JP2013156404A - Diffractive optical element, method for manufacturing the same, and optical system using diffractive optical element - Google Patents

Abstract

Disclosed is a diffractive optical element that suppresses the location dependence of diffraction efficiency in a grating plane based on thickness variation during assembly of a base layer in a diffraction grating, a method for manufacturing the same, and an optical system using the diffractive optical element. To do.
A diffractive optical element having a diffraction grating portion in which a first diffraction grating 1 and a second diffraction grating 2 formed of different materials are laminated so that their respective grating surfaces are in contact with each other. The diffraction grating 1 and the second diffraction grating 2 are provided with a first base layer and a second base layer, respectively, below the respective grating planes, and the different materials have a Young's modulus difference ΔE having a conditional expression ( 0 ≦ | ΔE | <3.0 GPa) is satisfied.
[Selection] Figure 1

Description

  The present invention relates to a diffractive optical element having a diffraction grating portion in which a first diffraction grating and a second diffraction grating are laminated, a manufacturing method thereof, and an optical system using the diffractive optical element.

  Conventionally, a method of reducing chromatic aberration of a lens system by providing a diffractive optical element having a diffractive action on the surface of the lens or a part of the lens system is known as opposed to a method of reducing chromatic aberration of a lens system by combining glass materials. . This method using a diffractive optical element utilizes the physical phenomenon that the deflection direction with respect to a light beam having a certain reference wavelength is reversed between the refracting surface and the diffractive surface in the optical system. In addition, the diffractive optical element can have an effect of an aspheric lens by appropriately changing the period of the periodic structure, and thus is effective in reducing various aberrations other than chromatic aberration.

  In general, the diffraction grating portion of the diffractive optical element has a blazed structure including a grating portion and a base portion (base layer). Such a blazed diffractive optical element can diffract light with high efficiency with respect to a specific one order (hereinafter also referred to as “specific order” or “design order”) and a specific wavelength.

  On the other hand, there is known a diffractive optical element configuration for obtaining this specific order diffraction efficiency sufficiently high over the entire visible wavelength band. Specifically, two diffraction gratings are arranged in close contact, and a low-refractive index high-dispersion material and a high-refractive index low-dispersion material are used as materials constituting each diffraction grating, and the height of the diffraction grating is appropriately set ( Hereinafter, such a diffractive optical element is referred to as “adherent two-layer DOE”). Thereby, high diffraction efficiency can be obtained in a wide wavelength band with respect to a specific order of diffracted light. The diffraction efficiency is defined as the ratio of the amount of diffracted light of each order to the amount of total transmitted light flux.

  Furthermore, as disclosed in Patent Document 1, in order to obtain a high diffraction efficiency of 99% or more in the entire visible wavelength range, the partial dispersion ratio θgF has a smaller value (linear anomalous dispersion) than that of a normal material. It is known to use materials. Further, as disclosed in Patent Document 2, it is known to improve the environmental resistance performance by defining the viscosity and elastic modulus of the material constituting the diffraction grating.

JP 2008-241734 A JP 2001-249208 A

  However, Patent Documents 1 and 2 do not disclose or suggest the location dependency of the diffraction efficiency in the grating plane based on the thickness variation at the time of producing the base layer in the diffraction grating, including the cause of occurrence. The applicant of the present application has come to recognize a new problem of the location dependence of diffraction efficiency in the grating plane based on the thickness variation during the production of the base layer in the diffraction grating.

  An object of the present invention is to provide a diffractive optical element that reduces the location dependence of diffraction efficiency in the grating plane based on thickness variations during the production of a base layer in a diffraction grating, a method for manufacturing the same, and an optical system using the diffractive optical element. To provide a system.

  In order to achieve the above object, a typical configuration of the diffractive optical element according to the present invention is such that a first diffraction grating and a second diffraction grating formed of different materials are laminated so that the respective grating surfaces are in contact with each other. The first and second diffraction gratings include a first base layer and a second base layer, respectively, below the respective grating surfaces. The different materials are characterized in that the Young's modulus difference ΔE satisfies the conditional expression (0 ≦ | ΔE | <3.0 GPa).

  The manufacturing method of the diffractive optical element and the optical system using the diffractive optical element also constitute one aspect of the present invention.

  According to the present invention, a diffractive optical element that reduces the location dependence of diffraction efficiency in the grating plane based on thickness variations during the production of a base layer in a diffraction grating, a method for manufacturing the same, and an optical device that uses the diffractive optical element A system can be provided.

(A) is the principal part schematic of the diffractive optical element which concerns on embodiment of this invention, (b) is a schematic diagram which shows the element structure of a diffractive optical element, (c) is the dispersion | variation in the thickness at the time of the assembly of a base layer. It is a figure explaining. It is a principal part schematic diagram of the imaging optical system carrying the diffractive optical element which concerns on embodiment of this invention. It is a figure which shows the diffraction efficiency of the diffractive optical element which concerns on the 1st Embodiment of this invention. It is a figure which shows the diffraction efficiency of the diffractive optical element which concerns on the 2nd Embodiment of this invention. It is a figure which shows the diffraction efficiency of the diffractive optical element of a comparative example.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the accompanying drawings. The configurations shown in the following embodiments are merely examples, and the present invention is not limited to the illustrated configurations.

<< First Embodiment >>
(Shooting optics)
FIG. 2 shows a photographing optical system such as a camera equipped with a diffractive optical element according to an embodiment of the present invention. In the figure, reference numeral 101 denotes a photographic lens, which has an internal aperture 40 and a refractive optical system including a diffractive optical element to be described later. Reference numeral 41 denotes a film which is an imaging plane or a photoelectric conversion element such as a CCD.

  The diffractive optical element corrects chromatic aberration of the taking lens 101. When the diffractive optical element of the present invention is applied, stable high diffraction efficiency is possible even with manufacturing variations, so that a high-performance photographic lens with less flare and less unevenness in image plane illuminance can be obtained. Although FIG. 2 shows that the diffraction grating portion 10 is provided on the bonding surface of the front lens, the present invention is not limited to this, and a plurality of diffractive optical elements may be used in the photographing lens.

(Diffraction optical element)
FIG. 1A is a front view and a side view of a diffractive optical element according to an embodiment of the present invention. A diffractive optical element having a diffraction grating portion 10 is formed at the boundary between substrate lenses 20 and 30 made of flat plates or lenses. The surfaces of the substrate lenses 20 and 30 on which the diffraction grating portion 10 is formed are curved surfaces, and the substrate lenses 20 and 30 form a refractive optical portion. The diffraction grating portion 10 has a concentric diffraction grating shape centered on the optical axis O and has a lens action. FIG. 1B shows a cross-sectional shape obtained by cutting the diffractive optical part 10 of FIG. 1A along the AA ′ cross section in the drawing. FIG. 1B is a considerably deformed view for easy understanding of the lattice shape.

  In FIG. 1B, the diffraction grating portion 10 has a configuration of a close contact DOE in which a first diffraction grating 1 and a second diffraction grating 2 are closely disposed (laminated). The first diffraction grating 1 includes a first base layer whose boundary surface is the curved surface 202 of the substrate lens 20 that is a first lens, and the second diffraction grating 2 is a substrate lens 30 that is a second lens. A second base layer having a curved surface 301 as a boundary surface. The first and second diffraction gratings have a concentric blazed grating shape, and a lens action (convergence action or diverging action) is obtained by gradually changing the grating pitch from the center (optical axis) to the periphery. ing. Each diffraction grating acts as one diffraction grating portion 10 through all layers.

  Further, by using the blazed structure, incident light incident on the diffraction grating unit 10 is concentrated and diffracted in a specific diffraction order (+ 1st order in the figure) direction.

(High refractive index low dispersion material and low refractive index high dispersion material)
In order to obtain high diffraction efficiency in a wide wavelength band in the two-layer DOE, a high refractive index and low dispersion material is used as a material for forming the diffraction grating 1 and a low refractive index and high dispersion material is used as a material for forming the diffraction grating 2. Furthermore, in order to obtain a diffraction efficiency of 99% or more in the entire visible range, it is necessary to use a material having a linear dispersion characteristic with a partial dispersion ratio θgF smaller than that of a normal material as a low refractive index and high dispersion material. In order to obtain this linear dispersion characteristic, there is known a method in which ITO (Indium-Tin Oxide) fine particles are finely dispersed and mixed with a base resin material.

  Unlike other inorganic oxides, in addition to the change in refractive index due to electronic transition, ITO generates free carriers due to tin doping or oxygen vacancies, and the refractive index changes. This electronic transition and free carriers have a very strong linear dispersion characteristic. Therefore, SnO2 and ATO (SnO2 doped with antimony) having the influence of free carriers as in the case of ITO can also be used.

  On the other hand, ITO is known as a material having a relatively high transmittance such as being used for a transparent electrode. However, this is not sufficient when ITO is used in an optical system that requires a higher transmittance. This decrease in the transmittance of ITO is caused by tin doping, and it is extremely difficult to obtain a material having a strong linear dispersion characteristic and an extremely high transmittance.

  For this reason, as shown in FIG. 1B, when the diffractive optical element having the two-layer DOE structure is formed on the boundary surface of the lens, the second diffraction grating 2 made of a resin in which ITO fine particles are dispersed. The thinner the base film thickness h2, the higher the transmittance. Here, the base film thickness is the thickness of the portion (base layer) where the lattice is not formed. Further, making the base film thickness (base layer thickness) of the second diffraction grating 2 more uniform over the entire lens reduces the location dependence of the transmittance in the grating plane, so the base film thickness is equal. Must be h2. Further, the curvature 21 of the curved surface connecting the valleys of the second diffraction grating 2 and the curvature 301 of the curved surface of the first surface of the substrate lens 30 are substantially equal.

(Production method)
As described above, since the base film thickness of the diffraction grating 2 made of a low refractive index and high dispersion material in which ITO fine particles are dispersed affects the transmittance, it is important to manufacture it thinly and uniformly over the entire lens. As a specific manufacturing method, first, in order to form the diffraction grating 2 of a low refractive index and high dispersion material in which ITO fine particles are dispersed thinly and with high precision uniformly over the entire lens area, a mold is used, and a substrate lens is used. 30 is formed in accordance with the curvature 301 of the curved surface of the first surface.

  Thereafter, the second diffraction grating 2 formed on the substrate lens 30 and the substrate lens 20 are bonded with the material constituting the first diffraction grating 1 and simultaneously molded (joint molding), whereby a diffractive optical element is formed. Can be produced. Further, centering may be performed at the same time in order to align the centers of the substrate lenses 20 and 30 simultaneously with the joint molding of the first diffraction grating 1.

(Base film thickness variation during assembly and location dependence of diffraction efficiency)
At the time of manufacturing the diffractive optical element, each substrate lens, a mold for forming the diffraction grating, the shape of the diffraction grating by the grating molding, and the like vary in manufacturing. In particular, the curvature of the curved surfaces 202 and 301 of the substrate lens, the curvature of the curved surface connecting the apex and trough portions of the diffraction grating of the mold for molding the diffraction grating, and the curvature of the curved surface 12 as a result of curing shrinkage when molding the resin. And 21 have variations.

  When forming the base film thickness with high accuracy in accordance with the curvature 301 of the curved surface of the first surface of the substrate lens 30 when the second diffraction grating 2 is formed, the above-described variation may occur when the first diffraction grating 1 is formed by bonding. As a result, the base film thickness of the first diffraction grating 1 varies. FIG. 1C shows a case where the base film thickness of the first diffraction grating 1 is different within the element plane. In particular, if the centering of the substrate lenses 20 and 30 is performed simultaneously with the joint molding of the first diffraction grating 1, the variation becomes large.

  When the first diffraction grating is bonded and formed, the second diffraction grating is caused by a difference in curing shrinkage due to a difference in Young's modulus between the material constituting the first diffraction grating and the material constituting the second diffraction grating. The fine particle-dispersed material is pulled, and the density changes because the volume does not change and the volume changes. When the base film thickness of the first diffraction grating differs depending on the location in the grating plane, the amount of pulling differs depending on the base film thickness, so that the density change differs depending on the location in the grating plane.

  In general, since the refractive index is proportional to the density, the fact that the change in density varies depending on the location in the lattice plane means that the change in refractive index varies depending on the location in the lattice plane. For this reason, when the location dependence of the density change amount occurs in the element plane, the refractive index change also increases, resulting in a difference in diffraction efficiency η1 and η2 of diffraction gratings having different base thicknesses, resulting in location dependence. When this diffractive optical element is applied to a photographic optical system, the resulting image performance is degraded.

  In particular, a material in which fine particles are dispersed does not change because the amount of fine particles dispersed inside is constant even if the volume of the resin material changes. The amount is large.

  In contrast to the second diffraction grating 2, the first diffraction grating 1 can be first formed into a grating, and then the second diffraction grating 2 can be joined and formed into a diffractive optical element. This is also not preferable because the base film thickness varies and the transmittance varies when the second diffraction grating 2 is bonded.

(Location dependence of Young's modulus difference and diffraction efficiency)
In this way, the inventor of the present invention has a place dependency on the base film thickness of one diffraction grating, the refractive index of the material constituting the other diffraction grating is changed by bonding, and the diffraction efficiency is changed to a place in the grating plane. An improvement was made in that the dependency occurred and the image performance deteriorated. That is, the present inventors have found a diffractive optical element that reduces the dependence of diffraction efficiency on the location in the lattice plane and can stably form high diffraction efficiency. Specifically, the base film thickness varies by selecting a material in which the Young's modulus difference ΔE falls within the following conditional expression as the material constituting the first diffraction grating and the material constituting the second diffraction grating. Even in this case, it has been found that the location dependence of the diffraction efficiency in the lattice plane can be reduced.

0 ≦ | ΔE | <3.0 GPa
If this is not satisfied, the location dependence of the diffraction efficiency becomes large when the base film thickness is different, which is not preferable.

  More preferably, the above conditions satisfy the following conditions: the difference ΔE in Young's modulus between different materials and the larger Young's modulus Em of different materials.

1.0 GPa <| ΔE | <3.0 GPa
5.5 GPa <Em <7.0 GPa
(Young's modulus difference and Abbe number difference)
The material that constitutes the first diffraction grating and the material that constitutes the second diffraction grating include a resin material having substantially the same composition of the organic substance in common and mixed with different inorganic fine particles. The difference in Abbe number of the inorganic fine particles used is preferably 10 or more. By using resin materials with substantially the same composition, the Young's modulus difference can be reduced, and fine particles with a large Abbe number difference are dispersed to form a high refractive index low dispersion material and a low refractive index high dispersion material. This is because a high diffraction efficiency can be obtained over the entire visible range.

  In order to obtain high diffraction efficiency in the entire visible range, it is preferable to use ITO having linear characteristics, and the base film thickness hi of the diffraction grating of the material containing ITO fine particles and the diffraction grating of the material containing fine particles different from ITO are used. The base film thickness h preferably satisfies the following conditions.

5 x hi <h
If this is not satisfied, the difference in base film thickness between the first diffraction grating and the second diffraction grating is reduced. As a result, it is difficult to compensate for manufacturing variations with the base film thickness of a diffraction grating made of a material containing fine particles different from ITO, which has relatively little influence on optical characteristics. Further, when centering the substrate lenses 20 and 30, if the base film thickness of the diffraction grating made of a material containing fine particles different from ITO is not thick, it is not preferable because it becomes difficult to perform centering.

  The grating height d of the diffractive optical element is preferably 15 μm or less. If this is not satisfied, the dependency of diffraction efficiency on the incident angle increases, and the applicable optical system is limited.

(Specific configuration of diffractive optical element)
"Example"
The specific configuration of the diffractive optical element according to this embodiment is an ultraviolet curable resin (nd = 1...) In which 20 vol% of ZrO2 fine particles are mixed in an acrylic ultraviolet curable resin as a first resin material with respect to the first diffraction grating. 6202, νd = 43.9, θgF = 0.572). Further, an ultraviolet curable resin (nd = 1.5686, νd = 19.4) in which 16 vol% of ITO fine particles different from ZrO 2 fine particles are mixed with acrylic ultraviolet curable resin as the second resin material for the second diffraction grating. , ΘgF = 0.416).

  The same resin (nd = 1.5241, νd = 51.6, θgF = 0.563) is used for the acrylic ultraviolet curable resin of the first diffraction grating material and the second diffraction grating material. The refractive indexes of the ZrO2 fine particles are nd = 1.910, νd = 45.1, θgF = 0.612, and the refractive indexes of the ITO fine particles are nd = 1.8289, νd = 7.47, and θgF = 0.360. The grating height d is 11.11 μm, and the design order is + 1st order. The partial dispersion ratio θgF is defined by the following equation.

θgF = (ng−nF) / (nF−nC)
FIG. 3 shows the characteristics of the diffraction efficiency at the designed order (+ 1st order) when the base film thickness of the diffractive optical element is different. The base film thicknesses of the first diffraction grating material and the second diffraction grating material in FIG. 1B are 35 μm, 30 μm, and 2.0 μm, respectively. η1 is the diffraction efficiency when the base thickness is h11, and η2 is the diffraction efficiency when the base thickness is h12. The incident angle is vertical. It can be seen that even if the base film thickness of the first diffraction grating is different, the diffraction efficiency is 99.5% or more in the entire visible region (wavelength 400 nm to 700 nm).

  When the Young's modulus of the material of the first diffraction grating and the second diffraction grating was evaluated using the nanoindentation method, respectively, it was 6.5 GPa and 4.9 GPa, respectively, and the Young's modulus difference ΔE was as low as 1.5 GPa. It was. Here, the nano-indentation method is to obtain a surface hardness from the load applied to the indenter and the projected area under the indenter by pushing an indenter with a regular triangular pyramid made of a diamond tip into the surface of the material. . The Young's modulus is almost determined by the base resin. By including the same base resin as in the present embodiment, the difference in Young's modulus between the first diffraction grating material and the second diffraction grating material can be reduced. it can.

<< Second Embodiment >>
In the present embodiment, the diffraction grating is formed of a material different from that of the first embodiment. That is, an ultraviolet curable resin (nd = 1.5843, νd = 46.6, θgF = 0.581) in which 13 vol% of ZrO 2 fine particles are mixed with an acrylic ultraviolet curable resin is used as the material of the first diffraction grating. Further, as a material of the second diffraction grating, an ultraviolet curable resin (nd = 1.5313, in which ITO fine particles are mixed in a volume of 16 vol% in a resin mixed with a material obtained by mixing an acrylic ultraviolet curable resin and a fluorine acrylic ultraviolet curable resin. νd = 19.1, θgF = 0.416).

  The materials of the second diffraction grating are acrylic ultraviolet curable resin (nd = 1.5241, νd = 51.6, θgF = 0.563) and fluorine acrylic ultraviolet curable resin (nd = 1.430, νd = 60. 6, θgF = 0.553) is mixed 1: 1. The first diffraction grating material and the second diffraction grating material both contain the same acrylic ultraviolet curable resin. The refractive indexes of the ZrO2 fine particles are nd = 1.910, νd = 45.1, θgF = 0.612, and the refractive indexes of the ITO fine particles are nd = 1.8289, νd = 7.47, and θgF = 0.360. The grating height d is 10.71 μm, and the design order is + 1st order.

  FIG. 4 shows the characteristics of the diffraction efficiency at the designed order (+ 1st order) when the base film thickness of the diffractive optical element is different. The base film thickness is the same as the base thicknesses h11, h12, and h2 in FIG. 1B of the first embodiment, and is 35 μm, 30 μm, and 2.0 μm, respectively. In FIG. 4, η1 is the diffraction efficiency when the base thickness is h11, and η2 is the diffraction efficiency when the base thickness is h12. The incident angle is vertical. From FIG. 4, it can be seen that even if the base film thickness of the first diffraction grating is different, the diffraction efficiency is 99.5% or more in the entire visible region (wavelength 400 nm to 700 nm).

  When the Young's modulus of the material of the first diffraction grating and the second diffraction grating was evaluated using the nanoindentation method, respectively, it was 6.5 GPa and 3.7 GPa, respectively, and the Young's modulus difference ΔE was as low as 2.8 GPa. It was. The Young's modulus is almost determined by the base resin, and since the resin of the same composition is included as in this embodiment, the difference in Young's modulus between the first diffraction grating material and the second diffraction grating material is small. As a result, even if the base film thickness of the first diffraction grating is different, the difference in diffraction efficiency is small. Compared with the first embodiment, since the Young's modulus difference is large, the location dependence of the diffraction efficiency in the element surface is slightly large, but 99.5% or more is obtained in the entire visible range.

(Comparative example)
In order to clarify the effect of the present embodiment, a comparative example is shown. The comparative example is the first embodiment,
The other configurations are the same as those of the first embodiment except that the second embodiment is different in material and lattice height. As a material for the first diffraction grating, an ultraviolet curable resin (nd = 1.5211, νd = 50.4, θgF = 0.570) in which 6 vol% of ZrO2 fine particles are mixed with an acrylic ultraviolet curable resin is used. In addition, as a material for the second diffraction grating, an ultraviolet curable resin (nd = 1.51010, νd = 19.2, θgF = 0.410) obtained by mixing 16 vol% of ITO fine particles with a fluorine acrylic ultraviolet curable resin. Use. The grating height d is 10.51 μm, and the design order is + 1st order.

  FIG. 5 shows the characteristics of the diffraction efficiency at the design order (+ 1st order) when the base film thickness of the diffractive optical element is different. As in the first embodiment, the base film thicknesses h11, h12, and h2 of the first diffraction grating material and the second diffraction grating material in FIG. 2 are 35 μm, 30 μm, and 2.0 μm, respectively. . η1 is the diffraction efficiency when the base thickness is h11, and η2 is the diffraction efficiency when the base thickness is h12. The incident angle is vertical. As can be seen from FIG. 5, in the material of the comparative example, when the base film thickness of the first diffraction grating is different, the diffraction efficiency has a location dependency in the element plane.

  When the Young's modulus of the material of the first diffraction grating and the second diffraction grating was evaluated using the nanoindentation method, respectively, it was 6.5 GPa and 2.5 GPa, respectively, and the Young's modulus difference ΔE was as large as 4.0 GPa. It was. The Young's modulus is almost determined by the base resin, and if a resin having a different material composition is used as in this comparative example, the difference in Young's modulus between the material of the first diffraction grating and the material of the second diffraction grating increases. As a result, when the base film thickness of the first diffraction grating is different, the difference in diffraction efficiency is increased.

(Modification 1)
In the above-described embodiment, regarding the conditional expression of 0 ≦ | ΔE | <3.0 GPa, the intermediate value embodiment and the embodiment in the vicinity of the upper limit value are specifically disclosed, but the theory in the vicinity of the lower limit value (near zero) is disclosed. It is apparent that the effect of the present invention can be obtained because the follow-up property is good in the vicinity of zero.

(Modification 2)
In the above-described embodiment, the same acrylic ultraviolet curable resin is included as the different materials for forming the first diffraction grating and the second diffraction grating, but both may include the same other organic matter. good. Or both may contain the same inorganic substance.

(Modification 3)
The present invention is not limited to using the diffraction grating material and the manufacturing method described in the above-described embodiment, and may be appropriately changed within the range of the conditional expression described above.

(Modification 4)
In the above-described embodiment, the photographing lens of the camera is shown, but the present invention is not limited to this. For example, the same effect can be obtained when used in an imaging optical system used in a wide wavelength region such as a video camera photographing lens, an office machine image scanner, or a digital copying machine reader lens.

1... First diffraction grating 2.. Second diffraction grating 10.. Optical element of diffraction grating part 20, 30 .. Substrate lens 101.

Claims (13)

A diffractive optical element having a diffraction grating portion in which a first diffraction grating and a second diffraction grating formed of different materials are stacked so that respective grating surfaces are in contact with each other,
The first diffraction grating and the second diffraction grating include a first base layer and a second base layer, respectively, below the respective grating surfaces;
The diffractive optical element is characterized in that the different materials satisfy the following conditional expression with respect to a difference ΔE in Young's modulus.
0 ≦ | ΔE | <3.0 GPa 2. The diffractive optical element according to claim 1, wherein a difference ΔE in Young's modulus between the different materials and a larger Young's modulus Em of the different materials satisfy the following conditions, respectively.
1.0 GPa <| ΔE | <3.0 GPa
5.5 GPa <Em <7.0 GPa   The diffractive optical element according to claim 1, wherein the different materials both contain the same organic or inorganic material.   4. The diffractive optical element according to claim 3, wherein the different materials are resin materials in which inorganic fine particles are dispersed.   The diffractive optical element according to claim 1, wherein the different materials have an Abbe number difference of 10 or more.   6. The diffractive optical element according to claim 3, wherein one of the different materials is ITO fine particles as inorganic fine particles. 7. The diffractive optical element according to claim 6, wherein a base film thickness hi of a diffraction grating made of a material containing ITO fine particles and a base film thickness h of a diffraction grating made of a material containing fine particles different from ITO satisfy the following conditions.
5 x hi <h   An ultraviolet curable resin in which 20 vol% of ZrO2 fine particles are mixed in an acrylic ultraviolet curable resin is used as the first resin material for the first diffraction grating, and an acrylic ultraviolet ray is used as the second resin material for the second diffraction grating. 8. The diffractive optical element according to claim 1, wherein an ultraviolet curable resin in which 16 vol% of ITO fine particles different from the ZrO2 fine particles are mixed with the curable resin is used. 9. The diffractive optical element according to claim 1, wherein the first diffraction grating and the second diffraction grating include the same resin material. 10.   The diffractive optical element according to claim 1, wherein a grating height of the diffraction grating is 15 μm or less.   The diffractive optical element according to any one of claims 1 to 10, further comprising two refracting optical units each having the diffractive optical element on a boundary surface, and having a refracting optical system in addition to the diffractive optical element. An optical system using the characteristic diffractive optical element. The diffractive optical element manufacturing method according to any one of claims 1 to 10, wherein the diffraction grating portion is provided at a boundary between the first lens and the second lens.
Performing a grating molding of the second diffraction grating composed of a second resin material in which ITO fine particles are dispersed on the second lens using a mold;
Using the first resin material in which inorganic fine particles different from ITO fine particles constituting the first diffraction grating are dispersed in the second lens provided with the second diffraction grating and the first lens. Joining and forming, and
A method for producing a diffractive optical element, comprising: A method for producing a diffractive optical element according to claim 12,
Using the first resin material in which inorganic fine particles different from ITO fine particles constituting the first diffraction grating are dispersed in the second lens provided with the second diffraction grating and the first lens. A method of manufacturing a diffractive optical element, wherein the first lens and the second lens are centered while being joined.