Projection substrate, method for manufacturing projection substrate, and glasses-type terminal

Abstract

The present invention relates to a method for manufacturing a projection substrate (100) for projecting image light onto a display surface, the method comprising: a step for preparing a substrate (101) in which a first surface (102) and a second surface (103) on the opposite side to the first surface (102) have a predetermined flatness and a predetermined surface roughness; a step for detecting a perforation (104) in the second surface (103) of the substrate (101); a step for processing the second surface (103) until the size of the detected perforation (104) is at most a predetermined diameter and at most a predetermined depth; and a step for forming, on the first surface (102) of the substrate, a plurality of diffraction gratings (210, 230) for diffracting the incident projection light and outputting the diffracted light as image light from the display surface.

Description

Projection substrate, projection substrate manufacturing method, and eyeglass-type terminal

[0001] The present invention relates to a projection substrate, a method for manufacturing 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). Furthermore, there is known a technique for forming an optical waveguide on a polished substrate (see, for example, Patent Document 4).

[0003] Japanese Patent Application Laid-Open No. 2017-207686 International Publication No. 2023 / 047488 US Patent No. 8,160,411 Japanese Patent Application Laid-Open No. 2023-126175

[0004] Such eyeglass-type devices have used projection substrates with diffraction gratings formed on the substrate. Such projection substrates have been manufactured using substrates whose front and back surfaces have been polished to a predetermined flatness and surface roughness. However, even substrates processed to a predetermined flatness and surface roughness may have perforations of a predetermined size remaining on the surface of the substrate. If such perforations exist in the light path, they reflect or absorb light in a way that prevents the light from passing through, which can result in parts of the image light becoming dark or not being able to be displayed, making it impossible to output uniform image light.

[0005] Therefore, the present invention has been made in consideration of these points, and aims to suppress variations in in-plane brightness in the display area of ​​image light caused by perforations formed on the surface of the substrate in a projection substrate that displays image light on a display surface using a diffraction grating formed on the surface of the substrate.

[0006] In a first aspect of the present invention, there is provided a method for manufacturing a projection substrate for projecting image light onto a display surface, the method comprising the steps of: preparing a substrate having a first surface and a second surface opposite to the first surface with a predetermined flatness and a predetermined surface roughness; detecting perforations on the second surface of the substrate; processing the second surface until the size of the detected perforations is equal to or less than a predetermined diameter and a predetermined depth; and forming a plurality of diffraction gratings on the first surface of the substrate for diffracting incident projection light and outputting it from the display surface as the image light.

[0007] In the step of preparing the substrate, the substrate may be prepared such that at least the second surface has a total thickness variation (TTV) value that is equal to or less than half the wavelength of the image light, and the second surface has a maximum cross-sectional height that is equal to or less than a predetermined value that is smaller than the TTV value of the second surface.

[0008] In the step of preparing the substrate, the substrate may have at least the second surface having a maximum cross-sectional height of 1 nm or less.

[0009] The step of processing the second surface may include a step of polishing the second surface. The step of processing the second surface may include a step of coating the second surface with a coating material.

[0010] The step of processing the second surface may further include a step of polishing the second surface coated with the coating material. In the step of processing the second surface, the second surface may be processed until the size of the perforations has a diameter of ½ or less of the wavelength of the image light and a depth of 150 nm or less.

[0011] The manufacturing method may further include, before the step of forming a plurality of the diffraction gratings, a step of detecting perforations on the first surface of the substrate, and a step of processing the first surface until the size of the detected perforations is equal to or smaller than a predetermined diameter and a predetermined depth.

[0012] In a second aspect of the present invention, there is provided a projection substrate for projecting image light onto a display surface, comprising: a substrate; an incident diffraction grating provided on a first surface of the substrate, onto which projection light for projecting the image light is incident and which guides at least a portion of the incident projection light toward a predetermined direction within the substrate; and an exit diffraction grating provided on the first surface of the substrate, at a position in the predetermined direction from the incident diffraction grating, onto which the projection light guided by the incident diffraction grating is incident and which emits at least a portion of the incident projection light from the display surface as the image light, wherein a TTV value of a second surface of the substrate opposite to the first surface is not more than 1 / 2 of the wavelength of the image light, a maximum cross-sectional height of the second surface of the substrate is not more than a predetermined value that is smaller than the TTV value, and a size of perforations in the second surface of the substrate is not more than a predetermined diameter and not more than a predetermined depth.

[0013] The size of the perforation in the first surface of the substrate may be equal to or smaller than a predetermined diameter and equal to or smaller than a predetermined depth.

[0014] In a third 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 second 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 image light onto the display surface with a surface facing the user's eye as the display surface; a frame that fixes the projection substrate; and a projection unit that is provided on the frame and irradiates the projection light onto the incident diffraction grating of the projection substrate to project the image light onto the display surface.

[0015] According to the present invention, in a projection substrate that displays image light on a display surface using a diffraction grating formed on the surface of the substrate, it is possible to suppress variations in in-plane brightness in the display area of ​​the image light that are caused by perforations formed on the surface of the substrate.

[0016] 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 projection substrate 100 according to the present embodiment. 8 shows an example of the configuration of the substrate 101 in the process of manufacturing the projection substrate 100 according to the present embodiment.

[0017] <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.

[0018] The projection board 100 projects the incident projection light onto a display surface as image light. For example, the projection board 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 board 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 board 100 is the surface that faces away from the user when the user is wearing the eyeglass-type terminal 10.

[0019] The second surface of the projection substrate 100 is the surface facing the user's eye when the user wears the eyeglass-type terminal 10, and is the display surface for image light. Fig. 1 shows an example in which the first and second surfaces of the projection substrate 100 are arranged substantially parallel to the XY plane. The projection substrate 100 is, for example, a glass substrate on which a diffraction grating that functions 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] FIG. 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 input diffraction grating 210 provided on the projection substrate 100. The projection light for projecting image light is incident on the input diffraction grating 210, which guides at least a portion of the incident projection light toward a predetermined direction within the substrate. The projection light guided by the input diffraction grating 210 is then incident on the output diffraction grating 230, which emits at least a portion of the incident projection light from the display surface as image light. In other words, the projection substrate 100 emits the projection light guided within the substrate from the output diffraction grating 230 as image light. The input diffraction grating 210 and the output diffraction grating 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 input diffraction grating 210, an intermediate diffraction grating 220, and an output diffraction grating 230. The projection light L enters the input diffraction grating 210, passes through the intermediate diffraction grating 220, and is output from the output diffraction grating 230 as image light P. The intermediate diffraction grating 220 guides the projection light L part by part to the output diffraction grating 230 as the projection light L travels away from the input diffraction grating 210.

[0026] Similarly, as the projection light L travels away from the intermediate diffraction grating 220, the output diffraction grating 230 outputs a portion of the projection light L as part of the image light P. In this way, the projection substrate 100 outputs the projection light L that is incident on the input diffraction grating 210 from the output diffraction grating 230 as image light P.

[0027] <Examples of Projection Light L and Image Light P> FIG. 4 shows an example of the projection light L irradiated onto the projection substrate 100 by the projection unit 120 according to this embodiment and the image light P emitted from the 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 substantially 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 an image M1 on a surface substantially 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 input diffraction grating 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 input diffraction grating 210 passes through the intermediate diffraction grating 220 and is output from the output diffraction grating 230 as image light P. The image light P is output from the output diffraction grating 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 ray bundles that are focused as image M2.

[0030] 4, five of the multiple ray bundles that are emitted from the circular region C of the output diffraction grating 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 input diffraction grating 210 to the output diffraction grating 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 output diffraction grating 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 board 100, superimposed on the scenery seen through the projection board 100. In other words, the output diffraction grating 230 functions as a display area 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 includes a substrate 101, an input diffraction grating 210, an intermediate diffraction grating 220, and an output diffraction grating 230. The substrate 101 is a plastic substrate or a glass substrate. The input diffraction grating 210, the intermediate diffraction grating 220, and the output diffraction grating 230 are provided on the substrate 101.

[0035] <Example of Incident Diffraction Grating 210> Projection light for projecting image light is incident on the incident diffraction grating 210, and the incident diffraction grating 210 diffracts the incident projection light toward the intermediate diffraction grating 220 in a first direction. Fig. 5 shows an example in which the incident diffraction grating 210 has a circular shape on a plane approximately parallel to the XY plane, but this is not limiting. The incident diffraction grating 210 may have any shape, such as an ellipse, a polygon, or a trapezoid, as long as it can guide the projection light to the intermediate diffraction grating 220. The incident diffraction grating 210 may be formed on the first surface of the substrate 101, or alternatively, on the second surface of the substrate 101.

[0036] The incident diffraction grating 210 has a plurality of first grooves 212 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 diffraction grating 210 has a reflective or transmissive incident diffraction grating and guides projection light toward the intermediate diffraction grating 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 diffraction grating 210 toward the intermediate diffraction grating 220. Here, the traveling direction of the projection light from the incident diffraction grating 210 toward the intermediate diffraction grating 220 is defined as the first direction. Figure 5 shows an example in which the first direction is 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 first direction. Since the projection light is incident on the incident diffraction grating 210 while converging, the incident diffraction grating 210 guides the projection light to the intermediate diffraction grating 220 so that the projection light has a divergence angle centered on the first direction within the plane of the projection substrate 100.

[0038] <Example of Intermediate Diffraction Grating 220> The intermediate diffraction grating 220 is provided in a first direction from the incident diffraction grating 210 and diffracts a portion of the projection light incident from the incident diffraction grating 210 toward the output diffraction grating 230 in a second direction. The intermediate diffraction grating 220 is provided in a region through which the projection light passes, on a plane substantially parallel to the XY plane. The intermediate diffraction grating 220 has a reflective diffraction grating and guides the projection light toward the output diffraction grating 230 by reflective diffraction. The intermediate diffraction grating 220 has, for example, a rectangular shape with its longitudinal direction in the first direction. The intermediate diffraction grating 220 may be formed on the first surface of the substrate 101, or alternatively, may be formed on the second surface of the substrate 101.

[0039] Since the projection light propagates while diverging around the first direction, it is preferable that the intermediate diffraction grating 220 has a shape that diverges as it moves away from the incident diffraction grating 210, away from the first direction, which is the direction of propagation of the projection light passing through the incident diffraction grating 210. The intermediate diffraction grating 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 intermediate diffraction grating 220 has a trapezoidal shape. An intermediate diffraction grating 220 of this shape can be formed to correspond to a region in which the projection light propagates while diverging in the XY plane, and can efficiently guide the projection light.

[0040] The intermediate diffraction grating 220 has a plurality of second grooves 222 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 predetermined groove widths and intervals, thereby functioning as a diffraction grating. The intermediate diffraction grating 220 functions as, for example, a reflective diffraction grating, and guides the projection light to the output diffraction grating 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 output diffraction grating 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 intermediate diffraction grating 220 toward the output diffraction grating 230 is defined as the second direction, and the angle between the first direction and the second direction is defined as the first angle. In this case, the plurality of second grooves 222 are formed in a direction tilted in the second direction by half the first angle with respect to the first direction. Figure 5 shows an example in which the second 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 tilted in the second direction by substantially 45 degrees with respect to the first direction.

[0043] The intermediate diffraction grating 220 has a plurality of first divided regions 224 arranged in the direction of propagation of the incident projection light. The second grooves 222 formed in the plurality of first divided regions 224 have different depths. In other words, the second grooves 222 are formed in the intermediate diffraction grating 220 so that the proportion of light that is guided to the output diffraction grating 230 out of the incident projection light differs for each first divided region 224.

[0044] It is desirable that the intermediate diffraction grating 220 have three or more first divided regions 224. In this way, the intermediate diffraction grating 220 is divided into a plurality of first divided regions 224, and the amount of projection light guided to the output diffraction grating 230 is varied for each first divided region 224, thereby guiding projection light whose intensity varies depending on the distance from the input diffraction grating 210 to the output diffraction grating 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 diffraction grating 210 than the one first divided region 224. In this case, the rate of change in the depth of the second grooves 222 of two adjacent first divided regions 224 among the multiple first divided regions 224 may be greater the further away from the incident diffraction grating 210.

[0046] 5, consider an intermediate diffraction grating 220 having three first divided regions 224. Here, the first divided region 224a, which is closest to the incident diffraction grating 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 diffraction grating 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 diffraction grating 210 is incident on the adjacent first divided region 224b.

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

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

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

[0050] <Example of Exit Diffraction Grating 230> The exit diffraction grating 230 is provided in the second direction from the intermediate diffraction grating 220, and diffracts at least a portion of the projection light incident from the intermediate diffraction grating 220 from the display surface toward a third direction. The exit diffraction grating 230 emits the projection light as image light from the display surface, which is the second surface of the projection substrate 100. The third direction is a direction from the projection substrate 100 toward the eyes of a user wearing the eyeglass-type terminal. The exit diffraction grating 230 may be formed on the first surface of the substrate 101, or alternatively, may be formed on the second surface of the substrate 101.

[0051] 5 shows an example in which the exit diffraction grating 230 has a rectangular shape with its longitudinal direction in the X-axis direction on a plane substantially parallel to the XY plane, but is not limited to this. The exit diffraction grating 230 only needs to be able to guide the projection light and emit it as image light, and may have, for example, a rectangular, square, trapezoid, or other shape with its longitudinal direction in the Y-axis direction.

[0052] The output diffraction grating 230 has a plurality of third groove portions 232 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 predetermined groove widths and intervals, thereby functioning as a diffraction grating. The output diffraction grating 230 has a reflective or transmissive diffraction grating and guides image light toward the user's eyes by reflective diffraction or transmissive diffraction.

[0053] The third period of the plurality of third grooves 232 provided in the output diffraction grating 230 is different from the second period of the plurality of second grooves 222 in the intermediate diffraction grating 220. The third period of the plurality of third grooves 232 in the output diffraction grating 230 may be the same as the first period of the plurality of first grooves 212 in the input diffraction grating 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 that occur 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.

[0054] The multiple third groove portions 232 are arranged, for example, in a second direction from the intermediate diffraction grating 220 toward the output diffraction grating 230. Fig. 5 shows an example in which the third groove portions 232 extending in the first direction are arranged in the second direction.

[0055] Like the intermediate diffraction grating 220, the output diffraction grating 230 has a plurality of second divided regions 234 arranged in the traveling direction of the projection light incident from the intermediate diffraction grating 220. The third grooves 232 formed in the plurality of second divided regions 234 have different depths. In other words, in the output diffraction grating 230, the third grooves 232 are formed so that the proportion of light that is output as image light out of the input projection light differs for each second divided region 234.

[0056] The output diffraction grating 230 desirably has two or more second divided regions 234. For example, the depth of the third grooves 232 provided in one second divided region 234 is greater than the depth of the third grooves 232 provided in a second divided region 234 that is closer to the intermediate diffraction grating 220 than one second divided region 234. Furthermore, when the output diffraction grating 230 has three or more second divided regions 234, the rate of change in the depth of the third grooves 232 between two adjacent second divided regions 234 may increase as the distance from the intermediate diffraction grating 220 increases.

[0057] As described above, output diffraction grating 230 is divided into a plurality of second divided regions 234, and the amount of light output as image light is made different for each second divided region 234. As a result, output diffraction grating 230, like the plurality of first divided regions 224 of intermediate diffraction grating 220, can guide projection light as image light, while adjusting the distribution of the light amount of the entire image to be approximately constant when an observer observes the image light as an image.

[0058] As described above, the projection substrate 100 according to this embodiment branches the projection light incident on the input diffraction grating 210 into different projection light beams for each of the plurality of first division regions 224 of the intermediate diffraction grating 220, and then outputs the branched projection light as image light from the output diffraction grating 230. This allows the projection substrate 100 to reduce variations in brightness of the projected image observed by the user. Furthermore, the projection substrate 100 can further reduce variations in brightness of the image by outputting image light beams for each of the plurality of second division regions 234 of the output diffraction grating 230.

[0059] Such a projection substrate 100 can be realized by forming diffraction gratings corresponding to the incident diffraction grating 210, the intermediate diffraction grating 220, and the exit diffraction grating 230 on the front or back surface of a glass substrate, a plastic substrate, or the like. The grooves forming the diffraction gratings are made of, for example, resist, resin, or the like.

[0060] Although the projection substrate 100 according to the present embodiment has been described above as including the input diffraction grating 210, the intermediate diffraction grating 220, and the output diffraction grating 230, the present invention is not limited to this. The projection substrate 100 may also include a two-dimensional diffraction grating that functions as the intermediate diffraction grating 220 and the output diffraction grating 230.

[0061] <Modification of Projection Board 100> Fig. 6 shows a modification of the projection board 100 according to this embodiment. The modified projection board 100 shows an example in which a two-dimensional diffraction grating is used. The projection board 100 has an incident diffraction grating 210 and a two-dimensional diffraction grating 240. Projection light L is incident on the incident diffraction grating 210. The incident diffraction grating 210 guides at least a portion of the incident projection light toward the two-dimensional diffraction grating 240 in the substrate 101. The projection light guided by the incident diffraction grating 210 is incident on the two-dimensional diffraction grating 240, which then emits at least a portion of the incident projection light as image light P from the display surface.

[0062] The two-dimensional diffraction grating 240 functions as the intermediate diffraction grating 220 and the exit diffraction grating 230 described in Fig. 2. The optical system can be simplified by using such a two-dimensional diffraction grating 240. Note that the two-dimensional diffraction grating 240 is well known, and therefore a detailed description thereof will be omitted here.

[0063] The above-described projection substrate 100 can be used to configure the eyeglass-type terminal 10, etc. Such a projection substrate 100 guides projection light inside the substrate 101, so that at least a portion of the first surface 102 and the second surface 103 of the substrate 101 also function as a reflective surface that reflects the projection light. Therefore, if the flatness, surface roughness, etc. of the substrate 101 exceed a predetermined value, the projection light cannot be guided as designed, which may result in variations in the in-plane brightness in the display area of ​​the image light. Therefore, it is desirable to form the projection substrate 100 using a substrate 101 whose flatness, surface roughness, etc. are equal to or less than a predetermined value.

[0064] However, even if the projection substrate 100 is formed using a substrate 101 whose flatness, surface roughness, etc. are below a predetermined value, variations in the in-plane brightness in the display area of ​​the image light may occur. For example, the authors have found that even if the surface of the substrate 101 is polished so that the surface roughness is below a predetermined value, small holes may remain locally. In this embodiment, such small holes are called perforations.

[0065] The authors have found that if perforations larger than a predetermined size exist in the path of the projection light, the perforations reflect or absorb the light in a manner that prevents the projection light from passing through, causing part of the image light to become dark or to become unable to be displayed, making it impossible to output uniform image light. For example, if perforations with a diameter larger than half the wavelength of the image light and a depth of approximately 150 nm are formed on the surface of the substrate 101, part of the image light on the display surface will become dark or to become unable to be displayed.

[0066] Therefore, in the method for manufacturing the projection substrate 100 according to this embodiment, the projection substrate 100 is formed so as to suppress variations in in-plane luminance in the display area of ​​the image light caused by such perforations. The method for manufacturing such a projection substrate 100 will be described next.

[0067] 7 shows an example of a manufacturing flow of the projection substrate 100 according to this embodiment. Also, Fig. 8 shows an example of the configuration of the substrate 101 in the process of manufacturing the projection substrate 100 according to this embodiment.

[0068] First, a substrate 101 is prepared (S11), in which the first surface 102 and the second surface 103 opposite the first surface 102 have a predetermined flatness and a predetermined surface roughness. As the flatness of the substrate 101, the total thickness variation (TTV) value of at least the second surface 103 of the substrate 101 is set to be equal to or less than half the wavelength of the image light. Note that the TTV value of the first surface 102 of the substrate 101 may also be equal to or less than half the wavelength of the image light.

[0069] For example, when red light is output as image light, the TTV is a value of approximately 0.4 μm or less. When light of the entire violet or visible light band is output as image light, the TTV is a value of approximately 0.2 μm or less. The substrate 101 having such flatness can be prepared by polishing the surface of the substrate 101 using a polishing device or the like. The polishing device that brings the surface of the substrate 101 to a predetermined flatness is referred to as the first polishing device.

[0070] The surface roughness of the substrate 101 is such that the maximum cross-sectional height of at least the second surface 103 of the substrate 101 is equal to or less than a predetermined value that is smaller than the TTV value of the second surface 103. The value of the maximum cross-sectional height of the first surface 102 of the substrate 101 may also be equal to or less than a predetermined value. For example, the maximum cross-sectional height may be equal to or less than 100 nm, or alternatively, may be equal to or less than 50 nm. The maximum cross-sectional height may be equal to or less than 10 nm, or alternatively, may be equal to or less than 5 nm. It is desirable that the maximum cross-sectional height be equal to or less than 1 nm.

[0071] A substrate 101 having such a surface roughness can be prepared by polishing the surface of the substrate 101 using a polishing apparatus or the like. The polishing apparatus that polishes the surface of the substrate 101 to a predetermined surface roughness is referred to as the second polishing apparatus. The first polishing apparatus and the second polishing apparatus may be the same apparatus or different apparatuses. Furthermore, the abrasive used by the first polishing apparatus (hereinafter referred to as the first abrasive) is different from the abrasive used by the second polishing apparatus (hereinafter referred to as the second abrasive). For example, the diameter of the second abrasive is smaller than the diameter of the first abrasive.

[0072] The first polishing apparatus and the second polishing apparatus are preferably capable of executing a predetermined program to perform polishing operations. The polishing process for achieving flatness of the substrate 101 and the polishing process for achieving surface roughness of the substrate 101 may be performed consecutively by executing the program.

[0073] 8A shows an example of a prepared substrate 101 according to this embodiment. The prepared substrate 101 has a total thickness variation (TTV) of 0.2 μm or less and a maximum cross-sectional height of 1 nm or less. Here, the substrate 101 may have at least a second surface 103 with a TTV of 0.2 μm or less and a maximum cross-sectional height of the second surface 103 of 1 nm or less. Additionally, the first surface 102 of the substrate 101 may have a TTV of 0.2 μm or less and a maximum cross-sectional height of the first surface 102 of 1 nm or less. The substrate 101 is a plastic substrate formed of resin or the like. The prepared substrate 101 has localized perforations 104.

[0074] Next, the perforation 104 on the second surface 103 of the substrate 101 is detected (S12). For example, a laser interferometer is used to measure the surface shape of the second surface 103 of the substrate 101. The laser interferometer generates interference fringes between light reflected from a reference surface and light reflected from a surface to be measured. If a perforation 104 is formed on the second surface 103 of the substrate 101, a disturbance, pattern, or the like of the interference fringes corresponding to the size of the perforation 104 will occur, allowing the perforation 104 to be quickly detected.

[0075] If a perforation 104 larger than a predetermined size is detected on the second surface 103 of the substrate 101 (S13: Yes), the second surface 103 of the substrate 101 is processed (S14). For example, if a perforation 104 having a diameter larger than half the wavelength of the image light and a depth larger than 150 nm is detected, the second surface 103 of the substrate 101 is processed. The depth of the perforation 104 to be detected may be larger than 100 nm, or alternatively, may be larger than 200 nm.

[0076] Step S14 of processing the second surface 103 of the substrate 101 includes, for example, polishing the second surface 103 of the substrate 101. Polishing of the second surface 103 may be performed by the first polishing apparatus and / or the second polishing apparatus used in the process of preparing the substrate 101, or alternatively, by a polishing apparatus (hereinafter referred to as a third polishing apparatus) different from the polishing apparatus used in the process of preparing the substrate 101. It is desirable that the third polishing apparatus be able to perform such a polishing operation by executing a predetermined program. Furthermore, the polishing agent may be the same as the first polishing agent and / or the second polishing agent, or alternatively, a polishing agent (hereinafter referred to as a third polishing agent) different from the first polishing agent and the second polishing agent may be used.

[0077] Alternatively or additionally, step S14 of processing the second surface 103 of the substrate 101 may include a process of coating the second surface 103 with a coating material. The coating material is preferably a material having a refractive index similar to that of the substrate 101. The coating material is also preferably a material containing a substance contained in the substrate 101. Such a coating can fill the perforations 104 in the second surface 103 of the substrate 101 with the coating material, thereby reducing the size and / or number of the perforations 104.

[0078] Furthermore, step S14 of processing the second surface 103 of the substrate 101 may further include polishing the second surface 103 coated with the coating material. The polishing process of the coated second surface 103 can reduce the size of new perforations 104 caused by coating the substrate 101, remaining perforations 104, etc.

[0079] Polishing of the coated second surface 103 may be performed by the first polishing device, the second polishing device, and / or the third polishing device, or alternatively, by a polishing device different from these polishing devices (hereinafter, referred to as the fourth polishing device). It is desirable that the fourth polishing device be able to perform such polishing operations by executing a predetermined program. Furthermore, the abrasive used may be the same as the first polishing device, the second polishing device, and / or the third polishing device, or alternatively, a polishing device different from these polishing devices may be used.

[0080] Next, the process returns to S12, and the perforations 104 on the second surface 103 of the substrate 101 are detected. The processes from S12 to S14 are repeated until no perforations 104 larger than a predetermined size are detected. In other words, the second surface 103 of the substrate 101 is processed until the size of the detected perforations 104 is equal to or smaller than a predetermined diameter and a predetermined depth. In this embodiment, the second surface 103 of the substrate 101 is processed until the size of the detected perforations 104 is equal to or smaller than a diameter half the wavelength of the image light and a depth of 150 nm or less. FIG. 8B shows an example of the substrate 101 whose second surface 103 has been processed.

[0081] If no perforations 104 larger than a predetermined size are detected on the second surface 103 of the substrate 101 (S13: No), multiple diffraction gratings are formed on the first surface 102 of the substrate 101 (S15). The multiple diffraction gratings diffract the projection light incident on the first surface 102 of the substrate 101, and output it as image light from the display surface of the second surface 103 of the substrate 101.

[0082] The multiple diffraction gratings are, for example, the above-described input diffraction grating 210, intermediate diffraction grating 220, and output diffraction grating 230. Alternatively, the multiple diffraction gratings may be the above-described input diffraction grating 210 and two-dimensional diffraction grating 240. Such a diffraction grating can be formed, for example, by known photolithography techniques, and therefore a detailed description of how to form the diffraction grating will be omitted.

[0083] Fig. 8(c) shows an example of a substrate 101 in which an input diffraction grating 210, an intermediate diffraction grating 220, and an output diffraction grating 230 are formed on the first surface 102. Note that Fig. 8(c) is a diagram in which the intermediate diffraction grating 220 is omitted. In this manner, the projection substrate 100 can be formed. In other words, Fig. 8(c) is an example of the cross-sectional configuration of the projection substrate 100 according to this embodiment.

[0084] In the projection substrate 100 formed as described above, the TTV value of the second surface 103 opposite the first surface 102 is equal to or less than half the wavelength of the image light. Furthermore, the maximum cross-sectional height of the second surface 103 of the projection substrate 100 is equal to or less than a predetermined value that is smaller than the TTV value. Furthermore, the size of the perforations 104 in the second surface 103 of the projection substrate 100 is equal to or less than a predetermined diameter and a predetermined depth. Projection light is incident on the projection substrate 100 from the second surface 103 opposite the first surface 102 of the substrate 101. Furthermore, the second surface 103 opposite the first surface 102 of the substrate 101 serves as a display surface. In other words, the exit diffraction grating 230 emits image light in the direction of the display surface of the second surface 103.

[0085] In the projection substrate 100, the second surface 103 of the substrate 101 through which the projection light propagates is processed until no perforations 104 exceeding a predetermined size are detected, thereby reducing the effect of the perforations 104 on the projection light. Therefore, the projection substrate 100 can suppress variations in in-plane brightness in the display area of ​​the image light caused by the perforations 104 formed on the surface of the substrate 101. Furthermore, according to the manufacturing flow for the projection substrate 100 according to this embodiment, such a projection substrate 100 can be easily manufactured.

[0086] In the above manufacturing flow of the projection substrate 100 according to the present embodiment, an example in which the second surface 103 of the substrate 101 is processed has been described, but the present invention is not limited to this. In addition, the first surface 102 of the substrate 101 may be processed to reduce the influence of the perforations 104 on the first surface 102 of the substrate 101 on the projection light. This makes it possible to form a projection substrate 100 in which the size of the perforations 104 on the first surface 102 of the substrate 101 is equal to or smaller than a predetermined diameter and a predetermined depth.

[0087] For example, before step S15 of forming a plurality of diffraction gratings, a step of detecting perforations 104 in the first surface 102 of the substrate 101 and a step of processing the first surface 102 of the substrate 101 until the size of the detected perforations 104 is equal to or smaller than a predetermined diameter and a predetermined depth are executed. In this case, it is desirable to process the first surface 102 of the substrate 101 by executing a flow similar to the flow from S12 to S14 described in Fig. 7. It goes without saying that the first surface 102 may be processed before the second surface 103, or the second surface 103 may be processed before the first surface 102.

[0088] In the above manufacturing flow of the projection substrate 100 according to the present embodiment, an example in which multiple diffraction gratings are formed on the first surface 102 of the substrate 101 has been described, but the present invention is not limited to this. For example, multiple diffraction gratings may be formed on the second surface 103 of the substrate 101. In this case, it is desirable to process the first surface 102 of the substrate 101 so as to reduce the effect of the perforations 104 on the first surface 102 of the substrate 101 on the projection light.

[0089] Furthermore, one or more diffraction gratings may be formed on the first surface 102 and the second surface 103 of the substrate 101. In this case, it is desirable to process the first surface 102 and the second surface 103 of the substrate 101 so as to reduce the influence of the perforations 104 on the projection light.

[0090] 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.

[0091] REFERENCE SIGNS LIST 10 Eyeglass-type terminal 20 Input light beam 30 Output light beam bundle 100 Projection substrate 101 Substrate 102 First surface 103 Second surface 104 Perforation 110 Frame 120 Projection section 210 Incident diffraction grating 212 First groove section 220 Intermediate diffraction grating 222 Second groove section 224 First division area 230 Outgoing diffraction grating 232 Third groove section 234 Second division area 240 Two-dimensional diffraction grating

Claims

1. A method for manufacturing a projection substrate for projecting image light onto a display surface, comprising the steps of: preparing a substrate having a first surface and a second surface opposite the first surface with a predetermined flatness and surface roughness; detecting perforations on the second surface of the substrate; processing the second surface until the size of the detected perforations is equal to or less than a predetermined diameter and a predetermined depth; and forming a plurality of diffraction gratings on the first surface of the substrate for diffracting incident projection light and outputting it from the display surface as the image light.

2. The manufacturing method according to claim 1, wherein in the step of preparing the substrate, the substrate is prepared such that the TTV (Total Thickness Variation) value of at least the second surface is equal to or less than 1 / 2 of the wavelength of the image light, and the maximum cross-sectional height of the second surface is equal to or less than a predetermined value that is smaller than the TTV value of the second surface.

3. The manufacturing method according to claim 2, wherein in the step of preparing a substrate, the substrate is prepared such that the maximum cross-sectional height of at least the second surface is 1 nm or less.

4. The manufacturing method according to claim 1, wherein the step of processing the second surface includes a step of polishing the second surface.

5. The manufacturing method according to claim 1, wherein the step of processing the second surface includes a step of coating the second surface with a coating material.

6. The manufacturing method according to claim 5, wherein the step of processing the second surface further comprises the step of polishing the second surface coated with the coating material.

7. The manufacturing method according to claim 1, wherein in the step of processing the second surface, the second surface is processed until the size of the perforations has a diameter of 1 / 2 or less of the wavelength of the image light and a depth of 150 nm or less.

8. The manufacturing method according to claim 1, further comprising, before the step of forming a plurality of said diffraction gratings, the steps of: detecting perforations on said first surface of said substrate; and processing said first surface until the size of the detected perforations is equal to or smaller than a predetermined diameter and a predetermined depth.

9. A projection substrate for projecting image light onto a display surface, comprising: a substrate; an incident diffraction grating provided on a first surface of the substrate, onto 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 substrate; and an exit diffraction grating provided on the first surface of the substrate, at a position in the predetermined direction from the incident diffraction grating, onto which the projection light guided by the incident diffraction grating is incident and which emits at least a portion of the incident projection light from the display surface as the image light; wherein a TTV value of a second surface of the substrate opposite to the first surface is not more than 1 / 2 of the wavelength of the image light, a maximum cross-sectional height of the second surface of the substrate is not more than a predetermined value that is smaller than the TTV value, and the size of perforations in the second surface of the substrate is not more than a predetermined diameter and not more than a predetermined depth.

10. The projection substrate according to claim 9, wherein the size of the perforations on the first surface of the substrate is equal to or smaller than a predetermined diameter and a predetermined depth.

11. A glasses-type terminal worn by a user, comprising: the projection substrate according to claim 9 or 10, 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 image light onto the display surface with a surface facing the user's eye as the display surface; a frame that fixes the projection substrate; and a projection unit that is provided on the frame and irradiates the projection light onto the incident diffraction grating of the projection substrate to project the image light onto the display surface.

Images