JP2021099404A - Diffraction optical element, optical instrument, and imaging apparatus - Google Patents

Abstract

To provide a diffraction optical element whose optical performance hardly varies even in a high-temperature and high-humidity environment.SOLUTION: A diffraction optical element 10 has a first substrate 2, a first resin 3, a second resin 8, and a second substrate 7 laminated in this order, and a concentric circular diffraction grating on a boundary surface where the first resin 3 and the second resin 8 are in contact with each other. The diffraction optical element has a first area S1 having the diffraction grating and a second area S2 adjacent to an outer periphery of the first area S1 where the first resin and the second resin are not laminated. In the second area S2, the second resin 8 and the first substrate 2 are opposite to each other across a gap. When a length in a radial direction of the second area S2 of the second resin 8 is U, the gap is provided from a position at a distance of 0.5U in a radial direction from at least an outer periphery 30 of the first resin 3 to a position at a distance of U. When a thickness of the gap is tv and a thickness of the outer periphery 30 of the first resin is t1, a ratio of tv to t1 is 0.1 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a diffractive optical element used in an imaging device or an optical device.

As an optical element used for a lens or the like, there is known a diffractive optical element in which two types of resins having different optical characteristics are provided between two base materials and a diffraction grating is formed at the interface between the two types of resins. This diffractive optical element is used for a lens or the like and is called a close contact two-layer diffractive optical element. It is known that when a close-contact two-layer diffractive optical element is used for a long period of time in a high temperature environment, peeling occurs at the interface between the base material and the resin. Patent Document 1 discloses that peeling at the interface between the base material and the resin is suppressed by setting the thickness and width of the outer peripheral portion of the resin of the diffractive optical element within a predetermined range.

JP-A-2016-061796

However, with the means disclosed in Patent Document 1, depending on the type and shape of the resin, if it is left in a high temperature and high humidity environment for a long time, peeling occurs at the interface between the base material and the resin, and the optical performance deteriorates. was there.

In the diffractive optical element for solving the above problems, the first base material, the first resin, the second resin, and the second base material are laminated in this order, and the interface between the first resin and the second resin is in contact with each other. A second resin that is a diffractive optical element having a concentric diffractive lattice and is not laminated with the first region having the diffractive grid, the first resin adjacent to the outer periphery of the first region, and the second resin. The second region has a region, and the second resin and the first base material face each other with a gap in the second region, and the gap is in the radial direction of the second region of the second resin. When the length is U, at least from the position of the distance 0.5U to the position of the distance U in the radial direction from the outer periphery of the first resin, the thickness of the void is tv, and the thickness of the outer periphery of the first resin is When t1, the ratio of the tv to the t1 is 0.1 or less.

According to the present invention, it is possible to provide a diffractive optical element whose optical performance does not easily fluctuate even in a high temperature and high humidity environment.

(A) is a schematic cross-sectional view showing a diffractive optical element according to an embodiment. (B) is an enlarged view of the area surrounded by the broken line in FIG. 1 (a). It is a figure explaining the 1st region and the 2nd region of a diffractive optical element. It is an enlarged view of the embodiment different from FIG. 1 (b) of the region surrounded by the broken line of FIG. 1 (a). It is a process drawing which shows the manufacturing method of the diffractive optical element which concerns on embodiment. It is the schematic which showed the image pickup apparatus which concerns on embodiment. It is a schematic cross-sectional view which showed the diffraction optical element of the comparative example.

[Diffractive optical element]
Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a diffractive optical element according to the present embodiment. FIG. 1A is an overall view, and FIG. 1B is an enlarged view of a region surrounded by a broken line in FIG. 1A. In FIG. 1B, the center of the diffractive optical element 10 is located on the left side of the figure, and the end portion of the diffractive optical element 10 is located on the right side of the figure. As shown in FIGS. 1A and 1B, in the diffractive optical element 10, the first base material 2, the first resin 3, the second resin 8 and the second base material 7 are laminated in this order. There is.

(Base material)
The first base material 2 has a first surface 2A on which the first resin 3 is provided. A transparent resin or transparent glass can be used for the first base material 2 and the second base material 7. It is preferable to use glass as the first base material 2 and the second base material 7, and for example, general optical glass typified by silicate glass, borosilicate glass, and phosphoric acid glass, quartz glass, and glass ceramics are used. be able to.

The shapes of the first base material 2 and the second base material 7 are not particularly limited, and the shape of the surface in contact with the resin can be selected from a concave spherical surface, a convex spherical surface, an axisymmetric aspherical surface, a flat surface, and the like. However, it is preferable that the shape of the surface of the first base material 2 in contact with the first resin 3 and the shape of the surface of the second base material 7 in contact with the second resin 8 are substantially the same. Further, the outer shape of the base material is preferably circular.

(1st resin, 2nd resin)
FIG. 2 is a diagram for explaining a first region S1 and a second region S2 of the diffractive optical element 10, and is a side view and a plan view of the diffractive optical element. For convenience of explanation, the second base material is omitted in FIG. The diffraction optical element 10 has a first region S1 in which a first resin 3 and a second resin 8 are laminated and has a diffraction grating. Further, the diffractive optical element 10 has a second region S2 having no diffraction grating adjacent to the outer periphery of the first region S1. In the second region S2, the first resin and the second resin are not laminated. That is, the first resin is not provided in the second region S2.

In the first region S1, O, which is the center of the diffractive optical element 10, is located. Here, the first region S1 is a circle having a radius r when viewed in a plan view. The second region S2 is a portion obtained by removing the circle of radius r from the circle of radius R, which is a concentric circle of circles of radius r when viewed in a plan view, and is a portion indicated by a diagonal line in the plan view of FIG. Is. The relationship of U = R−r> 0 holds between R and r shown in FIG. 2 and U shown in FIG. As will be described later, U is the radial length of the second resin 8 in the second region S2.

The second region S2 is a non-optically effective region. On the other hand, the first region S1 has an optically effective region. However, the first region S1 may also have a non-optical effective region. Here, it is preferable that the R and the r satisfy the relationship of 0.80 ≦ r / R ≦ 0.99. If r / R is less than 0.80, the optically effective region of the diffractive optical element becomes too small. On the other hand, when r / R exceeds 0.99, the amount of the second resin 8 existing in the second region S2 is small, so that the shape of the diffraction grating tends to change when water is absorbed. Further, when the diffractive optical element is manufactured, the precursor of the first resin may overflow on the side surface of the first base material.

The first region S1 has a concentric diffraction grating when viewed in a plan view at the interface where the first resin 3 and the second resin 8 are in contact with each other. The diffraction grating is a shape in which a plurality of diffraction gratings are continuously formed. The lattice shape is a repeating pattern of an inclined surface 31A that gently inclines in the radial direction from the center of the element toward the outer periphery, and a wall surface 31B that suddenly changes in the opposite direction of the inclination after traveling a predetermined distance. The intervals between the repeating patterns decrease continuously (diameterally) from the center to the outer circumference, and the steps are almost equal. The diffraction grating shape is a concentric relief pattern composed of N circles (N is an integer of 2 or more) centered on the center O of the element when viewed in a plan view.

The outer peripheral thickness of the first resin 3 is t1. Here, the thickness of the outer circumference is the first resin in the normal direction of the first surface 2A of the first base material in the range from the outer peripheral surface (outer peripheral end) 30 of the first resin to 1 mm toward the center O of the element. It is the average value of the thickness of.

The second resin 8 is a resin different from the first resin 3, and is provided on the first resin 3 and in contact with at least a part of the outer peripheral surface 30 of the first resin 3. Further, the second resin 7 is provided in contact with the second base material 8. In FIGS. 1A and 1B, the second resin 8 is provided in contact with the entire outer peripheral surface 30 of the first resin 3, but is in contact with only a part of the outer peripheral surface 30 as shown in FIG. It may be provided.

The radial end of the second resin 8 faces the first base material 2 via a gap in the second region S2. The gap is provided from a position of at least a distance of 0.5 U to a position of a distance U in the radial direction from the outer peripheral surface 30 of the first resin, where U is the radial length of the second resin 8 in the second region S2. Has been done. The second resin 8 is provided so as to be separated from the first base material 2 by a distance tv with respect to the normal direction of the first surface 2A of the first base material due to the gap. Here, the thickness tv of the void is 1/10 or less of the thickness t1 of the outer circumference of the first resin. In other words, the ratio of the void thickness tv to the outer peripheral thickness t1 of the first resin is 0.1 or less. By setting this ratio to 0.1 or less, it is possible to provide a diffractive optical element whose optical performance does not easily fluctuate even in a high temperature environment. Note that tv does not have to be a constant value. Further, as the value of tv, the average value of the separated regions can be adopted.

FIG. 6 is a schematic cross-sectional view showing a diffractive optical element of a comparative example, FIG. 6 (a) is an overall view, and FIG. 6 (b) is an enlargement of a region surrounded by a broken line in FIG. 6 (a). It is a figure.

In the diffractive optical element 10X, the first base material 2X, the first resin 3X, the second resin 8X, and the second base material 7X are laminated in this order. The diffraction optical element 10X has a first region S1X in which a first resin 3X and a second resin 8X are laminated and has a concentric diffraction grating. Further, the diffractive optical element 10X has a second region S2X that does not have a diffraction grating adjacent to the outer periphery of the first region S1X. Here, in the second region S2X, the first resin and the second resin are not laminated, and the first resin is not provided. Further, in the second region S2X, the second resin 8X is in direct contact with the first base material 2X without passing through a gap. In this respect, the diffractive optical element 10X has a different configuration from the diffractive optical element 10.

However, the inventor of the present application has left the diffractive optical element 10X in a high temperature and high humidity environment such as a temperature of 60 ° C. and a humidity of 85% for a long time (2000 hours), and the Z portion which is the interface between the second base material 7X and the second resin 8X It was found that the second resin 8X was peeled off from the second base material 7X at the starting point. As time passed, the peeling starting from the Z portion extended not only in the radial direction of the element but also in the central direction, and the optical performance such as diffraction efficiency deteriorated. I think this is due to the following.

First, the materials of the first resin 3X and the second resin 8X of the diffractive optical element are different. Therefore, since the first resin 3X and the second resin 8X have different swelling rates, the amount of volume expansion when water is absorbed is different. Since the second resin 8X is arranged so as to completely cover the first resin 3X, when the diffractive optical element 10X is left in a high temperature and high humidity environment for a long time, water permeates from the outer periphery from the second resin 8X. .. Further, the water that has permeated into the second resin 8X also permeates into the first resin 3X. Here, since the first resin 3X and the second resin 8X have different swelling rates, the volume expansion of the first resin 3X causes the second resin 8X not only to expand in volume but also from the first resin 3X. Receive stress. Therefore, tensile stress is generated in the second resin 8X in the Z portion in the direction away from the second base material 7X. When the tensile stress exceeds the adhesion between the second base material 7X and the second resin 8X, peeling occurs starting from the Z portion.

Therefore, in the diffractive optical element 10 of the present embodiment, the first base material 2 and the second resin 8 have a thickness tv of at least from the position of the distance 0.5U in the radial direction to the position of the distance U from the outer circumference of the first resin. A configuration was adopted in which they face each other through a gap. Then, by setting this tv to 1/10 or less of the thickness t1 of the outer circumference of the first resin, the stress received by the second resin 8 due to the water absorption and expansion of the first resin 3 is reduced as compared with the diffractive optical element 10X. I found that I could do it. As a result, even in a high temperature and high humidity environment, peeling is less likely to occur between the second base material 7 and the second resin 8, so that it is possible to provide a diffractive optical element whose optical performance is less likely to fluctuate. If the distance tv is larger than 1/10 of the thickness t1 of the outer circumference of the first resin, the first resin 3 easily absorbs water, so that the optical performance may fluctuate. The optical performance referred to here is the transmitted wavefront of the diffractive optical element. Further, the thickness of the void, tv, is preferably 2 μm or less. If the thickness tv of the voids exceeds 2 μm, the first resin 3 easily absorbs water, so that the optical performance may fluctuate.

Here, the position of the gap in the radial direction is at least from the position of the distance 0.5U to the position of the distance U in the radial direction from the outer periphery of the first resin 3. More preferably, there are voids in all of the first resin 3 from the outer circumference to the position of the distance U. On the other hand, if the void does not exist from the outer periphery of the first resin 3 to a position at a distance of 0.5 U, the tensile stress generated in the second resin 8 in the direction away from the second base material 7 cannot be sufficiently reduced.

Further, in the second region S2 shown in FIG. 1B, the radial distance w of the portion where the first base material 2 and the second resin 8 are in contact is preferably less than 1 mm. If w is 1 mm or more, the tensile stress generated in the second resin 8 in the direction away from the second base material 7 may not be sufficiently reduced. That is, the gap is preferably located within 1 mm in the radial direction from the outer peripheral surface 30 of the first resin.

The first resin 3 and the second resin 8 are made of a colorless and transparent resin, and the refractive index and Abbe number can be designed so that the diffractive optical element has desired optical characteristics. In order to obtain high diffraction efficiency in a wide wavelength band, the first resin 3 and the second resin 8 are preferably formed of a low refractive index high dispersion resin and a high refractive index low dispersion resin. Here, the low refractive index and the high refractive index mean the relative relationship between the refractive indexes of the first resin 3 and the second resin 8 (the refractive index nd of the d-line). Similarly, high dispersion and low dispersion mean the relative relationship between the dispersion characteristics (Abbe number νd) of the first resin 3 and the second resin 8. That is, the fact that the first resin 3 has a low refractive index and a high dispersion and the second resin 8 has a high refractive index and a low dispersion means that the refractive index of the first resin 3 is nd1, the Abbe number is νd1, and the refractive index of the second resin 8 is high. Is nd2 and the Abbe number is νd2, which means that nd1 <nd2 and νd1 <νd2 are satisfied. Depending on the desired optical characteristics, the first resin 3 may have a high refractive index and low dispersion, and the second resin 8 may have a low refractive index and high dispersion.

The first resin 3 preferably contains a thiol compound and a (meth) acrylate compound in order to obtain a high refractive index and a low dispersion. The first resin 3 cures an uncured first resin composition 3a containing a thiol compound monomer and / or an oligomer thereof and a (meth) acrylate-based monomer and / or an oligomer thereof. Obtained by The first resin composition 3a is an energy curable resin. An energy-curable resin is a resin that is cured by applying light energy and / or thermal energy from an uncured state.

Examples of the thiol compound contained in the first resin composition 3a used for forming the first resin 3 include 4-mercaptomethyl-3,6-dithia-1,8-octanedithiol and 4-mercaptomethyl-. 1,8-Dimercapto-3,6-dithiaoctane (4-mercaptomethyl-3,6-dithia-1,8-octanedithiol), 4,8-bis (mercaptomethyl) -1,11-dimercapto-3,6 , 9-Trithiaundecane (4,8-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane) and 5,7-bis (mercaptomethyl) -1,11-dimercapto-3, 6,9-Trithiandecane (5,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiawndecane) can be mentioned.

Examples of the (meth) acrylate compound contained in the first resin composition 3a used for forming the first resin 3 include tris (2-acryloxyethyl) isocyanurate, oligoethylene glycol di (meth) acrylate, and the like. Examples thereof include dimethylol tricyclodecanedi (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate and dipentaerythritol hexa (meth) acrylate.

The first resin composition 3a used for forming the first resin 3 contains a polymerization initiator. The polymerization initiator may be a photopolymerization initiator or a thermal polymerization initiator, which can be determined by the manufacturing process selected. However, when performing replica molding that facilitates the production of a diffraction grating shape, it is preferable that a photopolymerization initiator is contained. Examples of the photopolymerization initiator include 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -1-butanone, 1-hydroxy-cyclohexyl-phenyl-ketone, and bis (2,46, -Trimethylbenzoyl) -phenylphosphine oxide, 4-phenylbenzophenone, 4-phenoxybenzophenone, 4,4'-diphenylbenzophenone, 4,4'-diphenoxybenzophenone. The content of the photopolymerization initiator is preferably in the range of 0.01% by mass or more and 10% by mass or less with respect to the entire first resin composition 3a.

The second resin 8 contains an aromatic diol compound having fluorene as a functional group and a (meth) acrylate compound and / or a fluorine-based (meth) acrylate compound in order to obtain a low refractive index and a high dispersion. Is preferable. The second resin 8 is obtained by curing an uncured second resin composition 8a containing a monomer of an aromatic diol compound having fluorene as a functional group and / or an oligomer thereof. Further, the second resin composition 8a contains a monomer and / or oligomer of the (meth) acrylate compound and / or a monomer and / or an oligomer thereof of the fluorine-based (meth) acrylate compound. The second resin composition 8a is an energy curable resin like the first resin composition 3a.

Examples of the aromatic diol compound containing fluorene as a functional group contained in the second resin composition 8a used for forming the second resin 8 include 9,9-bis [4- (2-acryloyloxyethoxy)). Phenyl] Fluorene and the like can be mentioned.

Examples of the (meth) acrylate compound contained in the second resin composition 8a used for forming the second resin 8 include tris (2-acryloxyethyl) isocyanurate, oligoethylene glycol di (meth) acrylate, and the like. Examples thereof include dimethylol tricyclodecanedi (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate and dipentaerythritol hexa (meth) acrylate.

The second resin composition 8a used for forming the second resin 8 contains a polymerization initiator. The polymerization initiator may be a photopolymerization initiator or a thermal polymerization initiator, as in the case of the first resin composition 3a, and can be determined by a selected production process. However, when performing replica molding that facilitates the production of a diffraction grating shape, it is preferable that a photopolymerization initiator is contained. Examples of the photopolymerization initiator include 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -1-butanone, 1-hydroxy-cyclohexyl-phenyl-ketone, and bis (2,46, -Trimethylbenzoyl) -phenylphosphine oxide, 4-phenylbenzophenone, 4-phenoxybenzophenone, 4,4'-diphenylbenzophenone, 4,4'-diphenoxybenzophenone. Similar to the first resin composition 3a, the content of the photopolymerization initiator is preferably in the range of 0.01% by mass or more and 10% by mass or less with respect to the entire second resin composition 8a.

The swelling rates of the first resin 3 and the second resin 8 are not particularly limited, but when the swelling rate α of the first resin 3 is 1.1 times or more of the swelling rate β of the second resin 8, pulling is performed in the present embodiment. The effect of reducing stress becomes remarkable. When the swelling rate α of the first resin 3 is 1.1 times or more the swelling rate β of the second resin 8, the stress applied to the second resin 8 due to the water absorption expansion of the first resin 3 becomes larger. Therefore, in a structure such as the diffractive optical element 10X of the comparative example, the larger the swelling rate α of the first resin is larger than the swelling rate β of the second resin, the easier it is for the second resin to peel off from the second base material. The swelling rate is a percentage of the volume change caused by the absorption of water by the resin. When the swelling rate α of the first resin 3 is 1.5 times or more the swelling rate β of the second resin 8, the effect of reducing the tensile stress becomes more remarkable.

The thicknesses of the first resin 3 and the second resin 8 are not particularly limited, but if the thickness t2 of the second resin 8 is 1.5 times or more the thickness t1 of the outer circumference of the first resin 3, the tensile stress in the present embodiment. The reduction effect of is remarkable. When the thickness t2 of the second resin 8 is 1.5 times or more the thickness t1 of the outer periphery of the first resin 3, the volume fluctuation generated in the second resin 8 due to water absorption expansion becomes large and occurs in the second resin 8. The tensile stress is higher. Therefore, in a structure such as the diffractive optical element 10X of the comparative example, the larger the thickness of the second resin is larger than the thickness of the first resin, the easier it is for the second resin to peel off from the second base material. The thickness t2 is the thickness shown in FIG. 1 (b). Specifically, it is the thickness of the second resin 8 at the portion in contact with the outer circumference of the first resin 3, and is the average value of the thicknesses. The outer circumference of the first resin 3 is a range from the outer peripheral surface 30 to 1 mm toward the center of the element. Further, when the thickness t2 of the second resin 8 is 1.7 times or more the thickness t1 of the outer periphery of the first resin 3, the effect of reducing the tensile stress becomes more remarkable in the present embodiment.

From the following viewpoint, the thickness t1 of the outer circumference of the first resin is preferably in the range of 5 μm or more and 100 μm or less. If t1 is less than 5 μm, when the first resin composition 3a is cured to obtain the first resin 3, excessive stress is generated in the step difference between the peaks and valleys of the lattice, and the lattice shape is formed. It may not be transferred well. On the other hand, if t1 exceeds 100 μm, the volume fluctuation becomes large when water is absorbed, and the optical characteristics may fluctuate.

Further, the thickness t2 of the second resin is preferably in the range of 5 μm or more and 100 μm or less. If t2 is less than 5 μm, the lattice shape is easily deformed when the second resin composition 8a is cured to obtain the second resin 8, and if it is deformed, the diffraction efficiency may decrease. On the other hand, if t2 exceeds 100 μm, the volume fluctuation becomes large when water absorption occurs, and the optical characteristics may fluctuate.

[Manufacturing method of diffractive optical element]
The method for manufacturing the diffractive optical element is not particularly limited, but an example of a manufacturing process for the diffractive optical element for forming the two resins using an ultraviolet curable resin between the two glass substrates will be described below. Since the shape of the diffractive optical element is the same as that described above, the reference numerals used in the section [Diffractive optical element] will be described below.

In order to improve the adhesion of the glass substrate to the resin, it is preferable to pretreat the surface of the glass substrate that adheres to the resin. The pretreatment of the glass surface (first surface) is preferably a coupling treatment using a silane coupling agent having a good affinity with the resin. Specific examples of the coupling agent include hexamethyldisilazane, methyltrimethoxysilane, trimethylchlorosilane, and triethylchlorosilane.

First, the first resin 3 is formed. First, as shown in FIG. 4A, an uncured ultraviolet curable resin 3a is dropped onto the mold 1 as a first resin composition which is a precursor of the first resin. Further, the first base material 2 is placed on the ejector 4 and arranged so as to face the mold 1. The mold 1 used here has an inverted shape of a desired diffraction grating shape on the surface, and for example, a metal base material such as a stainless steel material or a steel material plated with NiP or oxygen-free copper is cut by a precision processing machine. It can be produced by doing.

Next, as shown in FIG. 4B, the ejector 4 is lowered to fill the uncured ultraviolet curable resin 3a between the mold 1 and the first base material 2, and then the ultraviolet light source 5 is used. The ultraviolet curable resin 3a is cured by irradiating ultraviolet rays from the first base material 2 side.

Then, as shown in FIG. 4C, the cured ultraviolet curable resin is released from the mold 1 to form the first resin 3 having a diffraction grating shape on the first base material 2. After forming the first resin 3, additional irradiation with ultraviolet rays or heat treatment may be performed in the air or an oxygen-free atmosphere.

Next, the second resin 8 is formed. First, as shown in FIG. 4D, an uncured ultraviolet curable resin 8a, which is a second resin composition that is a precursor of the second resin, is dropped onto the first resin 3. Further, the second base material 7 is placed on the ejector 9 and arranged so as to face the first base material 2. At this time, the release agent 11 is applied so as to surround the region where the first resin 3 of the first base material 2 is formed. The type of the release agent 11 is not particularly limited, and is, for example, a fluorine coating agent and a silicone oil. After applying the release agent 11, it is dried at a temperature of 80 ° C. W in FIG. 1B can be adjusted by the position and size of the region to which the release agent 11 is applied. Instead of applying the release agent 11, a spacer (for example, made of glass) that can be removed after the second resin is cured may be used. After forming the second resin, the first base material 2 may be deformed to partially peel off the first resin 3.

Next, as shown in FIG. 4 (e), the ejector 9 is lowered to cure the uncured ultraviolet as the second resin composition between the first base material 2 and the first resin 3 and the second base material 7. The resin 8a is filled. Then, the diffractive optical element 10 is obtained by irradiating ultraviolet rays from the second base material 7 side using the ultraviolet light source 5 and curing the ultraviolet curable resin 8a to form the second resin 8. At this time, when the second resin is cured and shrunk by irradiation with ultraviolet rays, the second resin 8 is separated from the first base material 2 in the region where the release agent 11 is applied. Then, at the radial end of the second resin 8, a gap is formed by separating the second resin from the first base material by a distance tv in the direction perpendicular to the first surface of the first base material 2. ..

Here, the distance tv can be adjusted by, for example, the filling amount of the ultraviolet curable resin 8a. The distance tv can be reduced by increasing the filling amount, and the distance tv can be increased by decreasing the filling amount. Further, when a spacer is used instead of applying the release agent 11, the distance tv can be adjusted by the thickness of the spacer used. After forming the second resin 8, additional irradiation with ultraviolet rays or heat treatment may be performed in the air or an oxygen-free atmosphere.

[Optical equipment]
Specific application examples of the diffractive optical element of the present invention include a lens constituting an optical device (shooting optical system) for a camera or a video camera, a lens constituting an optical device (projection optical system) for a liquid crystal projector, and the like. Can be mentioned. It can also be used as a pickup lens for a DVD recorder or the like. These optical systems include a housing and a plurality of lenses arranged in the housing, and at least one of the plurality of lenses can be used as the diffractive optical element of the present invention.

[Imaging device]
FIG. 5 shows the configuration of a single-lens reflex digital camera 600, which is an example of a preferred embodiment of an image pickup apparatus using the diffractive optical element of the present invention. In FIG. 5, the camera body 602 and the lens barrel 601 which is an optical device are coupled, and the lens barrel 601 is a so-called interchangeable lens that can be attached to and detached from the camera body 602.

The light from the subject is photographed through an optical system including a plurality of lenses 603, 605 and the like arranged on the optical axis of the photographing optical system in the housing 620 of the lens barrel 601. The diffractive optical element of the present invention can be used for, for example, lenses 603 and 605. Here, the lens 605 is supported by the inner cylinder 604 and is movably supported with respect to the outer cylinder of the lens barrel 601 for focusing and zooming.

During the observation period before shooting, the light from the subject is reflected by the main mirror 607 in the housing 621 of the camera body, passes through the prism 611, and then the shot image is projected to the photographer through the finder lens 612. The main mirror 607 is, for example, a half mirror, and the light transmitted through the main mirror is reflected by the sub mirror 608 in the direction of the AF (autofocus) unit 613, and this reflected light is used for distance measurement, for example. Further, the main mirror 607 is attached and supported on the main mirror holder 640 by adhesion or the like. During shooting, the main mirror 607 and the sub mirror 608 are moved out of the optical path via a drive mechanism (not shown), the shutter 609 is opened, and the image sensor 610 is incident from the lens barrel 601 and receives the light that has passed through the shooting optical system. To form an image of the photographed optical image. Further, the aperture 606 is configured so that the brightness and the depth of focus at the time of shooting can be changed by changing the aperture area.

Although the image pickup device using the diffractive optical element of the present invention is described here using a single-lens reflex digital camera, the diffractive optical element of the present invention can be similarly used for a smartphone, a compact digital camera, or the like.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. First, an evaluation method of Examples and Comparative Examples will be described.

(Evaluation method)
<D-line refractive index nd / Abbe number νd>
The refractive index and Abbe number of the first resin and the second resin of the diffractive optical elements of Examples and Comparative Examples were evaluated by preparing a sample for evaluating optical characteristics. It is also possible to peel off the base material from the diffractive optical element and take out the resin for evaluation without using a sample for evaluating optical characteristics. First, a method of preparing a sample for evaluating optical characteristics will be described.

On a glass (S-TIH11) having a thickness of 1 mm, a spacer having a thickness of 500 μm and an uncured resin composition which is a raw material of the resin to be measured were placed. Quartz glass having a thickness of 1 mm was placed on the quartz glass via a spacer, and the uncured resin composition was spread out. Next, the spacer is removed, and a high-pressure mercury lamp (manufactured by HOYA CANDEO OPTRONICS: UL750) is used from above the quartz glass at 20 mW / cm ² (= illuminance through the quartz glass) under the condition (50 J) for 2500 seconds. Irradiated with light. The resin composition was cured, the quartz glass was peeled off, and then annealed at 80 ° C. for 16 hours to prepare a sample for optical characteristic evaluation. The shape of the cured resin was 500 μm in thickness and 5 mm × 20 mm in size in the glass surface.

The obtained sample was subjected to f-line (486.1 nm), d-line (587.6 nm) and c-line (656.3 nm) from the glass side using a refractometer (KPR-30, Shimadzu Corporation). ), The refractive index of each wavelength was measured.

In addition, the Abbe number was calculated from the measured refractive index of each wavelength. The Abbe number νd was calculated by the following equation (1).
Abbe number νd = (nd-1) / (nf-nc) (1)

<Swelling rate>
The swelling rate α of the first resin and the swelling rate β of the second resin of the diffractive optical elements of Examples and Comparative Examples were evaluated by preparing a sample for evaluating the swelling rate. It is also possible to peel off the base material from the diffractive optical element and take out the resin for evaluation without using a sample for evaluating the swelling rate. The sample for swelling rate evaluation was prepared by the same procedure as the sample for optical characteristic evaluation.

First, the dimensions of the finished sample were measured with an optical microscope, and the volume was calculated. Subsequently, this sample was placed in a beaker containing pure water and immersed for 24 hours. Then, the dimensions of the sample were measured again with an optical microscope, and the volume was calculated. Then, the volume after immersion in pure water was divided by the volume before immersion in pure water to express the percentage, which was defined as the swelling rate.

<Resin thickness t1, t2, void thickness tv, distance w>
The diffracted optical elements of the manufactured Examples and Comparative Examples were cut in the stacking direction on the surface passing through the element center O. The cross section was observed with a metallurgical microscope (manufactured by Nikon Corporation, ECLIPSE ME600P) at a magnification of 1000 times (eyepiece: 10 times, objective lens: 100 times). The thickness tv of the void was measured from the feed amount of the XY stage of the observed image. At this time, tv was measured at 10 points, and the average value thereof was adopted. The outer peripheral thickness t1 of the first resin 3 was measured in a region of 1 mm in the direction from the outer peripheral surface 30 of the first resin 3 toward the element center O. The 1 mm region was divided into 10 equal parts, and the average value of the thickness at the center of each region was defined as the outer peripheral thickness t1 of the first resin. At this time, when the diffraction grating exists in a region 1 mm inward from the outer peripheral surface, the distance including the grating is set to the thickness t1. The thickness t2 of the second resin was also measured in the same manner as that of the first resin. Regarding the distance w, the distance of the second resin in the radial direction from the outer peripheral surface 30 of the first resin 3 toward the outer circumference was measured from an observation image of a microscope.

<Evaluation of resin peeling of diffractive optical elements>
The diffracted optical elements of the manufactured Examples and Comparative Examples were subjected to a durability test in a high temperature and high humidity environment (60 ° C., 85 RH%, 2000 hours), and the presence or absence of resin peeling of the elements after the durability test was visually checked and with an optical microscope. Observed.

<Measurement of transmitted wave surface>
The diffracted optical elements of the manufactured Examples and Comparative Examples were subjected to durability tests in a high temperature and high humidity environment (60 ° C., 85 RH%, 2000 hours), and the transmitted wave surfaces before and after the durability test were measured and compared. The element was designed as a diffractive lens so that the primary diffracted light was focused. First, using an interferometer (manufactured by ZYGO: GPI), the object to be measured and the reflection mirror were arranged in this order with respect to the interferometer. Then, the reflection mirror was adjusted to the focal position of the element, the transmitted wave surface of the element was measured, and the amount of change was calculated.

<Comprehensive evaluation>
A was designated as A in which no peeling of the resin was confirmed after the high temperature and high humidity durability test and the amount of transmitted wave surface deformation before and after the high temperature and high humidity durability test was less than 150 nm. Those in which resin peeling was confirmed or those having a transmitted wave surface deformation amount of 150 nm or more were evaluated as B.

(Example 1)
The diffractive optical element of Example 1 was manufactured by the manufacturing method shown in FIG. As the first base material 2, optical glass having a diameter of 60 mm (manufactured by OHARA Corporation, crystal species: S-TIM8) was used. The shape was a concave spherical shape with one surface flat and the other surface R190 mm. As the second base material 7, optical glass having a diameter of 58 mm (manufactured by OHARA Corporation, crystal species: S-FSL5) was used. The shape was a convex spherical shape with R70 mm on one surface and a convex spherical shape with R190 mm on the other surface. As the mold 1, a NiP layer plated on a metal base material was cut by a precision processing machine to form a shape in which the diffraction grating shape of the first resin 3 was inverted.

An uncured ultraviolet curable acrylic resin 3a, which is a precursor of the first resin, was filled between the mold 1 and the first base material 2. Then, in order to cure the acrylic resin 3a, the entire surface was irradiated with ultraviolet rays having a wavelength of 365 nm and an intensity of 10 mW / cm ^{2 for 200 seconds.} After the mold 1 was released, the first resin 3 was formed on the first base material 2 by heating at 80 ° C. for 24 hours.

Then, a mold release treatment was performed so as to surround the region where the first resin 3 of the first base material 2 was formed. The mold release treatment was carried out by applying DURASURF (Harves Co., Ltd.), which is a fluorine coating agent, and then drying in an oven at 80 ° C.

Subsequently, an uncured ultraviolet curable acrylic resin 8a, which is a precursor of the second resin 8, was filled between the first resin 3 and the second base material 7. Then, in order to cure the acrylic resin 8a, the entire surface was irradiated with ultraviolet rays having a wavelength of 365 nm and an intensity of 30 mW / cm ^{2 for 1000 seconds.} Finally, the diffractive optical element 10 of Example 1 was obtained by heating at 80 ° C. for 72 hours.

The d-line refractive index nd1 of the first resin 3 of the diffractive optical element of Example 1 is 1.62, the Abbe number νd1 is 40.0, and the d-line refractive index nd2 of the second resin 8 is 1.59, Abbe number. νd2 was 29.0. The swelling rate α of the first resin was 0.042%, and the swelling rate β of the second resin was 0.028%. That is, the swelling rate of the first resin was 1.5 times larger than the swelling rate of the second resin.

The lattice shape of the diffractive optical element of Example 1 had a gentle convex inclination with respect to the concave spherical surface of R190 mm which was the base. In the diffraction grating, the ring band width of the first ring band, which is a circle surrounding the element center O, is 3.5 mm, the ring band width of the second ring band is 1.5 mm, and the following ring band widths are continuous. It became narrower, and the outermost ring band was the 40th ring band, and the ring band width was 0.30 mm. The radial length U of the second resin 8 in the second region S2 was 2.0 mm. The thickness t1 of the first resin, the thickness t2 of the second resin, the thickness tv of the voids, and the distance w were t1 = 30 μm, t2 = 50 μm, tv = 0.3 μm, and w = 0 mm, respectively.

(Example 2)
In Example 2, the first base material was not subjected to the mold release treatment, and a glass spacer having a thickness of 1.1 μm was inserted so as to abut against the first resin 3. In addition, the amount of the first resin composition 3a used was reduced so that the thickness of the first resin 3 became thinner. Except for this point, the diffractive optical element of Example 2 was produced in the same manner as in Example 1. In the diffractive optical element of Example 2, the thickness t1 of the first resin, the thickness t2 of the second resin, the thickness tv of the void and the distance w are t1 = 20 μm, t2 = 50 μm, tv = 1.0 μm, w = 0 mm, respectively. Met.

(Example 3)
In Example 3, a glass spacer having a thickness of 2.0 μm was inserted so as to abut against the first resin 3. Except for this point, the diffractive optical element of Example 3 was produced in the same manner as in Example 2. In the diffractive optical element of Example 3, the thickness t1 of the first resin, the thickness t2 of the second resin, the thickness tv of the void and the distance w are t1 = 20 μm, t2 = 50 μm, tv = 1.8 μm, w = 0 mm, respectively. Met.

(Example 4)
In Example 4, the diffractive optical element of Example 4 was produced by the same method as in Example 1 except that the mold release treatment of the first base material 2 was performed to a position 1.5 mm from the outer circumference of the element. In the diffractive optical element of Example 4, the thickness t1 of the first resin, the thickness t2 of the second resin, the thickness tv of the void and the distance w are t1 = 30 μm, t2 = 50 μm, tv = 0.3 μm, w = 0, respectively. It was 5.5 mm.

(Example 5)
In Example 5, the diffractive optical element of Example 5 was produced by the same method as in Example 1 except that the mold release treatment of the first base material 2 was performed to a position 1.1 mm from the outer circumference of the element. In the diffractive optical element of Example 5, the thickness t1 of the first resin, the thickness t2 of the second resin, the thickness tv of the void and the distance w are t1 = 30 μm, t2 = 50 μm, tv = 0.3 μm, w = 0, respectively. It was 9.9 mm.

(Comparative Example 1)
In Comparative Example 1, the first base material was not subjected to the mold release treatment. In addition, the amount of the first resin composition used was reduced so that the thickness of the first resin was reduced. Except for this point, the diffractive optical element of Comparative Example 1 was produced in the same manner as in Example 1. In the diffractive optical element of Comparative Example 1, the thickness t1 of the first resin, the thickness t2 of the second resin, the thickness tv of the voids, and the distance w were t1 = 20 μm and t2 = 50 μm, respectively. There was no void between the second resin and the first base material.

(Comparative Example 2)
In Comparative Example 2, a glass spacer having a thickness of 1.1 μm was inserted from the outer circumference of the first base material 2 to a position 0.9 mm. Except for this point, the diffractive optical element of Comparative Example 2 was produced in the same manner as in Comparative Example 1. In the diffractive optical element of Comparative Example 2, the thickness t1 of the first resin, the thickness t2 of the second resin, the thickness tv of the void and the distance w are t1 = 20 μm, t2 = 50 μm, tv = 1.0 μm, w = 1, respectively. It was .1 mm.

(Comparative Example 3)
In Comparative Example 3, a glass spacer having a thickness of 4.0 μm was inserted so as to abut against the first resin. A diffractive optical element of Comparative Example 3 was produced in the same manner as in Example 1 except for this point. In the diffractive optical element of Comparative Example 3, the thickness t1 of the first resin, the thickness t2 of the second resin, the thickness tv of the void and the distance w are t1 = 30 μm, t2 = 50 μm, tv = 3.6 μm, w = 0 mm, respectively. Met.

Table 1 summarizes the length measurement results of the obtained diffractive optical element such as the thickness t1 of the first resin, the thickness t2 of the second resin, the thickness tv of the void, and the distance w.

In addition, the evaluation results of the diffractive optical elements obtained in Table 2 are summarized.

As shown in Table 2, the diffractive optical elements of Comparative Example 1 and Comparative Example 2 had resin peeling. It is presumed that this is because the diffractive optical element of Comparative Example 1 had the second resin and the first base material in close contact with each other, so that the second resin was excessively stressed at the upper part of the outer peripheral edge of the first resin. Further, since the diffractive optical element of Comparative Example 2 had a large w of 1.1 mm (0.55 U), the stress applied to the second resin located above the outer peripheral end of the first resin could not be sufficiently reduced. Guessed.

Further, in the diffractive optical element of Comparative Example 3, although the resin peeling was not confirmed, the change in the transmitted wavefront became as large as 160 nm. It is considered that this is because the thickness tv of the voids was larger than the thickness t1 of the first resin, and the optical performance of the first resin changed due to water absorption.

On the other hand, in Examples 1 to 5 in which w was 0.5 U or less with respect to U and the relationship between the first resin thickness t1 and the void thickness tv satisfied tv / t1 ≦ 0.1, resin peeling occurred. However, the change in the transmitted wave surface was also small.

2 1st base material 3 1st resin 7 2nd base material 8 2nd resin 10 Diffractive optical element 600 Single-lens reflex digital camera (imaging device)
601 Lens barrel (interchangeable lens, optical equipment)
602 Camera body 603 Lens 604 Inner cylinder 605 Lens 606 Aperture 607 Main mirror 608 Sub mirror 609 Shutter 610 Image sensor 611 Prism 621 Housing S1 First area S2 Second area

Claims (11)

A diffractive optical element in which a first base material, a first resin, a second resin, and a second base material are laminated in this order and have a concentric diffraction grating at the interface where the first resin and the second resin are in contact with each other. There,
It has a first region having the diffraction grating and a second region not provided with the first resin adjacent to the outer periphery of the first region.
In the second region, the second resin and the first base material face each other with a gap.
The gap is provided at least from a position of a distance of 0.5 U to a position of a distance U in the radial direction from the outer circumference of the first resin, where U is the radial length of the second region of the second resin. Be,
When the thickness of the void is tv and the thickness of the outer circumference of the first resin is t1,
A diffractive optical element characterized in that the ratio of the tv to the t1 is 0.1 or less. The diffractive optical element according to claim 1, wherein w, which is the radial distance of the portion where the second resin and the first base material are in contact with each other in the second region, is less than 1 mm. The diffractive optical element according to claim 1, wherein the second resin is not in contact with the first base material in the second region. The diffractive optical element according to any one of claims 1 to 3, wherein the thickness tv of the gap is 2 μm or less. The diffractive optical element according to any one of claims 1 to 4, wherein the second region is a non-optical effective region. The diffractive optical element according to any one of claims 1 to 5, wherein the outer peripheral thickness t1 of the first resin is in the range of 5 μm or more and 100 μm or less. The diffractive optical element according to any one of claims 1 to 5, wherein the swelling rate α of the first resin is 1.1 times or more the swelling rate β of the second resin. The diffractive optical element according to any one of claims 1 to 7, wherein t2, which is the thickness of the portion of the second resin in contact with the first resin, is 1.5 times or more the thickness t1 of the first resin. .. The diffractive optical element according to any one of claims 1 to 8, which is an optical device having a housing and an optical system having a plurality of lenses arranged in the housing, wherein at least one of the lenses is the diffractive optical element according to any one of claims 1 to 8. An optical device characterized by being. An image pickup apparatus comprising a housing, an optical system having a plurality of lenses arranged in the housing, and an image pickup element that receives light that has passed through the optical system.
An imaging device according to any one of claims 1 to 8, wherein at least one of the lenses is a diffractive optical element according to any one of claims 1 to 8. The imaging device according to claim 10, wherein the imaging device is a camera.

Images