Two-dimensional diffraction grating, projection substrate, eyeglass-type terminal, and production method for two-dimensional diffraction grating

Abstract

A two-dimensional diffraction grating according to the present invention is to diffract incident light in two directions and comprises a substrate and, on an upper surface of the substrate, a plurality of protruding structures that form a first diffraction grating that is organized at a first interval in a first direction and a second diffraction grating that is organized at a second interval in a second direction that is different from the first direction. Each of the protruding structures has a first staircase shape that has a plurality of surfaces that are parallel to the upper surface of the substrate and a plurality of surfaces that are oriented in the first direction and a second staircase shape that has a plurality of surfaces that are parallel to the upper surface of the substrate and a plurality of surfaces that are oriented in the second direction.

Description

Two-dimensional diffraction grating, projection substrate, glasses-type terminal, and method for manufacturing two-dimensional diffraction grating

[0001] The present invention relates to a two-dimensional diffraction grating, a projection substrate, a glasses-type terminal, and a method for manufacturing a two-dimensional diffraction grating.

[0002] Conventionally, glasses-type devices such as head-mounted displays that display a two-dimensional image for a user to observe using an optical system including a waveguide or the like are known (see, for example, Patent Documents 1 and 2). Also, two-dimensional diffraction gratings that diffract light in two directions are known (see, for example, Patent Document 3).

[0003] Japanese Patent Application Laid-Open No. 2017-207686 International Publication No. 2023 / 047488 U.S. Patent No. 8160411 Specification

[0004] Such glasses-type devices can be made into a simple optical system by using a two-dimensional diffraction grating. However, it has sometimes been difficult to manufacture a two-dimensional diffraction grating.

[0005] Therefore, the present invention has been made in view of these points, and an object thereof is to enable easy manufacture of a two-dimensional diffraction grating.

[0006] In a first aspect of the present invention, there is provided a two-dimensional diffraction grating for diffracting incident light in two directions, including a substrate, and a plurality of convex structures formed on the upper surface of the substrate and arranged at a first interval in a first direction and a second interval in a second direction different from the first direction, each of the convex structures having a first stepped shape having a plurality of surfaces parallel to the upper surface of the substrate and a plurality of surfaces facing the first direction, and a second stepped shape having a plurality of surfaces parallel to the upper surface of the substrate and a plurality of surfaces facing the second direction.

[0007] The length in the first direction of the plurality of surfaces parallel to the upper surface of the substrate in the first stepped shape may be different from the length in the second direction of the plurality of surfaces parallel to the upper surface of the substrate in the second stepped shape.

[0008] The cross-section of the first stepped shape formed by a plane perpendicular to the upper surface of the substrate and parallel to the first direction is inscribed in the hypotenuse of a predetermined first right triangle, and the cross-section of the second stepped shape formed by a plane perpendicular to the upper surface of the substrate and parallel to the second direction may be inscribed in the hypotenuse of a predetermined second right triangle different from the first right triangle.

[0009] In a second aspect of the present invention, there is provided a projection substrate for projecting image light onto a display surface, the projection substrate having an incident region having a diffraction grating for guiding at least a part of incident projection light for projecting the image light in a predetermined direction within the projection substrate, and a two-dimensional diffraction grating according to the first aspect provided at a position in the predetermined direction from the incident region, the projection light guided in the incident region being incident thereon, and at least a part of the incident projection light being emitted as the image light from the display surface.

[0010] In a third aspect of the present invention, there is provided a glasses-type terminal worn by a user, the glasses-type terminal including at least one of a lens for the user's right eye and a lens for the left eye, the projection substrate according to the second aspect for projecting the incident projection light as the image light onto the display surface, a frame for fixing the projection substrate, and a projection unit provided on the frame for irradiating the incident region of the projection substrate with the projection light for projecting the image light onto the two-dimensional diffraction grating.

[0011] In a fourth aspect of the present invention, there is provided a method for manufacturing a two-dimensional diffraction grating for diffracting incident light in two directions, the method including: applying a resin onto an upper surface of a substrate; pressing a mold having a plurality of recesses formed in advance against the resin applied to the substrate; curing the resin by irradiating the resin with light or applying heat while the mold is pressed against the resin; and removing the mold from the cured resin. The plurality of recesses formed in the mold are arranged at a first interval in a first direction and at a second interval in a second direction different from the first direction on a surface of the mold facing the substrate. Each of the recesses has a first stepped shape having a plurality of surfaces parallel to the surface of the mold facing the substrate and a plurality of surfaces facing the first direction, and a second stepped shape having a plurality of surfaces parallel to the surface of the mold facing the substrate and a plurality of surfaces facing the second direction.

[0012] According to the present invention, there is an effect that a two-dimensional diffraction grating can be easily manufactured.

[0013] A configuration example of the glasses-type terminal 10 according to the present embodiment is shown. A schematic of the optical path of the projection light in the glasses-type terminal 10 according to the present embodiment is shown. A schematic of the optical path of the projection light in the conventional projection substrate S is shown. An example of the conventional projection light L and image light P is shown. A configuration example of the conventional diffraction grating G1 is shown. A configuration example of the diffraction grating G2 with improved design freedom compared to the conventional diffraction grating G1 is shown. An example of the mold 50 for forming the diffraction grating G2 shown in FIG. 6 is shown. A configuration example of the projection substrate 100 according to the present embodiment is shown. A configuration example of the two-dimensional diffraction grating 300 according to the present embodiment is shown. An example of a cross-sectional view of the convex structure 320 according to the present embodiment is shown. An example of the manufacturing flow of the two-dimensional diffraction grating 300 according to the present embodiment is shown. A schematic configuration of the process of forming the two-dimensional diffraction grating 300 according to the present embodiment is shown.

[0014] <Example of the configuration of the glasses-type terminal 10> FIG. 1 shows an example of the configuration of the glasses-type terminal 10 according to the present embodiment. In this embodiment, three axes orthogonal to each other are defined as the X-axis, Y-axis, and Z-axis. The glasses-type terminal 10 is a wearable device, for example, worn by the user. The glasses-type terminal 10 projects image light onto a display area provided on the projection substrate 100 while allowing the user to observe the scenery through the glasses. The glasses-type terminal 10 includes a projection substrate 100, a frame 110, and a projection unit 120.

[0015] The projection substrate 100 projects the incident projection light as image light onto the display surface. For example, the projection substrate 100 transmits at least a part of the light incident from the first surface toward the user's eyes in the direction of the second surface. Also, the projection substrate 100 projects the light incident from the second surface as image light onto the display area provided on the second surface. Here, the first surface of the projection substrate 100 is the surface facing away from the user when the user wears the glasses-type terminal 10. Also, the second surface of the projection substrate 100 is the surface facing the user when the user wears the glasses-type terminal 10 and is the display surface of the image light. FIG. 1 shows an example in which the first surface and the second surface of the projection substrate 100 are arranged substantially parallel to the XY plane. The projection substrate 100 is, for example, a substrate on which a diffraction grating functioning as a waveguide is formed on a glass substrate. The projection substrate 100 will be described later.

[0016] The frame 110 fixes the projection substrate 100. At least one of the lenses for the user's right eye and the lens for the left eye is provided with the projection substrate 100 on the frame 110. FIG. 1 shows an example in which the projection substrate 100a is provided as the lens for the user's right eye and the projection substrate 100b is provided as the lens for the left eye on the frame 110.

[0017] Alternatively, the frame 110 may be provided with one projection substrate 100 as the lens for the user's right eye or the lens for the left eye. Also, the frame 110 may be provided with one projection substrate 100 as the lenses for both eyes of the user. In this case, the frame 110 may have the shape of goggles. The frame 110 has parts such as temples and straps so that the user can wear the glasses-type terminal 10.

[0018] The projection unit 120 is provided on the frame 110 and irradiates the projection substrate 100 with projection light for projecting image light onto the projection substrate 100. One or more such projection units 120 are provided on the frame 110. FIG. 1 shows an example in which a projection unit 120a for irradiating the projection substrate 100a with projection light L1 and a projection unit 120b for irradiating the projection substrate 100b with projection light L2 are provided on the frame 110.

[0019] The projection unit 120 may be provided at a portion of the frame 110 that fixes the projection substrate 100, or may be provided on a template or the like of the frame 110. It is desirable that the projection unit 120 is provided so as to be integrated with the frame 110. The projection unit 120 irradiates the projection substrate 100 with projection light including, for example, one wavelength, allowing the user to observe a monochromatic image. Further, the projection unit 120 may irradiate the projection substrate 100 with projection light including a plurality of wavelengths, allowing the user to observe an image including a plurality of colors.

[0020] FIG. 2 shows a schematic of the optical path of the projection light in the glasses-type terminal 10 according to the present embodiment. The projection unit 120 irradiates the projection light onto an incident region 210 provided on the projection substrate 100. The incident region 210 guides the projection light in the substrate of the projection substrate 100. Then, the projection substrate emits the projection light guided in the substrate as image light from an exit region 230. The incident region 210 and the exit region 230 will be described later.

[0021] <Optical path of the conventional projection substrate S> FIG. The projection substrate S has an incident region 210, a branching region 220, and an exit region 230. The projection light L enters the incident region 210, passes through the branching region and exits as image light P from the exit region 230. As the projection light L travels away from the incident region 210, the branching region guides the projection light L to the exit region 230 in portions.

[0022] Similarly, as the projection light L travels away from the branching region 220 in the emission region 230, the emission region 230 emits, as part of the image light P, the light of each part of the projection light L. As a result, the projection substrate S emits the projection light L incident on the incident region 210 as the image light P from the emission region 230.

[0023] <Example of Conventional Projection Light L and Image Light P>FIG. 4 shows an example of the projection light L irradiated by the projection unit 120 onto a conventional projection substrate S and the image light P emitted by the conventional projection substrate S. The projection unit 120 irradiates the projection light L, for example, toward the second surface of the projection substrate S located in the +Z direction. The projection light L corresponds to an image to be shown to the user. For example, when a screen or the like is installed on a plane substantially parallel to the XY plane and the projection light L is projected, an image M1 to be observed by the user is displayed on the screen. The image to be shown to the user is, for example, an AR (Augmented Reality) image or a VR (Virtual Reality) image created by a processor included in the projection unit 120. As described above, the projection unit 120 irradiates, as the projection light L, a plurality of light rays that form the image M1 on a plane substantially parallel to the XY plane.

[0024] In the present embodiment, an example in which the projection unit 120 projects a substantially rectangular image M1 having the X-axis direction as the longitudinal direction on a plane substantially parallel to the XY plane will be described. Also, in FIG. 4, five of the plurality of light rays irradiated by the projection unit 120 are shown as input light rays 20. For example, the light ray corresponding to the pixel in the upper left of the image is the first input light ray 20a, the light ray corresponding to the pixel in the lower left of the image is the second input light ray 20b, the light ray corresponding to the pixel in the center of the image is the third input light ray 20c, the light ray corresponding to the pixel in the upper right of the image is the fourth input light ray 20d, and the light ray corresponding to the pixel in the lower right of the image is the fifth input light ray 20e.

[0025] The projection unit 120 irradiates, for example, the incident region 210 of the projection substrate S with such projection light L so as to create a virtual upright image at infinity or a predetermined position. The projection light incident on the incident region 210 exits as image light P from the exit region 230 via the branching region 220. The image light P exits from the exit region 230 and enters the user's eye that is separated from the projection substrate S by a distance d. Then, the image light P forms an image M2 on the retina of the user's eye. Thus, the image light P includes a plurality of light beam bundles that form an image as the image M2.

[0026] In FIG. 4, five of the plurality of light beam bundles that are irradiated from the circular region C of the exit region 230 of the projection substrate S and form an image at a predetermined position are shown as output light beam bundles 30. For example, the light beam bundle that forms an image as the pixel in the lower right of the image is the first output light beam bundle 30a, the light beam bundle that forms an image as the pixel in the upper right of the image is the second output light beam bundle 30b, the light beam bundle that forms an image as the pixel in the center of the image is the third output light beam bundle 30c, the light beam bundle that forms an image as the pixel in the lower left of the image is the fourth output light beam bundle 30d, and the light beam bundle that forms an image as the pixel in the upper left of the image is the fifth output light beam bundle 30e.

[0027] Each light beam bundle corresponds to each of the plurality of input light rays 20 incident from the projection unit 120. For example, the first output light beam bundle 30a corresponds to the first input light ray 20a, and the first input light ray 20a includes a plurality of light rays generated by multiple branching and multiple diffractions or the like between the incident region 210 and the exit region 230 of the projection substrate S. Similarly, the second output light beam bundle 30b corresponds to the second input light ray 20b, the third output light beam bundle 30c corresponds to the third input light ray 20c, the fourth output light beam bundle 30d corresponds to the fourth input light ray 20d, and the fifth output light beam bundle 30e corresponds to the fifth input light ray 20e, respectively.

[0028] In other words, the image M2 formed by the image light P exiting from the exit region 230 on the retina of the user's eye corresponds to the image M1 projected by the projection light L irradiated by the projection unit 120. Thereby, the user wearing the glasses-type terminal 10 can feel as if the image M2 is projected on the second surface of the projection substrate S overlaid on the scenery seen through the projection substrate S. In other words, the exit region 230 functions as a display region for displaying the image M2 corresponding to the image M1 projected by the projection light L.

[0029] In FIG. 4, an example is shown where the image M2 observed by the user is an image obtained by inverting the image M1 projected by the projection light L vertically and horizontally. Note that the image M1 projected by the projection light L may be a still image, or instead, it may be a moving image.

[0030] According to the above-described conventional projection substrate S, the user can observe a still image, a moving image, etc. superimposed on the scenery viewed through the projection substrate S. However, in order to manufacture such a projection substrate S, it may be complicated and time-consuming to form three types of parts such as the incident region 210, the branching region 220, and the exit region 230 on the substrate.

[0031] In this case, it is conceivable to simplify the optical system by using a two-dimensional diffraction grating having the functions of the branching region 220 and the exit region 230. However, it has sometimes been difficult to manufacture a two-dimensional diffraction grating. Also, the design freedom of the diffraction grating has sometimes been limited as follows.

[0032] <Example of the configuration of the conventional diffraction grating G1> FIG. 5 shows an example of the configuration of the conventional diffraction grating G1. FIG. 5 shows a one-dimensional diffraction grating G1 in which a plurality of structures of width W

[0032] are arranged at intervals S ０ . Note that the width of the structure of the diffraction grating may be called a line, the interval between two adjacent structures may be called a space, and the period of a plurality of structures may be called a pitch. In this case, the pitch is the sum of the line and the space. Also, the value obtained by dividing the line by the pitch is called a fill factor.

[0033] The diffraction grating G1 transmits or diffracts the incident light. For example, the light incident on the exit region 230 shown in FIG. 2 is the light guided by being reflected a plurality of times inside the projection substrate 100. Therefore, the light incident on the diffraction grating of the exit region 230 enters the diffraction grating in an incident direction having a predetermined angle with respect to the surface (for example, the XY plane) of the projection substrate 100 on which the diffraction grating of the exit region 230 is formed.

[0034] Then, the diffraction grating in the light-emitting region 230 diffracts a part of the light incident in the direction where the user's eye is located while transmitting a part of the light incident on an adjacent diffraction grating. Therefore, it is desirable that the diffraction grating can be designed in a three-dimensional manner within a certain range for the incident direction of the incident light, the diffraction direction of the diffracted light, and the transmission direction of the transmitted light.

[0035] The diffraction grating G1 shown in FIG. 5 is formed such that the direction in which the structure extends is a predetermined direction on the plane (XY plane) where the diffraction grating G1 is formed. Thereby, the incident direction of the incident light, the diffraction direction of the diffracted light, and the transmission direction of the transmitted light of the diffraction grating G1 can be set in a direction corresponding to the predetermined direction. Note that adjusting the direction in which the structure extends corresponds to adjusting the incident angle of the incident light incident on the diffraction grating G1 in the XY plane parallel to one surface of the projection substrate 100.

[0036] <Configuration Example of Diffraction Grating G2> FIG. 6 shows a configuration example of a diffraction grating G2 with a higher degree of design freedom than the conventional diffraction grating G1. The diffraction grating G2 has a width W ０ and a plurality of structures are arranged at intervals S ０ . Each of the structures is formed such that the width of the structure decreases as it moves away from the plane (as an example, the XY plane) where the structure is formed in the vertical direction (+Z direction or -Z direction). For example, each of the structures has a cross-section perpendicular to the extending direction of the structure in the shape of a right triangle.

[0037] Such a diffraction grating G2 is formed such that, in addition to the direction in which the structure extends (the incident angle of the incident light incident on the diffraction grating G2), which is the same as that of the diffraction grating G1, the angle of the slope of the structure with respect to the plane where the diffraction grating G2 is formed (the angle φ shown in FIG. 6) becomes a predetermined angle. Thereby, the incident direction of the incident light, the diffraction direction of the diffracted light, and the transmission direction of the transmitted light of the diffraction grating G2 can be set in a direction corresponding to the incident angle and the predetermined angle φ. Therefore, the diffraction grating G2 can have a higher degree of design freedom than the diffraction grating G1. Note that the shape of such a diffraction grating G2 is a known shape called Blazed.

[0038] However, forming a plurality of structures having inclined surfaces can sometimes be difficult. For example, consider the case of forming a diffraction grating by filling a resin into a mold or the like. In this case, a mold having a concave portion corresponding to the structure to be formed must be formed in advance. For example, FIG. 7 shows an example of a mold 50 for forming the diffraction grating G2 shown in FIG. 6. FIG. 7 shows the cross-sectional shape of the mold 50 in the XZ plane parallel to the Z direction.

[0039] When forming the concave portion 51 in the mold 50, it is easy to form a hole in the vertical direction (Z direction) from one surface (XY plane) of the mold 50. However, as shown in FIG. 7, it is difficult to form the inclined surface 52. Further, when the cross-sectional shape of the concave portion 51 becomes smaller as it moves away from one surface of the mold 50 in the vertical direction, the shape of the end portion 53 of the concave portion 51 on the side opposite to one surface of the mold 50 becomes a narrow space. It is also difficult to form the shape of such an end portion 53.

[0040] Also, even if a mold 50 having such a concave portion 51 is formed, it may be difficult to fill the resin into the concave portion 51 without any gaps. Therefore, it may be difficult to form the diffraction grating G2 as shown in FIG. 6. Further, although FIG. 6 is an example of a one-dimensional diffraction grating, forming a two-dimensional diffraction grating having a plurality of structures having inclined surfaces in two directions may be even more difficult. Therefore, the projection substrate 100 according to the present embodiment constitutes a two-dimensional diffraction grating with improved design freedom without forming an inclined surface. Such a projection substrate 100 will be described next.

[0041] <Configuration Example of Projection Substrate 100> FIG. 8 shows a configuration example of the projection substrate 100 according to the present embodiment. FIG. 8 shows an example in which the first surface and the second surface of the projection substrate 100 are arranged substantially parallel to the XY plane. The projection substrate 100 has an incident region 210 and a two-dimensional diffraction grating 300. The projection light L is incident on the incident region 210 and is emitted as image light P from the two-dimensional diffraction grating 300. In other words, the two-dimensional diffraction grating 300 functions as the emission region 230 described in FIG. 2.

[0042] The projection substrate 100 is a substrate for projecting incident projection light as image light onto a display surface. The projection substrate 100 is a substrate formed of glass, plastic, resin, or the like. The projection substrate 100 includes an incident region 210 and a two-dimensional diffraction grating 300.

[0043] The incident region 210 receives projection light for projecting image light. The incident region 210 may be formed on the first surface of the projection substrate 100, or alternatively, may be formed on the second surface of the projection substrate 100. The incident region 210 has a diffraction grating that guides at least a part of the incident projection light in a predetermined direction within the projection substrate 100. Here, the predetermined direction is the direction in which the two-dimensional diffraction grating 300 is provided. In other words, the incident region 210 guides at least a part of the incident projection light to the two-dimensional diffraction grating 300.

[0044] The incident region 210 has, for example, an incident diffraction grating in which a plurality of groove portions are formed at a predetermined period. The plurality of groove portions function as a diffraction grating by being arranged in the same direction on one surface of the projection substrate 100 with a predetermined groove width and interval. The incident diffraction grating may be a reflective diffraction grating or a transmissive diffraction grating.

[0045] The predetermined period of the plurality of groove portions is, for example, in the range of about 10 nm to about 10 μm. The predetermined period is preferably in the range of about 100 nm to about 1 μm. The predetermined period is more preferably in the range of about 200 nm to about 800 nm. The depth of the plurality of groove portions is in the range of about 1 nm to about 10 μm. The depth of the plurality of groove portions is preferably in the range of about 10 nm to about 250 nm. The depth of the plurality of groove portions is more preferably in the range of about 50 nm to about 250 nm.

[0046] The fill factor of the plurality of groove portions ranges from about 0.05 to about 0.95. Preferably, the fill factor of the plurality of groove portions ranges from about 0.3 to about 0.7. Here, the fill factor is a value obtained by dividing the distance between two adjacent groove portions by the first period. Note that the distance between two adjacent groove portions may be referred to as a line, the width of the groove portion may be referred to as a space, and a predetermined period may be referred to as a pitch. In this case, the pitch is the sum of the line and the space, and the fill factor is a value obtained by dividing the line by the pitch.

[0047] The plurality of groove portions are arranged, for example, in a direction from the incident region 210 toward the two-dimensional diffraction grating 300. Since the projection light is incident on the incident region 210 while converging, the incident region 210 guides the projection light to the two-dimensional diffraction grating 300 so as to have a divergence angle centered on the direction toward the two-dimensional diffraction grating 300 in the plane of the projection substrate 100.

[0048] The two-dimensional diffraction grating 300 is provided at a position in a predetermined direction from the incident region 210. The projection light guided in the incident region 210 is incident on the two-dimensional diffraction grating 300, and at least a part of the incident projection light is emitted as image light from the second surface of the projection substrate 100. The two-dimensional diffraction grating 300 may be formed on the first surface of the projection substrate 100, or alternatively, may be formed on the second surface of the projection substrate 100. In the present embodiment, an example in which the two-dimensional diffraction grating 300 is formed on the second surface of the projection substrate 100 will be described.

[0049] FIG. 8 shows an example in which the two-dimensional diffraction grating 300 has a rectangular shape with the X-axis direction as the longitudinal direction in a plane substantially parallel to the XY plane, but is not limited thereto. The two-dimensional diffraction grating 300 only needs to be able to guide the projection light and emit it as image light. For example, it may have a shape such as a rectangle, a trapezoid, an oval, or an ellipse with the Y-axis direction as the longitudinal direction, or alternatively, may have a square or circular shape.

[0050] The two-dimensional diffraction grating 300 has a reflective or transmissive diffraction grating, and guides the image light in the direction of the user's eye by reflective diffraction or transmissive diffraction. A more specific configuration of such a two-dimensional diffraction grating 300 will be described next.

[0051] <Example of the configuration of the two-dimensional diffraction grating 300> Fig. 9 shows an example of the configuration of the two-dimensional diffraction grating 300 according to this embodiment. The two-dimensional diffraction grating 300 is a diffraction grating for diffracting incident light in two directions. The two-dimensional diffraction grating 300 diffracts the incident light in the XY plane and propagates it so as to form image light on the entire two-dimensional diffraction grating 300, and emits the image light toward the user's eye in the Z direction. The two-dimensional diffraction grating 300 includes a substrate 310 and a plurality of convex structures 320.

[0052] The substrate 310 is a substrate formed of glass, plastic, resin, or the like. The substrate 310 may be formed of the same material as the projection substrate 100, or alternatively, the substrate 310 may be a part of the projection substrate 100. When the substrate 310 is a part of the projection substrate 100, the plurality of convex structures 320 are formed in a partial region of the projection substrate 100. In other words, a partial region of the projection substrate 100 becomes the substrate 310.

[0053] The plurality of convex structures 320 are arranged at a first interval in a first direction on the upper surface of the substrate 310, and are also arranged at a second interval in a second direction different from the first direction. In other words, the plurality of convex structures 320 form a first diffraction grating arranged at a first interval in a first direction on the upper surface of the substrate 310, and form a second diffraction grating arranged at a second interval in a second direction different from the first direction. Thereby, the plurality of convex structures 320 function as a two-dimensional diffraction grating. The first direction and the second direction may be orthogonal or non-orthogonal. For example, in Fig. 9, the X direction is the first direction and the Y direction is the second direction.

[0054] The pitch, line, space, and fill factor of the first diffraction grating and the second diffraction grating are set to predetermined values. For example, the pitch of the first diffraction grating and the second diffraction grating is in the range of about 10 nm to about 10 μm. The pitch of the first diffraction grating and the second diffraction grating is preferably in the range of about 100 nm to about 1 μm. The pitch of the first diffraction grating and the second diffraction grating is more preferably in the range of about 200 nm to about 800 nm.

[0055] The fill factors of the first folding grating and the second folding grating are in the range of about 0.05 to about 0.95. The fill factors of the first folding grating and the second folding grating are preferably in the range of about 0.3 to about 0.7.

[0056] The height of the plurality of convex structures 320 is in the range of about 1 nm to about 10 μm. The height of the plurality of convex structures 320 is preferably in the range of about 10 nm to about 250 nm. The height of the plurality of convex structures 320 is more preferably in the range of about 50 nm to about 250 nm.

[0057] The two-dimensional diffraction grating 300 is formed such that the incident angle of incident light incident on the first diffraction grating is a predetermined angle in a plane parallel to the upper surface of the substrate 310. Similarly, the two-dimensional diffraction grating 300 is formed such that the incident angle of incident light incident on the second diffraction grating is a predetermined angle in a plane parallel to the upper surface of the substrate 310.

[0058] Each of the convex structures 320 has a plurality of surfaces parallel to the upper surface of the substrate 310. FIG. 9 shows an example in which the convex structure 320 has three surfaces, a first surface 321, a second surface 322, and a third surface 323, parallel to the upper surface of the substrate 310. Also, each of the convex structures 320 has a plurality of surfaces facing in the first direction. FIG. 9 shows an example in which the convex structure 320 has three surfaces, a fourth surface 324, a fifth surface 325, and a sixth surface 326, facing in the first direction.

[0059] The six surfaces from the first surface 321 to the sixth surface 326 of the convex structure 320 form a stepped shape facing in the first direction. In the present embodiment, the stepped shape facing in the first direction is referred to as the first stepped shape. FIG. 10 shows an example of an A-A cross-sectional view of the convex structure 320 according to the present embodiment. FIG. 10 shows an A-A cross-sectional view of the convex structure 320 by a plane parallel to the Z direction passing through the A-A line shown in FIG. 9. From FIG. 10, it can be seen that a part of the cross-section of the convex structure 320 has a cross-section of the first stepped shape.

[0060] The cross section of the first step shape is inscribed in the hypotenuse of a predetermined first right triangle. In FIG. 10 , the predetermined first right triangle is indicated by a dotted line. Here, the predetermined first right triangle has the same shape as the right triangle that is a cross section perpendicular to the extension direction of the structure of the diffraction grating G2 shown in FIG. 6 . The first diffraction grating of the two-dimensional diffraction grating 300 is formed by a plurality of convex structures 320 having such a first step shape. This allows the first diffraction grating to have a function similar to that of the diffraction grating G2.

[0061] In other words, the first diffraction grating of the two-dimensional diffraction grating 300 can set the diffraction direction of the diffracted light and the transmission direction of the transmitted light in accordance with the angle of incidence of the incident light on the first diffraction grating and the angle of the hypotenuse of the predetermined first right triangle. Therefore, like the diffraction grating G2, the first diffraction grating can have a higher degree of design freedom than the diffraction grating G1. Note that it is desirable that the number of steps, the step height, etc. of the first staircase shape be formed finer.

[0062] Each of the convex structures 320 further has a plurality of surfaces facing the second direction. Fig. 9 shows an example in which the convex structure 320 has three surfaces, a seventh surface 327, an eighth surface 328, and a ninth surface 329, facing the second direction. The six surfaces of the convex structure 320, the first surface 321 to the third surface 323 and the seventh surface 327 to the ninth surface 329, form a staircase shape similar to the first staircase shape. In this embodiment, the staircase shape facing the second direction is referred to as a second staircase shape.

[0063] As shown in the example of the cross-sectional view of the convex structure 320 in FIG. 10 , a portion of the cross-section of the convex structure 320 taken along a plane perpendicular to the upper surface of the substrate 310 and parallel to the second direction has a second step-shaped cross-section. The cross-section of the second step-shaped cross-section is also inscribed in the hypotenuse of a predetermined second right-angled triangle. Like the first right-angled triangle, the predetermined second right-angled triangle has the same shape as the right-angled triangle that is a cross-section perpendicular to the extension direction of the structure of the diffraction grating G2 shown in FIG. 6 . The second diffraction grating of the two-dimensional diffraction grating 300 is formed by a plurality of convex structures 320 having the second step-shaped cross-section, and thus, like the first diffraction grating, can have a function similar to that of the diffraction grating G2.

[0064] In other words, the second diffraction grating of the two-dimensional diffraction grating 300 can set the diffraction direction of the diffracted light and the transmission direction of the transmitted light in accordance with the angle of incidence of the incident light on the second diffraction grating and the angle of the hypotenuse of the predetermined second right triangle. Therefore, like the first diffraction grating, the second diffraction grating can have a higher degree of design freedom than the diffraction grating G1. Note that it is desirable that the number of steps, the step height, etc. of the second staircase shape be formed finer.

[0065] Here, the first and second staircase shapes may be the same shape, or alternatively, may be different shapes. The first and second staircase shapes are desirably determined in advance in accordance with the incident position of the projection light incident on the two-dimensional diffraction grating 300, the incident angle of the projection light, the shape of the two-dimensional diffraction grating 300 in a plane parallel to the top surface of the substrate 310, and the like.

[0066] For example, if the two-dimensional diffraction grating 300 has a rectangular shape and projection light is incident on one of the four vertices of the rectangle, the amount of light propagating in the long side direction of the rectangle will be different from the amount of light propagating in the short side direction. In this case, it is desirable that the first and second staircase shapes be formed in different shapes corresponding to the amount of light to be propagated.

[0067] For example, if the first staircase shape and the second staircase shape are different shapes, the length (depth) of one step of the first staircase shape is formed to be a value different from the length (depth) of the corresponding step of the second staircase shape. In other words, the length in a first direction of multiple faces parallel to the top surface of the substrate 310 in the first staircase shape is different from the length in a second direction of multiple faces parallel to the top surface of the substrate 310 in the second staircase shape.

[0068] For example, the length in the first direction of the first surface 321 of the convex structure 320 is a value different from the length in the second direction of the first surface 321. Similarly, the length in the first direction of the second surface 322 is a value different from the length in the second direction of the second surface 322, and the length in the first direction of the third surface 323 is a value different from the length in the second direction of the third surface 323.

[0069] In other words, by forming the lengths in the first direction and the second direction of the multiple faces of the convex structure 320 that are parallel to the upper surface of the substrate 310 to correspond to the transmission direction and diffraction direction of the projection light, it is possible to form a two-dimensional diffraction grating 300 that can be used for the projection substrate 100. The two-dimensional diffraction grating 300 according to this embodiment described above does not have the inclined surfaces 52 that are inclined with respect to the upper surface of the substrate 310, as in the diffraction grating G2 described in FIG. 6. Therefore, a mold for forming the two-dimensional diffraction grating 300 can be easily formed by forming holes in the vertical direction. A method for manufacturing the two-dimensional diffraction grating 300 using such a mold will now be described.

[0070] <Example of Manufacturing Flow of Two-Dimensional Diffraction Grating 300> FIG. 11 shows an example of a manufacturing flow of the two-dimensional diffraction grating 300 according to this embodiment. FIG. 12 shows a schematic configuration of the process of forming the two-dimensional diffraction grating 300 according to this embodiment. First, a resin 410 is applied to the upper surface of a substrate 310 (S11). The resin 410 preferably contains a material that hardens when exposed to light, heat, or the like. The resin 410 is, for example, a resin, a resist, or the like. The resin 410 is applied to the upper surface of the substrate 310 by a coating device or the like. FIG. 12(A) shows a substrate 310 on whose upper surface the resin 410 has been applied.

[0071] Next, a mold 420 in which a plurality of recesses 421 have been formed in advance is pressed against the resin 410 applied to the substrate 310 (S12). The recesses 421 of the mold 420 have a shape that, when filled with the resin 410, causes the filled resin 410 to form a plurality of convex structures 320 as shown in Fig. 9. For example, the plurality of recesses 421 formed in the mold 420 are arranged at a first interval in a first direction on the surface of the mold 420 facing the substrate 310, and are also arranged at a second interval in a second direction different from the first direction.

[0072] In addition, each of the recesses 421 has a first step shape having multiple faces parallel to the surface of the mold 420 facing the substrate 310 and multiple faces facing a first direction, and a second step shape having multiple faces parallel to the surface of the mold 420 facing the substrate 310 and multiple faces facing a second direction.

[0073] As described above, the recesses 421 of such mold 420 do not have slopes that are inclined with respect to the upper surface of substrate 310. Therefore, it is possible to easily form such recesses 421 in mold 420. Furthermore, since the recesses 421 of mold 420 do not have sharp edges or the like, by pressing mold 420 against resin 410, it is possible to easily fill the resin 410 to every corner of the recesses 421.

[0074] The mold 420 is handled so as to be movable relative to the substrate 310, for example, by a fixing jig and a moving device for the mold 420 (not shown), and is pressed against the upper surface (XY plane) of the substrate 310 in a direction perpendicular to the substrate 310 (Z direction). Note that the application device, the moving device, and the like are desirably controlled by a computer such as a CPU. Fig. 12(B) shows the substrate 310 with the mold 420 pressed against the resin 410.

[0075] Next, while the mold 420 is pressed against the resin 410, the resin 410 is hardened by irradiating it with light or applying heat (S13). Next, the mold 420 is removed from the hardened resin 410 (S14). The mold 420 is moved in a direction perpendicular to the upper surface of the substrate 310, for example, by a mold 420 fixing jig and moving device (not shown). In this manner, the two-dimensional diffraction grating 300 can be formed. FIG. 12(C) shows the two-dimensional diffraction grating 300 formed after the mold 420 is removed.

[0076] As described above, the two-dimensional diffraction grating 300 according to this embodiment can improve design freedom by not having an inclined surface inclined with respect to the upper surface of the substrate 310. Therefore, such a two-dimensional diffraction grating 300 can be easily manufactured.

[0077] In the above embodiment, an example has been described in which the two-dimensional diffraction grating 300 diffracts incident light in two directions, but the present invention is not limited to this. The two-dimensional diffraction grating 300 may also be used to diffract two incident light beams in one direction.

[0078] The present invention has been described above using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by functionally or physically distributing or integrating in any unit. Furthermore, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effects of the new embodiments resulting from the combination also have the effects of the original embodiments.

[0079] 10 Glasses-type terminal 20 Input light beam 30 Output light beam bundle 50 Mold 51 Recess 52 Slope 53 End 100 Projection substrate 110 Frame 120 Projection unit 210 Incident area 220 Branching area 230 Emission area 300 Two-dimensional diffraction grating 310 Substrate 320 Convex structure 321 First surface 322 Second surface 323 Third surface 324 Fourth surface 325 Fifth surface 326 Sixth surface 327 Seventh surface 328 Eighth surface 329 Ninth surface 410 Resin 420 Mold 421 Recess

Claims

1. A two-dimensional diffraction grating for diffracting incident light in two directions, comprising: a substrate; and a plurality of convex structures on an upper surface of the substrate, which form a first diffraction grating arranged at a first interval in a first direction and a second diffraction grating arranged at a second interval in a second direction different from the first direction, wherein each of the convex structures has a first step shape having a plurality of faces parallel to the upper surface of the substrate and a plurality of faces facing the first direction, and a second step shape having a plurality of faces parallel to the upper surface of the substrate and a plurality of faces facing the second direction.

2. The two-dimensional diffraction grating according to claim 1, wherein the lengths in the first direction of the multiple faces in the first step shape that are parallel to the top surface of the substrate are different from the lengths in the second direction of the multiple faces in the second step shape that are parallel to the top surface of the substrate.

3. The two-dimensional diffraction grating according to claim 1, wherein a cross section of the first step shape taken by a plane perpendicular to the upper surface of the substrate and parallel to the first direction is inscribed in the hypotenuse of a predetermined first right-angled triangle, and a cross section of the second step shape taken by a plane perpendicular to the upper surface of the substrate and parallel to the second direction is inscribed in the hypotenuse of a predetermined second right-angled triangle different from the first right-angled triangle.

4. A projection substrate for projecting image light onto a display surface, comprising: an incident area having a diffraction grating into which projection light for projecting the image light is incident and which guides at least a portion of the incident projection light in a predetermined direction within the projection substrate; and the two-dimensional diffraction grating according to any one of claims 1 to 3, which is provided at a position in the predetermined direction from the incident area, into which the projection light guided in the incident area is incident and which emits at least a portion of the incident projection light from the display surface as the image light.

5. A glasses-type terminal worn by a user, comprising: the projection board according to claim 4, which is provided as at least one of a lens for the right eye and a lens for the left eye of the user, and which projects the incident projection light onto the display surface as the image light; a frame that fixes the projection board; and a projection unit that is provided on the frame and irradiates the projection light onto the incident area of ​​the projection board to project the image light onto the two-dimensional diffraction grating.

6. A method for manufacturing a two-dimensional diffraction grating for diffracting incident light in two directions, comprising the steps of: applying a resin to an upper surface of a substrate; pressing a mold, on which a plurality of recesses have been formed, against the resin applied to the substrate; hardening the resin by irradiating the resin with light or applying heat while the mold is pressed against the resin; and removing the mold from the hardened resin, wherein the plurality of recesses formed in the mold are arranged at a first interval in a first direction on a surface of the mold facing the substrate, and are arranged at a second interval in a second direction different from the first direction, and each of the recesses has a first step shape having a plurality of faces parallel to the surface of the mold facing the substrate and a plurality of faces facing the first direction, and a second step shape having a plurality of faces parallel to the surface of the mold facing the substrate and a plurality of faces facing the second direction.

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