Metalens, image projection devices, light source devices, imaging devices, optical scanning devices, and methods for manufacturing metalens.

Abstract

By stacking multiple metalens with their microstructure surfaces facing inward, this provides a metalenx that protects fragile microstructure surfaces and suppresses the impact of defects caused by pillar shape errors on optical performance. [Solution] The metalens of the present invention is a metalens having a microstructure surface on which a plurality of microstructures are continuously formed on the light-transmitting surface, and the refractive index for the light is adjusted by the density of the microstructures, wherein the metalens has a plurality of microstructure surfaces, the two outermost of the microstructure surfaces are arranged to face each other, and the metalens is formed integrally such that a base layer is positioned outside the microstructure surfaces, sandwiching the microstructure surfaces.

Description

Technical Field

[0001] The present invention relates to a metalens, an image projection device using the metalens, a light source device, an imaging device, an optical scanning device, and a method for manufacturing a metalens.

Background Art

[0002] Metamaterials composed of periodic structures finer than the wavelength do not exist in nature and are artificial materials, and a two-dimensional form of them is called a metasurface. A metasurface generally has a fine metal structure, and depending on the content and state of the metal structure, it can generate an effect of generating a negative refractive index or function as a lens with a very high refractive index. As described above, since the metasurface can refract light in a direction that is not possible in its original form as a planar device, research on its applications has been progressing (see Patent Documents 1, 2, etc.). However, it has been a problem that the metasurface containing a metal structure has poor transmittance. To solve this problem, a configuration in which nanostructured fine pillar-like structures made of resin or glass are arranged on the surface of a substrate without using a metal structure has been considered. Such fine structures of non-metallic materials function as optical waveguides, and by controlling the diameter of the pillars, a phase difference is generated between adjacent pillars, and a device that refracts light with high transmittance by pseudo-reproducing the phase wavefront of transmitted light has been devised. This is called a metalens.

[0003] Although the metalens is expected to have high development potential due to its high degree of freedom, there are many problems and not many examples of commercialization. First, in the optical field using the visible light region, since the wavelength of the light used is short, the pillars become nanostructured. Such pillars are very fragile and may be severely damaged even by a light touch with a finger or tweezers. Furthermore, the difficulty of the manufacturing process is another issue. Due to the quirks of the metal lens manufacturing equipment, the pillar shape may not be as intended, which can lead to shape errors in the fine pattern and a decrease in light-gathering efficiency. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The present invention aims to solve the above-mentioned problems by stacking multiple metalens with the microstructure surface facing inward, thereby protecting the fragile microstructure surface and suppressing the impact of defects caused by pillar shape errors on optical performance. [Means for solving the problem]

[0005] The metalens of the present invention is a metalens having a microstructure surface on which a plurality of microstructures are continuously formed on the light-transmitting surface, and the refractive index for the light is adjusted by the density of the microstructures, wherein the metalens has a plurality of microstructure surfaces, the two outermost of the microstructure surfaces are arranged to face each other, and the metalens is formed integrally such that a base layer is positioned outside the microstructure surfaces, sandwiching the microstructure surfaces. [Effects of the Invention]

[0006] According to the present invention, by stacking multiple metalens with the microstructure surface facing inward, the fragile microstructure surface is protected, and the influence of defects due to pillar shape errors on optical performance is suppressed. [Brief explanation of the drawing]

[0007] [Figure 1] This is a diagram illustrating the schematic configuration of a typical metalens. [Figure 2] Figure 1 is a schematic diagram showing an example of the microstructure of the surface of the metalens shown. [Figure 3] This diagram schematically illustrates the refraction caused by a convex lens. [Figure 4]This figure schematically shows the change in refractive index caused by the microstructure shown in Figure 2. [Figure 5] This is a diagram showing the structure of the microstructure surface of a metalens. [Figure 6] This figure shows an example of the configuration of a metalens in the present invention. [Figure 7] This figure shows the changes in pillar diameter and phase change amount at a pillar height of 1 μm in the present invention. [Figure 8] This figure shows the changes in pillar diameter and phase change amount at a pillar height of 0.5 μm in the present invention. [Figure 9] This diagram schematically shows the variation in the height of the metal lens. [Figure 10] This figure illustrates an example of a method for producing a metalens according to the present invention. [Figure 11] This diagram illustrates one example of a method for generating metalens. [Figure 12] This figure illustrates another example of the method for producing metalens according to the present invention. [Figure 13] Figure 12 illustrates an example of a method for producing a metalens. [Figure 14] This figure shows an example of how the pillar distribution simulation works according to the present invention. [Figure 15] This figure shows another embodiment of the metal lens of the present invention. [Figure 16] This figure shows another embodiment of the metal lens of the present invention. [Figure 17] This figure shows an example in which the metalens of the present invention is applied in three or more layers. [Figure 18] This figure shows an example of a method for manufacturing a metal lens according to the present invention. [Figure 19] This figure shows an example of a method for manufacturing a metalens according to a second embodiment of the present invention. [Figure 20] This figure shows an example of an embodiment when the present invention is applied to an optical scanning device. [Figure 21] This figure shows an example of an embodiment when the present invention is applied to a light source device. [Figure 22] This is a diagram showing an example of an embodiment when the present invention is applied to an image projection device. [Figure 23] This is a diagram showing an example of an embodiment when the present invention is applied to an imaging device.

Embodiments for Carrying Out the Invention

[0008] Prior to explaining the configuration of the present invention, first, a meta-lens with a general configuration will be explained. In FIG. 1, a meta-lens 10 is shown as a comparative example. As shown in FIG. 1, the meta-lens 10 is an optical element including a substrate portion 11 made of plate-shaped quartz glass and a plurality of cylindrical pillars 13, which are a plurality of fine structures, provided on a light transmission surface 12 of the substrate portion 11. The substrate portion 11 is a base material layer in the meta-lens 10, and a plurality of pillars 13 are formed on the substrate portion 11 in a state where they are arranged side by side. The density of the pillars 13 is controlled by the filling rate when the substrate portion 11 is viewed from above, and the region occupied by the light transmission surface 12 where a plurality of pillars 13 are continuously formed is a fine structure surface.

[0009] FIG. 2 schematically shows, as a perspective view, a state where such a plurality of pillars 13 are continuously formed on the light transmission surface 12. In FIG. 2, although the pillar 13 is particularly described as a cylindrical fine structure with a diameter φ and a height H, it is not limited to such a configuration. For example, the upper surface thereof may be a polygonal prism such as a triangle, a quadrilateral, a hexagon, or a shape combined with rectangles, or a shape obtained by stretching them in one direction.

[0010] At this time, if the interval p between the pillars 13 is a sub-wavelength interval with respect to the transmitted light, the light transmission surface 12 functions as a so-called metasurface. The wavelength of such transmitted light may be arbitrary. For example, in the present embodiment, light with λ = 600 nm will be mainly handled as an example of light in the visible light region.

[0011] When the diameter of pillar 13 is φ and the distance between adjacent pillars 13 is the pitch p, the functionality of the transmissive surface 12 as a metasurface changes depending on the filling ratio of the pillars 13. This is because, when a light wave enters a subwavelength interval pitch p, pillar 13 acts as a meta-atom that inhibits the propagation of the light wave. Furthermore, it has been found that by changing the packing ratio, i.e., density, of these pillars 13, it is possible to give the entire transmissive surface 12 a refractive index different from that of the material of the pillars 13.

[0012] To illustrate this point, Figure 3 shows, as a simple example, the propagation of a light wave in a convex lens, along with its phase wavefront. In Figure 3, the region where the phases of adjacent parallel rays coincide is schematically shown as a phase wavefront using thin lines. Needless to say, the direction normal to the phase wavefront is the direction of light propagation. When light enters a convex lens 200 with refractive index n, the speed of light slows down by that amount according to the refractive index, so the phase wavefront with respect to parallel light rays tilts toward the convex direction of the convex lens 200. Since the direction in which this sequence of phase wavefronts propagates is the direction of light propagation, the direction of light propagation becomes tangential to this sequence of phase wavefronts, and as shown in Figure 3, it is bent toward the optical axis of the convex lens 200.

[0013] Figures 4(a) and 4(b) schematically illustrate the effect of pillars 13 on the metasurface, which is a transmissive surface 12. As shown in Figure 4(a), when pillars 13 smaller than the wavelength λ are densely arranged on the transmissive surface 12, the light of wavelength λ on the transmissive surface 12 does not recognize the pillars 13 as individual cylinders, but rather recognizes them in the form of the magnitude of the refractive index of the transmissive surface 12, depending on the magnitude of the packing density.

[0014] In other words, on the transmissive surface 12, which is a metasurface, the pseudo refractive index n2 changes depending on the diameter and height of the pillars 13, or the spacing (pitch) between the upright pillars 13. The magnitude of such pseudo refractive index n2 is roughly shown in Figure 4(a) by color coding based on the intensity of the gradient.

[0015] Therefore, as shown in Figure 4(b), when parallel light rays are incident on the transmission surface 12 from a direction perpendicular to it, considering the light rays incident on the transmission surface 12, the phase wavefront, as shown in Figure 4(b), propagates more slowly in areas with a larger refractive index. At this time, as already mentioned, the magnitude of the refractive index of the transmission surface 12 is the magnitude of the filling density in which the pillars 13 are formed. In other words, for transmitted light, a change in the filling density of the pillars 13 on the transmission surface 12 is equivalent to a change in the optical path length in that area. Therefore, similar to the refractive index of the convex lens 200 shown in Figure 3, by providing a delay due to the refractive index on the transmission surface 12 by the same amount as the delay caused by the difference in optical path length due to the lens thickness, it is possible to obtain a refractive effect similar to that of the convex lens 200.

[0016] Thus, when the pillar 13 is on the order of subwavelengths relative to the wavelength λ of light, and when the refractive index of the transmission surface 12 is given a gradient by its packing density as shown in Figure 4(b), the wavefront propagation is slowed down by the packing density of the pillar 13, so the phase wavefront tilts to the left in the figure as shown in Figure 4(b). If multiple pillars 13 of the subwavelength order are arranged regularly, this phenomenon acts as if they were atoms for light waves traveling through a molecular crystal lattice, causing the phase wavefront to be distorted as if it were refracted. Conversely, if such a distortion of the phase wavefront can be artificially created by the regularity of the pillar 13, then the transmission surface 12 will have optical functions equivalent to a lens surface with refractive index n2.

[0017] In other words, if a distribution of pillar diameters 13 can be created such that the phase wavefront of the transmitted light passing through the transmission surface 12 coincides with the phase wavefront of the light passing through the convex lens with refractive index n2, then the light passing through such a transmission surface 12 will be the same as the light that has passed through the convex lens with refractive index n2. This is a simplified principle of an optically functional surface called a metasurface, and in such an optically functional surface, microstructures like pillar 13 are likened to atoms and called metaatoms.

[0018] In this way, by appropriately changing the filling density of the pillars 13 formed on the transmission surface 12, the phase wavefront of light at various points on the transmission surface 12 can be controlled, making it possible to give the metalens 10 various optical lens-like functionalities while maintaining a macroscopic flat plate shape. Figure 5 shows an example of the transmission surface 12 of such a metalens 10, as well as an enlarged view showing the pillar 13. The pillars 13 formed on the transmissive surface 12 in this embodiment, as shown in Figure 5, are sufficiently small relative to the wavelength of light to be transmitted. Also, as is clear from Figure 5, in this embodiment, the diameter φ of the pillars 13 is controlled to vary the packing density. This pitch p can be appropriately set based on, for example, the length of the long side / short side or diagonal if the pillars 13 are rectangular prisms, or the length of one side if they are triangular prisms. In any case, the distance between the pillars 13 that is geometrically most typical when viewed from the vertical direction can be treated as the horizontal / vertical pitch p.

[0019] This is a simplified explanation of the operating principle of the metalens 10, which provides a refractive effect to transmitted light regardless of the lens shape.

[0020] Now, in such a metalensor 10, it is known that not all of the transmitted light is refracted; rather, some of the light is refracted and transmitted, while the rest of the light is transmitted as is. As mentioned above, this occurs because pillar 13 acts as an element that obstructs the propagation of transmitted light, thereby changing the phase of the transmitted light and creating a pseudo-refractory effect. Improving the efficiency of light ray utilization in this way has also been a challenge for conventional metalenses 10.

[0021] This phenomenon can be caused by factors such as a "gap" in the formation of the pillar 13, or by the relationship between the angle of incidence and the position of incidence on the transmissive surface 12, which causes the pillar 13 to travel in a straight line without exhibiting its effect as a meta-atom. This light is what is known as zero-order light, and various methods have been considered in conventional metalens to increase the amount of first-order light L1, which is given a refractive effect, and to decrease the proportion of this zero-order light L0.

[0022] It has been found that this type of zero-order light L0 can be reduced by decreasing the loss due to poor formation of pillar 13. However, as already mentioned, pillar 13 is a structure with a diameter shorter than the wavelength of transmitted light λ = 600 nm, and as is clear from Figures 2 and 5, many parts are formed in an orderly and dense manner, so even a light touch with a finger or tweezers can cause significant damage. Furthermore, as shown in Figure 2, if the surface on which the pillar 13 is formed is left exposed, it becomes extremely vulnerable to impact.

[0023] Therefore, in this embodiment of the present invention, as shown in Figure 6, a single metalens 20 is formed by stacking and joining two metalens 10, as shown in Figure 1. Thus, in the metalens 20 of the present invention, a pair of substrate portions 11 are integrally formed so as to be positioned opposite each other on both sides of the transmissive surface 12, which is a microstructure surface, in a manner that sandwiches the transmissive surface 12.

[0024] With this configuration, as shown in Figure 6, both sides of the metalens 20 are covered by the substrate layer, which is the base material, so fingers or tweezers cannot touch it at all, thus protecting the pillar 13. In other words, by stacking multiple metalens 10 with their microstructure surfaces facing inward, the surface on which the fragile pillar 13 is formed can be protected.

[0025] Furthermore, in this embodiment, in addition to simply sandwiching two metalens 10 between substrate layers with their microstructure surfaces facing inward, the height H of the pillar 13 is also halved compared to the conventional configuration.

[0026] The effects of this configuration will be explained. First, for the case where the height H=1μm of the pillar 13 made of quartz glass SiO2, which is the material of the substrate portion 11, Figure 7 shows the change in phase change amount and the change in pillar diameter φ plotted for each wavelength λ of the incident light. Similarly, Figure 8 shows a plot of the phase change and the change in pillar diameter φ for the case where the height H of pillar 13 is 0.5 μm. As is clear from Figures 7 and 8, when the height H of pillar 13 is changed from H=1μm to H=0.5μm, the amount of phase change is also halved. Therefore, to match the phase wavefront of the transmitted light to the simulation result for pillar 13 height H=1μm, two metalens with H=0.5μm should be stacked.

[0027] The effects of stacking multiple transparent surfaces 12 are described below. Let's assume that the height H of the pillar 13 is formed with variations including deviations ±σ from the design value due to manufacturing errors or other reasons. As shown in Figure 9, if the height H of pillar 13 is divided into h1 and h2, and set so that h1 + h2 = H, then the deviations of h1 ± σ1 and h2 ± σ2 due to independent manufacturing are highly likely to be |σ1 + σ2| < |σ|, and as a result the deviation of h1 + h2 from the design value will be averaged out, and the variance will decrease. This is because, as long as the opposing pillars 13 do not both experience a deviation in the same ± direction, the value will not deviate significantly from H. Note that Figure 9 exaggerates this variation to the extent that it is visually apparent; in reality, such variation is negligible.

[0028] As described above, in the metalens 20, by stacking multiple metalens 10 with their microstructure surfaces facing inward, it is possible to protect the fragile microstructure surfaces and suppress the impact of defects caused by shape errors in the pillars 13 on optical performance.

[0029] Next, we will explain the manufacturing method for these metalens 20. Conventionally, methods such as electron beam lithography (EBL) were used to form multiple microstructures like the one shown in Figure 5. Because this method has a resolution of less than 10 nm, it is widely used for fabricating metasurfaces. However, it is time-consuming and costly, so there has been a demand for more efficient manufacturing methods. As a method for manufacturing such a large area and with high efficiency, for example, a method of transferring a prototype 81 formed using lithography by nanoimprint is known.

[0030] An example of a method for manufacturing an optical element including a metalens 20 will be explained with reference to Figure 10. As shown in Figure 10(a), first, a substrate 86 is formed, which will be the material that constitutes the substrate portion 11 of the metalens 20 (step S101 in Figure 11). A prototype pattern 81 with cylindrical or polygonal prism-shaped voids formed according to processing data for a shape where the irregularities are reversed compared to the final pillar 23 is pressed onto the substrate 86, and a layer with the same shape as the pillar 13 is formed (step S103). Step S103 is a first microstructure generation step in which a plurality of pillars 13 are formed on the surface corresponding to the transparent layer 22 by molding the substrate 86 with the prototype 81. In the first microstructure generation step, a pattern is formed on the surface of the substrate 86 that mimics the shape of the pillars 13 manufactured by the prototype 81. Since these pillars 13 function as metaatoms, the first microstructure generation step is sometimes also called a metaatom formation step. In this first microstructure generation process, the height H from the lower end to the upper end of the formed pillar shape is generated such that H = h1, for example, for the reasons described in Figure 6. Furthermore, in this embodiment, metaatoms were formed by nanoimprint using the prototype 81, but they may also be formed by photolithography or other methods. Alternatively, any method capable of forming a microstructure pattern on the substrate 86 is acceptable, and the method is not particularly limited to nanoimprint. Furthermore, as shown in Figures 12 and 13, it is also possible to form the pillar 23 and the substrate 86 from different materials by using quartz glass for the substrate 86 and forming a resin-forming layer 89 on the substrate 86. In that case, if a photosensitive resin formation step of forming the resin-forming layer 89 is provided as step S102 after the substrate formation step S101 in Figure 11, the pillar 13 will be formed on the uppermost resin-forming layer 89 in the first microstructure generation step.

[0031] After the pillars 13 are formed on the substrate 86 in this manner, the substrate portion 11 is separated from the substrate 86 as shown in Figures 10(c) and 12(c). By this method, one metalens 10 with pillars 13 formed on the substrate portion 11 can be obtained. Subsequently, in this embodiment, another metalens 10, which has been prepared in the same manner, is joined so that the microstructure surface on which the pillars 13 are formed faces inward (step S104). Step S104 is a bonding process in which the two metalens 10 are bonded together so that the sides on which the pillars 13 are formed face inward. At this time, various methods can be considered for joining the two metalens, but for example, in order to avoid collision between the pillars 13, an outer frame of the substrate portion 11 surrounding the metalens 10 may be provided, and these outer frames may be joined together with an adhesive or the like.

[0032] As shown in Figures 6 and 9, the metalens 20 obtained by integrally joining two metalens 10 has two microstructured surfaces, or transmission surfaces 12, along the Z-direction, which is the direction of light transmission, in the vertical direction of the paper. In addition, a pair of substrate portions 11 are located outside the transmission surfaces 12. With this configuration, the metalens 20 suppresses the impact on optical performance due to variations in the pillars 13 on each transmission surface 12, and by closing and integrating the pillars 13 so that they are located inside the substrate portion 11, the impact resistance of the pillars 13 is enhanced, preventing damage and providing a metalens with stable performance.

[0033] Now, when designing the metalens 20 of the present invention, it is important that appropriate pillars 13 are formed in the first microstructure generation step. Figure 14 is a flowchart showing an example of running a simulation program to calculate the surface distribution of the pillar 13. Here, the surface distribution of pillar 13 represents the filling rate of pillar 13 at each position on the transparent surface 12.

[0034] First, once the calculation begins, a ray calculation is performed to create BSDF data with the surface of the metalens 10 as the diffusion surface, in order to inversely calculate the distribution of metaatoms on the metalens 10 (step S201). Next, a distribution map of the filling density of the pillars 13 is formed from the BSDF data such that the phase wavefronts of the light transmitted through the transmission surface 12 coincide (step S202). As previously mentioned, the packing density viewed from above the transmission surface 12 on which the pillars 13 are formed greatly affects the amount of phase change of the transmitted light. Therefore, in this invention, the pillar distribution formation process in step S202 is performed by determining the packing density of the pillars 13 in particular. In step S202, the height H of the pillars 13 is calculated to be approximately the same length as the wavelength λ of the transmitted light, for example, 1 μm. Step S202 is equivalent to the simulation result when the multiple transmission surfaces 12 on the final stacked metalens 20 are treated as a single transmission surface.

[0035] Once the filling density distribution of pillar 13 is calculated, a ray calculation is performed based on this filling density to determine whether the required optical performance is satisfied (step S203). If the required optical performance is not met in step 203, the parameters of pillar 13 are changed (step S204), and the process is repeated starting from step S201. Furthermore, if the required optical performance is met in step S203, the height component value of the pillar 13 generated in step S202 is reset to h1=h2=1 / 2·H, and the BSDF data is recalculated (step S205). As a result of the BSDF recalculation step in step S205, the data from step S201 becomes a data set with half the amount of phase change compared to the data calculated in step S202. Furthermore, in this embodiment, the phase wavefronts of the two transmission surfaces 12 were recalculated so that h1=h2=1 / 2·H. However, for example, when stacking n layers of transmission surfaces 12, the height of the pillar 13 may be divided into n parts and set so that h1=h2=h3···=hn=1 / n·H. Thus, step S205 is equivalent to recalculating the BSDF data, which was calculated as a single layer, into the amount of phase change per layer of the stacked transparent surfaces 12. Applying the data from each layer obtained in step S205, the distribution of pillar 13 is recalculated (step S206). Based on the data on the filling density distribution of the pillars 13 in each layer obtained in steps S205 and S206, it is determined whether the ray model when the metalens 10 of each layer are stacked satisfies the optical performance requirements (step S207). If the required optical performance anticipated in step S207 is not met, the process returns to step S204, changes the parameters of the pillar 13, and then returns to step S201. If the required optical performance is satisfied in step S207, the simulation is terminated, and each layer of the metalens 10 is produced according to the manufacturing method described in Figures 10 and 12, then stacked and bonded.

[0036] According to this method of manufacturing a metallens, two identical metallenses 10, each with half the height H of the pillar 13, are joined together so that the forming surfaces of the pillars 13 face inward. That is, of the transmissive surfaces 12, which are microstructure surfaces, the two outermost surfaces are arranged to face each other, and a pair of substrate layers, which are substrate portions 11, are located outside the transmissive surfaces 12. Specifically, as shown in Figure 6, the two metalens 10 are integrally formed in a manner in which they are joined together facing each other.

[0037] When stacking multiple metalens 10, this shape ensures that the substrate portion 11 is on the outermost side. As a result, the surface on which the pillar 13 is formed is protected by the substrate portion 11, thereby increasing the impact resistance of the pillar 13 in the metalens 20, preventing damage, and enabling stable performance. Furthermore, as shown in Figure 14, if the optical performance of the entire metalens 20 is evaluated before stacking by dividing it by height H, the shape errors of the individual metalenses 10 are averaged out, so defects due to shape errors can be reduced, resulting in a better yield and more stable optical performance.

[0038] Furthermore, as a modified example of this embodiment, as shown in Figure 15, an example is shown in which the distribution and height H of the pillars 13 calculated in step S202 are kept the same during manufacturing, and both sides are covered with the substrate portion 11. In the metalens 20 shown in Figure 15, the two are similar in that a pair of substrate layers, the substrate portion 11, is located outside the transparent surface 12, but they differ in that the transparent surface 12 is not particularly laminated.

[0039] Even with this configuration, the transmissive surface 12 on which the pillar 13 is formed functions as a metalens, and since both sides are covered by the substrate portion 11, the impact resistance of the pillar 13 is enhanced, preventing damage and enabling stable performance.

[0040] Furthermore, as another variation, when multiple metalens 10 with different functions are stacked and joined, as shown in Figure 16, instead of dividing into n equal parts in step S205, metalens 10A and 10B having different pillar 13 distributions may be joined to each other. In Figure 16, as with the metalens 20 shown in Figures 6 and 15, the respective transmissive surfaces 12A and 12B of the metalens 10A and 10B are integrally formed in such a manner that they are sandwiched between the substrate portions 11A and 11B. This enhances the impact resistance of the pillar 13, prevents damage, and ensures stable performance. In other words, in a metalens 20 formed by stacking multiple metalenses 10A and 10B, each of which has multiple microstructure surfaces that generate different phase wavefronts when light is transmitted, a pair of substrate portions 11 are integrally formed so as to be positioned opposite each other on both sides of the transmitting surfaces 12A and 12B of each metalens 10A and 10B, sandwiching the microstructure surfaces.

[0041] Furthermore, when stacking three or more metalens 10A, 10B, and 10C using this manufacturing method, for example, as shown in Figure 17, at least the two outermost metalens 10A and metalens 10C are integrally formed so that their transmissive surfaces 12 face each other. Thus, in this embodiment, when stacking the metalens 10, the outermost pair of metalens 10 are arranged to face each other, and a pair of substrate layers, substrate portion 11A and substrate portion 11C, are located outside the transparent surfaces 12A and 12C that constitute this pair. With this configuration, since each of the three or more transparent surfaces 12A, 12B, and 12C is integrally formed in such a manner that it is sandwiched between the substrate portions 11A and 11C, the impact resistance of the pillar 13 is enhanced, preventing damage and enabling stable performance.

[0042] Next, as a second embodiment of the present invention, another manufacturing method in which three or more transparent surfaces 12 are laminated will be described. When stacking three or more transparent surfaces 12, it is difficult to generate "only the transparent surfaces 12" using, for example, nanoimprint lithography. Furthermore, even if lithography or the like is used, if three or more layers of metalens 10A, 10B, etc., which generate different phase wavefronts in each layer, are stacked, as shown in Figure 17, it is ultimately difficult to eliminate the substrate portion 11B no matter how thin it is made. Therefore, while the method described as the first embodiment keeps the manufacturing difficulty low, it has limitations when the goal is to further thin the metalens 20.

[0043] Furthermore, it is necessary to consider that the thickness of the substrate portion 11B creates a gap for obliquely incident light. Specifically, consider the case in Figure 17 where light is incident from below, perpendicular to the transmission surface 12A. At that time, primary light L1 is refracted by the transmissive surface 12A, and zero-order light L0 is generated that is not refracted by the transmissive surface 12A. However, the primary light L1, which is the ray that we want to use as a metalensor, will always be incident at an oblique angle on the substrate portion 11B. This means that the thicker the substrate portion 11B becomes, the greater the deviation of the incident position of the light ray from the simulation results when only one layer of metalens is used. Therefore, it becomes necessary to take this gap in the substrate portion 11B into account when performing the light ray calculation shown in Figure 14. Furthermore, when the light rays incident on pillar 13 are obliquely incident, the effects on the polarization components P and S will differ depending on the direction of incidence, so this point also needs to be taken into consideration.

[0044] Therefore, in this embodiment, we will describe a manufacturing method when laminating transmissive surfaces 12A, 12B, and 12C having different pillar distributions, as shown in Figures 18 and 19. First, as shown in Figure 19(a), a metalens 10A is generated as the first metalens (step S301). This metalens 10A may be generated by nanoimprinting, for example, as shown in steps S101 to S104 in Figure 11. Thus, step S301 in this embodiment is a first microstructure generation step in which a pattern of microstructures is formed on quartz glass by nanoimprinting, and can also be called a metaatom formation step or a nanoimprinting step. Next, as shown in Figure 19(b), a thin film 14 is formed on the metalens 10A so as to fill the gaps in the pillars 13 (step S302). At this time, the material of the thin film 14 can be, for example, titanium oxide, tantalum pentoxide, niobium pentoxide, etc. Furthermore, since the thin film 14 penetrates into the gaps of the microstructure, it is desirable to apply a liquid material and form it by spinning coat. Step S302 is a coating process in which a film is formed using a material different from that of the pillar 13.

[0045] Next, a pattern is formed on the formed thin film 14 (step S303). In this pattern formation step, for example, as shown in Figure 19(c), a nanoimprint method may be used in which the prototype 81 is pressed onto the thin film 14 from above. In this way, the thin film 14 fills the voids of the pillars 13, and a transparent surface 12B is formed on top of it, on which pillars 13 made of the same material as the thin film 14 are formed (step S303). Step S303 is a second microstructure generation step, or second microstructure generation step, which generates a pattern of microstructures on the thin film 14 formed in the coating step. Finally, the metalens 10C, formed by the method described separately in Figures 10 and 12, is bonded together with the substrate portion 11 so that the transmissive surface 12C faces the transmissive surface 12A (step S304). With this configuration, it is possible to manufacture a metalens 20 in which transmissive surfaces 12A, 12B, and 12C, which are different microstructure surfaces, are formed in sequence.

[0046] Now, in the configuration shown in Figure 19(d), the transmissive surface 12A, shown as the bottom layer in Figure 19, consists of a quartz glass pillar 13 and a material with a different refractive index from the material constituting the pillar 13 (for example, titanium oxide, tantalum pentoxide, or niobium pentoxide) that fills the gap between them. On the other hand, when creating the distribution of pillar 13 based on BSDF data using Figure 14, the calculation implicitly includes the refractive index difference between the pillar 13 and the air filling the gap between them, as shown in Figure 4. Therefore, when calculating the phase wavefront for the metalens 10A from BSDF data, it is necessary to perform the calculation using the refractive index difference between the coated silicon oxide film and the quartz glass, rather than the refractive index difference with air, according to the configuration shown in Figure 19(d).

[0047] A configuration like that shown in Figure 19(d) has the advantage of reducing the overall thickness of the metalens 20 unit compared to the stacked configuration shown in Figure 15. Furthermore, since the thickness of the substrate portion 11B does not need to be considered, it is expected that the optical characteristics will be close to those obtained when the desired optical characteristics are achieved with a single metalens 10.

[0048] Thus, the present invention is characterized in that, after performing the nanoimprint process shown in step S301 and before performing the bonding process shown in step S304, a coating process (step S302) is performed in which a thin film is formed on at least one of the metalens 10A using a coated silicon oxide film with a refractive index different from that of the material constituting the microstructure so as to fill the gaps between the pillars 13, and a second microstructure generation process (step S303) is performed in which a pattern of microstructures is generated on the thin film 14 formed in the coating process S302. With this configuration, compared to simply bonding multiple metalens 10 together to form a stacked metalens 20, the thickness of the substrate portion of each intermediate layer can be reduced, making it possible to further thin the metalens 20 during manufacturing.

[0049] Furthermore, the metalens 20 of the present invention has a transmissive surface 12 on which a plurality of pillars 13 are formed along the direction of light transmission, and the two outermost transmissive surfaces 12 are arranged to face each other, and a pair of substrate portions 11A and 11C are located outside the transmissive surfaces 12A and 12C. With this configuration, by closing and integrating the pillar 13 so that it is located inside the substrate portion 11, the impact resistance of the pillar 13 is enhanced, preventing damage and providing a metalens with stable performance. Furthermore, in the metalens 20 of this embodiment, the multiple transmission surfaces 12A, 12B, and 12C each generate different phase wavefronts when light is transmitted. With this configuration, different functionalities can be provided to each layer, making it possible to realize a much thinner optical system as a metalens 20 compared to conventional spherical / aspherical lenses.

[0050] In this embodiment, of the two outermost transparent surfaces 12A and 12C, at least one of the transparent surfaces 12A is filled with a material having a different refractive index than the material constituting the microstructure that fills the gap between the transparent surfaces 12A. Furthermore, pillars 13 are formed on the transparent surface 12B adjacent to the transparent surface 12A by materials with different refractive indices (such as titanium oxide, tantalum pentoxide, and niobium pentoxide). With this configuration, the intermediate transparent surface 12B can be easily made into a metalens shape by nanoimprinting materials with different refractive indices, and since it is not necessary to form the substrate portion 11B, the thickness of the integrally formed metalens 20 can be further reduced.

[0051] Figure 20 shows an example configuration of an optical scanning device 100 as an example using the metalens 20 of the present invention. In this embodiment, the optical scanning device 100 includes a light source optical system composed of a laser light source 21, a coupling lens 22, an aperture 23, a cylinder lens 24, and a folding mirror 25. Furthermore, the light reflected by the optical deflector 26, which is a polygon mirror, passes through the metalens 20 and then enters the photoreceptor 510. Furthermore, the present invention includes an output detection sensor 310 and a distortion correction lens 29, which are detection means. The output detection sensor 310 is used to measure synchronization with the optical deflector 26 by receiving a portion of the 0th order light L0 of the metalens 20.

[0052] In this embodiment as well, the optical deflector 26 is a polygon mirror made of a hexahedron with mirrored sides, and rotates with the direction perpendicular to the plane of the paper as its axis of rotation, thereby scanning the light incident from the folding mirror 25 along the main scanning direction. Furthermore, at this time, the laser beam moves to scan the photoreceptor 510, and the laser beam moves such that the rotation angle θ of the optical deflector 26 is proportional to the image height in the main scanning direction.

[0053] In this embodiment, the metalens 20 is a metalens in which the filling ratio of the pillars 13 on the transmission surface 12 is determined so that the refraction of the primary light L1 follows a trajectory similar to that of an fθ lens.

[0054] Furthermore, these metalens 20 can be applied to various optical devices. For example, they can be used as part of the optical system 101 of an optical device 150 as shown in Figure 21. The optical system 101 shows an example of an optical system used in a light source device that emits uniform light using a light tunnel 103, for example, by using multiple laser light sources.

[0055] Alternatively, the image projection device 110 shown in Figure 22 is shown as an example of an image projection device that includes a light source 111, a projection optical system 112 including a metalens 20, a reflective mirror 113, and an image display element 115, and projects an image toward a screen 114 which is the projection surface. By using such an image projection device 110, the thickness of the lens can be reduced by using a metalens 20 in the optical system, making it possible to realize a space-saving and high-performance device.

[0056] Another example of the optical device 150 is its use in the imaging device 130 shown in Figure 23. Thus, the metalens 20 can be widely used as one of the optical elements constituting the existing optical system 101.

[0057] The embodiments of the present invention are as follows. [1] The metalens 20 of the present invention is a metalens having one or more light-transmitting surfaces on which a plurality of pillars 13 are continuously formed, and the refractive index for light is adjusted by the density of the pillars 13, and is formed integrally so that a pair of substrate portions 11 are positioned opposite each other on both sides of the light-transmitting surface 12, sandwiching the light-transmitting surface 12. With this configuration, the metalens 20 suppresses the impact on optical performance due to variations in the pillars 13 on each transmission surface 12, and by closing and integrating the pillars 13 so that they are located inside the substrate portion 11, the impact resistance of the pillars 13 is enhanced, preventing damage and providing a metalens with stable performance.

[0058] [2] The metalens 20 of the present invention has, in addition to the configuration of the metalens described in [1], a plurality of transmissive surfaces 12 along the direction of light transmission, the two outermost transmissive surfaces 12 being arranged to face each other, and a pair of substrate portions 11 being located outside the transmissive surfaces 12. With this configuration, the metalens 20 suppresses the impact on optical performance due to variations in the pillars 13 on each transmission surface 12, and by closing and integrating the pillars 13 so that they are located inside the substrate portion 11, the impact resistance of the pillars 13 is enhanced, preventing damage and providing a metalens with stable performance.

[0059] [3] In addition to the configurations described in [1] or [2], the metalens 20 has multiple transmission surfaces 12, each having a different arrangement of pillars 13, which generate different phase wavefronts when transmitting light. With this configuration, different functionalities can be provided to each layer, making it possible to realize a much thinner optical system as a metalens 20 compared to conventional spherical / aspherical lenses.

[0060] [4] In addition to any of the configurations described in [1] to [3], the metalens 20 has at least one of its two outermost transmissive surfaces 12A, 12C, the transmissive surface 12A, filled with a material having a different refractive index than the material constituting the pillars 13, so as to fill the gap between the pillars 13. With this configuration, the intermediate transparent surface 12B can be easily made into a metalens shape by nanoimprinting materials with different refractive indices, and since it is not necessary to form the substrate portion 11B, the thickness of the integrally formed metalens 20 can be further reduced.

[0061] [5] In addition to the configuration described in [4], the metalens 20 of the present invention has a microstructure formed by the material on the microstructure surface adjacent to the microstructure surface in which the gaps are filled with a material having a different refractive index. With this configuration, the intermediate transparent surface 12B can be easily made into a metalens shape by nanoimprinting materials with different refractive indices, and since it is not necessary to form the substrate portion 11B, the thickness of the integrally formed metalens 20 can be further reduced.

[0062] [6] The present invention is characterized by being an image projection device comprising a projection optical system having the configuration described in any of [1] to [5], a light source, and an image display element. With this configuration, by using a metalens as some of the lenses that make up the projection optical system, the entire optical system can be further miniaturized.

[0063] [7] Furthermore, the present invention is a light source device having a light source optical system including a metalens 20 having the configuration described in [1] to [5], and a light source that emits light. With this configuration, by constructing an optical system using the metalens 20, the light source device itself can be miniaturized.

[0064] [8] Furthermore, the present invention is an imaging device equipped with a metalens 20 having the configuration described in [1] to [5]. With this configuration, by constructing an optical system using the metalens 20, the light source device itself can be miniaturized.

[0065] [9] The present invention also relates to an optical scanning device 100 equipped with a metalens 20 having the configuration described in [1] to [5]. With this configuration, by constructing an optical system using the metalens 20, the light source device itself can be miniaturized.

[0066]

[10] Furthermore, the present invention provides a method for manufacturing a metalens 20, which is a method for manufacturing a metalens in which a plurality of microstructures are arranged on a light-transmitting surface, thereby adjusting the refractive index for light by the density of the microstructures, and is characterized by comprising: a first microstructure generation step of continuously generating a plurality of microstructures on a substrate; and a joining step of integrally joining at least two metalens generated by the first microstructure generation step so that the surfaces on which the microstructures are formed face inward. With this configuration, the metalens 20 suppresses the impact on optical performance due to variations in the pillars 13 on each transmission surface 12, and by closing and integrating the pillars 13 so that they are located inside the substrate portion 11, the impact resistance of the pillars 13 is enhanced, preventing damage and providing a metalens with stable performance.

[0067]

[11] Furthermore, the manufacturing method of the metalens 20 of the present invention is characterized by performing, after the first microstructure generation step and before the bonding step, a coating step in which a thin film is formed on at least one metalens using a material with a different refractive index than the material constituting the microstructure so as to fill the gaps between the microstructures, and a second microstructure generation step in which a pattern of microstructures is generated on the thin film formed in the coating step. With this configuration, the intermediate transparent surface 12B can be easily made into a metalens shape by nanoimprinting materials with different refractive indices, and since it is not necessary to form the substrate portion 11B, the thickness of the integrally formed metalens 20 can be further reduced.

[0068] Although preferred embodiments of the present invention have been described above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the spirit of the invention as described in the claims, unless otherwise specifically limited in the above description. For example, a metalens may be used as an optical element to replace a lens in applications other than the optical systems described above. Furthermore, the first and second microstructure generation steps may utilize existing microfabrication technologies such as electron beam lithography (EBL) and photolithography, in addition to the nanoimprint method. The effects described in the embodiments of the present invention are merely illustrative of the most preferred effects that may arise from the present invention, and the effects of the present invention are not limited to those described in the embodiments. [Explanation of Symbols]

[0069] 10, 20... Metalens 11...Base material layer 12... Transmissive surface (fine structure surface) 13. Pillar (microstructure) 14. Thin film 101...Optical system 115...Image display element 114...Projection surface 100... Optical scanning device 110...Image projection device 130... Imaging device 150...Light source device S101...Substrate formation process S102...Photosensitive resin formation process S103...Metaatom formation process (first microstructure formation process) S104...Joining process S301...Nanoimprint process (first microstructure generation process) S302...Coating process S303...Fine structure formation process (second microstructure generation process) S304...Joining process [Prior art documents] [Patent Documents]

[0070] [Patent Document 1] Patent No. 7328232 [Patent Document 2] Special Publication No. 2023-530252

Claims

1. A metalens comprising one or more microstructure surfaces in which a plurality of microstructures are continuously formed on the light-transmitting surface, and the refractive index for the light is adjusted by the density of the microstructures, A metalens characterized in that a pair of substrate layers are integrally formed so as to be positioned opposite each other on both sides of the aforementioned microstructure surface, sandwiching the microstructure surface.

2. A metal lens according to claim 1, Having a plurality of microstructure surfaces along the light transmission direction, Of the aforementioned microstructure surfaces, the two outermost ones are arranged to face each other. A metalens characterized in that the pair of substrate layers are located outside the microstructure surface.

3. A metalens according to claim 2, A metalens characterized in that multiple microstructured surfaces each generate different phase wavefronts when light is transmitted through them.

4. A metalens according to claim 2, A metalens characterized in that at least one of the two outermost microstructure surfaces is filled with a material having a different refractive index than the material constituting the microstructure, so as to fill the gaps between the microstructures.

5. A metalens according to claim 4, A metalens characterized in that a microstructure is formed on a microstructure surface adjacent to the microstructure surface in which the gap is filled with a material of a different refractive index, by the said material.

6. An optical system comprising a metalens according to any one of claims 1 to 5, The system comprises a light source that emits the aforementioned light and an image display element, An image projection device that projects light transmitted through the aforementioned metalens onto a projection surface.

7. An optical system comprising a metalens according to any one of claims 1 to 5, A light source device having a light source that emits the aforementioned light.

8. An imaging apparatus comprising a metalens according to any one of claims 1 to 5.

9. An optical scanning apparatus comprising a metalens according to any one of claims 1 to 5.

10. A method for manufacturing a metalens, wherein a plurality of the microstructures are arranged on the light-transmitting surface, and the refractive index for light is adjusted by the density of the microstructures, A first microstructure generation step in which multiple microstructures are continuously generated on a substrate, A method for manufacturing a metalens, characterized by performing a joining step of integrally joining at least two metalens produced by the first microstructure generation step so that the surfaces on which the microstructures are formed face inward.

11. A method for manufacturing a metalens according to claim 10, After the first microstructure generation step and before the bonding step, a coating step is performed in which a thin film is formed on at least one of the metalens using a material with a different refractive index than the material constituting the microstructure so as to fill the gaps between the microstructures. A method for manufacturing a metalens, characterized by performing a second microstructure generation step of generating a pattern of microstructures on a thin film formed in the coating step.

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