JPWO2013168740A1 - Diffractive optical element and imaging optical system - Google Patents

Abstract

The diffractive optical element of the present invention is a diffractive optical element that changes the traveling direction of incident light by utilizing the diffraction phenomenon of light, and has at least one transparent substrate, and the first is formed on the transparent substrate. The diffraction grating layer and the second diffraction grating layer are stacked at least in the effective region without any gap therebetween, and one of the interfaces of the first diffraction grating layer on the side where the second diffraction grating layer is located. And a part of the interface of the second diffraction grating layer on the side where the first diffraction grating layer is located have a concavo-convex structure that is combined with each other and acts as one diffraction grating, As a material for one diffraction grating layer, a zirconia composite material, an organic-inorganic hybrid material containing a phenyl group or a biphenyl group, or a monomer material containing a fluoro group and a phenyl group in a single molecule is used. thing And features. The diffractive optical element can be made of a material that can withstand practical use, and flare caused by the diffractive optical element can be more effectively suppressed in the imaging optical system.

Description

  The present invention relates to a diffractive optical element that generates a diffracted light beam with respect to incident light, and an imaging optical system that is an optical system for an imaging apparatus configured using such a diffractive optical element.

  In an optical system of a digital camera such as a single-lens reflex camera, a compact digital camera, or a portable camera, a refractive lens using a refractive action of light such as a concave lens or a convex lens has been used in many cases. In such an imaging optical system, Degradation of image quality due to chromatic aberration of the refractive lens has been a greater problem than before.

  In order to correct the chromatic aberration of the refractive lens, measures such as incorporating a chromatic aberration correction lens using a fluorite or anomalous dispersion material as a lens material into the optical system have been taken, but the correction effect is not sufficient, Many problems still remain in practical use, such as the increase in the optical system and the cost.

  In recent years, many attempts have been made to solve the problem of chromatic aberration by incorporating a diffractive optical element called a diffractive lens having a lens action into an imaging optical system. A diffractive lens is a lens that collects or diverges light by utilizing a light diffraction phenomenon, and is known to have characteristics that are not found in a refractive lens.

  For example, a diffractive lens and a refractive lens have different focal length changes with respect to changes in the wavelength of incident light. Specifically, the refractive lens has a positive Abbe number, whereas the amount corresponding to the Abbe number of the diffractive lens is a negative value. It is said that the problem of chromatic aberration of the optical system can be solved by utilizing such optical characteristics of the diffractive lens and combining the diffractive lens with a part of the refractive lens optical system.

  However, if a diffractive optical element is used, chromatic aberration can be effectively corrected and the optical system can be reduced, but a new problem arises in that the image quality deteriorates due to flare in the optical system. One cause of flare is the presence of a wavelength band with low diffraction efficiency in the diffractive optical element. That is, when light having a wavelength that does not have high diffraction efficiency is incident, light other than the target order is generated, which becomes scattered light and generates flare.

  For example, if the diffraction efficiency can be set sufficiently high over all wavelengths in the visible light region, the occurrence of flare as described above can be suppressed. For example, Patent Document 1 describes an example of selecting an optical material and parameter conditions for achieving a diffractive optical element having high diffraction efficiency at the design order regardless of the wavelength.

  However, in the selection examples and parameter conditions described in Patent Document 1, the choices of materials are very narrow. Even though the diffraction efficiency is maintained at a high value over the entire visible light range, that is, it is aimed to be flat, there is a part where the diffraction efficiency is reduced to some extent depending on the wavelength. It was something that was not reached.

  Therefore, Patent Document 2 describes a technique for solving the problem that the diffraction efficiency cannot be set sufficiently high over all wavelengths in the visible light region by electronically correcting the information received by the image sensor. Yes.

  Also, in Patent Document 3, in order to eliminate the cause of flare that is not caused by a decrease in diffraction efficiency, the angle of the side wall of the diffraction grating is controlled in order to suppress flare generated by light reflected by the side wall of the diffraction grating. The technology is described.

Japanese Unexamined Patent Publication No. 10-268116 Japanese Unexamined Patent Publication No. 2005-167485 Japanese Unexamined Patent Publication No. 2011-170028

  However, the electronic correction described in Patent Document 2 does not function sufficiently depending on the shooting environment. In the method described in Patent Document 3, the angle of the side wall of the grating is changed. If the angle of the side wall is changed, the diffraction efficiency of the designed order is lowered, which may adversely affect the optical characteristics. In addition, these methods alone are not sufficient as a countermeasure for flare using a diffractive lens.

  The problem is how to set the diffraction efficiency sufficiently high over all wavelengths in the visible light region.

  However, not only in Patent Document 1, but due to problems such as cost, workability, durability, and haze of materials, it is actually very difficult to set the diffraction efficiency sufficiently high over all wavelengths in the visible light region. It was. For example, the material that meets the requirements is expensive because it is a special material, or it is very difficult to create a diffractive structure using that material, and the environmental fluctuations such as durability and temperature of the material. It has been difficult to simultaneously achieve resistance to changes in optical properties against light, suppression of scattering generated on the surface and inside of the material, and the like.

  Therefore, an object of the present invention is to provide a diffractive optical element that can be made of a material that can be put into practical use and that can more effectively suppress flare caused by the diffractive optical element in an imaging optical system. Specifically, sufficient diffraction efficiency is achieved over all wavelengths in the visible light range, taking into account various issues to be considered when using diffractive optical elements in imaging optical systems, such as cost, workability, durability, and material haze. An object of the present invention is to provide a diffractive optical element and an imaging optical system that can be set high.

  A diffractive optical element according to the present invention is a diffractive optical element that changes a traveling direction of incident light by utilizing a light diffraction phenomenon, and includes at least one transparent substrate and a first substrate provided on the transparent substrate. A diffraction grating layer; and a second diffraction grating layer formed on the first diffraction grating layer and made of a material having optical characteristics different from the material of the first diffraction grating layer. A part of the interface of the diffraction grating layer on the side where the second diffraction grating layer is located and a part of the interface of the second diffraction grating layer on the side where the first diffraction grating layer is located include: A concavo-convex structure that functions as one diffraction grating is formed by combining with each other, and the transparent substrate, the first diffraction grating layer, and the second diffraction grating layer are spaced at least in the effective region. At least one diffraction layer Zirconia composite material, organic-inorganic hybrid material containing phenyl group or biphenyl group, or monomer material containing fluoro group and phenyl group in a single molecule is used for the material of the sublayer And

Note that the concavo-convex structure that functions as one diffraction grating in combination with each other is a shape in which each surface of the concavo-convex structure is in close contact with each other and bonded to each other. Is a set of concavo-convex structures arranged within a distance of 1 μm and without any gaps. In the above, as a material of at least one diffraction grating layer, a zirconia composite material, an organic-inorganic hybrid material containing a phenyl group or a biphenyl group, or a monomer material containing a fluoro group and a phenyl group in a single molecule These materials include, but are not limited to, organic and inorganic hybrid materials containing a phenyl group or biphenyl group and other materials mixed with each other, and monomer materials containing a fluoro group and a phenyl group in a single molecule. It includes other materials that are mixed and cured.
The effective area refers to an area within the effective diameter of the diffractive optical element.

  The diffractive optical element according to the present invention is a diffractive optical element that changes a traveling direction of incident light by utilizing a light diffraction phenomenon, and includes at least one transparent substrate and a first transparent substrate provided on the transparent substrate. A first diffraction grating layer, a second diffraction grating layer formed on the first diffraction grating layer and made of a material having optical characteristics different from the material of the first diffraction grating layer, and the second diffraction grating layer A third diffraction grating layer made of a material having optical characteristics different from the materials of the first diffraction grating layer and the second diffraction grating layer provided on the diffraction grating layer; A part of the interface of the grating layer on the side where the second diffraction grating layer is located and a part of the interface of the second diffraction grating layer on the side where the first diffraction grating layer is located are mutually connected. Are combined to form a concavo-convex structure that acts as one diffraction grating. A part of the interface of the second diffraction grating layer on the side where the third diffraction grating layer is located, and the interface of the third diffraction grating layer on the side where the second diffraction grating layer is located. A part is formed with a concavo-convex structure that is combined with each other to act as one diffraction grating, and the transparent substrate, the first diffraction grating layer, the second diffraction grating layer, and the third diffraction grating are formed. The diffraction grating layer is laminated at least in the effective region without interposing a gap therebetween, and at least one diffraction grating layer material includes a zirconia composite material, an organic-inorganic hybrid material containing a phenyl group or a biphenyl group, Alternatively, a monomer material containing a fluoro group and a phenyl group in a single molecule may be used.

  The diffractive optical element according to the present invention is a diffractive optical element that changes a traveling direction of incident light by utilizing a light diffraction phenomenon, and includes at least one transparent substrate and a first transparent substrate provided on the transparent substrate. A first diffraction grating layer, a second diffraction grating layer formed on the first diffraction grating layer and made of a material having optical characteristics different from the material of the first diffraction grating layer, and the second diffraction grating layer A third diffraction grating layer made of a material having optical properties different from at least the material of the second diffraction grating layer provided on the diffraction grating layer; and at least the above-mentioned provided on the third diffraction grating layer A fourth diffraction grating layer made of a material having optical characteristics different from the material of the third diffraction grating layer, and the interface of the first diffraction grating layer on the side where the second diffraction grating layer is located A portion of the second diffraction grating layer; A part of the interface on the side where the one diffraction grating layer is located is formed with a concavo-convex structure that is combined with each other to act as one diffraction grating, and the third diffraction grating layer has the third structure. The interface on the side where the diffraction grating layer is located and the interface on the side where the second diffraction grating layer of the third diffraction grating layer is located do not have a concavo-convex structure, and the third diffraction grating layer A part of the interface on the side where the fourth diffraction grating layer is located and a part of the interface on the side where the third diffraction grating layer of the third diffraction grating layer is located are combined with each other. An uneven structure that functions as one diffraction grating is formed, and the transparent substrate, the first diffraction grating layer, the second diffraction grating layer, the third diffraction grating layer, and the fourth diffraction grating layer are formed. Are stacked at least in the effective region without any gaps between them, Even if the material of one diffraction grating layer is a zirconia composite material, an organic-inorganic hybrid material containing a phenyl group or a biphenyl group, or a monomer material containing a fluoro group and a phenyl group in a single molecule Good.

Further, the combination of the material of the first diffraction grating layer and the material of the second diffraction grating layer is such that, for these two materials, the refractive index of g-line is ng, the refractive index of C-line is nC, and the ng of one material is ng. When the difference between the value of −nC and the value of ng−nC of the other material is Δ (ng−nC), and the difference between the value of ng of one material and ng of the other material is Δng, You may be comprised so that conditional expression (A) may be satisfy | filled.
Conditional expression (A):
−0.13 ≦ Δ (ng−nC) +0.506 (Δng) ≦ 0.16

Further, the combination of the material of the first diffraction grating layer and the material of the second diffraction grating layer is such that, for these two materials, the refractive index of the g-line is ng, the refractive index of the C-line is nC, and the refraction of the e-line. The rate is ne, and the difference between the value of ng−nC of one material and the value of ng−nC of the other material is Δ (ng−nC). Similarly, the value of ne of one material and the value of ne of the other material When the difference is Δne, the following conditional expression (B) may be satisfied.
Conditional expression (B):
−1.1 <Δ (ng−nC) / (Δne) ^1/2 <0.27

Moreover, if the refractive index of d-line is larger than 1.59, it will be a high refractive index material, if it is in the range of 1.51-1.59, it will be a medium refractive index material, and if it is less than 1.51, it will be a low refractive index material. In the case of a low refractive index material, if the Abbe number is 50 or less, it is a low refractive index high dispersion material, if the Abbe number is 60 or more, it is a low refractive index low dispersion material, and in the case of a medium refractive index material, If the Abbe number is 40 or less, the material is a medium refractive index high dispersion material. If the Abbe number is 50 or more, the material is a medium refractive index low dispersion material. In the case of a high refractive index material, if the Abbe number is 30 or less, the material is highly refractive. If the Abbe number is 40 or more, the first refractive grating layer material, the second diffraction grating layer, and the third diffraction grating layer material are used. The combination is one of the following six patterns in the order of lamination from the transparent substrate: It may be in crab applicable.
Pattern 1: The first layer is a low refractive index low dispersion material, the second layer is a high refractive index low dispersion material, and the third layer is a high refractive index high dispersion material.
Pattern 2: The first layer is a medium refractive index high dispersion material, the second layer is a high refractive index high dispersion material, and the third layer is a high refractive index low dispersion material.
Pattern 3: The first layer is a low refractive index high dispersion material, the second layer is a high refractive index high dispersion material, and the third layer is a high refractive index low dispersion material.
Pattern 4: The first layer is a medium refractive index high dispersion material, the second layer is a low refractive index material or medium refractive index material, and the third layer is a high refractive index low dispersion material.
Pattern 5: The first layer is a high refractive index and high dispersion material, the second layer is a low refractive index material or medium refractive index material, and the third layer is a high refractive index and low dispersion material.
Pattern 6: The first layer is a medium refractive index material, the second layer is a medium refractive index high dispersion material, and the third layer is a high refractive index low dispersion material.

Further, in the stacking order of each diffraction grating layer from the transparent substrate, the refractive index of g-line of the first layer material is ng ₁ , the refractive index of g-line of the second layer material is ng ₂ , and the third layer The refractive index of the g-line of the material is ng ₃ , the refractive index of the e-line of the first layer material is ne _1, and the refractive index of the e-line of the second layer material is ne _2. The e-line refractive index is ne ₃ , the C-line refractive index of the first layer material is nC ₁ , the C-line refractive index of the second layer material is nC _2, and the C-layer of the third layer material is C The refractive index of the line is nC ₃ and the difference in refractive index between the first and second e-lines (ne ₁ -ne ₂ ) is Δne _12, and the refractive index of the e-line in the second and third layers is The difference (ne ₂ −ne ₃ ) is Δne _23, and the difference in refractive index between the g-line and C-line of the first layer material and the difference in refractive index between the g-line and C-line of the second layer material {( ng ₁ -nC ₁ )-(ng ₂ −nC ₂ )} is Δ (ng−nC) ₁₂ and the difference in refractive index between the g-line and C-line of the second layer material and the difference in refractive index between the g-line and C-line of the third layer material When the difference {(ng ₂ −nC ₂ ) − (ng ₃ −nC ₃ )} is Δ (ng−nC) ₂₃ , the material of the first diffraction grating layer, the second diffraction grating layer, and the third diffraction When the combination of the materials of the lattice layer corresponds to the pattern 1, the value when A = 5.5 in the formula (5) described later is 0.65 or less, and the formula (9) described later. The value when E = 0.5 is 0.94 or less, and the value when C = −1.5 in formula (7) described later is 0 or less, or 1.5 or more, and The value when D = 0.7 in formula (8) described later is less than 1.55 and corresponds to the pattern 2 described later. The value when A = 5.5 in (5) is less than 0.85, and the value when B = 1.2 in formula (6) described later is less than 0.99, and will be described later. In equation (7), the value when C = −1.3 is 0 or less or 1.575 or more, and the value when B = 0.29 in equation (6) described later is 0.97. In the case of corresponding to the pattern 3, the value when A = 5.5 in the formula (5) described later is less than 0.85, and C = − in the formula (7) described later. The value when 1.3 is 0 or less or 1.575 or more, and the value when B = 1.2 in the formula (6) described later is 1.01 or less, and the formula ( 6) When B = 0.29, the value is less than 0.97. In this case, the value when A = 0.2 in equation (5) described later is less than 0.97, and the value when B = 0.1 in equation (6) described later is When the value is less than 1.017, and when A = 0.8 in formula (5) described later is less than 1.045, and B = 0.47 in formula (6) described later When the value is less than 0.98 and falls under the pattern 5, the value when A = 0.05 in the equation (5) described later is less than 0.975, and the equation (6) described later ) Is less than 1.005 when B = 0.2, and is less than 0.99 when A = 0.3 in equation (5) described later, and an equation described later. In (6), the value when B = 0.6 is less than 0.965. In this case, the value when A = 0.6 in formula (5) described later is larger than 1.00 and smaller than 1.01, and C = −5.0 in formula (7) described later. And the value when D = −2.0 in equation (8) described later is greater than 1.49 and less than 1.77, and equation (9) described later. In this case, the value when E = 4.0 may be larger than 1.125.

  In the diffractive optical element, the surface shape of the uppermost diffraction grating layer may be an aspherical surface.

  In the diffractive optical element, the curved surface connecting the vertices on the transparent substrate side of the diffraction grating formed by the concavo-convex structure formed in the first diffraction grating layer may be an aspherical surface.

  In addition, the concave and convex structures constituting the diffraction grating are all concentric, and the ratio of the width of the widest ring zone to the width of the second widest ring zone is the concentric ring zone. It may be 1 to 0.7.

  Further, the unevenness having the same height as that of the concavo-convex structure is formed on a part outside the effective region of the surface on which the concavo-convex structure is formed of the diffraction grating layer in which the concavo-convex structure constituting the diffraction grating is formed. A structure may be formed.

  The diffractive optical element is a diffractive optical element that functions as a lens, and a single diffraction grating is formed in the element. The direction of curvature of the lens surface and the direction of the slope of the saw of the diffraction grating are the same. The arrangement order of the materials of the respective diffraction grating layers may be configured so as to have an inclination in the direction.

  The diffractive optical element is a diffractive optical element that functions as a lens, and two diffractive gratings are formed in the element. Of the two diffractive gratings, the diffractive optical element having the larger optical path difference of the d-line is used. The optical path difference is 2λ or less, and the two diffraction gratings are made of a high refractive index material if the refractive index of d-line is larger than 1.59, and medium refractive index material if it is in the range of 1.51 to 1.59. If it is less than 1.51, a low refractive index material is used. In the case of a low refractive index material, if the Abbe number is 50 or less, a low refractive index high dispersion material is obtained. If the Abbe number is 60 or more, a low refractive index material is obtained. In the case of a low-dispersion material and a medium-refractive index material, if the Abbe number is 40 or less, a medium-refractive-index high-dispersion material is used. If the Abbe number is 50 or more, a medium-refractive-index low-dispersion material is used. In this case, if the Abbe number is 30 or less, a high refractive index and high dispersion material is used. When the Abbe number is 40 or more, when a high refractive index and low dispersion material is used, the combination of materials forming each diffraction grating is a combination of a low refractive index low dispersion material and a high refractive index and low dispersion material, and a high refractive index. It corresponds to one of the combination of low dispersion material and high refractive index and high dispersion material, one combination of medium refractive index high dispersion material and high refractive index and high dispersion material, and one combination of low refractive index high dispersion material and high refractive index and high dispersion material. The angle formed by the normal of the line closest to the incident light and the incident light among the lines connecting the bottoms of each of the four concavo-convex structures constituting the two diffraction gratings is defined as the incident light. When the incident angle is a positive rotation direction when the light beam incident from the optical axis side with respect to the normal line is a positive rotation direction, in the combination of the concavo-convex structure having a large optical path difference between the two diffraction gratings, Low refractive index material The arrangement order of the materials of each diffraction grating layer is configured so that the diffraction grating layer made of a material is located on the incident side, and when the incident angle is a negative rotation direction, the two diffraction grating layers Among them, in the combination of the concavo-convex structure having a large optical path difference, the arrangement order of the materials of the respective diffraction grating layers may be configured so that the diffraction grating layer made of a material having a high refractive index is located on the incident side.

  In addition, a thin film made of a metal oxide may be provided between the transparent substrate and the first diffraction grating layer or between the diffraction grating layers on which the concavo-convex structure forming the diffraction grating is formed.

  Further, the difference in refractive index of the diffraction grating layer in which the concavo-convex structure constituting the diffraction grating is formed or the difference in refractive index between the diffraction grating layer and the thin film provided between the diffraction grating layers is 0.15 or less. It may be.

  An imaging optical system according to the present invention is an imaging optical system including at least one lens, including any of the diffractive optical elements described above, and the diffractive optical element is a lens system included in the imaging optical system. It is characterized in that chromatic aberration that eliminates chromatic aberration that appears is developed.

  Further, the imaging optical system is configured such that the diffractive optical element is formed on a transparent substrate having a lens function, and the diffraction direction is a positive power if the refractive direction of the lens is a positive power, If the refractive direction of the lens is negative power, the diffraction direction may be negative power.

  According to the present invention, it is possible to provide a diffractive optical element that can be made of a material that can withstand practical use and that can more effectively suppress flare caused by the diffractive optical element in the imaging optical system.

(A) And (b) is a schematic cross section which shows typically the cross section of the diffractive optical element of 1st Embodiment. It is a schematic top view which shows typically the shape of the diffraction grating formed in the diffractive optical element of 1st Embodiment. It is explanatory drawing explaining the diffraction surface formed per grating | lattice period with the diffractive optical element of 1st Embodiment. It is a graph which shows an example of the refractive index for every wavelength of two materials used for the diffraction grating layers 12 and 13 of the diffractive optical element of 1st Embodiment. (A) And (b) is a graph which shows the example of the primary diffraction efficiency of the diffraction grating 100 formed in the diffractive optical element of 1st Embodiment compared with the single layer diffraction grating by quartz glass. . It is explanatory drawing which shows the example of the optical characteristic of the material of each diffraction grating layer of the diffractive optical element of 1st Embodiment. It is a graph which shows the correlation with the value R of material set, and the diffraction efficiency value of the minimum side of g line | wire and C line | wire. It is a graph which shows the relationship between the value Q of a material set, and the diffraction efficiency of e line of the diffraction grating formed using the material. It is a schematic cross section which shows the other example of the diffractive optical element of 1st Embodiment. (A) And (b) is a schematic cross section which shows typically the cross section of the diffractive optical element of 2nd Embodiment. It is explanatory drawing explaining the diffraction surface formed per grating | lattice period with the diffractive optical element of 2nd Embodiment. It is explanatory drawing which shows the example of the material set suitable for 2nd Embodiment. It is a graph which shows an example of the refractive index for every wavelength of three materials used for the diffraction grating layers 22-24 of the diffractive optical element of 2nd Embodiment. It is a graph which shows the example of the primary diffraction efficiency in the whole diffractive optical element of 2nd Embodiment. (A) And (b) is explanatory drawing which shows the example of a combination of the height direction of two diffraction gratings. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 1 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 1 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 1 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 1 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 2 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 2 of a combination, and the difference of refractive index, and the height of a diffraction grating. (A) And (b) is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 2 of a combination, and the difference of a refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 2 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 3 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 3 of a combination, and the difference of refractive index, and the height of a diffraction grating. (A) And (b) is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 3 of a combination, and the difference of a refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 3 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 4 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 4 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 4 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 4 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 5 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 5 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 5 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 5 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 6 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 6 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 6 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is explanatory drawing which shows the relationship between the difference of the refractive index difference of the diffraction grating material in the example 6 of a combination, and the difference of refractive index, and the height of a diffraction grating. It is a schematic cross section which shows the other example of the diffractive optical element of 2nd Embodiment. It is explanatory drawing which shows the relationship between the entrance plane of the incident light to the diffraction structure in the diffractive optical element of 2nd Embodiment, and a diffraction direction. It is a graph which shows an example of the change of the diffraction efficiency by the incident angle of a diffraction structure. It is explanatory drawing which shows the relationship between the entrance plane of the incident light to the diffraction structure in the diffraction optical element of 2nd Embodiment, and a diffraction direction. It is a graph which shows an example of the change of the diffraction efficiency by the incident angle of a diffraction structure. It is a schematic cross section which shows the other example of the diffractive optical element of 2nd Embodiment. (A) And (b) is a schematic cross section which shows typically the cross section of the diffractive optical element of 3rd Embodiment. It is explanatory drawing explaining the diffraction surface formed per grating | lattice period with the diffractive optical element of 3rd Embodiment. It is a schematic cross section which shows the other example of the diffractive optical element of 3rd Embodiment. It is a graph which shows the refractive index for every wavelength of the three materials which form the diffraction grating layers 32-35 of the diffractive optical element of 3rd Embodiment. It is a graph which shows an example of the primary diffraction efficiency of the diffractive optical element of 3rd Embodiment. (A) And (b) is a schematic cross section which shows typically the example of the diffractive optical element of 4th Embodiment. It is a schematic cross section which shows typically the other example of the diffractive optical element of 4th Embodiment. It is a schematic cross section which shows typically the example of the diffractive optical element of 5th Embodiment. It is a schematic cross section which shows typically the other example of the diffractive optical element of 5th Embodiment. (A) And (b) is explanatory drawing which shows typically the cross-sectional shape of the diffraction grating part of the diffractive optical element of 6th Embodiment. Explanatory drawing which shows the example of application to the phase transfer function of the uneven structure of the diffractive optical element of 6th Embodiment. is a graph showing the relationship between the product of the height and width of the annular ring-shaped zones when changing the [rho _0. It is a schematic cross section which shows typically the cross section of the laminated diffraction grating layer part of the diffractive optical element of 7th Embodiment. It is explanatory drawing which shows typically the mode of the scattering by the reflected light of a lattice side wall. It is a graph which shows the relationship between the refractive index difference between grating | lattices, and reflection amount. (A) And (b) is explanatory drawing which shows the correction principle of the chromatic aberration using a diffractive optical element. It is explanatory drawing which shows the correction principle of the chromatic aberration using a diffractive optical element. It is a graph which shows the diffraction efficiency of the diffractive optical element of a 1st Example. It is a graph which shows the diffraction efficiency of the diffractive optical element of a 2nd Example. It is a schematic cross section which shows typically the cross section of the diffractive optical element of a 3rd Example. It is a graph which shows the diffraction efficiency of the diffractive optical element of a 3rd Example. It is explanatory drawing which shows the specific example of the material set of the diffractive optical element 20 of 2nd Embodiment. It is a typical sectional view showing the section of the diffraction optical element of the 4th example.

  Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1. FIG.
FIG. 1 is a configuration diagram showing an example of the diffractive optical element according to the first embodiment of the present invention. FIG. 1A is a schematic cross-sectional view schematically showing a cross section of the diffractive optical element 10 according to the first embodiment of the present invention. FIG. 1B is an exploded cross-sectional view of the diffractive optical element 10 shown in FIG.

  As shown in FIG. 1, the diffractive optical element 10 of the present embodiment has at least one transparent substrate 11. On the transparent substrate 11, a first diffraction grating layer 12 (hereinafter also simply referred to as “diffraction grating layer 12”) and a second diffraction grating layer 13 (hereinafter also simply referred to as “diffraction grating layer 13”). And a diffraction grating 100 is formed at least at a part of the interface between the first diffraction grating layer 12 and the second diffraction grating layer 13. That is, a part of the interface of the first diffraction grating layer 12 on the second diffraction grating layer 13 side and a part of the interface of the second diffraction grating layer 13 on the first diffraction grating layer 12 side are: A concave / convex structure that functions as one diffraction grating is formed in combination, and the two layers of the concave / convex structures 121 and 131 are laminated so as to be in close contact with each other, whereby two different layers are formed on the transparent substrate 11. A diffraction grating 100 made of a material is formed.

  The surface of the transparent substrate 11 on which such a diffraction grating layer is laminated may be a flat surface or a curved surface. That is, the diffraction grating layers 12 and 13 may be bonded and laminated on the surface of the transparent substrate 11 having a single lens shape. The first diffraction grating layer 12 may be formed with a desired concavo-convex structure 121 by, for example, an imprint method or the like. The second diffraction grating layer 13 is filled with a monomer material and cured or filled with a thermoplastic resin so as to fill the concave portion of the concave-convex structure 121 after the first diffraction grating layer 12 is formed. Alternatively, it may be formed by molding or the like and bonded and laminated. At that time, the first diffraction grating layer 12 and the second diffraction grating layer 13 are subjected to plasma treatment or coupling treatment using silane or the like. It is preferable to improve the adhesion. The transparent substrate 11 and the first diffraction grating layer 12 may be made of the same material. That is, the surface of the transparent substrate 11 can be processed to form the uneven structure 121 directly on the substrate, so that the transparent substrate 11 can also serve as the first diffraction grating layer 12. As a means for processing, if the transparent substrate 11 is glass, there are a glass mold method, cutting, dry etching method and the like, and if the transparent substrate 11 is resin, it is processed by injection molding or the like.

  Further, one transparent substrate may be provided on the opposite side of the transparent substrate 11. In other words, the diffraction grating layers 12 and 13 may be sandwiched between two transparent substrates.

  The concavo-convex structures 121 and 131 constituting the diffraction grating 100 may be, for example, a structure in which serrated concavo-convex sections are periodically arranged. In addition, on the entire element surface, one of the concave and convex structures has a shape simulating a Fresnel lens, for example, a ring zone having a sawtooth cross-sectional shape arranged in a concentric manner rotationally symmetric with respect to the optical axis. May be. FIG. 2 is a schematic top view schematically showing the shape of the diffraction grating 100 formed in the diffractive optical element 10 of the present embodiment. The grating pitch and the grating height are appropriately selected according to the function of the diffractive optical element 10 and the selected material.

  Note that the diffractive optical element 10 of this embodiment is a so-called close-contact diffractive optical element in which two optical members are combined to form one diffraction grating, and as shown in FIG. The diffractive optical element 10 can be regarded as having one diffractive surface formed by using two different materials in terms of one period of the grating (see the broken line in FIG. 3).

  In the present embodiment, two materials for forming such a diffractive surface, that is, materials for the diffraction grating layers 12 and 13, a material having a low refractive index and a large refractive index wavelength dispersion, a high refractive index, and A material having a small refractive index wavelength dispersion is used in combination. Specifically, the large / small chromatic dispersion may be considered as small / large Abbe number. That is, the highly dispersed material may be a material having a small Abbe number. The low dispersion material may be a material having a large Abbe number. Here, the high / low refractive index, or the large / small dispersion or Abbe number represents a relative relationship between the two materials. Hereinafter, as an expression representing the two materials forming the diffractive surface of the present embodiment, a material having a lower refractive index and a larger wavelength dispersion of the refractive index may be referred to as a “relatively low refractive index high dispersion material”. Further, a material having a higher refractive index and a larger wavelength dispersion of the refractive index may be referred to as a “relatively high refractive index low dispersion material”.

  FIG. 4 is a graph showing an example of the refractive index for each wavelength of the two materials 1 and 2 used for the diffraction grating layers 12 and 13. It should be noted that which diffraction grating layer the materials 1 and 2 are used in is arbitrary. That is, the material 1 may be used as the material of the diffraction grating layer 12, the material 2 may be used as the material of the diffraction grating layer 13, the material 2 may be used as the material of the diffraction grating layer 12, and the material 1 may be used as the material of the diffraction grating layer 13. It may be used as a material.

  In the example shown in FIG. 4, it can be seen that the material 1 has a lower refractive index than the material 2 and is a highly dispersed material. On the other hand, it can be seen that the material 2 has a higher refractive index than the material 1 and is a low dispersion material. Examples of materials having such characteristics include, for example, relatively high refractive index and low dispersion materials, zirconia composite materials using a resin containing a cyclo ring, adamantane, and cyclopentanyl group as a matrix, resins containing sulfur, optical A glass material is mentioned. For example, as a relatively low refractive index and high dispersion material, an organic material containing many double bonds, a material containing a phenyl group, a biphenyl group, a terphenyl group, a fluorene skeleton, or a material containing a fluoro group and a phenyl group And composite materials using titania fine particles and barium titanate fine particles. These special optical materials have high refractive index and high Abbe number, and low refractive index and low Abbe number in consideration of durability, so the optical characteristics of the element can be freely controlled. it can.

  Here, the diffraction efficiency of the diffractive optical element 10 of the present embodiment will be described. The diffraction efficiency of a so-called two-layer close-contact laminated type optical diffraction element as in this embodiment is obtained by multiplying the difference Δn between the refractive indexes of two materials used for the diffraction grating by the height d of the diffraction grating. The condition where the value obtained by dividing the wavelength λ of the light is an integer, that is, the condition where Δnd / λ = m (m is an integer other than 0) is the highest. In order to obtain high diffraction efficiency over the entire region of the visible light band (for example, blue 430 nm to red 660 nm), Δnd / λ may be approximately m (for example, within m ± 0.1) in those regions. . However, if Δn does not change with respect to the wavelength, even if the above condition can be satisfied at a certain wavelength, Δnd / λ becomes a value other than m at other wavelengths. Then, the diffraction efficiency decreases in those wavelength bands.

  Therefore, in order to change Δn with respect to the wavelength, in the present embodiment, the diffraction grating 100 is formed by combining a material having a high refractive index and low dispersion and a material having a low refractive index and high dispersion. By doing this, Δn can be increased as the wavelength becomes longer, so that the change in refractive index with respect to the wavelength of both materials can be canceled and Δnd / λ can be made around m over the entire visible light region. As a result, the diffraction efficiency can be increased over the entire visible light band.

  The value of m is preferably ± 1, because the height of the diffraction grating can be lowered, manufacturing becomes easy, and the incident angle dependency tends to be small, and good characteristics are easily obtained. However, even when the value of m is other than ± 1, when the diffraction grating functions as a condensing lens or a diverging lens and the number of lenses of the optical system is reduced or the total length of the optical system is reduced, m≈ ± 1. On the other hand, since the state of occurrence of flare changes, a more optimal state may be obtained depending on the optical system. Therefore, it is preferable to select the best value of m. If | m | is too large, the lattice height will be too large, making it difficult to produce or flaring easily. Therefore, | m | ≦ 5 is preferable.

  FIG. 5A is a graph showing an example of the first-order diffraction efficiency of the diffraction grating 100 manufactured by combining the materials 1 and 2 shown in FIG. FIG. 5B is a graph showing the diffraction efficiency of the diffraction grating when a diffraction grating having the same shape as that of the diffraction grating 100 manufactured using only quartz glass is formed. However, the grating height in these examples is 12.8 μm in the diffraction grating 100 of the present embodiment, and 1.1 μm in the diffraction grating using only quartz glass. In the present invention, the grating height, that is, the height of the diffraction grating, refers to a height with respect to an average direction distribution in which e-ray light travels. As shown in FIG. 5B, the diffraction efficiency of a diffraction grating manufactured using only quartz glass, that is, having a diffraction surface made of quartz glass and air, varies depending on the wavelength in the entire visible light band. You can see that it is very different. On the other hand, the diffraction grating 100 of the present embodiment shown in FIG. 5A satisfies the above-described selection conditions for the materials of the diffraction grating layers 11 and 12, and peaks at wavelengths of 430 nm and 650 nm. It can be seen that the diffraction efficiency of 95% or more can be maintained in the entire band.

  Further, when selecting the material of the diffraction grating layers 11 and 12, flare can be produced in the imaging optical system by selecting a material having a high environmental durability such as temperature, high durability against sunlight, or a material having a low haze value. A diffractive optical element that can be more effectively suppressed and can withstand practical use can be manufactured.

  For example, as a relatively high refractive index and low dispersion material, a resin material containing a halogen-based element such as sulfur can be cited, and these are often colored. For this reason, the subject that it was weak to yellowing with respect to an ultraviolet-ray or a heat | fever, and a temperature fluctuation occurred. Moreover, since the composite material has a large haze, there is a problem that it is not suitable for an imaging optical system. Therefore, in consideration of such a large haze problem, for example, using a composite material of zirconia fine particles having an average particle size of 3 nm to 20 nm coated with a silane coupling agent and an organic acid having a carboxylic acid group. Also good. For example, a material containing the above zirconia fine particles using a material containing a cyclo ring, particularly an adamantyl group, a dicyclopentanyl group, or a phenyl group in the matrix material in an amount of 80 vol% or more may be used.

  In addition, as a relatively low refractive index and high dispersion material, for example, it has been proposed to use fine particles such as titania in a fluororesin, but the fine particles such as titania are stably mixed in a water- and oil-repellent fluororesin. It's pretty difficult. Similarly, there is a problem that even when another monomer material is mixed with the fluororesin, the refractive index varies greatly with temperature change due to the separation or characteristics of the fluororesin having a low glass transition point. In addition, a resin material containing many double bonds has been proposed, but there was a problem in yellowing with respect to ultraviolet rays and heat. Therefore, in consideration of such difficulty in production and problems with refractive index fluctuation and transparency with respect to temperature change, for example, a monomer having a fluoro group and a phenyl group having a carbon chain of 2 or more and 6 or less, in particular, A monomer having 11 to 21 carbon atoms may be used. With such a monomer, since it has a low refractive index and a low Abbe number, it is likely to be a relatively low refractive index and high dispersion material, and it is easy to mix with other resins, and the refractive index temperature fluctuation is suppressed, A resin that is excellent in transparency and resistant to yellowing can be obtained. For example, the same problem can be solved by using an organic-inorganic hybrid material containing a phenyl group or a biphenyl group. The organic-inorganic hybrid material containing a phenyl group or a biphenyl group may be, for example, a resin in which one or more phenyl groups or biphenyl groups are bonded together with Si atoms.

  Further, when the application of the diffractive optical element 10 of the present embodiment is limited to the imaging optical system, the following conditions more suitable than the conditions based on the difference in refractive index and Abbe number or main dispersion are used. It is preferable to select a material for forming the diffraction grating.

  In the calculation of the diffraction efficiency, when only the difference between the refractive index and the main dispersion is considered, the diffraction efficiency may decrease in the green to yellow wavelength band, or the diffraction efficiency may decrease in the wavelength band of 430 nm or less.

  When the inventor of the present invention selects a material based on the following conditions instead of the main dispersion and the Abbe number, as a diffractive lens more suitable for the imaging optical system, over a wide range (400 nm to 700 nm) including the visible light band, It was discovered that high diffraction efficiency (specifically, 90% or more) can be maintained.

  The main dispersion used to calculate the Abbe number is obtained using the refractive indexes of the F-line and C-line of the Fraunhofer line, which are considered based on the sensitivity of the human eye. For this reason, an optimum result may not be obtained when applied to an imaging optical system as it is. For example, the sensitivity of an image sensor such as a CMOS extends to a wavelength that is shorter than the human eye to recognize as blue. If material selection is performed by ignoring this difference in sensitivity and taking into consideration only the refractive index difference and the main dispersion, the diffraction efficiency tends to decrease in the wavelength band of 430 nm or less, and the light that has not reached the desired diffraction order is blue. Since it occurs as flare, the image quality is adversely affected. In addition, since the diffraction efficiency from green to yellow decreases, it is recognized as a flare of green or red, which also adversely affects the image quality. Therefore, when used in an imaging optical system, it is more preferable to use the following conditions as the optical characteristics of the two materials to be combined.

Conditional expression (A):
−0.13 ≦ Δ (ng−nC) +0.506 (Δng) ≦ 0.16

Conditional expression (B):
−1.1 <Δ (ng−nC) / (Δne) ^1/2 <0.27

  Here, ng represents the refractive index of g-line (wavelength 435.84 nm). NC represents the refractive index of C-line (wavelength 656.27 nm). Ne represents the refractive index of e-line (wavelength 546.07 nm). Δ represents the difference between the material 1 and the material 2 indicated by the following symbols. For example, Δ (ng−nC) represents a difference between the ng−nC value of the material 1 and the ng−nC value of the material 2.

  Conditional expression (A) is a condition for suppressing a decrease in diffraction efficiency in a wavelength band of 430 nm or less, and condition (B) is a condition in which the diffraction efficiency is decreased in a green to yellow wavelength band. This is a condition for deterrence. Conditional expressions (A) and (B) can be used as independent conditions depending on the purpose. That is, only one of them may be satisfied.

  FIG. 6 is an explanatory diagram for explaining conditional expressions (A) and (B), and is a graph showing an example of optical characteristics of two materials to be combined. In FIG. 6, the alternate long and short dash line indicates the difference in refractive index between the two members near the g line, and the alternate long and two short dashes line indicates the difference in refractive index between the two members near the C line. Moreover, the dotted line has shown the inclination with respect to the wavelength of the difference of the refractive index of each material's g line and C line.

  An image sensor that normally uses a color filter captures light from about 400 nm that is cut as ultraviolet light to about 700 nm that is blocked by a blue filter. For this reason, if both the diffraction efficiencies in the vicinity of the g-line and C-line (for example, about 436 nm and 656 nm) are set to be high, diffraction is not only performed in the blue and red wavelengths but also in the green to yellow wavelength band. It is possible to prevent the efficiency from decreasing.

Here, the condition that the diffraction efficiency near the g-line and the C-line is high is that the refractive index of the diffraction grating layer 12 is n ₁₂ , the refractive index of the diffraction grating layer 13 is n ₁₃ , and the g of the diffraction grating layer 12 is g. If the refractive index of the line is expressed as n12g, the refractive index of the C line is expressed as n12C, and the diffraction grating layer 13 is also expressed in the same manner, it can be expressed by the following formula (1).

_{(N 12 g-n 13 g} ) /435.84= (n 12 C-n 13 C) /656.27 ··· Equation (1)

From equation (1), the left side is summarized as the refractive index difference ratio term, the right side is summarized as the wavelength ratio term, both sides are multiplied by -1, and 1 is added.
_{1- (n 12 C-n 13} C) / (n 12 g-n 13 g) = 1-656.27 / 435.84
And further organizing
_{((N 12 g-n 12} C) - (n 13 g-n 13 C)) / (n 12 g-n 13 g) ≒ -0.506
It becomes.

Here, the following equation (2) is defined.
_{R = ((n 12 g-} n 12 C) - (n 13 g-n 13 C)) + 0.506 × (n 12 g-n 13 g) ··· Equation (2)

  FIG. 7 is a graph showing a correlation between the value R, the efficiency value on the minimum side of the g line and the C line. Conditional expression (A) can be derived from the results shown in FIG. That is, if −0.13 <R <0.16, the minimum value of the diffraction efficiency of the g-line and C-line is preferably 95% or more. In addition, if -0.1 <R <0.12, the minimum value of the diffraction efficiency of g-line and C-line is 97% or more, which is more preferable. Further, if -0.07 <R <0.08, the minimum value of the diffraction efficiency of g-line and C-line is 99% or more, which is more preferable. As described above, the allowable range of the condition (B) may be changed according to the desired diffraction efficiency of the g-line and C-line.

  On the other hand, in order to obtain a high diffraction efficiency over the entire visible light having a diffraction efficiency, it is also important that the diffraction efficiency of the e-line does not decrease, which tends to decrease.

  In the present invention, the value P of the following formula (3) is defined. As shown in FIG. 6, the smaller the value P, the more concave the refractive index curve in the green region (see the graph curve of Material 1).

P = (ne−nC) / (ng−nC) (3)

  In order to obtain a high diffraction efficiency over the entire visible light having a diffraction efficiency, it is important that the diffraction efficiency of the e-line does not decrease, which is likely to decrease. However, when the diffraction grating 100 of this embodiment is formed of a transparent material that does not absorb the entire visible light band, the optical path difference of the e-line is likely to be larger than the optical path difference of the C-line or the g-line, and is likely to be larger than 1. For this reason, the diffraction efficiency tends to decrease. Therefore, the lower the value P, the better the material with a low refractive index, and the higher the value P, the better the material with a high refractive index.

  Further, the inventor of the present invention uses the difference value between the value P of the material 1 and the value P of the material 2, the value Q of the square root quotient of the refractive index difference between the materials 1 and 2, and the diffraction formed by using the material. It has been found that there is a dependency on the diffraction efficiency of the e-line of the grating 100. Here, the following equation (4) is defined.

Q = ΔP / (Δne) ^1/2 Formula (4)

  FIG. 8 is a graph showing the relationship between the value Q of a certain material set and the e-line diffraction efficiency of the diffraction grating 100 formed using the material when the condition (a) is satisfied. When the grating height is determined so that the diffraction efficiency of g-line and C-line is high so that diffraction is performed in a visible light broadband using a relatively high refractive index low dispersion material and a relatively low refractive index high dispersion material In addition, as shown in FIG. 8, it has been found that the value Q of the above-described formula (4) shows a relationship that does not depend much on the difference in the refractive index of the material forming the grating and also depends on the diffraction efficiency well.

  The condition (B) can be derived from the result shown in FIG. That is, if -1.1 <Q <0.27, the line efficiency of the e line is preferably 95% or more. If -0.9 <Q <0.15, the line efficiency of the e-line is 97% or more, which is more preferable. If -0.7 <Q <0.06, the line efficiency of the e line is 99% or more, which is more preferable. Thus, the allowable range of the condition (B) may be changed according to the desired line efficiency of the e line.

  As shown in the equation (2), if the difference between the slope of the material 1 representing dispersion and the slope of the material 2 (both are shown by dotted lines in FIG. 6) is large, the refraction of the diffraction grating layer 12 and the diffraction grating layer 13 is increased. The rate difference can be increased. Therefore, the greater the difference in dispersion, the lower the grating height of the diffraction grating, which facilitates the manufacture and reduces the incidence angle dependency of the diffraction efficiency, which is preferable.

  By maintaining such a relationship in the combination of the materials of the diffraction grating layers 12 and 13, it is possible to effectively act on the broadband efficiency of diffraction efficiency.

  As described above, the flare can be effectively reduced by selecting a material that satisfies the various conditions described above in terms of the refractive index difference and dispersion characteristics of the material set as a combination of materials used as the two-layer close-contact laminated diffraction grating. Can be suppressed.

  In addition, when the diffractive optical element 10 of this embodiment is incorporated in an imaging optical system, a change in diffraction efficiency due to incident angle dependency may be a problem. When the diffractive optical element 10 is incorporated in the imaging optical system, it is conceivable that light enters the diffractive optical element 10 from various incident angles. Although it is known that the diffraction efficiency of the diffraction grating changes depending on the incident angle, the change in efficiency can be suppressed by reducing the aspect ratio of the diffraction grating 100. Therefore, the diffraction grating 100 of the present embodiment preferably has a grating height of 20 μm or less, and more preferably 15 μm or less.

  FIG. 9 is a schematic cross-sectional view showing another example of the diffractive optical element 10 of the first embodiment. For example, consider a diffractive optical element 10 in which diffraction grating layers 12 and 13 are stacked on a single-lens transparent substrate 11 shown in FIG. 9 so that the diffraction grating functions as a hybrid lens having positive power.

  If the transparent substrate 11 has a convex shape as shown in FIG. 9, a high refractive index and low dispersion material is used for the first diffraction grating layer 12 located in the first layer when viewed from the transparent substrate 11 side. When a low refractive index and high dispersion material is used for the second diffraction grating layer 13 positioned, the direction of the grating side wall can be tilted from the optical axis direction to the outer peripheral side. Therefore, the diffraction grating layer 12 is formed using an imprint process. When it does, there exists a merit which becomes easy to release from a type | mold and becomes easy to form an optimal lattice shape. When the power direction of the diffraction grating is negative, on the contrary, a low refractive index and high dispersion material may be used for the first diffraction grating layer 12.

  Further, if the transparent substrate 11 is concave and the power of the diffraction grating is positive, it is better to imprint a low refractive index and high dispersion material as the first diffraction grating layer 12, and the power of the diffraction grating should be negative. For example, a high refractive index and low dispersion material is preferably imprinted as the first diffraction grating layer 12.

  In other words, it is more preferable that the material of each diffraction grating layer is arranged so that the curvature direction of the lens surface to be laminated and the direction of the slope of the saw of the diffraction grating have the same inclination with respect to the lens surface. .

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described. FIG. 10 is a configuration diagram showing an example of a diffractive optical element according to the second embodiment of the present invention. FIG. 10A is a schematic cross-sectional view schematically showing a cross section of the diffractive optical element 20 of the second embodiment. FIG. 10B is an exploded cross-sectional view of the diffractive optical element 20 shown in FIG.

  As shown in FIG. 10, the diffractive optical element 20 of the present embodiment has at least one transparent substrate 21, and a first diffraction grating layer 22 (hereinafter simply referred to as “diffraction grating layer 22”) on the transparent substrate 21. And a second diffraction grating layer 23 (hereinafter also simply referred to as “diffraction grating layer 23”) and a third diffraction grating layer 24 (hereinafter also simply referred to as “diffraction grating layer 24”). The diffraction grating 201 is formed at least at a part of the interface between the first diffraction grating layer 22 and the second diffraction grating layer 23, and the second diffraction grating layer 23 and the third diffraction grating layer 24 are formed. A diffraction grating 202 is formed on at least a part of the interface. That is, a part of the interface of the first diffraction grating layer 22 on the second diffraction grating layer 23 side and a part of the interface of the second diffraction grating layer 23 on the first diffraction grating layer 22 side are: In combination, a concavo-convex structure that acts as one diffraction grating is formed, and the concavo-convex structures 221 and 231 of these two layers are laminated so as to be in close contact with each other, and the second diffraction grating layer 23 has a second structure. The third diffraction grating layer 24 side interface part and the third diffraction grating layer 24 side interface part of the second diffraction grating layer 23 side are combined to act as one diffraction grating. Two concavo-convex structures are formed, and two concavo-convex structures 232 and 241 of these two layers are laminated so as to be in close contact with each other. The diffraction gratings 201 and 202 are It has been made. Note that the diffraction gratings 201 and 202 have substantially the same grating pitch. Note that the lattice height may be different. Here, substantially the same lattice pitch means that the pitch difference is ± 2%.

  Also in the present embodiment, the surface of the transparent substrate 21 on which the diffraction grating layer is laminated may be a flat surface or a curved surface. The transparent substrate 21 and the first diffraction grating layer 22 may be made of the same material. Further, one transparent substrate may be provided on the opposite side of the transparent substrate 21. That is, a configuration in which the diffraction grating layers 22, 23, and 24 are sandwiched between two transparent substrates may be employed.

  Note that the diffractive optical element 20 of the present embodiment is a so-called three-layer close-contact diffractive optical element in which three different optical members are combined to form a total of two diffraction gratings, as shown in FIG. The diffractive optical element 20 of the present embodiment can be regarded as having two diffractive surfaces formed using three types of optical member layers in terms of one grating period (see the broken line in FIG. 11).

  It is preferable that the three materials forming the two diffractive surfaces, that is, the materials of the diffraction grating layers 22, 23, and 24 match any of the six combinations shown in FIG. 12. That is, if the three materials used for the diffraction grating layers 22, 23, and 24 are materials 3, 4, and 5, combination example 1) Material 3 is a low refractive index and low dispersion material, and Material 4 is a high refractive index and low dispersion material. Material 5 is a high refractive index high dispersion material or combination example 2) Material 3 is a medium refractive index high dispersion material, Material 4 is a high refractive index high dispersion material, and Material 5 is high refractive. Example 3) Material 3 is a low refractive index, high dispersion material, Material 4 is a high refractive index, high dispersion material, and Material 5 is a high refractive index, low dispersion material, or a combination Example 4) The material 3 is a medium refractive index high dispersion material, the material 4 is a material having a low refractive index to a medium refractive index, and the material 5 is a high refractive index low dispersion material. High refractive index high dispersion material, material 4 is a low refractive index to medium refractive index material, Whether a high refractive index and low dispersion material, a combination example 6) material 3 is the medium refractive index material, the material 4 is a medium refractive index and high dispersion material, the material 5 is a high refractive index and low dispersion material. Here, the first layer material in FIG. 12 is described as material 3, the second layer material is material 4, and the third layer material is material 5.

  In the above combination, a high refractive index material is used if the d-line refractive index is greater than 1.59, a low refractive index material is used if the refractive index is less than 1.51, and a medium refractive index material therebetween. In the case of a low refractive index material, a high dispersion material is used when the Abbe number is 50 or less, and a low dispersion material is used when the Abbe number is 60 or more. In the case of a medium refractive index material, if the Abbe number is 40 or less, it is a high dispersion material, and if it is 50 or more, it is a low dispersion material. In the case of a high refractive index material, if the Abbe number is 30 or less, it is a high dispersion material, and if it is 40 or more, it is a low dispersion material. In the above combination, when the material is simply a low refractive index material, it means a material that is a low refractive index material and may be either low dispersion or high dispersion. Similarly, a medium refractive index material means a medium refractive index material that may be either low dispersion or high dispersion. Furthermore, in the case of a high refractive index material, it means a material that is a high refractive index material and may be either low dispersion or high dispersion.

  FIG. 13 is a graph showing an example of the refractive index for each wavelength of the three materials 3, 4 and 5 used for the diffraction grating layers 22, 23 and 24. In addition, as long as the relationship between the refractive index difference and the chromatic dispersion described above can be held by two diffraction surfaces, it is arbitrary for which diffraction grating layer the materials 3 to 5 are used. For example, in the example shown in FIG. 13, the material 3 may be used for the diffraction grating layer 24, the material 4 may be used for the diffraction grating layer 23, and the material 5 may be used for the diffraction grating layer 22. Further, for example, the material 3 may be used for the diffraction grating layer 22, the material 4 may be used for the diffraction grating layer 23, and the material 5 may be used for the diffraction grating layer 24.

  As an optical material enabling such a combination, for example, as a high refractive index and low dispersion material, a zirconia composite material or optical glass having a cyclo ring, an adamantyl group or a dicyclopentanyl group as a matrix as described above. Etc. Examples of the medium refractive index low dispersion material include the zirconia composite material, a resin material containing an adamantyl group and a dicyclopentanyl group, and optical glass. Examples of the low refractive index and low dispersion material include hydrocarbon materials and optical glass that do not have a double bond other than a polymer group. In addition, for example, as a high refractive index and high dispersion material, a resin material obtained by curing a monomer in which phenyl or biphenyl is bonded to an Si atom, a resin material containing many benzene rings such as fluorene or terphenyl, a double bond, or a triple bond. Resin materials having a structure containing a large amount of. In addition, for example, as a medium refractive index high dispersion material, as already described, an organic-inorganic hybrid material obtained by curing a monomer in which phenyl or biphenyl is bonded to an Si atom, or a resin material such as a polycarbonate having many double bonds Etc. Further, for example, as a low refractive index and high dispersion material, a material containing a fluoro group and a phenyl group can be mentioned, and in particular, when a material containing a fluoro group and a phenyl group is used in the same monomer, a material having a high refractive index is used. It is preferable because it is easy to mix with. By appropriately selecting and combining these optical materials, the optical characteristics of the element can be freely controlled.

  The diffractive optical element 20 of this embodiment is intended to have the same function as the diffraction grating of the diffractive optical element 10 of the first embodiment by combining two diffraction gratings. Therefore, as described in the first embodiment, the basic principle of making the value of Δnd / λ closer to an integer value in the element remains unchanged. However, since the number of materials to be combined is increased, it is easier to adjust so that the value of Δnd / λ can take a value closer to a single integer value as compared with the first embodiment. For example, it is assumed that the diffraction grating 100 of the first embodiment is not a single diffraction grating, but two diffraction gratings of the material 1 and the material 2 having the same height are bonded together, and the diffraction gratings of the materials 3 and 4 are combined. Alternatively, the diffraction grating similar to that of the material 2 may be formed, and the diffraction grating similar to that of the material 1 may be formed by bonding the diffraction gratings of the materials 4 and 5 together. Then, in this embodiment, since the height can be changed with two types of diffraction gratings, the range of material selection can be expanded. As an example, the relationship between the refractive index and the dispersion of the material 2 in the first embodiment for the material 1 is replaced with the material 3 and the material 4, and the relationship between the refractive index and the dispersion of the material 1 in the first embodiment for the material 2 is replaced with the material 4. The material 5 may be designed to be replaced.

  For example, many transparent optical materials have a tendency that the Abbe number decreases as the refractive index increases. In other words, the main dispersion tends to increase as the refractive index increases. According to the configuration of the present embodiment, even if the diffraction grating is formed using a combination in which the main dispersion increases as the refractive index increases, the same or better effect as the first embodiment can be obtained.

  FIG. 14 is a graph showing an example of the first-order diffraction efficiency of the entire diffractive optical element 20 of this embodiment manufactured by combining the materials 3, 4, and 5 shown in FIG. In the graph shown in FIG. 14, the diffraction grating layer 22 made of the material 5 and the diffraction grating layer 23 made of the material 4 form a diffraction grating 201 having a height of 9.8 μm, and the diffraction grating layer 23 made of the material 4 and the material 3 This is an example in which a diffraction grating 202 having a height of 6.9 μm is formed with the diffraction grating layer 24 according to FIG. In the example shown in FIG. 14, not only can the diffraction efficiency of 95% or more be maintained in the entire visible light band with the wavelengths of 400 nm and 600 nm as peaks, but also the line efficiency can be improved in a wavelength region other than the peak such as the green to yellow wavelength band. It can be seen that the decrease is small and the high value is maintained over the entire visible light band.

  In the example of combination shown in FIG. 12, the material of each diffraction grating layer is defined as the first layer, the second layer, and the third layer as viewed from the transparent substrate 21 in the stacking order. Is not necessarily limited to this.

  Further, as a feature of the combination example illustrated in FIG. 12, for example, in the combination examples 1, 2, and 3, the difference in refractive index between the first layer and the second layer is large to some extent (for example, 0.04 or more). When a material having similar dispersion characteristics is selected, the third layer has a refractive index close to that of the higher refractive index of those materials, and the refraction of the first and second layers. The difference in refractive index between the second layer and the third layer is smaller than the difference in the refractive index, and the dispersion characteristics are different from those of these materials. In this case, if the wavelength band where the refractive index difference between the second layer and the third layer is the smallest is near green, the diffraction grating formed by the first layer and the second layer and the second and third layers are formed. In some cases, it is easy to suppress the influence of the positional deviation in the pitch direction and the incident angle dependency of the diffraction grating.

  In Example 1, the first layer and the second layer are both low-dispersion materials, and the third layer is a material having a higher refractive index among the materials of the first and second layers. This is an example of a highly dispersed material having a refractive index slightly higher than that of the eye. In Example 2, both the first layer and the second layer are highly dispersed materials, and the third layer is a material having a higher refractive index among the materials of the first layer and the second layer. This is an example of a low dispersion material having a slightly higher refractive index than the eye. In Example 3, the first layer and the second layer are both highly dispersed materials, and the third layer is a two-layer material having a higher refractive index among the first and second layer materials. This is an example of a low dispersion material having a refractive index slightly lower than that of the eye.

  In this way, in the combination of materials forming each diffraction grating, when the difference in refractive index between the materials is large, those having close wavelength dispersion (for example, a combination of a low dispersion material and a low dispersion material or a high dispersion material) When the difference in refractive index between the materials is small, the three materials are combined so that the chromatic dispersions are separated (for example, a low dispersion material and a high dispersion material). It is preferable to select. In the above example, if the combination of the low refractive index material and the high refractive index material or the combination of the medium refractive index material and the high refractive index material, the difference in refractive index between the materials is large, and the low refractive index material and If the combination is a low refractive index material or a combination of a high refractive index material and a high refractive index material, the refractive index difference between the materials is assumed to be small, but the criteria for determining whether the refractive index difference is large or small is not limited to this. . For example, in this embodiment, the difference between the refractive indices of the d-lines of the two materials is 0.04 or more, and the difference may be small if it is less than 0.04.

  In addition, when the pitch is reduced or the incident angle on the diffraction grating is increased, the height of the convex portion of the concavo-convex structure, that is, the grating height is not excessively increased in order to prevent a decrease in diffraction efficiency. It is preferable. More specifically, the grating height of the diffraction grating 201 is preferably 20 μm or less, and more preferably 15 μm or less. Hereinafter, as a condition for the refractive index, a range in which the grating height of the diffraction grating 201 is 20 μm or less and a range in which the grating height is 15 μm or less are shown. In the following, when the concave and convex height signs in the drawings to be described are the same, the convex and concave portions of the concave and convex structure are arranged so as to overlap (see FIG. 15A). And the concave are opposed to each other (see FIG. 15B), and the lattice height indicates a condition that the absolute value is within the above range. FIG. 15A is an explanatory diagram illustrating an example in which the height directions of two diffraction gratings are opposite, and FIG. 15B illustrates an example in which the height directions of two diffraction gratings are the same. It is explanatory drawing.

In the following description, the refractive index of the g-line of the first layer material is ng ₁ , the refractive index of the g-line of the second layer material is ng ₂ , and the refractive index of the g-line of the third layer material is ng _3. Yes. The refractive index of the e-line of the first layer material is ne ₁ , the refractive index of the e-line of the second layer material is ne ₂ , and the refractive index of the e-line of the third layer material is ne ₃ . The refractive index of the C-line of the first layer material is nC ₁ , the refractive index of the C-line of the second layer material is nC ₂ , and the refractive index of the C-line of the third layer material is nC ₃ . Also, the difference in refractive index between the first layer and the second layer e-line (ne ₁ -ne ₂ ) is Δne _12, and the difference in refractive index between the second layer and the third layer e-line (ne ₂ -ne _3). ) As Δne ₂₃ . Further, the difference in refractive index between the g-line and C-line of the first layer material and the difference in refractive index between the g-line and C-line of the second layer material {(ng ₁ −nC ₁ ) − (ng ₂ − nC ₂ )} is Δ (ng−nC) ₁₂ and the difference in refractive index between the g-line and C-line of the second layer material and the difference in refractive index between the g-line and C-line of the third layer material { (Ng ₂ −nC ₂ ) − (ng ₃ −nC ₃ )} is represented by Δ (ng−nC) ₂₃ .

  At this time, the first layer material shown in FIG. 12 is the material of the diffraction grating layer 22, the second layer material is the material of the diffraction grating layer 23, and the third layer material is the material of the diffraction grating layer 24.

  Here, the following formulas (5) to (9) are defined. In addition, A, B, C, D, and E in the following formulas (5) to (9) are lattices obtained when specific values and ranges of the above combination examples 1 to 6 are calculated. This is an empirical parameter when a value correlated with height is estimated.

  That is, when these parameters A, B, C, D, and E are set to predetermined values, it has been empirically found that the correlation with the lattice height can be obtained.

  First, it shows about the correlation with the value of the above-mentioned formula (5)-(9) by the material set which satisfies combination example 1, and the height of a diffraction grating. FIG. 15 shows a correlation between the value of Expression (5) and the height of the concavo-convex structure of the diffraction grating 201 when A = 5.5 is used using the material set that satisfies the combination example 1. FIG. 17 shows the correlation between the value of equation (9) and the height of the concavo-convex structure of the diffraction grating 201 when E = 0.5 is used for the material set that satisfies the combination example 1. From FIG. 15, it is found that if the value of formula (5) <0.65, the height of the concavo-convex structure of the diffraction grating 201, that is, the grating height is sufficiently 15 μm or less, and FIG. If the value of> 0.94, the height of the concavo-convex structure of the diffraction grating 201, that is, the grating height is sufficiently 15 μm or less. FIG. 18 shows the correlation between the value of Expression (7) and the height of the concavo-convex structure of the diffraction grating 202 when C = −1.5 using a material set satisfying the combination example 1. FIG. 19 shows the correlation between the value of equation (8) and the height of the concavo-convex structure of the diffraction grating 202 when D = 0.7 using a material set satisfying the combination example 1. As shown in FIG. 18, the height of the concavo-convex structure of the diffraction grating 202, that is, the grating height is 20 μm or less except for 0 <value of Formula (7) <1.5, and 15 μm or less is 0 < It can be seen that the value of formula (7) is other than <1.7. Further, from FIG. 19, the height of the concavo-convex structure of the diffraction grating 202, that is, the grating height is 20 μm or less because the value of Expression (8) <1.55, and 15 μm or less is the expression (8 ) Value <1.51.

  Next, the correlation between the values of the above formulas (5) to (9) and the height of the diffraction grating by the material set satisfying the combination example 2 will be described. FIG. 20 shows the correlation between the value of the equation (5) and the height of the concavo-convex structure of the diffraction grating 201 when A = 5.5, where a material set satisfying the combination example 2 is used. FIG. 21 shows the correlation between the value of equation (6) when B = 1.2 and the height of the concavo-convex structure of the diffraction grating 201. From FIG. 20, the height of the concavo-convex structure of the diffraction grating 201, that is, the grating height is 20 μm or less because the value of Equation (5) <0.85, and 15 μm or less is that of Equation (5). It can be seen that the value <0.78. Further, from FIG. 21, the height of the concavo-convex structure of the diffraction grating 201, that is, the grating height is 20 μm or less because the value of the expression (6) <0.99, and 15 μm or less is the expression (6 ) Value <0.975. FIG. 22 shows the correlation between the value of equation (7) and the height of the concavo-convex structure of the diffraction grating 202 when C = −1.3. 22A is an explanatory diagram showing a correlation with the height of the concavo-convex structure of the diffraction grating 202 in the range of the value of the expression (7) from −2 to 2, and FIG. It is explanatory drawing which shows the correlation with the height of the uneven | corrugated structure of the diffraction grating 202, enlarging and the value of Formula (7) in the range of 1.5-2.1. FIG. 23 shows the correlation between the value of equation (6) and the height of the concavo-convex structure of the diffraction grating 202 when B = 0.29. As shown in FIG. 22, the height of the concavo-convex structure of the diffraction grating 202, that is, the grating height is 20 μm or less except for 0 <value of Formula (7) <1.575, and 15 μm or less is 0 < It can be seen that the value of formula (7) is other than 1.65. Further, from FIG. 23, the height of the concavo-convex structure of the diffraction grating 202, that is, the grating height is 20 μm or less because the value of Expression (6) <0.97, and 15 μm or less is the expression (6 ) Value <0.96.

  Next, the correlation between the values of the above formulas (5) to (9) and the height of the diffraction grating by the material set satisfying the combination example 3 will be described. FIG. 24 shows the correlation between the value of the equation (5) when A = 5.5 and the height of the concavo-convex structure of the diffraction grating 201 when a material set satisfying the combination example 3 is used. FIG. 25 shows the correlation between the value of equation (6) and the height of the concavo-convex structure of the diffraction grating 202 when B = 1.2. From FIG. 24, the height of the concavo-convex structure of the diffraction grating 201, that is, the grating height is 20 μm or less because the value of Equation (5) <0.85, and 15 μm or less is that of Equation (5). It can be seen that the value <0.78. Further, FIG. 25 shows that the height of the concavo-convex structure of the diffraction grating 201, that is, the grating height is sufficiently 15 μm or less if the value of the expression (6) <1.01. FIG. 26 shows the correlation between the value of the equation (7) and the height of the concavo-convex structure of the diffraction grating 202 when C = −1.3. FIG. 26A is an explanatory diagram showing the correlation with the height of the concavo-convex structure of the diffraction grating 202 in the range where the value of the expression (7) is −2 to 2, and FIG. It is explanatory drawing which shows the correlation with the height of the uneven | corrugated structure of the diffraction grating 202, enlarging and the value of Formula (7) in the range of 1.5-2.1. FIG. 27 shows the correlation between the value of equation (6) and the height of the concavo-convex structure of the diffraction grating 202 when B = 0.29. From FIG. 26, the height of the concavo-convex structure of the diffraction grating 202, that is, the grating height is 20 μm or less except for 0 <the value of the expression (7) <1.575, and 15 μm or less is 0 < It can be seen that the value of formula (7) is other than 1.65. Further, from FIG. 27, the height of the concavo-convex structure of the diffraction grating 202, that is, the grating height is 20 μm or less because the value of Expression (6) <0.97, and 15 μm or less is the expression (6 ) Value <0.96.

  In the above combination examples 4 and 5, when a material having a small difference in refractive index (for example, less than 0.04) and a dispersive characteristic is selected as the material set of the first layer and the second layer The third layer has a higher refractive index than the higher refractive index of these materials (therefore, the difference in refractive index between the first and second layers is higher than the second and third layers). The difference in refractive index is large), and the dispersion characteristics are similar to those of those materials having a lower refractive index.

  The correlation between the values of the above-described formulas (5) to (9) and the height of the diffraction grating by the material set satisfying the combination example 4 will be described. FIG. 28 shows the correlation between the value of the equation (5) when A = 0.2 and the height of the concavo-convex structure of the diffraction grating 201 when a material set satisfying the combination example 4 is used. FIG. 29 shows the correlation between the value of equation (6) when B = 0.1 and the height of the concavo-convex structure of the diffraction grating 201. From FIG. 28, the height of the concavo-convex structure of the diffraction grating 201, that is, the grating height is 20 μm or less because the value of the formula (5) <0.97, and 15 μm or less is the formula (5). It can be seen that the value <0.965. Further, from FIG. 29, the height of the concavo-convex structure of the diffraction grating 201, that is, the grating height is 20 μm or less because the value of the expression (6) <1.017, and 15 μm or less is the expression (6 ) Value <1.015. FIG. 30 shows the correlation between the value of equation (5) and the height of the concavo-convex structure of the diffraction grating 202 when A = 0.8. Further, FIG. 31 shows the correlation between the value of equation (6) when B = 0.47 and the height of the concavo-convex structure of the diffraction grating 202. From FIG. 30, the height of the concavo-convex structure of the diffraction grating 202, that is, the grating height is 20 μm or less because the value of Expression (5) <1.045, and 15 μm or less is that of Expression (5). It can be seen that the value <1.025. Further, from FIG. 31, the height of the concavo-convex structure of the diffraction grating 202, that is, the grating height is 20 μm or less because the value of Expression (6) <0.98, and 15 μm or less is the expression (6 ) Value <0.97.

  Next, it shows about the correlation with the value of said Formula (5)-(9) by the material set which satisfy | fills the example 5 of a combination, and the height of a diffraction grating. FIG. 32 shows the correlation between the value of the equation (5) when A = 0.05 and the height of the concavo-convex structure of the diffraction grating 201 when a material set satisfying the combination example 5 is used. FIG. 33 shows the correlation between the value of equation (6) when B = 0.2 and the height of the concavo-convex structure of the diffraction grating 201. From FIG. 32, the height of the concavo-convex structure of the diffraction grating 201, that is, the grating height is 20 μm or less because the value of Equation (5) <0.975, and 15 μm or less is that of Equation (5). It can be seen that the value <0.97. Further, from FIG. 33, the height of the concavo-convex structure of the diffraction grating 201, that is, the grating height is 20 μm or less because the value of Expression (6) <1.005, and 15 μm or less is the expression (6 ) Value <1.000. FIG. 34 shows the correlation between the value of equation (5) when A = 0.3 and the height of the concavo-convex structure of the diffraction grating 202. FIG. 35 shows the correlation between the value of equation (6) and the height of the concavo-convex structure of the diffraction grating 202 when B = 0.6. From FIG. 34, the height of the concavo-convex structure of the diffraction grating 202, that is, the grating height is 20 μm or less when the equation (5) <0.99, and 15 μm or less is when the equation (5) <0. It turns out that it is 975. Further, from FIG. 35, the height of the concavo-convex structure of the diffraction grating 202, that is, the height of the grating is 20 μm or less is the formula (6) <0.965, and the height of 15 μm or less is the formula (6) < It turns out that it is 0.95.

  Further, in the above combination example 6, when a material having substantially the same refractive index and different dispersion characteristics is selected as the material set of the first layer and the second layer, the second layer is made a highly dispersed material, and 3 The layer is made of a material having a refractive index higher than that of the material of the second layer and having a dispersive characteristic.

  The correlation between the values of the above formulas (5) to (9) and the height of the diffraction grating by the material set satisfying such combination example 6 will be described. FIG. 36 shows the correlation between the value of Expression (5) and the height of the concavo-convex structure of the diffraction grating 201 when A = 0.6 is used in the case where a material set satisfying the combination example 6 is used. FIG. 37 shows the correlation between the value of equation (8) when D = −2.0 and the height of the concavo-convex structure of the diffraction grating 201. From FIG. 36, the height of the concavo-convex structure of the diffraction grating 201, that is, the grating height is 20 to 15 μm or less when the value of Equation (5) <1.00 or the value of Equation (5)> 1.01. I know that there is. Also, from FIG. 37, the height of the concavo-convex structure of the diffraction grating 201, that is, the grating height is 20 μm or less because 1.77> the value of formula (8)> 1.49, and 15 μm or less. It can be seen that 1.75> value of formula (8)> 1.52. FIG. 38 shows the correlation between the value of the equation (7) when C = −5.0 and the height of the concavo-convex structure of the diffraction grating 202. Further, FIG. 39 shows the correlation between the value of Expression (9) when E = 4.0 and the height of the concavo-convex structure of the diffraction grating 202. From FIG. 38, the height of the concavo-convex structure of the diffraction grating 202, that is, the grating height is sufficiently 20 μm or less if the value of formula (7) <2.15, and 15 μm or less. It can be seen that the value of <1.95. Further, from FIG. 39, the height of the concavo-convex structure of the diffraction grating 202, that is, the grating height is 20 μm or less because the value of the expression (9)> 1.125, and 15 μm or less is the expression (9 ) Value> 1.15.

  Further, in the configuration of the present embodiment, since the diffraction efficiency of the green region is likely to be lowered, the values of the expressions (10) and (11) defined below may be set within a certain range.

P ′ = P + 0.167ne−0.605 Formula (10)

Q ′ = ΔP ′ / (Δne) ^1/2 Formula (11)

  When the grating heights of the diffraction grating 201 and the diffraction grating 202 are different from each other by a factor of two or more, the difference between P ′ of the relatively high dispersion material and the low dispersion material in the second layer and the third layer is If it is 0.055 or less, a diffraction efficiency of 98% is preferable, and if it is 0.015 or less, a diffraction efficiency of 99% is obtained. In combination example 3, if it is 0.045 or less, 98% diffraction efficiency is preferable, and if it is 0.01 or less, 99% diffraction efficiency is obtained, it is more preferable. In combination example 6, if it is 0.065 or less, the diffraction efficiency is preferably 98%, and if it is 0.028 or less, the diffraction efficiency is 99%, more preferably.

  Further, when the grating heights of the diffraction grating 201 and the diffraction grating 202 are less than twice, the difference between P ′ of the relatively high dispersion material and the low dispersion material and the refraction of the e-line in the first and third layers. If the square root quotient value Q ′ of the rate difference is less than 0.3, the diffraction efficiency in the green region is preferably 98%, and if it is less than 0.1, the diffraction efficiency in the green region is 99% or more, more preferably.

  In this way, if the combination of the three materials is adjusted appropriately, the aspect ratio of the diffraction grating can be reduced without excessively increasing the height of the diffraction grating. A lattice is obtained.

  By the way, in this embodiment, it is preferable to consider the incident angle dependence relationship when determining the arrangement order of materials.

  Hereinafter, the incident angle dependency and the arrangement order of materials in the present embodiment will be described. Hereinafter, the diffractive optical element 20 that functions as a hybrid lens having a positive power by stacking the diffraction grating layers 22, 23, and 24 on the single-lens transparent substrate 21 as shown in FIG. 40 will be described as an example. To do.

  FIG. 41 is an explanatory diagram showing the relationship between the incident surface of incident light on the diffractive structure and the diffraction direction in the diffractive optical element 20 shown in FIG. FIG. 41 shows the diffraction direction when light is incident from the upper layer side of the laminated diffraction grating layer, that is, the diffraction grating layer 24 side.

  As shown in FIG. 41, when the lines connecting the bottoms of the diffraction gratings in the diffractive optical element 20 are 81 and 82, respectively, these two lines are assumed to be parallel to each other. Hereinafter, for convenience, the line connected in the diffraction grating layer 24 is denoted by 81, and the line connected in the diffraction grating layer 22 is denoted by 82. Then, the angle α formed by the normal line 81 on the side close to the incident light beam and the incident light beam becomes the incident angle to the diffraction structure. The incident angle is positive on the optical axis side from the normal direction. Now, it is assumed that the incident light beam 38 is incident from the line 81 side in relation to the normal line 84. At this time, the incident direction is positive, and the diffraction direction is a direction (direction shown in the figure) diffracted to the optical axis side from the imaginary line obtained by extending the incident light beam.

  FIG. 42 is a graph showing an example of the change in diffraction efficiency depending on the incident angle of the diffractive structure shown in FIG. As shown in FIG. 42, in the diffractive structure having the shape and diffraction direction as shown in FIG. 41, when oblique incidence occurs, the change in diffraction efficiency differs between the case where the incident angle is positive and the case where the incident angle is negative. I understand. In the example shown in FIG. 42, it can be seen that if the incident angle is positive, the incident angle dependency is weaker than that in the negative case.

  Next, let us consider that light is incident from the lower layer side of the laminated diffraction grating layer, that is, the diffraction grating layer 22 side as shown in FIG. FIG. 43 is an explanatory diagram showing the relationship between the incident surface of incident light on the diffractive structure in the diffractive optical element 20 shown in FIG. 40 and the diffraction direction. Also in the example shown in FIG. 43, among the lines connecting the bottoms of the diffraction gratings in the diffractive optical element 20, 81 is connected to the diffraction grating layer 24, and 82 is connected to the diffraction grating layer 22. It is assumed that the two lines 81 and 82 are parallel to each other. Then, an angle α formed by the normal of the line 82 closer to the incident light beam and the incident light beam becomes the incident angle to the diffractive structure. Now, it is assumed that the incident light beam 83 is incident from the side of the line 82 with respect to the normal line 84. At this time, since the incident direction is opposite to the optical axis side, it is negative, and the diffraction direction is a direction (direction shown in the figure) diffracted to the optical axis side from the imaginary line obtained by extending the incident light beam.

  FIG. 44 is a graph showing an example of a change in diffraction efficiency depending on the incident angle of the diffraction structure shown in FIG. 43 by the material set corresponding to any one of the above-described combination examples 1, 2, and 3. When the material set corresponding to the above combination examples 1, 2, and 3 is used, as shown in FIG. 44, when the diffractive structure having the shape and the diffraction direction shown in FIG. It can be seen that the change in diffraction efficiency differs between the case and the negative case. In the example shown in FIG. 44, it can be seen that if the incident angle is negative, the incident angle dependency is weaker than that in the positive case. Therefore, in this embodiment as well, it is preferable to adjust the positional relationship of the material arrangement of the diffractive structure so that the incident angle is in a direction in which the incident angle dependency is weak. Specifically, when a diffraction grating is formed on a substrate having a certain curvature, two diffraction gratings having a large optical path difference are formed when the incident light beam is diffracted to the optical axis side from the extended virtual line. Of the materials, it is preferable that a material having a small refractive index is disposed closer to the center of the radius of curvature, and when diffracting to the side opposite to the optical axis side, a material having a higher refractive index is closer to the center of the radius of curvature. It is preferable to arrange on the side.

  For example, in the case of the structure and application as shown in FIG. 41, for two diffraction gratings 201 and 202, the optical path difference between the deepest part and the shallowest part of the unevenness in one period of the diffraction grating is compared. Is preferably located on the exit side. That is, the optical path difference obtained by multiplying the refractive index of the material of the diffraction grating layer 22 forming the diffraction grating 201 and the material of the diffraction grating layer 23 by the height of the unevenness, and the material of the diffraction grating layer 23 forming the diffraction grating 202 When the refractive index of the material of the diffraction grating layer 24 is multiplied by the unevenness height and compared with the optical path difference obtained by taking the difference, the material of the diffraction grating layer 22 forming the diffraction grating 201 located on the output side and the diffraction grating are compared. The optical path difference formed by the material of the layer 23 is larger than the optical path difference formed by the material of the diffraction grating layer 23 forming the diffraction grating 202 located on the incident side and the material of the diffraction grating layer 24. It is preferable that each material is disposed on the surface.

  Further, for example, in the case of the structure and application shown in FIG. 43, the same optical path difference is compared between the two diffraction gratings 201 and 202, and the diffraction grating having a large optical path difference of the grating material is positioned on the incident side. It is preferable. That is, the optical path difference obtained by multiplying the refractive index of the material of the diffraction grating layer 22 forming the diffraction grating 201 and the material of the diffraction grating layer 23 by the height of the unevenness, and the material of the diffraction grating layer 23 forming the diffraction grating 202 When the refractive index of the material of the diffraction grating layer 24 is multiplied by the uneven height and compared with the optical path difference obtained by taking the difference, the material of the diffraction grating layer 22 forming the diffraction grating 201 located on the incident side and the diffraction grating The optical path difference formed by the material of the layer 23 is larger than the optical path difference formed by the material of the diffraction grating layer 23 forming the diffraction grating 202 positioned on the emission side and the material of the diffraction grating layer 24. It is preferable that each material is disposed on the surface. If the diffraction direction is reversed, this relationship may be reversed in either case.

  As the element configuration, when a diffractive structure is formed on a convex lens, a diffraction grating having a large optical path difference of the grating material may be arranged on the convex lens side, that is, closer to the transparent substrate 21. On the other hand, when forming on the concave lens, the arrangement order of the diffraction grating layers with respect to the incident direction may be reversed from that when forming on the convex lens. FIG. 45 shows an arrangement example of the diffraction grating layers 22, 23, and 24 when the diffraction grating structure of the present embodiment is formed on the concave lens. In the example shown in FIG. 45, as the magnitude relationship of the optical path difference of the materials of the diffraction gratings 201 and 202 laminated on the transparent substrate 21, the diffraction grating 202 positioned on the outer side, that is, on the side farther from the transparent substrate 21, Each material is preferably arranged so that the optical path difference is larger than that of the diffraction grating 201 located on the concave lens side, that is, on the side closer to the transparent substrate 21.

  The example of the combination of materials shown in FIG. 12 is an example of a preferable combination of materials for each layer in the configuration in which the diffractive structure of the present invention is incorporated in a convex lens having a positive power as shown in FIG. Therefore, it is preferable to change the arrangement of the combination of these materials depending on how the incident light is inclined with respect to the diffraction direction of the diffraction grating.

  As described above, since it is possible to arbitrarily adopt an optimum structure depending on the shape of the surface forming the diffractive structure and the angular distribution of incident light, it is possible to further suppress deterioration of diffraction efficiency due to the incident angle dependency.

  As described above, flare can be effectively suppressed by selecting materials having a refractive index difference and dispersion characteristics satisfying predetermined conditions in a combination of materials used as a three-layer close-contact laminated diffraction grating. In addition, according to the present embodiment, it is possible to obtain an effect equal to or greater than that of the first embodiment while expanding the selectivity of the material.

Embodiment 3. FIG.
Next, a third embodiment of the present invention will be described. FIG. 46 is a configuration diagram showing an example of a diffractive optical element according to the third embodiment of the present invention. FIG. 46A is a schematic cross-sectional view schematically showing a cross section of the diffractive optical element of the third embodiment. FIG. 46B is an exploded cross-sectional view of the diffractive optical element 30 shown in FIG.

  As shown in FIG. 46, the diffractive optical element 30 of this embodiment has at least one transparent substrate 31, and a first diffraction grating layer 32 (hereinafter simply referred to as “diffraction grating layer 32”) is formed on the transparent substrate 31. ), The second diffraction grating layer 33 (hereinafter also simply referred to as “diffraction grating layer 33”), the third diffraction grating layer 34 (hereinafter also simply referred to as “diffraction grating layer 34”), and the fourth. A diffraction grating layer 35 (hereinafter also simply referred to as “diffraction grating layer 35”) is laminated, and the diffraction grating 301 is formed at least at a part of the interface between the first diffraction grating layer 32 and the second diffraction grating layer 33. The diffraction grating 302 is formed on at least a part of the interface between the third diffraction grating layer 34 and the fourth diffraction grating layer 35. That is, a part of the interface of the first diffraction grating layer 32 on the second diffraction grating layer 33 side and a part of the interface of the second diffraction grating layer 33 on the first diffraction grating layer 32 side are: In combination, a concavo-convex structure that functions as one diffraction grating is formed, and the concavo-convex structures 321 and 331 of these two layers are stacked so as to be in close contact with each other, and the third diffraction grating layer 34 has a first structure. A part of the interface of the fourth diffraction grating layer 35 side and a part of the interface of the fourth diffraction grating layer 35 on the third diffraction grating layer 34 side are combined to act as one diffraction grating. The two concavo-convex structures are formed, and the concavo-convex structures 341 and 351 of these two layers are laminated so as to be in close contact with each other, thereby forming a combination of four different materials on the transparent substrate 31. Two diffraction gratings 301 and 302 It has been made. Also in this embodiment, the diffraction gratings 301 and 302 have substantially the same grating pitch. The substantially identical lattice pitch means that the pitch difference is within ± 2%. Note that the lattice height may be different.

  Also in this embodiment, the surface of the transparent substrate 31 on which the diffraction grating layer is laminated may be a flat surface or a curved surface. The transparent substrate 31 and the first diffraction grating layer 32 may be made of the same material. Further, one transparent substrate may be provided on the opposite side of the transparent substrate 31. In other words, the diffraction grating layers 32, 33, 34, and 35 may be sandwiched between two transparent substrates.

  Note that the diffractive optical element 30 of the present embodiment is a so-called four-layer close-contact diffractive optical element in which two different optical members are combined to form a total of two diffraction gratings, as shown in FIG. In addition, the diffractive optical element 30 of this embodiment can be regarded as having two diffractive surfaces formed by using four types of optical member layers in terms of one period of the grating (see the broken line in FIG. 47). .

  The four materials forming the two diffractive surfaces, that is, the materials of the diffraction grating layers 32, 33, 34, and 35 may be selected based on the same conditions as in the second embodiment. That is, in the combination of diffraction gratings forming one diffraction surface, the relative relationship between the refractive indices of the diffraction grating layers 32 and 33 and the relative refractive index of the materials of the diffraction grating layers 22 and 23 of the second embodiment. And the relative relationship between the refractive indexes of the diffraction grating layers 34 and 35 and the relative relationship between the refractive indexes of the materials of the diffraction grating layer 23 and the diffraction grating layer 24 of the second embodiment are the same. If it is. For example, since the above-described equations (5) to (9) are all defined by the difference in refractive index between adjacent materials forming the diffraction grating, they can be applied to this structure as they are. That is, the material of the second layer of the second embodiment may be considered separately as the 2-1st layer and the 2-2nd layer.

  In this embodiment, in order to further improve the wavelength dependence while satisfying such conditions, the advantages of the four-layer structure are utilized, the refractive index is almost the same, and the partial dispersion ratios are different in any combination. You may use the material which has.

  For example, when the diffractive optical element 20 shown in FIG. 40 is manufactured, when the diffraction grating layer 22, the diffraction grating layer 23, and the diffraction grating layer 24 are stacked, the side wall of the diffraction grating 202 faces inward. Considering that the process of releasing the mold becomes difficult when imprinting the diffraction grating layer 24 because of the structure, it is conceivable that the shape of the grating is broken from the ideal shape. In such a case, for example, the structure shown in FIG. 48 is used, and the diffraction grating layer 32 is made of the same material as that of the diffraction grating layer 22, and the diffraction grating layer 33 is made of the same material as that of the diffraction grating layer 23. 34 is made of the same material as that of the diffraction grating layer 24, the diffraction grating layer 35 is made of the same material as that of the diffraction grating layer 23, and the concavo-convex direction of the concavo-convex structure formed by the diffraction grating layers 23 and 24 is set to the diffraction grating layer 34 and the diffraction grating. By reversing the concavo-convex direction of the concavo-convex structure formed by the layer 35, the same diffraction efficiency can be obtained, the mold can be easily released, and an ideal shape can be easily created.

  FIG. 49 is a graph showing an example of the refractive index for each wavelength of the four materials 6, 7, 8, and 9 forming the diffraction grating layers 32, 33, 34, and 35. If the two diffraction gratings 301 and 302 can be configured to have the same operation as that of the diffraction gratings 201 and 202 of the second embodiment manufactured using the material set shown in FIG. Which diffraction grating layer is used is arbitrary. That is, when the second layer material of the second embodiment is divided into a 2-1 layer and a 2-2 layer and the relationship between the refractive index difference and wavelength dispersion in FIG. It is only necessary that the relationship between the material sets constituting the lattice satisfies at least the relationship shown in FIG. For example, in the example shown in FIG. 49, the material 6 is used for the diffraction grating layer 35, the material 7 is used for the diffraction grating layer 34, the material 8 is used for the diffraction grating layer 33, and the material 9 is used for the diffraction grating layer 32. Also good. Further, for example, the material 6 may be used for the diffraction grating layer 32, the material 7 may be used for the diffraction grating layer 33, the material 8 may be used for the diffraction grating layer 34, and the material 9 may be used for the diffraction grating layer 35. In the present embodiment, the incident angle dependency can be suppressed based on the same principle as in the second embodiment.

  The example shown in FIG. 49 is an example in which the materials 6 and 7 are one combination and have close chromatic dispersion. Further, the materials 8 and 9 are another combination, and are examples in which the wavelength dispersion is separated. In addition, the materials 6 and 8 have substantially the same refractive index and seem to be very close to the main dispersion, but it can be seen that the partial dispersion ratios are different. Such materials are used in combination with different grating heights to reduce the wavelength dependence of diffraction efficiency.

  FIG. 50 is a graph showing an example of the first-order diffraction efficiency of the diffractive optical element 30 of this embodiment, which is manufactured by combining the materials 6 to 9 shown in FIG. In the diffractive optical element 30 of this embodiment shown in FIG. 50, the diffraction grating layer 32 made of the material 9 and the diffraction grating layer 33 made of the material 8 form a diffraction grating 301 having a height of 12.9 μm, and the material 7 This is an example in which a diffraction grating 302 having a height of 7.4 μm is formed by the diffraction grating layer 34 and the diffraction grating layer 35 made of the material 6. As shown in FIG. 50, it can be seen that a diffraction efficiency of 99% or more can be maintained in the entire visible light band.

  As described above, according to the present embodiment, there are more options because only the relative relationship between the materials needs to be considered. Further, by increasing the choice of materials, even parameters that are difficult to change with the same refractive index, such as a partial dispersion ratio, can be used as design parameters. As an example of the method of selection, two types of materials that have significantly different partial dispersion ratios (for example, 0.02 or more) are picked up, and the two types of materials are respectively selected from the second embodiment. Materials that meet similar combination conditions may be selected. If the materials that can be selected are the same as those in the first embodiment and the second embodiment, the wavelength dependence of the visible light band can be made equal to or less than that.

Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described. The present embodiment is a configuration in which the shape of the surface of the diffraction grating layer forming each diffraction grating is an aspherical surface in the configuration of each of the above embodiments. In the case of producing a laminated diffraction grating, it is known that the aberration of the entire optical system can be suppressed by making the surface shape of the transparent substrate, on which the diffraction grating is laminated, an aspherical surface instead of a spherical surface. However, it is difficult to process a lens such as glass into an aspherical surface, which increases the cost.

  Therefore, in this embodiment, an optical system in which aberration is suppressed can be obtained at low cost by using an aspherical resin material that is easy to control the shape. Specifically, the shape of the surface on the side where the diffraction grating of the resin forming the diffraction grating is not present and not in contact with the transparent substrate may be an aspherical surface. Further, for example, a curve formed by the diffraction grating layer and connecting the apexes of the diffraction grating closest to the transparent substrate 11 (in this example, the apex in each blazed structure) may be an aspherical surface.

  FIG. 51A is a schematic cross-sectional view schematically showing an example of the diffractive optical element of this embodiment. FIG. 51 (b) is an explanatory diagram showing only the diffraction grating surface of the portion surrounded by the broken line in FIG. 51 (a) in an enlarged manner. The example shown in FIG. 51 is an example in which the constituent elements of this embodiment are applied to the diffractive optical element 10 of the first embodiment. On the transparent substrate 11, the concavo-convex structure 121 is provided on one surface. And a second diffraction grating layer 13 having a concavo-convex structure 131 on one surface are stacked in close contact with each other with the concavo-convex structure facing each other. In this example, a curved surface (see a broken line 122 in FIG. 51B) formed by the diffraction grating layer 12 and the diffraction grating layer 13 and connecting the vertex of the diffraction grating closest to the single-lens transparent substrate 11 is used. It is aspherical.

  With such a configuration, it is possible to add an aspherical surface capable of effectively removing aberrations simultaneously with chromatic aberration.

  FIG. 52 is a schematic cross-sectional view schematically showing another example of the diffractive optical element of the present embodiment. The example shown in FIG. 52 is an example in which the constituent elements of this embodiment are applied to the diffractive optical element 10 of the first embodiment. On the transparent substrate 11, an uneven structure (diffractive surface on one surface) is shown. ) 121 and the second diffraction grating layer 13 having a concavo-convex structure (diffraction surface) 131 on one surface are laminated with the diffraction surfaces in close contact with each other. In this example, the surface 132 which is the surface of the outermost layer among the laminated diffraction grating layers 12 is an aspherical surface.

  With such a configuration, an aspherical surface capable of effectively removing aberrations can be added simultaneously with chromatic aberration by a resin imprint method. Therefore, in addition to the aberration reduction effect, there is an advantage that the number of lenses of the optical system can be reduced.

  51 and 52 show an example in which the present embodiment is applied to the configuration of the first embodiment, the present embodiment is similar to the configurations of the second and third embodiments. It is applicable to.

Embodiment 5. FIG.
Next, a fifth embodiment of the present invention will be described. In this embodiment, in the configuration of each of the embodiments described above, a thin film is interposed between the transparent substrate and the diffraction grating layer and / or between the diffraction grating layer and the diffraction grating layer, so that a silane coupling agent or the like Increases the effect of coupling treatment by improving the adhesion, suppressing the reflection that occurs due to the difference in the refractive index of the transparent substrate and the diffraction grating layer, and the diffraction grating layer and the diffraction grating layer, the generation of flare Suppress.

  The diffractive optical element 10 shown in FIG. 53 is an example in which the coupling process is performed with the thin film 14 interposed between the transparent substrate 11 and the diffraction grating layer 12 in the configuration of the first embodiment. As shown in FIG. 53, in this embodiment, after processing the transparent substrate 11 into a desired shape, the thin film 14 made of silica or the like is formed on the transparent substrate 11. Thereafter, the thin film 14 formed on the transparent substrate 11 is subjected to coupling treatment using silane or the like, and the diffraction grating layer 12 is formed on the thin film 14.

  Further, the diffractive optical element 10 shown in FIG. 54 is an example in which the coupling process is performed with the thin film 14 interposed between the diffraction grating layers 12 and 13 in the configuration of the first embodiment. Note that the present invention may be implemented by combining the example of FIG. 53 and the example of FIG.

  In the example shown in FIG. 54, in a state where the diffraction grating layer 12 is formed on the transparent substrate 11, a thin film 14 made of silica or the like is used on the diffraction grating layer 12 by sputtering, vapor deposition, CVD, or the like. create. Thereafter, the thin film 14 formed on the diffraction grating layer 12 is subjected to a coupling treatment using silane or the like, and then the diffraction grating layer 13 is formed on the thin film 14. The thickness of the thin film 14 is preferably about 5 nm to 100 nm.

  Thus, by performing the coupling process with the thin film 14 interposed between the substrate and the diffraction grating layer or between each diffraction grating layer, the durability due to the improved adhesion can be improved. In addition, the occurrence of scattering due to peeling of the interface can be suppressed. Note that the same effect can be obtained at the interface of the substrate even when a coupling process is performed on the interface between the diffraction grating layer and the substrate.

  Further, an antireflection film can be formed by adjusting the refractive index, thickness, and film configuration of the thin film 14 to form a single layer film or a multilayer film. In such a case, it is possible to suppress not only the surface on which most of the light beams forming the diffraction grating are incident, but also the reflection of the side surfaces of the unevenness having an angle close to perpendicular. In order to effectively form an antireflection film on the side surface of the diffraction grating layer constituting the diffraction grating, a sputtering method using CVD or ion assist is used, and the diffraction grating is defined by the effective area of the image sensor. The film thickness and refractive index may be determined so that the reflectance at the average incident angle of light incident from an external incident angle becomes smaller than the effective angle of view, and the film is configured. In the case of a single layer film, reflection can be effectively suppressed over a wide wavelength range by forming a film having a refractive index between the refractive indexes of the materials forming the interface. In addition, flare generated by optimizing film thickness and refractive index to the average value of the position where the light source that exists outside the angle of view that causes flare is assumed is effective for both single layer films and multilayer films Can be suppressed. If the thickness of the thin film (more specifically, the antireflection film) between the diffraction grating layers constituting the diffraction grating is 1 μm or less, it substantially acts as a diffraction grating by a combination of diffraction grating layers.

  In the above description, the case where the thin film according to the present embodiment is generated in the configuration of the first embodiment and applied to the suppression of flare caused by the coupling process or the diffraction grating is described as an example. The thin film 14 can be applied to any of the above embodiments.

Embodiment 6. FIG.
Next, a sixth embodiment of the present invention will be described. In the configuration of each of the above embodiments, the present embodiment is configured to suppress the occurrence of unevenness due to resin shrinkage by devising a method for determining the constant term of the phase transfer function of the diffraction grating. FIG. 55 is an explanatory view schematically showing the cross-sectional shape of the diffraction grating portion of the diffractive optical element of this embodiment, as compared with a conventional diffractive lens.

  For example, when forming a diffractive lens, there may be a diffractive structure having a very large pitch near the center of the lens. Then, similar unevenness was generated on the surface of the resin in which the diffraction grating was buried due to the shrinkage of the resin, which sometimes caused deterioration of aberration and diffraction efficiency (see FIG. 55A). In the present embodiment, in consideration of such a case, the above problem is solved by changing the shape without changing the optical characteristics.

  FIG. 55B is an explanatory diagram schematically showing the determination result of the constant term of the phase transfer function in the diffractive optical element of the present embodiment. As a representation of the phase wavefront formed by the diffractive lens, consider the following phase transfer function (Equation (12)).

φ (rad) = ρ ₀ + Σρ _n r ²ⁿ Formula (12)

This term of ρ ₀ is set so that the aspect ratio of the unevenness at the center portion is lowered. Specifically, as shown in FIG. 56, the width of each ring zone is defined as P _n (n is 1 for the ring zone at the center of the optical axis, and the outer ring width is larger for each period of unevenness with respect to the diameter direction of the diffraction grating. integer value as a to.), when the height d _n of zones, set as the maximum value of the product (P _n × d _n) becomes smaller. By setting in this way, the influence of the contraction of the diffraction grating layer 13 on the aberration and diffraction efficiency is reduced.

Here, it is assumed that the diffractive lens has a function of only a condensing effect with a focal length of 1000 mm. At this time, P ₁ = −7.85. It should be noted that the coefficient of _{P 2} or later is 0. The phase transfer function for the for the differential value becomes monotonous behavior, think the maximum value of the product of the width P _n of the height d _n and each ring-shaped zone of the annular zone at that time, zonal central portion 2 Think of a ring zone. In general, it is only necessary to consider an annular zone with a differential value near 0 and an adjacent annular zone. FIG. 57 shows the relationship between the product of the height of the annular zone and the width of the annular zone when ρ ₀ is changed.

In the example shown in FIG. 57, if ρ ₀ = −2.5, the maximum value of the product of the width and height of each annular zone is minimized. In the case of this example, it was confirmed that the deviation of the aberration from the design value was suppressed in the range of −1.75 to −3.25. From the above, it is considered that an error of about ± 30% is recognized with respect to the value of ρ ₀ where the maximum value of the product of the width and height of each annular zone is minimized.

In the example shown in FIG. 56, the method for determining the constant term of the phase transfer function for one diffraction grating is shown as an example in the case of applying to the first embodiment, but a plurality of diffraction gratings are stacked. Also in the second and third embodiments, the occurrence of irregularities due to shrinkage on the surface of the resin filling the diffraction grating in the manufacturing process can cause deterioration of aberration and diffraction efficiency. It is preferable to set ρ _{0 of the} phase transfer function so that the aspect ratio of the unevenness in the central portion is lowered by the method.

Embodiment 7. FIG.
Next, a seventh embodiment of the present invention will be described. This embodiment is a configuration in which the same structure as the diffraction grating is created outside the effective region in the configuration of each of the above embodiments.

  FIG. 58 is a schematic cross-sectional view schematically showing a cross section of the laminated diffraction grating layer portion of the diffractive optical element of this embodiment. For example, in the configuration in which the diffraction grating layer is laminated only in the effective region, when any one of the diffraction grating layers is made of a resin that is a suitable material, the outer diameter of the effective diameter or the outer diameter of the effective diameter is different due to the difference in the shrinkage amount of the resin. It was found that abnormalities such as voids due to wrinkles, peeling, and insufficient filling resin occurred on the resin, and the light incident on the site where the abnormality occurred was reflected or scattered, causing flare. Therefore, as shown in FIG. 58, the resin layer is formed so as to extend to the end of the transparent substrate that becomes the base on which the diffraction grating layers are stacked. Further, at that time, it is more preferable to form a dummy concavo-convex structure at the end portion so that a large difference in the shrinkage amount of the resin does not occur depending on the region. That is, it is preferable that the two resin layers are laminated to form an uneven shape.

  As a result, it is possible to prevent the occurrence of abnormalities such as voids due to wrinkles and peeling on the resin and insufficient filling resin. It is preferable that the concavo-convex structure provided outside the effective region has a pitch equal to or greater than the minimum pitch within the effective diameter. For example, when the diffractive optical element of the present invention is realized as a diffractive lens whose shape is similar to a Fresnel lens, when the outermost grating pitch within the effective diameter of the Fresnel lens is px, the filling factor is outside the effective diameter of the Fresnel lens. May form a lattice structure having a lattice pitch of 2 px to 0.5 px with 0.35 to 0.65. In addition, outside the effective diameter, in order to facilitate manufacture, an uneven structure in which the lattice pitch increases toward the outer periphery may be used. In addition, in the terminal part, it may not have an uneven structure, for example, the structure by which the resin film only by one type of material may be formed may be sufficient. In addition, the area | region covered with a resin layer should just contain at least the outside of an effective diameter, and does not necessarily need to cover all the surfaces of a board | substrate. For example, it is not necessary to include a region used as a fitting portion with the support portion when incorporated in the optical system.

Embodiment 8. FIG.
Next, an eighth embodiment of the present invention will be described. In this embodiment, in the configuration of each of the above embodiments, in order to suppress the generation of scattered light due to the light reflected on the side wall of the diffraction grating when light enters the diffraction structure, the refraction of the material forming the diffraction structure The difference in rate was determined.

  FIG. 59 is an explanatory diagram schematically showing how light is reflected by the grating side walls. FIG. 59 schematically shows the state of scattering by the reflected light on the grating side walls. As shown in FIG. 59, when light is reflected on the grating side wall, large scattered light is generated depending on the angle. For example, light outside the effective angle of view may enter the image sensor and cause flare. In particular, the image quality deteriorated during backlighting.

  At this time, when the difference in the refractive index of the material for which the diffractive structure was created and the amount of scattered light generated at the reflected angle were measured, a tendency as shown in FIG. 60 was obtained.

  The area of the side wall portion can be reduced by increasing the refractive index difference between the gratings. However, if the refractive index difference is large, the reflectivity increases accordingly, and as a result, the amount of reflection is increased as shown in FIG. As a result of examination, it was found that the amount of reflection at the side wall tends to increase as a function close to the square of the refractive index.

  In the present embodiment, in addition to the configuration of each of the above embodiments, the refractive index difference between the gratings is set to 0.15 or less, so that the reflectance generally equal to the target reflectance of the antireflection film is achieved. The reflected light at a certain vertical incidence is 0.5% or less, and the reflectance of the reflected light reflected from the grating side walls by light outside the angle of view is also reduced, so that the occurrence of flare is suppressed.

  However, if the difference in refractive index is made too small, the height of the diffraction grating increases, and the diffraction efficiency tends to deteriorate. For this reason, in the configuration of the first embodiment, the difference in refractive index between the materials constituting the diffraction grating is more preferably in the range of 0.02 to 0.15, and the configurations of the second and third embodiments. Then, it is preferable that it is 0.15 or less between the materials which comprise each diffraction grating. In addition, even if the refractive index difference between the materials which form a diffraction grating and comprise a diffraction grating is in the said range, it is possible to interpose a thin film for a coupling process. Even in such a case, if the thickness of the thin film is 100 nm or less, or if it is an antireflection film, the reflectance is not greatly changed.

Embodiment 9. FIG.
Next, a ninth embodiment of the present invention will be described. In this embodiment, an example in which the diffractive optical element according to the present invention is incorporated in an imaging optical system will be described. 61 and 62 are explanatory views for explaining the principle of correcting chromatic aberration using a diffractive optical element.

  As with the refractive lens 90 shown in FIG. 61A, in a normal refractive convex lens, chromatic aberration occurs due to the wavelength dependence of the refractive index. That is, the condensing position varies depending on the wavelength, and images are formed in the order of blue, green, and red wavelengths. On the other hand, if the diffractive optical element 10 shown in FIG. 61B is configured so that the diffraction direction has a positive power, it can form an image in the order of the wavelengths of red, green, and blue. Then, as shown in FIG. 62, the imaging optical system 1000 is configured by combining the refractive optical lens 90 shown in FIG. 61A and the diffractive optical element 10 shown in FIG. It is possible to eliminate chromatic aberration.

  As described above, when the refraction direction of the combined lens system has a positive power, the chromatic aberration tends to be blue <green <red in order of increasing focal length. In contrast, in order to develop an achromatic effect, a diffractive optical element having a positive power in the diffraction direction may be combined. That is, when the diffraction direction of the diffractive optical element has a positive power, the focal position is red <green <blue, so that chromatic aberration can be corrected efficiently.

  On the contrary, when the refraction direction of the lens system to be combined has negative power, chromatic aberration can be efficiently corrected by combining diffractive optical elements having negative power in the diffraction direction. In the imaging optical system according to the present invention, it is assumed that the chromatic aberration of the refractive lens coincides with the chromatic aberration of the diffractive optical element. For example, in the case of a normal refractive optical lens, the imaging position is not evenly divided with respect to the wavelength, but in a diffractive optical element, it is equally divided. Therefore, the chromatic aberration generated in the refractive optical lens may be designed to be equally divided although it has a reverse tendency with respect to the wavelength. The correction amount of chromatic aberration can be adjusted by the grating pitch.

  The imaging optical system may include a plurality of lenses. Moreover, you may provide an image pick-up element like CCD and CMOS. The chromatic aberration generated by the lens system included in these imaging optical systems may be designed so as to cancel each other when finally combined with the diffraction grating.

  In the example shown in FIG. 62, the example in which the flat diffractive optical element 10 is incorporated in the existing optical system is shown. In addition to this, a diffractive structure is put in the lens of the existing optical system, It is also possible to incorporate the diffractive optical element 10 acting as a hybrid lens into the optical system. This can be created by forming the transparent substrate of the diffractive optical element into a lens shape. In addition, even if it is the structure which pinches | interposes a diffraction grating layer in a lens, the structure which laminates | stacks a diffraction grating layer on the surface of a lens may be sufficient. Such a diffractive optical element 10 can be obtained by processing the transparent substrate of the diffractive optical element 10 into a shape that functions as one of lenses of an existing optical system.

  When a diffraction grating is formed in or on the lens, the lens power and the power of the diffraction grating are set to the same sign, and the pitch of the diffraction grating is adjusted to give characteristics similar to those of an anomalous dispersion material lens. It is also possible. In this case, an expensive anomalous dispersion material lens can be replaced with a diffractive lens, and a similar optical system can be constructed at low cost. In addition, an optical system having the same concept as the conventional design can be used, and a lens system using a diffraction element can be easily designed.

  61 to 62 show an example in which the diffractive optical element 10 of the first embodiment is incorporated into an imaging optical system, the diffractive optical element may be any of the above embodiments. Moreover, as an imaging optical system incorporating a diffractive optical element, for example, a compact digital camera, a small camera for a mobile phone or a smartphone, a surveillance camera, an endoscope, an image sensor, and the like are conceivable.

  As described above, a diffractive optical element that can be manufactured using a material that can be put to practical use as described in each embodiment and that can maintain a high diffraction efficiency of the designed order over a wide range in the visible light region is used in the imaging optical system. By incorporating, flare can be effectively suppressed in the imaging optical system. In addition, since it can be replaced with a lens made of an anomalous dispersion material, the conventional design concept can be used, and a configuration with equivalent performance can be obtained at a low cost without using an expensive anomalous dispersion material.

  Hereinafter, examples of the present embodiment will be described using specific numerical values and the like. The first example is an example of the first embodiment, and the diffractive optical element 10 in which the surface of the transparent substrate 11 on which the diffraction grating layer as shown in FIG. 9 is laminated is a curved surface will be described. . In the diffractive optical element 10 of this example, first, a glass substrate is processed into a desired shape (in this example, a single lens shape) to obtain a spherical single lens 11 having an effective diameter of 10 mm.

  Next, a coupling process is performed on the surface of the single lens 11 with a silane coupling agent for improving the adhesion with the diffraction grating layer 12 to be laminated in the next step.

  Next, the first resin material, which is the material of the diffraction grating layer 12, is laminated on the single lens 11 while transferring a desired shape using the optical imprint method, thereby forming the diffraction grating layer 12. The material used for the diffraction grating layer 12 is an organic-inorganic hybrid material in which a silicon atom is bonded to a biphenyl group. The acrylic monomer is cured by UV light by a photoimprint method, and the diffraction grating layer 12 and the resin are cured. Later, the optical characteristics are Abbe number = 25.1 and nd (refractive index of d-line) = 1.597. Moreover, it is a material which does not have absorption in wavelength 400nm -700nm. At this time, the diffraction grating layer 12 acts as a diffraction grating 100 on the surface thereof, that is, the surface not in contact with the single lens 11, in combination with the concavo-convex structure of the diffraction grating layer 13 to be described later. And the cross section is formed to include a blazed uneven structure.

  In addition, the concavo-convex structure 121 provided in the diffraction grating layer 12 has a diffraction grating with respect to a direction that is an average of a direction distribution in which e-ray light travels at least within an effective diameter as a diffraction lens of the diffractive optical element 10. It is formed so that the height of 100 is 12.8 μm. In this example, the concavo-convex structure 121 is patterned so that the diffraction grating 100 has a condensing effect with a focal length of 1000 mm as a diffraction lens, and the minimum pitch is about 120 μm at the outermost periphery. Further, a concavo-convex structure having a pitch of 120 μm is formed outside the effective diameter, so that the concavo-convex structure is created on the entire surface of the single lens 11.

Next, the second resin material, which is the material of the diffraction grating layer 13, is transferred onto the surface of the diffraction grating layer 12, that is, the surface not in contact with the single lens 11, using the optical imprint method. Then, the diffraction grating layer 13 is formed by laminating. The material used for the diffraction grating layer 13 is a resin in which an acrylic monomer having an adamantyl group and an organic solvent sol of ZrO ₂ fine particles are mixed, and the organic solvent removed by drying under reduced pressure is cured with an Abbe number = 44.2, nd = 1.644. Moreover, it is a material which does not have absorption in wavelength 400nm -700nm. At this time, the diffraction grating layer 13 fills at least the recesses of the concavo-convex structure 121 provided on the surface of the diffraction grating layer 12 without any gaps, and the other surface has a lens shape.

  As a result, the diffraction grating 100 constituting one diffraction surface is formed by the diffraction grating layers 12 and 13.

  Thereafter, an antireflection film is formed on the diffraction grating layer 13 and on the surface of the single lens 11 using a sputtering method, and the diffractive optical element 10 acting as a hybrid lens is obtained.

  In addition, the value of the conditional expression (A) of the material of the diffraction grating layer 12 and the material of the diffraction grating layer 13 was 0.00147, and the value of the conditional expression (B) was −0.0743.

  FIG. 63 is a graph showing the diffraction efficiency in the produced diffractive optical element 10 of this example. When the diffraction efficiency was measured, it was 99.5% at a wavelength of 455 nm, 97.5% at a wavelength of 533 nm, and 99.8% at a wavelength of 660 nm. The peaks of diffraction efficiency are at wavelengths of 440 nm and 650 nm.

  By using the diffractive optical element 10 of the present embodiment, flare due to the diffractive optical element can be more effectively suppressed in the imaging optical system. In addition, since the diffractive optical element 10 of the present embodiment does not include an air layer outside the effective diameter, reflection and scattering generated when light incident outside the effective region enters the gap and the like are sufficiently small. ing.

  When the imaging optical system was constructed and photographed using the diffractive optical element 10 of this example, there was no deterioration in resolution due to chromatic aberration, and a good image in which resolution or contrast did not deteriorate due to the occurrence of flare or the like. Is obtained. In addition, even when light from a light source outside the angle of view enters the diffractive optical element 10, a good image can be obtained in which the contrast due to the occurrence of flare does not decrease.

  The second example is an example of the second embodiment, and the diffractive optical element 20 in which the surface of the transparent substrate 11 on which the diffraction grating layer as shown in FIG. 40 is laminated is a curved surface will be described. . In the diffractive optical element 20 of this example, first, a single lens 21 and a diffraction grating layer 22 of a first resin material laminated thereon are formed by the same method as in the first example.

  In this embodiment, the uneven structure 221 provided in the diffraction grating layer 22 is formed so that the height of the diffraction grating 201 is 5.1 μm. The material used for the diffraction grating layer 22 is a resin obtained by curing an acrylic monomer whose main component is an alkyl group, and has optical properties of Abbe number = 64.0 and nd = 1.383.

Next, on the surface of the diffraction grating layer 22, that is, the surface not in contact with the single lens 21, the second resin material that is the material of the diffraction grating layer 23 is transferred using the optical imprint method. Then, the diffraction grating layer 23 is formed by laminating. The material used for the diffraction grating layer 23 was a mixture of an acrylic monomer having a dicyclopentanyl group and an organic solvent sol of ZrO ₂ fine particles, and the organic solvent removed by drying under reduced pressure was cured at the time of photoimprinting. It is a resin and has optical characteristics of Abbe number = 44.9 and nd = 1.612. At this time, the diffraction grating layer 23 fills at least the concave portion of the concave-convex structure 221 provided in the diffraction grating layer 22 without a gap, and is combined with the concave-convex structure 241 formed on the diffraction grating layer 24 on the other surface. The diffraction grating 202 is formed so as to include a concavo-convex structure 232 having a Fresnel lens shape as a whole and a blazed cross section. The concavo-convex structure 232 provided on the surface of the diffraction grating layer 23 is formed to have substantially the same grating pitch as the diffraction grating 201 formed at the interface between the diffraction grating layer 22 and the diffraction grating 23. However, the diffraction grating 202 is formed to have a height of 13.2 μm. As shown in FIG. 40, the grating height direction is formed so as to face the diffraction gratings 201 and 202, that is, in the opposite direction. At this time, the distance between the diffraction gratings 201 and 202 in the diffraction grating layer 23 is 1.0 μm.

  By filling the members of the diffraction grating layer 23 into the concave portions of the concavo-convex structure 221 provided in the diffraction grating layer 22 without gaps, first, the diffraction grating 201 constituting one diffraction surface is formed.

  Next, a desired shape is transferred onto the surface of the diffraction grating layer 23, that is, the surface not in contact with the diffraction grating layer 22, by using the third resin material, which is the material of the diffraction grating layer 24, using the optical imprint method. Then, the diffraction grating layer 24 is formed by laminating. The material used for the diffraction grating layer 24 is a resin obtained by curing a monomer having a fluorene skeleton, and has optical properties of Abbe number = 25.2 and nd = 1.616. At this time, the diffraction grating layer 24 fills at least the concave portion of the concavo-convex structure provided on the surface of the diffraction grating layer 23 without a gap, and the other surface has a lens shape.

  As a result, the diffraction grating 202 constituting one diffraction surface is formed by the diffraction grating layers 23 and 24.

  Thereafter, an antireflection film is formed on the diffraction grating layer 24 and on the surface of the single lens 21 using a sputtering method, and the diffractive optical element 20 acting as a hybrid lens is obtained. The other points, such as the height of the central portion of each diffraction grating and the provision of irregular shapes outside the effective diameter, are the same as in the first embodiment.

  In this case, the relationship between the refractive indexes of the materials satisfies the combination example 1, and the value of the equation (5) when A = 5.5 is 0.31, and the equation (E = 0.5) ( The value of 9) is 0.99. From the correlation diagrams shown in FIGS. 15 and 17, the grating height of the diffraction grating 201 is about 5 μm, which is almost equivalent to the actual shape. The value of the formula (7) when C = −1.5 is 1.8, and the value of the formula (8) when D = 0.7 is 1.49. From the correlation diagram of FIG. 18 and FIG. 19, the grating height of the diffraction grating 202 is about 13 μm, which is almost equivalent to the actual shape.

  FIG. 64 is a graph showing the diffraction efficiency in the produced diffractive optical element 20 of this example. When the diffraction efficiency was measured, it was 99.8% at a wavelength of 455 nm, 99.0% at a wavelength of 533 nm, and 99.0% at a wavelength of 660 nm. The peaks of diffraction efficiency are wavelengths 445 nm and 610 nm.

  FIG. 42 is a graph showing the change in diffraction efficiency depending on the incident angle of the diffractive structure of the diffractive optical element 20 of the present embodiment. As shown in FIG. 42, it can be seen that in this embodiment, the diffractive structure is formed so that the change in the diffraction efficiency is suppressed even when oblique incidence occurs. This is because the diffractive structure is formed so that the incident angle is positive in the relationship between the lens shape acting as a convex lens and the arrangement position of each material.

  By using the diffractive optical element 20 of the present embodiment, flare due to the diffractive optical element can be more effectively suppressed in the imaging optical system. In addition, since the diffractive optical element 20 of the present embodiment does not include an air layer outside the effective diameter, reflection and scattering generated when light incident outside the effective region enters the air gap and the like are sufficiently small. ing.

  The third example is an example of the second embodiment, and is an example in which the height directions of the diffraction gratings are aligned as shown in FIG. FIG. 65 is a schematic cross-sectional view schematically showing a cross section of the diffractive optical element 20 of the present embodiment. As shown in FIG. 65, the configuration of the diffractive optical element 20 of this embodiment is basically the same as that of the second embodiment. However, in the second embodiment, the inclination direction of the hypotenuse of the diffraction grating is set so that the diffraction grating 201 and the diffraction grating 202 face each other. However, in this embodiment, the inclination directions are aligned. .

  In the diffractive optical element 20 of the present embodiment, first, a single lens 21 and a diffraction grating layer 22 of a first resin material laminated thereon are formed by the same method as in the second embodiment. In this embodiment, the concavo-convex structure 221 provided in the diffraction grating layer 22 is formed so that the height of the diffraction grating 201 is 10.2 μm.

  Next, the diffraction grating layer 23 is formed on the surface of the diffraction grating layer 22, that is, on the surface not in contact with the single lens 21 by the same method as in the second embodiment. In this embodiment, the concavo-convex structure 232 provided in the diffraction grating layer 23 is formed to have substantially the same grating pitch as the concavo-convex structure 221 provided in the diffraction grating layer 22. However, the diffraction grating 202 is formed to have a height of 14.5 μm. As shown in FIG. 65, the grating height direction is formed so as to be aligned with the diffraction gratings 201 and 202. In other words, the diffraction grating 201 and the diffraction grating 202 are formed so that the inclination directions of the oblique sides of the diffraction grating are aligned.

  Next, the diffraction grating layer 24 is formed on the surface of the diffraction grating layer 23, that is, on the surface not in contact with the diffraction grating layer 22 by the same method as in the second embodiment.

  Thereafter, an antireflection film is formed on the diffraction grating layer 24 and on the surface of the single lens 21 to obtain the diffractive optical element 20 acting as a hybrid lens.

  The material used for the diffraction grating layer 22 of the diffractive optical element 20 of this example is a resin obtained by curing an acrylic monomer containing a biphenyl group and a silicon atom in the same molecule, and has an Abbe number = 23.3 and nd = 1. .624 with optical properties. Moreover, it is a material which does not have absorption in wavelength 400nm -700nm.

  The material used for the diffraction grating layer 23 is a resin obtained by curing a mixture of an acrylic monomer containing a phenyl group and a silicon atom and an acrylic monomer containing an adamantyl group, and the Abbe number = 43.1, nd = 1. 546 optical properties. Moreover, it is a material which does not have absorption in wavelength 400nm -700nm.

The material used for the diffraction grating layer 24 is a resin obtained by mixing an acrylic monomer having an adamantyl group and an organic solvent sol of ZrO ₂ fine particles, and curing the organic solvent removed by drying under reduced pressure. The optical characteristics are Abbe number = 44.0, nd = 1.463. Moreover, it is a material which does not have absorption in wavelength 400nm -700nm.

  The relationship between the refractive indexes of the materials at this time satisfies the combination example 5, and the value of the equation (5) in which A = 0.05 is 0.953, and the equation in which B = 0.2 ( The value of 6) is 0.985. The grating height of the diffraction grating 201 is expected to be about 10 μm from FIGS. 32 and 33, and is almost the same as the actual shape. The value of the equation (5) when A = 0.3 is 0.974, and the value of the equation (6) when B = 0.6 is 0.947. The grating height of the diffraction grating 202 is expected to be about 15 μm from FIGS. 34 and 35, and is almost the same as the actual shape. Each diffraction grating has a grating height of 15 μm or less, and maintains high efficiency over the entire grating pattern.

  FIG. 66 is a graph showing the diffraction efficiency in the produced diffractive optical element 20 of this example. When the diffraction efficiency was measured, it was 99.9% at a wavelength of 455 nm, 99.2% at a wavelength of 533 nm, and 99.4% at a wavelength of 660 nm. The peaks of diffraction efficiency are at wavelengths of 440 nm and 610 nm.

  Hereinafter, some specific examples will be shown as other suitable examples of the material set of the diffractive optical element 20 of the second embodiment. 67 is an explanatory diagram of a specific example of the combination example depicted in FIG. In FIG. 67, the grating height 1 represents the height of the diffraction grating formed by the diffraction grating layers 22 and 23. The grating height 2 represents the height of the diffraction grating formed by the diffraction grating layers 23 and 24. A negative value at the diffraction grating heights 1 and 2 represents a state in which the grating height direction is reversed with respect to the other diffraction grating. In FIG. 67, the Abbe number is used to classify the dispersion characteristics of each material. However, the value shown in the equation (3) is more than the similarity of the dispersion characteristics represented by the Abbe number of each material. It is more preferable that the similarity of the dispersion characteristics represented by the magnitude relation of the difference using the above matches the combination of FIG.

  In the example shown in FIG. 67, a material having an Abbe number of 60 or more with an nd of less than 1.51 can be obtained, for example, by curing a monomer mainly composed of an acrylic monomer mainly composed of an alkyl group. In addition, a material having an Abbe number of less than 1.51 and an Abbe number of 50 or less is, for example, mainly composed of an acrylic monomer containing a phenyl group and a fluoro group in the same molecule, and mixed with an acrylic monomer containing a phenyl group. Can be obtained.

A material having an nd = 1.51 to 1.59 and an Abbe number of 40 or less includes, for example, an organic-inorganic hybrid acrylic monomer in which a biphenyl group is bonded to a silicon atom, a phenyl group, and a fluoro group in the same molecule. It can be obtained by selecting, mixing and curing an acrylic monomer. A material having nd = 1.51 to 1.59 and an Abbe number of 40 to 50 can be obtained, for example, by mixing and curing an acrylic monomer having a silicon atom and a phenyl group bonded to an acrylic monomer having an adamantyl group. For materials with nd = 1.51 to 1.59 and an Abbe number of 50 or more, an acrylic monomer having an adamantyl group, a dicyclopentanyl group or a cyclo ring is mixed and cured, or ZrO is added to the monomer. It is obtained by curing a monomer that can be obtained by mixing _two fine organic solvent sols and removing the organic solvent.

A material having an Abbe number greater than nd = 1.59 and 40 or more, for example, an adamantyl group, a dicyclopentanyl group, or a monomer having a cyclo ring and an organic solvent sol of ZrO ₂ fine particles are mixed, It can be obtained by curing a monomer that can be obtained by removing the organic solvent. A material having an Abbe number greater than nd = 1.59 and 30 or less is mainly composed of, for example, an acrylic monomer having a fluorene skeleton or an acrylic monomer in which a phenyl group or a biphenyl group is bonded to a silicon atom at the same time or a plurality of bonds. It is obtained by curing the acrylic monomer.

  As described above, various combinations of materials are possible in the second embodiment, but are not limited to the above. For example, FIG. 67 shows only one representative example in each combination example, and there are other suitable examples.

  The third example is an example of the second embodiment, and three diffraction grating layers 22, 23, and 24 using three materials are provided between two transparent substrates 21 and 25. The manufacturing method of the sandwiched diffractive optical element 20 will be mainly described. FIG. 68 is a schematic cross-sectional view showing a cross section of the diffractive optical element 20 of this example. As shown in FIG. 68, the diffractive optical element 20 of this example has a configuration in which three diffraction grating layers 22, 23, and 24 using three materials are sandwiched between two transparent substrates 21 and 25. It has become. This can be said to be a form in which a diffractive structure is incorporated in an existing lens.

  In the diffractive optical element 20 of the present embodiment, first, a single lens 21 and a diffraction grating layer 22 of a first resin material laminated thereon are formed by the same method as in the second embodiment. In this embodiment, the uneven structure 221 provided in the diffraction grating layer 22 is the same as that in the second embodiment.

  Next, using a glass mold method, a desired shape is processed on the surface of a glass substrate different from the substrate on which the single lens 21 is formed, and the single lens 25 is obtained.

  Next, a third resin material, which is the material of the diffraction grating layer 24, is laminated on the produced single lens 25 while transferring a desired shape using an optical imprint method, thereby forming the diffraction grating layer 24. . At this time, the uneven structure 241 provided on the surface of the diffraction grating layer 24 is provided on the diffraction grating 202 and the diffraction grating layer 22 formed by the uneven structure 241 when the single lenses 21 and 25 are bonded to each other. The diffraction grating 201 formed by the uneven structure 221 is formed so as to have substantially the same grating pitch. The height and the height direction of the grating are the same as those in the second embodiment. Thereby, the diffraction grating layer 24 having a structure equivalent to the diffraction grating layer 24 in the second embodiment is obtained.

  Next, the single lenses 21 and 25 are bonded to each other with a predetermined interval so that the diffraction grating layers 22 and 24 face each other. At that time, a monomer that becomes the diffraction grating layer 23 is dropped between the diffraction grating layer 22 and the diffraction grating layer 24, so that the concave / convex structure 221 of the diffraction grating layer 22 and the concave / convex structure 241 of the diffraction grating layer 24 are the most mutually. Pressurization and exposure are performed so that the distance in the vicinity is 0.5 μm. Thereby, the dropped monomer is cured to form the diffraction grating layer 23 having the uneven structures 231 and 232 between the diffraction grating layer 22 and the diffraction grating layer 24. Thereafter, an antireflection film is formed on the surface of each of the single lens 21 and the single lens 25 using a sputtering method, and the diffractive optical element 20 acting as a hybrid lens is obtained. The material used for each diffraction grating layer is the same as in the second embodiment.

  This example is an example of the fifth embodiment. In addition to the configuration of the first example, as shown in FIG. 54, the thin film 14 is interposed between the diffraction grating layer 12 and the diffraction grating layer 13. This is an example of improving the adhesion by performing the coupling treatment with the intervening layer.

  In the diffractive optical element 10 of this example, first, a single lens 11 and a diffraction grating layer 12 of a first resin material laminated thereon are formed by the same method as in the first example. In this embodiment, the uneven structure provided in the diffraction grating layer 12 is the same as that in the first embodiment.

  Next, a thin film 14 having a thickness of 15 nm made of silica is formed on the surface of the diffraction grating layer 12 using a sputtering method. The thin film 14 formed on the concavo-convex structure of the diffraction grating layer 12 is subjected to a coupling process using a silane coupling agent, and a desired shape is formed on the thin film 14. The diffraction grating layer 13 is formed by an optical imprint method.

  Thereby, it is possible to obtain a highly reliable diffractive optical element 10 that does not peel off the diffraction grating layer 13 even in an environment where the temperature changes drastically or in a high-temperature humidified environment over the front surface of the diffraction region.

  This example is an example of the eighth embodiment. In this embodiment, a diffractive optical element 10 in which the silica thin film 14 is changed to a SiON film in the configuration of the fifth embodiment will be described.

  In the configuration of the fifth embodiment, a SiON film that becomes the thin film 14 is formed on the surface of the diffraction grating layer 12 by the CVD method. Here, the film is formed so that the film thickness is 150 nm at the side wall portion of the diffraction grating 100.

  The refractive index of the SiON film is nd = 1.625, and the Abbe number is 47.2. The material used for the diffraction grating layer 12 is the same as that of the first embodiment, and the Abbe number = 25.1 and nd = 1.597. The material used for the diffraction grating layer 13 is the same as that of the first embodiment, and the Abbe number = 44.2 and nd = 1.644.

  According to the configuration of the present embodiment, when there is a light source outside the angle of view, the diffractive optical element 10 of this embodiment is compared with the peak of scattered light measured from the diffractive optical element 10 of the first embodiment. The peak of the scattered light to be measured is reduced to about 20%.

Although the present invention has been described in detail above, these are merely examples, and the present invention can be implemented in other modes, and various modifications can be made without departing from the spirit of the present invention.
This application is based on a Japanese patent application filed on May 9, 2012 (Japanese Patent Application No. 2012-107735), which is incorporated by reference in its entirety.

  The present invention can be applied to all types of optical systems, but is particularly suitable for applications that reduce flare and reduce flare in imaging optical systems incorporated in cameras, mobile phones, smartphones, endoscopes, image sensors, and the like. is there.

10, 20, 30 Diffraction optical element 11, 21, 31, 25 Transparent substrate 12, 22, 32 First diffraction grating layer 121, 221, 321 Uneven structure 13, 23, 33 Second diffraction grating layer 131, 231, 232, 331 Uneven structure 24, 34 Third diffraction grating layer 241, 341 Uneven structure 35 Fourth diffraction grating layer 351 Uneven structure 14 Thin film 100, 201, 202, 301, 302 Diffraction grating 1000 Imaging optical system

Claims (17)

A diffractive optical element that changes the traveling direction of incident light using the diffraction phenomenon of light,
At least one transparent substrate;
A first diffraction grating layer provided on the transparent substrate;
A second diffraction grating layer made of a material having optical characteristics different from the material of the first diffraction grating layer provided on the first diffraction grating layer;
Part of the interface of the first diffraction grating layer on the side where the second diffraction grating layer is located and part of the interface of the second diffraction grating layer on the side where the first diffraction grating layer is located And a concavo-convex structure that is combined with each other and acts as one diffraction grating,
The transparent substrate, the first diffraction grating layer, and the second diffraction grating layer are laminated at least in an effective region without interposing a gap therebetween,
The material of at least one diffraction grating layer is a zirconia composite material, an organic-inorganic hybrid material containing a phenyl group or a biphenyl group, or a monomer material containing a fluoro group and a phenyl group in a single molecule. A diffractive optical element. A diffractive optical element that changes the traveling direction of incident light using the diffraction phenomenon of light,
At least one transparent substrate;
A first diffraction grating layer provided on the transparent substrate;
A second diffraction grating layer made of a material having optical characteristics different from the material of the first diffraction grating layer provided on the first diffraction grating layer;
A third diffraction grating layer made of a material having optical characteristics different from the materials of the first diffraction grating layer and the second diffraction grating layer provided on the second diffraction grating layer;
Part of the interface of the first diffraction grating layer on the side where the second diffraction grating layer is located and part of the interface of the second diffraction grating layer on the side where the first diffraction grating layer is located And a concavo-convex structure that is combined with each other and acts as one diffraction grating,
Part of the interface of the second diffraction grating layer on the side where the third diffraction grating layer is located and part of the interface of the third diffraction grating layer on the side where the second diffraction grating layer is located And a concavo-convex structure that is combined with each other and acts as one diffraction grating,
The transparent substrate, the first diffraction grating layer, the second diffraction grating layer, and the third diffraction grating layer are stacked at least in an effective region without any gaps between them,
The material of at least one diffraction grating layer is a zirconia composite material, an organic-inorganic hybrid material containing a phenyl group or a biphenyl group, or a monomer material containing a fluoro group and a phenyl group in a single molecule. A diffractive optical element. A diffractive optical element that changes the traveling direction of incident light using the diffraction phenomenon of light,
At least one transparent substrate;
A first diffraction grating layer provided on the transparent substrate;
A second diffraction grating layer made of a material having optical characteristics different from the material of the first diffraction grating layer provided on the first diffraction grating layer;
A third diffraction grating layer made of a material having optical characteristics different from at least the material of the second diffraction grating layer provided on the second diffraction grating layer;
A fourth diffraction grating layer made of a material having optical characteristics different from at least the material of the third diffraction grating layer provided on the third diffraction grating layer;
Part of the interface of the first diffraction grating layer on the side where the second diffraction grating layer is located and part of the interface of the second diffraction grating layer on the side where the first diffraction grating layer is located And a concavo-convex structure that is combined with each other and acts as one diffraction grating,
An uneven structure is formed between the interface of the second diffraction grating layer on the side where the third diffraction grating layer is located and the interface of the third diffraction grating layer on the side where the second diffraction grating layer is located. Without
Part of the interface of the third diffraction grating layer on the side where the fourth diffraction grating layer is located and part of the interface of the third diffraction grating layer on the side where the third diffraction grating layer is located And a concavo-convex structure that is combined with each other and acts as one diffraction grating,
The transparent substrate, the first diffraction grating layer, the second diffraction grating layer, the third diffraction grating layer, and the fourth diffraction grating layer do not interpose a gap at least in the effective region. Are stacked,
The material of at least one diffraction grating layer is a zirconia composite material, an organic-inorganic hybrid material containing a phenyl group or a biphenyl group, or a monomer material containing a fluoro group and a phenyl group in a single molecule. A diffractive optical element. The combination of the material of the first diffraction grating layer and the material of the second diffraction grating layer is such that, for these two materials, the refractive index of g line is ng, the refractive index of C line is nC, and ng-nC of one material. When the difference between the value of ng−nC of the other material is Δ (ng−nC), and the difference between the ng value of one material and the ng of the other material is Δng, the following conditional expression The diffractive optical element according to claim 1, which satisfies (A).
Conditional expression (A):
−0.13 ≦ Δ (ng−nC) +0.506 (Δng) ≦ 0.16 The combination of the material of the first diffraction grating layer and the material of the second diffraction grating layer is such that, for these two materials, the refractive index of g-line is ng, the refractive index of C-line is nC, and the refractive index of e-line is The difference between the ng-nC value of one material and the ng-nC value of the other material is Δ (ng-nC), and the difference between the ne value of one material and the ne of the other material is The diffractive optical element according to claim 1, wherein, when Δne is satisfied, the following conditional expression (B) is satisfied.
Conditional expression (B):
−1.1 <Δ (ng−nC) / (Δne) ^1/2 <0.27 If the refractive index of d-line is larger than 1.59, it is a high refractive index material, if it is in the range of 1.51-1.59, it is a medium refractive index material, and if it is less than 1.51, it is a low refractive index material,
In the case of a low refractive index material, if the Abbe number is 50 or less, it is a low refractive index high dispersion material, and if the Abbe number is 60 or more, it is a low refractive index low dispersion material,
In the case of a medium refractive index material, if the Abbe number is 40 or less, it is a medium refractive index high dispersion material, and if the Abbe number is 50 or more, it is a medium refractive index low dispersion material,
In the case of a high refractive index material, when the Abbe number is 30 or less, it is a high refractive index high dispersion material, and when the Abbe number is 40 or more, a high refractive index low dispersion material is used.
The combination of the material of the first diffraction grating layer, the material of the second diffraction grating layer, and the material of the third diffraction grating layer corresponds to one of the following six patterns in the stacking order from the transparent substrate. The diffractive optical element according to claim 2.
Pattern 1: The first layer is a low refractive index low dispersion material, the second layer is a high refractive index low dispersion material, and the third layer is a high refractive index high dispersion material.
Pattern 2: The first layer is a medium refractive index high dispersion material, the second layer is a high refractive index high dispersion material, and the third layer is a high refractive index low dispersion material.
Pattern 3: The first layer is a low refractive index high dispersion material, the second layer is a high refractive index high dispersion material, and the third layer is a high refractive index low dispersion material.
Pattern 4: The first layer is a medium refractive index high dispersion material, the second layer is a low refractive index material or medium refractive index material, and the third layer is a high refractive index low dispersion material.
Pattern 5: The first layer is a high refractive index and high dispersion material, the second layer is a low refractive index material or medium refractive index material, and the third layer is a high refractive index and low dispersion material.
Pattern 6: The first layer is a medium refractive index material, the second layer is a medium refractive index high dispersion material, and the third layer is a high refractive index low dispersion material. In the stacking order of each diffraction grating layer from the transparent substrate,
The refractive index of the g-line of the first layer material is ng ₁ , the refractive index of the g-line of the second layer material is ng _2, and the refractive index of the g-line of the third layer material is ng ₃ .
The refractive index of the e-line of the first layer material is ne ₁ , the refractive index of the e-line of the second layer material is ne _2, and the refractive index of the e-line of the third layer material is ne ₃ .
The refractive index of the first layer of the C-line of the material and nC _1, the refractive index of the C line of the second layer of material and nC _2, the refractive index of the third layer of material C line and nC _3,
The difference in refractive index (ne ₁ -ne ₂ ) between the first layer and the second layer e-line is Δne _12, and the difference in refractive index between the second layer and the third layer e-line (ne ₂ -ne ₃ ) is Δne ₂₃ ,
Difference in refractive index between the g-line and C-line of the first layer material and difference in refractive index between the g-line and C-line of the second layer material {(ng ₁ −nC ₁ ) − (ng ₂ −nC ₂ )} Is Δ (ng−nC) ₁₂ and the difference in refractive index between the g-line and C-line of the second layer material and the difference in refractive index between the g-line and C-line of the third layer material {(ng ₂₋ nC ₂ ) − (ng ₃ −nC ₃ )} is Δ (ng−nC) ₂₃ ,
The combination of the material of the first diffraction grating layer, the material of the second diffraction grating layer, and the material of the third diffraction grating layer is
In the case of corresponding to the pattern 1, the value when A = 5.5 in the following formula (5) is 0.65 or less, and E = 0.5 in the following formula (9). When the value is 0.94 or less and C = −1.5 in the following formula (7), the value is 0 or less or 1.5 or more, and in the following formula (8), D = When 0.7, the value is less than 1.55,
In the case of corresponding to the pattern 2, the value when A = 5.5 in the following formula (5) is less than 0.85, and B = 1.2 in the following formula (6). And the value when C = −1.3 in the following formula (7) is 0 or less or 1.575 or more, and B in the following formula (6) = 0.29 is less than 0.97,
In the case of corresponding to the pattern 3, the value when A = 5.5 in the following formula (5) is less than 0.85, and B = 1.2 in the following formula (6). And the value when C = −1.3 in the following formula (7) is 0 or less or 1.575 or more, and B in the following formula (6) = 0.29 is less than 0.97,
In the case of corresponding to the pattern 4, the value when A = 0.2 in the following formula (5) is less than 0.97, and B = 0.1 in the following formula (6). When the value is less than 1.017, and when A = 0.8 in the following equation (5), the value is less than 1.045, and in the following equation (6), B = 0.47. And the value is less than 0.98,
In the case of corresponding to the pattern 5, the value when A = 0.05 in the following formula (5) is less than 0.975, and B = 0.2 in the following formula (6). And the value when A = 0.3 in the following formula (5) is less than 0.99, and B = 0.6 in the following formula (6) And the value is less than 0.965,
In the case of corresponding to the pattern 6, the value when A = 0.6 in the following formula (5) is larger than 1.00 and smaller than 1.01, and in the following formula (7), C = The value when −5.0 is smaller than 2.15, and the value when D = −2.0 in the following formula (8) is larger than 1.49 and smaller than 1.77, and the following 7. The diffractive optical element according to claim 6, wherein a value when E = 4.0 in the formula (9) is greater than 1.125.

The diffractive optical element according to claim 1, wherein a surface shape of the uppermost diffraction grating layer is an aspherical surface. The diffractive optical system according to any one of claims 1 to 8, wherein a curved surface connecting the vertices on the transparent substrate side of the diffraction grating formed by the uneven structure formed in the first diffraction grating layer is an aspherical surface. element. The concavo-convex structures constituting the diffraction grating are all concentric, and the ratio of the width of the widest annular zone to the width of the second widest annular zone among the concentric annular zones is 1 to The diffractive optical element according to claim 1, which is 0.7. A concavo-convex structure having the same height as the concavo-convex structure is formed on a portion outside the effective region of the surface on which the concavo-convex structure is formed of the diffraction grating layer in which the concavo-convex structure forming the diffraction grating is formed. The diffractive optical element according to any one of claims 1 to 10, wherein the diffractive optical element is formed. A diffractive optical element that functions as a lens,
One diffraction grating is configured in the element,
The diffractive optical element according to claim 1, wherein the arrangement order of the materials of the respective diffraction grating layers is configured such that the curvature direction of the lens surface and the direction of the slope of the saw of the diffraction grating have the same direction of inclination. A diffractive optical element that functions as a lens,
Two diffraction gratings are configured in the element,
Of the two diffraction gratings, the optical path difference of the diffraction grating having the larger optical path difference of d-line is 2λ or less,
The two diffraction gratings should be high refractive index materials if the d-line refractive index is greater than 1.59, and medium refractive index materials if they are in the range of 1.51-1.59, and should be less than 1.51. In the case of a low refractive index material, if the Abbe number is 50 or less, it is a low refractive index high dispersion material, and if the Abbe number is 60 or more, it is a low refractive index low dispersion material. In the case of materials, if the Abbe number is 40 or less, the material is a medium refractive index high dispersion material. If the Abbe number is 50 or more, the material is a medium refractive index low dispersion material. In the case of a high refractive index material, the Abbe number is 30 or less. If the Abbe number is 40 or more, the combination of the materials forming each diffraction grating is a combination of a low refractive index and low dispersion material. Combination of low refractive index low dispersion material, high refractive index low dispersion material and high refraction The combination of high dispersion material, the combination of the medium refractive index and high dispersion material and a high refractive index and high dispersion material, and any of the combination of low refractive index and high dispersion material and a high refractive index and high dispersion material,
Of the lines connecting the bottoms of the four concavo-convex structures constituting the two diffraction gratings, the angle formed by the normal of the line closest to the incident light and the incident light is the incident angle. When the light incident from the optical axis side with respect to the normal is set as the positive rotation direction,
When the incident angle is a positive rotation direction, in the combination of the concavo-convex structure having a large optical path difference between the two diffraction gratings, the diffraction grating layer made of a material having a low refractive index is positioned more on the incident side. The arrangement order of the materials of each diffraction grating layer is configured,
When the incident angle is in the negative rotation direction, in the combination of the concavo-convex structure having a large optical path difference between the two diffraction gratings, the diffraction grating layer made of a material having a high refractive index is positioned more on the incident side. The diffractive optical element according to any one of claims 2, 3, 6, and 7, wherein an arrangement order of materials of each diffraction grating layer is configured. A thin film made of a metal oxide is provided between the transparent substrate and the first diffraction grating layer or between the diffraction grating layers on which the concavo-convex structure constituting the diffraction grating is formed. Item 14. The diffractive optical element according to any one of Items 13. The refractive index difference of the diffraction grating layer in which the concavo-convex structure constituting the diffraction grating is formed or the refractive index difference between the diffraction grating layer and the thin film provided between the diffraction grating layers is 0.15 or less. The diffractive optical element according to any one of claims 1 to 14. An imaging optical system comprising at least one lens,
A diffractive optical element according to any one of claims 1 to 15,
The imaging optical system, wherein the diffractive optical element exhibits chromatic aberration that eliminates chromatic aberration that occurs in a lens system included in the imaging optical system. The diffractive optical element is formed on a transparent substrate having a lens function, and is configured such that if the refractive direction of the lens is positive, the diffractive direction is positive, and the refractive direction of the lens is negative. The imaging optical system according to claim 16, wherein the imaging optical system is configured such that the diffraction direction is a negative power if the power is.

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