal layer not covered with the pattern is removed by ion milling, and then the resist film is removed. Thus, the metal layer 43 is formed. As described above, the metasurface reflector 30 is formed on the inner surface 3a of the lens 3.
Subsequently, 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 rim 2a of the frame 2. As described above, the near-eye wearable device 1 is manufactured.
The metasurface reflector 30 is not required to be directly formed on the inner surface 3a of the lens 3. For example, the metasurface reflector 30 may be formed on a base material such as a sapphire substrate or a flexible sheet. The method of forming the metasurface reflector 30 on the base material is the same as the method of forming the metasurface reflector 30 on the lens 3. In this case, a plurality of metasurface reflectors 30 may be formed on the base material. Then, by cutting the base material, a portion including one metasurface reflector 30 is obtained. The metasurface reflector 30 is formed on the inner surface 3a of the lens 3 by attaching the portion of the base material to a predetermined area of the inner surface 3a of the lens 3.
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 the plurality of unit regions 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 (orthogonal to) the X-axis direction, and the metal unit 45 is provided in each reflection region 32 among the plurality of unit regions 31. All the metal units 45 are set for the same wavelength λ. The lengths in the X-axis direction of the metal units 45 included in one arrangement in the X-axis direction (that is, one row) are different from each other.
For example, in the case where the lengths in the X-axis direction of the metal units 45 provided in the reflection regions 32 within a certain range are the same, the metal units 45 having the same length in the X-axis direction are arranged, so that the periodicity of the metal units 45 occurs in the X-axis direction. On the other hand, in the near-eye wearable device 1, the projection device 10, and the metasurface reflector 30 described above, the metal units 45 having different lengths in the X-axis direction are arranged, so that the periodicity of the metal units 45 is less likely to occur in the X-axis direction. This makes it possible to reduce the possibility of generating unnecessary scattered light in the X-axis direction. As a result, unnecessary scattered light can be reduced.
For example, it is conceivable to make the lengths of the metal units 45 in the X-axis direction, which are provided in the reflection regions 32 within a single range, the same for each predetermined range. In this case, within the same range, the metal units 45 having the same length in the X-axis direction are arranged, and the reflection angles θr of the reflected light Lr reflected by the metal units 45 are substantially the same. Accordingly, a large change occurs in the reflection angle θr between the two adjacent ranges, and there is a possibility that light bleeding occurs when the reflected light Lr is combined.
On the other hand, in the near-eye wearable device 1, the projection device 10, and the metasurface reflector 30 described above, each metal unit 45 is configured such that the phase change amount φ of the reflected light Lr linearly changes from one end 32a to the other end 32b of the reflection region 32 where the metal unit 45 is provided. According to this configuration, a plane wave having the gradient of the function φ(x) indicating the relationship between the position x in the X-axis direction and the phase change amount φ of the reflected light Lr as the wave vector Φ is generated. In this case, since Equations (1) and (2) are satisfied, the length of the metal unit 45 in the X-axis direction is determined by the wavelength λ to be reflected, the incident angle θi and the reflection angle θr corresponding to the position of the reflection region 32 where the metal unit 45 is provided. Therefore, by adjusting the length of the metal unit 45 in the X-axis direction, a desired reflection angle θr can be obtained with respect to the incident angle θi corresponding to the position of the reflection region 32. Accordingly, since the reflection angles θr smoothly change in the X-axis direction, it is possible to suppress the light bleeding.
In the arrangement in the Y-axis direction, the reflection regions 32 and the missing regions 33 are arranged irregularly. Therefore, the metal units 45 are arranged irregularly in the Y-axis direction. Accordingly, since the periodicity of the metal units 45 is less likely to occur in the Y-axis direction, it is possible to reduce the possibility that unnecessary scattered light occurs in the Y-axis direction. As a result, unnecessary scattered light can be further reduced.
The number of missing regions 33 is 10% or more and 20% or less of the total number of unit regions 31 included in the metasurface reflector 30. This configuration makes it possible to reduce unnecessary scattered light while suppressing a decrease in the intensity of reflected light.
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 as compared with the case where the metal unit is composed of a plurality of metal bodies. Accordingly, the manufacturing of the metasurface reflector 30 can be facilitated.
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, the electromagnetic resonance with the metal layer 41 through the dielectric layer 42 is effectively generated, and the reflected light Lr having a strong electric field strength 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, 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) for the laser light Ls of the visible light. As described above, by setting the respective dimensions of the metal unit 45 within the above-described ranges, the reflection efficiency for visible light can be enhanced.
The metal layer 43 is made of a metal containing at least one element selected from the group consisting of silver, aluminum, copper, and gold. Therefore, the metal layer 43 having a relatively high reflectance in the visible light region and a relatively high electric conductivity is obtained. Accordingly, the electromagnetic resonance between the metal layer 41 and the metal layer 43 can be strengthened, and the reflection efficiency can be enhanced.
The dielectric layer 42 is made of a material transparent in the visible light region. Accordingly, the absorption rate of visible light in the dielectric layer 42 is suppressed, so that the reflection efficiency for visible light can be enhanced.
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 having a dielectric constant that does not interfere with the electromagnetic action is obtained. Accordingly, the electromagnetic resonance between the metal layer 41 and the metal layer 43 can be strengthened, and the reflection efficiency can be enhanced.
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 interferes with the electromagnetic action can be reduced, and the possibility that the laser light Ls passes through the metal layer 41 can be reduced. Accordingly, the reflection efficiency can be enhanced.
The metasurface reflector, the projection device, and the near-eye wearable device according to the present disclosure are not limited to the above-described embodiments.
The near-eye wearable device 1 may be virtual reality (VR) glasses.
In the above-described embodiments, the projection device 10 directly projects (draws) an image onto the retina RE of the user of the near-eye wearable device 1. The projection device 10 may project an image onto the metasurface reflector 30.
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 an image screen.
The plurality of unit regions 31 is not required to include any missing region 33. In other words, the metal unit 45 may be provided in each of all the unit regions 31 among the plurality of unit regions 31. In this case as well, the lengths in the X-axis direction of the metal units 45 included in one arrangement (that is, one row) in the X-axis direction are different from each other. Accordingly, since the periodicity of the metal units 45 is less likely to occur in the X-axis direction, it is possible to reduce the possibility that unnecessary scattered light occurs in the X-axis direction.
As shown in
As shown in
The plurality of unit regions 31R includes reflection regions 32R and missing regions 33R. Each of the reflection regions 32R is a unit region 31R in which the metal unit 45 is provided. Each of the missing regions 33R is a unit region 31R in which any metal unit 45 is not provided. The plurality of unit regions 31G includes reflection regions 32G and missing regions 33G. Each of the reflection regions 32G is a unit region 31G in which the metal unit 45 is provided. Each of the missing regions 33G is a unit region 31G in which any metal unit 45 is not provided. The plurality of unit regions 31B includes reflection regions 32B and missing regions 33B. Each of the reflection regions 32B is a unit region 31B in which the metal unit 45 is provided. Each of the missing regions 33B is a unit region 31B in which any metal unit 45 is not provided.
As in the example shown in
In this modification example as well, the reflection regions 32R, 32G, and 32B are configured so that the incident angles θj and the reflection angles θr corresponding to the positions where the reflection regions 32R, 32G, and 32B are provided are obtained. Accordingly, the lengths in the X-axis direction of the metal units 45 provided in the unit regions 31R (reflection regions 32R) included in one row are different from each other. Similarly, the lengths in the X-axis direction of the metal units 45 provided in the unit regions 31G (reflection regions 32G) included in one row are different from each other. The lengths in the X-axis direction of the metal units 45 provided in the unit regions 31B (reflection regions 32B) included in one row are different from each other.
The reflection angle θr by the metal unit 45 varies in accordance with the wavelength λ. Therefore, the laser light Ls having the red component, the green component, and the blue component may not be reflected at a desired reflection angle θr. In the configuration of the above modification example, since the unit regions 31R for the red component, the unit regions 31G for the green component, and the unit regions 31B for the blue component are provided, each component can be reflected at the desired reflection angle θr. Further, since the lengths of the metal units 45 for the same wavelength component in the X-axis direction are different from each other, the periodicity of the metal units 45 in the X-axis direction is less likely to occur. Accordingly, it is possible to reduce the possibility that unnecessary scattered light occurs in the X-axis direction. As a result, it is possible to reflect each component of the laser light Ls at the desired reflection angle θr while reducing unnecessary scattered light.
The method for determining the length Lx is not limited to the method described in the above-described embodiments. For example, the lengths Lx of the unit regions 31 located at both ends of the metasurface reflector 30 in the X-axis direction may be determined by the above-described method, and the lengths Lx of the unit regions 31 located therebetween may be determined so as to gradually change from the length Lx of the unit region 31 located at one end of the metasurface reflector 30 in the X-axis direction to the length Lx of the unit region 31 located at the other end thereof.
The metal unit 45 is not limited to one metal body having a trapezoidal shape, and may be composed of, for example, a plurality of metal bodies arranged in the X-axis direction.
(Additional Statements)
[Clause 1]
A metasurface reflector comprising:
[Clause 2]
The metasurface reflector according to clause 1,
[Clause 3]
The metasurface reflector according to clause 1 or 2,
[Clause 4]
The metasurface reflector according to clause 3,
[Clause 5]
The metasurface reflector according to any one of clauses 1 to 4,
[Clause 6]
The metasurface reflector according to clause 5,
[Clause 7]
The metasurface reflector according to clause 5 or 6,
[Clause 8]
The metasurface reflector according to any one of clauses 1 to 7,
[Clause 9]
The metasurface reflector according to any one of clauses 1 to 8,
[Clause 10]
The metasurface reflector according to any one of clauses 1 to 9,
[Clause 11]
The metasurface reflector according to clause 10,
[Clause 12]
The metasurface reflector according to any one of clauses 1 to 11,
[Clause 13]
A projection device mounted on a near-eye wearable device, the projection device comprising:
[Clause 14]
A near-eye wearable device comprising:
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-160135 | Sep 2023 | JP | national |
