Light guide plate, image display device

Abstract

The present invention provides a light guide plate for an image display device, which is excellent in color reproducibility, light in weight, and wide in viewing angle, even if using a lead-free glass. A light guide plate for an image display device, which guides image light incident from an image display element to be emitted toward a pupil of a user, is composed of a lead-free glass having a refractive index of 1.8 or more with respect to the wavelength of the image light, and is configured so that the internal light transmittance at a wavelength of 400 nm is 0.6 or more when the plate thickness is 10 mm.

Description

[0001] This application is a divisional application of the parent application, which is application number 201810757806.3 and filed on July 11, 2018. Technical Field

[0002] The present invention relates to a light guide plate used in image display devices such as head-mounted displays, and an image display device using the light guide plate. Background Technology

[0003] In recent years, head-mounted displays have been put into practical use as devices that use virtual image optical systems to magnify 2D images so that observers can view the magnified virtual images.

[0004] Head-mounted displays are classified into transparent and opaque types. Transparent head-mounted displays, used in conjunction with information terminals or as devices for AR (Augmented Reality), require a small size and excellent portability. Opaque head-mounted displays, used for movie viewing, gaming, VR (Virtual Reality), etc., require a wide field of view for an immersive experience.

[0005] Such a head-mounted display is described, for example, in Patent Document 1. The head-mounted display of Patent Document 1 includes: a display device that displays an image; a light guide member that allows the image displayed on the display element to be incident; and a transmission unit that causes the incident image to be totally internally reflected within the light guide member and transmitted toward the user's pupil. Furthermore, in order to obtain a specified viewing angle, the light guide member is formed of nitrile material with a refractive index of approximately 1.7.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent document 1: Japanese Patent Application Publication No. 2010-243787. Summary of the Invention

[0009] The technical problem that the invention aims to solve

[0010] According to Patent Document 1, the light guide component for a head-mounted display can obtain an image with a viewing angle of 10.0°. However, for VR applications, a wider viewing angle and excellent color reproduction are also required. Furthermore, for AR applications, small size and lightweight are required, necessitating a thinner light guide component. In addition, in recent years, from the perspective of environmental protection and efficient resource utilization, there has been a demand for lead-free light guide components.

[0011] In view of this situation, the present invention aims to provide a light guide plate for an image display device (such as a head-mounted display) that can achieve excellent color reproduction, is lightweight, and provides a wide viewing angle even when using lead-free glass, and an image display device using the light guide plate.

[0012] Technical solutions to solve technical problems

[0013] In order to achieve the above objectives, the light guide plate of the present invention is a light guide plate for an image display device that guides image light incident from an image display element toward the user's pupil. The light guide plate is made of lead-free glass with a refractive index of 1.8 or more relative to the wavelength of the image light, and has an internal light transmittance of 0.6 or more at a wavelength of 400 nm when the plate thickness is 10 mm.

[0014] Based on this structure of the light guide plate, an image display device with excellent color reproduction, thin and lightweight design, and wide viewing angle can be constructed.

[0015] Furthermore, it is preferable that the light guide plate has a first surface and a second surface that are opposite to each other, and the parallelism between the first surface and the second surface is 20 arcseconds or less. Additionally, in this case, it is preferable that the difference between the maximum and minimum distances from the first surface to the second surface is 5 μm or less.

[0016] In addition, when the transmitted light of the standard light source D65 with a plate thickness of 10mm is represented by an xy chromaticity coordinate diagram, the chromaticity of x is preferably 0.31 to 0.34 and the chromaticity of y is preferably 0.33 to 0.36.

[0017] In addition, the preferred plate thickness is 0.5 to 1.0 mm.

[0018] Furthermore, the light guide plate preferably includes a first optical element that diffracts the guided image light and directs it toward the user's pupil. Preferably, the first optical element is made of a material with a refractive index greater than that of air. More preferably, the first optical element is made of a material with a refractive index greater than that of the light guide plate.

[0019] Furthermore, it is preferable to include a second optical element that diffracts image light incident from the image display element and directs it onto the light guide plate. Preferably, the second optical element is made of a material with a refractive index greater than that of air. More preferably, the second optical element is made of a material with a refractive index greater than that of the light guide plate.

[0020] Furthermore, the image display device of the present invention includes: a light source that emits illumination light; an image display element that receives illumination light from the light source and outputs image light; and any one of the above-mentioned light guide plates that guides the image light incident from the image display element toward the user's pupil.

[0021] The effects of the invention

[0022] As described above, according to the present invention, a light guide plate for an image display device that achieves excellent color reproduction, is lightweight, and provides a wide viewing angle even when using lead-free glass can be realized. Furthermore, an image display device using this light guide plate can be realized. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating the structure of a head-mounted display that uses the light guide plate according to an embodiment of the present invention.

[0024] Figure 2 This is a side view schematically illustrating the structure of a head-mounted display using the light guide plate according to an embodiment of the present invention.

[0025] Figure 3 This is a coordinate graph representing the characteristics of the light guide plate according to Embodiment 1 of the present invention.

[0026] Figure 4 This is a diagram illustrating a simulation model of a head-mounted display using the light guide plate described in Embodiment 1 of the present invention.

[0027] Figure 5 This is a coordinate graph representing the characteristics of the light guide plate according to Embodiment 2 of the present invention.

[0028] Label Explanation:

[0029] 1-HMD;

[0030] 2-Eyeglasses frame;

[0031] 2a-Installation section;

[0032] 3-Spectacular lenses;

[0033] 4-Backlight;

[0034] 5-Signal processing equipment;

[0035] 6-speaker;

[0036] 7-FPC;

[0037] 10-Light guide plate;

[0038] 10a - Page 1;

[0039] 10b - Page 2;

[0040] 20 - Display element unit;

[0041] 21-Laser source;

[0042] 22-Diffusion optical system;

[0043] 23-microlens array;

[0044] 24 - Image display elements;

[0045] 32R, 32L, 52R, 52L-HOE. Detailed Implementation

[0046] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Furthermore, identical or equivalent parts in the drawings are labeled with the same reference numerals, and their descriptions are omitted.

[0047] Figure 1 This diagram illustrates the structure of a head-mounted display 1 (hereinafter referred to as "HMD1") using the light guide plate 10 according to an embodiment of the present invention. Figure 1 (a) is a frontal side perspective view. Figure 1 (b) is a rear-view perspective view. For example... Figure 1 (a) and Figure 1 As shown in (b), spectacle lenses 3 are mounted on the front of the eyeglasses frame 2 worn on the user's head. A backlight 4 for illuminating the image is mounted on the mounting portion 2a of the eyeglasses frame 2. A signal processing device 5 for displaying the image and a speaker 6 for reproducing sound are provided on the temple portion of the eyeglasses frame 2. The light guide plate 10 is a rectangular thin plate-shaped optical component, and FPCs (Flexible Printed Circuits) 7, which form wirings, are routed from the circuits of the signal processing device 5 along the eyeglasses frame 2. Display element units (e.g., liquid crystal display elements) 20 are routed to the center of the user's eyes using the FPCs 7 and are positioned approximately at the center of the backlight 4. The display element units 20 are fixed relative to the light guide plate 10 such that they are located approximately at the center of the light guide plate 10. Additionally, at the position in front of the user, HOE (Holographic Optical Element) 32R and 32L (first optical elements) are respectively firmly attached to the first surface 10a of the light guide plate 10 by adhesive or the like. At the position opposite to the display element unit 20 across the light guide plate 10, HOE 52R and 52L are stacked on the second surface 10b of the light guide plate 10.

[0048] Figure 2 This is a side view schematically illustrating the structure of the HMD1 according to this embodiment. Furthermore, in Figure 2 In order to make the accompanying drawings clear, only the main parts of the invention are shown; the eyeglass frame 2, etc., are omitted from the drawings. Figure 2As shown, the HMD1 has a configuration that is symmetrical about the center line X connecting the center of the image display element 24 and the center of the light guide plate 10. Furthermore, light of each wavelength incident from the image display element 24 to the light guide plate 10 is divided into two parts, as described later, and directed to the user's right and left eyes respectively. The light paths of each wavelength directed to each eye are also approximately symmetrical about the center line X.

[0049] like Figure 2 As shown, the backlight 4 includes a laser light source 21, a diffusion optical system 22, and a microlens array 23. The display element unit 20 is an image generation unit with an image display element 24, driven, for example, in a field-sequential manner. The laser light source 21 has laser light sources corresponding to wavelengths R (wavelength 436nm), G (wavelength 546nm), and B (wavelength 633nm), which sequentially irradiate light of each wavelength at high speed. The light of each wavelength is incident on the diffusion optical system 22 and the microlens array 23, and transformed into a uniform, highly directional parallel beam without light unevenness, which is incident perpendicularly on the display panel surface of the image display element 24.

[0050] The image display element 24 is, for example, a transmissive liquid crystal (LCD T-LCOS) panel driven in a field-sequence manner. The image display element 24 modulates light of each wavelength in accordance with the image signal generated by the image engine (not shown) of the signal processing device 5. Light of each wavelength, modulated by the pixels of the effective area of ​​the image display element 24, is incident on the light guide plate 10 with a predetermined beam profile (approximately the same shape as the effective area). Alternatively, the image display element 24 can be replaced, for example, with other forms of display elements such as a DMD (Digital Mirror Device) or reflective liquid crystal (LCOS) panel, MEMS (Micro-Electro-Mechanical Systems), organic EL (Electro-Luminescence), or inorganic EL.

[0051] Furthermore, the display element unit 20 is not limited to a field-sequential display element, but can also be an image generation unit for a simultaneous display element (a display element having a predetermined arrangement of RGB color filters in front of the emission face). In this case, a white light source is used, for example.

[0052] like Figure 2As shown, light of various wavelengths modulated by the image display element 24 is sequentially incident into the light guide plate 10 from the first surface 10a. HOE52R and 52L (second optical elements) are stacked on the second surface 10b of the light guide plate 10. HOE52R and 52L are, for example, rectangular reflective volume phase-type HOEs, having a structure composed of three layers of photopolymers on which interference fringes corresponding to the wavelengths of light R, G, and B are respectively recorded. That is, HOE52R and 52L are configured to have a wavelength selection function, namely, diffracting light of wavelengths R, G, and B while allowing light of other wavelengths to pass through.

[0053] Alternatively, HOE52R and 52L can also be a layer of optical polymer that records interference fringes corresponding to the wavelengths of light R, G, and B.

[0054] Alternatively, HOE52R and 52L can be constructed using two layers of photopolymer to provide wavelength selection functionality corresponding to each wavelength of light (R, G, B). For example, consider constructing HOE52R and 52L using a single layer of photopolymer containing interference fringes corresponding to each wavelength of light (R, G) and another layer containing interference fringes corresponding to the wavelength of light (B). Furthermore, HOE32R and 32L are also reflective volume-phase HOEs, having the same layer structure as HOE52R and 52L. For example, the spacing of the interference fringe patterns can also be approximately the same for HOE32R and 32L and 52R and 52L.

[0055] HOE52R and 52L are stacked with their centers aligned and their interference fringe patterns reversed by 180°. Furthermore, in their stacked state, they are tightly fixed to the second surface 10b of the light guide plate 10 by adhesive or the like, with their centers aligned with the center line X. Light of various wavelengths modulated by the image display element 24 is sequentially incident on HOE52R and 52L via the light guide plate 10.

[0056] To guide light to the right and left eyes, HOE52R and 52L diffract light of each wavelength incident sequentially at a predetermined angle. The light of each wavelength diffracted by HOE52R and 52L undergoes repeated total internal reflection at the interface between the light guide plate 10 and the air, propagating within the light guide plate 10 and incident on HOE32R and 32L. Here, HOE52R and 52L assign the same diffraction angle to each wavelength. Therefore, all wavelengths of light incident at approximately the same position relative to the light guide plate 10 (or, according to other interpretations, emitted from approximately the same coordinates within the effective area of ​​the image display element 24) propagate in approximately the same optical path within the light guide plate 10 and incident on approximately the same positions on HOE32R and 32L. Alternatively, HOE52R and 52L diffract light of each wavelength of RGB to faithfully reproduce the pixel position relationships within the effective area of ​​the image displayed on the image display element 24 on HOE32R and 32L.

[0057] As described above, in this embodiment, HOE52R and 52L diffract light of all wavelengths emitted from approximately the same coordinates within the effective area of ​​the image display element 24, so that they are incident on approximately the same positions on HOE32R and 32L. On the other hand, in other embodiments, HOE52R and 52L may also be configured to diffract light of all wavelengths that originally constitute the same pixel but are relatively offset within the effective area of ​​the image display element 24, so that they are incident on approximately the same positions on HOE32R and 32L.

[0058] Light of various wavelengths incident on HOE32R and 32L is diffracted by HOE32R and 32L and emitted sequentially and approximately perpendicularly outward from the second surface 10b of the light guide plate 10. Thus, the light of each wavelength emitted as approximately parallel light forms a virtual image I of the image generated by the image display element 24 and is imaged on the user's right and left retina, respectively. Alternatively, HOE32R and 32L can be configured as condensers to allow the user to observe the magnified virtual image I. That is, light incident on the peripheral areas of HOE32R and 32L can be emitted at an angle closer to the center of the pupil, forming an image on the user's retina. Alternatively, to allow the user to observe the magnified virtual image I, HOE52R and 52L can diffract light of various wavelengths of RGB, so that the pixel position relationship on HOE32R and 32L is a magnified shape similar to the pixel position relationship within the effective area of ​​the image displayed on the image display element 24.

[0059] Furthermore, it is preferable to use materials with a refractive index greater than that of air as the materials used to manufacture HOE32R, 32L, 52R, and 52L. Using such materials for HOE32R, 32L, 52R, and 52L effectively improves their diffraction efficiency. Additionally, it is more preferable that the refractive index of the materials used to manufacture HOE32R, 32L, 52R, and 52L is higher than that of the material forming the light guide plate 10. Using such materials for HOE32R, 32L, 52R, and 52L improves diffraction efficiency and effectively enhances image clarity. For example, materials containing one or more of Si3N4, TiO2, Nb2O5, and Ta2O5 can be used as the materials used to manufacture HOE32R, 32L, 52R, and 52L. Thus, light of each wavelength of RGB is sequentially imaged at high speed on the user's retina, allowing the user to recognize the generated image obtained by the image display element 24 as a color image. Furthermore, the actual distance between the user's eyes and the image display element 24 is no more than tens of millimeters. However, since light of each wavelength is incident on the eyeball as approximately parallel light, the user can clearly recognize the generated image obtained by the image display element 24 even at infinity. In addition, as volumetric phase-type reflective HOEs, HOE32R and 32L have a narrow half-maximum diffraction efficiency and high light transmittance of external images. Therefore, the user can clearly observe external images along with the displayed image on the image display element 24.

[0060] Furthermore, in this embodiment, a structure is adopted where there is a single-board image display element 24 instead of separate display elements for the right and left eyes. This results in reduced manufacturing costs. Additionally, light from the same point (i.e., the image from the single-board image display element 24) is guided to each of the user's eyes through the same optical path length. Therefore, synchronized images can be incident on each of the user's eyes.

[0061] In the structure of this embodiment as described above, since a higher refractive index results in a shorter air-converted optical path length for light entering the light guide plate 10, a higher refractive index leads to a larger viewing angle relative to the width of the image display element 24. Therefore, in this embodiment, in order to increase the viewing angle (i.e., to make the viewing angle θv relative to the virtual image I of the image display element 24, for example, 13.5° or more), a high refractive index lead-free glass with a refractive index of 1.8 or more at each wavelength of RGB and a plate thickness of 0.5 to 1.0 mm is used for the light guide plate 10. Furthermore, the higher the refractive index of the light guide plate 10, the better; preferably, it is 1.95 or more.

[0062] When the high-refractive-index lead-free glass described above is used for the light guide plate 10, the preferred composition ranges of the components constituting the glass are as follows:

[0063] SiO2: 0-35%;

[0064] B2O3: 0–55%;

[0065] ZnO: 0-35%;

[0066] Y2O3: 0-40%;

[0067] ZrO2: 0–30%;

[0068] TiO2: 0–20%.

[0069] Furthermore, the content of each component is the mass percentage of the total oxide equivalent composition relative to the total mass of the glass. Here, the oxide equivalent composition is defined as the composition of each component contained in the glass, assuming that all oxides, complex salts, metal fluorides, etc., used as raw materials that are components of the glass of the present invention are completely decomposed into oxides when melted, and the total mass of the generated oxides is set as 100% by mass.

[0070] SiO2 is a component that constitutes the basic structure of glass, which can improve the stability of glass and easily maintain a viscosity suitable for forming molten glass. When the SiO2 content is more than 35%, the refractive index decreases or the liquidus temperature or glass transition temperature increases; therefore, 0 to 35% is preferred. Moreover, the SiO2 content is more preferably 1 to 25%, and more preferably 1 to 15%.

[0071] B2O3 is a mesh-forming oxide that imparts low-dispersion properties to glass, thereby improving its stability and chemical durability. When the B2O3 content is greater than 55%, the refractive index decreases; therefore, 0-55% is preferred. Furthermore, the B2O3 content is more preferably 1-45%, and more preferably 1-40%.

[0072] ZnO is a component that maintains a high refractive index while imparting low dispersion characteristics, effectively reducing the melting temperature, liquidus temperature, and transition temperature of glass. When the ZnO content exceeds 35%, devitrification is likely, and chemical durability decreases; therefore, a content of 0-35% is preferred. Furthermore, the ZnO content is more preferably 0.5-25%, and more preferably 1-20%.

[0073] Y₂O₃ is a component that maintains a high refractive index while imparting low dispersion characteristics, thus improving the stability and chemical durability of glass. When the Y₂O₃ content exceeds 40%, devitrification is more likely, and the glass transition temperature or deformation point temperature increases; therefore, a content of 0–40% is preferred. Moreover, the Y₂O₃ content is more preferably 0–20%, and more preferably 0.1–8%.

[0074] ZrO2 is a component that adjusts optical constants and improves the stability and weather resistance of glass, thereby enhancing its stability. When the ZrO2 content exceeds 30%, the glass stability decreases, leading to increased dispersion; therefore, a content of 0-30% is preferred. Furthermore, the ZrO2 content is more preferably 0.5-15%, and more preferably 1-10%.

[0075] TiO2 acts as a decorative agent in glass structures, increasing the refractive index and stability of the glass. When the TiO2 content exceeds 20%, it leads to increased dispersion, decreased thermal stability, increased liquidus temperature, and deterioration of colorability; therefore, a content of 0-20% is preferred. Furthermore, the TiO2 content is more preferably 1-18%, and more preferably 1-15%.

[0076] Furthermore, in order to reliably guide the light of each wavelength of RGB to HOE32R and 32L, the parallelism between the first surface 10a and the second surface 10b of the light guide plate 10 in this embodiment is as high as possible. Therefore, the light guide plate 10 of this embodiment is manufactured such that the parallelism between the first surface 10a and the second surface 10b is 20 arcseconds or less. Furthermore, the parallelism between the first surface 10a and the second surface 10b is preferably 10 arcseconds or less, and more preferably 5 arcseconds or less. Moreover, if the parallelism between the first surface 10a and the second surface 10b is greater than 20 arcseconds, it will be impossible to accurately guide the light of each wavelength of RGB to HOE32R and 32L.

[0077] Therefore, the light guide plate 10 of this embodiment, since it uses high refractive index lead-free glass with a refractive index of 1.8 or more at each wavelength of RGB, can be configured as a thin, lightweight HMD1 with a wide viewing angle θv (e.g., 13.5° or more).

[0078] Furthermore, in order to accurately guide light of each wavelength of RGB (i.e., to accurately reproduce colors), the higher the transmittance of each wavelength of RGB in the light guide plate 10 of this embodiment, the better. In particular, the wavelength of RGB falls within the wavelength region of 400-500 nm. If the component of RGB decreases, the displayed image (virtual image I) will appear yellow overall. Therefore, it is desirable to construct the light guide plate in a way that does not reduce the component of RGB. Therefore, for the light guide plate 10 of this embodiment, a nitrile material with an internal transmittance of 0.6 or more at a wavelength of 400 nm is used when the plate thickness is 10 mm. In addition, the higher the internal transmittance, the better, preferably 0.65 or more, and more preferably 0.70 or more.

[0079] Furthermore, in the light guide plate 10 of this embodiment, in order to faithfully reproduce the color image obtained by the image display element 24, it is required to accurately (with good balance) guide the light of each wavelength of RGB. Typically, the xy chromaticity coordinates of the standard light source D65 under a 10-degree field of view are x: 0.3138, y: 0.3310. However, when absorption occurs in the light guide plate 10, a deviation will occur from these coordinates, thus changing the user's color perception. Therefore, the light guide plate 10 of this embodiment uses a material such that, when the transmitted light of the standard light source D65 with a plate thickness of 10 mm is represented by an xy chromaticity diagram (coordinates), x: 0.31–0.34, y: 0.33–0.36. Furthermore, x is preferably 0.31–0.33, more preferably 0.31–0.32. Additionally, y is preferably 0.33–0.35, more preferably 0.33–0.34. Furthermore, when the x value exceeds the range of 0.31 to 0.34, or when the y value exceeds the range of 0.33 to 0.36, the color of the displayed image (virtual image I) becomes larger, and the user will observe a displayed image (virtual image I) with a significantly different color perception.

[0080] Furthermore, in order to accurately guide light of each wavelength of RGB and obtain an image with minimal bleed, the flatness of the light guide plate 10 in this embodiment should be as high as possible. Therefore, the light guide plate 10 in this embodiment is ground such that the difference between the maximum and minimum values ​​of the thickness of the light guide plate 10 (i.e., the distance between the first surface 10a and the second surface 10b) (i.e., TTV (Total Thickness Variation)) is 5 μm or less. In addition, the flatness (i.e., TTV) is preferably 2 μm or less, more preferably 1 μm or less. Furthermore, if the TTV exceeds 5 μm, the displayed image (virtual image I) observed by the user will have more bleed.

[0081]

Example

[0082] The following shows a specific embodiment of the light guide plate 10. However, the light guide plate 10 of the present invention is not limited to this embodiment.

[0083]

Example 1

[0084] As the nitrile material, "TAFD55" manufactured by "HOYA Co., Ltd." was used, and it was processed into a length of 50mm × width of 20mm × thickness of 1.0mm to obtain the light guide plate 10. The main characteristics are as follows.

[0085] Refractive index (@436nm): 2.04600;

[0086] Refractive index (@546nm): 2.00912;

[0087] Refractive index (@633nm): 1.99406;

[0088] Parallelism between face 10a and face 10b: 15 arc seconds;

[0089] Flatness (TTV): 5μm;

[0090] Internal transmittance at 400nm wavelength for a plate thickness of 10mm: 0.749;

[0091] The chromaticity of the transmitted light from the standard light source D65 with a plate thickness of 10mm is: x = 0.3187, y = 0.3385.

[0092] The composition of “TAFD55” is as follows:

[0093] SiO2: 1-10%;

[0094] B2O3: 1-10%;

[0095] ZnO: 0-10%;

[0096] Y2O3: 0-1%;

[0097] ZrO2: 1-10%.

[0098] in addition, Figure 3 This is a coordinate graph representing the characteristics of this embodiment. Figure 3 (a) shows the spectral characteristics when the plate thickness is 10 mm. Figure 3 (b) is the chromaticity diagram of the transmitted light from the standard light source D65 when the plate thickness is 10mm.

[0099] When the light guide plate 10 obtained in this way is assembled into the HMD1, and the image is evaluated at the viewpoint, a high-brightness and high-contrast image can be observed from a wide viewing angle.

[0100] Table 1 shows the parameters and results (i.e., viewing angle θv) during the simulation of the viewing angle when the light guide plate 10 of this embodiment is assembled into the HMD1. Additionally, Figure 4 It is a diagram representing the simulation model. Figure 4 The parameters shown correspond to those in Table 1.

[0101] Table 1

[0102] <![CDATA[Diffraction angles of HOE52R and 52L: θ' D > 85.0 Thickness of light guide plate 10: t 1.0 Number of reflections within the light guide plate 10 15 Width of HOE52R and 52L 5.2 Refractive index of HOE52R, 52L, 32R, and 32L 1.80 Refractive index of light guide plate 10 2.04600 <![CDATA[Light angle within the light guide plate 10: θ' i > 61.2 <![CDATA[Offset per reflection: t / tanθ' i > 1.8 <![CDATA[L(=t / tanθ' i ×(Number of reflections + 1)]]> 27.3 <![CDATA[Optical path length per reflection: t / cosθ' i > 2.1 <![CDATA[Actual optical path length (= t / cosθ' i × (number of reflections + 1))]]> 31.1 Air-converted optical path length 15.2 Additional optical path length (distance from HOE32R, 32L to the pupil) 5.0 Viewpoint θv 14.7

[0103] like Figure 4 As shown, in this simulation model, light of each wavelength in RGB ( Figure 4The light (as shown by the dashed line in the image) is incident on HOE52R and 52L. Inside HOE52R and 52L, it is diffracted at a diffraction angle θ'D (85.0°) and incident on the light guide plate 10 at a light angle θ'i (61.2°). Figure 4 (a)). Furthermore, the RGB light of each wavelength incident on the light guide plate 10 is reflected a predetermined number of times (15 times) within the light guide plate 10 (thickness: t = 1.0 mm, refractive index: 2.04600) and emitted towards the user's pupil. Figure 4 (b)). Furthermore, in this case, the viewing angle θv is determined by the positional relationship between the pupil position P and HOE52R, 52L, as shown... Figure 4 (c) can be represented as the angle formed by the two ends of HOE52R and 52L with the pupil position P. The two ends of HOE52R and 52L are positioned at a distance from the pupil position P after deviating from the air-converted optical path length + the additional optical path length (the distance from HOE32R and 32L to the pupil). Furthermore, if calculated using the parameters in Table 1, the viewing angle θv of the HMD1 assembled with the light guide plate 10 of this embodiment becomes 14.7° (refer to Table 1). It can be seen that the light guide plate 10 according to this embodiment obtains a wider viewing angle compared with the current structure of the HMD.

[0104]

Example 2

[0105] As the nitrile material, "TAFD65" manufactured by "HOYA Co., Ltd." was used, and it was processed into a length of 50mm × width of 20mm × thickness of 1.0mm to obtain the light guide plate 10. The main characteristics are as follows.

[0106] Refractive index (@436nm): 2.10226;

[0107] Refractive index (@546nm): 2.06011;

[0108] Refractive index (@633nm): 2.04305;

[0109] Parallelism between face 10a and face 10b: 15 arc seconds;

[0110] Flatness (TTV): 5μm;

[0111] Internal transmittance at 400nm wavelength for a plate thickness of 10mm: 0.609;

[0112] The chromaticity of the transmitted light from the standard light source D65 with a plate thickness of 10mm is: x = 0.3227, y = 0.3440.

[0113] The composition of “TAFD65” is as follows:

[0114] SiO2: 1-10%;

[0115] B2O3: 1-10%;

[0116] ZnO: 0-1%;

[0117] Y2O3: 0-1%;

[0118] ZrO2: 1-10%;

[0119] TiO2: 10-20%.

[0120] in addition, Figure 5 This is a coordinate graph representing the characteristics of this embodiment. Figure 5 (a) shows the spectral characteristics when the plate thickness is 10 mm. Figure 5 (b) is the chromaticity diagram of the transmitted light from the standard light source D65 when the plate thickness is 10mm.

[0121] When the light guide plate 10 obtained in this way is assembled into the HMD1, a high-brightness and high-contrast image can be observed from a wide viewing angle when evaluating the image at the viewpoint.

[0122] Table 2 shows the parameters and results (i.e., viewing angle θv) when the light guide plate 10 of this embodiment is assembled into the HMD1 during the simulation of the viewing angle. Furthermore, the simulation model and representation... Figure 4 The same.

[0123] Table 2

[0124]

[0125]

[0126] If the parameters in Table 2 are used in the same way as those in Table 1 for simulation, the viewing angle θv of the HMD1 assembled with the light guide plate 10 of this embodiment becomes 15.9°. Therefore, it can be seen that the light guide plate 10 according to this embodiment achieves a wider viewing angle compared to the current structure of the HMD.

[0127] The above describes the embodiments of the present invention. The present invention is not limited to the structure and specific numerical configurations of each embodiment; various modifications are possible within the scope of the technical concept of the present invention.

[0128] HOE32R, 32L, 52R, and 52L can also be light-transmitting HOEs. In this case, HOE52R and 52L are, for example, tightly fixed on the first surface 10a of the light guide plate 10 opposite to the display element unit 20, and diffract light of each wavelength from the display element unit 20 so that it is totally internally reflected inside the light guide plate 10 and transmitted to HOE32R or 32L. HOE32R and 32L are, for example, tightly fixed on the second surface 10b of the light guide plate 10 opposite to the user's pupil, and diffract light of each wavelength transmitted inside the light guide plate 10 toward the user's pupil.

[0129] Furthermore, the HOE32R, 32L, 52R, and 52L of this embodiment have been described as being formed from photopolymers, but this structure is not limited to this. For example, an optical thin film may also be deposited on the surface of the light guide plate 10 to form it.

[0130] In addition, the laser light source 21 of the display element unit 20 may be, for example, an LED or LD (semiconductor laser) backlight that sequentially illuminates each wavelength of light of R, G, and B at high speed.

[0131] In addition, in this embodiment, the display element unit 20 is disposed on the first surface 10a side of the light guide plate 10 and the HOE52R and 52L are disposed on the second surface 10b side of the light guide plate 10. However, this structure is not limited to this. For example, the display element unit 20 may be disposed on the second surface 10b side of the light guide plate 10 and the HOE52R and 52L may be disposed on the first surface 10a side of the light guide plate 10.

Claims

1. A light guide plate, which is a light guide plate for an image display device that guides image light incident from an image display element to be emitted toward a pupil of a user, characterized by comprising: a lead-free glass having a refractive index of 2.046 or more with respect to a wavelength of the image light, and an internal light transmittance of 0.6 or more for light having a wavelength of 400 nm when a plate thickness is 10 mm; the lead-free glass including Si02 at a content rate of 1 to 25%, ZnO at a content rate of 0 to 10%, Zr02 at a content rate of 1 to 10%, B203 at a content rate of 0 to 55%, Y203 at a content rate of 0 to 40%, and Ti02 at a content rate of 0 to 20%, each content rate being a mass percentage with respect to a total mass of the lead-free glass in an entirety oxide conversion composition; and when a transmittance light of a standard light source D65 when the plate thickness is 10 mm is represented by an xy chromaticity coordinate diagram, a chromaticity of x is 0.31 to 0.34, and a chromaticity of y is 0.33 to 0.

36.

2. The light guide plate according to claim 1, characterized in that the lead-free glass includes B203 at a content rate of 1 to 45%.

3. The light guide plate according to claim 2, characterized in that the lead-free glass includes B203 at a content rate of 10% or less.

4. The light guide plate according to claim 1, characterized by having a first surface and a second surface that face each other, and a parallelism of the first surface and the second surface being 20 arcseconds or less.

5. The light guide plate according to claim 4, characterized by a difference between a maximum value and a minimum value of a distance from the first surface to the second surface being 5 μm or less.

6. The light guide plate according to any one of claims 1 to 5, characterized by a plate thickness being 0.5 to 1.0 mm.

7. The light guide plate according to any one of claims 1 to 5, characterized by comprising a first optical element that diffracts the image light guided to be emitted toward the pupil of the user.

8. The light guide plate according to claim 7, characterized in that the first optical element is made of a material having a refractive index greater than a refractive index of air.

9. The light guide plate according to claim 7, characterized in that the first optical element is made of a material having a refractive index greater than a refractive index of the light guide plate.

10. The light guide plate according to claim 7, characterized by comprising a second optical element that diffracts the image light incident from the image display element to be incident to the light guide plate.

11. The light guide plate according to claim 10, characterized in that the second optical element is made of a material having a refractive index greater than a refractive index of air.

12. The light guide plate according to claim 10, characterized in that the second optical element is made of a material having a refractive index greater than a refractive index of the light guide plate. having: a light source that emits illumination light; an image display element that outputs image light by receiving the illumination light from the light source; and a light guide plate that guides the image light output from the image display element to be emitted toward a pupil of a user. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 13. An image display device, characterized by comprising: ​ ​ ​ ​ The light guide plate according to any one of claims 1 to 12, which guides image light incident from the image display element and emits it toward a pupil of a user.

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