Manufacturing method for diffractive optical lement

Abstract

Provided is a manufacturing method for a diffractive optical element having a non-periodic relief structure that has a predetermined relief depth or more and is concentrically shaped in plan view, the manufacturing method making it possible to obtain a diffractive optical element in which air bubbles are suppressed and which has an excellent optical characteristic. A manufacturing method for a diffractive optical element according to an embodiment of the present invention is a method for manufacturing a diffractive optical element having a non-periodic relief structure that has a relief depth of 4.0 μm or more and is concentrically shaped in plan view. The manufacturing method comprises: a step for coating a base material with a photocurable resin composition to form a coating film; a step for pressing a replica mold having a pattern corresponding to the non-periodic relief structure of the diffractive optical element to be obtained against the coating film; and a step for irradiating the coating film with light in a state where the replica mold is pressed, so as to cure the coating film and transfer the pattern of the replica mold to the coating film. The viscosity of the photocurable resin composition is 100-5,000 mPa·s, and the pressing pressure of the replica mold is 3-45 bar.

Description

Method for manufacturing diffractive optical elements

[0001] This invention relates to a method for manufacturing a diffractive optical element.

[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, they enable the miniaturization, weight reduction, and thinning of optical systems, and are expected to be put into practical use. 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 can also adjust the phase of light during such focusing or diverging, and can deform the wavefront of transmitted light into a specific shape to appropriately focus it at the focal point. Such diffractive optical elements can be manufactured, for example, by nanoimprint lithography. However, depending on the specific shape of the non-periodic surface uneven structure (especially when the depth of the unevenness is deep), bubbles may form in the resulting diffractive optical element, resulting in insufficient function of the diffractive optical element.

[0003] Japanese Patent Publication No. 2003-270418, Japanese Patent Publication No. 2016-176981, Japanese Patent Publication No. 2022-014503, Japanese Patent Publication No. 2024-117790

[0004] The main object of the present invention is to provide a method for manufacturing a diffractive optical element having a non-periodic uneven structure with concentric circles in a plan view and having an unevenness depth greater than a predetermined value, wherein bubbles are suppressed and a diffractive optical element with excellent optical properties can be obtained.

[0005] [1] A method for manufacturing a diffractive optical element according to an embodiment of the present invention is a method for manufacturing a diffractive optical element having a non-periodic uneven structure with a depth of 4.0 μm or more and concentric circles in a plan view. The manufacturing method includes the steps of: applying a photocurable resin composition to a substrate to form a coating film; pressing a replica mold having a pattern corresponding to the non-periodic uneven structure of the obtained diffractive optical element onto the coating film; and irradiating the coating film with light while the replica mold is pressed onto it to cure the coating film and transfer the pattern of the replica mold to the coating film. The viscosity of the photocurable resin composition is 100 mPa·s to 5000 mPa·s, and the pressing pressure of the replica mold is 3 bar to 45 bar. [2] In [1] above, the thickness of the coating film is 5.0 μm or more. [3] In [1] or [2] above, the manufacturing method includes adjusting the pressing pressure by moving the replica mold and the roller relative to each other while the replica mold is pressed against the coating film. [4] In any of [1] to [3] above, the substrate is a polyethylene terephthalate film. [5] In any of [1] to [4] above, the diffractive optical element is a phase Fresnel lens or a metalens. [6] In any of [1] to [5] above, the radius of the diffractive optical element is 0.1 mm to 100 mm.

[0006] According to embodiments of the present invention, a method for manufacturing a diffractive optical element having a non-periodic uneven structure with a predetermined or greater unevenness depth and concentric circles in a plan view can be provided, which can produce a diffractive optical element that suppresses bubbles and has excellent optical properties.

[0007] This is a schematic plan view of a phase Fresnel lens, which is an example of a diffractive optical element that can be obtained by the manufacturing method of an embodiment of the present invention. This is a schematic cross-sectional view of the phase Fresnel lens of Figure 1A along the line B-B. This is an enlarged schematic cross-sectional view of the main part of the second lens portion (prism) in the phase Fresnel lens of Figure 1A. This is a schematic diagram to explain the meaning of the numerical aperture NA in a phase Fresnel lens, which is an example of a diffractive optical element that can be obtained by the manufacturing method of the present invention. This is a conceptual diagram to explain the use of second-order or higher diffraction of light in a phase Fresnel lens, which is an example of a diffractive optical element that can be obtained by the manufacturing method of an embodiment of the present invention. This is a schematic cross-sectional view of a metalens, which is another example of a diffractive optical element that can be obtained by the manufacturing method of an embodiment of the present invention.

[0008] Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. Note that, for ease of viewing and understanding, the drawings are schematic or conceptual, and the lengths, widths, heights, thicknesses, shapes, sizes, proportions, directions, and quantities may differ from those of the actual objects.

[0009] A. Overview of the Method for Manufacturing a Diffractive Optical Element The method for manufacturing a diffractive optical element according to an embodiment of the present invention is a method for manufacturing a diffractive optical element having a surface depth of 4.0 μm or more and a non-periodic surface structure that is concentric in a plan view. The manufacturing method includes: a step of applying a photocurable resin composition to a substrate to form a coating film (coating film formation step); a step of pressing a replica mold having a pattern corresponding to the non-periodic surface structure of the obtained diffractive optical element onto the coating film (replica mold pressing step); and a step of irradiating the coating film with light while the replica mold is pressed onto it to cure the coating film and transfer the pattern of the replica mold to the coating film (pattern transfer step). In the embodiment of the present invention, the viscosity of the photocurable resin composition is 100 mPa·s to 5000 mPa·s, and the pressing pressure of the replica mold is 3 bar to 45 bar.

[0010] Hereinafter, a diffractive optical element that can be obtained by the manufacturing method of the embodiment of the present invention will be described, followed by a description of the manufacturing method.

[0011] B. Diffractive Optical Elements B-1. Overview of Diffractive Optical Elements The diffractive optical elements that can be obtained by the manufacturing method of the embodiments of the present invention can be any suitable optical element that performs its function by diffraction. In the embodiments of the present invention, as described above, the diffractive optical element has a surface depth of 4 μm or more and has a non-periodic surface structure that is concentric in a plan view. Typical examples of diffractive optical elements include phase Fresnel lenses, metalenses, cylindrical lenses, and point focus lenses. 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-order diffraction.

[0012] The following primarily describes phase Fresnel lenses, with a brief explanation of metalenses.

[0013] B-2. Phase Fresnel Lens Figure 1A is a schematic plan view of a phase Fresnel lens; Figure 1B is a schematic cross-sectional view of the phase Fresnel lens of Figure 1A along the line B-B; Figure 1C is an enlarged schematic cross-sectional view of the main part of the second lens portion (prism) in the phase Fresnel lens of Figure 1A. The illustrated example of a phase Fresnel lens 100 comprises a first lens portion 10 provided in the center and a second lens portion 20 provided around the first lens portion 10. In the illustrated example, the first lens portion 10 and the second lens portion 20 are provided on the first main surface 100a side of the phase Fresnel lens. The first lens portion 10 and the second lens portion 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.

[0014] 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 a curved surface and an inclined surface. 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, when 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.

[0015] 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 and provided concentrically. That is, as explained in section B-1 above, the phase Fresnel lens 100 has a non-periodic uneven structure that is concentric in plan view. In such a configuration, the effects of the embodiment of the present invention can be remarkable. Specifically, the diffractive optical element (for example, the phase Fresnel lens) can be manufactured by a so-called nanoimprint method, as will be explained in section C below. The nanoimprint method includes pressing a replica mold having a pattern corresponding to the non-periodic uneven structure described above onto a coated film of a photocurable resin composition (diffractive optical element forming material) and transferring the pattern to the photocurable resin composition. Here, if the non-periodic uneven structure is concentric in plan view, the outermost prism among the multiple prisms constituting the second lens portion acts as a barrier, and when the replica mold is pressed, there is no escape route for the photocurable resin composition. As a result, bubbles may be generated in the resulting diffractive optical element. In contrast, according to the embodiment of the present invention, as will be explained in section C below, even a diffractive optical element having such a concentric non-periodic uneven structure in plan view can be manufactured with good suppression of bubbles.

[0016] Each of the multiple prisms 21 has: a Fresnel surface 21a 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 for example, 20 to 300 steps. 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 for example, 1° to 45°. The rise surface 21b may be flat (its cross-section may be straight as in the illustrated example), or it may be curved (its cross-section may be curved).

[0017] 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 periphery. The manner in which the prism pitch gradually narrows toward the outer periphery 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 periphery such that the position xi of the top of the i-th prism from the center of the lens satisfies the following equation (2). In equation (2), n is the refractive index of the phase Fresnel lens (essentially a prism), f is the focal length of the phase Fresnel lens, and d ０ k is the height of the prism. ０ k is a variable related to the radius of the first lens section, and can be arbitrarily set by the designer within the range of 0 to 1. For example, k ０ If is 0, the height of the first lens is d０ It is equal to , and as it increases, xi decreases (i.e., the radius of the first lens part decreases), and the height of the first lens part is d ０ It will be lower than that.

[0018] 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 periphery. 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 60 to 97, or 65 to 96, or 70 to 93, or 72 to 90, or 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). In equation (3), n is the refractive index of the prism, and NA is the numerical aperture. The numerical aperture NA is an indicator of the lens's focusing power; a larger numerical aperture NA means higher focusing power (higher lens power). The numerical aperture NA can be calculated from the following equation (4). In equation (4), R is the radius of the phase Fresnel lens, f is the focal length of the phase Fresnel lens, and θ is the focusing angle (see Figure 2).

[0019] 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.

[0020] 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). In equation (1), n ​​is the refractive index of the prism, f is the focal length of the phase Fresnel lens, and x is the distance from the center of the phase Fresnel lens.

[0021] 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 that utilize second-order or higher-order phases, 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).

[0022] Figure 3 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 3, 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 two 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 3, 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.

[0023] 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.

[0024] Configurations that can utilize second-order or higher diffraction can typically be achieved by controlling the height of the prism. The height of the prism is d. ０ This can be obtained from the following equation (5). In equation (5), n is the refractive index of the prism, m is the order of diffraction, and λ is the wavelength of light. For example, if the refractive index of the prism is 1.55, the height of the prism that can utilize third-order diffraction for a wavelength of 532 nm is 2902 nm (2.902 μm). Assuming that the refractive index does not change with wavelength, from equation (5), a prism height of 2902 nm can utilize fourth-order diffraction for light with a wavelength of 399 nm and second-order diffraction for light with a wavelength of 798 nm. In this way, a higher-order phase Fresnel lens can focus light of multiple wavelengths (colors) simultaneously. As a result, higher-order phase Fresnel lenses can be suitably applied to multi-color optical systems. By appropriately adjusting the height of the prism, the phase Fresnel lens can be applied in a wavelength range of, for example, 300 nm (ultraviolet region) to 2000 nm (infrared region).

[0025] As described above, the height of the prism may be constant, or it may be configured to gradually decrease towards the outer edge. In the configuration where the height of the prism is constant, d in equation (5) above ０ This is the height of all the prisms. In a configuration where the height of the prisms gradually decreases towards the outer edge, d ０ This is the height of the innermost prism (i.e., adjacent to the first lens portion). With a configuration in which the height of the prism gradually decreases toward the outer edge, even when using second-order or higher diffraction and when the numerical aperture of the lens is large (high light-gathering power), focusing noise can be suppressed (preferably eliminated).

[0026] In an embodiment of the present invention, as described above, the depth of the concavities and convexities in the aperiodic concavo-convex structure is 4.0 µm or more. When the depth of the concavities and convexities is large as described above, when a replica mold is pressed against a coating film of a photocurable resin composition, the photocurable resin does not spread to every corner of the concave portions of the replica mold, and air bubbles may occur in the resulting diffractive optical element. In contrast, according to an embodiment of the present invention, as described in Section C below, even a diffractive optical element having such a deep concavo-convex structure can be produced while satisfactorily suppressing air bubbles. The depth of the concavities and convexities is preferably 4.5 µm or more, more preferably 5.0 µm or more, still more preferably 8.0 µm or more, and particularly preferably 10.0 µm or more. According to an embodiment of the present invention, even when the depth of the concavities and convexities falls within the above range, a diffractive optical element with suppressed air bubbles can be produced. The depth of the concavities and convexities may be, for example, 20.0 µm or less, or may be, for example, 15.0 µm or less. The depth of the concavities and convexities corresponds to the height d of the prism ０ (when the height of the prism gradually decreases toward the outer peripheral side, the height of the innermost prism).

[0027] The numerical aperture NA of the phase Fresnel lens may be, for example, 0.05 to 0.8, may be, for example, 0.08 to 0.7, may be, for example, 0.1 to 0.6, and may be, for example, 0.2 to 0.5. The numerical aperture NA can be obtained from the above formula (4).

[0028] As briefly described above, and as will be described in detail in Section C below, the phase Fresnel lens is typically made of a photocurable resin. By using a photocurable resin, the phase Fresnel lens can be produced by optical nanoimprinting. Since optical nanoimprinting allows operations at normal temperature, it has the advantage of high pattern reproduction accuracy. The photocurable resin is preferably light-transmissive.

[0029] The refractive index n of the phase Fresnel lens (and therefore the refractive index of the first and second lens portions) may be, for example, 1.50 to 2.70, 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.

[0030] 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.

[0031] B-3. ​​Metalens Figure 4 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 4 (similarly, the arrangement when viewed from above is also aperiodic). In the embodiment of the present invention, the arrangement of the pillars is concentric as described above. 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 can correspond to the depth of the irregularities in the aperiodic irregularity structure. Therefore, the height of the pillars is 4.0 μm or more as described above, and may be, for example, 4.5 μm to 20.0 μm.

[0032] 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.

[0033] Metalens, like phase Fresnel lenses, can also be manufactured by the manufacturing method described in section C below.

[0034] C. Details of the Method for Manufacturing a Diffractive Optical Element The method for manufacturing a diffractive optical element according to the embodiment of the present invention includes, as described above, a coating film formation step, a replica mold pressing step, and a pattern transfer step. Each of these steps will be described in detail below.

[0035] C-1. Coating Film Formation Process First, a photocurable resin composition (diffractive optical element forming material) is applied to the substrate to form a coating film. 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 composition, 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. The substrate is preferably a resin film. Resin films are easy to roll form, and as a result, diffractive optical elements can be continuously formed on the substrate by a process that combines nanoimprinting and roll-to-roll. The substrate is more preferably a polyester resin film, even more preferably a polyethylene terephthalate (PET) film, and particularly preferably a biaxially oriented PET film. Such a polyester resin film can exhibit excellent adhesion to the coating film of the photocurable resin composition.

[0036] The thickness of the base material may be, for example, 20 μm to 200 μm, may be for example 20 μm to 150 μm, may be for example 20 μm to 120 μm, and may be for example 20 μm to 80 μm. When the thickness falls within such a range, a lens with high transmittance can be obtained without appearance defects such as wrinkles and creases.

[0037] The haze of the base material is preferably 3.0% or less, more preferably 2.0% or less, still more preferably 1.0% or less, and particularly preferably 0.8% or less. When the haze falls within such a range, there can be obtained the advantage that the light condensing performance of the lens is not impaired. The lower the haze is, the more preferable it is, and the lower limit thereof may be, for example, 0.1%. The haze can be measured in accordance with JIS C 2318.

[0038] The total light transmittance of the base material is preferably 75% or more, more preferably 80% or more, still more preferably 85% or more, and particularly preferably 88% or more. When the total light transmittance falls within such a range, a lens with low light loss can be obtained. The higher the total light transmittance is, the more preferable it is, and the upper limit thereof may be, for example, 98%. The total light transmittance can be measured in accordance with JIS C 2318.

[0039] The tensile strength of the base material is preferably 150 MPa to 350 MPa, more preferably 170 MPa to 320 MPa, still more preferably 180 MPa to 300 MPa, and particularly preferably 200 MPa to 290 MPa. When the tensile strength falls within such a range, a lens with high transferability (which is unlikely to deform and is unlikely to crack) during pressing in nanoimprinting can be obtained. The tensile strength can be measured in accordance with JIS C 2318.

[0040] The elongation percentage of the base material is preferably 60% to 200%, more preferably 70% to 180%, still more preferably 80% to 170%, and particularly preferably 85% to 160%. When the elongation percentage falls within such a range, a lens with high transferability (which is unlikely to deform and is unlikely to crack) during pressing in nanoimprinting can be obtained. The elongation percentage can be measured in accordance with JIS C 2318.

[0041] The heat shrinkage rate of the substrate (at 150°C) is preferably 1.5% or less, more preferably 1.3% or less, even more preferably 1.2% or less, and particularly preferably 1.0% or less. The heat shrinkage rate may be, for example, 0.1% or more, or for example, 0.2% or more. If the heat shrinkage rate is within this range, deterioration of lens performance due to heat during use can be suppressed. The heat shrinkage rate may be measured in accordance with JIS C 2318.

[0042] In one embodiment, the substrate may have a flat first main surface and a second main surface having a fine uneven structure. In this case, the photocurable resin composition can typically be applied to the second main surface. The surface roughness Ra of the second main surface is preferably 1 nm to 30 nm, and more preferably 2 nm to 20 nm. With such a configuration, the coating film can adhere closely to the substrate. As a result, defects that may occur when pressing the replica mold can be significantly suppressed. Consequently, since the photocurable resin composition constituting the coating film reaches every corner of the replica mold, the generation of air bubbles can be significantly suppressed. The surface roughness Ra can be measured in accordance with JIS B 0601.

[0043] In embodiments of the present invention, the viscosity of the photocurable resin composition is 100 mPa·s to 5000 mPa·s, preferably 200 mPa·s to 4700 mPa·s, more preferably 400 mPa·s to 4200 mPa·s, even more preferably 700 mPa·s to 3500 mPa·s, and particularly preferably 900 mPa·s to 3000 mPa·s. If the viscosity of the photocurable resin composition is within this range, a coating film of the desired thickness can be formed, and the photocurable resin composition can be spread to every corner of the replica mold when the replica mold is pressed. As a result, a diffractive optical element can be obtained in which the unevenness depth in the non-periodic uneven structure is 4 μm or more, and bubbles are suppressed.

[0044] Any suitable configuration can be employed for the photocurable resin composition, provided that the desired viscosity can be achieved. Typically, the photocurable resin composition comprises a curing component and a photopolymerization initiator. Typical curing components include (meth)acrylate monomers or oligomers. In this specification, "(meth)acrylate" means acrylate and / or methacrylate. Specific examples of curing components include dipropylene glycol di(meth)acrylate (DPGDA), hexanediol di(meth)acrylate (HDDA), tripropylene glycol di(meth)acrylate (TPGDA), pentaerythritol tri(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate (m+n=10), methoxypolyethylene glycol #400 (meth)acrylate, trimethylolpropane EO modified tri(meth)acrylate, benzyl (meth)acrylate, 1- or 2-naphthyl (meth)acrylate, 1- or 2-naphthylmethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, isobolonyl (meth)acrylate, and adamantyl (meth)acrylate. Typically, photopolymerization initiators generate radicals upon irradiation with ultraviolet light, initiating the 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. The photocurable resin (resin composition) may contain a release agent and / or viscosity modifier. Typical release agents include fluorine compounds, silicone compounds, and phosphorus compounds. The use of a release agent can improve release properties from the replica mold. Typical viscosity modifiers include monomers and low molecular weight oligomers. The use of a viscosity modifier can improve filling and transfer properties to the replica mold.

[0045] Commercially available photocurable resin compositions may be used. Examples of commercially available products include "NL-S1030," "NL-S1060 V1K," "NL-S1060 V2K," "NL-S1060 V4K," and "NX003" from Shin Nakamura Chemical Co., Ltd., "Sunrad TM-01," "Sunrad FM-01," and "Sunrad TS-02" from Sanyo Chemical Industries, Ltd., and "OGSOL EA-0200," "OGSOL EA-F5710," "OGSOL GA-5060P," "OGSOL EA-0300," and "OGSOL GA-2800" from Osaka Gas Chemical Co., Ltd. Appropriate additives (e.g., viscosity modifiers, solvents) may be added to the commercially available products. These photocurable resin compositions may be used individually or in combination of two or more types.

[0046] In the photocurable resin composition, inorganic nanoparticles may be added (substantially dispersed) to increase the refractive index of the resulting diffractive optical element (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 added may be, for example, 10 to 80 parts by weight per 100 parts by weight of resin.

[0047] Any suitable method can be used to apply the photocurable resin composition. Specific examples of application methods include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (comma coating).

[0048] The thickness of the coating film can be appropriately set according to the desired depth of the unevenness. The thickness of the coating film may be, for example, 5.0 μm or more, or for example, 6.0 μm or more. If the thickness of the coating film is within this range, an uneven structure with a depth of 4.0 μm or more can be formed. The thickness of the coating film is preferably within ±0.5 μm, and more preferably within ±0.3 μm, of the set thickness. By adjusting the viscosity of the photocurable resin composition to the above desired range, a coating film with a thickness that differs little from the set thickness can be obtained.

[0049] C-2. Replica Mold Pressing Process Next, a replica mold having a pattern corresponding to the non-periodic uneven structure of the obtained diffractive optical element is pressed onto the coated film on the substrate. In the embodiment of the present invention, the pressing pressure of the replica mold is 3 bar to 45 bar as described above. If the pressing pressure is within this range, bubbles can be suppressed well and the optical properties (typically, light-gathering performance) of the obtained diffractive optical element can be made excellent. If the pressing pressure is too low, bubble suppression may be insufficient. If the pressing pressure is too high, the optical properties of the diffractive optical element may be insufficient. In particular, the problems that occur when the pressing pressure is too high cannot be predicted from common technical knowledge, and the effect of setting the pressing pressure to 3 bar to 45 bar is an unexpectedly excellent effect. The pressing pressure may be, for example, 5 bar or more, or for example, 7 bar or more, or for example, 10 bar or more, or for example, 12 bar or more, or for example, 15 bar or more. On the other hand, the pressing pressure may be, for example, 40 bar or less, 35 bar or less, 32 bar or less, 30 bar or less, or 28 bar or less. If the pressing pressure is within this range, the above effects may become even more pronounced.

[0050] The replica mold can be pressed in any suitable manner. Specifically, the replica mold may be pressed in a batch or a continuous manner. The batch method typically involves pressing the replica mold onto the coating film of a laminate of sheet-like substrates / coated films. In the batch method, typically the side of the replica mold opposite to the side in contact with the coating film (the side with the pattern) is pressed by any suitable means. The pressing means may be a plate or a roll. When using a plate, typically the plate and the replica mold are moved relatively vertically to press. When using a roll, the roll and the replica mold are moved relatively horizontally to press. Pressing with a plate and pressing with a roll may be combined. A typical example of a continuous method is the roll-to-roll process. The roll-to-roll process typically involves pressing a replica mold, provided on a stamping roll, onto a long (roll-shaped) laminate of substrates / coated films while conveying it. The pressing pressure can be adjusted by the pressing as described above.

[0051] C-3. At the end of the pattern transfer process, the coated film is irradiated with light while the replica mold is pressed against it. Here, "pressed against the replica mold" means that the replica mold is pressed against the coated film. Therefore, the replica mold may be subjected to the desired pressing pressure described above, or it may be subjected to pressure sufficient to maintain adhesion (a pressure smaller than the desired pressing pressure described above), or no pressure may be applied as long as adhesion is maintained.

[0052] The light irradiated onto the coated film can be appropriately set according to the type of coated film (photocurable resin composition). The light may include electromagnetic waves. Examples of light include ultraviolet light, visible light, infrared light, and electron beams. Ultraviolet light is preferred because of its versatility and ease of handling. The amount of light irradiated can be appropriately set according to the type of coated film (photocurable resin composition). Light irradiation is preferably continued until the coated film (photocurable resin composition) no longer hardens. For example, when irradiating with ultraviolet light, the illuminance may be, for example, 40 mW to 2000 mW, and the integrated light amount may be, for example, 100 mJ / cm². ２ ~2000mJ / cm ２ This is possible. When irradiating with ultraviolet light, typical examples of 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 an even 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.

[0053] As described above, light irradiation hardens the coating film, and the pattern of the replica mold (a pattern corresponding to the non-periodic uneven structure of the diffractive optical element) is transferred (stamped) onto the coating film. In this way, optical nanoimprinting can yield a diffractive optical element having an unevenness depth of 4.0 μm or more, a non-periodic uneven structure that is concentric in plan view, suppressed bubbles, and excellent optical properties.

[0054] Furthermore, the replica mold pressing process and the pattern transfer process may be performed using a nanoimprint lithography apparatus configured to enable the above-described operations.

[0055] C-4. Fabrication of Replica Molds The following describes the fabrication of replica molds that can be used in optical nanoimprinting as described above.

[0056] C-4-1. Preparation of Master Mold First, a diffractive optical element similar to the target diffractive optical element is prepared. The obtained diffractive optical element is called a master mold. Master molds can typically be prepared by stereolithography. A typical stereolithography method is two-photon polymerization stereolithography. Two-photon polymerization (TPP) is a technology used in high-resolution 3D printers. Two-photon polymerization stereolithography typically uses photopolymerization to convert a liquid photocurable resin into a solid. 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 perform extremely fine processing on a nanometer scale. The monomer composition used for two-photon polymerization typically includes a radical polymerizable monomer and a two-photon polymerization initiator. Examples of radically polymerizable monomers include difunctional (meth)acrylic monomers, trifunctional (meth)acrylic monomers, and polyfunctional (meth)acrylic monomers. In this specification, "(meth)acrylic" means acrylic and / or methacrylic. Examples of trifunctional (meth)acrylic monomers include pentaerythritol tri(meth)acrylate (PETA) and trimethylolpropane tri(meth)acrylate (TMPTA). Examples of polyfunctional (meth)acrylic monomers include dipentaerythritol hexa(meth)acrylate (DPHA). Aromatic (meth)acrylic monomers (e.g., benzyl (meth)acrylate) may be used for refractive index adjustment. 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. The two-photon polymerization initiator preferably has a large two-photon absorption cross-section. With such a configuration, the reaction occurs only when using laser light of a higher intensity than that used for normal photon absorption, 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.

[0057] Two-photon polymerization can typically be carried out by irradiating the above monomer composition with laser light. Preferably, the laser light has a high energy density. Such a configuration allows for good two-photon absorption. Examples of lasers 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.

[0058] A specific procedure for two-photon polymerization may be as follows: Using a 780 nm femtosecond laser (pulse width = 100 femtoseconds), focusing 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 sections B-2 and B-3 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. Then, a master mold for a diffractive optical element can be obtained by immersing the fabricated object in a solvent with low surface tension (e.g., alcohol, hexane, methyl nonaflurobutyl ether) for, for example, 15 minutes and drying it.

[0059] 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.

[0060] C-4-2. Fabrication of Replica Molds Next, a replica mold is fabricated using the master mold. The replica mold may be fabricated using the following replication transfer technique, or it may be fabricated by the two-photon polymerization photolithography described above.

[0061] The fabrication of a replica mold using replication transfer technology can be carried out, for example, by the following procedure: A final photopolymerized object (a diffractive optical element such as a phase Fresnel lens) is formed on any suitable substrate to serve as a master mold. Next, a conductive thin film of metal (e.g., nickel) is formed on the surface of the master mold 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 master mold is removed with a solvent or chemical. The master mold and the replica mold may also be mechanically separated. In this way, a replica mold can be obtained.

[0062] Using such replica molds, diffractive optical elements can be fabricated by optical nanoimprinting as described in sections C-1 to C-3 above.

[0063] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The evaluation methods in the examples are as follows.

[0064] (1) A 5 μm thick flat film was prepared using the photocurable resin used in the refractive index examples and comparative examples of the diffractive optical element forming material (photocurable resin). The refractive index of the obtained flat film was measured using a 2010 / M prism coupler manufactured by Metricon.

[0065] (2) The diffractive optical elements (phase Fresnel lenses) obtained in the examples and comparative examples of bubbles in diffractive optical elements were observed with an optical microscope for the presence or absence of bubbles and evaluated according to the following criteria: A (Good): No bubbles were observed B (Acceptable): One to three bubbles were observed C (Poor): Four or more bubbles were observed

[0066] (3) Optical Characteristics of Diffractive Optical Elements The diffractive optical elements (phase Fresnel lenses) obtained in the examples and comparative examples were measured using an optical constant measuring device (manufactured by TriOptix, product name "Optisphere®") to determine the modulation transfer function (MTF) at a wavelength of 546 nm. The values ​​for spatial frequencies of 40 lp / mm and 100 lp / mm were compared with those of the master mold and evaluated according to the following criteria. Note that MTF is one of the indicators of the imaging performance (light-gathering performance) of the lens. A (Good): For both 40 lp / mm and 100 lp / mm, the MTF ratio to the master mold was 90% or more. B (Acceptable): For both 40 lp / mm and 100 lp / mm, the MTF ratio to the master mold was 80% or more and less than 90%. C (Poor) : For at least one of 40 lb / mm and 100 lb / mm, the MTF ratio to the master mold was less than 80%.

[0067] [Example of Use: Diffractive Optical Element Forming Material (Photocurable Resin)] Photocurable resins 1 to 11 shown in Table 1 (referred to simply as "resin" in the examples) were used as diffractive optical element forming materials. The meaning of the notation in the "Type" column of Table 1 is as follows. NL-S1030: Product name of a photocurable resin for nanoimprinting manufactured by Shin Nakamura Chemical Co., Ltd. NL-S1060-V1K: Product name of a photocurable resin for nanoimprinting manufactured by Shin Nakamura Chemical Co., Ltd. NL-S1060-V2K: Product name of a photocurable resin for nanoimprinting manufactured by Shin Nakamura Chemical Co., Ltd. NL-S1060-V4K: Product name of a photocurable resin for nanoimprinting manufactured by Shin Nakamura Chemical Co., Ltd. NX003: Product name of a photocurable resin for nanoimprinting manufactured by Shin Nakamura Chemical Co., Ltd. TM-01: "Sunrad TM-01" photocurable resin for nanoimprinting manufactured by Sanyo Chemical Co., Ltd. FM-01: "Sunrad FM-01" photocurable resin for nanoimprinting manufactured by Sanyo Chemical Co., Ltd. TS-02: "Sunrad TS-02" photocurable resin for nanoimprinting manufactured by Sanyo Chemical Co., Ltd. TS-02 + EA-0300: A mixture of "TS-02" and "OGSOL EA-0300" manufactured by Osaka Gas Chemical Co., Ltd. (The amount of each compound differs between resin 9 and resin 11) #18210: Product name of a photocurable resin for nanoimprinting manufactured by NTT Advanced Technology Corporation

[0068] The coating properties of resins 1 to 11 were evaluated according to the following criteria. Evaluations were performed for both set film thicknesses of 6 μm and 13 μm. Note that resin 10, which received a "C" rating, could not be used for nanoimprinting. A (Good): 5.5 μm or more for a set film thickness of 6 μm, and 12.5 μm or more for a set film thickness of 13 μm. B (Acceptable): 5 μm or more and less than 5.5 μm for a set film thickness of 6 μm, and 12 μm or more and less than 12.5 μm for a set film thickness of 13 μm. C (Poor): Less than 5 μm for a set film thickness of 6 μm, and less than 12 μm for a set film thickness of 13 μm.

[0069]

[0070] [Manufacturing Example 1: Master Mold Preparation] A diffractive optical element (phase Fresnel lens) as shown in Figures 1A and 1B was fabricated by two-photon polymerization photopolymerization. The obtained phase Fresnel lens was used as master mold 1. The specific fabrication procedure for master mold 1 was as follows. A 6-inch fused silica substrate (thickness: 750 μm) was prepared as the substrate. This 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 a phase Fresnel lens on the substrate. The conditions for two-photon polymerization were as follows. Laser light used: Femtosecond laser (wavelength 780 nm) Focusing: Focused by a high-lens-power lens with a numerical aperture (NA) of 1.4 Laser output: 25 mW Scanning speed: 80 mm / sec In-plane spacing of scan lines: 0.08 μm Thickness-direction spacing of scan lines: 0.08 μm

[0071] 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 immersed in isopropyl alcohol (IPA) for 1 minute, followed by air blowing, and finally, heating at 150°C for 1 hour. In this way, residual monomers and cleaning solvents were removed from the phase Fresnel lens.

[0072] The configuration of the obtained master mold 1 was as follows: Refractive index: 1.56 Prism height (depth of unevenness): 5.04 μm (constant height) Prism pitch: gradually narrows towards the outer edge Diffraction order: primary lens numerical aperture NA: 0.3 Lens radius: 2.5 mm

[0073] [Manufacturing Example 2: Preparation of Master Mold] Except for setting the prism height (depth of unevenness) to 12.05 μm (constant height), the same conditions as in Manufacturing Example 1 were used to fabricate a diffractive optical element (phase Fresnel lens) as shown in Figures 1A and 1B. The resulting phase Fresnel lens was used as Master Mold 2.

[0074] [Manufacturing Example 3: Fabrication of Replica Mold] A thin film of nickel (Ni) with a thickness of 200 nm was deposited on the uneven surface of the master mold 1 obtained in Manufacturing Example 1 by sputtering using a vacuum deposition apparatus, forming a Ni electroplating layer. The master mold with the Ni electroplating layer was immersed in a Ni electroplating bath for 7 hours to form a 1 mm thick Ni layer on the uneven surface of the master mold 1. Finally, these were peeled off without applying force to the interface between the master mold and the Ni layer, and the Ni layer was recovered. This Ni layer was used as replica mold 1. Replica mold 1 had a pattern corresponding to the non-periodic uneven structure of the master mold 1, and the unevenness depth was 5.04 μm.

[0075] [Manufacturing Example 4: Fabrication of Replica Mold] Replica mold 2 was fabricated in the same manner as in Manufacturing Example 3, except that master mold 2 obtained in Manufacturing Example 2 was used instead of master mold 1. Replica mold 2 had a pattern corresponding to the non-periodic uneven structure of master mold 2, and the unevenness depth was 12.05 μm.

[0076] [Example 1] A PET film (Toyobo Co., Ltd., "Cosmoshine® A4160": 50 μm thick) having a flat first main surface and a second main surface with a fine uneven structure was used as the substrate. Resin 1 (viscosity 300 mPa·s) was coated onto the second main surface (uneven surface) of this substrate to a set film thickness of 6 μm to form a coating film. The coating properties of resin 1 were rated "A" as described above. Next, a replica mold 1 was pressed onto the coating film with a pressing pressure of 10 bar to bond the coating film and the replica mold 1. The pressing pressure was adjusted by combining pressing with a plate and pressing with a roll. With the coating film and the replica mold 1 bonded together, an illuminance of 400 mW and an integrated light amount of 1000 mJ / cm² were applied from the coating film side. ２The coated film (resin 1) was cured by irradiating it with ultraviolet light, and the pattern of the replica mold 1 was transferred. In this way, a diffractive optical element (phase Fresnel lens) was fabricated. The obtained diffractive optical element was subjected to evaluation of the above-mentioned "bubbles" and "optical properties (MTF)". The results are shown in Table 2.

[0077] [Examples 2-23 and Comparative Examples 1-6] Diffractive optical elements (phase Fresnel lenses) were fabricated in the same manner as in Example 1, except that the type of resin (and therefore viscosity) and the pressing pressure were changed as shown in Table 2. The obtained diffractive optical elements were subjected to the same evaluation as in Example 1. The results are shown in Table 2.

[0078]

[0079] [Example 24] A diffractive optical element (phase Fresnel lens) was fabricated in the same manner as in Example 1, except that the set film thickness was 13 μm and replica mode 2 was used. The obtained diffractive optical element was subjected to the same evaluation as in Example 1. The results are shown in Table 3.

[0080] [Examples 25-42 and Comparative Examples 7-12] Diffractive optical elements (phase Fresnel lenses) were fabricated in the same manner as in Example 24, except that the type of resin (and therefore viscosity) and the pressing pressure were changed as shown in Table 3. The obtained diffractive optical elements were subjected to the same evaluation as in Example 1. The results are shown in Table 3.

[0081]

[0082] [Evaluation] As is clear from Tables 2 and 3, the manufacturing method of the embodiment of the present invention makes it possible to create diffractive optical elements with large depths of irregularities and a non-periodic irregularity structure that is concentric in a plan view, while suppressing bubbles, and achieving excellent light-gathering performance.

[0083] The diffractive optical elements obtained by embodiments of the present invention are expected to have applications in, for example, lenses in optical systems where miniaturization, weight reduction, and thinning 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.

[0084] 10 First lens section 20 Second lens section 21 Prism 21a Fresnel surface 21b Rise surface 21c Top 21d Bottom 100 Diffractive optical element 100a First principal surface 100b Second principal surface 100c Optical axis (central axis)

Claims

1. A method for manufacturing a diffractive optical element, wherein the diffractive optical element has a surface depth of 4.0 μm or more and a non-periodic surface structure that is concentric in a plan view, and the manufacturing method comprises the steps of: applying a photocurable resin composition to a substrate to form a coating film; pressing a replica mold having a pattern corresponding to the non-periodic surface structure of the obtained diffractive optical element onto the coating film; and irradiating the coating film with light while the replica mold is pressed onto it to cure the coating film and transfer the pattern of the replica mold onto the coating film, wherein the viscosity of the photocurable resin composition is 100 mPa·s to 5000 mPa·s, and the pressing pressure of the replica mold is 3 bar to 45 bar.

2. The method for manufacturing a diffractive optical element according to claim 1, wherein the thickness of the coating film is 5.0 μm or more.

3. A method for manufacturing a diffractive optical element according to claim 1, comprising adjusting the pressing pressure by moving the replica mold and the roller relative to each other while the replica mold is pressed against the coating film.

4. The method for manufacturing a diffractive optical element according to claim 1, wherein the substrate is a polyethylene terephthalate film.

5. The method for manufacturing a diffractive optical element according to any one of claims 1 to 4, wherein the diffractive optical element is a phase Fresnel lens or a metalens.

6. The method for manufacturing a diffractive optical element according to claim 5, wherein the radius of the diffractive optical element is 0.1 mm to 100 mm.

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