JP2022038039A - Fine projection for optical element - Google Patents

Abstract

To provide a fine projection for an optical element having a reflection preventing characteristic in a wide range, and an optical element with a reflection preventing structure having the fine particle for an optical element.SOLUTION: In order to achieve the above object, there is provided a fine projection for an optical element formed in a surface of an optical element base material to obtain a reflection preventing effect. The fine projection for an optical element includes a first structure part with a top end flat part and a second structure part in the shape of a ring protrusion formed along the outer edge of the top end flat part of the first structure part.SELECTED DRAWING: Figure 1

Description

The present invention relates to fine protrusions for an optical element having antireflection characteristics, an optical element and an optical system having an antireflection structure provided with fine protrusions for an optical element, and a method for manufacturing an optical element with an antireflection structure.

Optical elements made of light-transmitting materials such as glass and plastic are subjected to surface treatment such as providing antireflection films on the light incident surface and light emitting surface in order to reduce the loss of transmitted light due to surface reflection of incident light. Has been done. This antireflection film is a single-layer film made of a substance having a lower refractive index than the substrate constituting the optical element, or a multilayer film in which a substance having a low refractive index and a substance having a high refractive index are alternately laminated, and is vapor-deposited. It is formed by a method, a sputtering method, a painting method, or the like.

In order to improve the antireflection effect of such an antireflection film, precise film thickness control is required. Therefore, in the production of the antireflection film, a high-precision process capable of precisely controlling the film thickness may be used, which is a factor of increasing the production cost.

Further, since the antireflection effect of the antireflection film utilizes the interference of the reflected light generated at the surface and the interface of each film, the antireflection performance of the antireflection film is wavelength-dependent. Therefore, it is difficult to provide a good antireflection effect for optical devices such as digital cameras and projector devices that use a wide wavelength band. Further, since the antireflection film has a light incident angle dependence, it is difficult to obtain a good antireflection effect on the entire light incident surface and light emitting surface for an optical element having a curvature such as a lens. be.

Therefore, as an antireflection means instead of the antireflection film described above, a method of providing a fine concavo-convex structure having a size equal to or smaller than the wavelength of the incident light on the surface of the optical element has been studied. If a cone shape such as a cone or a quadrangular pyramid whose cross-sectional area gradually decreases as it approaches the air layer from the base material side is adopted as the protrusion shape of this fine uneven structure, the interface between the air layer and the surface of the optical element suddenly decreases. It is possible to suppress a change in the refractive index. As a result, antireflection performance with excellent wavelength band characteristics and incident angle characteristics can be expected.

Here, the fine protrusions are very fine because they have a size equal to or smaller than the wavelength of the incident light. Further, in order to smoothly change the refractive index at the interface between the air layer and the surface of the optical element, the fine protrusions have a structure as thin and sharp as the tip. For this reason, it was easily damaged by physical contact and had poor scratch resistance.

Therefore, Patent Document 1 discloses a fine protrusion having a structure of a truncated cone and a pyramid base and flattening the upper end of the fine protrusion in the fine protrusions arranged at intervals of visible light or less.

Japanese Unexamined Patent Publication No. 2009-75539

However, since the fine protrusion structure described in Patent Document 1 has a flat surface portion at the tip of the structure, the refractive index suddenly changes at the interface between the air layer and the flat surface portion of the fine protrusions. Therefore, the continuous and smooth change of the refractive index is insufficient, and the antireflection performance is not sufficient. In addition, the antireflection effect is also obtained by the interference consisting of two layers of reflected light between the flat surface portion at the tip and the flat surface portion between the fine protrusions, but the antireflection effect is limited to a specific wavelength. , The antireflection effect cannot be obtained in a wide band.

The present invention has been made in view of the above, and an object of the present invention is to provide a microprojection for an optical element having antireflection characteristics in a wide band and an optical element having an antireflection structure provided with the microprojection for an optical element. do.

As a result of diligent research, we came up with the following inventions in order to solve the above-mentioned problems.
The fine protrusion for an optical element according to the present invention is a fine protrusion for an optical element provided on the surface of an optical element base material to obtain an antireflection effect, and the fine protrusion for an optical element has a tip flat portion formed therein. It is characterized by comprising a first structure portion and a second structure portion which is an annular protrusion formed along the outer edge of the tip plane portion of the first structure portion.

The fine protrusions for optical elements according to the present invention are a first structure portion in which a tip flat portion is formed and a second structure which is an annular protrusion formed along the outer edge of the tip plane portion of the first structure portion. By forming the portion, the refractive index is smoothly changed at the interface where the fine protrusions for the optical element are present. The optical element with an antireflection structure according to the present invention can reduce the reflectance over a wide band by providing a plurality of fine protrusions for the optical element on the optical surface.

It is a schematic of the vertical cross section which extracted a part of the fine protrusions for a plurality of optical elements in this embodiment formed on an optical element. It is a schematic three-dimensional view which shows that the 2nd structure is an annular projection. It is a schematic sectional drawing for demonstrating the structure of the microprojection for an optical element. It is a schematic sectional drawing which shows an example of the optical element which concerns on this invention. It is a schematic cross-sectional view which shows the optical element with an antireflection structure of this embodiment. It is the evaluation result of the reflectance characteristic in an Example and a comparative example.

Hereinafter, embodiments of a method for manufacturing a microprojection for an optical element, an optical element with an antireflection structure, and an optical element with an antireflection structure according to the present invention will be described.

1. 1. Embodiment in the structure of the optical element microprojection The optical element microprojection according to the present invention is an optical element microprojection provided on the surface of the optical element base material to obtain an antireflection effect, and is used for the optical element. The microprojection is characterized by comprising a first structure portion in which the tip plane portion is formed and a second structure portion which is an annular projection formed along the outer edge of the tip plane portion of the first structure portion. It is supposed to be. FIG. 1 shows a schematic view of a vertical cross section of a part of the optical element microprojections extracted from a plurality of optical element microprojections formed on the optical element according to the present embodiment. show.

In the present specification, the surface of the first structure portion on the side opposite to the surface in contact with the base material is referred to as the "tip flat portion" of the first structure portion. The boundary surface that comes into contact with the base material of the first structure portion is referred to as a "bottom surface portion" of the first structure portion. In addition, the "vertical section" is defined as follows. When the plane includes a straight line passing through the optical center of the optical element and parallel to the optical axis, and the plane includes the center point of the tip plane portion of the first structure portion, the fine details for the optical element cut by the plane. The cross section of the protrusion or the first structure portion is referred to as a "longitudinal cross section", and is used as a "vertical cross section" of a fine protrusion for an optical element and a "longitudinal cross section" of the first structure portion.

The base material 11 on which the optical element is formed may be made of glass or plastic as long as it is formed by using an optical material, and the material thereof is not particularly limited. Then, on the surface of the base material 11, there are a protrusion-shaped first structure portion 21 on which the tip flat portion is formed, and an annular protrusion formed along the outer edge of the tip flat portion of the first structure portion 21. A plurality of fine protrusions 20 for optical elements including the second structure portion 22 are provided.

The first structure portion 21 has a shape in which the cross-sectional area of the first structure portion 21 in a cross section perpendicular to the optical axis direction gradually decreases as it approaches the air layer from the base material side. Then, it is preferable that the tip surface has a flat surface portion, that is, a truncated cone shape or a pyramidal trapezoidal shape in which the tip flat portion is formed. If the tip of the first structure portion 21 is sharp, the area of the tip plane portion becomes extremely narrow, which makes it difficult to form the second structure portion. Further, the degree of change in the slope of the frustum of the first structure portion 21 having a frustum shape or a pyramid shape may be linear or curved by a quadratic function or the like. good.

Further, a second structure portion 22 which is an annular protrusion is formed along the outer edge of the tip plane portion of the first structure portion 21. FIG. 2 shows a schematic three-dimensional diagram showing that the second structure portion 22 is an annular protrusion when the first structure portion 21 has a truncated cone shape. As shown in FIG. 2, the second structure portion 22 is an annular protrusion formed along the outer edge of the flat surface portion of the first structure portion 21.

Since the second structure portion 22 is an annular protrusion formed along the outer edge of the tip plane portion of the first structure portion 21, the contact surface of the second structure portion 22 with the first structure portion is It becomes a ring. The shape and size of the outer periphery of the contact surface of the second structure portion 22 with the first structure portion are the same as the outer circumference of the tip flat portion of the first structure portion. Further, the inner peripheral shape of the contact surface of the second structure portion 22 with the first structure portion is substantially similar to the outer peripheral shape. In a cross section on a plane perpendicular to the optical axis direction of the annular projection formed by the outer periphery and the inner circumference of the second structure portion, the cross-sectional area of the cross section is the surface side in contact with the first structure portion. It gradually becomes smaller as it approaches the air layer.

When the second structure portion 22 does not exist in the tip plane portion of the first structure portion 21 and is all flat, it is mainly between the tip plane portion of the first structure portion 21 and the fine protrusions for a plurality of optical elements. Since the antireflection effect is obtained only by the interference of the two layers of reflected light with the flat surface portion, the antireflection effect cannot be obtained in a wide band. By providing the second structure portion 22 on the tip plane portion of the first structure portion 21, the refractive index is continuously and smoothly changed even at the tip portion of the fine protrusion 20 for the optical element. As a result, the antireflection effect can be obtained in a wide band as compared with the case where the tip flat portion of the first structure portion 21 does not have the second structure portion and is all flat. Further, since the second structure portion 22 is provided on the tip flat portion of the first structure portion 21 in the fine protrusion 20 for the optical element, the tip of the fine protrusion 20 for the optical element is damaged as compared with the needle-shaped structure. It is difficult and has high scratch resistance.

Further, in the present embodiment, as will be described later, the optical element microprojection 20 composed of the first structure portion 21 and the second structure portion 22 has an optically effective surface (optical light passing through the effective light flux) of the base material 11 by a mold. Since the surface) is formed on the optically effective surface at the same time, it is preferably made of the same optical material as the base material 11.

1-1. First Structure Part The structures of the first structure part and the second structure part will be described with reference to FIG. The broken line Op in FIG. 3 represents the optical axis direction, and is a straight line parallel to the central axis of the curvature of the optical element. Here, FIG. 3A shows a microprojection 20 for an optical element composed of a first structure portion 21 and a second structure portion 22 when the surface of the base material 11 and the optical axis direction Op are in a vertical relationship. The vertical cross section is shown. 3 (b) shows the optical element microprojection 20 composed of the first structure portion 21 and the second structure portion 22 when the surface of the base material 11 and the optical axis direction Op are in a relationship other than vertical. The vertical cross section is shown. At this time, it is preferable that the above-mentioned first structure portion 21 satisfies at least one conditional expression among the following conditional expressions (1) and (2).

First, the conditional expression (1) will be described. The conditional expression (1) shown below is an expression that defines the ratio between the width of the tip plane portion of the first structure portion 21 and the width of the projection surface for specifying the structure of the first structure portion 21. In this specification, the surface on which the first structure portion is projected in the optical axis direction is referred to as a “projection surface”.
0.20 ≤ W1 / W2 ≤ 0.75 ... (1)
However, W1: the width of the tip plane portion of the first structure portion 21.
W2: The width of the projection plane of the first structure portion 21.

If W1 / W2 is less than 0.20, it becomes difficult to form the second structure portion described later, which is not preferable. Further, when W1 / W2 exceeds 0.75, the antireflection effect is lowered, which is not preferable.

The lower limit of the conditional expression (1) is preferably 0.38, more preferably 0.41. The upper limit of the conditional expression (1) is preferably 0.52, more preferably 0.47.

Next, the conditional expression (2) will be described. The conditional expression (2) shown below is an expression that defines the ratio between the height of the structure and the width of the bottom surface portion in the first structure portion 21 for specifying the structure of the first structure portion 21.
0.4 ≤ H / W2 <2.0 ... (2)
However, H: the length of a straight line parallel to the optical axis from the center of the tip plane portion of the first structure portion 21 to the bottom surface portion.

If H / W2 is less than 0.4, the antireflection effect is not sufficient, which is not preferable. Further, when H / W2 is 2.0 or more, the structure is easily damaged, which is not preferable.

The lower limit of the conditional expression (2) is preferably 0.56, more preferably 0.65. The upper limit of the conditional expression (2) is preferably 0.95, more preferably 0.75.

Further, the first structure portion 21 has a higher antireflection effect by satisfying all of the conditional expressions (1) and (2).

1-2. Second Structure Part 22 The second structure part 22 in FIG. 3 preferably satisfies at least one conditional expression among the following conditional expressions (3) and (4).

The conditional expression (3) will be described. The conditional expression (3) shown below is the width of the inner peripheral shape of the contact surface of the second structure portion 22 with the first structure portion and the first structure for specifying the structure of the second structure portion 22. It is an equation which defines the ratio with the width of the tip plane part in the body part 21.
0 <X1 / W1 ≦ 0.95 ・ ・ ・ (3)
However, X1: the width of the inner circumference of the second structure portion 22 on the contact surface with the first structure portion.

Since the second structure 22 is an annular projection, X1 / W1 has a numerical value exceeding 0. Further, when X1 / W1 exceeds 0.95, the difference between the size of the outer circumference and the size of the inner circumference on the contact surface of the second structure portion 22 with the first structure portion becomes small, so that the thickness is small. It is not preferable because it becomes an annular protrusion and is easily damaged.

It is desirable that X1 / W1 is smaller because the change in the refractive index at the interface between the air layer and the fine protrusions for the optical element can be smoothed.

Next, the conditional expression (4) will be described. The conditional expression (4) shown below includes a contact surface of the second structure portion 22 with the first structure portion and a tip portion of the second structure portion 22 for specifying the structure of the second structure portion 22. It is an equation which defines the ratio of the length of the straight line parallel to the optical axis connecting
0.3 ≤ Z / W1 ≤ 1.0 ... (4)
However, Z: the length of a straight line parallel to the optical axis connecting the contact surface of the second structure portion 22 with the first structure portion and the tip end portion of the second structure portion 22.

If Z / W1 is less than 0.3, the antireflection effect is insufficient, which is not preferable. Further, when Z / W1 exceeds 1.0, it is not preferable because it is difficult to manufacture and it is easily damaged.

The lower limit of the conditional expression (4) is preferably 0.35, more preferably 0.40, and even more preferably 0.45. The upper limit of the conditional expression (4) is preferably 0.7, more preferably 0.6.

Further, the first structure portion 21 has a higher antireflection effect by satisfying all of the conditional expressions (3) and (4).

2. 2. Embodiment in the structure of an optical element with an antireflection structure In the present invention, the optical element is not particularly limited, and various objects such as a lens, a filter, and a mirror can be used. As an example of the optical element used in this embodiment, FIG. 4 shows an optical element 10 which is a meniscus lens. The shape of the optical surface of the base material 11 of the optical element 10 may be flat or non-planar. The shape may be any shape such as a spherical surface, an aspherical surface, and a free curved surface as long as it is a non-planar surface. The base material 11 includes an optical surface 12 and an optical surface 13 that allow an effective luminous flux that contributes to image formation to pass through. On the other hand, the outer peripheral portion of the base material 11 is the edge portion 14. Further, the broken line O indicates the central axis of the curvature of the optical element 10.

It is preferable that the optical element with an antireflection structure according to the present invention is provided with a plurality of the above-mentioned fine protrusions 20 for an optical element on at least one of the optical surfaces of the surface of the base material. FIG. 5 shows a schematic cross-sectional view of the optical element 30 with an antireflection structure according to the present embodiment. The optical element microprojections 20 according to the present invention are provided on the surfaces of the optical surface 12 and the optical surface 13. Since the reflectance decreases if the refractive index of the fine protrusions 20 for the optical element changes continuously from the tip of the fine protrusions to the substrate side, the fine protrusions 20 for the optical element are arranged according to a certain interval. It may be arranged in six directions, or it may be arranged irregularly.

When a plurality of optical element microprojections 20 are arranged on the surface of the base material 11 of the optical element 30 with an antireflection structure according to the present invention, the distance between adjacent optical element microprojections 20 is λ / 5 or more and λ / 2 or less. Is preferable. However, λ is the wavelength (nm) of the incident light. If the distance between the adjacent fine protrusions 20 for optical elements is less than λ / 5, it becomes difficult to form the fine protrusion structure, which is not preferable. When the distance between adjacent fine protrusions exceeds λ / 2, unnecessary diffracted light is generated, which is not preferable.

Further, in the optical element 30 with an antireflection structure according to the present invention, the material forming the base material 11 and the fine protrusions 20 for the optical element, that is, the first structure portion 21 and the second structure portion 22 is the same. Is preferable. Since the material for forming the base material 11 and the optical element fine protrusions 20 is the same, the optical element 30 with an antireflection structure provided with a plurality of optical element fine protrusions 20 can be integrally molded.

3. 3. Embodiment 3-1 in the characteristics of the optical element with the antireflection structure. First Structure Part In the first structure part 21 of the present embodiment, the occupancy ratio of the air with the first structure part 21 in the tip plane part is large in air, and the first structure in the part in contact with the base material. The occupancy ratio of the portion 21 and the air is large in the first structure portion 21. Therefore, the refractive index changes continuously and smoothly from the tip flat portion to the bottom surface portion of the first structure portion 21, and there is no portion where the refractive index changes significantly. Therefore, the antireflection structure composed of the first structure portion 21 has a low reflectance and a high transmittance.

3-2. Second Structure Part A second structure part 22 is provided on the tip plane portion of the first structure part 21 of the present embodiment. When the second structure portion 22 is not present in the tip plane portion of the first structure portion 21 and is all flat, the incident light is reflected and the antireflection effect is impaired. On the other hand, by providing the second structure portion 22 on the flat surface portion of the first structure portion 21, the refractive index is continuous also in the second structure portion 22 formed on the tip plane portion of the first structure portion 21. It changes smoothly. As a result, the antireflection effect of the fine protrusions 20 for the optical element is improved as compared with the case where the tip flat portion of the first structure portion 21 does not have the second structure portion 22 and is all flat.

Further, since the second structure portion 22 formed on the tip plane portion of the first structure portion 21 is smaller than the first structure portion 21, it is shorter than the wavelength effective in the first structure portion 21. It also contributes to the antireflection effect in the wavelength region. Therefore, as compared with the case where only the first structure portion 21 is used, the wavelength band in which the antireflection effect of the fine protrusions 20 for the optical element is exhibited becomes wider.

Further, on the inside of the second structure portion 22 which is an annular protrusion, a part of the tip plane portion of the first structure portion 21 is exposed to the air layer. A plane between a part of the tip plane portion of the first structure portion 21 exposed inside the second structure portion 22 and a plurality of adjacent microprojections for optical elements 20 arranged on the surface of the base material 11. It is also possible to obtain an antireflection effect due to the interference effect of the reflected light from the respective flat surface portions.

3-3. Optical element with antireflection structure The optical element 30 with antireflection structure of the present embodiment has the above-mentioned fine antireflection structure for an optical element on at least one optical surface of the surface of the base material 11 of the optical element. It is provided with a plurality of protrusions 20. Therefore, the reflectance is low and the transmittance is high. The fine projection 20 for an optical element reduces reflection due to the characteristic that the refractive index continuously and smoothly changes at the interface between air and the optical element, unlike the method of reducing reflection by the interference effect using an optical thin film. Mainly, since the interference effect is not used, the wavelength range covered by the reflection reduction effect is wide, and the increase in reflectance is small even if the incident angle of light changes.

The refractive index of each of the optical element base material 11, the first structure portion 21, and the second structure portion 22 preferably satisfies the following conditional expression (5). By satisfying the conditional expression (5), a good antireflection effect can be obtained in a wide band.
Refractive index of the first structure part ≤ Refractive index of the second structure part ≤ Refractive index of the optical element base material ... (5)

It is more preferable that the refractive indexes of the optical element base material 11, the first structure portion 21, and the second structure portion 22 are the same. This is because the optical materials of the optical element base material 11, the first structure portion 21, and the second structure portion 22 can be the same.

4. Embodiment in an Optical System with an Optical Element with an Antireflection Structure It is preferable that the optical system according to the present invention includes the optical element 30 with an antireflection structure according to the present invention. An optical system is an instrument or device that creates an image of an object by utilizing properties such as reflection and refraction of light, and is a component of optical equipment that handles light such as cameras, telescopes, and laser equipment. Since the optical system according to the present invention includes the optical element 30 with the antireflection structure according to the present invention, the reflectance is low in a wide wavelength range, and the increase in reflectance is small even if the incident angle of light changes. .. Further, the microprojection 20 for an optical element, which is an antireflection structure, has a second structure portion 22 provided on the tip flat portion of the first structure portion 21, and therefore has high scratch resistance.

5. Embodiment 5-1 in the method for manufacturing an optical element with an antireflection structure. Mold The mold according to the present invention preferably has the inverted shape of the above-mentioned optical element 30 with an antireflection structure. The mold material may be any material as long as it has a hardness of HRC51 or higher and can be dry-etched, and tungsten carbide, SiC, glassy carbon, NiP plating, silicon nitride and the like are preferable. A precious metal and a carbon film may be applied to the surface of the mold for the purpose of improving the releasability of the member. The production of the mold before patterning for forming the fine protrusions for the optical element is not limited to a specific method.

Next, patterning is performed to form fine protrusions for optical elements on the mold. For example, a photoresist is applied to the mold substrate using a photolithography method, and the pattern is exposed using exposure using Talbot interference. After developing this, the mold according to the present invention can be produced by processing the pattern into a mold by dry etching based on the photoresist pattern.

The formation of the patterning layer on the mold is not limited to the above method, and may be formed by, for example, the following method using nanoimprint. First, a replica mold made of a soft resin such as PDMS (polydimethylsiloxane) is produced by heat or UV imprint from a flat master mold having an arrangement pattern of fine protrusions for optical elements on the surface. Next, a UV-curable imprint resist is spin-coated on the inverted mold of the optical element to be produced. Then, using an imprint device having a pneumatic press mechanism, the replica mold is crimped to the mold coated with the imprint resist, the replica mold is crimped, the imprint resist is UV-cured, and then the replica mold is formed. Peel off. Then, the imprint resist remaining thinly by crimping is removed by dry etching.

5-2. Manufacturing Method The manufacturing method of the optical element with an antireflection structure according to the present invention may be any method as long as the above-mentioned antireflection structure can be formed, but is called an injection molding method or a glass molding method. It is preferable to use hot press molding. The mold used for manufacturing the optical element with the antireflection structure according to the present invention is preferably the mold according to the present invention.

Further, as described above, it is preferable that the materials forming the base material 11, the first structure portion 21, and the second structure portion 22 are the same. By using the same material, the base material 11 and the fine protrusions 20 for optical elements can be simultaneously molded by the above-mentioned manufacturing method. The present invention is not limited to this, and for example, a configuration is adopted in which an optical element provided with fine protrusions 20 for an optical element formed of an optical material different from the base material 11 is joined to the base material 11. You can also.

The embodiment of the present invention described above is one aspect of the present invention and can be appropriately changed without departing from the spirit of the present invention. Further, the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples.

A. Fine protrusions for optical elements As shown in FIG. 1, the fine protrusions for optical elements provided in the optical element with an antireflection structure in the embodiment are composed of a first structure portion and a second structure portion.

B. The optical surface 12 of the optical element with an aspherical antireflection structure is an aspherical surface having an effective diameter of 13.62 mm. Here, the definition formula of the aspherical surface when the surface position (sag amount) in the optical axis direction at a position perpendicular to the optical axis and away from the optical axis is Sag (R) is shown in Equation 1.

但し、ｒ：曲率半径。
Ｋ：円錐常数。
Ａ３～Ａ１２：非球面多項式の高次係数。

However, r: radius of curvature.
K: Conical constant.
A3 to A12: Higher-order coefficients of aspherical polynomials.

At this time, the optical surface 12 has a shape that satisfies the following numerical values in Equation 1. The maximum inclination angle of this surface is 36.8 °.

r = 12.1367
k = -10.0000
A3 = -1.9184E-3
A4 = 2.5495E-3
A5 = -9.0719E-4
A6 = 2.2378E-4
A7 = -2.9361E-5
A8 = 6.0856E-7
A9 = 2.5801E-7
A10 = -9.3494E-9
A11 = -2.6479E-9
A12 = 1.8505E-10

The optical surface 13 of the optical element with an antireflection structure is an aspherical surface having an effective diameter of 8.95 mm. At this time, the optical surface 13 has a shape that satisfies the following numerical values in Equation 1. The maximum inclination angle of this surface is 17.6 °.

r = 13.2858
k = 0.6453
A3 = 0.0
A4 = 4.029E-5
A5 = 0.0
A6 = 1.1353E-5
A7 = 0.0
A8 = -9.7868E-7
A9 = 0.0
A10 = 4.7507E-8
A11 = 0.0
A12 = -1.0466E-9

C. Mold The manufacture of a mold used for manufacturing an optical element with an antireflection structure will be described. First, a SUS steel material is used as a mold base material, and processing is performed so that each surface of the optical element described above has an inverted shape. Specifically, SUS steel, which is a cylindrical material, was processed into the shape of an optical piece by a grinding machine, and then electroless NiP plating was performed only on the optical surface. Then, it was machined with an aspherical surface cutting machine having a control resolution of 1 nm so as to have the above-mentioned optical surface. Then, the optical surface was optically polished, and finally washed with an organic solvent. The surface roughness of the mold base material thus obtained was Ra 1.0 nm with a scanning white interferometer manufactured by Zygo Corporation.

Next, a SiN layer to be an etching layer was formed on the surface of the mold by a CVD method at 2000 nm. At this time, the film forming method is not particularly limited to the CVD method, and may be a sputtering method or the like. Then, a patterning layer made of a resist film was formed on the surface of the SiN film. The method for forming the patterning layer is not particularly limited, but here, it was carried out as follows. First, a positive photoresist was spin-coated on the surface of the SiN film. Next, a phase mask having a φ330 nm pattern arranged in a hexagonal arrangement at a pitch of 340 nm was set in an interference exposure device controlled so that the Talbot interference light from the mask could be integrated, and exposure was performed from the upper surface of the mold. Finally, by developing and dissolving the photosensitive portion, a patterning layer made of a resist film having a hole diameter distribution of 330 nm arranged in six directions at a pitch of 340 nm was formed on the surface of the SiN film.

The mold on which the patterning layer of the resist is formed as described above is dry-etched by a dry etching apparatus. Etching was performed for 4 minutes under CHF3 and CF4 gas with a dry etching apparatus. After that, an unnecessary patterning layer of the resist film was removed, and a mold in the example was prepared.

D. Molding The optical element with antireflection structure in the embodiment is molded by injection molding using the above-mentioned mold. As the injection molding apparatus, an injection molding machine manufactured by FANUC Corporation was used. The optical resin used for injection molding is polycarbonate having a glass transition temperature of 145 ° C. The mold temperature at the time of injection molding was 155 ° C. and the holding pressure was 95 MP. By performing the mold release while maintaining the mold temperature, the resin is deformed at the interface between the mold and the resin during the mold release, and the annular protrusion is formed along the outer edge of the flat surface portion of the first structure portion. A second structural part was formed.

When the cross-sectional shape of this structure was measured using an AFM (Atomic Force Microscope), it was a structure having an annular structure on a truncated cone-shaped structure. The first structure portion of the fine protrusion for the optical element had a bottom surface diameter of 330 nm, a top surface diameter of 220 nm, and a height of 200 nm. At this time, the value of W1 / W2 in the conditional expression (1) was 0.67, and the value of H / W2 in the conditional expression (2) was 0.606. The height of the annular projection, which is the second structure portion, was 100 nm, the width was 10 nm, and the cross-sectional shape of the annular projection was parabolic. At this time, X1 / W1 in the conditional expression (3) was 0.91, and Z / W1 in the conditional expression (4) was 0.455.

The optical element with an antireflection structure thus produced has a working wavelength of 905 nm, and has a first structure portion having a flat surface portion on the optical surface of the optical element with the antireflection structure and a flat surface of the first structure portion. It is provided with a plurality of fine protrusions for an optical element, which are composed of a second structure portion which is an annular protrusion provided along the outer edge of the portion. The material forming the optical element base material, the first structure portion, and the second structure portion is the same. That is, the refractive indexes of the optical element base material, the first structure portion, and the second structure portion have the same value.

[Comparative example]
In the comparative example, the shape and material of the optical element are the same as those in the embodiment. The mold was also created under the same conditions as in the examples. Then, as in the embodiment, the optical element with the antireflection structure was molded by injection molding using a mold. At this time, the injection molding apparatus uses an injection molding machine manufactured by FANUC Corporation as in the embodiment, but a temperature controller is attached so that the mold temperature can be arbitrarily controlled. Next, the mold was molded at a mold temperature of 155 ° C. and a holding pressure of 95 MP, and then the mold temperature was lowered to 135 ° C. and then mold release was performed. By setting the mold temperature to 95 ° C., deformation of the resin at the interface between the mold and the resin as described above at the time of mold release was prevented from occurring.

The optical element with an antireflection structure thus produced is provided with a plurality of fine protrusions for an optical element having only a first structure portion having a tip flat portion on the optical surface thereof. When the cross-sectional shape of this structure was measured using AFM, it was a truncated cone-shaped structure, and the diameter of the bottom surface was 330 nm, the diameter of the top surface was 220 nm, and the height was 200 nm.

〔Evaluation results〕
The reflectance of the optical element with an antireflection structure described in Examples and Comparative Examples was measured by a film thickness measuring machine FE3000 manufactured by Otsuka Electronics Co., Ltd. FIG. 6 shows the evaluation results of the reflectance characteristics in Examples and Comparative Examples. The horizontal axis of FIG. 6 shows the wavelength (nm), and the vertical axis shows the reflectance (%). From FIG. 6, it was clarified that the optical element with the antireflection structure of the embodiment has excellent reflectance characteristics. On the other hand, it was clarified that the optical element with the antireflection structure of the comparative example was inferior in the reflectance characteristic to the optical element with the antireflection structure of the example. Therefore, the optical element with an antireflection structure according to the present invention has a first structure portion having a tip flat portion and an annular protrusion provided along the outer edge of the tip flat portion of the first structure portion on the optical surface thereof. It has been clarified that it has good reflectance characteristics by providing a plurality of fine protrusions for an optical element composed of a certain second structure portion.

The fine protrusion for an optical element according to the present invention is composed of a first structure portion having a tip plane portion and a second structure portion which is an annular protrusion provided along the outer edge of the tip plane portion of the first structure portion. As a result, the refractive index has the property of continuously and smoothly changing, and the scratch resistance is high. Further, the optical element with an antireflection structure according to the present invention, which has a plurality of fine protrusions for an optical element having the above-mentioned characteristics on the optical surface, has a good antireflection effect in a wide bandwidth and can be produced by injection molding or the like. Because of this, productivity is high. Therefore, it is suitable for panels of in-vehicle devices, optical devices, and other devices that require scratch resistance.

10 Optical element 11 Base material 12 Optical surface 13 Optical surface 14 Edge part 20 Fine protrusion for optical element 21 First structure part 22 Second structure part 30 Optical element with antireflection structure

Claims (13)

It is a fine protrusion for an optical element provided on the surface of an optical element base material to obtain an antireflection effect.
The fine protrusions for optical elements are a first structure portion in which a tip flat portion is formed, and a second structure portion which is an annular protrusion formed along the outer edge of the tip flat portion of the first structure portion. A fine protrusion for an optical element, which is characterized by being composed of. The fine protrusion for an optical element according to claim 1, wherein the shape of the first structure portion is a truncated cone shape or a pyramidal cone shape. The fine protrusion for an optical element according to claim 1 or 2, wherein the first structure portion satisfies the following conditional expression.
0.20 ≤ W1 / W2 ≤ 0.75 ... (1)
0.4 ≤ H / W2 <2.0 ... (2)
However, W1: the width of the tip plane portion of the first structure portion.
W2: The width of the projection surface in the optical axis direction of the first structure portion.
H: The length of a straight line parallel to the optical axis from the center of the tip plane portion of the first structure portion to the bottom surface portion. The fine protrusion for an optical element according to any one of claims 1 to 3, wherein the second structure portion satisfies the following conditional expression.
0 <X1 / W1 ≦ 0.95 ・ ・ ・ (3)
0.3 ≤ Z / W1 ≤ 1.0 ... (4)
However, X1: the width of the inner circumference of the second structure portion on the contact surface with the first structure portion.
Z: The length of a straight line parallel to the optical axis connecting the contact surface of the second structure portion with the first structure portion and the tip end portion of the second structure portion. The optical element according to any one of claims 1 to 4, wherein the refractive index of each of the optical element base material, the first structure portion, and the second structure portion satisfies the following conditional expression. For fine protrusions.
Refractive index of the first structure part ≤ Refractive index of the second structure part ≤ Refractive index of the optical element base material ... (5) An optical element with an antireflection structure, characterized in that a plurality of fine protrusions for an optical element according to any one of claims 1 to 5 are provided on at least one optical surface of the surface of the optical element substrate. .. The optical element with an antireflection structure according to claim 6, wherein the distance between the plurality of fine protrusions for the optical element is λ / 5 or more and λ / 2 or less.
However, λ: wavelength of incident light (nm). The optical element with an antireflection structure according to claim 6 or 7, wherein the material forming the optical element base material, the first structure portion, and the second structure portion is the same. The optical element with an antireflection structure according to any one of claims 6 to 8, wherein the shape of the optical surface of the optical element base material is non-planar. An optical system comprising the optical element with an antireflection structure according to any one of claims 6 to 9. A mold comprising an inverted shape of the optical element with an antireflection structure according to claim 6. The method for manufacturing an optical element with an antireflection structure according to any one of claims 6 to 9.
A method for manufacturing an optical element with an antireflection structure, which comprises using injection molding or hot press molding. The method for manufacturing an optical element with an antireflection structure according to claim 12, wherein the mold according to claim 11 is used for molding.

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