Optical system and imaging device

Abstract

An optical system according to the present disclosure comprises: a plurality of diffraction lenses; and an aperture stop that is disposed between any two diffraction lenses among the plurality of diffraction lenses and in which an opening is filled with a substance.

Description

Optical system and imaging device

[0001] The present disclosure relates to an optical system and an imaging device.

[0002] Wide-angle optical systems are essential for high-performance sensing optical systems, but achieving wide-field imaging requires multiple optical lenses, which increases size and weight and complicates assembly. Metalenses, on the other hand, are optical elements that can control the phase, amplitude, and polarization of propagating light using subwavelength structures, and are expected to enable the realization of compact optical systems (see Patent Literatures 1 and 2). Patent Literature 2 proposes a technology that utilizes the aberration properties of metalenses to combine them with multiple refractive lenses (bulk lenses) to improve optical properties.

[0003] JP 2022-544213 A JP 2021-71727 A

[0004] The technology described in Patent Document 2 can achieve a smaller size compared to an optical system configured using only refractive lenses, but since a plurality of refractive lenses are used, the size reduction is insufficient.

[0005] Therefore, it is desirable to provide an optical system and an imaging device that can achieve both miniaturization and high performance.

[0006] A first optical system according to one embodiment of the present disclosure includes a plurality of diffractive lenses and an aperture stop disposed between any two of the plurality of diffractive lenses, the aperture of which is filled with a substance.

[0007] A second optical system according to one embodiment of the present disclosure comprises, in order from the object side to the image plane side, a first lens having a first surface and a second surface, the first surface and the second surface being planar; a second lens having a third surface and a fourth surface, the third surface and the fourth surface being planar, the third surface being cemented to the second surface without an air gap; and a medium having a refractive index greater than 1 that is arranged to fill the space from the fourth surface to the image plane without an air gap, and of the first surface to the fourth surface, at least the second surface or the third surface is a phase modulation surface.

[0008] A first imaging device according to one embodiment of the present disclosure includes an optical system and a solid-state imaging element that outputs an imaging signal corresponding to an optical image formed by the optical system, and the optical system is configured by the first optical system according to the embodiment of the present disclosure.

[0009] A second imaging device according to an embodiment of the present disclosure includes an optical system and an imaging element that receives light via the optical system, and the optical system includes, in order from the object side to the image plane side, a first lens having a first surface and a second surface, the first surface and the second surface being planar; a second lens having a third surface and a fourth surface, the third surface and the fourth surface being planar, the third surface being cemented to the second surface without an air gap; and a medium having a refractive index greater than 1 that is arranged so as to fill the space from the fourth surface to the imaging element without an air gap, and of the first surface to the fourth surface, at least the second surface or the third surface is a phase modulation surface.

[0010] In the first optical system or the first imaging device according to an embodiment of the present disclosure, the configuration of the multiple diffractive lenses and the aperture stop is optimized to enable miniaturization and high performance.

[0011] In the second optical system or the second imaging device according to an embodiment of the present disclosure, the configuration up to the image plane is optimized so as to enable miniaturization and high performance to be achieved.

[0012] FIG. 1 is an explanatory diagram showing the influence of reflected light components in a solid-state imaging element having a CSP structure. FIG. 2 is an explanatory diagram showing the influence of reflected light components in a solid-state imaging element having a CSP structure. FIG. 3 is an explanatory diagram showing an overview of chromatic aberrations occurring in a diffractive lens and chromatic aberrations occurring in a refractive lens. FIG. 4 is a cross-sectional view schematically showing an overview of an optical system according to a first embodiment of the present disclosure. FIG. 5 is an explanatory diagram showing an example of an imaging state when image deviation occurs in the optical system. FIG. 6 is a cross-sectional view schematically showing Configuration Example 1-1 of the optical system according to the first embodiment. FIG. 7 is an aberration diagram showing longitudinal aberrations in the optical system according to Configuration Example 1-1. FIG. 8 is a cross-sectional view schematically showing Configuration Example 1-2 of the optical system according to the first embodiment. FIG. 9 is an aberration diagram showing longitudinal aberrations in the optical system according to Configuration Example 1-2. FIG. 10 is a cross-sectional view schematically showing Configuration Example 1-3 of the optical system according to the first embodiment. FIG. 11 is a cross-sectional view showing an example of the actual shape of an aspherical lens in the optical system according to Configuration Example 1-3. FIG. 12 is an aberration diagram showing longitudinal aberration in an optical system according to Configuration Example 1-3. FIG. 13 is a cross-sectional view schematically showing an optical system according to a comparative example. FIG. 14 is an explanatory diagram showing a comparison of specifications of an optical system according to Configuration Example 1-1 with specifications of an optical system according to a comparative example. FIG. 15 is an explanatory diagram showing a comparison of specifications of optical systems according to Configuration Examples 1-1 to 1-3. FIG. 16 is a cross-sectional view showing an example configuration of an imaging device according to the first embodiment. FIG. 17 is a cross-sectional view schematically showing an overview of an optical system and an imaging device according to a second embodiment of the present disclosure. FIG. 18 is an explanatory diagram showing a state of light ray passage through an optical system according to a comparative example. FIG. 19 is an explanatory diagram showing a state of light ray passage when a first lens is arranged on the object side of a phase modulation surface. FIG. 20 is an explanatory diagram showing an example of a light ray passage when a second lens is arranged on the image plane side of a phase modulation surface. FIG. 21 is a cross-sectional view schematically showing Configuration Example 2-1 of an optical system according to the second embodiment. FIG. 22 is a cross-sectional view showing an example structure of a phase modulation surface. Fig. 23 is a cross-sectional view schematically showing a configuration example 2-2 of the optical system according to the second embodiment. Fig. 24 is a cross-sectional view schematically showing a configuration example 2-3 of the optical system according to the second embodiment.

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The description will be made in the following order: 1. First embodiment 1.0 Comparative example 1.1 Overview of optical system 1.2 Specific configuration example of optical system 1.3 Configuration example of imaging device 1.4 Effects 2. Second embodiment 2.0 Comparative example 2.1 Overview of optical system and imaging device 2.2 Actions and effects 2.3 Specific configuration example of optical system 3. Other embodiments

[0014] 1. First Embodiment [1.0 Comparative Example] In Patent Document 1 (JP-A 2022-544213), a wide-angle optical system of 120° or more is realized with a single metalens. Like a diffractive lens, a metalens has a periodically repeating structure and can impart desired optical properties by diffracting light in any direction, but the diffraction direction varies significantly depending on the wavelength of the light. For this reason, when light is incident from a light source having a FWHM (Full Width at Half Maximum) of several tens of nanometers, such as an LED (Light Emitting Diode), significant chromatic aberration occurs, significantly degrading the optical properties.

[0015] Patent Document 2 (JP 2021-71727 A) proposes a technology that utilizes the aberration characteristics of a metalens and combines it with multiple refractive lenses (bulk lenses) to improve optical properties. While this technology allows for a more compact optical system than one composed solely of refractive lenses, the use of multiple refractive lenses results in insufficient compactness.

[0016] Currently, it is difficult to ensure sufficient performance with metalenses only in a narrow band (laser wavelength level). Even in optical systems that combine metalenses and refractive lenses, multiple refractive lenses are required to ensure sufficient performance. This leads to increased size and cost.

[0017] The chip-size package (CSP) structure is known as one of the structures of solid-state imaging devices that achieves a high pixel count, miniaturization, and a low profile. The CSP structure is an extremely small package realized with a size comparable to that of a single chip. In a solid-state imaging device with a CSP structure, for example, pixels for converting incident light into electrical signals are formed on a semiconductor substrate, and a glass substrate is disposed over the light-receiving surface on which the pixels are formed to fix the solid-state imaging device and protect the light-receiving surface.

[0018] 1 and 2 are explanatory diagrams showing the influence of reflected light components in a solid-state imaging device with a CSP structure.

[0019] As shown in the upper sections of FIGS. 1 and 2 , in a solid-state imaging device with a CSP structure (CSP solid-state imaging device), for example, a glass substrate 102 is disposed opposite the light-receiving surface side of a solid-state imaging device 101 via an adhesive 131. Here, the upper surface side (the light-receiving surface side of the solid-state imaging device 101) of the glass substrate 102 is air, and the refractive index n is 1.0. The refractive index n of the glass substrate 102 is, for example, 1.5. In a CSP solid-state imaging device, as shown in the upper sections of FIGS. 1 and 2 , subject light directly incident on the light-receiving surface of the solid-state imaging device 101 may be totally reflected at the light-receiving surface. This totally reflected component may be reflected at the interface between the glass substrate 102 and the air and return to the light-receiving surface (total reflection aliasing component). If the thickness h1 of the glass substrate 102 is large, as in the example in the upper section of FIG. 1 , the above-mentioned total reflection aliasing component will be imaged around the original light source image, as in the example in the lower section of FIG. 1 . Therefore, the total reflection component at the light receiving surface appears in the captured image as, for example, flare or ghosting on the subject image, which causes a decrease in the image quality of the captured image. It is known that the effect of this phenomenon on the captured image can be reduced, as in the example in the lower part of Figure 2, by reducing the thickness h2 (

[0020] ​(Chromatic aberration of diffractive lenses and refractive lenses) Figure 3 is an explanatory diagram showing an overview of chromatic aberration that occurs in diffractive lenses and refractive lenses. In Figure 3, λ1, λ2, and λ3 represent the wavelengths of light rays, and the wavelength relationship is λ3>λ2>λ1 (relative to wavelength λ2, wavelength λ1 is a short wavelength and wavelength λ3 is a long wavelength).

[0021] As shown in the upper part of Figure 3, the refractive power of a diffractive lens decreases as the wavelength becomes shorter. For example, when NA is 0.315 and f=20, the dispersion is very high, equivalent to an Abbe number of -3.45. On the other hand, as shown in the lower part of Figure 3, the refractive power of a refractive lens increases as the wavelength becomes shorter. The Abbe number of a refractive lens is generally around 20 to 60.

[0022] When combining positive lenses, the chromatic aberration of a diffractive lens and that of a refractive lens cancel each other out. However, the sensitivity of a diffractive lens to chromatic aberration is greater than that of a refractive lens. This results in many design constraints, such as increasing the focal length of the diffractive lens as in the optical system described in Patent Document 2, or increasing the number of refractive lenses.

[0023] [1.1 Overview of Optical System] FIG. 4 is a cross-sectional view schematically illustrating an overview of an optical system according to the first embodiment of the present disclosure.

[0024] The optical system according to the first embodiment includes a plurality of diffractive lenses and an aperture stop St, which is disposed between any two of the diffractive lenses and has an aperture Sta filled with a material such as resin. Each of the diffractive lenses has a positive refractive power.

[0025] Fig. 4 shows an example configuration having multiple diffractive lenses, namely, a first diffractive lens 11 and a second diffractive lens 12. The example configuration in Fig. 4 includes, in order from the object side toward the image plane (imaging plane) side, the first diffractive lens 11, an aperture stop St, and the second diffractive lens 12.

[0026] 4, the object-side surface of the first diffractive lens 11 and the image-plane-side surface of the second diffractive lens 12 are diffractive surfaces. Each of the diffractive lenses has a positive refractive power. In this configuration example, the first diffractive lens 11 and the second diffractive lens 12 each have a positive refractive power.

[0027] In this configuration example, the opening Sta of the aperture stop St is filled with a material such as resin, and therefore the light passing range from the first diffractive lens 11 to the second diffractive lens 12 is filled with the material such as resin. By arranging two diffractive lenses opposite the aperture stop St, it is possible to reduce chromatic aberration of magnification, and the two diffractive lenses form an optical system that can accommodate a light source with a wavelength width equivalent to a monochromatic LED (several tens of nanometers).

[0028] In this configuration example, image shift due to wavelength can be reduced by arranging the first diffractive lens 11 and the second diffractive lens 12 opposite the aperture stop St. In order to prevent image shift due to wavelength, it is desirable that the refractive power of the first diffractive lens 11 and the refractive power of the second diffractive lens 12 are equal. In this case, if an air layer is interposed between the first diffractive lens 11 and the second diffractive lens 12, total reflection will occur at the exit interface of the first diffractive lens 11. For this reason, total reflection can be reduced by filling the opening Sta of the aperture stop St with a material such as resin.

[0029] FIG. 5 is an explanatory diagram showing an example of an image formation state when there is image deviation in the optical system.

[0030] Between the center 31 and peripheral 32 of the imaging surface, the focal position shifts significantly due to wavelength, and if the wavelength width of the light source is too broad, the resolution decreases. For this reason, it is desirable that the light source has a wavelength width equivalent to that of a monochromatic LED (several tens of nanometers). Note that in the peripheral 32 of the imaging surface, even if there is a wavelength width, there is little position shift due to wavelength.

[0031] [1.2 Specific Configuration Examples of Optical Systems] Next, specific configuration examples of optical systems according to the first embodiment of the present disclosure will be described. Note that the meanings of symbols shown in the tables and drawings of the following specific configuration examples are as follows. "Si" indicates the number of the i-th surface, with symbols increasing sequentially from the object side. "Ri" indicates the value (mm) of the paraxial radius of curvature of the i-th surface. "Di" indicates the value (mm) of the axial distance between the i-th surface and the (i+1)-th surface. "ndi" indicates the value of the refractive index at the d-line (wavelength 587.6 nm) of the material of the optical element that comprises the i-th surface. "νdi" indicates the value of the Abbe number at the d-line of the material of the optical element that comprises the i-th surface. "φi" indicates the value (mm) of the effective diameter of the i-th surface. "DOE" in the column of surface number (Si) indicates that the surface in question is a diffractive surface. "ASP" in the column of surface number (Si) indicates that the surface in question is an aspherical surface. "IMG" indicates that the surface is an image surface.

[0032] In the following specific configuration examples, the lens surface may be a diffractive surface or an aspherical surface.

[0033] The diffractive surface is defined by the following polynomial (A) that indicates the phase change amount Φ(r): where λ is the normalized wavelength, M is the diffraction order, α is the phase coefficient, and r is the distance from the optical axis Z1.

[0034]

[0035] The aspherical shape is defined by the following formula (B): where Z(r) is positive in the direction of light travel and indicates the distance (sag) from the vertex of the lens surface in the direction of the optical axis. C indicates the curvature (the reciprocal of the radius of curvature). k indicates the conic constant. A indicates the aspherical coefficient. r indicates the distance from the optical axis Z1.

[0036]

[0037] (Configuration Example 1-1) FIG. 6 is a cross-sectional view that schematically shows a configuration example 1-1 of the optical system according to the first embodiment.

[0038] The optical system 1 according to configuration example 1-1 has, as multiple diffractive lenses, a first diffractive lens 11 and a second diffractive lens 12. The optical system 1 according to configuration example 1-1 includes, in order from the object side toward the image plane (imaging plane) IMG side, the first diffractive lens 11, an aperture stop St, and a second diffractive lens 12. In addition, a band-pass filter is provided as a filter LF on the image plane IMG side of the second diffractive lens 12.

[0039] The first diffractive lens 11 and the second diffractive lens 12 each have positive refractive power. The object-side surface of the first diffractive lens 11 and the image-plane-side surface of the second diffractive lens 12 are diffractive surfaces. The opening Sta of the aperture stop St is filled with a material such as resin.

[0040] In the optical system 1 according to configuration example 1-1, the first diffractive lens 11 and the second diffractive lens 12 are disposed opposite each other with an aperture stop St sandwiched therebetween. The first diffractive lens 11 and the second diffractive lens 12 have substantially the same focal length. This allows the first diffractive lens 11 and the second diffractive lens 12 to cancel out chromatic aberration of magnification.

[0041] Table 1 shows basic lens data for the optical system 1 according to Configuration Example 1-1. Table 2 shows coefficient values ​​representing the diffractive surface defined by the polynomial (A) in the optical system 1 according to Configuration Example 1-1.

[0042]

[0043]

[0044] FIG. 7 is an aberration diagram showing longitudinal aberration in the optical system 1 according to configuration example 1-1. FIG. 7 shows spherical aberration, astigmatism (curvature of field), and distortion as longitudinal aberrations. In the spherical aberration diagram, the solid line indicates values ​​at a wavelength of 940 nm, the dashed-dotted line indicates values ​​at a wavelength of 920 nm, and the dashed line indicates values ​​at a wavelength of 960 nm. In the astigmatism diagram, S indicates values ​​at the sagittal image plane, and T indicates values ​​at the tangential (meridional) image plane. In the astigmatism diagram and distortion diagram, values ​​at a wavelength of 940 nm are shown. "ω" indicates the angle of view. Similar aberration diagrams will be shown in the other configuration examples below.

[0045] (Configuration Example 1-2) Fig. 8 is a cross-sectional view schematically showing a configuration example 1-2 of the optical system according to the first embodiment. Fig. 9 is an aberration diagram showing longitudinal aberration in the optical system 2 according to the configuration example 1-2.

[0046] The optical system 2 according to configuration example 1-2 has, as a plurality of diffractive lenses, a first diffractive lens 11, a second diffractive lens 12, and a third diffractive lens 13. The optical system 2 according to configuration example 1-2 includes, in order from the object side toward the image plane (imaging plane) IMG side, the first diffractive lens 11, an aperture stop St, the second diffractive lens 12, and the third diffractive lens 13.

[0047] The first diffractive lens 11, the second diffractive lens 12, and the third diffractive lens 13 each have positive refractive power. The object-side surface of the first diffractive lens 11, the object-side surface of the second diffractive lens 12, and the object-side surface of the third diffractive lens 13 are diffractive surfaces. The opening Sta of the aperture stop St is filled with a material such as resin.

[0048] In the optical system 2 according to configuration example 1-2, the first diffractive lens 11 and the third diffractive lens 13 are disposed opposite each other with the aperture stop St sandwiched therebetween. The first diffractive lens 11 and the third diffractive lens 13 have substantially the same focal length. This allows the first diffractive lens 11 and the third diffractive lens 13 to cancel out chromatic aberration of magnification.

[0049] The optical system 2 according to the configuration example 1-2 can achieve optical performance that is even higher than that of the optical system 1 according to the configuration example 1-1.

[0050] Table 3 shows basic lens data for the optical system 2 according to Configuration Example 1-2. Table 4 shows coefficient values ​​representing the diffractive surface defined by the above polynomial (A) in the optical system 2 according to Configuration Example 1-2.

[0051]

[0052]

[0053] 10 is a cross-sectional view schematically showing a configuration example 1-3 of the optical system according to the first embodiment. FIG. 12 is an aberration diagram showing longitudinal aberration in the optical system 3 according to the configuration example 1-3.

[0054] The optical system 3 according to configuration example 1-3 has, as the plurality of diffractive lenses, a first diffractive lens 11 and a second diffractive lens 12. The optical system 3 according to configuration example 1-3 includes, in order from the object side toward the image plane (imaging plane) IMG side, the first diffractive lens 11, an aperture stop St, a refractive lens 21, and the second diffractive lens 12.

[0055] The first diffractive lens 11 and the second diffractive lens 12 each have positive refractive power. The object-side surface of the first diffractive lens 11 and the object-side surface of the second diffractive lens 12 are diffractive surfaces. The opening Sta of the aperture stop St is filled with a material such as resin.

[0056] In the optical system 3 according to configuration example 1-3, the first diffractive lens 11 and the second diffractive lens 12 are disposed opposite each other with the aperture stop St sandwiched therebetween. The first diffractive lens 11 and the second diffractive lens 12 have substantially the same focal length. This allows the first diffractive lens 11 and the second diffractive lens 12 to cancel out chromatic aberration of magnification.

[0057] The object-side surface of the refractive lens 21 is aspherical. The sag of the object-side surface (aspherical surface) of the refractive lens 21 is 40 μm or less. In the numerical data of the aspherical surface shown below, the maximum sag of the aspherical surface is 13 μm.

[0058] 11 shows an example of the actual shape of the refractive lens 21, which is an aspherical lens in the optical system 3 according to Configuration Example 1-3. If the curvature of the aspherical surface of the refractive lens 21 becomes too large, the amount of sag increases, and the thickness of the adhesive layer bonding the first diffractive lens 11 and the refractive lens 21 varies significantly within the lens surface, resulting in a decrease in adhesive strength and reliability in terms of preventing lens cracking. For this reason, it is desirable that the amount of sag of the aspherical surface of the refractive lens 21 be 40 μm or less.

[0059] The optical system 3 according to the configuration example 1-3 can achieve optical performance that is even higher than that of the optical system 1 according to the configuration example 1-1.

[0060] Table 5 shows basic lens data for the optical system 3 according to Configuration Examples 1 to 3. Table 6 shows coefficient values ​​representing the diffractive surface defined by the above polynomial (A) in the optical system 3 according to Configuration Examples 1 to 3. Table 7 shows coefficient values ​​representing the aspherical shape defined by the above formula (B) in the optical system 3 according to Configuration Examples 1 to 3.

[0061]

[0062]

[0063]

[0064] (Comparison of Configuration Examples) FIG. 13 is a cross-sectional view that schematically shows an optical system according to a comparative example.

[0065] The optical system 100 according to the comparative example includes, in order from the object side toward the image plane (imaging plane) IMG side, a first refractive lens L1, a second refractive lens L2, a third refractive lens L3, and an optical member GC. The lens surfaces of the first refractive lens L1, the second refractive lens L2, and the third refractive lens L3 are aspherical.

[0066] Table 8 shows basic lens data for the optical system 100 according to the comparative example. Table 9 shows the values ​​of the coefficients representing the aspherical shape defined by the above formula (B) for the optical system 100 according to the comparative example.

[0067]

[0068]

[0069] 14 shows a comparison between the specifications of the optical system 100 according to the comparative example and the specifications of the optical system 1 according to Configuration Example 1-1. Also, FIG. 15 shows a comparison between the specifications of the optical systems 1 to 3 according to Configuration Examples 1-1 to 1-3.

[0070] 14 and 15 show the wavelength of the light source, the lens configuration, and the sensor diagonal length (the diagonal length of the light receiving surface of the solid-state imaging element to which the optical system is applied) as specifications. Further specifications include the field of view (FOV), F-number (Fno), chief ray angle (CRA), total optical length (the distance on the optical axis from the surface closest to the object to the image plane IMG), and maximum optical diameter. Further specifications include the relative illumination (RI) values ​​at FOVs of 60° and 120°.

[0071] In the optical systems 1 to 3 according to the above configuration examples 1-1 to 1-3, each diffractive lens has a positive refractive power. This makes it possible to realize the power distribution necessary for chromatic aberration correction. Furthermore, in each configuration example, the light source is preferably an LED light source. An LED can be implemented more inexpensively than a laser light source.

[0072] (Configuration Example of Diffractive Lens) In the optical system according to the first embodiment, the diffractive lens may be a metalens. Diffractive lenses of other types than metalens have diffraction efficiencies of approximately 80% or less. In contrast, metalens have diffraction efficiencies of approximately 90%, which is high efficiency.

[0073] The diffractive lens may be a metalens, a transmission grating, a blazed grating, or a volume phase holographic grating.

[0074] (Specific example of metalens) The material of the substrate of the metalens is, for example, glass (SiO ２ , Fused Silica, BK7, Quartz), or a resin substrate. The pillar material of the metasurface in the metalens may be, for example, titanium oxide (TiO), silicon, polysilicon (Poly-Si), or amorphous silicon (a-Si). The protective layer of the metasurface may be composed of, for example, silicon oxide, silicon nitride, silicon oxynitride, silicon carbide, Fused Silica, BK7, Quartz, siloxane-based resin, styrene-based resin, acrylic resin, or the like. The protective layer of the metasurface may be composed of a material in which any of these resins contains fluorine.

[0075] (Specific example of material filled in aperture stop St) In the optical system according to the first embodiment, it is preferable that the refractive index of the material filled in aperture stop Sta is 1.3 or more. If the refractive index of the material is too small, the ability to correct chromatic aberration of magnification decreases. If the refractive index of the material is too low, the critical angle of the exit surface of first diffractive lens 11 becomes small. As a result, it becomes difficult to provide first diffractive lens 11 with sufficient power equivalent to the required amount of chromatic aberration correction.

[0076] Furthermore, the material filled in the opening Sta may be a resin. For example, a UV-curable resin or a thermosetting resin may be used. Furthermore, the material filled in the opening Sta may be a material other than a resin, such as oil, glycerin, or water. When the material filled inside the aperture stop St is a resin, for example, in the configuration of the optical system 2 according to the above-described configuration example 1-2, the first diffractive lens 11, the aperture stop St, and the second diffractive lens 12 can be bonded together, making stacking easy.

[0077] (Modification) For example, the optical system 2 according to Configuration Example 1-2 may have a configuration in which the order of the aperture stop St and the second diffractive lens 12 is changed. That is, the first diffractive lens 11, the second diffractive lens 12, the aperture stop St, and the third diffractive lens 13 may be arranged in this order from the object side toward the image plane (imaging plane) IMG side.

[0078] Furthermore, the optical system 3 according to Configuration Examples 1-3 may have a configuration in which the order of the aperture stop St and the refractive lens 21 is changed. That is, the first diffractive lens 11, the refractive lens 21, the aperture stop St, and the second diffractive lens 12 may be arranged in this order from the object side toward the image plane (imaging plane) IMG side.

[0079] [1.3 Configuration Example of Imaging Device] FIG. 16 is a cross-sectional view showing a configuration example of the imaging device according to the first embodiment.

[0080] The imaging device according to the first embodiment may be configured to include the optical system according to the first embodiment described above and a solid-state imaging element 101 that outputs an imaging signal corresponding to the optical image formed by the optical system.

[0081] 16 shows an example of the configuration of an imaging device according to the first embodiment, which includes a solid-state imaging element with a CSP structure (CSP solid-state imaging element 120). The imaging device according to the first embodiment includes a solid-state imaging element 101, a glass substrate 102, and an optical system 104. The imaging device according to the first embodiment also includes a circuit board 106, a connector 108, a spacer 109, a semiconductor component 110, a fixing agent 111, a thin circuit board 112, an adhesive 131, and a black resin 141. The CSP solid-state imaging element 120 includes the solid-state imaging element 101, the glass substrate 102, the adhesive 131, and the black resin 141.

[0082] The solid-state imaging element 101 is an imaging element such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor, etc. The solid-state imaging element 101 has a light receiving surface formed by arranging light receiving elements in a two-dimensional lattice pattern.

[0083] The glass substrate 102 has a first surface and a second surface facing each other. The light receiving surface of the solid-state imaging element 101 is disposed opposite the first surface of the glass substrate 102, and the optical system 104 is disposed opposite the second surface of the glass substrate 102.

[0084] The adhesive 131 is a transparent adhesive (GLUE) that bonds the solid-state imaging element 101 and the glass substrate 102 together.

[0085] The optical system 104 forms a subject image on the light receiving surface of the solid-state imaging device 101. As the optical system 104, the optical systems 1 to 3 according to the above configuration examples 1-1 to 1-3 can be applied.

[0086] The black resin 141 is a black mask that cuts out light that is emitted from the optical system 104 and that is outside the light-receiving surface of the solid-state imaging element 101. The black resin 141 is also a cavity layer that functions as a spacer for connecting the optical system 104 and the solid-state imaging element 101 in parallel.

[0087] The circuit board 106 is a board that outputs an electric signal (image signal) from the solid-state image sensor 101 to the outside. The connector 108 is a connector for connecting the image signal to an external device. The spacer 109 is a spacer with a built-in circuit that fixes an actuator (not shown) to the circuit board 106.

[0088] The semiconductor components 110 are components such as a capacitor mounted on the circuit board 106 and the spacer 109 and a control LSI (Large Scale Integration) for an actuator (not shown).

[0089] The fixing agent 111 fixes the solid-state imaging element 101 (CSP solid-state imaging element 120), the optical system 104, and the semiconductor component 110. The fixing agent 111 is made of a material that has the characteristic of reducing refracted and reflected light at the side surfaces of the optical system 104 and the solid-state imaging element 101.

[0090] The thin circuit board 112 is connected to the solid-state imaging element 101 and outputs an imaging signal from the solid-state imaging element 101 to the circuit board 106 .

[0091] The imaging device according to the first embodiment can be miniaturized, including the optical system, while avoiding flare and ghosting caused by reflected light (see FIGS. 1 and 2 ) and ensuring the strength of the entire CSP solid-state imaging element 120. In the configuration shown in FIG. 2 , the thickness h2 of the glass substrate 102 and adhesive 131 disposed on the solid-state imaging element 101 is reduced, thereby reducing the strength of the solid-state imaging element 101 (CSP solid-state imaging element 120). In the imaging device according to the first embodiment, the strength can be improved by applying the optical system according to the first embodiment as the optical system 104.

[0092] [1.4 Effects] As described above, according to the optical system of the first embodiment, the configuration of the multiple diffractive lenses and the aperture stop St is optimized to enable miniaturization and high performance, thereby making it possible to provide an optical system and an imaging device that can achieve miniaturization and high performance.

[0093] The optical system according to the first embodiment can suppress image shift due to wavelength change by optimizing the configuration of the multiple diffractive lenses and the aperture stop St. The optical system according to the first embodiment can realize a small, low-cost optical system that can accommodate a light source with a wavelength width equivalent to that of a monochromatic LED (several tens of nanometers).

[0094] The effects described in this specification are merely examples and are not limiting, and other effects may also be achieved. The same applies to the effects of other embodiments described below.

[0095] 2. Second Embodiment [2.0 Comparative Example] Recent camera modules for mobile devices tend to have higher resolution sensor devices and smaller modules. While metalenses are used as a means of miniaturization, it is difficult to achieve good MTF imaging performance with a single lens, focusing light into a small spot at the high Nyquist frequency of the fine pixels. A method of combining a metalense with an aspherical lens to improve optical characteristics (see Patent Document 2) exists, but this method results in increased size due to an increase in the overall optical length and degradation of optical characteristics due to decentering errors in multiple lens groups. The optical system proposed in Patent Document 2 is configured by simply replacing some of the conventional module lenses with metalenses, and therefore has limited contribution to miniaturization in the in-plane direction perpendicular to the optical axis.

[0096] [2.1 Overview of Optical System and Imaging Apparatus] FIG. 17 is a cross-sectional view that schematically illustrates an overview of an optical system and an imaging apparatus according to a second embodiment of the present disclosure.

[0097] The imaging device according to the second embodiment includes the optical system according to the second embodiment and an imaging element 200 that receives light via the optical system.

[0098] The optical system includes, in order from the object side to the image plane side, a first lens 11A having a first surface and a second surface as optical surfaces, and a second lens 12A having a third surface and a fourth surface as optical surfaces. In the first lens 11A, the first surface, which is the object side surface, and the second surface, which is the image plane side surface, are both planar. In the second lens 12A, the third surface, which is the object side surface, and the fourth surface, which is the image plane side surface, are both planar.

[0099] Light from the object plane passes through the first lens 11A and the second lens 12A in this order, and is focused on an image plane IMG (imaging plane). The optical system is arranged so that the imaging plane coincides with the imaging plane of the image sensor 200. The image sensor 200 has a plurality of pixels arranged two-dimensionally, and converts the secondary optical image formed by the optical system into an electrical signal according to the light intensity distribution, and outputs the electrical signal as an imaging signal.

[0100] The first lens 11A and the second lens 12A are compound lenses cemented together. The third surface of the second lens 12A is cemented to the second surface of the first lens 11A without an air gap between them. Of the first to fourth surfaces, at least the second or third surface is a phase modulation surface Sp. In the configuration example of FIG. 17 , the third surface is a phase modulation surface Sp, but the second surface, rather than the third surface, may be a phase modulation surface Sp. Furthermore, at least one of the first and fourth surfaces may be a phase modulation surface Sp. A phase modulation surface Sp is a surface through which a phase change of light occurs when light passes through that surface.

[0101] In the optical system, the first lens 11A and the second lens 12A are made of a lens material with a refractive index greater than 1. The optical system and the image sensor 200 are cemented together. In the image pickup device, a medium with a refractive index greater than 1 is provided so as to fill the space from the fourth surface of the optical system to the image plane IMG (image pickup surface) without an air gap. An optical filter GF (Configuration Example 2-1) or an optical member GL (Configuration Examples 2-1, 2-2, and 2-3), which will be described later, may be disposed between the fourth surface and the image pickup surface as a medium with a refractive index greater than 1. This results in a structure in the image pickup device where no air gap is present between the first surface and the image plane IMG (image pickup surface).

[0102] Furthermore, the optical system is provided with an aperture stop St near surface 1. The aperture stop St may be disposed in close contact with the object side of surface 1 as in Configuration Example 2-1 described later, or may be disposed at a distance from the object side of surface 1 as in Configuration Examples 2-2 and 2-3 described later.

[0103] [2.2 Functions and Effects] According to the optical system according to the second embodiment, it is possible to realize a small, high-resolution, and bright optical system. This will be specifically described below.

[0104] (Regarding miniaturization) Fig. 18 is an explanatory diagram showing an example of a state in which a light ray passes through an optical system according to a comparative example. Fig. 19 is an explanatory diagram showing an example of a state in which a light ray passes through when the first lens 11A is disposed on the object side of the phase modulation surface Sp.

[0105] By arranging the first lens 11A on the object side of the phase modulation surface Sp as in the configuration example of Figure 19, there is an effect of lowering the ray height x, and the effective diameter can be made smaller, thereby realizing miniaturization in the in-plane direction. In contrast, when configured with only the phase modulation surface Sp as in the optical system according to the comparative example of Figure 18, the ray height x at the phase modulation surface Sp is expressed as in equation (1) using the angle of view α. A is the aperture diameter, d is the distance between the aperture stop St and the phase modulation surface Sp, and f is the distance between the phase modulation surface Sp and the image plane IMG. -A / 2+dtanα<x<A / 2+dtanα ... (1)

[0106] The optical system according to the second embodiment differs from the optical system according to the comparative example in that the first lens 11A is disposed on the object side of the phase modulation surface Sp, as shown in Fig. 19 . In the configuration example of Fig. 19 , the ray height x at the phase modulation surface Sp is expressed as in equation (2) using angle β. Furthermore, angle β is expressed as in equation (3) using angle of view α. Because angle β can be relaxed due to the influence of the refractive index of the first lens 11A, in the optical system according to the second embodiment, the ray height x can be reduced by equations (2) and (3).

[0107] -A / 2+dtanβ<x<A / 2+dtanβ...(2) β=asin(sinα / n)...(3)

[0108] (High-Resolution, Bright Optical System) FIG. 20 is an explanatory diagram showing an example of the state of light rays passing when the second lens 12A is disposed on the image plane side of the phase modulation surface Sp.

[0109] As in the configuration example of Figure 20, by placing the second lens 12A on the image plane side of the phase modulation surface Sp, there is an effect of reducing the spot diameter Ds, and high-resolution imaging can be achieved. The formula for calculating the spot diameter Ds is shown in equation (4). λ is the design wavelength of the phase modulation surface Sp, F is the Fno of the phase modulation surface Sp, NA is the numerical aperture of the phase modulation surface Sp, and n is the refractive index of the second lens 12A. Ds = λF = λ / (2NA) = λ / (2n sin θ) ... (4)

[0110] Table 10 shows the results of comparing the specifications of the optical system according to the comparative example in FIG. 18 with those of optical systems according to configuration examples 2-1 and 2-2, which will be described later. It can be seen that in configuration examples 2-1 and 2-2, which will be described later, the NA increases due to the influence of the refractive index of the second lens 12A, resulting in a small spot diameter Ds. In the optical system according to the comparative example, the medium in the portion of the second lens 12A is air, so the NA cannot, in principle, exceed 1. In the optical system according to the second embodiment, by using a medium with a refractive index greater than 1 for the second lens 12A, an NA of 1 or greater can, in principle, be achieved, which contributes to a reduction in the imaging spot diameter Ds for higher resolution.

[0111] In addition, the optical system according to the second embodiment can achieve a small F-number, thereby realizing a bright optical system. Furthermore, as described above, by lowering the ray height x, an optical effective diameter without vignetting can be ensured, thereby eliminating vignetting even in the peripheral areas. Therefore, a bright optical system with little peripheral light falloff can be provided even in a wide-angle lens system.

[0112]

[0113] As described above, according to the optical system of the second embodiment, the space between the phase modulation surface Sp and the image surface IMG is filled with a medium having a refractive index greater than 1 without an air layer in between, so that in principle, a bright, high-resolution lens can be realized since the NA can exceed 1. Furthermore, by arranging the first lens 11A on the object side of the phase modulation surface Sp, the ray height x at the phase modulation surface Sp can be lowered, so that the lens edge and lens holder can be eliminated, and a low-profile, compact optical module can be realized.

[0114] Furthermore, in the optical system according to the second embodiment, the first surface and the phase modulation surface Sp can bend the ray angle in stages to reduce the ray height x while creating a nearly telecentric optical system, thereby realizing a compact optical module with a wide angle and little peripheral shading.

[0115] Furthermore, in the optical system according to the second embodiment, since there is no air gap between the first surface and the image plane IMG (imaging plane), it is possible to reduce assembly costs, such as by eliminating the need for a lens holder, thereby realizing miniaturization and cost reduction. Since there is no air gap between the first surface and the image plane IMG (imaging plane), it is possible to prevent dust from adhering to the interior of the optical system and to prevent foreign matter from entering from the outside. Furthermore, since a medium with a refractive index greater than 1 is disposed between the fourth surface and the imaging plane, it is easy to design a filter film.

[0116] [2.3 Specific Configuration Examples of Optical Systems] (Configuration Example 2-1) FIG. 21 is a cross-sectional view schematically illustrating Configuration Example 2-1 of an optical system according to the second embodiment. Table 11 shows the design wavelength λ of the phase modulation surface Sp in the optical system 1A according to Configuration Example 2-1, the focal length f of the entire system, the F-number (Fno), the image height Y, and the total optical length L (the distance on the optical axis from the surface closest to the object to the image plane IMG). Table 12 shows basic lens data for the optical system 1A according to Configuration Example 2-1. In Table 12, "Si" indicates the number of the i-th surface, with symbols sequentially increasing from the surface closest to the object. "Ri" indicates the value (mm) of the paraxial radius of curvature of the i-th surface. "Di" indicates the value (mm) of the distance on the optical axis between the i-th surface and the (i+1)-th surface. "ndi" indicates the value of the refractive index at the d-line (wavelength 587.6 nm) of the material of the optical element comprising the i-th surface. "νdi" indicates the Abbe number at the d-line of the material of the optical element that has the i-th surface. "STO" in the surface number (Si) column indicates that the aperture stop St is located at the corresponding position. "IMG" indicates that the corresponding surface is the image plane.

[0117] Table 13 shows the values ​​of the coefficients that define the phase modulation surface Sp in the optical system 1A according to configuration example 2-1. λ represents the normalized wavelength, and M represents the diffraction order. The phase modulation surface Sp is defined by the following polynomial (C) that represents the phase change amount Φ. R is the distance (radius) from the optical axis Z1 within the lens surface, and is specified by the coefficient Cn of the phase polynomial, and Φ represents the phase amount, expressed in mm.

[0118]

[0119]

[0120]

[0121]

[0122] The optical system 1A according to configuration example 2-1 includes, in order from the object side to the image plane side, an aperture stop St, a first lens 11A having first and second optical surfaces, a second lens 12A having third and fourth optical surfaces, an optical filter GF made of a medium having a refractive index greater than 1, and an optical member GL.

[0123] The aperture stop St is disposed on the object side of the first lens 11A via an air layer. The aperture stop St is disposed on the object side with a gap therebetween from the first surface.

[0124] In the optical system 1A, the first lens 11A and the second lens 12A are cemented to each other without an air gap. The second lens 12A and the optical filter GF are also cemented to each other without an air gap. A medium having a refractive index greater than 1, including the optical filter GF and the optical member GL, is provided so as to fill the space from the fourth surface of the second lens 12A to the image plane IMG (imaging plane) without an air gap. The optical system 1A is disposed so that the image plane IMG (imaging plane) coincides with the imaging plane of the image sensor 200. This results in a structure in which no air gap is present between the first surface and the image plane IMG.

[0125] The first lens 11A is a glass substrate having planar first and second surfaces. The second lens 12A is a glass substrate having planar third and fourth surfaces, with the third surface cemented to the second surface of the first lens 11A without an air gap. The third surface of the second lens 12A is a phase modulation surface Sp. The third phase modulation surface Sp has a positive focal length, allowing the second lens 12A to function as a lens.

[0126] The optical filter GF is a filter that transmits only light in a required wavelength band from among the wavelength components of the incident light and blocks light in unnecessary wavelength bands. For example, a band pass filter (BPF) is used as the optical filter GF when passing light with a narrow wavelength width, such as an infrared laser. Furthermore, if the optical system 1A is a lens that forms an image of light in the visible light range, an IR (infrared) cut filter is used. The optical filter GF achieves desired spectral characteristics by using a coating configured by stacking multiple transmission films.

[0127] In the optical system 1A according to configuration example 2-1, the optical filter GF is disposed with its filter surface in contact with the fourth surface. The optical filter GF may be formed by coating a film having the desired spectral characteristics on a flat substrate different from the second lens 12A, and then bonding the filter surface to the fourth surface. Note that the function of the optical filter GF may be realized by directly coating the fourth surface with a film having the desired spectral characteristics.

[0128] FIG. 22 is a cross-sectional view showing an example of the structure of the phase modulation surface Sp.

[0129] A typical example of a phase modulation surface Sp is a metasurface structure using a dielectric. Figure 22 shows an example of a cross-sectional view of a metasurface structure as an example of the structure of a phase modulation surface Sp. This metasurface structure includes a first substrate 41 with flat surfaces on both sides, a second substrate 42 with flat surfaces on both sides, and an intermediate layer 50 disposed between the first substrate 41 and the second substrate 42. Multiple nanostructures smaller than the wavelength of the incident light are disposed in the intermediate layer 50, and a filler material 51 is filled in the area other than the nanostructures. A typical nanostructure is a cylindrical pillar 52 made of a dielectric. By adjusting the diameter and pitch of the multiple pillars 52, it is possible to impart a phase to the light that varies depending on the position of the pillar 52. This allows for the desired optical characteristics to be achieved. In the optical system 1A according to configuration example 2-1, the wavelength of the incident light is 940 nm, and a-Si, for example, can be used as the dielectric that constitutes the pillars 52. The height of the pillars 52 can be, for example, 800 nm, and the pillars can be disposed at intervals of 370 nm. A filler 51 is filled between the first substrate 41 and the second substrate 42 so as to bury the columns 52. The filler 51 is transparent, and a material having a large refractive index difference from that of the columns 52 is used. When, for example, a CVD (Chemical Vapor Deposition) method is used as a manufacturing method, a silicon oxide film is formed as the filler 51. However, the filler 51 is not limited to a silicon oxide film, and other inorganic or organic materials can be used. Although the phase modulation surface Sp actually has a finite thickness, considering it as a surface does not significantly affect the lens performance, so it is treated as a surface here. The same applies to the other configuration examples described below.

[0130] (Configuration Example 2-2) FIG. 23 is a cross-sectional view schematically illustrating Configuration Example 2-2 of the optical system according to the second embodiment. [Table 14] shows the values ​​of the design wavelength λ of the phase modulation surface Sp in the optical system 2A according to Configuration Example 2-2, the focal length f of the entire system, the F-number (Fno), the image height Y, and the total optical length L (the distance on the optical axis from the surface closest to the object to the image plane IMG). [Table 15] shows basic lens data for the optical system 2A according to Configuration Example 2-2. [Table 16] shows the values ​​of coefficients that define the phase modulation surface Sp in the optical system 2A according to Configuration Example 2-2. The meanings of the symbols in each table are the same as those in Configuration Example 2-1 above.

[0131]

[0132]

[0133]

[0134] The optical system 2A according to configuration example 2-2 comprises, in order from the object side to the image plane side, an aperture stop St, a first lens 11A having first and second optical surfaces, a second lens 12A having third and fourth optical surfaces, and an optical member GL made of a medium having a refractive index greater than 1.

[0135] The aperture stop St is disposed in close contact with the object side of the first surface of the first lens 11 A. The aperture stop St may have a structure in which an aperture structure is bonded to the object side of the first lens 11 A, or may have a structure in which a low-reflection resist material is patterned by photolithography on the first surface of the first lens 11 A.

[0136] In the optical system 2A, the first lens 11A and the second lens 12A are cemented to each other without an air gap. Furthermore, the second lens 12A and the optical member GL are cemented to each other without an air gap. A medium having a refractive index greater than 1, including the optical member GL, is provided so as to fill the space from the fourth surface of the second lens 12A to the image plane IMG (imaging plane) without an air gap. The optical system 2A is disposed so that the image plane IMG (imaging plane) coincides with the imaging plane of the image sensor 200. This results in a structure in which no air gap is present between the first surface and the image plane IMG.

[0137] The first lens 11A is a glass substrate having planar first and second surfaces. The second lens 12A is a glass substrate having planar third and fourth surfaces, with the third surface cemented to the second surface of the first lens 11A without an air gap between them. In the first lens 11A, the first surface is a phase modulation surface Sp. In the second lens 12A, the third surface is a phase modulation surface Sp. The phase modulation surface Sp of the first surface and the phase modulation surface Sp of the third surface each have a positive focal length, so that the first lens 11A and the second lens 12A each have a lens function.

[0138] According to the optical system 2A of configuration example 2-2, by providing a phase modulation surface Sp on each of the first and third surfaces, it is possible to correct aberrations over a wider range of pupil diameters, thereby realizing an optical system with a very high NA (small Fno).

[0139] (Configuration Example 2-3) FIG. 24 is a cross-sectional view schematically illustrating Configuration Example 2-3 of the optical system according to the second embodiment. Table 17 shows the values ​​of the design wavelength λ of the phase modulation surface Sp in the optical system 3A according to Configuration Example 2-3, the focal length f of the entire system, the F-number (Fno), the image height Y, and the total optical length L (the distance on the optical axis from the surface closest to the object to the image plane IMG). Table 18 shows basic lens data for the optical system 3A according to Configuration Example 2-3. Table 19 shows the values ​​of coefficients that define the phase modulation surface Sp in the optical system 3A according to Configuration Example 2-3. The meanings of the symbols in each table are the same as those in Configuration Example 2-1 above.

[0140]

[0141]

[0142]

[0143] The optical system 3A according to configuration example 2-3 includes, in order from the object side to the image plane side, an aperture stop St, a first lens 11A having first and second optical surfaces, a second lens 12A having third and fourth optical surfaces, and an optical member GL made of a medium having a refractive index greater than 1.

[0144] The aperture stop St is disposed in close contact with the object side of the first surface of the first lens 11 A. The aperture stop St may have a structure in which an aperture structure is bonded to the object side of the first lens 11 A, or may have a structure in which a low-reflection resist material is patterned by photolithography on the first surface of the first lens 11 A.

[0145] In the optical system 3A, the first lens 11A and the second lens 12A are cemented to each other without an air gap. Furthermore, the second lens 12A and the optical member GL are cemented to each other without an air gap. A medium having a refractive index greater than 1, including the optical member GL, is provided so as to fill the space from the fourth surface of the second lens 12A to the image plane IMG (imaging plane) without an air gap. The optical system 3A is disposed so that the image plane IMG (imaging plane) coincides with the imaging plane of the image sensor 200. This results in a structure in which no air gap is present between the first surface and the image plane IMG.

[0146] The first lens 11A is a glass substrate having planar first and second surfaces. The second lens 12A is a glass substrate having planar third and fourth surfaces, with the third surface cemented to the second surface of the first lens 11A without an air gap. In the first lens 11A, the first surface is a phase modulation surface Sp. In the second lens 12A, the third and fourth surfaces are each a phase modulation surface Sp. The phase modulation surface Sp of the first surface and the phase modulation surface Sp of the third surface each have a positive focal length. This allows the first lens 11A and the second lens 12A to each have a lens function.

[0147] According to the optical system 3A of configuration example 2-3, by providing a phase modulation surface Sp on each of the first, third, and fourth surfaces, it is possible to correct aberrations over a wider range of pupil diameters, thereby realizing an optical system with a very high NA (small Fno).

[0148] 3. Other Embodiments The technology according to the present disclosure is not limited to the above-described embodiments, and various modifications are possible.

[0149] For example, the shapes and numerical values ​​of each part of the optical system shown in each of the above embodiments are merely examples of specific embodiments for implementing the present technology, and the technical scope of the present technology should not be interpreted in a limited manner based on these.

[0150] For example, the present technology can be configured as follows. According to the present technology configured as follows, the configuration is optimized to achieve miniaturization and high performance. This makes it possible to provide a small, low-cost optical system and imaging device.

[0151] (1) An optical system comprising: a plurality of diffractive lenses; and an aperture stop disposed between any two of the plurality of diffractive lenses, the aperture being filled with a substance. (2) The optical system according to (1), having a first diffractive lens and a second diffractive lens as the plurality of diffractive lenses, comprising, in order from the object side to the image plane side, the first diffractive lens, the aperture stop, and the second diffractive lens. (3) The optical system according to (2), in which the object side surface of the first diffractive lens and the image plane side surface of the second diffractive lens are diffractive surfaces. (4) The optical system according to (1), having a first diffractive lens, a second diffractive lens, and a third diffractive lens as the plurality of diffractive lenses. (5) The optical system according to (4), comprising, in order from the object side to the image plane side, the first diffractive lens, the aperture stop, the second diffractive lens, and the third diffractive lens. (6) The optical system according to (5) above, wherein the object-side surface of the first diffractive lens, the object-side surface of the second diffractive lens, and the object-side surface of the third diffractive lens are diffractive surfaces. (7) The optical system according to (1) above, wherein the plurality of diffractive lenses include a first diffractive lens and a second diffractive lens, and wherein, in order from the object side to the image plane side, the first diffractive lens, the aperture stop, a refractive lens, and the second diffractive lens are provided. (8) The optical system according to (7) above, wherein the object-side surface of the first diffractive lens and the object-side surface of the second diffractive lens are diffractive surfaces. (9) The optical system according to (7) or (8) above, wherein the sag amount of the object-side surface of the refractive lens is 40 μm or less. (10) The optical system according to any one of (1) to (9) above, wherein the refractive index of the material filled in the aperture is 1.3 or more. (11) The optical system according to any one of (1) to (10) above. (12) The optical system according to any one of (1) to (11) above, wherein each of the plurality of diffractive lenses has a positive refractive power. (13) The optical system according to any one of (1) to (12) above, wherein each of the plurality of diffractive lenses is a metalens.(14) The optical system according to any one of (1) to (13) above, into which light from an LED light source is incident. (15) An imaging device including an optical system and a solid-state imaging element that outputs an imaging signal corresponding to an optical image formed by the optical system, wherein the optical system comprises: a plurality of diffractive lenses; and an aperture stop whose opening is filled with a substance, disposed between any two diffractive lenses of the plurality of diffractive lenses. (16) The imaging device according to (15) above, further including a glass substrate having a first surface and a second surface opposed to each other, wherein a light receiving surface of the solid-state imaging element is disposed opposite the first surface of the glass substrate, and the optical system is disposed opposite the second surface of the glass substrate. (17) An optical system comprising, in order from the object side to the image plane side, a first lens having a first surface and a second surface, the first surface and the second surface being planar; a second lens having a third surface and a fourth surface, the third surface and the fourth surface being planar, the third surface being cemented to the second surface without an air gap; and a medium having a refractive index greater than 1, the medium being provided so as to fill the area from the fourth surface to the image plane without an air gap, wherein at least the second surface or the third surface of the first surface to the fourth surface is a phase modulation surface. (18) The optical system according to (17) above, wherein the phase modulation surface is a metasurface on which a plurality of structures smaller than the wavelength of incident light are arranged. (19) The optical system according to (17) or (18) above, further comprising an aperture stop arranged in close contact with the first surface on the object side, or arranged at a distance from the first surface on the object side.(20) An imaging device including an optical system and an imaging element that receives light via the optical system, wherein the optical system comprises, in order from the object side to the image plane side, a first lens having a first surface and a second surface, the first surface and the second surface being planar; a second lens having a third surface and a fourth surface, the third surface and the fourth surface being planar, the third surface being cemented to the second surface without an air gap; and a medium having a refractive index greater than 1 that is provided so as to fill the space from the fourth surface to the imaging element without an air gap, wherein at least the second surface or the third surface of the first surface to the fourth surface is a phase modulation surface.

[0152] This application claims priority based on Japanese Patent Application No. 2024-34163, filed on March 6, 2024, in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0153] Those skilled in the art will recognize that various modifications, combinations, subcombinations, and variations may occur depending on design requirements and other factors, and are intended to be within the scope of the appended claims and their equivalents.

Claims

1. An optical system comprising: a plurality of diffractive lenses; and an aperture stop, the aperture of which is filled with a substance, disposed between any two of the plurality of diffractive lenses.

2. The optical system according to claim 1, wherein the plurality of diffractive lenses include a first diffractive lens and a second diffractive lens, and the optical system comprises, in order from the object side to the image plane side, the first diffractive lens, the aperture stop, and the second diffractive lens.

3. The optical system according to claim 2, wherein the object side surface of said first diffractive lens and the image plane side surface of said second diffractive lens are diffractive surfaces.

4. The optical system according to claim 1, wherein the plurality of diffractive lenses include a first diffractive lens, a second diffractive lens, and a third diffractive lens.

5. The optical system according to claim 4, comprising, in order from the object side to the image plane side, the first diffractive lens, the aperture stop, the second diffractive lens, and the third diffractive lens.

6. The optical system according to claim 5, wherein the object-side surface of the first diffractive lens, the object-side surface of the second diffractive lens, and the object-side surface of the third diffractive lens are diffractive surfaces.

7. The optical system according to claim 1, wherein the plurality of diffractive lenses include a first diffractive lens and a second diffractive lens, and the optical system comprises, in order from the object side to the image plane side, the first diffractive lens, the aperture stop, a refractive lens, and the second diffractive lens.

8. The optical system according to claim 7, wherein the object-side surface of the first diffractive lens and the object-side surface of the second diffractive lens are diffractive surfaces.

9. The optical system according to claim 7, wherein the sag of the object-side surface of said refractive lens is 40 μm or less.

10. The optical system according to claim 1, wherein the refractive index of the material filled in the opening is 1.3 or more.

11. The optical system according to claim 1, wherein the substance filled in the opening is a resin.

12. The optical system according to claim 1, wherein each of the plurality of diffractive lenses has a positive refractive power.

13. The optical system of claim 1, wherein each of the plurality of diffractive lenses is a metalens.

14. The optical system according to claim 1, wherein light is incident from an LED light source.

15. An imaging device comprising an optical system and a solid-state imaging element that outputs an imaging signal corresponding to an optical image formed by said optical system, said optical system comprising: a plurality of diffractive lenses; and an aperture stop whose opening is filled with a substance and is disposed between any two of said plurality of diffractive lenses.

16. The imaging device according to claim 15, further comprising a glass substrate having a first surface and a second surface facing each other, wherein the light receiving surface of the solid-state imaging element is disposed opposite the first surface of the glass substrate, and the optical system is disposed opposite the second surface of the glass substrate.

17. An optical system comprising, in order from the object side to the image plane side, a first lens having a first surface and a second surface, the first surface and the second surface being flat; a second lens having a third surface and a fourth surface, the third surface and the fourth surface being flat, the third surface being cemented to the second surface without an air gap; and a medium having a refractive index greater than 1 that is provided so as to fill the space from the fourth surface to the image plane without an air gap, wherein of the first surface to the fourth surface, at least the second surface or the third surface is a phase modulation surface.

18. The optical system according to claim 17, wherein the phase modulation surface is a metasurface in which a plurality of structures smaller than the wavelength of incident light are arranged.

19. The optical system according to claim 17, further comprising an aperture stop arranged in close contact with the first surface on the object side, or arranged at a distance from the first surface on the object side.

20. An imaging device comprising an optical system and an imaging element that receives light via the optical system, wherein the optical system comprises, in order from the object side to the image plane side, a first lens having a first surface and a second surface, the first surface and the second surface being planar; a second lens having a third surface and a fourth surface, the third surface and the fourth surface being planar, the third surface being cemented to the second surface without an air gap; and a medium having a refractive index greater than 1 that is provided so as to fill the space from the fourth surface to the imaging element without an air gap, wherein at least the second surface or the third surface of the first surface to the fourth surface is a phase modulation surface.

Images