JP7418079B2 - Diffractive optical elements, optical instruments, imaging devices - Google Patents

Description

The present invention relates to a diffractive optical element used in imaging devices and optical equipment.

BACKGROUND ART As an optical element used for lenses and the like, there is known a diffractive optical element in which two types of resins having different optical properties 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 lenses and the like, and is called a close-contact two-layer type diffractive optical element. It is known that when a close-contact two-layer diffractive optical element is used in a high-temperature environment for a long period of time, 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 can be suppressed by setting the thickness and width of the outer peripheral portion of the resin of the diffractive optical element within a predetermined range.

Japanese Patent Application Publication No. 2016-067196

However, with the means disclosed in Patent Document 1, depending on the shape of the resin, peeling may occur at the interface between the base material and the resin.

A diffractive optical element for solving the above problems is a diffractive optical element in which a first resin layer and a second resin layer are laminated in close contact between a first base material and a second base material, The first resin layer has a grating portion having a diffraction grating shape, and an outer peripheral portion adjacent to the outer periphery of the grating portion and having no diffraction grating shape , and the outer peripheral portion is formed of the first base material or the second resin layer. The thickness te of the outer circumferential portion , which has a lower surface in contact with the base material and an upper surface on the opposite side of the lower surface, is the distance between the upper surface and the lower surface, d is the height of the diffraction grating, and is the diffraction ratio of the grating portion. When the thickness excluding the height of the grating is t1, the following formula (1) t1+0.3d≦te≦t1+0.9d (1) is satisfied, and the diameter of the outer peripheral portion is the radial length of the upper surface. The length we in the direction is characterized by satisfying the following formula (2): 30d≦we (2).

According to the present invention, it is possible to provide a diffractive optical element that is unlikely to peel off at the interface between the base material and the resin.

FIG. 1 is a schematic cross-sectional view showing a diffractive optical element according to a first embodiment. FIG. 7 is a schematic cross-sectional view showing a diffractive optical element according to a second embodiment. FIG. 3 is a process diagram showing a method for manufacturing a diffractive optical element according to an embodiment. 1 is a schematic diagram showing an imaging device according to an embodiment. FIG. 2 is a schematic cross-sectional view showing a diffractive optical element of a comparative example.

[Diffractive optical element]
(First embodiment)
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 a first embodiment. FIG. 1(a) is an overall view, and FIG. 1(b) is an enlarged view of the area surrounded by the broken line in FIG. 1(a). In FIG. 1(b), the center of the diffractive optical element 10 is located on the left side of the figure, and the end 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 resin layer 3 and the second resin layer 8 are in close contact between the first base material 2 and the second base material 7. It is laminated.

(Base material)
The first base material 2 and the second base material 7 can be made of transparent resin or transparent glass. The first base material 2 and the second base material 7 are preferably made of glass, and for example, common optical glasses such as silicate glass, borosilicate glass, and phosphate 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 aspheric 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 layer 3 and the shape of the surface of the second base material 7 in contact with the second resin layer 8 are approximately the same shape. Further, the outer shape of the base material is preferably circular.

(resin layer)
The first resin layer 3 has a grating section 31 having a diffraction grating shape, and an outer peripheral section 32 around the outer periphery of the grating section 31 . The diffraction grating shape 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 slopes gently 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 slope after a predetermined distance. The interval between the repeating patterns decreases continuously from the center toward the outer periphery, and the steps are approximately equal. The lattice portion 31 and the outer peripheral portion 32 only need to be adjacent to each other, and do not necessarily need to be formed continuously. The distance between the grating portion 31 and the outer peripheral portion 32 is preferably 50 times or less d (the height of the diffraction grating). In FIG. 1, the outer peripheral portion 32 does not have a diffraction grating shape, but it may have a diffraction grating shape as long as it satisfies equations (1) and (2) described later.

The height of the diffraction grating in the grating section 31 is d. Further, the thickness of the grating portion 31 excluding the height of the diffraction grating (the length in the normal direction of the surface of the first base material 2 on which the first resin layer 3 is formed) is t1.

The thickness of the outer peripheral portion 32 (the length in the normal direction of the surface of the first base material 2 on which the first resin layer 3 is formed) is te, and te satisfies the following formula (1).
t1+0.3d≦te≦t1+0.9d (1)

Here, d, t1, and te are average values of at least five locations. Further, the length of the outer circumferential portion 32 in the radial direction (direction from the center of the element toward the outer circumference) (the length in the direction parallel to the surface of the first base material 2 on which the first resin layer 3 is formed) is we. , we satisfy the following formula (2).
30d≦we (2)

By satisfying formulas (1) and (2), the diffractive optical element of the present invention is less likely to peel off at the interface between the first base material 7 and the first resin layer 3. The mechanism will be explained below while explaining the form of a diffractive optical element of a comparative example.

FIG. 5 is a schematic cross-sectional view showing a diffractive optical element 10X of a comparative example. FIG. 5(a) is an overall view, and FIG. 5(b) is an enlarged view of the area surrounded by the broken line in FIG. 5(a). In the diffractive optical element 10X, a first resin layer 3X and a second resin layer 8X are laminated in close contact between a first base material 2X and a second base material 7X.

The first resin layer 3X has a grating portion 31X having a diffraction grating shape, and an outer peripheral portion 32X having no diffraction grating shape and provided adjacent to the outer periphery of the grating portion 31X. Further, the thickness te of the outer peripheral portion 32X is greater than or equal to t1+d, and greater than or equal to the thickness of the first resin layer 3X. When such a shape is formed by curing uncured resin in the order of the first resin layer 3 Tensile stress remains in the direction in which the resin layer 3X tends to separate. This tensile stress is the sum of a tensile stress that depends on the grid height and a tensile stress that depends on the thickness of the outer circumference. The stress that depends on the lattice height is caused by the amount of curing shrinkage of the resin of the second resin layer formed on the thinnest part of the lattice part 31X and the thickest part of the lattice part 31X. Occurs due to differences. The stress that depends on the thickness of the outer peripheral part is caused by the amount of curing shrinkage of the resin of the second resin layer formed on the thinnest part of the lattice part 31X and the thickest part of the outer peripheral part 32X. Occurs due to differences. When the diffractive optical element 10X is used for a long period of time, the adhesion between the first resin layer 3X and the first base material 2 gradually decreases due to moisture entering from the air. Therefore, if the tensile stress remaining in the lattice portion 31 exceeds the adhesion force between the first resin layer 3X and the first base material 2, peeling will occur.

Therefore, the diffractive optical element of the present invention is configured such that the thickness of the outer peripheral portion 32 satisfies the following formula (1).
t1+0.3d≦te≦t1+0.9d (1)

By setting the thickness of the outer peripheral part 32 to t1 + 0.9d (the sum of 0.9 times t1 and d) or less, the thickness of the outer peripheral part 32 becomes thinner than the thickness of the first resin layer 3, so that no resin remains in the lattice part 31. The tensile stress caused by this is only the stress that depends on the grid height. Therefore, since the tensile stress remaining in the grating portion 31 is smaller than that of the diffractive optical element of the comparative example, peeling at the interface between the first base material 2 and the first resin layer 3 is less likely to occur. On the other hand, if the thickness of the outer peripheral portion 32 is made too thin, sink marks will occur during manufacturing, the shape of the diffraction grating will be distorted, and the diffraction efficiency will decrease. Therefore, the thickness of the outer peripheral portion 32 is t1+0.3d (the sum of 0.3 times t1 and d) or more. In addition, in FIG. 1(b), the thickness of the outer peripheral part 32 is constant from the center to the outer periphery, but the thickness of the outer peripheral part 32 does not need to be constant. Moreover, when the maximum value of the height of the diffraction grating is dmax, the above-mentioned te is less than t1+dmax (the sum of t1 and dmax).

Moreover, at the same time as formula (1) is satisfied, the radial length we of the outer peripheral portion 32 satisfies the following formula (2).
30d≦we (2)

By making the radial length of the outer circumferential portion 32 30 times or more d, it is possible to prevent sink marks from occurring during manufacturing. This is because when molding the resin with a mold, the resin pool can be increased. In addition, since the length in the radial direction is long, stress is not locally concentrated on the outer circumferential portion 32 when forming the second resin layer 8, and the occurrence of peeling from locations other than the lattice portion is suppressed. be able to. On the other hand, if the length in the radial direction of the outer circumferential portion 32 is less than 30 times d, there will be a small amount of resin pooling, sink marks will occur during manufacturing, the shape of the diffraction grating will be distorted, and the diffraction efficiency will decrease. Furthermore, since the length in the radial direction is short, stress is locally concentrated on the outer circumferential portion 32 when forming the second resin layer 8, and peeling may occur from locations other than the lattice portion.

Further, it is preferable that the radial length we of the outer peripheral portion 32 satisfies the following formula (3).
50d≦we≦100d (3)

By making the radial length of the outer circumferential portion 32 50 times or more d, it is possible to further reduce the possibility of sink marks occurring during manufacturing. Further, since the length of the outer circumferential portion 32 in the radial direction is 100 d or less, the non-optically effective portion does not become large, so that a wide optically effective portion of the diffractive optical element can be secured.

Thickness excluding the height d of the diffraction grating at the portion of the second resin layer 8 facing the grating portion 31 (length in the normal direction of the surface of the second base material 7 on which the second resin layer 8 is formed) When t2 is t2, it is preferable that t2 satisfies the following formula (4).
1.5d≦t2≦3d (4)

When t2 is within this range, good diffraction efficiency can be obtained. If t2 is less than 1.5 times d, there will be a difference in the refractive index between the thicker and thinner parts of the second resin layer 8 facing the grating part 31, and there is a risk that the diffraction efficiency will deteriorate. be. When t2 becomes larger than 3 times d, the volume of the second resin layer 8 increases, so that changes in the refractive index due to changes in volume due to temperature changes are likely to occur, and there is a possibility that the diffraction efficiency will change.

The height d of the diffraction grating is preferably in the range of 8 μm or more and 25 μm or less. When the height of the diffraction grating is within this range, it is possible to achieve both good diffraction efficiency and a reduction in tensile stress generated in the grating portion 31. If it is less than 8 μm, the diffraction efficiency determined by the product of the refractive index difference between the first resin layer 3 and the second resin layer 8 and the height d of the diffraction grating may not be sufficiently high. Moreover, if it exceeds 25 μm, there is a risk that the tensile stress that remains in the grating portion 31 and depends on the grating height will become large.

It is preferable that the thickness t1 of the grating portion 31 excluding the height d of the diffraction grating is in the range of 1 μm or more and 50 μm or less. When t1 is within this range, the shape of the grating portion 31 can be stably obtained, and good diffraction efficiency can be obtained. When t1 is less than 1 μm, stress is concentrated at the tips of the lattice portions 31, and there is a possibility that shape defects are likely to occur. When t1 exceeds 50 μm, since the volume of the resin increases, refractive index fluctuations due to volume changes due to temperature fluctuations are likely to occur, and there is a possibility that the diffraction efficiency will fluctuate.

It is preferable that the outer circumferential surface 32A of the outer circumferential portion 32 is in contact with the second resin layer 8. Since the outer circumferential surface 32A is in contact with the second resin layer 8, the time for water from the air to reach the lattice portion 31 is increased, so even if used for a long period of time, the first base material 2 and the first resin layer 3 will remain in contact with each other. Peeling is less likely to occur at the interface.

The first resin layer 3 and the second resin layer 8 are made of 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 over a wide wavelength band, the first resin layer 3 and the second resin layer 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 refer to the relative relationship between the refractive indexes (d-line refractive index nd) of the first resin layer 3 and the second resin layer 8. Similarly, high dispersion and low dispersion mean the relative relationship between the dispersion characteristics (Abbe number νd) of the first resin layer 3 and the second resin layer 8. In other words, the first resin layer 3 has a low refractive index and high dispersion, and the second resin layer 8 has a high refractive index and low dispersion. This means that nd1<nd2 and ν1<ν2 are satisfied, where nd2 is the refractive index of 8, and ν2 is the Abbe number. Note that, depending on desired optical properties, the first resin layer 3 may have a high refractive index and low dispersion, and the second resin layer 8 may have a low refractive index and high dispersion.

As the resin forming the first resin layer 3 and the second resin layer 8, it is preferable to use an energy curable resin. Among these, it is preferable to use an ultraviolet curable resin, and as the ultraviolet curable resin, acrylic resin, epoxy resin, etc. can be used. Furthermore, the resin forming the first resin layer 3 and the second resin layer 8 may contain organic or inorganic substances other than the energy-curable resin in order to adjust optical properties and mechanical properties.

(Second embodiment)
FIG. 2 is a schematic cross-sectional view showing a diffractive optical element according to a second embodiment. FIG. 2(a) is an overall view, and FIG. 2(b) is an enlarged view of the area surrounded by the broken line in FIG. 2(a). As shown in FIGS. 2A and 2B, the diffractive optical element 100 has a first resin layer 30 and a first resin layer 30 between a first base material 20 and a second base material 70, as in the first embodiment. The two resin layers 80 are laminated in close contact with each other. The first resin layer 30 has a grating section 310 having a diffraction grating shape, and an outer peripheral section 320 adjacent to the outer circumference of the grating section 310 .

Regarding the second embodiment, only the points different from the first embodiment will be described.

In the second embodiment, the shapes of the first base material 20 and the second base material 70 are different from those of the first embodiment. The first base material 20 and the second base material 70 are made of flat glass.

Further, in the second embodiment, the shape of the lattice portion 310 of the first resin layer is different from the shape of the lattice portion in the first embodiment. Although the shape of the lattice section 31 in the first embodiment was a convex shape, the shape of the lattice section 310 in the second embodiment is a concave shape.

The other parts have the same configuration as the first embodiment, and the second embodiment can also provide a diffractive optical element in which peeling does not easily occur at the interface between the first base material 20 and the first resin layer 30. .

[Method for manufacturing diffractive optical element]
Although the method for manufacturing a diffractive optical element in the present invention is not particularly limited, an example of a process for manufacturing a diffractive optical element in which two resin layers are formed using an ultraviolet curable resin between two glass substrates is described below. explain. Since the shape of the diffractive optical element is the same as that in the first embodiment, the reference numerals used in the first embodiment will be used in the following description.

In order to improve the adhesion with the resin layer, it is preferable that the surface of the glass substrate that comes into close contact with the resin layer is pretreated. Preferably, the glass surface is pretreated by coupling treatment using a silane coupling agent that has good affinity with the resin layer. Specific coupling agents include hexamethyldisilazane, methyltrimethoxysilane, trimethylchlorosilane, triethylchlorosilane, and the like.

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

Next, as shown in FIG. 3(b), the ejector 4 is lowered to fill the space between the mold 1 and the first base material 2 with uncured ultraviolet curable resin 3a, and then the ultraviolet light source 5 is used to fill the space between the mold 1 and the first base material 2. Then, ultraviolet rays are irradiated from the first base material 2 side to cure the ultraviolet curing resin 3a.

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

Next, a second resin layer 8 is formed. First, as shown in FIG. 3(d), an uncured ultraviolet curable resin 8a, which is a precursor of the second resin layer 8, is dropped onto the first resin layer 3. Further, the second base material 7 is placed on the ejector 9 and placed so as to face the first base material 2. Note that the ultraviolet curing resin 8a is a different resin having different optical properties (refractive index and Abbe number) from the ultraviolet curing resin 3a.

Next, as shown in FIG. 3(e), the ejector 9 is lowered to fill the space between the first base material 2 and the first resin layer 3 and the second base material 7 with uncured ultraviolet curable resin 8a. . Thereafter, 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 curing resin 8a to form the second resin layer 8. Note that after forming the second resin layer 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 lenses constituting optical equipment for cameras and video cameras (photographing optical systems), lenses constituting optical equipment for liquid crystal projectors (projection optical systems), etc. Can be mentioned. Moreover, it can also be used for a pickup lens of a DVD recorder or the like. These optical systems consist of a housing and a plurality of lenses arranged within the housing, and at least one of the plurality of lenses can be the diffractive optical element of the present invention.

[Imaging device]
FIG. 4 shows the configuration of a single-lens reflex digital camera 600, which is an example of a preferred embodiment of an imaging device using the diffractive optical element of the present invention. In FIG. 4, a camera body 602 and a lens barrel 601, which is an optical device, are combined, but the lens barrel 601 is a so-called interchangeable lens that can be attached to and detached from the camera body 602.

Light from the subject is photographed via an optical system including a plurality of lenses 603, 605, etc. arranged on the optical axis of the photographing optical system within the housing 620 of the lens barrel 601. The diffractive optical element of the present invention can be used for lenses 603 and 605, for example. Here, the lens 605 is supported by an inner tube 604 and movably supported relative to the outer tube of the lens barrel 601 for focusing and zooming.

During the observation period before photographing, 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 photographed 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 a submirror 608 in the direction of an AF (autofocus) unit 613, and this reflected light is used, for example, for distance measurement. Further, the main mirror 607 is mounted and supported by a main mirror holder 640 by adhesive or the like. During photographing, the main mirror 607 and sub-mirror 608 are moved out of the optical path through a drive mechanism (not shown), the shutter 609 is opened, and the image sensor 610 receives the light that has entered from the lens barrel 601 and passed through the photographic optical system. to form a photographic light image. Further, the diaphragm 606 is configured so that brightness and depth of focus during photographing can be changed by changing the aperture area.

Note that although an imaging device using the diffractive optical element of the present invention has been described here using a single-lens reflex digital camera, the diffractive optical element of the present invention can be similarly used for smartphones, compact digital cameras, and the like.

First, a method for evaluating the diffractive optical element produced in the example will be explained.

(Measurement method of grid height d, resin thickness t1, t2, te, resin length we)
A cut was made along a plane passing through the center of the optical axis with respect to the stacking direction of the diffractive optical element. The cut surface was observed at a magnification of 1000 times (eyepiece: 10 times, objective lens: 100 times) using a metallurgical microscope (manufactured by Nikon Corporation, ECLIPSE ME600P). The grating height d, resin thicknesses t1, t2, te, and resin length we were measured from the feed amount of the XY stage. The lattice height d is the length from the top of the lattice in the normal direction to the surface on which the first resin layer of the first base material is formed, with respect to the straight line connecting the two bottoms adjacent to the top of the lattice. It was measured. The objects of measurement were ring zones that are multiples of 8 (8th ring zone, 16th ring zone, . . . 40th ring zone), and calculation was made from the average value thereof.

The resin thickness was determined by measuring the length in the normal direction of the first base material surface. The thickness t1 of the lattice portion of the first resin layer excluding the lattice height d is the resin width of the lattice-shaped portion (tangential direction of the surface of the first base material on which the first resin layer is formed) divided into 10 equal parts. The area was divided, and the center of each divided area was used as the measurement target, and the average value was calculated. Similarly, the average thickness t2 of the second resin layer excluding the grid height d in the part facing the grid part of the first resin layer is the same as the resin width of the grid-shaped part (the second resin layer of the second base material is formed). (the tangential direction of the surface) was divided into 10 equal parts, and the center of each divided area was used as the measurement target, and the average value was calculated. The maximum value of the thickness te of the outer peripheral portion was measured.

The resin length we was determined by measuring the maximum length in the tangential direction of the surface of the first base material on which the first resin layer was formed.

(Evaluation of resin peeling)
The prepared diffractive optical element was left in a constant temperature bath set in a high temperature and high humidity environment (temperature 60°C, humidity 85RH%) for 1000 hours, and after 1000 hours, it was removed from the constant temperature bath and left in a temperature environment of 23℃ to check whether the resin peeled off or not. was observed visually and with an optical microscope. Those in which no resin peeling was observed were rated A, and those in which resin peeling was confirmed were rated C. A was passed and C was rated fail.

(Evaluation of diffraction efficiency)
Diffraction efficiency is measured by injecting measurement light with a diameter of approximately 2 mm and a wavelength of 400 nm to 700 nm into the outer periphery of a grating shape, and detecting the intensity of the first-order diffracted light emitted from the diffractive optical element with a spectrophotometer. did. The measurements were carried out in an environment with a temperature of 23±0.5° C. and a humidity of 50±10 RH%. Through this measurement, the shape accuracy of the lattice shape of approximately the 35th to 40th annular zones of the first lattice shape having 45 annular zones was evaluated. Diffraction efficiency of 95% or more was rated A, 93% or more but less than 95% was rated B, and less than 93% was rated C.

(comprehensive evaluation)
Among the evaluations of resin peeling and the evaluation of diffraction efficiency, those that were A in both evaluations were rated A. A case where one side is A and the other side is B is called B, and a case where one side is A and the other side is C is called C.

(Example 1)
The diffractive optical element of Example 1 was manufactured using the manufacturing method shown in FIG. As the first base material 2, optical glass (manufactured by Ohara Corporation, crystal type: S-TIM8) with a diameter of 60 mm was used. The shape was a concave spherical shape with one surface being flat and the other surface having an radius of 190 mm. As the second base material 7, optical glass (manufactured by Ohara Corporation, crystal type: S-FSL5) with a diameter of 58 mm was used. One surface had a convex spherical shape with an radius of 70 mm, and the other surface had a convex spherical shape with an radius of 190 mm. The mold 1 used was one in which a NiP layer plated on a metal base material was cut using a precision processing machine to form a shape that was an inversion of the diffraction grating shape of the first resin layer.

A space between the mold 1 and the first base material 2 was filled with an uncured ultraviolet curable acrylic resin 3a, which was a precursor of the first resin layer 3. Thereafter, in order to cure the acrylic resin 3a, the entire surface was irradiated with ultraviolet light having a wavelength of 365 nm and an intensity of 10 mW/cm ² for 200 seconds. After releasing the mold 1, the first resin layer 3 was formed on the first base material 2 by heating at 80° C. for 24 hours.

Thereafter, an uncured ultraviolet curable acrylic resin 8a, which is a precursor of the second resin layer 8, was filled between the first resin layer 3 and the second base material 7. Thereafter, 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 was obtained by heating at 80° C. for 72 hours.

The first resin layer 3 of the diffractive optical element of Example 1 had a refractive index of 1.62 and an Abbe number of 40.0, and the second resin layer 8 had a refractive index of 1.59 and an Abbe number of 29.0. .

The grating shape of the diffractive optical element of Example 1 had a gentle convex slope with respect to the concave spherical surface of the first base material 2 with an radius of 190 mm. Further, the ring width of the first ring zone is 3.5 mm, the ring width of the second ring zone is 1.5 mm, and the ring width becomes continuously narrower, and the ring zone is the outermost ring zone. The width of the 40th ring zone was 0.30 mm.

The grating height d of the diffraction grating shape was 20.0 μm. Further, the thickness t1 of the lattice portion of the first resin layer excluding the lattice height d was 30.0 μm. Further, the thickness t2 of the second resin layer excluding the height d of the diffraction grating at the portion facing the grating portion of the first resin layer was 50.0 μm. That is, the distance between the two glass substrates was 100 μm.

The thickness te of the outer peripheral portion was 41.5 μm, and the radial length we was 1.2 mm (1200 μm).

The shape of the diffractive optical element of Example 1 is summarized in Table 1.

Next, the diffraction efficiency and resin peeling of the diffractive optical element of Example 1 were evaluated. Since the diffraction efficiency was 95.8%, the evaluation was given as A. Further, since no resin peeling was observed, the evaluation was given as A. Since both evaluations were A, the overall evaluation was A. These evaluation results are summarized in Table 2.

(Examples 2 to 8 and Comparative Examples 1 to 3)
In Examples 2 to 8 and Comparative Examples 1 to 3, the shape of the mold 5 was different so that the shape of the resin layer was different from that of the diffractive optical element of Example 1, or the movement of the ejector 9 was changed so that the thickness of the second resin layer was different. A diffractive optical element was produced in the same manner as in Example 1, except that .

Table 1 summarizes the shapes of the diffractive optical elements of Examples 2 to 8 and Comparative Examples 1 to 3.

Furthermore, the evaluation results of Examples 2 to 8 and Comparative Examples 1 to 3 are summarized in Table 2.

In Examples 1 to 8 that satisfied formula (1) and formula (2), no resin peeling occurred. Moreover, since the diffraction efficiency was 93% or more, the overall evaluation was A or B in both cases. Among them, Examples 1 to 3 and Examples 7 and 8, which also satisfied formulas (3) and (4), had diffraction efficiencies of 95% or more, so the overall evaluation was A. Note that te in Examples 1 to 8 was less than the sum of the maximum height dmax of the diffraction grating and t1 (te<t1+dmax).

On the other hand, in Comparative Example 1, although the diffraction efficiency was high, the thickness of te was equal to the sum of t1 and d, and the formula (1) was not satisfied, so resin peeling occurred. Further, in Comparative Example 2, the thickness of te was t1+0.24d, and the formula (1) was not satisfied. Similarly, in Comparative Example 3, the length of we was 25 d, and the formula (2) was not satisfied. It is thought that in Comparative Examples 2 and 3, the diffraction efficiency was low because sink marks occurred during the formation of the first resin layer.

From the above results, by satisfying t1+0.3d≦te≦t1+0.9d (1) and satisfying 30d≦we (2), it is possible to provide a diffractive optical element that is unlikely to peel off at the interface between the base material and the resin. I found out that it can be done.

1 Mold 2, 2X, 20 First base material 3, 3X, 30 First resin layer 3a Ultraviolet curing resin 4 Ejector 5 Ultraviolet light source 7, 7X, 70 Second base material 8, 8X, 80 Second resin layer 9 Ejector 10, 100 Diffractive optical element 31, 31X, 310 Grating section 32, 32X, 320 Outer peripheral section 600 Single-lens reflex digital camera (imaging device)
601 Lens barrel (interchangeable lenses, optical equipment)
602 Camera body 603, 605 Lens 604 Inner tube 606 Aperture 607 Main mirror 608 Sub mirror 609 Shutter 610 Image sensor 611 Prism 621 Housing

Claims (9)

A diffractive optical element in which a first resin layer and a second resin layer are laminated in close contact between a first base material and a second base material,
The first resin layer has a grating portion having a diffraction grating shape, and an outer peripheral portion adjacent to the outer periphery of the grating portion and having no diffraction grating shape ,
The outer peripheral portion has a lower surface in contact with the first base material or the second base material, and an upper surface on the opposite side of the lower surface,
The thickness te of the outer peripheral portion, which is the distance between the upper surface and the lower surface, is calculated by the following formula ( 1)
t1+0.3d≦te≦t1+0.9d (1)
The filling,
The radial length we of the outer peripheral portion, which is the radial length of the upper surface , is expressed by the following formula (2)
30d≦we (2)
A diffractive optical element characterized by satisfying the following. The radial length we of the outer circumferential portion is expressed by the following formula (3)
50d≦we≦100d (3)
The diffractive optical element according to claim 1, which satisfies the following. When the thickness of the second resin layer excluding the height of the diffraction grating in the portion facing the grating portion of the first resin layer is t2, the t2 is expressed by the following formula (4).
1.5d≦t2≦3d (4)
The diffractive optical element according to claim 1 or 2, which satisfies the following. The diffractive optical element according to any one of claims 1 to 3, wherein the height d of the diffraction grating is in a range of 8 μm or more and 25 μm or less. The diffractive optical element according to any one of claims 1 to 4, wherein a thickness t1 of the grating portion excluding the height of the diffraction grating is in a range of 1 μm or more and 50 μm or less. The diffractive optical element according to any one of claims 1 to 5, wherein an outer peripheral surface of the outer peripheral portion is in contact with the second resin layer. An optical device comprising 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 6. An optical device characterized by: An imaging device comprising a housing, an optical system having a plurality of lenses arranged in the housing, and an imaging element that receives light passing through the optical system, the imaging device comprising:
An imaging device characterized in that at least one of the lenses is the diffractive optical element according to any one of claims 1 to 6. The imaging device according to claim 8, wherein the imaging device is a camera.

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