Projection substrate, glasses-type terminal, projection substrate design method, and program

Abstract

Provided is a projection substrate comprising: a first substrate; a first incident diffraction grating; a first intermediate diffraction grating; a first emission diffraction grating; and a first low refractive material. When the refractive index of the first substrate is ns1, the refractive index of the first low refractive material is nt1, the size of a first light vector from the first incident diffraction grating toward the first intermediate diffraction grating is V1, and the size of a second light vector from the first intermediate diffraction grating toward the first emission diffraction grating is V2, the following expression is satisfied: nt1<V1<ns1 and nt1<V2<ns1 (1).

Description

Projection board, eyeglass-type terminal, projection board design method, and program

[0001] The present invention relates to a projection board, an eyeglass-type terminal, a method for designing a projection board, and a program.

[0002] BACKGROUND ART 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).

[0003] JP 2017-207686 A International Publication No. 2023 / 047488

[0004] Such eyeglass-type devices used a projection substrate with a diffraction grating formed on the substrate. Conventional projection substrates diffract incident light using the difference in refractive index between the material forming the diffraction grating and air, so the diffraction grating was formed so that it was in contact with an air layer. However, diffraction gratings in contact with an air layer are vulnerable to impact, and the substrate itself can easily become distorted. Therefore, it is considered to provide a low-refractive index material with a lower refractive index than the substrate between the substrate and the air layer. However, because such substrates have a low-refractive index material in the direction of light propagation, it can be difficult to design them to output uniform image light compared to substrates without a low-refractive index material.

[0005] Therefore, the present invention has been made in consideration of these points, and aims to enable the output of uniform image light using a diffraction grating on a projection substrate in which the surface of a substrate on which a diffraction grating is provided is covered with a low refractive index material.

[0006] In a first aspect of the present invention, there is provided a projection substrate for projecting image light onto a display surface, the projection substrate including: a first substrate; a first incident diffraction grating provided on the first substrate, the first incident diffraction grating receiving projection light for projecting the image light and diffracting the incident projection light in a first direction; a first intermediate diffraction grating provided in the first direction from the first incident diffraction grating and diffracting the projection light incident from the first incident diffraction grating in a second direction; a first exit diffraction grating provided in the second direction from the first intermediate diffraction grating and diffracting the projection light incident from the first intermediate diffraction grating in a third direction toward the outside via the display surface; and a first exit diffraction grating formed on at least one surface of the first substrate, the first incident diffraction grating, the a first intermediate diffraction grating, and a first low-refractive index material covering the first exit diffraction grating and having a refractive index smaller than that of the first substrate, wherein the refractive index of the first substrate is ns1, the refractive index of the first low-refractive index material is nt1, and when the light in the first direction from the first entrance diffraction grating to the first intermediate diffraction grating is expressed as a first light vector which is a normalized wave vector of k-space, the magnitude of the first light vector is V1, and when the light in the second direction from the first intermediate diffraction grating to the first exit diffraction grating is expressed as a second light vector which is a normalized wave vector of k-space, the magnitude of the second light vector is V2, the magnitude V1 of the first light vector and the magnitude V2 of the second light vector satisfy the following equations: nt1<V1<ns1 and nt1<V2<ns1 (1).

[0007] The wavelength in vacuum of the projection light incident on the first incident diffraction grating is λ ０ , the direction cosines of the projection light in the X direction and the Y direction orthogonal to each other in a plane parallel to the first substrate are respectively i ｘ , i ｙ and the period (pitch) of the grooves of the first incident diffraction grating in the X direction is Λ １１ｘ , the pitch in the Y direction is Λ １１ｙ and the pitch of the grooves of the first intermediate diffraction grating in the X direction is Λ １２ｘ , the pitch in the Y direction is Λ １２ｙ When the first light vector (i １１ｘ , i １１ｙ ) is expressed by the following formula: The second light vector (i １２ｘ , i １２ｙ ) may be expressed as follows:

[0008] The first low refractive index material, the first input diffraction grating, the first intermediate diffraction grating, and the first output diffraction grating may be configured so that the magnitude V1 of the first light vector expressed by equation (2) and the magnitude V2 of the second light vector expressed by equation (3) of the light that is incident on the first input diffraction grating and that is output as the image light from a predetermined range on the display surface satisfy equation (1).

[0009] The predetermined range of the display surface may be a range of the projection board from which the image light enters the field of view of a user.

[0010] The first low refractive index material, the first input diffraction grating, the first intermediate diffraction grating, and the first output diffraction grating may be configured so that the magnitude V1 of the first light vector and the magnitude V2 of the second light vector of light in a predetermined wavelength range among the light emitted as the image light from a predetermined range on the display surface satisfy equation (1).

[0011] When the light in the third direction output from the first exit diffraction grating to the outside through the display surface is expressed as a third light vector which is a normalized wave vector in k space, the end point of the third light vector is the incident light (i ｘ , i ｙ ) may be equal to the end point of

[0012] a second substrate disposed parallel to the first substrate and having an area overlapping with the first substrate in a plan view; a second incident diffraction grating provided on the second substrate, on which the projection light for projecting the image light is incident and which diffracts the incident projection light in a fourth direction; a second intermediate diffraction grating provided in the fourth direction from the second incident diffraction grating and which diffracts the projection light incident from the second incident diffraction grating in a fifth direction; a second exit diffraction grating provided in the fifth direction from the second intermediate diffraction grating and which diffracts the projection light incident from the second intermediate diffraction grating onto the display surface provided in a third direction; and a second exit diffraction grating formed on at least one surface of the second substrate, which is disposed between the second incident diffraction grating and the second intermediate diffraction grating. the second substrate, and a second low refractive index material covering the second exit diffraction grating and having a refractive index lower than that of the second substrate, wherein the refractive index of the second substrate is ns2, the refractive index of the second low refractive index material is nt2, and when the light in the fourth direction from the second entrance diffraction grating to the second intermediate diffraction grating is expressed as a fourth light vector which is a normalized wave vector of k space, the magnitude of the fourth light vector is V4, and when the light in the fifth direction from the second intermediate diffraction grating to the second exit diffraction grating is expressed as a fifth light vector which is a normalized wave vector of k space, the magnitude of the fifth light vector is V5, the magnitude V4 of the fourth light vector and the magnitude V5 of the fifth light vector may satisfy the following equations: nt2<V4<ns2 and nt2<V5<ns2 (4)

[0013] On the first substrate, light in a first wavelength band of the projection light may not satisfy formula (1), and on the second substrate, light in the first wavelength band of the projection light may satisfy formula (4).

[0014] On the first substrate, light of the projection light in a second wavelength band different from the first wavelength band may satisfy equation (1), and on the second substrate, light of the projection light in the second wavelength band may not necessarily satisfy equation (4).

[0015] In a second 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 first 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 first incident diffraction grating of the projection substrate to project the image light onto the display surface.

[0016] In a third aspect of the present invention, there is provided a computer-implemented method for designing a projection substrate according to the first aspect, the method including: acquiring information on a refractive index ns1 of the first substrate and a refractive index nt1 of the first low refractive index material; acquiring information on a diffraction grating to be formed on the first substrate; and calculating direction cosines i of the projection light in the X and Y directions orthogonal to each other in a plane parallel to the first substrate. ｘ , i ｙ and calculating a magnitude V1 of the first light vector as follows: Calculating a magnitude V2 of the second light vector as follows: and confirming that the calculated magnitude V1 of the first light vector and the magnitude V2 of the second light vector satisfy equation (1).

[0017] In a fourth aspect of the present invention, there is provided a program which, when executed by a computer, causes the computer to execute the design method of the third aspect.

[0018] According to the present invention, in a projection substrate in which the surface of a substrate on which a diffraction grating is provided is covered with a low refractive index material, an effect is achieved in that uniform image light can be output by the diffraction grating.

[0019] 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 that the projection unit 120 irradiates onto the projection substrate 100 according to the present embodiment, and an example of the image light P that the projection substrate 100 emits. 5 shows an example of the configuration of the projection substrate 100 according to the present embodiment. 6 shows an example of the cross-sectional configuration of the projection substrate 100 according to the present embodiment. 7 shows an example of the process in which the projection light according to the present embodiment is diffracted by a diffraction grating, expressed in k-space. 8 shows a modified example of the projection substrate 100 according to the present embodiment. 9 shows an example of the design flow for the projection substrate 100 according to the present embodiment.

[0020] <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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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 a first input diffraction grating 210 provided on the projection board 100. The first input diffraction grating 210 guides the projection light within the substrate of the projection board 100. The projection board 100 then emits the projection light guided within the substrate from a first output diffraction grating 230 as image light. The first input diffraction grating 210 and the first output diffraction grating 230 will be described later.

[0028] 3 shows an outline of the optical path of projection light in the projection substrate 100 according to this embodiment. The projection substrate 100 has a first input diffraction grating 210, a first intermediate diffraction grating 220, and a first output diffraction grating 230. The projection light L is incident on the first input diffraction grating 210, passes through the first intermediate diffraction grating 220, and is output from the first output diffraction grating 230 as image light P. The first intermediate diffraction grating 220 guides the projection light L part by part to the first output diffraction grating 230 as the projection light L travels away from the first input diffraction grating 210.

[0029] Similarly, as the projection light L travels away from the first intermediate diffraction grating 220, the first exit diffraction grating 230 also 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 first entrance diffraction grating 210 from the first exit diffraction grating 230 as image light P.

[0030] <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.

[0031] 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.

[0032] The projection unit 120, for example, irradiates the projection light L onto the first 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 first input diffraction grating 210 passes through the first intermediate diffraction grating 220 and is output from the first output diffraction grating 230 as image light P. The image light P is output from the first 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.

[0033] 4, five of the multiple ray bundles that are emitted from the circular region C of the first 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 first output ray bundle 30a, the ray bundle that forms an image as the upper right pixel of the image is designated as second output ray bundle 30b, the ray bundle that forms an image as the central pixel of the image is designated as third output ray bundle 30c, the ray bundle that forms an image as the lower left pixel of the image is designated as fourth output ray bundle 30d, and the ray bundle that forms an image as the upper left pixel of the image is designated as fifth output ray bundle 30e.

[0034] 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 first input diffraction grating 210 to the first 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.

[0035] In other words, the image M2 formed on the retina of the user's eye by the image light P emitted from the first exit 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 first exit diffraction grating 230 functions as a display area that displays the image M2 corresponding to the image M1 projected by the projection light L.

[0036] 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.

[0037] <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 has a first substrate 101, a first input diffraction grating 210, a first intermediate diffraction grating 220, a first output diffraction grating 230, and a first low refractive index material 240.

[0038] The first substrate 101 is, for example, a glass substrate. The first input diffraction grating 210, the first intermediate diffraction grating 220, the first output diffraction grating 230, and the first low refractive index material 240 are provided on the first substrate 101. In Fig. 5, the first low refractive index material 240 formed on the surface of the first substrate 101 is omitted. The first low refractive index material 240 will be described later.

[0039] <Example of First Incident Diffraction Grating 210> Projection light for projecting image light is incident on the first incident diffraction grating 210, and the first incident diffraction grating 210 diffracts the incident projection light toward the first intermediate diffraction grating 220 in a first direction. While FIG. 5 shows an example in which the first incident diffraction grating 210 has a circular shape on a plane substantially parallel to the XY plane, this is not limiting. The first 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 first intermediate diffraction grating 220. The first incident diffraction grating 210 may be formed on the first surface of the first substrate 101, or alternatively, on the second surface of the first substrate 101.

[0040] The first 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 first incident diffraction grating 210 has a reflective or transmissive incident diffraction grating and guides projection light toward the first 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.

[0041] The multiple first grooves 212 are arranged, for example, in a direction from the first incident diffraction grating 210 to the first intermediate diffraction grating 220. Here, the traveling direction of the projection light from the first incident diffraction grating 210 to the first 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 first incident diffraction grating 210 while converging, the first incident diffraction grating 210 guides the projection light to the first 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.

[0042] <Example of First Intermediate Diffraction Grating 220> The first intermediate diffraction grating 220 is disposed in a first direction from the first input diffraction grating 210 and diffracts a portion of the projection light incident from the first input diffraction grating 210 toward the first output diffraction grating 230 in a second direction. The first intermediate diffraction grating 220 is disposed in a region through which the projection light passes, on a plane substantially parallel to the XY plane. The first intermediate diffraction grating 220 has a reflective diffraction grating and guides the projection light toward the first output diffraction grating 230 by reflective diffraction. The first intermediate diffraction grating 220 has, for example, a rectangular shape with its longitudinal direction in the first direction. The first intermediate diffraction grating 220 may be formed on the first surface of the first substrate 101, or alternatively, on the second surface of the first substrate 101.

[0043] Since the projection light propagates while spreading around the first direction, it is preferable that the first intermediate diffraction grating 220 has a shape that spreads away from the first direction, which is the propagation direction of the projection light passing through the first incident diffraction grating 210, as it moves away from the first incident diffraction grating 210. The first 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 first intermediate diffraction grating 220 has a trapezoidal shape. A first intermediate diffraction grating 220 with such a shape can be formed to correspond to a region where the projection light propagates while spreading in the XY plane, and can efficiently guide the projection light.

[0044] The first 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 a predetermined groove width and interval, thereby functioning as a diffraction grating. The first intermediate diffraction grating 220 functions as, for example, a reflective diffraction grating, and guides the projection light to the first output diffraction grating 230.

[0045] 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 first output diffraction grating 230. The second period is, for example, in the range of about 10 nm to about 10 μm.

[0046] The plurality of second grooves 222 are arranged, for example, in a predetermined direction. For example, the direction from the first intermediate diffraction grating 220 to the first 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.

[0047] The first 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 first intermediate diffraction grating 220 so that the proportion of light that is guided to the first output diffraction grating 230 out of the incident projection light differs for each first divided region 224.

[0048] The first intermediate diffraction grating 220 desirably has three or more first divided regions 224. In this way, the first intermediate diffraction grating 220 is divided into a plurality of first divided regions 224, and the amount of projection light guided to the first 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 first input diffraction grating 210 to the first 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.

[0049] 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 first 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 farther away from the first incident diffraction grating 210.

[0050] 5, consider a first intermediate diffraction grating 220 having three first divided regions 224. Here, the first divided region 224a, which is closest to the first input diffraction grating 210 among the three first divided regions 224, has the second grooves 222a formed to a depth such that approximately one-quarter of the amount of incident projection light is guided to the first 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 first input diffraction grating 210 is incident on the adjacent first divided region 224b.

[0051] The first divided region 224b, which is second closest to the first input diffraction grating 210, has a depth of the second grooves 222b formed such that it guides approximately one-third of the amount of incident projection light to the first output diffraction grating 230. In other words, the depth of the second grooves 222b of the first divided region 224b, which is second closest to the first input diffraction grating 210, is greater than the depth of the second grooves 222a so that it guides 4 / 3 times the amount of light to the first output diffraction grating 230 compared to the first divided region 224a closest to the first input diffraction grating 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 first input diffraction grating 210 to the first output diffraction grating 230.

[0052] The remaining approximately half of the amount of projection light incident on the first divided region 224a closest to the first input diffraction grating 210 is incident on the adjacent first divided region 224c. The first divided region 224c third closest to the first input diffraction grating 210 has the second grooves 222c formed to a depth such that approximately half of the amount of incident projection light is guided to the first output diffraction grating 230. In other words, the depth of the second grooves 222c of the first divided region 224c third closest to the first input diffraction grating 210 is greater than the depth of the second grooves 222b so that 3 / 2 times the amount of light is guided to the first output diffraction grating 230 compared to the first divided region 224b second closest to the first input diffraction grating 210.

[0053] 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 the rate of change in the depth increases with increasing distance from the first input diffraction grating 210. The first divided region 224c, which is third closest to the first input diffraction grating 210, guides to the first output diffraction grating 230 approximately one-fourth the amount of projection light incident on the first divided region 224a, which is closest to the first input diffraction grating 210. As in the above example, by varying the amount of projection light guided to the first output diffraction grating 230 for each first divided region 224 to a predetermined value, it can be seen that the first intermediate diffraction grating 220 can guide the projection light to the first output diffraction grating 230 while maintaining a substantially constant distribution of the amount of projection light guided to the first output diffraction grating 230 corresponding to each first divided region 224.

[0054] <Example of First Exit Diffraction Grating 230> The first exit diffraction grating 230 is provided in the second direction from the first intermediate diffraction grating 220, and diffracts at least a portion of the projection light incident from the first intermediate diffraction grating 220 from the display surface toward a third direction. The first 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 first exit diffraction grating 230 may be formed on the first surface of the first substrate 101, or alternatively, may be formed on the second surface of the first substrate 101.

[0055] 5 shows an example in which the first 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 first 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.

[0056] The first exit 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 first exit 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.

[0057] The third period of the plurality of third grooves 232 provided in the first exit diffraction grating 230 is different from the second period of the plurality of second grooves 222 in the first intermediate diffraction grating 220. The third period of the plurality of third grooves 232 in the first exit diffraction grating 230 may be the same as the first period of the plurality of first grooves 212 in the first entrance 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, distortion 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.

[0058] The multiple third groove portions 232 are arranged, for example, in a second direction from the first intermediate diffraction grating 220 toward the first 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.

[0059] Similar to the first intermediate diffraction grating 220, the first output diffraction grating 230 has a plurality of second divided regions 234 arranged in the traveling direction of the projection light incident from the first intermediate diffraction grating 220. The third grooves 232 formed in the plurality of second divided regions 234 have different depths. In other words, the third grooves 232 are formed in the first output diffraction grating 230 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.

[0060] The first 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 first intermediate diffraction grating 220 than one second divided region 234. Furthermore, when the first 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 first intermediate diffraction grating 220 increases.

[0061] As described above, the first 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, like the plurality of first divided regions 224 of the first intermediate diffraction grating 220, the first output diffraction grating 230 can guide the projection light as image light, and adjust the distribution of the light amount of the entire image to be approximately constant when the observer observes the image light as an image.

[0062] As described above, the projection substrate 100 according to this embodiment branches the projection light incident on the first input diffraction grating 210 into different portions for each of the plurality of first divided regions 224 of the first intermediate diffraction grating 220, and then outputs the branched projection light as image light from the first 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 also emitting image light from the first output diffraction grating 230 at different portions for each of the plurality of second divided regions 234.

[0063] Such a projection substrate 100 can be realized by forming diffraction gratings corresponding to the first incident diffraction grating 210, the first intermediate diffraction grating 220, and the first 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.

[0064] The above-described projection substrate 100 can be used to configure the eyeglasses-type terminal 10, etc. However, conventionally, it has been difficult to manufacture the substrates used in the eyeglasses-type terminal 10, etc. A diffraction grating formed on a conventional substrate diffracts incident light by utilizing the difference in refractive index between the material forming the diffraction grating and air.

[0065] Therefore, since the diffraction grating is formed in contact with an air layer, it is vulnerable to impacts and the substrate itself is prone to distortion. Furthermore, vacuum bonding processes and the like cannot be used in the process of forming conventional substrates that are in contact with an air layer. Furthermore, conventional substrates are prone to contamination by foreign matter such as water droplets. To protect such substrates, a complex structure, such as a layer structure to protect the diffraction grating on top of the air layer, was required. Therefore, the projection substrate 100 of this embodiment has a simple structure, is resistant to impacts, is resistant to distortion, can be subjected to vacuum bonding processes and the like, and reduces the intrusion of foreign matter such as water droplets. Such a projection substrate 100 is now described.

[0066] <Example of Cross-Sectional Configuration of Projection Substrate 100> Fig. 6 shows an example of the cross-sectional configuration of the projection substrate 100 according to this embodiment. In this embodiment, an example is shown in which a first input diffraction grating 210, a first intermediate diffraction grating 220, and a first output diffraction grating 230 are formed on the first surface 102 of the first substrate 101. Note that Fig. 6 is a diagram in which the first intermediate diffraction grating 220 is omitted.

[0067] 6 , projection light is incident on the first input diffraction grating 210 from the second surface 103 opposite the first surface 102 of the first substrate 101. The second surface 103 opposite the first surface 102 of the first substrate 101 is the display surface. In other words, the first output diffraction grating 230 outputs image light in the direction of the display surface of the second surface 103 (third direction).

[0068] The projection substrate 100 further includes a first low-refractive index material 240. The first low-refractive index material 240 is formed on at least one surface of the first substrate 101 and covers the first entrance diffraction grating 210, the first intermediate diffraction grating 220, and the first exit diffraction grating 230. The first low-refractive index material 240 fills the grooves of the first entrance diffraction grating 210, the first intermediate diffraction grating 220, and the first exit diffraction grating 230. The first low-refractive index material 240 is a material with a smaller refractive index than the first substrate 101, the first entrance diffraction grating 210, the first intermediate diffraction grating 220, and the first exit diffraction grating 230. The first low-refractive index material 240 includes, for example, mesoporous silica with a porous structure.

[0069] Mesoporous silica has a porous structure with multiple pores. Furthermore, since mesoporous silica is a spherical material with a diameter of approximately 20 nm, many gaps are formed between the spherical material when it is formed into a film. Since the pores and gaps of such mesoporous silica are filled with air, which has a refractive index of 1, the refractive index of a film formed from mesoporous silica is close to that of air, which is 1. Furthermore, even when mesoporous silica is formed into a film with a thickness similar to that of the grooves of a diffraction grating, there are few areas that block visible light, so the transmittance of visible light and the haze value are also close to those of air.

[0070] The first low-refractive index material 240 containing such mesoporous silica has, for example, a refractive index of less than 1.2, a visible light transmittance of more than 90%, and a haze value of less than 0.5. Such a first low-refractive index material 240 has properties similar to those of air with respect to visible light. Therefore, even when the first low-refractive index material 240 is filled in the grooves of the first input diffraction grating 210, the first intermediate diffraction grating 220, and the first output diffraction grating 230, the first input diffraction grating 210, the first intermediate diffraction grating 220, and the first output diffraction grating 230 can diffract and guide incident light in the same manner as when the first low-refractive index material 240 is not filled in the grooves.

[0071] As described above, the first entrance diffraction grating 210, the first intermediate diffraction grating 220, and the first exit diffraction grating 230 have their grooves filled with the first low refractive index material 240, making them less susceptible to damage by impact and less susceptible to the intrusion of foreign matter such as water droplets. The first low refractive index material 240 functions to reinforce the first entrance diffraction grating 210, the first intermediate diffraction grating 220, and the first exit diffraction grating 230, making the first substrate 101 less susceptible to distortion. Furthermore, because the first entrance diffraction grating 210, the first intermediate diffraction grating 220, and the first exit diffraction grating 230 do not need to be in contact with an air layer, a vacuum bonding process or the like can be used in the manufacturing process of the projection substrate 100.

[0072] It is desirable that the first low refractive index material 240 be formed over the entire first surface 102 of the first substrate 101, as shown in FIG. 6 . The first low refractive index material 240 is desirably laminated to a thickness equal to or greater than a predetermined thickness on the first entrance diffraction grating 210, the first intermediate diffraction grating 220, and the first exit diffraction grating 230. The predetermined thickness is, for example, about five times the width of the grooves on the first entrance diffraction grating 210, the first intermediate diffraction grating 220, and the first exit diffraction grating 230. The predetermined thickness is desirably about ten times the width of the grooves on the first entrance diffraction grating 210, the first intermediate diffraction grating 220, and the first exit diffraction grating 230.

[0073] The first input diffraction grating 210, the first intermediate diffraction grating 220, and the first output diffraction grating 230 are formed on the first surface 102, which is the opposite side to the display surface (second surface 103) of the first substrate 101. Projection light that passes through the inside of the first substrate 101 from the second surface 103 is incident on the first input diffraction grating 210. It is desirable for the first input diffraction grating 210 to be able to diffract all of the input projection light, but some of the light may leak from the first surface 102 to the outside of the first substrate 101. In this embodiment, this leaked light is called leakage light.

[0074] Such leakage light may enter the eyes of a person facing the user and cause discomfort. However, when the first low refractive index material 240 is laminated to a thickness equal to or greater than a predetermined thickness in the first incident diffraction grating 210, the first low refractive index material 240 reinforces the first incident diffraction grating 210 while dispersing and reducing the leakage light from the first incident diffraction grating 210 within the first low refractive index material 240.

[0075] Similarly, the first exit diffraction grating 230 causes at least a portion of the incident projection light to pass through the inside of the first substrate 101 and exit from the display surface. It is desirable that the first exit diffraction grating 230 be able to diffract all of the incident projection light, but some of the light may leak as leakage light from the first surface 102 to the outside of the first substrate 101. In this case as well, by stacking the first low refractive index material 240 to a thickness equal to or greater than a predetermined thickness on the first exit diffraction grating 230, the first low refractive index material 240 can reinforce the first exit diffraction grating 230 while dispersing and reducing the leakage light of the first exit diffraction grating 230 inside the first low refractive index material 240.

[0076] As described above, the first low refractive index material 240 covers the first entrance diffraction grating 210, the first intermediate diffraction grating 220, and the first exit diffraction grating 230, and thus the first low refractive index material 240 can reduce leakage light while reinforcing the first entrance diffraction grating 210, the first intermediate diffraction grating 220, and the first exit diffraction grating 230. The projection substrate 100 can emit incident projection light as image light without the first entrance diffraction grating 210, the first intermediate diffraction grating 220, and the first exit diffraction grating 230 being in contact with an air layer, and can protect the first entrance diffraction grating 210, the first intermediate diffraction grating 220, and the first exit diffraction grating 230 without a complex configuration.

[0077] Because this projection substrate 100 diffracts and guides the projection light via the first low-refractive index material 240, the optical design may be more complex than with a conventional substrate that does not have the first low-refractive index material 240. For example, designing the projection substrate 100 can be difficult when uniformly projecting image light onto a larger display surface or when uniformly projecting image light having more colors onto the display surface. Therefore, the inventors clarified the appropriate configuration conditions for the optical system of the projection substrate 100 by using a wave vector that uses wave numbers in k-space, and discovered a simple method for designing the projection substrate 100. Therefore, the conditions that the optical system of the projection substrate 100 must satisfy will first be described.

[0078] First, the wavelength in vacuum of the projection light incident on the first incident diffraction grating 210 is λ ０ The direction cosines of the incident projection light in the X direction and the Y direction, which are orthogonal to each other on a plane parallel to the first substrate 101, are respectively expressed as i ｘ , i ｙ In other words, the projection light incident on the first incident diffraction grating 210 in a plane parallel to the first substrate 101 is defined as the incident light (i ｘ , i ｙ ) and expressed as a wave vector.

[0079] Incident light (i ｘ , i ｙ ) is the wave number k (= 2π / λ ０ ) is a wave vector expressed as follows: ｘ , i ｙ The magnitude V0 of the incident light (i) is expressed as follows: where L and M are unit vectors. ｘ , i ｙ ) is shown in k-space in FIG.

[0080] <Example of k-space representation of the process of diffraction of projection light> Figure 7 shows an example of k-space representation of the process of diffraction of projection light by a diffraction grating according to this embodiment. Note that, because the effective projection light output as image light is light diffracted by the diffraction grating in the XY plane substantially parallel to the first substrate 101, the Z axis perpendicular to the first substrate 101 is omitted in Figure 7. The horizontal axis of Figure 7 indicates the wave number in the X direction, and the vertical axis indicates the wave number in the Y direction.

[0081] Incident light (i ｘ , i ｙ ) is preferably a normalized wave vector that is normalized to a predetermined value. For example, the incident light (i ｘ , i ｙ ) so that the magnitude of the incident light (i ｘ , i ｙ ) components are normalized. ｘ , i ｙ ) is in an area A with a radius of 1.

[0082] Although the incident light can be expressed as a collection of multiple light rays that are incident at various angles of incidence and have various wavelengths, four of the multiple light rays will be described here. The four light rays correspond to, for example, the light rays at the four corners of the image light, and are the first input light ray 20a, the second input light ray 20b, the fourth input light ray 20d, and the fifth input light ray 20e described in Fig. 4. In Fig. 7, the end points of these four light rays are indicated by four points near the center of region A.

[0083] The first incident diffraction grating 210 is configured to receive such incident light (i ｘ , i ｙ ) toward the first intermediate diffraction grating 220. In k-space, such a first incident diffraction grating 210 diffracts the incident light (i ｘ , i ｙ The end point of the first wave vector (D １ｘ , D １ｙ ), where m is the diffraction order, Λ is the period (pitch) of the grooves of the first incident diffraction grating 210, and f ｘ and f ｙis a unit vector representing the direction of the periodicity of the first incident diffraction grating 210. The diffraction order m is often set to −1 or 1, and in this embodiment, m=1.

[0084] Here, the first incident diffraction grating 210 divides the incident light (i ｘ , i ｙ ) into the first wave vector (D １ｘ , D １ｙ ) is defined as the first light vector (i １１ｘ , i １１ｙ ) In other words, the first light vector (i １１ｘ , i １１ｙ ) is a normalized wave vector representing the light in the first direction traveling from the first incident diffraction grating 210 to the first intermediate diffraction grating 220 in the k-space. １１ｘ , i １１ｙ ) is expressed by the following formula: where Λ １１ｘ is the pitch of the grooves of the first incident diffraction grating 210 in the X direction, Λ １１ｙ is the pitch of the grooves of the first input diffraction grating 210 in the Y direction.

[0085] The first light vector (i １１ｘ , i １１ｙ The magnitude V1 of the distance θ can be calculated as follows:

[0086] In the k-space, such a first light vector (i １１ｘ , i １１ｙ ) end point position (first wave vector (D １ｘ , D １ｙ When the end point of the incident light (i ｘ , i ｙ ) is refracted without being diffracted by the first incident diffraction grating 210. In this case, the incident light (i ｘ , i ｙ ) cannot be output as image light from the display surface of the projection board 100.

[0087] In k-space, the first light vector (i １１ｘ , i １１ｙWhen the end point of the incident light (i ｘ , i ｙ ) is diffracted by the first incident diffraction grating 210 to a position corresponding to region B. Region B is a region whose radius is greater than 1 and less than or equal to nt1. Here, the refractive index of the first low refractive index material 240 is defined as nt1.

[0088] In other words, the first light vector (i １１ｘ , i １１ｙ If the end point of the incident light (i ｘ , i ｙ ) is diffracted into the first low refractive index material 240 in the first direction. The first low refractive index material 240 has a lower light transmittance and diffraction efficiency than air and the first substrate 101. Therefore, the incident light (i ｘ , i ｙ ) the amount of light output from the display surface of the projection board 100 as image light is reduced.

[0089] In k-space, the first light vector (i １１ｘ , i １１ｙ When the end point of the incident light (i ｘ , i ｙ ) is diffracted by the first incident diffraction grating 210 to a position corresponding to region C. Region C is a region whose radius is greater than nt1 and less than ns1. Here, the refractive index of the first substrate 101 is defined as ns1.

[0090] In other words, the first light vector (i １１ｘ , i １１ｙ If the end point of the incident light (i ｘ , i ｙ ) is diffracted toward the first substrate 101 in the first direction. In the first substrate 101, the first intermediate diffraction grating 220 is formed in the first direction from the first incident diffraction grating 210, so that the incident light (i ｘ , i ｙ ) can be efficiently guided to the first intermediate diffraction grating 220.

[0091] In k-space, the first light vector (i １１ｘ , i １１ｙ When the end point of the incident light (i ｘ , i ｙ ) corresponds to the case where the first light vector (i １１ｘ , i １１ｙ If the end point of the incident light (i ｘ , i ｙ ) cannot be output as image light from the display surface of the projection board 100.

[0092] From the above, in the k-space, the first light vector (i １１ｘ , i １１ｙ It is desirable to configure the pitch of the first incident diffraction grating 210, the refractive index nt1 of the first low refractive index material 240, and the refractive index ns1 of the first substrate 101 so that the end point of the incident light (i ｘ , i ｙ ) are incident on the first light vector (i １１ｘ , i １１ｙ ) end point (first wave vector (D １ｘ , D １ｙ ) and the end point of the four points shown.

[0093] Similarly, the first intermediate grating 220 receives the first light vector (i １１ｘ , i １１ｙ ) into the second wave vector (D ２ｘ , D ２ｙ ) to the second light vector (i １２ｘ , i １２ｙ ) In other words, the second light vector (i １２ｘ , i １２ｙ ) is a normalized wave vector representing the light in the second direction traveling from the first intermediate diffraction grating 220 to the first output diffraction grating 230 in the k-space. １２ｘ , i １２ｙ ) is expressed by the following formula: where Λ １２ｘ is the pitch of the grooves of the first intermediate diffraction grating 220 in the X direction, Λ１２ｙ is the pitch of the grooves of the first intermediate diffraction grating 220 in the Y direction.

[0094] The second light vector (i １２ｘ , i １２ｙ The magnitude V2 of the distance θ can be calculated as follows:

[0095] In the k-space, such a second light vector (i １２ｘ , i １２ｙ ) end point position (second wave vector (D ２ｘ , D ２ｙ If the end position of the first light vector (i １１ｘ , i １１ｙ ) is refracted without being diffracted by the first intermediate diffraction grating 220. In this case, the first light vector (i １１ｘ , i １１ｙ ) cannot be output as image light from the display surface of the projection board 100.

[0096] In k-space, the second light vector (i １２ｘ , i １２ｙ If the end point of the first light vector (i １１ｘ , i １１ｙ ) is diffracted into the first low refractive index material 240 in the second direction. １１ｘ , i １１ｙ ) the amount of light output from the display surface of the projection board 100 as image light is reduced.

[0097] In k-space, the second light vector (i １２ｘ , i １２ｙ If the end point of the first light vector (i １１ｘ , i １１ｙ ) corresponds to the case where the first light vector (i １１ｘ , i １１ｙ ) can be efficiently guided to the first exit grating 230. FIG. 7 shows the first light vector (i １１ｘ , i １１ｙ) end point (first wave vector (D １ｘ , D １ｙ The four points shown as the end points of the second light vector (i １２ｘ , i １２ｙ ) end point (second wave vector (D ２ｘ , D ２ｙ ) and the end point of the four points shown.

[0098] In k-space, the second light vector (i １２ｘ , i １２ｙ If the end point of the first light vector (i １１ｘ , i １１ｙ ) corresponds to the case where the first light vector (i １１ｘ , i １１ｙ ) cannot be output as image light from the display surface of the projection board 100.

[0099] From the above, it can be seen that in order for the projection substrate 100 having one first substrate 101 whose surface is covered with the first low refractive index material 240 to be able to diffract the projection light with the diffraction grating and output the image light from the display surface, at least the following equation must be satisfied: In other words, the projection substrate 100 is configured such that the pitch of the diffraction grating, the refractive index nt1 of the first low refractive index material 240, and the refractive index ns1 of the first substrate 101 satisfy the following equation: (Equation 7) nt1<V1<ns1 and nt1<V2<ns1

[0100] Furthermore, in order for the projection board 100 to output image light as an image with a uniform light intensity from the display surface, it is sufficient to make the light intensity of the plurality of image light beams output from a predetermined area of ​​the display surface that constitutes the screen approximately constant. The predetermined area of ​​the display surface is the area from which the projection board 100 emits the image light that enters the user's field of view.

[0101] In this case, of the projection light incident on the first incident diffraction grating 210, the first light vector (i １１ｘ , i １１ｙ ) and the magnitude V1 of the second light vector (i １２ｘ , i １２ｙThe first substrate 101, the first low refractive index material 240, the first input diffraction grating 210, the first intermediate diffraction grating 220, and the first output diffraction grating 230 are configured so that the size V2 of the input diffraction grating 210 satisfies the formula (7).

[0102] Furthermore, in order to output a color image from a predetermined range of the display surface with a uniform light amount, it is sufficient to further make the light amount of image light in a predetermined wavelength range approximately constant. In this case, among the light emitted as image light from the predetermined range of the display surface, the first light vector (i １１ｘ , i １１ｙ ) and the magnitude V1 of the second light vector (i １２ｘ , i １２ｙ The first substrate 101, the first low refractive index material 240, the first input diffraction grating 210, the first intermediate diffraction grating 220, and the first output diffraction grating 230 are configured so that the size V2 of the first input diffraction grating 210 satisfies the formula (7).

[0103] The first exit grating 230 then receives the second light vector (i １２ｘ , i １２ｙ ) into the third wave vector (D ３ｘ , D ３ｙ ) to the third light vector (i １３ｘ , i １３ｙ ) In other words, the third light vector (i １２ｘ , i １２ｙ ) is a normalized wave vector that represents, in k-space, the light in the third direction that is output from the first exit diffraction grating 230 to the outside through the display surface. １３ｘ , i １３ｙ ) is expressed by the following formula: where Λ １３ｘ is the pitch of the grooves of the first exit diffraction grating 230 in the X direction, Λ １３ｙ is the pitch of the grooves of the first exit diffraction grating 230 in the Y direction.

[0104] In k-space, the third light vector (i １３ｘ , i １３ｙ ) end point (third wave vector (D ３ｘ , D ３ｙ The end point of the incident light (i ｘ , i ｙ) in the area C. This allows the projection board 100 to output image light with reduced image distortion from the display surface while making the amount of light uniform across the entire screen. １２ｘ , i １２ｙ ) end point (second wave vector (D ２ｘ , D ２ｙ ) are moved to four points near the center of region A by first exit diffraction grating 230.

[0105] As described above, the projection substrate 100 according to this embodiment can improve the strength of the first substrate 101 by covering the surface of the first substrate 101 with the first low refractive index material 240. Furthermore, it has been found that, in such a projection substrate 100, by expressing the optical path of the incident projection light in k-space, it is possible to identify the parameter conditions that make the amount of image light output by the projection substrate 100 uniform. Therefore, the projection substrate 100 can be easily created without performing complex optical design or complex optical simulation.

[0106] The projection substrate 100 according to the present embodiment has been described above as an example in which incident projection light is output as image light using one first substrate 101, but the present invention is not limited to this. The projection substrate 100 may have multiple substrates. Therefore, an example in which the projection substrate 100 has two substrates will be described next.

[0107] <Modification of Projection Board 100> Fig. 8 shows a modification of the projection board 100 according to the present embodiment. The projection board 100 of the modification has a first board 101 and a second board 301. The first board 101 has the same configuration as that described in Fig. 6, and therefore description thereof will be omitted here.

[0108] The second substrate 301 is disposed parallel to the first substrate 101 and has an area that overlaps with the first substrate 101 in a plan view. The second substrate 301 has a first surface 302 on which a second input diffraction grating 310, a second intermediate diffraction grating 320, a second output diffraction grating 330, and a second low refractive index material 340 are formed. Note that the second intermediate diffraction grating 320 is omitted from FIG. 8 .

[0109] The operation of each part of the second substrate 301 is substantially the same as the operation of each part of the first substrate 101. For example, projection light is incident on the second incident diffraction grating 310 from a second surface 303 opposite to the first surface 302 of the second substrate 301. The projection light for projecting image light is incident on the second incident diffraction grating 310, and the second incident diffraction grating 310 diffracts the incident projection light in a fourth direction.

[0110] The second intermediate diffraction grating 320 is disposed in the fourth direction from the second input diffraction grating 310 and diffracts the projection light incident from the second input diffraction grating 310 in a fifth direction. The second output diffraction grating 330 is disposed in the fifth direction from the second intermediate diffraction grating 320 and diffracts the projection light incident from the second intermediate diffraction grating 320 toward a display surface disposed in the third direction. The second output diffraction grating 330 emits image light from a second surface 303 opposite to the first surface 302 of the second substrate 301 toward the display surface of the first substrate 101.

[0111] The direction from the second exit diffraction grating 330 to the display surface is the third direction described above. The fourth and fifth directions are directions parallel to the surface of the second substrate 301. The fourth direction may be the same as the first direction. The fifth direction may be the same as the second direction. The arrangement of each part of the second substrate 301 may be the same as the arrangement of each part of the first substrate 101. In FIG. 5, the symbols of each part of the second substrate 301 are indicated in parentheses around each part of the first substrate 101.

[0112] The second low refractive index material 340 is formed on at least one surface of the second substrate 301 and covers the second input diffraction grating 310, the second intermediate diffraction grating 320, and the second output diffraction grating 330. The second low refractive index material 340 is filled in the grooves of the second input diffraction grating 310, the second intermediate diffraction grating 320, and the second output diffraction grating 330. The second low refractive index material 340 has a smaller refractive index than the second substrate 301, the second input diffraction grating 310, the second intermediate diffraction grating 320, and the second output diffraction grating 330. The second low refractive index material 340 includes, for example, mesoporous silica with a porous structure. The second low refractive index material 340 may be the same material as the first low refractive index material 240.

[0113] The second substrate 301 described above, like the first substrate 101, includes the second low refractive index material 340, and is therefore resistant to breakage due to impact, to contamination with foreign matter such as water droplets, and to distortion. Furthermore, the second substrate 301 can reduce leakage light. Like the first substrate 101, the second substrate 301 can be designed simply.

[0114] For example, the refractive index of the second substrate 301 is set to ns2, and the refractive index of the second low refractive index material 340 is set to nt2. The light in the fourth direction traveling from the second incident diffraction grating 310 to the second intermediate diffraction grating 320 is represented by a fourth light vector (i ２１ｘ , i ２１ｙ ), the magnitude of the fourth light vector is V4. ２１ｘ , i ２１ｙ ), the fourth light vector (i ２１ｘ , i ２１ｙ The magnitude V4 of the vector Λ is expressed by the following equation: ２１ｘ is the pitch of the grooves of the second incident diffraction grating 310 in the X direction, Λ ２１ｙ is the pitch of the grooves of the second input diffraction grating 310 in the Y direction.

[0115] Similarly, the light in the fifth direction from the second intermediate diffraction grating 320 toward the second output diffraction grating 330 is represented by a fifth light vector (i ２２ｘ , i ２２ｙ ), the magnitude of the fifth light vector is V5. ２２ｘ , i ２２ｙ ), the fifth light vector (i ２２ｘ , i ２２ｙ The magnitude V5 of the voltage V is given by the following equation:

[0116] In this second substrate 301, in order for the projection light to be diffracted by the diffraction grating and image light to be output from the display surface, it is understood that at least the following equation must be satisfied. In other words, the projection substrate 100 is configured such that the pitch of the diffraction grating of the second substrate 301, the refractive index nt2 of the second low refractive index material 340, and the refractive index ns2 of the second substrate 301 satisfy the following equations: nt2<V4<ns2 and nt2<V5<ns2 (Equation 11)

[0117] Furthermore, the light in the third direction going out from the second exit diffraction grating 330 through the display surface is converted into a sixth light vector (i ２３ｘ , i ２３ｙ ) is expressed as the sixth light vector (i ２３ｘ , i ２３ｙ ) is expressed by the following formula: where Λ ２３ｘ is the pitch of the grooves of the second exit diffraction grating 330 in the X direction, Λ ２３ｙ is the pitch of the grooves of the second exit diffraction grating 330 in the Y direction.

[0118] In the k-space, the sixth light vector (i ２３ｘ , i ２３ｙ The end point of the incident light (i ｘ , i ｙ ) is preferably equal to the end point of the projection board 100. This allows the projection board 100 to output image light with reduced image distortion from the display surface while making the amount of light uniform across the entire screen.

[0119] The second substrate 301 guides projection light having a wavelength different from that of the projection light guided by the first substrate 101. For example, light in a first wavelength band is incident on the second substrate 301 as projection light, and light in a second wavelength band different from the first wavelength band is incident on the first substrate 101 as projection light. As an example, the first wavelength band has a wavelength band including red and a wavelength band including a portion of green. In this case, the second wavelength band has a wavelength band including blue and a wavelength band including the remaining portion of green.

[0120] When the second substrate 301 outputs projection light of the first wavelength band to the display surface as image light, and the first substrate 101 outputs projection light of the second wavelength band to the display surface as image light, the projection substrate 100 can output color image light that is a combination of red, green, and blue light from the display surface.

[0121] Here, the first substrate 101 only needs to guide the light of the second wavelength band, and does not need to guide the light of the first wavelength band to the display surface. In other words, in the first substrate 101, the light of the second wavelength band among the projection light satisfies equation (7), but the light of the first wavelength band does not have to satisfy equation (7). In this case, at least one of V1 and V2 of the light of the first wavelength band will satisfy the following equation: (Equation 13) 1<V1≦nt1 or ns1<V1 1<V2≦nt1 or ns1<V2

[0122] Similarly, the second substrate 301 only needs to guide the light of the first wavelength band, and does not need to guide the light of the second wavelength band to the display surface. In other words, in the second substrate 301, the light of the first wavelength band among the projection light satisfies equation (11), and the light of the second wavelength band does not have to satisfy equation (11). In this case, at least one of V4 and V5 of the light of the second wavelength band will satisfy the following equations: (Equation 14) 1<V4≦nt1 or ns1<V4 1<V5≦nt1 or ns1<V5

[0123] As described above, the first substrate 101 and the second substrate 301 only need to be designed so that the part of the projection light that is output as image light satisfies equations (7) and (11). This improves the degree of freedom in designing the first substrate 101 and the second substrate 301, and makes it possible to more easily form the projection substrate 100. A method for designing such a projection substrate 100 will now be described.

[0124] <Example of Design Flow of Projection Substrate 100> Fig. 9 shows an example of a design flow of the projection substrate 100 according to this embodiment. The design flow shown in Fig. 9 is an example of a design flow for designing the projection substrate 100 having the first substrate 101 described in Fig. 6. The design flow is an example of an operation flow of a program executed by a computer.

[0125] First, information on the refractive index ns1 of the first substrate 101 and the refractive index nt1 of the first low-refractive index material 240 is acquired (S11). For example, data on the refractive index ns1 corresponding to the substrate material used for the first substrate 101 and the refractive index nt1 corresponding to the material used for the first low-refractive index material 240 is acquired from data stored in a storage unit, an external database, or the like. Alternatively, data input from an input device or the like may be acquired.

[0126] Next, information on the diffraction grating to be formed on the first substrate 101 is obtained (S12). The diffraction grating information includes the pitch Λ of the grooves of the first incident diffraction grating 210 in the X direction. １１ｘ , pitch Λ in the Y direction １１ｙ The diffraction grating information also includes information on the pitch Λ of the grooves of the first intermediate diffraction grating 220 in the X direction. １２ｘ , pitch Λ in the Y direction １２ｙ The diffraction grating information is acquired in the same manner as the refractive index information, for example. The diffraction grating information may be acquired from the design data of the first substrate 101.

[0127] Next, the direction cosines i of the projection light in the X and Y directions that are orthogonal to each other on a plane parallel to the first substrate 101 are calculated. ｘ , i ｙ For example, the direction cosine i is calculated using the input direction and the input intensity of the projection light incident on the first incident diffraction grating 210. ｘ , i ｙ Calculate.

[0128] Next, the first light vector (i １１ｘ , i １１ｙ ) is calculated using equation (4) (S14). １２ｘ , i １２ｙ The magnitude V2 of the calculated first light vector (i １１ｘ , i １１ｙ ) and the magnitude V1 of the second light vector (i １２ｘ , i １２ｙ It is confirmed that the magnitude V2 of the vector θ satisfies the formula (7) (S16).

[0129] If V1 and / or V2 do not satisfy the formula (7) (S16: No), the design parameters are changed (S17). The design parameters are the refractive index ns1 of the first substrate 101, the refractive index nt1 of the first low refractive index material 240, and the pitch Λ of the grooves of the first incident diffraction grating 210. １１ｘ and pitch Λ １１ｙ , the pitch Λ of the grooves of the first intermediate diffraction grating 220 １２ｘ and pitch Λ １２ｙ In S17, for example, a predetermined parameter among the design parameters is changed by a predetermined value. Also, a parameter input from an input device or the like may be changed by the input value.

[0130] The operations from S14 to S17 may be repeated until V1 and V2 satisfy the formula (7). If V1 and V2 satisfy the formula (7) (S16: Yes), then the third light vector (i １３ｘ , i １３ｙ ) end point of the incident light (i ｘ , i ｙ ) the pitch Λ of the grooves of the first exit diffraction grating 230 in the X direction. １３ｘ , pitch Λ in the Y direction １３ｙ (S18) According to the above operation flow, it is possible to easily design a projection substrate 100 that can output uniform image light.

[0131] In the above description of the projection substrate 100 according to the present embodiment, the projection substrate 100 has a first substrate 101, and the projection substrate 100 has a first substrate 101 and a second substrate 301, but the present invention is not limited to this. The projection substrate 100 may have three or more substrates.

[0132] 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.

[0133] REFERENCE SIGNS LIST 10 Eyeglass-type terminal 20 Input light beam 30 Output light beam bundle 100 Projection substrate 101 First substrate 102 First surface 103 Second surface 110 Frame 120 Projection unit 210 First input diffraction grating 212 First groove portion 220 First intermediate diffraction grating 222 Second groove portion 224 First division region 230 First output diffraction grating 232 Third groove portion 234 Second division region 240 First low refractive index material 301 Second substrate 302 First surface 303 Second surface 310 Second input diffraction grating 320 Second intermediate diffraction grating 330 Second output diffraction grating 340 Second low refractive index material

Claims

1. A projection substrate for projecting image light onto a display surface, comprising: a first substrate; a first incident diffraction grating provided on the first substrate, onto which projection light for projecting the image light is incident and which diffracts the incident projection light in a first direction; a first intermediate diffraction grating provided in the first direction from the first incident diffraction grating and which diffracts the projection light incident from the first incident diffraction grating in a second direction; a first exit diffraction grating provided in the second direction from the first intermediate diffraction grating and which diffracts the projection light incident from the first intermediate diffraction grating in a third direction toward the outside via the display surface; and a first low refractive index material formed on at least one surface of the first substrate, which covers the first incident diffraction grating, the first intermediate diffraction grating, and the first exit diffraction grating and has a refractive index smaller than that of the first substrate, wherein the refractive index of the first substrate is defined as ns1 and the refractive index of the first low refractive index material is defined as nt1, When the light in the first direction from the first input diffraction grating to the first intermediate diffraction grating is expressed as a first light vector which is a normalized wave vector in k-space, the magnitude of the first light vector is V1, and when the light in the second direction from the first intermediate diffraction grating to the first output diffraction grating is expressed as a second light vector which is a normalized wave vector in k-space, the magnitude of the second light vector is V2, the magnitude V1 of the first light vector and the magnitude V2 of the second light vector satisfy the following equations: nt1<V1<ns1 and nt1<V2<ns1 (1). Projection substrate.

2. The wavelength in vacuum of the projection light incident on the first incident diffraction grating is λ ０ , the direction cosines of the projection light in the X direction and the Y direction orthogonal to each other in a plane parallel to the first substrate are respectively i ｘ , i ｙ The period (pitch) of the grooves of the first incident diffraction grating in the X direction is defined as Λ １１ｘ , the pitch in the Y direction is Λ １１ｙ The pitch of the grooves of the first intermediate diffraction grating in the X direction is Λ １２ｘ , the pitch in the Y direction is Λ １２ｙ When the first light vector (i １１ｘ , i １１ｙ ) is expressed by the following formula: The second light vector (i １２ｘ , i １２ｙ ) is expressed by the following formula: The projection substrate according to claim 1 .

3. The projection substrate according to claim 2, wherein the first low refractive index material, the first incident diffraction grating, the first intermediate diffraction grating, and the first exit diffraction grating are configured so that the magnitude V1 of the first light vector expressed by equation (2) and the magnitude V2 of the second light vector expressed by equation (3) of the light that is incident on the first incident diffraction grating and exits as the image light from a predetermined range on the display surface satisfy equation (1).

4. The projection board according to claim 3, wherein the predetermined range of the display surface is a range from which the image light enters the field of view of a user of the projection board.

5. The projection board according to claim 3, wherein the first low refractive index material, the first input diffraction grating, the first intermediate diffraction grating, and the first output diffraction grating are configured so that the magnitude V1 of the first light vector and the magnitude V2 of the second light vector of light within a predetermined wavelength range, among the light emitted as the image light from a predetermined range on the display surface, satisfy equation (1).

6. When the light in the third direction output from the first exit diffraction grating to the outside through the display surface is expressed as a third light vector which is a normalized wave vector in k-space, the end point of the third light vector is the incident light (i ｘ , i ｙ 3. The projection substrate according to claim 2, wherein the end point of the projection substrate is equal to the end point of the projection substrate.

7. A second substrate disposed parallel to the first substrate and having an area overlapping with the first substrate in a plan view; a second incident diffraction grating provided on the second substrate, onto which the projection light for projecting the image light is incident and which diffracts the incident projection light in a fourth direction; a second intermediate diffraction grating provided in the fourth direction from the second incident diffraction grating and which diffracts the projection light incident from the second incident diffraction grating in a fifth direction; a second exit diffraction grating provided in the fifth direction from the second intermediate diffraction grating and which diffracts the projection light incident from the second intermediate diffraction grating onto the display surface provided in a third direction; and a second low refractive index material formed on at least one surface of the second substrate, which covers the second incident diffraction grating, the second intermediate diffraction grating, and the second exit diffraction grating, and which has a refractive index smaller than that of the second substrate, wherein the refractive index of the second substrate is ns2 and the refractive index of the second low refractive index material is nt2, 2. The projection board according to claim 1, wherein when the light in the fourth direction from the second input diffraction grating to the second intermediate diffraction grating is expressed as a fourth light vector which is a normalized wave vector in k-space, the magnitude of the fourth light vector is V4, and when the light in the fifth direction from the second intermediate diffraction grating to the second output diffraction grating is expressed as a fifth light vector which is a normalized wave vector in k-space, the magnitude of the fifth light vector is V5, the magnitude V4 of the fourth light vector and the magnitude V5 of the fifth light vector satisfy the following equations: nt2<V4<ns2 and nt2<V5<ns2 (4).

8. The projection substrate according to claim 7, wherein, on the first substrate, light in a first wavelength band of the projection light does not satisfy formula (1), and, on the second substrate, light in the first wavelength band of the projection light satisfies formula (4).

9. The projection substrate according to claim 8, wherein, on the first substrate, light in a second wavelength band different from the first wavelength band among the projection light satisfies formula (1), and, on the second substrate, light in the second wavelength band among the projection light does not satisfy formula (4).

10. A glasses-type terminal worn by a user, comprising: a projection substrate according to any one of claims 1 to 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 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 first incident diffraction grating of the projection substrate to project the image light onto the display surface.

11. A computer-implemented method for designing the projection substrate according to any one of claims 1 to 9, comprising: a step of acquiring information on the refractive index ns1 of the first substrate and the refractive index nt1 of the first low refractive index material; a step of acquiring information on a diffraction grating to be formed on the first substrate; and a step of calculating direction cosines i of the projection light in the X and Y directions orthogonal to each other in a plane parallel to the first substrate. ｘ , i ｙ a step of calculating a magnitude V1 of the first light vector as follows: Calculating a magnitude V2 of the second light vector as follows: and a step of confirming that the calculated magnitude V1 of the first light vector and the magnitude V2 of the second light vector satisfy equation (1).

12. A program which, when executed by a computer, causes the computer to carry out the design method according to claim 11.

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