Metalens, manufacturing method therefor and laminating device

Abstract

To provide a metalens capable of conversing a beam profile from Gaussian distribution to top-hat distribution with a nanostructure on only one main surface of a substrate.SOLUTION: A metalens (1) is composed of a plurality of nano-sized pillars (3) arranged on one principal surface of an optically transparent substrate (2). The pillars (3), which are located inside an optical center at a distance r, are typically arranged so that change in a cross section is expressed by a function that satisfies three specific conditions.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a metalens, a method for manufacturing the same, and an illumination device.

Background Art

[0002] In illumination such as pathological diagnosis, generally, a wide illumination range, high and uniform intensity distribution are required. In addition, a laser or a light-emitting diode is used as the light source for the illumination. The emitted light from such a light source is usually a Gaussian beam having a Gaussian distribution of radiation intensity. Therefore, in the above illumination, it is required to convert the beam profile of the emitted light from the light source from a Gaussian distribution to a top-hat profile having a substantially uniform radiation intensity distribution.

[0003] The conversion of the beam profile from a Gaussian distribution to a top-hat profile can be realized by an optical system including an aspherical lens. However, in an illumination device in a small device such as an endoscope, a smaller optical system for converting the above beam profile is required.

[0004] As a technique for converting the beam profile with such a small optical system, there is known a technique of disposing a double-sided metalens having pillars on both main surfaces on the optical path of the emitted light from the light source. In this technique, the emitted light from the light source is collimated by the nanostructure on the incident side, and the radiation angle of the emitted light is controlled by the nanostructure on the emission side (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the prior art as described above, in order to control the emitted light, it is necessary to form nanostructures with different functions on each of the two main surfaces of the substrate. There remains room for consideration from the perspective of forming nanostructures only on one main surface of the substrate to control the beam profile.

[0007] One aspect of the present invention aims to provide a metasurface capable of converting a beam profile from a Gaussian distribution to a top-hat distribution by nanostructures on only one main surface of a substrate.

Means for Solving the Problems

[0008] In order to solve the above problems, a metasurface according to one aspect of the present invention is a metasurface composed of a light-transmissive substrate and a plurality of light-transmissive nano-sized pillars disposed on one main surface of the substrate, wherein when the optical center of the metasurface is taken as the origin, the area S of each of the pillars located at a point where the distance from the optical center is r is represented by a function S(r) that satisfies the following three conditions. (1) It is continuous in -r0 ≦ r ≦ r0 (r0 > 0). (2) It takes a minimum value at r = 0. (3) It takes a maximum value at r = ±r1 (0 < r1 < r0).

[0009] Alternatively, in order to solve the above problems, a metasurface according to one aspect of the present invention is a metasurface composed of a light-transmissive substrate and a plurality of light-transmissive nano-sized pillars disposed on one main surface of the substrate, wherein when the optical center of the metasurface is taken as the origin, the area occupancy ratio Σ of the pillars at a point where the distance from the optical center is r is represented by a function Σ(r) that satisfies the following three conditions. (1) It is continuous in -r0 ≦ r ≦ +r0 (r0 > 0). (2) It takes a minimum value at r = 0. (3) It takes a maximum value at r = ±r1 (0 < r1 < r0).

[0010] Also, in order to solve the above problems, a lighting device according to an aspect of the present invention includes a light source that emits a Gaussian beam and the above-mentioned metalens disposed in the optical path of the emitted light from the light source.

[0011] Also, in order to solve the above problems, a method for manufacturing a metalens according to an aspect of the present invention is to dispose light-transmissive pillars on one main surface of a light-transmissive substrate such that the phase distribution of light transmitted through the metalens becomes a phase distribution obtained by adding a first phase distribution of a lens that converts a specific Gaussian beam into collimated light and a second phase distribution of a metasurface that converts the beam profile of the collimated light of the specific Gaussian beam into a top-hat type.

Advantages of the Invention

[0012] According to one aspect of the present invention, it is possible to provide a metalens capable of converting a beam profile from a Gaussian distribution to a top-hat distribution by a nanostructure on only one main surface of a substrate.

Brief Description of the Drawings

[0013]

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Mode for Carrying Out the Invention

[0014] 〔Metalens〕 Hereinafter, an embodiment of the present invention will be described. FIG. 1 is a diagram schematically showing the configuration of a metalens according to an embodiment of the present invention. FIG. 2 is a diagram for explaining the arrangement of pillars in the metalens according to an embodiment of the present invention. As shown in FIG. 1, the metalens 1 is composed of a substrate 2 having light transmissivity and a plurality of nano-sized pillars 3 having light transmissivity. The substrate 2 is, for example, a circular flat plate when viewed in plan.

[0015] The pillars 3 are arranged over the entire one main surface of the substrate 2. In the present embodiment, one main surface of the substrate 2 is microscopically divided into lattice-like unit compartments, and one pillar 3 is arranged for each unit compartment. The pillars 3 are arranged in each unit compartment in an appropriate form according to the position of the unit compartment on the main surface and the optical characteristics required for the metalens 1.

[0016] On one main surface of the substrate 2, apart from the above unit partitions, macroscopically, as shown in FIG. 2, it is divided into a circular central portion 10 and an annular peripheral portion 20 surrounding the central portion 10. In the present embodiment, the peripheral portion 20 is divided into an annular first peripheral portion 21, a second peripheral portion 22, ··· and an n-th peripheral portion 2n from the inside. n represents the order of the peripheral portion when counting the annular peripheral portions from the central portion 10, and is a positive integer of 1 or more. When the diameter of the metalens increases, usually n also increases. For example, when the diameter of the metalens is 50 μm, n can be 3. At this time, as shown in FIG. 2, the peripheral portion is shown as a triple annular region.

[0017] In the present embodiment, when the optical center of the metalens (for example, the center of the central portion 10) is taken as the origin, the respective areas S of the pillars 3 located at points where the distance from the optical center is r can be represented by a function S(r) that satisfies the following three conditions. Alternatively, in the present embodiment, the area occupancy ratio Σ of the pillars 3 at a point where the distance from the optical center is r can be represented by a function Σ(r) that satisfies the following three conditions. Alternatively, in the present embodiment, the width W of the pillars 3 at a point where the distance from the optical center is r can be represented by a function W(r) that satisfies the following three conditions. (1) It is continuous when -r0 ≤ r ≤ r0 (r0 > 0). (2) It takes a minimum value at r = 0. (3) It takes a maximum value at r = ±r1 (0 < r1 < r0).

[0018] The "area of the pillar" may be a representative value of the size of the area occupied by the pillar on the main surface of the substrate. For example, the area of the pillar may be the area when the pillar is projected onto the main surface along the optical axis. In this case, when the pillar has a straight-barrel shape, the area of the pillar may be the bottom area of the pillar or the cross-sectional area. In the following description, the embodiments of the present invention will be described by taking the case where the shape of the pillar is a regular square prism or a cylinder as an example, and the area of the pillar will be described as the cross-sectional area of the pillar.

[0019] FIG. 3 is a diagram showing an example of the distribution of the widths of the pillars in the metalens according to the present embodiment, FIG. 4 is a diagram showing an example of the distribution of the cross-sectional areas of the pillars in the metalens according to the present embodiment, and FIG. 5 is a diagram showing an example of the distribution of the area occupancy ratios of the pillars in the metalens according to the present embodiment. FIGS. 3 to 5 show an example of the metalens in which n is 3 in FIG. 2. In the metalens 1 of the present embodiment, the center-to-center distance between adjacent pillars 3 is constant, and the height of the pillars 3 is constant. Further, in the present specification, the "area occupancy ratio of the pillars" means the ratio Sp / Su of the cross-sectional area Sp of the pillars to the area Su of the unit section of the substrate.

[0020] FIG. 3 shows the distribution of the phase (also referred to as the "wrapped phase distribution") folded (wrapped) in the range of 0 to 2π. In the folded phase distribution, a discontinuous step of 2π occurs. The first peripheral portion 21 to the third peripheral portion 23 correspond to the folding of the phase. As shown in FIG. 3, the width of the pillar continuously changes such that it takes a minimum value at the optical center in the central portion 10 and takes a maximum value outside thereof. From the central portion 10 to the first peripheral portion 21, from the first peripheral portion 21 to the second peripheral portion 22, and from the second peripheral portion 22 to the third peripheral portion 23, the width of the pillar changes discontinuously and increases greatly. In each of the first peripheral portion 21, the second peripheral portion 22, and the third peripheral portion 23, the width of the pillar continuously changes so as to gradually decrease from the inside to the outside.

[0021] As shown in FIG. 4, the distribution of the cross-sectional area of the pillars in the metalens changes in the same manner as the distribution of the widths of the pillars described above with respect to FIG. 3. Also, as shown in FIG. 5, the distribution of the area occupancy ratio of the pillars in the metalens changes in the same manner as the distribution of the widths of the pillars described above with respect to FIG. 3.

[0022] Since the metalens of the present embodiment has the characteristics of the arrangement (distribution) of the pillars as described above, it can emit incident Gaussian beam light as light having a substantially top-hat type beam profile. This point will be described more specifically in the examples described later. Hereinafter, a method for manufacturing the metalens of the present embodiment will be described.

[0023] [Method for manufacturing a metasurface lens] The metasurface lens of the present embodiment can be manufactured by arranging light-transmissive pillars on one main surface of a light-transmissive substrate such that the phase distribution of the light transmitted through the metasurface lens becomes a phase distribution obtained by adding a specific first phase distribution and a second phase distribution.

[0024] Here, the incident light set in the design of the metasurface lens will be described. FIG. 6 is a diagram showing an example of the radiation intensity distribution of the laser light irradiating the metasurface lens according to the present embodiment. As shown in FIG. 6, the laser light is a Gaussian beam and has a radiation intensity distribution of a Gaussian distribution.

[0025] FIG. 7 is a diagram for explaining the beam shape regarding the metasurface lens according to the present embodiment. The laser light emitted from a laser as a light source has a divergence angle α as shown in FIG. 7. α is represented by "n × sin α" when the numerical aperture of the light source (an optical element such as a laser or a lens or an optical fiber attached to the light emitting device) is NA and the refractive index of the medium of the optical element attached to the light emitting device is n. Further, the Gaussian beam that has passed through the optical element arranged on the optical path of the laser light and is converted into a top-hat type beam profile may have a top-hat beam divergence angle θ different from the aforementioned α.

[0026] The first phase distribution is the phase distribution of a lens that converts a specific Gaussian beam into collimated light, and is represented by, for example, the following formula (1). In the following formula (1), x represents the distance from the optical axis on the x-axis orthogonal to the optical axis of the lens, y represents the distance from the optical axis on the y-axis orthogonal to both the optical axis and the x-axis, and f represents the focal length of the lens, respectively.

[0027] [Equation]

[0028] Note that although Equation (1) represents the phase distribution when the above lens is a spherical lens, the first phase distribution is not limited to the phase distribution of a spherical lens. The first phase distribution can be determined according to the conditions of the incident light, and it only needs to be the phase distribution of a lens for collimating the incident light into collimated light. For this reason, it may also be the phase distribution of an aspherical lens.

[0029] The second phase distribution is the phase distribution of a metasurface that converts the beam profile of the collimated light of a specific Gaussian beam into a top-hat type, and is represented by the following Equation (2) described in, for example, "Diffractive phase elements for beam shaping: a new design method" by Xin Tan et al., APPLIED OPTICS, Vol. 34, No. 8, 10 March 1995, p1317. In Equation (2) below, r represents the distance from the optical axis of the metasurface, λ represents the wavelength of a specific Gaussian beam, D represents the diameter of the metasurface, w1 represents the beam waist diameter of a specific Gaussian beam, w2 represents the beam diameter of a beam having a substantially uniform intensity distribution, l represents the propagation distance, and ξ represents the radial distance from the origin of the metasurface.

[0030]

Equation

[0031] For the sake of convenience, among the optical elements having pillars, those of the present embodiment are referred to as "metalens", and the others are referred to as "metasurface".

[0032] By adding the first phase distribution and the second phase distribution, a phase distribution that satisfies the above-described Conditions 1 to 3 can be obtained. FIG. 8 shows an example of (1) the phase distribution of a spherical lens (SL) for collimated light, (2) a Gaussian-top hat conversion metasurface (GTBS), and (3) the phase distribution of their sum (GTBS+SL) when the numerical aperture NA = 0.22 at the light source and the divergence angle θ = 5° (on the top-hat beam side).

[0033] The three upper diagrams in Fig. 8 all show the distribution of continuous phase (unwrap phase distribution), and the three lower diagrams all show the distribution of phase folded in the range of 0 to 2π (wrap phase distribution). The two diagrams on the left side facing the paper surface of Fig. 8 are the unwrap phase distribution and wrap phase distribution of SL, the two diagrams in the center are the unwrap phase distribution and wrap phase distribution of GTBS, and the two diagrams on the right side are the unwrap phase distribution and wrap phase distribution of GTBS+SL (i.e., for this embodiment). In the phase distribution of GTBS+SL, there is a curve satisfying the above-mentioned three conditions in the central part.

[0034] Note that the diagram of the phase distribution in this embodiment is a diagram showing the phase delay as positive unless otherwise specified.

[0035] In the manufacture of the metasurface in this embodiment, next, a plurality of light-transmissive pillars are arranged on one main surface of the substrate. The positions of the pillars are the unit partitions in the substrate described above. The size of the pillars to be arranged in the unit partition can be determined based on the phase distribution of GTBS+SL. For example, when the shape of the pillar is a regular quadrangular prism and the height of the pillar is constant, in the unit partition, a pillar having a cross-sectional area corresponding to the phase amount at that position is arranged. Thus, in the above case, the cross-sectional area of the pillar arranged in the unit partition is determined based on the correlation between the cross-sectional area of the pillar and the phase shift amount.

[0036] For such a correlation, for example, in the case of the cross-sectional area of the pillar, pillars of a single shape (such as all regular quadrangular prisms) are used, the height and cross-sectional area of the pillar are scanned for the transmittance, and the height and cross-sectional area of the pillar are scanned for the phase shift amount. Based on those results, the correlation between the phase shift amount and the cross-sectional area of the pillar when the height is constant is obtained. Such a correlation can also be obtained for information regarding the size of the pillar other than the cross-sectional area of the pillar, such as the height of the pillar, the width of the pillar, or the area occupancy rate of the pillar, in the same manner as the cross-sectional area of the pillar.

[0037] FIG. 9 is a diagram showing an example of the relationship between the distance from the optical center of the metasurface and the "width" of the pillars when pillars of regular square prisms of the same height are arranged according to the (1) wrap phase distribution of SL, (2) wrap phase distribution of GTBS, and (3) wrap phase distribution of GTBS+SL in FIG. 8. In FIG. 9, the upper diagram shows the distance from the center of the substrate and the width of the pillars of the regular square prisms located there, indicating that the higher the position, the larger the width of the pillars. The lower diagram shows the width of the pillars and their distribution when the metasurface is viewed in plan view, indicating that the blacker the position, the smaller the width of the pillars at that position, and the whiter the position, the larger the width of the pillars at that position.

[0038] The distribution of the width of the pillars in the central part of the SL metasurface arranged based on the phase distribution of SL is convex upward like the phase distribution, and the distribution of the width of the pillars in the central part of the GTBS metasurface based on the phase distribution of GTBS is convex downward like the phase distribution. In contrast, the distribution of the width of the pillars in the central part of the metasurface of this embodiment based on the phase distribution of GTBS+SL constitutes a curve that satisfies the three conditions described above like the phase distribution. Thus, the distribution of the width of the pillars in GTBS+SL is characteristic compared to those in the SL metasurface and the GTBS metasurface.

[0039] FIG. 10 is a diagram showing an example of the relationship between the distance from the optical center of the metasurface and the "cross-sectional area" of the pillars when pillars of regular square prisms of the same height are arranged according to the (1)-(3) wrap phase distributions in FIG. 8. The upper diagram shows that the higher the position, the larger the cross-sectional area of the pillars. The lower diagram shows the cross-sectional area of the pillars and their distribution when the metasurface is viewed in plan view, indicating that the blacker the position, the smaller the cross-sectional area of the pillars at that position, and the whiter the position, the larger the cross-sectional area of the pillars at that position.

[0040] Further, FIG. 11 is a diagram showing an example of the relationship between the distance from the optical center of the metalens and the "area occupancy rate" of the pillars when pillars of regular square prisms of the same height are arranged according to the wrap phase distributions of (1) to (3) in FIG. 8. The upper diagram shows that the higher the position, the larger the area occupancy rate of the pillars. The lower diagram shows the area occupancy rate of the pillars and its distribution when the metalens is viewed from above. The darker the color, the smaller the area occupancy rate of the pillars at that position, and the lighter the color, the larger the area occupancy rate of the pillars at that position.

[0041] In each of FIGS. 10 and 11, that is, the cross-sectional area of the pillars and the area occupancy rate of the pillars, a similar tendency to that in FIG. 9, that is, the width of the pillars, is confirmed.

[0042] Similarly, the case of cylindrical pillars is shown in FIGS. 12 to 14. FIG. 12 is a diagram showing an example of the relationship between the distance from the optical center of the metalens and the radius of the pillars when cylindrical pillars of the same height are arranged according to the wrap phase distributions of (1) to (3) in FIG. 8. FIG. 13 shows an example of the relationship between the distance from the optical center of the metalens and the cross-sectional area of the pillars when cylindrical pillars of the same height are arranged according to the wrap phase distributions of (1) to (3) in FIG. 8, and FIG. 14 shows an example of the relationship between the distance from the optical center of the metalens and the area occupancy rate of the pillars when cylindrical pillars of the same height are arranged according to the wrap phase distributions of (1) to (3) in FIG. 8. As shown in FIGS. 12 to 14, in the case of cylindrical pillars as well, a similar tendency to that of the regular square prism pillars shown in FIGS. 9 to 11 is confirmed.

[0043] Here, the beam shape before entering the metalens is considered. FIG. 15 is a diagram showing an example of the unwrapped phase distribution and the wrapped phase distribution of GTBS+SL when NA = 0.1, 0.2, or 0.3 and θ = 5°. The upper three diagrams in FIG. 15 show the unwrapped phase distribution, and the lower three diagrams show the wrapped phase distribution. Also, the left two diagrams in FIG. 15 show the phase distribution when NA is 0.1 (α is 5.7°), the middle two diagrams show the phase distribution when NA is 0.2 (α is 11.5°), and the right two diagrams show the phase distribution when NA is 0.3 (α is 17.5°).

[0044] From FIG. 15, it is confirmed that as NA increases, the value of the phase increases, and the difference between the maximum value and the minimum value in the central part tends to decrease. Also, according to FIG. 15, when the divergence angle α of the incident light is larger than the top-hat beam divergence angle θ, the bending degree of the inflection point of the phase distribution becomes smaller, and the shape of the phase distribution is considered to approach that of the SL more closely.

[0045] FIG. 16 shows an example of the relationship between the distance from the optical center and the width of the pillar when pillars of a regular square prism of the same height are arranged according to the wrapped phase distribution of FIG. 15. Also, FIG. 17 shows an example of the relationship between the distance from the optical center and the area occupancy rate of the pillar when pillars of a regular square prism of the same height are arranged according to the wrapped phase distribution of FIG. 15. Both FIG. 16 and FIG. 17 show the width or area occupancy rate of the pillar and its distribution when NA is 0.1, 0.2, and 0.3 in order from the left.

[0046] According to FIGS. 16 and 17, the curve showing the change in the information regarding the size of the pillar with respect to the distance from the optical center satisfies the above-described three conditions. And when NA(α) increases with respect to θ, the maximum value of the curve becomes smaller, and the length of the curve in the direction along the main surface of the substrate tends to become shorter (contracts toward the optical center). Also, when NA(α) decreases with respect to θ, the maximum value of the curve becomes larger, the length of the curve in the direction along the main surface of the substrate becomes longer, and the position of the maximum value in the direction along the main surface of the substrate tends to move farther from the optical center.

[0047] As shown in FIGS. 15 to 17, the metalens of the present embodiment can be configured by arranging pillars based on the phase distribution shown in FIG. 15. Thus, the metalens of the present embodiment can be configured by arranging the pillars as described above even when considering the beam shape of the incident light.

[0048] Also, the beam shape emitted from the metalens is considered. FIG. 18 shows an example of the wrap phase distributions of SL, GTBS, and GTBS+SL when NA = 0.1 and θ = 15°. FIG. 18 shows the wrap phase distributions of SL, GTBS, and GTBS+SL in order from the left. According to FIG. 18, when the top-hat beam divergence angle θ is larger than the divergence angle α of the incident light, the inflection point of the phase distribution moves farther from the optical center and the change in the value of the phase becomes larger, and it is considered that the shape of the phase distribution approaches that of GTBS even more.

[0049] FIG. 19 shows an example of the wrap phase distribution of GTBS+SL when NA = 0.1, 0.2, 0.3, or 0.4 and θ = 15°. In FIG. 19, the wrap phase distributions of GTBS+SL are shown when NA = 0.1 at the upper left, NA = 0.2 at the upper left, NA = 0.3 at the upper right, and NA = 0.4 at the lower right. According to FIG. 19, as the top-hat beam divergence angle θ increases and NA(α) also increases, the phase distribution approaches the phase distribution of GTBS+SL from the phase distribution of GTBS, and it is confirmed that the aforementioned inflection point peculiar to the phase distribution of GTBS+SL tends to be shifted toward the central part.

[0050] According to FIGS. 15 to 19, in the present embodiment in which desired optical characteristics are exhibited by pillars having different cross-sectional areas only at a fixed position on the substrate, when θ is 5 to 30° and NA is 0.1 to 0.4, it is considered preferable that the ratio of α to θ (α / θ) is 0 to 0.6 from the viewpoint of realizing the aforementioned function (curve) satisfying the aforementioned three conditions at the central part of the metalens. Depending on the use of the metalens, the beam shapes of the incident light and the emitted light may be limited. In such a case, by performing the manufacturing process as described above within a range according to the beam shape conditions, the metalens of the present embodiment corresponding to the use can be manufactured.

[0051] According to the manufacturing method according to the present embodiment, a metalens that does not satisfy at least any one of the three conditions regarding the pillars of the metalens according to the present embodiment described above can be manufactured, but a metalens that can substantially convert the beam profile of a Gaussian beam into a top-hat type can be easily designed and manufactured. Thus, it can also be said that a metalens that can substantially convert the beam profile of a Gaussian beam into a top-hat type is a metalens manufactured by the manufacturing method of the present embodiment described above.

[0052] The metalens according to the manufacturing method of the present embodiment can substantially convert the beam profile of a Gaussian beam into a top-hat type by the aforementioned simple design, but there are circumstances where it is impossible to directly specify it by its structure or characteristics, or it is not approximately practical. As a remarkable feature of such a simple design, the metalens is represented by a characteristic change regarding the shape of the pillar in the central part. On the other hand, considering that generally a lens is designed according to the incident beam, it is obvious that it can also be realized by a structure other than the above-mentioned remarkable features. However, it is impossible to generally specify in words what kind of state the structure other than the above-mentioned remarkable features should be in order to bring about the above-mentioned conversion function. The work of specifying the structure that brings about this function up to the range other than the above-mentioned remarkable features may be possible by comparing and examining the arrangement of the pillars and the conditions of the target beam in a large number and various states. However, such an examination work requires an enormous amount of time and cost, and is not approximately practical in view of the nature of patent applications that require rapidity and the like.

[0053] 〔Illumination device〕 The illumination device according to an embodiment of the present invention includes a light source that emits a Gaussian beam and the metalens of the present embodiment disposed in the optical path of the emitted light from the light source. One aspect of the illumination device is shown in FIG. 20.

[0054] As shown in FIG. 20, the illumination device 100 includes a laser 31, an optical fiber 32, and a metalens 1. The laser 31 generates laser light having a wavelength of, for example, 805 nm. The optical fiber 32 is optically connected to the laser 31, transmits the laser light generated by the laser, and emits it from the tip. Laser light, which is a Gaussian beam, is emitted from the tip of the optical fiber 32. The laser 31 and the optical fiber 32 constitute the light source 30 in the illumination device 100.

[0055] The metalens 1 is the metalens of the present embodiment described above. The metalens 1 is located at a position away from the tip of the optical fiber 32 and is disposed on the optical path of the light emitted from the optical fiber 32 with the main surface having the pillar facing forward. Further, the tip of the optical fiber 32 and the metalens 1 may be held by a probe. Such a configuration is suitable from the viewpoint of constituting an illumination device applied to an endoscope.

[0056] Since the illumination device of the present embodiment has a Gaussian beam light source and the metalens of the present embodiment described above, it can emit light rays having a substantially top-hat type beam profile.

[0057] Alternatively, the illumination device according to the embodiment of the present invention may be configured such that the metalens directly receives the laser light from the laser without passing through the optical fiber. A configuration including only an optical system of a laser, an optical fiber, and a metalens, or a simpler configuration including only a laser and a metalens as shown in FIG. 20 is suitable from the viewpoint of miniaturization of the illumination device.

[0058] Alternatively, the illumination device according to the embodiment of the present invention may further include a further optical configuration such as an optical element disposed in the optical system of the light source for adjusting the divergence angle α of the laser. A configuration including such a further optical configuration is suitable from the viewpoint of improving the performance of the illumination device and the like.

[0059] Note that the light source preferably includes a laser from the viewpoint that the height of the output and the width of the applicable range thereby can be expected, but may include other than the laser within the range of generating a Gaussian beam. For example, the light source may include a light emitting diode as a beam generation source.

[0060] 〔Summary〕 The first aspect of the present invention is a metasurface (1) composed of a light-transmissive substrate (2) and a plurality of light-transmissive nano-sized pillars (3) arranged on one main surface of the substrate, wherein when the optical center of the metasurface is taken as the origin, the area S of each pillar located at a point where the distance from the optical center is r is represented by a function S(r) that satisfies the following three conditions. (1) It is continuous when -r0 ≤ r ≤ r0 (r0 > 0), (2) It takes a minimum value at r = 0, (3) It takes a maximum value at r = ±r1 (0 < r1 < r0).

[0061] Further, the second aspect of the present invention is a metasurface composed of a light-transmissive substrate and a plurality of light-transmissive nano-sized pillars arranged on one main surface of the substrate, wherein when the optical center of the metasurface is taken as the origin, the area occupancy ratio Σ of the pillars at a point where the distance from the optical center is r is represented by a function Σ(r) that satisfies the following three conditions. (1) It is continuous when -r0 ≤ r ≤ +r0 (r0 > 0), (2) It takes a minimum value at r = 0, (3) It takes a maximum value at r = ±r1 (0 < r1 < r0).

[0062] According to the first or second aspect of the present invention, there is provided a metasurface having pillars on one main surface of a substrate, which can substantially convert a Gaussian beam into a top-hat type. Therefore, according to the first or second aspect, there is provided a metasurface capable of converting a beam profile from a Gaussian distribution to a top-hat distribution by a nanostructure only on one main surface of the substrate.

[0063] The third aspect of the present invention is that in the first aspect or the second aspect, each of the pillars is arranged in each of the unit partitions regularly set on the main surface, the pillars have the same shape and the same height, and have different cross-sectional areas according to the position of the unit partition from the optical center. According to the third aspect, by adjusting any one of the shape, height, and cross-sectional area of the pillar, the pillar that brings about a desired phase can be easily determined. Therefore, the third aspect is more effective from the viewpoint of the simplicity of the design of the metalens.

[0064] The fourth aspect of the present invention is an illumination device having a light source that emits a Gaussian beam and the above-described metalens arranged in the optical path of the emitted light from the light source. In the fourth aspect, the above-described metalens is arranged in the optical path of the Gaussian beam from the light source. Therefore, according to the fourth aspect, it is possible to realize a small-sized illumination device in which the beam profile is substantially converted from a Gaussian distribution to a top-hat distribution by a metalens having a simple configuration on only one main surface of the substrate.

[0065] The fifth aspect of the present invention is that in the fourth aspect, the light source includes a laser. The fifth aspect is more effective from the viewpoint of the high energy intensity of the irradiation light and the improvement of the versatility of the illumination device.

[0066] The sixth aspect of the present invention is a method for manufacturing a metalens, in which pillars having light transmissivity are arranged on one main surface of a light-transmissive substrate such that the phase distribution of the light transmitted through the metalens becomes a phase distribution obtained by adding a first phase distribution of a lens that converts a specific Gaussian beam into collimated light and a second phase distribution of a metasurface that converts the specific Gaussian beam into a top-hat shape. According to the sixth aspect, a metalens having pillars on one main surface of a substrate can be designed and manufactured by a simple operation of adding the first phase distribution and the second phase distribution, both of which can be calculated, and the metalens can substantially convert the beam profile of a Gaussian beam into a top-hat shape. Therefore, according to the sixth aspect, it is possible to provide a metalens capable of converting the beam profile from a Gaussian distribution to a top-hat distribution by a nanostructure on only one main surface of the substrate.

[0067] The seventh aspect of the present invention is, in the sixth aspect, the first phase distribution is represented by the following formula (1). In formula (1), x represents the distance from the optical axis on the x-axis orthogonal to the optical axis of the spherical lens, y represents the distance from the optical axis on the y-axis orthogonal to both the optical axis and the x-axis, and f represents the focal length of the spherical lens, respectively. The seventh aspect is more effective from the viewpoint of easily determining the arrangement of the pillars of the metalens that can substantially convert the beam profile of a Gaussian beam into a top-hat shape.

[0068]

Equation

[0069] The eighth aspect of the present invention is that in the sixth aspect or the seventh aspect, the second phase distribution is represented by the following formula (2). In formula (2), r is the distance from the optical axis of the metasurface, λ is the wavelength of light having a radiation intensity distribution of a specific Gaussian beam Gaussian distribution, D is the diameter of the metasurface, w1 is the beam waist diameter of a specific Gaussian beam of light having a radiation intensity distribution of a Gaussian distribution, w2 is the diameter of the beam when the radiation intensity distribution of light having a radiation intensity distribution of a beam Gaussian distribution with a substantially uniform intensity distribution becomes uniform, l is the propagation distance, and ξ is the radial distance from the origin of the metasurface, respectively. The eighth aspect is more effective from the viewpoint of easily determining the arrangement of the pillars of the metasurface that can substantially convert the beam profile of the Gaussian beam into a top-hat type.

[0070]

Number

[0071] The ninth aspect of the present invention is that in any one of the sixth aspect to the eighth aspect, based on the correlation between the information on the size of the pillar and the phase shift amount when the shape of the pillar and the arrangement of the pillars on the main surface are specified, the information on the size of the pillar is determined, and a pillar having the size of the determined information is arranged on the main surface. The ninth aspect is more effective from the viewpoint of easily determining the arrangement of the pillars of the metasurface that can substantially convert the beam profile of the Gaussian beam into a top-hat type.

[0072] According to the present invention, it is possible to easily design and realize a metasurface that substantially converts a Gaussian beam into a top-hat type beam. The present invention having such an effect is expected to contribute to the promotion of industries using metasurfaces or the expansion of technological innovation, and for example, is expected to contribute to the achievement of Goal 9, "Build the infrastructure for industry and innovation" of the Sustainable Development Goals (SDGs) proposed by the United Nations.

[0073] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. Hereinafter, specific examples of embodiments of the present invention will be described.

Example

[0074] 〔Example 1〕 The metalens 1 according to the present embodiment was manufactured by the method described in the present embodiment, and an illumination device as shown in FIG. 20 was configured. Then, the intensity distribution of the beam was measured by the beam profiler 110. An 805 nm fiber-coupled laser was used as the light source 30. The optical path length of the incident light to the metalens (the distance from the tip of the optical fiber 32 to the other main surface of the substrate of the metalens 1) was 2 cm, and the transmission distance D2 was 20 cm. The diameter of the metalens 1 was 5 mm, the incident light to the metalens 1 was a Gaussian beam, and the numerical aperture NA of the optical fiber 32 was 0.1. The metalens 1 was arranged along the X-Y plane perpendicular to the optical axis when the direction along the optical axis at the tip of the optical fiber 32 was defined as the Z direction. FIG. 21 shows the intensity distribution at a propagation distance of 20 cm by the beam profiler 110 of the light emitted from the metalens 1.

[0075] As shown in FIG. 21, in the metalens 1, an intensity distribution including portions with high radiation intensity not only at the optical center but also on both sides thereof was confirmed. Thus, in the metalens 1, a top-hat type beam profile having a relatively uniform intensity distribution was confirmed.

[0076] 〔Comparative Example 1〕 The intensity distribution of the beam was measured in the same manner as in Example 1 except that the GTBS metasurface was used instead of the metalens 1. The GTBS metasurface is configured by arranging pillars with different cross-sectional areas in the same manner as in the present embodiment based on the phase distribution obtained from the above-described formula (2). FIG. 22 shows the intensity distribution at a propagation distance of 20 cm of the light emitted from the GTBS metasurface.

[0077] As shown in FIG. 22, the radiation intensity distribution of the GTBS metasurface is strong at the optical center and weakens as the distance from the optical center increases. Thus, in the GTBS metasurface, a Gaussian-type beam profile in which the radiation intensity decreases as the distance from the optical center increases was confirmed.

[0078] 〔Example 2〕 According to the method described in the embodiment of the present invention, the phase distribution of GTBS+SL was obtained under the following conditions, and a metalens was designed in which pillars of regular square prisms with different cross-sectional areas were arranged on one main surface of a substrate according to the phase distribution. The beam diameter of the designed uniform irradiation area at a propagation distance of 100 μm is 39.4 μmΦ. NA = 0.22 α = 12.7° θ = 5°

[0079] The relationship between the area occupancy ratio of the pillars in the metalens of this example and the distance from the optical center of the pillars is shown in FIG. 23.

[0080] Further, the calculation result of the beam intensity distribution in the x-z plane of the metalens when the Gaussian beam of the above α is incident along the Z direction which is the optical axis direction on the metalens of this example is shown in FIG. 24. Also, the calculation result of the beam profile of the emitted light at a propagation distance of 100 μm of the metalens is shown in FIG. 25.

[0081] As shown in FIG. 25, in the model of the metalens of this example, a substantially top-hat type beam profile is confirmed. Also, in the model of the metalens of this example, a result of substantially uniform beam intensity is obtained within a range equivalent to the beam diameter (39.4 μmΦ) of the designed uniform irradiation area.

[0082] 〔Comparative Example 2〕 According to the method for obtaining the phase distribution of GTBS from the above-described formula (2), the phase distribution of GTBS was obtained under the same conditions as in Example 2. According to the phase distribution, a GTBS metasurface was designed in which pillars of regular square prisms having different cross-sectional areas were arranged on one main surface of a substrate, similar to Example 2. The relationship between the area occupancy ratio of the pillars in the GTBS metasurface of this comparative example and the distance from the optical center of the pillar is shown in FIG. 26.

[0083] Also, for the model of the GTBS metasurface of this comparative example, the beam profile was calculated in the same manner as in Example 2. The calculation result of the distribution of the beam intensity in the x-z plane of the GTBS metasurface is shown in FIG. 27. Further, the calculation result of the beam profile of the emitted light at a propagation distance of 100 μm of the GTBS metasurface is shown in FIG. 28.

[0084] As shown in FIG. 28, in the model of the GTBS metasurface of this comparative example, the illuminance distribution in the illumination area is poor, and a bright portion is generated in the center. Further, as is clear from the comparison between FIG. 25 and FIG. 28, although the beam diameter of the designed uniform illumination area is 39.4 μmΦ, the same as that of Example 2, the illumination area spreads wider than the design value, and the illuminance is lower even with the same laser output as in Example 2.

[0085] [Example 3] Similar to Example 2, the phase distribution of GTBS+SL was obtained under the following conditions according to the method described in the embodiments of the present invention, and a metalens was designed in which pillars of regular square prisms having different cross-sectional areas were arranged on one main surface of a substrate according to the phase distribution. The beam diameter of the designed uniform illumination area at a propagation distance of 100 μm is 57.2 μmΦ. NA = 0.4 α = 23.6° θ = 10°

[0086] The relationship between the area occupancy ratio of the pillars in the metalens of this example and the distance from the optical center of the pillar is shown in FIG. 29.

[0087] Further, Fig. 30 shows the calculation result of the beam intensity distribution in the x-z plane of the metalens when the Gaussian beam of the above α is incident along the Z direction which is the optical axis direction on the metalens of this embodiment. Fig. 31 shows the calculation result of the beam profile of the emitted light at the propagation distance of 100 μm of the metalens.

[0088] As shown in Fig. 31, in the model of the metalens of this embodiment, similar to Example 2, a substantially top-hat type beam profile is confirmed. Also, in the model of the metalens of this embodiment, similar to Example 2, a result of substantially uniform beam intensity is obtained within a range equivalent to the beam diameter (57.2 μmΦ) of the designed uniform irradiation area.

[0089] [Comparative Example 3] According to the method for obtaining the phase distribution of GTBS from the above-described formula (2), the phase distribution of GTBS was obtained under the same conditions as in Example 3, and according to the phase distribution, a GTBS metasurface was designed in which pillars of regular square prisms with different cross-sectional areas were arranged on one main surface of the substrate in the same manner as in Example 3. Fig. 32 shows the relationship between the area occupancy ratio of the pillars in the GTBS metasurface of this comparative example and the distance from the optical center of the pillars.

[0090] Also, for the model of the GTBS metasurface of this comparative example, the beam profile was calculated in the same manner as in Example 3. Fig. 33 shows the calculation result of the beam intensity distribution in the x-z plane of the GTBS metasurface. Fig. 34 shows the calculation result of the beam profile of the emitted light at the propagation distance of 100 μm of the GTBS metasurface.

[0091] As shown in Fig. 34, in the model of the GTBS metasurface of this comparative example, the uniformity of the illuminance distribution within the illumination area is low. Also, as is clear from the comparison between Fig. 31 and Fig. 34, although the beam diameter of the designed uniform irradiation area is the same as that of Example 3, which is 57.2 μmΦ, the illumination area spreads wider than the design value, and the illuminance is lower even with the same laser output as in Example 3.

Explanation of Signs

[0092] 1 metalens 2 substrate 3 pillar 10 central part 20 peripheral part 21 first peripheral part 22 second peripheral part 23 third peripheral part 2n nth peripheral part 30 light source 31 laser 32 optical fiber 100 lighting device 110 beam profiler

Claims

1. A metalens composed of a substrate having light transmissivity and a plurality of nano-sized pillars having light transmissivity disposed on one main surface of the substrate, wherein when the optical center of the metalens is taken as the origin, the area S of each of the pillars located at a point where the distance from the optical center is r is represented by a function S(r) that satisfies the following three conditions: (1) It is continuous in -r0 ≤ r ≤ r0 (r0 > 0), (2) It takes a minimum value at r = 0, (3) It takes a maximum value at r = ±r1 (0 < r1 < r0).

2. A metalens composed of a substrate having light transmissivity and a plurality of nano-sized pillars having light transmissivity disposed on one main surface of the substrate, wherein when the optical center of the metalens is taken as the origin, the area occupancy ratio Σ of the pillars at a point where the distance from the optical center is r is represented by a function Σ(r) that satisfies the following three conditions: (1) It is continuous in -r0 ≤ r ≤ +r0 (r0 > 0), (2) It takes a minimum value at r = 0, (3) It takes a maximum value at r = ±r1 (0 < r1 < r0).

3. Each of the pillars is disposed in each of the regularly set unit compartments on the main surface, wherein the pillars have the same shape and the same height, and have different cross-sectional areas according to the position of the unit compartment from the optical center, the metalens according to claim 1 or 2.

4. An illumination device having a light source that emits a Gaussian beam and the metalens according to claim 1 or 2 disposed in the optical path of the light emitted from the light source.

5. The illumination device according to claim 4, wherein the light source includes a laser.

6. A method for manufacturing a metalens, wherein pillars having light transmissivity are disposed on one main surface of a substrate having light transmissivity such that the phase distribution of the light transmitted through the metalens becomes a phase distribution obtained by adding the first phase distribution of a lens that converts a specific Gaussian beam into collimated light and the second phase distribution of a metasurface that converts the specific Gaussian beam into a top-hat type.

7. The method for manufacturing a metalens according to claim 6, wherein the first phase distribution is represented by the following formula (1). 【Number 1】 In formula (1), x represents the distance from the optical axis on the x-axis orthogonal to the optical axis of the lens, y represents the distance from the optical axis on the y-axis orthogonal to both the optical axis and the x-axis, and f represents the focal length of the lens, respectively.

8. The method for manufacturing a metasurface lens according to claim 6, wherein the second phase distribution is represented by the following formula (2). 【Number 2】 In formula (2), r represents the distance from the optical axis of the metasurface, λ represents the wavelength of the specific Gaussian beam, D represents the diameter of the metasurface, w1 represents the beam waist diameter of the specific Gaussian beam, w2 represents the diameter of the beam having a substantially uniform intensity distribution, l represents the propagation distance, and ξ represents the radial distance from the origin of the metasurface, respectively.

9. The method for manufacturing a metasurface lens according to claim 6, wherein information regarding the size of the pillar is determined based on the correlation between the shape of the pillar and the information regarding the size of the pillar and the phase shift amount when the arrangement of the pillar on the main surface is specified, and the pillar having the determined size information is arranged on the main surface.

Images