Optical system and imaging apparatus and lens device having the same

Abstract

To provide an optical system that is small-sized and can satisfactorily correct various aberrations from a center of a screen to a periphery of the screen.SOLUTION: An optical system has at least one or more lenses and a meta-lens. The meta-lens includes a lens surface that causes a phase change on a wave front of passing light. A phase function of the lens surface representing the amount of phase change on the wave front corresponding to a position in a radial direction of the meta-lens includes at least one of a critical point and an inflection point.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical system suitable for digital video cameras, digital still cameras, broadcast cameras, silver halide film cameras, surveillance cameras, vehicle-mounted cameras, distance measuring cameras, and the like. [Background technology]

[0002] In recent years, there has been a demand for optical systems used in imaging devices to be compact. Patent Document 1 discloses an optical system having a so-called metalens with positive refractive power. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-71727 Summary of the Invention [Problem to be solved by the invention]

[0004] The metalens of Patent Document 1 corrects chromatic aberration, but has a small refractive power and cannot share the refractive power of other lenses. Therefore, the metalens of Patent Document 1 has a limited effect of correcting various aberrations other than chromatic aberration, such as spherical aberration, coma aberration, curvature of field, astigmatism, and distortion aberration. In addition, the metalens of Patent Document 1 has a phase function that monotonically decreases from the center to the periphery, but the refractive power becomes monotonically stronger from the center to the periphery, so that spherical aberration, curvature of field, astigmatism, and the like are likely to occur. Note that the phase function is a function that represents the amount of phase change in the wavefront of light passing through the metalens corresponding to the radial position of the metalens (the amount of phase change in the wavefront before and after passing through the metalens). As described above, it is difficult for the optical system of Patent Document 1 to satisfactorily correct various aberrations other than chromatic aberration from the center of the screen to the periphery of the screen.

[0005] An object of the present invention is to provide an optical system which is compact and capable of effectively correcting various aberrations from the center of the screen to the periphery of the screen. [Means for solving the problem]

[0006] An optical system as one aspect of the present invention comprises at least one lens and a metalens, the metalens having a lens surface that induces a phase change in a wavefront of light passing through it, and a phase function of the lens surface, which represents an amount of phase change in the wavefront corresponding to a radial position of the metalens, includes at least one of a critical point and an inflection point. Effect of the Invention

[0007] According to the present invention, it is possible to provide an optical system which is small in size and capable of effectively correcting various aberrations from the center of the screen to the periphery of the screen. [Brief description of the drawings]

[0008] [Figure 1] 4 is a longitudinal aberration diagram of the optical system of Example 1 when focusing at infinity. FIG. [Diagram 2] 4 is a longitudinal aberration diagram of the optical system of Example 1 when focusing at infinity. FIG. [Diagram 3] FIG. 1 shows the phase function of the metalens surface of Example 1. [Figure 4] FIG. 13 is a diagram illustrating the change in filling factor near the critical point of the phase function of the metalens surface of Example 1. [Diagram 5] FIG. 13 is a diagram showing the change in filling factor near the inflection point of the phase function of the metalens surface of Example 1. [Figure 6] FIG. 11 is a cross-sectional view of the optical system of the second embodiment when focusing at infinity. [Figure 7] FIG. 11 is a longitudinal aberration diagram of the optical system of Example 2 when focusing at infinity. [Figure 8] FIG. 13 shows the phase function of the metalens surface of Example 2. [Figure 9] FIG. 13 is a diagram illustrating the change in filling factor near the inflection point of the phase function of the metalens surface of Example 2. [Figure 10]FIG. 11 is a cross-sectional view of the optical system of Example 3 when focusing at infinity. [Figure 11] 11A to 11C are longitudinal aberration diagrams of the optical system of Example 3 when focusing at infinity. [Figure 12] FIG. 13 shows the phase function of the metalens surface of Example 3. [Figure 13] FIG. 13 is a diagram illustrating the change in filling factor near the inflection point of the phase function of the metalens surface of Example 3. [Figure 14] FIG. 11 is a cross-sectional view of the optical system of Example 4 at the time of focusing at infinity. [Figure 15] 13A to 13C are longitudinal aberration diagrams of the optical system of Example 4 when focusing at infinity. [Figure 16] FIG. 13 shows the phase function of the metalens surface of Example 4. [Figure 17] FIG. 13 is a diagram illustrating the change in filling factor near the critical point of the phase function of the metalens surface of Example 4. [Figure 18] FIG. 13 is a diagram illustrating the change in filling factor near the inflection point of the phase function of the metalens surface of Example 4. [Figure 19] FIG. 1 is a schematic diagram of a subwavelength structure of a metalens. [Figure 20] FIG. 2 is an explanatory diagram of a rectangular columnar structure. [Figure 21] FIG. 2 is an explanatory diagram of a cylindrical columnar structure. [Figure 22] FIG. 2 is an explanatory diagram of a columnar structure of a hexagonal column. [Figure 23] FIG. 13 is a schematic diagram of a metalens surface having a phase function that includes an inflection point. [Figure 24] FIG. 13 is a schematic diagram of a metalens surface having a phase function that includes a critical point. [Diagram 25] 1 is a diagram showing the relationship between the ratio of the length of a columnar structure to the size of a substrate and the filling rate. [Figure 26] 11 is a diagram illustrating the relationship between the filling rate and the amount of phase change. [Figure 27] FIG. 1 is a schematic diagram of an imaging device. [Figure 28] FIG. 2 is a schematic diagram of a lens device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In each drawing, the same reference numerals are given to the same members, and duplicated explanations will be omitted.

[0010] 1, 6, 10, and 14 are cross-sectional views of the optical system L0 of Examples 1 to 4 when focused at infinity. The optical system L0 of each Example is used in imaging devices such as digital video cameras, digital still cameras, broadcast cameras, silver halide film cameras, surveillance cameras, car-mounted cameras, and distance measuring cameras, as well as optical instruments including interchangeable lenses.

[0011] In each cross-sectional view, the left side is the object side and the right side is the image side. When the optical system L0 of each embodiment is used in an optical device such as a projector, the left side is the screen side and the right side is the projected image side.

[0012] The arrows in each cross-sectional view indicate the direction of lens movement during focusing from infinity to close range. In each embodiment, the entire optical system L0 moves from the image side to the object side during focusing. Focusing may also be performed by moving only some of the lenses in the optical system L0 from the image side to the object side, or from the object side to the image side.

[0013] In each cross-sectional view, SP is an aperture stop. IP is an image plane, and when the optical system L0 of each embodiment is used as the photographing optical system of a digital still camera or digital video camera, the imaging surface of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor is disposed thereon. When the optical system L0 of each embodiment is used as the photographing optical system of a silver halide film camera, a photosensitive surface equivalent to the film surface is disposed on the image plane IP. FL is an optical block equivalent to an optical filter, a face plate, a crystal low-pass filter, an infrared cut filter, etc.

[0014] The optical system L0 in each example has at least one or more lenses (one or more lenses) and a metalens (optical element) ML. In this embodiment, the metalens ML has a lens surface MLS which is at least one lens surface, which is a lens surface on the object side and a lens surface on the image side. The lens surface MLS has a subwavelength structure including a plurality of columnar structures (convex portions) of subwavelength size, and generates a phase change in the wavefront of light passing through the lens surface MLS along the traveling direction of the light.

[0015] Here, the principle of light refraction by the subwavelength structure of the metalens ML will be described. FIG. 19 is a schematic diagram of the subwavelength structure of the metalens ML. In the subwavelength structure, a columnar structure is provided on the surface of a substrate so that the size (thickness) of the columnar structure of subwavelength size changes in the radial direction of the lens surface according to a predetermined rule. The substrate may be flat or curved. The size of each columnar structure is equal to or smaller than the design wavelength. Each columnar structure is invisible to light, and the columnar structure behaves as an average effective medium in which the refractive index of air and the refractive index of the material constituting the columnar structure are averaged under approximation. In this case, the refractive index of the effective medium becomes closer to the refractive index of the material constituting the columnar structure as the size of the columnar structure becomes larger, and becomes closer to the refractive index of air as the ratio (filling rate) of the columnar structure to the air becomes smaller as the size of the columnar structure becomes smaller. Note that the medium filling the space between the columnar structures is not limited to air, since the same effect can be obtained even if any medium is filled instead of air.

[0016] In this way, by changing the size of the columnar structures in the radial direction, it is possible to obtain the effect that the refractive index of the effective medium changes continuously in the radial direction. That is, under approximation, the metalens ML can be regarded as a kind of gradient index lens in which the refractive index changes in the radial direction. If the refractive index is different, the optical distance changes even with the same thickness, so the amount of phase change of the wavefront of light passing through the metalens ML before and after passing through the metalens ML changes depending on the refractive index of the effective medium. In the metalens ML, since the size of the columnar structures changes in the radial direction, the amount of phase change differs at each position in the radial direction. That is, for example, when a plane wave (parallel light beam) with a uniform phase is incident on the metalens ML, the phase of the wavefront of the plane wave shifts according to the amount of phase change at each position in the radial direction of the metalens ML. As a result, the metalens ML acts as a lens that converges or diverges the plane wave. Note that in this embodiment, an example of a plane wave has been described for simplicity, but it goes without saying that the metalens ML acts as a lens that converges or diverges light according to the same principle for the wavefront of light that is not a plane wave.

[0017] 2, 7, 11 and 15 are aberration diagrams of the optical systems of Examples 1 to 4 when focused at infinity, respectively.

[0018] In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the design wavelength (the design wavelength for each embodiment is shown separately). In the astigmatism diagram, S shows the amount of astigmatism on the sagittal image plane, and M shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the design wavelength is shown.

[0019] Next, the characteristic configuration of the optical system L0 in each embodiment will be described.

[0020] The phase function Φ(h) of the lens surface LMS includes at least one of a critical point and an inflection point. The phase function φ(h) is a function that represents the amount of phase change in the wavefront of light passing through the metalens ML corresponding to the radial position h of the metalens ML (the amount of phase change in the wavefront before and after passing through the metalens; the integrated value of the phase change). As described above, the metalens surface ML generates a phase change in the wavefront of the light passing through it due to the subwavelength structure. When the amount of phase change on the optical axis is set to 0, a phase change occurs at the radial position h relative to the optical axis as shown in FIG. 19. In the following description, unless otherwise specified, the amount of phase change represents the amount of phase change relative to the amount of phase change on the optical axis being 0, and the phase is expressed in radians (rad). In addition, the critical point is a point where the value of the first-order derivative of the phase function φ(h) becomes 0, and the sign of the value of the first-order derivative of the phase function φ(h) changes before and after the critical point. An inflection point is a point where the value of the second derivative of the phase function φ(h) becomes 0 and the sign of the value of the second derivative of the phase function φ(h) changes around that point.

[0021] In FIG. 19(A), in the sub-wavelength structure of the lens surface MLS, the columnar structure is provided on the substrate surface so that the size (thickness) of the columnar structure increases with distance from the optical axis center (center of the lens surface MLS) at the left end in the radial direction of the lens surface MLS. The change in which the size of the columnar structure increases with distance from the optical axis center in the radial direction of the lens surface MLS is repeated periodically along the radial direction of the lens surface MLS. In this case, one period is defined as the period until the phase change amount becomes -2π. Since a wavefront with a phase change of -2π is continuously connected to a wavefront with a phase change of 0, in order to generate a phase change smaller than -2π (large absolute value), it is sufficient to repeat one period again starting from the columnar structure with a phase change of 0. In this way, an arbitrary negative phase change amount can be obtained by repeating the phase change from 0 to 2π. As shown in FIG. 19(A), when a columnar structure is provided, the phase function starts from 0 and takes a negative value, so that the metalens surface MLS has a positive refractive power near the optical axis.

[0022] In Fig. 19(B), in the sub-wavelength structure of the lens surface MLS, a columnar structure is provided on the substrate surface such that the size (thickness) of the columnar structure decreases with increasing distance from the optical axis center (center of the lens surface MLS) at the left end in the radial direction of the lens surface MLS. The change in which the size of the columnar structure increases with increasing distance from the optical axis center in the radial direction of the lens surface MLS is repeated periodically along the radial direction of the lens surface MLS. In this case, as in the case of Fig. 19(A), an arbitrary positive phase change amount can be obtained by repeating the phase change from 0 to 2π, and the metalens surface MLS has negative refractive power near the optical axis.

[0023] As described above, the phase function φ(h) expresses the amount of positive or negative phase change as an integrated value of the phase change from the center of the optical axis. The reference for making the value of the phase function φ(h) 0 does not necessarily have to be the center of the optical axis, and in reality, there may be a constant amount of uncertainty. In addition, since an axisymmetric optical system is assumed in this embodiment, the phase function is also expressed as axisymmetric, but in a non-axisymmetric optical system, the phase function does not need to be axisymmetric.

[0024] The relationship between the amount of phase change and the columnar structure will be described below. As mentioned above, when the ratio (filling rate) of the columnar structure changes according to the size of the columnar structure, the effective refractive index of the effective medium changes, causing a phase change. The amount of phase change in the columnar structure can be obtained by performing an electromagnetic field analysis based on, for example, the rigorous coupled wave theory (RCWA) or the finite difference time domain method (FDTD).

[0025] First, the definition of the filling ratio F will be described. Fig. 20(A) shows a schematic diagram of a unit cell (a set of one columnar structure and its corresponding substrate) virtually cut out from the continuous structure shown in Fig. 19. Fig. 20(B) shows an elevation view and a plan view of the unit cell in Fig. 20(A).

[0026] The columnar structure in FIG. 20 is a quadrangular prism with a square bottom. Here, the area of ​​the substrate of the unit cell is S0. The bottom area of ​​the columnar structure (the area of ​​the substrate occupied by the columnar structure) is S1, and the height of the columnar structure is H. In this case, the filling rate F is (S1×H) / (S0×H). The area S0 and the bottom area S1 are w0×w0 and w1×w1, respectively. That is, in general, the filling rate is defined as the ratio of the volume of the columnar structure to the volume of the space of the height H on the substrate of the unit cell. According to this definition, the filling rate can be calculated even if the structure is not necessarily a column. For example, the filling rate can be calculated in the case of the columnar structure with a circular bottom in FIG. 21 and the columnar structure with a regular hexagonal bottom in FIG. 22. In the columnar structure in FIG. 21, the filling rate F is (S1×H) / (S0×H). In addition, the area S0 and the base area S1 are w0×w0 and (π×w1×w1) / 4, respectively. In the structure of FIG. 22, the packing ratio F is (S1×H) / (S0×H). In addition, the area S0 and the base area S1 are {3×(√3)×w0×w0} / 8 and {3×(√3)×w1×w1} / 8, respectively.

[0027] 20 to 22 are cylindrical pillars having two similar and parallel planar figures as the top and bottom surfaces, but in reality, the two planar figures do not have to be completely similar, and the top and bottom surfaces do not have to be completely parallel. Even in such cases, the effective refractive index of the effective medium can be controlled from the viewpoint of the filling factor described above.

[0028] Furthermore, when viewed as a whole, the substrate in the unit cells of Figures 20 to 22 actually exists as a single substrate, and a columnar structure is provided on the substrate.

[0029] In addition, in FIGS. 20 to 22, the center of the substrate and the center of the columnar structure in the unit cell are substantially aligned, but the present invention is not limited to this.

[0030] Furthermore, the shape of the columnar structure is not limited to the shapes in Figures 20 to 22. For example, it may be a prism with a polygonal bottom surface, a prism with a trapezoidal bottom surface, a prism with a convex bottom surface, a prism with a substantially regular polygonal bottom surface, a prism with an L-shaped bottom surface, or the like.

[0031] Below, we will explain the effect of the phase function φ(h) of the metalens surface MLS including at least one of a critical point and an inflection point.

[0032] When the phase function φ(h) includes a critical point, it has the effect of greatly changing the refractive power at the center of the lens surface MLS and the refractive power at the periphery, or changing the sign of the refractive power. For example, as in Example 1 and Example 4, by using aspherical lenses in front of the optical system L0 or near the aperture stop SP, it is possible to correct spherical aberration and coma aberration while increasing the refractive power of the aspherical lenses and achieving size reduction. However, in this case, the curvature of field and astigmatism tend to have a wavy shape from the center to the periphery of the screen (image surface). In this case, by arranging a metalens in which the phase function φ(h) includes a critical point, it is possible to satisfactorily correct the wavy aberration by utilizing the difference in refractive power between the center and the periphery.

[0033] When the phase function φ(h) includes an inflection point, it has the effect of reducing the refractive power of the periphery with respect to the refractive power of the center of the lens surface MLS. For example, as in the second and third embodiments, by increasing the refractive power near the center of the lens surface MLS, it is possible to reduce the refractive power of the periphery relatively while miniaturizing the lens, and to refract the peripheral light beam gently with respect to the light beam near the center. This makes it possible to effectively correct spherical aberration and coma aberration.

[0034] Furthermore, by positioning a metalens MLS, in which the phase function φ(h) includes a critical point or an inflection point, on the object side of the aperture stop SP, it is possible to significantly change the refractive power of the lens surface MLS at the position where the on-axis light beam and the off-axis light beam are radially separated, thereby making it possible to effectively correct distortion.

[0035] As described above, by having the phase function φ(h) of the metalens surface MLS include at least one of a critical point and an inflection point, it is possible to satisfactorily correct various aberrations in the optical system L0. Furthermore, if one were to try to obtain the above effect simply with an aspheric lens, the thickness of the optical system L0 would increase by the amount of the aspheric lens, but when the metalens ML is used, the increase in thickness is kept to a minimum, and the optical system L0 can be made more compact.

[0036] Next, a description will be given of configurations that are preferably satisfied in the optical system L0 of each embodiment.

[0037] It is preferable that the size of the columnar structure varies in the radial direction of the lens surface MLS according to a predetermined rule. This allows an arbitrary phase change amount to be obtained at the radial position h. In this embodiment, the filling rate is used as the size of the columnar structure, but the present invention is not limited to this. For example, the volume of the columnar structure, the diameter of the columnar structure, and the area occupied by the columnar structure on the lens surface MLS (the bottom area of ​​the columnar structure) may be used as the size of the columnar structure.

[0038] The subwavelength structure preferably includes a configuration in which the columnar structures are provided such that the size of the columnar structures increases or decreases with increasing distance from the center of the lens surface MLS in the radial direction of the lens surface MLS. It is also more preferable that such a configuration is provided periodically along the radial direction of the lens surface MLS in at least a portion of the lens surface MLS. This makes it possible to continuously change the phase function φ(h) as a repetition of phase changes from 0 to 2π or 0 to −2π in the radial direction of the metalens surface MLS, allowing the metalens ML as a whole to function as a lens.

[0039] When the above-mentioned configurations are provided in a plurality of configurations along the radial direction of the lens surface MLS in at least a portion of the metalens surface MLS, it is preferable that the distance (spacing, period) in the radial direction of the lens surface MLS of the first configuration and the second configuration included in the plurality of configurations is different. It is also more preferable that the distance in the radial direction of the plurality of configurations in at least a portion of the metalens surface MLS becomes shorter as it moves away from the center, and then changes to become longer as it moves away from the center. The effect of such a change in configuration will be described with reference to FIG. 23.

[0040] FIG. 23 is a schematic diagram of a metalens surface MLS having a phase function φ(h) including an inflection point. In FIG. 23, the lens surface MLS is provided with a plurality of configurations in which the packing rate of the columnar structure decreases with distance from the center of the lens surface MLS in the radial direction of the lens surface MLS. Although the intermediate columnar structures are omitted, they are provided in the same manner as in FIG. 19. D(i) is the radial distance of the lens surface MLS of the i-th (i is a natural number) configuration among the plurality of configurations, counting from the center of the lens surface. In FIG. 24, the distance D(i) is longer than the distance D(i+1), and the distance D(i+1) is shorter than the distance D(i+2). That is, in the i-th and i+1-th configurations, the phase change from 0 to -2π in the i+1-th period occurs at a narrower interval than the phase change from 0 to -2π in the i-th period. At this time, the slope (absolute value) of the phase function φ(h) becomes steep along the radial direction of the lens surface MLS. Furthermore, in the (i+1)th and (i+2)th configurations, the phase change from 0 to -2π in the (i+2)th period occurs at a wider interval than the phase change from 0 to -2π in the (i+1)th period. At this time, the (absolute value of) the gradient of the phase function φ(h) becomes gentle along the radial direction of the lens surface MLS. As described above, in FIG. 23, the (absolute value of) the gradient of the phase function φ(h) becomes gradually steep along the radial direction of the lens surface MLS, and then gradually becomes gentle halfway through. That is, this means that the phase function φ(h) includes an inflection point, and the inclusion of the inflection point in the phase function φ(h) can provide an aberration correction effect.

[0041] In addition, in FIG. 23, the columnar structures are provided so that the filling rate decreases with increasing distance from the center of the lens surface MLS in the radial direction of the lens surface MLS, but they may be provided so that the filling rate increases.

[0042] In Example 1, as shown in Figures 3 and 5, the phase function φ(h) of the metalens ML includes an inflection point. The filling factor corresponding to the actual columnar structure periodically changes from a small value to a large value, and the interval of the period narrows (from 0.0086 mm to 0.0084 mm) and then widens (from 0.0084 mm to 0.0086 mm) before and after the inflection point. In other words, the columnar structure is provided such that the phase function φ(h) includes an inflection point before and after it. The inflection point of the phase function φ(h) in Example 1 is 1.0058 mm away from the optical axis in the radial direction.

[0043] In Example 2, as shown in Figures 8 and 9, the phase function φ(h) of the metalens ML includes an inflection point. The filling rate corresponding to the actual columnar structure periodically changes from a large value to a small value, and the interval of the period narrows (from 0.0250 mm to 0.0245 mm) and then widens (from 0.0245 mm to 0.0250 mm) before and after the inflection point. In other words, the columnar structure is provided such that the phase function φ(h) includes an inflection point before and after it. The inflection point of the phase function φ(h) in Example 2 is 0.7135 mm away from the optical axis in the radial direction.

[0044] In Example 3, as shown in Figures 12 and 13, the phase function φ(h) of the metalens ML includes an inflection point. The filling factor corresponding to the actual columnar structure periodically changes from a large value to a small value, and the interval of the period narrows (from 0.0126 mm to 0.0124 mm) and then widens (from 0.0124 mm to 0.0126 mm) before and after the inflection point. In other words, the columnar structure is provided such that the phase function φ(h) includes an inflection point before and after it. The inflection point of the phase function φ(h) in Example 3 is 0.7490 mm away from the optical axis in the radial direction.

[0045] In Example 4, as shown in FIGS. 16 and 18, the phase function φ(h) of the metalens ML includes an inflection point. The filling factor corresponding to the actual columnar structure periodically changes from a small value to a large value, and the interval of the period narrows (from 0.0070 mm to 0.0069 mm) and then widens (from 0.0069 mm to 0.0070 mm) before and after the inflection point. In other words, the columnar structure is provided such that the phase function φ(h) includes an inflection point before and after the inflection point. The inflection point of the phase function φ(h) in Example 4 is 0.9342 mm away from the optical axis in the radial direction.

[0046] In the case where the above-mentioned configurations are provided in at least a part of the metalens surface MLS along the radial direction of the lens surface MLS, it is preferable that the change in size of the columnar structure in the first configuration and the second configuration included in the multiple configurations is different. For example, in the first configuration, the columnar structure is provided so that the size of the columnar structure increases with distance from the center of the lens surface MLS in the radial direction of the lens surface MLS. In addition, in the second configuration, the columnar structure is provided so that the size of the columnar structure decreases with distance from the center of the lens surface MLS in the radial direction of the lens surface MLS. In addition, it is more preferable that at least a part of the metalens surface MLS is provided with a configuration in which the first configuration is periodically repeated and a configuration in which the second configuration is periodically repeated in the radial direction of the lens surface MLS. That is, the configuration in which the first configuration is periodically repeated and the configuration in which the second configuration is periodically repeated are switched at a predetermined position in the radial direction of the metalens surface MLS. The effect of the above configuration will be described with reference to FIG. 24.

[0047] FIG. 24 is a schematic diagram of a metalens surface MLS having a phase function φ(h) including a critical point. In FIG. 24, configurations that cause a phase change from 0 to 2π (or −2π) are repeatedly provided, and the i-th (i is a natural number), i+1-th, i+2-th, and i+3-th configurations are shown counting from the center of the lens surface. The i+1-th configuration ends just before a phase change of 2π occurs, and switches to the i+2-th configuration. Up to the i+1-th configuration, the columnar structures are provided so that their size decreases with distance from the center of the lens surface MLS in the radial direction of the lens surface MLS. On the other hand, from the i+2-th configuration, the columnar structures are provided so that their size decreases with distance from the center of the lens surface MLS in the radial direction of the lens surface MLS. With this configuration, the phase function φ(h) of the lens surface MLS decreases in phase until halfway through the i+1th period (before switching to the i+2th period), and increases in phase after switching to the i+2th period. As described above, in FIG. 24, the phase function φ(h) decreases in phase along the radial direction of the lens surface MLS, and then starts to increase halfway through. This means that the phase function φ(h) includes a critical point, and the inclusion of the critical point in the phase function φ(h) can provide an aberration correction effect.

[0048] In addition, in Fig. 24, the columnar structure changes so that the filling rate decreases and then increases as the distance from the center of the lens surface MLS increases in the radial direction of the lens surface MLS, but the present invention is not limited to this. The columnar structure may change so that the filling rate increases and then decreases as the distance from the center of the lens surface MLS increases in the radial direction of the lens surface MLS. In this case, the phase function φ(h) includes a critical point where the phase function changes from increasing to decreasing.

[0049] In Example 1, as shown in Figures 3 and 4, the phase function φ(h) of the metalens ML includes a critical point. The filling factor corresponding to the actual columnar structure periodically changes from a small value to a large value, while periodically changing from a large value to a small value in the middle. In other words, the columnar structure is provided such that the phase function φ(h) includes a critical point before and after it. The critical point of the phase function φ(h) in Example 1 is 2.0417 mm away from the optical axis in the radial direction.

[0050] In Example 4, as shown in Figures 16 and 17, the phase function φ(h) of the metalens ML includes a critical point. The filling factor corresponding to the actual columnar structure periodically changes from a small value to a large value, while periodically changing from a large value to a small value in the middle. In other words, the columnar structure is provided such that the phase function φ(h) includes a critical point before and after it. The critical point of the phase function φ(h) in Example 4 is 1.8459 mm away from the optical axis in the radial direction.

[0051] Although the characteristic structure of the metalens ML and its aberration correction effect have been described above, if the optical system L0 is composed of only the metalens ML, there is a limit to the aberration correction. Therefore, it is preferable to perform aberration correction by combining the metalens ML with an aspheric lens. In addition, by using the metalens ML in combination with an aspheric lens, a synergistic effect can be achieved in the aberration correction. Therefore, it is preferable that the optical system L0 in each embodiment has at least one aspheric lens, and at least one of the object side lens surface or image side lens surface of the aspheric lens is aspheric, and the aspheric surface is an aspheric surface having at least one of an inflection point and a critical point.

[0052] In Examples 1 and 4, spherical aberration and coma aberration are corrected by an aspheric lens with large refractive power arranged near the aperture stop SP, but this inevitably leads to undulating field curvature. Therefore, by placing a metalens ML, in which the phase function φ(h) includes a critical point or an inflection point, near the image plane, it is possible to selectively correct the field curvature.

[0053] In Examples 2 and 3, spherical aberration and coma aberration are offset by an aspheric lens with negative refractive power and a metalens ML with positive refractive power. In addition, a large number of metalens MLs can be used to obtain a sufficient aberration correction effect, but in that case, the reduction in efficiency due to unnecessary diffracted light derived from the subwavelength structure and the impact on image quality due to flare cannot be ignored. For this reason, it is preferable to use the metalens ML in combination with an aspheric lens.

[0054] The shape of the columnar structure is preferably a cylindrical column having two substantially similar and substantially parallel planar figures as the upper and lower surfaces. If the shape of the columnar structure is similar to, for example, a cone or pyramid, it is not preferable because it is difficult to manufacture the columnar structure using a semiconductor manufacturing process such as lithography.

[0055] Next, conditions that the optical system L0 of each embodiment should preferably satisfy will be described. The optical system L0 of each embodiment should preferably satisfy one or more of the following conditional expressions (1) to (12).

[0056] 0.050 <r / D<0.425 (1) 0.1<|fM| / f<10.0 (2) 0.1 <fP / f<10.0 (3) -10.0 <fN / f<-0.1 (4) 1.0 <H / λ<3.0 (5) 0.3 <rmax / λ<0.9 (6) 0.05 <rmin / λ<0.5 (7) Here, r is the distance from the center of the lens surface MLS in the radial direction of the metalens surface ML to the position of the lens surface MLS corresponding to the critical point or inflection point of the phase function φ(h) of the metalens surface MLS. D is the effective diameter of the metalens surface MLS (the distance twice the distance from the optical axis to the light ray that is the furthest from the optical axis in the radial direction among the light rays passing through the metalens surface MLS). f is the focal length of the optical system L0. fM is the focal length of the metalens ML. fP is the focal length of at least one lens with positive refractive power (positive lens) included in the optical system L0. fN is the focal length of at least one lens with negative refractive power (negative lens) included in the optical system L0. H is the maximum height of the columnar structure (the length in the direction parallel to the optical axis direction). λ is the design wavelength, for example, the wavelength at which the transmittance of light (approximately parallel light) incident on the metalens ML along the optical axis, i.e., the ratio of the intensity of the emitted light to the intensity of the incident light, is maximized. rmax and rmin are the maximum and minimum diameters of the columnar structures provided on the metalens surface MLS, respectively. Note that the diameter of the columnar structure is the diameter of a circle circumscribing the shape of the base when the base of the columnar structure is an approximate circle or an approximate regular polygon, and is the maximum length of a straight line connecting any two points on the base when the base has any other shape.

[0057] Conditional formula (1) specifies the value of the ratio of the distance from the center of the metalens surface MLS in the radial direction of the metalens surface MLS to the critical point or inflection point of the phase function φ(h) of the metalens surface MLS to the effective diameter of the metalens surface MLS. As described above, the metalens ML has the effect of significantly changing the refractive power of the metalens surface MLS between the vicinity of the optical axis and the periphery, or changing the sign of the refractive power. Therefore, by arranging the metalens ML near the image plane away from the aperture stop SP, the curvature of field and astigmatism can be well corrected from the center of the screen (image plane) to the periphery by utilizing the difference in refractive power between the center and the periphery. In addition, when the metalens ML is arranged near the aperture stop SP, spherical aberration and coma aberration can be well corrected. Furthermore, when the metalens ML is arranged closer to the object side than the aperture stop SP, distortion aberration can be well corrected. If the distance from the center of the lens surface MLS to the critical point or inflection point of the phase function φ(h) of the metalens surface MLS becomes short by falling below the lower limit of conditional formula (1), the change in refractive power within the metalens surface MLS becomes too steep, and the aberration correction effect becomes excessive, which is undesirable. If the distance from the center of the lens surface MLS to the critical point or inflection point of the phase function φ(h) of the metalens surface MLS becomes long by exceeding the upper limit of conditional formula (1), the position corresponding to the critical point or inflection point of the metalens surface MLS will be too far to the periphery. In this case, the aberration correction effect utilizing the difference in refractive power between the center and the periphery will be limited, which is undesirable.

[0058] Conditional formula (2) specifies the value of the ratio of the focal length of the metalens ML to the focal length of the optical system L0. In general, in order to correct aberrations or suppress the occurrence of aberrations, it is preferable for multiple lenses to share the refractive power of the optical system L0. Therefore, in order to perform aberration correction using the metalens ML, it is preferable for the metalens ML to share a certain degree of the refractive power of the optical system L0. This makes it possible to reduce the refractive power of lenses other than the metalens ML, and to appropriately obtain the aberration correction effect while suppressing the occurrence of aberrations. If the absolute value of the focal length of the metalens ML becomes small below the lower limit of conditional formula (2), the refractive power of the metalens ML becomes too large, which is undesirable because the aberration correction is excessive. If the absolute value of the focal length of the metalens ML becomes large above the upper limit of conditional formula (2), the refractive power sharing effect becomes small, and the refractive power of the other lenses becomes relatively large. In this case, the aberrations generated become large and the aberration correction effect of the metalens ML also becomes small, which is undesirable.

[0059] Conditional formula (3) specifies the value of the ratio of the focal length of at least one lens having positive refractive power in the optical system L0 to the focal length of the optical system L0. By combining a lens having positive refractive power with a metalens ML, the refractive power can be shared to suppress the occurrence of aberrations, or the respective aberrations can be offset, thereby enabling better aberration correction. If the focal length of the lens having positive refractive power is shortened below the lower limit of conditional formula (3), the refractive power of the lens having positive refractive power becomes too large, which is undesirable because spherical aberration and curvature of field occur significantly under the surface. If the focal length of the lens having positive refractive power is lengthened above the upper limit of conditional formula (3), it is undesirable because the effect of sharing the refractive power and the effect of correcting the aberration of the lens having positive refractive power become small.

[0060] Conditional formula (4) specifies the value of the ratio of the focal length of at least one lens having negative refractive power in the optical system L0 to the focal length of the optical system L0. Combining a lens having negative refractive power with a metalens ML allows the refractive power to be shared, suppressing the occurrence of aberrations, or canceling out the respective aberrations, thereby enabling better aberration correction. If the focal length of the lens having negative refractive power is shortened below the lower limit of conditional formula (4), the refractive power of the lens having negative refractive power becomes too large, which is undesirable because spherical aberration and curvature of field occur excessively. If the focal length of the lens having negative refractive power is increased above the upper limit of conditional formula (4), it is undesirable because the effect of sharing the refractive power and the effect of correcting the aberration of the lens having negative refractive power become small.

[0061] Conditional formula (5) specifies the value of the ratio of the maximum height of the columnar structure to the design wavelength. By satisfying conditional formula (5), an optical path length equivalent to the design wavelength or more is generated on the metalens surface ML, and the metalens ML can realize a continuous desired phase change by repeating a periodic configuration that generates a phase change from 0 to 2π as described above. If the maximum height of the columnar structure is reduced below the lower limit of conditional formula (5), a phase change from 0 to 2π (2π in width) cannot be generated, the phase jumps discontinuously at the boundary of the repeated period, and the wavefront of the design wavelength is not continuously connected, which is undesirable. If the maximum height of the columnar structure is increased above the upper limit of conditional formula (5), the maximum height of the columnar structure becomes too high, making manufacturing difficult, which is undesirable.

[0062] Conditional formula (6) specifies the value of the ratio of the maximum diameter of the diameters of the columnar structures provided on the metalens surface MLS to the design wavelength. By satisfying conditional formula (6), the metalens ML can behave as an average effective medium for light. If the maximum diameter is smaller than the lower limit of conditional formula (6), it is not possible to obtain the filling rate required to cause a phase change from 0 to 2π (2π in width), and the wavefront of the design wavelength is not continuous, which is undesirable. If the maximum diameter is larger than the upper limit of conditional formula (6), the columnar structures become too large for light of the design wavelength, which is undesirable because unintended diffracted light, flare, and reflected light occur.

[0063] Conditional formula (7) specifies the value of the ratio of the minimum diameter of the diameters of the columnar structures provided on the metalens surface MLS to the design wavelength. By satisfying conditional formula (7), the metalens ML can behave as an average effective medium for light. If the minimum diameter is smaller than the lower limit of conditional formula (7), the columnar structures become too thin and manufacturing becomes difficult, which is undesirable. If the minimum diameter is larger than the upper limit of conditional formula (7), it is not possible to obtain the filling rate required to cause a phase change from 0 to 2π (2π in width), and the wavefront of the design wavelength is not continuous, which is undesirable.

[0064] It is preferable that the numerical ranges of the conditional expressions (1) to (7) are set to the numerical ranges of the following conditional expressions (1a) to (7a).

[0065] 0.085 <r / D<0.415 (1a) 0.3<|fM| / f<9.0 (2a) 0.15 <fP / f<9.70 (3a) -9.5 <fN / f<-0.4 (4a) 1.1 <H / λ<2.5 (5a) 0.35 <rmax / λ<0.87 (6a) 0.07 <rmin / λ<0.45 (7a) It is more preferable that the numerical ranges of the conditional expressions (1) to (7) be the numerical ranges of the following conditional expressions (1b) to (7b).

[0066] 0.095 <r / D<0.405 (1b) 0.6<|fM| / f<8.0 (2b) 0.30 <fP / f<9.50 (3b) -9.0 <fN / f<-0.7 (4b) 1.15 <H / λ<2.20 (5b) 0.40 <rmax / λ<0.85 (6b) 0.09 <rmin / λ<0.40 (7b) It is further preferable that the numerical ranges of the conditional expressions (1) to (7) be the numerical ranges of the following conditional expressions (1c) to (7c).

[0067] 0.110<2×r / D<0.395 (1c) 0.8<|fM| / f<7.0 (2c) 0.40 <fP / f<9.20 (3c) -8.0 <fN / f<-1.0 (4c) 1.2 <H / λ<2.0 (5c) 0.45 <rmax / λ<0.83 (6c) 0.14 <rmin / λ<0.35 (7c) Next, the optical system L0 of each embodiment will be described in detail.

[0068] In Example 1, the optical system L0 includes a first lens G1 to a sixth lens G6, which have positive, negative, positive, positive, negative, and negative refractive powers, arranged in this order from the object side to the image side. In Example 1, the design wavelength is 940 nm. The metalens ML in Example 1 is the sixth lens G6, and the metalens surface MLS is the image-side lens surface of the sixth lens G6. The metalens ML also has a negative refractive power near the optical axis. The refractive index of the columnar structure of the metalens surface MLS is 2.0164 at the design wavelength. The metalens surface MLS is provided with a cylindrical columnar structure shown in FIG. 21 in accordance with FIG. 25 and FIG. 26, while changing the diameter w1 of the circle so as to produce the phase change of FIG. 3. In Example 1, the length w0 of the substrate is 0.75 μm, the height H of the columnar structure is 1.45 μm, and the diameter w1 varies in the range from 0.200 μm to 0.685 μm.

[0069] In Example 2, the optical system L0 includes a first lens G1 to a sixth lens G6, which have negative, positive, negative, positive, positive, and negative refractive powers, arranged in this order from the object side to the image side. In Example 2, the design wavelength is 587.56 nm. The metalens ML in Example 2 is the fourth lens G4, and the metalens surface MLS is the object-side lens surface of the fourth lens G6. The metalens ML also has a positive refractive power near the optical axis. The refractive index of the columnar structure of the metalens surface MLS is 2.0458 at the design wavelength. The rectangular columnar structure shown in FIG. 20 is provided on the metalens surface MLS in accordance with FIGS. 25 and 26, with the length w1 of the side of the rectangle being changed so as to produce the phase change of FIG. 8. In Example 2, the length w0 of the substrate is 0.40 μm, the height H of the columnar structure is 0.84 μm, and the side length w1 varies in the range from 0.100 μm to 0.335 μm.

[0070] In Example 3, the optical system L0 includes a first lens G1 to a fourth lens G4, which have positive, positive, negative, and negative refractive powers, arranged in this order from the object side to the image side. In Example 3, the design wavelength is 940 nm. The metalens ML in Example 3 is the second lens G2, and the metalens surface MLS is the image-side lens surface of the second lens G2. The metalens ML has a positive refractive power near the optical axis. The refractive index of the columnar structure of the metalens surface MLS is 2.0164 at the design wavelength. The metalens surface MLS is provided with a hexagonal columnar structure shown in FIG. 22 in accordance with FIG. 25 and FIG. 26, while changing the length w1 of one side of the hexagon so as to generate the phase change of FIG. 12. In Example 3, the length w0 of the substrate is 0.75 μm, the height H of the columnar structure is 1.45 μm, and the side length w1 varies in the range from 0.180 μm to 0.607 μm.

[0071] In Example 4, the optical system L0 includes a first lens G1 to a sixth lens G6, which have positive, negative, positive, positive, negative, and negative refractive powers, arranged in this order from the object side to the image side. In Example 4, the design wavelength is 587.56 nm. The metalens ML in Example 4 is the sixth lens G6, and the metalens surface MLS is the image-side lens surface of the sixth lens G6. The metalens ML also has a negative refractive power near the optical axis. The refractive index of the columnar structure of the metalens surface MLS is 2.0458 at the design wavelength. The metalens surface MLS is provided with the cylindrical columnar structure shown in FIG. 21 in accordance with FIG. 25 and FIG. 26, while changing the diameter w1 of the circle so as to produce the phase change of FIG. 16. In Example 4, the length w0 of the substrate is 0.40 μm, the height H of the columnar structure is 0.84 μm, and the diameter w1 varies in the range from 0.180 μm to 0.367 μm.

[0072] Numerical examples 1 to 4 corresponding to the first to fourth embodiments, respectively, are shown below.

[0073] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial spacing (distance on the optical axis) between the mth surface and the (m+1)th surface. Here, m is the surface number counted from the light incident side. Additionally, nd represents the refractive index of each optical component with respect to the d-line, and νd represents the Abbe number of the optical component. Additionally, n940 is the refractive index of each optical component with respect to a wavelength of 940 nm. The Abbe number νd of a certain material is given by the following when the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines are Nd, NF, and NC, respectively: νd=(Nd-1) / (NF-NC) It is expressed as:

[0074] In each numerical example, d, focal length (mm), F-number, and half angle of view (°) are all values ​​when the optical system L0 of each example is focused on an object at infinity. The back focus BF is the distance on the optical axis from the final lens surface (the lens surface closest to the image) of the optical system L0 to the image surface, expressed as an air-equivalent length. The total lens length is the distance from the foreground (the lens surface closest to the object) of the optical system L0 to the final lens surface (not including the optical block FL) plus the back focus.

[0075] If the optical surface is aspheric, a * symbol is added to the right of the surface number. The aspheric shape is expressed as follows, where X is the displacement from the apex of the surface in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, A10, and A12 are the aspheric coefficients of each order: X = (h 2 / R) / [1+{1-(1+K)(h / R) 2} 1 / 2 +A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 ] In addition, "e±XX" in each aspheric coefficient is "×10± XX " It means.

[0076] In addition, MLS indicates that the surface is a metalens surface. The phase function φ of the metalens surface is expressed as follows, where B4, B6, B8, B10, and B12 are the coefficients of each order when the phase function φ is expressed as a power series polynomial: φ=B2×h 2 +B4×h 4 +B6×h 6 +B8×h 8 +B10×h 10 +B12×h 12 +B14×h 14 It is expressed as:

[0077] Similarly, when the optical path difference function of the metalens surface is Φ, the design wavelength is λ, and C4, C6, C8, C10, and C12 are the coefficients of each order when the optical path difference function is expressed as a power series polynomial, Φ=φ×λ / (2π)=C2×h 2 +C4×h 4 +C6×h 6 +C8×h 8 +C10×h 10 +C12×h 12 +C14×h 14 In this case, if the focal length of the metalens surface is fM, 1 / fM=-2×C2=-2×λ×B2 / (2π) It is.

[0078] In addition, "e±XX" in each coefficient is "×10± XX " It means.

[0079] [Numerical Example 1] Unit: mm Surface Data Surface number rd n940 νd Effective diameter 1* -3.433 0.50 1.52639 55.7 3.38 2* -2.603 0.10 2.53 3* 1.322 0.40 1.63455 20.4 2.04 4* 0.961 0.29 1.61 5(Aperture) ∞ 0.00 1.61 6* 6.494 0.42 1.52639 55.7 1.54 7* -27.169 0.11 1.53 8* -19.890 0.65 1.52639 55.7 1.56 9* -1.623 0.74 1.61 10* 3.480 0.40 1.64307 19.3 2.62 11* 1.970 1.40 3.18 12 ∞ 0.50 1.50792 64.1 6.91 13(MLS) ∞ 0.40 7.61 Image plane ∞ Aspheric Data Front page K = 0.00000e+00 A 4= 8.31829e-02 A 6=-6.80816e-03 A 8= 4.96011e-05 2nd side K =-7.83575e+00 A 4= 1.39114e-01 A 6=-2.53752e-02 A 8= 1.68533e-02 3rd page K =-4.53662e+00 A 4= 1.33684e-01 A 6=-4.83426e-02 A 8= 1.34721e-02 Side 4 K =-3.57529e+00 A 4= 1.07508e-01 A 6=-2.00095e-02 A 8=-4.70803e-02 Side 6 K = 1.00000e+01 A 4= 9.41213e-03 A 6= 6.12387e-02 A 8=-1.55783e-01 A10=-2.77809e-03 Side 7 K =-1.86654e+01 A 4= 1.49386e-01 A 6= 1.09103e-01 A 8=-8.78459e-02 A10= 8.49814e-03 Side 8 K = 0.00000e+00 A 4= 7.25912e-02 A 6= 5.61224e-02 A 8=-2.60104e-02 9th page K = 0.00000e+00 A 4=-3.42408e-02 A 6= 1.36192e-02 A 8=-2.08664e-02 Side 10 K = 0.00000e+00 A 4=-1.22987e-01 A 6= 2.69464e-02 A 8= 4.87787e-03 A10=-3.34934e-03 Page 11 K = 0.00000e+00 A 4=-1.24895e-01 A 6= 3.36893e-02 A 8=-5.67529e-03 Page 13 (MLS) C 2= 8.55017e-02 C 4=-1.73660e-02 C 6= 1.38018e-03 C 8=-4.37175e-05 Focal length 4.11 F-number: 2.57 Half angle of view (°) 43.35 Image height 3.88 Lens length 5.90 BF 0.40 Single lens data Lens starting surface focal length 1 1 16.93 2 3 -9.73 3 6 10.00 4 8 3.32 5 10 -7.88 6 12 -5.85 [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1* 16.001 0.44 1.53504 55.7 1.85 2* 2.788 0.12 1.66 3* 1.746 0.77 1.53504 55.7 1.72 4* -3.594 -0.07 1.72 5(Aperture) ∞ 0.23 1.67 6* -5.055 0.40 1.66080 20.4 1.61 7* 55.707 0.19 1.91 8(MLS) ∞ 0.40 1.51633 64.1 2.30 9 ∞ 0.34 2.72 10* 2.141 0.40 1.53499 55.8 3.65 11* 2.257 0.94 4.26 12* 2.031 0.50 1.53504 55.7 4.57 13* 1.357 0.43 6.01 14 ∞ 0.40 1.51633 64.1 7.31 15 ∞ 0.40 7.67 Image plane ∞ Aspheric Data Front page K = 0.00000e+00 A 4=-1.91087e-02 A 6= 1.37174e-03 A 8= 3.95640e-04 2nd side K =-3.18548e+00 A 4=-2.03665e-02 A 6= 9.72944e-03 A 8= 1.63619e-02 3rd page K =-4.74707e+00 A 4= 4.76470e-02 A 6=-6.23112e-02 A 8= 6.19068e-03 A10=-1.74582e-02 Page 4 K = 1.00000e+01 A 4=-9.55121e-02 A 6= 7.92232e-02 A 8=-4.93316e-02 A10= 2.73523e-02 Page 6 K = 9.96250e+00 A 4=-1.14053e-01 A 6= 1.84047e-01 A 8=-3.60989e-02 A10= 6.22275e-03 Page 7 K = 1.99999e+01 A 4=-7.25652e-02 A 6= 1.37502e-01 A 8=-5.40950e-02 A10= 2.59535e-02 Page 8 (MLS) C 2=-2.50984e-02 C 4= 8.41972e-03 C 6= 5.93566e-04 C 8=-7.84988e-04 C10=-1.55749e-04 Page 10 K = 0.00000e+00 A 4=-9.20501e-02 A 6= 1.21058e-02 A 8=-2.32952e-03 Page 11 K = 0.00000e+00 A 4=-8.08606e-02 A 6= 9.29348e-03 A 8=-1.34130e-03 Page 12 K =-1.00000e+01 A 4=-6.35885e-02 A 6=-1.18290e-02 A 8= 2.86576e-03 Page 13 K =-4.66528e+00 A 4=-3.78185e-02 A 6= 2.45314e-03 A 8=-9.86812e-05 Focal length 4.28 F-number: 2.57 Half angle of view (°) 42.15 Image height 3.88 Lens length 5.76 BF 1.10 Single lens data Lens starting surface focal length 1 1 -6.38 2 3 2.31 3 6 -6.99 4 8 19.92 5 10 35.26 6 12 -10.31 [Numerical Example 3] Unit: mm Surface Data Surface number rd n940 νd Effective diameter 1* 2.085 0.50 1.83150 40.1 1.90 2* 2.845 0.31 1.58 3 (Aperture) ∞ 0.10 1.53 4 ∞ 0.50 1.50792 64.1 1.50 5(MLS) ∞ 0.74 1.99 6* -24.138 0.45 1.64307 19.3 3.25 7* -27.261 0.87 3.75 8* 3.912 0.50 1.64307 19.3 5.09 9* 3.080 0.33 5.71 10 ∞ 0.50 1.50792 64.1 7.34 11 ∞ 0.40 7.77 Image plane ∞ Aspheric Data Front page K = 0.00000e+00 A 4=-8.51198e-03 A 6=-1.87386e-03 A 8=-8.21259e-03 2nd side K = 0.00000e+00 A 4=-8.82492e-03 A 6=-1.39205e-02 A 8=-1.00226e-02 Page 5 (MLS) C 2=-6.42581e-02 C 4= 5.80317e-03 C 6= 8.18128e-03 C 8=-3.64839e-03 C10 = 5.41249e-03 Side 6 K = 0.00000e+00 A 4=-1.32164e-02 A 6= 3.81982e-03 Side 7 K = 0.00000e+00 A 4=-1.66429e-02 A 6= 1.04823e-02 A 8=-1.22743e-03 Side 8 K = 0.00000e+00 A 4=-7.50759e-02 A 6= 4.47157e-03 A 8= 7.75616e-04 A10=-7.39618e-05 9th page K = 0.00000e+00 A 4=-6.50080e-02 A 6= 6.71184e-03 A 8=-4.14732e-04 Focal length 4.17 F-number 2.40 Half angle of view(°) 42.91 Image height 3.88 Lens length 5.03 BF 1.06 Single lens data Lens starting surface focal length 1 1 7.22 2 4 7.78 3 6 -347.26 4 8 -29.43 5 10 0.00 [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1* -3.896 0.50 1.53504 55.7 3.31 2* -3.046 0.10 2.55 3* 1.403 0.46 1.66080 20.4 2.11 4* 1.017 0.29 1.64 5(Aperture) ∞ 0.00 1.64 6* 10.150 0.44 1.53504 55.7 1.60 7* -10.748 0.11 1.63 8* -27.778 0.70 1.53504 55.7 1.67 9* -1.670 0.78 1.71 10* 3.880 0.40 1.67070 19.3 2.61 11* 1.944 1.51 3.13 12 ∞ 0.50 1.51633 64.1 6.94 13(MLS) ∞ 0.40 7.62 Image plane ∞ Aspheric Data Front page K = 0.00000e+00 A 4= 7.76296e-02 A 6=-5.96239e-03 2nd side K = 0.00000e+00 A 4= 1.58973e-01 A 6=-2.43158e-02 A 8= 1.36084e-02 3rd page K =-3.59362e+00 A 4= 8.65247e-02 A 6=-2.20609e-02 A 8= 7.58096e-03 Page 4 K =-3.07327e+00 A 4= 8.03389e-02 A 6=-1.81655e-02 A 8=-2.75557e-02 Page 6 K = 0.00000e+00 A 4= 2.52416e-02 A 6=-1.56320e-03 A 8=-7.66220e-02 Page 7 K = 0.00000e+00 A 4= 1.48521e-01 Page 8 K = 0.00000e+00 A 4= 8.55980e-02 A 6=-4.07608e-03 A 8= 4.28876e-03 Page 9 K = 0.00000e+00 A 4=-1.84767e-02 A 6= 3.70582e-03 A 8=-5.13414e-03 Page 10 K = 0.00000e+00 A 4=-1.10959e-01 A 6= 2.08304e-02 A 8= 7.15666e-03 A10=-3.97014e-03 Page 11 K = 0.00000e+00 A 4=-1.21890e-01 A 6= 3.34359e-02 A 8=-6.00247e-03 Page 13 (MLS) C 2= 7.06468e-02 C 4=-1.63034e-02 C 6= 1.36101e-03 C 8=-4.39037e-05 Focus distance 4.39 Fナンバー2.57 Half angle of view (°) 41.42 Image height 3.88 Lens length 6.20 BF 0.40 Single lens data Lens starting surface focal length 1 1 21.65 2 3 -10.68 3 6 9.83 4 8 3.29 5 10 -6.33 6 12 -7.08 Various values ​​in each numerical example are summarized in Table 1 below.

[0080] [Table 1]

[0081] [Imaging device] Next, an embodiment of a digital still camera (imaging device) using the optical system L0 of each embodiment as an imaging optical system will be described with reference to FIG. 27. In FIG. 27, 10 denotes a camera body, and 11 denotes an imaging optical system configured by any of the optical systems L0 described in the first to fourth embodiments. 12 denotes an imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that is built into the camera body and receives an optical image formed by the imaging optical system 11 and photoelectrically converts it. The camera body 10 may be a so-called single-lens reflex camera having a quick-turn mirror, or a so-called mirrorless camera having no quick-turn mirror. In addition, various aberrations such as distortion aberration and chromatic aberration of the image acquired by the imaging element 12 may be electrically corrected to improve the image quality of the output image.

[0082] In this way, by applying the optical system L0 of each embodiment to an imaging device such as a digital still camera, it is possible to obtain an imaging device with a small lens. [Lens device] 14 is a schematic external view of a lens device 20 using the optical system L0 of each embodiment as a photographing optical system. The lens device 20 is a so-called interchangeable lens that is detachably attached to a camera body (not shown). 21 is a photographing optical system configured with any of the optical systems L0 described in the first to fourth embodiments. The photographing optical system 21 is held by a holding unit (not shown). The lens device 20 also has a focus operating means 22 and an operating means 23 for changing the photographing mode.

[0083] When the user operates the focus operation means 22, the arrangement of the photographing optical system 21 is changed mechanically or electrically, and the focal position can be changed.

[0084] Furthermore, the user may operate the operation means 23 to change the arrangement of the lens groups in the photographing optical system 21 for a purpose other than focusing. For example, the arrangement of the lens groups in the photographing optical system 21 may be mechanically or electrically changed in response to the operation of the operation means 23 to change the aberration of the photographing optical system 21. In this case, it is preferable that the focal position does not substantially change.

[0085] The disclosure of this embodiment includes the following configuration. (Configuration 1) having at least one lens and a metalens; the metalens has a lens surface that induces a phase change in a wavefront of light passing therethrough; 11. An optical system comprising: a phase function of the lens surface, which represents an amount of phase change in the wavefront corresponding to a radial position of the metalens, the phase function including at least one of a critical point and an inflection point. (Configuration 2) When the distance in the radial direction from the center of the lens surface to a position corresponding to at least one critical point or inflection point included in the phase function is r and the effective diameter of the lens surface is D, 0.050 <r / D<0.425 2. The optical system according to claim 1, wherein the following condition is satisfied: (Configuration 3) the lens surface has a structure including a plurality of convex portions, 3. The optical system according to configuration 1 or 2, wherein the size of the convex portion changes in the radial direction according to a predetermined rule. (Configuration 4) The optical system described in configuration 3, wherein the size of the convex portion is at least one of a filling rate of the convex portion, a volume of the convex portion, a diameter of the convex portion, and an area of ​​the lens surface occupied by the convex portion. (Configuration 5) 5. The optical system according to claim 3 or 4, wherein the structure includes a configuration in which the convex portions are provided such that the size of the convex portions increases or decreases with increasing distance from the center of the lens surface in the radial direction. (Configuration 6) The optical system described in configuration 5, wherein the configurations are provided periodically along the radial direction. (Configuration 7) the structure includes a plurality of configurations including at least one of a configuration in which the convex portions are provided so that the size of the convex portions increases with increasing distance from the center of the lens surface in the radial direction and a configuration in which the convex portions are provided so that the size of the convex portions decreases with increasing distance from the center of the lens surface in the radial direction, the plurality of configurations includes a first configuration and a second configuration, The optical system according to any one of configurations 3 to 6, wherein the radial spacing of the first configuration is different from the radial spacing of the second configuration. (Configuration 8) 8. The optical system of configuration 7, wherein, over at least a portion of the metalens surface, the radial distance between the plurality of features decreases with distance from the center and then changes to increase with distance from the center. (Configuration 9) the structure includes a plurality of configurations including at least one of a configuration in which the convex portions are provided so that the size of the convex portions increases with increasing distance from the center of the lens surface in the radial direction and a configuration in which the convex portions are provided so that the size of the convex portions decreases with increasing distance from the center of the lens surface in the radial direction, the plurality of configurations includes a first configuration and a second configuration, The optical system described in any one of configurations 3 to 8, characterized in that the change in size of the convex portion in the first configuration is different from the change in size of the convex portion in the second configuration. (Configuration 10) 10. The optical system of configuration 9, wherein at least a portion of the metalens surface has a configuration in which a first configuration is periodically repeated and a configuration in which a second configuration is periodically repeated in the radial direction. (Configuration 11) 11. The optical system according to any one of configurations 3 to 10, wherein the convex portion is a cylindrical column having two substantially similar and substantially parallel planar figures as upper and lower surfaces. (Configuration 12) Let f be the focal length of the optical system, and f be the focal length of the metalens: 0.1<|fM| / f<10.0 12. The optical system according to any one of configurations 1 to 11, wherein the following condition is satisfied: (Configuration 13) The optical system includes at least one positive lens, When the focal length of the optical system is f and the focal length of the positive lens is fP, 0.1 <fP / f<10.0 13. The optical system according to any one of configurations 1 to 12, wherein the following condition is satisfied: (Configuration 14) The optical system includes at least one negative lens, When the focal length of the optical system is f and the focal length of the negative lens is fN, -10.0 <fN / f<-0.1 14. The optical system according to any one of configurations 1 to 13, wherein the following condition is satisfied: (Configuration 15) When the maximum height of the convex portion in the direction along the optical axis is H and the design wavelength is λ, 1.0 <H / λ<3.0 15. The optical system according to any one of configurations 1 to 14, wherein the following condition is satisfied: (Configuration 16) The maximum diameter and the minimum diameter of the diameters of the plurality of protrusions are respectively defined as rmax and rmin, and the design wavelength is λ. 0.3 <rmax / λ<0.9 0.05 <rmin / λ<0.50 16. The optical system according to any one of configurations 1 to 15, wherein the following condition is satisfied: (Configuration 17) the optical system includes at least one aspheric lens; 17. The optical system according to any one of configurations 1 to 16, wherein the aspheric lens has an aspheric surface that includes at least one of a critical point and an inflection point. (Configuration 18) having at least one lens and a metalens; the lens surface has a structure including a plurality of convex portions, An optical system, characterized in that the size of the convex portion changes in the radial direction according to a predetermined rule. (Configuration 19) A lens surface that causes a phase change in the wavefront of light passing through the lens surface. An optical element, characterized in that a phase function of the lens surface, which represents an amount of phase change on the wavefront corresponding to a radial position on the lens surface, includes at least one of a critical point and an inflection point. (Configuration 20) 19. An imaging apparatus comprising: an optical system according to any one of configurations 1 to 18; and an imaging element that receives an image formed by the optical system. (Configuration 21) 19. A lens device comprising: an optical system according to any one of configurations 1 to 18; and a holder for holding the optical system.

[0086] Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0087] L0 optical system ML Metalens MLS Metalens Surface

Claims

1. having at least one lens and a metalens; the metalens has a lens surface that induces a phase change in a wavefront of light passing therethrough; 11. An optical system comprising: a phase function of the lens surface, which represents an amount of phase change in the wavefront corresponding to a radial position of the metalens, the phase function including at least one of a critical point and an inflection point.

2. When the distance in the radial direction from the center of the lens surface to a position corresponding to at least one critical point or inflection point included in the phase function is r and the effective diameter of the lens surface is D, 0.050<r / D<0.425 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. the lens surface has a structure including a plurality of convex portions, The optical system according to claim 1 , wherein the size of the convex portion changes in the radial direction according to a predetermined rule.

4. 4. The optical system according to claim 3, wherein the size of the convex portion is at least one of a packing rate of the convex portion, a volume of the convex portion, a diameter of the convex portion, and an area of ​​the lens surface occupied by the convex portion.

5. The optical system according to claim 3 , wherein the structure includes a configuration in which the convex portions are provided so that the size of the convex portions increases or decreases with increasing distance from the center of the lens surface in the radial direction.

6. The optical system according to claim 5 , wherein the configurations are provided periodically along the radial direction.

7. the structure includes a plurality of configurations including at least one of a configuration in which the convex portions are provided so that the size of the convex portions increases with increasing distance from the center of the lens surface in the radial direction and a configuration in which the convex portions are provided so that the size of the convex portions decreases with increasing distance from the center of the lens surface in the radial direction, the plurality of configurations includes a first configuration and a second configuration, The optical system of claim 3 , wherein the radial spacing of the first configuration is different than the radial spacing of the second configuration.

8. 8. The optical system of claim 7, wherein, over at least a portion of the metalens surface, the radial distance between the plurality of features decreases with distance from the center and then changes to increase with distance from the center.

9. the structure includes a plurality of configurations including at least one of a configuration in which the convex portions are provided so that the size of the convex portions increases with increasing distance from the center of the lens surface in the radial direction and a configuration in which the convex portions are provided so that the size of the convex portions decreases with increasing distance from the center of the lens surface in the radial direction, the plurality of configurations includes a first configuration and a second configuration, 4. The optical system according to claim 3, wherein a change in size of the convex portion in the first configuration is different from a change in size of the convex portion in the second configuration.

10. 10. The optical system of claim 9 , wherein at least a portion of the metalens surface has a configuration in which the first configuration is periodically repeated and a configuration in which the second configuration is periodically repeated in the radial direction.

11. 4. The optical system according to claim 3, wherein the convex portion is a columnar body having two substantially similar and substantially parallel planar figures as upper and lower surfaces.

12. When the focal length of the optical system is f and the focal length of the metalens is fM, 0.1<|fM| / f<10.0 3. The optical system according to claim 1, wherein the following condition is satisfied:

13. The optical system includes at least one positive lens, When the focal length of the optical system is f and the focal length of the positive lens is fP, 0.1<fP / f<10.0 3. The optical system according to claim 1, wherein the following condition is satisfied:

14. The optical system includes at least one negative lens, When the focal length of the optical system is f and the focal length of the negative lens is fN, -10.0<fN / f<-0.1 3. The optical system according to claim 1, wherein the following condition is satisfied:

15. When the maximum height of the convex portion in the direction along the optical axis is H and the design wavelength is λ, 1.0<H / λ<3.0 3. The optical system according to claim 1, wherein the following condition is satisfied:

16. The maximum diameter and the minimum diameter of the diameters of the plurality of protrusions are denoted by rmax and rmin, respectively, and the design wavelength is denoted by λ. 0.3<rmax / λ<0.9 0.05<rmin / λ<0.50 3. The optical system according to claim 1, wherein the following condition is satisfied:

17. the optical system includes at least one aspheric lens; 3. The optical system of claim 1, wherein the aspheric lens has an aspheric surface that includes at least one of a critical point and an inflection point.

18. having at least one lens and a metalens; the lens surface has a structure including a plurality of convex portions, An optical system, characterized in that the size of the convex portion changes in the radial direction according to a predetermined rule.

19. A lens surface that causes a phase change in the wavefront of light passing through the lens surface. An optical element, characterized in that a phase function of the lens surface, which represents an amount of phase change on the wavefront corresponding to a radial position on the lens surface, includes at least one of a critical point and an inflection point.

20. 3. An imaging apparatus comprising: the optical system according to claim 1; and an imaging element for receiving an image formed by the optical system.

21. 3. A lens device comprising: an optical system according to claim 1; and a holder for holding the optical system.

Images