JPWO2010140341A1 - Diffractive optical element - Google Patents

Abstract

The diffractive optical element of the present invention comprises a first optical material containing one resin, a substrate having a diffraction grating on its surface, a second optical material containing a second resin and inorganic particles, and is provided on the diffraction grating. The optical adjustment layer has a maximum thickness of 15 μm to 100 μm, and the second resin is a polymer of a photocurable resin composition containing a bifunctional monomer or oligomer. .

Description

  The present invention relates to a diffractive optical element, and relates to a diffractive optical element constituted by two or more members containing different resins.

  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.

  The diffractive optical element has a 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 includes a base made of an optical material and provided with a diffraction grating on the surface, and an optical adjustment layer made of an optical material different from the base and covering the diffraction grating. A phase difference type diffractive optical element 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 m-order diffraction efficiency for light of wavelength λ is 100%. Here, m is an integer and indicates the diffraction order.

  Accordingly, if an optical material having a refractive index n1 (λ) and an optical material having a refractive index n2 (λ) having a wavelength dependency such that d is substantially constant within the wavelength band of the light to be used can be combined, The wavelength dependency of diffraction efficiency can be reduced. 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 optical material constituting the substrate, and ultraviolet curable resin is used as the optical material constituting the optical adjustment layer.

  Patent Document 2 discloses that in a phase difference type diffractive optical element having a similar structure, glass is used as an optical material constituting a substrate, and an energy curable resin is used as an optical material constituting an optical adjustment layer. Yes. Patent Document 2 discloses that this structure can reduce the wavelength dependency of diffraction efficiency, and can effectively prevent color unevenness and flare generation due to unnecessary order light.

Japanese Patent Laid-Open No. 10-268116 JP 2001-249208 A

  When glass is used as an optical material constituting a substrate in a retardation type diffractive optical element, it is difficult to make fine processing compared to resin, so it is not easy to narrow the diffraction grating pitch and improve diffraction performance. . For this reason, it is difficult to improve the optical performance while reducing the size of the retardation type diffractive 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 optical material constituting the substrate, diffraction grating processing and molding are easier than glass. However, it is difficult to achieve various values of refractive index compared to glass, and the difference in refractive index between the optical material constituting the substrate and the optical material constituting the optical adjustment layer is reduced. For this reason, as apparent from the equation (1), the depth d of the diffraction grating is increased.

  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 formed in the mold into a sharp shape. It becomes difficult to process. 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 inventor of the present application examined the use of a composite material in which inorganic particles are dispersed in a matrix resin as the optical adjustment layer. In the 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. It is thought that the wavelength characteristic of can be obtained.

  However, when a retardation type diffractive optical element was produced using various composite materials, it was found that there was a problem that the refractive index of the optical adjustment layer was not stable.

  In the phase difference type diffractive optical element, when the refractive index of the optical adjustment layer changes, the constancy of d in the equation (1) is lost, and therefore unnecessary diffracted light is generated. As a result, the diffraction efficiency at the design order is greatly reduced. For example, in the diffraction efficiency simulation, when the refractive index of the optical adjustment layer decreases by 0.002, the diffraction efficiency at a wavelength of 640 nm decreases by 3.05% from 97.95% to 94.90%. When the refractive index increases by 0.002, the diffraction efficiency at the wavelength of 440 nm decreases by 4.98% from 98.06% to 93.07%.

  An object of the present invention is to solve the above-described problems and provide a diffractive optical element having good optical characteristics.

  The diffractive optical element of the present invention comprises a first optical material containing one resin, a substrate having a diffraction grating on its surface, a second optical material containing a second resin and inorganic particles, and is provided on the diffraction grating. The optical adjustment layer has a maximum thickness of 15 μm to 100 μm, and the second resin is a polymer of a photocurable resin composition containing a bifunctional monomer or oligomer. .

  In a preferred embodiment, the photocurable resin composition further includes a tri- or higher functional monomer or oligomer.

  In a preferred embodiment, the photocurable resin composition contains the bifunctional monomer or oligomer in a proportion of 10 wt% to 100 wt%.

  In a preferred embodiment, the first resin is polycarbonate.

  In a preferred embodiment, the bifunctional monomer or oligomer is a bifunctional epoxy acrylate.

  In a preferred embodiment, the trifunctional or higher functional monomer or oligomer is a trifunctional or higher functional acrylate.

  In a preferred embodiment, the second resin is an aliphatic resin.

  In a preferred embodiment, 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 first optical material is larger than the wavelength dispersion of the second optical material.

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

  According to the present invention, since the second resin of the composite material, which is the second optical material constituting the optical adjustment layer, is composed of the photocurable resin composition containing a bifunctional monomer or oligomer, the curing reaction proceeds sufficiently. In addition, a decrease in the refractive index of the optical adjustment layer and a refractive index distribution accompanying the film thickness distribution do not occur. In addition, even in a use environment that receives ultraviolet rays or is in a high temperature state, fluctuations in the refractive index of the optical adjustment layer are suppressed. Furthermore, the first optical material constituting the substrate is not altered or deteriorated by the ultraviolet rays used when forming the optical adjustment layer. For this reason, generation | occurrence | production of unnecessary diffracted light and stray light can be suppressed, and the diffractive optical element which has a favorable optical characteristic can be obtained.

It is a figure which shows typically the cross-sectional structure of the diffractive optical element of a prior art. It is a figure which shows typically the relationship between the integrated light quantity and the refractive index of the irradiated ultraviolet-ray in the 2nd optical material used for normal resin and the conventional composite material, and the diffractive optical element of this invention. (A) is a figure explaining the mechanism by which a normal polyfunctional monomer hardens | cures, (b) is a figure explaining the hardening mechanism of the composite material containing a polyfunctional monomer, (c) is polyfunctional. It is a figure explaining the hardening mechanism of the composite material containing a monomer and a bifunctional monomer. (A) And (b) is sectional drawing and top view which show embodiment of the diffractive optical element by this invention. A graph explaining the definition of effective particle size It is sectional drawing which shows other embodiment of the diffractive optical element by this invention.

  The inventor of the present application examined in detail the cause of the refractive index becoming unstable when a composite material is used as the optical material constituting the optical adjustment layer. FIG. 1 schematically shows a cross-sectional structure of a conventional diffractive optical element 111. The conventional diffractive optical element 111 is made of a first optical material and has a base 101 provided with a diffraction grating 2 on the surface, and an optical adjustment layer 103 made of a second optical material and provided to cover the diffraction grating 2. It has.

  The resin material has a narrower range of selectable refractive index and wavelength dependency than inorganic materials such as glass and ceramic. For this reason, when a resin is used as the substrate 101, only a normal optical resin satisfies the formula (1) and hardly satisfies the refractive index characteristics required as an optical adjustment layer, so that a wide wavelength region is obtained. It is very difficult to realize a diffractive optical element having high diffraction efficiency.

  In order to solve this problem and obtain high diffraction efficiency in a phase difference type diffractive optical element using a substrate made of resin, the present inventor dispersed inorganic particles in the resin as the second optical material constituting the optical adjustment layer. We have been studying the use of composite materials.

  Specifically, resin is used for the first optical material constituting the substrate 101, various composite materials containing resin and inorganic particles are used for the second optical material constituting the optical adjustment layer 103, and the characteristics of the diffractive optical element and The refractive index of the optical adjustment layer was evaluated in detail. As a result, when the thickness of the optical adjustment layer 103 is 15 μm or more and 100 μm or less, and the optical adjustment layer 103 is made of a composite material containing an ultraviolet curable resin composed only of a polyfunctional resin as the second resin, It has been found that there is a problem in that the refractive index does not reach the design value even when sufficient irradiation is performed.

  Here, the design value is a design value of the refractive index of the composite material calculated from the blending ratio of the materials, and is a value of the refractive index realized when the composite material is formed with a thickness of 2 μm or less. The thickness of the optical adjustment layer is the thickness of the optical adjustment layer at the deepest part of the diffraction step, that is, the maximum film thickness of the optical adjustment layer.

  FIG. 2 shows the refractive indexes of the resin and composite material obtained by irradiating the ultraviolet curable resin composition and the ultraviolet curable composite material composition having a thickness of 15 μm or more with ultraviolet rays and polymerizing the composition. The results are shown schematically. In FIG. 2, the horizontal axis indicates the integrated light quantity of the irradiated ultraviolet rays, and the vertical axis indicates the refractive index of the obtained resin and composite material.

  A curve C1 shows the relationship between the refractive index and the accumulated amount of ultraviolet light when an ultraviolet curable resin composition containing only a polyfunctional monomer or oligomer is cured. Curve C2 shows the relationship between the refractive index and the cumulative amount of ultraviolet light when a composite material composition containing only a polyfunctional monomer or oligomer as a resin component is cured. As shown in FIG. 2, in the curve C1, in the region R1, the refractive index increases as the integrated light amount increases. When the integrated light amount exceeds a predetermined amount that is the upper limit of the region R1, the refractive index becomes constant.

  This is presumably because the polymerization reaction and crosslinking reaction of the monomers and oligomers are not complete and unreacted functional groups remain in the region where the integrated light quantity is small. As a result, it is considered that the optical adjustment layer in a state where the unreacted functional group remains is cured by ultraviolet rays that pass through the diffractive optical element while the diffractive optical element is used, and the refractive index is increased. On the other hand, when ultraviolet rays are irradiated until the refractive index becomes constant, the optical adjustment layer has almost no unreacted functional group, so the refractive index of the optical adjustment layer has almost reached the design value. It is considered that the refractive index does not change even when irradiated with ultraviolet rays. Accordingly, the region R1 in the curve C1 is a region where the refractive index is unstable, and the refractive index is stable in a region where the accumulated amount of ultraviolet rays irradiated is larger than that in the region R1.

  On the other hand, as a result of detailed research by the inventor of the present application, as shown by a curve C2 in FIG. 2, when a composite material composition containing only a polyfunctional monomer or oligomer as a resin component is cured, the accumulated light quantity of ultraviolet rays As the refractive index increases, the refractive index of the cured optical adjustment layer does not readily become constant, and it has been found that the region R2 where the refractive index is unstable is significantly wider than the curve C1. According to the results of detailed experiments, it was found that the cumulative amount of ultraviolet light for stabilizing the refractive index in the curve C2 is about 10 times or more that in the case of the curve C1.

  Furthermore, as a result of various experiments, a composite material composition containing only a bifunctional monomer or oligomer as a resin component was cured, or a composite material composition containing only a polyfunctional monomer or oligomer as a resin component was obtained. When cured, or when a composite material composition containing a bifunctional monomer or oligomer and a trifunctional or higher functional monomer or oligomer as a resin component is cured, the refractive index is unstable as shown by curve C3. It has been found that such a region R3 has a smaller integrated light amount with a constant refractive index than a composite material composition containing only a polyfunctional monomer or oligomer as a resin component. That is, it was found that the refractive index is stabilized even with a small amount of ultraviolet irradiation by including a bifunctional monomer or oligomer in the resin component of the composite material composition.

  Based on these results, when the resin component of the composite material consists of a photocurable resin composition containing a polyfunctional monomer or oligomer, and from a photocurable resin composition containing a bifunctional and polyfunctional monomer or oligomer The mechanism of the curing reaction was investigated. This will be specifically described with reference to FIGS.

  In order to express the intrinsic properties of the photo-curable resin, in the curing reaction stage, the reactive functional groups between the monomers or oligomers of the resin (hereinafter collectively referred to as “monomer”) molecules are brought close to the reactable region. It is necessary to increase the polymerization and crosslinking density by advancing the chain reaction efficiently. The tendency of the change in the refractive index indicated by the curves C1 to C3 in FIG. 2 indicates that the density increases due to the shrinkage of the material accompanying the progress of the curing reaction due to polymerization and crosslinking, and the refractive index increases accordingly. it is conceivable that. For this reason, it is considered that when there is no unreacted reactive functional group, the shrinkage of the material stops and the refractive index becomes constant.

  The polyfunctional resin is a resin having three or more reactive functional groups in the monomer molecule, and forms a rigid network structure having a higher crosslink density compared to monofunctional and bifunctional resins. In other words, in the polyfunctional resin, the distance between the crosslinking points is relatively small, and it is considered that the degree of freedom in which the reactive functional group can move during the curing reaction is small.

  As shown in FIG. 3 (a), in the photocurable resin composition composed only of the polyfunctional monomer molecule Pm, there is no substance that inhibits the curing reaction such as inorganic particles, and therefore the reactivity between the monomer molecules Pm. The functional group can be easily accessed to the reactive region. For this reason, the chain reaction once started proceeds efficiently. That is, the curing proceeds sufficiently with a small amount of ultraviolet rays and reaches a region where the refractive index is stable. In the cured resin, the reactive functional group te of the monomer molecule Pm is bonded to the reactive functional group te of another monomer molecule, and there is no unreacted reactive functional group.

  On the other hand, when only the polyfunctional monomer molecule is used as a resin component, the inorganic particles are dispersed and the composite material composition is cured, as shown in FIG. 3B, the inorganic particles F are reactive functional groups between the monomer molecules Pm. Physically obstruct the approach of the base te. When it is disturbed by the inorganic particles F, it becomes difficult for the reactive functional group te between the monomer molecules Pm to approach the reactive region, and thus the initiated curing chain reaction stops before it proceeds sufficiently. A large number of unreacted functional groups tu remain.

  As a result, in order to complete the curing reaction of the composite material composition and reach the region where the refractive index is stable, the UV irradiation amount is increased compared with the case of curing only the polyfunctional monomer molecule, and the curing chain reaction Will need to increase the opportunity to start. This point becomes more remarkable as the film thickness increases and the number of monomer molecules present per unit area irradiated with ultraviolet rays increases.

  In particular, when only the monomer component of the polyfunctional resin is used as the resin component of the composite material, that is, the matrix resin, the reactive functional group of the monomer molecule forms a bond with the reactive functional group of another monomer molecule to form a network. The degree of freedom of movement of the reactive functional group during the curing reaction is reduced, and the distance between molecules is also reduced. For this reason, the effect | action which the inorganic particle prevents the approach of the reactive functional group between monomer molecules acts comparatively largely also with the monomer molecule of monofunctional resin or bifunctional resin. As a result, it is considered that the amount of UV irradiation necessary to react the unreacted reactive functional group and to keep the refractive index of the cured resin constant will further increase.

  In order to obtain high diffraction efficiency when an inexpensive and highly productive resin is used as the substrate, it is preferable to use a composite material as the optical adjustment layer. On the other hand, resin materials tend not to have high durability against ultraviolet rays compared to inorganic materials used for optical applications because of their molecular structures. Therefore, when a resin material is used as the substrate, it is also important to suppress the substrate deterioration due to ultraviolet rays necessary for curing the matrix resin in the composite material.

  As described above, when only a polyfunctional monomer molecule is used as a resin component, inorganic particles are dispersed and the composite material composition is cured, a large amount of ultraviolet rays are irradiated to complete the polymerization and crosslinking reaction, and the refractive index changes. There is a need to cure the composite material composition to a stable state. However, according to the study by the present inventor, when a large amount of ultraviolet rays is irradiated until the refractive index of the composite material becomes constant, the resin constituting the base of the diffractive optical element is changed in quality, specifically high-polarity light. It has been found that yellowing and light transmittance decrease due to generation of decomposition products, and color reproducibility and brightness decrease in a diffractive optical element used in the visible light region.

  As a result of detailed research, as shown in FIG. 2, the region Rd of the integrated light quantity of ultraviolet rays in which the resin constituting the substrate 101 of the diffractive optical element is altered is composed of only polyfunctional monomer molecules as resin components and inorganic particles. It was found that when the optical adjustment layer 103 was formed by dispersing and curing the composite material composition, it partially overlapped with the region R2 having an unstable refractive index.

  In other words, from the curve C2, even if an optical adjustment layer is formed using a composite material composition containing only a polyfunctional monomer or oligomer as a resin component, the refractive index will not be constant unless the irradiation amount of ultraviolet rays is increased considerably. However, it is understood that when the substrate 101 is irradiated with ultraviolet rays so that the refractive index is constant, the substrate 101 is irradiated with a large amount of ultraviolet rays, thereby causing deterioration or deterioration of the resin constituting the substrate 101. It was.

  For this reason, when only the polyfunctional resin is used as the resin component of the composite material constituting the optical adjustment layer, the refractive index is stabilized if priority is given to the suppression of the deterioration or deterioration of the resin constituting the substrate 101. It is difficult to irradiate the composite material composition with a sufficient amount of ultraviolet rays, and the refractive index of the optical adjustment layer does not show a predetermined design value. As a result, as shown in FIG. 2, the refractive index difference between the substrate and the optical adjustment layer becomes smaller than the design value, and unnecessary diffracted light is generated. In addition, if the refractive index obtained in a state in which the polymerization and crosslinking reaction of the composite material constituting the optical adjustment layer is incomplete satisfies the above-described formula (1), ultraviolet rays are irradiated during use. By being received or held at a high temperature, the remaining reactive functional group reacts to increase the refractive index, thereby generating unnecessary diffracted light.

  Further, in a diffractive optical element in which the diffraction grating has a sawtooth shape or a step shape, a film thickness distribution corresponding to the shape of the diffraction grating inevitably occurs in the optical adjustment layer. On the other hand, as described above, the amount of ultraviolet irradiation necessary to reach the design value of the refractive index of the composite material increases as the thickness increases. For this reason, if the amount of ultraviolet irradiation at the portion where the optical adjustment layer has the maximum thickness is not sufficient to reach the design value of the refractive index of the composite material, that is, with respect to the curve C2 in FIG. When the ultraviolet light irradiation amount is in the R2 region, the refractive index varies within the optical adjustment layer, leading to a further decrease in diffraction efficiency.

  For these reasons, when only the polyfunctional resin is used as the resin component of the composite material constituting the optical adjustment layer 101, it is difficult to realize the diffractive optical element 111 having optical characteristics as designed.

  In order to solve this problem, the inventor of the present application paid attention to the resin component of the composite material constituting the optical adjustment layer. When the resin component is a polymer of a photocurable resin composition containing a bifunctional monomer or oligomer, even if it is a composite material, the monomer or It has been found that almost all reactive functional groups of the oligomer can be reacted, and the refractive index of the cured composite material can be reached to the design value.

  Since the bifunctional monomer Pd has only two reactive functional groups te, even if one reactive functional group te forms a bond with the reactive functional group of another monomer, the other reactive functional group te's freedom of movement is high. Therefore, as shown in FIG. 3C, when the bifunctional monomer Pd is included in addition to the polyfunctional monomer Pm as the resin component of the composite material, the reactive functional group te of the bifunctional monomer Pd during the curing reaction is included. Therefore, even if inorganic particles that inhibit the reaction coexist, there are many opportunities to come close to the reactive functional group te of the other polyfunctional monomer Pm. For this reason, since the polymerization and crosslinking reaction between the monomers can proceed sufficiently in a chain, unreacted functional groups can be reduced. In FIG. 2, when the resin component of the composite material is a polymer of a photocurable resin composition containing a bifunctional monomer and a polyfunctional monomer, as shown by a curve C3, the refractive index of the composite material indicated by the region R3. The region where the is not constant becomes narrower than the composite material composition having only the polyfunctional monomer molecule as the resin component. As a result, the region Rd in which the resin constituting the substrate 101 is altered by ultraviolet rays does not overlap with the region R3 where the refractive index of the composite material is not constant. Therefore, the composite material composition can be completely cured and the refractive index of the optical adjustment layer can reach the design value even with the amount of irradiation light of ultraviolet rays that does not change the resin constituting the substrate 101 by ultraviolet rays. As a result, it is possible to realize a diffractive optical element that maintains the optical performance as designed without substantially changing the refractive index of the optical adjustment layer in the use environment.

  Hereinafter, embodiments of the diffractive optical element according to the present invention will be described in detail. FIGS. 4A and 4B are a cross-sectional view and a top view showing the first embodiment of the diffractive optical element according to the present invention. A diffractive optical element 21 shown in FIGS. 4A and 4B includes a base 1 and an optical adjustment layer 3.

  The substrate 1 is made of a first optical material containing a first resin and has a diffraction grating 2 on the surface. In the present embodiment, the first optical material contains only the first resin. The cross-sectional shape, arrangement, pitch and depth of the diffraction grating 2 are determined based on the optical characteristics of the substrate 1 and the optical adjustment layer 3 and the optical characteristics required for the diffractive optical element 21. For example, when the diffractive optical element 21 has a lens function, a ring-shaped diffraction grating having a sawtooth cross-sectional shape is continuously changed so that the pitch decreases from the center to the periphery of the lens. It arranges concentrically. The diffraction grating in this case only needs to have a cross-sectional shape having a lens action, an arrangement, and a pitch. As shown in FIG. 4A, the diffraction grating 2 may be formed on a curved surface or on a plane. You may form in. In particular, when the diffraction grating 2 is formed so that the envelope surface passing through the grooves 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 through an optimal combination of the refraction action and the diffraction action. A lens having high imaging performance can be obtained.

  The depth of the diffraction grating 2 can be determined using Equation (1). When a base is produced by molding using a resin-containing material, the depth (step) of the diffraction grating shape is preferably 20 μm or less. This is because when a die having a diffraction grating shape with a depth exceeding 20 μm is to be machined, it is necessary to cut the die deeply. This is because it becomes difficult. Further, in this case, since it is necessary to perform processing with a cutting tool having a large curvature radius at the tip, it is difficult to narrow the diffraction pitch, and it is necessary to increase the diffraction pitch. As a result, it is difficult to obtain the effect of providing a diffraction grating and reducing aberrations.

  Although the base 1 of the diffractive optical element 21 shown in FIGS. 4A and 4B has the diffraction grating 2 on one surface, the diffraction grating 2 may be provided on both sides of the base 1. As shown in FIG. 4A, the substrate 1 has a convex surface and a flat surface, and the diffraction grating 2 is provided on the convex surface. The shape of the two opposing main surfaces of the substrate 1 is not limited to this combination, and may be a combination of other shapes. Specifically, the two main surfaces facing each other of the base body 1 may be a biconvex surface, a convex surface and a concave surface, a biconcave surface, a concave surface and a flat surface, or both flat surfaces. In this case, the diffraction grating 2 may be formed on only one surface or may be formed on both surfaces. In addition, when diffraction gratings are formed on both sides, the shape, arrangement, pitch, and diffraction grating depth of the diffraction gratings on both sides do not need to match as long as they satisfy the performance required for the diffractive optical element. .

  As the first resin constituting the first optical material, the wavelength dependence of the diffraction efficiency in the design order of the diffractive optical element 21 can be reduced from among translucent resin materials generally used as the base of the optical element. A resin having refractive index characteristics and wavelength dispersion is selected. By using a resin as the material of the substrate 1, the molding process is easy and the productivity is high, and the finally obtained diffractive optical element 21 can be reduced in size and weight. For example, as the first resin, selecting a polycarbonate resin, polymethyl methacrylate (PMMA), an acrylic resin such as an alicyclic acrylic resin, an alicyclic olefin resin, or the like is excellent in translucency. Is preferable. These resins may be copolymerized with other resins, alloyed with other resins, or blended with other resins for the purpose of improving moldability, mechanical properties, and the like. As described above, the first resin may include only a single resin, or may include two or more resins.

  In addition to the first resin, the first optical material includes inorganic particles for adjusting optical properties such as refractive index and mechanical properties such as thermal expansion, and dyes and pigments that absorb electromagnetic waves in a specific wavelength region. An agent may be included. These inorganic particles and additives are not main components constituting the first optical material.

  The optical adjustment layer 3 is made of a second optical material including the second resin 4 and the inorganic particles 5, and is provided on the surface of the substrate 1 so as to cover the diffraction grating 2. The optical adjustment layer 3 is provided for the purpose of reducing the wavelength dependence of the diffraction efficiency by the substrate 1.

  The optical adjustment layer 3 is preferably formed so as to completely fill at least the grooves (steps) of the diffraction grating 2, and the thickest part of the optical adjustment layer 3 is the deepest part (step part) of the diffraction grating 2. It is preferable that the depth is larger than the depth (the sawtooth-shaped root portion). When the optical adjustment layer 3 and the main component of the substrate 1 are made of resin and the diffractive optical element 21 is used in the visible light region, the depth of the deepest part of the diffraction grating 2 is about 10 μm or more. The maximum thickness is preferably 15 μm or more including a margin for completely filling the step of the diffraction grating.

  As long as the optical adjustment layer 3 completely fills the grooves (steps) of the diffraction grating 2, an effect of reducing the wavelength dependency of the diffraction efficiency can be obtained. However, if the optical adjustment layer 3 is too thick, the effect of Rayleigh scattering by the inorganic particles is remarkably generated, and the light transmittance of the optical adjustment layer 3 is lowered. In addition, when a photo-curable resin is used as the matrix resin, the possibility of cracks is increased due to the stress generated with the curing shrinkage. For this reason, it is preferable that the maximum thickness of the optical adjustment layer 3 is 100 μm or less. That is, the maximum thickness of the optical adjustment layer 3 is preferably 15 μm or more and 100 μm or less.

  When the optical adjustment layer 3 is installed on the substrate 1 on which the diffraction grating 2 is formed such that the envelope surface passing through the groove of the diffraction grating 2 is an aspheric surface having a lens action, the surface of the optical adjustment layer 3 is By matching the aspherical shape, the refracting action and the diffractive action are fused, and the lens characteristics can be improved by reducing chromatic aberration and field curvature.

  In the second optical material constituting the optical adjustment layer 3, the second resin 4 functions as a matrix resin, and the inorganic particles 5 are dispersed in the second resin 4. Thereby, the 2nd resin 4 and the inorganic particle 5 comprise the composite material. The second resin 4 is a photocurable resin.

  More specifically, the second resin 4 is a polymer of a photocurable resin composition containing a bifunctional monomer or oligomer. The second resin 4 is not particularly limited as long as it is a polymer of a photocurable resin composition containing a bifunctional monomer or oligomer. By including a photocurable resin composition containing a bifunctional monomer or oligomer, the degree of freedom of movement of reactive functional groups is high even in the presence of inorganic particles, as described with reference to FIG. The curing chain reaction proceeds efficiently. For this reason, the refractive index of the optical adjustment layer reaches a value at which the refractive index of the optical adjustment layer does not increase any further even with a smaller UV irradiation amount. Moreover, compared with the case where a monofunctional monomer or oligomer is used, the mechanical properties of the optical adjustment layer 3 after curing are excellent. That is, when the composite material in which the inorganic particles are dispersed is used for the optical adjustment layer of the diffractive optical element, an excellent balance between optical characteristics and mechanical characteristics can be realized.

  In the present specification, “functional” and “reactive functional group” mean a site where a monomer or oligomer can form a bond with another monomer or oligomer by a polymerization reaction or a crosslinking reaction. In particular, in the present invention, since a photocurable resin is used, it refers to a site where a bond is formed by irradiation with light, specifically, ultraviolet rays. More specifically, it refers to a carbon-carbon double or triple bond. Also, conventionally, such a monomer monofunctional monomer containing one reactive functional group, a monomer containing two reactive functional groups are called a bifunctional monomer, and a monomer containing three or more reactive functional groups is called a polyfunctional monomer.

  The reactive functional group changes to a carbon-carbon bond by polymerization or crosslinking and disappears. For this reason, unless the unreacted reactive functional group remains, the reactive functional group does not remain in the polymer resin. However, by analyzing the structure of the resin, it is possible to specify how many reactive functional groups the monomer or oligomer had. For this reason, a polymerized or crosslinked resin is also called a bifunctional resin, a polyfunctional resin, or the like.

  The photo-curable resin composition constituting the second resin may contain only one type of bifunctional monomer or oligomer as a raw material for the resin component, and in order to satisfy requirements such as optical properties and mechanical properties, etc. Any one or more of a bifunctional monomer or oligomer, a monofunctional monomer or oligomer, and a tri- or higher functional monomer or oligomer may be further included. In the photocurable resin composition constituting the second resin, it is preferable to contain a bifunctional monomer or oligomer at a ratio of 10 wt% to 100 wt%. This is to increase the efficiency of the curing chain reaction that cures the second optical material. The photocurable resin composition contains a photopolymerization initiator in addition to the resin component raw material. The second optical material may contain an additive such as a dye or a pigment that absorbs electromagnetic waves in a specific wavelength region. These additives are not main components constituting the resin component.

（１）

（２）

（３）

（４）

（５）Specific examples of the bifunctional monomer or oligomer that can be used in the photocurable resin composition constituting the second resin include epoxy acrylates represented by the following chemical formulas (1), (2), and (3). And dimethylol-tricyclodecane diacrylate represented by the chemical formula (4), triethylene glycol diacrylate represented by the chemical formula (5), and the like.

(1)

(2)

(3)

(4)

(5)

（６）

（７）

（８）

（９）Specific examples of the tri- or higher functional monomer or oligomer include pentaerythritol triacrylate represented by the following chemical formula (6), pentaerythritol tetraacrylate represented by the chemical formula (7), and pentaerythritol tetraacrylate represented by the chemical formula (8). Examples thereof include methacrylate and trimethylolpropane triacrylate represented by the chemical formula (9).

(6)

(7)

(8)

(9)

  Among these bifunctional monomers or oligomers and tri- or higher functional monomers or oligomers, an aliphatic resin having no benzene ring is particularly preferable. This is because the conjugated double bond of the benzene ring absorbs ultraviolet rays and can be decomposed or altered. Specifically, it is preferable to use dimethylol-tricyclodecane diacrylate represented by the above chemical formulas (4) and (5), triethylene glycol diacrylate, or the like.

  Moreover, since it is preferable that the optical adjustment layer 3 has a high Abbe number, it is more preferable to use a second resin that also exhibits a high Abbe number. In particular, when a resin having an Abbe number of 40 or more is used, it is easy to satisfy the formula (1) when a composite material in which inorganic particles are dispersed is used. Therefore, by selecting a bifunctional monomer or oligomer described above or a trifunctional or higher functional monomer or oligomer having an alicyclic structure, a siloxane structure, a fluorine atom, or the like, the polymerized second resin can be increased. It is possible to have an Abbe number.

In order to reduce the wavelength dependence of the diffraction efficiency by the substrate 1, the refractive index at the wavelength λ of the first optical material constituting the substrate 1 is n 1 (λ), and the second optical material constituting the optical adjustment layer 3 is formed. When the refractive index at the wavelength λ is n2 (λ), it is preferable to select the first optical material and the second optical material that substantially satisfy the expression (1) for the wavelength λ in a desired range. More specifically, if the depth d of the diffraction grating satisfies the following formula (2), it can be said that the practically sufficient condensing function can be obtained, and the formula (1) is almost satisfied.

  For this purpose, for example, a material having a wavelength dependency of the refractive index showing a tendency opposite to the wavelength dependency of the refractive index in the first optical material may be selected as the second optical material. More specifically, in the wavelength range of light using the diffractive optical element 21, 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. That is, the first optical material needs to be a low refractive index and high dispersion material than 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 needs to be smaller than the refractive index of the second optical material, and the Abbe number of the first optical material needs to be smaller than the Abbe number of the second optical material. By using the composite material in which the inorganic particles 5 are dispersed using the second resin 4 as a matrix, the refractive index and Abbe number of the second optical material can be adjusted. And the diffraction efficiency in the wavelength band which uses a diffractive optical element can be improved by using for the optical adjustment layer 3 the 2nd optical material which has a suitable refractive index and Abbe number.

  If the inorganic particles 5 dispersed in the second resin have a high refractive index, the second optical material can have a high refractive index that cannot be achieved by the second resin alone. For this reason, the difference in refractive index between the first optical material and the second optical material can be enlarged, and the depth of the diffraction grating 2 can be reduced as is apparent from the equation (1). As a result, when the substrate 1 is produced by molding, the transferability of the diffraction grating 2 is improved. Further, since the step of the diffraction grating 2 can be made shallow, transfer is easy even if the step interval is narrowed. Therefore, the diffraction performance can be improved by narrowing the pitch of the diffraction grating 2. Furthermore, it is possible to use materials having various physical properties for the second resin, and it is easier to achieve compatibility with properties other than optics.

  When the first optical material containing the first resin is used for the substrate 1 and the second optical material made of the composite material containing the second resin 4 and the inorganic particles 5 is used as the optical adjustment layer 3, the inorganic particles 5 are generally made of resin. Often has a high refractive index. For this reason, it is preferable that the second optical material has a higher refractive index and lower wavelength dispersibility than the first optical material because more materials can be selected as the inorganic particles 5. In other words, the first optical material preferably has a lower refractive index and higher dispersion than the second optical material.

The refractive index of the second optical material that is a composite material can be estimated from the refractive index of the second resin that is a matrix resin and the inorganic particles 5 by, for example, Maxwell-Garnet theory expressed by the following formula (3).

In Formula (3), n _COM λ is the average refractive index of the second optical material at a specific wavelength λ, and n _p λ and n _m λ are the refractive indexes of the inorganic particles and the second resin at this wavelength λ, respectively. . P is a volume ratio of the inorganic particles to the entire second optical material. In (Expression 2), the Abbe number of the composite material is further calculated by estimating the refractive index of the D-line (589.2 nm), the F-line (486.1 nm), and the C-line (656.3 nm) of Fraunhofer as the wavelength λ. It is also possible to estimate. Conversely, the mixing ratio between the second resin 4 and the inorganic particles 5 may be determined from the estimation based on this theory.

In the formula (3), when the inorganic particles 5 absorb light or the inorganic particles 5 contain a metal, the refractive index of the formula (3) is calculated as a complex refractive index. Equation (3) is an equation that holds when n _p λ ≧ n _m λ. When n _p λ <n _m λ, the refractive index is estimated using the following equation (4).

  When a second optical material made of a composite material is used as the optical adjustment layer 3, the second optical material has a higher refractive index than the first optical material and a lower wavelength dispersion than the first optical material. is required. For this reason, the inorganic particles 5 to be dispersed in the second resin are also preferably composed mainly of a material having a low wavelength dispersibility, that is, a high Abbe number. In particular, when a polycarbonate-based resin is used as the first resin, the inorganic particles 5 are preferably composed mainly of a material having an Abbe number of 30 or more. For example, zirconium oxide (Abbe number: 35), yttrium oxide (Abbe number: 34), lanthanum oxide (Abbe number: 35), hafnium oxide (Abbe number: 32), scandium oxide (Abbe number: 27), alumina (Abbe number) It is particularly preferable that the main component is at least one oxide selected from the group consisting of (number: 76) and silica (Abbe number: 68). Moreover, you may use these complex oxides. In the wavelength band of light in which the diffractive optical element 22 is used, as long as the formula (1) or (2) is satisfied, in addition to these inorganic particles, a high refractive index represented by, for example, titanium oxide or zinc oxide is exhibited. Inorganic particles may coexist.

  The effective particle size of the inorganic particles 5 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. 5, the horizontal axis represents the particle size of the inorganic particles, and the left vertical axis represents the frequency of the inorganic particles with respect to the particle size on 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 of the inorganic particles 5 defined in this way 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 diffractive optical element 21 can be produced, for example, by the following method. First, the base 1 having the diffraction grating 2 provided on one side is manufactured by injection molding using the first optical material constituting the base 1.

  Next, the 2nd optical material used as the raw material of the optical adjustment layer 3 is prepared. As described above, as the second resin, a bifunctional monomer or oligomer, or a bifunctional monomer or oligomer and a polyfunctional monomer or oligomer, a dispersion in which inorganic particles are dispersed in a solvent, a photopolymerization initiator, Mix.

  The raw material of the second optical material is dropped onto the substrate 1 using a dispenser, the solvent is dried using a vacuum dryer or the like, and then placed in a mold. The raw material is cured by irradiating ultraviolet rays from the back surface of the substrate 1. Let A diffractive optical element 21 is obtained by separating the substrate 1 provided with the hardened optical adjustment layer 3 from the mold.

  As described above, according to the diffractive optical element of this embodiment, the second resin of the composite material, which is the second optical material constituting the optical adjustment layer, is composed of a photocurable resin composition containing a bifunctional monomer or oligomer. The curing reaction proceeds sufficiently, and the refractive index of the optical adjustment layer does not decrease and the refractive index distribution accompanying the film thickness distribution does not occur. In addition, even in a use environment that receives ultraviolet rays or is in a high temperature state, fluctuations in the refractive index of the optical adjustment layer are suppressed. Furthermore, the first optical material constituting the substrate is not altered or deteriorated by the ultraviolet rays used when forming the optical adjustment layer. Therefore, it is possible to obtain a diffractive optical element that can achieve a desired high diffraction efficiency and condensing characteristics.

  When a diffractive optical element is combined with another optical element such as a lens to form a wide-angle optical system, flare occurs in the captured image due to the oblique incident light that has passed through the step surface of the diffraction grating, and the contrast of the image is reduced. May be significantly worse. In such a case, flare can be suppressed by providing a plurality of diffraction steps having different heights and forming the optical adjustment layer only on diffraction steps having a large height.

  FIG. 6 schematically shows a cross-sectional structure of such a diffractive optical element 22. The diffractive optical element 22 includes a base 11 and an optical adjustment layer 13. A first diffraction grating 12 a and a second diffraction grating 12 b are provided on one surface of the base 11. Each of the first diffraction grating 12a and the second diffraction grating 12b includes a plurality of concentric annular zones with the optical axis 10 as the center, and the second diffraction grating 12b is more peripheral than the first diffraction grating 12a. On the side. The step of the first diffraction grating 12a is higher than the step of the second diffraction grating 12b. The height of the step between the first diffraction grating 12a and the second diffraction grating 12b may be reduced as the distance from the optical axis 10 increases.

  The optical adjustment layer 13 covers the first diffraction step 12 a, and the second diffraction grating 12 b is not covered by the optical adjustment layer 13. The surface 16 on which the diffraction step of the substrate 11 is not provided has an aspherical shape.

  According to the diffractive optical element 22, the second diffraction grating 12 b provided on the outer peripheral side is not covered with the optical adjustment layer 13. As can be seen from the equation (1), the step depth d of the second diffraction grating 12b can be reduced. Thereby, when light is incident obliquely with respect to the optical axis 10 of the diffractive optical element 22, the outer side diffraction grating that is likely to be incident at a larger angle with respect to the optical axis, that is, the step of the second diffraction grating 12b. The amount of light passing through the stepped surface of the diffraction grating can be reduced. Since such light does not contribute to diffraction and causes flare, the generation of flare can be suppressed by reducing the amount of light passing through the step surface.

  In the diffractive optical elements 21 and 22 of the above embodiment, an antireflection layer may be further provided on the surfaces of the optical adjustment layers 3 and 13. The antireflection layer has a single layer structure made of a film having a lower refractive index than that of the optical adjustment layers 3 and 13, or a multilayer structure made of a film made of a material having a lower refractive index than that of the optical adjustment layers 3 and 13 and a film made of a higher material. Have. Examples of the material used for the antireflection layer include a resin, a composite material of resin and inorganic particles, or an inorganic thin film formed by vacuum deposition, sputtering, CVD, or the like. When a composite material is used as the antireflection layer, silica, alumina, magnesium oxide, or the like having a low refractive index can be used as the inorganic particles.

  The diffractive optical elements 21 and 22 may have nanostructure antireflection shapes on the surfaces of the optical adjustment layers 3 and 13. The antireflection shape of the nanostructure can be easily formed, for example, by a transfer method (nanoimprint) using a mold.

  Furthermore, the diffractive optical elements 21 and 22 may further include a surface layer having an effect of adjusting mechanical properties such as friction resistance and thermal expansion on the surface of the optical adjustment layers 3 and 13 or the antireflection layer. .

  Hereinafter, the results of producing the diffractive optical element according to the present invention and evaluating the characteristics will be described in detail.

Example 1
A diffractive optical element 21 having the structure shown in FIG. 4 was produced by the following method. The diffractive optical element 21 has a lens action and is designed to use first-order diffracted light. The same applies to the following embodiments.

（１０）First, as the first resin of the first optical material constituting the substrate 1, bisphenol A polycarbonate resin (d-line refractive index 1.585, Abbe number 28) is injection-molded so that the envelope surface at the base of the diffraction grating is not A base body 1 having a spherical shape and a diffraction grating 2 having a ring-like shape with a depth of 15 μm provided on one side was produced. The effective radius of the lens portion is 0.828 mm, the number of annular zones is 29, the minimum annular zone pitch is 14 μm, and the paraxial R (curvature radius) of the diffraction surface is −1.0144 mm. The bisphenol A-based polycarbonate resin is represented by the following chemical formula (10).

(10)

  Next, the 2nd optical material used as the raw material of the optical adjustment layer 3 was prepared as follows. As the second resin, a bifunctional acrylate resin B (d-line refractive index 1.531, Abbe number 52, the above chemical formula (4)) is used, and zirconium oxide (primary particle size 3 to 10 nm, effective by light scattering method) is used. Disperse PGME (propylene glycol monomethyl ether) dispersion with a particle size of 20 nm and a silane surface treatment agent so that the weight ratio of zirconium oxide in the total solid content excluding PGME as a dispersion medium is 56% by weight. And mixed with a photopolymerization initiator. The optical properties of the second optical material after drying and curing are as follows: the refractive index at d-line is 1.623, the Abbe number is 43, and the light transmittance at a wavelength of 400 to 700 nm is 90% or more (film Thickness is 30 μm). In addition, about the refractive index, the raw material of the optical adjustment layer 3 was used on the flat plate, the film | membrane was formed on the same conditions, and the measurement was performed using the prism coupler (the Metricon company make, MODEL2010). The measurement was performed at three wavelengths (405 nm, 532 nm, and 633 nm), and the refractive index and Abbe number of other wavelengths were calculated by an approximate expression using the respective measured refractive index values.

0.4 μL of this second optical material was dropped on the substrate 1 using a dispenser, dried with a vacuum dryer (25 ° C., internal pressure of vacuum dryer 1300 Pa, 3 hours), and then a mold (stainless steel) was placed in a nickel plating film formed) on the alloy surface, the back surface of the substrate 1 (the surface opposite to the dropped surface composite material), by irradiation with ultraviolet rays (illuminance 120 mW / cm ^2, accumulated light quantity 4000 mJ / cm ²⁾ The second resin was cured. Thereafter, it was separated from the mold and formed as the optical adjustment layer 3. The surface shape of the optical adjustment layer 3 was formed so as to coincide with the aspheric shape along the envelope shape at the base of the diffraction grating 2. The thickness of the optical adjustment layer 3 is 30 μm at the thickest part (that is, the part corresponding to the deepest part of the diffractive optical element), and 15 μm at the thinnest part (that is, the part corresponding to the tip part of the diffractive optical element). Formed.

The diffraction efficiency of the diffractive optical element 21 produced through the above steps was measured. The light from the white light source is transmitted through the diffractive optical element 21, and the maximum luminance at the condensing point corresponding to each diffraction order is measured using an ultra-precision three-dimensional measuring device (manufactured by Mitaka Kogyo Co., Ltd.). The first-order diffraction efficiency was calculated by the calculation shown in Equation (5). In the following examples and comparative examples, higher-order diffracted light higher than third-order diffracted light was not detected.

  The first-order diffraction efficiency of the diffractive optical element 21 of this example was 92% or more at all wavelengths. In a general application, if the first-order diffraction efficiency is 90% or more, the diffractive optical element is sufficiently practical.

Further, when the diffraction efficiency was examined again after irradiating the diffractive optical element of this example with ultraviolet rays of 4000 mJ / cm ² , there was no decrease in diffraction efficiency due to the refractive index change of the optical adjustment layer.

  In addition, it can be seen from this example that when the second resin constituting the optical adjustment layer 3 contains a bifunctional monomer, the refractive index is stabilized in a thickness range of 15 μm to 30 μm. It was.

(Example 2)
As an example of the present invention, a diffractive optical element 21 having the same configuration as that of Example 1 was produced by the same method as that of Example 1. However, the polyfunctional acrylate resin A (d-line refractive index 1.529, Abbe number 50, mixture of the above chemical formula (6) and chemical formula (7)) is used as the second resin of the second optical material constituting the optical adjustment layer 3. And bifunctional epoxy acrylate resin D (d-line refractive index 1.569, Abbe number 35, the above chemical formula (3)) are mixed at a weight ratio of 4: 1, and 2-propanol (IPA) is used as a solvent. The point used is different from Example 1. The optical adjustment layer 3 was formed to have a thickness of 30 μm.

  When the first-order diffraction efficiency of the diffractive optical element of this example was calculated by the same method as in Example 1, it was 91% or more at all wavelengths.

Further, when the diffraction efficiency was examined again after irradiating the diffractive optical element of this example with ultraviolet rays of 4000 mJ / cm ² , there was no decrease in diffraction efficiency due to the refractive index change of the optical adjustment layer.

(Example 3)
As an example of the present invention, a diffractive optical element 21 having the same configuration as that of Example 2 was produced by the same method as that of Example 2. However, the acrylate resin A used in Example 2 as the second resin of the second optical material constituting the optical adjustment layer 3 and the epoxy acrylate resin D (d-line refractive index 1.569, Abbe number 35, the above chemical formula (3 )) In a ratio of 3: 1 by weight is different from Example 2. The optical adjustment layer 3 was formed to have a thickness of 40 μm.

When the first-order diffraction efficiency of the diffractive optical element of this example was calculated by the same method as in Example 1, it was 91% or more at all wavelengths. Further, when the diffraction efficiency was examined again after irradiating the diffractive optical element of this example with ultraviolet rays of 4000 mJ / cm ² , there was no decrease in diffraction efficiency due to the refractive index change of the optical adjustment layer.

Example 4
As an example of the present invention, a diffractive optical element 21 having the same configuration as that of Example 2 was produced by the same method as that of Example 2. However, the acrylate resin A used in Example 2 as the second resin of the second optical material constituting the optical adjustment layer 3 and the epoxy acrylate resin D (d-line refractive index 1.569, Abbe number 35, the above chemical formula (3 )) In a ratio of 9: 1 by weight is different from Example 2. The optical adjustment layer 3 was formed to have a thickness of 40 μm.

When the first-order diffraction efficiency of the diffractive optical element of this example was calculated by the same method as that of Example 1, it was 92% or more at all wavelengths. Further, when the diffraction efficiency was examined again after irradiating the diffractive optical element of this example with ultraviolet rays of 4000 mJ / cm ² , there was no decrease in diffraction efficiency due to the refractive index change of the optical adjustment layer.

(Example 5)
As an example of the present invention, a diffractive optical element 22 having the structure shown in FIG. 6 was prepared by the following method. The diffractive optical element 22 has a lens action and is designed to use first-order diffracted light.

  First, a bisphenol A-based polycarbonate resin (d-line refractive index 1.585, Abbe number 28, the above chemical formula (10)) is injection-molded as a first resin of the first optical material constituting the substrate 11 to obtain a diffraction grating. A base body 11 having ring-shaped diffraction gratings 12a and 12b having a base envelope surface of an aspherical shape, a first diffraction step depth of 15 μm, and a second diffraction step depth of 1 μm on one side was prepared. The effective radius of the lens portion is 0.828 mm, the number of annular zones is 26 for the first diffraction step and 3 for the second diffraction step, the minimum annular zone pitch is 14 μm, and the paraxial axis of the diffraction surface. R (radius of curvature) is -1.0144 mm.

  As a 2nd optical material which comprises the optical adjustment layer 13, the material similar to Example 2 was used, and the optical adjustment layer 13 was formed with the same method. The thickness of the optical adjustment layer 13 is 30 μm at the thickest part (that is, the part corresponding to the deepest part of the diffractive optical element 22), and 15 μm at the thinnest part (that is, the part corresponding to the tip part of the diffractive optical element). Formed as follows.

  When the first-order diffraction efficiency of the diffractive optical element 22 of this example was calculated by the same method as that of Example 1, it was 94% or more at all wavelengths.

Further, when the diffraction efficiency was examined again after irradiating the diffractive optical element 22 of this example with ultraviolet rays of 4000 mJ / cm ² , there was no decrease in the diffraction efficiency due to the refractive index change of the optical adjustment layer 13.

(Comparative Example 1)
As Comparative Example 1, a diffractive optical element 21 having the same configuration as that of Example 2 was produced by the same method as that of Example 2. However, the as 2 resin, using only polyfunctional acrylate resin A, the amount of ultraviolet irradiation in Example 2 of the second optical material composing the optical adjustment layer 3 (illuminance 120 mW / cm ^2, accumulated light quantity 4000 mJ / cm ²⁾ Thus, the second optical material is different from the second embodiment in that the second optical material is manufactured by increasing the weight ratio of zirconium oxide so that the refractive index at the d-line is 1.623 and the Abbe number is 40. The thickness of the optical adjustment layer 3 is 30 μm at the thickest part (that is, the part corresponding to the deepest part of the diffractive optical element), and 15 μm at the thinnest part (that is, the part corresponding to the tip part of the diffractive optical element). Formed.

  When the first-order diffraction efficiency of the diffractive optical element of this comparative example was calculated by the same method as in Example 1, it was 93% or more at all wavelengths.

However, when the diffraction efficiency was measured again after irradiating the diffractive optical element with ultraviolet rays of 4000 mJ / cm ² , it decreased to 86%. This is because the refractive index of the optical adjustment layer is changed by additional irradiation with ultraviolet rays.

(Comparative Example 2)
As Comparative Example 2, a diffractive optical element 21 having the same configuration as that of Example 2 was produced by the same method as that of Example 2. However, the second embodiment is different from the second embodiment in that only the polyfunctional acrylate resin A is used as the second resin of the second optical material constituting the optical adjustment layer 3. The thickness of the optical adjustment layer 3 is 30 μm at the thickest part (that is, the part corresponding to the deepest part of the diffractive optical element), and 15 μm at the thinnest part (that is, the part corresponding to the tip part of the diffractive optical element). Formed.

  When the first-order diffraction efficiency of the diffractive optical element of this comparative example was calculated in the same manner as in Example 1, it was 87% at all wavelengths. The refractive index of the optical adjustment layer was 1.618, which did not reach the design value of 1.623. That is, since the refractive index of the optical adjustment layer is changed by additional irradiation with ultraviolet rays, it is not preferable as an optical element.

(Consideration of results)
Table 1 below shows the composition of the matrix resin used in the optical adjustment layers of Examples 1 to 5 and Comparative Examples 1 and 2 and the ratio of the blending. Further, the measurement results of the maximum and minimum thicknesses of the optical adjustment layer and the diffraction efficiency of the produced diffractive optical element are shown.

  The maximum film thickness in Table 1 is the thickness of the optical adjustment layers 3 and 13 at the root position of the sawtooth shape of the diffraction grating. The minimum film thickness is the thickness of the optical adjustment layers 3 and 13 at the position of the tip of the diffraction grating saw blade shape.

  In the diffractive optical elements of Examples 1 to 5 in Table 1, a first-order diffraction efficiency of 90% or more is obtained before additional irradiation with ultraviolet rays. This is presumably because the optical adjustment layers 3 and 13 having a refractive index substantially equal to the design value are formed in the diffractive optical elements of Examples 1 to 5. Further, the first-order diffraction efficiency of the diffractive optical elements of Examples 1 to 5 does not change even when ultraviolet rays are additionally irradiated. That is, it can be seen that the refractive indexes of the optical adjustment layers 3 and 13 are stable and the characteristics of the diffractive optical element do not vary.

  Since the first-order diffraction efficiency of the diffractive optical element of Comparative Example 2 is 90% or less, the optical adjustment layer 3 is obtained by including a bifunctional monomer or oligomer in the photocurable resin composition constituting the second resin. , 13 can reach a value substantially equal to the design value. Further, since the first-order diffraction efficiency does not change even after additional irradiation with ultraviolet rays, it is considered that almost no unreacted reactive functional group remains in the second resin.

  In addition, from the results of Examples 1 to 5, the above-described effects can be obtained when the content of the bifunctional monomer or oligomer is 10 wt% or more and 100 wt% or less in the photocurable resin composition constituting the second resin. I understand that.

  On the other hand, as can be seen from the results of Comparative Example 2, when the second resin is a polymer of a photocurable resin composition containing only a polyfunctional monomer or oligomer, the first-order diffraction efficiency is 10% or more lower than the design value. . This is because the refractive index is smaller than the design value because the polymerization and crosslinking reaction of the second resin is insufficient even when irradiated with ultraviolet rays having the same integrated light amount as in Examples 1 to 5. It is thought that it has declined.

  Further, as can be seen from the results of Comparative Example 1, even if the polymerization and crosslinking reaction of the second resin are insufficient, if the inorganic particles to be dispersed are increased, the refractive index of the second optical material constituting the optical adjustment layer is increased. Therefore, the manufactured diffractive optical element exhibits a first-order diffraction efficiency in a practical range. However, the first-order diffraction efficiency is reduced by additional irradiation with ultraviolet rays. This is because an unreacted reactive functional group reacts by irradiation with ultraviolet rays, and the refractive index of the second resin increases, so that the refractive index of the second optical material constituting the optical adjustment layer exceeds the design value. It is considered that the first-order diffraction efficiency is lowered and the first-order diffraction efficiency is lowered.

  As described above, according to the diffractive optical element according to the present embodiment, since the change in the refractive index of the material constituting the element can be suppressed, there is no generation of unnecessary diffracted light, excellent optical characteristics and high productivity An optical element can be obtained.

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

1,11,101 Substrate 2,12a, 12b Diffraction grating 3,13,103 Optical adjustment layer 4,14 Matrix resin 5,15 Inorganic particle 21,22 Diffractive optical element

[0008]
It has been found that the region R2 is significantly wider than the curve C1. According to the results of detailed experiments, it was found that the cumulative amount of ultraviolet light for stabilizing the refractive index in the curve C2 is about 10 times or more that in the case of the curve C1.
[0038]
Furthermore, as a result of various experiments, when a composite material composition containing only a bifunctional monomer or oligomer as a resin component is cured, or a bifunctional monomer or oligomer and a tri- or higher functional monomer or oligomer are used as a resin component. When the composite material composition is cured, as shown by the curve C3, the region R3 where the refractive index is unstable has only a polyfunctional monomer or oligomer whose refractive index is constant and whose integrated light quantity is constant. It was found to be less than the composite material composition contained as That is, it was found that the refractive index is stabilized even with a small amount of ultraviolet irradiation by including a bifunctional monomer or oligomer in the resin component of the composite material composition.
[0039]
Based on these results, when the resin component of the composite material consists of a photocurable resin composition containing a polyfunctional monomer or oligomer, and from a photocurable resin composition containing a bifunctional and polyfunctional monomer or oligomer The mechanism of the curing reaction was investigated. This will be specifically described with reference to FIGS.
[0040]
In order to express the intrinsic properties of the photo-curable resin, in the curing reaction stage, the reactive functional groups between the monomers or oligomers of the resin (hereinafter collectively referred to as “monomer”) molecules are brought close to the reactable region. It is necessary to increase the polymerization and crosslinking density by advancing the chain reaction efficiently. The tendency of the change in the refractive index indicated by the curves C1 to C3 in FIG. 2 indicates that the density increases due to the shrinkage of the material accompanying the progress of the curing reaction due to polymerization and crosslinking, and the refractive index increases accordingly. it is conceivable that. For this reason, it is considered that when there is no unreacted reactive functional group, the shrinkage of the material stops and the refractive index becomes constant.
[0041]
A polyfunctional resin is a resin having three or more reactive functional groups in the monomer molecule.

Claims (10)

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 inorganic particles, and provided on the diffraction grating;
The maximum thickness of the optical adjustment layer is 15 μm or more and 100 μm or less,
The diffractive optical element, wherein the second resin is a polymer of a photocurable resin composition containing a bifunctional monomer or oligomer.   The diffractive optical element according to claim 1, wherein the photocurable resin composition further includes a trifunctional or higher functional monomer or oligomer.   The diffractive optical element according to claim 1, wherein the photocurable resin composition contains the bifunctional monomer or oligomer in a proportion of 10 wt% to 100 wt%.   The diffractive optical element according to claim 3, wherein the first resin is polycarbonate.   The diffractive optical element according to claim 4, wherein the bifunctional monomer or oligomer is a bifunctional epoxy acrylate.   The diffractive optical element according to claim 5, wherein the trifunctional or higher functional monomer or oligomer is a trifunctional or higher functional acrylate.   The diffractive optical element according to claim 1, wherein the second resin is an aliphatic resin.   2. The diffractive optical element according to claim 1, wherein 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 first optical material is larger than the wavelength dispersion of the second optical material. .   2. The diffractive optical element according to claim 1, wherein the inorganic particles include 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 1, wherein an effective particle diameter of the inorganic particles is 1 nm or more and 100 nm or less.

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