Optical stack

Abstract

To provide an optical laminate that includes a diffractive optical element having a non-periodic uneven structure and that can appropriately perform the function of the diffractive optical element. [Solution] An optical laminate according to an embodiment of the present invention comprises: a substrate; a diffractive optical element having a non-periodic uneven structure provided on the substrate; and an optical functional auxiliary layer provided so as to cover the diffractive optical element, wherein the refractive index of the diffractive optical element is 1.50 to 2.70, and the refractive index of the optical functional auxiliary layer is less than 1.30. In one embodiment, the diffractive optical element is a phase Fresnel lens or a metalens.

Description

[Technical Field]

[0001] This invention relates to an optical laminate. [Background technology]

[0002] Theoretical research is progressing on diffractive optical elements. Because diffractive optical elements exhibit optical functions through a surface uneven structure on the order of the wavelength of light, it is possible to miniaturize, lighten, and thin optical systems, and practical applications are expected. Furthermore, the part of a diffractive optical element that exhibits optical functions (i.e., the surface uneven structure) typically has a non-periodic structure, and such a non-periodic surface uneven structure can control the phase, polarization state, amplitude, etc., of the light transmitted through the diffractive optical element. Examples of diffractive optical elements having a non-periodic surface uneven structure include phase Fresnel lenses and metalenses. Both phase Fresnel lenses and metalenses not only have the function of focusing or diverging light like ordinary lenses, but they can also adjust the phase of light during such focusing or diverging, and deform the wavefront of transmitted light into a specific shape to appropriately focus it at the focal point. When such diffractive optical elements are applied to an optical laminate, if the diffractive optical element is placed on the outermost surface, the surface (essentially the non-periodic surface uneven structure) may be damaged, which may reduce or eliminate the function of the diffractive optical element. On the other hand, even if one attempts to protect the surface of a diffractive optical element (essentially a non-periodic uneven structure) with, for example, an adhesive, the protective structure may reduce or eliminate the function of the diffractive optical element. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2003-270418 [Patent Document 2] Japanese Patent Publication No. 2016-176981 [Patent Document 3] Japanese Patent Publication No. 2022-014503 [Patent Document 4] Japanese Patent Publication No. 2024-117790 [Overview of the project] [Problems that the invention aims to solve]

[0004] The main object of the present invention is to provide an optical laminate that includes a diffractive optical element having a non-periodic uneven structure and that can appropriately perform the function of said diffractive optical element. [Means for solving the problem]

[0005] [1] An optical laminate according to an embodiment of the present invention comprises: a substrate; a diffractive optical element having a non-periodic uneven structure provided on the substrate; and an optical function auxiliary layer provided so as to cover the diffractive optical element, wherein the refractive index of the diffractive optical element is 1.50 to 2.70, and the refractive index of the optical function auxiliary layer is less than 1.30. [2] In the above [1], the diffractive optical element is a phase Fresnel lens or a metalens. [3] In [1] or [2] above, the radius of the diffractive optical element is 0.1 mm to 100 mm. [4] In any of the above [1] to [3], the height of the uneven structure of the diffractive optical element is 0.5 μm to 2.0 μm. [5] In any of the above [1] to [4], the thickness of the optical functional auxiliary layer is three times or more the height of the uneven structure of the diffractive optical element. [6] In any of the above [1] to [5], the diffractive optical element is made of a photocurable resin, a thermoplastic resin, or a thermosetting resin. [7] In any of the above [1] to [6], the radius of the substrate is 1.05 to 30 times the radius of the diffractive optical element. [8] In any of the above [1] to [7], the optical laminate further has a protective layer on the side of the optical functional auxiliary layer opposite to the diffractive optical element, and the surface of the optical functional auxiliary layer on the protective layer side is a flat surface. [9] In the above [8], the optical functional auxiliary layer and the protective layer are laminated with an adhesive layer in between, and the storage modulus of the adhesive layer at 23°C is 1.0 × 10 5 (Pa) or higher.

[10] In any of the above [1] to [9], the optical functional auxiliary layer is a porous layer, and its porosity is 20% by volume to 60% by volume.

[11] In any of the above [1] to

[10] , the optical functional auxiliary layer has a total light transmittance of 85% to 99% and a haze of less than 5%. [Effects of the Invention]

[0006] According to embodiments of the present invention, an optical laminate can be provided that includes a diffractive optical element having a non-periodic uneven structure, and that is capable of appropriately performing the function of the diffractive optical element. [Brief explanation of the drawing]

[0007] [Figure 1A] This is a schematic plan view of an optical laminate according to one embodiment of the present invention. [Figure 1B] Figure 1A is a schematic cross-sectional view of the optical laminate along the BB line. [Figure 2A] This is a schematic plan view of a phase Fresnel lens that can be used in an optical laminate according to an embodiment of the present invention. [Figure 2B] Figure 2A is a schematic cross-sectional view of a phase Fresnel lens along the BB line. [Figure 2C] Figure 2A is a schematic cross-sectional view of the main part of the second lens section (prism) in the phase Fresnel lens. [Figure 3] This is a schematic diagram illustrating the meaning of the numerical aperture (NA) in a phase Fresnel lens that can be used in an optical laminate according to an embodiment of the present invention. [Figure 4] This is a conceptual diagram illustrating the use of second-order or higher diffraction of light in a phase Fresnel lens that can be used in an optical laminate according to an embodiment of the present invention. [Figure 5] This is a schematic cross-sectional view of a metalens that can be used in an optical laminate according to an embodiment of the present invention. [Figure 6] This is a laser microscope image showing the state of the emitted light from the optical laminate of Example 1. [Modes for carrying out the invention]

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. For ease of viewing and understanding, the drawings are drawn schematically or conceptually, and lengths, widths, heights, thicknesses, shapes, sizes, ratios, directions, numbers, etc. may be different from the actual ones.

[0009] A. Overall configuration of the optical laminate FIG. 1A is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention; FIG. 1B is a schematic cross-sectional view taken along line B-B of the optical laminate of FIG. 1A. The optical laminate 200 in the illustrated example has a base material 120, a diffractive optical element 100, and an optical function auxiliary layer 140 in this order. The diffractive optical element 100 typically has an aperiodic uneven structure. The diffractive optical element 100 may be formed directly on the base material 120, or may be laminated on the base material 120 via any appropriate adhesive layer (for example, an adhesive layer, a tackifier layer: not shown). The diffractive optical element 100 is typically formed directly on the base material 120 as in the illustrated example. The optical function auxiliary layer 140 is provided so as to cover the diffractive optical element 100. The optical laminate may further have a protective layer 180 as in the illustrated example. In the illustrated example, the protective layer 180 is laminated on the surface of the optical function auxiliary layer 140 opposite to the base material 120 via an adhesive layer 160. The protective layer 180 is typically provided to protect the diffractive optical element 100.

[0010] The optical laminate 200 in the illustrated example is circular in plan view. More specifically, both the diffractive optical element 100 and the substrate 120 are circular in plan view. In the illustrated example, the diffractive optical element 100 and the substrate 120 are arranged coaxially. However, the optical laminate may have any appropriate plan view shape depending on the purpose. The plan view shape of the optical laminate may be, for example, elliptical, rectangular, square, or polygonal. Furthermore, although the diffractive optical element 100 and the substrate 120 have the same shape in plan view in the illustrated example, the plan view shapes of the diffractive optical element 100 and the substrate 120 may be different. The planar shape of the diffractive optical element / substrate may be, for example, one of the following combinations: circular / rectangle, circular / square, circular / polygon, circular / ellipse, rectangular / circular, rectangular / rectangle, rectangular / square, rectangular / polygon, rectangular / ellipse, square / circular, square / rectangle, square / square, square / polygon, square / ellipse, polygon / circular, polygon / rectangle, polygon / square, polygon / polygon, polygon / ellipse, ellipse / circular, ellipse / rectangle, ellipse / square, ellipse / polygon, ellipse / ellipse. The optical function auxiliary layer 140 only needs to be formed to cover the diffractive optical element 100, and the protective layer 180 only needs to be formed to protect the diffractive optical element 100 (so that when viewed from above, all of the diffractive optical elements are located within the protective layer). Therefore, the planar shapes of the optical function auxiliary layer and the protective layer are not particularly limited.

[0011] As the diffractive optical element 100, any suitable optical element having a non-periodic uneven structure and exhibiting function through diffraction can be used. Typical examples of diffractive optical elements 100 include phase Fresnel lenses, metalenses, cylindrical lenses, and point focus lenses. The illustrated example is a phase Fresnel lens. The phase Fresnel lens may be a first-order phase Fresnel lens utilizing first-order diffraction, or a higher-order phase Fresnel lens utilizing second-order or higher diffraction. Details of the diffractive optical element will be explained in section C below.

[0012] As described above, the optical function auxiliary layer 140 is provided so as to cover the diffractive optical element 100. Preferably, as shown in the illustrated example, the optical function auxiliary layer 140 fills the recesses of the uneven structure of the diffractive optical element 100 so that the surface on the protective layer 180 side is flat. With such a configuration, the occurrence of undesirable lens effects caused by the optical function auxiliary layer is suppressed or prevented, so that an optical laminate with light-gathering performance that is well in line with the design can be obtained. Typically, the optical function auxiliary layer 140 is formed directly on the diffractive optical element 100 (i.e., without an adhesive layer). The optical function auxiliary layer 140 can be formed, for example, by coating or printing an optical function auxiliary layer forming coating solution onto the diffractive optical element 100. Details of the optical function auxiliary layer will be described in section D below.

[0013] In embodiments of the present invention, the refractive index of the diffractive optical element 100 is 1.50 to 2.70, and the refractive index of the optical function auxiliary layer 140 is less than 1.30. With such a configuration, the optical functions resulting from the non-periodic uneven structure of the diffractive optical element (typically, functions that can control the phase, polarization state, amplitude, and combinations thereof of light) can be well maintained. The difference between the refractive index of the diffractive optical element 100 and the refractive index of the optical function auxiliary layer 140 may be, for example, 0.20 to 1.60, or for example, 0.25 to 1.00, or for example, 0.25 to 0.80, or for example, 0.30 to 0.60. If the difference is within such a range, a diffractive optical element (and consequently an optical laminate) with excellent light-gathering performance and excellent light-transmitting performance can be obtained.

[0014] The radius R0 of the substrate 120 may be, for example, 1.05 to 750 times, 1.05 to 50 times, or 1.05 to 30 times the radius R of the diffractive optical element 100. If the radius R0 of the substrate and the radius R of the diffractive optical element are in this relationship, the coating liquid for forming the optical functional auxiliary layer will flow outside the diffractive optical element, making it less likely for thickness variations to occur in the resulting optical functional auxiliary layer, and as a result, unwanted lens effects caused by thickness variations in the optical functional auxiliary layer can be avoided. Furthermore, although the coating thickness of the coating liquid for forming the optical functional auxiliary layer may be thicker or thinner in the center due to surface tension, the region where such thickness variations are formed can be located outside the diffractive optical element, so that even if thickness variations occur, adverse effects on the diffractive optical element can be avoided. Here, if the planar shape of the substrate and / or diffractive optical element is elliptical, the length of half the major axis can be treated as the radius; if it is rectangular, square, or polygonal, the length of half the diagonal can be treated as the radius. As described above (and further details will be provided in Section C-1-2), the optical function auxiliary layer 140 can be formed, for example, by coating or printing an optical function auxiliary layer forming coating solution onto the diffractive optical element 100. In this case, a coating margin of approximately 200 μm should be ensured. That is, from the viewpoint of the coating margin, the radius R0 of the substrate 120 should be approximately 200 μm larger than the radius R of the diffractive optical element 100.

[0015] Typically, only one diffractive optical element 100 is provided on the substrate 120, as shown in the illustrated example. However, depending on the purpose and application, multiple (e.g., two, three, four, or more) diffractive optical elements may be provided on the substrate. In one embodiment, multiple diffractive optical elements may be provided on a long substrate. The diffractive optical elements may be formed at predetermined intervals in the longitudinal and / or width directions of the substrate, or they may be formed randomly. Thus, an optical laminate in which diffractive optical elements are provided on a long substrate can also be included in embodiments of the present invention. In this case, diffractive optical elements (and therefore, the optical function auxiliary layer as well) can be continuously formed on the substrate while the substrate is being roll-transported. Furthermore, if necessary, a sheet-shaped optical laminate of a predetermined size (e.g., as shown in the illustrated example) can be obtained by cutting the long optical laminate. As described above, the sheet-shaped optical laminate may have one diffractive optical element on the substrate, or it may have multiple diffractive optical elements.

[0016] <Variation> The optical laminate may further have a refractive lens (not shown) on the outside of the protective layer 180 (opposite the optical function auxiliary layer 140) or on the outside of the substrate 120 (opposite the optical function auxiliary layer 140). Alternatively, either the protective layer 180 or the substrate 120 may be composed of a refractive lens. Since refractive lenses and diffractive optical elements have opposite wavelength dependencies with respect to light focusing, their respective wavelength dependencies can be canceled out. As a result, an optical laminate with good light focusing performance over a very wide wavelength range can be realized. Typically, a refractive lens has a flat surface and a refractive surface (concave or convex). Typically, the flat surface can be used in lamination with other components.

[0017] The components of the optical laminate are described in detail below.

[0018] B. Base material The substrate 120 can be any suitable configuration as long as a diffractive optical element can be formed on it. The substrate may be composed of, for example, a resin film or a glass plate. Examples of resins that make up the resin film include polyester resins, polycarbonate resins, acrylic resins, olefin resins, cycloolefin resins, and cellulose resins. Examples of glass that makes up the glass plate, according to composition, include soda-lime glass, boric acid glass, aluminosilicate glass, and quartz glass. Examples of glass that makes up the glass plate, according to alkali component, include alkali-free glass and low-alkali glass. In one embodiment, fused silica (a type of quartz glass) may be used. The substrate is typically light-transmitting. The substrate may also be flexible, for example.

[0019] The thickness of the substrate may be, for example, 10 μm to 2000 μm. When a resin film is used as the substrate, the thickness of the substrate may be, for example, 20 μm to 200 μm.

[0020] C. Diffractive optical elements As mentioned above, typical examples of diffractive optical elements include phase Fresnel lenses, metalenses, cylindrical lenses, and point focus lenses. Here, we will mainly explain phase Fresnel lenses and briefly describe metalenses.

[0021] C-1. Phase Fresnel Lens C-1-1. Specific configuration of a phase Fresnel lens Figure 2A is a schematic plan view of a phase Fresnel lens; Figure 2B is a schematic cross-sectional view of the phase Fresnel lens of Figure 2A along the line BB; and Figure 2C is an enlarged schematic cross-sectional view of the main part of the second lens section (prism) in the phase Fresnel lens of Figure 2A. The illustrated example of a phase Fresnel lens 100 comprises a first lens section 10 provided in the center and a second lens section 20 provided around the first lens section 10. In the illustrated example, the first lens section 10 and the second lens section 20 are provided on the first main surface 100a side of the phase Fresnel lens. The first lens section 10 and the second lens section 20 may also be provided on the second main surface 100b side of the phase Fresnel lens, or on both sides of the phase Fresnel lens. In the illustrated example, the first main surface 100a is typically the exit surface, but it may also be the incident surface.

[0022] As described above, the first lens section 10 is located in the center of the phase Fresnel lens 100. Typically, the optical axis of the first lens section 10 coincides with the optical axis (central axis) 100c of the phase Fresnel lens 100. Any appropriate surface shape can be adopted for the first lens section depending on the purpose. Examples of surface shapes for the first lens section include curved surfaces and inclined surfaces. Examples of curved surfaces include the surface shape near the optical axis of a convex lens (illustrated example) and the surface shape near the optical axis of a concave lens. The height of the first lens section can be appropriately set depending on the purpose. For example, the height of the first lens section may be the same as or different from the height of the innermost (i.e., adjacent to the first lens section) prism (described later) among the multiple prisms constituting the second lens section. For example, if the radius of the first lens section is designed to be small, the height of the first lens section may be less than the height of the prism.

[0023] As described above, the second lens section 20 is provided around the first lens section 10. The second lens section 20 has a plurality of prisms 21 arranged toward the outer circumference. Typically, the plurality of prisms 21 are provided coaxially with respect to the optical axis (central axis) 100c of the phase Fresnel lens 100. In a phase Fresnel lens that is circular in plan view, as shown in the illustrated example, the plurality of prisms 21 are annular. Each of the plurality of prisms 21 has: a Fresnel surface 21a that is inclined toward the outer circumference; a rise surface 21b provided between adjacent Fresnel surfaces 21a, 21a and extending in the direction of the optical axis 100c of the phase Fresnel lens 100 (vertical direction in the illustrated example); a top portion 21c which is the connection between the upper part of the Fresnel surface 21a and the upper part of the rise surface 21b; and a bottom portion 21d which is the connection between the lower part of the Fresnel surface 21a and the lower part of the rise surface 21b. The Fresnel surface 21a may be inclined linearly, curved, or stepped, as shown in the illustrated example. If the Fresnel surface is inclined curved, the curve may be convex upwards, convex downwards, or a combination of these (i.e., a shape with an inflection point). If the Fresnel surface is inclined stepped, the number of steps may be, for example, 10 or more, or 20 to 300. The inclination angle of the Fresnel surface (angle with respect to the direction perpendicular to the optical axis 100c of the Fresnel lens: in the illustrated example, the angle with respect to the horizontal direction) may be, for example, 1° to 55°, or 1° to 45°. The rise surface 21b may have a flat surface (its cross-section may be linear, as shown in the illustrated example), or it may be a curved surface (its cross-section may be curved).

[0024] The second lens section 20 is typically configured such that the distance between the tops 21c of adjacent prisms 21 (hereinafter sometimes referred to as the prism pitch) gradually narrows toward the outer edge. The manner in which the prism pitch gradually narrows toward the outer edge can be appropriately set depending on the purpose. In one embodiment, this manner can satisfy the following equation (2). That is, with the innermost prism as the first, the prism pitch can gradually narrow toward the outer edge such that the position xi of the top of the i-th prism from the center of the lens satisfies the following equation (2).

number

[0025] In one embodiment, the second lens section 20 may be configured such that the heights of the multiple prisms 21 gradually decrease toward the outer edge. In this case, regarding the height of the prisms, for example, if the height of the innermost prism (i.e., adjacent to the first lens section) is 100, the height of the outermost prism may be, for example, 97 or less, or for example, 60 to 97, or for example, 65 to 96, or for example, 70 to 93, or for example, 72 to 90, or for example, 73 to 85. In one embodiment, the ratio "height of the outermost prism / height of the innermost prism" is expressed by the following formula (3).

number

number

[0026] The height of the prism refers to the vertical distance from the bottom 21d to the top 21c of the prism. In the illustrated example, since the rise surface 21b extends vertically, the height of the prism 21 is synonymous with the height of the rise surface 21b.

[0027] The prism height reduction profile can be appropriately set depending on the purpose. For example, the prism height reduction profile may be a linear reduction with a constant slope, or a curved reduction that is convex upwards, and may be constant from the first lens portion side up to a predetermined range, and outside the predetermined range it may be a linear reduction with a constant slope or a curved reduction that is convex upwards. In one embodiment, the prism height reduction profile A satisfies the following formula (1).

number

[0028] As described above, a phase Fresnel lens may be a first-order phase Fresnel lens that utilizes first-order diffraction, or a higher-order phase Fresnel lens that utilizes second-order or higher-order diffraction. First-order phase Fresnel lenses can focus light more efficiently because most of the energy is concentrated in first-order diffraction. As a result, compared to lenses utilizing higher-order phases (second order or higher), there is less light loss, and the overall efficiency of the optical system can be improved. Higher-order phase Fresnel lenses (typically phase Fresnel lenses using higher-order diffraction with a diffraction order of 2 or higher in visible light) can function as diffraction lenses with the same or substantially the same integer order of focal length for multiple wavelengths in visible and near-infrared light. Therefore, they are useful for color displays and / or color optical systems that handle these multiple wavelengths (colors).

[0029] Figure 4 is a conceptual diagram illustrating the case where the second order diffraction of light is utilized in a phase Fresnel lens (i.e., a second-order phase Fresnel lens). As shown in Figure 4, incident light (parallel light) of wavelength λ is emitted from each prism at a predetermined angle so as to be directed toward the focusing direction. In the case of the second-order phase Fresnel lens shown in the example, the wavefronts of the emitted light from adjacent prisms are shifted by 2 wavelengths (2λ). That is, the optical path difference of the emitted light from adjacent prisms is 2λ. Therefore, the phases of the emitted light from adjacent prisms coincide. The fact that the optical path difference of the emitted light from adjacent prisms is 2λ means that, as shown in Figure 4, the optical path difference of the emitted light from all adjacent prisms is 2λ. As a result, the phases of the emitted light from all prisms coincide, and the intensity of the light focused by the phase Fresnel lens becomes very strong. In the case of a third-order Fresnel lens, the optical path difference of the light emitted from adjacent prisms is 3λ; in the case of an n-order Fresnel lens, the optical path difference of the light emitted from adjacent prisms is nλ.

[0030] As described above, the phase Fresnel lens may be a first-order phase Fresnel lens that utilizes first-order diffraction, or a higher-order phase Fresnel lens that utilizes second-order or higher diffraction. The diffraction order of the phase Fresnel lens may be, for example, 1 to 6, or for example, 2 to 5, or for example, 3 to 4.

[0031] Configurations that can utilize second-order or higher diffraction can typically be achieved by controlling the height of the prism. The height d0 of the prism can be determined from the following equation (5).

number

[0032] As described above, the height of the prism may be constant, or it may be configured to gradually decrease toward the outer edge. In the configuration where the height of the prism is constant, d0 in equation (5) above is the height of all the prisms. In the configuration where the height of the prism gradually decreases toward the outer edge, d0 is the height of the innermost prism (i.e., adjacent to the first lens portion). With the configuration where the height of the prism gradually decreases toward the outer edge, even when diffraction of the second order or higher is used and the numerical aperture of the lens is large (high light-gathering power), focusing noise can be suppressed (preferably eliminated). In the embodiment of the present invention, the height d0 of the prism may correspond to the height of the non-periodic uneven structure.

[0033] The height d0 of the prism can be appropriately set according to the wavelength (color) of the light to be focused, the order of diffraction, the refractive index of the prism, etc. The height d0 of the prism may be, for example, 0.5 μm to 2.0 μm, or for example, 0.7 μm to 1.8 μm, or for example, 0.8 μm to 1.7 μm, or for example, 1.0 μm to 1.6 μm.

[0034] The numerical aperture (NA) of the phase Fresnel lens may be, for example, 0.05 to 0.8, 0.08 to 0.7, 0.1 to 0.6, or 0.2 to 0.5. The numerical aperture (NA) can be calculated from the above formula (4).

[0035] Phase Fresnel lenses are typically composed of light-transmitting materials. These light-transmitting materials can be appropriately selected depending on the purpose, desired light transmittance, and applicability to the manufacturing method. For example, the light-transmitting material may be a photocurable resin, a thermoplastic resin, or a thermosetting resin. Specific examples of light-transmitting materials include (meth)acrylic resins such as polymethyl (meth)acrylate, polycarbonate resins, olefin resins such as polyethylene and polypropylene, and cyclic olefin resins such as polynorbornene. The constituent materials of phase Fresnel lenses, in relation to the manufacturing method, will be explained in section C-1-2 below.

[0036] The refractive index n of the phase Fresnel lens (and therefore the refractive index of the first and second lens parts) may be, for example, 1.50 to 2.70 as described above, or for example, 1.52 to 2.20, or for example, 1.54 to 2.00, or for example, 1.55 to 1.95, or for example, 1.56 to 1.90.

[0037] The radius R of the phase Fresnel lens may be, for example, 0.1 mm to 100 mm, or for example, 0.5 mm to 50 mm, or for example, 1 mm to 30 mm. The radius of the phase Fresnel lens may also be, for example, 1.2 mm to 20 mm, or for example, 1.5 mm to 10 mm, or for example, 1.8 mm to 8 mm, or for example, 2 mm to 5 mm.

[0038] C-1-2. Method for manufacturing diffractive optical elements The diffractive optical element (essentially the first lens portion and the second lens portion) may be formed by stereolithography or by nanoimprint lithography. The stereolithography and nanoimprint lithography methods will be described below.

[0039] A typical example of stereolithography is two-photon polymerization (TPP). Two-photon polymerization is a technology used in high-resolution 3D printers. Typically, two-photon polymerization converts liquid photocurable resin into a solid using photopolymerization. Two-photon polymerization is based on the nonlinear interaction of light, and the polymerization reaction occurs only in a very small region around the focal point of the light, making it possible to process extremely fine materials on the nanometer scale. The monomer composition used for two-photon polymerization typically includes a radical polymerizable monomer and a two-photon polymerization initiator. Examples of radical polymerizable monomers include bifunctional acrylic monomers, trifunctional acrylic monomers, and polyfunctional acrylic monomers. Examples of trifunctional acrylic monomers include pentaerythritol triacrylate (PETA) and trimethylolpropane triacrylate (TMPTA). Examples of polyfunctional acrylic monomers include dipentaerythritol hexaacrylate (DPHA). For refractive index adjustment, aromatic acrylic monomers (e.g., benzyl acrylate) may be used. Two-photon polymerization initiators are typically photopolymerization initiators that, when activated by two-photon absorption, generate radicals and / or acids, which trigger the photopolymerization reaction. Two-photon polymerization initiators can be appropriately selected depending on the wavelength of light used for two-photon polymerization. Preferably, two-photon polymerization initiators have a large two-photon absorption cross-section. With such a configuration, the reaction occurs only when laser light of a higher intensity than normal photon absorption is used, and as a result, high resolution can be achieved. A typical example of a two-photon polymerization initiator is bis(4-diallylaminobenzylidene)ketone. This compound is highly sensitive and can achieve high resolution.

[0040] Two-photon polymerization can typically be carried out by irradiating the above monomer composition with laser light. The laser light preferably has a high energy density. Such a configuration allows for good two-photon absorption. Examples of laser light with high energy density include femtosecond lasers. Typical wavelengths of the laser light can be in the near-infrared region (e.g., around 800 nm). Laser irradiation devices of such wavelengths can be high-powered and inexpensive.

[0041] A specific procedure for two-photon polymerization may be as follows: Using a 780 nm femtosecond laser (pulse width = 100 femtoseconds), focusing it with a high-lens-power lens with a numerical aperture NA = 1.4, and scanning with a laser output of 25 mW, a scan speed of 80 mm / sec, an in-plane spacing of 0.2 μm between scan lines, and a thickness-direction spacing of 0.4 μm between scan lines, a microstructure with controllable phase can be fabricated. The specific configuration of the microstructure is as described in section C-1-1 above. After polymerization (fabrication), the unpolymerized monomers can be removed from the fabricated object by immersing it in a solvent (e.g., ketones, esters) that easily dissolves or disperses unpolymerized monomers for, for example, 5 to 120 minutes. Next, the fabricated object is immersed in a solvent with low surface tension (e.g., alcohol, hexane, methyl nonaflubutyl ether) for, for example, 15 minutes and dried to obtain the final stereolithography object (e.g., a phase Fresnel lens) or a master mold or replica mold for a phase Fresnel lens.

[0042] The above describes a method for converting a liquid photocurable resin into a solid using photopolymerization. However, it is also possible to change the solubility of the resin in a solvent by a chemical reaction caused by light, and then create a microstructure by washing with the solvent. In this case, only the parts that reacted with light may be dissolved, or only the parts that reacted with light may be left intact.

[0043] Nanoimprint lithography typically involves using a replica mold with a shape corresponding to the final photopolymerized object (e.g., a phase Fresnel lens) to transfer (stamp) that shape onto a resin or resin precursor coated on a substrate. The replica mold may be fabricated using the following replication transfer techniques, or by the two-photon polymerization photopolymerization method described above.

[0044] The fabrication of a replica mold using replication transfer technology can be carried out, for example, by the following procedure: A final stereolithographic object (phase Fresnel lens) is formed on any suitable substrate, and then a conductive thin film of metal (e.g., nickel) is formed on the surface of the stereolithographic object and the surrounding substrate surface by sputtering. The thickness of the conductive thin film may be, for example, 10 nm to 500 nm. Next, electrolytic metal plating is performed using the conductive thin film as a seed film. It is preferable that the metal used for electrolytic metal plating is the same as that of the conductive thin film. A metal replica mold with a thickness of 0.5 mm or more is formed by electrolytic metal plating, and finally, the stereolithographic object is removed with a solvent or chemical. In this way, a replica mold can be obtained.

[0045] Nanoimprinting can be either optical nanoimprinting or thermal nanoimprinting. Optical nanoimprinting typically involves pressing a replica mold pattern onto a photocurable resin (typically using ultraviolet light), irradiating it with ultraviolet light to cure the resin, and then replicating the pattern. Optical nanoimprinting can be performed at room temperature, resulting in high pattern reproduction accuracy. Thermal nanoimprinting typically involves pressing a replica mold pattern onto a thermosetting resin or thermoplastic resin and then replicating the pattern by heating. When using a thermosetting resin, the pattern is replicated by pressing the replica mold onto the uncured (liquid) thermosetting resin and then heating it to cure the resin. When using a thermoplastic resin, the pattern is replicated by pressing the replica mold pattern onto a thermoplastic resin film, heating it, and then cooling it. Thermal nanoimprinting can be performed directly on any material that hardens or softens upon heating.

[0046] Photocurable resins (resin compositions) typically contain a curing component and a photopolymerization initiator. Typical curing components include acrylate monomers or oligomers. Specific examples of curing components include dipropylene glycol diacrylate (DPGDA), hexanediol diacrylate (HDDA), and tripropylene glycol diacrylate (TPGDA). Photopolymerization initiators typically generate radicals upon irradiation with ultraviolet light, initiating polymerization of monomers and / or oligomers. Examples of photopolymerization initiators include benzoin ether-based initiators, acetophenone-based initiators, and oxime ester-based initiators. The photopolymerization initiator can be appropriately selected depending on the type of monomer and / or oligomer used, the wavelength of ultraviolet light, etc. Photocurable resins (resin compositions) may also contain a release agent and / or viscosity modifier. Typical release agents include fluorine compounds and silicone compounds. The use of a release agent can improve release properties from replica molds. Typical viscosity modifiers include monomers and low molecular weight oligomers. Using viscosity modifiers can improve the filling and transferability of the replica mold.

[0047] Examples of thermoplastic resins include polymethyl methacrylate (PMMA), polycarbonate (PC), and polyethylene terephthalate (PET).

[0048] Examples of thermosetting resins include epoxy resins and phenolic resins.

[0049] The above-mentioned photocurable resin, thermoplastic resin, and thermosetting resin may each be compounded (substantially dispersed) with inorganic nanoparticles to increase the refractive index of the resulting molded article (for example, to 1.60 or higher). Examples of materials constituting the inorganic nanoparticles include titanium dioxide, niobium oxide, silicon nitride, and zirconium oxide. The particle size of the inorganic nanoparticles may be, for example, 3 nm to 50 nm. The amount of inorganic nanoparticles compounded may be, for example, 10 to 80 parts by weight per 100 parts by weight of resin.

[0050] An example of a specific procedure for nanoimprint lithography is described below. Here, optical nanoimprint lithography is used as an example. First, an uncured resin is uniformly applied to a replica mold or substrate. Examples of application methods include spin coating and dip coating. Next, the applied resin is sandwiched between the replica mold and the substrate, and uniform pressure is applied. By applying pressure, the resin fills the microstructure of the replica mold. Heat is applied as needed to increase the fluidity of the resin and promote filling. With the resin sandwiched between the replica mold and the substrate, the resin is cured by irradiation with, for example, ultraviolet light. The curing process may vary depending on the type of monomer, light irradiation conditions, etc. Light irradiation is preferably continued until the resin no longer hardens. For example, when irradiating with ultraviolet light, typical light sources include high-pressure mercury lamps, metal halide lamps, and UV-LEDs. High-pressure mercury lamps have a peak wavelength of 365 nm and can provide high output over a wide range of wavelengths. Metal halide lamps can irradiate over a wider wavelength range. UV-LEDs have high output at specific wavelengths. The light source can be appropriately selected depending on the type of resin, etc. Finally, the cured resin is peeled off the replica mold. A peeling roll may be used if necessary. By using a peeling roll, the problem of cured material residue remaining on the replica mold can be suppressed.

[0051] In the case of thermal nanoimprinting, the same procedure can be adopted, except that ultraviolet light irradiation is replaced with heating. The heating temperature can be appropriately set depending on the type of resin, etc. For example, in the case of thermoplastic resins, the heating temperature can be set to a temperature 20°C or more higher than the glass transition temperature. Furthermore, delamination can be performed after the resin, replica mold, and substrate have cooled.

[0052] C-2. Metal Lens Figure 5 is a schematic cross-sectional view of a metalens. In the illustrated example, the metalens is provided with independent pillars (columnar structures) of nanometer width on the base. When the metalens is viewed from above, the phase, polarization state, amplitude, etc. of light can be individually controlled by controlling the width, shape, anisotropy, direction, arrangement, etc. of the pillars. As described above, the arrangement of the pillars can be set according to the desired control of light. As a result, the arrangement of the pillars is typically aperiodic, as shown in Figure 5 (similarly, the arrangement when viewed from above is also aperiodic). The width of the pillars may be, for example, 5 nm to 500 nm, or for example, 30 nm to 200 nm. The height of the pillars is typically constant. The height of the pillars may be, for example, 200 μm to 1000 μm, or for example, 300 μm to 600 μm. In embodiments of the present invention, the height of the pillars may correspond to the height of the aperiodic uneven structure.

[0053] Examples of light control methods using metalens include controlling the phase by the width of the pillar, controlling the phase by resonance, and the Pancharanum-Berry phase method. The Pancharanum-Berry phase method is a method that controls the phase of circularly polarized light by the direction of anisotropic nanofins.

[0054] Examples of materials that make up a metalens include dielectric materials, metallic materials, and composite materials. Examples of dielectric materials include silicon, barium titanate, and titanium oxide. Examples of metallic materials include gold and silver. Composite materials are combinations (hybrid materials) of dielectric materials and metallic materials.

[0055] The thickness of the metalens (the sum of the thickness of the base and the height of the pillar) may be, for example, 10 μm to 2000 μm, or for example, 11 μm to 200 μm.

[0056] Metalens can be fabricated, for example, by the following method. First, a thin film is formed using the above-mentioned material. Examples of thin film formation methods include sputtering or vapor deposition. The formed thin film is then patterned based on the width, shape, anisotropy, arrangement, etc., of the pillars designed according to the desired light control. Examples of patterning methods include electron beam lithography (EBL), extreme ultraviolet (EUV) photolithography, nanoimprint lithography (NIL), atomic layer deposition (ALD), and plasma etching.

[0057] D. Optical function auxiliary layer Any suitable configuration with a refractive index of less than 1.30 can be adopted for the optical functional auxiliary layer 140. In one embodiment, the optical functional auxiliary layer 140 may be a porous layer containing spaces such as voids and gaps inside. With such a configuration, the refractive index can be controlled by adjusting the porosity. Below, a specific configuration will be described for the case where the optical functional auxiliary layer 140 is a porous layer.

[0058] The refractive index of the optical function auxiliary layer is less than 1.30, as described above, with a lower limit of greater than 1.00. The refractive index of the optical function auxiliary layer is preferably 1.13 to 1.28, more preferably 1.14 to 1.27, even more preferably 1.15 to 1.26, and particularly preferably 1.16 to 1.25. If the refractive index of the optical function auxiliary layer is within this range, the deterioration of the function of the diffractive optical element due to covering the diffractive optical element can be suppressed very well. Unless otherwise specified, the refractive index refers to the refractive index measured at a wavelength of 550 nm. The refractive index can be measured, for example, as follows: The optical function auxiliary layer is formed on a predetermined film, and the resulting laminate is cut to a predetermined size. The cut laminate is bonded to the surface of a glass plate via an adhesive, and the center of the back surface of the glass plate (approximately 20 mm in diameter) is colored in with a black marker to create a sample that does not reflect light from the back surface of the glass plate. The above sample is placed in an ellipsometer (JAWoollam Japan: VASE), and the refractive index is measured under conditions of a wavelength of 550 nm and an incident angle of 50 to 80 degrees.

[0059] The total light transmittance of the optical functional auxiliary layer is preferably 85% to 99%, more preferably 87% to 98%, and even more preferably 89% to 97%. With such a configuration, excellent transparency can be achieved for the entire optical laminate. The total light transmittance can be measured, for example, by a haze meter as described later.

[0060] The haze of the optical functional auxiliary layer is preferably less than 5%, and more preferably less than 3%. On the other hand, the haze may be, for example, 0.1% or more, and 0.2% or more. With such a configuration, excellent transparency can be achieved for the optical laminate as a whole. The haze can be calculated using the following formula, for example, by using a haze meter (for example, "HM-150" manufactured by Murakami Color Technology Laboratory Co., Ltd.). Haze (%) = [Diffuse transmittance (%) / Total light transmittance (%)] × 100 (%)

[0061] The thickness of the optical function auxiliary layer is preferably three times or more the height of the uneven structure of the diffractive optical element. With such a configuration, it is easy to make the surface of the optical function auxiliary layer on the protective layer side a flat surface. As a result, the occurrence of undesirable lens effects caused by the optical function auxiliary layer is suppressed or prevented, so that an optical laminate with light-gathering performance that is well in line with the design can be obtained. The thickness of the optical function auxiliary layer can be set appropriately as long as the above flat surface can be realized. The thickness of the optical function auxiliary layer may be, for example, four times or more the height of the uneven structure of the diffractive optical element, or for example, five times or more. On the other hand, the thickness of the optical function auxiliary layer may be, for example, 10 times or less the height of the uneven structure of the diffractive optical element. If the thickness of the optical function auxiliary layer is too large, Drying can take a long time, and uneven thickness may occur in the optical function auxiliary layer. The thickness of the optical function auxiliary layer may be, for example, 2.0 μm to 15 μm, or 3.0 μm to 10 μm, or 3.5 μm to 8.0 μm, or 4.0 μm to 7.0 μm. If the thickness of the optical function auxiliary layer is within this range, it is above the wavelength of visible light and near-infrared light, so the phase, polarization state, amplitude, etc. of these lights can be controlled well.

[0062] Materials that can constitute the optical functional auxiliary layer (porous layer) include, for example, those described in International Publication No. 2004 / 113966, Japanese Patent Publication No. 2013-254183, and Japanese Patent Publication No. 2012-189802. Typical examples of materials that constitute the optical functional auxiliary layer include silicon compounds. Examples of silicon compounds include silica compounds; hydrolyzable silanes, and their partial hydrolysates and dehydration condensates; silicon compounds containing silanol groups; and activated silica obtained by contacting silicates with acids or ion exchange resins. Other materials that can constitute the optical functional auxiliary layer include organic polymers; polymerizable monomers (e.g., (meth)acrylic monomers and styrene monomers); and curable resins (e.g., (meth)acrylic resins, fluorine-containing resins, and urethane resins). These materials may be used individually or in combination of two or more.

[0063] In one embodiment, the optical functional auxiliary layer may contain spaces such as voids and gaps within it. In this case, the porosity of the optical functional auxiliary layer is preferably 20% to 60% by volume, more preferably 25% to 55% by volume, even more preferably 30% to 50% by volume, and particularly preferably 35% to 45% by volume. Such porosity allows the refractive index of the optical functional auxiliary layer to be within an appropriate range while ensuring strength. Here, the porosity is a value calculated from the refractive index measured with an ellipsometer using the Lorentz-Lorenz formula.

[0064] The size of the voids that may be included in the optical functional auxiliary layer can be adjusted to a desired size depending on the purpose and application. For example, the size of the voids that may be included in the optical functional auxiliary layer is 2 nm or larger, preferably 5 nm or larger, more preferably 10 nm or larger, and even more preferably 20 nm or larger. On the other hand, the size of the voids that may be included in the optical functional auxiliary layer is 500 nm or smaller, preferably 200 nm or smaller, and more preferably 100 nm or smaller. Note that the size of the void refers to the diameter of the major axis of the void, of the diameter of the major axis and the diameter of the minor axis.

[0065] The size of the pores can be quantified by the BET test method. In one embodiment, 0.1 g of the sample to be measured (e.g., the formed optical functional auxiliary layer) is placed in the capillary of a specific surface area measuring device (e.g., "ASAP2020" from Micromeritic), and then the sample is dried under reduced pressure at room temperature for 24 hours to remove any gas contained in the sample. Then, nitrogen gas is adsorbed onto the sample to create an adsorption isotherm, and the pore distribution is determined. This allows for the evaluation of the pore size.

[0066] The optical functional auxiliary layer (porous layer) typically includes an aerogel and / or particles (e.g., hollow microparticles and / or porous particles). The optical functional auxiliary layer preferably includes a nanoporous layer (specifically, a layer in which 90% or more of the pores have a diameter of 10 -1 nm~10 3 It may be a porous layer within the range of nm.

[0067] Any suitable particles can be used as the above-mentioned particles. Typically, the particles are composed of silica-based compounds. Examples of particle shapes include spherical, plate-shaped, needle-shaped, string-shaped, and grape cluster-shaped. Examples of string-shaped particles include particles in which multiple spherical, plate-shaped, or needle-shaped particles are linked together in a chain-like manner, short fibrous particles (for example, short fibrous particles described in Japanese Patent Publication No. 2001-188104), and combinations thereof. String-shaped particles may be linear or branched. Examples of grape cluster-shaped particles include those formed by the aggregation of multiple spherical, plate-shaped, and needle-shaped particles to form a grape cluster. The shape of the particles can be confirmed, for example, by observation using a transmission electron microscope.

[0068] An example of an optical functional auxiliary layer is a structure composed of one or more types of constituent units that form a fine void structure, and these constituent units are bonded together (for example, chemically bonded via catalytic action). Examples of the shapes of the constituent units include particulate, fibrous, rod-shaped, and plate-shaped. The constituent units may have only one shape, or they may have a combination of two or more shapes.

[0069] One specific example of an optical functional auxiliary layer is a porous layer composed of a porous body in which particles having micropores (hereinafter referred to as microporous particles) are chemically bonded together. Such a porous layer can be obtained, for example, by chemically bonding microporous particles together. The shape of the microporous particles is not particularly limited and may be spherical, for example, or other shapes. The microporous particles may also be, for example, sol-gel bead-like particles, nanoparticles (e.g., hollow nanosilica nanoballoon particles), nanofibers, etc. The microporous particles typically include inorganic substances. Specific examples of inorganic substances include silicon (Si), magnesium (Mg), aluminum (Al), titanium (Ti), zinc (Zn), and zirconium (Zr). These may be used individually or in combination of two or more. In one embodiment, the microporous particles are, for example, microporous particles of a silicon compound, and the porous body is, for example, a silicone porous body. The microporous particles of a silicon compound include, for example, pulverized gel-like silica compounds.

[0070] Another example of an optical function auxiliary layer is a layer containing fibrous material such as nanofibers, in which spaces are formed by the entanglement of these fibrous materials. Yet another example of an optical function auxiliary layer is a layer formed using hollow nanoparticles or nanoclay, or a layer formed using hollow nanoballoons or magnesium fluoride. The optical function auxiliary layer may be composed of a single constituent material or of multiple constituent materials. The optical function auxiliary layer may be composed of a single form as in the above example or of multiple forms as in the above example.

[0071] The porous layer described above may be, for example, a continuous cell structure in which the pore structure is continuous. A continuous cell structure means that in a porous material (for example, a silicone porous material), the pore structure is connected in three dimensions, and can also be described as a state in which the space of the pore structure is continuous. By having a continuous cell structure in the porous layer, the porosity can be increased. It is difficult to form a continuous cell structure using closed-cell particles that each have a pore structure, such as hollow particles (for example, hollow silica), but when silica sol particles (pulverized gel-like silicon compounds that form a sol) are used, for example, the silica sol particles may have a three-dimensional dendritic structure, and the dendritic particles settle and accumulate in the coating film (a coating film of a sol containing pulverized gel-like silicon compounds), thereby easily forming a continuous cell structure. It is preferable that the porous layer has a monolithic structure in which the continuous cell structure includes multiple pore distributions. A monolithic structure means, for example, a hierarchical structure that includes a structure in which nano-sized fine pores exist and a continuous cell structure in which nano-sized fine pores are aggregated. According to the monolithic structure, for example, it is possible to achieve both film strength and high porosity by providing film strength with fine pores and high porosity with a coarse, interconnected cell structure.

[0072] For example, the above monolithic structure can be formed by controlling the pore distribution of the void structure generated in the gel (gel-like silicon compound) prior to pulverization into silica sol particles. Alternatively, for example, when pulverizing a gel-like silicon compound, a monolithic structure can be formed by controlling the particle size distribution of the silica sol particles after pulverization to a predetermined size. The particle size distribution can be measured, for example, by particle size distribution evaluation devices such as dynamic light scattering and laser diffraction, and by electron microscopes such as scanning electron microscopes (SEM) and transmission electron microscopes (TEM).

[0073] As described above, the porous layer may contain pulverized gel-like compounds such as gel-like silicon compounds, and these pulverized particles are chemically bonded to each other (chemical bonds). The chemical bonds are not particularly limited and include, for example, cross-linking bonds, covalent bonds, and hydrogen bonds. The volume-average particle diameter of the pulverized material in the porous layer is, for example, 0.10 μm or more, preferably 0.20 μm or more, and more preferably 0.40 μm or more. On the other hand, the volume-average particle diameter of the pulverized material in the porous layer is, for example, 2.00 μm or less, preferably 1.50 μm or less, and more preferably 1.00 μm or less. Note that the volume-average particle diameter is an indicator of the variation in particle size of the pulverized material and can be determined by particle size distribution measurement.

[0074] The optical functional auxiliary layer may contain silicon atoms. For example, the silicon atoms contained in the optical functional auxiliary layer are preferably bonded to siloxane bonds. The proportion of unbonded silicon atoms (specifically, residual silanols) among all silicon atoms contained in the optical functional auxiliary layer is, for example, less than 50%, preferably 30% or less, and more preferably 15% or less.

[0075] An optical function auxiliary layer can be formed, for example, by coating or printing an optical function auxiliary layer forming coating solution (sometimes also referred to as a coating solution) onto the first main surface (uneven surface) of a diffractive optical element. More specifically, an optical function auxiliary layer can be formed by heating a coating film or printed layer of the optical function auxiliary layer forming coating solution formed on the first main surface (uneven surface) of the optical function layer.

[0076] In one embodiment, the coating film may be formed using a coating solution containing microporous particles, and the microporous particles may be chemically bonded together by heating (including drying) this coating solution. The coating solution containing microporous particles is, for example, a suspension. A catalyst (crosslinking reaction accelerator) and / or a substance that generates a catalyst (catalyst generator) that promotes crosslinking between microporous particles (for example, the dehydration condensation reaction of residual silanol groups that may be contained in the microporous particles) may be added to the coating solution. Examples of catalysts include photoactive catalysts and thermally activated catalysts. Examples of catalyst generators include photocatalyst generators and thermal catalyst generators. Examples of photocatalyst generators include photobase generators (catalysts that generate a basic catalyst by light irradiation) and photoacid generators (substances that generate an acidic catalyst by light irradiation). For example, the microporous particles are pulverized gel-like compounds (preferably gel-like silicon compounds), and the optical function auxiliary layer is a porous layer composed of a porous body (preferably a silicone porous body) containing the pulverized gel-like compounds. Such microporous particles may have a state in which the three-dimensional structure of the gel-like compound before pulverization is dispersed in a three-dimensional basic structure, and by using such microporous particles, a structure based on the three-dimensional basic structure can be formed. Specifically, a new structure different from the three-dimensional structure of the gel-like compound can be formed. Thus, the final optical function auxiliary layer (porous layer) may have a low refractive index, for example, similar to that of an air layer. Furthermore, by chemically bonding the microporous particles together, the above three-dimensional basic structure can be fixed, and sufficient strength can be ensured in the final optical function auxiliary layer (porous layer). Details of the specific composition and formation method of the optical function auxiliary layer (porous layer) are described, for example, in International Publication No. 2019 / 151073. The description in that publication is incorporated herein by reference.

[0077] The coating thickness of the above coating liquid can be set according to the desired thickness of the optical function auxiliary layer. The heating temperature of the coating film (coating liquid) is, for example, 20°C or higher, preferably 50°C or higher. On the other hand, the heating temperature of the coating film (coating liquid) is, for example, 200°C or lower, preferably 150°C or lower. The heating time of the coating film (coating liquid) is, for example, 10 seconds or longer. On the other hand, the heating time of the coating film (coating liquid) is, for example, 24 hours or shorter, preferably 1 hour or shorter, more preferably 30 minutes or shorter, and even more preferably 10 minutes or shorter.

[0078] E. Adhesive Layer The adhesive constituting the adhesive layer 160 has a hardness such that it does not penetrate into the voids of the optical function auxiliary layer (porous layer) in the normal state. With such a configuration, the characteristics resulting from the porosity of the optical function auxiliary layer can be maintained well. The storage elastic modulus of the adhesive at 23°C is preferably 1.0×10 5 (Pa) or more, more preferably 1.2×10 5 (Pa) or more, and even more preferably 1.3×10 5 (Pa) or more. On the other hand, considering the durability of the adhesive layer, the storage elastic modulus of the adhesive at 23°C is preferably 5.0×10 7 (Pa) or less, more preferably 4.0×10 7 (Pa) or less, even more preferably 3.0×10 7 (Pa) or less, particularly preferably 2.0×10 7 (Pa) or less, and especially preferably 1.0×10 7 (Pa) or less. Also, for example, the storage elastic modulus of the adhesive at 23°C may be 1.0×10 6 (Pa) or less. Such an adhesive has a buffering function (cushion function) against external forces and has a softness that can suppress damage to the porous layer. The storage elastic modulus is obtained by reading the value at 23°C when measured in accordance with the method described in JIS K 7244-1 "Plastics - Test Methods for Dynamic Mechanical Properties" under the condition of a frequency of 1 Hz and a heating rate of 5°C / min in the range of -50°C to 150°C.

[0079] Any suitable adhesive can be used as the adhesive constituting the adhesive layer, as long as it has the characteristics described above. Typical adhesives include acrylic adhesives (acrylic adhesive compositions). Typical acrylic adhesive compositions contain (meth)acrylic polymers as the main component (base polymer). (Meth)acrylic polymers may be contained in the adhesive composition in a proportion of, for example, 50% or more by weight, preferably 70% or more by weight, and more preferably 90% or more by weight, of the solid content of the adhesive composition. (Meth)acrylic polymers contain alkyl (meth)acrylate as the main component as monomer units. (Meth)acrylate refers to acrylate and / or methacrylate. Examples of alkyl groups in alkyl (meth)acrylate include linear or branched alkyl groups having 1 to 18 carbon atoms. The average number of carbon atoms in the alkyl group is preferably 3 to 9. Examples of monomers constituting (meth)acrylic polymers include alkyl (meth)acrylates, as well as comonomers such as carboxyl group-containing monomers, hydroxyl group-containing monomers, amide group-containing monomers, aromatic ring-containing (meth)acrylates, and heterocyclic (meth)acrylates. The comonomers are preferably hydroxyl group-containing monomers and / or heterocyclic (meth)acrylates, and more preferably N-acryloylmorpholine. The acrylic adhesive composition may preferably contain a silane coupling agent and / or a crosslinking agent. Examples of silane coupling agents include epoxy group-containing silane coupling agents. Examples of crosslinking agents include isocyanate-based crosslinking agents and peroxide-based crosslinking agents. Details of the acrylic adhesive composition are described, for example, in Japanese Patent No. 4140736, and the description in said patent publication is incorporated herein by reference.

[0080] The thickness of the adhesive layer is preferably 3 μm to 30 μm, and more preferably 5 μm to 15 μm. Within this thickness range, damage to the optical function auxiliary layer (porous layer) can be effectively suppressed, and as a result, the function of the diffractive optical element can be well maintained.

[0081] F. Protective layer The protective layer 180 can be any suitable configuration as long as it protects the diffractive optical element 100 and the optical function auxiliary layer 140 from external forces such as impact, moisture, and oxygen, and suppresses scratches, damage, and chemical deterioration. The protective layer can typically be composed of a resin film. The resin constituting the resin film may be a thermoplastic resin, a thermosetting resin, or an active energy ray (e.g., ultraviolet light, electron beam) curable resin. Examples of resin film forming materials include (meth)acrylic resins, cellulose resins such as diacetylcellulose and triacetylcellulose, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyester resins such as polyethylene terephthalate resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. Preferably, it is a (meth)acrylic resin or a polyester resin. Note that "(meth)acrylic resin" refers to acrylic resins and / or methacrylic resins.

[0082] The thickness of the protective layer may be, for example, 3 μm to 200 μm. Within this range, the thickness of the protective layer enables thinning of the optical laminate and, when the optical laminate is put into practical use, provides excellent surface protection and suppresses damage to the diffractive optical elements. The thickness of the protective layer may vary depending on the purpose, constituent materials, etc. For example, the thickness of the protective layer may be 5 μm to 190 μm, or 10 μm to 150 μm, or 15 μm to 130 μm, or 20 μm to 100 μm.

[0083] A hard coat layer may be provided on the outer surface of the protective layer (opposite the diffractive optical element). By providing a hard coat layer, damage to the diffractive optical element can be further suppressed. The hard coat layer preferably has a pencil hardness of H or higher, more preferably 2H or higher, and even more preferably 3H or higher. On the other hand, the pencil hardness of the hard coat layer is preferably 6H or lower, more preferably 5H or lower. The pencil hardness can be measured according to the "pencil hardness test" of JIS K 5400. The thickness of the hard coat layer may be, for example, 0.5 μm to 30 μm, or for example 1 μm to 20 μm, or for example 2 μm to 15 μm. Details of the hard coat layer are described, for example, in Japanese Patent Publication No. 2011-237789 and Japanese Patent Publication No. 2016-224443. The descriptions in those publications are incorporated herein by reference.

[0084] The tensile modulus of the protective layer is, for example, 20 MPa or more, preferably 30 MPa or more, more preferably 50 MPa or more, even more preferably 100 MPa or more, and particularly preferably 300 MPa or more. On the other hand, the tensile modulus of the protective layer is preferably 10 GPa or less, more preferably 8 GPa or less, and even more preferably 6 GPa or less. If the tensile modulus of the protective layer is within this range, when the optical laminate is put into practical use, it can provide excellent surface protection performance and suppress damage to the diffractive optical elements. The tensile modulus can be measured, for example, in accordance with JIS K 7161.

[0085] The glass transition temperature (Tg) of the protective layer is preferably 20°C or higher, more preferably 40°C or higher, even more preferably 60°C or higher, and particularly preferably 70°C or higher. On the other hand, the Tg of the protective layer may be, for example, 250°C or lower. If the Tg of the protective layer is within this range, similar to the effect of setting the tensile modulus within the above range, when the optical laminate is put into practical use, it is possible to provide excellent surface protection performance and suppress damage to the diffractive optical elements.

[0086] According to embodiments of the present invention, by providing a protective layer and an optical function auxiliary layer on the first main surface (main surface having an uneven structure) side of the diffractive optical element, the diffractive optical element can be protected from physical and / or chemical damage during actual use. As a result, the optical function of the diffractive optical element can be well maintained against visible light and near-infrared light. Here, visible light may be, for example, electromagnetic waves with wavelengths of 380 to 780 nm; near-infrared light may be, for example, electromagnetic waves with wavelengths of 780 to 1600 nm. Specific examples of damage include contamination by sebum, contamination by chemicals, destruction of fine irregularities due to pressure from protrusions, deformation of fine irregularities due to pressure, and deterioration of fine irregularities due to harmful electromagnetic waves such as ultraviolet rays. [Examples]

[0087] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0088] (1) Refractive index (1-1) Refractive index of a phase Fresnel lens A 5 μm thick flat film was fabricated using the same material as that used to make up the phase Fresnel lens, as described in Example 1 below. The refractive index of the obtained flat film was measured using a 2010 / M prism coupler manufactured by Metricon. (1-2) Refractive index of the optical auxiliary layer The optical functional auxiliary layer used in the example was formed on an acrylic film. The resulting laminate was cut to a size of 25 mm x 50 mm. The cut laminate was bonded to the surface of a glass plate (thickness: 3 mm) using an adhesive. The center of the back surface of the glass plate (approximately 20 mm in diameter) was colored black with a black marker to create a sample that did not reflect light from the back surface of the glass plate. The sample was set in an ellipsometer (JAWoollam Japan: VASE) and the refractive index was measured under conditions of a wavelength of 550 nm and an incident angle of 50° to 80°.

[0089] [Manufacturing Example 1] Preparation of coating solution for forming an optical functional auxiliary layer (1) Gelation of silicon compounds Mixture A was prepared by dissolving 0.95 g of methyltrimethoxysilane (MTMS), a precursor of silicon compounds, in 2.2 g of dimethyl sulfoxide (DMSO). To this mixture A, 0.5 g of 0.01 mol / L aqueous oxalic acid solution was added, and the mixture was stirred at room temperature for 30 minutes to hydrolyze the MTMS and produce mixture B containing tris(hydroxy)methylsilane. To 5.5 g of DMSO, 0.38 g of 28% by weight aqueous ammonia and 0.2 g of pure water were added. Then, the above mixture B was added, and the mixture was stirred at room temperature for 15 minutes to gel tris(hydroxy)methylsilane, obtaining mixture C containing a gel-like silicon compound. (2) Aging process The mixed solution C containing the gel-like silicon compound prepared as described above was incubated at 40°C for 20 hours to perform the maturation process. (3) Grinding Next, the gel-like silicon compound, which had been aged as described above, was crushed into granules of several mm to several cm in size using a spatula. Then, 40 g of isopropyl alcohol (IPA) was added to mixture C, and after light stirring, it was left to stand at room temperature for 6 hours to decantate the solvent and catalyst in the gel. By performing the same decantation treatment three times, the solvent was replaced to obtain mixture D. Next, the gel-like silicon compound in mixture D was subjected to pulverization (high-pressure medialess pulverization). For the pulverization (high-pressure medialess pulverization), a homogenizer (manufactured by SMT Co., Ltd., product name "UH-50") was used, and 1.85 g of the gel-like compound and 1.15 g of IPA from mixture D were weighed into a 5 cc screw bottle, and pulverization was performed at 50 W, 20 kHz for 2 minutes. This grinding process pulverized the gel-like silicon compound in the above-mentioned mixture D, resulting in the mixture D becoming a sol E of the pulverized material. The volume-average particle size, which indicates the particle size variation of the pulverized material contained in sol E, was confirmed to be 0.50 to 0.70 μm using a dynamic light scattering nanotrack particle size analyzer (Nikkiso Co., Ltd., UPA-EX150). Furthermore, to 0.75 g of sol E, 0.015 g of a 1.5 wt% MEK (methyl ethyl ketone) solution of a photobase generator (Wako Pure Chemical Industries, Ltd., product name: WPBG266) and 0.005 g of a 5% MEK solution of a bis-crosslinking accelerator ((trimethoxysilyl)hexane) were added in a ratio, and a mixed solvent of isobutyl alcohol / ethylene glycol dimethyl ether (1 / 1) was added to obtain a coating solution for forming an optical functional auxiliary layer with a solid content of 3 wt%.

[0090] [Manufacturing Example 2] Preparation of the adhesive constituting the adhesive layer In a four-necked flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser, 90.7 parts butyl acrylate, 6 parts N-acryloylmorpholine, 3 parts acrylic acid, 0.3 parts 2-hydroxybutyl acrylate, and 0.1 parts by weight of 2,2'-azobisisobutyronitrile as a polymerization initiator were charged together with 100 g of ethyl acetate. After introducing nitrogen gas and purging the mixture with nitrogen while gently stirring, the polymerization reaction was carried out for 8 hours while maintaining the liquid temperature in the flask at around 55°C to prepare an acrylic polymer solution. An acrylic adhesive solution was prepared by adding 0.2 parts isocyanate crosslinking agent (Coronate L, manufactured by Nippon Polyurethane Industries, Ltd., an adduct of trimethylolpropane tolylene diisocyanate), 0.3 parts benzoyl peroxide (Nippon Oil & Fats Co., Ltd., Niper BMT), and 0.2 parts γ-glycidoxypropyl methoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.: KBM-403) to 100 parts of the solids of the obtained acrylic polymer solution. Next, the above acrylic adhesive solution was applied to one side of a silicone-treated polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Polyester Films Co., Ltd., thickness: 38 μm) so that the thickness of the adhesive layer after drying would be 10 μm. The film was then dried at 150°C for 3 minutes to form the adhesive layer. The storage modulus of the obtained adhesive was 1.3 × 10⁻⁶. 5It was (Pa).

[0091] [Example 1] 1. Fabrication of diffractive optical elements (phase Fresnel lenses) A 6-inch fused silica substrate (thickness: 750 μm) was prepared as the substrate. On this substrate, phase Fresnel lenses as shown in Figures 2A and 2B were fabricated by two-photon polymerization photolithography. Specifically, the substrate was placed in a high-resolution 3D printer (Nanoscribe, product name "QuantumX"), and a monomer composition containing a radical polymerizable monomer and a photopolymerization initiator (Nanoscribe, product name "IP-Dip2") was subjected to two-photon polymerization to fabricate the phase Fresnel lenses on the substrate. The conditions for two-photon polymerization were as follows. Laser light used: Femtosecond laser (wavelength 780nm) Light focusing: Light focusing is achieved by a high-power lens with a numerical aperture (NA) of 1.4. Laser output: 25mW Scanning speed: 80mm / sec In-plane spacing of scan lines: 0.08 μm Scanning line spacing in the thickness direction: 0.08 μm

[0092] The polymerization (3D printing) process took 36 hours. After printing, the phase Fresnel lens / substrate laminate was removed from the 3D printer, immersed in propylene glycol monomethyl ether acetate (PGMEA) for 15 minutes, then in isopropyl alcohol (IPA) for 1 minute, followed by air blowing, and finally heating at 150°C for 1 hour. In this manner, residual monomers and cleaning solvents were removed from the phase Fresnel lens.

[0093] The resulting phase Fresnel lens configuration was as follows: Refractive index: 1.56 Prism height: 1.49 μm (constant height) Prism pitch: Gradually narrows towards the outer edge. Diffraction order: 1st order Lens numerical aperture (NA): 0.3 Lens radius: 2.5mm

[0094] 2. Fabrication of optical stacks The optical function auxiliary layer forming solution from Manufacturing Example 1 was applied to the surface of the phase Fresnel lens of the phase Fresnel lens / substrate laminate obtained above, and dried at 100°C for 30 minutes to form an optical function auxiliary layer with a thickness of 5 μm. The surface of the optical function auxiliary layer opposite to the substrate was flat. The refractive index of the optical function auxiliary layer was 1.18. Next, the adhesive layer from Manufacturing Example 2 was transferred to the surface of the optical function auxiliary layer. Furthermore, an HC-TAC film (Nitto Denko "HC3", thickness 45 μm) was laminated to the surface of the adhesive layer. The HC-TAC film is a triacetylcellulose (TAC) film with a hard coat (HC) layer formed on it, and it was laminated so that the TAC film was on the adhesive layer side. In this way, an optical laminate having the configuration of HC layer / TAC film / adhesive layer / optical function auxiliary layer / phase Fresnel lens / substrate was obtained.

[0095] 3. Evaluation of optical laminates 3-1. Light-gathering performance Parallel light (wavelength 532 nm) was incident on the substrate side of the obtained optical laminate, and the state of the light emitted from the phase Fresnel lens was observed using a laser microscope (Keyence Corporation, product name "VK-X3000"). The observed image is shown in Figure 6. As is clear from Figure 6, the phase Fresnel lens showed good light-gathering performance.

[0096] 3-2. Durability of optical functions After autoclaving the obtained optical laminate (5 atmospheres, 50°C, 15 minutes), we confirmed whether the optical laminate possessed practically acceptable optical durability. Specifically, we touched the surface of the optical laminate directly with a finger, then rubbed it firmly with a finger, and finally rubbed it back and forth 10 times with a cloth. Subsequently, when we observed the optical laminate with a laser microscope, no change was observed in the appearance of the phase Fresnel lens. In other words, it was confirmed that the optical laminate (essentially a phase Fresnel lens) possessed practically acceptable optical durability. [Industrial applicability]

[0097] The optical laminate according to the embodiment of the present invention is expected to have applications in, for example, lenses in optical systems where miniaturization, lightness, and thinness are required, AR / VR devices, LiDAR in autonomous driving or facial recognition systems, surveillance systems such as IR or machine vision cameras, CMOS image sensors, and medical devices such as endoscopes. [Explanation of Symbols]

[0098] 10. First lens section 20 Second lens section 21 Prisms 21a Fresnel surface 21b Rise surface 21c top 21d bottom 100 diffractive optical elements 100a First main surface 100b Second main surface 100c optical axis (center axis) 120 Base material 140 Optical function auxiliary layer 160 Adhesive layer 180 protective layer 200 Optical laminate

Claims

1. The device comprises: a substrate; a diffractive optical element having a non-periodic uneven structure provided on the substrate; and an optical functional auxiliary layer provided so as to cover the diffractive optical element; The refractive index of the diffractive optical element is 1.50 to 2.

70. The refractive index of the optical functional auxiliary layer is less than 1.

30. Optical laminate.

2. The optical laminate according to claim 1, wherein the diffractive optical element is a phase Fresnel lens or a metalens.

3. The optical laminate according to claim 2, wherein the radius of the diffractive optical element is 0.1 mm to 100 mm.

4. The optical laminate according to claim 3, wherein the height of the uneven structure of the diffractive optical element is 0.5 μm to 2.0 μm.

5. The optical laminate according to claim 4, wherein the thickness of the optical functional auxiliary layer is three times or more the height of the uneven structure of the diffractive optical element.

6. The optical laminate according to any one of claims 1 to 5, wherein the diffractive optical element is composed of a photocurable resin, a thermoplastic resin, or a thermosetting resin.

7. The optical laminate according to any one of claims 1 to 5, wherein the radius of the substrate is 1.05 to 30 times the radius of the diffractive optical element.

8. The optical laminate according to any one of claims 1 to 5, further comprising a protective layer on the side of the optical functional auxiliary layer opposite to the diffractive optical element, wherein the surface of the optical functional auxiliary layer on the protective layer side is a flat surface.

9. The optical function auxiliary layer and the protective layer are laminated with an adhesive layer in between, and the storage modulus of the adhesive layer at 23°C is 1.0 × 10⁻⁶. ５ The optical laminate according to claim 8, wherein the pressure is (Pa) or higher.

10. The optical laminate according to claim 9, wherein the optical functional auxiliary layer is a porous layer and its porosity is 20% by volume to 60% by volume.

11. The optical laminate according to claim 10, wherein the optical functional auxiliary layer has a total light transmittance of 85% to 99% and a haze of less than 5%.

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