Diffractive optical element and manufacturing method thereof

Abstract

A diffractive optical element (100) is provided with a substrate (1) having a first surface (11) on which a diffraction grating is formed, a second surface (12) facing the first surface (11), and a side part (13) connecting the first surface (11) and the second surface (12). The side part (13) includes a first curved surface (13a) connected, so as to be continuous, to one of the first surface (11) and the second surface (12).

Description

Diffractive optical element and method for manufacturing the same

[0001] The present disclosure relates to a diffractive optical element and a method for manufacturing a diffractive optical element.

[0002] Diffractive optical elements having diffraction gratings have been used in displays such as head-mounted displays (HMDs). The exit pupil expansion element (diffractive optical element) disclosed in Patent Document 1 includes a stray light reduction section at the end of a waveguide section that guides light.

[0003] Japanese Patent Application Laid-Open No. 2020-112614

[0004] In conventional diffractive optical elements, a diffraction grating is formed on the surface of a substrate made of a material such as glass, and then the substrate's outer shape is formed (cut out) by laser processing. Because the outer shape of the substrate is cut out by laser processing, chipping or breakage occurs on the outer periphery of the substrate. This can lead to the inclusion of foreign matter in the diffractive optical element or a decrease in the mounting accuracy of the diffractive optical element, resulting in a decrease in the yield of the diffractive optical element.

[0005] Therefore, an object of the present disclosure is to provide a diffractive optical element that suppresses the occurrence of chipping or cracking in the outer periphery of the substrate, and a method for manufacturing a diffractive optical element.

[0006] In order to achieve the above object, a diffractive optical element according to one embodiment of the present disclosure comprises a substrate having a first surface on which a diffraction grating is formed, a second surface opposite to the first surface, and a side portion connecting the first surface and the second surface, wherein the side portion includes a first curved surface that is continuously connected to either the first surface or the second surface.

[0007] According to the present disclosure, it is possible to prevent chipping or chipping from occurring on the outer periphery of the substrate.

[0008] FIG. 1 is a plan view of a diffractive optical element according to the first embodiment. FIG. 2 is a cross-sectional view taken along line AA' in FIG. 1. FIG. 3 is a cross-sectional view of a mold according to the first embodiment. FIG. 4 is a flowchart for explaining a method for manufacturing a diffractive optical element according to the first embodiment. FIG. 5 is a diagram for explaining a method for manufacturing a diffractive optical element according to the first embodiment. FIG. 6 is a cross-sectional view of a diffractive optical element according to a second embodiment. FIG. 7 is a cross-sectional view of a mold according to the second embodiment. FIG. 8 is a cross-sectional view of a mold according to a modified example.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the present invention, its applications, or its uses. In the following description, the same parts will be designated by the same reference numerals, and detailed description will be omitted as appropriate.

[0010] (First embodiment) (Configuration of diffractive optical element) Fig. 1 is a plan view of a diffractive optical element according to the first embodiment. Fig. 2 is a cross-sectional view taken along line A-A' in Fig. 1. In the following description, the left-right direction in Fig. 1 is the X direction, the up-down direction in Fig. 1 is the Y direction, and the depth direction in Fig. 1 is the Z direction.

[0011] As shown in FIG. 1, the diffractive optical element 100 according to the first embodiment includes a substrate 1 .

[0012] The substrate 1 is a sheet-like, flat-plate-like or film-like substrate. The material of the substrate 1 is, for example, glass or resin that satisfies optical properties and is a material that can be reheat-press molded as described below.

[0013] The substrate 1 has a first surface 11 , a second surface 12 opposite to the first surface 11 , and a side portion 13 connecting the first surface 11 and the second surface 12 .

[0014] A diffraction section 2 including a plurality of diffraction gratings is formed on a first surface 11 of the substrate 1 .

[0015] The diffraction section 2 includes an incident section 21 , an extension section 22 , and an exit section 23 .

[0016] The incident portion 21 is composed of a diffraction grating. The diffraction gratings of the incident portion 21 are arranged in a line in the X direction at a constant pitch. The incident portion 21 diffracts light incident on the first surface 11 of the substrate 1 (light in the depth direction (Z direction) in FIG. 1 ) toward the extension portion 22 (to the right side (X direction) in FIG. 1 ). The light diffracted by the incident portion 21 is totally reflected by the first surface 11 and the second surface 12 of the substrate 1, propagates within the substrate 1, and enters the extension portion 22.

[0017] The extension section 22 is composed of a diffraction grating. The diffraction gratings of the extension section 22 are arranged side by side at a constant pitch in a direction at an angle of 45° to the X direction. The extension section 22 diffracts the light diffracted by the incident section 21 (light toward the right (X direction) in FIG. 1 ) toward the exit section 23 (downward (Y direction) in FIG. 1 ). The light diffracted by the incident section 21 is totally reflected by the first surface 11 and the second surface 12 of the substrate 1, propagates within the substrate 1, and enters the exit section 23.

[0018] The exit section 23 is composed of a diffraction grating. The diffraction gratings of the exit section 23 are arranged in the Y direction at a constant pitch. The exit section 23 diffracts (emits) the light diffracted by the extension section 22 (light directed downward (Y direction) in FIG. 1 ) toward the first surface 11 of the substrate 1 (light directed forward (Z direction) in FIG. 1 ). At this time, the exit section 23 diffracts (emits) only a portion of the incident light and propagates the remaining light within the substrate 1. When this light re-enters the exit section 23, the exit section diffracts (emits) only a portion of the light and propagates the remaining light again within the substrate 1. By repeating this process, the exit pupil of the diffractive optical element is expanded (divided into multiple parts). As a result, even if the position of the eye (observation position) moves, any of the exit pupils can be observed.

[0019] 2, a first curved surface 13a, a second curved surface 13b, and a flat surface 13c are formed on the outer periphery of the side portion 13 of the substrate 1. The first curved surface 13a is a curved surface whose upper end is continuously connected to the outer periphery of the first surface 11. The second curved surface 13b is a curved surface whose lower end is continuously connected to the outer periphery of the second surface 12. The flat surface 13c is a plane that connects the lower end of the first curved surface 13a and the upper end of the second curved surface 13b, and extends in the Z direction.

[0020] In the configuration of the first embodiment, the side portion 13 includes a first curved surface 13a that is continuously connected to the outer periphery of the first surface 11 of the substrate 1, and a second curved surface 13b that is continuously connected to the outer periphery of the second surface 12 of the substrate 1. This continuously connects the first surface 11 and the second surface 12 of the substrate 1 to the side portion 13, making it possible to suppress chipping or chipping from occurring on the outer periphery of the substrate.

[0021] The side portion 13 also includes a flat surface 13c that connects the first curved surface 13a and the second curved surface 13b, making the side portion 13 of the substrate 1 flat and facilitating positioning of the substrate.

[0022] In Figure 2, the first curved surface 13a and the second curved surface 13b have an arc-shaped cross section, but this is not limited to this and may be a fan shape or a free curve, etc., and the first curved surface 13a and the second curved surface 13b may have any shape as long as the first surface 11 and the second surface 12 of the substrate 1 are continuously connected to the side portion 13.

[0023] (Method of Manufacturing Diffractive Optical Element) Fig. 3 is a cross-sectional view of a mold according to the first embodiment. The mold 3 in Fig. 3 is a mold used when forming the substrate 1.

[0024] The mold 3 is composed of an upper mold 31, a lower mold 32, and a body mold 33. When forming the substrate 1, a material 1' for the substrate 1 is placed in an internal space 34 formed between the upper mold 31, the lower mold 32, and the body mold 33.

[0025] FIG. 4 is a flowchart illustrating a method for manufacturing a diffractive optical element according to the first embodiment.

[0026] First, the material 1' of the substrate 1 is supplied into the internal space 34 of the mold 3 (step S1). The material 1' placed in the internal space 34 of the mold 3 is reheat-pressed (step S2). Specifically, the material 1' placed in the internal space 34 is heated (e.g., to approximately 400°C to 800°C), and then the material 1' is pressed (e.g., at approximately 0.1 to 10 MPa) by the upper mold 31 and the lower mold 32. At this time, the bottom surface of the upper mold 31 is positioned to correspond to the first surface 11 of the substrate 1, the top bottom of the lower mold 32 is positioned to correspond to the second surface 12 of the substrate 1, and the inner surface of the body mold 33 is positioned to correspond to the side portion 13 (flat surface 13c) of the substrate 1. Here, the volume of the material 1' supplied into the internal space 34 of the mold 3 is smaller than the volume of the internal space 34 (volume inside the mold) during reheat pressing. As a result, curved surfaces (first curved surface 13a and second curved surface 13b) are formed on the outer periphery (side portion 13) of the substrate 1 (material 1'). Thereafter, the substrate 1 is formed by cooling the material 1'.

[0027] After forming the substrate 1, the diffractive section 2 (diffraction grating) is formed by UV imprinting. Specifically, the substrate 1 is moved onto the stage 4, and a UV resin is applied onto the substrate 1 using a dispenser 5 to form a UV resin layer 2' (step S3, see FIG. 5(a)). Then, a mold 6 with a concave-convex pattern is roll-transferred onto the UV resin layer 2' using a pressure roll 7 (step S4, see FIG. 5(b)). The concave-convex pattern formed on the mold 6 corresponds to the shape of the diffraction grating to be formed in the diffractive section 2. Then, ultraviolet (UV) rays are irradiated onto the UV resin layer 2' from a UV light source 8 to harden the UV resin layer 2' (step S5, see FIG. 5(c)). Then, the mold 6 is peeled off from the UV resin layer 2' by the pressure roll 7 (step S6, see FIG. 5(d)). This forms the diffractive section 2 (UV resin layer 2') on the substrate 1, thereby forming the diffractive optical element 1.

[0028] In the manufacturing method of the diffractive optical element according to the first embodiment, the substrate 1 is molded using a mold 3. In conventional diffractive optical elements, after the substrate is formed, the outer shape of the substrate is cut out by laser processing, which causes chipping and breakage in the outer periphery of the substrate. In contrast, in this embodiment, the outer shape (side portion 13) of the substrate 1 is formed in advance by the mold 3, so cutting out the outer shape of the substrate by laser processing is not necessary. This makes it possible to prevent chipping and breakage in the outer periphery of the substrate.

[0029] Furthermore, in conventional diffractive optical elements, the first and second surfaces of the substrate are polished to make them flat. This causes surface waviness on the first and second surfaces of the substrate, resulting in a deterioration in the image quality of displays using the diffractive optical element. In contrast, in this embodiment, the first and second surfaces 11 and 12 of the substrate 1 are formed in advance using the mold 3, so there is no need to polish the first and second surfaces 11 and 12 of the substrate 1. This makes it possible to suppress a deterioration in the image quality of displays using the diffractive optical element.

[0030] It is to be noted that only one of the first curved surface 13a and the second curved surface 13b may be formed on the side portion 13 of the substrate 1.

[0031] The first curved surface 13a and the second curved surface 13b may be directly connected to each other.

[0032] The flat surface 13c may be omitted.

[0033] Second Embodiment Fig. 6 is a cross-sectional view of a diffractive optical element according to a second embodiment. In the second embodiment, the diffractive optical element 100 includes a plurality of substrates (two in this example). Each substrate has a first surface 11 on which a convex portion 14 is formed on the outer periphery.

[0034] 6, the diffractive optical element 100 includes substrates 1a and 1b. The substrates 1a and 1b are arranged side by side in the Z direction inside a housing 200. The housing 200 is used to fix the positions of the substrates 1a and 1b in the X, Y, and Z directions.

[0035] 1 and 2, but a convex portion 14 that protrudes in the Z direction is formed on the outer periphery of the first surface 11. A side portion 13 (flat surface 13c) is formed on the side of this convex portion 14.

[0036] 6, by providing a protrusion 14 on the first surface 11 of the substrate 1b, the distance between the substrates 1a and 1b can be maintained at a predetermined distance. In other words, the positions of the substrates 1a and 1b can be regulated by the protrusion 14 of the substrate 1b.

[0037] Furthermore, by providing the convex portions 14 on the first surface 11 of the substrate 1a, the diffractive portion 2 and the like can be protected from impacts from above and both the left and right sides of the substrate 1a in the drawing.

[0038] Furthermore, in the substrates 1a and 1b, side portions 13 are formed on the sides of the protrusions 14. A flat surface 13c extending in the Z direction is formed on the side portions 13. Since the flat surface 13c can be arranged along the inner surface of the housing 200, the positions of the substrates 1a and 1b in the X and Y directions can be regulated.

[0039] The diffraction gratings formed on the first surfaces 11 of the substrates 1a and 1b diffract light of different wavelengths, for example. That is, the diffraction gratings formed on the first surfaces 11 of the substrates 1a and 1b have different diffraction grating pitches. This allows the diffractive optical element to expand the exit pupil of a color image.

[0040] Fig. 7 is a cross-sectional view of a mold according to the second embodiment. As shown in Fig. 7, in the second embodiment, a recess 31a is formed in an upper mold 31 of the mold 3. This recess 31a is formed at a position corresponding to the protrusion 14 on the substrates 1a and 1b. In the second embodiment, the mold 3 shown in Fig. 7 is used in steps S1 to S3 of Fig. 4.

[0041] In the manufacturing method of the diffractive optical element according to the second embodiment, the substrate 1 is formed using a mold 3. In conventional diffractive optical elements, the first and second surfaces of the substrate are polished to make them flat. Therefore, when arranging multiple substrates side by side in the Z direction, it is necessary to form a diffraction grating on the first surface and then provide a restricting member on the first surface to restrict the position of the substrates relative to each other. In this case, in order to fix the positions of the multiple substrates, the lengths of the restricting member in the Z direction must be aligned, making it difficult to manufacture the diffractive optical element. Furthermore, a separate process for providing the restricting member is required. In contrast, in the manufacturing method of the diffractive optical element according to the second embodiment, the recessed portion 31a is formed in the mold 3. Therefore, by forming the substrates 1a and 1b using the mold 3, the protrusions 14 that restrict the positions of the substrates 1a and 1b are formed in advance on the substrate 1. This eliminates the need to align the lengths of the members that restrict the positions of the substrates 1a and 1b in the Z direction, facilitating the manufacture of the diffractive optical element. Furthermore, the process for providing the protrusions 14 is unnecessary.

[0042] In the present embodiment, the protrusions 14 are formed on the outer periphery of the first surface 11, but this is not limiting. For example, the protrusions 14 may be provided at a plurality of locations (at least three locations) on the first surface 11, or may be provided on the second surface 12. The protrusions 14 may have any shape as long as they can regulate the positions of the substrates 1a and 1b.

[0043] In addition, in this embodiment, the recess 31 a is formed in the upper mold 31 of the mold 3, but a recess may be formed in the lower mold 32. If a structure corresponding to the protrusion 14 can be formed on the substrate 1, the protrusion may be formed on the upper mold 31 or the lower mold 32 of the mold 3.

[0044] Other Embodiments The mold 3 may have other configurations.

[0045] FIG. 8( a) is a cross-sectional view of a mold according to a modified example. The mold 3 in FIG. 8( a) has a recess 31b formed in the upper mold 31. This recess 31a provides an alignment mark 15 to the substrate 1 when the material 1′ is reheat-pressed. In conventional diffractive optical elements, the first and second surfaces of the substrate are polished to make them flat. Therefore, providing the alignment mark 15 to the diffractive optical element requires a separate process for providing the alignment mark 15. In contrast, in this modified example, the recess 31b provides the alignment mark 15 to the substrate 1 (material 1′) when the material 1′ is reheat-pressed. This eliminates the need for the process for providing the alignment mark 15, facilitating the manufacture of diffractive optical elements.

[0046] Fig. 8(b) is a cross-sectional view of a mold according to a modified example. In Figs. 4 and 7, the bottom surface of the upper mold 31 of the mold 3 is flat, but in Fig. 8(b), the bottom surface 31c of the upper mold 31 is curved. This allows the substrate 1 to have a cylindrical shape. At least one of the upper surface of the lower mold 32 of the mold 3 and the inner surface of the trunk mold 33 may be curved. Furthermore, the shapes of the bottom surface of the upper mold 31, the upper surface of the lower mold 32, and the inner surface of the trunk mold 33 of the mold 3 may be curved, spherical, free-form, or any other shape.

[0047] Fig. 8(c) is a cross-sectional view of a mold according to a modified example. The mold 3 in Fig. 8(c) has a fine uneven pattern formed on the bottom surface 31d of the upper mold 31. This allows an anti-reflection structure (moth-eye structure) to be formed on the first surface 11 of the substrate 1, eliminating the need for a separate process of providing the first surface 11 of the substrate 1 with an anti-reflection function (such as an anti-reflection structure or an anti-reflection film (AR coating)).

[0048] The diffractive optical element of the present disclosure can be used in displays such as head-mounted displays (HMDs), for example.

[0049] REFERENCE SIGNS LIST 100 Diffractive optical element 1, 1a, 1b Substrate 1' Material 11 First surface 12 Second surface 13 Side portion 13a First curved surface 13b Second curved surface 13c Flat surface 14 Convex portion 15 Alignment mark 2 Diffraction portion 2' UV resin layer 21 Incident portion 22 Extension portion 23 Emitting portion 3 Mold 31 Upper mold 32 Lower mold 33 Body mold 34 Internal space

Claims

1. A diffractive optical element comprising: a substrate having a first surface on which a diffraction grating is formed; a second surface opposite said first surface; and a side portion connecting said first surface and said second surface, said side portion including a first curved surface that is continuously connected to either said first surface or said second surface.

2. A diffractive optical element according to claim 1, wherein the side portion includes a second curved surface that is continuously connected to the other of the first surface and the second surface, and a plane that connects the first curved surface and the second curved surface.

3. The diffractive optical element according to claim 1, wherein a convex portion is formed on at least one of the first surface and the second surface.

4. The diffractive optical element according to claim 3, wherein the convex portion is formed on the outer periphery of at least one of the first surface and the second surface.

5. A diffractive optical element according to claim 1, comprising a plurality of said substrates.

6. A method for manufacturing a diffractive optical element having a substrate, comprising: a first step of supplying a moldable glass material to a mold and forming the substrate by reheat pressing; and a second step of forming a diffraction grating on a first surface of the substrate after the first step.

7. The method for manufacturing a diffractive optical element according to claim 6, wherein in the second step, the diffraction grating is formed by UV imprinting.

8. A method for manufacturing a diffractive optical element as described in claim 6, wherein the volume of the material supplied to the mold in the first step is smaller than the volume inside the mold during the reheat press molding in the first step.

9. A method for manufacturing a diffractive optical element as described in claim 6, wherein the mold has at least one of a convex portion and a concave portion formed at a position corresponding to either the first surface or a second surface opposite the first surface of the substrate.

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