Transmissive meta-lens, optical device, image projection device, light source device, imaging device, and optical scanning device

Abstract

To provide a refractive meta-lens with higher performance by breaking periodicity occurring in the arrangement of meta-atoms and eliminating elements that become a diffractive lens.SOLUTION: The present invention is a transmissive meta-lens in which a plurality of micro-structures are continuously formed on a light transmitting surface, and the refractive index for the light is adjusted by the density of the micro-structures. A dimension d of the micro-structures in a horizontal direction relative to the transmitting surface satisfies λ≥d, where λ is the wavelength of the light. The transmissive meta-lens is characterized in that the density of the micro-structures is determined by a phase amount corresponding to a phase wavefront of the light, and the repetition range of the phase amount is irregular in the horizontal direction of the transmitting surface.SELECTED DRAWING: Figure 16

Description

[Technical Field]

[0001] The present invention relates to a transmissive metalens and an optical device, an image projection device, a light source device, an imaging device, and an optical scanning device that use a metalens. [Background technology]

[0002] Metamaterials, which consist of periodic structures smaller than the wavelength, are artificial materials that do not exist in nature, and when they are made two-dimensional, they are called metasurfaces. Since the spacing or size of the tiny periodic structures (metaatoms) that make up metasurfaces depends on the wavelength, in the field of relatively large wavelength ranges (Radio Frequency), active development is underway, including intelligent reflectors and beam-scanning antennas.

[0003] On the other hand, in the optical field that uses the visible light region, the wavelength is short, so the size of the required meta-atoms is small, at several hundred nanometers, making them difficult to process, which has been an obstacle. However, in recent years, advances have been made in the application of semiconductor processing technology to precisely engrave glass and dielectrics, and the development of optical elements using such metasurfaces is also progressing in the optical field (see, for example, Patent Documents 1 and 2, Non-Patent Document 1, etc.).

[0004] Among the metasurfaces that utilize this technology, metalenses are nanodevices composed of tiny nano-sized structures. They have a lens-like light-focusing effect and can be significantly thinner than conventional refractive lenses. There are several operating principles, but it is already known that they basically control the amplitude and phase of light when it passes through or is reflected by the metalenses. However, when such metalenses are actually created, it has become clear that the resulting periodic structure causes strong diffraction phenomena. This is thought to occur because the phase wavefront of light is expressed by the arrangement of meta-atoms, and when the meta-atom structure is viewed macroscopically, the refractive index changes repeatedly at a constant period (basically a phase of 2π). These diffractive lens characteristics exhibit different aberration characteristics from those of refractive lenses, which makes them useful in some ways, but also poses a challenge in that they require optical design that is different from that of conventional refractive lenses. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention is intended to solve the above-mentioned problems, and aims to provide a refractive metalens with higher performance by breaking the periodicity that occurs in the arrangement of meta-atoms and eliminating the elements that act as diffractive lenses. [Means for solving the problem]

[0006] The metalens of the present invention is a transmissive metalens in which a plurality of microstructures are continuously formed on a light transmitting surface, and the refractive index for the light is adjusted by the density of the microstructures, wherein a dimension d of the microstructures in a horizontal direction relative to the transmitting surface satisfies λ≧d where λ is the wavelength of the light, and the transmissive metalens is characterized in that the density of the microstructures is determined by a phase amount corresponding to a phase wavefront of the light, and the repetition range of the phase amount is irregular in the horizontal direction of the transmitting surface. [Effects of the Invention]

[0007] According to the present invention, by breaking the periodicity that occurs in the arrangement of meta-atoms and eliminating the elements that become diffractive lenses, it is possible to provide a refractive metalens with higher performance. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a metalens as a first embodiment of the present invention. [Figure 2]FIG. 2 is a diagram schematically illustrating an example of the microstructure of the surface of the metalens shown in FIG. 1. [Figure 3] FIG. 1 is a diagram schematically illustrating refraction by a convex lens. [Figure 4] FIG. 3 is a diagram illustrating a schematic change in refractive index caused by the microstructure shown in FIG. 2. [Figure 5] FIG. 10 is a diagram illustrating an example of a method for generating a metasurface. [Figure 6] FIG. 10 is a diagram illustrating an example of a method for producing a metalens. [Figure 7] FIG. 10 is a diagram showing a comparative example when a conventional metalens is used. [Figure 8] FIG. 1 is a diagram illustrating the diffraction effect that occurs in a conventional metalens. [Figure 9] FIG. 10 is a diagram illustrating an example of a method for calculating a filling rate in the present invention. [Figure 10] FIG. 4 is a diagram showing an example of a method for calculating a first annular zone in the present invention. [Figure 11] FIG. 11 is a diagram showing an example of a first annular zone calculated from FIG. [Figure 12] FIG. 10 is a diagram showing an example of a method for calculating a second annular zone in the present invention. [Figure 13] FIG. 13 is a diagram showing an example of a second annular zone calculated from FIG. 12. [Figure 14] FIG. 10 is a diagram showing an example of a method for calculating a third annular zone in the present invention. [Figure 15] FIG. 15 is a diagram showing an example of a third annular zone calculated from FIG. 14. [Figure 16] FIG. 10 is a diagram showing an example of the calculation results for each annular zone in the present invention. [Figure 17] 1A and 1B are diagrams illustrating the principle of reducing the diffraction effect in the present invention. [Figure 18] FIG. 1 is a diagram showing an example of the configuration of an optical device using a metalens of the present invention. [Figure 19] FIG. 1 is a diagram showing an example of the configuration of an image projection device using a metalens of the present invention. [Figure 20]FIG. 1 is a diagram showing an example of the configuration of an optical system of a light source device using a metalens of the present invention. [Figure 21] FIG. 1 is a diagram showing an example of the configuration of an imaging device using a metalens of the present invention. [Figure 22] FIG. 1 is a diagram showing an example of the configuration of an optical scanning device using a metalens of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] FIG. 1 shows an example of the configuration of a metalens having a metasurface as a first embodiment of the present invention. In the figure, metalens 10 is shown as an example of an optical element having a substrate 11 made of plate-like quartz glass, and a plurality of cylindrical pillars 13, which are microstructures, provided on a light transmitting surface 12 of the substrate 11. Note that, although pillars 13 are particularly shown as cylindrical microstructures with a diameter R in Fig. 2, they are not limited to this configuration and may be, for example, polygonal pillars whose upper surfaces are polygonal, such as triangular, rectangular, or hexagonal, or may have a shape that combines rectangular shapes, or may have a shape obtained by extending any of these in one direction.

[0010] In this case, if the interval between the pillars 13 is a sub-wavelength interval for the transmitted light, the transmitting surface 12 functions as a so-called metasurface. The wavelength of the transmitted light may be any wavelength, but in this embodiment, for example, light of λ=532 nm is used as an example of light in the visible light region.

[0011] When the diameter of the pillars 13 is R and the distance between adjacent pillars 13 is a pitch p, the functionality of the transmitting surface 12 as a metasurface changes depending on the filling rate of the pillars 13. This is because, when a light wave enters the sub-wavelength pitch p, the pillars 13 act as meta-atoms that block the progression of the light wave. It has also been found that by changing the packing ratio of these pillars 13, that is, the density, it is possible to give the entire transmitting surface 12 a refractive index different from the refractive index of the material of the pillars 13.

[0012] To explain this point, first, as a simple example, Figure 3 shows the progression of a light wave through a convex lens, along with the phase wavefront. In Figure 3, the portion where the phases of adjacent parallel light rays match is shown as a phase wavefront by a thin line. Needless to say, the normal direction to the phase wavefront is the direction of light propagation. When light enters convex lens 200 with refractive index n, the speed of light slows down in proportion to the refractive index, and the phase wavefront is tilted relative to the parallel light beam toward the convex direction of convex lens 200. Since the direction in which the series of phase wavefronts travels is the direction in which light travels, the direction in which light travels is tangent to the series of phase wavefronts, and the light is bent toward the optical axis of convex lens 200 as shown in FIG.

[0013] 4(a) and 4(b) are schematic diagrams showing the effect of pillars 13 on a metasurface, i.e., a transmitting surface 12. As shown in Fig. 4(a), when pillars 13 smaller than the wavelength λ are arranged in a forest on the transmitting surface 12, light of wavelength λ does not recognize the pillars 13 as individual cylinders on the transmitting surface 12, but rather recognizes them as the refractive index of the transmitting surface 12, which varies depending on the filling rate.

[0014] That is, on the transmitting 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 standing pillars 13. The magnitude of such pseudo-refractive index n2 is roughly shown in Figure 4(a) by color-coding according to the gradation intensity.

[0015] Therefore, as shown in Figure 4(b), when parallel light rays are incident on the transmitting surface 12 from a direction perpendicular to the transmitting surface 12, the phase wavefront of the light rays incident on the transmitting surface 12 will move more slowly in areas with a larger refractive index, as shown in Figure 4(b). As already mentioned, the magnitude of the refractive index of the transmitting surface 12 depends on the filling rate at which the pillars 13 are formed. In other words, for the transmitted light, a change in the filling rate of the pillars 13 on the transmitting surface 12 is equivalent to a change in the optical path length of 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 at the transmitting surface 12 equal to the phase wavefront that is delayed due to the difference in optical path length caused by the thickness of the lens, it is possible to achieve a refractive effect similar to that of the convex lens 200. In this way, if the pillars 13 are of the subwavelength order with respect to the wavelength λ of light and the refractive index of the transmitting surface 12 is gradient due to their filling rate, as shown in Figure 4(b), the progression of the wavefront will be slowed down by the filling rate of the pillars 13, and the phase wavefront will be tilted to the left as shown in Figure 4(b). When multiple pillars 13 of the subwavelength order are arranged in a regular pattern, this phenomenon plays a role similar to that of atoms for light waves traveling within a molecular crystal lattice, distorting the phase wavefront as if it were refracted. Conversely, if such distortion of the phase wavefront can be artificially created by the regularity of the pillars 13, the transmitting surface 12 will have an optical function equivalent to that of a lens surface with a refractive index n2. This is the simple principle of optically functional surfaces called metasurfaces, and in such optically functional surfaces, microstructures such as pillar 13 are sometimes called meta-atoms, likening them to atoms.

[0016] It is known that the conditions for changing the phase wavefront based on this principle are practically equivalent to conditional formula (1). Here, λ is the wavelength of the transmitted light, and R is the diameter of the pillar 13. Furthermore, for shapes other than cylinders, this formula can also be written as λ≧d, where d is the horizontal dimension of the microstructure relative to the transmitting surface 12. For example, if the pillar 13 is a rectangular prism, d can be the length of the long side / short side or the diagonal, or if the pillar 13 is a triangular prism, it can be the length of one side. In either case, the geometrically most typical distance when viewing the pillar 13 from the vertical direction can be treated as the horizontal dimension d.

[0017]

number

[0018] Extending this concept, it can be seen that adjacent light waves arrive with a delay, and so the degree of inclination of the convex lens can be reproduced in a pseudo manner by varying the density of the pillars 13 on the surface. In other words, if the surface pillars 13 can be appropriately positioned using an optical element that satisfies conditional formula (1), the refractive index n2 at each point on the transmitting surface 12 can be adjusted by adjusting the density of the pillars 13, which are called meta-atoms.By distributing the refractive index n2 of the transmitting surface 12, for example, concentrically, it is possible to obtain a refracted wavefront similar to that of a convex lens 200 simply by passing light through the flat transmitting surface 12.

[0019] As described above, the pseudo refractive index n2 of the transmitting surface 12 can be controlled by the degree of density of the pillars 13, that is, the area (filling rate) occupied by the pillars 13 in a plane perpendicular to the transmitted light. In this embodiment, the degree of density is adjusted by changing the diameter R of the pillars 13 to change the filling rate of the pillars 13.

[0020] In other words, if it is possible to create a distribution of the diameters of the pillars 13 such that the phase wavefront of the transmitted light passing through the transmitting surface 12 matches the phase wavefront of the light passing through a convex lens with a refractive index n2, the light passing through such transmitting surface 12 will be the same as light that has passed through a convex lens with a refractive index n2.

[0021] Now, a method for realizing such a transmitting surface 12 will be described. Conventionally, methods such as electron beam lithography (EBL) have been used to form multiple microstructures such as those shown in Figure 2. This method has a resolution of less than 10 nm and is therefore widely used to fabricate metasurfaces. However, this method is time-consuming and cost-intensive, so a more efficient manufacturing method has been sought. As a method for manufacturing such a large area and with high efficiency, for example, a method of transferring by nanoimprint using a prototype 81 formed by lithography is known.

[0022] An example of a method for manufacturing an optical element including such a metalens 10 will be described with reference to FIG. As shown in FIG. 5(a), first, synthetic silica glass 88 is formed on a quartz substrate 86, which is the material that will form the substrate portion 11 of the metalens 10 (step S101 in FIG. 6). Next, a resist layer 89 made of a photosensitive resin is formed in a layer shape on the synthetic quartz glass 88 (step S102). A pattern prototype 81 having cylindrical or polygonal prism-shaped voids formed therein according to processing data having a shape that is the reverse of the desired pillar 13 in terms of concavity and convexity is pressed against a resist layer 89 formed on synthetic quartz glass 88, and a layer having the same shape as the pillar 13 is formed (step S103). Step S103 is a mask formation process in which a mask pattern is formed using the resist layer 89. In the mask formation process, a pattern is formed on the surface of the synthetic quartz glass 88 using the resist layer 89 so as to resemble the shape of the pillars 13 to be manufactured. In this mask formation process, it is desirable that the height from the bottom to the top of the pillar shape formed by the resist layer 89, in other words, the thickness of the resist layer 89, be approximately the same as the thickness of the synthetic silica glass 88 layer. In addition, in this embodiment, the mask is formed by nanoimprint using the prototype 81, but it may also be formed by photolithography or the like.

[0023] Next, a dry etching process such as ECR plasma etching or RIE etching is performed using an etching gas that is a mixture of oxygen gas for etching photosensitive resin and fluorocarbon gas for etching synthetic quartz glass (step S104). In the etching process of step S104, the resist layer 89 and the synthetic quartz glass 88 are etched in a state in which the shape of the resist layer 89 is transferred onto the synthetic quartz glass 88, as shown in FIG. 5(c).

[0024] When the etching process is continued until the resist layer 89 is removed, the shape of the resist layer 89 is transferred to the synthetic quartz glass 88, and pillars 13 are formed as shown in FIG. 5(d). This method can be used in a similar manner even if the substrate 86 and the synthetic quartz glass 88 are made of the same material, and may also be used for a substrate formed of multiple layers. In this embodiment, the thickness of the resist layer 89 and the thickness of the synthetic quartz glass 88 are approximately the same, and the etching rates are also approximately the same, so when the resist layer 89 is removed, the synthetic quartz glass 88 forms pillars 13 that are spaced apart from each other. In this case, if a material for the substrate 86 is selected that is not or is difficult to etch by the etching gas, pillars 13 can be formed in the same manner even if the thickness of the resist layer 89 is different from the thickness of the synthetic quartz glass 88. Similarly, the etching rate may be controlled in accordance with the layer thickness by changing the mixture ratio of the etching gas or the materials of the substrate 86 and synthetic quartz glass 88 .

[0025] A typical example of a metalens 10 produced in this way, with different patterns depending on the filling rate of the pillars 13, is shown in FIG. The reason why such a substantially concentric filling rate is shown will also be explained. Simply finding a correspondence between the filling factor and the numerical value obtained by quantifying the phase wavefront of incident light using, for example, ray simulation software results in values ​​that are similar to the discretization of the lens surface, as shown in Figure 8(a), and the range of possible sparseness and denseness becomes wide. Also, the diameter of the pillars 13 formed in metalens 10 is usually finite, and when the filling factor is controlled by the diameter R of the cylindrical pillars 13, the top surfaces of the pillars 13 are circular, so the filling factor of the circle relative to the rectangle is approximately 78% at most. Furthermore, as shown in conditional formula (1), the pillars 13 must be arranged so that their diameter R is equal to or less than the wavelength. Therefore, simply determining the filling factor based on a coefficient proportional to the numerical value of the phase wavefront does not allow the metasurface properties of metalens 10 to be fully utilized, so the filling factor of pillars 13 must be kept within a certain range.

[0026] Therefore, a typical method for making the phase wavefront equivalent to that of a refractive lens using a filling factor is to digitize the phase wavefront obtained as shown in Figure 8(a), and then calculate the remainder when dividing each value by 2π as the filling factor. This is equivalent to "folding" the graph in Figure 8(a) so that the specified pillar packing density (≒ pillar diameter) is not exceeded. If the phase wavefront quantified by this calculation method is graphed with the degree of density of the pillars 13, in other words, the filling rate of the pillars 13, on the vertical axis and the radial direction of the metalens 10 on the horizontal axis, the shape shown in FIG. 8(b) will result. As is clear from Figures 8(a) and (b), this operation is similar to dividing a normal convex lens into a Fresnel lens, which is thinned while maintaining the inclination of the lens surface.

[0027] Furthermore, since the phase wavefront of light with wavelength λ naturally repeats with a phase cycle of 2π, the quantized calculation results also have this periodicity. Furthermore, the numerical values ​​of these phase wavefronts ultimately have a periodicity that oscillates with a period of 2π in the radial direction of Figure 7, and due to this radial periodicity, the density of pillars 13 should also be formed so that it is repeatedly distributed in concentric circles of a predetermined width within the width of the sub-wavelength range, as shown in Figure 7. For convenience, let us call the innermost concentric circle in Figure 7 the first annular zone 31, and then the subsequent annular zones 32, 33, etc., going outwards. This means that each of these annular zones has a periodicity of 2π along its radial width.

[0028] That is, as is clear from the diagram in FIG. 8(b), this periodicity occurs throughout the entire area of ​​the metalens 10, and the diffractive properties of the metalens 10 itself become strongly apparent. It is widely known that if one attempts to form a metalens 10 by simply associating a phase wavefront with the filling rate of the pillars 13, some of the transmitted light will exhibit diffractive behavior.

[0029] However, because this type of diffraction exhibits different aberration characteristics from refractive lenses, it is useful in some respects, but it also poses a challenge in that it requires a different optical design from conventional refractive lenses. Another problem is that it behaves like a concentric diffraction grating, resulting in the generation of concentric diffraction fringes.

[0030] Therefore, in order to reduce diffraction fringes when using the metalens 10, in the present embodiment, the calculation formula used to quantify the phase wavefront is deliberately modified to remove periodicity, thereby disrupting the macroscopic periodicity of the density of the pillars 13 in the radial direction of the metalens 10, thereby reducing the diffraction fringes.

[0031] To break this periodicity, it would be easy to add a certain amount of randomness to the pillar diameter, but this would also break the periodicity in the relationship between the phase wavefront and the pillar diameter, which is not desirable.

[0032] Therefore, there is a need for a method for breaking the long-term periodicity without losing the periodicity in wavelength units required for the metalens 10. A specific method for doing this will be described with reference to FIG. 9. First, a zero-point correction is performed on the raw data of the phase wavefront, with a predetermined phase set as the zero point (step S201). This corresponds to setting a reference point. The following calculations are performed on the numerical data of the phase wavefront based on this reference point as the reference numerical data of the phase wavefront. Next, as shown in Fig. 8, a "folding" operation is performed so that the pillar diameter, which indicates the filling rate, falls within a predetermined range (step S202). The folding operation is an operation in which the reference numerical data of the phase wavefront is divided by a predetermined value 2π+α, the quotient is discarded, and the remainder is converted into data. Here, the predetermined value used is (1-0.4) x 2π, which is a value that is changed by -40% from 2π. In other words, the calculation is performed as α = -0.4 x 2π. FIG. 10 is a graph of the radial distribution of this converted data, with the distribution passing through the center of the metalens 10. Note that, because correction was performed in step S201 so that the center point of the metalens 10 was the zero point, the center point of the metalens 10 is also drawn as 0 in FIG.

[0033] From the data digitized in step S202, a size in which the phase change falls within one period is cut out as the first annular zone 31 shown in FIG. 11 (step S203). In this embodiment, in step S203, the diameter of the first annular zone 31 is 1.2π, and therefore the phase amount from the center of the metalens 10 to a radius of 1.885 rad is treated as the first annular zone 31. Furthermore, each piece of numerical data included in this first annular zone 31 is the first periodic original data in this embodiment.

[0034] Next, the original numerical data of the phase wavefront calculated in step S201 is subjected to zero point correction again by setting the numerical value of the outer edge of the first annular zone 31 to zero (step S204). As a result, as shown in FIG. 12, a new numerical data waveform of the phase wavefront adjusted with the outer edge of the first annular zone 31 set to 0 is obtained as the first period correction data. For the numerical data obtained in step S204, the predetermined value is changed to (2+0.5)×π this time, and the folding operation is similarly performed on the numerical data of step S204 (step S205). In this case, in step S205, (2+0.5)×π is used as the predetermined value, that is, the calculation is performed as α2=+0.5π.

[0035] As in step S202, a size in which the phase change falls within one period is cut out from the digitized data as the second annular zone 32 shown in FIG. 12 (step S206). When this operation is performed, the area from the center of the metalens 10 up to a radius of 7.85 rad is treated as the second annular zone 32, as shown by the diagonal lines in FIG. When step S206 is performed, the areas that have already been removed as the first annular zones 31 in step S203 are deleted and treated as 0. Similarly, the portions outside the second annular zones 32 are also treated as 0, so when the numerical data for the second annular zones 32 are graphed along the radial direction passing through the center position of the metalens 10, the graph shown in Fig. 13 is obtained. Each piece of numerical data included in the second annular zones 32 is the second periodic original data in this embodiment.

[0036] Next, the original numerical data of the phase wavefront calculated in step S201 is subjected to zero point correction again by setting the numerical value of the outer edge of the second annular zone 32 to zero (step S207). Since the diameter of the second zone 32 is shifted from 2π by 50%, the outer edge of the second zone 32 is positioned 2.5π away from the outer edge of the first zone 31 in step S206. Next, the predetermined value is changed to (2-0.3) x π, and the folding operation is similarly performed on the numerical data of step S204 (step S208). As a result, the area indicated by diagonal lines in Fig. 14 is treated as the third annular zone 33. When this area is extracted in the same manner as in step S206, the numerical data of the third annular zone 33 shown in Fig. 15 is obtained.

[0037] These operations are repeated multiple times (step S209), and n nth zones are created by dividing the (n-1)th period correction data, which has been zero-point corrected by setting the numerical value of the outer edge of the (n-1)th zone to zero, by the period (2π+αn) and cutting the remainder to a width that will change the phase by one period (step S210). These operations maintain the degree of change in filling rate within one period for each of the first ring zone 31, the second ring zone 32, and the third ring zone 33, and the boundary conditions of these numerical data are adjusted to match by zero-point correction. Therefore, the numerical data of the phase wavefront obtained by performing steps S201 to S210 is equivalent to cutting out a metalens surface such as that shown in Fig. 8(a) while changing the width of each adjacent annular zone as shown in Fig. 16. By changing the width of each annular zone in this way, while maintaining periodicity within each annular zone, long-range periodicity that crosses over adjacent annular zones is eliminated.

[0038] In this way, the degree of density of pillar 13 in this embodiment is represented by a series of numerical values ​​consisting of first period original data, which is the remainder when the numerical data of the phase wavefront is divided by the period (2π+α1), second period original data, which is the remainder when the first period corrected data obtained from the numerical data of the phase wavefront by performing zero point correction at the outer edge of the first period original data, is divided by the period (2π+α2), and nth period original data, which is the remainder when the (n-1)th period corrected data obtained by repeating these processes is divided by the period (2π+αn). In this embodiment, the deviation from the period 2π is defined as the deviation amount α1 to αn. Experiments have shown that the larger the deviation amount, the more effective it is at eliminating diffraction factors, but at the same time, it also results in a larger deviation in the focusing position. Therefore, it is preferable to provide randomness to the deviation amount between ±5% and ±80%. When 2π is used as the reference, the width of each annular zone is changed to any value between 0.4π and 3.6π in the case of ±80%.

[0039] By recombining these n layers of zones, from the first to the nth, it is possible to obtain a metalens 10 in which multiple zones are combined, each with a different width for the repeat range of adjacent phase amounts, as shown by the solid lines in FIG. 17 for the comparative example and the example. The vertical axis of the metalens 10 shown in FIG. 17 is expressed as the filling rate of the pillars 13 at each location. As is clear from FIG. 17 , the metalens 10 shown in the example of this embodiment is formed so that the repeat width of the phase amount in adjacent zones, such as the first zone 31, the second zone 32, and the third zone 33, is irregular. Although only one direction has been described in this embodiment, as can be seen from FIG. 2 and other figures, metalens 10 is a two-dimensionally arranged cylinder, and therefore what has been described with reference to FIGS. 8 to 15 also applies to any direction passing through the center of metalens 10. With this configuration, the metasurface effect due to the microscopic periodicity of the filling rate of the pillars 13 can be maintained while eliminating the long-term periodicity that occurs when cutting out each ring zone, thereby eliminating the element that becomes a diffractive lens and reducing the effects of interference fringes or diffraction fringes that occur in the metalens 10.

[0040] Furthermore, these metalenses 10 can be applied to various optical devices by being used as part of the optical system 101 of an optical device 100 such as that shown in FIG.

[0041] For example, the image projection device 110 shown in FIG. 19 is an example of an image projection device that has a light source 111, a projection optical system 112 including a metalens 10, and a reflective mirror 113, and projects an image toward a screen 114, which is a projection surface. By using such an image projection device 110, it is possible to reduce the thickness of the lens by using metalens 10 in the optical system, while also reducing the diffracted light that is unique to metalens 10, making it possible to realize a more space-saving and high-performance device. Note that such projection optical systems employ optical systems with decentered optical axes. In such cases, off-axis light is incident on metalens 10, and the optical path length to the image plane or screen surface varies depending on the incident position, and the magnification varies in the horizontal and vertical directions, making it necessary to adjust the filling rate in accordance with changes in the imaging characteristics for each incident position. Therefore, in order to prevent the occurrence of diffraction fringes, it is desirable to break up the periodic density of pillars 13, taking into account changes in the diameter of the incident light beam for each incident position on metalens 10. Specifically, the "shift amount" may be changed in the vertical and horizontal directions according to the respective magnifications, or if pillars 13 are made into elliptical cylinders or square prisms with rectangular cross sections instead of cylindrical, the filling rate in the vertical direction and the filling rate in the horizontal direction will vary according to the ratio of the long and short sides of the ellipse or rectangle, so this may also be implemented.

[0042] Other examples of the optical device 100 include an optical system 101 as shown in FIG. 20, an imaging device 130 as shown in FIG. 21, and an optical scanning device 140 as shown in FIG. In this way, it is possible to use the metalens 10 as one optical element that constitutes an existing optical system 101. Furthermore, for example, optical scanning device 140 is shown to have a configuration in which metalens 10 is used as a replacement for an fθ lens in an existing optical system. Optical scanning device 140 is described as an optical scanning device that scans light onto photoconductor 146 via light source 111, polygon mirror 145, and metalens 10. Note that an optical system having fθ characteristics is used in the scanning optical system that constitutes such an optical scanning device 140. In this case, off-axis light is incident on the metalens 10, and the optical path length to the image plane or photosensitive surface varies depending on the incident position, and the magnification varies in the horizontal and vertical directions, so it is necessary to adjust the filling rate in accordance with changes in the imaging characteristics for each incident position. Therefore, in order to prevent the occurrence of diffraction fringes, it is desirable to break up the periodic density of the pillars 13, taking into account changes in the diameter of the incident light beam for each incident position on the metalens 10. Specifically, the "shift amount" may be changed in the vertical and horizontal directions according to the respective magnifications, or if pillars 13 are made into elliptical cylinders or square prisms with rectangular cross sections instead of cylindrical, the filling rate in the vertical direction and the filling rate in the horizontal direction will vary according to the ratio of the long and short sides of the ellipse or rectangle, so this may also be implemented.

[0043] The aspects of the present invention are as follows. [1] Metalens 10 of the present invention is a transmissive metalens that adjusts the refractive index for light by varying the density of pillars 13, which are microstructures, and the dimension d in the horizontal direction relative to transmitting surface 12 of the microstructure satisfies λ≧d, where λ is the wavelength of light. Furthermore, metalens 10 is characterized in that the density of pillars 13 is determined by a phase amount corresponding to the phase wavefront of light, and the repetition range of the phase amount is irregular in the horizontal direction of transmitting surface 12. With this configuration, the long-term periodicity that occurs in the arrangement of meta-atoms is disrupted, and the elements that become diffractive lenses are eliminated, making it possible to realize a refractive metalens 10 with higher performance.

[0044] [2] Metalens 10 of the present invention is a transmissive metalens as described in [1], characterized in that the correspondence between the phase difference and the density of the microstructures changes every predetermined width of the phase difference repetition range, and this predetermined width changes within a range of 2π±5% to 2π±80%. With this configuration, the long-term periodicity that occurs in the arrangement of meta-atoms is disrupted, and the elements that become diffractive lenses are eliminated, making it possible to realize a refractive metalens 10 with higher performance.

[0045] [3] In addition to the configuration described in [1] or [2], metalens 10 is characterized in that the predetermined widths of the repetition ranges of adjacent phase amounts are different from each other. With this configuration, the long-term periodicity that occurs in the arrangement of meta-atoms is disrupted, and the elements that become diffractive lenses are eliminated, making it possible to realize a refractive metalens 10 with higher performance.

[0046] [4] In addition to the configuration described in any one of [1] to [3], the phase amount of the metalens 10 is represented by a series of numerical values ​​consisting of first periodic original data obtained by dividing the numerical data of the phase wavefront by the period (2π+α1) and cutting the remainder over a width sufficient to change the phase by one period; second periodic original data obtained by deleting the first periodic original data from the numerical data and performing zero-point correction again at the outer edge of the first periodic original data and dividing the remainder over a width sufficient to change the phase by one period; and nth periodic original data obtained by repeating these steps and dividing the (n-1)th periodic corrected data by the period (2π+αn) and cutting the remainder over a width sufficient to change the phase by one period; and the density of the pillars 13 is determined according to the first to nth periodic original data. With this configuration, the long-term periodicity that occurs in the arrangement of meta-atoms is disrupted, and the elements that become diffractive lenses are eliminated, making it possible to realize a refractive metalens 10 with higher performance.

[0047] [5] In addition to the configuration described in any one of [1] to [4], α1 to αn in metalens 10 are defined as shift amounts with respect to the period 2π, and the shift amounts are within the range of ±5% to ±80%. With this configuration, the width of each of the first zone 31 through the nth zone is calculated with a certain degree of randomness depending on the amount of shift, thereby disrupting the long-term periodicity that occurs in the arrangement of meta-atoms and eliminating the elements that would become diffractive lenses, thereby achieving a refractive metalens 10 with higher performance.

[0048] [6] Furthermore, metalens 10 of the present invention is a transmissive metalens in which a plurality of pillars 13 are formed continuously on a light transmitting surface, and the refractive index for transmitted light is adjusted by the density of the pillars 13, and the dimension d of pillars 13 in the horizontal direction relative to transmitting surface 12 satisfies λ≧d, where λ is the wavelength of light. Furthermore, metalens 10 is characterized by having a plurality of concentric ring zones, each with a different relationship between the density of pillars 13 and the phase wavefront of light, and each ring zone has a different width. With this configuration, the width of each of the first zone 31 through the nth zone is calculated with a certain degree of randomness depending on the amount of shift, thereby disrupting the long-term periodicity that occurs in the arrangement of meta-atoms and eliminating the elements that would become diffractive lenses, thereby achieving a refractive metalens 10 with higher performance.

[0049] [7] The present invention also provides an optical device having the metalens 10 according to any one of the configurations described in [1] to [6]. With this configuration, it is possible to realize a refractive metalens 10 with higher performance by breaking the long-term periodicity that occurs in the arrangement of meta-atoms and eliminating the element that becomes a diffractive lens, which allows the thickness of the optical elements in the optical device to be reduced, contributing to space savings.

[0050] [8] The present invention also provides an image projection device 110 that includes a metalens 10 having any one of the configurations described in [1] to [6] and a light source 111 that emits light, and that projects at least a portion of the light that has passed through the metalens 10 onto a screen 114 that is a projection surface. With this configuration, it is possible to realize a refractive metalens 10 with higher performance by breaking the long-term periodicity that occurs in the arrangement of meta-atoms and eliminating the elements that become diffractive lenses, which allows the thickness of the optical elements in the image projection device 110 to be reduced, contributing to space savings.

[0051] [9] The present invention also provides a light source device having metalens 10 according to any one of the configurations described in [1] to [6] and a light source 111 that emits light. With this configuration, it is possible to realize a refractive metalens 10 with higher performance by breaking the long-term periodicity that occurs in the arrangement of meta-atoms and eliminating the element that becomes a diffractive lens, which allows the thickness of the optical elements in the optical device to be reduced, contributing to space savings.

[0052]

[10] The present invention also provides an imaging device 130 equipped with an optical system 101 including a metalens 10 according to any one of the configurations described in [1] to [6]. With this configuration, it is possible to realize a refractive metalens 10 with higher performance by breaking the long-term periodicity that occurs in the arrangement of meta-atoms and eliminating the elements that become diffractive lenses, which allows the thickness of the lenses in the imaging device 130 to be reduced, contributing to space savings.

[0053]

[11] The present invention also provides an optical scanning device 140 equipped with an optical system including a metalens 10 according to any one of the configurations described in [1] to [6]. With this configuration, it is possible to realize a refractive metalens 10 with higher performance by breaking the long-term periodicity that occurs in the arrangement of meta-atoms and eliminating the elements that become diffractive lenses, and therefore it is possible to reduce the thickness of the fθ lens in the optical scanning device 140, contributing to space savings.

[0054] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to such specific embodiments, and unless otherwise specifically limited in the above description, various modifications and changes are possible within the scope of the spirit of the present invention as described in the claims. The effects described in the embodiments of the present invention are merely examples of the most preferable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments of the present invention. [Explanation of symbols]

[0055] 10. Transmissive metalens (metalens) 12...Transparent surface 13. Microstructure (pillar) 100...optical device 101...Light source optical system (optical system) 110 Image projection device 114...Projection surface 130 Imaging device 140 Optical scanning device d...dimension n1, n2... refractive index λ...Wavelength S201 Zero point correction S203: First period original data S204: First cycle correction data S206: Second cycle original data [Prior art documents] [Patent documents]

[0056] [Patent Document 1] Special Publication No. 2022-502715 [Patent Document 2] Japanese Patent Application Laid-Open No. 2024-45435 [Non-patent literature]

[0057] [Non-Patent Document 1] ACS Photonics 2024, 11(3), 816-865 Publication Date:February 27, 2024

Claims

1. A transmissive metalens having a plurality of microstructures continuously formed on a light transmitting surface, and adjusting the refractive index for the light depending on the density of the microstructures, a dimension d of the microstructure in a horizontal direction relative to the transmission surface satisfies λ≧d where λ is the wavelength of the light; the transmission metalens, wherein the density of the microstructures is determined by a phase amount corresponding to a phase wavefront of the light, and the repetition range of the phase amount is irregular in the horizontal direction of the transmission surface.

2. 10. The transmissive metalens of claim 1, a transmission metalens, wherein the correspondence relationship between the phase amount and the density of the microstructures changes for each predetermined width of a repetition range of the phase amount, and the predetermined width changes within a range from 2π±5% to 2π±80%.

3. 3. The transmissive metalens of claim 2, A transmissive metalens, wherein the predetermined widths of adjacent repeat ranges of the phase amount are different from each other.

4. 10. The transmissive metalens of claim 1, the phase amount is represented by a series of numerical values ​​consisting of first periodic original data obtained by dividing the numerical data of the phase wavefront by a period (2π + α1) and cutting the remainder over a width sufficient to change the phase by one period; second periodic original data obtained by deleting the first periodic original data from the numerical data and performing zero-point correction again at the outer edge of the first periodic original data, and dividing the remainder by a period (2π + α2), which is obtained by cutting the remainder over a width sufficient to change the phase by one period; and nth periodic original data obtained by repeating these steps and dividing the (n-1)th periodic corrected data by a period (2π + αn), which is obtained by cutting the remainder over a width sufficient to change the phase by one period; and the density of the microstructures is determined in accordance with the first to nth periodic original data.

5. 5. The transmissive metalens of claim 4, The α1 to αn are defined as amounts of shift with respect to a period 2π, and the amounts of shift are within a range of ±5% to ±80%.

6. A transmissive metalens having a plurality of microstructures continuously formed on a light transmitting surface, and adjusting the refractive index for the light depending on the density of the microstructures, a dimension d of the microstructure in a horizontal direction relative to the transmission surface satisfies λ≧d where λ is the wavelength of the light; The transmissive metalens has a plurality of concentric ring zones, each of which has a different relationship between the density of the microstructures and the phase wavefront of the light, and each of the ring zones has a different width.

7. 7. An optical device comprising the transmissive metalens of claim 1.

8. A transmission metalens according to any one of claims 1 to 6; and a light source that emits the light, An image projection device that projects at least a portion of the light that has passed through the transmission metalens onto a projection surface.

9. a light source optical system including the transmissive metalens according to any one of claims 1 to 6; a light source that emits the light.

10. An imaging device comprising an optical system including the transmissive metalens according to claim 1 .

11. An optical scanning device comprising an optical system including the transmission metalens according to any one of claims 1 to 6.

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