Light guide plate and manufacturing method thereof, light guide plate module and image display device

Abstract

The present invention realizes the plasticization of a light guide plate and realizes a safe and lightweight light guide plate. The light guide plate comprises a substrate, an incident diffraction grating for diffracting incident light, and an emission diffraction grating for emitting light diffracted by the incident diffraction grating from the substrate. The emission diffraction grating is formed by a concave-convex pattern formed on the substrate surface, the concave-convex pattern being composed of a first parallel straight line group and a second parallel straight line group intersecting the first parallel straight line group, and the spacing between the first parallel straight line group and the spacing between the second parallel straight line group are equal. Furthermore, the characteristic is that, as the relationship between the spacing P between the first parallel straight line group and the second parallel straight line group and the width W of the concave-convex pattern, W / P is greater than 0.15 and less than 0.85.

Description

Technical Field

[0001] The present invention relates to a technology that combines a light guide plate and a diffraction element to be small, lightweight, and capable of performing image display such as augmented reality. Background Art

[0002] In an augmented reality image display device, the user can not only see the projected image, but also see the surroundings at the same time. The projected image can overlap with the real world known to the user. As uses other than these displays, video games and wearable devices such as glasses can be cited. By wearing a translucent light guide plate and a projector (light source) integrated into a pair of glasses or goggles, the user can visually confirm the image supplied from the projector overlapping with the real world.

[0003] One of such image display devices is described in "Patent Document 1" to "Patent Document 3". In these patent documents, the light guide plate is composed of a plurality of concave-convex diffraction gratings formed on a glass substrate. The light emitted from the projector is transmitted inside the light guide plate while being totally reflected by the incident diffraction grating in combination with the light guide plate. The light is further converted into a plurality of replicated light rays by another diffraction grating, and is totally reflected and propagated inside the light guide plate, and finally emitted from the light guide plate. A portion of the emitted light is formed on the retina through the user's pupil and is recognized as an augmented reality image that overlaps with the image of the real world.

[0004] In such a light guide plate using a concave-convex diffraction grating, the wave vector K of the light emitted from the projector is refracted in the light guide plate, and according to Snell's law, the wave vector is K0. Moreover, it is converted into a wave vector K1 that can be totally reflected and propagated inside the light guide plate by the diffraction grating used for incidence. Through another one or more diffraction gratings provided on the light guide plate, it is diffracted, and the wave vector changes in the manner of K2, K3, etc. every time the diffraction is repeated. If the wave vector of the light finally emitted from the light guide plate is set to K', then |K'|=|K|, and when the projector is located on the opposite side of the eye across the light guide plate, K'=K. On the other hand, when the projector is located on the opposite side of the eye across the light guide plate, with respect to the wave vector, the light guide plate has the same function as a reflector. If the normal vector of the light guide plate is taken along the z direction and the x, y, and z components of the wave vector are compared, it can be expressed as Kx'=Kx, Ky'=Ky, and Kz'=-Kz.

[0005] The function of the light guide plate is to copy the light emitted from the projector into multiple pieces and guide the light so that the multiple light rays emitted are recognized by the user as image information equivalent to the original image. At this time, the copied light group has a wave vector equivalent to the light with image information emitted from the projector and has spatial expansion. A part of the copied light group enters the pupil and is visually confirmed by forming an image on the retina together with the external information, which can provide the user with augmented reality information with the external information added.

[0006] The size of the wave vector of light with image information varies depending on its wavelength. The concave-convex diffraction grating has a constant wave vector, and the diffracted wave vector K1 varies depending on the wavelength of the incident light, and propagates at different angles in the light guide plate. The refractive index of the glass substrate that constitutes the light guide plate is approximately constant with respect to the wavelength, and the range of conditions for guiding light while total reflection varies depending on the wavelength of the incident light. Therefore, in order for users to recognize wide-angle images, it is necessary to overlap multiple different light guide plates for each wavelength. Generally speaking, the number of light guide plates is considered to be about two to four, corresponding to the number of R, G, and B, or set to ±1.

[0007] The image display device described in "Patent Document 1" is an image display device for amplifying input light in two dimensions, and is provided with three linear diffraction gratings. One is a diffraction grating for incidence, and the other two diffraction gratings for emission are typically arranged overlapping each other on the surface and back of a light guide plate, realizing the functions of a diffraction grating for replication and emission. In addition, the following example is described in "Patent Document 1": a diffraction grating for emission is formed on one side by a cylindrical photonic crystal-type periodic structure.

[0008] The image display device described in "Patent Document 2" is a technology that is composed of a plurality of linear side surfaces in order to solve the problem that the image projected by the photonic crystal in "Patent Document 1" has high brightness in the central portion of the field of view.

[0009] In the image display devices described in "Patent Document 3" and "Patent Document 4", three diffraction gratings serving as an incident diffraction grating, a deflection diffraction grating, and an emission diffraction grating are arranged in a light guide plate without overlapping regions. In "Patent Document 3", a suspended triangular diffraction grating is disclosed in order to improve the diffraction efficiency of the incident diffraction grating.

[0010] "Patent Document 5" and "Patent Document 6" disclose technologies that use two reflective volume holograms for incident and emitting as diffraction gratings formed on a light guide plate. Among them, the volume hologram forms diffraction gratings corresponding to multiple wavelengths in space multiple times, and diffracts light of multiple wavelengths at the same angle, unlike the concave-convex diffraction grating above. Therefore, users can recognize RGB images through a single light guide plate. On the other hand, in the above concave-convex diffraction grating, a wide viewing angle can be achieved by replicating the light in a two-dimensional direction within the light guide plate. In contrast, they only provide a one-dimensional replication function, so there is a relatively narrow viewing angle.

[0011] Prior art literature

[0012] Patent Literature

[0013] Patent Document 1: Japanese Patent Application No. 2017-528739

[0014] Patent Document 2: WO 2018 / 178626

[0015] Patent Document 3: US2016 / 0231566A1

[0016] Patent Document 4: U.S. Patent Application No. 6580529

[0017] Patent Document 5: Japanese Patent Application Publication No. 2007-94175

[0018] Patent Document 6: Japanese Patent Application Publication No. 2013-200467 Summary of the invention

[0019] Problems to be solved by the invention

[0020] In the light guide plates (image display elements) described in "Patent Documents 1" to "Patent Documents 4" and image display devices using the same, which are advantageous for achieving a wide viewing angle, by making the light guide plates plastic, a new light guide plate can be provided that achieves improved safety against scattering and reduced weight compared to the existing glass-made ones. In this specification, "plastic" refers to a material composed of a polymer compound, and is a concept that does not include glass but includes resins, polycarbonates, acrylate resins, photocurable resins, and the like.

[0021] In the following, in the present invention, the light guide plate is limited to a light guide plate having a concave-convex diffraction grating and is described. In addition, for ease of understanding, the image inversion caused by the lens action of the eye and the effect of reversing the image projected to the retina in the brain and recognizing it are omitted, and the relationship between the pixel position and the brightness of the projected image projected from the image light source arranged on the same side as the eye with respect to the light guide plate to the screen in front is discussed. The image actually recognized visually is reversed upside down.

[0022] In "Patent Document 1", regarding the substrate material of the light guide plate, Fig.15A , Fig. 15B As shown, a technique is disclosed in which a glass material provided on the surface of a glass plate is used for a grating. As for a diffraction grating, a technique is disclosed in which a waveguide (=glass plate) surface is formed by etching.

[0023] In "Patent Document 1" Figure 3 A perspective view of the light guide plate is shown. In addition, Patent Document 1 discloses a technique for forming two emission grids on one surface using photonic crystals. Fig.16 The configuration of the cylinders of the photonic crystal formed in "Patent Document 1" is shown. The configuration period of the cylinders of the photonic crystal needs to be less than the wavelength in order to form a photonic band gap. The refractive index of the cylindrical structure of Patent Document 1 is higher than that of the substrate. However, as described later, when a cylindrical photonic crystal is formed on the surface of a light guide plate by injection molding or the like, the refractive index of the cylinder is equal to that of the waveguide (or substrate). In this case, if the ratio of the diameter to the height of the cylinder, that is, the aspect ratio, is not greater than about 2, the brightness of the projected image is insufficient.

[0024] The photonic crystal with improved high brightness in the central part of the projected image described in "Patent Document 2" is composed of multiple linear side faces in order to solve the problem that the image projected by the photonic crystal that is not cylindrical but linear is high brightness in the central part of the field of view. Figure 4 of "Patent Document 2" shows the shape of the photonic crystal. In "Patent Document 2", as described in the 34th line of page 1 and the 8th line of page 2, the striped high brightness part in the central part is improved. In "Patent Document 2", the striped high brightness part in the central part that becomes the subject is not clearly disclosed by figures, etc.

[0025] "Patent Document 3" Figure 5 The incident diffraction grating disclosed in C has an overhanging triangular cross section, and can efficiently couple the image light incident from the upper direction (air side) in the figure to the interior of the light guide plate with the hatching.

[0026] The light with image information is coupled with the incident diffraction grating provided in the light guide plate in a manner having a wave number capable of total reflection light guiding in the light guide plate, and propagates in the light guide plate. A portion of the light that crosses the outgoing diffraction grating is diffracted, and is emitted from the light guide plate with a wave number equivalent to that of the original image light. The image information provided to the user has the travel angle information corresponding to the pixel position of the original image information, that is, the wave number. In order for the image information of one pixel to be emitted from the light guide plate and reach the pupil of the user, it is necessary to emit from a specific position in the light guide plate determined by the travel angle, the distance between the light guide plate and the pupil of the user, and the size of the pupil of the user. As described above, in the light guide plate, the light is copied and emitted by expanding in space, so the greater the expansion in space, the less light is visually recognized by the user, and the smaller the brightness visually recognized becomes. On the other hand, the emission position visually recognized by the user changes according to the pixel position of the original image information, so in an image display device using a light guide plate, the brightness inevitably changes according to the pixel position.

[0027] In the prior art, methods suitable for making light guide plates include direct etching of glass substrates, or nanoimprinting methods suitable for forming patterns with high aspect ratios. In the photonic crystals of "Patent Document 2" and "Patent Document 3" based thereon, the ratio of a representative length such as the diameter of the bottom surface to its height, i.e., the aspect ratio, needs to be about 2 or more.

[0028] The aspect ratio of the surface concavo-convex pattern formed by injection molding technology, which has been a practical method for manufacturing optical disc media, does not exceed 1. Therefore, when the aspect ratio is greater than 2, the accuracy of pattern transfer decreases and it is difficult to apply. This is a problem caused by the limitation of the essential manufacturing method that the molten polycarbonate resin, acrylic resin, polyolefin resin, etc. has high viscosity and the resin cannot enter the high aspect ratio concavo-convex formed with nano-periods with high accuracy.

[0029] Furthermore, when using a suspended diffraction grating as described in "Patent Document 3", the master mold (stamp) and the light guide plate cannot be separated in injection molding technology, so it cannot be applied.

[0030] Therefore, an object of the present invention is to realize a light guide plate made of plastic and to realize a safe and lightweight light guide plate.

[0031] Solutions to Solve Problems

[0032] A preferred embodiment of the present invention is a light guide plate, which includes: a substrate; an incident diffraction grating that diffracts incident light; and an emission diffraction grating that emits the light diffracted by the incident diffraction grating from the substrate. The emission diffraction grating is formed by a concave-convex pattern formed on the substrate surface, the concave-convex pattern is composed of a first parallel straight line group and a second parallel straight line group intersecting the first parallel straight line group, and the spacing between the first parallel straight line group and the spacing between the second parallel straight line group are equal. Moreover, it is characterized in that, as a relationship between the spacing P between the first parallel straight line group and the second parallel straight line group and the width W of the concave-convex pattern, W / P is greater than 0.15 and less than 0.85.

[0033] Another preferred embodiment of the present invention is a light guide plate module formed by stacking a plurality of the above-mentioned light guide plates.

[0034] Another preferred embodiment of the present invention is an image display device including the above-mentioned light guide plate module and a projector for irradiating image light onto the light guide plate module, wherein the image light is incident on an incident diffraction grating.

[0035] Another preferred embodiment of the present invention is a method for manufacturing the light guide plate, comprising: a step of preparing a substrate formed of a material composed of a polymer compound; and a step of forming an incident diffraction grating and an output diffraction grating on the substrate using a mold.

[0036] Another preferred embodiment of the present invention is a light guide plate, comprising: a substrate; an incident diffraction grating that diffracts incident light; and an emission diffraction grating that emits light. The emission diffraction grating is formed by a linear concave-convex pattern formed on the substrate surface, so that light propagating from the incident diffraction grating in the substrate is diffracted in a direction perpendicular to the linear concave-convex pattern at a diffraction efficiency of η1, and in a direction perpendicular to the substrate at a diffraction efficiency of η2. 11 Diffraction, and the diffraction efficiency is related to η 11 <η1.

[0037] Effects of the Invention

[0038] According to the present invention, a light guide plate can be made of plastic, thereby realizing a safe and lightweight light guide plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a conceptual diagram showing an example of a phase function of an output diffraction grating.

[0040] Figure 2 It is a schematic diagram of a mesh diffraction grating.

[0041] Figure 3 This is a conceptual diagram showing the definition of a projection circle.

[0042] Figure 4AIt is an image showing the intensity distribution of light propagating inside the light guide toward the center of the image.

[0043] Figure 4B This is an image showing the intensity distribution of light traveling inside the light guide plate toward the end of the image.

[0044] Figure 5 1 is a schematic plan view of a light guide plate according to an embodiment.

[0045] Figure 6 1 is a schematic side view of a light guide plate according to an embodiment.

[0046] Fig. 7A It is an explanatory diagram showing a projection image of a photonic crystal diffraction grating.

[0047] Figure 7B It is an explanatory diagram showing a projection image of a mesh-type diffraction grating.

[0048] Figure 8 This is a graph showing a projection image when the pattern width is changed in a mesh-type output diffraction grating.

[0049] Fig. 9 It is a graph showing the relationship between the brightness unevenness index and the aspect ratio of the pattern.

[0050] Fig. 10A This is an image diagram showing the diffracted light incident on a transmission-type diffraction grating.

[0051] Fig. 10B This is an image diagram showing the diffracted light incident on a reflective diffraction grating.

[0052] Fig.11A It is a graph showing the relationship between pattern width and diffraction efficiency.

[0053] Fig. 11B It is a graph showing the relationship between pattern width and aspect ratio.

[0054] Fig. 11C This is a conceptual diagram showing the definition of the duty ratio.

[0055] Fig.12 The figure is a side view of an embodiment of a light guide plate for improving uneven brightness.

[0056] Fig.13A This is a schematic diagram of an example in which a projector and a pupil are arranged on the same side of a light guide plate.

[0057] Fig. 13B This is a schematic diagram of an example in which a projector and a pupil are arranged on opposite sides of a light guide plate.

[0058] Fig.14AThis is a schematic diagram for explaining a projection image when the light guide plate of the embodiment is not deformed.

[0059] Fig. 14B This is a schematic diagram showing the influence on the projection image when the light guide plate of the embodiment is deformed.

[0060] Fig.15A 1 is a side view of an embodiment of a light guide plate that suppresses deformation.

[0061] Fig. 15B 1 is a top view of an embodiment of a light guide plate that suppresses deformation.

[0062] Fig. 15C FIG. 1 is a side view of an embodiment of a light guide plate module that suppresses deformation.

[0063] Fig.16 It is a schematic diagram showing the structure of the image display device of the embodiment. DETAILED DESCRIPTION

[0064] Hereinafter, the embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the description of the embodiments described below. It is easy for those skilled in the art to understand that the specific structure can be changed within the scope of the idea or purpose of the present invention.

[0065] In the configuration of the invention described below, the same parts or parts having the same functions are denoted by the same reference numerals in different drawings, and overlapping descriptions may be omitted.

[0066] When there are a plurality of elements that are the same or have the same function, different subscripts may be assigned to the same reference numerals for description. However, when there is no need to distinguish between a plurality of elements, the subscripts may be omitted for description.

[0067] The expressions "first", "second", "third", etc. in this specification are used to identify the components and do not necessarily limit the number, order or content. In addition, the numbers used to identify the components are used in each context, and the use of numbers in one context does not necessarily indicate the same structure in other contexts. In addition, it does not prevent a component identified by a certain number from having the function of a component identified by another number.

[0068] In order to facilitate understanding of the invention, the position, size, shape, range, etc. of each structure shown in the drawings and the like may not represent the actual position, size, shape, range, etc. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings and the like.

[0069] The publications, patents and patent applications cited in this specification constitute part of the description of this specification as they are.

[0070] Unless clearly stated otherwise in the context, a constituent element expressed in the singular form in the present specification includes a plural form.

[0071] In the embodiment described below, a two-dimensional mesh pattern is provided as the output diffraction grating. Thus, by setting the aspect ratio of the concavo-convex pattern transferred to the surface of the light guide plate to 1 or less, a light guide plate using a plastic molding technology with practical results such as injection molding can be provided.

[0072] Photonic crystals or diffraction gratings spatially affect phase modulation with respect to incident light through surface irregularities. The magnitude of phase modulation increases in proportion to the difference in refractive index between the surface structure and air and the height of the surface irregularities.

[0073] Figure 1 The wave number of the emitted diffraction grating is schematically shown. The phase functions of the diffraction gratings with wave numbers K1 and K2 having an azimuth angle of ±60 degrees relative to the Y axis are represented by (a) and (b), respectively, and each has a sinusoidal phase distribution. The phase modulation amount is standardized to 1. If they are synthesized, (c) is obtained. It can be said that the photonic crystal is formed on the surface of the light guide plate by approximating it to a pillar, etc., and made of a high refractive index material.

[0074] like Figure 1 As shown in (c), the maximum value of the phase modulation amount of K1+K2 is 2. If it is approximated by an isolated cylinder, etc., it is judged to be the same as Figure 1 (a) Figure 1 Compared to the single sinusoidal wave diffraction grating in (b), it requires twice the height (aspect ratio).

[0075] Figure 2 is a schematic diagram of the mesh-shaped outgoing diffraction grating of this embodiment. Figure 1 (c) Compared with the sine wave structure, it has high-order wave number components when Fourier transform is performed, but when used as a light guide plate, by appropriately selecting the period, it is possible to prevent the wave number components of the second order and above from being diffracted with respect to the incident light (the wave number is an imaginary number). Moreover, the mesh diffraction grating overlaps the rectangular diffraction gratings of ±60 degrees, and compared with the cylinder, it does not have wave number components other than the directions of the fundamental waves K1 and K2, so the diffraction efficiency can be improved.

[0076] The incident diffraction grating of this embodiment is a reflective diffraction grating rather than a transmissive diffraction grating as disclosed in "Patent Document 3", so that a low aspect ratio can be achieved by utilizing reflection which is larger than the deflection effect of refraction.

[0077] Thus, a two-dimensional emission diffraction grating with a reduced aspect ratio can be provided, which can be realized by plastic molding technology such as injection molding, and a safe and lightweight light guide plate can be provided. The present invention is intended to produce a light guide plate by applying plastic molding technology, so the aspect ratio is described in consideration of the transferability of the resin of the concave-convex pattern. When the period of the concave-convex pattern is set to p, the width of the convex portion is set to w, and the height is set to h, the transferability of the resin is determined by the transfer of the resin to the narrower width of the concave-convex portion. Therefore, the aspect ratio is defined by h / min(w, p-w). Here, min(w, p-w) means selecting the smaller of w and p-w. Refer to the following Fig. 11C .

[0078] In the following embodiments, the Z axis is set as the optical axis direction and the XY plane is set as the coordinate system of the surface of the light guide plate. In addition, if the user's pupil is approximated to a circle, the emission position in the light guide plate visually recognized by the user corresponding to the pixel position is also a circle. Hereinafter, it is referred to as an emission circle.

[0079] Figure 3 3 is a schematic diagram for explaining the emission circle. Here, the projector 300 as a light source for forming an image and the user's pupil 400 are arranged on opposite sides relative to the light guide plate 10. The wave vector of the incident diffraction grating 100 is set to the y direction, Figure 3 The arrows in represent light rays in the x-z plane. In the case where the incident diffraction grating 100 does not have a wave vector component in the x direction, the straight-propagating light ray 301 irradiated from the projector 300 moves in the direction to the right in the figure. On the other hand, in order for the user to recognize the light as a projected image, light rays of the same angle need to reach the user's pupil 400 through the path of the light ray 302 shown in the figure as being visually recognized. The emission circle 303 is an imaginary circle located on the emission diffraction grating 200 and moving parallel to the user's pupil 400 in the direction of the light ray being visually recognized. Only the light ray 302 emitted from the emission circle 303 on the emission diffraction grating 200 is recognized by the user as a projected image, and other light rays are not recognized.

[0080] Figure 4A and Figure 4B The intensity distribution of light propagating inside the light guide plate is calculated using a simulation method described later. In the figure, the incident diffraction grating is arranged on the upper side, and the pupil (Pupil) equivalent to the user's eye is arranged below it.

[0081] Figure 4AIt is the intensity distribution of light toward the center of the image, indicating the situation where the pixel position is the center of the projected image. The output circle in the figure indicates the area where the light reaching the pupil is finally diffracted on the output diffraction grating. The area with high brightness on the straight line from the incident diffraction grating toward the y direction indicates the main light group (hereinafter referred to as the principal light group) that is diffracted by the incident diffraction grating and propagates inside the light guide plate. As shown in the figure, it has the characteristic that the intensity gradually decays according to the propagation of the principal light group. The light group with low brightness that extends to the periphery of the principal light group is a light group that is diffracted by the output diffraction grating and deflected in the direction of travel in the x-y plane. Under this condition, the projected light is in the z-axis direction, so it is judged that the output circle and the pupil are consistent in the x-y plane. Therefore, the light that reaches the pupil and is recognized as an image is part of the principal light group with high intensity.

[0082] Figure 4B It is the intensity distribution of light toward the end of the image, and is the case of the pixel position in the upper right corner of the projected image. As shown in the figure, the main light group travels from the incident diffraction grating toward the lower right direction. The position of the pupil is constant, but the emission circle is the emission position of the light group traveling toward the upper right of the pupil, so it moves to the lower left relative to the pupil in the x-y plane. In this case, the emission circle is at a position separated from the main light group, so the brightness of the light group that reaches the pupil and is recognized as an image is lower than the above case. The above is the main reason for the uneven brightness when using a light guide plate to project an image.

[0083] Figure 5 The structure plan view and wave number of the light guide plate of the embodiment are schematically shown. The light guide plate 10 is provided with an incident diffraction grating 100 and an outgoing diffraction grating 200 having a single grating pitch.

[0084] If the grating pitch is set to P, the size of the wave vector of the diffraction grating is represented by K = 2π / P. If represented by a coordinate system with the optical axis direction as the z-axis, the wave vector of the incident diffraction grating 100 is K1 = (0, -K, 0). The outgoing diffraction grating 200 has two wave vectors with an angle of 120 degrees, which are K2 = (+K / √3, K / 2, 0) and K3 = (-K / √3, K / 2, 0). It can be seen that if the wave vector of the light incident on the light guide plate 10 is k i =(k i x , k i y , k i z ), let the wave vector of the emitted light be k o =(k o x , k o y , k oz ), so that K1, K2, and K3 act on k in sequence i , then k becomes as follows o =k i , emitting light with the same wave vector as the incident light, that is, light with the same image information.

[0085] k 0 =k i

[0086]

[0087] k 0 y =k i y + K - (K / 2) - (K / 2) = k i y

[0088] k 0 z =k i z

[0089] …(1)

[0090] Considering that the wave vector of the diffraction grating is added to the wave vector of the light by diffraction, when the light is emitted from the light guide plate after N-fold diffraction, the following relationship holds.

[0091] [Number 1]

[0092]

[0093] m i and K i is the diffraction order of the i-th intersection and the wave vector of the diffraction grating.

[0094] The left side of the above equation represents the change of wave vector caused by diffraction. When it is not zero, the light is totally reflected on the surface of the light guide plate, expands in space, and propagates. (Equation 1) and (Equation 2) represent the magnification function of the entrance pupil brought by the light guide plate.

[0095] The output diffraction grating 200 is composed of a two-dimensional concave-convex pattern formed on the surface of the substrate. The diffraction generated by the intersection of the light and the output diffraction grating is K2, K3 and K2+K3. The first and second diffraction K2 and K3 are primary diffraction caused by the usual diffraction grating. According to symmetry, the diffraction efficiency η1 is equal. According to (Formula 2), the image light is emitted from the light guide plate through two diffraction, and is accompanied by the movement of the emission point along the x direction. Therefore, the product of the diffraction efficiency η1×η1=(η1) 2 It is the parameter that mainly determines the brightness of the peripheral field of view.

[0096] On the other hand, the diffraction K2+K3 generated by the intersection of the emission diffraction gratings is a two-dimensional first-order diffraction, and the image light is emitted from the light guide plate through the first-order diffraction. Therefore, the diffraction efficiency η 11 It is a parameter that mainly determines the brightness of the center of the field of view. Here, the index of the brightness of the projection image and the index of the uneven brightness between the center and the periphery are defined as follows.

[0097] Brightness factor B=(η1) 2 ····(3)

[0098] Uneven brightness factor U=η 11 / (η1) 2 ····(4)

[0099] Next, the simulation method for analyzing the image display element used in the embodiment is briefly described. The ray tracing method advocated by GH Spencer et al. in 1962 [GH Spencer and MBTK Murty, "General Ray-Tracing Procedure", J. Opt. Soc. Am. 52, p. 672 (1962).] is a method that focuses on the particle nature of light and traces the path to calculate the image observed at a certain point, and has been continuously improved with the computer graphics field as the center [16-18]. The Monte Carlo ray tracing method based on the ray tracing method [I. Powell "Ray Tracing through sysytems containing holographic optical elements", Appl. Opt. 31, pp. 2259-2264 (1992).] is a method that prevents the exponential growth of the amount of calculation by randomly processing the separation of the path caused by diffraction or reflection, etc., and is suitable for the simulation of light guide plates that propagate through repeated diffraction and total reflection. In the Monte Carlo ray tracing method, reflection and refraction can be faithfully reproduced, but regarding diffraction, it is necessary to develop an appropriate model.

[0100] In the light guide plate for head-mounted displays, a diffraction model corresponding to the wavelength range (about 400-700nm) covering the entire visible light region and the incident angle range corresponding to the 40° viewing angle of the projection image is essential, and the amount of calculation on the market becomes huge. Here, considering that the light that is visually recognized is a part of the total light, the following algorithm is used: by pre-stopping the calculation of the light guided to the area that is not visually recognized, the amount of calculation is reduced to less than 1 / 1000. The angle and wavelength dependence of the diffraction efficiency based on the diffraction grating is based on the method of pre-tabulating the calculation results based on the FDTD (Finite Differential Time Domain) method for reference.

[0101] Example 1

[0102] Figure 6 1 is a side view showing the structure of the image display element of this embodiment. The light guide plate 10 in the figure is formed with an incident diffraction grating 100 and an outgoing diffraction grating 200. The incident diffraction grating 100 is composed of a linear grating along the x direction, and the period of the pattern is P. The outgoing diffraction grating 200 is a linear grating with a pattern period of P. The angle between each grating and the x axis is θo. As the outgoing diffraction grating 200, Figure 2 The diffraction grating of the mesh type with the linear gratings shown is crossed. θo is, for example, 60 degrees, but it can also be adjusted according to the size and size of the light guide plate. In the following embodiments, θo = 60 degrees is used for explanation. The period P of the pattern is, for example, 0.3 to 0.6 μm, but it can also be changed according to the wavelength of the light source and the purpose.

[0103] The projection images of the diffraction grating of the photonic crystal in Patent Document 1 and the mesh diffraction grating of this embodiment are compared when the aspect ratio is the same as 0.8. The simulation conditions are as follows: pattern pitch P = 420nm, pattern height = 80nm, wavelength of light = 550nm, thickness of light guide plate = 1.0mm, refractive index of light guide plate = 1.58. The viewing angle of the projection image is 40 degrees.

[0104] exist Figure 6 In the embodiment of FIG. 1 , from the viewpoint of achieving a low aspect ratio, a reflective diffraction grating is used as the incident diffraction grating 100. For process reasons, the outgoing diffraction grating 200 is formed on the same side of the light guide plate 10 as the incident diffraction grating 100.

[0105] Fig. 7A These are simulation results of an image diagram of a diffraction grating of a pillar-type photonic crystal described in "Patent Document 1" and its projection image. Figure 7BThe figure is a simulation result of the image diagram of the mesh diffraction grating of this embodiment and its projection image. The aspect ratio of the diffraction grating is always less than 1. Here, the height of the pillar is set to h, and the diameter of the pillar is set to d, and the aspect ratio of the pillar-type photonic crystal is defined by h / d.

[0106] As shown in the figure, it can be seen that when the aspect ratio is less than 1, Fig. 7A In the photonic crystal, the brightness of the central part of the projected image is high, and the visual confirmation is poor. In contrast, the mesh diffraction grating of this embodiment can obtain a good projected image by using a pattern with a low aspect ratio. The reason is that Fig. 7A In the photonic crystal, the diffraction efficiency η mainly determines the brightness of the projection image in the center of the field of view. 11 The product of the diffraction efficiency (η1) mainly determines the brightness of the surrounding projection image. 2 big.

[0107] Figure 8 The simulation calculation results of the projected image (Projected image) when the line width (Line width) of the mesh-type output diffraction grating of this embodiment is changed are shown. The line pitch (Line pitch) and the line height (Line height) of the pattern are the same. The image of the pattern (Pattern) is also published.

[0108] As shown in the figure, when the pattern width is 40 nm, η 11 / (η1) 2 When η is less than 1, the central part of the projected image is dark. On the other hand, when the pattern width is 200 nm, η 11 / (η1) 2 When the pattern width is 100 nm, η 11 / (η1) 2 When it is close to 1, the brightness distribution of the projected image is close to uniform.

[0109] Based on the above, it can be judged that in the mesh diffraction grating of this embodiment, by appropriately setting the pattern width, the brightness distribution of the projected image can be controlled. 11 / (η1) 2 )-1” is used as the brightness unevenness index. The smaller the value, the smaller the brightness unevenness, so it is more convenient intuitively.

[0110] Fig. 9 It is the brightness unevenness index brightness|η 11 / (η1) 2-1| and the aspect ratio of the pattern. The calculation conditions are set to be the same as above, and the pattern width is changed to change the aspect ratio. As shown in the figure, it can be judged that the mesh diffraction grating of this embodiment can minimize the brightness unevenness when the aspect ratio is less than 1, preferably the aspect ratio is greater than 0.25 and less than 1.0. Therefore, if the mesh diffraction grating of this embodiment is used as an emission diffraction grating, a lightweight and low-cost plastic light guide plate can be provided by injection molding or the like.

[0111] According to the above research, the output diffraction grating of this embodiment causes the image light beam that is totally reflected from the incident diffraction grating to be diffracted mainly in the direction perpendicular to the straight line pattern of the diffraction grating with a diffraction efficiency of η1, and causes a part of the image light beam to be directly directed to the user's pupil (in the direction substantially perpendicular to the light guide plate) with a diffraction efficiency of η1. 11 At this time, in order to reduce the uneven brightness of the user's field of view, it is desirable to reduce |η 11 / (η1) 2 -1|. That is, η 11 and (η1) 2 For example, let η 11 is (η1) 2 In addition, in order to make the center of the field of view not too bright, it is expected that η 11 <η1, further, it is more desirable that η 11 <<η1.

[0112] Next, the incident diffraction grating will be described.

[0113] Fig. 10A This is the simulation result of the same transmission-type diffraction grating as that of Patent Document 3. In the transmission-type diffraction grating, incident light is transmitted and diffracted and propagates inside the light guide plate (substrate). The incident diffraction grating is formed on the surface of the light guide plate close to the light source.

[0114] The image light 1000 is a structure that is incident from the left, and the right half of the figure represents the substrate (Sub). In a transmission-type diffraction grating, the maximum diffraction efficiency is obtained under the conditions of refraction caused by the blazing surface and diffraction phase tuning caused by the periodic structure. As shown in the figure, in order to achieve this goal, the height of the concave-convex pattern needs to be large, the angle of the pattern needs to be 70 degrees to 80 degrees, and the aspect ratio of the height of the pattern divided by the period is greater than 10. In general plastic molding methods such as injection molding, if the aspect ratio exceeds 1, problems such as deterioration of transferability will occur, and the yield rate during mass production will be reduced. It can be judged that the transmission-type diffraction grating shown here is not suitable as the incident diffraction grating of this embodiment.

[0115] Fig. 10BThis is the simulation result of a reflective diffraction grating. In a reflective diffraction grating, incident light is reflected and diffracted, that is, it is reflected toward the light source and propagates inside the light guide plate (substrate). The position of the incident diffraction grating is formed on the surface of the light guide plate away from the light source.

[0116] The image light is also incident from the left, and the left half of the figure represents the substrate (Sub). In the reflective diffraction grating, the maximum diffraction efficiency is obtained under the conditions of reflection caused by the blazing surface and diffraction phase tuning caused by the periodic structure. As shown in the figure, it can be judged that compared with the transmission type, the condition can be met by a concave-convex pattern with a low aspect ratio. At this time, the height of the concave-convex pattern is about 250nm, and the aspect ratio is about 0.57. In the above-mentioned prototype element, a triangular concave-convex pattern with a pattern height of 374nm can be well transferred. It can be said that the light guide plate of this embodiment preferably uses a reflective diffraction grating.

[0117] Fig.11A and Fig. 11B is the simulation result showing the relationship between the pattern duty cycle, diffraction efficiency and aspect ratio. Fig. 11C As shown in FIG. 1 , if the pitch of the diffraction grating pattern is set to p and the width of the pattern is set to w, the duty cycle is represented by w / p. Here, the settings are: pattern pitch P = 460nm, pattern height = 70nm, wavelength of light = 550nm, thickness of light guide plate = 1.0mm, refractive index of light guide plate = 1.58. The viewing angle of the projected image is 40 degrees.

[0118] Fig.11A The figure shows the relationship between the first diffraction efficiency η1 and w / p. As shown in the figure, it can be judged that the first diffraction efficiency η1 has the following characteristics: it reaches a maximum value of about 4.2% when w / p = 0.5, and decreases as w / p approaches 0 or 1. It can be said that in order to obtain a diffraction efficiency of about 0.6%, the w / p of the mesh diffraction grating of this embodiment needs to be in the range of 0.15 to 0.85. In addition, it can be said that when w / p is in the range of 0.3 to 0.7, the efficiency is high, and when w / p is in the range of 0.4 to 0.6, the efficiency is the highest.

[0119] Fig. 11B Indicates the aspect ratio of the pattern. It is fixed to pattern height = 70nm, so if w / p approaches 1 or 0, the aspect ratio increases. If the aspect ratio of the pattern is set to 1 or less as a benchmark for the application of injection molding, etc., it can be said that the w / p of the mesh diffraction grating of this embodiment needs to be in the range of 0.15 to 0.85. In addition, the smallest aspect ratio and the easiest to manufacture is w / p = 0.5.

[0120] In summary, it can be said that, in principle, when w / p=0.5, that is, w=pw, the diffraction efficiency of the diffraction grating is maximum and the aspect ratio of the pattern is minimum.

[0121] Fig.12 1 is a schematic diagram of the light guide plate of this embodiment that further reduces brightness unevenness. In the figure, 10 represents the light guide plate, 100 represents the incident diffraction grating, and 200 represents the emission diffraction grating. As shown in the figure, by changing the duty ratio of the concave-convex pattern of the emission diffraction grating according to the distance from the incident diffraction grating 100, the diffraction efficiency can be distributed. In this way, the brightness unevenness of the projected image can be further improved. As a specific example, Fig.11A As shown, the portion of the output diffraction grating 200 close to the incident diffraction grating 100 is set to a duty ratio of about 0.2 with low diffraction efficiency. On the other hand, the portion of the output diffraction grating 200 far from the incident diffraction grating 100 is set to a duty ratio of about 0.5 with high diffraction efficiency.

[0122] As described above, if the mesh diffraction grating of this embodiment is used, a light guide plate can be provided by a plastic molding technique such as injection molding.

[0123] Example 2

[0124] On the other hand, the mechanical strength (Young's modulus) of the plastic light guide plate is lower than that of the conventional glass light guide plate, and therefore deformation due to ambient temperature or air pressure is increased. The solution of this embodiment to this problem is shown below.

[0125] Fig.13A and Fig. 13B is a schematic diagram showing the effect of the relative tilt of two light guide plates. Fig.13A and Fig. 13B In FIG. 1 , the light guide plate 10 is composed of light guide plates 11 and 12 corresponding to different wavelengths. Reference numeral 300 denotes a projector for image projection, 400 denotes a user's pupil, and 500 denotes projected image light.

[0126] In this example, based on Fig. 10B According to the view of the invention, the incident diffraction grating adopts a reflective diffraction grating. Therefore, the incident diffraction grating 100 is formed on the surface of the light guide plate 10 far from the projector 300 (the right surface in the figure). As for the output diffraction grating 200, for the convenience of the process, since it can improve the accuracy by forming it on the same surface as the incident diffraction grating 100, it is also formed on the surface far from the projector 300.

[0127] Fig.13AThis is a case where the projector 300 and the user's pupil 400 are arranged on the same side relative to the light guide plate 10. As shown in the figure, the light guide plate 10 finally reflects the image light 500 so that it reaches the user. Therefore, if the light guide plate 12 is tilted compared to the light guide plate 11, the position of the pixel visually recognized will move according to the wavelength of the projected light, and the image quality will be reduced. The resolution of the light angle of a user with a visual acuity of 1.0 is 1 / 60 degrees, so if this is used as a reference, the relative tilt of the two light guide plates needs to be sufficiently smaller than 1 / 60 degrees, and it is difficult to install it as a head-mounted display, especially in a plastic light guide plate.

[0128] Fig. 13B This is a case where the projector 300 and the user's pupil 400 are arranged on opposite sides relative to the light guide plate 10. As shown in the figure, the light guide plate 10 finally transmits the image light 500 to reach the user. Since the angles of the incident light and the emitted light are basically the same, even if there is a relative tilt between the light guide plates 11 and 12, in principle, there will be no movement of the projected image due to the wavelength. Therefore, when the plastic light guide plate of this embodiment is installed on a head-mounted display, it is expected that the projector light source is on the opposite side of the user relative to the light guide plate (transmission type). In fact, the angle conditions of the light beam for total reflection light guidance inside the light guide plate are affected, so it is noted that the relative tilt of the light guide plates 11 and 12 is expected to be suppressed to less than about 3 degrees.

[0129] Compared with 13A, Fig. 13B The relationship between the position of the projector and the user's eyes is reversed with respect to the light guide plate. This influence can be addressed by inverting the projected image.

[0130] Example 3

[0131] The following is an example of another solution that takes deformation of the plastic light guide plate into consideration. Fig.14A and Fig. 14B This is a schematic diagram showing the bending of the light guide plates due to the ambient temperature, air pressure, etc. when two light guide plates are held by a holding frame or the like.

[0132] like Fig.14A As shown, the two light guide plates 11 and 12 are held in a frame 15 for mechanical strength and positioning. From the perspective of mechanical accuracy, the interval between the two light guide plates is considered to be about 100 μm. In order to prevent dust and the like from entering between the light guide plates or condensation, the frame 15 has appropriate airtightness.

[0133] Fig. 14B The following situation is schematically shown: due to the stress generated by the change of air pressure or ambient temperature, the plastic light guide plate with less strength than glass is deformed. As in the above case, the position visually recognized by the user is shifted according to the wavelength (color), so the projected image is degraded.

[0134] Fig.15A , Fig. 15B , Fig. 15C Schematic diagram of the light guide plate of this embodiment showing improvement in deflection caused by environmental conditions.

[0135] Fig.15A A light guide plate is shown. An incident diffraction grating 100 and an outgoing diffraction grating 200 are formed on the surface of the light guide plate 10 , and a columnar gap retaining pattern 1501 is formed on the back surface.

[0136] Fig. 15B 1 shows the arrangement of the gap holding pattern 1501 in the xy plane. For example, when the light guide plate 10 is sized to be a rectangle with a side of 40 mm, the gap holding pattern 1501 can be formed to have a diameter of 10 μm, a height of 10 μm, and an interval of 200 μm. In a plastic molding method such as injection molding, two-sided molding can be easily performed by inserting two molds that determine the surface pattern into a mold.

[0137] Fig. 15C 1 is a schematic diagram showing a combination of two light guide plates 11 and 12. As shown in the figure, the two light guide plates are arranged close to each other with a gap-retaining pattern 1501 therebetween. The joint 1502 can be joined using a plastic joining method such as ultrasound, laser beam, heat treatment, etc. An adhesive can also be used. By adopting such a structure, the interval between the two light guide plates can be maintained at the height of the gap-retaining pattern 1501.

[0138] The results of the deformation simulation caused by periodic boundary conditions can be judged as follows: Fig. 14B The deflection of the light guide plate shown is reduced to less than 1 / 100. In order to reduce the deflection while maintaining the quality of the projected image, the area occupied by the gap holding pattern 1501 is preferably about 0.1 to 5.0% of the area of ​​the light guide plate.

[0139] A note on the stamp used here. The stamp of the incident diffraction grating and the output diffraction grating can use, for example, the following Ni stamp: the pattern is transferred using the Ni electroforming technology on a Si master mold that has been patterned on a Si wafer using a reduction exposure method, an EB drawing method, etc. In addition, the stamp for the gap holding pattern can also use a Ni stamp obtained by transferring the pattern using the Ni electroforming technology on a Si master mold that has been patterned on a Si wafer using a close exposure method such as an i-line. They can also be formed by changing the position on a Si wafer in a clean room, and the Ni stamp produced by mechanical cutting is used. As a result, the thickness of the Ni stamp is the same, so it is easy to improve the molding accuracy. At this time, it is further preferred to compose the marks 1503 such as the reference mark for determining the relative position of the two light guide plates and the reference mark for cutting out the Ni stamp at the same time as the diffraction grating.

[0140] Example 4

[0141] Fig.16 Schematic diagram showing the structure of the image display device of this embodiment. The light with image information emitted from the projector 300 in the figure reaches the user's pupil 400 through the action of the B, G, R light guide plates 11, 12, 13, thereby realizing augmented reality. The B, G, R light guide plates 11, 12, 13 are combined Figure 6 In the light guide plate of the present embodiment shown, the pitch and depth of the diffraction grating formed are optimized for each color.

[0142] Fig.16 In the embodiment, the image display device is composed of a light guide plate 10, a projector 300, and a display image control unit (not shown). Here, the light guide plate 10 corresponds to color display and integrates the R, G, B light guide plates 11, 12, and 13. In addition, as the image forming unit, for example, an image forming device composed of a reflective or transmissive spatial light modulator, a light source, and a lens, an image forming device based on an organic or inorganic EL (Electro Luminescence) element array and a lens, an image forming device based on a light emitting diode array and a lens, an image forming device combining a light source, a semiconductor MEMS mirror array, and a lens, and other well-known image forming devices can be used.

[0143] In addition, a device that resonates an LED or laser light source and the front end of an optical fiber through MEMS technology or PZT can also be used. Among them, the most common is an image forming device composed of a reflective or transmissive spatial light modulator, a light source, and a lens. Here, as a spatial light modulation device, a transmissive or reflective liquid crystal display device such as LCOS (Liquid Crystal On Silicon) and a digital micromirror device (DMD) can be cited. As a light source, a white light source can be separated into RGB and used, and LEDs or lasers corresponding to each color can also be used.

[0144] Furthermore, the reflective spatial light modulation device can adopt a structure composed of a liquid crystal display device and a polarization beam splitter, which reflects a part of the light from the light source and guides it to the liquid crystal display device, and allows a part of the light reflected by the liquid crystal display device to pass through and guide it to a collimating optical system using a lens. As light-emitting elements constituting the light source, red light-emitting elements, green light-emitting elements, blue light-emitting elements, and white light-emitting elements can be cited. The number of pixels can be determined based on the specifications required by the image display device. As specific values ​​of the number of pixels, in addition to the 1280×720 shown above, 320×240, 432×240, 640×480, 1024×768, and 1920×1080 can also be exemplified.

[0145] In the image display device of the present embodiment, the light beams including the image information emitted from the projector 300 are positioned so as to illuminate the incident diffraction gratings of the light guide plates 11 , 12 , and 13 , and are formed integrally with the light guide plate 10 .

[0146] In addition, a display image control unit (not shown) controls the operation of the projector 300 to realize a function of appropriately providing image information to the pupil 400 of the user.

[0147] In the above-described embodiment, in a light guide plate (image display element) having a surface concavoconvex diffraction grating, at least a mesh-type diffraction grating is used as an emission diffraction grating, and is integrally molded from a material having the same refractive index as the waveguide using an injection molding method or the like, thereby enabling plasticization of the light guide plate, thereby enabling a safe and lightweight light guide plate. That is, by using a mesh-type diffraction grating, a light guide plate having good performance can be manufactured by injection molding with a surface concavoconvexity having an aspect ratio of 1 or less, thereby enabling improvement in safety and lightweighting of the light guide plate due to plasticization.

[0148] This embodiment shows a situation in which image information is improved for the user, but in addition to this, the image display device of this embodiment can also have various sensors such as touch sensors, temperature sensors, acceleration sensors, etc. for obtaining information from the user or the outside world, and an eye tracking mechanism for measuring the movement of the user's eyes.

[0149] Availability in production

[0150] The present invention can be used in various image display devices.

[0151] Explanation of symbols

[0152] 10—light guide plate, 100—incident diffraction grating, 200—exit diffraction grating, 300—projector, 400—user's pupil, 500—image light.

Claims

1. A light guide plate, characterized in that: have: substrate; an incident diffraction grating that diffracts incident light; and an output diffraction grating that emits the light diffracted by the incident diffraction grating from the substrate, The output diffraction grating is formed by a concave-convex pattern formed on the substrate surface. The concavo-convex pattern is composed of a first parallel straight line group and a second parallel straight line group intersecting the first parallel straight line group, and the spacing between the first parallel straight line group and the spacing between the second parallel straight line group are equal. As the relationship between the pitch P of the first parallel straight line group and the second parallel straight line group and the width W of the concavo-convex pattern, W / P is greater than or equal to 0.15 and less than or equal to 0.85, The above-mentioned outgoing diffraction grating has two wave vectors with an angle of 120 degrees. The concavo-convex pattern is formed by injection molding technology so that the aspect ratio of the concavo-convex pattern is 1 or less.

2. The light guide plate according to claim 1, characterized in that: The substrate is formed of a material composed of a polymer compound.

3. The light guide plate according to claim 1, characterized in that: The aspect ratio of the concavo-convex pattern is 0.25 or more and 1.0 or less.

4. The light guide plate according to claim 1, characterized in that: The spacing P between the first parallel straight line group and the second parallel straight line group is equal to the spacing of the incident diffraction grating.

5. The light guide plate according to claim 1, characterized in that: The incident diffraction grating is a reflection type diffraction grating that reflects and diffracts incident light and propagates it inside the substrate, and is formed on the same surface of the substrate as the outgoing diffraction grating.

6. The light guide plate according to claim 1, characterized in that: The above-mentioned W / P is 0.3 or more and 0.7 or less.

7. The light guide plate according to claim 1, characterized in that: Regarding the output diffraction grating, the relationship between the pitch P of the first parallel straight line group and the second parallel straight line group and the width W of the concavo-convex pattern changes according to the positional relationship between the output diffraction grating and the incident diffraction grating.

8. The light guide plate according to claim 1, characterized in that: The output diffraction grating includes a portion where the W / P is greater than or equal to 0.4 and less than or equal to 0.

6.

9. The light guide plate according to claim 1, characterized in that: The output diffraction grating diffracts the light propagating from the incident diffraction grating in the substrate at a diffraction efficiency η1 in a direction perpendicular to the concave-convex pattern, and diffracts the light at a diffraction efficiency η in a direction perpendicular to the substrate. 11 Diffraction, and the diffraction efficiency is related to η 11 <η1.

10. The light guide plate according to claim 9, characterized in that: η 11 is (η1) 2 0.8 to 1.2 times of.

11. A light guide plate module, characterized in that: The light guide plate according to claim 1 is stacked in plurality.

12. The light guide plate module according to claim 11, characterized in that: The substrate of the light guide plate includes alignment marks on the same surface as the incident diffraction grating and the outgoing diffraction grating.

13. The light guide plate module according to claim 11, characterized in that: A gap retaining pattern is provided on the surface of the substrate of the light guide plate. The gap retaining pattern has an occupied area of ​​0.1% to 5.0% compared with the area of ​​the light guide plate.

14. An image display device comprising the light guide plate module according to claim 12 and a projector for irradiating image light onto the light guide plate module, It is characterized in that The image light is incident on the incident diffraction grating.

15. The image display device according to claim 14, characterized in that: The substrate is formed of a material composed of a polymer compound. The aspect ratio of the concavo-convex pattern is 1 or less.

16. The image display device according to claim 14, characterized in that: The light guide plate module emits the image light toward a side opposite to a side where the projector is arranged.

17. A method for manufacturing a light guide plate, the light guide plate being the light guide plate according to claim 1, It is characterized in that have: a step of preparing the above-mentioned substrate formed of a material composed of a polymer compound; and The step of forming the incident diffraction grating and the output diffraction grating on the substrate by using a stamp.

Images