WO2010087208A1

WO2010087208A1 - Diffractive optical element and manufacturing method thereof

Info

Publication number: WO2010087208A1
Application number: PCT/JP2010/000587
Authority: WO
Inventors: 村田晶子; 岡田夕佳; 高原範久
Original assignee: パナソニック株式会社
Priority date: 2009-02-02
Filing date: 2010-02-01
Publication date: 2010-08-05

Abstract

Disclosed is a diffractive optical element comprising a substrate (1) which is formed of a first optical material including a first resin and which is provided with a diffraction grating (2) on a surface of the substrate, an optical regulation layer (4) which is formed of a second optical material including a second resin and which is provided on the substrate (1)to cover the diffraction grating (2), and an intermediate layer (3) which is formed of a third optical material including a third resin and which is provided between the substrate (1) and the optical regulation layer (4). The refractive index of the first optical material is smaller than the refractive index of the second optical material and the wavelength dispersion of refractive index of the first optical material is greater than the wavelength dispersion of refractive index of the second optical material.

Description

Diffractive optical element and manufacturing method thereof

The present invention relates to a diffractive optical element, and more particularly to a diffractive optical element constituted by two or more members containing different resins and a method for manufacturing the same.

The diffractive optical element has a structure in which a diffraction grating for diffracting light is provided on a base made of an optical material such as glass or resin. A diffractive optical element is used in an optical system of various optical devices including an imaging device and an optical recording device. For example, a lens designed to collect diffracted light of a specific order at one point, or a spatial low-pass filter A polarization hologram or the like is known.

A diffractive optical element has the feature that the optical system can be made compact. In contrast to refraction, longer wavelength light diffracts more greatly, so it is possible to improve chromatic aberration and curvature of field of the optical system by combining a diffractive optical element and a normal optical element using refraction. It is.

However, since the diffraction efficiency theoretically depends on the wavelength of light, designing a diffractive optical element so that the diffraction efficiency for light of a specific wavelength is optimal reduces the diffraction efficiency for light of other wavelengths. Challenges arise. For example, when a diffractive optical element is used in an optical system that uses white light, such as a camera lens, the wavelength dependence of this diffraction efficiency causes color unevenness and flare due to unnecessary order light. It is difficult to construct an optical system having

In order to solve such a problem, Patent Document 1 provides a diffraction grating on a surface of a base made of an optical material, and covers the diffraction grating with an optical adjustment layer made of an optical material different from that of the base. By configuring the element and selecting two optical materials so that the optical characteristics satisfy a predetermined condition, the diffraction efficiency at the designed diffraction order is increased regardless of the wavelength, that is, the wavelength dependence of the diffraction efficiency is increased. A method of reducing is disclosed.

When the wavelength of light transmitted through the diffractive optical element is λ, the refractive indices at the wavelengths λ of the two types of optical materials are n1 (λ) and n2 (λ), and the depth of the diffraction grating is d, the following formula ( When 1) is satisfied, the diffraction efficiency for light of wavelength λ is 100%.

Therefore, in order to reduce the wavelength dependence of the diffraction efficiency, an optical material having a refractive index n1 (λ) and a refractive index n2 (with a wavelength dependence such that d is substantially constant within the wavelength band of the light used. The optical material of λ) may be combined. In general, a material having a high refractive index and a low wavelength dispersion is combined with a material having a low refractive index and a high wavelength dispersion. Patent Document 1 discloses that glass or resin is used as the first optical material serving as a base and ultraviolet curable resin is used as the second optical material.

Patent Document 2 discloses that, in a phase difference type diffractive optical element having a similar structure, glass is used as a first optical material, and an energy beam curable resin having a viscosity of 5000 mPa · s or less is used as a second optical material. In addition, it is disclosed that the wavelength dependency of diffraction efficiency can be reduced and color unevenness and flare generation due to unnecessary order light can be effectively prevented.

When glass is used as the first optical material serving as a substrate, it is difficult to perform fine processing as compared with resin, and thus it is not easy to reduce the pitch of the diffraction grating and improve the diffraction performance. For this reason, it is difficult to improve the optical performance while reducing the size of the optical element. In addition, since the glass molding temperature is higher than that of the resin, the durability of the mold for molding the glass is lower than that of the mold for molding the resin, and there is a problem in productivity.

On the other hand, when a resin is used as the first optical material serving as the substrate, it is superior to glass in terms of workability and moldability of the diffraction grating. However, it is difficult to realize various values of refractive index as compared with glass, and the difference in refractive index between the first optical material and the second optical material is small. Therefore, as is clear from Equation (1), the diffraction grating The depth d of becomes larger.

As a result, although the workability of the substrate itself is excellent, it is necessary to deeply process the mold for forming the diffraction grating, or to form the tip of the groove into a sharp shape, making it difficult to process the mold. Become. Further, as the diffraction grating becomes deeper, it is necessary to increase the pitch of the diffraction grating due to processing restrictions on at least one of the base and the mold. For this reason, the number of diffraction gratings cannot be increased, and the restrictions on the design of the diffractive optical element increase.

In order to solve such problems, the applicant of the present application described in Patent Document 3 uses a composite material containing inorganic particles having an average particle diameter of 1 nm to 100 nm in a matrix material made of resin as an optical adjustment layer. is suggesting. In this composite material, the refractive index and the Abbe number can be controlled by the material of the inorganic particles to be dispersed and the addition amount of the inorganic particles, and the refractive index and the Abbe number that are not found in conventional resins can be obtained. Therefore, by using the composite material for the optical adjustment layer, the degree of freedom in designing the diffraction grating when resin is used as the first optical material as the substrate is increased, the moldability is improved, and the excellent diffraction efficiency is achieved. Wavelength characteristics can be obtained.

Japanese Patent Laid-Open No. 10-268116 JP 2001-249208 A International Publication No. 07/026597 Pamphlet

In the phase difference type diffractive optical element disclosed in Patent Documents 1 to 3, the inventor of the present application, when the base and the optical adjustment layer are made of a resin material, depending on the type of the resin material, the base and the optical adjustment layer may be It has been found that there is a problem in that the substrate swells or dissolves at the contact portion, and the shape of the diffraction grating deviates from the design value.

The present invention has been made in view of such problems of the prior art, and even when a resin excellent in productivity and workability is used as a substrate and an optical adjustment layer, a diffractive optical element having good optical characteristics. An object is to provide an element and a method for manufacturing the element.

The optical element of the present invention is made of a first optical material containing a first resin, has a base having a diffraction grating on the surface, and a second optical material containing a second resin, and covers the base so as to cover the diffraction grating. An optical adjustment layer provided and a third optical material containing a third resin, and an intermediate layer provided between the base and the optical adjustment layer, wherein the refractive index of the first optical material is It is smaller than the refractive index of the second optical material, and the wavelength dispersion of the refractive index of the first optical material is larger than the wavelength dispersion of the refractive index of the second optical material.

In a preferred embodiment, the second resin is a thermosetting resin or an energy curable resin.

In a preferred embodiment, the second optical material further includes inorganic particles, and the inorganic particles are dispersed in the second resin.

In a preferred embodiment, the refractive index of the third optical material is larger than the refractive index of the first optical material and smaller than the refractive index of the second optical material.

In a preferred embodiment, the difference in solubility parameter between the first resin and the third resin is 0.8 [cal / cm ³ ] ^1/2 or more.

In a preferred embodiment, the difference in solubility parameter between the second resin and the third resin is 0.8 [cal / cm ³ ] ^1/2 or more.

In a preferred embodiment, the thickness of the intermediate layer is 5% or less of the minimum value of the grating interval of the diffraction grating.

In a preferred embodiment, the thickness of the intermediate layer is 1% or less of the minimum value of the grating interval of the diffraction grating.

In a preferred embodiment, the third resin is a thermosetting resin or an energy curable resin.

In a preferred embodiment, the inorganic particles contain at least one selected from the group consisting of zirconium oxide, yttrium oxide, lanthanum oxide, hafnium oxide, scandium oxide, alumina, and silica as a main component.

In a preferred embodiment, the effective particle size of the inorganic particles is 1 nm or more and 100 nm or less.

In a preferred embodiment, the first resin is polycarbonate.

In a preferred embodiment, the intermediate layer has a thickness of 10 nm or more.

The method for producing a diffractive optical element according to the present invention includes a step of preparing a base having a diffraction grating on a surface thereof, the first optical material including a first resin, and covering the surface of the diffraction grating of the base Including a step of forming an intermediate layer on a substrate and a step of forming an optical adjustment layer made of a second optical material containing a second resin on the intermediate layer, and the step of forming the intermediate layer includes: A step of disposing a three-resin raw material on the base so as to cover a surface of the diffraction grating of the base; and curing the third resin raw material to form the intermediate layer made of a third optical material. A process.

In a preferred embodiment, the difference between the solubility parameter of the first resin and the solubility parameter of the raw material of the third resin is 0.8 [cal / cm ³ ] ^1/2 or more.

According to the present invention, since the intermediate layer is provided between the base and the optical adjustment layer, the base and the optical adjustment layer are not in direct contact, and the base and the optical adjustment layer are made of a material containing a resin. In addition, the resin of the optical adjustment layer penetrates into the substrate, and the diffraction grating shape is prevented from being deformed or the refractive index changing layer is generated.

FIG. 6 is a diagram schematically showing a state where a diffraction grating is deformed in a diffractive optical element of a conventional technique. (A) is a figure which shows typically the state in which the refractive index change layer produced | generated in the interface of a base | substrate and an optical adjustment layer in the diffractive optical element of a prior art, (b) is the figure which expanded the part. . (A) And (b) is a figure explaining the relationship between the material of an optical adjustment layer, and unnecessary diffracted light in the diffractive optical element of a prior art in which a refractive index change layer is formed in the interface of a base | substrate and an optical adjustment layer. is there. It is a figure which shows typically the refraction of the light in the optical element in which the layer from which the refractive index changed was formed in the interface of a base | substrate and an optical adjustment layer. (A) is typical sectional drawing which shows 1st Embodiment of the diffractive optical element of this invention, (b) is the figure which expanded the part. It is a graph which shows the relationship between the difference of SP value of a polycarbonate and an acrylate resin, and the refractive index of the refractive index change layer produced | generated on the surface of a base | substrate when an acrylate resin is formed on the base | substrate which consists of polycarbonates. FIG. 6 is an enlarged schematic view showing a grating portion in the diffractive optical element shown in FIG. 5. 6 is a graph showing a simulation result of the first-order diffraction efficiency when the thickness of the intermediate layer in the diffractive optical element shown in FIG. 5 is 5% of the minimum pitch. It is a graph explaining the definition of the effective particle diameter of particle | grains. It is typical sectional drawing which shows an example of the diffractive optical element produced by embodiment of the manufacturing method of the diffractive optical element of this invention. (A) to (e) are partial process diagrams for explaining an embodiment of a method for manufacturing a diffractive optical element. It is sectional drawing which shows the other form of the diffractive optical element of this invention. It is sectional drawing of the diffractive optical element of a comparative example. It is a figure which shows the result of the 1st-order diffraction efficiency with respect to the intermediate | middle layer thickness in an Example and a comparative example.

The inventor of the present application has examined in detail the swelling of the base caused by using a material containing a resin for both the base and the optical adjustment layer in the conventional diffractive optical element. Hereinafter, the examination results will be described.

A conventional diffractive optical element 111 shown in FIG. 1 includes a base 101 having a diffraction grating 102 provided on the surface thereof, and an optical adjustment layer 103 provided so as to cover the diffraction grating 102. When the optical adjustment layer 103 and the base 101 are formed of an optical material containing a resin and the interaction between the two optical materials is strong, the base 101 may swell at a portion where the base 101 and the optical adjustment layer 103 are in contact with each other. By melting, the shape of the diffraction grating 102 is broken as shown in FIG. If the shape of the diffraction grating 102 collapses, a desired order of diffracted light may not be obtained with sufficient intensity, or unnecessary diffracted light may be generated.

The inventor of the present application has found that unnecessary diffracted light may be generated in the diffractive optical element 111 even if the shape of the diffraction grating 102 is not changed. 2A, in the conventional diffractive optical element 112, when the resin contained in the optical adjustment layer 103 penetrates from the surface of the base 101, the shape of the diffraction grating 102 provided on the surface of the base 101 changes greatly. Even if it does not, the refractive index of the base | substrate 101 of the part which the resin osmose | permeated changes. In this case, it was confirmed that a layer 101a (hereinafter referred to as “refractive index changing layer”) having a refractive index different from that of the base 101 was formed at the interface between the base 101 and the optical adjustment layer 103. The refractive index changing layer 101a can be confirmed by an optical microscope, and the thickness of the refractive index changing layer 101a is about 500 nm to 5000 nm. In particular, as shown in FIG. 2B, since the thickness of the tip 102t of the diffraction step of the diffraction grating 102 is thin, the resin contained in the optical adjustment layer 103 is more likely to penetrate into the substrate 101. For this reason, the refractive index changing layer 101a tends to be thick at the tip portion 102t of the diffraction step.

As described above, when the shape change of the diffraction grating 102 and the generation of the refractive index change layer 101a can be confirmed by visual observation or observation with an optical microscope, it is understood that the diffractive optical element 112 does not exhibit the optical characteristics as designed. .

Next, the mechanism by which the unnecessary diffracted light of the optical element is generated when the refractive index changing layer is generated in the diffractive optical element will be specifically described with reference to FIGS. 3 (a) and 3 (b).

As shown in FIG. 3A, a diffractive optical element 113 that uses first-order diffracted light using different resins for the substrate 101 (refractive index N1) and the optical adjustment layer 103 (refractive index N2) is considered. According to the study of the present inventor, the resin constituting the optical adjustment layer 103 permeates into the base 101, whereby the refractive index changing layer 101b having a changed refractive index is generated. When the refractive index of the base 101 and the optical adjustment layer 103 satisfies the relationship of N1 <N2, the refractive index N3 of the generated refractive index changing layer 101b satisfies the relationship of N1 <N3 <N2.

When the refractive indexes N1 and N2 are designed to satisfy the formula (1) within the wavelength band used, the difference in optical distance of the steps constituting the diffraction grating is caused by the refractive index changing layer 101b formed at the interface. That is, the phase difference becomes smaller than the design value, and Formula (1) is not satisfied. As a result, the diffraction efficiency of the diffractive optical element 113 when the light B in the wavelength band to be used is incident, that is, the emission efficiency of the _first- order diffracted light B ₁ becomes lower than the design value. At this time, 0th-order diffracted light B ₀ is mainly generated as unnecessary diffracted light. The zero-order diffracted light B ₀ has a longer focal length than the _first-order diffracted light B ₁ .

On the other hand, when a composite material as disclosed in Patent Document 3 is used as the optical adjustment layer, the above-described problem occurs due to the matrix material contained in the composite material penetrating into the substrate. As shown in FIG. 3B, a diffractive optical element 114 that uses a first-order diffracted light using a base 101 and an optical adjustment layer 103 ′ formed by dispersing inorganic particles 104 in a matrix material 103 is considered. . The refractive indexes of the substrate 101 and the optical adjustment layer 103 'are N1 and N2, respectively, and the refractive index of the matrix material 103 is N4. In this case, as described above, only the matrix material 103 of the optical adjustment layer 103 ′ permeates the base 101, thereby generating the refractive index changing layer 101 c having a changed refractive index.

When the refractive indexes of the base 101, the optical adjustment layer 103 ′, and the matrix material 103 satisfy the relationship of N1 <N2 and N4 <N1, the refractive index N3 of the generated refractive index changing layer 101c is N1> N3 <N2. Satisfy the relationship. This is because the nanometer-order inorganic particles 4 cannot move to the base 101, and the refractive index changing layer 101c is generated by the permeation of the matrix material 103 having a refractive index lower than that of the base 101.

As in the case described above, when the refractive indexes N1 and N2 are designed to satisfy the formula (1) within the wavelength band used, the steps constituting the diffraction grating are formed by the refractive index changing layer 101c formed at the interface. The optical distance difference, that is, the phase difference becomes larger than the design value, and the expression (1) is not satisfied. As a result, the diffraction efficiency of the diffractive optical element 113 when the light B in the wavelength band to be used is incident, that is, the emission efficiency of the _first- order diffracted light B ₁ becomes lower than the design value. At this time, second-order diffracted light B ₂ is mainly generated as unnecessary diffracted light. The second-order diffracted light B ₂ has a shorter focal length than the _first-order diffracted light B ₁ .

In an optical system using only a normal refraction phenomenon, as shown in FIG. 4, even if the refractive index changing layer 201d is generated between the base 201 and the optical adjustment layer 203, the refractive index changing layer 201d and the base 201 Is about 0.01, the angle at which the light C entering from the base 201 is refracted at the interface between the base 201 and the refractive index changing layer 201d is small. If the refractive index changing layer 201d is thin, the distance that the light C travels at the refracted angle is short. For this reason, even when the refractive index changing layer 201d is generated, the incident angle and the incident position of the light C incident on the optical adjustment layer 203 are almost the same as when the refractive index changing layer 201d is not generated, and the optical performance is affected. Is small enough to be ignored. That is, even if the refractive index change layer 201d that cannot be observed with an optical microscope is generated, the influence can be ignored.

However, as described above, in the case of a diffractive optical element, the generation of the refractive index changing layer does not satisfy the diffraction condition (1), and thus the generation of the refractive index changing layer is directly connected to the generation of unnecessary diffracted light. As a result, the diffraction efficiency at the design order is greatly reduced.

In particular, when a material containing an ultraviolet curable resin or a thermosetting resin is used as the optical adjustment layer from the viewpoint of productivity, an uncured resin, that is, a monomer or an oligomer is in contact with the substrate in the process of forming the optical adjustment layer. To do. Since monomers and oligomers have a smaller molecular weight than the cured resin, the reactivity and permeability to the substrate 101 are greater than those after the cured resin. That is, the diffraction grating is easily deformed, and the diffraction efficiency is lowered due to the generation of the refractive index changing layer and the refractive index changing layer.

In addition, when using a composite material for the optical adjustment layer, the optical adjustment layer is formed to uniformly disperse the inorganic particles in the matrix material or to adjust the viscosity of the optical adjustment layer in the process of forming the optical adjustment layer. A solvent may be added to the starting material. Such a solvent, like the resin material in the optical adjustment layer, causes a refractive index change due to dissolution of the substrate and penetration into the substrate, and causes the above-described problems.

In order to solve such a problem, the present invention provides an intermediate layer between the base and the optical adjustment layer to suppress the interaction between the base and the optical adjustment layer. Hereinafter, embodiments of the diffractive optical element according to the present invention will be described in detail.

(First embodiment)
FIG. 5A is a cross-sectional view showing a first embodiment of a diffractive optical element according to the present invention. As shown in FIG. 5A, the diffractive optical element 51 includes a base 1, an intermediate layer 3, and an optical adjustment layer 4. The base 1 is made of a first optical material containing a first resin. The optical adjustment layer 4 and the intermediate layer 3 are also made of a second optical material containing a second resin and a third optical material containing a third resin, respectively.

The substrate 1 has a main surface 1a, and a diffraction grating 2 is provided on the main surface 1a. The reason why a material containing a resin is used as the first optical material is that it is preferable to use a resin rather than glass from the viewpoint of productivity and workability. Optical elements such as lenses can be manufactured with high productivity by molding. In this case, the life of the mold depends on the material to be molded, and the life of the mold is about 10 times longer and the manufacturing cost can be reduced by using resin compared to the case of using glass. Moreover, although it may be difficult to shape | mold glass to fine shapes, such as a diffraction grating shape, since techniques, such as injection molding, can be utilized if it is resin, the optical element which has a fine shape can be shape | molded. When the resin is used, it is excellent in fine workability, so that the performance of the diffractive optical element 51 can be improved or the diffractive optical element 51 can be downsized by reducing the pitch of the diffraction grating 2. Furthermore, it is possible to reduce the weight of the diffractive optical element 51.

As the first resin, among the translucent resin materials generally used as the base of the optical element, the refractive index characteristic and the wavelength dispersion that can reduce the wavelength dependency of the diffraction efficiency at the design order of the diffractive optical element. Select a material with In particular, an aromatic polycarbonate resin and a copolymer resin containing an aromatic polycarbonate structure are preferable.

The first optical material may contain, in addition to the first resin, one or more components that adjust optical properties such as refractive index and Abbe number and mechanical properties such as impact resistance. In addition to the first resin, the first optical material includes optical particles such as refractive index, inorganic particles for adjusting mechanical properties such as thermal expansion, dyes and pigments that absorb electromagnetic waves in a specific wavelength region, etc. The additive may be included.

In the present embodiment, the main surface 1a of the substrate 1 includes a region r1 where the optical axis O of the diffractive optical element 51 is located, r2 surrounding the region r1, and r3 surrounding the region r2. The main surface 1a has a concave aspheric shape having a lens action in the region r1. A diffraction grating 2 is provided in the region r2 of the main surface 1a. As shown in FIG. 5B, the diffraction grating 2 is constituted by a grating 2a having a concentric step shape centered on the optical axis O. From the optical characteristics of the substrate 1 and the optical adjustment layer 4 and the optical design of the finally obtained diffractive optical element 51, the cross-sectional shape, pitch, and groove depth of the grating 2a are determined. For example, when the diffraction grating 2 has a lens action, the pitch may be changed so as to decrease continuously or intermittently from the center of the lens toward the periphery, and the grating 2a may be arranged concentrically. In the present embodiment, the diffraction grating 2 is formed on a flat surface, but may be formed on a curved surface in order to further improve the light collecting function. In particular, when the diffraction grating 2 is formed so that the envelope surface passing through the groove of the diffraction grating is an aspheric surface having a lens action, the chromatic aberration, curvature of field, etc. are improved in a balanced manner by an optimal combination of the refraction action and the diffraction action. A lens having high imaging performance can be obtained. The depth d of the diffraction grating 2 can be determined using Equation (1).

In the present embodiment, the diffraction grating 2 is provided only on one main surface 1a of the base body 1. However, a diffraction grating may be provided on the other main surface 1b, and diffraction is also performed on the region r1 of the main surface 1a. A grid may be provided. In the present embodiment, the main surface 1a has a concave shape in the central region r1, and the envelope surface and the main surface 1b passing through the grooves of the diffraction grating in the region r2 are planes. The shape may be independently a plane, a convex shape, and a concave shape.

Further, when diffraction gratings are provided on the main surface 1a and the main surface 1b, the shape, arrangement, pitch, and diffraction grating depth of the diffraction gratings on both surfaces are not necessarily the same as long as they satisfy the performance required for the diffractive optical element. There is no need to let them. The same applies to the following embodiments.

In the intermediate layer 3, the resin or solvent contained in the optical adjustment layer 4 penetrates into the substrate 1 in the step of heat-curing and energy-curing the optical adjustment layer 4 made of resin (curing by ultraviolet rays, visible light, electron beams, etc.). The diffraction grating 2 provided on the main surface 1a of the base 1 is prevented from being deformed and the refractive index of the base 1 from being changed. For this reason, it is preferable that the intermediate layer 3 is provided in the region r <b> 2 in the main surface 1 a of the substrate 1 so as to cover at least the diffraction grating 2. In the present embodiment, the intermediate layer 3 covers the regions r1 and r2. As described above, the intermediate layer 3 is made of the third optical material containing the third resin. It is desirable that the third optical material has sufficient translucency so as not to deteriorate the characteristics of the diffractive optical element 51 and does not erode the substrate 1. For this reason, examples of the third resin included in the third optical material include acrylic resin, epoxy resin, polyester resin, polystyrene resin, polyolefin resin, polyamide resin, polyimide resin, polyvinyl alcohol, butyral resin, vinyl acetate resin, and fat. Of the resins represented by cyclic polyolefin resin, polycarbonate, liquid crystal polymer, polyphenylene ether, polysulfone, polyethersulfone, polyarylate, etc., those that do not erode the substrate 1 and satisfy translucency may be appropriately selected. .

Particularly, it is more preferable to use a thermosetting resin or an energy ray curable resin as the third resin because it is excellent in productivity. Examples of energy rays used for curing include ultraviolet rays, visible rays, and electron beams. Examples of the energy ray curable resin include monomers and oligomers having a methacryl group, an acrylic group, an epoxy group, an oxetane group, and the like, and an ene-thiol resin.

When a monomer is used as a raw material for the third resin, it is preferable that the viscosity of the monomer is low in order to apply thinly. An oligomer may be used as a raw material for the third resin. However, the oligomer has a higher viscosity than the monomer. For this reason, when using an oligomer as a raw material of 3rd resin, it is preferable to dilute an oligomer with a solvent and to apply | coat to the area | region in which the diffraction grating 2 of the base | substrate 1 was formed. In this case, it is necessary to select a solvent that does not penetrate the substrate 1 as the solvent to be used.

In order for the intermediate layer 3 not to erode the substrate 1, it is necessary to reduce the interaction between the third optical material of the intermediate layer 3 and the first optical material of the substrate 1. Therefore, there is a difference in solubility parameter between the third resin contained in the third optical material, the raw material of the third resin in an uncured or unpolymerized state, and the solvent contained in the raw material and the first resin of the first optical material. It is preferably 0.8 [cal / cm ³ ] ^1/2 or more. As will be described in detail below, the third resin contained in the third optical material, the raw material of the third resin in an uncured or unpolymerized state, the solvent contained in the raw material, and the second constituting the optical adjustment layer 4 The difference in solubility parameter between the optical material and the second resin is preferably 0.8 [cal / cm ³ ] ^1/2 or more.

The solubility parameter is the square root of the cohesive energy density in regular solution theory, and the solubility parameter δ of a certain substance is defined by the following equation using the molar volume V and cohesive energy ΔE per mol.
δ = (ΔE / V) ^1/2

The solubility parameter is an index of the intermolecular force of the substance, and it is considered that the closer the solubility parameter, the higher the affinity, that is, the stronger the interaction. There are various derivation methods for the solubility parameter. For example, a value obtained by a method of calculating from a molecular structure formula by Fedors et al. Can be used. The solubility parameter used in the present specification is a value obtained by a method of calculating from this molecular structural formula. Examples of the structure that increases the solubility parameter include highly polar functional groups such as OH groups and amide bonds. On the other hand, examples of the structure having a low solubility parameter include a fluorine atom, a hydrocarbon group, and a siloxane bond.

FIG. 6 shows changes in the refractive index formed in a region in the vicinity of the surface in contact with the acrylate resin of the substrate when acrylate resins having various SP values (solubility parameters) are formed on the substrate made of aromatic polycarbonate. The result of having measured the refractive index of the layer is shown. The horizontal axis indicates the difference in SP value between the substrate and the acrylate resin formed on the substrate surface, and the vertical axis indicates the refractive index of the refractive index changing layer formed on the substrate surface. A prism coupler (manufactured by Metricon Corporation, MODEL 2010) was used for the measurement of the refractive index. FIG. 6 shows that the refractive index is almost constant when the difference in SP value between the substrate and the acrylate resin is 0.8 [cal / cm ³ ] ^1/2 or more. This is because, if the difference in SP value is 0.8 [cal / cm ³ ] ^1/2 or more, the acrylate resin does not penetrate into the substrate so that the refractive index changes, and the interaction occurs substantially. This is probably because it is not. Therefore, even when the above-described resin is used as the first resin of the first optical material constituting the substrate 1, the difference in SP value from the third resin is 0.8 [cal / cm ³ ] ^1/2 or more. If it exists, it is thought that interaction does not arise substantially.

When an energy beam curable resin or a thermosetting resin is used as the third resin, the cured resin is three-dimensionally cross-linked, so that the resin and solvent contained in the optical adjustment layer 4 penetrate into the substrate 1 and erode. The effect of suppressing this is increased.

A transparent inorganic material such as silicon oxide, silicon nitride, titanium oxide, zinc oxide, zirconium oxide, magnesium fluoride, or ITO may be used as the third optical material of the intermediate layer 3. However, when an inorganic material is used, it is necessary to employ a vacuum process such as sputtering or vapor deposition, and the manufacturing cost may be increased due to an increase in the cost of the apparatus and an increase in the takt time. On the other hand, when the organic material described above is used, it can be formed in a short time using simple equipment, and thus there is an advantage that the manufacturing cost can be reduced. In addition, when using an inorganic material as the 3rd optical material of the intermediate | middle layer 3, interaction does not arise between an inorganic material, the 1st optical material of the base | substrate 1, and the optical adjustment layer 4 mentioned later, and an inorganic material osmose | permeates. Thus, the refractive index changing layer is not formed on the surface of the substrate 1. In addition, the solubility parameter is defined for organic substances and not for inorganic substances.

As described above, the solubility parameter of the third resin contained in the third optical material, the raw material of the third resin in an uncured or unpolymerized state, and the solvent contained in the raw material and the first resin of the first optical material When the difference is 0.8 [cal / cm ³ ] ^1/2 or more, the interaction between the intermediate layer 3 and the substrate 1 hardly occurs. However, if the intermediate layer 3 is thin, when the intermediate layer 3 cannot be formed with a uniform thickness, the base 1 and the optical adjustment layer 4 are in direct contact with each other or are too thin, so that the first optical material of the base 1 and the optical layer There is a possibility that the interaction of the adjustment layer 4 with the second optical material cannot be suppressed. For this reason, it is preferable that the thickness of the intermediate layer 3 is 10 nm or more. Here, “10 nm” refers to a range including variations such as a manufacturing error of about 10%. Depending on the material of the intermediate layer 3 and the method of forming the intermediate layer 3, if the intermediate layer 3 has a thickness of about 9 nm, the interaction may be sufficiently suppressed, and a thickness of about 11 nm is required. It means that there are cases.

Further, when the intermediate layer 3 is thick, the optical characteristics of the diffractive optical element 51, particularly the diffraction efficiency of the diffraction grating 2, is reduced. Hereinafter, this decrease in diffraction efficiency will be described. FIG. 7 is a schematic cross-sectional view showing the enlarged grating 2a of the diffraction grating 2. As shown in FIG. As shown in FIG. 7, the intermediate layer 3 is provided so as to cover the surface of the grating 2 a of the diffraction grating 2. Assuming that the interval between the gratings 2a in the diffraction grating 2 is T, among the light 40 transmitted from the base 1 to the optical adjustment layer 4 side between the gratings 2a, the light that passes through the region r11 has the inclined portion 3a of the intermediate layer 3 Advancing from the substrate 1 to the optical adjustment layer 4 across the substrate. On the other hand, the light 40 transmitted through the region r12 corresponding to the thickness t of the intermediate layer 3 is substantially perpendicular to the thickness direction in the wall surface portion 3b of the intermediate layer 3 provided along the wall surface of the grating 2a. Direction, that is, parallel to the intermediate layer 3.

As described above, the diffraction efficiency of the diffractive optical element 51 is designed to be 100% when Expression (1) is satisfied, and the presence of the intermediate layer 3 is not considered in this Expression (1). However, in the case where the thickness t of the intermediate layer 3 is sufficiently smaller than the distance T of the grating 2a in the diffraction grating 2, there is no intermediate layer 3 generated by crossing the inclined portion 3a of the intermediate layer in the region r11. The optical path difference with respect to the case can be ignored, and a diffraction efficiency close to 100% can be obtained by substantially satisfying the equation (1). On the other hand, the light 40 transmitted through the region r12 is transmitted through the wall surface portion 3b of the intermediate layer 3 by the length of the step d of the grating 2a. Therefore, the optical path difference with respect to the case without the intermediate layer 3 cannot be ignored. The transmitted light 40 cannot substantially satisfy the formula (1). For this reason, as the thickness t of the intermediate layer 3 increases, the amount of light that cannot satisfy Expression (1) increases, and the diffraction efficiency of the diffraction grating 2 decreases.

In FIG. 8, an intermediate layer 3 having a thickness corresponding to 5% of the minimum value of the grating interval T of the diffraction grating 2 (hereinafter referred to as “minimum pitch”) is provided between the substrate 1 and the optical adjustment layer 4. It is a simulation result which shows the wavelength dependence of the diffraction efficiency of the diffraction grating 2 in the case of being provided. In FIG. 8, the horizontal axis represents the wavelength (μm) of light transmitted through the diffractive optical element, and the vertical axis represents the first-order diffraction efficiency (%). As shown in FIG. 8, it was found that a first-order diffraction efficiency of 80% or more can be obtained in the wavelength range of 400 nm to 700 nm. According to a detailed examination, it was found that when the thickness of the intermediate layer 3 is within 1% of the minimum pitch of the grating interval of the diffraction grating 2, a first-order diffraction efficiency of 95% can be obtained.

From these results, the thickness of the intermediate layer 3 is preferably 10 nm or more and 5% or less of the minimum pitch of the diffraction grating 2, and more preferably 10 nm or more and 1% or less of the minimum pitch of the diffraction grating 2. It can be said that it is preferable. It is preferable that at least the slope portion 3a and the wall surface portion 3b of the intermediate layer 3 have a uniform thickness.

Regarding the translucency of the intermediate layer 3, it is sufficient that the transmittance of all light rays is 90% or more in the thickness of the intermediate layer 3 to be formed. Further, as described above, the refractive index of the intermediate layer 3 may be selected as long as the presence of the intermediate layer 3 does not adversely affect the diffraction efficiency. Regardless of the value of the refractive index, the intermediate layer 3 prevents the diffraction grating shape of the substrate 1 from being deformed and the refractive index from being changed due to the interaction between the substrate 1 and the optical adjustment layer 4, thereby reducing the decrease in diffraction efficiency. Can do. In particular, when the refractive index of the material constituting the intermediate layer 3 is larger than the refractive index of the first optical material constituting the substrate 1 and smaller than the refractive index of the second optical material constituting the optical adjustment layer 4, the intermediate layer 3 An antireflection effect can be achieved.

As described with reference to FIG. 2B, the refractive index change layer is generated by the interaction between the substrate and the optical adjustment layer, and the refractive index change layer becomes thick at the tip of the lattice shape (FIG. 2 (b) tip 101t). For this reason, when the refractive index changing layer is generated, the ratio of the light transmitted through the portion located at the tip of the grating of the refractive index changing layer is increased, and the diffraction efficiency of the optical element is likely to be lowered. As a result, it is considered that the diffraction efficiency is greatly reduced even when the thickness of the other part of the refractive index changing layer is 5% or less of the minimum pitch of the grating interval.

On the other hand, the intermediate layer 3 is formed on the lattice 2 of the substrate 1 and can be formed with a substantially uniform thickness although it depends on the forming method. That is, the intermediate layer 3 is not formed as thick as the refractive index changing layer even at the tip portion of the lattice shape. Therefore, practically sufficient diffraction efficiency can be achieved if the thickness of the intermediate layer 3 is 5% or less of the minimum pitch of the lattice spacing as described above.

The optical adjustment layer 4 is provided so as to cover the intermediate layer 2 on the main surface 1a of the substrate 1 so as to fill at least the step of the diffraction grating 2 in order to reduce the wavelength dependency of the diffraction efficiency in the diffractive optical element 51. ing. In the present embodiment, the main surface 1a of the substrate 1 on which the diffraction grating 2 is provided is a flat surface, and therefore the surface of the optical adjustment layer 4 that is not in contact with the substrate 1 is also configured by a flat surface. However, by combining the effect of refraction by making the surface aspherical and the effect of diffraction by forming it on the diffraction grating shape of the substrate, the lens characteristics are improved by reducing chromatic aberration and curvature of field. Can be made.

In order to reduce the wavelength dependency of diffraction efficiency, it is preferable that the substrate 1 and the optical adjustment layer 4 satisfy the formula (1) in the entire wavelength region of light to be used. For this purpose, the first optical material of the substrate 1 and the second optical material of the optical adjustment layer 4 exhibit a tendency that the wavelength dependence of the refractive index is opposite, and cancel each other in the change of the refractive index with respect to the wavelength. It is preferable to provide. More specifically, the refractive index of the first optical material is smaller than the refractive index of the second optical material, and the wavelength dispersion of the refractive index of the first optical material is greater than the wavelength dispersion of the refractive index of the second optical material. Is preferred. Alternatively, the refractive index of the first optical material is preferably larger than the refractive index of the second optical material, and the wavelength dispersion of the refractive index of the first optical material is preferably smaller than the wavelength dispersion of the refractive index of the second optical material. The wavelength dispersion of the refractive index is expressed by, for example, the Abbe number. The larger the Abbe number, the smaller the wavelength dispersion of the refractive index. Therefore, the refractive index of the first optical material is preferably smaller than the refractive index of the second optical material, and the Abbe number of the first optical material is preferably smaller than the Abbe number of the second optical material. Alternatively, the refractive index of the first optical material is preferably larger than the refractive index of the second optical material, and the Abbe number of the first optical material is preferably larger than the Abbe number of the second optical material.

When the 1st optical material and 2nd optical material which comprise the base | substrate 1 and the optical adjustment layer 4 each contain resin like this embodiment, it can be used as 2nd resin of a 2nd optical material, and the light to be used is used. In general, there are few resins having a high refractive index and low wavelength dispersion that satisfy the formula (1) in the entire wavelength region. In such a case, by using a composite material in which inorganic particles having a high refractive index are dispersed in the second resin as the second optical material, the choice of materials can be increased and the refractive index and the Abbe number can be finely adjusted. . In addition, since the composite material uses a resin as a matrix material, the composite material has a feature of being excellent in workability while being a material having both high refractive index and low wavelength dispersion.

In this case, the resin used as the matrix material of the composite material, that is, the second resin includes methacrylic resin such as polymethyl methacrylate, epoxy resin; polyester resin such as polyethylene terephthalate, polybutylene terephthalate and polycaprolactone; polystyrene resin such as polystyrene. Olefin resin such as polypropylene; polyamide resin such as nylon; polyimide resin such as polyimide and polyetherimide; polyvinyl alcohol; butyral resin; vinyl acetate resin; alicyclic polyolefin resin. Further, engineering plastics such as polycarbonate, liquid crystal polymer, polyphenylene ether, polysulfone, polyethersulfone, polyarylate, and amorphous polyolefin may be used. Also, a mixture or copolymer of these resins (polymers) may be used. Moreover, you may use what modified | denatured these resin. In particular, it is more preferable to use a thermosetting resin or an energy beam curable resin as the second resin because of excellent productivity. As the energy ray curable resin, a resin similar to that exemplified as the third resin can be used.

Examples of the inorganic particles dispersed in the second resin include zirconium oxide, titanium oxide, zinc oxide, tantalum oxide, niobium oxide, tungsten oxide, indium oxide, tin oxide, hafnium oxide, lanthanum oxide, scandium oxide, cerium oxide, and oxide. Yttrium, barium titanate, silica, alumina and the like can be used, but are not necessarily limited thereto. Moreover, you may use these complex oxides. Among these, from the viewpoint of ensuring the low wavelength dispersibility of the composite material, the inorganic particles dispersed in the second resin are selected from the group consisting of zirconium oxide, yttrium oxide, lanthanum oxide, hafnium oxide, scandium oxide, alumina, and silica. It is more preferable that at least one selected as a main component.

The effective particle size of the inorganic particles 4 is preferably 1 nm or more and 100 nm or less. When the effective particle size is 100 nm or less, loss due to Rayleigh scattering can be reduced and the transparency of the optical adjustment layer 3 ′ can be increased. Further, by setting the effective particle size to 1 nm or more, it is possible to suppress the influence of light emission or the like due to the quantum effect. The 2nd optical material may further contain additives, such as a dispersing agent which improves the dispersibility of inorganic particles, a polymerization initiator, and a leveling agent, as needed.

Here, the effective particle diameter will be described with reference to FIG. In FIG. 9, the horizontal axis represents the particle size (nm) of the inorganic particles, and the left vertical axis represents the frequency (%) of the inorganic particles with respect to the particle size of the horizontal axis. The vertical axis on the right represents the cumulative frequency of particle size. The effective particle size means that the particle size at which the cumulative frequency is 50% in the particle size frequency distribution of the entire inorganic particles is the central particle size (median diameter: d50), and the cumulative frequency is centered on the central particle size. It refers to the particle size range B in the range A of 50%. Therefore, it is preferable that the range of the effective particle size defined as described above of the inorganic particles 4 is in the range of 1 nm to 100 nm. In order to accurately determine the value of the effective particle size, for example, it is preferable to measure 200 or more inorganic particles.

The optical adjustment layer 4 contains a solvent in the raw material of the optical adjustment layer 4 for the purpose of adjusting the workability in the manufacturing process when forming the optical adjustment layer 4 and the surface property of the optical adjustment layer 4. May be. The type of the solvent is appropriately selected from the viewpoints of the solubility of the second resin contained in the second optical material constituting the optical adjustment layer 4 and raw materials such as monomers and oligomers, workability, and surface property control of the optical adjustment layer 4. Selected.

As described above, the second resin or solvent contained in the second optical material constituting the optical adjustment layer 4 does not interact with the third resin or solvent contained in the third optical material constituting the intermediate layer 3. It is preferable that the difference in solubility parameter between the second resin or solvent and the third resin or solvent contained in the second optical material is 0.8 [cal / cm ³ ] ^1/2 or more. However, when the optical adjustment layer 4 is formed, if the intermediate layer 3 is already cured or polymerized, the second optical material included in the second optical material is compared with the organic material included in the cured third optical material. The difference in the solubility parameter of the resin or solvent may be 0.8 [cal / cm ³ ] ^1/2 or more.

In this case, since the intermediate layer 3 functions as a barrier, the solubility parameter of the second resin and the solvent contained in the second optical material of the optical adjustment layer 4 and the solubility parameter of the first resin of the first optical material constituting the substrate 1. The difference may not be 0.8 [cal / cm ³ ] ^1/2 or more. Accordingly, the range of selection of materials that can be used as the first optical material and the second optical material is widened, and it becomes easier to select a material that satisfies the relationship of the expression (1).

According to the diffractive optical element of this embodiment, the intermediate layer is provided between the base and the optical adjustment layer. For this reason, the substrate and the optical adjustment layer are not in direct contact with each other, and even if a material containing a resin is used for the substrate and the optical adjustment layer, the resin contained in the optical adjustment layer penetrates the substrate and the shape of the diffraction grating is destroyed. Or generation of a refractive index changing layer is suppressed. Further, since the thickness of the intermediate layer is 5% or less of the minimum value of the grating spacing of the diffraction grating, the influence of the decrease in diffraction efficiency due to the intermediate layer is suppressed. As a result, it is possible to realize a diffractive optical element having high diffraction efficiency by using a resin for the substrate and the optical adjustment layer. Further, since it is not necessary to select a combination of resins contained in the base and the optical adjustment layer from the viewpoint of chemical interaction, there is an advantage that the choice of materials for the optical adjustment layer is widened. In particular, from the viewpoint of productivity, when a material containing an ultraviolet curable resin or a thermosetting resin is used as the optical adjustment layer, in the step of forming the optical adjustment layer, the uncured resin constituting the optical adjustment layer is There is no contact with the substrate. Thereby, reaction and penetration of the optical adjustment layer into the substrate can be suppressed, and a decrease in diffraction efficiency can be suppressed. Similarly, when a composite material is used for the optical adjustment layer, even if a material in which a solvent is added to the raw material for forming the optical adjustment layer is used, the solvent does not come into contact with the substrate. Thereby, similarly to the resin material in the optical adjustment layer, it is possible to suppress a change in refractive index and a decrease in diffraction efficiency due to the solvent dissolving and penetrating into the substrate.

In the diffractive optical element 51 of this embodiment, an antireflection layer may be provided on the surface of the optical adjustment layer 4. The material of the antireflection layer is not particularly limited as long as it has a refractive index smaller than that of the optical adjustment layer 4. For example, either a resin, a composite material of resin and inorganic particles, an inorganic thin film formed by vacuum deposition, or the like can be used. Examples of the inorganic particles used in the composite material as the antireflection layer include silica, alumina, and magnesium oxide having a low refractive index. Further, a nanostructure antireflection shape may be formed on the surface of the optical adjustment layer 4. The antireflection shape of the nanostructure can be easily formed by, for example, a transfer method (nanoimprint) using a mold. Further, a surface layer having an effect of adjusting mechanical properties such as friction resistance and thermal expansion may be separately formed on the surface of the optical adjustment layer 4 or the antireflection layer.

(Second Embodiment)
Hereinafter, embodiments of a method for manufacturing a diffraction grating according to the present invention will be described.

FIG. 10 schematically shows the structure of the diffractive optical element 52 manufactured according to this embodiment. The diffractive optical element 52 covers the base 11, the diffraction grating 12 provided on the surface of the base 11, the intermediate layer 13 provided on the surface of the base 11 so as to cover the diffraction grating 2, and the diffraction grating 22. And an optical adjustment layer 14 provided on the intermediate layer 13. The second optical material constituting the optical adjustment layer 14 includes a second resin 15 and inorganic particles 16, and is a nanocomposite material in which the inorganic particles 16 are dispersed in the second resin.

As shown in FIG. 11A, first, a base 11 having a diffraction grating 12 formed on the surface is prepared. For example, as represented by injection molding, press molding, etc., a method of performing molding by supplying the material of the substrate 11 in a softened or molten state to a mold in which the shape of the diffraction grating 12 is formed, and a diffraction grating shape. A method of polymerizing the resin raw material by heating and / or irradiation with energy rays, or forming the diffraction grating 12 on the preformed substrate 12 by cutting, polishing, or the like, by casting a resin raw material monomer or oligomer into the formed mold And the like. You may prepare the base | substrate 11 in which the diffraction grating 12 was formed by methods other than these.

Subsequently, as shown in FIG. 11B, an intermediate layer is formed on the diffraction grating 12 of the substrate 11. The intermediate layer is formed by applying a liquid monomer or oligomer, which is the raw material 13 'of the intermediate layer, and then curing, applying a resin having fluidity by heating and melting, cooling and solidifying, and plasma. Examples thereof include a method of directly forming an intermediate layer from a raw material 13 ′ such as a monomer or an oligomer by gas phase polymerization represented by polymerization or vapor deposition polymerization. In the figure, a state in which the liquid raw material 13 ′ is applied by the spray coating device 17 is shown. When a transparent inorganic material such as silicon oxide is used as the third optical material, a known inorganic thin film forming method such as a vapor deposition method, a sputtering method, or a CVD method can be used.

Examples of the method of applying the intermediate layer raw material 13 'include dip coating, coating using a liquid injection nozzle such as a dispenser, spray coating by an ink jet method or spray coating, coating by rotation such as spin coating, screen printing or padding. Application by squeezing such as printing, transfer, or the like can be used. Moreover, you may combine these methods suitably. Examples of a method for curing the applied raw material 13 ′ include irradiation with energy rays such as ultraviolet rays, electron beams, and radiation, and thermal curing. By curing, an intermediate layer 13 is formed on the surface of the diffraction grating 12 as shown in FIG. As described above, when the vapor phase polymerization method is used, the intermediate layer 13 is formed directly instead of the raw material 13 '. Even when a transparent inorganic material such as silicon oxide is used as the third optical material, the intermediate layer 13 can generally be formed directly.

Next, an optical adjustment layer is formed on the intermediate layer 13. The method for forming the optical adjustment layer is appropriately selected from existing coating layer formation processes depending on the material and the shape accuracy determined by the characteristics of the diffractive optical element. For example, spray coating, dip coating, coating using a liquid injection nozzle such as a dispenser, spray coating such as an inkjet method, coating by rotation such as spin coating, coating by squeezing such as screen printing or pad printing, transfer, etc. are applied Thereby, an optical adjustment layer can also be formed. Moreover, you may combine these processes suitably. FIG. 11C shows a state in which a monomer or oligomer that is a raw material 14 ′ of the optical adjustment layer is applied on the intermediate layer 13 using a liquid injection nozzle 18 such as a dispenser.

For the curing of the raw material 14 ′, a process such as thermal curing or energy beam irradiation can be used. For example, in the case of curing with ultraviolet rays, a photopolymerization initiator is added to the uncured resin 14 '. When the uncured resin 14 'is cured with an electron beam, a photopolymerization initiator is usually unnecessary. If the raw material 14 'contains a solvent, the solvent is dried before curing as shown in FIG. 11 (d). The solvent can be dried by a method such as heat drying or reduced pressure drying. Depending on the material used, it is necessary to adjust the drying temperature, pressure, time, and the like. However, if the solvent remains, the refractive index of the optical adjustment layer fluctuates and must be completely removed.

Thereafter, as shown in FIG. 11 (d), the raw material 14 ′ is cured in a desired shape using the mold 10, and the mold 10 is removed, and the optical adjustment is performed as shown in FIG. 11 (e). Layer 14 is formed to complete the diffractive optical element 52. In the case where the shape of the optical adjustment layer 4 is regulated using the mold 10, it is possible to arrange the raw material 14 ′ of the optical adjustment layer 14 in the mold and press it against the substrate 11 after drying. However, it is more preferable to arrange the raw material 14 ′ of the optical adjustment layer 14 on the base 11 side. This is because the raw material 14 ′ of the optical adjustment layer 14 before curing (before drying depending on the material) has a low viscosity, so that it is easy to go around the substrate 11 having the diffraction grating shape formed on the surface, and the entrapment of bubbles is suppressed. This is because the adhesion between the optical adjustment layer 14 after curing and the substrate is also improved.

The material constituting the mold 10 may be appropriately selected according to required accuracy and durability. For example, metals such as iron, aluminum, alloys thereof, and brass can be used. You may use the metal which surface-treated, such as nickel plating, as needed. In addition, resins such as quartz, glass, epoxy resin, polyester resin, and polyolefin resin can be used. The resin material often shrinks when cured, but when using a composite composed of resin and inorganic particles, it may be considered that the shrinkage rate is lower than when using the resin material alone. desirable.

When using the mold 10 to regulate the shape of the optical adjustment layer 14, it is common to perform mold release after the curing step. However, if the raw material 14 ′ of the optical adjustment layer 14 is not deformed before the curing process is performed, the curing process may be performed after first releasing the mold. When mold release is performed after curing by energy beam irradiation, energy beam irradiation is performed in a state where the raw material 14 ′ of the optical adjustment layer 14 is regulated by the mold 10. When an opaque material such as metal is used as the mold 10, energy beam irradiation is performed through the substrate 11 from the surface opposite to the surface on which the raw material 9 of the optical adjustment layer is disposed. On the other hand, if a material transparent to energy rays, such as quartz for ultraviolet rays, is used as the mold 10, energy beam irradiation can be performed through the mold 10 from the surface on which the raw material 14 ′ of the optical adjustment layer 14 is disposed. Is possible.

Thereby, the diffractive optical element 52 is completed as shown in FIG.

According to the method for manufacturing a diffractive optical element of this embodiment, an intermediate layer is provided between the base and the optical adjustment layer. For this reason, the base and the optical adjustment layer are not in direct contact, and even if a material containing a resin is used for the base and the optical adjustment layer, the resin of the optical adjustment layer penetrates into the base, and the shape of the diffraction grating collapses. Generation of the refractive index changing layer is suppressed. As a result, it is possible to realize a diffractive optical element having high diffraction efficiency by using a resin for the base and the optical adjustment layer. Further, since it is not necessary to select a combination of resins contained in the base and the optical adjustment layer from the viewpoint of chemical interaction, there is an advantage that the choice of materials for the optical adjustment layer is widened.

Particularly, the intermediate layer is formed by disposing the raw material of the intermediate layer on the substrate and then curing the raw material. For this reason, when the raw material for the optical adjustment layer is disposed on the substrate, the intermediate layer does not contain monomers, oligomers, solvents, etc., and the interaction between the intermediate layer and the raw material for the optical adjustment layer is suppressed. For this reason, there is a merit that options for the material of the optical adjustment layer are further expanded.

In the first and second embodiments, the diffractive optical element has one diffraction grating, but a diffractive optical element having a plurality of diffraction gratings may be realized. For example, as shown in FIG. 12, the diffractive optical element 53 includes a base 21, two diffraction gratings 22 provided on the surface of the base 21, an optical adjustment layer 24 provided so as to cover the diffraction grating 22, the base 21, and the optical element. And an intermediate layer 23 provided between the adjustment layers 24.

Hereinafter, the results of producing the diffractive optical element according to the present invention and evaluating the characteristics will be described in detail. Table 1 summarizes the material and thickness of the intermediate layer, the SP value difference with the substrate, the presence or absence of erosion, and the first-order diffraction efficiency used in the examples and comparative examples described below.

Example 1
A diffractive optical element 52 having the structure shown in FIG. 10 was produced by the following method. The diffractive optical element 21 has a lens action and is designed to use first-order diffracted light. This also applies to the following examples and comparative examples.

First, a bisphenol A-based polycarbonate resin (d-line refractive index 1.585, Abbe number 28, SP value 9.8 [cal / cm ³ ] ^1/2 ) is injection-molded, so that the envelope of the root of the diffraction grating is obtained. A base body 11 having an aspherical shape and having an annular diffraction grating 2 having a depth of 15 μm on one side was produced. The effective radius of the lens part is 0.828 mm, the number of annular zones is 29, the minimum annular zone pitch is 14 μm, and the paraxial radius R (curvature radius) of the diffraction surface is −1.0144 mm. Next, annealing was performed by holding the base 11 at 120 ° C. for 1 hour.

Next, pentaerythritol triacrylate (refractive index: 1.485, SP value 11.3) is applied onto the diffraction grating 2 of the substrate 11 by spray coating, and cured by irradiating with ultraviolet rays to form the intermediate layer 13. did. The thickness of the intermediate layer 13 was 420 nm. This value is 3% of the minimum pitch of the grating interval of the diffraction grating 12.

Next, a composite material as a material for the optical adjustment layer 4 was prepared as follows. Alicyclic acrylic resin A (d-line refractive index 1.53, Abbe number 52, SP value 9.0 [cal / cm ³ ] ^1/2 ) and zirconium oxide (primary particle size 3 to 10 nm, by light scattering method) A PGME (propylene glycol monomethyl ether) dispersion having an effective particle size of 20 nm and a silane surface treatment agent of 30 wt% was dispersed and mixed so that the weight ratio of zirconium oxide in the solid content was 56 wt%. . The composite material has a cured d-line refractive index of 1.623 and an Abbe number of 43. The light transmittance at a wavelength of 400 to 700 nm at a film thickness of 30 μm is 90% or more. The SP value of PGME is 10.5 [cal / cm ³ ] ^1/2 .

After 0.4 μL of this composite material is dropped onto the intermediate layer 13 of the base 11 by a dispenser, it is dried by a dryer and pressed with a mold, and the back side of the base (the side opposite to the side on which the composite material is dropped). Then, ultraviolet irradiation (illuminance 120 mW / cm ² , integrated light quantity 4000 mJ / cm ² ) was performed and released from the mold to form the optical adjustment layer 14. The surface shape of the optical adjustment layer 14 has an aspherical shape of the diffraction grating 2 of the substrate along the envelope shape at the base of the diffraction grating, and the thickness was 30 μm.

The diffraction efficiency of the diffractive optical element 52 produced by the above steps was measured. Using a white light source and a color filter (R: 640 nm, G: 540 nm, B: 440 nm), using an ultra-precise three-dimensional measuring device (manufactured by Mitaka Kogyo Co., Ltd.) for brightness at each diffraction order at each wavelength. And calculated from the following equation (2). The first-order diffraction efficiency was 90% or more at each wavelength. In addition, higher-order diffracted light higher than third-order diffracted light was not detected.

Since the diffractive optical element of the present invention is characterized by having a high diffraction efficiency with respect to all white light, the first-order diffraction efficiency is required to be 80% or more for all the R, G, and B wavelengths. The diffractive optical element 52 formed by such a method is cut along a cross section passing through the optical axis, and the boundary portion between the substrate 11 and the intermediate layer 12 and the boundary portion between the intermediate layer 12 and the optical adjustment layer 13 are observed with an optical microscope. As a result, no shape change or discoloration due to the interaction of materials was observed.

(Example 2)
A diffractive optical element having the same structure as in Example 1 was produced by the same method as in Example 1. In this example, as a raw material for the intermediate layer 12, an epoxy acrylate resin (refractive index: 1.600, SP value: 11.2) diluted with IPA (isopropyl alcohol) was applied, dried after application, and then cured. This is different from the first embodiment. The thickness of the obtained intermediate layer 12 is 700 nm, and this value is 5% of the minimum pitch of the grating interval of the diffraction grating 12.

The diffraction efficiency was calculated by the same method as in Example 1. As a result, the diffraction efficiency was 80% or more for all wavelengths of R, G, and B.

The diffractive optical element was cut along a cross section passing through the optical axis, and the boundary portion between the substrate and the optical adjustment layer was observed with an optical microscope. As a result, no erosion due to the interaction of the materials was observed.

(Example 3)
A diffractive optical element having the same structure as that of Example 1 was produced in the same manner as in Example 1. This example is different from Example 1 in that an acrylate resin (refractive index: 1.65, SP value: 11.1) is used as a raw material for the intermediate layer 12. The thickness of the obtained intermediate layer 12 is 420 nm, and this value is 3% of the minimum pitch of the grating interval of the diffraction grating 12.

The diffraction efficiency was calculated by the same method as in Example 1. As a result, the diffraction efficiency was 85% or more for all the R, G, and B wavelengths.

(Comparative Example 1)
As a comparative example, as shown in FIG. 13, among the diffractive optical elements of Example 1, a diffractive optical element 54 having a structure having no intermediate layer was produced by the same method as in Example 1. This comparative example differs from Example 1 in that the optical adjustment layer 14 was formed directly on the substrate 11 without forming an intermediate layer.

The produced diffractive optical element 54 was cut along a cross section passing through the optical axis, and the boundary portion between the substrate and the optical adjustment layer was observed with an optical microscope. As a result, as shown in FIG. It was done. In addition, the diffraction efficiency could not be measured because it did not have a light collecting function due to erosion of the diffraction grating shape.

(Comparative Example 2)
As a comparative example, a diffractive optical element having the same structure as in Example 1 was produced by the same method as in Example 1. In this comparative example, trimethylolpropane triacrylate (TMPTA) (refractive index: 1.475, SP value of 9.7) having a difference from the SP value of the base polycarbonate of 0.1 or less is used as the intermediate layer. This is different from the first embodiment in that it is formed.

The thickness of the intermediate layer is 420 nm (3% of the minimum pitch of the grating interval of the diffraction grating 12).

The produced diffractive optical element was cut along a cross section passing through the optical axis, and the boundary between the substrate and the optical adjustment layer was observed with an optical microscope. As a result, erosion due to the interaction of materials was observed as shown in FIG. It was. In addition, the diffraction efficiency could not be measured because it did not have a light collecting function due to erosion of the diffraction grating shape.

(Comparative Example 3)
As a comparative example, a diffractive optical element having the same structure as in Example 1 was produced by the same method as in Example 1. This comparative example differs from Example 1 in that the thickness of the intermediate layer is 840 nm, which is 6% of the minimum pitch.

The produced diffractive optical element was cut along a cross section passing through the center, and the boundary portion between the substrate and the optical adjustment layer was observed with an optical microscope. As a result, no erosion due to the interaction of the materials was observed.

The diffraction efficiency was calculated by the same method as in Example 1. As a result, the R and G wavelengths were 80% or more, but the B wavelength was 80% or less.

(Comparative Example 4)
As a comparative example, a diffractive optical element having the same structure as in Example 1 was produced by the same method as in Example 1. This comparative example differs from Example 1 in that the thickness of the intermediate layer is 1.12 μm, which is 8% of the minimum pitch.

The diffraction efficiency was calculated by the same method as in Example 1. As a result, it was 80% or less for all the R, G, and B wavelengths.

FIG. 14 shows the results of the first-order diffraction efficiency with respect to the intermediate layer thickness in Examples and Comparative Examples. FIG. 14 also shows the result of the diffraction efficiency obtained by simulation when the thickness of the intermediate layer is 1% of the minimum pitch. In the simulation, an acrylate resin having a refractive index of 1.600 and an Abbe number of 33 was used as the material of the intermediate layer.

As can be seen from the results of Examples 1, 2, and 3, if the difference in solubility parameter between the intermediate layer and the substrate is 0.8 or more, the substance contained in the intermediate layer penetrates into the substrate, and the refractive index changing layer is formed. Generation can be suppressed. Further, if the thickness of the intermediate layer is 5% or less of the minimum pitch, the diffraction efficiency of the primary light is 80% or more for light of any wavelength, and a diffractive optical element having optical characteristics almost as designed is obtained. I can see that this is possible.

On the other hand, as can be seen from the results of Comparative Example 1, when the intermediate layer is not formed, the optical adjustment layer penetrates into the substrate, resulting in the formation of a refractive index change layer, which significantly reduces the diffraction efficiency. Further, as can be seen from the result of Comparative Example 2, even when the substance contained in the intermediate layer penetrates into the substrate, a refractive index changing layer is generated, and the diffraction efficiency is remarkably lowered.

Furthermore, as can be seen from the results of Comparative Example 3, even when the difference in solubility parameter between the intermediate layer and the substrate is 0.8 or more, the intermediate layer has a thickness greater than 5% of the minimum pitch. It can be seen that the diffraction efficiency decreases due to the influence of the above.

As shown in FIG. 14, if the thickness of the intermediate layer is 5% or less of the minimum pitch, the diffraction efficiency of the primary light is 80%, and if it is 3% or less of the minimum pitch, the diffraction efficiency of the primary light. Is 85% or more for light of any wavelength, and it is found that the average is 90% or more. Further, from the simulation results, it can be seen that if the thickness of the intermediate layer is 1% or less of the minimum pitch, the diffraction efficiency is 95% or more.

Thus, according to the optical element of the example, since the thickness of the intermediate layer is 5% or less of the minimum value of the grating interval of the diffraction grating, the influence of the decrease in diffraction efficiency due to the intermediate layer is suppressed. In addition, since the difference in solubility parameter between the resin contained in the third optical material of the intermediate layer and the resin contained in the first optical material of the base is 0.8 or more, the generation of the refractive index changing layer is suppressed. The

The diffractive optical element of the present invention can be suitably used as, for example, a camera lens, a spatial low-pass filter, a polarization hologram, or the like.

1, 11, 21, 101

Substrate

2, 12, 22, 102

Diffraction gratings

3, 14, 24, 103 Optical adjustment layers 4, 13, 23 Intermediate layer 10 Mold 17 Spray coating device 18 Dispenser 101a Refractive

index changing layers

51, 52 53, 54, 111, 112 Diffractive optical element

Claims

A substrate made of a first optical material containing a first resin and having a diffraction grating on its surface;
An optical adjustment layer made of a second optical material containing a second resin and provided on the base so as to cover the diffraction grating;
It comprises a third optical material containing a third resin, and comprises an intermediate layer provided between the base and the optical adjustment layer,
The refractive index of the first optical material is smaller than the refractive index of the second optical material, and the wavelength dispersion of the refractive index of the first optical material is larger than the wavelength dispersion of the refractive index of the second optical material.
The diffractive optical element according to claim 1, wherein the second resin is a thermosetting resin or an energy curable resin.
The diffractive optical element according to claim 2, wherein the second optical material further includes inorganic particles, and the inorganic particles are dispersed in the second resin.
The diffractive optical element according to claim 3, wherein a refractive index of the third optical material is larger than a refractive index of the first optical material and smaller than a refractive index of the second optical material.
The diffractive optical element according to claim 4, wherein a difference in solubility parameter between the first resin and the third resin is 0.8 [cal / cm 3 ] 1/2 or more.
The diffractive optical element according to claim 5, wherein a difference in solubility parameter between the second resin and the third resin is 0.8 [cal / cm 3 ] 1/2 or more.
The diffractive optical element according to claim 6, wherein the thickness of the intermediate layer is 5% or less of the minimum value of the grating interval of the diffraction grating.
The diffractive optical element according to claim 7, wherein a thickness of the intermediate layer is 1% or less of a minimum value of a grating interval of the diffraction grating.
The diffractive optical element according to claim 8, wherein the third resin is a thermosetting resin or an energy curable resin.
The diffractive optical element according to claim 3, wherein the inorganic particles contain at least one selected from the group consisting of zirconium oxide, yttrium oxide, lanthanum oxide, hafnium oxide, scandium oxide, alumina and silica as a main component.
The diffractive optical element according to claim 10, wherein an effective particle diameter of the inorganic particles is 1 nm or more and 100 nm or less.
The diffractive optical element according to claim 1, wherein the first resin is polycarbonate.
The diffractive optical element according to claim 7, wherein the intermediate layer has a thickness of 10 nm or more.
A step of preparing a substrate made of a first optical material containing a first resin and having a diffraction grating on the surface;
Forming an intermediate layer on the base so as to cover the surface of the diffraction grating of the base;
Forming an optical adjustment layer made of a second optical material containing a second resin on the intermediate layer,
The step of forming the intermediate layer includes
Disposing a third resin material on the base so as to cover the surface of the diffraction grating of the base;
And a step of forming the intermediate layer made of a third optical material by curing the raw material of the third resin.
The method of manufacturing a diffractive optical element according to claim 14, wherein the second optical material further includes inorganic particles, and the inorganic particles are dispersed in the second resin.
The method of manufacturing a diffractive optical element according to claim 15, wherein a refractive index of the third optical material is larger than a refractive index of the first optical material and smaller than a refractive index of the second optical material.
The method of manufacturing a diffractive optical element according to claim 16, wherein a difference between the solubility parameter of the first resin and the solubility parameter of the raw material of the third resin is 0.8 [cal / cm 3 ] 1/2 or more. .