Diffraction optical element and optical device

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 instrument. [Background technology]

[0002] Conventionally, a method for reducing chromatic aberration in a lens system has been known in which a diffractive optical element having a diffractive effect is provided as a part of the optical system. In addition to correcting chromatic aberration, diffractive optical elements are known to have an aspheric 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 band by arranging two diffraction gratings in close contact with each other and appropriately setting the material and grating height 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. As a result, in the diffractive optical element described in Patent Document 1, cracks due to stress generated in the optical adjustment layer due to the hardening shrinkage of the second optical material during manufacturing are prevented.

[0005] On the other hand, optical elements used in optical devices such as cameras and head-mounted displays are often symmetrical with respect to 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 in order to reduce size, weight, 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 stresses concentrating locally on the optical adjustment layer during hardening and shrinkage by making the thickness of the optical adjustment layer, which is a resin layer on a substrate, constant. However, when the substrate is a partially cut circular shape, the diffraction grating on the substrate is circular on the inside and arc-shaped 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 hardening is different from that in the case of only a circular diffraction grating. Therefore, in the case of a diffractive optical element in which a circular diffraction grating and an arc-shaped diffraction grating are provided on a substrate, even if the thickness of the resin layer on the substrate is constant as in the technique disclosed in Patent Document 1, the diffraction efficiency is reduced due to the density difference of the resin layer, and the optical characteristics are likely to deteriorate.

[0008] An object of the present invention is to provide a diffractive optical element that can reduce or prevent degradation of optical characteristics when a diffraction grating that is circular and a diffraction grating that is arc-shaped in a 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 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, the diffractive optical element has a region in which a first gradient in the thickness of the resin layer increases from the center of the circle of the diffraction grating toward the outside is 0.4 or more. Effect 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 description 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. [Diagram 2] 1 is a schematic diagram showing a diffractive optical element according to a first embodiment of the present invention. [Diagram 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. [Diagram 5] 1 is a schematic cross-sectional view showing a diffractive optical element according to a first embodiment of the present invention. [Figure 6] 5A to 5C 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. 11 is a schematic diagram showing an imaging device according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 the present 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 the present embodiment in a plan view seen in the optical axis direction. The lower part of FIG. 1 is a cross-sectional view taken along the 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 the present embodiment. FIG. 3 is a schematic diagram showing the boundary region 16 and the boundary region 17 in the diffractive optical element 10 according to the present 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 the present embodiment, and show the region 18 surrounded by the dashed line in FIG. 3.

[0014] 1, the diffractive optical element 10 according to this embodiment has two optical elements, a substrate 11 which is 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. The substrate 11 has a diffraction grating 13 provided on one surface. 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 molded 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 aspheric 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 targeted by the diffractive optical element 10. The term "transparent" means that the transmittance of light having a wavelength in the range of 420 nm to 700 nm is 10% or more, for example.

[0016] The substrate 11 has a partially cut circular shape surrounded by an arc and a line connecting both ends of the arc in a plan view in the optical axis direction of the diffractive optical element 10. Here, the line connecting both ends of the arc may be a straight line or a curved line. Also, there may be one or more arcs. That is, in the partially cut circular shape, there may be one or more portions missing from the circular shape. The center of the partially cut 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 the planar shape, is not limited to the shape shown in FIG. 1, and may be an appropriate shape depending on the application of the diffractive optical element 10, etc.

[0017] Since substrate 11 has a planar shape of a partially cut 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 more. In addition, the line connecting both ends of the arc may be a curve.

[0018] The diffractive optical element 10 including the substrate 11 has a first region 14 having the grating pattern of the diffraction grating 13, and a second region 15 arranged outside the first region 14 and not having the grating pattern of the diffraction grating 13. The first region 14 is a region in which the diffraction grating 13 is provided, and the second region 15 is a region in which the diffraction grating is not provided. The first region 14 is a region through which light targeted by the diffractive optical element 10 generally transmits. The second region 15 is a region through which light targeted by the diffractive optical element 10 does not transmit.

[0019] As shown in Fig. 3, an arc-shaped diffraction grating 13 is present on the outside 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 are 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 side of the circumferential portion of the arc-shaped diffraction grating 13.

[0020] The diffraction grating 13 is provided on one surface of the substrate 11 having a planar shape of a partially cut circular shape, concentrically about the center of the partially cut circular circle through which the optical axis of the diffractive optical element 10 passes. In one example, the diffraction grating 13 is formed so that a gently descending slope and a steeply rising wall surface are continuously repeated from the element center passing through the optical axis to the periphery, as shown in Fig. 4. In another example, the diffraction grating 13 is formed so that a gently ascending slope and a steeply descending wall surface are continuously repeated from the element center passing through the optical axis to 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 is preferably a photocurable resin or a thermosetting resin from the viewpoint of ease of manufacture.

[0022] 1, resin layer 12 is formed on substrate 11 so as to adhere closely to substrate 11, fill in the unevenness of diffraction grating 13, and cover diffraction grating 13. Resin layer 12 is formed across first region 14 in which diffraction grating 13 is provided and second region 15 in which 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 the inorganic material 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 so as to cover the grating surface of the diffraction grating 13 along the grating surface. The transparent inorganic film can be provided by using various film forming 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 the 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 the light targeted by the diffractive optical element 10 transmits, the resin layer 12 is provided to have substantially the same resin layer thickness t with respect to the envelope surface, which is a surface 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 more in the 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 is discontinuous. The thickness increase gradient G of the resin layer 12 here is the gradient at which the thickness t of the resin layer 12 increases from the center of the circle of the diffraction grating 13 toward the outside, that is, the degree to which the thickness t of the resin layer changes from the center of the circle of the 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 inside and 0.5 mm outside the boundary 19, into 20 sections with a width of 0.05 mm each, and dividing the boundary region 16 by 0.5 mm outside, into 20 sections with a width of 0.05 mm each. The change in the average thickness of the resin layer 12 between adjacent sections is calculated by dividing the boundary region 16 by the distance of 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 can be the average thickness of the resin layer 12 from the envelope surface of the diffraction grating 13 in the first region 14. The thickness t of the resin layer 12 can be the average thickness of the resin layer 12 provided on the substrate 11 in the second region 15. The thickness t of the resin layer can be measured using a shape measuring machine or the like. The thickness t of the resin layer can be obtained by taking the difference between the measured value of the surface shape of the diffractive optical element 10 by the shape measuring machine 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 at 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 where 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 to take into consideration the shrinkage of the resin constituting the resin layer 12 when it hardens, and to suppress the density difference of the resin due to hardening to a small value.

[0029] The phenomenon in which a difference in resin density occurs due to curing will be described with reference to Figs. 6 to 8 along with the manufacturing method of the diffractive optical element 10 according to this embodiment. Fig. 6 is a schematic cross-sectional view showing the steps of the manufacturing method of the diffractive optical element 10 according to this embodiment. Figs. 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 contraction of the resin during curing.

[0030] In manufacturing the diffractive optical element 10 according to the present embodiment, first, as shown in FIG. 6(a), liquid resin 121 is discharged into a mold 21 for forming a 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 provided. 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 a resin layer 12 composed of the cured resin 121. The resin 121 used at this time 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 for curing the resin 121 through the substrate 11. In particular, a photocurable resin is more preferable because it has a fast curing speed and is cost-effective. Examples of photocurable resins include acrylic, methacrylic, epoxy, thiol, and episulfide resins. In this manner, resin 121 can be molded on 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, integral with substrate 11, from mold 21. In this manner, diffractive optical element 10 can be manufactured.

[0031] 7 and 8 show the shrinkage behavior during curing of the resin 121 constituting the resin layer 12 in the diffractive optical element 10. 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-sectional view of 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-sectional view 71 of the boundary region 17 on the side where the diffraction grating 13 in Fig. 7 is continuous.

[0032] In the manufacturing method as shown in FIG. 6, the outside of the substrate 11 is restrained when the resin 121 constituting the resin layer 12 is cured. Therefore, when the resin 121 is cured, the resin 121 of the diffractive optical element 10 mainly shrinks in the radial direction from the outer periphery to the inner periphery as shown by the solid arrow 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, so in addition to the radial shrinkage, the resin 121 shrinks in the direction along the diffraction grating 13 as shown by the dashed arrow in FIG. 7. Therefore, when the thickness of the resin layer 12 is approximately constant, the boundary region 16 on the side where the diffraction grating 13 is discontinuous and the resin 121 in the vicinity thereof become lower in density. As a result, the refractive index of the resin layer 12 in the boundary region 16 on the side where the diffraction grating 13 is discontinuous and the vicinity thereof 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 more in the 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 is discontinuous. For this reason, in this embodiment, as shown in FIG. 8, the mold 21 for providing the resin layer 12 has a gradient such that the resin layer 12 in the second region 15 is thicker. Therefore, the resin 121 can be supplied from the second region 15 to the first region 14 when the resin 121 hardens and shrinks. As a result, in this embodiment, the radial shrinkage of the resin 121 can be improved, and the shrinkage of the resin 121 in the boundary region 16 on the side where the diffraction grating 13 is discontinuous and in the vicinity thereof can also be improved. Thus, in this embodiment, by improving 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 suppressed or prevented, and the decrease in the diffraction efficiency of the resin layer 12 can be suppressed or prevented.

[0034] Furthermore, if the thickness increase gradient Ga of the resin layer 12 is 1.8 or more, the resin 121 can be sufficiently supplied during hardening 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 hardening shrinkage stress is generated in the thickness direction during the hardening 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 is 1.8 or more and 12 or less, that is, 1.8≦Ga≦12. Note that it is sufficient that the diffractive optical element 10 has at least a region where the thickness increase gradient Ga is 1.8 or more and 12 or less.

[0035] The shrinkage of the resin 121 in the 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 the 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 the 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 the boundary region 17 on the side where the diffraction grating 13 is continuous. In other words, it is preferable that Ga>Gb. It is preferable 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 the 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. The 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, the internal refractive index becomes uneven, resulting in a decrease in diffraction efficiency, whereas if the thickness 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. 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, 17 including 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 effect of the diffractive optical element 10 can be sufficiently obtained.

[0039] Thus, according to this embodiment, in the diffractive optical element 10 provided with the circular diffraction grating 13 and the arc-shaped diffraction grating 13, it is possible to reduce or prevent deterioration of the optical characteristics. 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, when the change in the 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 manufacturing method of a diffractive optical element according to the first embodiment will be described with reference to Figures 1 and 6. In the first embodiment, a diffractive optical element 10 having the shape shown in Figure 1 was manufactured.

[0042] In Example 1, first, a substrate molded by injection molding a polycarbonate-based resin material (EP4500, manufactured by Mitsubishi Gas Chemical) was prepared as the substrate 11. The substrate 11 had an outer diameter of φ46 mm, a region diameter of φ42 mm where the diffraction grating was located, a central thickness of 2.5 mm, and a peripheral thickness of 1.0 mm. One surface had a convex shape, 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 with respect to the center of the outer diameter of the substrate 11, and the grating interval became smaller from the center to the periphery. The substrate 11 had a segmented circular shape in a plan view seen in the optical axis direction, and had a shape in which a circle was cut by a straight line at a position 18 mm from the center. 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 formed by cutting a circle with a straight line at a position 16 mm from the center in the same direction as the substrate 11.

[0043] Next, the resin layer 12 was molded using the mold 21 according to the process shown in FIG. 6. The resin 121 used at this time was an episulfide-based resin material of a photocurable resin. The mold 21 had an outer diameter of φ48 mm, and the portion corresponding to the first region 14 in which the grating shape of the diffraction grating 13 was located had an aspheric shape corresponding to the envelope surface through which the apex of the diffraction grating 13 provided on the substrate 11 passed. The mold 21 had a shape in which the resin layer 12 was formed so that the resin layer 12 had a region in which the thickness increase gradient Ga of the resin layer 12 was 1.8 in the 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, 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 as shown in FIG. 6(b). At this time, the filling area of ​​the resin 121 was set to a size larger than the area 21 mm where the grating shape of the substrate 11 is present, and to a radius of 23 mm from the outer periphery of the substrate 11, in the boundary area 17 on the side where the diffraction grating 13 is continuous. The outer edge of the filling area of ​​the resin 121 was set to be between 21.1 mm and 22.5 mm as much as possible. Also, the filling area of ​​the resin 121 was set to be between 2 mm outside the outer periphery, which is the area where the grating shape of the substrate 11 is present, and to the outer periphery of the substrate 11, in the boundary area 16 on the side where the diffraction grating 13 is discontinuous. The outer edge of the filling area of ​​the resin 121 was set to be 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, thereby forming the resin layer 12. Next, the ejector 20 was raised to release the resin layer 12 together 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 optical axis center to the end at least three points in each 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 points, and the maximum Ga at each of the three points was 1.8. Specifically, the average thickness of the resin layer 12 from the position 15.5 mm from the center of the diffraction grating 13 to 16.5 mm at 0.05 mm intervals was as follows. That is, the average thickness of the resin layer 12 was 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 away from the center of the diffraction grating 13 .

[0046] In addition, the thickness increase gradient Gb of the resin layer in the boundary region 17 on the side where the diffraction grating 13 is continuous, including the boundary 19 between the first region 14 and the second region 15, was measured at three points, and the maximum Gb at each of the three points was 0.8. Specifically, the average thickness of the resin layer 12 from the position 20.5 mm from the center of the diffraction grating 13 to 21.5 mm at 0.05 mm intervals was as follows. That is, the average thickness of the 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 the 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 shape was located 21 mm away from the center of the diffraction grating 13 .

[0047] As an evaluation of the optical performance of the diffractive optical element 10 according to the embodiment 1, the diffraction efficiency in the wavelength region from 420 nm to 700 nm was measured. In the optical performance evaluation, when the change in the diffraction efficiency compared to the design value is 1% or less, the optical performance is not significantly affected, and the evaluation was made as "a" which means very good. When the change in the diffraction efficiency compared to the design value is more than 1% and less than 2%, the optical performance is not significantly affected, and the evaluation was made as "b" which means good. When the change in the diffraction efficiency compared to the design value is more than 2%, the deterioration of the optical performance cannot be ignored, and the evaluation was made as "c" which means poor. In addition, as an evaluation of the shape accuracy of the diffractive optical element 10, the shape of the surface of the resin layer 12 was compared with the design shape. When the difference from the design shape is 1 μm or less, the optical performance is not significantly affected, and the evaluation was made as "a" which means very good. When the difference from the design shape is more than 1 μm and less than 2 μm, the optical performance is not significantly affected, and the evaluation was made as "b" which means good. When the difference from the design shape is more than 2 μm, the deterioration of the optical performance cannot be ignored, and the evaluation was made as "c" which means poor. 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 the substrate 11. The mold 21 was shaped so that the resin layer 12 was formed so that the resin layer 12 had a region in which the thickness increase gradient Ga of the resin layer 12 in the boundary region 16 on the side where the diffraction grating 13 was discontinuous was 0.4. The mold 21 was shaped so that the resin layer 12 had a region in which the thickness increase gradient Gb of the resin layer 12 in the boundary region 17 on the side where the diffraction grating 13 was continuous was 0.2. 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.

[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. Also, 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 for optical performance and shape accuracy in the same manner as in Example 1. 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 the substrate 11. The mold 21 was shaped so that the resin layer 12 was formed so that the resin layer 12 had a region in which the thickness increase gradient Ga of the resin layer 12 was 1.8 in the boundary region 16 on the side where the diffraction grating 13 was discontinuous. The mold 21 was shaped so that the resin layer 12 was formed so that the resin layer 12 had a region in which the thickness increase gradient Gb of the resin layer 12 was 1.8 in the boundary region 17 on the side where the diffraction grating 13 was continuous. 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.

[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 of 1.8. The thickness increase gradient Gb at each of the three locations had a maximum 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. 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 the resin layer 12 had a region in which the thickness increase gradient Ga of the resin layer 12 in the boundary region 16 on the side where the diffraction grating 13 was discontinuous was 0.4. The mold 21 was shaped so that the resin layer 12 was formed so that the resin layer 12 had a region in which the thickness increase gradient Gb of the resin layer 12 in the boundary region 17 on the side where the diffraction grating 13 was continuous was 0.8. 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.

[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 for optical performance and shape accuracy in the same manner as in Example 1. As shown in Table 1, it was confirmed that both the optical performance and shape accuracy were excellent.

[0057] Example 5 In Example 5, a diffractive optical element 10 having the shape shown in FIG. 2 was manufactured as the substrate 11. The substrate 11 had an outer diameter of φ46 mm, a diameter of the region where the diffraction grating 13 was located of φ42 mm, a central thickness of 2.5 mm, and a peripheral thickness of 1.0 mm. One surface had a convex shape, and the other surface was flat, and a diffraction grating 13 with a grating height of 10 μm was provided. The substrate 11 had a missing circular shape with two missing parts symmetrical to the optical axis in a planar view in the optical axis direction, and had a shape in which a circle was cut by a curve at a position approximately 18 mm from the center. The diffraction grating 13 was provided in a circular shape from the center to 16 mm, i.e., up to a diameter of 32 mm, and the diffraction grating 13 from 32 mm to 42 mm had an arc shape in which a circle was cut by a curve at a position approximately 16 mm from the center in the same direction as the substrate 11. Moreover, the shape of the mold 21 was such that the resin layer 12 was formed so as to have a region in which the thickness increase gradient Ga of the resin layer 12 was 1.8 in the boundary region 16 on the side where the diffraction grating 13 was discontinuous. Moreover, the shape of the mold 21 was such that the resin layer 12 was formed so as to have a region in which the thickness increase gradient Gb of the resin layer 12 was 0.8 in the boundary region 17 on the side where the diffraction grating 13 was continuous. 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.

[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 for optical performance and shape accuracy in the same manner as in Example 1. 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. Except for this, 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 for optical performance and shape accuracy in the same manner as in Example 1. 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 the 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 the boundary region 16 on the side where the diffraction grating 13 was discontinuous was 0, that is, the resin layer 12 was flat. The mold 21 was shaped so that the thickness increase gradient Gb of the resin layer 12 in the boundary region 17 on the side where the diffraction grating 13 was continuous was 0, that is, the resin layer 12 was flat. In other respects, the resin layer 12 was molded in the same manner as in Example 1 to manufacture the diffractive optical element 10.

[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 for optical performance and shape accuracy in the same manner as in Example 1. 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 instruments, display devices, imaging devices, etc. In the second embodiment, optical instruments, 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 made up 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 the lenses.

[0069] (Display device (projection optical system)) 9(a) to 9(c) are schematic diagrams showing a 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 such 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 has a display panel 104, an optical system 105, and a 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 eye or right eye. The optical system 105 is for forming an image of 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, an optical path changing element such as a mirror or a polarizing beam splitter (PBS), or the like. The diffractive optical element 10 is installed so as to be located between the optical system 105 and the eye E, and corrects chromatic aberration of the image light emitted from the optical system 105 and formed 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 above using an HMD, the diffractive optical element 10 can also be used in a projector or the like.

[0073] (Imaging device) Fig. 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 is detachable from the camera body 202.

[0074] Light from a subject is captured via an optical system consisting of multiple lenses 203, 205, etc., arranged on the optical axis of the capturing optical system in 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 supported movably with respect to the outer barrel of the lens barrel 201 for focusing and zooming.

[0075] During an observation period before shooting, light from a subject is reflected by a main mirror 207 in a housing 221 of the camera body, passes through a prism 211, and then a shot image is projected to the photographer through a viewfinder lens 212. The main mirror 207 is, for example, a half mirror, and the light that passes through the main mirror 207 is reflected by a sub-mirror 208 in the direction of an AF (autofocus) unit 213, and this reflected light is used, for example, for distance measurement. The main mirror 207 is attached and supported by a main mirror holder 240 by adhesive or the like. During shooting, the main mirror 207 and the sub-mirror 208 are moved out of the optical path via a driving mechanism (not shown), the shutter 209 is opened, and the image sensor 210 receives light that has entered from the lens barrel 201 and passed through the shooting optical system, and forms a shooting light image. The aperture 206 is configured to change the brightness and focal depth during shooting by changing the opening area.

[0076] Although the imaging device has been described above 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 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 in a first gradient of 0.4 or more. 1. A diffractive optical element comprising: (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 a 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. The 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 as defined in 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 as defined in any one of configurations 1 to 10. [Explanation of symbols]

[0078] 10 Diffractive optical elements 11 Substrate 12 Resin layer 13 Diffraction Grating 14 First Area 15 The 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 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 in a first gradient of 0.4 or more.

1. A diffractive optical element comprising:

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 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 a diffractive optical element according to claim 1.

12. A display device including 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, 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 a diffractive optical element according to claim 1.

Images