Optical elements, optical instruments, imaging devices

Abstract

To reduce uneven refractive index while maintaining diffraction efficiency.SOLUTION: An optical element comprises: a first optical layer; a second optical layer; and a transparent base material, the first optical layer disposed between the second optical layer and the transparent base material, and a diffraction grating formed on a boundary face between the first optical layer and the second optical layer. Refractive index of d-line of the second optical layer is greater than refractive index of d-line of the first optical layer, and Abbe number of the second optical layer is greater than Abbe number of the first optical layer. The first optical layer includes first resin and inorganic particles dispersed in the first optical layer. The second optical layer includes second resin the elastic modulus of which is 0.1 GPa or more and 3.0 GPa or less at 22°C or more and 24°C or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical element.

Background Art

[0002] When white light passes through a lens, chromatic aberration occurs because the refractive index varies depending on the color. Therefore, in a diffractive optical system, a technique is known in which chromatic aberration is reduced and diffraction efficiency is improved by laminating resins made of materials having different dispersion characteristics.

[0003] For example, Patent Document 1 proposes a diffractive optical element in which a high-refractive-index and low-dispersion material having a diffractive grating shape on its surface and zirconia fine particles dispersed as inorganic fine particles in an organic resin, and a low-refractive-index and high-dispersion material having a diffractive grating shape on its surface and ITO fine particles dispersed as inorganic fine particles in an organic resin are laminated.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The thickness of low-refractive-index, high-dispersion materials is not uniform because they have a diffraction grating shape on their surface. Therefore, gaps are created in the film thickness of high-refractive-index, low-dispersion materials. Because the amount of shrinkage during curing differs depending on the film thickness, strain occurs within the high-refractive-index, low-dispersion material, resulting in residual stress. This residual stress tends to increase in correlation with the elastic modulus of the high-refractive-index, low-dispersion material. High-refractive-index, low-dispersion materials containing dispersed inorganic fine particles generally have a high elastic modulus, leading to excessive residual stress and causing refractive index unevenness within the material. When light is incident on a high-refractive-index, low-dispersion material with refractive index unevenness, a phase difference occurs compared to when light is incident on a high-refractive-index, low-dispersion material without refractive index unevenness. In the defocused state, ring-shaped unevenness may occur, where the density increases in correlation with the phase difference. Therefore, the present invention aims to provide laminated optical elements and optical instruments with reduced refractive index unevenness. [Means for solving the problem]

[0006] A means for solving the above problem is an optical element having a first optical layer, a second optical layer, and a transparent substrate, wherein the first optical layer is disposed between the second optical layer and the transparent substrate, and a diffraction grating is formed at the interface between the first optical layer and the second optical layer, The refractive index of the d line in the second optical layer is higher than the refractive index of the d line in the first optical layer. The Abbe number of the second optical layer is higher than the Abbe number of the first optical layer. The first optical layer consists of a first resin and inorganic particles dispersed in the first resin. The second optical layer is made of a second resin having an elastic modulus of 0.1 GPa to 3.0 GPa at at least one temperature in the range of 22°C to 24°C. The second resin is an enthiol-based resin, and the inorganic particles dispersed in the first resin are indium tin compounds, which are transparent and conductive substances. The proportion of inorganic particles in the first resin is between 10.8% and 16.76% and The average primary particle diameter of the inorganic particles is between 3 nm and 20 nm. the law of nature, The diffraction efficiency of the optical element in the visible light region is 99% or more, and the phase difference near the central ring body generated when the second resin is irradiated with a laser using a laser interferometer is 40 nm or less. It is characterized by the following. [Effects of the Invention]

[0007] This technology offers advantages in reducing refractive index unevenness while maintaining diffraction efficiency. [Brief explanation of the drawing]

[0008] [Figure 1] These are a top view and a side view of the optical element according to this embodiment. [Figure 2] This is a schematic diagram showing a method for manufacturing optical elements. [Figure 3] This is a schematic diagram showing the manufacturing method of the evaluation sample used in the example. [Figure 4] This table shows the evaluation results for the examples and comparative examples. [Figure 5] This is an explanatory diagram of an imaging device as an example of a device using an optical element according to the embodiment. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the embodiments described below are only one embodiment of the invention and are not limited thereto. Common components will be described with reference to multiple drawings, and components with common reference numerals will be omitted from description as appropriate. Different items with the same name can be distinguished by adding "item number ○," such as "item number 1," "item number 2," etc.

[0010] <First Embodiment> Figure 1 shows a top view and a side view of the optical element 100 according to this embodiment.

[0011] The optical element 100 is composed of a substrate 10, a resin part 1 provided on the substrate 10, a resin part 2 provided on the resin part 1, and a substrate 11 provided on the resin part 2. Here, the substrates 10 and 11 are transparent substrates that transmit light in the visible light region. The optical element 100 is, for example, a diffractive optical element. The substrate 10, the resin part 1, the resin part 2, and the substrate 11 are laminated in this order. The resin part 1 and the resin part 2 are in close contact with each other, and a diffraction grating is formed at the interface between the resin part 1 and the resin part 2. The resin part 1 is, for example, the first optical layer, and the resin part 2 is, for example, the second optical layer.

[0012] The refractive index of the resin part 1 at a certain wavelength is nA, and the refractive index of the resin part 2 at the same wavelength is nB. In this case, nA is smaller than nB. (nA < nB) As the wavelength for comparison, the d-line (587.6 nm) is typical, but wavelengths such as the c-line or g-line may also be used. The refractive index nA at the d-line is, for example, 1.54 or more and 1.58 or less, and the refractive index nB at the d-line is, for example, 1.57 or more and 1.63 or less. The difference between the refractive index nA at the d-line and the refractive index nB at the d-line is 0.027 or more and 0.047 or less.

[0013] The Abbe number of the resin part 1 is νA, and the Abbe number of the resin part 2 is νB. In this case, νA is smaller than νB. (νA < νB) The Abbe number νA is, for example, 19 or more and 28 or less, and the Abbe number νB is, for example, 38 or more and 43 or less. Here, ν d is exemplified, but it is not ν d but ν c or ν g may also be used.

[0014] If the refractive index and the Abbe number do not satisfy the above ranges, the height of the diffraction grating described later will vary, and there is a risk that refractive index unevenness will easily occur due to ambient environmental changes such as temperature.

[0015] Hereinafter, the resin part 1 will be described in detail.

[0016] The resin part 1 is composed of a resin 1a and inorganic particles. The resin 1a, together with the resin 2a that constitutes the resin part 2, is designed in terms of refractive index, Abbe number, and secondary dispersion so that the optical element 100 can obtain desired optical properties. The resin part 1 contains inorganic particles surface-treated with a dispersant and a curable resin 1a. The resin 1a and the resin 2a can be a first resin and a second resin, respectively.

[0017] Here, the resin can be, for example, a polymer or an organic resin that partially contains an inorganic component such as silicone.

[0018] The refractive index of the resin part 1 is lower than that of the resin part 2, and the Abbe number of the resin part 1 is lower than that of the resin part 2.

[0019] Here, the Abbe number and the secondary dispersion are indices representing the slope of the refractive index in the visible light region (wavelength: 435.8 nm to 656.3 nm), and are calculated by the following formulas (1) and (2). Abbe number ν d =(n d -1) / (n F -n c ) (1) Secondary dispersion θ gF =(n F -1) / (n F -n c ) (2) n g : Refractive index of g-line (435.8 nm) n F : Refractive index of F-line (486.1 nm) n d : Refractive index of d-line (587.6 nm) n c : Refractive index of c-line (656.3 nm)

[0020] Here, the Abbe number ν d is the slope of n c from n F in the range of n d , but an arbitrary refractive index range can be selected. When nA < nB at the d-line, the Abbe number is preferably ν d , but the Abbe number is ν dThis may also be the case. The resin 2a constituting the resin part 2 is an enthiol-based resin containing a thiol compound and a (meth)acrylate compound in order to achieve a high refractive index and low dispersion. Resin 2a is obtained by curing an uncured resin composition containing a monomer and / or oligomer of a thiol compound and a monomer and / or oligomer of a (meth)acrylate-based resin. Resin 2a is an energy-curable resin. An energy-curable resin is a resin that hardens from an uncured state by applying light energy and / or thermal energy.

[0021] Examples of thiol compounds contained in the resin 2a used to form the resin portion 2 include 4-mercaptomethyl-3,6-dithia-1,8-octanedithiol, 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane (4-mercaptomethyl-3,6-dithia-1,8-octanedithiol), 4,8-bis(mercaptomethyl)-1,11-dimercapto-3,6,9-trithiaundecane (4,8-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane), and 5,7-bis(mercaptomethyl)-1,11-dimercapto-3,6,9-trithiaundecane (5,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane).

[0022] Examples of (meth)acrylate compounds contained in the resin 2a used to form the resin part 2 include tris(2-acryloxyethyl) isocyanurate, oligoethylene glycol di(meth)acrylate, dimethylol tricyclodecane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0023] Furthermore, the proportion of thiol compounds in resin 2a is preferably in the range of 30% by mass or more and 80% by mass or less. When the thiol compound content is within the above range, optical properties and moldability are good. If the thiol compound content is less than 30% by mass, it may not be possible to increase the refractive index. On the other hand, if the thiol compound content exceeds 80% by mass, the moldability when forming resin part 2 may not be sufficient.

[0024] The resin 2a used to form the resin part 2 contains a polymerization initiator. The polymerization initiator may be a photopolymerization initiator or a thermal polymerization initiator, and can be determined by the selected manufacturing process. However, when performing replica molding which facilitates the production of diffraction grating shapes, it is preferable to contain a photopolymerization initiator. Examples of photopolymerization initiators include 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone, 1-hydroxycyclohexyl-phenyl-ketone, bis(2,46-trimethylbenzoyl)-phenylphosphine oxide, 4-phenylbenzophenone, 4-phenoxybenzophenone, 4,4'-diphenylbenzophenone, and 4,4'-diphenoxybenzophenone. From the viewpoint of good transparency of the resin part 2, 1-hydroxycyclohexyl-phenyl-ketone is preferred.

[0025] The content of the photopolymerization initiator is preferably in the range of 0.01% by mass or more and 10% by mass or less relative to the total amount of resin 2a. Depending on the reactivity with oligomers, etc., and the wavelength of irradiation used during photocuring, one type of photopolymerization initiator may be used, or two or more types may be used in combination.

[0026] By configuring the resin part 2 as described above, it is possible to obtain a material with an elastic modulus of 0.1 GPa to 3.0 GPa at temperatures between 22°C and 24°C, and with a high refractive index and low dispersion relative to the resin part 1. Preferably, it is more preferable if the elastic modulus is between 0.1 GPa and 2.5 GPa. If the elastic modulus is less than 0.1 GPa, the temperature dependence of the refractive index becomes large, and the desired optical properties may not be obtained. If the elastic modulus is greater than 3.0 GPa, it is difficult to reduce refractive index unevenness of the optical element 100. When light is incident on the resin part 2 where refractive index unevenness occurs, a phase difference occurs compared to when light is incident on the resin part 2 without refractive index unevenness. In the defocused state, ring-shaped unevenness occurs, where the density increases in correlation with the phase difference.

[0027] Here, "22°C to 24°C" means that it is sufficient for at least one point around 23°C to satisfy the above range of elastic modulus; it is not necessary for all points between 22°C and 24°C to satisfy the above range of elastic modulus.

[0028] By setting the elastic modulus of the resin part 2 within the above range, residual stress generated during the curing of resin 2a can be reduced, and refractive index unevenness within the resin part 2 can be reduced. By reducing refractive index unevenness, the phase difference can be reduced, and the density of ring body unevenness during defocusing can be thinned.

[0029] The thickness D2 of the resin part 2, that is, the length from the lattice top 101 of the resin part 1 to the base material 11, is preferably 20 μm or more and 80 μm or less, and more preferably 30 μm or more and 70 μm or less.

[0030] Next, the resin 1a contained in the resin part 1 will be described. Resin 1a is a resin that is liquid at room temperature and hardens through a radical generation mechanism using a polymerization initiator such as a photopolymerization initiator or a thermal polymerization initiator. Therefore, the resin 1a of this embodiment can be suitably used for replica molding of optical elements such as lenses.

[0031] The resin 1a contained in the resin part 1 of this embodiment is a curable resin, obtained by curing an uncured resin. Examples of resin 1a include, but are not limited to, acrylic resins, methacrylic resins, vinyl resins, epoxy resins, etc. Only one type of resin 1a may be used, or two or more types may be used in combination. Here, acrylic resins are preferred from the viewpoint of having excellent optical properties. As the acrylic resin, monomers or oligomers of compounds containing polymerizable reactive groups such as acrylate groups and methacrylate groups can be used. The monomer or oligomer is preferably one that is well compatible with the solvent and dispersant in which the metal oxide particles are dispersed. As the monomer, there is no particular limit to the type as long as it is an unsaturated group-containing compound having one or more double or triple bonds in the molecule. Specific examples of monomers or oligomers of unsaturated group-containing compounds include 1,4-divinylcyclohexane, 1,4-cyclohexanedimethanol divinyl ether, 4,4-dimethylhepta-1-ene-6-yne, divinylbenzene, 1,6-divinylnaphthalene, N-vinylpyrrolidone, N-vinylcaprolactam, ethoxylated bisphenol A divinyl ether, propoxylated bisphenol A divinyl ether, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, phenoxyethyl( Examples include monofunctional acrylates and methacrylates such as meth)acrylate; polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, trimethylolethane tri(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, hexanediol di(meth)acrylate, tri(acryloyloxyethyl) isocyanurate, etc.

[0032] Here, the monomer content is between 25% and 90% by volume relative to the resin portion 1. By satisfying the range of dispersant content described later in the resin portion 1, and by satisfying the above range of monomer content, light scattering can be reduced, and volume expansion due to moisture absorption in the cured resin composition can be minimized. This is because, in resin 1a, the metal oxide particles are suitably dispersed by the dispersant, and the monomers act as crosslinking components, making it possible to suppress volume expansion. On the other hand, if the monomer content is less than 25% by volume relative to the resin portion 1, moldability deteriorates. Also, if the monomer content is more than 90% by volume, the content of metal oxide particles decreases relatively, and sufficient optical properties cannot be obtained.

[0033] The inorganic particles consisting of metal oxides contained in the resin part 1 will be described below.

[0034] In the resin part 1 of this embodiment, the inorganic particles play a role in adjusting the wavelength dispersion of the refractive index of the resin 1a.

[0035] From the perspective of not affecting light scattering and transmission performance, the preferred average primary particle size of metal oxide particles is between 3 nm and 20 nm. If the particle size, including aggregates, exceeds 20 nm, light scattering may increase significantly. On the other hand, if the particle size is smaller than 3 nm, the surface energy of the particles increases, which may lead to re-aggregation and make dispersion difficult.

[0036] If particles with a particle size exceeding 20 nm are present in the resin part 1, such particles can be removed by processes such as centrifugation or ultrafiltration. When removing particles, it is preferable to remove the solvent while the particles are dispersed in the solvent (particle dispersion). One method for measuring the average primary particle size (number-average particle size of primary particles) of inorganic particles is the dynamic light scattering method. A particle size analyzer can be used for this measurement, such as the ELSZ-2000ZS (manufactured by Otsuka Electronics Co., Ltd.).

[0037] The inorganic particle content is preferably 1% by volume or more and 29% by volume or less relative to the resin part 1. When the inorganic particle content is within the above range, the resin part 1 has low viscosity and excellent processability. Furthermore, the cured resin 1a has high refractive index and high transparency optical properties. On the other hand, if the inorganic particle content is less than 1% by volume relative to the resin part 1, the cured resin 1a may have a high scattering rate and insufficient transparency. Furthermore, if the inorganic particle content is greater than 29% by volume, the viscosity of the resin part 1 may increase and moldability may deteriorate.

[0038] Depending on the desired optical properties, various metal oxides can be used for the inorganic particles. Examples of usable particles include silicon dioxide (SiO2), titanium dioxide (TiO2), strontium titanate (SrTiO3), zirconium oxide (ZrO2), and hafnium oxide (HfO2). Other examples include aluminum oxide (Al2O3), indium oxide (In2O3), tin oxide (SnO2), indium tin oxide (ITO), antimony-doped tin oxide (ATO), and zinc oxide (ZnO). By increasing the wavelength dispersion, the Appe number ν is... d To reduce the diffraction efficiency, titanium dioxide or strontium titanate can be used. Furthermore, to improve the diffraction efficiency of the optical element in the visible light region, a transparent conductive material can be used. Specific materials include indium oxide, tin oxide, indium tin oxide, antimony-doped tin oxide, and zinc oxide, with indium tin compounds being preferred.

[0039] Since the optical properties (linear dispersion properties) that enable high-precision diffraction efficiency in the visible light region depend on the conductive carriers (electrons, holes, etc.), it is preferable to use conductive materials.

[0040] In the case of organic microparticles, transparency is worse compared to inorganic particles, which is undesirable.

[0041] It is desirable to apply surface treatment to the inorganic particles as needed. Surface treatment may be performed during the synthesis and fabrication of the fine particles, or it may be performed separately after the fine particles have been obtained.

[0042] Furthermore, it is desirable to use a surface treatment agent, such as a dispersant like a surfactant, to uniformly disperse the inorganic particles so that they do not aggregate.

[0043] In this embodiment, pigment derivatives, resin-type, or surfactant-type surface treatment agents and dispersants can be suitably used. Cationic, weakly cationic, nonionic, or amphoteric surfactants are effective as surface treatment agents and dispersants. In particular, polyester-based, ε-caprolactone-based, polycarboxylates, polyphosphates, hydrostearates, amidosulfonates, polyacrylates, olefin maleate copolymers, acrylic-maleate copolymers, alkylamine acetates, alkyl fatty acid salts, fatty acid polyethylene glycol esters, silicones, and fluorine-based surfactants can be used, but in this embodiment, it is preferable to use at least one basic type selected from ammonia and organic amines. Specifically, these include alkylamine PO or EO modified products such as Dispervic 161, 162, 163, and 164 from the Dispervic series (manufactured by Big Chemie Japan), Solspers 3000, 9000, 17000, 20000, 24000, and 41090 from the Solspers series (manufactured by Zenega), and TAMN-15 from the TAMN series (manufactured by Nikko Chemical).

[0044] The amount of surface treatment agent and dispersant added is preferably in the range of 0.1% to 35.0% by weight relative to the weight of the fine particles. If too much dispersant is added, it will cause clouding and optical scattering, and the properties of the composition obtained containing the fine particles (refractive index, Abbe number, secondary dispersion properties, elastic modulus, etc.) will be reduced more than necessary. Preferably, it is in the range of 4.0% to 25.0% by weight. Furthermore, the surface treatment agent and dispersant can be used individually or in combination of two or more types.

[0045] The polymerization initiator used in resin part 1 may be the same as or different from the one used in resin part 2. It can be appropriately selected according to the curing conditions (irradiation wavelength, irradiation dose) of the curable resin.

[0046] The manufacturing method for the resin part 1 will be described below.

[0047] First, in addition to the untreated inorganic particle dispersant, a process is performed to adsorb the dispersant onto the surface of the inorganic particles.

[0048] Specifically, conductive microparticles such as ITO and AZO can be used as inorganic particles. For the solvent in the dispersion solution, for example, xylene or toluene can be used. Furthermore, for the surface adsorption treatment, aggregates are loosened using a bead mill or the like, and the dispersant is adsorbed onto the exposed surface, stabilizing it as a primary particle size. The desired amount of photopolymerizable monomers, oligomers, and photopolymerization initiators is calculated from the particle concentration in the dispersion solution and dissolved.

[0049] Furthermore, filtering can be performed as needed to remove aggregated particles. After confirming that the particles are well dispersed without precipitation, the solvent can be removed, for example, using an evaporator. In this case, it is preferable to appropriately adjust the degree of reduced pressure according to the boiling point of the solvent, the amount of residual solvent, etc. Rapid evaporation and removal of the solvent may worsen the degree of particle aggregation and impair dispersibility. Also, when removing the solvent by reduced pressure, it is possible to heat the mixture to an extent that does not impair dispersibility, if necessary.

[0050] By following the above steps, the resin part 1 of this embodiment can be obtained.

[0051] The resulting resin portion 1 may contain residual solvent that could not be removed. If the amount of residual solvent is greater than 0.1% by mass, it may promote particle movement during photocuring, potentially leading to an increased refractive index gradient (GI) and light scattering. Therefore, it is preferable that the residual solvent content be 0.1% by mass or less.

[0052] The thickness D1 of the resin portion 1, that is, the length from the lattice apex 101 or lattice valley 102 to the base material 10, is preferably 1 μm or more and 30 μm or less, and more preferably 2 μm or more and 25 μm or less. If the resin portion 1 is thinner than 1 μm, the optical properties of the optical element 100 will deteriorate, and if the resin portion 1 is thicker than 30 μm, the transparency of the optical element 100 may deteriorate. In this embodiment, the thickness D1 is smaller than the thickness D2. It is more preferable that the length from the lattice valley 102 to the base material 10 is within the above range.

[0053] The length L1 from the lattice valley 102 to the lattice apex 101 of the resin part 1 is preferably 5 μm or more and 25 μm or less. The length L1 is the length from the lattice apex 101 to the lattice valley 102, and it is sufficient if at least one of the optical elements 100 satisfies this condition. By designing the thickness D1 of the resin part 1, the thickness D2 of the resin part 2, and the length L1 within the above range, an optical element 100 with high diffraction efficiency can be obtained.

[0054] The method for manufacturing the optical element 100 will be described below.

[0055] Figure 2 is a schematic diagram showing the manufacturing method of the optical element 100 according to this embodiment. The manufacturing process of the optical element 100 will be described below with reference to Figure 2. In Figure 2, the same reference numerals are used for components that are the same as those in Figure 1.

[0056] First, an appropriate amount of uncured resin 1a is filled between a mold 12 having a shape that is an inversion of the desired diffraction grating shape and a substrate 10. The resin 1a is designed to have a high refractive index and low dispersion relative to the resin part 2 after curing. Here, the substrate 10 and the mold 12 are held in a release jig 15.

[0057] Next, the mold 12 and the substrate 10 are moved to spread the uncured resin 1a to the desired thickness, covering the outside of the optically effective area. During filling, pressure or heat may be applied to the mold 12 and / or the substrate 10 as needed.

[0058] Next, the filled, uncured resin 1a is cured by applying light or thermal energy. In Figure 2(a), light energy is applied by an ultraviolet light source 60. At this time, heat may be added in addition to light to accelerate the curing reaction of the uncured resin 1a.

[0059] Next, as shown in Figure 2(b), the release jig 15 is moved to release the mold 12, forming a resin part 1 having a diffraction grating shape, which is made of cured resin 1a.

[0060] Furthermore, as shown in Figure 2(c), the substrate 10 on which the resin part 1 is formed is held by the molding jig 16. Next, an appropriate amount of uncured resin 2a is filled between the diffraction grating shape of the resin part 1 and the substrate 11. Since the objective is to form the resin part 2, a mold different from the mold 12 may be used instead of the substrate 11.

[0061] Then, as shown in Figure 2(d), the uncured resin 2a is spread to cover the optically effective inside and outside until it reaches the desired thickness. Furthermore, light and thermal energy are applied to the filled uncured resin 2a by the light source 60 to cure it, forming a resin part 2 having a diffraction grating shape, which is made of cured resin 2a.

[0062] The base material 11 may be separated after the resin part 2 has been formed.

[0063] The pitch between the gratings in the formed diffraction grating shape increases towards the center of the optical element 100 and decreases towards the radial ends of the optical element 100. The pitch between the gratings is the distance from the grating vertex 101 to the adjacent grating vertex, or the distance from the grating valley 102 to the adjacent grating valley, and is the distance from the grating valley 102 to the adjacent grating valley.

[0064] The optical element 100 can be manufactured through the above process.

[0065] <Examples> The resins 1a and 2a and the optical element 100 of this embodiment will be described in detail below. First, the evaluation method for the optical element of this embodiment will be explained.

[0066] The refractive index and Abbe number of the resin parts 1 and 2 of the optical element 100 in the example, or of the optical element in the comparative example, were evaluated by preparing samples for optical property evaluation. It is also possible to evaluate the resin by peeling the substrate from the optical element and extracting it, without using samples for optical property evaluation. First, the method for preparing the optical property evaluation samples will be described.

[0067] As shown in Figure 3(a), on a 1 mm thick glass 4 (S-TIH11), the resin part 1 was placed on a 12.5 μm thick spacer 9, and the resin part 2 was placed on a 50 μm thick spacer 9, along with the uncured resin 5a, which is the raw material for the resin to be measured. A 1 mm thick quartz glass 8 was then placed on top of this, via the spacer 9, and the uncured resin 5a was spread out.

[0068] Next, as shown in Figure 3(b), the spacer 9 was removed. Then, as shown in Figure 4(c), a high-pressure mercury lamp (HOYA CANDEO OPTRONICS: UL750), which was the light source 18, was used to irradiate the quartz glass 8 with light at 20 mW / cm2 (illuminance through the quartz glass) for 2500 seconds (50 J). After curing the resin 5a and peeling off the quartz glass, the resin was annealed at 80°C for 16 hours and used as a sample for optical property evaluation. The shape of the cured resin 5 was 500 μm thick and 5 mm × 20 mm in size on the glass surface.

[0069] The refractive indices of the obtained samples were measured from the glass 4 side using a refractometer (KPR-30, Shimadzu Corporation) at each wavelength: g-line (435.8 nm), F-line (486.1 nm), d-line (587.6 nm), and c-line (656.3 nm).

[0070] Furthermore, the Abbe number was calculated from the refractive index of each measured wavelength. The Abbe number ν was calculated using equation (1) described above.

[0071] <Evaluation of diffraction efficiency> The diffraction efficiency of the optical elements in the examples and comparative examples was measured using an automated optical element measuring device (Spectrometer Co., Ltd.: ASP-32). An arbitrary spot light was shone onto the optical element, and first the amount of transmitted light was measured. Next, the amount of first-order diffracted light, which is the design order, was measured, and the diffraction efficiency was defined as the ratio of the design-order light amount to the total transmitted light amount, expressed as a percentage.

[0072] <Evaluation of transmitted wavefronts> A laser interferometer was used on the optical element to confirm the phase shift near the central ring. If the phase shift in the optical element is exactly an integer wavelength, the result is 0 nm.

[0073] (Example 1) Resin 1a was prepared as follows.

[0074] 52.74 g of a fine particle dispersion (average particle size 15 nm, indium tin oxide concentration 9.90 w%, dispersant amount 2.07 w%: dispersant type [high molecular weight dispersant] manufactured by CIK Nanotech) in which indium tin oxide (ITO) was dispersed in xylene solvent was mixed with 3.69 g of a mixture of UV-curable acrylic resins consisting of 20 w% tris(2-acryloxyethyl) isocyanurate, 25 w% pentaerythritol triacrylate, 40 w% dicyclopentenyloxyethyl methacrylate, 13 w% urethane-modified polyester acrylate, and 2 w% 1-hydroxycyclohexyl phenyl ketone.

[0075] The particle size was measured using a laser-type particle size analyzer (ELS: Otsuka Electronics) for the fine particle dispersion. This mixed solution was placed in an evaporator, and after removing the xylene solvent at a minimum pressure of 4 hPa, the mixture was passed through a 0.5 μm filter (SHPX-005-M25DKC: Rokitechno) to prepare energy-curable resin 1a.

[0076] Resin 1a was fired using a TGA (PerkinElmer) and the amount of inorganic solids in resin 1a was quantified. It was 52.1% by weight.

[0077] The residual solvent (xylene) was detected by gas chromatography (5890 series II: Hewlett Packard) and found to be 0.002 w%.

[0078] The refractive index was measured on a sample that was cured at 50 J and then annealed at 80°C for 72 hours. g ,n F ,n e ,n d ,n C )=(1.601, 1.589, 1.577, 1.570, 1.559), (ν d ,θ gF )=(19.1,0.41).

[0079] Resin 2a was prepared as follows.

[0080] Thiol compounds and (meth)acrylic compounds were prepared so that the resin 2a amounted to 100 parts by mass. 49.8 parts by mass of the thiol compound 4-mercapto-3,6-dithia-1,8-octanedithiol, 28.4 parts by mass of the (meth)acrylic compound tris(2-acryloxyethyl) isocyanurate, and 0.1 parts by mass of triethylamine were placed in a bottle and mixed.

[0081] After mixing, the mixture was stirred at 23°C for 72 hours to adjust the viscosity, and then filtered through an adsorbent to remove triethylamine. Subsequently, 4.8 parts by weight of dicyclopentenyloxyethyl methacrylate, 22.9 parts by weight of tris(2-acryloxyethyl) isocyanurate, and 2.1 parts by weight of 1-hydroxycyclohexylphenyl ketone were added and mixed until homogeneous to obtain resin 2a.

[0082] The refractive index was measured on a sample that was cured at 50 J and then annealed at 80°C for 72 hours. g ,n F ,n e ,n d ,n C )=(1.635, 1.626, 1.619, 1.615, 1.611), (ν d ,θ gF)=(39.6,0.59).

[0083] The elastic modulus of the resin portion 2 containing resin 2a at 23°C was 1.8 GPa.

[0084] The optical element 100 was manufactured using the manufacturing method shown in Figure 2.

[0085] First, as shown in Figure 2(a), an uncured resin 1a was placed on a mold 12 having a diffraction grating shape. A substrate 10 made of 2 mm thick glass was placed on top of the resin 1a. Next, a high-pressure mercury lamp (EXECURE250, manufactured by HOYA CANDEO OPTRONICS), which was the light source 18, was used to irradiate the resin 1a at an intensity of 14.2 mW / cm2 to 20 mW / cm2 for 2500 to 3500 seconds.

[0086] Next, as shown in Figure 2(b), the mold 12 was released and annealed in air at 80°C for 72 hours to form a resin part 1 having a diffraction grating shape. The height of the lattice apex 101 of the diffraction grating was 12.85 μm, the distance from the substrate 10 (which is the base thickness of the diffraction grating) to the lattice valleys 102 was 3 μm, and the lattice pitch was 200 μm.

[0087] Next, as shown in Figure 2(c), the substrate 10 on which the resin part 1 was formed was held in a molding jig 16. Uncured resin 2a was dropped onto the diffraction grating shape of the resin part 1. Then, as shown in Figure 2(d), a substrate 11, which is a flat glass plate, was placed on top of the resin 2a, and the resin 2a was spread out so that the radial length of the resin part 2 was 300 μm from the radial end of the resin part 1.

[0088] Finally, the sample was irradiated from the substrate 11 side with a high-pressure mercury lamp (manufactured by HOYA CANDEO OPTRONICS Co., Ltd.: UL750), which was the light source 60, at 20 mW / cm2 (illuminance through quartz glass) for 2500 seconds (50 J). The resin 2a was cured and annealed at 80°C for 72 hours to obtain the resin part 2, and the optical element 100 was obtained. The thickness of the resin part 2 was 50 μm from the lattice vertex of the resin part 1.

[0089] The diffraction efficiency of the optical element 100 in Example 1 across the entire visible light region (wavelength: 435.8 nm to 656.3 nm) was 99% or higher. The phase difference near the center was 15 nm.

[0090] (Example 2) Resin 1a was prepared as follows.

[0091] 39.31 g of a fine particle dispersion (average particle size 15 nm, indium tin oxide concentration 9.90 w%, dispersant amount 2.07 w%: dispersant type [high molecular weight dispersant] manufactured by CIK Nanotech) in which indium tin oxide (ITO) was dispersed in xylene solvent was mixed with 5.25 g of a mixture of UV-curable acrylic resins consisting of 20 w% tris(2-acryloxyethyl) isocyanurate, 25 w% pentaerythritol triacrylate, 40 w% dicyclopentenyloxyethyl methacrylate, 13 w% urethane-modified polyester acrylate, and 2 w% 1-hydroxycyclohexyl phenyl ketone.

[0092] This mixed solution was placed in an evaporator, and after removing the xylene solvent at a minimum pressure of 4 hPa, energy-curable resin 1d was prepared by passing it through a 0.5 μm filter (SHPX-005-M25DKC: manufactured by Rokitechno). Energy-curable resin 1d was calcined using a TGA (manufactured by PerkinElmer), and the amount of inorganic solids in energy-curable resin 1d was quantified. It was 39.31% by weight. The residual solvent (xylene) was determined to be less than 0.001 wt% by gas chromatography (5890 series II: manufactured by Hewlett Packard).

[0093] The refractive index was measured on a sample that was cured at 50 J and then annealed at 80°C for 72 hours. g ,n F ,n e ,n d ,n C )=(1.580, 1.570, 1.561, 1.555, 1.547), (ν d ,θ gF )=(24.1,0.44).

[0094] Resin 2a was prepared as follows.

[0095] A thiol compound and (meth)acrylic compound were prepared so that the resin 2a amounted to 100 parts by mass. 32.0 parts by mass of the thiol compound 4-mercapto-3,6-dithia-1,8-octanedithiol, 18.8 parts by mass of the (meth)acrylic compound tris(2-acryloxyethyl) isocyanurate, and 0.1 parts by mass of triethylamine were placed in a bottle and mixed.

[0096] After mixing, the mixture was stirred at 23°C for 72 hours to adjust the viscosity, and then filtered through an adsorbent to remove triethylamine. Subsequently, 8.9 parts by weight of dicyclopentenyloxyethyl methacrylate, 37.2 parts by weight of tris(2-acryloxyethyl) isocyanurate, and 2.1 parts by weight of 1-hydroxycyclohexylphenyl ketone were added and mixed until homogeneous to obtain resin 2a.

[0097] The refractive index was measured on a sample that was cured at 50 J and then annealed at 80°C for 72 hours. g ,n F ,n e ,n d ,n C )=(1.602, 1.594, 1.587, 1.584, 1.580), (ν d ,θ gF )=(42.4,0.58).

[0098] The elastic modulus of the resin portion 2 containing resin 2a at 23°C was 2.5 GPa.

[0099] An optical element 100 was manufactured using the method shown in Figure 2, similar to Example 1. However, a resin portion 1 having a diffraction grating shape was formed. The height of the lattice apex 101 of the diffraction grating was 20.0 μm, the distance from the substrate 10 (which is the base thickness of the diffraction grating) to the lattice valley 102 was 3 μm, and the lattice pitch was 200 μm.

[0100] Furthermore, the thickness of the resin portion 2 in the optical element 100 was 50 μm from the lattice vertex of the resin portion 1.

[0101] The diffraction efficiency of the optical element 100 in Example 2 across the entire visible light region (wavelength: 435.8 nm to 656.3 nm) was 99% or higher. The phase difference near the center was 30 nm.

[0102] (Example 3) Resin 1a was prepared using the same resin 1a as in Example 2.

[0103] Resin 2a was prepared as follows.

[0104] A thiol compound and (meth)acrylic compound were prepared so that the resin 2a amounted to 100 parts by mass. 32.0 parts by mass of the thiol compound 4-mercapto-3,6-dithia-1,8-octanedithiol, 18.8 parts by mass of the (meth)acrylic compound tris(2-acryloxyethyl) isocyanurate, and 0.1 parts by mass of triethylamine were placed in a bottle and mixed.

[0105] After mixing, the mixture was stirred at 23°C for 72 hours to adjust the viscosity, and then filtered through an adsorbent to remove triethylamine. Subsequently, 4.5 parts by weight of dicyclopentenyloxyethyl methacrylate, 41.7 parts by weight of tris(2-acryloxyethyl) isocyanurate, and 2.1 parts by weight of 1-hydroxycyclohexylphenyl ketone were added and mixed until homogeneous to obtain resin 2a.

[0106] The refractive index was measured on a sample that was cured at 50 J and then annealed at 80°C for 72 hours. g ,n F ,n e ,n d ,n C )=(1.602, 1.594, 1.587, 1.584, 1.580), (ν d ,θ gF )=(42.4,0.58).

[0107] The elastic modulus of the resin portion 2 containing resin 2a at 23°C was 2.7 GPa.

[0108] An optical element 100 was manufactured using the method shown in Figure 2, similar to Example 1. However, a resin portion 1 having a diffraction grating shape was formed. The height of the lattice apex 101 of the diffraction grating was 20.0 μm, the distance from the substrate 10 (which is the base thickness of the diffraction grating) to the lattice valley 102 was 3 μm, and the lattice pitch was 200 μm.

[0109] Furthermore, the thickness of the resin portion 2 in the optical element 100 was 50 μm from the lattice vertex of the resin portion 1.

[0110] The diffraction efficiency of the optical element 100 in Example 3 across the entire visible light region (wavelength: 435.8 nm to 656.3 nm) was 99% or higher. The phase difference near the center was 18 nm.

[0111] (Example 4) Resin 1a was prepared using the same resin 1a as in Example 2.

[0112] Resin 2a was prepared as follows.

[0113] A thiol compound and (meth)acrylic compound were prepared so that the resin 2a amounted to 100 parts by mass. 32.0 parts by mass of the thiol compound 4-mercapto-3,6-dithia-1,8-octanedithiol, 18.8 parts by mass of the (meth)acrylic compound tris(2-acryloxyethyl) isocyanurate, and 0.1 parts by mass of triethylamine were placed in a bottle and mixed.

[0114] After mixing, the mixture was stirred at 23°C for 72 hours to adjust the viscosity, and then filtered through an adsorbent to remove triethylamine. Subsequently, 0 parts by weight of dicyclopentenyloxyethyl methacrylate, 46.1 parts by weight of tris(2-acryloxyethyl) isocyanurate, and 2.1 parts by weight of 1-hydroxycyclohexylphenyl ketone were added and mixed until homogeneous to obtain resin 2a.

[0115] The refractive index was measured on a sample that was cured at 50 J and then annealed at 80°C for 72 hours. g ,n F ,n e ,n d ,n C )=(1.602, 1.594, 1.587, 1.584, 1.580), (ν d ,θ gF )=(42.4,0.58).

[0116] The elastic modulus of the resin portion 2 containing resin 2a at 23°C was 3.0 GPa.

[0117] An optical element 100 was manufactured using the method shown in Figure 2, similar to Example 1. However, a resin portion 1 having a diffraction grating shape was formed. The height of the lattice apex 101 of the diffraction grating was 20.0 μm, the distance from the substrate 10 (which is the base thickness of the diffraction grating) to the lattice valley 102 was 3 μm, and the lattice pitch was 200 μm.

[0118] Furthermore, the thickness of the resin portion 2 in the optical element 100 was 50 μm from the lattice vertex of the resin portion 1.

[0119] The diffraction efficiency of the optical element 100 in Example 4 across the entire visible light region (wavelength: 435.8 nm to 656.3 nm) was 99% or higher. The phase difference near the center was 20 nm.

[0120] (Comparative Example 1) Resin 1b was prepared as follows.

[0121] 52.07 g of a fine particle dispersion (average particle size 15 nm, indium tin oxide concentration 9.90 w%, dispersant amount 2.07 w%: dispersant type [high molecular weight dispersant] manufactured by CIK Nanotech) in which indium tin oxide (ITO) was dispersed in xylene solvent was mixed with 3.77 g of a mixture of UV-curable acrylic resins consisting of 20 w% tris(2-acryloxyethyl) isocyanurate, 25 w% pentaerythritol triacrylate, 40 w% dicyclopentenyloxyethyl methacrylate, 13 w% urethane-modified polyester acrylate, and 2 w% 1-hydroxycyclohexyl phenyl ketone.

[0122] This mixed solution was placed in an evaporator, and after removing the xylene solvent at a minimum pressure of 4 hPa, the energy-curable resin 1b was prepared by passing it through a 0.5 μm filter (SHPX-005-M25DKC: manufactured by Rokitechno).

[0123] Resin 1b was fired using a TGA (PerkinElmer) and the amount of inorganic solids in resin 1b was quantified. It was 51.55% by weight.

[0124] Residual solvent (xylene) was detected by gas chromatography (5890 series II: Hewlett Packard) and found to be less than 0.001 w%.

[0125] The refractive index was measured on a sample that was cured at 50 J and then annealed at 80°C for 72 hours. g ,n F ,n e ,n d ,n C )=(1.600, 1.588, 1.576, 1.569, 1.558), (ν d ,θ gF )=(19.3,0.41).

[0126] Resin 2b was prepared as follows.

[0127] A dispersion of zirconium oxide in methanol solvent (manufactured by Sakai Chemical Industry Co., Ltd.: average particle size of metal oxide particles 5 nm, zirconium oxide concentration 31.2% by mass) was prepared in 47.48 g. In addition, 5.04 g of ω-carboxy-polycaprolactone monoacrylate (manufactured by Toagosei Co., Ltd.: M-5300) was prepared as a dispersant. Furthermore, 4.08 g of tris(2-acryloxyethyl) isocyanurate, 0.70 g of pentaerythritol triacrylate, and 5.74 g of dicyclopentenyloxyethyl methacrylate were prepared as UV-curable resins. In addition, 0.33 g of 1-hydroxycyclohexylphenyl ketone was prepared as a photopolymerization initiator, and each was placed in a bottle and mixed.

[0128] The mixture was treated with an ultrasonic cleaner (Emerson Japan: BRANSON 1210) for 30 minutes, after which aggregates were removed using syringe filters (PTFE 0.8 μm and 0.2 μm). Subsequently, the mixture was heated in an oil bath at 41°C and concentrated under reduced pressure using an evaporator to remove the methanol solvent and obtain resin 2b.

[0129] The refractive index was measured on a sample that was cured at 50 J and then annealed at 80°C for 72 hours. g ,n F ,n e ,n d ,n C )=(1.637, 1.629, 1.622, 1.619, 1.615), (ν d ,θ gF )=(45.0,0.57).

[0130] The elastic modulus of the resin portion 2 containing resin 2a at 23°C was 4.0 GPa.

[0131] An optical element 100 was manufactured using the method shown in Figure 2, similar to Example 1. However, a resin portion 1 having a diffraction grating shape was formed. The height of the lattice apex 101 of the diffraction grating was 10.2 μm, the distance from the substrate 10 (which is the base thickness of the diffraction grating) to the lattice valley 102 was 3 μm, and the lattice pitch was 200 μm.

[0132] Furthermore, the thickness of the resin portion 2 in the optical element 100 was 50 μm from the lattice vertex of the resin portion 1.

[0133] The diffraction efficiency of the optical element in Comparative Example 1 across the entire visible light region (wavelength: 435.8 nm to 656.3 nm) was 99% or higher. The phase difference near the center was 60 nm.

[0134] The results of Examples 1-4 and Comparative Example 1 are shown in Figure 4. In Examples 1-4, by setting the elastic modulus between 0.1 GPa and 3.0 GPa at temperatures between 22°C and 24°C, it was possible to maintain a diffraction efficiency of 99% or higher while also reducing the phase difference near the center due to refractive index unevenness. However, in Comparative Example 1, the elastic modulus of the resin part 2 at temperatures between 22°C and 24°C was greater than 3.0 GPa, so the phase difference near the center due to refractive index unevenness could not be reduced. As a result, dense ring-shaped unevenness occurred during defocusing.

[0135] <Second Embodiment> Figure 5 shows an imaging device 600 as an example of a device equipped with the optical element 100 of this embodiment. In Figure 5, the camera body 602 and the lens barrel 601, which is an optical instrument, are coupled together, but the lens barrel 601 is preferably an interchangeable lens that can be attached to and detached from the camera body 602.

[0136] Light from the subject passes through an optical system consisting of multiple lenses 603, 605, etc., arranged on the optical axis of the imaging optical system within the housing 620 of the lens barrel 601, and is received by the image sensor 610. The light received by the image sensor 610 is in the visible light region (wavelength: 300 nm to 800 nm). The optical element 100 of this embodiment can be used, for example, as lens 605, or as a lens other than lens 605. It can also be applied to various lenses such as printer lenses, microscope lenses, eyeglasses, and contact lenses.

[0137] Here, the lens 605 is supported by the inner cylinder 604 within the housing and is movably supported relative to the outer cylinder of the lens barrel 601 for focusing and zooming. Preferably, the size of the lens 605 is 40 mm or more and 60 mm or less in diameter.

[0138] During the observation period before shooting, light from the subject is reflected by the main mirror 607 inside the camera body housing 621, passes through the prism 611, and the image is projected onto the photographer through the viewfinder lens 612. The main mirror 607 is, for example, a half-mirror, and the light that passes through the main mirror is reflected by the sub-mirror 608 towards the AF (autofocus) unit 613, and this reflected light is used, for example, for distance measurement. The main mirror 607 is also attached and supported by the main mirror holder 640 by adhesive or other means. During shooting, the main mirror 607 and sub-mirror 608 are moved out of the optical path via a drive mechanism (not shown), the shutter 609 is opened, and the image of the photographic light incident from the lens barrel 601 is projected onto the image sensor 610. The aperture 606 is configured to change the brightness and depth of field during shooting by changing the aperture area.

[0139] The embodiments described above can be modified as appropriate without departing from the technical concept.

[0140] For example, multiple embodiments can be combined. Furthermore, some elements of at least one embodiment can be deleted or replaced.

[0141] Furthermore, new matters may be added to at least one embodiment. The disclosures of this specification include not only those explicitly stated herein, but also all matters that can be understood from this specification and the accompanying drawings.

[0142] Furthermore, the disclosures in this specification include the complements of the individual concepts described herein. That is, if this specification contains a statement such as "A is greater than B," then even if it omits a statement such as "A is not greater than B," it can be said that this specification discloses "A is not greater than B." This is because the statement "A is greater than B" presupposes that the case where "A is not greater than B" is being considered. [Explanation of Symbols]

[0143] 1 1st optical layer 2 Second optical layer 10 Transparent base material 1a First resin 2a 2nd resin

Claims

1. An optical element comprising a first optical layer, a second optical layer, and a transparent substrate, wherein the first optical layer is disposed between the second optical layer and the transparent substrate, and a diffraction grating is formed at the interface between the first optical layer and the second optical layer, The refractive index of the d line in the second optical layer is higher than the refractive index of the d line in the first optical layer. The Abbe number of the second optical layer is higher than the Abbe number of the first optical layer. The first optical layer consists of a first resin and inorganic particles dispersed in the first resin. The second optical layer is made of a second resin having an elastic modulus of 0.1 GPa or more and 3.0 GPa or less at at least one temperature in the range of 22°C or more and 24°C or less. The second resin is an enthiol-based resin, and the inorganic particles dispersed in the first resin are an indium tin compound, which is a transparent and conductive substance. The proportion of the inorganic particles in the first resin is between 10.8% and 16.76% and the average primary particle diameter of the inorganic particles is between 3 nm and 20 nm. An optical element characterized in that the diffraction efficiency of the optical element in the visible light region is 99% or more, and the phase difference near the central ring body generated when the second resin is irradiated with a laser using a laser interferometer is 40 nm or less.

2. The optical element according to claim 1, characterized in that the refractive index of the first optical layer is 1.54 or more and 1.58 or less.

3. The optical element according to claim 2, characterized in that the second resin has an elastic modulus of 0.1 GPa or more and 2.5 GPa or less at at least one temperature in the range of 22°C or more and 24°C or less.

4. The optical element according to any one of claims 1 to 3, characterized in that the Abbe number of the first optical layer is 19 or more and 28 or less.

5. The optical element according to any one of claims 1 to 4, characterized in that the Abbe number is an Abbe number in the range of 435.8 nm to 656.3 nm.

6. The optical element according to any one of claims 1 to 5, characterized in that the difference between the refractive index of the first optical layer and the refractive index of the second optical layer is 0.027 or more and 0.047 or less.

7. The optical element according to any one of claims 1 to 6, characterized in that the second optical layer is bonded to the first optical layer and to a transparent substrate different from the transparent substrate, and is bonded and arranged between the first optical layer and the transparent substrate different from the transparent substrate.

8. The optical element according to any one of claims 1 to 7, characterized in that the length from the top of the lattice of the first optical layer to the lattice valley adjacent to the top of the lattice is 1 μm or more and 30 μm or less.

9. The optical element according to claim 8, characterized in that the aforementioned length is smaller than the thickness of the second optical layer.

10. The optical element according to any one of claims 1 to 9, characterized in that the thickness of the second optical layer is 20 μm or more and 80 μm or less.

11. An optical device having a housing and a lens inside the housing that is equipped with an optical element according to any one of claims 1 to 10.

12. The optical device according to claim 11, characterized in that the lens is 40 mm or more and 60 mm or less in diameter.

13. The imaging apparatus according to claim 12, further comprising the optical instrument and an image sensor that receives light that has passed through the optical instrument.

Images