Method for manufacturing diffraction grating, diffraction grating, projection substrate, and eyewear-type terminal

Abstract

A method for manufacturing a diffraction grating includes: a step of applying a resin to a first diffraction grating region of a substrate; a step of pressing a mold against the resin applied to the substrate, the mold such that a plurality of recesses are formed in advance in a region facing the first diffraction grating region of the substrate; a step of curing the resin by irradiating the resin with light or applying heat thereto, while the mold is pressed against the resin; and a step of removing the mold from the cured resin. The resin is blown onto the upper surface of the substrate so that the thickness of the resin applied to a first region within the first diffraction grating region of the substrate is different from the thickness of the resin applied to a second region, different from the first region, within the first diffraction grating region of the substrate.

Description

Diffraction grating manufacturing method, diffraction grating, projection substrate, and eyeglass-type terminal

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

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

[0003] Japanese Patent Application Publication No. 2017-207686 International Publication No. 2023 / 047488 U.S. Patent No. 8,160,411

[0004] Such eyeglass-type devices can be made into a simple optical system by using a projection substrate with a diffraction grating formed on the substrate, but it can be difficult to easily form a diffraction grating on the substrate.

[0005] The present invention has been made in view of these points, and has as its object to make it possible to easily form a diffraction grating on a substrate.

[0006] a mold having a plurality of recesses pre-formed in a region of the substrate facing the first diffraction grating region, against the resin applied to the substrate; curing the resin by irradiating the resin with light or by applying heat to the resin while the mold is pressed against the resin; and removing the mold from the cured resin, wherein in the resin applying step, the resin is sprayed onto the upper surface of the substrate such that a thickness of the resin applied to a first region within the first diffraction grating region of the substrate is different from a thickness of the resin applied to a second region within the first diffraction grating region of the substrate that is different from the first region; and wherein the recesses formed in the mold are arranged at a first interval in a first direction, and a depth of the recesses in the region of the substrate facing the first region is different from a depth of the recesses in a region of the substrate facing the second region.

[0007] In the step of applying the resin, the resin may be sprayed onto the upper surface of the substrate by an inkjet method.

[0008] In the step of applying the resin, the resin may be applied so that the thickness of the resin applied to the first region is smaller than the thickness of the resin applied to the second region, and the multiple recesses formed in the mold may be formed so that the depth of the recesses in the region facing the first region of the substrate is shallower than the depth of the recesses in the region facing the second region of the substrate.

[0009] The first direction may be a direction from the first region toward the second region, and in the step of applying the resin, the resin may be applied so that the thickness of the resin gradually increases in the first direction, and the multiple recesses formed in the mold may be formed so that the depths of adjacent recesses are the same or deeper in the first direction from the region of the substrate facing the first region toward the region facing the second region.

[0010] In the step of pressing the mold, the mold may be pressed so that a region of a surface of the mold facing the upper surface of the substrate, excluding the recess, comes into contact with the upper surface of the substrate.

[0011] The step of applying the resin may further include a step of applying the resin to a second diffraction grating region different from the first diffraction grating region, and in the step of applying the resin to the second diffraction grating region, the resin may be sprayed onto the upper surface of the substrate such that a thickness of the resin applied to a third region within the second diffraction grating region is different from a thickness of the resin applied to a fourth region within the second diffraction grating region, and the plurality of recesses formed in the mold may be arranged at second intervals in a second direction different from the first direction, and a depth of the recesses in a region of the substrate facing the third region may be different from a depth of the recesses in a region of the substrate facing the fourth region.

[0012] The second direction may be a direction from the third region toward the fourth region, and in the step of applying the resin to the second diffraction grating region, the resin may be applied so that the thickness of the resin gradually increases in the second direction, and the multiple recesses formed in the mold may be formed so that the depths of adjacent recesses are the same or deeper in the second direction from the region of the substrate facing the third region toward the region facing the fourth region.

[0013] In a second aspect of the present invention, there is provided a diffraction grating comprising: a substrate; and a plurality of structures formed of resin, the structures being arranged in a first direction at a first interval in a first diffraction grating region on an upper surface of the substrate; wherein, within the first diffraction grating region of the substrate, the plurality of structures formed in a first region have a different height from the upper surface of the substrate in a direction perpendicular to the substrate, compared to the plurality of structures formed in a second region different from the first region.

[0014] In a third aspect of the present invention, there is provided a projection substrate for projecting image light onto a display surface, comprising: an incident region into which projection light for projecting the image light is incident and which has a diffraction grating that guides at least a portion of the incident projection light toward a predetermined direction within the projection substrate; and an exit region that is located at a position in the predetermined direction from the incident region, into which the projection light guided in the incident region is incident and which emits at least a portion of the incident projection light from the display surface as the image light, wherein at least one of the incident region and the exit region has the diffraction grating of the second aspect and diffracts at least a portion of the incident projection light from the display surface as the image light.

[0015] In a fourth aspect of the present invention, there is provided a glasses-type terminal worn by a user, the glasses-type terminal comprising: the projection substrate of the third aspect, which is provided as at least one of a lens for the user's right eye and a lens for the user's left eye, and which projects the incident projection light onto the display surface as the image light; a frame that fixes the projection substrate; and a projection unit that is provided on the frame and irradiates the projection light onto the entrance area of ​​the projection substrate to project the image light onto the exit area.

[0016] According to the present invention, an effect is achieved in that a diffraction grating can be easily formed on a substrate.

[0017] 1 shows an example of the configuration of the eyeglass-type terminal 10 according to the present embodiment. 2 shows an outline of the optical path of the projection light in the eyeglass-type terminal 10 according to the present embodiment. 3 shows an outline of the optical path of the projection light in the projection substrate 100 according to the present embodiment. 4 shows an example of the projection light L irradiated onto the projection substrate 100 by the projection unit 120 according to the present embodiment, and an example of the image light P emitted from the projection substrate 100. 5 shows an example of the configuration of the projection substrate 100 according to the present embodiment. 6 shows a modified example of the projection substrate 100 according to the present embodiment. 7 shows an example of the manufacturing flow of the diffraction grating according to the present embodiment. 8 shows an example in which a resin 410 is applied to the upper surface of the substrate 300 according to the present embodiment. 9 shows an example of the configuration of a mold 420 according to the present embodiment. 10 shows an example in which a mold 420 is pressed against the resin 410 applied to the substrate 300 according to the present embodiment. 11 shows a diffraction grating G formed on the upper surface of the substrate 300 according to the present embodiment. 12 shows an example of the configuration of a conventional diffraction grating. 13 shows a modified example of the mold 420 according to the present embodiment.

[0018] <Configuration example of eyeglasses-type terminal 10> Fig. 1 shows a configuration example of an eyeglasses-type terminal 10 according to this embodiment. In this embodiment, three mutually orthogonal axes are defined as an X-axis, a Y-axis, and a Z-axis. The eyeglasses-type terminal 10 is, for example, a wearable device worn by a user. The eyeglasses-type terminal 10 projects image light onto a display area provided on a projection substrate 100 while allowing the user to observe a scene through the glasses. The eyeglasses-type terminal 10 includes the projection substrate 100, a frame 110, and a projection unit 120.

[0019] The projection substrate 100 projects incident projection light onto a display surface as image light. For example, the projection substrate 100 transmits at least a portion of the light incident from the first surface toward the user's eyes in the direction of the second surface. The projection substrate 100 also projects the light incident from the second surface as image light onto a 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 eyeglass-type terminal 10. The second surface of the projection substrate 100 is the surface facing the user when the user wears the eyeglass-type terminal 10, and is the display surface for the image light. FIG. 1 shows an example in which the first and second surfaces of the projection substrate 100 are arranged approximately parallel to the XY plane. The projection substrate 100 is, for example, a glass substrate on which a diffraction grating functioning as a waveguide is formed. The projection substrate 100 will be described later.

[0020] The frame 110 fixes the projection substrate 100. The frame 110 is provided with the projection substrate 100 as at least one of a lens for the user's right eye and a lens for the left eye. Fig. 1 shows an example in which the frame 110 is provided with a projection substrate 100a as a lens for the user's right eye and a projection substrate 100b as a lens for the left eye.

[0021] Alternatively, the frame 110 may be provided with one projection board 100 as a lens for the user's right eye or left eye. The frame 110 may also be provided with one projection board 100 as lenses for both eyes of the user. In this case, the frame 110 may have a goggle shape. The frame 110 has temples, a strap, and other parts that allow the user to wear the eyeglass-type terminal 10.

[0022] The projection unit 120 is provided on the frame 110 and irradiates projection light toward the projection substrate 100 to project 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 projection light L1 onto the projection substrate 100a and a projection unit 120b for irradiating projection light L2 onto the projection substrate 100b are provided on the frame 110.

[0023] The projection unit 120 may be provided at a portion of the frame 110 where the projection substrate 100 is fixed, or may be provided at a temple or the like of the frame 110. It is desirable that the projection unit 120 be provided so as to be integrated with the frame 110. For example, the projection unit 120 irradiates the projection substrate 100 with projection light including one wavelength, allowing the user to observe a monochromatic image. Alternatively, the projection unit 120 may irradiate the projection substrate 100 with projection light including multiple wavelengths, allowing the user to observe an image including multiple colors.

[0024] 2 shows an outline of the optical path of projection light in the eyeglass-type terminal 10 according to this embodiment. The projection unit 120 irradiates the projection light onto an incident area 210 provided on the projection substrate 100. The incident area 210 guides the projection light within the substrate of the projection substrate 100. The projection substrate 100 then emits the projection light guided within the substrate from an emission area 230 as image light. The incident area 210 and the emission area 230 will be described later.

[0025] 3 shows an outline of the optical path of projection light on the projection substrate 100 according to this embodiment. The projection substrate 100 has an incident region 210, a branching region 220, and an exit region 230. Projection light L enters the incident region 210, passes through the branching region 220, and exits from the exit region 230 as image light P. The branching region 220 guides the projection light L part by part to the exit region 230 as the projection light L travels away from the incident region 210.

[0026] Similarly, as the projection light L travels away from the branching region 220, the emission region 230 also emits a portion of the projection light L as part of the image light P. In this way, the projection board 100 emits the projection light L that has entered the entrance region 210 from the emission region 230 as image light P.

[0027] <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 the conventional projection substrate 100 and the image light P emitted from the conventional projection substrate 100. The projection unit 120 irradiates the projection light L, for example, toward the second surface of the projection substrate 100 located in the +Z direction. The projection light L corresponds to an image to be shown to the user. For example, when the projection light L is projected onto a screen or the like placed on a surface approximately parallel to the XY plane, an image M1 is displayed on the screen for the user to observe. The image to be shown to the user is, for example, an augmented reality (AR) image or a virtual reality (VR) image created by a processor included in the projection unit 120. In this way, the projection unit 120 irradiates, as the projection light L, a plurality of light rays that form the image M1 on a surface approximately parallel to the XY plane.

[0028] In this embodiment, an example will be described in which the projection unit 120 projects a substantially rectangular image M1 with the X-axis direction as the longitudinal direction on a plane substantially parallel to the XY plane. Also, in Fig. 4, five of the multiple light rays emitted by the projection unit 120 are shown as input light rays 20. For example, the light ray corresponding to the upper left pixel of the image is the first input light ray 20a, the light ray corresponding to the lower left pixel of the image is the second input light ray 20b, the light ray corresponding to the central pixel of the image is the third input light ray 20c, the light ray corresponding to the upper right pixel of the image is the fourth input light ray 20d, and the light ray corresponding to the lower right pixel of the image is the fifth input light ray 20e.

[0029] The projection unit 120, for example, irradiates the projection light L onto the entrance region 210 of the projection substrate 100 so as to create an erect virtual image at infinity or at a predetermined position. The projection light incident on the entrance region 210 passes through the branching region 220 and is emitted from the exit region 230 as image light P. The image light P is emitted from the exit region 230 and enters the user's eye, which is a distance d away from the projection substrate 100. The image light P is then focused as image M2 on the retina of the user's eye. In this way, the image light P includes a plurality of light beams that are focused as image M2.

[0030] 4, five of the multiple ray bundles that are emitted from the circular region C of the emission region 230 of the projection substrate 100 and form an image at a predetermined position are shown as output ray bundles 30. For example, the ray bundle that forms an image as the lower right pixel of the image is designated as the first output ray bundle 30a, the ray bundle that forms an image as the upper right pixel of the image is designated as the second output ray bundle 30b, the ray bundle that forms an image as the central pixel of the image is designated as the third output ray bundle 30c, the ray bundle that forms an image as the lower left pixel of the image is designated as the fourth output ray bundle 30d, and the ray bundle that forms an image as the upper left pixel of the image is designated as the fifth output ray bundle 30e.

[0031] Each ray bundle corresponds to one of the multiple input light rays 20 incident from the projection unit 120. For example, the first output ray bundle 30a corresponds to the first input light ray 20a, and includes multiple light rays generated by multiple branching and multiple diffractions of the first input light ray 20a as it travels from the incident region 210 to the exit region 230 of the projection substrate 100. Similarly, the second output ray bundle 30b corresponds to the second input light ray 20b, the third output ray bundle 30c corresponds to the third input light ray 20c, the fourth output ray bundle 30d corresponds to the fourth input light ray 20d, and the fifth output ray bundle 30e corresponds to the fifth input light ray 20e.

[0032] In other words, the image M2 formed on the retina of the user's eye by the image light P emitted from the emission region 230 corresponds to the image M1 projected by the projection light L emitted by the projection unit 120. This allows the user wearing the eyeglass-type terminal 10 to feel as if the image M2 is being projected onto the second surface of the projection substrate 100, superimposed on the scenery seen through the projection substrate 100. In other words, the emission region 230 functions as a display region that displays the image M2 corresponding to the image M1 projected by the projection light L.

[0033] 4, an example is shown in which the image M2 observed by the user is an image obtained by vertically and horizontally inverting the image M1 projected by the projection light L. Note that the image M1 projected by the projection light L may be a still image, or alternatively, may be a moving image. Next, a more specific example of the projection substrate 100 will be described.

[0034] <Configuration Example of Projection Substrate 100> Fig. 5 shows a configuration example of the projection substrate 100 according to this embodiment. Fig. 5 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 a substrate for projecting incident projection light onto a display surface as image light. The projection substrate 100 is, for example, a glass substrate. The projection substrate 100 has an incident region 210, a branching region 220, and an exit region 230.

[0035] <Example of Incident Region 210> The incident region 210 receives projection light for projecting image light and guides the incident projection light toward the branching region 220. Fig. 5 shows an example in which the incident region 210 has a circular shape on a plane substantially parallel to the XY plane, but is not limited to this. The incident region 210 may have any shape, such as an ellipse, a polygon, or a trapezoid, as long as it can guide the projection light toward the branching region 220.

[0036] The incident region 210 has an incident diffraction grating in which a plurality of first grooves 212 are formed at a first period. In other words, the plurality of first grooves 212 are arranged in the same direction on the upper surface of the projection substrate 100 with a predetermined groove width and interval, thereby functioning as a diffraction grating. The incident region 210 has a reflective or transmissive incident diffraction grating and guides projection light toward the branching region 220 by reflective diffraction or transmissive diffraction. The first period of the plurality of first grooves 212 is, for example, in the range of approximately 10 nm to 10 μm.

[0037] The multiple first grooves 212 are arranged, for example, in a direction from the incident region 210 toward the branching region 220. Here, the traveling direction of the projection light from the incident region 210 toward the branching region 220 is defined as a third direction. Fig. 5 shows an example in which the third direction is a direction substantially parallel to the X-axis direction, and the first grooves 212 extending in a direction substantially parallel to the Y-axis direction are arranged in the third direction. Since the projection light is incident on the incident region 210 while converging, the incident region 210 guides the projection light to the branching region 220 so that the projection light has a divergence angle centered on the third direction within the plane of the projection substrate 100.

[0038] <Example of Branching Region 220> The branching region 220 guides a portion of the projection light incident from the entrance region 210 toward the exit region 230. The branching region 220 is provided in a region through which the projection light passes, on a plane substantially parallel to the XY plane. The branching region 220 has a reflective intermediate diffraction grating, and guides the projection light toward the exit region 230 by reflective diffraction. The branching region 220 has, for example, a rectangular shape with the third direction as its longitudinal direction.

[0039] Since the projection light propagates while spreading around the third direction, it is preferable that the branching region 220 has a shape that spreads away from the entrance region 210 and away from the third direction, which is the propagation direction of the projection light passing through the entrance region 210, as it moves away from the entrance region 210. The branching region 220 has, for example, a trapezoidal, fan-shaped, or other shape on a plane substantially parallel to the XY plane. Figure 5 shows an example in which the branching region 220 has a trapezoidal shape. A branching region 220 of this shape can be formed corresponding to a region where the projection light propagates while spreading in the XY plane, and can efficiently guide the projection light.

[0040] The branching region 220 has an intermediate diffraction grating in which a plurality of second grooves 222 are formed at a second period. In other words, the plurality of second grooves 222 are arranged in the same direction on the upper surface of the projection substrate 100 with a predetermined groove width and interval, thereby functioning as a diffraction grating. The branching region 220 functions as, for example, a reflective intermediate diffraction grating and guides the projection light to the emission region 230.

[0041] The second period of the plurality of second groove portions 222 is different from the first period of the plurality of first groove portions 212. It is desirable to select an appropriate second period for guiding the projection light to the emission region 230. The second period is, for example, in the range of about 10 nm to about 10 μm.

[0042] The plurality of second grooves 222 are arranged, for example, in a predetermined direction. For example, the direction from the branching region 220 toward the emission region 230 is defined as the fourth direction, and the angle between the third direction and the fourth direction is defined as the first angle. In this case, the plurality of second grooves 222 are formed in a direction inclined toward the fourth direction by an angle that is half the first angle with respect to the third direction. Figure 5 shows an example in which the fourth direction is substantially parallel to the Y-axis direction, the first angle is substantially 90 degrees, and the plurality of second grooves 222 are arranged in a direction inclined toward the fourth direction by approximately 45 degrees with respect to the third direction.

[0043] The branching region 220 has a plurality of first dividing regions 224 arranged in the traveling direction of the incident projection light. The second grooves 222 formed in the plurality of first dividing regions 224 have different depths. In other words, the second grooves 222 are formed in the branching region 220 so that the proportion of the incident projection light that is guided to the emission region 230 differs for each first dividing region 224.

[0044] It is desirable that the branching region 220 has three or more first divided regions 224. In this way, the branching region 220 is divided into a plurality of first divided regions 224, and the amount of projection light guided to the emission region 230 is varied for each first divided region 224, thereby guiding projection light whose intensity varies depending on the distance from the incidence region 210 to the emission region 230, while adjusting the distribution of the light amount in the direction perpendicular to the traveling direction of the projection light to be approximately constant.

[0045] For example, the second grooves 222 are formed so that the depth of the second grooves 222 provided in one first divided region 224 is greater than the depth of the second grooves 222 provided in a first divided region 224 that is closer to the incident region 210 than the one first divided region 224. In this case, the rate of change in the depth of the second grooves 222 between two adjacent first divided regions 224 among the plurality of first divided regions 224 may be greater the farther away from the incident region 210.

[0046] 5, consider a branch region 220 having three first divided regions 224. Here, the first divided region 224a, which is closest to the incident region 210 among the three first divided regions 224, has a depth of the second groove 222a formed so that approximately one-quarter of the amount of incident projection light is guided to the output region 230. In this case, the remaining approximately three-quarters of the amount of projection light that is incident on the first divided region 224a closest to the incident region 210 is incident on the adjacent first divided region 224b.

[0047] The depth of the second groove 222b of the first divided region 224b second closest to the entrance region 210 is formed so that the second groove 222b guides approximately one-third of the amount of incident projection light to the exit region 230. In other words, the depth of the second groove 222b of the first divided region 224b second closest to the entrance region 210 is formed greater than the depth of the second groove 222a so that the first divided region 224b guides 4 / 3 times the amount of light to the exit region 230 compared to the first divided region 224a closest to the entrance region 210. This first divided region 224b guides approximately one-quarter of the amount of projection light incident on the first divided region 224a closest to the entrance region 210 to the exit region 230.

[0048] The remaining approximately half of the amount of projection light that is incident on the first divided region 224a that is closest to the incident region 210 is incident on the adjacent first divided region 224c. The first divided region 224c that is third closest to the incident region 210 has a depth of the second groove 222c formed so as to guide approximately half of the amount of incident projection light to the output region 230. In other words, the depth of the second groove 222c of the first divided region 224c that is third closest to the incident region 210 is formed greater than the depth of the second groove 222b so as to guide 3 / 2 times the amount of light to the output region 230 compared to the first divided region 224b that is second closest to the incident region 210.

[0049] Furthermore, the rate of change in the depth of the second groove portions 222 of two adjacent first divided regions 224 out of the three first divided regions 224 is formed so that the rate of change increases the farther away from the incident region 210. The first divided region 224c, which is third closest to the incident region 210, guides to the output region 230 approximately one-fourth the amount of projection light that was incident on the first divided region 224a, which is closest to the incident region 210. As in the above example, by varying the amount of projection light guided to the output region 230 for each first divided region 224 to a predetermined value, it can be seen that the branch region 220 can guide the projection light to the output region 230 while maintaining a substantially constant distribution of the amount of projection light guided to the output region 230 corresponding to each first divided region 224.

[0050] <Example of Emission Region 230> The emission region 230 guides at least a portion of the projection light incident from the branch region 220 and emits it as image light from the second surface of the projection substrate 100. Fig. 5 shows an example in which the emission region 230 has a rectangular shape with its longitudinal direction in the X-axis direction on a plane approximately parallel to the XY plane, but this is not limiting. The emission region 230 only needs to be able to guide the projection light and emit it as image light, and may have a shape such as a rectangle, square, or trapezoid with its longitudinal direction in the Y-axis direction.

[0051] The emission region 230 has an emission diffraction grating in which a plurality of third groove portions 232 are formed at a third period. In other words, the plurality of third groove portions 232 are arranged in the same direction on the upper surface of the projection substrate 100 with a predetermined groove width and interval, thereby functioning as a diffraction grating. The emission region 230 has a reflective or transmissive emission diffraction grating and guides image light toward the user's eyes by reflective diffraction or transmissive diffraction.

[0052] The third period of the plurality of third groove portions 232 provided in the emission region 230 is different from the second period of the plurality of second groove portions 222 in the branch region 220. The third period of the plurality of third groove portions 232 in the emission region 230 may be the same as the first period of the plurality of first groove portions 212 in the incidence region 210. In this way, by substantially matching the periods of the diffraction gratings provided in the region where the projection light enters and the region where the image light exits, distortions and the like occurring in the image observed by the user can be reduced. The third period is, for example, in the range of approximately 10 nm to 10 μm.

[0053] The plurality of third grooves 232 are arranged, for example, in a fourth direction from the branching region 220 toward the emission region 230. Fig. 5 shows an example in which the third grooves 232 extending in the third direction are arranged in the fourth direction.

[0054] Like the branching region 220, the emission region 230 has a plurality of second division regions 234 arranged in the traveling direction of the projection light incident from the branching region 220. The third groove portions 232 formed in the plurality of second division regions 234 have different depths. In other words, the third groove portions 232 are formed in the emission region 230 so that the proportion of light that is emitted as image light out of the input projection light differs for each second division region 234.

[0055] It is desirable that the emission region 230 has two or more second divide regions 234. For example, the depth of the third groove portion 232 provided in one second divide region 234 is formed to be greater than the depth of the third groove portion 232 provided in a second divide region 234 that is closer to the branch region 220 than the one second divide region 234. Furthermore, when the emission region 230 has three or more second divide regions 234, the rate of change in the depth of the third groove portion 232 of two adjacent second divide regions 234 may be greater the farther away from the branch region 220.

[0056] As described above, the emission region 230 is divided into a plurality of second divided regions 234, and the amount of light emitted as image light is made different for each second divided region 234. As a result, like the plurality of first divided regions 224 of the branch region 220, the emission region 230 can guide the projection light as image light, and can adjust the distribution of the amount of light across the entire image to be approximately constant when the observer observes the image light as an image.

[0057] As described above, the projection substrate 100 according to this embodiment branches the projection light incident on the entrance region 210 into different proportions for each of the plurality of first divided regions 224 of the branch region 220, and then emits the projection light as image light from the exit region 230. This allows the projection substrate 100 to reduce variations in the brightness of the projected image observed by the user. Furthermore, the projection substrate 100 can further reduce variations in the brightness of the image by emitting image light at different proportions for each of the plurality of second divided regions 234 in the exit region 230 as well.

[0058] Such a projection substrate 100 can be realized by forming diffraction gratings corresponding to the incident region 210, the branching region 220, and the exit region 230 on the front or back surface of a glass substrate or the like. The grooves forming the diffraction gratings are made of, for example, resist, resin, or the like. However, manufacturing such a projection substrate 100 can be complicated and time-consuming because three types of regions, namely the incident region 210, the branching region 220, and the exit region 230, are formed on the substrate. Furthermore, forming diffraction gratings with different groove depths in each region can also be time-consuming.

[0059] It is possible to simplify the optical system by using a two-dimensional diffraction grating that functions as the branching region 220 and the exit region 230. FIG. 6 shows a modified example of the projection substrate 100 according to this embodiment. The modified projection substrate 100 shows an example in which a two-dimensional diffraction grating is used. The projection substrate 100 has an entrance region 210 and a two-dimensional diffraction grating 240. Projection light L is incident on the entrance region 210 and exits from the two-dimensional diffraction grating 240 as image light P. In other words, the two-dimensional diffraction grating 240 functions as the branching region 220 and the exit region 230 described in FIG. 2 .

[0060] Such a modified projection substrate 100 can reduce the area where the diffraction grating is formed. However, a two-dimensional diffraction grating has a more complicated structure than a one-dimensional diffraction grating, and can be difficult to manufacture. Therefore, the method for manufacturing a diffraction grating according to this embodiment makes it possible to easily form various diffraction gratings on a substrate. Next, a method for manufacturing such a diffraction grating G will be described.

[0061] <Example of a Manufacturing Flow of a Diffraction Grating> FIG. 7 shows an example of a manufacturing flow of a diffraction grating G according to this embodiment. First, resin 410 is sprayed onto the upper surface of substrate 300 to apply the resin to the first diffraction grating region 310 of the substrate 300 (S11). It is desirable that the resin 410 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 substrate 300 using a coating device or the like. It is desirable that the resin 410 is sprayed onto the upper surface of substrate 300 using an inkjet method. This makes it possible to easily apply the resin 410 to a predetermined region of the substrate 300 using a simple device.

[0062] The first diffraction grating region 310 is a region where the diffraction grating G is formed on the upper surface of the substrate 300. The first diffraction grating region 310 is, for example, at least one of the incident region 210, the branching region 220, and the exit region 230 described in FIG.

[0063] It is desirable that the resin 410 has a viscosity sufficient to maintain the shape of the applied resin. For example, when forming a diffraction grating G with a uniform groove depth, the resin 410 is applied to the first diffraction grating region 310 so that the resin 410 has a thickness equal to or greater than the thickness of the diffraction grating G on the upper surface of the substrate 300. Furthermore, when forming a diffraction grating G with different groove depths, the resin 410 may be applied to the first diffraction grating region 310 so that the resin 410 has a thickness that varies depending on the depth of the groove to be formed on the upper surface of the substrate 300.

[0064] 8 shows an example in which resin 410 is applied to the upper surface of substrate 300 according to this embodiment. In this embodiment, an example will be described in which resin 410 is sprayed onto the upper surface of substrate 300 so that the thickness of resin 410 applied to first region 311 in first diffraction grating region 310 of substrate 300 is different from the thickness of resin 410 applied to second region 312, which is different from first region 311 in first diffraction grating region 310 of substrate 300. The example in FIG. 8 shows an example in which resin 410 is applied so that the thickness of resin 410 applied to first region 311 is smaller than the thickness of resin 410 applied to second region 312.

[0065] When forming a diffraction grating in which the depth of the second grooves 222 increases in the direction away from the incident region 210, as in the plurality of first dividing regions 224 of the branching region 220, it is desirable to form the resin 410 so that the thickness varies in one direction. For example, if the direction from the first region 311 toward the second region 312 is defined as the first direction, the resin 410 is applied so that the thickness of the resin 410 gradually increases in the first direction. For example, when the branching region 220 is formed in the first diffraction grating region 310, the first direction is the same as the third direction described in FIG. 5 .

[0066] 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 300 (S12). Fig. 9 shows an example of the configuration of the mold 420 according to this embodiment. The plurality of recesses 421 are provided on the surface of the mold 420 facing the substrate 300, in an area facing the first diffraction grating region 310 of the substrate 300. Here, the width of the recesses 421 in the first direction corresponds to the spacing between the grooves of the diffraction grating formed in the first diffraction grating region 310 of the substrate 300.

[0067] The plurality of recesses 421 formed in the mold 420 are arranged at a predetermined first interval in a first direction, and are formed so that the depth of the recesses 421 in a region facing the first region 311 of the substrate 300 is different from the depth of the recesses 421 in a region facing the second region 312 of the substrate 300. The first interval corresponds to the width of the grooves of the diffraction grating formed in the first diffraction grating region 310 of the substrate 300. In this embodiment, an example will be described in which the plurality of recesses 421 formed in the mold 420 are formed so that the depth of the recesses 421 in a region facing the first region 311 of the substrate 300 is shallower than the depth of the recesses 421 in a region facing the second region 312 of the substrate 300.

[0068] 10 shows an example in which a mold 420 is pressed against a resin 410 applied to a substrate 300 according to this embodiment. Fig. 10 shows an example in which a plurality of recesses 421 are formed in the mold 420 so that the depths of adjacent recesses 421 are the same or deeper in the first direction. This makes it possible to form a diffraction grating in which the depths of adjacent grooves are the same or deeper in the first direction.

[0069] 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 300, for example, by a fixing jig and a moving device for the mold 420 (not shown). In this way, the diffraction grating G can be formed on the upper surface of the substrate 300.

[0070] 11 shows a diffraction grating G formed on the upper surface of a substrate 300 according to this embodiment. In other words, the diffraction grating G includes the substrate 300 and a plurality of structures 430 formed of resin 410 and arranged at a first interval in a first direction in a first diffraction grating region 310 on the upper surface of the substrate 300. The first interval, which is the interval between adjacent structures 430, corresponds to the width of the grooves in the diffraction grating. Furthermore, the width of the structures 430 in the first direction corresponds to the interval between the grooves in the diffraction grating.

[0071] In the first diffraction grating region 310 of the substrate 300, the plurality of structures 430 formed in the first region 311 have a different height in the direction perpendicular to the substrate 300 from the upper surface of the substrate 300, compared to the plurality of structures 430 formed in a second region 312 different from the first region 311. Figure 11 shows an example of a diffraction grating G in which the plurality of structures 430 formed in the first region 311 are formed to be lower in height than the plurality of structures 430 formed in the second region 312.

[0072] It is desirable that the plurality of structures 430 be formed from the upper surface of the substrate 300. For example, a diffraction grating can be formed by forming recesses or the like in a direction perpendicular to the upper surface of the substrate 300. Fig. 12 shows an example of the configuration of a conventional diffraction grating. In the case of such a conventional diffraction grating, if the groove depth is varied, the position of the bottom surface of the groove in the direction perpendicular to the upper surface of the substrate 300 will also vary (ΔD in the figure).

[0073] As described with reference to FIG. 2 , projection light is guided inside the projection substrate 100. Therefore, projection light is obliquely incident on the diffraction grating formed on the upper surface of the projection substrate 100 from inside the projection substrate 100. In the case of the conventional diffraction grating shown in FIG. 12 , of the light incident from inside the substrate 300, the amount of light incident on the portions of the diffraction grating where the bottoms of the grooves are formed deeper may differ significantly from the amount of light incident on the portions of the diffraction grating where the bottoms of the grooves are formed shallower. In such conventional diffraction gratings, the diffraction efficiency may be reduced.

[0074] In contrast, in the diffraction grating G according to this embodiment, the plurality of structures 430 can be formed from the upper surface of the substrate 300. For example, in step S12 of pressing the mold 420 against the substrate 300 described in Fig. 7 , the mold 420 is pressed so that the area of ​​the surface facing the upper surface of the substrate 300, excluding the recesses 421, comes into contact with the upper surface of the substrate 300.

[0075] As a result, the bottom surfaces of the multiple grooves of the diffraction grating G can be made to substantially coincide with the upper surface of the substrate 300, even if the height of the structures 430 varies. As a result, compared to conventional diffraction gratings, the diffraction grating G can make the projection light incident almost uniformly over the entire diffraction grating G, even if the projection light is incident obliquely from inside the substrate 300. Therefore, the diffraction grating G can improve the diffraction efficiency compared to conventional diffraction gratings.

[0076] As described above, the projection substrate 100 can be formed by forming the diffraction grating G on the upper surface of the substrate 300 and, if necessary, forming other regions and performing other processing on the substrate 300. Note that, in this embodiment, an example has been described in which one region out of the incident region 210, the branching region 220, and the exit region 230 is formed as the diffraction grating G on the upper surface of the substrate 300, but this is not limitative. Two or more regions out of the incident region 210, the branching region 220, and the exit region 230 may also be formed as the diffraction grating G on the upper surface of the substrate 300.

[0077] Furthermore, when the branching region 220 and the emission region 230 are formed as a common two-dimensional diffraction grating 240, the incidence region 210 and the two-dimensional diffraction grating 240 (in this case, the two-dimensional diffraction grating 240 may also be referred to as an emission region) may be formed as a diffraction grating G on the upper surface of the substrate 300. In these cases, a diffraction grating G is further formed in one or more regions different from the first diffraction grating region 310 on the upper surface of the substrate 300.

[0078] 7 may be repeated multiple times to form multiple diffraction gratings G on the upper surface of the substrate 300. Alternatively, multiple diffraction gratings G may be formed in a single manufacturing flow. For example, step S11 of applying resin 410 to the substrate 300 described in FIG. 7 may further include a step of applying resin 410 to a second diffraction grating region different from the first diffraction grating region 310.

[0079] In the step of applying resin 410 to the second diffraction grating region, similar to the first diffraction grating region 310, the resin 410 is sprayed onto the upper surface of the substrate 300 so that the thickness of the resin 410 applied to the third region within the second diffraction grating region is different from the thickness of the resin applied to the fourth region within the second diffraction grating region. Here, similar to the first diffraction grating region 310, the resin 410 is applied so that the thickness of the resin 410 gradually increases in a second direction from the third region toward the fourth region. Note that the second direction is different from the first direction. For example, when forming the emission region 230 in the first diffraction grating region, the second direction is the same as the fourth direction described in FIG. 5 .

[0080] In this case, among the plurality of recesses 421 formed in the mold 420, the plurality of recesses 421 formed at positions corresponding to the second diffraction grating region are arranged at a predetermined second interval in the second direction. The depth of the recesses 421 in the region facing the third region of the substrate 300 is formed to be different from the depth of the recesses 421 in the region facing the fourth region of the substrate 300. For example, the plurality of recesses 421 are formed so that the depth of adjacent recesses 421 in the second direction is the same or deeper.

[0081] As described above, according to the method for manufacturing the diffraction grating G of this embodiment, different diffraction gratings G can be formed in the first diffraction grating region 310 and the second diffraction grating region of the substrate 300. It goes without saying that different diffraction gratings G can also be formed in three or more regions of the substrate 300 using a similar process. Therefore, for example, it is possible to easily manufacture a projection substrate 100 in which different diffraction gratings G are formed as the entrance region 210, the branching region 220, and the exit region 230 on the upper surface of the substrate 300.

[0082] The method for manufacturing the diffraction grating G according to the present embodiment described above can form diffraction gratings G of various shapes corresponding to the shapes of the plurality of recesses 421 formed in the mold 420. For example, in the present embodiment, the mold 420 has been described in which the plurality of recesses 421 having a rectangular cross section are formed so that the cross section of the structure 430 of the diffraction grating G taken along the XZ plane has a rectangular shape, but the present invention is not limited to this.

[0083] FIG. 13 shows a modified example of the mold 420 according to this embodiment. For example, as shown in FIG. 13A, the mold 420 may have a plurality of recesses 421 whose cross section taken along the XZ plane is in the shape of a right triangle. In this case, a diffraction grating G having a known shape known as a blazed grating can be formed. Also, as shown in FIG. 13B, the mold 420 may have a cross section taken along the XZ plane that is inscribed in a right triangle and has a stepped shape. In this case, a diffraction grating G having a pseudo function of a blazed diffraction grating can be formed. Also, the mold 420 may have a plurality of recesses 421 so as to form a two-dimensional diffraction grating.

[0084] 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.

[0085] REFERENCE SIGNS LIST 10 Glasses-type terminal 20 Input light beam 30 Output light beam bundle 100 Projection substrate 110 Frame 120 Projection unit 210 Incident area 212 First groove 220 Branching area 222 Second groove 224 First division area 226 First reflection area 230 Exit area 232 Third groove 234 Second division area 236 Second reflection area 240 Two-dimensional diffraction grating 300 Substrate 310 First diffraction grating area 311 First area 312 Second area 410 Resin 420 Mold 421 Recess 430 Structure

Claims

1. A method for manufacturing a diffraction grating, comprising the steps of: spraying a resin onto an upper surface of a substrate to apply the resin to a first diffraction grating region of the substrate; pressing a mold, the mold having a plurality of recesses pre-formed in a region of the substrate facing the first diffraction grating region, 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 in the step of applying resin, the resin is sprayed onto the upper surface of the substrate so that a thickness of the resin applied to a first region within the first diffraction grating region of the substrate is different from a thickness of the resin applied to a second region of the substrate different from the first region within the first diffraction grating region, and the plurality of recesses formed in the mold are arranged at a first interval in a first direction, and are formed so that a depth of the recesses in the region facing the first region of the substrate is different from a depth of the recesses in a region facing the second region of the substrate.

2. The method for manufacturing a diffraction grating according to claim 1, wherein in the step of applying the resin, the resin is sprayed onto the upper surface of the substrate by an inkjet method.

3. A method for manufacturing a diffraction grating as described in claim 1, wherein in the step of applying the resin, the resin is applied so that the thickness of the resin applied to the first region is smaller than the thickness of the resin applied to the second region, and the multiple recesses formed in the mold are formed so that the depth of the recesses in the region facing the first region of the substrate is shallower than the depth of the recesses in the region facing the second region of the substrate.

4. A method for manufacturing a diffraction grating as described in claim 3, wherein the first direction is a direction from the first region toward the second region, and in the step of applying the resin, the resin is applied so that the thickness of the resin gradually increases in the first direction, and the multiple recesses formed in the mold are formed so that the depths of adjacent recesses are the same or deeper in the first direction from the region of the substrate facing the first region toward the region facing the second region.

5. A method for manufacturing a diffraction grating as described in claim 1, wherein in the step of pressing the mold, the mold is pressed so that the area of ​​the surface facing the top surface of the substrate, excluding the recess, is in contact with the top surface of the substrate.

6. A method for manufacturing a diffraction grating according to any one of claims 1 to 5, wherein the step of applying the resin further comprises a step of applying the resin to a second diffraction grating region different from the first diffraction grating region, and in the step of applying the resin to the second diffraction grating region, the resin is sprayed onto the upper surface of the substrate so that a thickness of the resin applied to a third region within the second diffraction grating region is different from a thickness of the resin applied to a fourth region within the second diffraction grating region, and the multiple recesses formed in the mold are arranged at second intervals in a second direction different from the first direction, and are formed so that a depth of the recesses in a region of the substrate facing the third region is different from a depth of the recesses in a region of the substrate facing the fourth region.

7. A method for manufacturing a diffraction grating as described in claim 6, wherein the second direction is a direction from the third region toward the fourth region, and in the step of applying the resin to the second diffraction grating region, the resin is applied so that the thickness of the resin gradually increases in the second direction, and the multiple recesses formed in the mold are formed so that the depths of adjacent recesses are the same or deeper in the second direction from the region of the substrate facing the third region toward the region facing the fourth region.

8. A diffraction grating comprising: a substrate; and a plurality of structures formed of resin and arranged in a first direction at a first interval in a first diffraction grating region on the top surface of the substrate, wherein, within the first diffraction grating region of the substrate, the plurality of structures formed in a first region have a different height in the direction perpendicular to the top surface of the substrate than the plurality of structures formed in a second region different from the first region.

9. A projection substrate for projecting image light onto a display surface, comprising: an entrance region 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 an exit region provided at a position in the predetermined direction from the entrance region, into which the projection light guided in the entrance region is incident and which emits at least a portion of the incident projection light from the display surface as the image light, wherein at least one of the entrance region and the exit region has the diffraction grating described in claim 8 and diffracts at least a portion of the incident projection light from the display surface as the image light.

10. A glasses-type terminal worn by a user, comprising: the projection board according to claim 9, which is provided as at least one of a lens for the user's right eye and a lens for the user's left eye, 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 entrance area of ​​the projection board to project the image light onto the exit area.

Images