Diffractive optical elements and optical devices

Abstract

To provide a diffraction optical element which can reduce or prevent deterioration of optical characteristics, when a circular diffraction grating and an arc shaped diffraction grating are provided in plan view.SOLUTION: A diffraction optical element has a substrate having a surface where a diffraction grating is provided, and a resin layer provided so as to coat the diffraction grating on a surface of the substrate, wherein the diffraction grating includes a circular first diffraction grating and an arc shaped second diffraction grating arranged in outside of the first diffraction grating, in plan view when being viewed in an optical axis direction, the diffraction optical element has a first region where the diffraction grating is provided and a second region which is arranged in outside of the first region and where the diffraction grating is not provided, and a third region including a boundary between the first region and the second region on a side where the diffraction grating is discontinuous has a region with a first gradient that a thickness of the resin layer increases from a center of a circle of the diffraction grating to outside of 0.4 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a diffractive optical element and an optical device. [Background technology]

[0002] A conventional method for reducing chromatic aberration in a lens system is to provide a diffractive optical element with diffractive properties in part of the optical system. Diffractive optical elements are known to not only correct chromatic aberration, but also to have an aspherical effect by appropriately changing the grating pitch of their periodic structure.

[0003] It is also known that in diffractive optical elements used in lenses in optical systems, high diffraction efficiency can be obtained over a wide wavelength range by arranging two diffraction gratings in close contact and appropriately setting the materials and grating heights that make up each diffraction grating.

[0004] Patent Document 1 describes a diffractive optical element including a substrate made of a first optical material and having a diffraction grating on its surface, and an optical adjustment layer made of a second optical material and provided on the substrate so as to cover the diffraction grating. In the diffractive optical element described in Patent Document 1, the optical adjustment layer made of the second optical material containing a resin has a uniform thickness in the normal direction from the envelope surface, which is a curved surface passing through the tip of the diffraction grating. This prevents cracks caused by stress in the optical adjustment layer due to, for example, the curing shrinkage of the second optical material during manufacturing.

[0005] On the other hand, optical elements used in optical devices such as cameras and head-mounted displays are often symmetrical about the optical axis, i.e., circular in shape. However, in recent years, there has been an increasing demand for optical elements with shapes other than circular, with the goals of miniaturization, weight reduction, design, and shape adaptation to the human body. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2012 / 176388 Summary of the Invention [Problem to be solved by the invention]

[0007] Patent Document 1 discloses a technique for preventing cracks from occurring due to localized concentration of stress in the optical adjustment layer during curing shrinkage by maintaining a constant thickness of the optical adjustment layer, which is a resin layer on a substrate. However, when the substrate has a segmented circular shape, such as a cut-off circular lens, the diffraction grating on the substrate has a circular shape on the inside and an arc-shaped shape on the outside in a plan view in the optical axis direction. In the case of an arc-shaped diffraction grating, the shrinkage behavior of the resin formed on the diffraction grating during curing differs from that in the case of a circular diffraction grating alone. Therefore, in the case of a diffractive optical element having a circular diffraction grating and an arc-shaped diffraction grating provided on a substrate, even if the thickness of the resin layer on the substrate is maintained constant as in the technique disclosed in Patent Document 1, the diffraction efficiency is likely to decrease due to differences in the density of the resin layer, resulting in deterioration of the optical characteristics.

[0008] An object of the present invention is to provide a diffractive optical element that can reduce or prevent deterioration of optical characteristics when a diffraction grating that is circular and a diffraction grating that is arc-shaped in plan view are provided. [Means for solving the problem]

[0009] According to one aspect of the present invention, there is provided a diffractive optical element having a substrate having a surface on which a diffraction grating is provided, and a resin layer provided on the surface of the substrate so as to cover the diffraction grating, wherein, in a planar view seen along the optical axis direction, the diffraction grating includes a first diffraction grating having a circular shape and a second diffraction grating having an arc shape and arranged outside the first diffraction grating, the diffractive optical element has a first region in which the diffraction grating is provided, and a second region arranged outside the first region and in which the diffraction grating is not provided, and a third region including a boundary between the first region and the second region on the side where the diffraction grating is discontinuous, wherein the thickness of the resin layer increases at a first gradient of 0.4 or more from the center of the circle of the diffraction grating toward the outside. [Effects of the Invention]

[0010] According to the present invention, in the case where a diffraction grating having a circular shape and a diffraction grating having an arc shape in a plan view are provided, it is possible to reduce or prevent deterioration of optical characteristics. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing a diffractive optical element according to a first embodiment of the present invention. [Figure 2] 1 is a schematic diagram showing a diffractive optical element according to a first embodiment of the present invention. [Figure 3] 1 is a schematic diagram showing a diffractive optical element according to a first embodiment of the present invention. [Figure 4] 1 is a schematic cross-sectional view showing a diffractive optical element according to a first embodiment of the present invention. [Figure 5] 1 is a schematic cross-sectional view showing a diffractive optical element according to a first embodiment of the present invention. [Figure 6] 1A to 1C are schematic cross-sectional views showing steps in a method for manufacturing a diffractive optical element according to the present invention. [Figure 7] 5A to 5C are schematic diagrams illustrating a curing process for the diffractive optical element according to the first embodiment of the present invention. [Figure 8]5A to 5C are schematic cross-sectional views showing a curing process for the diffractive optical element according to the first embodiment of the present invention. [Figure 9] FIG. 4 is a schematic diagram showing a display device according to a second embodiment of the present invention. [Figure 10] FIG. 10 is a schematic diagram showing an imaging device according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] [First embodiment] A diffractive optical element and a method for manufacturing a diffractive optical element according to a first embodiment of the present invention will be described with reference to FIGS.

[0013] First, the configuration of the diffractive optical element according to this embodiment will be described with reference to FIGS. 1 to 5. FIG. 1 is a schematic diagram showing a diffractive optical element 10 according to the first embodiment. The upper part of FIG. 1 is a plan view showing the diffractive optical element 10 according to this embodiment in a plan view seen in the optical axis direction. The lower part of FIG. 1 is a cross-sectional view taken along line AA′ in the plan view in the upper part of FIG. 1. FIG. 2 is a plan view showing another planar shape of the diffractive optical element 10 according to this embodiment. FIG. 3 is a schematic diagram showing boundary regions 16 and 17 in the diffractive optical element 10 according to this embodiment. FIGS. 4 and 5 are cross-sectional views showing examples of the cross-sectional shape of the diffraction grating 13 in the diffractive optical element 10 according to this embodiment, and show the region 18 surrounded by the dashed line in FIG. 3.

[0014] As shown in Fig. 1, the diffractive optical element 10 according to this embodiment has two optical elements: a substrate 11 serving as a base, and a resin layer 12. The diffractive optical element 10 according to this embodiment is used in optical devices such as digital cameras, video cameras, binoculars, and head-mounted displays. A diffraction grating 13 is provided on one surface of the substrate 11. The resin layer 12 is provided on the surface of the substrate 11 on which the diffraction grating 13 is provided, so as to cover the diffraction grating 13.

[0015] The substrate 11 is, for example, a substrate having a convex lens shape, and may be a resin substrate formed by injection molding, or may be a glass substrate. The shape of the substrate 11 may be a convex lens shape, a concave lens shape, a convex spherical shape, a concave spherical shape, an aspherical shape, a flat shape, or the like. The material constituting the substrate 11 is not particularly limited as long as it is a transparent material that is transparent to light such as visible light that is the target of the diffractive optical element 10. Note that transparency means, for example, that the transmittance of light in the wavelength range of 420 nm to 700 nm is 10% or more.

[0016] In a plan view seen in the optical axis direction of the diffractive optical element 10, the substrate 11 has a segmented circular shape, which is a shape surrounded by an arc and a line connecting both ends of the arc. Here, the line connecting both ends of the arc may be straight or curved. The arc may be one or more. That is, the segmented circular shape may have one or more missing portions. The center of the segmented circular shape is the center of the diffraction grating 13, which is the optical center of the diffractive optical element 10. The shape of the substrate 11, including its planar shape, is not limited to the shape shown in FIG. 1 and can be any appropriate shape depending on the intended use of the diffractive optical element 10, etc.

[0017] Because substrate 11 has a planar shape of a broken circle, diffraction grating 13 includes a circular diffraction grating 13 on the inside of substrate 11 and an arc-shaped diffraction grating 13 on the outside of substrate 11. As shown in Fig. 2, the planar shape of substrate 11 may have two arcs, or may have more. Furthermore, the line connecting both ends of the arc may be curved.

[0018] A diffractive optical element 10 including a substrate 11 has a first region 14 having the grating pattern of a diffraction grating 13, and a second region 15 located outside the first region 14 and not having the grating pattern of the diffraction grating 13. The first region 14 is a region where the diffraction grating 13 is provided, and the second region 15 is a region where no diffraction grating is provided. The first region 14 is a region where light targeted by the diffractive optical element 10 is generally transmitted. The second region 15 is a region where light targeted by the diffractive optical element 10 is not transmitted.

[0019] As shown in Fig. 3, an arc-shaped diffraction grating 13 is present on the outer side of the substrate 11. Therefore, in a region including a boundary 19 (see Figs. 4 and 5) between the first region 14 and the second region 15, there is a boundary region 16 on the side where the diffraction grating 13 is discontinuous, and a boundary region 17 on the side where the diffraction grating 13 is continuous. The boundary region 16 is a region including the boundary 19 between the first region 14 and the second region 15 on the side where the diffraction grating 13 is discontinuous, i.e., on both end sides of the arc-shaped diffraction grating 13. The boundary region 17 is a region including the boundary 19 between the first region 14 and the second region 15 on the side where the diffraction grating 13 is continuous, i.e., on the circumferential side of the arc-shaped diffraction grating 13.

[0020] Diffraction grating 13 is provided on one surface of substrate 11, which has a partially circular planar shape, in a concentric pattern centered on the center of the partially circular circle through which the optical axis of diffractive optical element 10 passes. In one example, diffraction grating 13 is formed so that gently descending slopes and steeply rising wall surfaces are continuously repeated from the element center passing through the optical axis toward the periphery, as shown in Fig. 4. In another example, diffraction grating 13 is formed so that gently ascending slopes and steeply descending wall surfaces are continuously repeated from the element center passing through the optical axis toward the periphery, as shown in Fig. 5.

[0021] Resin layer 12 is provided on one surface of substrate 11 so as to cover diffraction grating 13. The resin constituting resin layer 12 is not particularly limited as long as it is a transparent resin that is transmissive to light such as visible light that is the target of diffractive optical element 10, but from the viewpoint of ease of manufacture, it is preferably a photocurable resin or a thermosetting resin.

[0022] 1, resin layer 12 is formed on substrate 11 so as to adhere closely to substrate 11, fill in the uneven portions of diffraction grating 13, and cover diffraction grating 13. Resin layer 12 is formed across first region 14 where diffraction grating 13 is provided and second region 15 where diffraction grating 13 is not provided.

[0023] A transparent inorganic film may be provided between the substrate 11 and the resin layer 12. That is, a transparent inorganic film may be provided on the diffraction grating 13 of the substrate 11, and the resin layer 12 may be provided on the substrate 11 via the transparent inorganic film. In this case, the transparent inorganic film is a thin film made of a transparent inorganic material that is transparent to light such as visible light that is the target of the diffractive optical element 10. Examples of inorganic materials include aluminum oxide (Al2O3), silicon oxide (SiO2, SiO), titanium oxide (TiO x ), tantalum oxide (TaO x ), niobium oxide (NbO x ) are examples. The transparent inorganic film can be provided along the grating surface of the diffraction grating 13 so as to cover the grating surface. The transparent inorganic film can be provided using various film formation methods such as vacuum deposition and sputtering. When the substrate 11 is made of resin, the provision of the transparent inorganic film reduces or prevents penetration and dissolution of the resin material between the substrate 11 and the resin layer 12, thereby reducing or preventing deterioration of the diffraction efficiency.

[0024] 4 and 5, in the first region 14, which is a region through which light targeted by the diffractive optical element 10 passes, the resin layer 12 is provided to have substantially the same resin layer thickness t with respect to the envelope plane, which is a plane passing through the tips of the diffraction grating 13. On the other hand, in the second region 15, the resin layer 12 is provided to have a resin layer thickness t that is thicker than that of the first region 14.

[0025] Furthermore, the diffractive optical element 10 according to this embodiment has at least a region in which the thickness increase gradient G of the resin layer 12 is 0.4 or greater in boundary region 16, which includes boundary 19 between first region 14 and second region 15 on the side where diffraction grating 13 is discontinuous. The thickness increase gradient G of the resin layer 12 here refers to the gradient at which the thickness t of the resin layer 12 increases from the center of the circle of diffraction grating 13 toward the outside, i.e., the degree to which the thickness t of the resin layer changes from the center of the circle of diffraction grating 13 toward the outside. The thickness increase gradient G can be calculated by dividing the boundary region 16, which is 0.5 mm inward and 0.5 mm outward from boundary 19 at its center, into 20 sections, each 0.05 mm wide, and dividing the boundary region 16 by 0.5 mm, and then dividing the boundary region 16 by 0.5 mm, and then dividing the boundary region 16 by 0.05 mm, and then dividing the boundary region 16 by 0.5 mm toward the outside, and then dividing the boundary region 16 by 0.05 mm.

[0026] The thickness increase gradient G includes a thickness increase gradient Ga and a thickness increase gradient Gb. The thickness increase gradient Ga is the thickness increase gradient G in the boundary region 16 including the boundary 19 on the side where the diffraction grating 13 is discontinuous. The thickness increase gradient Gb is the thickness increase gradient G in the boundary region 17 including the boundary 19 on the side where the diffraction grating 13 is continuous. As described above, the diffractive optical element 10 according to this embodiment has at least a region where the thickness increase gradient Ga is 0.4 or more.

[0027] The thickness t of the resin layer 12 in the first region 14 can be the average thickness of the resin layer 12 from the envelope surface of the diffraction grating 13. Furthermore, the thickness t of the resin layer 12 in the second region 15 can be the average thickness of the resin layer 12 provided on the substrate 11. The thickness t of the resin layer can be measured using a shape measuring instrument or the like. The thickness t of the resin layer can be obtained by taking the difference between the measurement value of the surface shape of the diffractive optical element 10 obtained by the shape measuring instrument or the like and the shape of the substrate 11. Alternatively, the thickness t of the resin layer can be measured by cutting the diffractive optical element 10 along a plane passing through the center of the circle of the diffraction grating and measuring the cross-sectional shape.

[0028] As described above, the diffractive optical element 10 according to this embodiment has at least a region in which the thickness increase gradient Ga of the resin layer 12 is 0.4 or more in the boundary region 16 including the boundary 19 on the side where the diffraction grating 13 is discontinuous. This is because, taking into consideration the shrinkage of the resin that makes up the resin layer 12 when it hardens, the density difference of the resin due to hardening is kept small.

[0029] The phenomenon of resin density differences occurring due to curing will be described together with the method for manufacturing the diffractive optical element 10 according to this embodiment using Figures 6 to 8. Figure 6 is a schematic cross-sectional view showing the steps of the method for manufacturing the diffractive optical element 10 according to this embodiment. Figures 7 and 8 are a schematic view and a schematic cross-sectional view showing the curing step of the diffractive optical element 10, and are schematic views showing the shrinkage of the resin during curing.

[0030] To manufacture the diffractive optical element 10 according to this embodiment, first, as shown in FIG. 6( a), a liquid resin 121 is ejected onto a mold 21 for forming the resin layer 12. Next, the ejector 20 is lowered to bring the resin 121 on the mold 21 into contact with the surface of the substrate 11 on which the diffraction grating 13 is formed. Next, as shown in FIG. 6( b), the resin 121 is filled between the mold 21 and the substrate 11 while controlling the distance between them. Next, as shown in FIG. 6( c), the filled resin 121 is cured to form the resin layer 12 composed of the cured resin 121. The resin 121 used here is preferably a photocurable resin or a thermosetting resin. When a photocurable resin is used as the resin 121, a light irradiator 22 irradiates the resin 121 with light L, such as ultraviolet light, through the substrate 11 to cure the resin 121. Photocurable resins are particularly preferred because of their fast curing speed and cost-effectiveness. Examples of photocurable resins include acrylic, methacrylic, epoxy, thiol, and episulfide resins. In this manner, resin 121 can be molded onto substrate 11 using mold 21 to provide resin layer 12. Next, ejector 20 is raised to release resin layer 12, which is made of cured resin 121, integrally with substrate 11, from mold 21. In this manner, diffractive optical element 10 can be manufactured.

[0031] 7 and 8 show the shrinkage behavior of the resin 121 that constitutes the resin layer 12 in the diffractive optical element 10 when cured. Fig. 7 shows a plan view of the diffractive optical element 10 as viewed in a plane along the optical axis direction. Fig. 8 shows a cross-section 61 of the boundary region 16 on the side where the diffraction grating 13 in Fig. 7 is discontinuous, and a cross-section 71 of the boundary region 17 on the side where the diffraction grating 13 in Fig. 7 is continuous.

[0032] In the manufacturing method shown in FIG. 6 , the outer side of the substrate 11 is constrained when the resin 121 constituting the resin layer 12 hardens. Therefore, when the resin 121 hardens, the resin 121 shrinks in the diffractive optical element 10 primarily in the radial direction from the outer periphery to the inner periphery, as indicated by the solid arrows in FIG. 7 . Furthermore, in the boundary region 16 on the side where the diffraction grating 13 is discontinuous, the cross section of the diffraction grating 13 is exposed, and therefore, in addition to the radial shrinkage, the resin 121 shrinks in the direction along the diffraction grating 13, as indicated by the dashed arrows in FIG. 7 . Therefore, when the thickness of the resin layer 12 is substantially constant, the density of the resin 121 in and around the boundary region 16 on the side where the diffraction grating 13 is discontinuous becomes lower. As a result, the refractive index of the resin layer 12 in and around the boundary region 16 on the side where the diffraction grating 13 is discontinuous changes from the design value.

[0033] The diffractive optical element 10 according to this embodiment has at least a region in which the thickness increase gradient Ga of the resin layer 12 is 0.4 or greater in a boundary region 16 including a boundary 19 between the first region 14 and the second region 15 on the side where the diffraction grating 13 is discontinuous. Therefore, in this embodiment, as shown in FIG. 8 , the mold 21 for providing the resin layer 12 has a gradient shape such that the resin layer 12 is thicker in the second region 15. Therefore, when the resin 121 cures and shrinks, the resin 121 can be supplied from the second region 15 to the first region 14. This reduces the radial shrinkage of the resin 121 and also reduces the shrinkage of the resin 121 in and around the boundary region 16 on the side where the diffraction grating 13 is discontinuous. By reducing the shrinkage of the resin 121, the occurrence of a refractive index difference due to a density difference in the resin layer 12 formed by the resin 121 can be reduced or prevented, thereby minimizing or preventing a decrease in the diffraction efficiency of the resin layer 12.

[0034] Furthermore, if the thickness increase gradient Ga of the resin layer 12 is 1.8 or greater, the resin 121 can be supplied sufficiently during cure shrinkage, and a decrease in diffraction efficiency can be more effectively prevented. However, if the thickness increase gradient Ga of the resin layer 12 is greater than 12, a large cure shrinkage stress is generated in the thickness direction during the curing process of the resin 121, which may cause deformation of the diffractive optical element 10. Therefore, it is preferable that the thickness increase gradient Ga be 1.8 or greater and 12 or less, i.e., 1.8≦Ga≦12. It is preferable that the diffractive optical element 10 have at least a region where the thickness increase gradient Ga is 1.8 or greater and 12 or less.

[0035] Note that the shrinkage of the resin 121 in boundary region 16 on the side where the diffraction grating 13 is discontinuous tends to be greater than the shrinkage of the resin 121 in boundary region 17 on the side where the diffraction grating 13 is continuous. For this reason, it is preferable that the thickness increase gradient Ga of the resin layer 12 in boundary region 16 on the side where the diffraction grating 13 is discontinuous is greater than the thickness increase gradient Gb of the resin layer 12 in boundary region 17 on the side where the diffraction grating 13 is continuous. In other words, it is preferable that Ga > Gb. Note that it is sufficient that the diffractive optical element 10 has at least a region where the thickness increase gradient Ga is greater than the thickness increase gradient Gb.

[0036] Furthermore, the grating height d of diffraction grating 13 is preferably 1 μm or more and 30 μm or less in order to fully obtain the effect of diffractive optical element 10. Note that grating height d is the height from the boundary between the convex portion of diffraction grating 13 and the base to the tip of the convex portion of diffraction grating 13. Grating height d can be an average value for diffraction gratings 13 provided on substrate 11.

[0037] Furthermore, if the thickness t of the resin layer 12 is thinner than 10 μm, unevenness in the internal refractive index occurs, resulting in reduced diffraction efficiency, while if it is too thick, the diffractive optical element 10 becomes thick and heavy. Therefore, the thickness t of the resin layer 12 is preferably 10 μm or more and 300 μm or less. Note that the thickness t of the resin layer 12 here can be the average thickness of the resin layer 12 formed across the first region 14 and the second region 15.

[0038] Furthermore, the pitch of the diffraction grating 13 in the boundary regions 16 and 17, which include the boundary 19 between the first region 14 and the second region 15, is preferably 10 μm or more and 300 μm or less, so that the diffractive optical element 10 can fully achieve its effect.

[0039] As described above, according to this embodiment, it is possible to reduce or prevent deterioration of the optical characteristics of the diffractive optical element 10 provided with a circular diffraction grating 13 and an arc-shaped diffraction grating 13. The optical characteristics of the diffractive optical element 10 can be evaluated by measuring the diffraction efficiency in a desired wavelength range, such as the wavelength range from 420 nm to 700 nm, as an optical performance evaluation. In this case, for example, if the change in diffraction efficiency compared to the design value is 2% or less, the optical characteristics are not significantly affected, and therefore the optical characteristics can be evaluated as being good.

[0040] [Example] Next, the diffractive optical element 10 according to the first embodiment will be specifically described using examples.

[0041] Example 1 A diffractive optical element and a method for manufacturing a diffractive optical element according to Example 1 will be described with reference to Figures 1 and 6. In Example 1, a diffractive optical element 10 having the shape shown in Figure 1 was manufactured.

[0042] In Example 1, a substrate 11 was prepared by injection molding a polycarbonate resin material (EP4500, manufactured by Mitsubishi Gas Chemical Company, Ltd.). The substrate 11 had an outer diameter of 46 mm, a diffraction grating region diameter of 42 mm, a central thickness of 2.5 mm, and a peripheral thickness of 1.0 mm. One surface was convex, and the other surface was flat, and a diffraction grating 13 with a grating height of 10 μm was provided. The diffraction grating 13 was arranged concentrically around the center of the outer diameter of the substrate 11, with the grating spacing decreasing from the center toward the periphery. The substrate 11 had a segmented circular shape in a planar view in the optical axis direction, with the shape being such that the circle was cut 18 mm from the center by a straight line. The diffraction grating 13 was circular and extended up to 16 mm from the center, i.e., up to a diameter of 32 mm. The diffraction grating 13 from 32 mm to 42 mm in diameter had an arc shape, with the circle cut by a straight line at a position 16 mm from the center in the same direction as the substrate 11.

[0043] Next, a resin layer 12 was molded using a mold 21 according to the process shown in FIG. 6. The resin 121 used here was a photocurable episulfide resin material. The mold 21 had an outer diameter of 48 mm, and the portion corresponding to the first region 14, where the grating shape of the diffraction grating 13 was located, had an aspherical shape corresponding to the envelope surface through which the vertices of the diffraction grating 13 formed on the substrate 11 passed. The mold 21 was also shaped so that the resin layer 12 would have a region where the thickness increase gradient Ga of the resin layer 12 was 1.8 in a boundary region 16 including the boundary 19 between the first region 14 and the second region 15 on the side where the diffraction grating 13 was discontinuous. The resin 121 was dripped onto the mold 21 as shown in FIG. 6(a). Next, as shown in FIG. 6(b), the ejector 20 was lowered to fill the space between the mold 21 and the substrate 11 with the resin 121 so that the thickness of the resin layer 12 from the envelope surface of the diffraction grating 13 was 100 μm. At this time, the filling area of ​​the resin 121 in the boundary region 17 on the side where the diffraction grating 13 is continuous was larger than the region 21 mm where the grating shape of the substrate 11 is located and was within a radius of 23 mm from the outer periphery of the substrate 11. The filling area of ​​the resin 121 was arranged to have its outer edge between 21.1 mm and 22.5 mm as much as possible. Furthermore, in the boundary region 16 on the side where the diffraction grating 13 is discontinuous, the filling area of ​​the resin 121 was arranged to be 2 mm outward from the outer periphery of the substrate 11, where the grating shape of the substrate 11 is located, and extend to the outer periphery of the substrate 11. The filling area of ​​the resin 121 was arranged to have its outer edge between 1.9 mm and 0.5 mm from the outer periphery as much as possible. Thereafter, as shown in FIG. 6(c), ultraviolet light was irradiated from the light irradiator 22 to harden the resin 121, forming a resin layer 12. Next, the ejector 20 was raised to release the resin layer 12 integrally with the substrate 11 from the mold 21, thereby producing the diffractive optical element 10 having the shape shown in FIG.

[0044] The diffractive optical element 10 according to Example 1 manufactured as described above was subjected to shape measurement after being released from the mold 21. A surface profiler Form Talysurf (manufactured by Taylor Hobson) was used for the shape measurement. To measure the thickness of the resin layer 12, the surface profile of the diffractive optical element 10 on the resin layer 12 side was measured from the center of the optical axis to the edge at least three locations in the direction of the boundary region 16 on the side where the diffraction grating 13 is discontinuous and in the direction of the boundary region 17 on the side where the diffraction grating 13 is continuous.

[0045] The thickness increase gradient Ga of the resin layer 12 in the boundary region 16 on the side where the diffraction grating 13 is discontinuous, including the boundary 19 between the first region 14 and the second region 15, was measured at three locations. The maximum Ga at each of the three locations was 1.8. Specifically, the average thickness of the resin layer 12 from a position 15.5 mm from the center of the diffraction grating 13 to 16.5 mm in 0.05 mm increments was as follows: 100 μm (15.5 mm to 15.9 mm), 190 μm (15.95 mm), 280 μm (16 mm), and 370 μm (16.05 mm to 16.5 mm). The thickness increase gradient Ga of the resin layer 12 was calculated to be 0.0 (15.5 mm to 15.9 mm), 1.8 (15.95 mm to 16.05 mm), and 0.0 (16.1 mm to 16.5 mm). The boundary 19 between the first region 14 and the second region 15 was located 16 mm from the center of the diffraction grating 13 .

[0046] Furthermore, the thickness increase gradient Gb of the resin layer in boundary region 17 on the side where diffraction grating 13 is continuous, including boundary 19 between first region 14 and second region 15, was measured at three locations. Gb at each of the three locations was found to have a maximum value of 0.8. Specifically, the average thickness of resin layer 12 from a position 20.5 mm from the center of diffraction grating 13 to 21.5 mm in 0.05 mm increments was as follows: That is, the average thickness of resin layer 12 was 100 μm (20.5 mm to 20.9 mm), 140 μm (20.95 mm), 180 μm (21 mm), and 220 μm (21.05 mm to 21.5 mm). The thickness increase gradient Gb of resin layer 12 was calculated to be 0.0 (20.5 mm to 20.9 mm), 0.8 (20.95 mm to 21.05 mm), and 0.0 (21.1 mm to 21.5 mm). The boundary 19 between the first region 14 and the second region 15 having no grating pattern was located 21 mm from the center of the diffraction grating 13 .

[0047] The optical performance of the diffractive optical element 10 according to Example 1 was evaluated by measuring the diffraction efficiency in the wavelength range from 420 nm to 700 nm. In the optical performance evaluation, when the change in diffraction efficiency compared to the design value was 1% or less, the optical performance was not significantly affected and the result was evaluated as "very good" (a). When the change in diffraction efficiency compared to the design value was between 1% and 2%, the optical performance was not significantly affected and the result was evaluated as "good" (b). When the change in diffraction efficiency compared to the design value was more than 2%, the deterioration of the optical performance was not negligible and the result was evaluated as "poor" (c). Furthermore, the shape of the surface of the resin layer 12 was compared with the design shape to evaluate the shape accuracy of the diffractive optical element 10. When the difference from the design shape was 1 μm or less, the optical performance was not significantly affected and the result was evaluated as "very good" (a). When the difference from the design shape was between 1 μm and 2 μm, the optical performance was not significantly affected and the result was evaluated as "good" (b). When the difference from the design shape was more than 2 μm, the deterioration of the optical performance was not negligible and the result was evaluated as "poor" (c). As a result, it was confirmed that the diffractive optical element 10 according to Example 1 was excellent in both optical performance and shape accuracy, as shown in Table 1.

[0048] Example 2 In Example 2, the same substrate as in Example 1 was used as substrate 11. The mold 21 was shaped so that resin layer 12 was formed so that boundary region 16 on the side where diffraction grating 13 is discontinuous had a region where thickness increase gradient Ga of 0.4. The mold 21 was shaped so that resin layer 12 was formed so that boundary region 17 on the side where diffraction grating 13 is continuous had a region where thickness increase gradient Gb of 0.2. Except for this, resin layer 12 was molded in the same manner as in Example 1, and a diffractive optical element 10 was manufactured.

[0049] The shape of the diffractive optical element 10 according to Example 2 was measured after demolding in the same manner as in Example 1. The thickness increase gradient Ga at each of the three locations had a maximum of 0.4. The thickness increase gradient Gb at each of the three locations had a maximum of 0.2.

[0050] The diffractive optical element 10 according to Example 2 was evaluated by measuring its optical performance and shape accuracy in the same manner as in Example 1, and as shown in Table 1, it was confirmed that the optical performance was good and the shape accuracy was very good.

[0051] Example 3 In Example 3, the same substrate as in Example 1 was used as substrate 11. The mold 21 was shaped so that resin layer 12 was formed so that it had a region in boundary region 16 on the side where diffraction grating 13 is discontinuous, where the thickness increase gradient Ga of resin layer 12 was 1.8. The mold 21 was shaped so that resin layer 12 was formed so that it had a region in boundary region 17 on the side where diffraction grating 13 is continuous, where the thickness increase gradient Gb of resin layer 12 was 1.8. Except for this, resin layer 12 was molded in the same manner as in Example 1, and a diffractive optical element 10 was manufactured.

[0052] The shape of the diffractive optical element 10 according to Example 3 was measured after demolding in the same manner as in Example 1. The thickness increase gradient Ga at each of the three locations had a maximum value of 1.8. The thickness increase gradient Gb at each of the three locations had a maximum value of 1.8.

[0053] The diffractive optical element 10 according to Example 3 was evaluated for optical performance and shape accuracy in the same manner as in Example 1, and as shown in Table 1, it was confirmed that the optical performance was very good and the shape accuracy was good.

[0054] Example 4 In Example 4, the same substrate as in Example 1 was used as the substrate 11. The mold 21 was shaped so that the resin layer 12 was formed so that it had a region in the boundary region 16 on the side where the diffraction grating 13 was discontinuous, where the thickness increase gradient Ga of the resin layer 12 was 0.4. The mold 21 was shaped so that the resin layer 12 was formed so that it had a region in the boundary region 17 on the side where the diffraction grating 13 was continuous, where the thickness increase gradient Gb of the resin layer 12 was 0.8. Except for this, the resin layer 12 was molded in the same manner as in Example 1, and a diffractive optical element 10 was manufactured.

[0055] The shape of the diffractive optical element 10 according to Example 4 was measured after demolding in the same manner as in Example 1. The thickness increase gradient Ga at each of the three locations had a maximum of 0.4. The thickness increase gradient Gb at each of the three locations had a maximum of 0.8.

[0056] The diffractive optical element 10 according to Example 4 was evaluated by measuring its optical performance and shape accuracy in the same manner as in Example 1, and as shown in Table 1, it was confirmed that both the optical performance and shape accuracy were good.

[0057] Example 5 In Example 5, a diffractive optical element 10 was manufactured using a substrate 11 having the shape shown in FIG. 2. The substrate 11 had an outer diameter of 46 mm, a diameter of 42 mm in the region where the diffraction grating 13 was located, a central thickness of 2.5 mm, and a peripheral thickness of 1.0 mm. One surface was convex, and the other surface was flat, with a diffraction grating 13 having a grating height of 10 μm. When viewed in a plan view in the optical axis direction, the substrate 11 had a segmented circular shape with two missing points symmetrical about the optical axis, and the shape was a circle cut by a curve approximately 18 mm from the center. The diffraction grating 13 was circular up to 16 mm from the center, i.e., up to a diameter of 32 mm. The diffraction grating 13 from 32 mm to 42 mm in diameter had an arc shape cut by a curve approximately 16 mm from the center in the same direction as the substrate 11. The mold 21 was shaped so that the resin layer 12 would be formed in a region where the boundary region 16 on the side where the diffraction grating 13 is discontinuous has a thickness increase gradient Ga of 1.8. The mold 21 was shaped so that the resin layer 12 would be formed in a region where the boundary region 17 on the side where the diffraction grating 13 is continuous has a thickness increase gradient Gb of 0.8. In all other respects, the resin layer 12 was molded in the same manner as in Example 1, and the diffractive optical element 10 was manufactured.

[0058] The shape of the diffractive optical element 10 according to Example 5 was measured after demolding in the same manner as in Example 1. The thickness increase gradient Ga at each of the three locations had a maximum of 1.8. The thickness increase gradient Gb at each of the three locations had a maximum of 0.8.

[0059] The diffractive optical element 10 according to Example 5 was evaluated by measuring the optical performance and shape accuracy in the same manner as in Example 1, and as shown in Table 1, it was confirmed that both the optical performance and shape accuracy were very good.

[0060] Example 6 In Example 6, the resin layer 12 was molded so that the thickness from the envelope surface of the diffraction grating 13 was 12 μm. In other respects, the resin layer 12 was molded in the same manner as in Example 1, and the diffractive optical element 10 was manufactured.

[0061] The shape of the diffractive optical element 10 according to Example 6 was measured after demolding in the same manner as in Example 1. The thickness increase gradient Ga at each of the three locations had a maximum of 1.8. The thickness increase gradient Gb at each of the three locations had a maximum of 0.8.

[0062] The diffractive optical element 10 according to Example 6 was evaluated by measuring its optical performance and shape accuracy in the same manner as in Example 1, and as shown in Table 1, it was confirmed that both the optical performance and shape accuracy were very good.

[0063] (Comparative Example 1) In Comparative Example 1, the same substrate as in Example 1 was used as substrate 11. The mold 21 was shaped so that the resin layer 12 was formed such that the thickness increase gradient Ga of the resin layer 12 in boundary region 16 on the side where diffraction grating 13 is discontinuous was 0, i.e., the resin layer 12 was flat. The mold 21 was shaped so that the thickness increase gradient Gb of the resin layer 12 in boundary region 17 on the side where diffraction grating 13 is continuous was 0, i.e., the resin layer 12 was flat. Except for this, molding of the resin layer 12 was carried out in the same manner as in Example 1, and a diffractive optical element 10 was manufactured.

[0064] The shape of the diffractive optical element 10 according to Comparative Example 1 was measured after demolding in the same manner as in Example 1. The thickness increase gradient Ga at each of the three locations had a maximum of 0.0. The thickness increase gradient Gb at each of the three locations had a maximum of 0.0.

[0065] The diffractive optical element 10 according to Comparative Example 1 was evaluated by measuring the optical performance and shape accuracy in the same manner as in Example 1, and as shown in Table 1, it was confirmed that both the optical performance and shape accuracy were poor.

[0066] The evaluation results for the above-mentioned Examples 1 to 6 and Comparative Example 1 are shown in Table 1 below. [Table 1]

[0067] [Second embodiment] The diffractive optical element 10 according to the first embodiment can be applied to various devices and apparatuses such as optical equipment, display devices, imaging devices, etc. In the second embodiment, optical equipment, display devices, and imaging devices will be described as specific application examples of the diffractive optical element 10 according to the first embodiment.

[0068] (optical equipment) Specific application examples of the diffractive optical element 10 according to the first embodiment include lenses constituting optical devices (projection optical systems) for head-mounted displays and liquid crystal projectors, and lenses constituting optical devices (photography optical systems) for head cameras and video cameras. It can also be used as a pickup lens for DVD recorders and the like. These optical systems are composed of at least one lens arranged in a housing, and the diffractive optical element 10 according to the first embodiment can be used for at least one of these lenses.

[0069] (Display device (projection optical system)) 9(a) to 9(c) are schematic diagrams showing the configuration of a head-mounted display (HMD) 100, which is an example of a preferred embodiment of a display device using the diffractive optical element 10 according to the first embodiment. FIG. 9(a) is a side view showing the HMD 100. FIG. 9(b) is a side view showing the HMD 100. FIG. 9(c) is a schematic diagram showing the optical system of the HMD 100.

[0070] 9(a) and 9(b), the HMD 100 has a housing 101, a wearing device 102, and display units 103 for the left and right eyes. Each display unit 103 is provided inside the housing 101. The HMD 100 is worn on the user's head H by the wearing device 102 so that the display units 103 for the left and right eyes are positioned corresponding to the user's left and right eyes, respectively.

[0071] As shown in FIG. 9( c), each display unit 103 includes a display panel 104, an optical system 105, and the diffractive optical element 10 according to the first embodiment. The display panel 104 is a display unit such as an organic electroluminescence (EL) panel or a liquid crystal panel, and displays an image for the corresponding left or right eye. The optical system 105 focuses the image light emitted from the display panel 104 at the position of the user's eye E. Depending on the design of the HMD 100, the optical system 105 may include a transmissive optical element such as a convex lens or a concave lens, a reflective optical element such as a concave mirror, or an optical path changing element such as a mirror or a polarizing beam splitter (PBS). The diffractive optical element 10 is disposed between the optical system 105 and the eye E and corrects chromatic aberration of the image light emitted from the optical system 105 and focused on the eye E via the diffractive optical element 10. The diffractive optical element 10, together with the optical system 105, constitutes an optical system that guides image light, which is light emitted from the display panel 104, to the user's eye E, and functions as at least one of the lenses in the optical system.

[0072] Although the display device has been described here using an HMD, the diffractive optical element 10 can also be used in a projector or the like.

[0073] (imaging device) 10 is a schematic diagram showing the configuration of a single-lens reflex digital camera 200, which is an example of a preferred embodiment of an imaging device using the diffractive optical element 10 according to the first embodiment. In Fig. 10, a camera body 202 and a lens barrel 201, which is an optical device, are coupled together, and the lens barrel 201 is a so-called interchangeable lens that can be attached to and detached from the camera body 202.

[0074] Light from a subject is captured through an optical system consisting of multiple lenses 203, 205, etc., arranged on the optical axis of the imaging optical system inside a housing 220 of a lens barrel 201. The diffractive optical element 10 according to the first embodiment can be used for the lenses 203, 205, for example. Here, the lens 205 is supported by an inner barrel 204, and is movably supported relative to the outer barrel of the lens barrel 201 for focusing and zooming.

[0075] During the observation period before shooting, light from the subject is reflected by a main mirror 207 inside the housing 221 of the camera body, passes through a prism 211, and then is projected to the photographer through a viewfinder lens 212 as a captured image. The main mirror 207 is, for example, a half mirror, and light transmitted through the main mirror 207 is reflected by a sub-mirror 208 toward an AF (autofocus) unit 213. This reflected light is used, for example, for distance measurement. The main mirror 207 is attached and supported by a main mirror holder 240, for example, by adhesive. During shooting, a drive mechanism (not shown) moves the main mirror 207 and sub-mirror 208 out of the optical path, opens a shutter 209, and allows an image sensor 210 to receive light that has entered through the lens barrel 201 and passed through the shooting optical system, forming a captured optical image. The aperture 206 is configured so that the brightness and depth of focus during shooting can be changed by changing the aperture area.

[0076] Although the imaging device has been described here using a single-lens reflex digital camera, the diffractive optical element 10 can also be used in smartphones, compact digital cameras, drones, and the like.

[0077] The disclosure of this embodiment includes the following configuration. (Configuration 1) a substrate having a surface on which a diffraction grating is provided; a resin layer provided on the surface of the substrate so as to cover the diffraction grating, when viewed in a plan view along the optical axis direction, the diffraction grating includes a first diffraction grating having a circular shape and a second diffraction grating having an arc shape arranged outside the first diffraction grating, the diffractive optical element has a first region in which the diffraction grating is provided and a second region that is disposed outside the first region and in which the diffraction grating is not provided, In a third region including a boundary between the first region and the second region on the side where the diffraction grating is discontinuous, the thickness of the resin layer increases from the center of the circle of the diffraction grating toward the outside at a first gradient of 0.4 or more. A diffractive optical element characterized by: (Configuration 2) The first gradient has a region of 1.8 or more and 12 or less. 2. The diffractive optical element according to configuration 1, (Configuration 3) The first gradient has at least a region where the thickness of the resin layer is greater than the second gradient in a fourth region including the boundary on the side where the diffraction grating is continuous, the thickness of the resin layer increasing from the center of the circle of the diffraction grating toward the outside. 3. The diffractive optical element according to configuration 1 or 2. (Configuration 4) The average thickness of the resin layer is 10 μm or more and 300 μm or less. 4. The diffractive optical element according to any one of configurations 1 to 3. (Configuration 5) The grating height of the diffraction grating is 1 μm or more and 30 μm or less. 5. The diffractive optical element according to any one of configurations 1 to 4. (Configuration 6) The pitch of the diffraction grating in the third region is 10 μm or more and 300 μm or less. 6. A diffractive optical element according to any one of configurations 1 to 5. (Configuration 7) The resin layer is made of a photocurable resin. 7. The diffractive optical element according to any one of configurations 1 to 6. (Configuration 8) The photocurable resin is an episulfide-based resin. 8. The diffractive optical element according to configuration 7. (Configuration 9) An inorganic film is provided between the substrate and the resin layer. 9. The diffractive optical element according to any one of configurations 1 to 8, (Configuration 10) The substrate is a resin substrate or a glass substrate. 10. The diffractive optical element according to any one of configurations 1 to 9, (Configuration 11) 1. An optical instrument comprising: a housing; and an optical system having at least one lens disposed within the housing, 11. An optical device, wherein at least one of the lenses is a diffractive optical element according to any one of configurations 1 to 10. (Configuration 12) A display device having a housing, an optical system having at least one lens disposed in the housing, and a display unit that emits light guided by the optical system, 11. A display device, wherein at least one of the lenses is a diffractive optical element according to any one of configurations 1 to 10. (Configuration 13) An imaging device having a housing, an optical system having at least one lens disposed in the housing, and an imaging element that receives light that has passed through the optical system, 11. An imaging device, wherein at least one of the lenses is a diffractive optical element according to any one of configurations 1 to 10. [Explanation of symbols]

[0078] 10 Diffractive optical element 11 Circuit Board 12 Resin layer 13 Diffraction Grating 14 First Area 15 Second Area 16 Boundary area 17 Boundary area 19 boundaries 20 Ejector 21 Mold 22 Light irradiation machine

Claims

1. a substrate having a surface on which a diffraction grating is provided; a resin layer provided on the surface of the substrate so as to cover the diffraction grating, when viewed in a plan view along the optical axis direction, the diffraction grating includes a first diffraction grating having a circular shape and a second diffraction grating having an arc shape arranged outside the first diffraction grating, the diffractive optical element has a first region in which the diffraction grating is provided and a second region that is disposed outside the first region and in which the diffraction grating is not provided, In a third region including a boundary between the first region and the second region on the side where the diffraction grating is discontinuous, the thickness of the resin layer increases from the center of the circle of the diffraction grating toward the outside at a first gradient of 0.4 or more. A diffractive optical element characterized by:

2. The first gradient has at least a region in which it is 1.8 or more and 12 or less.

2. The diffractive optical element according to claim 1.

3. The first gradient has a region where the thickness of the resin layer is greater than the second gradient in a fourth region including the boundary on the side where the diffraction grating is continuous, the region being larger than the second gradient in a thickness of the resin layer increasing from the center of the circle of the diffraction grating toward the outside.

3. A diffractive optical element according to claim 1 or 2.

4. The average thickness of the resin layer is 10 μm or more and 300 μm or less.

3. A diffractive optical element according to claim 1 or 2.

5. The grating height of the diffraction grating is 1 μm or more and 30 μm or less.

3. A diffractive optical element according to claim 1 or 2.

6. The pitch of the diffraction grating in the third region is 10 μm or more and 300 μm or less.

3. A diffractive optical element according to claim 1 or 2.

7. The resin layer is made of a photocurable resin.

3. A diffractive optical element according to claim 1 or 2.

8. The photocurable resin is an episulfide-based resin.

8. A diffractive optical element according to claim 7.

9. An inorganic film is provided between the substrate and the resin layer.

3. A diffractive optical element according to claim 1 or 2.

10. The substrate is a resin substrate or a glass substrate.

3. A diffractive optical element according to claim 1 or 2.

11. 1. An optical instrument comprising: a housing; and an optical system having at least one lens disposed within the housing, 3. An optical instrument, wherein at least one of the lenses is the diffractive optical element according to claim 1.

12. A display device having a housing, an optical system having at least one lens disposed in the housing, and a display unit that emits light guided by the optical system, 3. A display device, wherein at least one of the lenses is a diffractive optical element according to claim 1.

13. An imaging device having a housing, an optical system having at least one lens disposed in the housing, and an imaging element that receives light that has passed through the optical system, 3. An imaging device, wherein at least one of the lenses is the diffractive optical element according to claim 1.

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