Metalens and light-emitting device

Abstract

The present invention suppresses any increase in the difference in the amount of phase delay when two or more light beams having mutually different wavelengths are transmitted through a metalens. This metalens comprises a substrate that transmits light, and a plurality of microstructures disposed in a specific region of the substrate. In the metalens, the shape of each of the plurality of microstructures is such that the width in a first direction and the width in a second direction different from the first direction are mutually different as seen in the central-axis direction of the metalens. This metalens is used in, e.g., an illumination device or a measurement device.

Description

Meta lens and light-emitting device

[0001] The technology disclosed in this specification relates to a meta lens and a light-emitting device.

[0002] A meta lens (also referred to as a metasurface lens) includes a substrate that transmits light and a plurality of microstructures (also referred to as meta-atoms) disposed on the surface of the substrate. By controlling the structure, shape, orientation of each micro-structure, and the arrangement of the plurality of micro-structures on the substrate, the meta lens can refract and reflect light and radio waves in an arbitrary direction, control the phase, or absorb a specific wavelength. For each micro-structure in a conventional meta lens, the shape when viewed in the direction of the central axis of the meta lens is circular. Such a meta lens is used as an optical system provided in a measuring device such as LiDAR (light detection and ranging) or a lighting device (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 特開2024-005895号公報

[0004] Here, the amount of phase delay when light passes through the meta lens depends on the wavelength of the light. Therefore, if the wavelengths of the lights incident on the meta lens are different, the amount of delayed phase also differs accordingly. For this reason, when two lights with different wavelengths are incident on a conventional meta lens, a difference occurs in the amount of phase delay between the two lights. The difference in the amount of phase delay between the two lights may, for example, reduce the condensing properties of the two lights.

[0005] This specification discloses a technology capable of solving the above-described problems.

[0006] The technology disclosed in this specification can be realized, for example, in the following forms.

[0007] (1) The meta lens disclosed in this specification includes a substrate that transmits light and a plurality of microstructures disposed in a specific region of the substrate. The shape of each of the plurality of microstructures is a shape in which the width in a first direction and the width in a second direction different from the first direction are different from each other when viewed in the direction of the central axis of the meta lens.

[0008] In this configuration, the shape of each microstructure constituting the metalens is such that its width differs in at least two directions. Therefore, the metalens in this configuration can reduce the difference in phase delay between at least two light beams with different wavelengths. Specifically, each microstructure generates a phase delay for the light component of the incident light along a specific polarization direction, corresponding to the wavelength of the light and the width of the microstructure in that specific direction. Furthermore, the longer the wavelength of the incident light, the smaller the positional delay at the metalens. For example, if the width of the microstructure in a first direction is longer than the width in a second direction, the phase delay of the light component of the first light beam with a relatively longer wavelength along the first polarization direction will be greater than the phase delay of the light component of the second light beam with a relatively shorter wavelength along the second polarization direction. Therefore, this configuration can reduce the difference in phase delay between at least two light beams with different wavelengths compared to a configuration in which the microstructure is a perfect circle.

[0009] (2) In the metalens described above, the first direction and the second direction may be configured to be orthogonal to each other. With this configuration, the shape of the microstructure can be made relatively simple.

[0010] (3) The light-emitting device comprises the metalens, a first light-emitting element that emits first light having a first wavelength and including a light component in a first polarization direction along the first direction toward the metalens, and a second light-emitting element that emits second light having a second wavelength shorter than the first wavelength and including a light component in a second polarization direction along the second direction toward the metalens. The width in the first direction of the microstructure may be longer than the width in the second direction. With this configuration, the light-emitting device can emit at least two lights with different wavelengths while reducing the difference in phase delay between at least two lights.

[0011] (4) In the above-described light-emitting device, the first light emitted by the first light-emitting element may include only the light component in the first polarization direction, and the second light emitted by the second light-emitting element may include only the light component in the second polarization direction. This configuration makes it possible to improve the light-gathering ability of the entire first light emitted by the first light-emitting element and the entire second light emitted by the second light-emitting element.

[0012] (5) A metalens disclosed herein comprises a substrate that allows light transmission and a plurality of microstructures arranged in a specific region of the substrate, wherein the plurality of microstructures have a shape that makes the phase delay amount of at least two lights that differ from each other in both wavelength and polarization state an integer multiple of 2π. With this metalens, it is possible to reduce the difference in the phase delay amount of at least two lights that differ from each other in wavelength.

[0013] Furthermore, the technologies disclosed herein can be realized in various forms, for example, as metalens, light-emitting devices equipped with metalens as an optical system (e.g., floodlights, measuring devices, and lighting devices).

[0014] A schematic cross-sectional view showing the configuration of the illumination device of the embodiment. A schematic diagram showing the emission surface of the metalens of the first embodiment. A schematic diagram showing the process of yellow light passing through the metaatom. A schematic diagram showing the process of blue light passing through the metaatom. An explanatory diagram showing a modified example of the metaatom.

[0015] (Embodiment) This embodiment will be described with reference to Figures 1 to 4. Each figure shows mutually orthogonal X, Y, and Z axes for specifying direction. For convenience, in this specification, the X-axis direction will be referred to as the "front-back direction," the negative Y-axis direction as the "left-right direction," and the Z-axis direction as the "up-down direction." However, the lighting device 10 may actually be installed in a direction different from these. The lighting device 10 is an example of a light-emitting device.

[0016] As described later, the lighting device 10 of this embodiment includes a yellow light-emitting element 30Y and a blue light-emitting element 30B. The lighting device 10 mixes the yellow light LY emitted by the yellow light-emitting element 30Y and the blue light LB emitted by the blue light-emitting element 30B to generate white light LW, which is then irradiated to the outside. The lighting device 10 can be mounted on a vehicle as a lamp, or on a lighting fixture, for example.

[0017] As shown in Figure 1, the lighting device 10 includes a metalens 20, a yellow light-emitting element 30Y, a blue light-emitting element 30B, a semiconductor substrate 40, and a reflective member 50.

[0018] The reflective member 50 is a block body in which a through-passage 52 for passing light is formed. The through-passage 52 penetrates the reflective member 50 in a straight line in the front-to-back direction. The through-passage 52 has a shape that opens radially from the entrance 53 toward the exit 55. The inner circumferential surface 54 of the through-passage 52 is a reflective surface that is, for example, mirror-finished or has a reflective film formed on it.

[0019] The yellow light-emitting element 30Y is a light-emitting member that emits yellow light LY. The yellow light LY is visible light having a wavelength in the yellow wavelength region (550 nm or more, 590 nm or less). The yellow light LY contains only the vertically polarized light component. The yellow light-emitting element 30Y is positioned on the entrance 53 side of the reflecting member 50 and emits yellow light LY toward the through passage 52. The yellow light LY is an example of the first light, the yellow wavelength region is an example of the first wavelength, and the direction of vertical polarization (up and down direction) is an example of the first polarization direction (first direction).

[0020] Specifically, the yellow light-emitting element 30Y includes a yellow LED 31Y and a vertical polarizing element 32Y. The yellow LED 31Y is an LED (Light Emitting Diode) that emits unpolarized yellow light LYp (laser light). The vertical polarizing element 32Y is an element that converts the yellow light LYp emitted from the yellow LED 31Y into vertically polarized yellow light LY. The vertical polarizing element 32Y is composed of, for example, a polarizer, a waveplate (such as a quarter-wave plate), a polarization separation element, a polarization filter, etc.

[0021] The blue light-emitting element 30B is a light-emitting member that emits blue light LB. The blue light LB is visible light having a wavelength in the blue wavelength region (430 nm or more, 490 nm or less). The blue light LB contains only transversely polarized light components. The blue light-emitting element 30B is positioned on the entrance port 53 side of the reflecting member 50 and emits blue light LB toward the through passage 52. The blue light LB is an example of a second type of light, the blue wavelength region is an example of a second type of wavelength, and the direction of transverse polarization (left-right direction) is an example of a second type of polarization direction.

[0022] Specifically, the blue light-emitting element 30B includes a blue LED 31B and a transverse polarizing element 32B. The blue LED 31B is an LED that emits unpolarized blue light LBp. The transverse polarizing element 32B is an element that converts the blue light LBp emitted from the blue LED 31B into transversely polarized blue light LB. The transverse polarizing element 32B is configured to include, for example, a polarizer, a waveplate (such as a quarter-wave plate), a polarization separation element, a polarization filter, etc.

[0023] The semiconductor substrate 40 is positioned on the side of the reflective member 50 facing the entrance port 53. A yellow light-emitting element 30Y and a blue light-emitting element 30B are mounted on the surface of the semiconductor substrate 40 facing the entrance port 53. The semiconductor substrate 40 also has multiple circuit elements mounted on it, for example, for controlling the light emission of the yellow light-emitting element 30Y and the blue light-emitting element 30B.

[0024] The metalens 20 is positioned on the exit port 55 side of the reflecting member 50. As shown in Figure 2, the metalens 20 comprises a substrate 22 and a plurality of metaatoms 24 arranged on the surface of the substrate 22. The metalens 20 can achieve desired optical performance by arranging a large number of metaatoms 24 on the surface of the substrate 22 and appropriately designing the shape and arrangement pattern of these metaatoms 24. In other words, the desired optical performance can be achieved with a single metalens 20. The metaatoms 24 are an example of microstructures (also called subwavelength structures).

[0025] The substrate 22 is a rectangular plate material that allows light emitted from the yellow light-emitting element 30Y and the blue light-emitting element 30B to pass through. The surface of the substrate 22 includes a flat exit surface SO (the surface of the metalens) and a flat incident surface SI (the surface of the metalens) located on the opposite side of the exit surface SO. The central portion of the exit surface SO is the effective region Ab. The material of the substrate 22 is, for example, glass, TiO ２ SiO ２ It is a synthetic resin. In this embodiment, the substrate 22 is made of glass. The thickness of the substrate 22 may be, for example, 100 nm or more and 3 mm or less. The effective region Ab is an example of a specific region.

[0026] Metaatoms 24 are fine protrusions that project from the surface of the substrate 22. The metaatoms 24 are arranged in a predetermined pattern in the effective region Ab. The arrangement pattern of the metaatoms 24, as well as the shape and size of each metaatom 24, are designed according to the optical function required of the metalens 20. In this embodiment, the metaatoms 24 are designed to function as focusing lenses that concentrate light in the metalens 20. The distance between adjacent metaatoms 24 is set to be sufficiently small compared to the wavelength of light incident on the metalens 20. In this embodiment, the distance between adjacent metaatoms 24 is set to be sufficiently small compared to the wavelength of light emitted from the yellow light-emitting element 30Y and the blue light-emitting element 30B, that is, the wavelength of yellow light LY and blue light LB. The material of the metaatoms 24 is, for example, silicon (Si), glass, or TiO ２ SiO ２ In this embodiment, the material of the metaatom 24 is silicon with a refractive index of about 1.5-4. The height of the metaatom 24 from the exit surface SO may be about 1 μm or more and 2 μm or less.

[0027] Figure 3 shows the process of yellow light LY passing through the metaatom 24, and Figure 4 shows the process of blue light LB passing through the metaatom 24. In Figures 3 and 4, only the shape of the metaatom 24 as viewed in the direction of the central axis (front-to-back direction) of the metalens 20 is shown.

[0028] For each meta-atom 24, the shape of the meta-atom 24 when viewed in the direction of the central axis of the meta-lens 20 (hereinafter sometimes referred to as the "cross-sectional shape") is such that the vertical width H (for example, about 500 nm) is longer than the horizontal width W (for example, about 200 nm). The shape and size of the cross-section of each meta-atom 24 are substantially uniform over the entire length in the direction of the central axis (front-to-back direction) of the meta-lens 20. The ratio of the vertical width H to the horizontal width W of the meta-atom 24 (= H / W) preferably correlates with the wavelength ratio of the wavelength λY of vertically polarized yellow light LY to the wavelength λB of transversely polarized blue light LB. The width ratio may be, for example, 1.5 or more, 2 or more, or 2.5 or more. Specifically, the cross-sectional shape of the meta-atom 24 is an elongated ellipse in the vertical direction (see Figures 3 and 4).

[0029] In this embodiment, the optical axis of the yellow light-emitting element 30Y is parallel to the central axis direction of the metalens 20 (the direction perpendicular to the substrate 22), and the yellow light-emitting element 30Y is positioned to emit yellow light LY toward the metalens 20 along the central axis direction of the metalens 20. The optical axis of the blue light-emitting element 30B is parallel to the central axis direction of the metalens 20, and the blue light-emitting element 30B is positioned to emit blue light LB toward the metalens 20 along the central axis direction of the metalens 20.

[0030] Here, the longer the wavelength of the light incident on the metalens 20 (meta-atom 24), the smaller the phase delay when the light passes through the metalens. The wavelength λY of the yellow light LY (LYp) used in this embodiment is longer than the wavelength λB of the transversely polarized blue light LB (LBp). Therefore, if a conventional metalens with a circular cross-sectional shape of the meta-atom were used instead of the metalens 20, the phase of the blue light LB passing through the metalens would lag behind the phase of the yellow light LY passing through the metalens. As a result, it would not be possible to focus the yellow light LY and the blue light LB to a predetermined position.

[0031] In contrast, this embodiment utilizes the fact that, with respect to the light component of the light incident on the metalens 20 (meta-atom 24) along a specific polarization direction, the narrower the width of the meta-atom 24 in that specific direction, the smaller the phase delay when the light passes through the metalens. That is, in the metalens 20 of this embodiment, the cross-sectional shape of the meta-atom 24 is such that the vertical width H is longer than the horizontal width W. Therefore, the meta-atom 24 generates a phase delay for the light components of the incident light along the vertical and horizontal polarization directions, respectively, corresponding to the wavelength of the light and the vertical and horizontal widths of the meta-atom 24.

[0032] As shown in Figure 3, vertically polarized yellow light LY is transmitted through the meta-atom 24. The phase delay of the yellow light LY is relatively larger depending on the vertical width H of the meta-atom 24. As shown in Figure 4, horizontally polarized blue light LB is transmitted through the meta-atom 24. The phase delay of the blue light LB is relatively smaller depending on the horizontal width W of the meta-atom 24. In short, the phase delay due to the difference in wavelength between the yellow light LY and the blue light LB is reduced by the difference in the widths (vertical width H and horizontal width W) of the respective meta-atoms 24 in the polarization direction of the yellow light LY and the polarization direction of the blue light LB. In this embodiment, the ratio of the vertical width H and horizontal width W of the meta-lens 20 is adjusted so that the phase delay of both the yellow light LY and the blue light LB is 2π. As a result, the meta-atom 24 can mix the yellow light LY and the blue light LB to generate white light LW and focus it at a predetermined position.

[0033] The relationship between the phase delay amount Φ and the width of the meta-atom 24 (vertical width H, horizontal width W) is as follows. From this equation, the width of the meta-atom 24 can be determined in order to set the phase delay amount Φ to a desired value. Φ = {β(w) - k ０}・h = (2π / λ)・{n ｅｆｆ (w) - 1} * h β(w): Amount of phase modulation per unit length w: Width of the cross-section of the metaatom 24 in a predetermined direction k ０ : Wave vector n in air ｅｆｆ λ: Effective refractive index λ: Wavelength of incident light h: Protrusion length of the metaatom 24 from the substrate 22

[0034] (Modifications) The technologies disclosed herein are not limited to the embodiments described above and can be modified in various forms without departing from the spirit thereof, for example, the following modifications are possible.

[0035] In the above embodiment, a metalens 20 having a light-gathering function was exemplified as the metalens, but the metalens may also have other functions, such as a diffusion function or a collimating function. In the above embodiment, the microstructure was arranged on the exit surface of the substrate, but the microstructure may also be arranged on the ingress surface of the substrate.

[0036] In the above embodiment, both the incident surface SI and the exit surface SO of the substrate 22 were flat surfaces. However, one of the incident surface SI and the exit surface SO may be flat, a part of the incident surface SI may be flat, a part of the exit surface SO may be flat, and the entire incident surface SI and the exit surface SO may not be flat. The specific region is not limited to the central region of the substrate 22, but may be a region offset from the center. The specific region is not limited to a part of the surface of the substrate 22, but may be the entire surface. Among the plurality of metaatoms 24 arranged on the substrate 22, the cross-section of only some of the metaatoms 24 may be elongated in a predetermined direction.

[0037] In the above embodiment, the first light was yellow light LY containing only the vertically polarized light component, but it may also be light containing other polarization components in addition to the vertically polarized light component (for example, unpolarized light). The second light was blue light LB containing only the transversely polarized light component, but it may also be light containing other polarization components in addition to the transversely polarized light component (for example, unpolarized light). The first and second wavelengths may be in the wavelength range of color combinations other than yellow and blue (for example, a combination of red, green, and blue). The first and second polarization directions are not limited to the up-and-down and left-and-right directions, but may also be directions that are inclined with respect to the up-and-down direction, for example. The first and second polarization directions are not limited to directions that are orthogonal to each other, but may be directions that intersect each other. The combination of polarization of the first and second light is not limited to a combination of vertical and transverse polarization, but may also include combinations of linear polarization, random polarization, circular polarization, and elliptic polarization in other directions, for example.

[0038] In the above embodiment, the light-emitting element has a configuration with an LED, but it is not limited to this, and a configuration having other semiconductor light-emitting elements or a light source such as a light bulb may also be used.

[0039] In the above embodiment, the cross-sectional shape of the meta-atom 24 has a vertical width H longer than the horizontal width W. However, for example, a shape with a horizontal width W longer than the vertical width H may also be used. Further, the cross-sectional shape of the meta-atom 24 is not limited to a shape in which the widths in directions orthogonal to each other are different, and any shape in which the widths in intersecting directions are different may be used.

[0040] In the above embodiment, the phase delay amount of the yellow light LY and the phase delay amount of the blue light LB are both 2π, but values other than 2π may also be used, and they may be different from each other. In short, in the above embodiment, for example, compared with a configuration in which the shape of the meta-atom 24 is a perfect circle, it is sufficient if the difference between the phase delay amount of the yellow light LY and the phase delay amount of the blue light LB is reduced.

[0041] The cross-sectional shape of the micro-structure is not limited to an ellipse, and for example, the shape shown in FIG. 5 may also be used. As shown in (A) of FIG. 5, the cross-sectional shape of the micro-structure may be a shape in which a relatively long straight portion (H1) and a relatively short straight portion (W1) intersect. The intersection angle of the two straight portions is not limited to 90 degrees, and may be, for example, 45 degrees, 60 degrees, or the like. For a micro-structure having such a shape, it is possible to suppress an increase in the difference in the phase delay amount when two lights having different wavelengths pass through the metalens.

[0042] As shown in (B) of FIG. 5, the cross-sectional shape of the micro-structure may be a substantially rhombus shape in which the lengths of the two diagonals (H2, W2) are different. In this case, each side of the cross-sectional shape of the micro-structure may be linear, concave, or convex. For a micro-structure having such a shape, it is possible to suppress an increase in the difference in the phase delay amount when two lights having different wavelengths pass through the metalens.

[0043] As shown in (C) of FIG. 5, the cross-sectional shape of the micro-structure may be a shape in which three or more straight portions having different lengths (H3, W3, W4) from each other and different extending directions intersect each other. For such a micro-structure, it is possible to suppress an increase in the difference in the amount of phase delay when transmitting through the metalens for three or more lights having different wavelengths from each other.

[0044] In the above embodiment, the condensing property of two or more lights is improved by focusing on the propagation phase delay. However, the present invention is not limited to this, and a configuration that improves the condensing property of two or more lights by focusing on the resonance phase delay may also be used. In short, the micro-structure may be a shape that makes the phase delay amounts of at least two lights having different wavelengths and polarization states from each other an integer multiple of 2π.

[0045] In the above embodiment, the lighting device 10 is exemplified as the light-emitting device. However, the light-emitting device may be, for example, a LiDAR used in an in-vehicle autonomous driving system (AD: autonomous driving) or an advanced driver assistance system (ADAS: advanced driver assistance system), or a measuring device used in a system other than AD and ADAS. The metalens may be a lens provided in a device or component different from the measuring device or the lighting device. For example, it may be a lens provided in an in-vehicle camera. The metalens may be a lens provided in a component for a different use than for vehicles. For example, it may be a lens provided in a security camera or a lens provided in a camera for a smartphone.

[0046] This international application claims priority based on Japanese Patent Application No. 2025-006563, which was filed on January 17, 2025, and the entire contents of the Japanese Patent Application No. 2025-006563 are incorporated herein by reference.

[0047] The above description of specific embodiments of the present invention is presented for purposes of illustration. They are not intended to be exhaustive or to limit the invention to the forms described. It will be apparent to those skilled in the art that numerous modifications and variations are possible in light of the above description.

[0048] 10: Lighting device 20: Metalens 22: Substrate 24: Metaatom 30B: Blue light-emitting element 30Y: Yellow light-emitting element 31B: Blue LED 31Y: Yellow LED 32B: Transverse polarizing element 32Y: Vertical polarizing element 40: Semiconductor substrate 50: Reflective element 52: Through passage 53: Entrance opening 54: Inner surface 55: Exit opening Ab: Effective area SI: Entrance surface SO: Exit surface

Claims

1. A metalens comprising a light-transmitting substrate and a plurality of microstructures arranged in a specific region of the substrate, wherein the shape of each of the plurality of microstructures is such that, when viewed in the direction of the central axis of the metalens, the width in a first direction and the width in a second direction different from the first direction are different from each other.

2. A metalens according to claim 1, wherein the first direction and the second direction are orthogonal to each other.

3. A light-emitting device comprising: a metalens according to claim 1 or claim 2; a first light-emitting element that emits first light toward the metalens, which has a first wavelength and includes a light component in a first polarization direction along the first direction; and a second light-emitting element that emits second light toward the metalens, which has a second wavelength shorter than the first wavelength and includes a light component in a second polarization direction along the second direction, wherein the width of the microstructure in the first direction is longer than the width in the second direction.

4. A light-emitting device according to claim 3, wherein the first light emitted by the first light-emitting element includes only the light component in the first polarization direction, and the second light emitted by the second light-emitting element includes only the light component in the second polarization direction.

5. A metalens comprising a substrate that allows light transmission, and a plurality of microstructures arranged in a specific region of the substrate, wherein the plurality of microstructures have a shape that causes the phase delay amount of at least two lights, each having a different wavelength and polarization state from the others, to be an integer multiple of 2π.

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